二維材料為探索基礎物理與化學提供了新的機會。最廣泛研究的過渡金屬二硫族化物中的材料，像是二硫化鉬，它能夠通過調整層數來改變材料的基本性質。例如塊材的二硫化鉬具有間接帶隙的半導體性質，能階的大小能隨著層數減少而增加。然而，單層二硫化鉬中具有直接帶隙的半導體性質。這種能力使二硫化鉬成為以光催化方式來還原二氧化碳的光催化劑材料。光吸收性能是光催化劑的關鍵要素之一，增加厚度顯著增加吸收性能。
本論文研究了超薄二硫化鉬薄膜對光還原二氧化碳的影響。為了實現光還原二氧化碳，需要考慮六個重要因素 : 能隙、電荷分離和運輸、帶位置與氧化還原電位、吸附物質和電荷攜帶之間的反應、光催化劑表面上化學物質的吸附、以及脫附化學產物等。本文的主題是研究薄膜厚度和基板效應，通過後硫化製程來製備了超薄二硫化鉬薄膜。首先，沉積三氧化鉬薄膜在基板上，然後加熱通入氫氣來轉化為二氧化鉬薄膜，最後通入硫化氫氣體，成功的硫化成二硫化鉬薄膜。透過原子力顯微鏡用來確認薄膜的實際厚度，命名為MS3，MS7和MS17，對應於3nm，7nm，17nm和25nm的原始氧化物層。使用測量紫外線可見光光譜儀，量測薄膜的能隙和吸收性能。根據吸光度數據計算的tauc圖，MS3，MS7和MS17薄膜的能隙分別為1.7 eV，1.65 eV和1.58 eV，以及吸收性能分別為10％，12％和30％。使用拉曼光譜確認薄膜的A1g和E2g1特徵峰之間的頻率差異為23.27, 24.76, 25.76和26.24 cm-1，利用氣相層析儀來分析光還原二氧化碳的氣體產率和產物的選擇性。從氣相層析儀測量中，超薄二硫化鉬薄膜樣品獲得三種碳氫化合物的產物，分別是甲烷（0.095 μmole），乙醛（0.12 μmole）和丙酮（0.04 μmole）。本實驗的結果發現，碳氫化合物的產物的生產速率與超薄二硫化鉬薄膜厚度增加成比例增加，但在超過17 nm後產率開始下降。另外，製鍍超薄二硫化鉬薄膜在不同基板，也呈現碳氫化合物的產物選擇性。
我們成功地證實了超薄二硫化鉬薄膜可以用來光還原二氧化碳的應用，超薄二硫化鉬薄膜的厚度與基板等因素，具有氫化合物的產率與選擇性之相關聯性，提供一個用來研究光還原二氧化碳的學理機制的未來可行方向。

Two Dimensional (2D) materials offer a new opportunity to explore fundamental physics and overcome the scaling limit of bulk materials. The most extensively studied materials are 2H phase in group VI TMDCs such as molybdenum disulfide (MoS2). MoS2 is one of TMDs with adjustable optical properties by tuning the layer number. Bulk MoS2 has an indirect bandgap, which increases monotonically as the number of layer decreases. This ability makes MoS2 as a promising material for photocatalytic CO2 reduction. Light absorption performance is one of the keys to determine the performance metric of the photo-catalyst for CO2 photo-reduction.
This thesis studies MoS2 ultrathin film for CO2 photo-reduction. To make CO2 photo-reduction happen, there are 6 important factors to be considered. Bandgap (Absorption), charge separation and transportation, band position vs redox potential, reaction between adsorbed species and charge carries, adsorption of chemical species on the photo-catalyst surface, and desorption of chemical products. This thesis is to investigate the thickness dependence and substrate effect on the CO2 reduction of MoS2. MoS2 ultrathin film was successfully prepared by post sulfurization.
First step was to deposit MoO3 then converted to MoO2 and sulfurized into MoS2. AFM confirm the thickness, were named as MS3, MS7, and MS17 corresponding to the original oxide layer of 3 nm, 7 nm, 17 nm and 25 nm. UV visible measurement was performed to find out the bandgap and absorption property. From tauc plot calculated from absorbance data, the bandgap are 1.7 eV, 1.65 eV and 1.58 eV, and the absorption performance are 10%, 12% and 30% for MS3, MS7 and MS17 respectively. Raman Spectroscopy confirm the frequency differences between A1g and E2g1 with 23.27, 24.76, 25.76 and 26.24 cm-1 are for MS3, MS7, MS17 and bulk respectively. The grain size was ranging from 40 to 235Å.
The gas chromatography has been performed to understand the productivity and selectivity. 2 x 2 sample inserted to the 7 cm3 chamber with nitrogen, CO2 and H2O entered later. From the GC measurement, 3 products obtained from all samples are methane (0.095 µmole), acetaldehyde (0.12 µmole) and acetone (0.04 µmole). From the thickness dependent measurement, the production rate increase proportional to increased thickness but decreases after exceeding 17 nm. The production rate also revealed if the C1 product not sensitive to thickness inversely proportional with C2 and C3 product.
Finally, MoS2 ultrathin film successfully demonstrated for CO2 photo-reduction. Thickness dependent and substrate effect play a role for selectivity and productivity. Detailed mechanism need further investigation.

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