Co-reporter:Jing Zhang, Shuai Jia, Iskandar Kholmanov, Liang Dong, Dequan Er, Weibing Chen, Hua Guo, Zehua Jin, Vivek B. Shenoy, Li Shi, and Jun Lou
ACS Nano August 22, 2017 Volume 11(Issue 8) pp:8192-8192
Publication Date(Web):August 3, 2017
DOI:10.1021/acsnano.7b03186
The crystal configuration of sandwiched S–Mo–Se structure (Janus SMoSe) at the monolayer limit has been synthesized and carefully characterized in this work. By controlled sulfurization of monolayer MoSe2, the top layer of selenium atoms is substituted by sulfur atoms, while the bottom selenium layer remains intact. The structure of this material is systematically investigated by Raman, photoluminescence, transmission electron microscopy, and X-ray photoelectron spectroscopy and confirmed by time-of-flight secondary ion mass spectrometry. Density functional theory (DFT) calculations are performed to better understand the Raman vibration modes and electronic structures of the Janus SMoSe monolayer, which are found to correlate well with corresponding experimental results. Finally, high basal plane hydrogen evolution reaction activity is discovered for the Janus monolayer, and DFT calculation implies that the activity originates from the synergistic effect of the intrinsic defects and structural strain inherent in the Janus structure.Keywords: HER; Janus SMoSe; Raman; sulfurization; TOF-SIMS;
Co-reporter:Pei Dong, Marco-Tulio F. Rodrigues, Jing Zhang, Raquel S. Borges, Kaushik Kalaga, Arava L.M. Reddy, Glaura G. Silva, Pulickel M. Ajayan, Jun Lou
Nano Energy 2017 Volume 42(Volume 42) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.nanoen.2017.10.035
Both flexible energy harvesting and storage devices have been widely reported separately to satisfy part of the needs in the emerging areas, including wearable electronics, and low-density applications such as rooftop solar collectors. However, a flexible energy system with mechanical robustness and light-weight is the integrated device that will serve the real demand. Herein, a flexible printable dye-sensitized solar cell/supercapacitor integrated energy device has been designed, fabricated and characterized. This new device has several advantages: flexible, portable, high voltage capacity (up to 1.8 V), lightweight, environmental friendly and expanded indoor-use capabilities. The device demonstrated very stable performances under various extreme mechanical loading conditions in outdoor testing. This work paves way for future development of highly flexible integrated energy system for many potential applications.Download high-res image (188KB)Download full-size image
Co-reporter:Yingchao Yang;Nam Dong Kim;Vikas Varshney;Sangwook Sihn;Yilun Li;Ajit K. Roy;James M. Tour
Nanoscale (2009-Present) 2017 vol. 9(Issue 8) pp:2916-2924
Publication Date(Web):2017/02/23
DOI:10.1039/C6NR09897E
Hierarchically organized three-dimensional (3D) carbon nanotubes/graphene (CNTs/graphene) hybrid nanostructures hold great promises in composite and battery applications. Understanding the junction strength between CNTs and graphene is crucial for utilizing such special nanostructures. Here, in situ pulling an individual CNT bundle out of graphene is carried out for the first time using a nanomechanical tester developed in-house, and the measured junction strength of CNTs/graphene is 2.23 ± 0.56 GPa. The post transmission electron microscopy (TEM) analysis of remained graphene after peeling off CNT forest confirms that the failure during pull-out test occurs at the CNT–graphene junction. Such a carefully designed study makes it possible to better understand the interfacial interactions between CNTs and graphene in the 3D CNTs/graphene nanostructures. The coupled experimental and computational effort suggests that the junction between the CNTs and the graphene layer is likely to be chemically bonded, or at least consisting of a mixture of chemical bonding and van der Waals interactions.
Co-reporter:Jing Zhang;Jingjie Wu;Hua Guo;Weibing Chen;Jiangtan Yuan;Ulises Martinez;Gautam Gupta;Aditya Mohite;Pulickel M. Ajayan
Advanced Materials 2017 Volume 29(Issue 42) pp:
Publication Date(Web):2017/11/01
DOI:10.1002/adma.201701955
AbstractHere, the hydrogen evolution reaction (HER) activities at the edge and basal-plane sites of monolayer molybdenum disulfide (MoS2) synthesized by chemical vapor deposition (CVD) are studied using a local probe method enabled by selected-area lithography. Reaction windows are opened by e-beam lithography at sites of interest on poly(methyl methacrylate) (PMMA)-covered monolayer MoS2 triangles. The HER properties of MoS2 edge sites are obtained by subtraction of the activity of the basal-plane sites from results containing both basal-plane and edge sites. The catalytic performances in terms of turnover frequencies (TOFs) are calculated based on the estimated number of active sites on the selected areas. The TOFs follow a descending order of 3.8 ± 1.6, 1.6 ± 1.2, 0.008 ± 0.002, and 1.9 ± 0.8 × 10−4 s−1, found for 1T′-, 2H-MoS2 edges, and 1T′-, 2H-MoS2 basal planes, respectively. Edge sites of both 2H- and 1T′-MoS2 are proved to have comparable activities to platinum (≈1–10 s−1). When fitted into the HER volcano plot, the MoS2 active sites follow a trend distinct from conventional metals, implying a possible difference in the reaction mechanism between transition-metal dichalcogenides (TMDs) and metal catalysts.
Co-reporter:Yi Zeng;Xing Li;Weibing Chen;Jianhui Liao;Qing Chen
Advanced Materials Interfaces 2017 Volume 4(Issue 21) pp:
Publication Date(Web):2017/11/01
DOI:10.1002/admi.201700739
AbstractMonolayer MoS2 normally has weak photoluminescence (PL) because of the poor light absorption due to the atomic thickness. Here, the highly enhanced PL of chemical vapor deposited (CVD)-grown monolayer MoS2 with uniform self-assembled sub-monolayer Au nanoparticle arrays is reported. The PL intensity of monolayer MoS2 can be enhanced by up to 200 times. The dependence of the enhancement factor upon the excitation wavelength, the density of Au nanoparticles, and the thickness of the dielectric layer, is systematically investigated. The results indicate that the PL enhancement indeed stems from the local surface plasmon resonance of Au nanoparticles. The study provides a bottom-up, low-cost, large scale, and highly effective route to enhance the PL of CVD-grown monolayer MoS2.
Co-reporter:Peter Samora Owuor;Chra Sekhar Tiwary;Ryota Koizumi;Matias Soto;Amelia C. Hart;Enrique V. Barrera;Robert Vajtai;Pulickel M. Ajayan
Advanced Engineering Materials 2017 Volume 19(Issue 5) pp:
Publication Date(Web):2017/05/01
DOI:10.1002/adem.201600756
Strong van der Waals forces between individual carbon nanotubes pose a major hurdle for effective use of nanotubes as reinforcement in nanocomposite due to agglomeration. In this paper, the authors show that van der Waals forces in combination with functionalization of carbon nanotubes, can be utilized to design nanocomposites mimicking stiffening behavior normally observed in biological materials such as fibrin gels, health bones, actin filaments in cytoskeletons etc. Carbon nanotube spheres are used as reinforcement in an elastomer matrix and when subjected to dynamic loads exhibit significant self-stiffening. Increased stiffness is also observed in dynamic loading after every relaxation cycle. The authors further show high energy absorption of the nanocomposite in impact tests. Authors study shows that the rational design of macroscale materials from nano-scale constituents can be achieved utilizing simple methodology to produce multifunctional materials with broad applications.
