Shuit-Tong Lee

Self-healing is the way by which nature repairs damage and prolongs the life of bio entities. A variety of practical applications require self-healing materials in general and self-healing polymers in particular. Different (complex) methods provide the rebonding of broken bonds, suppressing crack, or local damage propagation. Here, a simple, versatile, and cost-effective methodology is reported for initiating healing in bulk polymers and self-healing and anticorrosion properties in polymer coatings: introduction of carbon dots (CDs), 5 nm sized carbon nanocrystallites, into the polymer matrix forming a composite. The CDs are blended into polymethacrylate, polyurethane, and other common polymers. The healing/self-healing process is initiated by interfacial bonding (covalent, hydrogen, and van der Waals bonding) between the CDs and the polymer matrix and can be optimized by modifying the functional groups which terminate the CDs. The healing properties of the bulk polymer–CD composites are evaluated by comparing the tensile strength of pristine (bulk and coatings) composites to those of fractured composites that are healed and by following the self-healing of scratches intentionally introduced to polymer–CD composite coatings. The composite coatings not only possess self-healing properties but also have superior anticorrosion properties compared to those of the pure polymer coatings.

C3N—A 2D Crystalline, Hole-Free, Tunable-Narrow-Bandgap Semiconductor with Ferromagnetic Properties

Co-reporter:Siwei Yang;Wei Li;Caichao Ye;Gang Wang;He Tian;Chong Zhu;Peng He;Guqiao Ding;Xiaoming Xie;Yang Liu;Yeshayahu Lifshitz;Zhenhui Kang;Mianheng Jiang

Advanced Materials 2017 Volume 29(Issue 16) pp:

Publication Date(Web):2017/04/01

DOI:10.1002/adma.201605625

Graphene has initiated intensive research efforts on 2D crystalline materials due to its extraordinary set of properties and the resulting host of possible applications. Here the authors report on the controllable large-scale synthesis of C3N, a 2D crystalline, hole-free extension of graphene, its structural characterization, and some of its unique properties. C3N is fabricated by polymerization of 2,3-diaminophenazine. It consists of a 2D honeycomb lattice with a homogeneous distribution of nitrogen atoms, where both N and C atoms show a D6h-symmetry. C3N is a semiconductor with an indirect bandgap of 0.39 eV that can be tuned to cover the entire visible range by fabrication of quantum dots with different diameters. Back-gated field-effect transistors made of single-layer C3N display an on–off current ratio reaching 5.5 × 1010. Surprisingly, C3N exhibits a ferromagnetic order at low temperatures (<96 K) when doped with hydrogen. This new member of the graphene family opens the door for both fundamental basic research and possible future applications.

Carbon Nanodot Surface Modifications Initiate Highly Efficient, Stable Catalysts for Both Oxygen Evolution and Reduction Reactions

Co-reporter:Juan Liu;Shunyan Zhao;Chuanxi Li;Manman Yang;Yanmei Yang;Yang Liu;Yeshayahu Lifshitz;Zhenhui Kang

Advanced Energy Materials 2016 Volume 6( Issue 9) pp:

Publication Date(Web):

DOI:10.1002/aenm.201502039

Efficient, stable, and low-cost electrocatalysts for the oxygen evolution and reduction reactions (OER and ORR) are essential components of energy conversion. Although much progress has been achieved in the development of platinum-based electrocatalysts for ORR and iridium-based electrocatalysts for OER, they are still not yet viable for large-scale commercialization because of the high cost and scanty supply of the noble metals. Here, it is demonstrated that carbon nanodots surface-modified with either phosphorus or amidogen can respectively achieve electrocatalytic activity approaching that of the benchmark Pt/C and IrO₂ /C catalysts for ORR and OER. Furthermore, phosphorus (amidogen)-modified carbon nanodots with attached Au nanoparticles exhibit superior ORR (OER) activity better than commercial Pt/C (IrO₂/C) catalysts as well as excellent electrochemical stability under visible light.

Reversible and Precise Self-Assembly of Janus Metal-Organosilica Nanoparticles through a Linker-Free Approach

Co-reporter:Huicheng Hu, Fei Ji, Yong Xu, Jiaqi Yu, Qipeng Liu, Lei Chen, Qian Chen, Peng Wen, Yeshayahu Lifshitz, Yan Wang, Qiao Zhang, and Shuit-Tong Lee

ACS Nano 2016 Volume 10(Issue 8) pp:7323

Publication Date(Web):July 8, 2016

DOI:10.1021/acsnano.6b03396

Reversible self-assembly of nanoparticles into ordered structures is essential for both fundamental study and practical applications. Although extensive work has been conducted, the demand for simple, cheap, reversible, and versatile ordering methods is still a central issue in current nanoscience and nanotechnology. Here we report a reversible and precise self-assembly of nanoparticles through a linker-free and fast approach by manipulating the interparticle forces, e.g., van der Waals (VDW) force and electrostatic force. Because VDW force is nondirectional, an oriented interaction is achieved to induce the directional binding of nanoparticles utilizing the Janus nanostructure. An effective sol–gel approach has been developed to synthesize metal-organosilica Janus nanoparticles. Dimers and trimers can be obtained by tuning the steric hindrance. After assembly, “hot-spots” can be generated between adjacent nanoparticles, and dramatic enhancement has been observed in surface-enhanced Raman scattering. The present strategy overcomes several limitations of existing approaches and allows the controlled assembly of small particles into various structures.Keywords: Janus nanoparticle; reversible self-assembly; surface plasmon resonance; surface-enhanced raman spectroscopy; van der Waals force

Two-dimensional layered material/silicon heterojunctions for energy and optoelectronic applications

