This paper provides a fresh perspective and new insights into nanoscale friction by investigating it through molecular dynamics(MD)simulation and atomic force microscope(AFM)nanoscratch experiments.This work considere...This paper provides a fresh perspective and new insights into nanoscale friction by investigating it through molecular dynamics(MD)simulation and atomic force microscope(AFM)nanoscratch experiments.This work considered gallium arsenide,an importantⅢ-Ⅴdirect bandgap semiconductor material residing in the zincblende structure,as a reference sample material due to its growing usage in 5G communication devices.In the simulations,the scratch depth was tested as a variable in the fine range of 0.5-3 nm to understand the behavior of material removal and to gain insights into the nanoscale friction.Scratch force,normal force,and average cutting forces were extracted from the simulation to obtain two scalar quantities,namely,the scratch cutting energy(defined as the work performed to remove a unit volume of material)and the kinetic coefficient of friction(defined as the force ratio).A strong size effect was observed for scratch depths below 2 nm from the MD simulations and about 15 nm from the AFM experiments.A strong quantitative corroboration was obtained between the specific scratch energy determined by the MD simulations and the AFM experiments,and more qualitative corroboration was derived for the pile-up and the kinetic coefficient of friction.This conclusion suggests that the specific scratch energy is insensitive to the tool geometry and the scratch speed used in this investigation.However,the pile-up and kinetic coefficient of friction are dependent on the geometry of the tool tip.展开更多
GaAs nanocrystals were prepared via a simple mechanical ball milling technique. The prepared GaAs nanocrystals have high purity and could form colloidal ethanol suspension without any surfactant additives. The colloid...GaAs nanocrystals were prepared via a simple mechanical ball milling technique. The prepared GaAs nanocrystals have high purity and could form colloidal ethanol suspension without any surfactant additives. The colloidal GaAs nanocrystal suspension displayed excellent two-photon absorption property over the visible and near-infrared region from 490 nm to 1064 nm, which enables it to become a promising broadband optical limiting material.展开更多
Ultrafast laser inscription(ULI)inside semiconductors offers new perspectives for 3D monolithic structures to be fabricated and new functionalities to be added in electronic and photonic microdevices.However,important...Ultrafast laser inscription(ULI)inside semiconductors offers new perspectives for 3D monolithic structures to be fabricated and new functionalities to be added in electronic and photonic microdevices.However,important challenges remain because of nonlinear effects such as strong plasma generation that distort the energy delivery at the focal point when exposing these materials to intense infrared light.Up to now,the successful technological demonstrations have primarily concentrated on silicon(Si).In this paper,we target at another important semiconductor:gallium arsenide(GaAs).With nonlinearities higher than those of Si,3D-machining of GaAs with femtosecond pulses becomes even harder.However,we show that the difficulty can be circumvented by burst-mode irradiation.We generate and apply trains of pulses at terahertz repetition rates for efficient pulse-to-pulse accumulation of laser-induced free carriers in the focal region,while avoiding an overdose of prefocal excitations.The superior performance of burst-mode irradiation is confirmed by a comparative study conducted with infrared luminescence microscopy.The results indicate a successful reduction of the plasma density in the prefocal region so that higher pulse energy reaches the focal spot.The same method is applied to identify optimum irradiation conditions considering particular cases such as asymmetric pulse trains and aberrated beams.With 64-pulse trains,we successfully manage to cross the writing threshold providing a solution for ULI inside GaAs.The application potential is finally illustrated with a stealth dicing demonstration by taking benefit of the burst mode.The irradiation method opens wide possibilities for 3D structuring inside GaAs by ULI.展开更多