Co-reporter:Peter Samora Owuor, Thierry Tsafack, Hye Yoon Hwang, Ok-Kyung Park, Sehmus Ozden, Sanjit Bhowmick, Syed Asif Syed Amanulla, Robert Vajtai, Jun Lou, Chandra Sekhar TiwaryPulickel M. Ajayan
ACS Nano 2017 Volume 11(Issue 1) pp:
Publication Date(Web):December 15, 2016
DOI:10.1021/acsnano.6b07249
Building three-dimensional (3D) structures from their constituent zero-, one-, and two-dimensional nanoscale building blocks in a bottom-up assembly is considered the holey grail of nanotechnology. However, fabricating such 3D nanostructures at ambient conditions still remains a challenge. Here, we demonstrate an easily scalable facile method to fabricate 3D nanostructures made up of entirely zero-dimensional silicon dioxide (SiO2) nanoparticles. By combining functional groups and vacuum filtration, we fabricate lightweight and highly structural stable 3D SiO2 materials. Further synergistic effect of material is shown by addition of a 2D material, graphene oxide (GO) as reinforcement which results in 15-fold increase in stiffness. Molecular dynamics (MD) simulations are used to understand the interaction between silane functional groups (3-aminopropyl triethoxysilane) and SiO2 nanoparticles thus confirming the reinforcement capability of GO. In addition, the material is stable under high temperature and offers a cost-effective alternative to both fire-retardant and oil absorption materials.Keywords: functionalization; graphene oxide (GO); molecular dynamics; silanes; silicon dioxide (SiO2); stiffness;
Co-reporter:Jingjie Wu, Mingjie Liu, Pranav P. Sharma, Ram Manohar Yadav, Lulu Ma, Yingchao Yang, Xiaolong Zou, Xiao-Dong Zhou, Robert Vajtai, Boris I. Yakobson, Jun Lou, and Pulickel M. Ajayan
Nano Letters 2016 Volume 16(Issue 1) pp:466-470
Publication Date(Web):December 9, 2015
DOI:10.1021/acs.nanolett.5b04123
The practical recycling of carbon dioxide (CO2) by the electrochemical reduction route requires an active, stable, and affordable catalyst system. Although noble metals such as gold and silver have been demonstrated to reduce CO2 into carbon monoxide (CO) efficiently, they suffer from poor durability and scarcity. Here we report three-dimensional (3D) graphene foam incorporated with nitrogen defects as a metal-free catalyst for CO2 reduction. The nitrogen-doped 3D graphene foam requires negligible onset overpotential (−0.19 V) for CO formation, and it exhibits superior activity over Au and Ag, achieving similar maximum Faradaic efficiency for CO production (∼85%) at a lower overpotential (−0.47 V) and better stability for at least 5 h. The dependence of catalytic activity on N-defect structures is unraveled by systematic experimental investigations. Indeed, the density functional theory calculations confirm pyridinic N as the most active site for CO2 reduction, consistent with experimental results.
Co-reporter:I. Abid, A. Bohloul, S. Najmaei, C. Avendano, H.-L. Liu, R. Péchou, A. Mlayah and J. Lou
Nanoscale 2016 vol. 8(Issue 15) pp:8151-8159
Publication Date(Web):15 Mar 2016
DOI:10.1039/C6NR00829A
In this work we investigate the interaction between plasmonic and excitonic resonances in hybrid MoSe2@Au nanostructures. The latter were fabricated by combining chemical vapor deposition of MoSe2 atomic layers, Au disk processing by nanosphere lithography and a soft lift-off/transfer technique. The samples were characterized by scanning electron and atomic force microscopy. Their optical properties were investigated experimentally using optical absorption, Raman scattering and photoluminescence spectroscopy. The work is focused on a resonant situation where the surface plasmon resonance is tuned to the excitonic transition. In that case, the near-field interaction between the surface plasmons and the confined excitons leads to interference between the plasmonic and excitonic resonances that manifests in the optical spectra as a transparency dip. The plasmonic–excitonic interaction regime is determined using quantitative analysis of the optical extinction spectra based on an analytical model supported by numerical simulations. We found that the plasmonic–excitonic resonances do interfere thus leading to a typical Fano lineshape of the optical extinction. The near-field nature of the plasmonic–excitonic interaction is pointed out experimentally from the dependence of the optical absorption on the number of monolayer stacks on the Au nanodisks. The results presented in this work contribute to the development of new concepts in the field of hybrid plasmonics.
Co-reporter:Pei Dong, Alin Cristian Chipara, Phillip Loya, Yingchao Yang, Liehui Ge, Sidong Lei, Bo Li, Gustavo Brunetto, Leonardo D. Machado, Liang Hong, Qizhong Wang, Bilan Yang, Hua Guo, Emilie Ringe, Douglas S. Galvao, Robert Vajtai, Mircea Chipara, Ming Tang, Jun Lou, and Pulickel M. Ajayan
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 3) pp:2142
Publication Date(Web):December 31, 2015
DOI:10.1021/acsami.5b10667
A solid–liquid self-adaptive composite (SAC) is synthesized using a simple mixing–evaporation protocol, with poly(dimethylsiloxane) (PDMS) and poly(vinylidene fluoride) (PVDF) as active constituents. SAC exists as a porous solid containing a near equivalent distribution of the solid (PVDF)–liquid (PDMS) phases, with the liquid encapsulated and stabilized within a continuous solid network percolating throughout the structure. The pores, liquid, and solid phases form a complex hierarchical structure, which offers both mechanical robustness and a significant structural adaptability under external forces. SAC exhibits attractive self-healing properties during tension, and demonstrates reversible self-stiffening properties under compression with a maximum of 7-fold increase seen in the storage modulus. In a comparison to existing self-healing and self-stiffening materials, SAC offers distinct advantages in the ease of fabrication, high achievable storage modulus, and reversibility. Such materials could provide a new class of adaptive materials system with multifunctionality, tunability, and scale-up potentials.Keywords: hierarchical structure; self-adaptive; self-healing; self-stiffening; solid−liquid composite
Co-reporter:Jingjie Wu;Mingjie Liu;Kuntal Chatterjee;Ken P. Hackenberg;Jianfeng Shen;Xiaolong Zou;Yong Yan;Jing Gu;Yingchao Yang;Pulickel M. Ajayan
Advanced Materials Interfaces 2016 Volume 3( Issue 9) pp:
Publication Date(Web):
DOI:10.1002/admi.201500669
The scarcity of inexpensive and efficient electrocatalyst for acid water oxidation to molecular oxygen presents the development of nonprecious catalysts for water oxidation a scientific priority. For water splitting, transition-metal dichalcogenides have attracted great interest as advanced catalysts for hydrogen evolution reaction, but there has been no sincere attention to generate significant anodic current density of oxygen evolution reaction (OER) with these materials. Addressing this unmet need, here, the outstanding catalytic performance of MoS2 and TaS2 in OER is demonstrated. Chemically exfoliated 2D thin sheets of MoS2 and TaS2, in both of their 1T and 2H polymorph, have been employed for OER catalysis in acid medium. The best performance for oxygen evolution, which is also comparable to benchmark IrO2, comes out from 1T-MoS2 followed by 1T-TaS2, 2H-MoS2, and 2H-TaS2. Theoretical study reveals that the dominant catalytic activity is on edge sites instead of surface and corroborates the experimental results of polymorphic dependence of electrocatalytic activity. The materials have also shown moderate durability in the harsh acidic medium. The study brings up new set of electrocatalyst for oxygen evolution in acid regime that hitherto has remained largely unrevealed.
Co-reporter:Jingjie Wu;Zhili Hu;Zehua Jin;Sidong Lei;Hua Guo;Kuntal Chatterjee;Jing Zhang;Yingchao Yang;Bo Li;Yang Liu;Jiawei Lai;Robert Vajtai;Boris Yakobson;Ming Tang;Pulickel M. Ajayan
Advanced Materials Interfaces 2016 Volume 3( Issue 16) pp:
Publication Date(Web):
DOI:10.1002/admi.201600383
Although a lot of work has been reported on the growth and properties of 2D atomic layered materials, the growth mechanism for these crystals via the chemical vapor deposition method (CVD) has remained elusive. Here, a screw dislocation–driven spiral growth of SnSe2 crystal flakes via CVD is reported. The polymorph of as-synthesized SnSe2 crystals is verified as 1T-phase by both experimental characterization and theoretical calculation. The density functional theory study reveals morphology transformation during the growth process while phase-field modeling unravels the screw dislocation propagation to form the pyramid-like structure of SnSe2. The optical band gap of SnSe2 crystals relates to an indirect band gap of 1.0 eV. The photodetector devices based on SnSe2 crystals exhibit high responsivity and ultrafast response time in the microsecond regime.
