ZhenYu Li

Electronic Structure Engineering via On-Plane Chemical Functionalization: A Comparison Study on Two-Dimensional Polysilane and Graphane

Co-reporter:Ning Lu;Jinlong Yang

The Journal of Physical Chemistry C September 24, 2009 Volume 113(Issue 38) pp:16741-16746

Publication Date(Web):2017-2-22

DOI:10.1021/jp904208g

Two-dimensional materials are important for electronics applications. A natural way of electronic structure engineering for two-dimensional systems is on-plane chemical functionalization. On the basis of density functional theory, we study the electronic structures of fluorine-substituted planar polysilane and graphane. We find that carbon and silicon present very different surface chemistries. The indirect energy gap of planar polysilane becomes direct upon fluorine decoration, and its gap width is mainly determined by fluorine coverage regardless of its distribution on the surface. However, the electronic structure of fluorine doped graphane is very sensitive to the doping configuration, due to the competition between antibonding states and nearly free electron (NFE) states. With specific fluorine distribution patterns, zero-dimensional and one-dimensional NFE states can be obtained. Our results demonstrate the advantages of two-dimensional silicon based materials compared with carbon based materials, in the viewpoint of practical electronic structure engineering by surface chemical functionalization.

Two-Dimensional Stoichiometric Boron Oxides as a Versatile Platform for Electronic Structure Engineering

Co-reporter:Ruiqi Zhang, Zhenyu Li, and Jinlong Yang

The Journal of Physical Chemistry Letters September 21, 2017 Volume 8(Issue 18) pp:4347-4347

Publication Date(Web):August 25, 2017

DOI:10.1021/acs.jpclett.7b01721

Oxides of two-dimensional (2D) atomic crystals have been widely studied due to their unique properties. In most 2D oxides, oxygen acts as a functional group, which makes it difficult to control the degree of oxidation. Because borophene is an electron-deficient system, it is expected that oxygen will be intrinsically incorporated into the basal plane of borophene, forming stoichiometric 2D boron oxide (BO) structures. By using first-principles global optimization, we systematically explore structures and properties of 2D BO systems with well-defined degrees of oxidation. Stable B–O–B and OB3 tetrahedron structure motifs are identified in these structures. Interesting properties, such as strong linear dichroism, Dirac node-line (DNL) semimetallicity, and negative differential resistance, have been predicted for these systems. Our results demonstrate that 2D BO represents a versatile platform for electronic structure engineering via tuning the stoichiometric degree of oxidation, which leads to various technological applications.

A Kinetic Pathway toward High-Density Ordered N Doping of Epitaxial Graphene on Cu(111) Using C5NCl5 Precursors

Co-reporter:Ping Cui, Jin-Ho Choi, Changgan Zeng, Zhenyu Li, Jinlong Yang, and Zhenyu Zhang

Journal of the American Chemical Society May 31, 2017 Volume 139(Issue 21) pp:7196-7196

Publication Date(Web):May 12, 2017

DOI:10.1021/jacs.6b12506

Pristine graphene possesses high electrical mobility, but its low charge carrier density severely limits its technological significance. Past efforts to increase graphene’s carrier density via chemical doping have shown limited successes, accompanied by substantial reductions in the mobility caused by disordered dopants. Here, based on first-principles calculations, we propose to grow graphene on Cu(111) via self-assembly of C5NCl5 molecular precursors to achieve high-density (1/6) and highly ordered nitrogen doping. Such a process relies on the elegant concerted roles played by the London dispersion, chemical, and screened Coulomb repulsive forces in enhancing molecular adsorption, facilitating easy dechlorination, and dictating the overall orientation of the C5N radicals, respectively. Further growth from the orientationally correlated graphene islands is accompanied by significantly minimized density of grain boundaries as the grains coalesce to form larger N-doped graphene sheets, which are further shown to possess superb electronic properties for future device applications. Initial kinetic processes involved in N-doped graphene growth using C5NH5 precursors are also investigated and contrasted with that of C5NCl5.

Thickness-Dependent Adsorption of Melamine on Cu/Au(111) Films

Co-reporter:Li Wang, Pai Li, Hexia Shi, Zhenyu Li, Kai Wu, and Xiang Shao

The Journal of Physical Chemistry C April 13, 2017 Volume 121(Issue 14) pp:7977-7977

Publication Date(Web):March 15, 2017

DOI:10.1021/acs.jpcc.7b00938

Supported metal films represent a model binary metallic system wherein the surface properties can be finely tuned with the composition/thickness of the film. Thus, it has raised increasing research interests from various aspects. In this work, the adsorption and assembly behavior of melamine on the Cu films grown on the (22 × √3) reconstructed Au(111) substrate were investigated as a function of Cu thickness. The atomically resolved scanning tunneling microscopy (STM) images in combination with density functional theory (DFT) calculations reveal that the ultrathin submonolayer copper film forms a pseudomorphic (1 × 1) lattice by agglomerating at the subsurface, while the true Cu adlayers start to appear on the three-layer thick films and hold the bulk Cu(111) lattice. Correspondingly, the adsorption and assembly of the melamine molecules significantly differ from those on pure metals, experiencing a gradual transformation from physisorption to chemisorption assemblies with the Cu film thickening. These findings shed light on the self-assembly behavior of organics on binary metallic surfaces. In addition, the evaporated metal films also register a diversified substrate for tuning the properties of adsorbed molecular films.

