Co-reporter:Thomas G. Schuhmann Jr., Jun Yao, Guosong Hong, Tian-Ming Fu, and Charles M. Lieber
Nano Letters September 13, 2017 Volume 17(Issue 9) pp:5836-5836
Publication Date(Web):August 8, 2017
DOI:10.1021/acs.nanolett.7b03081
Syringe-injectable mesh electronics represent a new paradigm for brain science and neural prosthetics by virtue of the stable seamless integration of the electronics with neural tissues, a consequence of the macroporous mesh electronics structure with all size features similar to or less than individual neurons and tissue-like flexibility. These same properties, however, make input/output (I/O) connection to measurement electronics challenging, and work to-date has required methods that could be difficult to implement by the life sciences community. Here we present a new syringe-injectable mesh electronics design with plug-and-play I/O interfacing that is rapid, scalable, and user-friendly to nonexperts. The basic design tapers the ultraflexible mesh electronics to a narrow stem that routes all of the device/electrode interconnects to I/O pads that are inserted into a standard zero insertion force (ZIF) connector. Studies show that the entire plug-and-play mesh electronics can be delivered through capillary needles with precise targeting using microliter-scale injection volumes similar to the standard mesh electronics design. Electrical characterization of mesh electronics containing platinum (Pt) electrodes and silicon (Si) nanowire field-effect transistors (NW-FETs) demonstrates the ability to interface arbitrary devices with a contact resistance of only 3 Ω. Finally, in vivo injection into mice required only minutes for I/O connection and yielded expected local field potential (LFP) recordings from a compact head-stage compatible with chronic studies. Our results substantially lower barriers for use by new investigators and open the door for increasingly sophisticated and multifunctional mesh electronics designs for both basic and translational studies.Keywords: flat flexible cable (FFC) connector; Mesh electronics; nanoelectronics interface; nanowire field-effect transistor; neural interface; zero insertion force (ZIF) connection;
Co-reporter:Tuncay Ozel, Benjamin A. Zhang, Ruixuan Gao, Robert W. Day, Charles M. Lieber, and Daniel G. Nocera
Nano Letters July 12, 2017 Volume 17(Issue 7) pp:4502-4502
Publication Date(Web):June 16, 2017
DOI:10.1021/acs.nanolett.7b01950
Development of new synthetic methods for the modification of nanostructures has accelerated materials design advances to furnish complex architectures. Structures based on one-dimensional (1D) silicon (Si) structures synthesized using top-down and bottom-up methods are especially prominent for diverse applications in chemistry, physics, and medicine. Yet further elaboration of these structures with distinct metal-based and polymeric materials, which could open up new opportunities, has been difficult. We present a general electrochemical method for the deposition of conformal layers of various materials onto high aspect ratio Si micro- and nanowire arrays. The electrochemical deposition of a library of coaxial layers comprising metals, metal oxides, and organic/inorganic semiconductors demonstrate the materials generality of the synthesis technique. Depositions may be performed on wire arrays with varying diameter (70 nm to 4 μm), pitch (5 μ to 15 μ), aspect ratio (4:1 to 75:1), shape (cylindrical, conical, hourglass), resistivity (0.001–0.01 to 1–10 ohm/cm2), and substrate orientation. Anisotropic physical etching of wires with one or more coaxial shells yields 1D structures with exposed tips that can be further site-specifically modified by an electrochemical deposition approach. The electrochemical deposition methodology described herein features a wafer-scale synthesis platform for the preparation of multifunctional nanoscale devices based on a 1D Si substrate.Keywords: Core−shell structures; electrochemistry; hybrid layers; one-dimensional structures; silicon nanowire arrays; wafer-scale deposition;
Co-reporter:Tian-Ming Fu;Guosong Hong;Robert D. Viveros;Tao Zhou
PNAS 2017 114 (47 ) pp:E10046-E10055
Publication Date(Web):2017-11-21
DOI:10.1073/pnas.1717695114
Implantable electrical probes have led to advances in neuroscience, brain−machine interfaces, and treatment of neurological
diseases, yet they remain limited in several key aspects. Ideally, an electrical probe should be capable of recording from
large numbers of neurons across multiple local circuits and, importantly, allow stable tracking of the evolution of these
neurons over the entire course of study. Silicon probes based on microfabrication can yield large-scale, high-density recording
but face challenges of chronic gliosis and instability due to mechanical and structural mismatch with the brain. Ultraflexible
mesh electronics, on the other hand, have demonstrated negligible chronic immune response and stable long-term brain monitoring
at single-neuron level, although, to date, it has been limited to 16 channels. Here, we present a scalable scheme for highly
multiplexed mesh electronics probes to bridge the gap between scalability and flexibility, where 32 to 128 channels per probe
were implemented while the crucial brain-like structure and mechanics were maintained. Combining this mesh design with multisite
injection, we demonstrate stable 128-channel local field potential and single-unit recordings from multiple brain regions
in awake restrained mice over 4 mo. In addition, the newly integrated mesh is used to validate stable chronic recordings in
freely behaving mice. This scalable scheme for mesh electronics together with demonstrated long-term stability represent important
progress toward the realization of ideal implantable electrical probes allowing for mapping and tracking single-neuron level
circuit changes associated with learning, aging, and neurodegenerative diseases.
Co-reporter:Tian-Ming Fu;Guosong Hong;Robert D. Viveros;Tao Zhou
PNAS 2017 114 (47 ) pp:E10046-E10055
Publication Date(Web):2017-11-21
DOI:10.1073/pnas.1717695114
Implantable electrical probes have led to advances in neuroscience, brain−machine interfaces, and treatment of neurological
diseases, yet they remain limited in several key aspects. Ideally, an electrical probe should be capable of recording from
large numbers of neurons across multiple local circuits and, importantly, allow stable tracking of the evolution of these
neurons over the entire course of study. Silicon probes based on microfabrication can yield large-scale, high-density recording
but face challenges of chronic gliosis and instability due to mechanical and structural mismatch with the brain. Ultraflexible
mesh electronics, on the other hand, have demonstrated negligible chronic immune response and stable long-term brain monitoring
at single-neuron level, although, to date, it has been limited to 16 channels. Here, we present a scalable scheme for highly
multiplexed mesh electronics probes to bridge the gap between scalability and flexibility, where 32 to 128 channels per probe
were implemented while the crucial brain-like structure and mechanics were maintained. Combining this mesh design with multisite
injection, we demonstrate stable 128-channel local field potential and single-unit recordings from multiple brain regions
in awake restrained mice over 4 mo. In addition, the newly integrated mesh is used to validate stable chronic recordings in
freely behaving mice. This scalable scheme for mesh electronics together with demonstrated long-term stability represent important
progress toward the realization of ideal implantable electrical probes allowing for mapping and tracking single-neuron level
circuit changes associated with learning, aging, and neurodegenerative diseases.
Co-reporter:Tian-Ming Fu;Guosong Hong;Robert D. Viveros;Tao Zhou
PNAS 2017 114 (47 ) pp:E10046-E10055
Publication Date(Web):2017-11-21
DOI:10.1073/pnas.1717695114
Implantable electrical probes have led to advances in neuroscience, brain−machine interfaces, and treatment of neurological
diseases, yet they remain limited in several key aspects. Ideally, an electrical probe should be capable of recording from
large numbers of neurons across multiple local circuits and, importantly, allow stable tracking of the evolution of these
neurons over the entire course of study. Silicon probes based on microfabrication can yield large-scale, high-density recording
but face challenges of chronic gliosis and instability due to mechanical and structural mismatch with the brain. Ultraflexible
mesh electronics, on the other hand, have demonstrated negligible chronic immune response and stable long-term brain monitoring
at single-neuron level, although, to date, it has been limited to 16 channels. Here, we present a scalable scheme for highly
multiplexed mesh electronics probes to bridge the gap between scalability and flexibility, where 32 to 128 channels per probe
were implemented while the crucial brain-like structure and mechanics were maintained. Combining this mesh design with multisite
injection, we demonstrate stable 128-channel local field potential and single-unit recordings from multiple brain regions
in awake restrained mice over 4 mo. In addition, the newly integrated mesh is used to validate stable chronic recordings in
freely behaving mice. This scalable scheme for mesh electronics together with demonstrated long-term stability represent important
progress toward the realization of ideal implantable electrical probes allowing for mapping and tracking single-neuron level
circuit changes associated with learning, aging, and neurodegenerative diseases.
Co-reporter:Tian-Ming Fu;Guosong Hong;Robert D. Viveros;Tao Zhou
PNAS 2017 114 (47 ) pp:E10046-E10055
Publication Date(Web):2017-11-21
DOI:10.1073/pnas.1717695114
Implantable electrical probes have led to advances in neuroscience, brain−machine interfaces, and treatment of neurological
diseases, yet they remain limited in several key aspects. Ideally, an electrical probe should be capable of recording from
large numbers of neurons across multiple local circuits and, importantly, allow stable tracking of the evolution of these
neurons over the entire course of study. Silicon probes based on microfabrication can yield large-scale, high-density recording
but face challenges of chronic gliosis and instability due to mechanical and structural mismatch with the brain. Ultraflexible
mesh electronics, on the other hand, have demonstrated negligible chronic immune response and stable long-term brain monitoring
at single-neuron level, although, to date, it has been limited to 16 channels. Here, we present a scalable scheme for highly
multiplexed mesh electronics probes to bridge the gap between scalability and flexibility, where 32 to 128 channels per probe
were implemented while the crucial brain-like structure and mechanics were maintained. Combining this mesh design with multisite
injection, we demonstrate stable 128-channel local field potential and single-unit recordings from multiple brain regions
in awake restrained mice over 4 mo. In addition, the newly integrated mesh is used to validate stable chronic recordings in
freely behaving mice. This scalable scheme for mesh electronics together with demonstrated long-term stability represent important
progress toward the realization of ideal implantable electrical probes allowing for mapping and tracking single-neuron level
circuit changes associated with learning, aging, and neurodegenerative diseases.
Co-reporter:Anqi Zhang and Charles M. Lieber
Chemical Reviews 2016 Volume 116(Issue 1) pp:215
Publication Date(Web):December 21, 2015
DOI:10.1021/acs.chemrev.5b00608
Nano-bioelectronics represents a rapidly expanding interdisciplinary field that combines nanomaterials with biology and electronics and, in so doing, offers the potential to overcome existing challenges in bioelectronics. In particular, shrinking electronic transducer dimensions to the nanoscale and making their properties appear more biological can yield significant improvements in the sensitivity and biocompatibility and thereby open up opportunities in fundamental biology and healthcare. This review emphasizes recent advances in nano-bioelectronics enabled with semiconductor nanostructures, including silicon nanowires, carbon nanotubes, and graphene. First, the synthesis and electrical properties of these nanomaterials are discussed in the context of bioelectronics. Second, affinity-based nano-bioelectronic sensors for highly sensitive analysis of biomolecules are reviewed. In these studies, semiconductor nanostructures as transistor-based biosensors are discussed from fundamental device behavior through sensing applications and future challenges. Third, the complex interface between nanoelectronics and living biological systems, from single cells to live animals, is reviewed. This discussion focuses on representative advances in electrophysiology enabled using semiconductor nanostructures and their nanoelectronic devices for cellular measurements through emerging work where arrays of nanoelectronic devices are incorporated within three-dimensional cell networks that define synthetic and natural tissues. Last, some challenges and exciting future opportunities are discussed.
Co-reporter:You-Shin No, Ruixuan Gao, Max N. Mankin, Robert W. Day, Hong-Gyu Park, and Charles M. Lieber
Nano Letters 2016 Volume 16(Issue 7) pp:4713-4719
Publication Date(Web):June 23, 2016
DOI:10.1021/acs.nanolett.6b02236
Semiconductor nanowires and other one-dimensional materials are attractive for highly sensitive and spatially confined electrical and optical signal detection in biological and physical systems, although it has been difficult to localize active electronic or optoelectronic device function at one end of such one-dimensional structures. Here we report a new nanowire structure in which the material and dopant are modulated specifically at only one end of nanowires to encode an active two-terminal device element. We present a general bottom-up synthetic scheme for these tip-modulated nanowires and illustrate this with the synthesis of nanoscale p–n junctions. Electron microscopy imaging verifies the designed p-Si nanowire core with SiO2 insulating inner shell and n-Si outer shell with clean p-Si/n-Si tip junction. Electrical transport measurements with independent contacts to the p-Si core and n-Si shell exhibited a current rectification behavior through the tip and no detectable current through the SiO2 shell. Electrical measurements also exhibited an n-type response in conductance versus water-gate voltage with pulsed gate experiments yielding a temporal resolution of at least 0.1 ms and ∼90% device sensitivity localized to within 0.5 μm from the nanowire p–n tip. In addition, photocurrent experiments showed an open-circuit voltage of 0.75 V at illumination power of ∼28.1 μW, exhibited linear dependence of photocurrent with respect to incident illumination power with an estimated responsivity up to ∼0.22 A/W, and revealed localized photocurrent generation at the nanowire tip. The tip-modulated concept was further extended to a top-down/bottom-up hybrid approach that enabled large-scale production of vertical tip-modulated nanowires with a final synthetic yield of >75% with >4300 nanowires. Vertical tip-modulated nanowires were fabricated into >50 individually addressable nanowire device arrays showing diode-like current–voltage characteristics. These tip-modulated nanowire devices provide substantial opportunity in areas ranging from biological and chemical sensing to optoelectronic signal and nanoscale photodetection.