Co-reporter:Will J. Hardy, Jiangtan Yuan, Hua Guo, Panpan Zhou, Jun Lou, and Douglas Natelson
ACS Nano 2016 Volume 10(Issue 6) pp:5941
Publication Date(Web):May 10, 2016
DOI:10.1021/acsnano.6b01269
With materials approaching the 2D limit yielding many exciting systems with intriguing physical properties and promising technological functionalities, understanding and engineering magnetic order in nanoscale, layered materials is generating keen interest. One such material is V5S8, a metal with an antiferromagnetic ground state below the Néel temperature TN ∼ 32 K and a prominent spin-flop signature in the magnetoresistance (MR) when H∥c ∼ 4.2 T. Here we study nanoscale-thickness single crystals of V5S8, focusing on temperatures close to TN and the evolution of material properties in response to systematic reduction in crystal thickness. Transport measurements just below TN reveal magnetic hysteresis that we ascribe to a metamagnetic transition, the first-order magnetic-field-driven breakdown of the ordered state. The reduction of crystal thickness to ∼10 nm coincides with systematic changes in the magnetic response: TN falls, implying that antiferromagnetism is suppressed; and while the spin-flop signature remains, the hysteresis disappears, implying that the metamagnetic transition becomes second order as the thickness approaches the 2D limit. This work demonstrates that single crystals of magnetic materials with nanometer thicknesses are promising systems for future studies of magnetism in reduced dimensionality and quantum phase transitions.Keywords: antiferromagnet; magnetic layered material; magnetoresistance; quantum critical point; V5S8
Co-reporter:Sina Najmaei, Jiangtan Yuan, Jing Zhang, Pulickel Ajayan, and Jun Lou
Accounts of Chemical Research 2015 Volume 48(Issue 1) pp:31
Publication Date(Web):December 9, 2014
DOI:10.1021/ar500291j
The unique physical properties of two-dimensional (2D) molybdenum disulfide (MoS2) and its promising applications in future optoelectronics have motivated an extensive study of its physical properties. However, a major limiting factor in investigation of 2D MoS2 is its large area and high quality preparation. The existence of various types of defects in MoS2 also makes the characterization of defect types and the understanding of their roles in the physical properties of this material of critical importance.In this Account, we review the progress in the development of synthetic approaches for preparation of 2D MoS2 and the understanding of the role of defects in its electronic and optical properties. We first examine our research efforts in understanding exfoliation, direct sulfurization, and chemical vapor deposition (CVD) of MoS2 monolayers as main approaches for preparation of such atomic layers. Recognizing that a natural consequence of the synthetic approaches is the addition of sources of defects, we initially focus on identifying these imperfections with intrinsic and extrinsic origins in CVD MoS2. We reveal the predominant types of point and grain boundary defects in the crystal structure of polycrystalline MoS2 using transmission electron microscopy (TEM) and understand how they modify the electronic band structure of this material using first-principles-calculations. Our observations and calculations reveal the main types of vacancy defects, substitutional defects, and dislocation cores at the grain boundaries (GBs) of MoS2. Since the sources of defects in two-dimensional atomic layers can, in principle, be controlled and studied with more precision compared with their bulk counterparts, understanding their roles in the physical properties of this material may provide opportunities for changing their properties. Therefore, we next examine the general electronic properties of single-crystalline 2D MoS2 and study the role of GBs in the electrical transport and photoluminescence properties of its polycrystalline counterparts. These results reveal the important role played by point defects and GBs in affecting charge carrier mobility and excitonic properties of these atomic layers.In addition to the intrinsic defects, growth process induced substrate impurities and strain induced band structure perturbations are revealed as major sources of disorder in CVD grown 2D MoS2. We further explore substrate defects for modification and control of electronic and optical properties of 2D MoS2 through interface engineering. Self-assembled monolayer based interface modification, as a versatile technique adaptable to different conventional and flexible substrates, is used to promote significant tunability in the key MoS2 field-effect device parameters. This approach provides a powerful tool for modification of native substrate defect characteristics and allows for a wide range of property modulations. Our results signify the role of intrinsic and extrinsic defects in the physical properties of MoS2 and unveil strategies that can utilize these characteristics.
Co-reporter:Jiangtan Yuan;Jingjie Wu;Will J. Hardy;Philip Loya;Minhan Lou;Yingchao Yang;Sina Najmaei;Menglei Jiang;Fan Qin;Kunttal Keyshar;Heng Ji;Weilu Gao;Jiming Bao;Junichiro Kono;Douglas Natelson;Pulickel M. Ajayan
Advanced Materials 2015 Volume 27( Issue 37) pp:5605-5609
Publication Date(Web):
DOI:10.1002/adma.201502075
Co-reporter:Jia Liang, Yingchao Yang, Jing Zhang, Jingjie Wu, Pei Dong, Jiangtan Yuan, Gengmin Zhang and Jun Lou
Nanoscale 2015 vol. 7(Issue 36) pp:14813-14816
Publication Date(Web):10 Aug 2015
DOI:10.1039/C5NR03724G
In this communication, nickel diselenide (NiSe2) nanoparticles are synthesized by a facile and low-cost hydrothermal method. The synthesis method can be extended to other metal diselenides as well. The electrode made of NiSe2 exhibits superior electrocatalytic activity in the hydrogen evolution reaction (HER). A low Tafel slope of 31.1 mV per decade is achieved for NiSe2, which is comparable to that of platinum (∼30 mV per decade). Moreover, the catalytic activity of NiSe2 is very stable and no obvious degradation is found even after 1000 cyclic voltammetric sweeps.