First-Principles Study of Molecular Clusters Formed by Nitric Acid and Ammonia

Co-reporter:Jinfei Ling, Xunlei Ding, Zhenyu LiJinlong Yang

The Journal of Physical Chemistry A 2017 Volume 121(Issue 3) pp:

Publication Date(Web):January 1, 2017

DOI:10.1021/acs.jpca.6b09185

Molecular clusters formed by m nitric acid molecules and n ammonia molecules are studied with density functional theory. For smaller clusters with m, n ≤ 4, all possible combinations of m and n are considered, while for larger clusters in the 5 ≤ m, n ≤ 8 range we only consider the possibilities with |m – n| ≤ 1. Hydrogen bond network formation is an important stabilization mechanism in these clusters. At the same time, proton transfer is generally preferred except in the smallest clusters. Nitric acid and ammonia evaporation rates of these clusters are calculated with both collision activation barriers and reaction thermodynamics explicitly considered. However, unlike in the case of cluster growth from sulfuric acid and ammonia, activation barriers do not play an important role here. If m and n are unequal, evaporation of the abundant species is always preferred. For clusters with m = n > 2, ammonia evaporation is faster than nitric acid. Stabilities of all clusters can be quantitatively evaluated by the evaporation rate of the preferred species. Larger clusters are generally more stable. However, exceptions can occur at structure motif transition point. Deviation from the stoichiometry of m = n significantly lowers the cluster stability. For a cluster pair formed by the same number of molecules, the nitric acid abundant one is more stable, which determines the growth pathway of these clusters.

Contrasting Structural Reconstructions, Electronic Properties, and Magnetic Orderings along Different Edges of Zigzag Transition Metal Dichalcogenide Nanoribbons

Co-reporter:Ping Cui, Jin-Ho Choi, Wei Chen, Jiang Zeng, Chih-Kang Shih, Zhenyu LiZhenyu Zhang

Nano Letters 2017 Volume 17(Issue 2) pp:

Publication Date(Web):December 28, 2016

DOI:10.1021/acs.nanolett.6b04638

Two-dimensional transition metal dichalcogenides represent an emerging class of layered materials exhibiting various intriguing properties, and integration of such materials for potential device applications will necessarily invoke further reduction of their dimensionality. Using first-principles approaches, here we investigate the structural, electronic, and magnetic properties along the two different edges of zigzag MX2 (M = Mo, W; X = S, Se) nanoribbons. Along the M edges, we reveal a previously unrecognized but energetically strongly preferred (2 × 1) reconstruction pattern, which is universally operative for all the four systems (and possibly more), characterized by an elegant self-passivation mechanism through place exchanges of the outmost X and M edge atoms. In contrast, the X edges undergo a much milder (2 × 1) or (3 × 1) reconstruction for MoX2 or WX2, respectively. These contrasting structural preferences of the edges can be exploited for controlled fabrication of properly tailored transition metal dichalcogenide nanoribbons under nonequilibrium growth conditions. We further use the zigzag MoX2 nanoribbons to demonstrate that the Mo and X edges possess distinctly different electronic and magnetic properties, which are significant for catalytic and spintronic applications.Keywords: edge reconstruction; electronic and magnetic properties; First-principles calculations; nanoribbons; transition metal dichalcogenides;

Epitaxial Growth of Single Layer Blue Phosphorus: A New Phase of Two-Dimensional Phosphorus

Co-reporter:Jia Lin Zhang, Songtao Zhao, Cheng Han, Zhunzhun Wang, Shu Zhong, Shuo Sun, Rui Guo, Xiong Zhou, Cheng Ding Gu, Kai Di Yuan, Zhenyu Li, and Wei Chen

Nano Letters 2016 Volume 16(Issue 8) pp:4903-4908

Publication Date(Web):June 30, 2016

DOI:10.1021/acs.nanolett.6b01459

Blue phosphorus, a previously unknown phase of phosphorus, has been recently predicted by theoretical calculations and shares its layered structure and high stability with black phosphorus, a rapidly rising two-dimensional material. Here, we report a molecular beam epitaxial growth of single layer blue phosphorus on Au(111) by using black phosphorus as precursor, through the combination of in situ low temperature scanning tunneling microscopy and density functional theory calculation. The structure of the as-grown single layer blue phosphorus on Au(111) is explained with a (4 × 4) blue phosphorus unit cell coinciding with a (5 × 5) Au(111) unit cell, and this is verified by the theoretical calculations. The electronic bandgap of single layer blue phosphorus on Au(111) is determined to be 1.10 eV by scanning tunneling spectroscopy measurement. The realization of epitaxial growth of large-scale and high quality atomic-layered blue phosphorus can enable the rapid development of novel electronic and optoelectronic devices based on this emerging two-dimensional material.Keywords: 2D material; blue phosphorus; MBE; STM;