Co-reporter:Yuming Wang;Ke Ding;Baoquan Sun;Jiansheng Jie

Nano Research 2016 Volume 9( Issue 1) pp:72-93

Publication Date(Web):2016 January

DOI:10.1007/s12274-016-1003-3

As one of the most important semiconductor materials, silicon (Si) has been widely used in current energy and optoelectronic devices, such as solar cells and photodetectors. However, the traditional Si p–n junction solar cells need complicated fabrication processes, leading to the high cost of Si photovoltaic devices. The wide applications of Si-based photodetectors are also hampered by their low sensitivity to ultraviolet and infrared light. Recently, two-dimensional (2D) layered materials have emerged as a new material system with tremendous potential for future energy and optoelectronic applications. The combination of Si with 2D layered materials represents an innovative approach to construct high-performance optoelectronic devices by harnessing the complementary advantages of both materials. In this review, we summarize the recent advances in 2D layered material/Si heterojunctions and their applications in photovoltaic and optoelectronic devices. Finally, the outlook and challenges of 2D layered material/Si heterojunctions for high-performance device applications are presented.

Highly Fluorescent, Photostable, and Ultrasmall Silicon Drug Nanocarriers for Long-Term Tumor Cell Tracking and In-Vivo Cancer Therapy

Co-reporter:Xiaoyuan Ji;Fei Peng;Yiling Zhong;Yuanyuan Su;Xiangxu Jiang;Chongxi Song;Liu Yang;Binbin Chu;Yao He

Advanced Materials 2015 Volume 27( Issue 6) pp:1029-1034

Publication Date(Web):

DOI:10.1002/adma.201403848

MoO3 Nanodots Decorated CdS Nanoribbons for High-Performance, Homojunction Photovoltaic Devices on Flexible Substrates

Co-reporter:Zhibin Shao, Jiansheng Jie, Zheng Sun, Feifei Xia, Yuming Wang, Xiaohong Zhang, Ke Ding, and Shuit-Tong Lee

Nano Letters 2015 Volume 15(Issue 5) pp:3590-3596

Publication Date(Web):April 13, 2015

DOI:10.1021/acs.nanolett.5b01087

The p–n homojunctions are essential components for high-efficiency optoelectronic devices. However, the lack of p-type doping in CdS nanostructures hampers the fabrication of efficient photovoltaic (PV) devices from homojunctions. Here we report a facile solution-processed method to achieve efficient p-type doping in CdS nanoribbons (NRs) via a surface charge transfer mechanism by using spin-coated MoO3 nanodots (NDs). The NDs-decorated CdS NRs exhibited a hole concentration as high as 8.5 × 1019 cm–3, with the p-type conductivity tunable in a wide range of 7 orders of magnitude. The surface charge transfer mechanism was characterized in detail by X-ray photoelectron spectroscopy, Kelvin probe force microscopy, and first-principle calculations. CdS NR-homojunction PV devices fabricated on a flexible substrate exhibited a power conversion efficiency of 5.48%, which was significantly better than most of the CdS nanostructure-based heterojunction devices, presumably due to minimal junction defects. Devices made by connecting cells in series or in parallel exhibited enhanced power output, demonstrating the promising potential of the homojunction PV devices for device integration. Given the high efficiency of the surface charge transfer doping and the solution-processing capability of the method, our work opens up unique opportunities for high-performance, low-cost optoelectronic devices based on CdS homojunctions.

MoS2/Si Heterojunction with Vertically Standing Layered Structure for Ultrafast, High-Detectivity, Self-Driven VisibleNear Infrared Photodetectors

Co-reporter:Liu Wang;Jiansheng Jie;Zhibin Shao;Qing Zhang;Xiaohong Zhang;Yuming Wang;Zheng Sun

Advanced Functional Materials 2015 Volume 25( Issue 19) pp:2910-2919

Publication Date(Web):

DOI:10.1002/adfm.201500216

As an interesting layered material, molybdenum disulfide (MoS₂) has been extensively studied in recent years due to its exciting properties. However, the applications of MoS₂ in optoelectronic devices are impeded by the lack of high-quality p–n junction, low light absorption for mono-/multilayers, and the difficulty for large-scale monolayer growth. Here, it is demonstrated that MoS₂ films with vertically standing layered structure can be deposited on silicon substrate with a scalable sputtering method, forming the heterojunction-type photodetectors. Molecular layers of the MoS₂ films are perpendicular to the substrate, offering high-speed paths for the separation and transportation of photo-generated carriers. Owing to the strong light absorption of the relatively thick MoS₂ film and the unique vertically standing layered structure, MoS₂/Si heterojunction photodetectors with unprecedented performance are actualized. The self-driven MoS₂/Si heterojunction photodetector is sensitive to a broadband wavelength from visible light to near-infrared light, showing an extremely high detectivity up to ≈10¹³ Jones (Jones = cm Hz^1/2 W⁻¹), and an ultrafast response speed of ≈3 μs. The performance is significantly better than the photodetectors based on mono-/multilayer MoS₂ nanosheets. Additionally, the MoS₂/Si photodetectors exhibit excellent stability in air for a month. This work unveils the great potential of MoS₂/Si heterojunction for optoelectronic applications.

Charge-Transfer Emission of Mixed Organic Cocrystal Microtubes over the Whole Composition Range

Co-reporter:Yan-Qiu Sun, Yi-Long Lei, Xu-Hui Sun, Shuit-Tong Lee, and Liang-Sheng Liao

Chemistry of Materials 2015 Volume 27(Issue 4) pp:1157

Publication Date(Web):December 26, 2014

DOI:10.1021/cm5027249

A series of crystalline mixed cocrystal microtubes comprising organic charge-transfer (CT) complexes has been prepared. The emission colors of the mixed cocrystal microtubes can be tailored from green to orange at low dopant concentrations (0 < x ⩽ 5%), while their hexagonal cross sections can transform into square ones gradually at higher concentrations (0.15 < x < 1). In addition, we can further extend the solvent-processed synthetic route to other CT pairs based on structural compatibility consideration.

