金属衬底在石墨烯化学气相沉积生长中的作用

以过渡金属为催化衬底的化学气相沉积法(Chemical Vapor Deposition，CVD)已经可以制备与机械剥离样品相媲美的石墨烯，是实现石墨烯工业应用的关键技术之一。原子尺度理论研究能够帮助我们深刻理解石墨烯生长机理，为实验现象提供合理的解释，并有可能成为将来实验设计的理论指导。本文从理论计算的角度，总结了各种金属衬底在石墨烯CVD生长过程中的各种作用与相应的机理，包括在催化碳源裂解、降低石墨烯成核密度等，催化加快石墨烯快速生长，修复石墨烯生长过程中产生的缺陷，控制外延生长石墨烯的晶格取向，以及在降温过程中石墨烯褶皱与金属表面台阶束的形成过程等。在本文最后，我们对当前石墨烯生长领域中亟需解决的理论问题进行了深入探讨与展望。     

气相输运沉积制备c轴择优取向的碘化铋薄膜

铋基卤化物材料因其无毒和优良的光电性能而显示出巨大的应用潜力。BiI₃作为一种层状重金属半导体,已被用于X射线检测、γ射线检测和压力传感器等领域,最近其作为一种薄膜太阳能电池吸收材料备受关注。本文采用简单的气相输运沉积(VTD)法,以BiI₃晶体粉末作为蒸发源,在玻璃基底上得到高质量c轴择优取向的BiI₃薄膜。并通过研究蒸发源温度和沉积距离对薄膜物相和形貌的影响,分析了BiI₃薄膜择优生长的机理。结果表明VTD法制备的BiI₃薄膜属于三斜晶系,其光学带隙为~1.8 eV。沉积温度对薄膜的择优取向有较大影响,在沉积温度低于270 ℃时,沉积的薄膜具有沿c轴择优取向生长的特点,超过此温度,c轴择优取向生长消失。在衬底温度为250 ℃、沉积距离为15 cm时制备的薄膜结晶性能最好,晶体形貌为片状八面体。     

雾化辅助化学气相沉积法氧化镓薄膜生长研究

采用自主设计搭建的雾化辅助化学气相沉积系统设备,开展了Ga₂O₃薄膜制备及其特性研究工作。通过X射线衍射研究了沉积温度、系统沉积压差对Ga₂O₃薄膜结晶质量的影响。结果表明,Ga₂O₃在425~650 ℃温度区间存在物相转换关系。随着沉积温度从425 ℃升高至650 ℃,薄膜结晶分别由非晶态、纯α-Ga₂O₃结晶状态向α-Ga₂O₃、β-Ga₂O₃两相混合结晶状态改变。通过原子力显微镜表征探究了生长温度对Ga₂O₃薄膜表面形貌的影响,从475 ℃升高至650 ℃时,薄膜表面粗糙度由26.8 nm下降至24.8 nm。同时,高分辨X射线衍射仪测试表明475 ℃、5 Pa压差条件下的α-Ga₂O₃薄膜样品半峰全宽仅为190.8″,为高度结晶态的单晶α-Ga₂O₃薄膜材料。     

Synthesis of flower-like WS2 by chemical vapor deposition

Flower-like tungsten disulfide (WS₂) with a diameter of 5-10 μm is prepared by chemical vapor deposition (CVD). Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Raman spectroscopy, and ultraviolet-visible (UV-vis) spectroscopy are used to characterize its morphological and optical properties, and its growth mechanism is discussed. The key factors for the formation of flower-like WS₂ are determined. Firstly, the cooling process causes the generation of nucleation dislocations, and then the "leaf" growth of flower-like WS₂ is achieved by increasing the temperature.     