Precursor Triggering Synthesis of Self-Coupled Sulfide Polymorphs with Enhanced Photoelectrochemical Properties

Co-reporter:Shi-Kui Han, Chao Gu, Songtao Zhao, Sen Xu, Ming Gong, Zhenyu Li, and Shu-Hong Yu

Journal of the American Chemical Society 2016 Volume 138(Issue 39) pp:12913-12919

Publication Date(Web):July 26, 2016

DOI:10.1021/jacs.6b06609

Heteronanostructures have attracted intensive attention due to their electronic coupling effects between distinct components. Despite tremendous advances of nanostructure fabrication, combining independent polymorphs by forming heterojunction is still challenging but fascinating, such as copper sulfides (Cu2–xS), exhibiting varying band gaps and crystal structures with various stoichiometries. Herein, self-coupled Cu2–xS polymorphs (Cu1.94S-CuS) by a facile one-pot chemical transformation route have been reported for the first time. Unprecedentedly, a manganous precursor plays a crucial role in inducing and directing the formation of such a dumbbell-like architecture, which combines 1D Cu1.94S with 2D CuS. During the transformation, Mn2+ ions mediate the Cu+ ions diffusion and phase conversion process particularly. Furthermore, this self-coupled polymorphic structure exhibits significantly enhanced photoelectrochemical properties compared with the individual Cu1.94S nanocrystals and CuS nanoplates, originating from the unique heterointerfaces constructed by intrinsic band alignment and the enhanced contact between high conductivity hexagonal planes and the working electrode revealed by density functional theory (DFT) calculations. So we anticipate this emerging interfacial charge separation could provide useful hints for applications in optoelectronic devices or photocatalysis.

Mo2C nanoparticles embedded within bacterial cellulose-derived 3D N-doped carbon nanofiber networks for efficient hydrogen evolution

Co-reporter:Zhen-Yu Wu, Bi-Cheng Hu, Ping Wu, Hai-Wei Liang, Zhi-Long Yu, Yue Lin, Ya-Rong Zheng, Zhenyu Li and Shu-Hong Yu

NPG Asia Materials 2016 8(7) pp:e288

Publication Date(Web):2016-07-01

DOI:10.1038/am.2016.87

Molybdenum carbide (Mo2C) has been considered as a promising non-noble-metal hydrogen evolution reaction (HER) electrocatalyst for future clean energy devices. In this work, we report a facile, green, low-cost and scalable method for the synthesis of a Mo2C-based HER electrocatalyst consisting of ultrafine Mo2C nanoparticles embedded within bacterial cellulose-derived 3D N-doped carbon nanofiber networks (Mo2C@N-CNFs) using 3D nanostructured biomass as a precursor. The electrocatalyst exhibits remarkable HER activity (an overpotential of 167 mV achieves 10 mA cm−2 and a high exchange current density of 4.73 × 10−2 mA cm−2) and excellent stability in acidic media as well as high HER activity in neutral and basic media. Further theoretical calculations indicate a strong synergistic effect between Mo2C nanoparticles and N-CNFs in the Mo2C@N-CNF catalyst, which leads to an impressive HER performance.

The Nanoparticle Size Effect in Graphene Cutting: A Pac-Man Mechanism

Co-reporter:Zongyang Qiu; Li Song; Jin Zhao; Zhenyu Li; Jinlong Yang

Angewandte Chemie International Edition 2016 Volume 55( Issue 34) pp:9918-9921

Publication Date(Web):

DOI:10.1002/anie.201602541

Abstract

Metal-nanoparticle-catalyzed cutting is a promising way to produce graphene nanostructures with smooth and well-aligned edges. Using a multiscale simulation approach, we unambiguously identified a “Pac-Man” cutting mechanism, characterized by the metal nanoparticle “biting off” edge carbon atoms through a synergetic effect of multiple metal atoms. By comparing the reaction rates at different types of edge sites, we found that etching of an entire edge carbon row could be triggered by a single zigzag-site etching event, which explains the puzzling linear dependence of the overall carbon-atom etching rate on the nanoparticle surface area observed experimentally. With incorporation of the nanoparticle size effect, the mechanisms revealed herein open a new avenue to improve controllability in graphene cutting.