Controlled synthesis and synergistic effects of graphene-supported PdAu bimetallic nanoparticles with tunable catalytic properties

Co-reporter:Chang-Hai Liu, Rui-Hua Liu, Qi-Jun Sun, Jian-Bing Chang, Xu Gao, Yang Liu, Shuit-Tong Lee, Zhen-Hui Kang and Sui-Dong Wang

Nanoscale 2015 vol. 7(Issue 14) pp:6356-6362

Publication Date(Web):09 Mar 2015

DOI:10.1039/C4NR06855F

Graphene-supported bimetallic nanoparticles are promising nanocatalysts, which can show strong and tunable catalytic activity and selectivity. Herein room-temperature-ionic-liquid-assisted metal sputtering is utilized to synthesize PdAu bimetallic nanoparticles on graphene with bare surface, small size, high surface density and controlled Pd-to-Au ratio. This controllable synthetic approach is green-chemistry compatible and totally free of additives and byproducts. The supported PdAu nanoparticles show excellent catalytic capabilities for both oxidation and reduction reactions, strongly dependent on the Pd-to-Au ratio. A strong correlation among catalytic performance, bimetallic composition and charge redistribution in the PdAu nanoparticles has been demonstrated. The results suggest that sufficient Au d-holes appear to be significant to the catalysis of oxidation reaction, and a metallic Pd surface is critical to the catalysis of reduction reaction. By the present method, the bimetallic combination can be tailored for distinct types of catalytic reactions.

Fluorescent N-Doped Carbon Dots as in Vitro and in Vivo Nanothermometer

Co-reporter:Yanmei Yang, Weiqian Kong, Hao Li, Juan Liu, Manman Yang, Hui Huang, Yang Liu, Zhongyang Wang, Zhiqiang Wang, Tsun-Kong Sham, Jun Zhong, Chao Wang, Zhuang Liu, Shuit-Tong Lee, and Zhenhui Kang

ACS Applied Materials & Interfaces 2015 Volume 7(Issue 49) pp:27324

Publication Date(Web):November 23, 2015

DOI:10.1021/acsami.5b08782

The fluorescent N-doped carbon dots (N-CDs) obtained from C3N4 emit strong blue fluorescence, which is stable with different ionic strengths and time. The fluorescence intensity of N-CDs decreases with the temperature increasing, while it can recover to the initial one with the temperature decreasing. It is an accurate linear response of fluorescence intensity to temperature, which may be attributed to the synergistic effect of abundant oxygen-containing functional groups and hydrogen bonds. Further experiments also demonstrate that N-CDs can serve as effective in vitro and in vivo fluorescence-based nanothermometer.Keywords: cellular imaging; in vivo imaging; linear response; N-doped carbon dots; nanothermometer; temperature-dependent fluorescence

Semiconducting Graphene on Silicon from First-Principles Calculations

Co-reporter:Xuejie Dang, Huilong Dong, Lu Wang, Yanfei Zhao, Zhenyu Guo, Tingjun Hou, Youyong Li, and Shuit-Tong Lee

ACS Nano 2015 Volume 9(Issue 8) pp:8562

Publication Date(Web):July 27, 2015

DOI:10.1021/acsnano.5b03722

Graphene is a semimetal with zero band gap, which makes it impossible to turn electric conduction off below a certain limit. Transformation of graphene into a semiconductor has attracted wide attention. Owing to compatibility with Si technology, graphene adsorbed on a Si substrate is particularly attractive for future applications. However, to date there is little theoretical work on band gap engineering in graphene and its integration with Si technology. Employing first-principles calculations, we study the electronic properties of monolayer and bilayer graphene adsorbed on clean and hydrogen (H)-passivated Si (111)/Si (100) surfaces. Our calculation shows that the interaction between monolayer graphene and a H-passivated Si surface is weak, with the band gap remaining negligible. For bilayer graphene adsorbed onto a H-passivated Si surface, the band gap opens up to 108 meV owing to asymmetry introduction. In contrast, the interaction between graphene and a clean Si surface is strong, leading to formation of chemical bonds and a large band gap of 272 meV. Our results provide guidance for device designs based on integrating graphene with Si technology.Keywords: band gap; graphene; graphene−Si interaction; silicon;

Solution-Processed Graphene Quantum Dot Deep-UV Photodetectors

Co-reporter:Qing Zhang, Jiansheng Jie, Senlin Diao, Zhibin Shao, Qiao Zhang, Liu Wang, Wei Deng, Weida Hu, Hui Xia, Xiaodong Yuan, and Shuit-Tong Lee

ACS Nano 2015 Volume 9(Issue 2) pp:1561

Publication Date(Web):January 27, 2015

DOI:10.1021/acsnano.5b00437

Fast-response and high-sensitivity deep-ultraviolet (DUV) photodetectors with detection wavelength shorter than 320 nm are in high demand due to their potential applications in diverse fields. However, the fabrication processes of DUV detectors based on traditional semiconductor thin films are complicated and costly. Here we report a high-performance DUV photodetector based on graphene quantum dots (GQDs) fabricated via a facile solution process. The devices are capable of detecting DUV light with wavelength as short as 254 nm. With the aid of an asymmetric electrode structure, the device performance could be significantly improved. An on/off ratio of ∼6000 under 254 nm illumination at a relatively weak light intensity of 42 μW cm–2 is achieved. The devices also exhibit excellent stability and reproducibility with a fast response speed. Given the solution-processing capability of the devices and extraordinary properties of GQDs, the use of GQDs will open up unique opportunities for future high-performance, low-cost DUV photodetectors.Keywords: asymmetric electrodes; deep-UV; graphene; photodetectors; quantum dots;