Co-reporter:Ram Manohar Yadav, Jingjie Wu, Raji Kochandra, Lulu Ma, Chandra Sekhar Tiwary, Liehui Ge, Gonglan Ye, Robert Vajtai, Jun Lou, and Pulickel M. Ajayan
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 22) pp:11991
Publication Date(Web):May 13, 2015
DOI:10.1021/acsami.5b02032
Oxygen reduction and evolution reactions are essential for broad range of renewable energy technologies such as fuel cells, metal-air batteries and hydrogen production through water splitting, therefore, tremendous effort has been taken to develop excellent catalysts for these reactions. However, the development of cost-effective and efficient bifunctional catalysts for both reactions still remained a grand challenge. Herein, we report the electrocatalytic investigations of bamboo-shaped carbon nitrogen nanotubes (CNNTs) having different diameter distribution synthesized by liquid chemical vapor deposition technique using different nitrogen containing precursors. These CNNTs are found to be efficient bifunctional electrocatalyst for oxygen reduction and evolution reactions. The electrocatalytic activity strongly depends on the nanotube diameter as well as nitrogen functionality type. The higher diameter CNNTs are more favorable for these reactions. The increase in nanotube diameter itself enhances the catalytic activity by lowering the oxygen adsorption energy, better conductivity, and further facilitates the reaction by increasing the percentage of catalytically active nitrogen moieties in CNNTs.Keywords: carbon nitrogen nanotubes; nanotube diameter; nitrogen moieties; oxygen reduction and evolution reactions;
Co-reporter:Jingjie Wu, Lulu Ma, Ram Manohar Yadav, Yingchao Yang, Xiang Zhang, Robert Vajtai, Jun Lou, and Pulickel M. Ajayan
ACS Applied Materials & Interfaces 2015 Volume 7(Issue 27) pp:14763
Publication Date(Web):June 19, 2015
DOI:10.1021/acsami.5b02902
The nitrogen-doped graphene (NG) with dominance of the pyridinic-N configuration is synthesized via a straightforward process including chemical vapor deposition (CVD) growth of graphene and postdoping with a solid nitrogen precursor of graphitic C3N4 at elevated temperature. The NG fabricated from CVD-grown graphene contains a high N content up to 6.5 at. % when postdoped at 800 °C but maintains high crystalline quality of graphene. The obtained NG exhibits high activity, long-standing stability, and outstanding crossover resistance for electrocatalysis of oxygen reduction reaction (ORR) in alkaline medium. The NG treated at 800 °C shows the best ORR performance. Further study of the dependence of ORR activity on different N functional groups in these metal-free NG electrodes provides deeper insights into the origin of ORR activity. Our results reveal that the pyridinic-N tends to be the most active N functional group to facilitate ORR at low overpotential via a four-electron pathway.Keywords: low defect; metal-free; nitrogen functionality; nitrogen-doped graphene; oxygen reduction reaction; pyridinic nitrogen;
Co-reporter:Jiangnan Zhang, Jin Haeng Lee, Jun Lou, Yanfei Gao
Extreme Mechanics Letters 2015 Volume 2() pp:60-64
Publication Date(Web):March 2015
DOI:10.1016/j.eml.2015.01.005
Nano-asperity friction force has been found to depend on both the sliding velocity and the contact size. The former is a consequence of stress-assisted, thermally activated process, which is often explained by the one-degree-of-freedom Tomlinson model that assumes a virtual point contact sliding over a periodic tip–surface interaction potential. However, this model cannot provide an accurate description of the rate-determining process when coupled with the contact size dependence. In this synergistic experimental/modeling study, atomic friction measurements were conducted on cleaved mica and HOPG surfaces with varying normal force and sliding velocity, and the spatially-nonuniform saddle-point configurations were calculated from a Peierls framework. The agreement between experiments and theory suggests that the detailed characteristics of the interface slip field govern the atomic friction.
Co-reporter:Jiangtan Yuan, Sina Najmaei, Zhuhua Zhang, Jing Zhang, Sidong Lei, Pulickel M. Ajayan, Boris I. Yakobson, and Jun Lou
ACS Nano 2015 Volume 9(Issue 1) pp:555
Publication Date(Web):January 8, 2015
DOI:10.1021/nn505809d
Transition metal dichalcogenides monolayers and black phosphorus thin crystals are emerging two-dimensional materials that demonstrated extraordinary optoelectronic properties. Exotic properties and physics may arise when atomic layers of different materials are stacked together to form van der Waals solids. Understanding the important interlayer couplings in such heterostructures could provide avenues for control and creation of characteristics in these artificial stacks. Here we systematically investigate the optical and optoelectronic properties of artificial stacks of molybdenum disulfide, tungsten disulfide, and black phosphorus atomic layers. An anomalous photoluminescence quenching was observed in tungsten disulfide–molybdenum disulfide stacks. This was attributed to a direct to indirect band gap transition of tungsten disulfide in such stacks while molybdenum disulfide maintains its monolayer properties by first-principles calculations. On the other hand, due to the strong build-in electric fields in tungsten disulfide–black phosphorus or molybdenum disulfide–black phosphorus stacks, the excitons can be efficiently splitted despite both the component layers having a direct band gap in these stacks. We further examine optoelectronic properties of tungsten disulfide–molybdenum disulfide artificial stacks and demonstrate their great potentials in future optoelectronic applications.Keywords: black phosphorus; charge transfer; optoelectronics; photoluminescence; transition metal dichalcogenides;
Co-reporter:Jingjie Wu, Ram Manohar Yadav, Mingjie Liu, Pranav P. Sharma, Chandra Sekhar Tiwary, Lulu Ma, Xiaolong Zou, Xiao-Dong Zhou, Boris I. Yakobson, Jun Lou, and Pulickel M. Ajayan
ACS Nano 2015 Volume 9(Issue 5) pp:5364
Publication Date(Web):April 21, 2015
DOI:10.1021/acsnano.5b01079
The challenge in the electrosynthesis of fuels from CO2 is to achieve durable and active performance with cost-effective catalysts. Here, we report that carbon nanotubes (CNTs), doped with nitrogen to form resident electron-rich defects, can act as highly efficient and, more importantly, stable catalysts for the conversion of CO2 to CO. The unprecedented overpotential (−0.18 V) and selectivity (80%) observed on nitrogen-doped CNTs (NCNTs) are attributed to their unique features to facilitate the reaction, including (i) high electrical conductivity, (ii) preferable catalytic sites (pyridinic N defects), and (iii) low free energy for CO2 activation and high barrier for hydrogen evolution. Indeed, DFT calculations show a low free energy barrier for the potential-limiting step to form key intermediate COOH as well as strong binding energy of adsorbed COOH and weak binding energy for the adsorbed CO. The highest selective site toward CO production is pyridinic N, and the NCNT-based electrodes exhibit no degradation over 10 h of continuous operation, suggesting the structural stability of the electrode.Keywords: carbon nanotubes; CO2 reduction; high durability; high selectivity; low overpotential; pyridinic nitrogen;
Co-reporter:Pranav P. Sharma;Dr. Jingjie Wu;Dr. Ram Manohar Yadav;Mingjie Liu;Christopher J. Wright;Dr. Chra Sekhar Tiwary; Boris I. Yakobson; Jun Lou; Pulickel M. Ajayan; Xiao-Dong Zhou
Angewandte Chemie International Edition 2015 Volume 54( Issue 46) pp:13701-13705
Publication Date(Web):
DOI:10.1002/anie.201506062
Abstract
Nitrogen-doped carbon nanotubes (NCNTs) have been considered as a promising electrocatalyst for carbon-dioxide-reduction reactions, but two fundamental chemistry questions remain obscure: 1) What are the active centers with respect to various defect species and 2) what is the role of defect density on the selectivity of NCNTs? The aim of this work is to address these questions. The catalytic activity of NCNTs depends on the structural nature of nitrogen in CNTs and defect density. Comparing with pristine CNTs, the presence of graphitic and pyridinic nitrogen significantly decreases the overpotential (ca. −0.18 V) and increases the selectivity (ca. 80 %) towards the formation of CO. The experimental results are in congruent with DFT calculations, which show that pyridinic defects retain a lone pair of electrons that are capable of binding CO2. However, for graphitic-like nitrogen, electrons are located in the π* antibonding orbital, making them less accessible for CO2 binding.
Co-reporter:Pranav P. Sharma;Dr. Jingjie Wu;Dr. Ram Manohar Yadav;Mingjie Liu;Christopher J. Wright;Dr. Chra Sekhar Tiwary; Boris I. Yakobson; Jun Lou; Pulickel M. Ajayan; Xiao-Dong Zhou
Angewandte Chemie 2015 Volume 127( Issue 46) pp:13905-13909
Publication Date(Web):
DOI:10.1002/ange.201506062
Abstract
Nitrogen-doped carbon nanotubes (NCNTs) have been considered as a promising electrocatalyst for carbon-dioxide-reduction reactions, but two fundamental chemistry questions remain obscure: 1) What are the active centers with respect to various defect species and 2) what is the role of defect density on the selectivity of NCNTs? The aim of this work is to address these questions. The catalytic activity of NCNTs depends on the structural nature of nitrogen in CNTs and defect density. Comparing with pristine CNTs, the presence of graphitic and pyridinic nitrogen significantly decreases the overpotential (ca. −0.18 V) and increases the selectivity (ca. 80 %) towards the formation of CO. The experimental results are in congruent with DFT calculations, which show that pyridinic defects retain a lone pair of electrons that are capable of binding CO2. However, for graphitic-like nitrogen, electrons are located in the π* antibonding orbital, making them less accessible for CO2 binding.