Back Cover: The Nanoparticle Size Effect in Graphene Cutting: A Pac-Man Mechanism (Angew. Chem. Int. Ed. 34/2016)

Co-reporter:Zongyang Qiu; Li Song; Jin Zhao; Zhenyu Li; Jinlong Yang

Angewandte Chemie International Edition 2016 Volume 55( Issue 34) pp:

Publication Date(Web):

DOI:10.1002/anie.201605489

Rcktitelbild: The Nanoparticle Size Effect in Graphene Cutting: A Pac-Man Mechanism (Angew. Chem. 34/2016)

Co-reporter:Zongyang Qiu; Li Song; Jin Zhao; Zhenyu Li; Jinlong Yang

Angewandte Chemie 2016 Volume 128( Issue 34) pp:

Publication Date(Web):

DOI:10.1002/ange.201605489

The Nanoparticle Size Effect in Graphene Cutting: A Pac-Man Mechanism

Co-reporter:Zongyang Qiu; Li Song; Jin Zhao; Zhenyu Li; Jinlong Yang

Angewandte Chemie 2016 Volume 128( Issue 34) pp:10072-10075

Publication Date(Web):

DOI:10.1002/ange.201602541

Abstract

Metal-nanoparticle-catalyzed cutting is a promising way to produce graphene nanostructures with smooth and well-aligned edges. Using a multiscale simulation approach, we unambiguously identified a “Pac-Man” cutting mechanism, characterized by the metal nanoparticle “biting off” edge carbon atoms through a synergetic effect of multiple metal atoms. By comparing the reaction rates at different types of edge sites, we found that etching of an entire edge carbon row could be triggered by a single zigzag-site etching event, which explains the puzzling linear dependence of the overall carbon-atom etching rate on the nanoparticle surface area observed experimentally. With incorporation of the nanoparticle size effect, the mechanisms revealed herein open a new avenue to improve controllability in graphene cutting.

Aerobic Oxidation of Cyclohexane on Catalysts Based on Twinned and Single-Crystal Au75Pd25 Bimetallic Nanocrystals

Co-reporter:Liangbing Wang, Songtao Zhao, Chenxuan Liu, Chen Li, Xu Li, Hongliang Li, Youcheng Wang, Chao Ma, Zhenyu Li, and Jie Zeng

Nano Letters 2015 Volume 15(Issue 5) pp:2875-2880

Publication Date(Web):April 3, 2015

DOI:10.1021/nl5045132

Bimetallic Au75Pd25 nanocrystals with shapes of icosahedron and octahedron were synthesized by adding different amounts of iodide ions, and were employed as catalysts for solvent-free aerobic oxidation of cyclohexane. Although both icosahedrons and octahedrons were bounded by {111} facets, the turnover frequency number of Au75Pd25 icosahedrons reached 15 106 h–1, almost three times as high as that of Au75Pd25 octahedrons. The conversion of cyclohexane reached 28.1% after 48 h using Au75Pd25 icosahedrons, with the selectivity of 84.3% to cyclohexanone. Density functional theory calculations along with X-ray photoelectron spectroscopy examinations reveal that the excellent catalytic performance of AuPd icosahedrons could be ascribed to twin-induced strain and highly negative charge density of Au atoms on the surface.

Single-Molecule Imaging of Activated Nitrogen Adsorption on Individual Manganese Phthalocyanine

Co-reporter:Jia Lin Zhang, Zhunzhun Wang, Jian Qiang Zhong, Kai Di Yuan, Qian Shen, Lei Lei Xu, Tian Chao Niu, Cheng Ding Gu, Christopher A. Wright, Anton Tadich, Dongchen Qi, He Xing Li, Kai Wu, Guo Qin Xu, Zhenyu Li, and Wei Chen

Nano Letters 2015 Volume 15(Issue 5) pp:3181-3188

Publication Date(Web):April 23, 2015

DOI:10.1021/acs.nanolett.5b00290

An atomic-scale understanding of gas adsorption mechanisms on metal-porphyrins or metal-phthalocyanines is essential for their practical application in biological processes, gas sensing, and catalysis. Intensive research efforts have been devoted to the study of coordinative bonding with relatively active small molecules such as CO, NO, NH3, O2, and H2. However, the binding of single nitrogen atoms has never been addressed, which is both of fundamental interest and indeed essential for revealing the elementary chemical binding mechanism in nitrogen reduction processes. Here, we present a simple model system to investigate, at the single-molecule level, the binding of activated nitrogen species on the single Mn atom contained within the manganese phthalocyanine (MnPc) molecule supported on an inert graphite surface. Through the combination of in situ low-temperature scanning tunneling microscopy, scanning tunneling spectroscopy, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, and density functional theory calculations, the active site and the binding configuration between the activated nitrogen species (neutral nitrogen atom) and the Mn center of MnPc are investigated at the atomic scale.

