Unconventional lattice dynamics in few-layer h-BN and indium iodide crystals

Unusual quadratic dispersion of flexural vibrational mode and red-shift of Raman shift of in-plane mode with increasing layer-number are quite common and interesting in low-dimensional materials, but their physical origins still remain open questions. Combining ab initio density functional theory calculations with the empirical force-constant model, we study the lattice dynamics of two typical two-dimensional(2 D) systems, few-layer h-BN and indium iodide(In I). We found that the unusual quadratic dispersion of flexural mode frequency on wave vector may be comprehended based on the competition between atomic interactions of different neighbors. Long-range interaction plays an essential role in determining the dynamic stability of the 2 D systems. The frequency red-shift of in-plane Raman-active mode from monolayer to bulk arises mainly from the reduced long-range interaction due to the increasing screening effect.     

Tailoring electronic properties of two-dimensional antimonene with isoelectronic counterparts

Using ab initio density functional theory calculations, we explore the three most stable structural phases, namely, α,β, and cubic(c) phases, of two-dimensional(2D) antimonene, as well as its isoelectronic counterparts SnTe and InI. We find that the band gap increases monotonically from Sb to SnTe to InI along with an increase in ionicity, independent of the structural phases. The band gaps of this material family cover the entire visible-light energy spectrum, ranging from 0.26 eV to 3.37 eV, rendering them promising candidates for optoelectronic applications. Meanwhile, band-edge positions of these materials are explored and all three types of band alignments can be achieved through properly combining antimonene with its isoelectronic counterparts to form heterostructures. The richness in electronic properties for this isoelectronic material family sheds light on possibilities to tailor the fundamental band gap of antimonene via lateral alloying or forming vertical heterostructures.     

电子快门照相机

<正> 本文以一个具体的电子快门照相机的设计为例,论述电子快门照相机的设计原理。重点讨论光圈优先,快门自动控制的一种半自动照相机(简称电快相机)是如何通过传感器系统的作用,使物镜的光圈数、快门速度、底片感光速度等诸因素有机地结合起来,从而实现景     

光栏在连续变倍显微镜设计中的作用

<正> 任何从事光学系统设计的同志都知道每一个光学系统都明显的存在三种形式的光栏,即视场光栏,孔径光栏,杂光光栏。三种光栏作用各异。但在光学设计计算阶段孔径光栏的作用将是十分重要的。因此本文将重点讨论一下孔径光栏在变倍显微镜及其附加大物镜的设计中的地位及处理方法。孔径光栏是光学系统对物体的投影中心,更重要的是:它的中心应是通过光学系统参与成像的优良光束的中心。这就意味着光栏位置