The pentacene films on the glass/ITO surface: structure and optical properties

Abstract

The structure, morphology and optical transmittance spectra of pentacene films on the (glass/ITO) surface were studied. The films were grown by two methods - the thermal vacuum deposition (TVD) and pulsed laser deposition (PLD). The electron diffraction pattern from thermally deposited pentacene films confirms their polycrystalline structure while the diffraction pattern of PLD-coated layers has a diffusion character. The results obtained showed that layers deposited by the TVD method has an optical spectrum that is characteristic for the pentacene film in contrary to the layers deposited by the PLD method. It is found a sensitivity of the optical transmittance of pentacene films to the ammonia action, which may be used for development the optical gas sensor.     

A new endocytic model based on the co-rotational grid method

Endocytosis plays important roles in many cellular physiological processes, such as metabolism and immune. Many theoretical models have been proposed to study the endocytic process, but little has considered the tensile deformation of the membrane and the actin forces. In this paper, a new endocytic model is proposed based on the co-rotational grid method. Our model gives a direct estimation of the in-plane strain of the plasma membrane and provides a basis for the calculation of further scission process of the vesicle. The results fit well with experimental data in the literature. Moreover, it is suggested that the active forces of actin at the endocytic site is the main mechanism driving the invagination of the plasma membrane.     

Growth and characterization of two-dimensional crystals for communication and energy applications

This review article covers the growth and characterization of two-dimensional (2D) crystals of transition metal chalcogenides, h-BN, graphene, etc. The chemical vapor transport method for bulk single crystal growth is discussed in detail. Top-down methods like mechanical and liquid exfoliation and bottom-up methods like chemical vapor deposition and molecular beam epitaxy for mono/few-layer growth are described. The optimal characterization techniques such as optical, atomic force, scanning electron, and Raman spectroscopy for identification of mono/few-layer(s) of the 2D crystals are discussed. In addition, a survey was done for the application of 2D crystals for both creation and deterministic transfer of single-photon sources and photovoltaic systems. Finally, the application of plasmonic nanoantenna was proposed for enhanced solar-to-electrical energy conversion and faster/brighter quantum communication devices.     

单晶金刚石p型和n型掺杂的研究

超宽禁带半导体材料金刚石在热导率、载流子迁移率和击穿场强等方面表现出优异的性质,在功率电子学领域具有广阔的应用前景。实现p型和n型导电是制备金刚石半导体器件的基础要求,其中p型金刚石的发展较为成熟,主流的掺杂元素是硼,但在高掺杂时存在空穴迁移率迅速下降的问题;n型金刚石目前主流的掺杂元素是磷,还存在杂质能级深、电离能较大的问题,以及掺杂之后金刚石晶体中的缺陷造成载流子浓度和迁移率都比较低,电阻率难以达到器件的要求。因此制备高质量的p型和n型金刚石成为研究者关注的焦点。本文主要介绍金刚石独特的物理性质,概述化学气相沉积法和离子注入法实现金刚石掺杂的基本原理和参数指标,进而回顾两种方法进行单晶金刚石薄膜p型和n型掺杂的研究进展,系统总结了其面临的问题并对未来方向进行了展望。     

基于Ni-SnO2纳米颗粒的GS-PUF设计

气敏传感器具有气体识别、探测和监测等功能, 广泛应用于工业生产等领域, 但在泄漏预警时缺乏迅速识别和定位等功能. 本文基于传感器制备工艺偏差分析, 通过对传感器气敏机制的研究, 提出一种基于Ni-SnO2纳米颗粒的气敏传感器物理不可克隆函数(Gas Sensor-Physical Unclonable Function, GS-PUF)设计方案. 该方案利用掺杂Ni元素的方法, 结合静电喷雾沉积技术制备Ni-SnO2气敏传感器, 以获取更加稳定可靠的物理特征值, 然后采集气敏传感器对不同浓度下气体的响应数据, 最后利用随机阻值多位平衡算法比较不同组气敏传感器响应电信号值, 实现PUF数据输出. 制备每组样本可产生128位二进制数据的多组PUF样本, 进行对比实验. 结果表明, 所设计的GS-PUF具有气体泄漏源头识别定位的功能, 且随机性提升至99%, 唯一性达49.80%.