Co-reporter:Robert W. Day, Max N. Mankin, and Charles M. Lieber
Nano Letters 2016 Volume 16(Issue 4) pp:2830-2836
Publication Date(Web):March 1, 2016
DOI:10.1021/acs.nanolett.6b00629
One-dimensional (1D) structures offer unique opportunities for materials synthesis since crystal phases and morphologies that are difficult or impossible to achieve in macroscopic crystals can be synthesized as 1D nanowires (NWs). Recently, we demonstrated one such phenomenon unique to growth on a 1D substrate, termed Plateau–Rayleigh (P-R) crystal growth, where periodic shells develop along a NW core to form diameter-modulated NW homostructures with tunable morphologies. Here we report a novel extension of the P-R crystal growth concept with the synthesis of heterostructures in which Ge (Si) is deposited on Si (Ge) 1D cores to generate complex NW morphologies in 1, 2, or 3D. Depositing Ge on 50 nm Si cores with a constant GeH4 pressure yields a single set of periodic shells, while sequential variation of GeH4 pressure can yield multimodulated 1D NWs with two distinct sets of shell periodicities. P-R crystal growth on 30 nm cores also produces 2D loop structures, where Ge (Si) shells lie primarily on the outside (inside) of a highly curved Si (Ge) core. Systematic investigation of shell morphology as a function of growth time indicates that Ge shells grow in length along positive curvature Si cores faster than along straight Si cores by an order of magnitude. Short Ge deposition times reveal that shells develop on opposite sides of 50 and 100 nm Si cores to form straight 1D morphologies but that shells develop on the same side of 20 nm cores to produce 2D loop and 3D spring structures. These results suggest that strain mediates the formation of 2 and 3D morphologies by altering the NW’s surface chemistry and that surface diffusion of heteroatoms on flexible freestanding 1D substrates can facilitate this strain-mediated mechanism.
Co-reporter:Jae-Hyun Lee, Anqi Zhang, Siheng Sean You, and Charles M. Lieber
Nano Letters 2016 Volume 16(Issue 2) pp:1509-1513
Publication Date(Web):January 8, 2016
DOI:10.1021/acs.nanolett.6b00020
Semiconductor nanowire (NW) devices that can address intracellular electrophysiological events with high sensitivity and spatial resolution are emerging as key tools in nanobioelectronics. Intracellular delivery of NWs without compromising cellular integrity and metabolic activity has, however, proven difficult without external mechanical forces or electrical pulses. Here, we introduce a biomimetic approach in which a cell penetrating peptide, the trans-activating transcriptional activator (TAT) from human immunodeficiency virus 1, is linked to the surface of Si NWs to facilitate spontaneous internalization of NWs into primary neuronal cells. Confocal microscopy imaging studies at fixed time points demonstrate that TAT-conjugated NWs (TAT-NWs) are fully internalized into mouse hippocampal neurons, and quantitative image analyses reveal an ca. 15% internalization efficiency. In addition, live cell dynamic imaging of NW internalization shows that NW penetration begins within 10–20 min after binding to the membrane and that NWs become fully internalized within 30–40 min. The generality of cell penetrating peptide modification method is further demonstrated by internalization of TAT-NWs into primary dorsal root ganglion (DRG) neurons.
Co-reporter:Yunlong Zhao, Jun Yao, Lin Xu, Max N. Mankin, Yinbo Zhu, Hengan Wu, Liqiang Mai, Qingjie Zhang, and Charles M. Lieber
Nano Letters 2016 Volume 16(Issue 4) pp:2644-2650
Publication Date(Web):March 21, 2016
DOI:10.1021/acs.nanolett.6b00292
Large-scale, deterministic assembly of nanowires and nanotubes with rationally controlled geometries could expand the potential applications of one-dimensional nanomaterials in bottom-up integrated nanodevice arrays and circuits. Control of the positions of straight nanowires and nanotubes has been achieved using several assembly methods, although simultaneous control of position and geometry has not been realized. Here, we demonstrate a new concept combining simultaneous assembly and guided shaping to achieve large-scale, high-precision shape controlled deterministic assembly of nanowires. We lithographically pattern U-shaped trenches and then shear transfer nanowires to the patterned substrate wafers, where the trenches serve to define the positions and shapes of transferred nanowires. Studies using semicircular trenches defined by electron-beam lithography yielded U-shaped nanowires with radii of curvature defined by inner surface of the trenches. Wafer-scale deterministic assembly produced U-shaped nanowires for >430 000 sites with a yield of ∼90%. In addition, mechanistic studies and simulations demonstrate that shaping results in primarily elastic deformation of the nanowires and show clearly the diameter-dependent limits achievable for accessible forces. Last, this approach was used to assemble U-shaped three-dimensional nanowire field-effect transistor bioprobe arrays containing 200 individually addressable nanodevices. By combining the strengths of wafer-scale top-down fabrication with diverse and tunable properties of one-dimensional building blocks in novel structural configurations, shape-controlled deterministic nanowire assembly is expected to enable new applications in many areas including nanobioelectronics and nanophotonics.
Co-reporter:Ning Gao;Teng Gao;Xiao Yang;Wei Zhou;Xiaochuan Dai;Anqi Zhang
PNAS 2016 Volume 113 (Issue 51 ) pp:14633-14638
Publication Date(Web):2016-12-20
DOI:10.1073/pnas.1625010114
Nanomaterial-based field-effect transistor (FET) sensors are capable of label-free real-time chemical and biological detection
with high sensitivity and spatial resolution, although direct measurements in high–ionic-strength physiological solutions
remain challenging due to the Debye screening effect. Recently, we demonstrated a general strategy to overcome this challenge
by incorporating a biomolecule-permeable polymer layer on the surface of silicon nanowire FET sensors. The permeable polymer
layer can increase the effective screening length immediately adjacent to the device surface and thereby enable real-time
detection of biomolecules in high–ionic-strength solutions. Here, we describe studies demonstrating both the generality of
this concept and application to specific protein detection using graphene FET sensors. Concentration-dependent measurements
made with polyethylene glycol (PEG)-modified graphene devices exhibited real-time reversible detection of prostate specific
antigen (PSA) from 1 to 1,000 nM in 100 mM phosphate buffer. In addition, comodification of graphene devices with PEG and
DNA aptamers yielded specific irreversible binding and detection of PSA in pH 7.4 1x PBS solutions, whereas control experiments
with proteins that do not bind to the aptamer showed smaller reversible signals. In addition, the active aptamer receptor
of the modified graphene devices could be regenerated to yield multiuse selective PSA sensing under physiological conditions.
The current work presents an important concept toward the application of nanomaterial-based FET sensors for biochemical sensing
in physiological environments and thus could lead to powerful tools for basic research and healthcare.
Co-reporter:Guosong Hong, Tian-Ming Fu, Tao Zhou, Thomas G. Schuhmann, Jinlin Huang, and Charles M. Lieber
Nano Letters 2015 Volume 15(Issue 10) pp:6979-6984
Publication Date(Web):August 28, 2015
DOI:10.1021/acs.nanolett.5b02987
Syringe-injectable mesh electronics with tissue-like mechanical properties and open macroporous structures is an emerging powerful paradigm for mapping and modulating brain activity. Indeed, the ultraflexible macroporous structure has exhibited unprecedented minimal/noninvasiveness and the promotion of attractive interactions with neurons in chronic studies. These same structural features also pose new challenges and opportunities for precise targeted delivery in specific brain regions and quantitative input/output (I/O) connectivity needed for reliable electrical measurements. Here, we describe new results that address in a flexible manner both of these points. First, we have developed a controlled injection approach that maintains the extended mesh structure during the “blind” injection process, while also achieving targeted delivery with ca. 20 μm spatial precision. Optical and microcomputed tomography results from injections into tissue-like hydrogel, ex vivo brain tissue, and in vivo brains validate our basic approach and demonstrate its generality. Second, we present a general strategy to achieve up to 100% multichannel I/O connectivity using an automated conductive ink printing methodology to connect the mesh electronics and a flexible flat cable, which serves as the standard “plug-in” interface to measurement electronics. Studies of resistance versus printed line width were used to identify optimal conditions, and moreover, frequency-dependent noise measurements show that the flexible printing process yields values comparable to commercial flip-chip bonding technology. Our results address two key challenges faced by syringe-injectable electronics and thereby pave the way for facile in vivo applications of injectable mesh electronics as a general and powerful tool for long-term mapping and modulation of brain activity in fundamental neuroscience through therapeutic biomedical studies.
Co-reporter:Ning Gao, Wei Zhou, Xiaocheng Jiang, Guosong Hong, Tian-Ming Fu, and Charles M. Lieber
Nano Letters 2015 Volume 15(Issue 3) pp:2143-2148
Publication Date(Web):February 9, 2015
DOI:10.1021/acs.nanolett.5b00133
Transistor-based nanoelectronic sensors are capable of label-free real-time chemical and biological detection with high sensitivity and spatial resolution, although the short Debye screening length in high ionic strength solutions has made difficult applications relevant to physiological conditions. Here, we describe a new and general strategy to overcome this challenge for field-effect transistor (FET) sensors that involves incorporating a porous and biomolecule permeable polymer layer on the FET sensor. This polymer layer increases the effective screening length in the region immediately adjacent to the device surface and thereby enables detection of biomolecules in high ionic strength solutions in real-time. Studies of silicon nanowire field-effect transistors with additional polyethylene glycol (PEG) modification show that prostate specific antigen (PSA) can be readily detected in solutions with phosphate buffer (PB) concentrations as high as 150 mM, while similar devices without PEG modification only exhibit detectable signals for concentrations ≤10 mM. Concentration-dependent measurements exhibited real-time detection of PSA with a sensitivity of at least 10 nM in 100 mM PB with linear response up to the highest (1000 nM) PSA concentrations tested. The current work represents an important step toward general application of transistor-based nanoelectronic detectors for biochemical sensing in physiological environments and is expected to open up exciting opportunities for in vitro and in vivo biological sensing relevant to basic biology research through medicine.
Co-reporter:Max N. Mankin, Robert W. Day, Ruixuan Gao, You-Shin No, Sun-Kyung Kim, Arthur A. McClelland, David C. Bell, Hong-Gyu Park, and Charles M. Lieber
Nano Letters 2015 Volume 15(Issue 7) pp:4776-4782
Publication Date(Web):June 9, 2015
DOI:10.1021/acs.nanolett.5b01721
Integration of compound semiconductors with silicon (Si) has been a long-standing goal for the semiconductor industry, as direct band gap compound semiconductors offer, for example, attractive photonic properties not possible with Si devices. However, mismatches in lattice constant, thermal expansion coefficient, and polarity between Si and compound semiconductors render growth of epitaxial heterostructures challenging. Nanowires (NWs) are a promising platform for the integration of Si and compound semiconductors since their limited surface area can alleviate such material mismatch issues. Here, we demonstrate facet-selective growth of cadmium sulfide (CdS) on Si NWs. Aberration-corrected transmission electron microscopy analysis shows that crystalline CdS is grown epitaxially on the {111} and {110} surface facets of the Si NWs but that the Si{113} facets remain bare. Further analysis of CdS on Si NWs grown at higher deposition rates to yield a conformal shell reveals a thin oxide layer on the Si{113} facet. This observation and control experiments suggest that facet-selective growth is enabled by the formation of an oxide, which prevents subsequent shell growth on the Si{113} NW facets. Further studies of facet-selective epitaxial growth of CdS shells on micro-to-mesoscale wires, which allows tuning of the lateral width of the compound semiconductor layer without lithographic patterning, and InP shell growth on Si NWs demonstrate the generality of our growth technique. In addition, photoluminescence imaging and spectroscopy show that the epitaxial shells display strong and clean band edge emission, confirming their high photonic quality, and thus suggesting that facet-selective epitaxy on NW substrates represents a promising route to integration of compound semiconductors on Si.