We report accurate, calculated electronic, transport, and bulk properties of zinc blende gallium arsenide (GaAs). Our ab-initio, non-relativistic, self-con-sistent calculations employed a local density approximation (...We report accurate, calculated electronic, transport, and bulk properties of zinc blende gallium arsenide (GaAs). Our ab-initio, non-relativistic, self-con-sistent calculations employed a local density approximation (LDA) potential and the linear combination of atomic orbital (LCAO) formalism. We strictly followed the Bagayoko, Zhao, and William (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). Our calculated, direct band gap of 1.429 eV, at an experimental lattice constant of 5.65325 Å, is in excellent agreement with the experimental values. The calculated, total density of states data reproduced several experimentally determined peaks. We have predicted an equilibrium lattice constant, a bulk modulus, and a low temperature band gap of 5.632 Å, 75.49 GPa, and 1.520 eV, respectively. The latter two are in excellent agreement with corresponding, experimental values of 75.5 GPa (74.7 GPa) and 1.519 eV, respectively. This work underscores the capability of the local density approximation (LDA) to describe and to predict accurately properties of semiconductors, provided the calculations adhere to the conditions of validity of DFT.展开更多
Negative thermal expansion of gallium arsenide has been investigated through temperature dependent Extended X-ray Absorption Fine Structure (EXAFS) measurements. The bond thermal expansion coefficient αbond has been ...Negative thermal expansion of gallium arsenide has been investigated through temperature dependent Extended X-ray Absorption Fine Structure (EXAFS) measurements. The bond thermal expansion coefficient αbond has been evaluated and compared to negative expansion coefficient αtens due to tension effects. The overall thermal expansion coefficient is the sum?of?αbond?and αtens. Below 60 K, αtens is greater than αbond? yielding to a negative expansion in this temperature region. Tension effects are progressively overcome by the stretching effects in the region 60 - 300 K. The asymmetry of nearest neighbors distribution is not negligible since the gaussian approximation underestimates the bond expansion by about 0.00426 Å. This error decreases when the temperature is lowered. The accuracy in the thermal expansion evaluation and the connection between third cumulant and thermal expansion are discussed.展开更多
This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical...This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical atomic-centered orbital basis sets. The electronic band structure, total density of state (DOS) and band gap energy were calculated for Gallium-Arsenide and Aluminium-Arsenide in diamond structures. The result of minimum total energy and computational time obtained from the experimental lattice constant 5.63 A for both Gallium Arsenide and Aluminium Arsenide is -114,915.7903 eV and 64.989 s, respectively. The electronic band structure analysis shows that Aluminium-Arsenide is an indirect band gap semiconductor while Gallium-Arsenide is a direct band gap semiconductor. The energy gap results obtained for GaAs is 0.37 eV and AlAs is 1.42 eV. The band gap in GaAs observed is very small when compared to AlAs. This indicates that GaAs can exhibit high transport property of the electron in the semiconductor which makes it suitable for optoelectronics devices while the wider band gap of AlAs indicates their potentials can be used in high temperature and strong electric fields device applications. The results reveal a good agreement within reasonable acceptable errors when compared with the theoretical and experimental values obtained in the work of Federico and Yin wang [1] [2].展开更多
For the last several years, the linear array x-ray detector for x-ray imaging with gallium arsenide direct conversion sensitive elements has been developed and tested at the In-stitute for High Energy Physics. The arr...For the last several years, the linear array x-ray detector for x-ray imaging with gallium arsenide direct conversion sensitive elements has been developed and tested at the In-stitute for High Energy Physics. The array consists of 16 sensitive modules. Each module has 128 gallium arsenide (GaAs) sensitive elements with 200 μm pitch. Current article describes two key program procedures of initial dark current compensation of each sensitive element in the linear array, and sensitivity adjustment for alignment of strip pattern in the raw image data. As a part of evaluation process a modular transfer function (MTF) was measured with the slanted sharp-edge object under RQA5 technique as it described in the International Electrotechnical Commission 62220-1 standard (high voltage 70 kVp, additional aluminium filter 21 mm) for images with compensated dark currents and adjusted sensitivity of detector elements. The 10% level of the calculated MTF function has spatial resolution within 2 - 3 pair of lines per mm for both vertical and horizontal orientation.展开更多
