Modification of Soft Inorganic Thin Films through the use of van der Waals Epitaxial Strain

人类社会对更好的信息传播手段的一贯追求和对它的有效利用？的能源供应，需要不断创新的基础技术材料基础设施。变革性技术依赖于其科学基础的突破，如材料和加工。近年来，一些无机软固体在能量转换和信息处理方面显示出了潜在的应用前景，并有望为奇异态物质的物理学提供新的见解。理论工作表明，这些材料的可逆机械变形可能导致其物理性质的逐渐或突然变化。然而，这些软材料，特别是重卤化物和硫属化物，由于其独特的材料结构和原子排列，难以利用常规的化学方法诱导变形。这项工作解决了这个问题，探索通过货车德瓦尔斯外延拉伸软，但重卤化物和硫属化物材料的可能性。这项研究将以应变薄膜的形式引入一套新的有用的光电、电光、逻辑和存储材料。研究人员还将通过建立一个“图形学习”计划来追求教育目标，该计划将通过信息的图形呈现来培训工程本科生，特别是来自代表性不足的群体的学生。 外延电子和光学材料内的应变已被用于产生在未应变状态下无法实现的期望的材料性质。虽然在传统的半导体中使用效果很好，但将应变引入到货车德瓦尔斯键合化合物中是困难的。由周期表中较深的元素形成的货车德瓦尔斯化合物，称为重卤化物和硫属化物，可能为应变改性这些材料提供新的机会。这项授权旨在通过货车德瓦尔斯外延将较重的元素合成为薄膜，并在导致外延层内显著弹性应变的条件下将其外延到有用的衬底上。重点将放在两种模型材料：货车德瓦尔斯固体PbI 2和非货车德瓦尔斯固体CH 3 NH3 PbCl 3。其他几种材料，包括CdTe，CdS，SbI 3和Sb 2S 3也将被研究。通过X射线衍射、拉曼光谱、透射电子显微镜和角分辨光致发光光谱对应变大小、应变弛豫机制和应变引起的物理性质进行表征。第一性原理计算将被用来阐明实验观察。在建立了卤化物和硫属化物的货车德瓦尔斯成核/生长模型之后，对这些外延材料的合成的修改将针对通过货车德瓦尔斯外延工艺实现弹性应变工程。外延应变的大小和各向异性以及对材料性能的影响将用于对外延“重”货车范德华材料的潜在变化和行为进行机械理解。

Human society's consistent pursuit of better means of information communication and effective use of it?s energy supplies, requires continual innovation in the underlying technological materials infrastructure. Transformative technologies rely on breakthroughs in their scientific foundations, such as materials and processing. Recently, a number of soft inorganic solids have shown potential for applications in energy conversion and information manipulation, and promising new insight into the physics of exotic states of matter. Theoretical works suggest that reversible mechanical deformations in these materials could lead to either gradual or abrupt shifts of their physical properties. However, these soft materials, particularly, heavy halides and chalcogenides, experience difficulty in utilizing conventional chemical approaches to induce for deformation purpose due to their unique materials structures and atomic arrangement. This work addresses this problem by exploring the possibility of stretching soft but heavy halide and chalcogenide materials through van der Waals epitaxy. The research will introduce a new set of useful optoelectronic, electro-optic, logic and memory materials in the form of strained thin films. Researchers will also pursue educational goals by establishing a 'Graphics for Learning' program, which will train engineering undergraduate students, especially from underrepresented groups, through the graphical presentation of information. Strain within epitaxial electronic and optical materials has been used to produce desirable materials properties unachievable in the unstrained state. While used to great effect in conventional semiconductors, the introduction of strain into the class of van der Waals bonded compounds has been difficult. The van der Waals compounds formed from elements deeper in the periodic table, termed heavy halides and chalcogenides, may offer new opportunity to strain-modify these materials. This grant looks to synthesize 'soft' and 'heavy' materials as thin films out of the heavier elements via van der Waals epitaxy onto useful substrates under conditions that lead to significant elastic strains within the epitaxial layers. The focus will be on two model materials: the van der Waals solid PbI2 and non-van der Waals solid CH3NH3PbCl3. Several other materials including CdTe, CdS, SbI3 and Sb2S3 will also be studied. The strain magnitude, strain relaxation mechanisms and strain-induced physical properties will be characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy and angle-resolved photoluminescence spectroscopy. First-principle calculations will be employed to elucidate the experimental observations. After establishing a van der Waals nucleation/growth model for halides and chalcogenides, modifications to the synthesis of these epitaxial materials will be directed at achieving elastic strain engineering via the van der Waals epitaxial process. The magnitude and anisotropy of the epitaxial strain and the effect on materials properties will be used to develop a mechanistic understanding of the underlying changes in and behavior of the epitaxial 'heavy' van der Waals materials.