Co-reporter:Zhiguo Wang
ACS Applied Materials & Interfaces May 10, 2017 Volume 9(Issue 18) pp:15893-15893
Publication Date(Web):April 21, 2017
DOI:10.1021/acsami.7b03659
Self-charging lithium ion batteries (SCLIBs) that hybridize mechanical energy harvesting and storage processes into one process can be fabricated using a piezoelectric polyvinylidene fluoride (PVDF) film as a separator in lithium ion batteries. In this paper, the deintercalation reaction at LiCoO2 and intercalation reaction at graphite were studied under an internal piezoelectric field using density functional theory. It was found that the internal piezoelectric field applied on the anode can increase intercalation energies and diffusion behavior, at the same time, and the internal piezoelectric field facilitates the deintercalation reaction at the cathode. The simulation results revealed the self-charging mechanism of SCLIBs, in which the piezoelectric potential can assist the deintercalation and intercalation proccesses at the cathode and anode upon self-charging, which may be responsible for the experimentally observed efficiency of SCLIBs.Keywords: deintercalation; density functional theory; intercalation; piezoelectric potential; self-charging lithium ion batteries;
Co-reporter:Wei Jin
RSC Advances (2011-Present) 2017 vol. 7(Issue 70) pp:44547-44551
Publication Date(Web):2017/09/11
DOI:10.1039/C7RA07899D
The adsorption and magnesiation behavior of Mg onto α-Sn and Mg2Sn through (100), (110) and (111) surfaces were investigated by using first-principles calculations. It was found that the Mg atom prefers to be adsorbed on the surface rather than diffuse into the sub-surface of Sn. The diffusion energy barrier is higher for Mg diffusing from the surface to the subsurface compared with the internal diffusion. Mg diffuses much faster along the <100> direction than along the <110> and <111> directions. The diffusion process from the surface to the subsurface is a rate-limiting step for Mg intercalation into Sn. The surface magnesiation is also a rate-limiting step for Mg intercalation into Mg2Sn though (100) and (110) surfaces, whereas the surface magnesiation of the Mg2Sn (111) surface is easier than the (100) and (110) surfaces. Surface modification is necessary to improve the magnesiation behavior of Sn as an anode for MIBs, especially when the anode materials are reduced to the nanoscale.
Co-reporter:Wenwu Shi;Yong Qing Fu
Journal of Nanoparticle Research 2017 Volume 19( Issue 9) pp:296
Publication Date(Web):24 August 2017
DOI:10.1007/s11051-017-3996-2
In this paper, mechanisms behind enhancement of catalytic activity of MoS2 mono-layer (three atomic layers) for hydrogen evolution reaction (HER) by mechanically applying bending strain were investigated using density functional theory. Results showed that with the increase of bending strains, the Gibbs free energy for hydrogen adsorption on the MoS2 mono-layer was decreased from 0.18 to −0.04 eV and to 0.13 eV for the bend strains applied along the zigzag and armchair directions, respectively. The mechanism for the enhanced catalytic activity comes from the changes of density of electronic states near the Fermi energy level, which are induced by the changes of the Mo-S and Mo-Mo bonds upon bending. This report provides a new design methodology to improve the catalytic activity of catalysts based on two-dimensional transition metal dichalcogenides through a simple mechanical bending.
Co-reporter:Jianjian Shi;Y. Q. Fu
Journal of Materials Science 2017 Volume 52( Issue 1) pp:605-612
Publication Date(Web):07 September 2016
DOI:10.1007/s10853-016-0357-y
First-principle calculation was employed to investigate the surface stability for (100), (110), and (111) low-index facets of LiNi0.5Mn1.5O4 (LNMO) crystallographic structures with a P4332 space group and phase transitions at the surface regions of Ni0.5Mn1.5O4. The calculated surface energies of (100) and (111) facets with Li-terminations are 1.39 and 1.40 eV, respectively, indicating that both these facets of the LNMO are stable according to the calculation results. Defect formation energies and diffusion barriers of Ni and Mn in surface facets of the Ni0.5Mn1.5O4 are much lower than those in the bulk. This suggests that the Ni and Mn ions in the surface regions of the LNMO easily occupy the tetrahedral Li-positions during delithiation process, which supports the experimental results and explains the surface structure changes of the LNMO upon delithiation.