Co-reporter:Thomas J. Kempa; D. Kwabena Bediako; Evan C. Jones; Charles M. Lieber;Daniel G. Nocera
Journal of the American Chemical Society 2015 Volume 137(Issue 11) pp:3739-3742
Publication Date(Web):March 5, 2015
DOI:10.1021/ja5118717
The development of high-throughput and scalable techniques for patterning inorganic structures is useful for the improved function and efficiency of photonic and energy conversion devices. Here we demonstrate a facile and rapid electrochemical method for patterning periodic metallic and nonmetallic submicron structures over large areas. Si substrates have been patterned with arrays of periodically spaced lines, rings, squares, and terraces of main-group and transition-metal oxides. In addition to planar substrates, three-dimensional surfaces and their vertical sidewalls have been patterned. The features are 20(±1) nm high and 360(±15) nm wide, and their period is finely tunable in situ from 500 nm to 7 μm. These features exhibit <3% variation in period and are rapidly patterned in <2 min. We demonstrate the versatility of the technique by rapidly patterning an efficient water splitting catalyst, Co phosphate oxide (CoPi), and show that the integrated materials system performs water splitting with complete Faradaic efficiency. More generally, the ability to pattern submicron structures over large areas in a facile, reliable, and timely manner may be useful for the fabrication of devices for energy, meta-material, and sensing applications.
Co-reporter:Xiaojie Duan
Nano Research 2015 Volume 8( Issue 1) pp:1-22
Publication Date(Web):2015 January
DOI:10.1007/s12274-014-0692-8
Co-reporter:Wei Zhou, Xiaochuan Dai, Tian-Ming Fu, Chong Xie, Jia Liu, and Charles M. Lieber
Nano Letters 2014 Volume 14(Issue 3) pp:1614-1619
Publication Date(Web):January 30, 2014
DOI:10.1021/nl500070h
Nanowire nanoelectronic devices have been exploited as highly sensitive subcellular resolution detectors for recording extracellular and intracellular signals from cells, as well as from natural and engineered/cyborg tissues, and in this capacity open many opportunities for fundamental biological research and biomedical applications. Here we demonstrate the capability to take full advantage of the attractive capabilities of nanowire nanoelectronic devices for long term physiological studies by passivating the nanowire elements with ultrathin metal oxide shells. Studies of Si and Si/aluminum oxide (Al2O3) core/shell nanowires in physiological solutions at 37 °C demonstrate long-term stability extending for at least 100 days in samples coated with 10 nm thick Al2O3 shells. In addition, investigations of nanowires configured as field-effect transistors (FETs) demonstrate that the Si/Al2O3 core/shell nanowire FETs exhibit good device performance for at least 4 months in physiological model solutions at 37 °C. The generality of this approach was also tested with in studies of Ge/Si and InAs nanowires, where Ge/Si/Al2O3 and InAs/Al2O3 core/shell materials exhibited stability for at least 100 days in physiological model solutions at 37 °C. In addition, investigations of hafnium oxide-Al2O3 nanolaminated shells indicate the potential to extend nanowire stability well beyond 1 year time scale in vivo. These studies demonstrate that straightforward core/shell nanowire nanoelectronic devices can exhibit the long term stability needed for a range of chronic in vivo studies in animals as well as powerful biomedical implants that could improve monitoring and treatment of disease.
Co-reporter:Wooyoung Shim, Jun Yao, and Charles M. Lieber
Nano Letters 2014 Volume 14(Issue 9) pp:5430-5436
Publication Date(Web):August 18, 2014
DOI:10.1021/nl502654f
Programmable logic arrays (PLA) constitute a promising architecture for developing increasingly complex and functional circuits through nanocomputers from nanoscale building blocks. Here we report a novel one-dimensional PLA element that incorporates resistive switch gate structures on a semiconductor nanowire and show that multiple elements can be integrated to realize functional PLAs. In our PLA element, the gate coupling to the nanowire transistor can be modulated by the memory state of the resistive switch to yield programmable active (transistor) or inactive (resistor) states within a well-defined logic window. Multiple PLA nanowire elements were integrated and programmed to yield a working 2-to-4 demultiplexer with long-term retention. The well-defined, controllable logic window and long-term retention of our new one-dimensional PLA element provide a promising route for building increasingly complex circuits with nanoscale building blocks.
Co-reporter:Xiaocheng Jiang, Jinsong Hu, Alexander M. Lieber, Charles S. Jackan, Justin C. Biffinger, Lisa A. Fitzgerald, Bradley R. Ringeisen, and Charles M. Lieber
Nano Letters 2014 Volume 14(Issue 11) pp:6737-6742
Publication Date(Web):October 13, 2014
DOI:10.1021/nl503668q
Microbial fuel cells (MFCs) have been the focus of substantial research interest due to their potential for long-term, renewable electrical power generation via the metabolism of a broad spectrum of organic substrates, although the low power densities have limited their applications to date. Here, we demonstrate the potential to improve the power extraction by exploiting biogenic inorganic nanoparticles to facilitate extracellular electron transfer in MFCs. Simultaneous short-circuit current recording and optical imaging on a nanotechnology-enabled platform showed substantial current increase from Shewanella PV-4 after the formation of cell/iron sulfide nanoparticle aggregates. Detailed characterization of the structure and composition of the cell/nanoparticle interface revealed crystalline iron sulfide nanoparticles in intimate contact with and uniformly coating the cell membrane. In addition, studies designed to address the fundamental mechanisms of charge transport in this hybrid system showed that charge transport only occurred in the presence of live Shewanella, and moreover demonstrated that the enhanced current output can be attributed to improved electron transfer at cell/electrode interface and through the cellular-networks. Our approach of interconnecting and electrically contacting bacterial cells through biogenic nanoparticles represents a unique and promising direction in MFC research and has the potential to not only advance our fundamental knowledge about electron transfer processes in these biological systems but also overcome a key limitation in MFCs by constructing an electrically connected, three-dimensional cell network from the bottom-up.
Co-reporter:Sun-Kyung Kim, Kyung-Deok Song, Thomas J. Kempa, Robert W. Day, Charles M. Lieber, and Hong-Gyu Park
ACS Nano 2014 Volume 8(Issue 4) pp:3707
Publication Date(Web):March 11, 2014
DOI:10.1021/nn5003776
Recent investigations of semiconductor nanowires have provided strong evidence for enhanced light absorption, which has been attributed to nanowire structures functioning as optical cavities. Precise synthetic control of nanowire parameters including chemical composition and morphology has also led to dramatic modulation of absorption properties. Here we report finite-difference time-domain (FDTD) simulations for silicon (Si) nanowire cavities to elucidate the key factors that determine enhanced light absorption. The FDTD simulations revealed that a crystalline Si nanowire with an embedded 20-nm-thick amorphous Si shell yields 40% enhancement of absorption as compared to a homogeneous crystalline Si nanowire, under air-mass 1.5 global solar spectrum for wavelengths between 280 and 1000 nm. Such a large enhancement in absorption results from localization of several resonant modes within the amorphous Si shell. A nanowire with a rectangular cross section exhibited enhanced absorption at specific wavelengths with respect to a hexagonal nanowire. The pronounced absorption peaks were assigned to resonant modes with a high symmetry that red-shifted with increasing size of the rectangular nanowire. We extended our studies to investigate the optical properties of single- and multilayer arrays of these horizontally oriented nanowire building blocks. The absorption efficiency of a nanowire stack increases with the number of nanowire layers and was found to be greater than that of a bulk structure or even a single nanowire of equivalent thickness. Lastly, we found that a single-layer nanowire array preserves the structured absorption spectrum of a single nanowire and ascribed this result to a diffraction effect of the periodic nanowire array. The results from these provide insight into the design of nanowire optical cavities with tunable and enhanced light absorption and thus, could help enable the development of ultrathin solar cells and other nanoscale optoelectronic devices.Keywords: core−shell nanowire; finite-difference time-domain simulations; nanoelectronic device; periodic structures; solar energy; subwavelength optical cavities
Co-reporter:Charles M. Lieber;Jun Yao;Hao Yan;James C. Ellenbogen;Shamik Das;James F. Klemic
PNAS 2014 Volume 111 (Issue 7 ) pp:2431-2435
Publication Date(Web):2014-02-18
DOI:10.1073/pnas.1323818111
Implementation of complex computer circuits assembled from the bottom up and integrated on the nanometer scale has long been
a goal of electronics research. It requires a design and fabrication strategy that can address individual nanometer-scale
electronic devices, while enabling large-scale assembly of those devices into highly organized, integrated computational circuits.
We describe how such a strategy has led to the design, construction, and demonstration of a nanoelectronic finite-state machine.
The system was fabricated using a design-oriented approach enabled by a deterministic, bottom–up assembly process that does
not require individual nanowire registration. This methodology allowed construction of the nanoelectronic finite-state machine
through modular design using a multitile architecture. Each tile/module consists of two interconnected crossbar nanowire arrays,
with each cross-point consisting of a programmable nanowire transistor node. The nanoelectronic finite-state machine integrates
180 programmable nanowire transistor nodes in three tiles or six total crossbar arrays, and incorporates both sequential and
arithmetic logic, with extensive intertile and intratile communication that exhibits rigorous input/output matching. Our system
realizes the complete 2-bit logic flow and clocked control over state registration that are required for a finite-state machine
or computer. The programmable multitile circuit was also reprogrammed to a functionally distinct 2-bit full adder with 32-set
matched and complete logic output. These steps forward and the ability of our unique design-oriented deterministic methodology
to yield more extensive multitile systems suggest that proposed general-purpose nanocomputers can be realized in the near
future.
Co-reporter:Tian-Ming Fu;Xiaochuan Dai;Zhe Jiang;Ping Xie;Zengguang Cheng;Xiaojie Duan
PNAS 2014 Volume 111 (Issue 4 ) pp:1259-1264
Publication Date(Web):2014-01-28
DOI:10.1073/pnas.1323389111
The miniaturization of bioelectronic intracellular probes with a wide dynamic frequency range can open up opportunities to
study biological structures inaccessible by existing methods in a minimally invasive manner. Here, we report the design, fabrication,
and demonstration of intracellular bioelectronic devices with probe sizes less than 10 nm. The devices are based on a nanowire–nanotube
heterostructure in which a nanowire field-effect transistor detector is synthetically integrated with a nanotube cellular
probe. Sub-10-nm nanotube probes were realized by a two-step selective etching approach that reduces the diameter of the nanotube
free-end while maintaining a larger diameter at the nanowire detector necessary for mechanical strength and electrical sensitivity.
Quasi-static water-gate measurements demonstrated selective device response to solution inside the nanotube, and pulsed measurements
together with numerical simulations confirmed the capability to record fast electrophysiological signals. Systematic studies
of the probe bandwidth in different ionic concentration solutions revealed the underlying mechanism governing the time response.
In addition, the bandwidth effect of phospholipid coatings, which are important for intracellular recording, was investigated
and modeled. The robustness of these sub-10-nm bioelectronics probes for intracellular interrogation was verified by optical
imaging and recording the transmembrane resting potential of HL-1 cells. These ultrasmall bioelectronic probes enable direct
detection of cellular electrical activity with highest spatial resolution achieved to date, and with further integration into
larger chip arrays could provide a unique platform for ultra-high-resolution mapping of activity in neural networks and other
systems.
Co-reporter:Thomas J. Kempa, Robert W. Day, Sun-Kyung Kim, Hong-Gyu Park and Charles M. Lieber
Energy & Environmental Science 2013 vol. 6(Issue 3) pp:719-733
Publication Date(Web):16 Jan 2013
DOI:10.1039/C3EE24182C
Over the past decade extensive studies of single semiconductor nanowire and nanowire array photovoltaic devices have explored the potential of these materials as platforms for a new generation of efficient and cost-effective solar cells. This feature review discusses strategies for implementation of semiconductor nanowires in solar energy applications, including advances in complex nanowire synthesis and characterization, fundamental insights from characterization of devices, utilization and control of the unique optical properties of nanowires, and new strategies for assembly and scaling of nanowires into diverse arrays that serve as a new paradigm for advanced solar cells.
Co-reporter:Thomas J. Kempa ; Sun-Kyung Kim ; Robert W. Day ; Hong-Gyu Park ; Daniel G. Nocera
Journal of the American Chemical Society 2013 Volume 135(Issue 49) pp:18354-18357
Publication Date(Web):November 26, 2013
DOI:10.1021/ja411050r
Enhanced synthetic control of the morphology, crystal structure, and composition of nanostructures can drive advances in nanoscale devices. Axial and radial semiconductor nanowires are examples of nanostructures with one and two structural degrees of freedom, respectively, and their synthetically tuned and modulated properties have led to advances in nanotransistor, nanophotonic, and thermoelectric devices. Similarly, developing methods that allow for synthetic control of greater than two degrees of freedom could enable new opportunities for functional nanostructures. Here we demonstrate the first regioselective nanowire shell synthesis in studies of Ge and Si growth on faceted Si nanowire surfaces. The selectively deposited Ge is crystalline, and its facet position can be synthetically controlled in situ. We use this synthesis to prepare electrically addressable nanocavities into which solution soluble species such as Au nanoparticles can be incorporated. The method furnishes multicomponent nanostructures with unique photonic properties and presents a more sophisticated nanodevice platform for future applications in catalysis and photodetection.