Gas-phase dynamics in graphene growth by chemical vapour deposition

Co-reporter:Gan Li, Sheng-Hong Huang and Zhenyu Li

Physical Chemistry Chemical Physics 2015 vol. 17(Issue 35) pp:22832-22836

Publication Date(Web):30 Jul 2015

DOI:10.1039/C5CP02301G

Chemical vapour deposition on a Cu substrate is becoming a very important approach to obtain high quality graphene samples. Previous studies of graphene growth on Cu mainly focus on surface processes. However, recent experiments suggest that gas-phase dynamics also plays an important role in graphene growth. In this article, gas-phase processes are systematically studied using computational fluid dynamics. Our simulations clearly show that graphene growth is limited by mass transport under ambient pressures while it is limited by surface reactions under low pressures. The carbon deposition rate at different positions in the tube furnace and the concentration of different gas phase species are calculated. Our results confirm that the previously realized graphene thickness control by changing the position of the Cu foil is a result of gas-phase methane decomposition reactions.

Obtaining Two-Dimensional Electron Gas in Free Space without Resorting to Electron Doping: An Electride Based Design

Co-reporter:Songtao Zhao ; Zhenyu Li ;Jinlong Yang

Journal of the American Chemical Society 2014 Volume 136(Issue 38) pp:13313-13318

Publication Date(Web):September 4, 2014

DOI:10.1021/ja5065125

Nearly free electron (NFE) states are widely existed on atomically smooth surfaces in two-dimensional materials. Since they are mainly distributed in free space, these states can in principle provide ideal electron transport channels without nuclear scattering. Unfortunately, NFE states are typically unoccupied, and electron doping is required to shift them toward the Fermi level and, thus, to be involved in electron transport. Instead of occupying these NFE states, it is more desirable to have intrinsic nucleus-free two-dimensional electron gas in free space (2DEG-FS) at the Fermi level without relying on doping. Inspired by a recently identified electride material, we suggest that Ca2N monolayer should possess such a 2DEG-FS state, which is then confirmed by our first-principles calculations. Phonon dispersion in Ca2N monolayer shows no imagery frequency indicating that the monolayer structure is stable. A mechanical analysis demonstrates that Ca2N bulk exfoliation is feasible to produce a freestanding monolayer. However, in real applications, the strong chemical activity of 2DEG-FS may become a practical issue. It is found that some ambient molecules can dissociatively adsorb on the Ca2N monolayer, accompanying with a significant charge transfer from the 2DEG-FS state to adsorbates. To protect the 2DEG-FS state from molecule adsorption, we predict that graphane can be used as an effective encapsulating material. A well-encapsulated intrinsic 2DEG-FS state is expected to play an important role in low-dimensional electronics by realizing nuclear scattering free transport.

Bilayer Graphene Growth via a Penetration Mechanism

Co-reporter:Ping Wu ; Xiaofang Zhai ; Zhenyu Li ;Jinlong Yang

The Journal of Physical Chemistry C 2014 Volume 118(Issue 12) pp:6201-6206

Publication Date(Web):March 7, 2014

DOI:10.1021/jp4108156

From both fundamental and technical points of view, precise control of the layer number of graphene samples is very important. To reach this goal, atomic-scale mechanisms of multilayer graphene growth on metal surfaces should be understood. Although it is a geometrically favorable pathway to transport carbon species to interface and then form a new graphene layer there, penetration of a graphene overlayer is not a chemically straightforward process. In this study, the possibility of different active species penetrating a graphene overlayer on Cu(111) surface is investigated by first-principles calculations. It is found that carbon atom penetration can be realized via an atom-exchange process, which leads to a new graphene growth mechanism. Based on this result, a bilayer graphene growth protocol is proposed to obtain high-quality samples. Such a penetration possibility also provides great flexibility for designed growth of graphene nanostructures.

Lattice Mismatch Induced Nonlinear Growth of Graphene

Co-reporter:Ping Wu ; Huijun Jiang ; Wenhua Zhang ; Zhenyu Li ; Zhonghuai Hou ;Jinlong Yang

Journal of the American Chemical Society 2012 Volume 134(Issue 13) pp:6045-6051

Publication Date(Web):March 8, 2012

DOI:10.1021/ja301791x

As a two-dimensional material, graphene can be obtained via epitaxial growth on a suitable substrate. Recently, an interesting nonlinear behavior of graphene growth has been observed on some metal surfaces, but the underlying mechanism is still elusive. Taking the Ir(111) surface as an example, we perform a mechanistic study on graphene growth using a combined approach of first-principles calculations and kinetic Monte Carlo (kMC) simulations. Small carbon clusters on the terrace or at step sites are studied first. Then, we investigate how these small carbon species are attached to graphene edges. Generally, attachment of carbon atoms is thermodynamically favorable. However, due to substrate effect, there are also some edge sites where graphene growth must proceed via cluster attachment. The overall growth rate is determined by these cluster attachment processes, which have a much lower chance of happening compared to the monomer attachment. On the basis of such an inhomogeneous growth picture, kMC simulations are performed by separating different time scales, and the experimentally found quintic-like behavior is well reproduced. Different nonlinear growth behaviors are predicted for different graphene orientations, which is consistent with previous experiments. Inhomogeneity induced by lattice mismatch revealed in this study is expected to be a universal phenomenon and will play an important role in the growth of many other heteroepitaxial systems.

