過渡金屬二硫族化物(Transition-metal Dichalcogenides, TMDCs)，為一種二維材料的統稱，由元素週期表上部分過渡金屬元素與硫族元素組合而成。此材料具有半導體特性，塊材時為非直接能隙，當材料為單層時，因為量子侷限的效應，大部分材料轉變為直接能隙(1~2 eV)，此時材料為原子級厚度具有高穿透度與可撓性，適合應用在可撓式電子元件與光學元件。目前最常見的材料製備方法為化學氣相沉積，然而與機械剝離法的樣品比較後，化學氣相沉積所合成的材料載子遷移率通常比較低，這可能是材料合成過程中，有許多缺陷產生。本實驗合成的二硒化鎢單晶，在光致螢光光譜面掃描中，可以看到螢光強度由單晶中間向外遞減，為了理解其原因，利用掃描式穿透電子顯微鏡，觀察材料的晶格結構。雖然目前化學氣相沉積已經可以成長大面積的二維材料薄膜，然而這些薄膜大部分都是由不同晶格方向的晶體組成，為多晶的薄膜，薄膜中有許多晶界，在電性傳導中扮演很重要的角色。本實驗另一個重點為尋找化學氣相沉積的二硒化鎢晶界處，經由製作二硒化鎢背閘極式電晶體，觀察電晶體通道跨過與無跨過晶界的電學性質。另外在有氧環境下，經由連續多次量測，觀察通道跨過晶界的電晶體其電性變化。

Transition-metal Dichalcogenides (TMDCs) collectively name a series of two - dimensional materials, composed of transition metal groups and chalcogenides in the periodic table. These material have semiconducting properties, have shown atom-scale thickness, direct band gap, high transmittance and flexibility, etc. Besides these properties, TMDCs have shown outstanding performance in both flexible electronic device and optical electronic device. Very recently, it has been shown that synthesis of large film of polycrystalline monolayer TMDCs could be achieved using chemical vapor deposition (CVD). However, as compared to mechanically exfoliated samples, the CVD grown thin film typically have much lower carrier mobility, due to the growth process imperfections that induce various structural defects in the material. The first part of this thesis is inspecting the point defect in our CVD-synthesized WSe2, which exhibited PL intensity inhomogeneous.

Synthetic 2D crystal films grown by chemical vapor deposition are typically polycrystalline, which contain many grain boundaries, these grain boundaries play an import role in the electron transport. The second part of this thesis is observing the grain boundary effects on electronic transport by fabricating WSe2 into back-gate structure field-effect transistors. Comparing the electron transport properties to the channel across the grain boundary and without the grain boundary, and using the continuous measurement to observe how the grain boundary effect with electrical transport properties in ambient condition.

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