Co-reporter:Chong Xie;Jia Liu;Xiaochuan Dai;Lihua Jin;Wei Zhou
PNAS 2013 Volume 110 (Issue 17 ) pp:6694-6699
Publication Date(Web):2013-04-23
DOI:10.1073/pnas.1305209110
Seamless and minimally invasive integration of 3D electronic circuitry within host materials could enable the development
of materials systems that are self-monitoring and allow for communication with external environments. Here, we report a general
strategy for preparing ordered 3D interconnected and addressable macroporous nanoelectronic networks from ordered 2D nanowire
nanoelectronic precursors, which are fabricated by conventional lithography. The 3D networks have porosities larger than 99%,
contain approximately hundreds of addressable nanowire devices, and have feature sizes from the 10-μm scale (for electrical
and structural interconnections) to the 10-nm scale (for device elements). The macroporous nanoelectronic networks were merged
with organic gels and polymers to form hybrid materials in which the basic physical and chemical properties of the host were
not substantially altered, and electrical measurements further showed a >90% yield of active devices in the hybrid materials.
The positions of the nanowire devices were located within 3D hybrid materials with ∼14-nm resolution through simultaneous
nanowire device photocurrent/confocal microscopy imaging measurements. In addition, we explored functional properties of these
hybrid materials, including (i) mapping time-dependent pH changes throughout a nanowire network/agarose gel sample during external solution pH changes,
and (ii) characterizing the strain field in a hybrid nanoelectronic elastomer structures subject to uniaxial and bending forces.
The seamless incorporation of active nanoelectronic networks within 3D materials reveals a powerful approach to smart materials
in which the capabilities of multifunctional nanoelectronics allow for active monitoring and control of host systems.
Co-reporter:Xiaojie Duan, Tian-Ming Fu, Jia Liu, Charles M. Lieber
Nano Today 2013 Volume 8(Issue 4) pp:351-373
Publication Date(Web):August 2013
DOI:10.1016/j.nantod.2013.05.001
•Novel nanoscale 2D and 3D probes for action potential recording in cultured cells, tissue slices, whole organs, and 3D synthetic nanoelectronic/tissue constructs are reviewed.•The uniqueness enabled by the use of nanometer scale functional elements is highlighted. Exciting future applications of these new probes in biophysical, electrophysiological, and neural activity mapping studies are discussed.Semiconductor nanowires configured as the active channels of field-effect transistors (FETs) have been used as detectors for high-resolution electrical recording from single live cells, cell networks, tissues and organs. Extracellular measurements with substrate supported silicon nanowire (SiNW) FETs, which have projected active areas orders of magnitude smaller than conventional microfabricated multielectrode arrays (MEAs) and planar FETs, recorded action potential and field potential signals with high signal-to-noise ratio and temporal resolution from cultured neurons, cultured cardiomyocytes, acute brain slices and whole animal hearts. Measurements made with modulation-doped nanoscale active channel SiNW FETs demonstrate that signals recorded from cardiomyocytes are highly localized and have improved time resolution compared to larger planar detectors. In addition, several novel three-dimensional (3D) transistor probes, which were realized using advanced nanowire synthesis methods, have been implemented for intracellular recording. These novel probes include (i) flexible 3D kinked nanowire FETs, (ii) branched intracellular nanotube SiNW FETs, and (iii) active silicon nanotube FETs. Following phospholipid modification of the probes to mimic the cell membrane, the kinked nanowire, branched intracellular nanotube and active silicon nanotube FET probes recorded full-amplitude intracellular action potentials from spontaneously firing cardiomyocytes. Moreover, these probes demonstrated the capability of reversible, stable, and long-term intracellular recording, thus indicating the minimal invasiveness of the new nanoscale structures and suggesting biomimetic internalization via the phospholipid modification. Simultaneous, multi-site intracellular recording from both single cells and cell networks were also readily achieved by interfacing independently addressable nanoprobe devices with cells. Finally, electronic and biological systems have been seamlessly merged in 3D for the first time using macroporous nanoelectronic scaffolds that are analogous to synthetic tissue scaffold and the extracellular matrix in tissue. Free-standing 3D nanoelectronic scaffolds were cultured with neurons, cardiomyocytes and smooth muscle cells to yield electronically-innervated synthetic or ‘cyborg’ tissues. Measurements demonstrate that innervated tissues exhibit similar cell viability as with conventional tissue scaffolds, and importantly, demonstrate that the real-time response to drugs and pH changes can be mapped in 3D through the tissues. These results open up a new field of research, wherein nanoelectronics are merged with biological systems in 3D thereby providing broad opportunities, ranging from a nanoelectronic/tissue platform for real-time pharmacological screening in 3D to implantable ‘cyborg’ tissues enabling closed-loop monitoring and treatment of diseases. Furthermore, the capability of high density scale-up of the above extra- and intracellular nanoscopic probes for action potential recording provide important tools for large-scale high spatio-temporal resolution electrical neural activity mapping in both 2D and 3D, which promises to have a profound impact on many research areas, including the mapping of activity within the brain.
Co-reporter:Zhe Jiang, Quan Qing, Ping Xie, Ruixuan Gao, and Charles M. Lieber
Nano Letters 2012 Volume 12(Issue 3) pp:1711-1716
Publication Date(Web):February 6, 2012
DOI:10.1021/nl300256r
Semiconductor nanowires and other semiconducting nanoscale materials configured as field-effect transistors have been studied extensively as biological/chemical (bio/chem) sensors. These nanomaterials have demonstrated high-sensitivity from one- and two-dimensional sensors, although the realization of the ultimate pointlike detector has not been achieved. In this regard, nanoscale p–n diodes are attractive since the device element is naturally localized near the junction, and while nanowire p–n diodes have been widely studied as photovoltaic devices, their applications as bio/chem sensors have not been explored. Here we demonstrate that p–n diode devices can serve as a new and powerful family of highly localized biosensor probes. Designed nanoscale axial p–n junctions were synthetically introduced at the joints of kinked silicon nanowires. Scanning electron microscopy images showed that the kinked nanowire structures were achieved, and electrical transport measurements exhibited rectifying behavior with well-defined turn-on in forward bias as expected for a p–n diode. In addition, scanning gate microscopy demonstrated that the most sensitive region of these nanowires was localized near the kinked region at the p–n junction. High spatial resolution sensing using these p–n diode probes was carried out in aqueous solution using fluorescent charged polystyrene nanobeads. Multiplexed electrical measurements show well-defined single-nanoparticle detection, and experiments with simultaneous confocal imaging correlate directly the motion of the nanobeads with the electrical signals recorded from the p–n devices. In addition, kinked p–n junction nanowires configured as three-dimensional probes demonstrate the capability of intracellular recording of action potentials from electrogenic cells. These p–n junction kinked nanowire devices, which represent a new way of constructing nanoscale probes with highly localized sensing regions, provide substantial opportunity in areas ranging from bio/chem sensing and nanoscale photon detection to three-dimensional recording from within living cells and tissue.
Co-reporter:Tzahi Cohen-Karni, Didier Casanova, James F. Cahoon, Quan Qing, David C. Bell, and Charles M. Lieber
Nano Letters 2012 Volume 12(Issue 5) pp:2639-2644
Publication Date(Web):April 2, 2012
DOI:10.1021/nl3011337
Nanostructures, which have sizes comparable to biological functional units involved in cellular communication, offer the potential for enhanced sensitivity and spatial resolution compared to planar metal and semiconductor structures. Silicon nanowire (SiNW) field-effect transistors (FETs) have been used as a platform for biomolecular sensors, which maintain excellent signal-to-noise ratios while operating on lengths scales that enable efficient extra- and intracellular integration with living cells. Although the NWs are tens of nanometers in diameter, the active region of the NW FET devices typically spans micrometers, limiting both the length and time scales of detection achievable with these nanodevices. Here, we report a new synthetic method that combines gold-nanocluster-catalyzed vapor–liquid–solid (VLS) and vapor–solid–solid (VSS) NW growth modes to produce synthetically encoded NW devices with ultrasharp (<5 nm) n-type highly doped (n++) to lightly doped (n) transitions along the NW growth direction, where n++ regions serve as source/drain (S/D) electrodes and the n-region functions as an active FET channel. Using this method, we synthesized short-channel n++/n/n++ SiNW FET devices with independently controllable diameters and channel lengths. SiNW devices with channel lengths of 50, 80, and 150 nm interfaced with spontaneously beating cardiomyocytes exhibited well-defined extracellular field potential signals with signal-to-noise values of ca. 4 independent of device size. Significantly, these “pointlike” devices yield peak widths of ∼500 μs, which is comparable to the reported time constant for individual sodium ion channels. Multiple FET devices with device separations smaller than 2 μm were also encoded on single SiNWs, thus enabling multiplexed recording from single cells and cell networks with device-to-device time resolution on the order of a few microseconds. These short-channel SiNW FET devices provide a new opportunity to create nanoscale biomolecular sensors that operate on the length and time scales previously inaccessible by other techniques but necessary to investigate fundamental, subcellular biological processes.
Co-reporter:Ruixuan Gao, Steffen Strehle, Bozhi Tian, Tzahi Cohen-Karni, Ping Xie, Xiaojie Duan, Quan Qing, and Charles M. Lieber
Nano Letters 2012 Volume 12(Issue 6) pp:3329-3333
Publication Date(Web):May 14, 2012
DOI:10.1021/nl301623p
Nanowire-based field-effect transistors, including devices with planar and three-dimensional configurations, are being actively explored as detectors for extra- and intracellular recording due to their small size and high sensitivities. Here we report the synthesis, fabrication, and characterization of a new needle-shaped nanoprobe based on an active silicon nanotube transistor, ANTT, that enables high-resolution intracellular recording. In the ANTT probe, the source/drain contacts to the silicon nanotube are fabricated on one end, passivated from external solution, and then time-dependent changes in potential can be recorded from the opposite nanotube end via the solution filling the tube. Measurements of conductance versus water-gate potential in aqueous solution show that the ANTT probe is selectively gated by potential changes within the nanotube, thus demonstrating the basic operating principle of the ANTT device. Studies interfacing the ANTT probe with spontaneously beating cardiomyocytes yielded stable intracellular action potentials similar to those reported by other electrophysiological techniques. In addition, the straightforward fabrication of ANTT devices was exploited to prepare multiple ANTT structures at the end of single probes, which enabled multiplexed recording of intracellular action potentials from single cells and multiplexed arrays of single ANTT device probes. These studies open up unique opportunities for multisite recordings from individual cells through cellular networks.
Co-reporter:Sun-Kyung Kim, Robert W. Day, James F. Cahoon, Thomas J. Kempa, Kyung-Deok Song, Hong-Gyu Park, and Charles M. Lieber
Nano Letters 2012 Volume 12(Issue 9) pp:4971-4976
Publication Date(Web):August 13, 2012
DOI:10.1021/nl302578z
Subwavelength diameter semiconductor nanowires can support optical resonances with anomalously large absorption cross sections, and thus tailoring these resonances to specific frequencies could enable a number of nanophotonic applications. Here, we report the design and synthesis of core/shell p-type/intrinsic/n-type (p/i/n) Si nanowires (NWs) with different sizes and cross-sectional morphologies as well as measurement and simulation of photocurrent spectra from single-NW devices fabricated from these NW building blocks. Approximately hexagonal cross-section p/i/n coaxial NWs of various diameters (170–380 nm) were controllably synthesized by changing the Au catalyst diameter, which determines core diameter, as well as shell deposition time, which determines shell thickness. Measured polarization-resolved photocurrent spectra exhibit well-defined diameter-dependent peaks. The corresponding external quantum efficiency (EQE) spectra calculated from these data show good quantitative agreement with finite-difference time-domain (FDTD) simulations and allow assignment of the observed peaks to Fabry–Perot, whispering-gallery, and complex high-order resonant absorption modes. This comparison revealed a systematic red-shift of equivalent modes as a function of increasing NW diameter and a progressive increase in the number of resonances. In addition, tuning shell synthetic conditions to enable enhanced growth on select facets yielded NWs with approximately rectangular cross sections; analysis of transmission electron microscopy and scanning electron microscopy images demonstrate that growth of the n-type shell at 860 °C in the presence of phosphine leads to enhanced relative Si growth rates on the four {113} facets. Notably, polarization-resolved photocurrent spectra demonstrate that at longer wavelengths the rectangular cross-section NWs have narrow and significantly larger amplitude peaks with respect to similar size hexagonal NWs. A rectangular NW with a diameter of 260 nm yields a dominant mode centered at 570 nm with near-unity EQE in the transverse-electric polarized spectrum. Quantitative comparisons with FDTD simulations demonstrate that these new peaks arise from cavity modes with high symmetry that conform to the cross-sectional morphology of the rectangular NW, resulting in low optical loss of the mode. The ability to modulate absorption with changes in nanoscale morphology by controlled synthesis represents a promising route for developing new photovoltaic and optoelectronic devices.