Excitons have significant impacts on the properties of semiconductors.They exhibit significantly different properties when a direct semiconductor turns in to an indirect one by doping.Huybrecht variational method is a...Excitons have significant impacts on the properties of semiconductors.They exhibit significantly different properties when a direct semiconductor turns in to an indirect one by doping.Huybrecht variational method is also found to influence the study of exciton ground state energy and ground state binding energy in Al_(x)Ga_(1−x)As semiconductor spherical quantum dots.The Al_(x)Ga_(1−x)As is considered to be a direct semiconductor at AI concentration below 0.45,and an indirect one at the concentration above 0.45.With regards to the former,the ground state binding energy increases and decreases with AI concentration and eigenfrequency,respectively;however,while the ground state energy increases with AI concentration,it is marginally influenced by eigenfrequency.On the other hand,considering the latter,while the ground state binding energy increases with AI concentration,it decreases with eigenfrequency;nevertheless,the ground state energy increases both with AI concentration and eigenfrequency.Hence,for the better practical performance of the semiconductors,the properties of the excitons are suggested to vary by adjusting AI concentration and eigenfrequency.展开更多
High-pressure has been widely utilized to improve material performances such as thermal conductiv-ityκand interfacial thermal conductance G.Gallium arsenide(GaAs)as a functional semiconductor has attracted extensive ...High-pressure has been widely utilized to improve material performances such as thermal conductiv-ityκand interfacial thermal conductance G.Gallium arsenide(GaAs)as a functional semiconductor has attracted extensive attention in high-pressure studies for its technological importance and complex structure transitions.Thermal properties of GaAs under high pressure are urgent needs in physics but remain elusive.Herein,we systematically investigateκGaAs and G Al/GaAs of multi-structure up to -23 GPa.We conclude that:(1)in pressurization,phonon group velocity,lattice defects,and electrons play a central role inκGaAs in elastic,plastic,and metallization regions,respectively.The increased phonon density of states(PDOS)overlap,group velocity,and interfacial bonding enhances G Al/GaAs.(2)In depressurization,electrons remain the dominant factor on κ GaAs from 23 to 13.5 GPa.G Al/GaAs increases dramatically at -12 GPa due to the larger PDOS overlap.With decompressing to ambient,lattice defects including grain size reduction,arsenic vacancies,and partial amorphization reduce κ GaAs to a glass-like value.Remarkably,the released G Al/GaAs is 2.6 times higher than that of the initial.Thus our findings open a new dimension in synergistically realizing glass-like κ and enhancing G,which can facilitate thermoelectric performance and its potential engineering applications.展开更多
基于表面沟道型平面肖特基势垒二极管基本结构,采用GaAs 0.15μm伪高电子迁移率晶体管(pseudomorphic high electron mobility transistors,pHEMT)工艺制程,提出了一种垂直沟道长跨度空气桥的肖特基二极管模型.研究了不同阳极直径对肖...基于表面沟道型平面肖特基势垒二极管基本结构,采用GaAs 0.15μm伪高电子迁移率晶体管(pseudomorphic high electron mobility transistors,pHEMT)工艺制程,提出了一种垂直沟道长跨度空气桥的肖特基二极管模型.研究了不同阳极直径对肖特基二极管级联电阻的影响,对比分析了不同焊盘间距下肖特基二极管模型的S参数仿真结果,得到最优空气桥长度;仿真了最优焊盘间距下二极管肖特基结的TCAD模型,根据仿真得到的特性曲线提取肖特基二极管的SPICE参数.经实验测试,该二极管具有极低的零偏置结电容,截止频率高达9 THz,仿真结果与实测结果吻合度较高,可用于太赫兹频段上.展开更多
基金The authors would like to thank EPSRC(EP/K018345/1,EP/T024844/1)the Royal Society-NSFC Interna-tional Exchange Program(IECINSFC181474)for providing financial support to this research.SG is particularly thankful for the research support provided by the UKRI via Grant Nos.EP/L016567/1,EP/S013652/1,EP/T001100/1,EP/S036180/1,and EP/T024607/1+4 种基金The authors also acknowledge the support received from H2020(Cost Actions CA18125,CA18224,CA17136,and CA16235)the Royal Academy of Engineering via Grant Nos.IAPP18-19)295,TSP1332,and EXPP2021\11277and the Newton Fellowship award from the Royal Society(NIFR1191571)SG also accessed the Isambard Bris-tol,a UK supercomputing service,via the Resource Allocation Panel and ARCHER2 resources(Project e648)The authors also acknowledge the use of the EPSRC(EP/K000586/1)-funded ARCHIE WeSt High-Performance Computer at the University of Strathclyde.
