The effect of piezoelectricity on phonon properties and thermal conductivity of gallium nitride （GaN） nanofilms is theoretically investigated. The elasticity model is utilized to derive the phonon properties in spat...The effect of piezoelectricity on phonon properties and thermal conductivity of gallium nitride （GaN） nanofilms is theoretically investigated. The elasticity model is utilized to derive the phonon properties in spatially confined GaN nanofilms. The piezoelectric constitutive relation in GaN nanofilms is taken into account in calculating the phonon dispersion relation. The modified phonon group velocity and phonon density of state as well as the phonon thermal conductivity are also obtained due to the contribution of piezoelectricity. Theoretical results show that the piezoelectricity in GaN nanofilms can change significantly the phonon properties such as the phonon group velocity and density of states, resulting in the variation of the phonon thermal conductivity of GaN nanofilms remarkably. Moreover, the piezoelectricity of GaN can modify the dependence of thermal conductivity on the geometrical size and temperature. These results can be useful in modeling the thermal performance in the active region of GaN-based electronic devices.展开更多
We show the results of first-principles calculations of structural,phonon,elastic,thermal and electronic properties of the Mg-X inter-metallics in their respective ground state phase and meta-stable phases at equilibr...We show the results of first-principles calculations of structural,phonon,elastic,thermal and electronic properties of the Mg-X inter-metallics in their respective ground state phase and meta-stable phases at equilibrium geometry and the studied pressure range.Phonon dispersion spectra for these compounds were investigated by using the linear response technique.The phonon spectra do not show any abnormality in their respective ground state phase.The respective ground states phases of the studied system remain stable within the studied pressure range.Electronic and thermodynamic properties were derived by analysis of the electronic structures and quasi-harmonic approximation.The mixed bonding character of the Mg-X intermetallics is revealed by Mg-X bonds,and it leads the metallic nature.Most of the contribution originated from X ions d like states at Fermi level compared to that of Mg ion in these intermetallics.In this work,we also predicted the melting temperature of these intermetallics and evaluated the Debye temperature by using elastic constants.展开更多
We investigate the effects of pre-stress and surface tension on the electron–acoustic phonon scattering rate and the mobility of rectangular silicon nanowires. With the elastic theory and the interaction Hamiltonian ...We investigate the effects of pre-stress and surface tension on the electron–acoustic phonon scattering rate and the mobility of rectangular silicon nanowires. With the elastic theory and the interaction Hamiltonian for the deformation potential, which considers both the surface energy and the acoustoelastic effects, the phonon dispersion relation for a stressed nanowire under spatial confinement is derived. The subsequent analysis indicates that both surface tension and pre-stress can dramatically change the electron–acoustic phonon interaction. Under a negative（positive） surface tension and a tensile（compressive） pre-stress, the electron mobility is reduced（enhanced） due to the decrease（increase） of the phonon energy as well as the deformation-potential scattering rate. This study suggests an alternative approach based on the strain engineering to tune the speed and the drive current of low-dimensional electronic devices.展开更多
The thermal conductivity of GaN nanofilm is simulated by using the molecular dynamics(MD)method to explore the influence of the nanofilm thickness and the pre-strain field under different temperatures.It is demonstrat...The thermal conductivity of GaN nanofilm is simulated by using the molecular dynamics(MD)method to explore the influence of the nanofilm thickness and the pre-strain field under different temperatures.It is demonstrated that the thermal conductivity of GaN nanofilm increases with the increase of nanofilm thickness,while decreases with the increase of temperature.Meanwhile,the thermal conductivity of strained GaN nanofilms is weakened with increasing the tensile strain.The film thickness and environment temperature can affect the strain effect on the thermal conductivity of GaN nanofilms.In addition,the analysis of phonon properties of GaN nanofilm shows that the phonon dispersion and density of states of GaN nanofilms can be significantly modified by the film thickness and strain.The results in this work can provide the theoretical supports for regulating the thermal properties of GaN nanofilm through tailoring the geometric size and strain engineering.展开更多