A first-principles prediction of two-dimensional superconductivity in pristine B2C single layers

Co-reporter:Jun Dai, Zhenyu Li, Jinlong Yang and Jianguo Hou

Nanoscale 2012 vol. 4(Issue 10) pp:3032-3035

Publication Date(Web):29 Mar 2012

DOI:10.1039/C2NR12018F

Based on first-principles lattice dynamics and electron–phonon coupling calculations, B2C sheets are predicted to be a two-dimensional (2D) phonon-mediated superconductors with a relatively high transition temperature (Tc). The electron–phonon coupling parameter was calculated to be 0.92 and it is mainly contributed by low frequency out-of-plane phonon modes and electronic states with a π character. When the Coulomb pseudopotential, μ*, is set to 0.10, the estimated temperature, Tc, is 19.2 K. To the best of our knowledge, B2C is the first pristine 2D superconductor with a Tc higher than the boiling point of liquid helium.

Graphene Thickness Control via Gas-Phase Dynamics in Chemical Vapor Deposition

Co-reporter:Zhancheng Li, Wenhua Zhang, Xiaodong Fan, Ping Wu, Changgan Zeng, Zhenyu Li, Xiaofang Zhai, Jinlong Yang, and Jianguo Hou

The Journal of Physical Chemistry C 2012 Volume 116(Issue 19) pp:10557-10562

Publication Date(Web):April 27, 2012

DOI:10.1021/jp210814j

Why the Band Gap of Graphene Is Tunable on Hexagonal Boron Nitride

Co-reporter:Erjun Kan ; Hao Ren ; Fang Wu ; Zhenyu Li ; Ruifeng Lu ; Chuanyun Xiao ; Kaiming Deng ;Jinlong Yang

The Journal of Physical Chemistry C 2012 Volume 116(Issue 4) pp:3142-3146

Publication Date(Web):January 3, 2012

DOI:10.1021/jp2106988

The electronic properties of a graphene–boron nitride (G/BN) bilayer have been carefully investigated by first-principles calculations. We find that the energy gap of graphene is tunable from 0 to 0.55 eV and sensitive to the stacking order and interlayer distances of the G/BN bilayer. By electronic structure analysis and tight-binding simulations, we conclude that the charge redistribution within graphene and charge transfer between graphene and BN layers determine the energy gap of graphene, through modification of the on-site energy difference of carbon p orbitals at two sublattices. On the basis of the revealed mechanism, we also predict how to engineer the band gap of graphene.

High-Pressure Phase Favored by a Symmetry-Recognized Nanoconfinement Effect

Co-reporter:Shengnan Wang, Di Yin, Zhenyu Li, and Jinlong Yang

The Journal of Physical Chemistry Letters 2012 Volume 3(Issue 16) pp:2154-2158

Publication Date(Web):July 26, 2012

DOI:10.1021/jz3007047

Recently, a high-pressure phase (B2) of KI has been experimentally observed in the inner space of single-walled carbon nanotubes. Our first-principles calculations indicate that in a confined nanospace, relative stabilities of the high-pressure B2 phase and the low-pressure B1 phase of KI are not necessarily determined by their external pressures. As a result of crystal symmetry differences, different phases are preferred at different K/I ratios. Such a symmetry-recognized confinement effect opens a new avenue for nanomaterials synthesis.Keywords: carbon nanotubes; confinement; DFT; potassium iodide;

Density functional predictions of new silicon allotropes: Electronic properties and potential applications to Li-battery anode materials

Co-reporter:Fang Wu, Dai Jun, Erjun Kan, Zhenyu Li

Solid State Communications 2011 Volume 151(Issue 18) pp:1228-1230

Publication Date(Web):September 2011

DOI:10.1016/j.ssc.2011.06.001

In terms of first-principles density functional calculations, we investigate the stabilities and electronic properties of two hypothetical allotropes of silicon, the body-centered tetragonal (Bct) and monoclinic (M4) phases. The calculated electronic structures and phonon dispersions reveal that both phases are stable and have a band gap smaller than that of the diamond form of silicon by a factor of ∼2. We also discuss the possible applications of Bct and M4 phases as lithium-battery anode material.Highlights► We predict two hypothetical allotropes of silicon with DFT calculations. ► Both allotropes are very stable, with a band gap about 0.3 eV. ► These hypothetical allotropes are better lithium-battery anode materials than diamond-one.