Co-reporter:Thomas J. Kempa;James F. Cahoon;Sun-Kyung Kim;Robert W. Day;Hong-Gyu Park;David C. Bell
PNAS 2012 Volume 109 (Issue 5 ) pp:
Publication Date(Web):2012-01-31
DOI:10.1073/pnas.1120415109
Silicon nanowires (NWs) could enable low-cost and efficient photovoltaics, though their performance has been limited by nonideal
electrical characteristics and an inability to tune absorption properties. We overcome these limitations through controlled
synthesis of a series of polymorphic core/multishell NWs with highly crystalline, hexagonally-faceted shells, and well-defined
coaxial (p/n) and p/intrinsic/n (p/i/n) diode junctions. Designed 200–300 nm diameter p/i/n NW diodes exhibit ultralow leakage currents of approximately 1 fA, and open-circuit voltages and fill-factors up to 0.5 V
and 73%, respectively, under one-sun illumination. Single-NW wavelength-dependent photocurrent measurements reveal size-tunable
optical resonances, external quantum efficiencies greater than unity, and current densities double those for silicon films
of comparable thickness. In addition, finite-difference-time-domain simulations for the measured NW structures agree quantitatively
with the photocurrent measurements, and demonstrate that the optical resonances are due to Fabry-Perot and whispering-gallery
cavity modes supported in the high-quality faceted nanostructures. Synthetically optimized NW devices achieve current densities
of 17 mA/cm2 and power-conversion efficiencies of 6%. Horizontal integration of multiple NWs demonstrates linear scaling of the absolute
photocurrent with number of NWs, as well as retention of the high open-circuit voltages and short-circuit current densities
measured for single NW devices. Notably, assembly of 2 NW elements into vertical stacks yields short-circuit current densities
of 25 mA/cm2 with a backside reflector, and simulations further show that such stacking represents an attractive approach for further
enhancing performance with projected efficiencies of > 15% for 1.2 μm thick 5 NW stacks.
Co-reporter:Xiaocheng Jiang;Gengfeng Zheng;Bozhi Tian;Hongtao Wang;Liqiang Mai;Jie Xiang;Fang Qian
PNAS 2011 Volume 108 (Issue 30 ) pp:
Publication Date(Web):2011-07-26
DOI:10.1073/pnas.1108584108
Branched nanostructures represent unique, 3D building blocks for the “bottom-up” paradigm of nanoscale science and technology.
Here, we report a rational, multistep approach toward the general synthesis of 3D branched nanowire (NW) heterostructures.
Single-crystalline semiconductor, including groups IV, III–V, and II–VI, and metal branches have been selectively grown on
core or core/shell NW backbones, with the composition, morphology, and doping of core (core/shell) NWs and branch NWs well
controlled during synthesis. Measurements made on the different composition branched NW structures demonstrate encoding of
functional p-type/n-type diodes and light-emitting diodes (LEDs) as well as field effect transistors with device function
localized at the branch/backbone NW junctions. In addition, multibranch/backbone NW structures were synthesized and used to
demonstrate capability to create addressable nanoscale LED arrays, logic circuits, and biological sensors. Our work demonstrates
a previously undescribed level of structural and functional complexity in NW materials, and more generally, highlights the
potential of bottom-up synthesis to yield increasingly complex functional systems in the future.
Co-reporter:Soon-Hong Kwon, Ju-Hyung Kang, Christian Seassal, Sun-Kyung Kim, Philippe Regreny, Yong-Hee Lee, Charles M. Lieber and Hong-Gyu Park
Nano Letters 2010 Volume 10(Issue 9) pp:3679-3683
Publication Date(Web):August 12, 2010
DOI:10.1021/nl1021706
We report the experimental demonstration of an optically pumped silver-nanopan plasmonic laser with a subwavelength mode volume of 0.56(λ/2n)3. The lasing mode is clearly identified as a whispering-gallery plasmonic mode confined at the bottom of the silver nanopan from measurements of the spectrum, mode image, and polarization state, as well as agreement with numerical simulations. In addition, the significant temperature-dependent lasing threshold of the plasmonic mode contrasts and distinguishes them from optical modes. Our demonstration and understanding of these subwavelength plasmonic lasers represent a significant step toward faster, smaller coherent light sources.
Co-reporter:Tzahi Cohen-Karni, Quan Qing, Qiang Li, Ying Fang and Charles M. Lieber
Nano Letters 2010 Volume 10(Issue 3) pp:1098-1102
Publication Date(Web):February 5, 2010
DOI:10.1021/nl1002608
Nanowire field-effect transistors (NW-FETs) have been shown to be powerful building blocks for nanoscale bioelectronic interfaces with cells and tissue due to their excellent sensitivity and their capability to form strongly coupled interfaces with cell membranes. Graphene has also been shown to be an attractive building block for nanoscale electronic devices, although little is known about its interfaces with cells and tissue. Here we report the first studies of graphene field effect transistors (Gra-FETs) as well as combined Gra- and NW-FETs interfaced to electrogenic cells. Gra-FET conductance signals recorded from spontaneously beating embryonic chicken cardiomyocytes yield well-defined extracellular signals with signal-to-noise ratio routinely >4. The conductance signal amplitude was tuned by varying the Gra-FET working region through changes in water gate potential, Vwg. Signals recorded from cardiomyocytes for different Vwg result in constant calibrated extracellular voltage, indicating a robust graphene/cell interface. Significantly, variations in Vwg across the Dirac point demonstrate the expected signal polarity flip, thus allowing, for the first time, both n- and p-type recording to be achieved from the same Gra-FET simply by offsetting Vwg. In addition, comparisons of peak-to-peak recorded signal widths made as a function of Gra-FET device sizes and versus NW-FETs allowed an assessment of relative resolution in extracellular recording. Specifically, peak-to-peak widths increased with the area of Gra-FET devices, indicating an averaged signal from different points across the outer membrane of the beating cells. One-dimensional silicon NW- FETs incorporated side by side with the two-dimensional Gra-FET devices further highlighted limits in both temporal resolution and multiplexed measurements from the same cell for the different types of devices. The distinct and complementary capabilities of Gra- and NW-FETs could open up unique opportunities in the field of bioelectronics in the future.
Co-reporter:Quan Qing;Sumon K. Pal;Bozhi Tian;Xiaojie Duan;Brian P. Timko;Tzahi Cohen-Karni;Venkatesh N. Murthy;
Proceedings of the National Academy of Sciences 2010 107(5) pp:1882-1887
Publication Date(Web):January 19, 2010
DOI:10.1073/pnas.0914737107
Revealing the functional connectivity in natural neuronal networks is central to understanding circuits in the brain. Here,
we show that silicon nanowire field-effect transistor (Si NWFET) arrays fabricated on transparent substrates can be reliably
interfaced to acute brain slices. NWFET arrays were readily designed to record across a wide range of length scales, while
the transparent device chips enabled imaging of individual cell bodies and identification of areas of healthy neurons at both
upper and lower tissue surfaces. Simultaneous NWFET and patch clamp studies enabled unambiguous identification of action potential
signals, with additional features detected at earlier times by the nanodevices. NWFET recording at different positions in
the absence and presence of synaptic and ion-channel blockers enabled assignment of these features to presynaptic firing and
postsynaptic depolarization from regions either close to somata or abundant in dendritic projections. In all cases, the NWFET
signal amplitudes were from 0.3–3 mV. In contrast to conventional multielectrode array measurements, the small active surface
of the NWFET devices, ∼0.06 μm2, provides highly localized multiplexed measurements of neuronal activities with demonstrated sub-millisecond temporal resolution
and, significantly, better than 30 μm spatial resolution. In addition, multiplexed mapping with 2D NWFET arrays revealed spatially
heterogeneous functional connectivity in the olfactory cortex with a resolution surpassing substantially previous electrical
recording techniques. Our demonstration of simultaneous high temporal and spatial resolution recording, as well as mapping
of functional connectivity, suggest that NWFETs can become a powerful platform for studying neural circuits in the brain.
Co-reporter:Bradley R. Ringeisen;Jinsong Hu;Lisa A. Fitzgerald;Justin C. Biffinger;Ping Xie;Xiaocheng Jiang
PNAS 2010 Volume 107 (Issue 39 ) pp:16806-16810
Publication Date(Web):2010-09-28
DOI:10.1073/pnas.1011699107
Microbial fuel cells (MFCs) represent a promising approach for sustainable energy production as they generate electricity
directly from metabolism of organic substrates without the need for catalysts. However, the mechanisms of electron transfer
between microbes and electrodes, which could ultimately limit power extraction, remain controversial. Here we demonstrate
optically transparent nanoelectrodes as a platform to investigate extracellular electron transfer in Shewanella oneidensis MR-1, where an array of nanoholes precludes or single window allows for direct microbe-electrode contacts. Following addition
of cells, short-circuit current measurements showed similar amplitude and temporal response for both electrode configurations,
while in situ optical imaging demonstrates that the measured currents were uncorrelated with the cell number on the electrodes.
High-resolution imaging showed the presence of thin, 4- to 5-nm diameter filaments emanating from cell bodies, although these
filaments do not appear correlated with current generation. Both types of electrodes yielded similar currents at longer times
in dense cell layers and exhibited a rapid drop in current upon removal of diffusible mediators. Reintroduction of the original
cell-free media yielded a rapid increase in current to ∼80% of original level, whereas imaging showed that the positions of
> 70% of cells remained unchanged during solution exchange. Together, these measurements show that electron transfer occurs
predominantly by mediated mechanism in this model system. Last, simultaneous measurements of current and cell positions showed
that cell motility and electron transfer were inversely correlated. The ability to control and image cell/electrode interactions
down to the single-cell level provide a powerful approach for advancing our fundamental understanding of MFCs.
Co-reporter:Bozhi Tian;Tzahi Cohen-Karni;Quan Qing;Xiaojie Duan;Ping Xie
Science 2010 Volume 329(Issue 5993) pp:830-834
Publication Date(Web):13 Aug 2010
DOI:10.1126/science.1192033
Nanoprobes of Cell Potential
Direct electrical measurements of cell potentials usually face design compromises. Microelectrodes probe within the cytosol of cells but have a minimum size (hundreds of nanometers in width) for obtaining useful signals. Nanoscale field effect transistors (FETs) can have an active probe size of only tens of nanometers but generally allow only the outer cell potential to be measured. Tian et al. (p. 830) fabricated nanowires in which kinks could be introduced to create a sharp probe tip pointing away from the fabrication substrate. Coating the tip with a phospholipid bilayer allowed the probe to be inserted through the membranes of beating cardiac cells, where it could be used to follow temporal changes in cell potential.
Co-reporter:Brian P. Timko;Fernando Patolsky
Science 2009 Vol 323(5920) pp:1429
Publication Date(Web):13 Mar 2009
DOI:10.1126/science.1155917
Abstract
Fromherz and Voelker make incorrect assumptions about our experiments that raise serious questions about the validity of their claims. We show that our calibrated signals are consistent with previously published data and a general model with biophysically relevant parameters. Additionally, the wide variation in previously published signal amplitudes suggests caution in applying and drawing conclusions from the models of Fromherz and Voelker.
Co-reporter:Bozhi Tian, Thomas J. Kempa and Charles M. Lieber
Chemical Society Reviews 2009 vol. 38(Issue 1) pp:16-24
Publication Date(Web):06 Nov 2008
DOI:10.1039/B718703N
This tutorial review focuses on recent work addressing the properties and potential of semiconductor nanowires as building blocks for photovoltaic devices based on investigations at the single nanowire level. Two central nanowire motifs involving p-i-n dopant modulation in axial and coaxial geometries serve as platforms for fundamental studies. Research illustrating the synthesis of these structural motifs will be reviewed first, followed by an examination of recent studies of single axial and coaxial p-i-n silicon nanowire solar cells. Finally, challenges and opportunities for improving efficiency enabled by controlled synthesis of more complex nanowire structures will be discussed, as will their potential applications as power sources for emerging nanoelectronic devices.