XB_(2)(X=Mg and Al)compounds have drawn great attention for their superior electronic characteristics and potential applications in semiconductors and superconductors.The study of phonon thermal transport properties o...XB_(2)(X=Mg and Al)compounds have drawn great attention for their superior electronic characteristics and potential applications in semiconductors and superconductors.The study of phonon thermal transport properties of XB_(2)is significant to their application and mechanism behind research.In this work,the phonon thermal transport properties of three-dimensional(3D)and two-dimensional(2D)XB_(2)were studied by first-principles calculations.After considering the electron-phonon interaction(EPI),the thermal conductivities(TCs)of 3D Mg B_(2)and 3D Al B_(2)decrease by 29%and 16%which is consistent with experimental values.Moreover,the underlying mechanisms of reduction on lattice TCs are the decrease in phonon lifetime and heat capacity when considering quantum confinement effect.More importantly,we are surprised to find that there is a correlation between quantum confinement effect and EPI.The quantum confinement will change the phonon and electron characteristics which has an impact on EPI.Overall,our work is expected to provide insights into the phonon thermal transport properties of XB_(2)compounds considering EPI and quantum confinement effect.展开更多
The elastic, dynamical, and electronic properties of cubic LiHg and Li3Hg were investigated based on first-principles methods. The elastic constants and phonon spectral calculations confirmed the mechanical and dynami...The elastic, dynamical, and electronic properties of cubic LiHg and Li3Hg were investigated based on first-principles methods. The elastic constants and phonon spectral calculations confirmed the mechanical and dynamical stability of the materials at ambient conditions. The obtained elastic moduli of LiHg are slightly larger than those of Li3Hg. Both LiHg and Li3Hg are ductile materials with strong shear anisotropy as metals with mixed ionic, covalent, and metallic interactions. The calculated Debye temperatures are 223.5 K and 230.6 K for LiHg and Li3Hg, respectively. The calculated phonon frequency of the T2g mode in Li3Hg is 326.8 cm-1. The p states from the Hg and Li atoms dominate the electronic structure near the Fermi level. These findings may inspire further experimental and theoretical study on the potential technical and engineering applications of similar alkali metal-based intermetallic compounds.展开更多
基金support received from the National Natural Science Foundation of China (11472243, 11302189, 11321202)the Doctoral Fund of Ministry of Education of China (20130101120175)
文摘The effect of piezoelectricity on phonon properties and thermal conductivity of gallium nitride （GaN） nanofilms is theoretically investigated. The elasticity model is utilized to derive the phonon properties in spatially confined GaN nanofilms. The piezoelectric constitutive relation in GaN nanofilms is taken into account in calculating the phonon dispersion relation. The modified phonon group velocity and phonon density of state as well as the phonon thermal conductivity are also obtained due to the contribution of piezoelectricity. Theoretical results show that the piezoelectricity in GaN nanofilms can change significantly the phonon properties such as the phonon group velocity and density of states, resulting in the variation of the phonon thermal conductivity of GaN nanofilms remarkably. Moreover, the piezoelectricity of GaN can modify the dependence of thermal conductivity on the geometrical size and temperature. These results can be useful in modeling the thermal performance in the active region of GaN-based electronic devices.
基金The present work was financially supported by a Grant-Aid for Science and Engineering Research Board(Grant No.SERB/F/922/2014-15),Department of Science&Technology,Government of India.