Facile, Large-Quantity Synthesis of Stable, Tunable-Color Silicon Nanoparticles and Their Application for Long-Term Cellular Imaging

Co-reporter:Yiling Zhong, Xiaotian Sun, Siyi Wang, Fei Peng, Feng Bao, Yuanyuan Su, Youyong Li, Shuit-Tong Lee, and Yao He

ACS Nano 2015 Volume 9(Issue 6) pp:5958

Publication Date(Web):May 31, 2015

DOI:10.1021/acsnano.5b00683

We herein introduce a facile, low-cost photochemical method capable of rapid (<40 min) and large-quantity (∼10 g) production of highly fluorescent (quantum yield: 25%) silicon nanoparticles (SiNPs) of tunable optical properties (peak emission wavelength in the range of 470–560 nm) under ambient air conditions, by introducing 1,8-naphthalimide as a reducing agent and surface ligands. The as-prepared SiNPs feature robust storage stability and photostability preserving strong and stable fluorescent during long-term (>3 h) high-power UV irradiation, in contrast to the rapid fluorescence quenching within 2 h of conventional organic dyes and II–VI quantum dots under the same conditions. The as-prepared SiNPs serving as photostable nanoprobes are workable for cellular imaging in long-term manners. Our findings provide a powerful method for mild-condition and low-cost, large-quantity production of highly fluorescent and photostable SiNPs for various promising applications.Keywords: bioimaging; large-quantity; long-term; photochemical; silicon nanoparticles;

Silicon Nanomaterials Platform for Bioimaging, Biosensing, and Cancer Therapy

Co-reporter:Fei Peng, Yuanyuan Su, Yiling Zhong, Chunhai Fan, Shuit-Tong Lee, and Yao He

Accounts of Chemical Research 2014 Volume 47(Issue 2) pp:612

Publication Date(Web):January 7, 2014

DOI:10.1021/ar400221g

Silicon nanomaterials are an important class of nanomaterials with great potential for technologies including energy, catalysis, and biotechnology, because of their many unique properties, including biocompatibility, abundance, and unique electronic, optical, and mechanical properties, among others. Silicon nanomaterials are known to have little or no toxicity due to favorable biocompatibility of silicon, which is an important precondition for biological and biomedical applications. In addition, huge surface-to-volume ratios of silicon nanomaterials are responsible for their unique optical, mechanical, or electronic properties, which offer exciting opportunities for design of high-performance silicon-based functional nanoprobes, nanosensors, and nanoagents for biological analysis and detection and disease treatment. Moreover, silicon is the second most abundant element (after oxygen) on earth, providing plentiful and inexpensive resources for large-scale and low-cost preparation of silicon nanomaterials for practical applications. Because of these attractive traits, and in parallel with a growing interest in their design and synthesis, silicon nanomaterials are extensively investigated for wide-ranging applications, including energy, catalysis, optoelectronics, and biology. Among them, bioapplications of silicon nanomaterials are of particular interest.In the past decade, scientists have made an extensive effort to construct a silicon nanomaterials platform for various biological and biomedical applications, such as biosensors, bioimaging, and cancer treatment, as new and powerful tools for disease diagnosis and therapy. Nonetheless, there are few review articles covering these important and promising achievements to promote the awareness of development of silicon nanobiotechnology.In this Account, we summarize recent representative works to highlight the recent developments of silicon functional nanomaterials for a new, powerful platform for biological and biomedical applications, including biosensor, bioimaging, and cancer therapy. First, we show that the interesting photoluminescence properties (e.g., strong fluorescence and robust photostability) and excellent biocompatibility of silicon nanoparticles (SiNPs) are superbly suitable for direct and long-term visualization of biological systems. The strongly fluorescent SiNPs are highly effective for bioimaging applications, especially for long-term cellular labeling, cancer cell detection, and tumor imaging in vitro and in vivo with high sensitivity. Next, we discuss the utilization of silicon nanomaterials to construct high-performance biosensors, such as silicon-based field-effect transistors (FET) and surface-enhanced Raman scattering (SERS) sensors, which hold great promise for ultrasensitive and selective detection of biological species (e.g., DNA and protein). Then, we introduce recent exciting research findings on the applications of silicon nanomaterials for cancer therapy with encouraging therapeutic outcomes. Lastly, we highlight the major challenges and promises in this field, and the prospect of a new nanobiotechnology platform based on silicon nanomaterials.

Synchrotron Soft X-ray Absorption Spectroscopy Study of Carbon and Silicon Nanostructures for Energy Applications

Co-reporter:Jun Zhong;Hui Zhang;Xuhui Sun

Advanced Materials 2014 Volume 26( Issue 46) pp:7786-7806

Publication Date(Web):

DOI:10.1002/adma.201304507

Carbon and silicon materials are two of the most important materials involved in the history of the science and technology development. In the last two decades, C and Si nanoscale materials, e.g., carbon nanotubes, graphene, and silicon nanowires, and quantum dots, have also emerged as the most interesting nanomaterials in nanoscience and nanotechnology for their myriad promising applications such as for electronics, sensors, biotechnology, etc. In particular, carbon and silicon nanostructures are being utilized in energy-related applications such as catalysis, batteries, solar cells, etc., with significant advances. Understanding of the nature of surface and electronic structures of nanostructures plays a key role in the development and improvement of energy conversion and storage nanosystems. Synchrotron soft X-ray absorption spectroscopy (XAS) and related techniques, such as X-ray emission spectroscopy (XES) and scanning transmission X-ray microscopy (STXM), show unique capability in revealing the surface and electronic structures of C and Si nanomaterials. In this review, XAS is demonstrated as a powerful technique for probing chemical bonding, the electronic structure, and the surface chemistry of carbon and silicon nanomaterials, which can greatly enhance the fundamental understanding and also applicability of these nanomaterials in energy applications. The focus is on the unique advantages of XAS as a complementary tool to conventional microscopy and spectroscopy for effectively providing chemical and structural information about carbon and silicon nanostructures. The employment of XAS for in situ, real-time study of property evolution of C and Si nanostructures to elucidate the mechanisms in energy conversion or storage processes is also discussed.