Co-reporter:Zhiguo Wang, Yang He, Meng Gu, Yingge Du, Scott X. Mao, and Chongmin Wang
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 37) pp:24567
Publication Date(Web):August 30, 2016
DOI:10.1021/acsami.6b06581
Reversible insertion/extraction of foreign ions into/from a host lattice constitutes the fundamental operating principle of rechargeable battery and electrochromic materials. The insertion of foreign ions is a far more commonly observed structural evolution of the host lattice, and for the most cases such a lattice evolution is subtle. However, it has not been clear what factors control such a lattice structural evolution. Based on the tungsten trioxide (WO3) model crystal, we use in situ transmission electron microscopy (TEM) combined with density functional theory calculations to explore the nature of Li ions intercalation induced crystal symmetry evolution of WO3. We discovered that Li insertion into the octahedral cavity of the WO3 lattice will lead to a low to high symmetry transition, featuring a sequential monoclinic → tetragonal → cubic phase transition. The density functional theory results reveal that the phase transition is essentially governed by the electron transfer from Li to the WO6 octahedrons, which effectively leads to the weakening the W–O bond and modifies system band structure, resulting in an insulator-to-metal transition. The observation of the electronic effect on crystal symmetry and conductivity is significant, providing deep insights on the intercalation reactions in secondary rechargeable ion batteries and the approach for tailoring the functionalities of material based on insertion of ions in the lattice.Keywords: electron transfer; first-principles calculation; in situ TEM; insulator-to-metal transition; ion intercalation; phase transformation; tungsten trioxide
Co-reporter:Zhijie Li, Ningning Wang, Zhijie Lin, Junqiang Wang, Wei Liu, Kai Sun, Yong Qing Fu, and Zhiguo Wang
ACS Applied Materials & Interfaces 2016 Volume 8(Issue 32) pp:20962
Publication Date(Web):July 22, 2016
DOI:10.1021/acsami.6b02893
Porous CuO nanosheets were prepared on alumina tubes using a facile hydrothermal method, and their morphology, microstructure, and gas-sensing properties were investigated. The monoclinic CuO nanosheets had an average thickness of 62.5 nm and were embedded with numerous holes with diameters ranging from 5 to 17 nm. The porous CuO nanosheets were used to fabricate gas sensors to detect hydrogen sulfide (H2S) operating at room temperature. The sensor showed a good response sensitivity of 1.25 with respond/recovery times of 234 and 76 s, respectively, when tested with the H2S concentrations as low as 10 ppb. It also showed a remarkably high selectivity to the H2S, but only minor responses to other gases such as SO2, NO, NO2, H2, CO, and C2H5OH. The working principle of the porous CuO nanosheet based sensor to detect the H2S was identified to be the phase transition from semiconducting CuO to a metallic conducting CuS.Keywords: CuO; gas sensor; hydrogen sulfide; hydrothermal method; nanosheet
Co-reporter:Wei Jin, Guangqiang Yin, Zhiguo Wang, Y.Q. Fu
Applied Surface Science 2016 Volume 385() pp:72-79
Publication Date(Web):1 November 2016
DOI:10.1016/j.apsusc.2016.05.096
Highlights
- •
Surface of spinel MgMn2O4 and MgNi0.5Mn1.5O4 cathodes were investigated.
- •
The surface energies show less dependence on the Ni-doping.
- •
Atomic reconstruction occurred due to atomic relaxation at the surface.
Co-reporter:Zhijie Li, Xinyue Niu, Zhijie Lin, Ningning Wang, Huahai Shen, Wei Liu, Kai Sun, Yong Qing Fu, Zhiguo Wang
Journal of Alloys and Compounds 2016 Volume 682() pp:647-653
Publication Date(Web):15 October 2016
DOI:10.1016/j.jallcom.2016.04.311
•The CeO2 nanowires were synthesized by hydrothermal route.•The sensor based on CeO2 film shows a high performance in detecting H2S gas.•The sensor’s detection limit towards H2S gas is as low as 50 ppb.•The sensor shows a short response/recovery time (24 s and 15 s, respectively for 50 ppb H2S).CeO2 nanowires were synthesized using a facile hydrothermal process without any surfactant, and their morphological, structural and gas sensing properties were systematically investigated. The CeO2 nanowires with an average diameter of 12.5 nm had a face-centered cubic fluorite structure and grew along [111] of CeO2. At the room temperature of 25 °C, hydrogen sulfide (H2S) gas sensor based on the CeO2 nanowires showed excellent sensitivity, low detection limit (50 ppb), and short response and recovery time (24 s and 15 s for 50 ppb H2S, respectively).
Co-reporter:Wei Jin, Zhijie Li, Zhiguo Wang, Y.Q. Fu
Materials Chemistry and Physics 2016 Volume 182() pp:167-172
Publication Date(Web):1 October 2016
DOI:10.1016/j.matchemphys.2016.07.019
•Diffusion of Mg ions in Bi and β-Sn were investigated using density functional theory.•Bi and β-Sn are good anode material for Mg ion batteries.•Bi is better a candidate than the β-Sn to be used as anode material for the MIBs.Based on density functional theory computation, we systematically investigated diffusion behavior of Mg ions in β-tin (Sn), bismuth (Bi), and their magnesiation compounds of Bi2Mg3 and Mg2Sn. Results showed that the β-Sn and Bi are good candidates for the anode materials for Mg ion batteries with small diffusion barriers. The dynamic simulations and the obtained energy barriers showed that compared with β-Sn, Bi is a better anode candidate with fast charge/discharge rates for the Mg ion batteries.
