以化學氣相沉積法合成二硫化鉬薄膜並應用於可撓式壓電感測元件

Abstract

二硫化鉬與石墨烯同為研究熱門的二維材料，但在單層結構上卻有著截然不同的性質，在量子侷限效應下，單層二硫化鉬具有1.8電子伏特的直接能隙。此特性除了能展現良好的發光性質，在場效電晶體之應用上則提供了高開關電流比，基於這些特性，高品質二硫化鉬的合成受到了關注及重視。 以機械剝離法製備薄層二硫化鉬難以控制尺寸、層數，也難以大量產出。利用化學氣相沉積的合成方式，則能夠生產大面積單層二硫化鉬。我們以三氧化鉬(MoO3)及硫粉作為前驅物，成功地以化學氣相沉積方式合成二硫化鉬於矽基板上，並使用光學顯微鏡、拉曼光譜、光致螢光光譜、原子力顯微鏡及高解析穿透式電子顯微鏡進行鑑定。 隨著科技進步，人們對於高性能之電子產品的需求日益提高，如可撓曲、輕薄化之電子基板等，也因此具壓電、壓阻、高機械強度的二維半導體材料成了熱門研究主題。本研究以二硫化鉬在聚二甲基矽氧烷(polydimethylsiloxane, PDMS)薄膜上製成可撓式電子元件，並架設一個壓電感測平台，以量測二硫化鉬電晶體上下彎折時，拉伸與擠壓產生的電流的起伏變化。未來可以進一步應用在可撓曲的電子產品，人體脈動感測，或是其他新穎二維材料壓電鑑定上。

Molybdenum sulfide (MoS2) is one of the most common transition metal dichalcogenides (TMDCs), which have been studied for catalytic and electronic applications. Monolayer MoS2 is a two-dimensional material with a direct bandgap of 1.8 eV. The monolayer MoS2-based field-effect transistors have high on/off ratio and are suitable for fabrication of advanced high-performance electronics. Therefore, high-quality monolayer MoS2 holds great potential for future electronic applications. Using a mechanical exfoliation method to prepare MoS2 is difficult to control the number of layers and the size of flakes. However, a chemical vapor deposition (CVD) method can be used to synthesize high-quality monolayer MoS2 with lower cost and mass production. In this study, we successfully used molybdenum trioxide and sulfur powder as precursors to synthesize MoS2 films on a silicon wafer with the CVD method. Subsequently, we used an optical microscope (OM), Raman spectroscopy, photoluminescence (PL), atomic-force microscopy (AFM), and high-resolution transmission electron microscope (HRTEM) to characterize the as-synthesized MoS2 films. In future, smart electronic systems are expected to afford arbitrary form factors, robust elasticity, high-speed charge transport, and low-power consumption. With these characteristics, 2D layered semiconductors with high mechanical and piezo-trionic properties have attracted much attention in research. In this work, we fabricated a device with the CVD-grown MoS2 on a bendable, flexible PDMS thin film to examine the change of the electric transport in the device as the film was subject to tensile and compressive strains. With the capability of detecting these strain changes, this MoS2-based device can be employed as a vessel pulsation sensor. Accordingly, other novel 2D materials-based piezotronic devices can be characterized by the same way as this thesis demonstrated.