Silicon/Hematite Core/Shell Nanowire Array Decorated with Gold Nanoparticles for Unbiased Solar Water Oxidation

Co-reporter:Xin Wang, Kui-Qing Peng, Ya Hu, Fu-Qiang Zhang, Bo Hu, Li Li, Meng Wang, Xiang-Min Meng, and Shuit-Tong Lee

Nano Letters 2014 Volume 14(Issue 1) pp:18-23

Publication Date(Web):December 16, 2013

DOI:10.1021/nl402205f

We report the facile fabrication of three-dimensional (3D) silicon/hematite core/shell nanowire arrays decorated with gold nanoparticles (AuNPs) and their potential application for sunlight-driven solar water splitting. The hematite and AuNPs respectively play crucial catalytic and plasmonic photosensitization roles, while silicon absorbs visible light and generates high photocurrent. Under simulated solar light illumination, solar water splitting with remarkable efficiency is achieved with no external bias applied. Such a nanocomposite photoanode design offers great promise for unassisted sunlight-driven water oxidation, and further stability and efficiency improvements to the device will lead to exciting prospects for practical solar water splitting and artificial photosynthesis.

Metal-Catalyzed Electroless Etching of Silicon in Aerated HF/H2O Vapor for Facile Fabrication of Silicon Nanostructures

Co-reporter:Ya Hu, Kui-Qing Peng, Zhen Qiao, Xing Huang, Fu-Qiang Zhang, Rui-Nan Sun, Xiang-Min Meng, and Shuit-Tong Lee

Nano Letters 2014 Volume 14(Issue 8) pp:4212-4219

Publication Date(Web):July 18, 2014

DOI:10.1021/nl500361u

Inspired by metal corrosion in air, we demonstrate that metal-catalyzed electroless etching (MCEE) of silicon can be performed simply in aerated HF/H2O vapor for facile fabrication of three-dimensional silicon nanostructures such as silicon nanowires (SiNW) arrays. Compared to MCEE commonly performed in aqueous HF solution, the present pseudo gas phase etching offers exceptional simplicity, flexibility, environmental friendliness, and scalability for the fabrication of three-dimensional silicon nanostructures with considerable depths because of replacement of harsh oxidants such as H2O2 and AgNO3 by environmental-green and ubiquitous oxygen in air, minimum water consumption, and full utilization of HF.

Silicon nanowire-based therapeutic agents for in vivo tumor near-infrared photothermal ablation

Co-reporter:Yuanyuan Su, Fei Peng, Xiaoyuan Ji, Yimei Lu, Xinpan Wei, Binbin Chu, Chongxi Song, Yanfeng Zhou, Xiangxu Jiang, Yiling Zhong, Shuit-Tong Lee and Yao He

Journal of Materials Chemistry A 2014 vol. 2(Issue 19) pp:2892-2898

Publication Date(Web):24 Feb 2014

DOI:10.1039/C4TB00100A

The first example of silicon nanowire (SiNW)-based in vivo tumor phototherapy is presented. Gold nanoparticle (AuNP)-decorated SiNWs are employed as high-performance NIR hyperthermia agents for highly efficacious in vivo tumour ablation. Significantly, the overall survival time of SiNW-treated mice is drastically prolonged, with 100% of mice being alive and tumor-free for over 8 months, which is the longest survival time ever reported for tumor-bearing mice treated with nanomaterial-based NIR hyperthermia agents.

Ordered Ag/Si Nanowires Array: Wide-Range Surface-Enhanced Raman Spectroscopy for Reproducible Biomolecule Detection

Co-reporter:Jian-An Huang, Ying-Qi Zhao, Xue-Jin Zhang, Li-Fang He, Tai-Lun Wong, Ying-San Chui, Wen-Jun Zhang, and Shuit-Tong Lee

Nano Letters 2013 Volume 13(Issue 11) pp:5039-5045

Publication Date(Web):September 27, 2013

DOI:10.1021/nl401920u

Surface-enhanced Raman scattering (SERS) systems utilizing the interparticle nanogaps as hot spots have demonstrated ultrasensitive single-molecule detection with excellent selectivity yet the electric fields are too confined in the small nanogaps to enable reproducible biomolecule detections. Here, guided by finite-difference-time-domain simulation, we report hexagonal-packed silver-coated silicon nanowire (Ag/SiNW) arrays as a nanogap-free SERS system with wide-range electric fields and controlled interwire separation. Significantly, the system achieves a SERS detection of long double-strand DNA of 25–50 nm in length with a relative standard deviation (RSD) of 14% for measurements of above 4000 spots over an area of 200 × 200 μm2. The high reproducibility in the SERS detection is attributed to (1) the large interwire spacing of 150 nm that allows access and excitation of large biomolecules; and (2) 600 nm wide-range electric field generated by propagating surface plasmons along the surface of continuous Ag coating on a SiNW. Moreover, a reproducible multiplex SERS measurement is also demonstrated with RSDs of 7–16% with an enhancement factor of ∼106. The above results show that the ordered Ag/SiNW array system may serve as an excellent SERS platform for practical chemical and biological detection.