Co-reporter:Wenwu Shi, Zhiguo Wang, Zhijie Li, Y.Q. Fu
Materials Chemistry and Physics 2016 Volume 183() pp:392-397
Publication Date(Web):1 November 2016
DOI:10.1016/j.matchemphys.2016.08.043
•Effect of electric field on the adsorption and diffusion were investigated.•Adsorption energies of the adatoms in the MoS2 monolayer were enhanced.•Diffusion barriers of the adatoms in the MoS2 monolayer were decreased.•Electric field can be used to realize a fast charging rate of rechargeable ion batteries.A new phenomenon, electric field enhanced adsorption and diffusion of lithium, magnesium and aluminum ions in a MoS2 monolayer, was investigated using density functional theory in this study. With the electric field increased from 0 to 0.8 V/Å, the adsorption energies of the Li, Mg and Al atoms in the MoS2 monolayer were decreased from −2.01 to −2.49 eV, from −0.80 to −1.28 eV, and −2.71 to −3.01 eV, respectively. The corresponding diffusion barriers were simultaneously decreased from 0.23 to 0.08 eV, from 0.15 to 0.10 eV, and 0.24 to 0.21 eV for the Li, Mg and Al ions, respectively. We concluded that the external electric field can increase the charging speed of rechargeable ion batteries based on the MoS2 anode materials.
Co-reporter:Zhijie Li, Shiyun Wu, Zhiguo Wang, Y.Q. Fu
Journal of Alloys and Compounds 2016 672() pp: 155-160
Publication Date(Web):5 July 2016
DOI:10.1016/j.jallcom.2016.02.082
•Solid state transformations induced by doping in WO3 were investigated.•Mechanisms of structure transformation induced by doping were clarified.•RexW1-xO3 has a cubic structure as x is larger than 0.375.•Electron doping induces the monoclinic to cubic transformation.Effects of dopants on structural stability of monoclinic WO3 were studied using density functional theory. Transformation from monoclinic to cubic crystal structures was obtained by gradually increasing doping concentrations of both rhenium (Re) and electrons inside the monoclinic WO3, whereas a large distortion of WO6 octahedra was observed by gradually increasing doping concentrations of both niobium (Nb) and holes inside the monoclinic WO3. It was verified that RexW1-xO3 has a cubic structure if x is larger than 0.375, and the transformation from monoclinic to cubic structure is mainly dependent on the occupancy of the W 5d orbital. The elastic characteristics of the RexW1-xO3 decrease with the increase of the content of Re in the range of 0.375 ≤ x ≤ 0.875.
Co-reporter:Wenwu Shi, Shiyun Wu, Zhiguo Wang
Physica E: Low-dimensional Systems and Nanostructures 2016 Volume 81() pp:192-195
Publication Date(Web):July 2016
DOI:10.1016/j.physe.2016.03.014
The electronic properties of SiC nanotubes (SiCNTs) under external transverse electric field were investigated using density functional theory. The pristine SiCNTs were semiconductors with band-gaps of 2.03, 2.17 and 2.25 eV for (6,6), (8,8) and (10,10) SiCNTs, respectively. It was found the band gaps was reduced with the external transverse electric filed applied. The (8,8) and (10,10) SiCNTs changed from semiconductor to metals as the intensity of electric field reached 0.7 and 0.5 V/Å. The results indicate that the electronic properties of SiCNTs can be tuned by the transvers electric field with integrality of the nanotubes.
Co-reporter:Zhijie Li, Zhijie Lin, Ningning Wang, Junqiang Wang, Wei Liu, Kai Sun, Yong Qing Fu, Zhiguo Wang
Sensors and Actuators B: Chemical 2016 Volume 235() pp:222-231
Publication Date(Web):1 November 2016
DOI:10.1016/j.snb.2016.05.063
•The network nano-sheet Co3O4 arrays were synthesized by hydrothermal route.•The sensor based on Co3O4 film shows a high performance in detecting NH3 gas.•The sensor’s detection limit towards NH3 gas is as low as 0.2 ppm.•The sensor exhibits an excellent selectivity against other toxic and noxious gases.Network nano-sheet arrays of Co3O4 for high precision NH3 sensing application were prepared on alumina tube using a facile hydrothermal process without template or surfactant, and their morphology, nanostructures and NH3 gas sensing performance were investigated. The prepared nano-sheet Co3O4 arrays showed a network structure with an average sheet thickness of 39.5 nm. Detailed structural analysis confirmed that the synthesized Co3O4 nano-sheets were consisted of nanoparticles with an average diameter of 20.0 nm. NH3 gas sensor based on these network Co3O4 nano-sheet arrays showed a low detection limit (0.2 ppm), rapid response/recovery time (9 s/134 s for 0.2 ppm NH3), good reproducibility and long-term stability for NH3 detection at room temperature.
