本研究透過電漿輔助化學氣相還原法(PACVR)，利用硒蒸氣與二氧化鉬前
驅物薄膜進行氣相化學反應合成二硒化鉬，並透過電漿解離硒蒸氣降低反應能障，成功在相較於傳統的氣相沉積法低的溫度下合成二硒化鉬。本研究結果指出，基板溫度在攝氏450 度的製程所合成的二硒化鉬能得到最好的氣體響應。此外相較於一般的化學氣相沈積製程，電漿輔助製程所需的基板溫度至少低了150 度，且具有大面積連續薄膜的製程能力，適合作為未來量產與可撓式元件的應用。
PACVR 製程除了可以降低合成溫度外，本研究透過調整硒化過程載流氣體
中氫氣與氮氣的成分比來調控二硒化鉬薄膜的相變化；氮氣較多時會形成1T 與2H相比例約1:1 的均勻薄膜，氫氣較高時會形成表面為1T 相較高(1T:2H=6:4)，而深層為2H 相主導的異質接面。由於載子在均質材料與異質界面具有不同的分佈狀況，因此會影響氣體分子與MoSe2的電荷轉移。實驗結果證明1T/2H異質接面產生朝下的能帶彎曲，導致電子累積在二硒化鉬表面。當NO2 與MoSe2 接觸時電子會從MoSe2 轉移到NO2 上，因此接觸NO2 時電阻變化的響應較為敏感。反之對NH3 因為是電子轉移至MoSe2，在初始電子密度較高的情況下響應較不敏感。相反的，氮氣較多時所合成的均質二維材料由於具有許多1T 與2H的局域接面與空乏區，會降低電子密度形成等效的p 型半導體，因此對於NH3 的響應較高。
最後本研究的最佳條件能夠順利的在室溫下進行氣體的吸附和脫附，且感測
結果也有重複性。在低濃度的感測中，對1 ppm 的阿摩尼亞有66 %的靈敏度；0.5ppm 的二氧化氮有17 %的靈敏度。

Our research exploits an alternative technique of plasma assisted chemical vaporreduction (PACVR), which reduces the reaction barrier through the dissociation ofselenium vapor, to facilitate the chemical reaction with the molybdenum oxide precursorand successfully synthesized MoSe2 at lower temperatures than that of the conventional
chemical vapor deposition process. Our results revealed that MoSe2 synthesized at 450 ℃exhibits the best sensing performance. In comparison to the conventional chemical vapor deposition, out PACVR method shows the advantages of the lower substrate temperature
of at least 150 ℃ and the potential of large area fabrication of continuous film, which is benefit to applications of mass production and flexible electronic device in the future.
In this work, the phase engineering of MoSe2 is also achieved by tuning the ratio of H2/N2 within the carrier gas. First, a uniform film with coexistence of 1T and 2H phases with ratio about 1:1 was synthesized in a N2-rich environment. On the contrary, a higher
concentration of H2 results in a self-assembled vertical heterojunction, including a 1T-rich phase (1T:2H ≈ 6:4) film near the surface, and a 2H-rich phase beneath. This heterojunction then influences the distribution of carrier and the charge transfer between materials and gas molecular. Our result proved that the heterojunction result from 1T/2H interface creates a downward band bending, leading the accumulation of electrons near the surface of MoSe2. Since electrons are extracted by absorbed NO2 molecules, the higher initial electron density results in a higher response. On the contrary, since electrons are transferred from NH3 molecular to MoSe2, the response is less sensitive because the initial state of surface consists of higher density of electrons. On the other hand, when carrier gas composed of
more N2 during PACVR, a coexisting MoSe2 films inhibit vertical heterojunction. However, since there are much more 1T/2H local heterojunctions in the basal plane, the presence of depletion regions leads to a lower density of electron, forming an equivalent p-type semiconductor, and promoting the response to NH3 instead.
Finally, the best parameter from this research exhibit the capability of absorption, desorption at room temperature, and repeatable sensing response. In low concentration, the response of 66 % and 17 % to 1 ppm NH3 and 0.5 ppm NO2 was acquired

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