Grain Size Effect on Electrical Conductivity and Giant Magnetoresistance of Bulk Magnetic Polycrystals

By solving the Boltzmann transport equation and considering the spin-dependent grain boundary scattering, the distribution of electrons in grains and the electrical transport properties in the applied magnetic field are studied. With regard to the dominant influence of grain boundary scattering which is taken as a boundary condition for the electrical transport, the grain size-dependent electrical conductivity is investigated. In addition, the reorientation of the relative magnetization between grains brings the change of the electron spin when the magnetonanocrystailine material is subjected to the magnetic field, resulting in the remarkable giant magnetoresistance effect.     

Influence of surface scattering on the thermal properties of spatially confined GaN nanofilm

Gallium nitride(GaN), the notable representative of third generation semiconductors, has been widely applied to optoelectronic and microelectronic devices due to its excellent physical and chemical properties. In this paper, we investigate the surface scattering effect on the thermal properties of GaN nanofilms. The contribution of surface scattering to phonon transport is involved in solving a Boltzmann transport equation(BTE). The confined phonon properties of GaN nanofilms are calculated based on the elastic model. The theoretical results show that the surface scattering effect can modify the cross-plane phonon thermal conductivity of GaN nanostructures completely, resulting in the significant change of size effect on the conductivity in GaN nanofilm. Compared with the quantum confinement effect, the surface scattering leads to the order-of-magnitude reduction of the cross-plane thermal conductivity in GaN nanofilm. This work could be helpful for controlling the thermal properties of Ga N nanostructures in nanoelectronic devices through surface engineering.     

纳米孪晶和梯度纳米结构金属强韧特性研究进展

金属材料在航空、航天工业以及民用工业等领域具有广泛的应用,如何获取同时具备高强度和良好塑性的金属材料一直是材料、物理、力学等不同学科长期以来亟待解决的难题.传统的强化方法包括应变强化、固溶强化、相变强化、晶粒细化强化和第二相弥散强化等,均会使材料的韧性或塑性降低.近年来,实验研究发现通过界面设计和微结构调控来可以制备出高强高韧的金属材料,认为位错与各类界面的相互作用、以及微结构优化对应力集中的削弱是材料强化和韧化的主要原因.根据已有实验观察,人们通过原子尺度方法定量分析高强高韧金属材料的变形机理,揭示其强化和韧化机制;同时,发展出基于变形机理的理论模型和有限元方法定量描述高强高韧金属的力学行为.论文将重点介绍纳米孪晶金属和梯度纳米结构金属的强韧特性研究进展,并对新型纳米结构金属材料的强韧特性优化进行展望.     

Electron–acoustic phonon interaction and mobility in stressed rectangular silicon nanowires

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.