Co-reporter:Jianjian Shi, Zhiguo Wang, Y.Q. Fu
Electrochimica Acta 2015 Volume 186() pp:71-75
Publication Date(Web):20 December 2015
DOI:10.1016/j.electacta.2015.10.144
Lithium ion dynamics in crystalline lithium silicide Li12Si7 were studied using density functional theory. Vacancy formation and diffusion of lithium ions showed a strong dependence on crystallographic sites of the lithium ions. The thirteen crystallographic lithium ions in the Li12Si7 can be divided into three types based on their mobilities, and their typical diffusion energy barriers are 0.18, 0.36 and 0.52 eV, respectively. These crystallographic lithium ions take part in the fast diffusion process and are distributed within one dimensional column. The result agrees well with experimental report of the quasi-one dimensional fast diffusion channel in the Li12Si7.
Co-reporter:Guoqiang Li, Tamas Varga, Pengfei Yan, Zhiguo Wang, Chongmin Wang, Scott A. Chambers and Yingge Du
Physical Chemistry Chemical Physics 2015 vol. 17(Issue 23) pp:15119-15123
Publication Date(Web):11 May 2015
DOI:10.1039/C5CP01344E
We investigated the impact of crystallographic orientation on the photocatalytic activity of single crystalline WO3 thin films prepared by molecular beam epitaxy on the photodegradation of rhodamine B (RhB). A clear effect is observed, with (111) being the most reactive surface, followed by (110) and (001). Photoreactivity is directly correlated with the surface free energy determined by density functional theory calculations. The RhB photodegradation mechanism is found to involve hydroxyl radicals in solution formed from photo-generated holes and differs from previous studies performed on nanoparticles and composites.
Co-reporter: Zhiguo Wang;Qiulei Su; Huiqiu Deng; Yongqing Fu
ChemElectroChem 2015 Volume 2( Issue 9) pp:1292-1297
Publication Date(Web):
DOI:10.1002/celc.201500201
Abstract
The lithiation process of silicon was investigated by using ab initio molecular dynamics. Diffusion coefficients of Li in Li–Si alloys were calculated to be in the range between 2.08×10−9 and 3.53×10−7 cm2 s−1 at room temperature. The results showed that the Li mobility is strongly dependent on the composition of the LixSi alloys. The Li diffusivity in a LixSi alloy can be enhanced by two orders of magnitude when x is increased from 1.0 to 3.75, which can be explained by the instability of the Si network, owing to charge transfer from Li to Si.
Co-reporter: Zhiguo Wang;Dr. Qiulei Su; Huiqiu Deng; Yongqing Fu
ChemElectroChem 2015 Volume 2( Issue 8) pp:1182-1186
Publication Date(Web):
DOI:10.1002/celc.201500059
Abstract
In this work, we investigated the effect of oxygen deficiency on defect chemistry in delithiated spinel LiNi0.5Mn1.5O4 cathodes by using first principles density functional calculations. Results show that the oxygen deficiency assists the migration of Ni and Mn ions from octahedral sites to tetrahedral ones, and the migration assists the formation of oxygen vacancies. These results shed light on the atomic-level structural changes of the delithiated spinel LiNi0.5Mn1.5O4, in which transition-metal ions migrate from octahedral sites to tetrahedral ones, accompanied by oxygen release upon heating. Oxygen deficiency plays key roles in oxygen release in the LiNi0.5Mn1.5O4 cathodes.
Co-reporter:Zhiguo Wang, Qiulei Su, Huiqiu Deng, Weidong He, Junhao Lin and Y. Q. Fu
Journal of Materials Chemistry A 2014 vol. 2(Issue 34) pp:13976-13982
Publication Date(Web):03 Jul 2014
DOI:10.1039/C4TA01614A
Improvements in the electrical conductivity and lithium (Li) mobility for Li ion batteries are of particular importance for their high-power applications. Mapping of electron energy loss spectroscopy shows that the electrochemical reaction front region is under electron-rich conditions during lithiation. In this paper, the electron-rich effect on the diffusion behaviors of Li in pristine and phosphorus-doped group IVA elements, e.g., silicon, germanium and tin, were investigated using the first principles density functional theory (DFT) calculations in combination with a climbing-image nudged elastic band and ab initio DFT molecular dynamics. Phosphorus doping was found to be a non-critical factor for enhanced Li diffusion into Si. Instead, the results showed that the diffusion barriers and diffusivity of Li are mainly affected by the electron-rich effect, i.e. the energy barriers decrease and diffusivity increases in an electron-rich environment. The decrease in diffusion barriers was attributed to the relaxation of Si–Si bonds with extra electrons, which can also apply to the case of Ge but not for metallic Sn. These new findings provide a theoretical and experimental basis for the design and fabrication of next generation batteries with a high power density.