Co-reporter:Sina Najmaei, Xiaolong Zou, Dequan Er, Junwen Li, Zehua Jin, Weilu Gao, Qi Zhang, Sooyoun Park, Liehui Ge, Sidong Lei, Junichiro Kono, Vivek B. Shenoy, Boris I. Yakobson, Antony George, Pulickel M. Ajayan, and Jun Lou
Nano Letters 2014 Volume 14(Issue 3) pp:1354-1361
Publication Date(Web):February 11, 2014
DOI:10.1021/nl404396p
We demonstrate how substrate interfacial chemistry can be utilized to tailor the physical properties of single-crystalline molybdenum disulfide (MoS2) atomic-layers. Semiconducting, two-dimensional MoS2 possesses unique properties that are promising for future optical and electrical applications for which the ability to tune its physical properties is essential. We use self-assembled monolayers with a variety of end termination chemistries to functionalize substrates and systematically study their influence on the physical properties of MoS2. Using electrical transport measurements, temperature-dependent photoluminescence spectroscopy, and empirical and first-principles calculations, we explore the possible mechanisms involved. Our data shows that combined interface-related effects of charge transfer, built-in molecular polarities, varied densities of defects, and remote interfacial phonons strongly modify the electrical and optical properties of MoS2. These findings can be used to effectively enhance or modulate the conductivity, field-effect mobility, and photoluminescence in MoS2 monolayers, illustrating an approach for local and universal property modulations in two-dimensional atomic-layers.
Co-reporter:Jing Zhang, Sina Najmaei, Hong Lin and Jun Lou
Nanoscale 2014 vol. 6(Issue 10) pp:5279-5283
Publication Date(Web):21 Feb 2014
DOI:10.1039/C3NR05979K
A novel MoS2 transparent counter electrode for dye-sensitized solar cells is reported. In order to enhance the catalytic activity of the electrode, active edge sites are created artificially by patterning holes on MoS2 atomic layers. Electrochemical analysis shows that the electrochemical activity is significantly improved after the patterning of holes. The photon-to-electron efficiency of the dye-sensitized solar cells based on MoS2 atomic layer counter electrodes is increased remarkably from 2% to 5.8% after the hole patterning.
Co-reporter:Pei Dong, Yu Zhu, Jing Zhang, Feng Hao, Jingjie Wu, Sidong Lei, Hong Lin, Robert H. Hauge, James M. Tour and Jun Lou
Journal of Materials Chemistry A 2014 vol. 2(Issue 48) pp:20902-20907
Publication Date(Web):31 Oct 2014
DOI:10.1039/C4TA05264A
Dye-sensitized solar cells (DSSCs) are an emerging photovoltaic technology with both low costs and good efficiency. However, the cathode used in most DSSCs is fluorine-doped tin oxide glass coated with a Pt film, which is both expensive and brittle and therefore limits the flexibility and large-scale implementation of this promising technology. We report here work which showed that flexible, seamlessly covalently bonded, three-dimensional vertically aligned few-walled carbon nanotubes (VAFWCNTs)/graphene on metal foil can act as a novel cathode free from transparent conducting oxide and Pt for application in DSSCs. This cathode has a lower charge transfer resistance and lower contact resistance between the catalyst and the substrate than the conventional combination in a brittle Pt/fluorine-doped tin oxide cathode. The covalently bonded graphene and VAFWCNTs ensure excellent electron transport through the electrode and the large surface area of the hybrid carbon materials rivals the catalytic capability of the Pt analogue. DSSCs utilizing this flexible VAFWCNTs/graphene hybrid cathode outperformed the Pt-based cells in both rigid (8.2% vs. 6.4%) and flexible (3.9% vs. 3.4%) assemblies. The VAFWCNTs/graphene on metal foil combination is a novel, inexpensive, high-performance, flexible cathode for application in solar cells.
Co-reporter:Pei Dong ; Yu Zhu ; Jing Zhang ; Cheng Peng ; Zheng Yan ; Lei Li ; Zhiwei Peng ; Gedeng Ruan ; Wanyao Xiao ; Hong Lin ; James M. Tour
The Journal of Physical Chemistry C 2014 Volume 118(Issue 45) pp:25863-25868
Publication Date(Web):October 8, 2014
DOI:10.1021/jp505735j
Metal grids covered by graphene were used as transparent conductive electrodes in dye sensitized solar cells. The efficiency of dye sensitized solar cells with graphene-on-Pt grids was 0.4%. Compared to the control group, in which the platinum grids were used as a transparent conductive layer, the efficiency of dye sensitized solar cells with graphene was more than 2 times better. To our knowledge, it is the most efficient dye sensitized solar cell to use a graphene-based transparent conductive electrode without a conductive oxide support such as fluorine-doped tin oxide or indium-doped tin oxide. The dye sensitized solar cell prepared by 150 °C as the low temperature processes, which are essential for fabricating flexible dye sensitized solar cells, was fabricated using a hybrid graphene on Ni grids transparent conductive electrode, and it exhibited an efficiency of 0.25%. The mechanical properties of the flexible hybrid transparent electrode are better than the oxide-based transparent conductive electrode in both bending and stretching tests. Therefore, the long-term stability of the flexible dye sensitized solar cells could be enhanced by using this new transparent conductive layer.
Co-reporter:Sina Najmaei, Adnen Mlayah, Arnaud Arbouet, Christian Girard, Jean Léotin, and Jun Lou
ACS Nano 2014 Volume 8(Issue 12) pp:12682
Publication Date(Web):December 3, 2014
DOI:10.1021/nn5056942
We report on the fabrication of monolayer MoS2-coated gold nanoantennas combining chemical vapor deposition, e-beam lithography surface patterning, and a soft lift-off/transfer technique. The optical properties of these hybrid plasmonic–excitonic nanostructures are investigated using spatially resolved photoluminescence spectroscopy. Off- and in-resonance plasmonic pumping of the MoS2 excitonic luminescence showed distinct behaviors. For plasmonically mediated pumping, we found a significant enhancement (∼65%) of the photoluminescence intensity, clear evidence that the optical properties of the MoS2 monolayer are strongly influenced by the nanoantenna surface plasmons. In addition, a systematic photoluminescence broadening and red-shift in nanoantenna locations is observed which is interpreted in terms of plasmonic enhanced optical absorption and subsequent heating of the MoS2 monolayers. Using a temperature calibration procedure based on photoluminescence spectral characteristics, we were able to estimate the local temperature changes. We found that the plasmonically induced MoS2 temperature increase is nearly four times larger than in the MoS2 reference temperatures. This study shines light on the plasmonic–excitonic interaction in these hybrid metal/semiconductor nanostructures and provides a unique approach for the engineering of optoelectronic devices based on the light-to-current conversion.Keywords: nanostructure; photoluminescence; plasmonic;
Co-reporter:Sina Najmaei, Matin Amani, Matthew L. Chin, Zheng Liu, A. Glen Birdwell, Terrance P. O’Regan, Pulickel M. Ajayan, Madan Dubey, and Jun Lou
ACS Nano 2014 Volume 8(Issue 8) pp:7930
Publication Date(Web):July 14, 2014
DOI:10.1021/nn501701a
Semiconducting MoS2 monolayers have shown many promising electrical properties, and the inevitable polycrystallinity in synthetic, large-area films renders understanding the effect of structural defects, such as grain boundaries (GBs, or line-defects in two-dimensional materials), essential. In this work, we first examine the role of GBs in the electrical-transport properties of MoS2 monolayers with varying line-defect densities. We reveal a systematic degradation of electrical characteristics as the line-defect density increases. The two common MoS2 GB types and their specific roles are further examined, and we find that only tilt GBs have a considerable effect on the MoS2 electrical properties. By examining the electronic states and sources of disorder using temperature-dependent transport studies, we adopt the Anderson model for disordered systems to explain the observed transport behaviors in different temperature regimes. Our results elucidate the roles played by GBs in different scenarios and give insights into their underlying scattering mechanisms.Keywords: electronic transport; grain boundaries; MoS2; polycrystallinity; two-dimensional materials
Co-reporter:Sina Najmaei, Pulickel M. Ajayan and J. Lou
Nanoscale 2013 vol. 5(Issue 20) pp:9758-9763
Publication Date(Web):31 Jul 2013
DOI:10.1039/C3NR02567E
Raman spectroscopy is utilized to quantify the temperature dependency of the vibrational modes in molybdenum disulfide (MoS2) atomic layers. These analyses are essential for understanding the structural properties and phononic behaviors of this two-dimensional (2D) material. We quantitatively analyze the temperature dependent shifts of the Raman peak positions in the temperature range from 300 to 550 K, and find that both planar and out-of-plane characteristic modes are highly sensitive to temperature variations. This temperature dependency is linear and can be fully explained by the first-order temperature coefficient. Using a semi-quantitative model, we evaluate the contributions of the material's thermal expansion and intrinsic temperature effects to this dependency. We reveal that the dominating source of shift in the peak position of planar mode E2g1 for samples of all thicknesses investigated is the four-phonon process. In addition to the four-phonon process, thermal expansion plays a significant role in the temperature dependency of the out-of-plane mode, A1g. The thickness dependency of the temperature coefficient for MoS2 and a drastic change in behaviors of samples from bi- to single-layered are also demonstrated. We further explore the role of defects in the thermal properties of MoS2 by examining the temperature dependency of Raman modes in CVD-grown samples.
