中文摘要：

在常压条件下使用CVD法生长单层WS_2,通过改变实验条件实现控制晶粒大小或生长成薄膜的目的。采用光学显微镜、拉曼、光致发光谱等对制备的样品进行表征,得到了结晶质量高、尺寸达120μm的单层WS_2晶粒。同时讨论了几个重要参数如温度、生长时间以及钨源用量等对生长单层WS_2的影响。结果表明：温度对CVD生长WS_2影响最大,高温有助于生长高结晶质量的WS_2。调节生长时间可以控制WS_2晶粒的大小,较长时间能生长出连续的薄膜。过量的S蒸汽会抑制WS_2生长,影响结晶质量。

英文摘要：

Single layer WS_2 was synthesized by atmospheric pressure CVD method. The mono-WS_2 of triangular grain was grown by the single controlled quartz tube furnaces on well cleaned sapphire substrates. The grain size could be controlled by adjusting the experimental conditions. Optical microscopy,Raman spectroscopy,and photoluminescence emission spectroscopy were utilized to characterize WS_2 samples. The Optical microscopy shows the length of triangle domain up to 120 μm and the uniform of WS_2. Raman spectrum of a WS_2 single domain demonstrates the characteristic E12g（ in-plane vibrational）mode and A1g（ out-of-plane vibrational） mode at 355. 1 cm-1and 418. 1 cm-1,respectively. The frequency difference between E12 gmode and A1 gmode is 64 cm（-1） which matches the single-layer-thick WS_2 films. The PL peak of WS_2 is located at 619 nm（ 2. 0 e V） which consistents with its direct-band-gap.Furthermore,the PL intensity of monolayer WS_2 is very strong,which reveals its high crystalline. The experiment results demonstrate that the large size mono-WS_2 flakes with high crystalline can be synthesized controllable on sapphire. The effects of some essential growth parameters such as the temperature,the growth time and the precursor on the controlled growth of mono-layer WS_2 are also discussed.