Co-reporter:Zhiguo Wang, Qiulei Su, Jianjian Shi, Huiqiu Deng, G. Q. Yin, J. Guan, M. P. Wu, Y. L. Zhou, H. L. Lou, and Y. Q. Fu
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 9) pp:6786
Publication Date(Web):April 2, 2014
DOI:10.1021/am500554y
Using first-principles calculation based on density functional theory, diffusion of Mg atom into α- and β-Sn was investigated. The diffusion barriers are 0.395 and 0.435 eV for an isolated Mg atom in the α- and β-Sn, respectively. However, the diffusion barriers of the Mg atom decrease in the α-Sn, whereas they increase in the β-Sn, when an additional Mg atom was inserted near the original diffusing Mg atom, which is mainly due to strong binding of Mg–Mg atoms in the β-Sn. Therefore, it is better to use the α-Sn, rather than the β-Sn, as an anode material for Mg ion batteries.Keywords: anode materials; density functional theory; diffusion batteries; Mg ion batteries; Mg−Mg interaction; tin;
Co-reporter:Zhiguo Wang, Qiulei Su, G.Q. Yin, Jianjian Shi, Huiqiu Deng, J. Guan, M.P. Wu, Y.L. Zhou, H.L. Lou, Y.Q. Fu
Materials Chemistry and Physics 2014 Volume 147(Issue 3) pp:1068-1073
Publication Date(Web):15 October 2014
DOI:10.1016/j.matchemphys.2014.06.060
•Atomistic structures of GBs in MX2 (M = Mo, W, Nb; X = S, Se) monolayer were identified.•Stability of GBs in the MX2 (M = Mo, W, Nb; X = S, Se) monolayer were studied.•Electronic properties of GBs in the MX2 (M = Mo, W, Nb; X = S, Se) monolayer were studied.•Defect levels induced by the GBs are located within the band gap of semiconducting MX2.•NbS2 and NbSe2 remain as metallic materials within grain boundaries.Layered transition metal dichalcogenides with unique mechanical, electronic, optical, and chemical properties can be used for novel nanoelectronic and optoelectronic devices. Large-area monolayers synthesized using chemical vapor deposition are often polycrystals with many dislocations and grain boundaries (GBs). In the present paper, atomic structure and electronic properties of MX2 (M = Mo, W, Nb; X = S, Se) with the GBs were investigated using first principles based on density functional theory. Simulation results revealed that the zigzag-oriented GBs (which consist of pentagon/heptagons (5-7) pairs) were more stable than the armchair-oriented GBs (which consist of pentagon/heptagons (5-7-5-7) pairs). The GBs induced defect levels are located within the band gap for the semiconductor materials of MX2 (M = Mo, W; X = S, Se) monolayers, and the NbS2 and NbSe2 remained as metallic materials with GBs. Results provided a possible pathway to build these nano-layered materials into nanoelectronic devices.
Co-reporter:Zhiguo Wang, Meng Gu, Yungang Zhou, Xiaotao Zu, Justin G. Connell, Jie Xiao, Daniel Perea, Lincoln J. Lauhon, Junhyeok Bang, Shengbai Zhang, Chongmin Wang, and Fei Gao
Nano Letters 2013 Volume 13(Issue 9) pp:4511-4516
Publication Date(Web):August 14, 2013
DOI:10.1021/nl402429a
The physical and chemical behaviors of materials used in energy storage devices, such as lithium-ion batteries (LIBs), are mainly controlled by an electrochemical process, which normally involves insertion/extraction of ions into/from a host lattice with a concurrent flow of electrons to compensate charge balance. The fundamental physics and chemistry governing the behavior of materials in response to the ions insertion/extraction is not known. Herein, a combination of in situ lithiation experiments and large-scale ab initio molecular dynamics simulations are performed to explore the mechanisms of the electrochemically driven solid-state amorphization in Li–Si systems. We find that local electron-rich condition governs the electrochemically driven solid-state amorphization of Li–Si alloys. This discovery provides the fundamental explanation of why lithium insertion in semiconductor and insulators leads to amorphization, whereas in metals, it leads to a crystalline alloy. The present work correlates electrochemically driven reactions with ion insertion, electron transfer, lattice stability, and phase equilibrium.