Co-reporter:J. Zhang, H. Lu, Y. Sun, L. Ci, P. M. Ajayan, and J. Lou
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 19) pp:9501
Publication Date(Web):September 4, 2013
DOI:10.1021/am402221u
We evaluated the interfacial properties of vertically and transversely aligned multiwalled carbon nanotubes (CNTs) carpets using atomic force microscopy (AFM) under ambient (26%–52% relative humidity (RH)), mild (10% RH), and dry conditions (<3.3% RH). The frictional forces on a transversely aligned CNT (TAMWCNT) surface are lower than those on a vertically aligned CNT (VAMWCNT) surface, and they decrease as the relative humidity decreases for both TAMWCNT and VAMWCNT surfaces. Similar trends are found for adhesion forces on both surfaces. Contact mechanics theories are applied and compared in an attempt to better understand these results. The tribological behavior of CNT carpets unveiled in this paper is expected to inspire tunable friction surface engineering strategies.Keywords: adhesion and friction; anisotropy; carbon nanotube; humidity;
Co-reporter:Cheng Peng;Zheng Jia;Henry Neilson;Teng Li
Advanced Engineering Materials 2013 Volume 15( Issue 4) pp:250-256
Publication Date(Web):
DOI:10.1002/adem.201200169
Abstract
Indium Tin Oxide (ITO) films are widely used as transparent electrodes in electronic displays and solar cells. However, the small fracture strain of brittle ITO films poses significant challenge to their applications in flexible electronics devices that often undergo large deformation. Inspired by recent development of inorganic/organic hybrid permeation barriers for flexible electronics, we design and fabricate ITO-based multilayer electrodes with enhanced electro-mechanical durability. In situ electro-mechanical experiments of five structural designs of ITO-based multilayer electrodes are performed to investigate the evolution of crack density and the corresponding variance of electrical resistance of such electrodes. A coherent mechanics model is established to determine the driving force for crack propagation in the ITO layer in these electrodes. The mechanics model suggests that a top protective polymeric coating above and an intermediate polymeric layer below the ITO layer can effectively enhance the mechanical durability of the ITO electrodes by reducing the crack driving force up to 10-folds. The modeling results offer mechanistic understanding of the in situ experimental measurements of the critical fracture strains of the five types of ITO-based multilayer electrodes. The findings in this work provide quantitative guidance for the material selection and structural optimization of ITO-based multilayer transparent electrodes of high mechanical durability.
Co-reporter:Zheng Jia, Cheng Peng, Jun Lou, Teng Li
Thin Solid Films 2012 Volume 520(Issue 21) pp:6576-6580
Publication Date(Web):31 August 2012
DOI:10.1016/j.tsf.2012.07.011
Our in situ experiments of polyimide-supported thin indium tin oxide (ITO) films reveal buckling-driven film cracking in some samples and buckling-driven interfacial delamination in other samples. Although studies of individual buckling-driven failure mode exist, it still remains unclear what governs the competition between these two different failure modes in a given film/substrate structure. Through theoretical analysis and numerical simulations, we delineate a map of competing buckling-driven failure modes of substrate-supported thin brittle films in the parameter space of interfacial adhesion and interfacial imperfection size. Such a map can offer insight on the mechanical durability of functional thin films. For example, interestingly, we show that strongly bonded thin brittle films are more prone to buckling-driven cracking, a more detrimental failure mode for thin brittle ITO transparent conductors widely used in displays and flexible electronics.Highlights► Map of buckling-driven failure modes of thin brittle films on substrates. ► We study key parameters that govern buckling-driven failure modes. ► The map offers insights on optimal design of functional thin films.
Co-reporter:Zheng Liu, Li Song, Shizhen Zhao, Jiaqi Huang, Lulu Ma, Jiangnan Zhang, Jun Lou, and Pulickel M. Ajayan
Nano Letters 2011 Volume 11(Issue 5) pp:2032-2037
Publication Date(Web):April 13, 2011
DOI:10.1021/nl200464j
Graphene (G) and atomic layers of hexagonal boron nitride (h-BN) are complementary two-dimensional materials, structurally very similar but with vastly different electronic properties. Recent studies indicate that h-BN atomic layers would be excellent dielectric layers to complement graphene electronics. Graphene on h-BN has been realized via peeling of layers from bulk material to create G/h-BN stacks. Considering that both these layers can be independently grown via chemical vapor deposition (CVD) of their precursors on metal substrates, it is feasible that these can be sequentially grown on substrates to create the G/h-BN stacked layers useful for applications. Here we demonstrate the direct CVD growth of h-BN on highly oriented pyrolytic graphite and on mechanically exfoliated graphene, as well as the large area growth of G/h-BN stacks, consisting of few layers of graphene and h-BN, via a two-step CVD process. The G/h-BN film is uniform and continuous and could be transferred onto different substrates for further characterization and device fabrication.
Co-reporter:Zheng Liu, Lijun Hu, Ji Liu, Caiyu Qiu, Haiqing Zhou, Daniel P. Hashim, Gang Shi, Cheng Peng, Sina Najmaei, Lianfeng Sun, Jun Lou, and Pulickel M. Ajayan
Nano Letters 2011 Volume 11(Issue 12) pp:5117-5122
Publication Date(Web):October 28, 2011
DOI:10.1021/nl201910j
In this paper, a method of strain actuation of single-walled carbon nanotube (SWNT) films using droplets is examined, and the physical origin of an open-circuit voltage (Voc)—observed across the film during this process—is explored. We demonstrate that droplet actuation is driven by the formation of a capillary bridge between the suspended SWNT films and the substrates, which deforms the films by wetting forces during evaporation. The induced strain is further evaluated and analyzed using dynamic Raman and two-dimensional correlation spectra. Supported by theoretical calculations, our experiments reveal the time and strain dependency of the capillary bridge’s midpoint directional movement. This relationship is applied to display the correlation between the induced strain and the measured Voc.