文摘This paper provides a fresh perspective and new insights into nanoscale friction by investigating it through molecular dynamics(MD)simulation and atomic force microscope(AFM)nanoscratch experiments.This work considered gallium arsenide,an importantⅢ-Ⅴdirect bandgap semiconductor material residing in the zincblende structure,as a reference sample material due to its growing usage in 5G communication devices.In the simulations,the scratch depth was tested as a variable in the fine range of 0.5-3 nm to understand the behavior of material removal and to gain insights into the nanoscale friction.Scratch force,normal force,and average cutting forces were extracted from the simulation to obtain two scalar quantities,namely,the scratch cutting energy(defined as the work performed to remove a unit volume of material)and the kinetic coefficient of friction(defined as the force ratio).A strong size effect was observed for scratch depths below 2 nm from the MD simulations and about 15 nm from the AFM experiments.A strong quantitative corroboration was obtained between the specific scratch energy determined by the MD simulations and the AFM experiments,and more qualitative corroboration was derived for the pile-up and the kinetic coefficient of friction.This conclusion suggests that the specific scratch energy is insensitive to the tool geometry and the scratch speed used in this investigation.However,the pile-up and kinetic coefficient of friction are dependent on the geometry of the tool tip.
基金The work was financially supported by the National Natural Science Foundation of China (Nos. 10104003, 10204003, 90206003, and 90101027) and the National Key Basic Research Special Foundation of China (No.TG1999075207).
文摘GaAs nanocrystals were prepared via a simple mechanical ball milling technique. The prepared GaAs nanocrystals have high purity and could form colloidal ethanol suspension without any surfactant additives. The colloidal GaAs nanocrystal suspension displayed excellent two-photon absorption property over the visible and near-infrared region from 490 nm to 1064 nm, which enables it to become a promising broadband optical limiting material.
基金This research has received funding from the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation program(Grant Agreement No.724480).
文摘Ultrafast laser inscription(ULI)inside semiconductors offers new perspectives for 3D monolithic structures to be fabricated and new functionalities to be added in electronic and photonic microdevices.However,important challenges remain because of nonlinear effects such as strong plasma generation that distort the energy delivery at the focal point when exposing these materials to intense infrared light.Up to now,the successful technological demonstrations have primarily concentrated on silicon(Si).In this paper,we target at another important semiconductor:gallium arsenide(GaAs).With nonlinearities higher than those of Si,3D-machining of GaAs with femtosecond pulses becomes even harder.However,we show that the difficulty can be circumvented by burst-mode irradiation.We generate and apply trains of pulses at terahertz repetition rates for efficient pulse-to-pulse accumulation of laser-induced free carriers in the focal region,while avoiding an overdose of prefocal excitations.The superior performance of burst-mode irradiation is confirmed by a comparative study conducted with infrared luminescence microscopy.The results indicate a successful reduction of the plasma density in the prefocal region so that higher pulse energy reaches the focal spot.The same method is applied to identify optimum irradiation conditions considering particular cases such as asymmetric pulse trains and aberrated beams.With 64-pulse trains,we successfully manage to cross the writing threshold providing a solution for ULI inside GaAs.The application potential is finally illustrated with a stealth dicing demonstration by taking benefit of the burst mode.The irradiation method opens wide possibilities for 3D structuring inside GaAs by ULI.