Co-reporter:Zhiguo Wang, Qiulei Su and Huiqiu Deng
Physical Chemistry Chemical Physics 2013 vol. 15(Issue 22) pp:8705-8709
Publication Date(Web):12 Apr 2013
DOI:10.1039/C3CP51167G
Using first principles calculations based on density functional theory, the adsorption and diffusion properties of Li and Mg atoms on single-layered and bulk V2O5 are investigated. The simulation results show that the diffusion barrier of Li on the single-layered V2O5 is decreased compared with that of the bulk V2O5, which indicates that the Li mobility can be significantly enhanced on the single-layered V2O5. The increased binding energies of Li to single-layered V2O5 make them more attractive for promising cathode materials. Although the diffusion barrier of Mg on the single-layered V2O5 does not decrease, the binding energies of Mg to single-layered V2O5 is increased compared with that of bulk V2O5, thus the single-layered V2O5 is an attractive cathode material for rechargeable ion batteries.
Co-reporter:Zhiguo Wang, Xinyue Niu, Qiulei Su, Huiqiu Deng, Zhijie Li, Wangyu Hu, and Fei Gao
The Journal of Physical Chemistry C 2013 Volume 117(Issue 34) pp:17644-17649
Publication Date(Web):July 30, 2013
DOI:10.1021/jp405104z
We present an ab initio molecular dynamics study of the effect of transition metal (TM) adatoms (Sc–Zn) on the threshold displacement energy (TDE) of graphene. Our calculations predict that it is substantially easier to displace one of the carbon atoms near the adatoms. Substitutional TM atoms at carbon vacancies and Stone–Wales defects are the main defect structures formed after irradiation in the TM adatoms–graphene systems. Defect can be formed at low energy electron irradiation (electron energy below 55 keV for the V, Cr, Mn, Fe, and Co adatoms). Thus, the absorption of TM atoms on graphene enables patterning the graphene by controlling deposition and electron irradiation, as well as graphene modification under transmission electron microscope condition. Also, the result provides an easy pathway to dope the graphene with TM substitutional atoms for the spin-electronic devices through electron-beam or ion-beam lighography.
Co-reporter:Zhiguo Wang ; Y.G. Zhou ; Junhyeok Bang ; M.P. Prange ; S.B. Zhang ;Fei Gao
The Journal of Physical Chemistry C 2012 Volume 116(Issue 30) pp:16070-16079
Publication Date(Web):July 9, 2012
DOI:10.1021/jp303905u
Defects play an important role on the unique properties of the sp2-bonded materials, such as graphene. The creation and evolution of monovacancy, divacancy, Stone-Wales (SW), and grain boundaries (GBs) under irradiation in graphene are investigated using density functional theory and time-dependent density functional theory molecular dynamics simulations. It is of great interest that the patterns of these defects can be controlled through electron irradiation. The SW defects can be created by electron irradiation with energy above the displacement threshold energy (Td, ∼19 eV) and can be healed with an energy (14–18 eV) lower than Td. The transformation between four types of divacancies—V2(5–8–5), V2(555–777), V2(5555–6–7777), and V2(55–77)—can be realized through bond rotation induced by electron irradiation. The migrations of divancancies, SW defects, and GBs can also be controlled by electron irradiation. Thus, electron irradiation can serve as an important tool to modify morphology in a controllable manner and to tailor the physical properties of graphene.
Co-reporter:Yungang Zhou, Zhiguo Wang, Ping Yang, and Fei Gao
The Journal of Physical Chemistry C 2012 Volume 116(Issue 13) pp:7581-7586
Publication Date(Web):March 7, 2012
DOI:10.1021/jp300593q
Novel electronic and magnetic properties of various-sized graphene nanoflakes (GNFs) embedded in a boron nitride (BN) layer were studied by ab initio methods. The feasibility of synthesizing hybrid GNF-BN structure, a desirable quantum dot structure, was explored. In this structure, photoexcited electrons and holes occupy the same spatial region—the GNF region—which offers an effective way to generate a GNF-based light-emitting device and adjust its emitted optical properties by controlling the size and array of GNF in the BN layer. On the basis of the important magnetism properties of embedded GNF, we propose a specific configuration to obtain a large spin. Together with the high stability of spin alignment, the proposed configuration can be exploited for spintronic devices.
Co-reporter:Zhiguo Wang ; Yungang Zhou ; Yanwen Zhang ;Fei Gao
The Journal of Physical Chemistry C 2012 Volume 116(Issue 3) pp:2271-2277
Publication Date(Web):December 27, 2011
DOI:10.1021/jp208229b
Structure and electronic properties of carbon nanotubes (CNTs) with grain boundaries (GBs) are investigated using density-functional calculations, where the GBs parallel and perpendicular to the tube axis are considered. Simulation results show that the GBs have a great effect on the electronic properties of the CNTs. For the GBs along the tube axis, the CNTs are narrow or zero band gap (<0.16 eV) materials, independent of the misoritentaion angle and diameter. For the GBs perpendicular to the tube axis, localized electronic states appear within the GBs regions, leading to a larger band gap of up to 0.6 eV. It is convenient to transport and localize the electrons and holes by engineering the GBs. These findings are of great significance for developing carbon-based nanomaterials and electronic devices.