Low-Temperature Growth of Graphene by Chemical Vapor Deposition Using Solid and Liquid Carbon Sources

Co-reporter:Zhancheng Li, Ping Wu, Chenxi Wang, Xiaodong Fan, Wenhua Zhang, Xiaofang Zhai, Changgan Zeng, Zhenyu Li, Jinlong Yang, and Jianguo Hou

ACS Nano 2011 Volume 5(Issue 4) pp:3385

Publication Date(Web):March 25, 2011

DOI:10.1021/nn200854p

Graphene has attracted a lot of research interest owing to its exotic properties and a wide spectrum of potential applications. Chemical vapor deposition (CVD) from gaseous hydrocarbon sources has shown great promises for large-scale graphene growth. However, high growth temperature, typically 1000 °C, is required for such growth. Here we demonstrate a revised CVD route to grow graphene on Cu foils at low temperature, adopting solid and liquid hydrocarbon feedstocks. For solid PMMA and polystyrene precursors, centimeter-scale monolayer graphene films are synthesized at a growth temperature down to 400 °C. When benzene is used as the hydrocarbon source, monolayer graphene flakes with excellent quality are achieved at a growth temperature as low as 300 °C. The successful low-temperature growth can be qualitatively understood from the first principles calculations. Our work might pave a way to an undemanding route for economical and convenient graphene growth.Keywords: chemical vapor deposition; graphene; liquid carbon sources; low temperature growth; solid carbon sources

First-Principles Thermodynamics of Graphene Growth on Cu Surfaces

Co-reporter:Wenhua Zhang ; Ping Wu ; Zhenyu Li ;Jinlong Yang

The Journal of Physical Chemistry C 2011 Volume 115(Issue 36) pp:17782-17787

Publication Date(Web):August 4, 2011

DOI:10.1021/jp2006827

Chemical vapor deposition (CVD) is an important method to synthesis graphene on a substrate. Recently, Cu became the most popular CVD substrate for graphene growth. Here, we combine electronic structure calculation, molecular dynamics simulation, and thermodynamics analysis to study the graphene growth process on Cu surfaces. As a fundamentally important but previously overlooked fact, we find that carbon atoms are thermodynamically unfavorable on a Cu surface under typical experimental conditions. The active species for graphene growth should thus mainly be CHx instead of atomic carbon. On the basis of this new picture, the nucleation behavior can be understood, which explains many experimental observations and also provides us a guide to improve graphene sample quality.

Structure of Graphene Oxide: Thermodynamics versus Kinetics

Co-reporter:Ning Lu ; Di Yin ; Zhenyu Li ;Jinlong Yang

The Journal of Physical Chemistry C 2011 Volume 115(Issue 24) pp:11991-11995

Publication Date(Web):May 19, 2011

DOI:10.1021/jp204476q

Graphene oxide (GO) is an important intermediate to prepare graphene, and it is also a versatile material with various applications. However, despite its importance, the detailed structure of GO is still unclear. For example, previous theoretical studies based on energetics have suggested that hydroxyl chain is an important structural motif of GO, which, however, is found to be contrary to nuclear magnetic resonance (NMR) experiments. In this study, by calculating vibrational frequencies, we find that hydroxyl chain structure is also inconsistent with infrared experiment. To resolve this controversy, we check both thermodynamic and kinetic aspects of GO structure. First-principles thermodynamics gives a free-energy based stability ordering similar to that solely based on inner energy, and the hydroxyl chain is indeed thermodynamically very favorable. Therefore, kinetics during GO synthesis is expected to have an important role in GO structure. Transition state calculations predict large energy barriers between local minima, which suggests that experimentally obtained GO samples have kinetically constrained structures.

Boron K4 crystal: a stable chiral three-dimensional sp2 network

Co-reporter:Jun Dai, Zhenyu Li and Jinlong Yang

Physical Chemistry Chemical Physics 2010 vol. 12(Issue 39) pp:12420-12422

Publication Date(Web):31 Aug 2010

DOI:10.1039/C0CP00735H

Based on first-principles equation-of-state and lattice dynamics calculations, a new boron allotrope with K4 structure is proposed, which gives the first example of a three-dimensional all sp2 network.

Single-stranded DNA adsorption on chiral molecule coated Au surface: a molecular dynamics study

Co-reporter:Haiqing Liang, Zhenyu Li and Jinlong Yang

Physical Chemistry Chemical Physics 2010 vol. 12(Issue 17) pp:4431-4434

Publication Date(Web):24 Feb 2010

DOI:10.1039/B923012B

All-atomistic molecular dynamics simulations with explicit water solution are performed to investigate the interaction between single-stranded DNA (ssDNA) molecules and chiral N-isobutyryl-cysteine (NIBC) molecule coated Au surfaces. Different contributions to the force exerted on ssDNA are analyzed. It turns out that the experimentally observed stereospecific adsorption behavior of ssDNA on D/L-NIBC self-assembled monolayer surface mainly originates from the interaction between the dipole moment of NIBC and the negative charge carried by ssDNA.