Co-reporter:Yang Lu;Jun Song;Jian Yu Huang
Advanced Functional Materials 2011 Volume 21( Issue 20) pp:3982-3989
Publication Date(Web):
DOI:10.1002/adfm.201101224
Abstract
Fracture of metals at the nanoscale and corresponding failure mechanisms have recently attracted considerable interest. However, quantitative in situ fracture experiments of nanoscale metals are rarely reported. Here it is shown that, under uni-axial tensile loading, single crystalline ultrathin gold nanowires may fracture in two modes, displaying distinctively different fracture morphologies and ductility. In situ high resolution transmission electron microscopy (HRTEM) studies suggest that the unexpected brittle-like fracture was closely related to the observed twin structures, which is very different from surface dislocation nucleation/propagation mediated mechanism in ductile fracture mode. Molecular dynamics (MD) simulations further reveal the processes of shear-induced twin formation and damage initiation at the twin structure/free surface interface, confirming the experimentally observed differences in fracture morphology and ductility. Finally, a fracture criterion based on competition between twin formation and surface dislocation nucleation/propagation as a function of misalignment angle is discussed.
Co-reporter:Yogeeswaran Ganesan, Cheng Peng, Yang Lu, Phillip E. Loya, Padraig Moloney, Enrique Barrera, Boris I. Yakobson, James M. Tour, Roberto Ballarini, and Jun Lou
ACS Applied Materials & Interfaces 2011 Volume 3(Issue 2) pp:129
Publication Date(Web):January 7, 2011
DOI:10.1021/am1011047
Traditional single-fiber pull-out type experiments were conducted on individual multiwalled carbon nanotubes (MWNT) embedded in an epoxy matrix using a novel technique. Remarkably, the results are qualitatively consistent with the predictions of continuum fracture mechanics models. Unstable interface crack propagation occurred at short MWNT embedments, which essentially exhibited a linear load−displacement response prior to peak load. Deep embedments, however, enabled stable crack extension and produced a nonlinear load−displacement response prior to peak load. The maximum pull-out forces corresponding to a wide range of embedments were used to compute the nominal interfacial shear strength and the interfacial fracture energy of the pristine MWNT-epoxy interface.Keywords (keywords): epoxy composite; interfacial strength; multiwall carbon nanotubes; single-fiber pull-out
Co-reporter:Pei Dong, Cary L. Pint, Mel Hainey, Francesca Mirri, Yongjie Zhan, Jing Zhang, Matteo Pasquali, Robert H. Hauge, Rafael Verduzco, Mian Jiang, Hong Lin, and Jun Lou
ACS Applied Materials & Interfaces 2011 Volume 3(Issue 8) pp:3157
Publication Date(Web):July 19, 2011
DOI:10.1021/am200659y
A novel dye-sensitized solar cell (DSSC) structure using vertically aligned single-walled carbon nanotubes (VASWCNTs) as the counter electrode has been developed. In this design, the VASWCNTs serve as a stable high surface area and highly active electrocatalytic counter-electrode that could be a promising alternative to the conventional Pt analogue. Utilizing a scalable dry transfer approach to form a VASWCNTs conductive electrode, the DSSCs with various lengths of VASWCNTs were studied. VASWCNTs-DSSC with 34 μm original length was found to be the optimal choice in the present study. The highest conversion efficiencies of VASWCNTs-DSSC achieved 5.5%, which rivals that of the reference Pt DSSC. From the electrochemical impedance spectroscopy analysis, it shows that the new DSSC offers lower interface resistance between the electrolyte and the counter electrode. This reproducible work emphasizes the promise of VASWCNTs as efficient and stable counter electrode materials in DSSC device design, especially taking into account the low-cost merit of this promising material.Keywords: counter electrodes; dye-sensitized solar cells; electrocatalytic activity; vertically aligned single-walled carbon nanotubes;
Co-reporter:Yang Lu;Jun Song;Jian Yu Huang
Nano Research 2011 Volume 4( Issue 12) pp:1261-1267
Publication Date(Web):2011 December
DOI:10.1007/s12274-011-0177-y
The plastic deformation and the ultrahigh strength of metals at the nanoscale have been predicted to be controlled by surface dislocation nucleation. In situ quantitative tensile tests on individual 〈111〉 single crystalline ultrathin gold nanowires have been performed and significant load drops observed in stress-strain curves suggest the occurrence of such dislocation nucleation. High-resolution transmission electron microscopy (HRTEM) imaging and molecular dynamics simulations demonstrated that plastic deformation was indeed initiated and dominated by surface dislocation nucleation, mediating ultrahigh yield and fracture strength in sub-10-nm gold nanowires.
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Co-reporter:Yang Lu
JOM 2011 Volume 63( Issue 9) pp:
Publication Date(Web):2011 September
DOI:10.1007/s11837-011-0155-6
This paper reviews recent studies on in-situ quantitative mechanical characterization of metallic nanowires with diameters from a few nanometers to hundreds of nanometers, with particular emphasis placed on tensile loading geometry. Critical challenges and pitfalls in manipulating, clamping, and quantitatively testing nanowire specimens, with drastically different dimensions, are discussed. Two general experimental strategies are employed: microelectrochemical systems-based technology for testing of larger-diameter metal nanowires (D ∼ 30–300 nm), and insitu transmission electron microscopyatomic force microscopy platform for testing of ultrathin metallic nanowires (D < 20 nm). Size-dependent mechanical behaviors of gold nanowires, as well as the transition of different deformation mechanisms at corresponding length scales, are clearly revealed.
Co-reporter:Yogeeswaran Ganesan, Cheng Peng, Yang Lu, Lijie Ci, Anchal Srivastava, Pulickel M. Ajayan, and Jun Lou
ACS Nano 2010 Volume 4(Issue 12) pp:7637
Publication Date(Web):November 11, 2010
DOI:10.1021/nn102372w
We report on the usage of a simple microfabricated device that works in conjunction with a quantitative Nanoindenter within a scanning electron microscope (SEM) chamber, for the in situ quantitative tensile testing of individual catalytically grown pristine and nitrogen-doped multiwall carbon nanotubes (MWNTs). The two types of MWNTs were found to possess similar strengths but different load-bearing abilities owing to the differences in their wall structures. Also, stress versus strain curves and fracture surfaces showed that while the pristine MWNTs deform and fail in a brittle fashion, the nitrogen-doped MWNTs deform plastically to varying degrees prior to failure. High resolution transmission electron microscope (TEM) images of the nitrogen-doped MWNT fracture specimens showed the presence of regions of reduced cross-section areas and kinks in close proximity to the fracture surfaces. The presence of nitrogen atoms in the graphitic sheets was assumed to have led to the formation of kinks whose motion induced by straining could have resulted in the plastic deformation of the carbon nanotubes.Keywords: fracture; in situ tensile testing; multiwall carbon nanotube; nitrogen doping; plasticity
Co-reporter:Y. Lu;Y. Ganesan;J. Lou
Experimental Mechanics 2010 Volume 50( Issue 1) pp:47-54
Publication Date(Web):2010 January
DOI:10.1007/s11340-009-9222-0
A novel micromechanical device was developed to convert the compressive force applied by a nanoindenter into pure tensile loading at the sample stages inside a scanning electron microscope or a transmission electron microscope, in order to mechanically deform a one-dimensional nanostructure, such as a nanotube or a nanowire. Force vs. displacement curves for samples with Young’s modulus above a threshold value can be obtained independently from readings of a quantitative high resolution nanoindenter with considerable accuracy, using a simple conversion relationship. However, in-depth finite element analysis revealed the existence of limitations for the device when testing samples with relatively low Young’s modulus, where forces applied on samples derived from nanoindenter readings using a predetermined force conversion factor will no longer be accurate. In this paper, we will demonstrate a multi-step method which can alleviate this problem and make the device capable of testing a wide range of samples with considerable accuracy.