Co-reporter:Zhiguo Wang
Journal of Nanoparticle Research 2012 Volume 14( Issue 3) pp:
Publication Date(Web):2012 March
DOI:10.1007/s11051-012-0756-1
Using first-principles calculations, the structure, stability, and electronic properties of BN sheets with grain boundaries (GBs) are investigated. Two types of GBs, i.e., zigzag- and armchair-oriented GBs, are considered. Simulation results reveal that the zigzag-oriented GBs are more stable than the armchair-oriented ones. The GBs induce defect levels located within the band gap, which must be taken into account when building nanoelectronic devices.
Co-reporter:Zhiguo Wang;Shengjie Wang;Chunlai Zhang;Jingbo Li
Journal of Nanoparticle Research 2011 Volume 13( Issue 1) pp:185-191
Publication Date(Web):2011 January
DOI:10.1007/s11051-010-0017-0
The electronic properties of saturated and unsaturated twinned SiC nanowires grown along [111] direction and surrounded by {111} facets are investigated using first-principles calculations with density functional theory and generalized gradient approximation. All the nanowires considered, including saturated and unsaturated ones, exhibit semiconducting characteristics. The saturated nanowires have a direct band gap and the band gap decreases with increasing diameters of the nanowires. The hexagonal (2H) stacking inside the cubic (3C) stacking has no effect on electronic properties of the SiC nanowires. The highest occupied molecular orbitals and the lowest unoccupied molecular orbitals are distributed along the nanowire axis uniformly, which indicates that the twinned SiC nanowires are good candidates in realizing nano-optoelectronic devices.
Co-reporter:Z.G. Wang, J.B. Li, F. Gao, W.J. Weber
Acta Materialia 2010 Volume 58(Issue 6) pp:1963-1971
Publication Date(Web):April 2010
DOI:10.1016/j.actamat.2009.11.039
Abstract
Molecular dynamics simulations with the Tersoff potential were used to study the response of twinned SiC nanowires under tensile and compressive strain. The critical strain of the twinned nanowires can be enhanced by twin stacking faults, and their critical strains are larger than those of perfect nanowires with the same diameters. Under axial tensile strain, the bonds of the nanowires are stretched just before failure. The failure behavior is found to depend on the twin segment thickness and the diameter of the nanowires. An atomic chain is observed for thin nanowires with small twin segment thickness under tension strain. Under axial compressive strain, the collapse of twinned SiC nanowires exhibits two different failure modes, depending on the length and diameter of the nanowires, i.e., shell buckling for short nanowires and columnar buckling for longer nanowires.
Co-reporter:Zhiguo Wang, Chunlai Zhang, Jingbo Li, Fei Gao, William J. Weber
Computational Materials Science 2010 Volume 50(Issue 2) pp:344-348
Publication Date(Web):December 2010
DOI:10.1016/j.commatsci.2010.08.024
The electronic properties of hydrogen-saturated GaN nanowires with different orientations and sizes are investigated using first principles calculations, and three types of nanowires oriented along the [0 0 1], [1 1 0] and [1 −1 0] crystal directions are considered. The electronic properties of nanowires in all three directions are extremely similar. All the hydrogen-saturated GaN nanowires show semiconducting behavior with a direct band gap larger than that of bulk wurtzite GaN. Quantum confinement leads to a decrease in the band gap of the nanowires with increasing nanowire size. The [0 0 1]-oriented nanowires with hexagonal cross sections are energetically more favorable than the [1 0 0]- and [1 −1 0]-oriented nanowires with triangular cross sections.
Co-reporter: Zhiguo Wang; Jingbo Li;Dr. Fei Gao;Dr. William J. Weber
ChemPhysChem 2010 Volume 11( Issue 15) pp:3329-3332
Publication Date(Web):
DOI:10.1002/cphc.201000244
Abstract
The electronic properties of wurtzite/zinc-blende (WZ/ZB) heterojunction GaN are investigated using first-principles methods. A small component of ZB stacking formed along the growth direction in the WZ GaN nanowires does not show a significant effect on the electronic property, whereas a charge separation of electrons and holes occurs along the directions perpendicular to the growth direction in the ZB stacking. The later case provides an efficient way to separate the charge through controlling crystal structure. These results have significant implications for most state of the art excitonic solar cells and the tuning region in tunable laser diodes.