Co-reporter:Yajie Dong, Bozhi Tian, Thomas J. Kempa and Charles M. Lieber
Nano Letters 2009 Volume 9(Issue 5) pp:2183-2187
Publication Date(Web):April 21, 2009
DOI:10.1021/nl900858v
Coaxial core/shell nanowires represent an important class of nanoscale building blocks with substantial potential for exploring new concepts and materials for solar energy conversion. Here, we report the first experimental realization of coaxial group III−nitride nanowire photovoltaic (PV) devices, n-GaN/i-InxGa1−xN/p-GaN, where variation of indium mole fraction is used to control the active layer band gap and hence light absorption. Current−voltage data reveal clear diode characteristics with ideality factors from 3.9 to 5.6. Electroluminescence measurements demonstrate tunable emission from 556 to 371 nm and thus confirm band gap variations in the InxGa1−xN active layer from 2.25 to 3.34 eV as In composition is varied. Simulated one-sun AM 1.5G illumination yielded open-circuit voltages (Voc) from 1.0 to 2.0 V and short-circuit current densities (Jsc) from 0.39 to 0.059 mA/cm2 as In composition is decreased from 0.27 to 0 and a maximum efficiency of ∼0.19%. The n-GaN/i-InxGa1−xN/p-GaN nanowire devices are highly robust and exhibit enhanced efficiencies for concentrated solar light illuminations as well as single nanowire Jsc values as high as 390 mA/cm2 under intense short-wavelength illumination. The ability to rationally tune the structure and composition of these core/shell III−nitride nanowires will make them a powerful platform for exploring nanoenabled PVs in the future.
Co-reporter:Brian P. Timko, Tzahi Cohen-Karni, Guihua Yu, Quan Qing, Bozhi Tian and Charles M. Lieber
Nano Letters 2009 Volume 9(Issue 2) pp:914-918
Publication Date(Web):January 26, 2009
DOI:10.1021/nl900096z
We show that nanowire field-effect transistor (NWFET) arrays fabricated on both planar and flexible polymeric substrates can be reproducibly interfaced with spontaneously beating embryonic chicken hearts in both planar and bent conformations. Simultaneous recordings from glass microelectrode and NWFET devices show that NWFET conductance variations are synchronized with the beating heart. The conductance change associated with beating can be tuned substantially by device sensitivity, although the voltage-calibrated signals, 4−6 mV, are relatively constant and typically larger than signals recorded by microelectrode arrays. Multiplexed recording from NWFET arrays yielded signal propagation times across the myocardium with high spatial resolution. The transparent and flexible NWFET chips also enable simultaneous electrical recording and optical registration of devices to heart surfaces in three-dimensional conformations not possible with planar microdevices. The capability of simultaneous optical imaging and electrical recording also could be used to register devices to a specific region of the myocardium at the cellular level, and more generally, NWFET arrays fabricated on increasingly flexible plastic and/or biopolymer substrates have the potential to become unique tools for electrical recording from other tissue/organ samples or as powerful implants.
Co-reporter:Tzahi Cohen-Karni;Brian P. Timko;Lucien E. Weiss
PNAS 2009 Volume 106 (Issue 18 ) pp:7309-7313
Publication Date(Web):2009-05-05
DOI:10.1073/pnas.0902752106
Semiconductor nanowires (NWs) have unique electronic properties and sizes comparable with biological structures involved in
cellular communication, thus making them promising nanostructures for establishing active interfaces with biological systems.
We report a flexible approach to interface NW field-effect transistors (NWFETs) with cells and demonstrate this for silicon
NWFET arrays coupled to embryonic chicken cardiomyocytes. Cardiomyocyte cells were cultured on thin, optically transparent
polydimethylsiloxane (PDMS) sheets and then brought into contact with Si-NWFET arrays fabricated on standard substrates. NWFET
conductance signals recorded from cardiomyocytes exhibited excellent signal-to-noise ratios with values routinely >5 and signal
amplitudes that were tuned by varying device sensitivity through changes in water gate–voltage potential, Vg. Signals recorded from cardiomyocytes for Vg from −0.5 to +0.1 V exhibited amplitude variations from 31 to 7 nS whereas the calibrated voltage remained constant, indicating
a robust NWFET/cell interface. In addition, signals recorded as a function of increasing/decreasing displacement of the PDMS/cell
support to the device chip showed a reversible >2× increase in signal amplitude (calibrated voltage) from 31 nS (1.0 mV) to
72 nS (2.3 mV). Studies with the displacement close to but below the point of cell disruption yielded calibrated signal amplitudes
as large as 10.5 ± 0.2 mV. Last, multiplexed recording of signals from NWFET arrays interfaced to cardiomyocyte monolayers
enabled temporal shifts and signal propagation to be determined with good spatial and temporal resolution. Our modular approach
simplifies the process of interfacing cardiomyocytes and other cells to high-performance Si-NWFETs, thus increasing the experimental
versatility of NWFET arrays and enabling device registration at the subcellular level.
Co-reporter:Xiaocheng Jiang;Qihua Xiong;SungWoo Nam;Donhee Ham
PNAS 2009 Volume 106 (Issue 50 ) pp:21035-21038
Publication Date(Web):2009-12-15
DOI:10.1073/pnas.0911713106
Three-dimensional (3D), multi-transistor-layer, integrated circuits represent an important technological pursuit promising
advantages in integration density, operation speed, and power consumption compared with 2D circuits. We report fully functional,
3D integrated complementary metal-oxide-semiconductor (CMOS) circuits based on separate interconnected layers of high-mobility
n-type indium arsenide (n-InAs) and p-type germanium/silicon core/shell (p-Ge/Si) nanowire (NW) field-effect transistors (FETs).
The DC voltage output (Vout) versus input (Vin) response of vertically interconnected CMOS inverters showed sharp switching at close to the ideal value of one-half the
supply voltage and, moreover, exhibited substantial DC gain of ≈45. The gain and the rail-to-rail output switching are consistent
with the large noise margin and minimal static power consumption of CMOS. Vertically interconnected, three-stage CMOS ring
oscillators were also fabricated by using layer-1 InAs NW n-FETs and layer-2 Ge/Si NW p-FETs. Significantly, measurements
of these circuits demonstrated stable, self-sustained oscillations with a maximum frequency of 108 MHz, which represents the
highest-frequency integrated circuit based on chemically synthesized nanoscale materials. These results highlight the flexibility
of bottom-up assembly of distinct nanoscale materials and suggest substantial promise for 3D integrated circuits.
Co-reporter:Ping Xie;Yongjie Hu;Ying Fang;Jinlin Huang
PNAS 2009 Volume 106 (Issue 36 ) pp:15254-15258
Publication Date(Web):2009-09-08
DOI:10.1073/pnas.0906943106
We report studies defining the diameter-dependent location of electrically active dopants in silicon (Si) and germanium (Ge)
nanowires (NWs) prepared by nanocluster catalyzed vapor-liquid-solid (VLS) growth without measurable competing homogeneous
decomposition and surface overcoating. The location of active dopants was assessed from electrical transport measurements
before and after removal of controlled thicknesses of material from NW surfaces by low-temperature chemical oxidation and
etching. These measurements show a well-defined transition from bulk-like to surface doping as the diameter is decreased <22–25
nm for n- and p-type Si NWs, although the surface dopant concentration is also enriched in the larger diameter Si NWs. Similar diameter-dependent
results were also observed for n-type Ge NWs, suggesting that surface dopant segregation may be general for small diameter NWs synthesized by the VLS approach.
Natural surface doping of small diameter semiconductor NWs is distinct from many top-down fabricated NWs, explains enhanced
transport properties of these NWs and could yield robust properties in ultrasmall devices often dominated by random dopant
fluctuations.
Co-reporter:Yongjie Hu, Jie Xiang, Gengchiau Liang, Hao Yan and Charles M. Lieber
Nano Letters 2008 Volume 8(Issue 3) pp:925-930
Publication Date(Web):February 6, 2008
DOI:10.1021/nl073407b
Ge/Si core/shell nanowires (NWs) are attractive and flexible building blocks for nanoelectronics ranging from field-effect transistors (FETs) to low-temperature quantum devices. Here we report the first studies of the size-dependent performance limits of Ge/Si NWFETs in the sub-100 nm channel length regime. Metallic nanoscale electrical contacts were made and used to define sub-100 nm Ge/Si channels by controlled solid-state conversion of Ge/Si NWs to NiSixGey alloys. Electrical transport measurements and modeling studies demonstrate that the nanoscale metallic contacts overcome deleterious short-channel effects present in lithographically defined sub-100 nm channels. Data acquired on 70 and 40 nm channel length Ge/Si NWFETs with a drain−source bias of 0.5 V yield transconductance values of 78 and 91 µS, respectively, and maximum on-currents of 121 and 152 µA. The scaled transconductance and on-current values for a gate and bias voltage window of 0.5 V were 6.2 mS/µm and 2.1 mA/µm, respectively, for the 40 nm device and exceed the best reported values for planar Si and NW p-type FETs. In addition, analysis of the intrinsic switching delay shows that terahertz intrinsic operation speed is possible when channel length is reduced to 70 nm and that an intrinsic delay of 0.5 ps is achievable in our 40 nm device. Comparison of the experimental data with simulations based on a semiclassical, ballistic transport model suggests that these sub-100 nm Ge/Si NWFETs with integrated high-κ gate dielectric operate near the ballistic limit.
Co-reporter:Won Il Park, Gengfeng Zheng, Xiaocheng Jiang, Bozhi Tian and Charles M. Lieber
Nano Letters 2008 Volume 8(Issue 9) pp:3004-3009
Publication Date(Web):August 19, 2008
DOI:10.1021/nl802063q
We report the nanocluster-catalyzed growth of ultralong and highly uniform single-crystalline silicon nanowires (SiNWs) with millimeter-scale lengths and aspect ratios up to approximately 100 000. The average SiNW growth rate using disilane (Si2H6) at 400 °C was 31 μm/min, while the growth rate determined for silane (SiH4) reactant under similar growth conditions was 130 times lower. Transmission electron microscopy studies of millimeter-long SiNWs with diameters of 20−80 nm show that the nanowires grow preferentially along the ⟨110⟩ direction independent of diameter. In addition, ultralong SiNWs were used as building blocks to fabricate one-dimensional arrays of field-effect transistors (FETs) consisting of approximately 100 independent devices per nanowire. Significantly, electrical transport measurements demonstrated that the millimeter-long SiNWs had uniform electrical properties along the entire length of wires, and each device can behave as a reliable FET with an on-state current, threshold voltage, and transconductance values (average ±1 standard deviation) of 1.8 ± 0.3 μA, 6.0 ± 1.1 V, 210 ± 60 nS, respectively. Electronically uniform millimeter-long SiNWs were also functionalized with monoclonal antibody receptors and used to demonstrate multiplexed detection of cancer marker proteins with a single nanowire. The synthesis of structurally and electronically uniform ultralong SiNWs may open up new opportunities for integrated nanoelectronics and could serve as unique building blocks linking integrated structures from the nanometer through millimeter length scales.
Co-reporter:Thomas J. Kempa, Bozhi Tian, Dong Rip Kim, Jinsong Hu, Xiaolin Zheng and Charles M. Lieber
Nano Letters 2008 Volume 8(Issue 10) pp:3456-3460
Publication Date(Web):September 3, 2008
DOI:10.1021/nl8023438
Nanowires represent a promising class of materials for exploring new concepts in solar energy conversion. Here we report the first experimental realization of axial modulation-doped p-i-n and tandem p-i-n+−p+-i-n silicon nanowire (SiNW) photovoltaic elements. Scanning electron microscopy images of selectively etched nanowires demonstrate excellent synthetic control over doping and lengths of distinct regions in the diode structures. Current−voltage (I−V) characteristics reveal clear and reproducible diode characteristics for the p-i-n and p-n SiNW devices. Under simulated one-sun solar conditions (AM 1.5G), optimized p-i-n SiNW devices exhibited an open circuit voltage (Voc) of 0.29 V, a maximum short-circuit current density of 3.5 mA/cm2, and a maximum efficiency of 0.5%. The response of the short-circuit current versus Voc under varying illumination intensities shows that the diode quality factor is improved from n = 1.78 to n = 1.28 by insertion of the i-type SiNW segment. The temperature dependence of Voc scales as −2.97 mV/K and extrapolates to the crystalline Si band gap at 0 K, which is in excellent agreement with bulk properties. Finally, a novel single SiNW tandem solar cell consisting of synthetic integration of two photovoltaic elements with an overall p-i-n+−p+-i-n structure was prepared and shown to exhibit a Voc that is on average 57% larger than that of the single p-i-n device. Fundamental studies of such well-defined nanowire photovoltaics will enable their intrinsic performance limits to be defined.