A density functional study on cationic AunCum+clusters and their monocarbonyls

Co-reporter:Yu Zhao, Zhenyu Li and Jinlong Yang

Physical Chemistry Chemical Physics 2009 vol. 11(Issue 13) pp:2329-2334

Publication Date(Web):11 Feb 2009

DOI:10.1039/B817806B

Small cationic AunCum+ (n + m≤ 6) clusters and their monocarbonyls AunCumCO+ have been studied by first-principles calculations. The trend for small Au clusters to form planar structures is weaker when some Au atoms are substituted by Cu atoms. A significant odd–even oscillation of the electron affinity of the cationic clusters with the number of their Au or Cu atoms is observed. CO prefers binding to Cu, which can be understood by the frontier molecular orbital theory. Its binding energy on AunCum+ generally decreases with the increase of the Cu content in the cluster, which is highly related to the electron transfer between CO and the cluster. Our calculation suggests that reactive collision between CO and Au3Cu+ may lead to the dissociation of the cluster with an Au atom loss.

Electron Transport in Butane Molecular Wires with Different Anchoring Groups Containing N, S, and P: A First Principles Study

Co-reporter:X. Y. Feng, Zhenyu Li and Jinlong Yang

The Journal of Physical Chemistry C 2009 Volume 113(Issue 52) pp:21911-21914

Publication Date(Web):December 7, 2009

DOI:10.1021/jp908347s

Using butane molecular wire as an example, based on density functional theory and the nonequilibrium Green’s function technique, we study the effect of anchoring groups on the transport properties of the corresponding molecular junctions. Consistent with available experimental data, we observe a conductance increase from amine to sulfide and phosphide anchoring groups. This behavior can be understood with the tunneling barrier model, where the p orbital energy of N, S, or P determines the energy of the highest occupied molecular orbital and thus the barrier height. Our results demonstrate the critical role of anchoring group chemistry in molecular electronics.

Boron K4 crystal: a stable chiral three-dimensional sp2 network

Co-reporter:Jun Dai, Zhenyu Li and Jinlong Yang

Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 39) pp:NaN12422-12422

Publication Date(Web):2010/08/31

DOI:10.1039/C0CP00735H

Based on first-principles equation-of-state and lattice dynamics calculations, a new boron allotrope with K4 structure is proposed, which gives the first example of a three-dimensional all sp2 network.

Gas-phase dynamics in graphene growth by chemical vapour deposition

Co-reporter:Gan Li, Sheng-Hong Huang and Zhenyu Li

Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 35) pp:NaN22836-22836

Publication Date(Web):2015/07/30

DOI:10.1039/C5CP02301G

Chemical vapour deposition on a Cu substrate is becoming a very important approach to obtain high quality graphene samples. Previous studies of graphene growth on Cu mainly focus on surface processes. However, recent experiments suggest that gas-phase dynamics also plays an important role in graphene growth. In this article, gas-phase processes are systematically studied using computational fluid dynamics. Our simulations clearly show that graphene growth is limited by mass transport under ambient pressures while it is limited by surface reactions under low pressures. The carbon deposition rate at different positions in the tube furnace and the concentration of different gas phase species are calculated. Our results confirm that the previously realized graphene thickness control by changing the position of the Cu foil is a result of gas-phase methane decomposition reactions.

Single-stranded DNA adsorption on chiral molecule coated Au surface: a molecular dynamics study

Co-reporter:Haiqing Liang, Zhenyu Li and Jinlong Yang

Physical Chemistry Chemical Physics 2010 - vol. 12(Issue 17) pp:NaN4434-4434

Publication Date(Web):2010/02/24

DOI:10.1039/B923012B

All-atomistic molecular dynamics simulations with explicit water solution are performed to investigate the interaction between single-stranded DNA (ssDNA) molecules and chiral N-isobutyryl-cysteine (NIBC) molecule coated Au surfaces. Different contributions to the force exerted on ssDNA are analyzed. It turns out that the experimentally observed stereospecific adsorption behavior of ssDNA on D/L-NIBC self-assembled monolayer surface mainly originates from the interaction between the dipole moment of NIBC and the negative charge carried by ssDNA.

A density functional study on cationic AunCum+clusters and their monocarbonyls

Co-reporter:Yu Zhao, Zhenyu Li and Jinlong Yang

Physical Chemistry Chemical Physics 2009 - vol. 11(Issue 13) pp:NaN2334-2334

Publication Date(Web):2009/02/11

DOI:10.1039/B817806B

Small cationic AunCum+ (n + m≤ 6) clusters and their monocarbonyls AunCumCO+ have been studied by first-principles calculations. The trend for small Au clusters to form planar structures is weaker when some Au atoms are substituted by Cu atoms. A significant odd–even oscillation of the electron affinity of the cationic clusters with the number of their Au or Cu atoms is observed. CO prefers binding to Cu, which can be understood by the frontier molecular orbital theory. Its binding energy on AunCum+ generally decreases with the increase of the Cu content in the cluster, which is highly related to the electron transfer between CO and the cluster. Our calculation suggests that reactive collision between CO and Au3Cu+ may lead to the dissociation of the cluster with an Au atom loss.

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Abstract

Abstract