Selective Growth of Dual-Color-Emitting Heterogeneous Microdumbbells Composed of Organic Charge-Transfer Complexes

Co-reporter:Yi Long Lei ; Liang Sheng Liao ;Shuit Tong Lee

Journal of the American Chemical Society 2013 Volume 135(Issue 10) pp:3744-3747

Publication Date(Web):March 4, 2013

DOI:10.1021/ja3114278

We report a simple yet versatile solution route for constructing heterojunctions from luminescent organic charge-transfer (CT) complexes through a two-step seeded-growth method. Using this method, we achieved anisotropic and selective growth of anthracene–1,2,4,5-tetracyanobenzene (TCNB) complexes onto the tips of naphthalene–TCNB microtubes, resulting in the formation of microdumbbells. Significantly, the two-component microdumbbells appear as dual-color-emitting heterojunctions arising from integration of two distinct color-emitting materials. We further elucidated the two-step seeded-growth mechanism of the dumbbell-like organic heterostructures on the basis of structural analysis of the two crystals and surface–interface energy balance. In principle, the present synthetic route may be used to fabricate a wide range of sophisticated dual- or multicolor-emitting organic heterostructures via judicious choice of the CT complexes.

Large-Scale Aqueous Synthesis of Fluorescent and Biocompatible Silicon Nanoparticles and Their Use as Highly Photostable Biological Probes

Co-reporter:Yiling Zhong ; Fei Peng ; Feng Bao ; Siyi Wang ; Xiaoyuan Ji ; Liu Yang ; Yuanyuan Su ; Shuit-Tong Lee ;Yao He

Journal of the American Chemical Society 2013 Volume 135(Issue 22) pp:8350-8356

Publication Date(Web):April 12, 2013

DOI:10.1021/ja4026227

A large-scale synthetic strategy is developed for facile one-pot aqueous synthesis of silicon nanoparticles (SiNPs) yielding ∼0.1 g SiNPs of small sizes (∼2.2 nm) in 10 min. The as-prepared SiNPs feature strong fluorescence (photoluminescence quantum yield of 20–25%), favorable biocompatibility, and robust photo- and pH-stability. Moreover, the SiNPs are naturally water dispersible, requiring no additional post-treatment. Such SiNPs can serve as highly photostable bioprobes and are superbly suitable for long-term immunofluorescent cellular imaging.

Opto-electronic conversion logic behaviour through dynamic modulation of electron/energy transfer states at the TiO2–carbon quantum dot interface

Co-reporter:Fang Wang, Yonglai Zhang, Yang Liu, Xuefeng Wang, Mingrong Shen, Shuit-Tong Lee and Zhenhui Kang

Nanoscale 2013 vol. 5(Issue 5) pp:1831-1835

Publication Date(Web):21 Jan 2013

DOI:10.1039/C3NR33985H

Here we show a bias-mediated electron/energy transfer process at the CQDs–TiO2 interface for the dynamic modulation of opto-electronic properties. Different energy and electron transfer states have been observed in the CQDs–TNTs system due to the up-conversion photoluminescence and the electron donation/acceptance properties of the CQDs decorated on TNTs.

Germanium–graphene composite anode for high-energy lithium batteries with long cycle life

Co-reporter:Jian-Guo Ren, Qi-Hui Wu, Hao Tang, Guo Hong, Wenjun Zhang and Shuit-Tong Lee

Journal of Materials Chemistry A 2013 vol. 1(Issue 5) pp:1821-1826

Publication Date(Web):10 Dec 2012

DOI:10.1039/C2TA01286C

The high-energy lithium ion battery is an ideal power source for electric vehicles and grid-scale energy storage applications. Germanium is a promising anode material for lithium ion batteries due to its high specific capacity, but still suffers from poor cyclability. Here, we report a facile preparation of a germanium–graphene nanocomposite using a low-pressure thermal evaporation approach, by which crystalline germanium particles are uniformly deposited on graphene surfaces or embedded into graphene sheets. The nanocomposite exhibits a high Coulombic efficiency of 80.4% in the first cycle and a capacity retention of 84.9% after 400 full cycles in a half cell, along with high utilization of germanium in the composite and high rate capability. These outstanding properties are attributed to the monodisperse distribution of high-quality germanium particles in a flexible graphene framework. This preparation approach can be extended to other active elements that can be easily evaporated (e.g., sulfur, phosphorus) for the preparation of graphene-based composites for lithium ion battery applications.

Bioinspired Photoelectric Conversion System Based on Carbon-Quantum-Dot-Doped Dye–Semiconductor Complex

Co-reporter:Zheng Ma, Yong-Lai Zhang, Lei Wang, Hai Ming, Haitao Li, Xing Zhang, Fang Wang, Yang Liu, Zhenhui Kang, and Shuit-Tong Lee

ACS Applied Materials & Interfaces 2013 Volume 5(Issue 11) pp:5080

Publication Date(Web):May 13, 2013

DOI:10.1021/am400930h

Compared to nature’s photoelectric conversion processes, artificial devices are still far inferior in efficiency and stability. Inspired by light absorption and resonance energy transfer processes of chlorophyll, we developed a highly efficient photoelectric conversion system by introducing Carbon quantum dots (CQDs) as an electron transfer intermediary. Compared with conventional dye-sensitized semiconductor systems, the present CQD-doped system showed significantly higher photoelectric conversion efficiency, as much as 7 times that without CQDs. The CQD-doped dye/semiconductor system may provide a powerful approach to the development of highly efficient photoelectric devices.Keywords: carbon quantum dots; dye−semiconductor complex; energy transfer; enhanced UV−vis light absorbance; photoelectric conversion; power conversion efficiency;

Electronic structure of MoO3−x/graphene interface

Co-reporter:Qi-Hui Wu, Yingqi Zhao, Guo Hong, Jian-Guo Ren, Chundong Wang, Wenjun Zhang, Shuit-Tong Lee

Carbon 2013 Volume 65() pp:46-52

Publication Date(Web):December 2013

DOI:10.1016/j.carbon.2013.07.091

The interfacial electronic structure of MoO3−x/graphene has been investigated using photoemission spectroscopy. The experimental data showed that upon deposition of MoO3−x, the Fermi level of graphene shifts downward gradually from its Dirac point due to the p-type doping effect. From the Fermi level shift of −0.28 eV, the hole density of graphene was estimated to be 5.44 × 1012 cm−2. The formation of surface negative dipole due to electron transfer from graphene to the deposited MoO3−x films increased the sample′s work function. The existence of gap states in MoO3−x induced by oxygen vacancies greatly reduced the hole injection barrier at the MoO3−x/graphene interface.