Co-reporter:Guihua Yu, Xianglong Li, Charles M. Lieber and Anyuan Cao
Journal of Materials Chemistry A 2008 vol. 18(Issue 7) pp:728-734
Publication Date(Web):11 Jan 2008
DOI:10.1039/B713697H
Developing flexible and scalable methods for controlled assembly of nanomaterials remains a critical challenge in nanotechnology. In this article, we review the progress in assembly of nanostructures with a focus on the recently reported method utilizing a bubble expansion process to align one-dimensional nanostructures embedded in blown bubble films. This approach is general and enables efficient assembly of a variety of nanomaterials over large areas on both rigid and flexible substrates, with good control on the orientation and density. The basic blown bubble film process, generality, mechanism, unique characteristics, and potential applications are discussed.
Co-reporter:Bozhi Tian,
Xiaolin Zheng,
Thomas J. Kempa,
Ying Fang,
Nanfang Yu,
Guihua Yu,
Jinlin Huang
&
Charles M. Lieber
Nature 2007 449(7164) pp:885
Publication Date(Web):2007-10-18
DOI:10.1038/nature06181
Solar cells are attractive candidates for clean and renewable power1, 2; with miniaturization, they might also serve as integrated power sources for nanoelectronic systems. The use of nanostructures or nanostructured materials represents a general approach to reduce both cost and size and to improve efficiency in photovoltaics1, 2, 3, 4, 5, 6, 7, 8, 9. Nanoparticles, nanorods and nanowires have been used to improve charge collection efficiency in polymer-blend4 and dye-sensitized solar cells5, 6, to demonstrate carrier multiplication7, and to enable low-temperature processing of photovoltaic devices3, 4, 5, 6. Moreover, recent theoretical studies have indicated that coaxial nanowire structures could improve carrier collection and overall efficiency with respect to single-crystal bulk semiconductors of the same materials8, 9. However, solar cells based on hybrid nanoarchitectures suffer from relatively low efficiencies and poor stabilities1. In addition, previous studies have not yet addressed their use as photovoltaic power elements in nanoelectronics. Here we report the realization of p-type/intrinsic/n-type (p-i-n) coaxial silicon nanowire solar cells. Under one solar equivalent (1-sun) illumination, the p-i-n silicon nanowire elements yield a maximum power output of up to 200 pW per nanowire device and an apparent energy conversion efficiency of up to 3.4 per cent, with stable and improved efficiencies achievable at high-flux illuminations. Furthermore, we show that individual and interconnected silicon nanowire photovoltaic elements can serve as robust power sources to drive functional nanoelectronic sensors and logic gates. These coaxial silicon nanowire photovoltaic elements provide a new nanoscale test bed for studies of photoinduced energy/charge transport and artificial photosynthesis10, and might find general usage as elements for powering ultralow-power electronics11 and diverse nanosystems12, 13.
Co-reporter:Fernando Patolsky;Brian P. Timko;Guihua Yu;Ying Fang;Andrew B. Greytak;Gengfeng Zheng
Science 2006 Vol 313(5790) pp:1100-1104
Publication Date(Web):25 Aug 2006
DOI:10.1126/science.1128640
Abstract
We report electrical properties of hybrid structures consisting of arrays of nanowire field-effect transistors integrated with the individual axons and dendrites of live mammalian neurons, where each nanoscale junction can be used for spatially resolved, highly sensitive detection, stimulation, and/or inhibition of neuronal signal propagation. Arrays of nanowire-neuron junctions enable simultaneous measurement of the rate, amplitude, and shape of signals propagating along individual axons and dendrites. The configuration of nanowire-axon junctions in arrays, as both inputs and outputs, makes possible controlled studies of partial to complete inhibition of signal propagation by both local electrical and chemical stimuli. In addition, nanowire-axon junction arrays were integrated and tested at a level of at least 50 “artificial synapses” per neuron.
Co-reporter:Jie Xiang, Wei Lu, Yongjie Hu, Yue Wu, Hao Yan
and Charles M. Lieber
Nature 2006 441(7092) pp:489
Publication Date(Web):
DOI:10.1038/nature04796
Co-reporter:Chen Yang;Zhaohui Zhong
Science 2005 Vol 310(5752) pp:1304-1307
Publication Date(Web):25 Nov 2005
DOI:10.1126/science.1118798
Abstract
We describe the successful synthesis of modulation-doped silicon nanowires by achieving pure axial elongation without radial overcoating during the growth process. Scanning gate microscopy shows that the key properties of the modulated structures—including the number, size, and period of the differentially doped regions—are defined in a controllable manner during synthesis, and moreover, that feature sizes to less than 50 nanometers are possible. Electronic devices fabricated with designed modulation-doped nanowire structures demonstrate their potential for lithography-independent address decoders and tunable, coupled quantum dots in which changes in electronic properties are encoded by synthesis rather than created by conventional lithography-based techniques.
Co-reporter:Wayne U. Wang;Chuo Chen;Keng-hui Lin;Ying Fang;
Proceedings of the National Academy of Sciences 2005 102(9) pp:3208-3212
Publication Date(Web):February 16, 2005
DOI:10.1073/pnas.0406368102
Development of miniaturized devices that enable rapid and direct analysis of the specific binding of small molecules to proteins
could be of substantial importance to the discovery of and screening for new drug molecules. Here, we report highly sensitive
and label-free direct electrical detection of small-molecule inhibitors of ATP binding to Abl by using silicon nanowire field-effect
transistor devices. Abl, which is a protein tyrosine kinase whose constitutive activity is responsible for chronic myelogenous
leukemia, was covalently linked to the surfaces of silicon nanowires within microfluidic channels to create active electrical
devices. Concentration-dependent binding of ATP and concentration-dependent inhibition of ATP binding by the competitive small-molecule
antagonist STI-571 (Gleevec) were assessed by monitoring the nanowire conductance. In addition, concentration-dependent inhibition
of ATP binding was examined for four additional small molecules, including reported and previously unreported inhibitors.
These studies demonstrate that the silicon nanowire devices can readily and rapidly distinguish the affinities of distinct
small-molecule inhibitors and, thus, could serve as a technology platform for drug discovery.
Co-reporter:Jie Xiang;Brian P. Timko;Yue Wu;Wei Lu
PNAS 2005 Volume 102 (Issue 29 ) pp:10046-10051
Publication Date(Web):2005-07-19
DOI:10.1073/pnas.0504581102
Two-dimensional electron and hole gas systems, enabled through band structure design and epitaxial growth on planar substrates,
have served as key platforms for fundamental condensed matter research and high-performance devices. The analogous development
of one-dimensional (1D) electron or hole gas systems through controlled growth on 1D nanostructure substrates, which could
open up opportunities beyond existing carbon nanotube and nanowire systems, has not been realized. Here, we report the synthesis
and transport studies of a 1D hole gas system based on a free-standing germanium/silicon (Ge/Si) core/shell nanowire heterostructure.
Room temperature electrical transport measurements clearly show hole accumulation in undoped Ge/Si nanowire heterostructures,
in contrast to control experiments on single-component nanowires. Low-temperature studies show well-controlled Coulomb blockade
oscillations when the Si shell serves as a tunnel barrier to the hole gas in the Ge channel. Transparent contacts to the hole
gas also have been reproducibly achieved by thermal annealing. In such devices, we observe conductance quantization at low
temperatures, corresponding to ballistic transport through 1D subbands, where the measured subband energy spacings agree with
calculations for a cylindrical confinement potential. In addition, we observe a “0.7 structure,” which has been attributed
to spontaneous spin polarization, suggesting the universality of this phenomenon in interacting 1D systems. Lastly, the conductance
exhibits little temperature dependence, consistent with our calculation of reduced backscattering in this 1D system, and suggests
that transport is ballistic even at room temperature.
Co-reporter:Fernando Patolsky;Gengfeng Zheng;Oliver Hayden;Melike Lakadamyali;Xiaowei Zhuang
PNAS 2004 Volume 101 (Issue 39 ) pp:14017-14022
Publication Date(Web):2004-09-28
DOI:10.1073/pnas.0406159101
We report direct, real-time electrical detection of single virus particles with high selectivity by using nanowire field effect
transistors. Measurements made with nanowire arrays modified with antibodies for influenza A showed discrete conductance changes
characteristic of binding and unbinding in the presence of influenza A but not paramyxovirus or adenovirus. Simultaneous electrical
and optical measurements using fluorescently labeled influenza A were used to demonstrate conclusively that the conductance
changes correspond to binding/unbinding of single viruses at the surface of nanowire devices. pH-dependent studies further
show that the detection mechanism is caused by a field effect, and that the nanowire devices can be used to determine rapidly
isoelectric points and variations in receptor-virus binding kinetics for different conditions. Lastly, studies of nanowire
devices modified with antibodies specific for either influenza or adenovirus show that multiple viruses can be selectively
detected in parallel. The possibility of large-scale integration of these nanowire devices suggests potential for simultaneous
detection of a large number of distinct viral threats at the single virus level.
Co-reporter:Yue Wu,
Jie Xiang,
Chen Yang,
Wei Lu
and
Charles M. Lieber
Nature 2004 430(6995) pp:61
Publication Date(Web):
DOI:10.1038/nature02674
Co-reporter:Deli Wang
Nature Materials 2003 2(6) pp:
Publication Date(Web):
DOI:10.1038/nmat908
Inorganic colloids now come in many forms — spheres, discs and rods. With the addition of branched tetrapods to this list, the potential for creating materials with interesting mechanical, optical and electrical properties is even greater.
Co-reporter:Zhaohui Zhong;Deli Wang;Yi Cui;Marc W. Bockrath
Science 2003 Vol 302(5649) pp:1377-1379
Publication Date(Web):21 Nov 2003
DOI:10.1126/science.1090899
Abstract
The development of strategies for addressing arrays of nanoscale devices is central to the implementation of integrated nanosystems such as biological sensor arrays and nanocomputers. We report a general approach for addressing based on molecular-level modification of crossed semiconductor nanowire field-effect transistor (cNW-FET) arrays, where selective chemical modification of cross points in the arrays enables NW inputs to turn specific FET array elements on and off. The chemically modified cNW-FET arrays function as decoder circuits, exhibit gain, and allow multiplexing and demultiplexing of information. These results provide a step toward the realization of addressable integrated nanosystems in which signals are restored at the nanoscale.
Co-reporter:Xiangfeng Duan,
Yu Huang,
Ritesh Agarwal
and
Charles M. Lieber
Nature 2003 421(6920) pp:241
Publication Date(Web):
DOI:10.1038/nature01353
Co-reporter:Evan T. Powers ;Sung Ik Yang Dr. ;Jeffery W. Kelly
Angewandte Chemie 2002 Volume 114(Issue 1) pp:
Publication Date(Web):4 JAN 2002
DOI:10.1002/1521-3757(20020104)114:1<135::AID-ANGE135>3.0.CO;2-1
Die Peptidlänge beeinflusst die Form der mit Kraftmikroskopie (AFM) aufgenommenen Grate der Langmuir-Blodgett-Filme aus amphiphilen Peptiden: Wohlgeordnete LB-Filme (links) können aus einem 14-gliedrigen amphiphilen Peptid, weniger geordnete LB-Filme mit einem breiteren Gitter (rechts) aus einem 18-gliedrigen Peptid hergestellt werden. Die gezeigten Bilder mit einer Auflösung von 100×100 nm wurden mit AFM unter Verwendung von Spitzen aus Kohlenstoff-Nanoröhren erhalten.
Co-reporter:Evan T. Powers ;Sung Ik Yang Dr. ;Jeffery W. Kelly
Angewandte Chemie International Edition 2002 Volume 41(Issue 1) pp:
Publication Date(Web):2 JAN 2002
DOI:10.1002/1521-3773(20020104)41:1<127::AID-ANIE127>3.0.CO;2-F
Peptide length affects the size of the ridges observed in the atomic force microscopy (AFM) images of the Langmuir–Blodgett films of amphiphilic peptides: Well-ordered LB films can be prepared from a 14-residue amphiphilic peptide (left), while ordered LB films with a wider lattice (right) are obtained from an 18-residue peptide. The 100 nm×100 nm images pictured were obtained by AFM using carbon nanotube tips.