文摘We report accurate, calculated electronic, transport, and bulk properties of zinc blende gallium arsenide (GaAs). Our ab-initio, non-relativistic, self-con-sistent calculations employed a local density approximation (LDA) potential and the linear combination of atomic orbital (LCAO) formalism. We strictly followed the Bagayoko, Zhao, and William (BZW) method, as enhanced by Ekuma and Franklin (BZW-EF). Our calculated, direct band gap of 1.429 eV, at an experimental lattice constant of 5.65325 Å, is in excellent agreement with the experimental values. The calculated, total density of states data reproduced several experimentally determined peaks. We have predicted an equilibrium lattice constant, a bulk modulus, and a low temperature band gap of 5.632 Å, 75.49 GPa, and 1.520 eV, respectively. The latter two are in excellent agreement with corresponding, experimental values of 75.5 GPa (74.7 GPa) and 1.519 eV, respectively. This work underscores the capability of the local density approximation (LDA) to describe and to predict accurately properties of semiconductors, provided the calculations adhere to the conditions of validity of DFT.
文摘Negative thermal expansion of gallium arsenide has been investigated through temperature dependent Extended X-ray Absorption Fine Structure (EXAFS) measurements. The bond thermal expansion coefficient αbond has been evaluated and compared to negative expansion coefficient αtens due to tension effects. The overall thermal expansion coefficient is the sum?of?αbond?and αtens. Below 60 K, αtens is greater than αbond? yielding to a negative expansion in this temperature region. Tension effects are progressively overcome by the stretching effects in the region 60 - 300 K. The asymmetry of nearest neighbors distribution is not negligible since the gaussian approximation underestimates the bond expansion by about 0.00426 Å. This error decreases when the temperature is lowered. The accuracy in the thermal expansion evaluation and the connection between third cumulant and thermal expansion are discussed.
文摘This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical atomic-centered orbital basis sets. The electronic band structure, total density of state (DOS) and band gap energy were calculated for Gallium-Arsenide and Aluminium-Arsenide in diamond structures. The result of minimum total energy and computational time obtained from the experimental lattice constant 5.63 A for both Gallium Arsenide and Aluminium Arsenide is -114,915.7903 eV and 64.989 s, respectively. The electronic band structure analysis shows that Aluminium-Arsenide is an indirect band gap semiconductor while Gallium-Arsenide is a direct band gap semiconductor. The energy gap results obtained for GaAs is 0.37 eV and AlAs is 1.42 eV. The band gap in GaAs observed is very small when compared to AlAs. This indicates that GaAs can exhibit high transport property of the electron in the semiconductor which makes it suitable for optoelectronics devices while the wider band gap of AlAs indicates their potentials can be used in high temperature and strong electric fields device applications. The results reveal a good agreement within reasonable acceptable errors when compared with the theoretical and experimental values obtained in the work of Federico and Yin wang [1] [2].
文摘For the last several years, the linear array x-ray detector for x-ray imaging with gallium arsenide direct conversion sensitive elements has been developed and tested at the In-stitute for High Energy Physics. The array consists of 16 sensitive modules. Each module has 128 gallium arsenide (GaAs) sensitive elements with 200 μm pitch. Current article describes two key program procedures of initial dark current compensation of each sensitive element in the linear array, and sensitivity adjustment for alignment of strip pattern in the raw image data. As a part of evaluation process a modular transfer function (MTF) was measured with the slanted sharp-edge object under RQA5 technique as it described in the International Electrotechnical Commission 62220-1 standard (high voltage 70 kVp, additional aluminium filter 21 mm) for images with compensated dark currents and adjusted sensitivity of detector elements. The 10% level of the calculated MTF function has spatial resolution within 2 - 3 pair of lines per mm for both vertical and horizontal orientation.