Co-reporter:Zhiguo Wang, Shengjie Wang, Jingbo Li, Fei Gao and William J. Weber
The Journal of Physical Chemistry C 2009 Volume 113(Issue 44) pp:19281-19285
Publication Date(Web):October 9, 2009
DOI:10.1021/jp907657z
The atomic and electronic structures of saturated and unsaturated GaN nanotubes along the [001] direction with (100) lateral facets are studied using first-principles calculations. Atomic relaxation of nanotubes shows that appreciable distortion occurs in the unsaturated nanotubes. All the nanotubes considered, including saturated and unsaturated ones, exhibit semiconducting, with a direct band gap. Surface states arisen from the 3-fold-coordinated N and Ga atoms at the lateral facets exist inside the bulklike band gap. When the nanotubes are saturated with hydrogen, these dangling bond bands are removed from the band gap, but the band gap decreases with increasing the wall thickness of the nanotubes.
Co-reporter:Xiaoli Sun, Zhiguo Wang, Yong Qing Fu
Carbon (May 2017) Volume 116() pp:
Publication Date(Web):May 2017
DOI:10.1016/j.carbon.2017.01.024
Effects of grain boundaries (GBs) in graphene on adsorption and diffusion of sodium were investigated using first principle calculations. Results showed that the presence of GBs in graphene enhanced the adsorption of sodium, with their adsorption energies in the range of −1.32∼-0.79 eV, which were lower than the value of −0.67 eV for sodium adsorbed on pristine graphene. The diffusion energy barriers were in the range of 0.09–0.35 eV when sodium was diffused along GBs of graphene, whereas they were decreased when sodium was gradually diffused into the GBs. Results showed that graphene with GBs had a larger energy storage capacity for sodium than the pristine one, indicating that it can be used as a good anode material for sodium ion batteries.Figure optionsDownload full-size imageDownload high-quality image (243 K)Download as PowerPoint slide
Co-reporter:Guoqiang Li, Tamas Varga, Pengfei Yan, Zhiguo Wang, Chongmin Wang, Scott A. Chambers and Yingge Du
Physical Chemistry Chemical Physics 2015 - vol. 17(Issue 23) pp:NaN15123-15123
Publication Date(Web):2015/05/11
DOI:10.1039/C5CP01344E
We investigated the impact of crystallographic orientation on the photocatalytic activity of single crystalline WO3 thin films prepared by molecular beam epitaxy on the photodegradation of rhodamine B (RhB). A clear effect is observed, with (111) being the most reactive surface, followed by (110) and (001). Photoreactivity is directly correlated with the surface free energy determined by density functional theory calculations. The RhB photodegradation mechanism is found to involve hydroxyl radicals in solution formed from photo-generated holes and differs from previous studies performed on nanoparticles and composites.
Co-reporter:Zhiguo Wang, Qiulei Su and Huiqiu Deng
Physical Chemistry Chemical Physics 2013 - vol. 15(Issue 22) pp:NaN8709-8709
Publication Date(Web):2013/04/12
DOI:10.1039/C3CP51167G
Using first principles calculations based on density functional theory, the adsorption and diffusion properties of Li and Mg atoms on single-layered and bulk V2O5 are investigated. The simulation results show that the diffusion barrier of Li on the single-layered V2O5 is decreased compared with that of the bulk V2O5, which indicates that the Li mobility can be significantly enhanced on the single-layered V2O5. The increased binding energies of Li to single-layered V2O5 make them more attractive for promising cathode materials. Although the diffusion barrier of Mg on the single-layered V2O5 does not decrease, the binding energies of Mg to single-layered V2O5 is increased compared with that of bulk V2O5, thus the single-layered V2O5 is an attractive cathode material for rechargeable ion batteries.
Co-reporter:Zhiguo Wang, Qiulei Su, Huiqiu Deng, Weidong He, Junhao Lin and Y. Q. Fu
Journal of Materials Chemistry A 2014 - vol. 2(Issue 34) pp:NaN13982-13982
Publication Date(Web):2014/07/03
DOI:10.1039/C4TA01614A
Improvements in the electrical conductivity and lithium (Li) mobility for Li ion batteries are of particular importance for their high-power applications. Mapping of electron energy loss spectroscopy shows that the electrochemical reaction front region is under electron-rich conditions during lithiation. In this paper, the electron-rich effect on the diffusion behaviors of Li in pristine and phosphorus-doped group IVA elements, e.g., silicon, germanium and tin, were investigated using the first principles density functional theory (DFT) calculations in combination with a climbing-image nudged elastic band and ab initio DFT molecular dynamics. Phosphorus doping was found to be a non-critical factor for enhanced Li diffusion into Si. Instead, the results showed that the diffusion barriers and diffusivity of Li are mainly affected by the electron-rich effect, i.e. the energy barriers decrease and diffusivity increases in an electron-rich environment. The decrease in diffusion barriers was attributed to the relaxation of Si–Si bonds with extra electrons, which can also apply to the case of Ge but not for metallic Sn. These new findings provide a theoretical and experimental basis for the design and fabrication of next generation batteries with a high power density.