Co-reporter:Lincoln J. Lauhon;Mark S. Gudiksen;Deli Wang
Nature 2002 420(6911) pp:57-61
Publication Date(Web):2002-11-07
DOI:10.1038/nature01141
Semiconductor heterostructures with modulated composition and/or doping enable passivation of interfaces and the generation of devices with diverse functions1. In this regard, the control of interfaces in nanoscale building blocks with high surface area will be increasingly important in the assembly of electronic and photonic devices2, 3, 4, 5, 6, 7, 8, 9, 10. Core–shell heterostructures formed by the growth of crystalline overlayers on nanocrystals offer enhanced emission efficiency7, important for various applications8, 9, 10. Axial heterostructures have also been formed by a one-dimensional modulation of nanowire composition11, 12, 13 and doping11. However, modulation of the radial composition and doping in nanowire structures has received much less attention than planar1 and nanocrystal7 systems. Here we synthesize silicon and germanium core–shell and multishell nanowire heterostructures using a chemical vapour deposition method applicable to a variety of nanoscale materials14. Our investigations of the growth of boron-doped silicon shells on intrinsic silicon and silicon–silicon oxide core–shell nanowires indicate that homoepitaxy can be achieved at relatively low temperatures on clean silicon. We also demonstrate the possibility of heteroepitaxial growth of crystalline germanium–silicon and silicon–germanium core–shell structures, in which band-offsets drive hole injection into either germanium core or shell regions. Our synthesis of core–multishell structures, including a high-performance coaxially gated field-effect transistor, indicates the general potential of radial heterostructure growth for the development of nanowire-based devices.
Co-reporter:Mark S. Gudiksen,
Lincoln J. Lauhon,
Jianfang Wang,
David C. Smith
and
Charles M. Lieber
Nature 2002 415(6872) pp:617
Publication Date(Web):
DOI:10.1038/415617a
The assembly of semiconductor nanowires and carbon nanotubes into nanoscale devices and circuits could enable diverse applications in nanoelectronics and photonics1. Individual semiconducting nanowires have already been configured as field-effect transistors2, photodetectors3 and bio/chemical sensors4. More sophisticated light-emitting diodes5 (LEDs) and complementary and diode logic6, 7, 8 devices have been realized using both n- and p-type semiconducting nanowires or nanotubes. The n- and p-type materials have been incorporated in these latter devices either by crossing p- and n-type nanowires2, 5, 6, 9 or by lithographically defining distinct p- and n-type regions in nanotubes8, 10, although both strategies limit device complexity. In the planar semiconductor industry, intricate n- and p-type and more generally compositionally modulated (that is, superlattice) structures are used to enable versatile electronic and photonic functions. Here we demonstrate the synthesis of semiconductor nanowire superlattices from group III–V and group IV materials. (The superlattices are created within the nanowires by repeated modulation of the vapour-phase semiconductor reactants during growth of the wires.) Compositionally modulated superlattices consisting of 2 to 21 layers of GaAs and GaP have been prepared. Furthermore, n-Si/p-Si and n-InP/p-InP modulation doped nanowires have been synthesized. Single-nanowire photoluminescence, electrical transport and electroluminescence measurements show the unique photonic and electronic properties of these nanowire superlattices, and suggest potential applications ranging from nano-barcodes to polarized nanoscale LEDs.
Co-reporter:Xiangfeng Duan,
Yu Huang,
Yi Cui,
Jianfang Wang
and
Charles M. Lieber
Nature 2001 409(6816) pp:66
Publication Date(Web):
DOI:10.1038/35051047
Nanowires and nanotubes carry charge and excitons efficiently, and are
therefore potentially ideal building blocks for nanoscale electronics and
optoelectronics1, 2. Carbon nanotubes have already been exploited
in devices such as field-effect3, 4 and single-electron5, 6 transistors, but the practical utility of nanotube components
for building electronic circuits is limited, as it is not yet possible to
selectively grow semiconducting or metallic nanotubes7, 8. Here
we report the assembly of functional nanoscale devices from indium phosphide
nanowires, the electrical properties of which are controlled by selective
doping. Gate-voltage-dependent transport measurements demonstrate that the
nanowires can be predictably synthesized as either n- or p-type. These doped
nanowires function as nanoscale field-effect transistors, and can be assembled
into crossed-wire p–n junctions that exhibit rectifying behaviour. Significantly,
the p–n junctions emit light strongly and are perhaps the smallest light-emitting
diodes that have yet been made. Finally, we show that electric-field-directed
assembly can be used to create highly integrated device arrays from nanowire
building blocks.
Co-reporter:Chin Li Cheung;Jason H. Hafner
PNAS 2000 Volume 97 (Issue 8 ) pp:3809-3813
Publication Date(Web):2000-04-11
DOI:10.1073/pnas.050498597
Carbon nanotubes are potentially ideal atomic force microscopy probes because they can have diameters as small as one nanometer,
have robust mechanical properties, and can be specifically functionalized with chemical and biological probes at the tip ends.
This communication describes methods for the direct growth of carbon nanotube tips by chemical vapor deposition (CVD) using
ethylene and iron catalysts deposited on commercial silicon-cantilever-tip assemblies. Scanning electron microscopy and transmission
electron microscopy measurements demonstrate that multiwalled nanotube and single-walled nanotube tips can be grown by predictable
variations in the CVD growth conditions. Force-displacement measurements made on the tips show that they buckle elastically
and have very small (≤ 100 pN) nonspecific adhesion on mica surfaces in air. Analysis of images recorded on gold nanoparticle
standards shows that these multi- and single-walled carbon nanotube tips have radii of curvature of 3–6 and 2–4 nm, respectively.
Moreover, the nanotube tip radii determined from the nanoparticle images are consistent with those determined directly by
transmission electron microscopy imaging of the nanotube ends. These molecular-scale CVD nanotube probes have been used to
image isolated IgG and GroES proteins at high-resolution.
Co-reporter:Jiangtao Hu,
Min Ouyang,
Peidong Yang
and
Charles M. Lieber
Nature 1999 399(6731) pp:48
Publication Date(Web):
DOI:10.1038/19941
Nanometre-scale electronic structures are of both fundamental and technological interest: they provide a link between molecular and solid state physics, and have the potential to reach far higher device densities than is possible with conventional semiconductor technology1,2. Examples of such structures include quantum dots,which can function as single-electron transistors3,4 (although theirsensitivity to individual stray charges might make them unsuitable for large-scale devices) and semiconducting carbon nanotubes several hundred nanometres in length, which have been used to create a field-effect transistor5. Much smaller devices could be made by joining two nanotubes or nanowires to create, for example, metal–semiconductor junctions, in which the junction area would be about 1 nm2 for single-walled carbon nanotubes. Electrical measurements of nanotube 'mats' have shown the behaviour expected for a metal–semiconductor junction6. However, proposed nanotube junction structures7 have not been explicitly observed, nor have methods been developed to prepare them. Here we report controlled, catalytic growth of metal–semiconductor junctions between carbon nanotubes and silicon nanowires, and show that these junctions exhibit reproducible rectifying behaviour.
Co-reporter:Stanislaus S. Wong,
Ernesto Joselevich,
Adam T. Woolley,
Chin Li Cheung
and
Charles M. Lieber
Nature 1998 394(6688) pp:52
Publication Date(Web):
DOI:10.1038/27873
Carbon nanotubes combine a range of properties that make them well suited for use as probe tips in applications such as atomic force microscopy (AFM)1, 2, 3. Their high aspect ratio, for example, opens up the possibility of probing the deep crevices4 that occur in microelectronic circuits, and the small effective radius of nanotube tips significantly improves the lateral resolution beyond what can be achieved using commercial silicon tips5. Another characteristic feature of nanotubes is their ability to buckle elastically4,6, which makes them very robust while limiting the maximum force that is applied to delicate organic and biological samples. Earlier investigations into the performance of nanotubes as scanning probe microscopy tips have focused on topographical imaging, but a potentially more significant issue is the question of whether nanotubes can be modified to create probes that can sense and manipulate matter at the molecular level7. Here we demonstrate that nanotube tips with the capability of chemical and biological discrimination can be created with acidic functionality and by coupling basic or hydrophobic functionalities or biomolecular probes to the carboxyl groups that are present at the open tip ends. We have used these modified nanotubes as AFM tips to titrate the acid and base groups, to image patterned samples based on molecular interactions, and to measure the binding force between single protein–ligand pairs. As carboxyl groups are readily derivatized by a variety of reactions8, the preparation of a wide range of functionalized nanotube tips should be possible, thus creating molecular probes with potential applications in many areas of chemistry and biology.
Co-reporter:Teri Wang Odom,
Jin-Lin Huang,
Philip Kim
and
Charles M. Lieber
Nature 1998 391(6662) pp:62
Publication Date(Web):
DOI:10.1038/34145
Carbon nanotubes1 are predicted to be metallic or semiconducting depending on their diameter and the helicity of the arrangement of graphitic rings in their walls2, 3, 4, 5. Scanning tunnelling microscopy (STM) offers the potential to probe this prediction, as it can resolve simultaneously both atomic structure and the electronic density of states. Previous STM studies of multi-walled nanotubes6, 7, 8, 9 and single-walled nanotubes (SWNTs)10 have provided indications of differing structures and diameter-dependent electronic properties, but have not revealed any explicit relationship between structure and electronic properties. Here we report STM measurements of the atomic structure and electronic properties of SWNTs. We are able to resolve the hexagonal-ring structure of the walls, and show that the electronic properties do indeed depend on diameter and helicity. We find that the SWNT samples exhibit many different structures, with no one species dominating.
Co-reporter:Peter B. Kruskal, Zhe Jiang, Teng Gao, Charles M. Lieber
Neuron (8 April 2015) Volume 86(Issue 1) pp:21-24
Publication Date(Web):8 April 2015
DOI:10.1016/j.neuron.2015.01.004
The patch clamp is a fundamental tool for neuroscientists, offering insights that have shaped our understanding of the brain. Advances in nanotechnology suggest that the next generation of recording methods is now within reach. We discuss the complexity and future promise of applying nanoscience to neural recording.
Co-reporter:Lin Xu ; Zhe Jiang ; Quan Qing ; Liqiang Mai ; Qingjie Zhang
Nano Letter () pp:
Publication Date(Web):December 30, 2012
DOI:10.1021/nl304435z
Functional kinked nanowires (KNWs) represent a new class of nanowire building blocks, in which functional devices, for example, nanoscale field-effect transistors (nanoFETs), are encoded in geometrically controlled nanowire superstructures during synthesis. The bottom-up control of both structure and function of KNWs enables construction of spatially isolated point-like nanoelectronic probes that are especially useful for monitoring biological systems where finely tuned feature size and structure are highly desired. Here we present three new types of functional KNWs including (1) the zero-degree KNW structures with two parallel heavily doped arms of U-shaped structures with a nanoFET at the tip of the “U”, (2) series multiplexed functional KNW integrating multi-nanoFETs along the arm and at the tips of V-shaped structures, and (3) parallel multiplexed KNWs integrating nanoFETs at the two tips of W-shaped structures. First, U-shaped KNWs were synthesized with separations as small as 650 nm between the parallel arms and used to fabricate three-dimensional nanoFET probes at least 3 times smaller than previous V-shaped designs. In addition, multiple nanoFETs were encoded during synthesis in one of the arms/tip of V-shaped and distinct arms/tips of W-shaped KNWs. These new multiplexed KNW structures were structurally verified by optical and electron microscopy of dopant-selective etched samples and electrically characterized using scanning gate microscopy and transport measurements. The facile design and bottom-up synthesis of these diverse functional KNWs provides a growing toolbox of building blocks for fabricating highly compact and multiplexed three-dimensional nanoprobes for applications in life sciences, including intracellular and deep tissue/cell recordings.
Co-reporter:Guihua Yu, Xianglong Li, Charles M. Lieber and Anyuan Cao
Journal of Materials Chemistry A 2008 - vol. 18(Issue 7) pp:NaN734-734
Publication Date(Web):2008/01/11
DOI:10.1039/B713697H
Developing flexible and scalable methods for controlled assembly of nanomaterials remains a critical challenge in nanotechnology. In this article, we review the progress in assembly of nanostructures with a focus on the recently reported method utilizing a bubble expansion process to align one-dimensional nanostructures embedded in blown bubble films. This approach is general and enables efficient assembly of a variety of nanomaterials over large areas on both rigid and flexible substrates, with good control on the orientation and density. The basic blown bubble film process, generality, mechanism, unique characteristics, and potential applications are discussed.
Co-reporter:Bozhi Tian, Thomas J. Kempa and Charles M. Lieber
Chemical Society Reviews 2009 - vol. 38(Issue 1) pp:NaN24-24
Publication Date(Web):2008/11/06
DOI:10.1039/B718703N
This tutorial review focuses on recent work addressing the properties and potential of semiconductor nanowires as building blocks for photovoltaic devices based on investigations at the single nanowire level. Two central nanowire motifs involving p-i-n dopant modulation in axial and coaxial geometries serve as platforms for fundamental studies. Research illustrating the synthesis of these structural motifs will be reviewed first, followed by an examination of recent studies of single axial and coaxial p-i-n silicon nanowire solar cells. Finally, challenges and opportunities for improving efficiency enabled by controlled synthesis of more complex nanowire structures will be discussed, as will their potential applications as power sources for emerging nanoelectronic devices.
