The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation （GGA） as well as the on-sit...The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation （GGA） as well as the on-site Coulomb interaction correction （＋U）. The Seebeck coefficient of TiS2 is calculated based on the electronic structure obtained within the GGA under the consideration of the on-site Coulomb interaction. The calculated Seebeck coefficient at 300K shows that Coulomb interaction U in the range of 4.97-5.42eV is important to reproduce the experimental data. The obtained energy gap Eg around 0.05 eV indicates that TiS2 is an indirect narrow-gap semiconductor.展开更多
The anisotropic properties of 1T- and 2H-TaS2 axe investigated by the density functional theory within the framework of full-potential linearized augmented plane wave method. The band structures of 1T- and 2H-TaS2 exh...The anisotropic properties of 1T- and 2H-TaS2 axe investigated by the density functional theory within the framework of full-potential linearized augmented plane wave method. The band structures of 1T- and 2H-TaS2 exhibit anisotropic properties and the calculated electronic specific-heat coefficient γ of 2H-TaS2 accords well with the existing experimental value. The anisotropic frequency-dependent dielectric functions including the effect of the Drude term are analysed, where the ε^xx（ω） spectra corresponding to the electric field E perpendicular to the z axis show excellent agreement with the measured results except for the ε1^xx（ω） of 1T-TaS2 below the energy level of 2.6 eV which is due to the lack of the enough CDW information for reference in our calculation. Furthermore, based on the values of optical effective mass ratio P of 1T and 2H phases it is found that the anisotropy in 2H-TaS2 is stronger than that in 1T-TaS2.展开更多
The temperature in the active region of semiconductor modules can be measured by a vacuum system method.The test device is positioned on a vacuum test platform and heated in two ways,from the chip and from the case,to...The temperature in the active region of semiconductor modules can be measured by a vacuum system method.The test device is positioned on a vacuum test platform and heated in two ways,from the chip and from the case,to identify the required heat to establish stable temperature gradients for the two processes,respectively.A complementary relationship between the temperatures under the two heating methods is found.By injecting the total heat into the device,the resulting uniform temperature can be derived from the temperature curves of the chip and case.It is demonstrated that the temperature obtained from this vacuum system method is equivalent to the normal operating temperature of the device in the atmosphere.Further comparison of our result with that of the electrical method also shows good agreement.展开更多
基金Supported by the National Science Foundation of China under Grant Nos 10504036 and 50472097, the Special Funds for Major State Basic Research Project of China under Grant No 2005CB623603, the Knowledge Innovation Programme of Chinese Academy of Sciences, and Director Grants of Hefei Institutes of Physical Sciences.
文摘The thermoelectric compound TiS2 is studied by using the full-potential linearized augmented plane-wave method on the density functional theory with the generalized gradient approximation （GGA） as well as the on-site Coulomb interaction correction （＋U）. The Seebeck coefficient of TiS2 is calculated based on the electronic structure obtained within the GGA under the consideration of the on-site Coulomb interaction. The calculated Seebeck coefficient at 300K shows that Coulomb interaction U in the range of 4.97-5.42eV is important to reproduce the experimental data. The obtained energy gap Eg around 0.05 eV indicates that TiS2 is an indirect narrow-gap semiconductor.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 90503005 and 50472097）, the State Key Development Program for Basic Research of China （Grant No 2005CB623603）, Knowledge Innovation Program of Chinese Academy of Sciences, and Director Grants of Hefei Institutes of Physical Sciences. Acknowledgment Part of the calculations were performed at the Centre for Computational Science, Hefei Institute of Physics China.
文摘The anisotropic properties of 1T- and 2H-TaS2 axe investigated by the density functional theory within the framework of full-potential linearized augmented plane wave method. The band structures of 1T- and 2H-TaS2 exhibit anisotropic properties and the calculated electronic specific-heat coefficient γ of 2H-TaS2 accords well with the existing experimental value. The anisotropic frequency-dependent dielectric functions including the effect of the Drude term are analysed, where the ε^xx（ω） spectra corresponding to the electric field E perpendicular to the z axis show excellent agreement with the measured results except for the ε1^xx（ω） of 1T-TaS2 below the energy level of 2.6 eV which is due to the lack of the enough CDW information for reference in our calculation. Furthermore, based on the values of optical effective mass ratio P of 1T and 2H phases it is found that the anisotropy in 2H-TaS2 is stronger than that in 1T-TaS2.
基金Supported by the Beijing Municipal Natural Science Fund,under Grant No 4092005the Research Fund for Doctoral Program of Ministry of Education of China under Grant No 20091103110006.
文摘The temperature in the active region of semiconductor modules can be measured by a vacuum system method.The test device is positioned on a vacuum test platform and heated in two ways,from the chip and from the case,to identify the required heat to establish stable temperature gradients for the two processes,respectively.A complementary relationship between the temperatures under the two heating methods is found.By injecting the total heat into the device,the resulting uniform temperature can be derived from the temperature curves of the chip and case.It is demonstrated that the temperature obtained from this vacuum system method is equivalent to the normal operating temperature of the device in the atmosphere.Further comparison of our result with that of the electrical method also shows good agreement.