Molecule design and isomorphism synthesis towards artificial enzymes

Co-reporter:Weisong Zhang, Jingjing Gong, Zhenhui Kang, Hailiang Hu, Zhenyu Guo, Youyong Li, Yang Liu, Hengchao Zhang, Lili Zhang, Yanan Yang and Shuit-Tong Lee

CrystEngComm 2013 vol. 15(Issue 4) pp:662-665

Publication Date(Web):14 Nov 2012

DOI:10.1039/C2CE26820E

Design and construction of artificial enzymes via crystal engineering of organic–inorganic hybrid systems having two functional domains; with one domain serving as the reaction active site, and the other providing the reaction driving force have been demonstrated.

Modification of CuPc/graphene interfacial electronic structure with F16CuPc

Co-reporter:Qi-Hui Wu, Guo Hong, S.T. Lee

Organic Electronics 2013 Volume 14(Issue 2) pp:542-547

Publication Date(Web):February 2013

DOI:10.1016/j.orgel.2012.11.024

The electronic structure between organic and solid electrode is a crucial issue in obtaining high-performance organic-based electronic devices (e.g. organic photovoltaic and organic light-emitting diode). In this communication we report that the electronic properties of phthalocyanine CuPc/graphene interface can be modified by sequential deposition of hexadecafluorophthalocyaninatocopper (F16CuPc) on the CuPc/graphene interface due to the interactions of F16CuPc with graphene. This method can be used to alter the energy barrier heights between graphene Dirac point and organic’s highest occupied molecular orbital and lowest unoccupied molecular orbital at the organic/graphene interface by simple deposition of another electron acceptor or donor layer on this interface.Graphical abstractThe electronic properties of CuPc/graphene interface could be altered by simply coating a layer of F16CuPc, which results in p-doping of graphene and causes the downward shift of the Fermi level from the graphene Dirac point.Highlights► Energy barriers between CuPc HOMO/LUMO and graphene Dirac point have been aligned. ► F16CuPc coating layer has been used to modify the electronic structure of CuPc/graphene interface. ► Electronic structure of organic/graphene interface can be modified by another subsequently deposited organic layer.

Silicon nanowires for advanced energy conversion and storage

Co-reporter:Kui-Qing Peng, Xin Wang, Li Li, Ya Hu, Shuit-Tong Lee

Nano Today 2013 Volume 8(Issue 1) pp:75-97

Publication Date(Web):February 2013

DOI:10.1016/j.nantod.2012.12.009

Due to their unique structural, electrical, optical, and thermal properties, silicon nanowires (SiNWs) are attracting immense interest as a promising material for advanced energy conversion and storage applications. In this feature article, we review the recent achievements on SiNWs for advanced energy conversion and storage applications including photovoltaics, photocatalysis, thermoelectrics, lithium-ion batteries and supercapacitors. We also offer our prospective on the outstanding challenges in this emerging field.Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (301 K)Download as PowerPoint slideHighlights► A brief overview of the popular methods for the low-cost fabrication of high-quality silicon nanowires is given. ► Silicon nanowires for energy conversion and storage applications including photovoltaics, photocatalysis, thermoelectrics, lithium-ion batteries and supercapacitors are summarized. ► Future challenges and prospects for silicon nanowires in the arena of energy-related applications are discussed.

Recent progress in organic molecule/graphene interfaces

Co-reporter:Guo Hong, Qi-Hui Wu, Jianguo Ren, Chundong Wang, Wenjun Zhang, Shuit-Tong Lee

Nano Today 2013 Volume 8(Issue 4) pp:388-402

Publication Date(Web):August 2013

DOI:10.1016/j.nantod.2013.07.003

•We review recent progress on the studies of organic/graphene interfaces.•Organic molecular assembly structure on graphene surface prepared on different substrates.•Interfacial electronic properties between organic molecule and graphene.•Outlook on the development and application of organic/graphene interface in organic devices.Graphene holds great promise in wide-ranging applications due to its novel electronic, thermal, mechanical, and chemical properties. In many applications, graphene needs to be integrated with other materials, it is thus important to understand the surface physics and chemistry of graphene. Understanding the adsorption behavior of organic molecules on graphene is an important issue to develop the full potential of graphene-based organic electronic devices. This article reviews the interfacial morphologies and electronic structures between organic molecules and graphene, prepared on different substrates. Generally, adsorption of organic molecules on graphene exhibits two important characteristics: (1) formation of well-ordered organic layers based on the graphene template and (2) occurrence of charge transfer between adsorbed molecules and graphene, offering the promise in tuning the electronic properties of graphene.