基金supported by the National Natural Science Foundation of China(Nos.12164032 and 11964026)the Natural Science Foundation of Inner Mongolia(No.2019MS01010)+3 种基金Scientific Research Projects in Colleges and Universities in Inner Mongolia(No.NJZZ19145)Graduate Science Innovative Research Projects(No.S20210281Z)the Natural Science Foundation of Inner Mongolia(No.2022MS01014)Doctor Research Start-up Fund of Inner Mongolia Minzu University(No.BS625).
文摘Excitons have significant impacts on the properties of semiconductors.They exhibit significantly different properties when a direct semiconductor turns in to an indirect one by doping.Huybrecht variational method is also found to influence the study of exciton ground state energy and ground state binding energy in Al_(x)Ga_(1−x)As semiconductor spherical quantum dots.The Al_(x)Ga_(1−x)As is considered to be a direct semiconductor at AI concentration below 0.45,and an indirect one at the concentration above 0.45.With regards to the former,the ground state binding energy increases and decreases with AI concentration and eigenfrequency,respectively;however,while the ground state energy increases with AI concentration,it is marginally influenced by eigenfrequency.On the other hand,considering the latter,while the ground state binding energy increases with AI concentration,it decreases with eigenfrequency;nevertheless,the ground state energy increases both with AI concentration and eigenfrequency.Hence,for the better practical performance of the semiconductors,the properties of the excitons are suggested to vary by adjusting AI concentration and eigenfrequency.
基金financially supported by the National Natural Science Foundation of China(Nos.51720105007,51976025,and 52206219)the Fundamental Research Funds for the Central Universities(No.DUT22ZD216).
文摘High-pressure has been widely utilized to improve material performances such as thermal conductiv-ityκand interfacial thermal conductance G.Gallium arsenide(GaAs)as a functional semiconductor has attracted extensive attention in high-pressure studies for its technological importance and complex structure transitions.Thermal properties of GaAs under high pressure are urgent needs in physics but remain elusive.Herein,we systematically investigateκGaAs and G Al/GaAs of multi-structure up to -23 GPa.We conclude that:(1)in pressurization,phonon group velocity,lattice defects,and electrons play a central role inκGaAs in elastic,plastic,and metallization regions,respectively.The increased phonon density of states(PDOS)overlap,group velocity,and interfacial bonding enhances G Al/GaAs.(2)In depressurization,electrons remain the dominant factor on κ GaAs from 23 to 13.5 GPa.G Al/GaAs increases dramatically at -12 GPa due to the larger PDOS overlap.With decompressing to ambient,lattice defects including grain size reduction,arsenic vacancies,and partial amorphization reduce κ GaAs to a glass-like value.Remarkably,the released G Al/GaAs is 2.6 times higher than that of the initial.Thus our findings open a new dimension in synergistically realizing glass-like κ and enhancing G,which can facilitate thermoelectric performance and its potential engineering applications.
文摘基于表面沟道型平面肖特基势垒二极管基本结构,采用GaAs 0.15μm伪高电子迁移率晶体管(pseudomorphic high electron mobility transistors,pHEMT)工艺制程,提出了一种垂直沟道长跨度空气桥的肖特基二极管模型.研究了不同阳极直径对肖特基二极管级联电阻的影响,对比分析了不同焊盘间距下肖特基二极管模型的S参数仿真结果,得到最优空气桥长度;仿真了最优焊盘间距下二极管肖特基结的TCAD模型,根据仿真得到的特性曲线提取肖特基二极管的SPICE参数.经实验测试,该二极管具有极低的零偏置结电容,截止频率高达9 THz,仿真结果与实测结果吻合度较高,可用于太赫兹频段上.