化學氣相沉積二硫化鉬薄膜成長以及微結構分析

Abstract

二硫化鉬是一種被大量研究的二維材料，其結構類似石墨烯，都是六角形平面之結構，鉬原子層被上下各一層硫原子層包夾，形成三明治之結構。二硫化鉬最讓人矚目之性質是當厚度由塊材減少至單層時，會由非直接能隙1.0 eV轉變為直接能隙1.8 eV。這讓單層的二硫化鉬被期待成為各種電子元件的材料。得到單層二硫化鉬的方法有許多，其中最受到青睞的製程方式為化學氣相沉積法，可以得到大面積單層的二硫化鉬。化學氣相沉積成長的二硫化鉬薄膜會受到許多參數的影響，包含成長溫度、氣流量、擺放方式、前驅物量以及添加氯化鈉進行成長等。本實驗會依序討論這些參數造成製程的影響並作分析。為了測量單顆二硫化鉬之性質，我們調整參數將原本晶粒尺寸從約數百奈米增加至數十微米。最後發現在高溫下成長出的第一層二硫化鉬晶粒上會有許多微小第二層二硫化鉬晶粒，我們猜測這造成晶粒單位面積內有許多產氫反應的活性點，會比完美單層二硫化鉬晶粒的產氫效率好。

Molybdenum disulfide is one of the 2D materials which has been widely studied. Similar to graphene, its lattice is hexagonal. The most interesting property of molybdenum disulfide is when the layer thickness is reduced from bulk to single layer, its bandgap will change from an indirect bandgap of 1.0 eV to a direct bandgap of 1.8 eV. This makes single layer of molybdenum disulfide expected to be a material for various electronic or optical devices. There are many methods to get single layer molybdenum disulfide, especially chemical vapor deposition(CVD) is an extensive method to synthesize large-area single layer molybdenum disulfide. In our experiments, we tuned parameters such as growth temperature, carrier gas flow, placement of substrate, addition of sodium chloride to investigate and analyze influences. In order to measure property of single grain molybdenum disulfide, we adjusted parameters to increase grain size from 200 nanometers to 30 microns. It was found that there are many tiny second layers of molybdenum disulfide grains on the first layer grains grown at high temperatures. We assume that this results in many active sites for hydrogen evolution reaction in the unit area of the grain, which makes hydrogen evolution reaction (HER) efficiency better than perfect single-layer molybdenum disulfide grain.