Silicon-Nanowire-Based Nanocarriers with Ultrahigh Drug-Loading Capacity for InVitro and InVivo Cancer Therapy

Co-reporter:Fei Peng;Dr. Yuanyuan Su;Xinpan Wei;Yimei Lu;Yanfeng Zhou;Yiling Zhong; Shuit-Tong Lee; Yao He

Angewandte Chemie International Edition 2013 Volume 52( Issue 5) pp:1457-1461

Publication Date(Web):

DOI:10.1002/anie.201206737

Silicon-Nanowire-Based Nanocarriers with Ultrahigh Drug-Loading Capacity for InVitro and InVivo Cancer Therapy

Co-reporter:Fei Peng;Dr. Yuanyuan Su;Xinpan Wei;Yimei Lu;Yanfeng Zhou;Yiling Zhong; Shuit-Tong Lee; Yao He

Angewandte Chemie 2013 Volume 125( Issue 5) pp:1497-1501

Publication Date(Web):

DOI:10.1002/ange.201206737

Carbon nanodots: synthesis, properties and applications

Co-reporter:Haitao Li, Zhenhui Kang, Yang Liu and Shuit-Tong Lee

Journal of Materials Chemistry A 2012 vol. 22(Issue 46) pp:24230-24253

Publication Date(Web):29 Aug 2012

DOI:10.1039/C2JM34690G

Carbon nanodots (C-dots) have generated enormous excitement because of their superiority in water solubility, chemical inertness, low toxicity, ease of functionalization and resistance to photobleaching. In this review, by introducing the synthesis and photo- and electron-properties of C-dots, we hope to provide further insight into their controversial emission origin (particularly the upconverted photoluminescence) and to stimulate further research into their potential applications, especially in photocatalysis, energy conversion, optoelectronics, and sensing.

Growth of TiO2 nanorod arrays on reduced graphene oxide with enhanced lithium-ion storage

Co-reporter:Lifang He, Ruguang Ma, Ning Du, Jianguo Ren, Tailun Wong, Yangyang Li and Shuit Tong Lee

Journal of Materials Chemistry A 2012 vol. 22(Issue 36) pp:19061-19066

Publication Date(Web):25 Jul 2012

DOI:10.1039/C2JM33571A

We demonstrate the synthesis of a sandwich-like nanocomposite by planting rutile TiO2 nanorods onto reduced graphene oxide (RGO) via a modified seed-assisted hydrothermal growth method. The synthetic process consists of functionalization of graphene oxide (GO), followed by hydrolytic deposition of TiO2 nanoparticles on GO and reduction, and finally hydrothermal growth of rutile TiO2 nanorods on RGO. The resultant nanocomposite, i.e. rutile TiO2 nanorod arrays on RGO (TONRAs–RGO), exhibits largely enhanced reversible charge–discharge capacity and rate capability compared to bare TiO2 nanorods (TONRs) due to its unique structure and superior conductivity. The rate performance of the nanocomposite is also better than that of anatase TiO2 nanoparticles. This study will inspire better design of RGO-based nanocomposites for high energy density lithium-ion battery applications.

Fe2TiO5-incorporated hematite with surface P-modification for high-efficiency solar water splitting

Co-reporter:Xiaolin Lv, Kaiqi Nie, Huiwen Lan, Xin Li, Youyong Li, Xuhui Sun, Jun Zhong, Shuit-Tong Lee

Nano Energy (February 2017) Volume 32() pp:

Publication Date(Web):February 2017

DOI:10.1016/j.nanoen.2017.01.001

•We show a discrete Fe2TiO5-incorporation in hematite to improve the performance.•It can be well coupled with surface P-modification with a synergetic effect.•It shows a high photocurrent of 2.90 mA/cm2 at 1.23 VRHE with Co-Pi catalysts.•It provides a good insight to understand other Ti-based treatments of hematite.Hematite is a promising photocatalyst for solar water splitting while its performance has been severely limited by various factors. Recently surface Fe2TiO5 layer was widely reported to enhance the performance of hematite with a favorable band position to facilitate hole transport. Here we further show that the Fe2TiO5-incorporation in bulk hematite can also improve the performance with faster charge separation. Moreover, it can be well coupled with surface P-modification to simultaneously improve charge separation and hole transfer with a synergetic effect. The Ti and P co-modified hematite shows a significantly enhanced photocurrent of 2.37 mA/cm2 at 1.23 V vs. RHE when compared to the pristine value of 0.85 mA/cm2. After coupling with Co-Pi catalysts, the hematite sample can even achieve a stable, high photocurrent of 2.90 mA/cm2 at 1.23 V vs. RHE. The design of Ti and P co-modified hematite hollow nanostructures can be used as a promising candidate for solar water splitting applications. The discrete Fe2TiO5-incorporation also provides a good insight on the mechanism to understand other Ti-based treatments of hematite.

Silicon nanowire-based therapeutic agents for in vivo tumor near-infrared photothermal ablation

Co-reporter:Yuanyuan Su, Fei Peng, Xiaoyuan Ji, Yimei Lu, Xinpan Wei, Binbin Chu, Chongxi Song, Yanfeng Zhou, Xiangxu Jiang, Yiling Zhong, Shuit-Tong Lee and Yao He

Journal of Materials Chemistry A 2014 - vol. 2(Issue 19) pp:NaN2898-2898

Publication Date(Web):2014/02/24

DOI:10.1039/C4TB00100A

Growth of TiO2 nanorod arrays on reduced graphene oxide with enhanced lithium-ion storage

Co-reporter:Lifang He, Ruguang Ma, Ning Du, Jianguo Ren, Tailun Wong, Yangyang Li and Shuit Tong Lee

Journal of Materials Chemistry A 2012 - vol. 22(Issue 36) pp:NaN19066-19066

Publication Date(Web):2012/07/25

DOI:10.1039/C2JM33571A

Carbon nanodots: synthesis, properties and applications

Co-reporter:Haitao Li, Zhenhui Kang, Yang Liu and Shuit-Tong Lee

Journal of Materials Chemistry A 2012 - vol. 22(Issue 46) pp:NaN24253-24253

Publication Date(Web):2012/08/29