自2004年石墨烯被證實能單獨穩定的存在於自然界中，為世人開啟了名為二維材料領域的序幕，而擁有半導體能隙特性的過渡金屬二硫族化物(Transition Metal Dichalcogenides)包括二硫化鉬、二硒化鎢等其他類似結構及特性的材料，具有材料在單層及多層上特性明顯之差異、多元的材料選擇、可調控之載子遷移率、可撓性、透光性、易整合於電子裝置等特性，因這些特性使該材料在未來的電子和光電應用中展現出巨大的潛力。在本文中我們的實驗以二硫化鎢為主要研究對象，在化學氣相沉積生長二維二硫化鎢的方法中，三氧化鎢粉末是較為廣泛地被使用的前驅物。但是由於鎢-氧鍵的高度穩定性，使得三氧化鎢需提供非常高的溫度來產生足夠的前驅物蒸氣作為生長過程的鎢來源。在本文中，我們選擇了仲鎢酸銨(ammonium paratungstate, APT)，一種鎢礦提煉的初級產物，常用於精煉成高純度三氧化鎢或工業常見的藍色或紫色氧化鎢，作為本文所使用的二硫化鎢一步驟合成法的替代前驅物。在先前的研究中通常以高純度的三氧化鎢或藍色氧化鎢作為前驅物，而使用仲鎢酸銨作為前驅物可以節省使用其他前驅物在製備上所消耗的能量和浪費。本文中使用仲鎢酸銨作為前驅物可於一步驟製程中進行前驅物的熱分解及合成二維二硫化鎢樣品，並透過原子力顯微鏡，拉曼光譜和光致發光光譜來證實樣品為單層，而在參數優化的樣品中最大的晶粒尺寸可達到24 µm。艾克斯射線數據的結果表明，仲鎢酸銨最終形成較穩定的低化學劑量比氧化鎢如紫鎢(WO2.72)，這是仲鎢酸銨在熱分解中可提供生成二氧化鎢之前驅物的證據之一。在初期樣品合成中不僅有三角形晶粒亦會存在奈米線，而在後續的實驗中證實樣品中所生長的奈米線是前驅物的結晶，並找出可以控制的奈米線形成的方法。最後，與先前的研究相比，我們提供了一種新的前驅物選擇，可節省生產高純度前驅物過程所需的能量並降低成本，可以用於未來大規模的生產。

關鍵字：二維材料、仲鎢酸銨、化學氣相沉積、二硫化鎢

Two-dimensional layered materials have attracted much attention due to their unique electronic, optoelectronic, thermal, and mechanical properties. The existence of a semiconductor bandgap in transitional metal dichalcogenides including MoS2, WS2, MoSe2, and WSe2 with transformation from indirect to direct bandgaps when scaling down to the monolayer provide great potential for the development of future electronics and optoelectronics applications. In the case of WS2, WO3 and S powders have been most widely used as precursors for the chemical vapor deposition growth. However, WO3 cannot be directly sulfurized by sulfur due to the highly stable W-O bonding in the process of WS2 growth. Therefore, WO3 should be initially reduced into intermediates-WO3-x to facilitate the growth procedure. In this work, we have selected ammonium paratungstate (APT) - the primary raw material for the extraction of WO3, as an alternative precursor to synthesize WS2 via one-step process. Compared to WO3, the amount of APT and process complexity are both significantly reduced through the synthesis of WS2. The x-ray diffraction data result shows that most of APT ultimately form WO3-x, which plays an important role in the growth of WS2. In addition, monolayer triangular WS2 flakes have been successfully grown and confirmed by atomic force microscope profiles, Raman spectra, and photoluminescence spectra. In contrast to previous studies, we have successfully synthesized large area monolayer triangular flakes without the assistance of salts, seed particles, and hydrogen. As a result, the growth process reported herein provides a practical and feasible solution for low-cost and efficient synthesis of WS2 for future mass production.

Keywords: 2D materials, ammonium paratungstate, chemical vapor deposition, tungsten disulfide

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