Co-reporter:Yogeeswaran Ganesan
JOM 2009 Volume 61( Issue 1) pp:32-37
Publication Date(Web):2009 January
DOI:10.1007/s11837-009-0005-y
A polymer nanocomposite is created by introducing nanoparticulates into a macroscopic polymer matrix. Polymer nanocomposites represent a new class of material alternative to conventional filled polymers and possess some extremely interesting properties. The alteration/ enhancement of the properties of these materials can partially be attributed to the fact that the properties of the nanoparticulate fillers are substantially different/better than that of the micrometer-scale fillers and partially owing to the fact that when a good dispersion is obtained the filler-matrix interfacial area tends to be dramatically larger when compared to that in traditional composites. This paper presents an overview of past work done on the mechanical characterization of one such type of polymer matrix nanocomposite, the carbon-nanotube-reinforced polymer-matrix composite. The primary emphasis is on the properties of the filler/matrix interface and the methods used for interfacial charaterization.
Co-reporter:H. Lu, J. Goldman, F. Ding, Y. Sun, M.X. Pulikkathara, V.N. Khabashesku, B.I. Yakobson, J. Lou
Carbon 2008 Volume 46(Issue 10) pp:1294-1301
Publication Date(Web):August 2008
DOI:10.1016/j.carbon.2008.05.010
Sliding friction and adhesion properties of vertically aligned multi-walled carbon nanotube (VAMWCNT) arrays and fluoro-nanodiamond (F-ND) films on glass substrate have been quantitatively investigated in current study using atomic force microscopy. It was found that VAMWCNT arrays result in lower friction compared to F-ND films. Friction forces were also found to be consistently higher in nitrogen environment than in ambient environment for both samples and a surface chemistry based hypothesis was proposed. However, no apparent dependence of relative humidity was found on adhesion forces for both F-ND and VAMWCNT samples, indicating lack of correlation between nanoscale adhesion and friction. The implications from current study for designing movable components in micro- and nanoelectromechanical system devices were also discussed.
Co-reporter:Yingchao Yang, Charlotte Flatebo, Jia Liang, Pei Dong, Jiangtan Yuan, Tianxiao Wang, Jing Zhang, Weibing Chen, Jingjie Wu, Pulickel M. Ajayan, Lijie Ci, Qilin Li, Jun Lou
Applied Materials Today (June 2016) Volume 3() pp:
Publication Date(Web):1 June 2016
DOI:10.1016/j.apmt.2016.03.004
TiO2 nanoparticles are successfully synthesized on carbonized cotton T-shirt through a low-cost hydrothermal process. The photocatalytic performance of the fabricated hybrid material system is examined by the degradation of methyl orange (MO). It is shown that 98.6% MO in solution can be decomposed within thirty minutes by direct natural sunlight, demonstrating better photodegradation efficiency than TiO2, doped TiO2, and other semiconductor nanoparticles. The stability of this hybrid photocatalyst is also quite attractive. After ten cycles of usage, it can still degrade up to 93% of MO in solutions. The anchoring of TiO2 nanoparticles on the framework of carbonized cotton T-shirt creates a unique architecture overcoming the difficulty of dispersing and recycling nanoparticle photocatalysts. It also introduces beneficial synergistic effects such as carbon doping and enhanced charge migration, making it very promising for the practical application of degrading water-borne, organic contaminants.The photocatalytic performance of the fabricated hybrid TiO2/carbonized cotton T-shirt examined by the degradation of methyl orange (MO) shows that MO in solution can be decomposed up to 98.6% within thirty minutes by direct natural sunlight, demonstrating better photodegradation efficiency than TiO2, doped TiO2, and other semiconductor nanoparticles.Download full-size image
Co-reporter:Xinlu Li, Yingchao Yang, Yujie Zhao, Jun Lou, Xiyu Zhao, Ronghua Wang, Qinghua Liang, Zhenghong Huang
Carbon (April 2017) Volume 114() pp:
Publication Date(Web):April 2017
DOI:10.1016/j.carbon.2016.12.082
Graphene nanoribbons (GNRs) with opened edges and less structural defects are embedded in polyacrylonitrile (PAN)-based carbon nanofibers (CNFs) by electrospinning followed by stabilization and carbonization. GNRs not only can be used as one-dimensional nanofillers, but also act as nanoplatelet template to promote the formation of graphitic carbon in PAN matrix. X-ray diffraction, Raman spectroscopy and N2 absorption are used to analyze the microstructure of GNR-reinforced CNFs. In situ tensile test using a micromechanical device inside a scanning electron microscope (SEM) is carried out to evaluate the mechanical performance of individual GNR-reinforced CNF. The tensile strength and elastic modulus of CNFs reinforced by 2 wt% GNRs with a diameter of ∼160 nm are 3.52 GPa and 70.07 GPa, respectively, which are higher than those of pristine PAN CNFs with similar size, i.e. 2.44 GPa and 28.97 GPa. The rough fracture surface for all GNR-reinforced CNFs suggests that the GNRs can dramatically toughen the fibers. A sword-in-sheath failure is observed in 4 wt% GNR reinforced CNFs, confirming that GNRs are entirely embedded and well aligned along the fiber axis. This study demonstrates the potential of GNRs as a promising reinforcement to improve the formation of graphitic carbon and mechanical performance of CNFs.
Co-reporter:Jiangtan Yuan, Weibing Chen, Jun Lou
Science Bulletin (30 March 2017) Volume 62(Issue 6) pp:381-382
Publication Date(Web):30 March 2017
DOI:10.1016/j.scib.2017.02.007
Co-reporter:Yongjie Zhan, Yang Lu, Cheng Peng, Jun Lou
Journal of Crystal Growth (15 June 2011) Volume 325(Issue 1) pp:76-80
Publication Date(Web):15 June 2011
DOI:10.1016/j.jcrysgro.2011.04.031
Single crystalline copper nanorings were synthesized through the solvothermal process. The N-methyl-2-pyrrolidone (NMP)/water system is thought to be the key factor to form the novel structure, and a growth-stress induced bending mechanism is proposed to explain the formation mechanism. Micro-manipulation experiments revealed excellent mechanical properties of these copper nanorings.Highlights► A simple solvothermal method to prepare discrete, single crystalline Cu nanorings. ► Polyvinyl acetate (PVA) selected as reductant and CuCl as copper resource. ► N-methyl-2-pyrrolidone (NMP) proved to be a key factor to form the ring structure. ► As-prepared copper nanorings show excellent mechanical properties.
Co-reporter:Pei Dong, Yu Zhu, Jing Zhang, Feng Hao, Jingjie Wu, Sidong Lei, Hong Lin, Robert H. Hauge, James M. Tour and Jun Lou
Journal of Materials Chemistry A 2014 - vol. 2(Issue 48) pp:NaN20907-20907
Publication Date(Web):2014/10/31
DOI:10.1039/C4TA05264A
Dye-sensitized solar cells (DSSCs) are an emerging photovoltaic technology with both low costs and good efficiency. However, the cathode used in most DSSCs is fluorine-doped tin oxide glass coated with a Pt film, which is both expensive and brittle and therefore limits the flexibility and large-scale implementation of this promising technology. We report here work which showed that flexible, seamlessly covalently bonded, three-dimensional vertically aligned few-walled carbon nanotubes (VAFWCNTs)/graphene on metal foil can act as a novel cathode free from transparent conducting oxide and Pt for application in DSSCs. This cathode has a lower charge transfer resistance and lower contact resistance between the catalyst and the substrate than the conventional combination in a brittle Pt/fluorine-doped tin oxide cathode. The covalently bonded graphene and VAFWCNTs ensure excellent electron transport through the electrode and the large surface area of the hybrid carbon materials rivals the catalytic capability of the Pt analogue. DSSCs utilizing this flexible VAFWCNTs/graphene hybrid cathode outperformed the Pt-based cells in both rigid (8.2% vs. 6.4%) and flexible (3.9% vs. 3.4%) assemblies. The VAFWCNTs/graphene on metal foil combination is a novel, inexpensive, high-performance, flexible cathode for application in solar cells.
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