文摘We show the results of first-principles calculations of structural,phonon,elastic,thermal and electronic properties of the Mg-X inter-metallics in their respective ground state phase and meta-stable phases at equilibrium geometry and the studied pressure range.Phonon dispersion spectra for these compounds were investigated by using the linear response technique.The phonon spectra do not show any abnormality in their respective ground state phase.The respective ground states phases of the studied system remain stable within the studied pressure range.Electronic and thermodynamic properties were derived by analysis of the electronic structures and quasi-harmonic approximation.The mixed bonding character of the Mg-X intermetallics is revealed by Mg-X bonds,and it leads the metallic nature.Most of the contribution originated from X ions d like states at Fermi level compared to that of Mg ion in these intermetallics.In this work,we also predicted the melting temperature of these intermetallics and evaluated the Debye temperature by using elastic constants.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11472243,11302189,and 11321202)the Doctoral Fund of Ministry of Education of China(Grant No.20130101120175)+1 种基金the Zhejiang Provincial Qianjiang Talent Program,China(Grant No.QJD1202012)the Educational Commission of Zhejiang Province,China(Grant No.Y201223476)
文摘We investigate the effects of pre-stress and surface tension on the electron–acoustic phonon scattering rate and the mobility of rectangular silicon nanowires. With the elastic theory and the interaction Hamiltonian for the deformation potential, which considers both the surface energy and the acoustoelastic effects, the phonon dispersion relation for a stressed nanowire under spatial confinement is derived. The subsequent analysis indicates that both surface tension and pre-stress can dramatically change the electron–acoustic phonon interaction. Under a negative（positive） surface tension and a tensile（compressive） pre-stress, the electron mobility is reduced（enhanced） due to the decrease（increase） of the phonon energy as well as the deformation-potential scattering rate. This study suggests an alternative approach based on the strain engineering to tune the speed and the drive current of low-dimensional electronic devices.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11772294 and 11621062)the Fundamental Research Funds for the Central Universities(Grant No.2017QNA4031)。
文摘The thermal conductivity of GaN nanofilm is simulated by using the molecular dynamics(MD)method to explore the influence of the nanofilm thickness and the pre-strain field under different temperatures.It is demonstrated that the thermal conductivity of GaN nanofilm increases with the increase of nanofilm thickness,while decreases with the increase of temperature.Meanwhile,the thermal conductivity of strained GaN nanofilms is weakened with increasing the tensile strain.The film thickness and environment temperature can affect the strain effect on the thermal conductivity of GaN nanofilms.In addition,the analysis of phonon properties of GaN nanofilm shows that the phonon dispersion and density of states of GaN nanofilms can be significantly modified by the film thickness and strain.The results in this work can provide the theoretical supports for regulating the thermal properties of GaN nanofilm through tailoring the geometric size and strain engineering.
基金financially supported by the National Natural Science Foundation of China(Nos.51720105007,52076031 and 51806031)the Fundamental Research Funds for the Central Universities(No.DUT19RC(3)006)the computing resources from Super-computing Center of Dalian University of Technology。
文摘XB_(2)(X=Mg and Al)compounds have drawn great attention for their superior electronic characteristics and potential applications in semiconductors and superconductors.The study of phonon thermal transport properties of XB_(2)is significant to their application and mechanism behind research.In this work,the phonon thermal transport properties of three-dimensional(3D)and two-dimensional(2D)XB_(2)were studied by first-principles calculations.After considering the electron-phonon interaction(EPI),the thermal conductivities(TCs)of 3D Mg B_(2)and 3D Al B_(2)decrease by 29%and 16%which is consistent with experimental values.Moreover,the underlying mechanisms of reduction on lattice TCs are the decrease in phonon lifetime and heat capacity when considering quantum confinement effect.More importantly,we are surprised to find that there is a correlation between quantum confinement effect and EPI.The quantum confinement will change the phonon and electron characteristics which has an impact on EPI.Overall,our work is expected to provide insights into the phonon thermal transport properties of XB_(2)compounds considering EPI and quantum confinement effect.
基金This study was supported by the National Natural Science Foundation of China under Grant Nos. 11347007 and 11674131, the Qing Lan Project, the Colleges and Universities in Jiangsu Province Natural Science Research Project under Grant No 14KJB460013, and the Priority Academic Program Develop- ment of Jiangsu Higher Education Institutions. Y. L. Li thanks the support from the Chinese Scholarship Council. C. M. Hao thanks the support from the Postgraduate Research 8z Practice Innovation Program of Jiangsu Province under Grant No. KYCX17_1652.
文摘The elastic, dynamical, and electronic properties of cubic LiHg and Li3Hg were investigated based on first-principles methods. The elastic constants and phonon spectral calculations confirmed the mechanical and dynamical stability of the materials at ambient conditions. The obtained elastic moduli of LiHg are slightly larger than those of Li3Hg. Both LiHg and Li3Hg are ductile materials with strong shear anisotropy as metals with mixed ionic, covalent, and metallic interactions. The calculated Debye temperatures are 223.5 K and 230.6 K for LiHg and Li3Hg, respectively. The calculated phonon frequency of the T2g mode in Li3Hg is 326.8 cm-1. The p states from the Hg and Li atoms dominate the electronic structure near the Fermi level. These findings may inspire further experimental and theoretical study on the potential technical and engineering applications of similar alkali metal-based intermetallic compounds.
