低溫電漿輔助硒化調控二維二硒化鎢/氧化鎢生成比例及其高靈敏NOX氣體感測應用

Highly Sensitive NOx Gas Sensors Operating at Room Temperature based on Hybrid WO3WSe2 Films Synthesized from the Reduction of WO3Through Plasma-Enhanced Selenization at Low Temperature

李建廣(Li, Chien Kuang)

指導教授 ： 闕郁倫

國立清華大學/工學院/材料科學工程學系/碩士(2015年)

摘要

本實驗透過電漿輔助硒化的方式達到低溫合成大面積二維材料二硒化鎢，大約在攝氏300度下即可讓氧化鎢完全轉變，此方法和其他傳統電化學氣相沈積或是一般硒化的製成相比，其製成溫度是相對低許多，因此也相當有機會運用在軟性電子元件上，其實在合成端，我們探討許多影響，像是氣氛比例和電漿瓦數大小對硒化的程度，前驅物的結晶性對於二硒化鎢的合成是否有品質上的提升，還有基板的平坦度對於透過熱蒸度的方式鍍膜其連續性的影響等等。除此之外，我們可以利用控制前驅物的厚度來達到二硒化鎢的層數控制，如果是以二氧化矽當作基板，最少層數約3層。
我們知道二維材料由於具備半導體性和高體表面積比，因此相當俱有潛力當作氣體感測器，文獻上雖已有人展示過其運用，但是仍有些問題存在於二維材料的表現，例如重複性使用性的能力相當差，需要透過長時間來回到原本的電流狀態，還有目前的偵測極限為ppm等級，而本實驗成功透過電漿來部分硒化氧化鎢，讓二硒化鎢以片狀的方式堆疊在表面或是嵌入在氧化鎢裡，如此的結構可以產生較多的缺陷和懸鍵，其相當有助於偵測物一氧化氮的吸附，借此來達到更低濃度的偵測，目前偵測極限最低為25 ppb，在二維材料的表現中算是相當好的，除此之外我們發現混合的氧化鎢/二硒化鎢薄膜透過紫外線照光的方式，可以加速偵測物的脫附，讓脫附時間縮短到只需要大約250秒，比純的二維材料在紫外光照射下脫附的更快速，因此能解決二維材料在氣體感測上重複使用性的問題。

關鍵字

混合二硒化鎢 氧化鎢 ； 電漿硒化 ； 氣體感測

並列摘要

In this work, we have successfully synthesized tungsten trioxide (WO3) / tungsten diselenide (WSe2) hybrid films in different ratios at low temperature through plasma-enhanced selenization process. The temperature for the synthesis of transition metal dichalcogenides (TMDs) through conventional chemical vapor deposition or selenization/sulfurization processes usually require temperatures higher than 500oC. It means that the thermal budget is still too high. But for our method, the synthesis temperature can be lower than 300oC. Lowering the process temperature not only can lower the cost; but also, show the potential for fabrication of flexible electrical, optoelectrical and sensing devices between other applications. Parameters such as the effect of plasma power, forming gas ratio (H2/N2), crystallinity of precursor and the substrate have major influence in the reduction process of WO3. Besides, the thickness control for synthesis of WSe2 is also addressed in this work.
Recent reports have demonstrated that TMDs at atomic thickness are suitable to serve as gas sensors due to its high surface-to-volume ratio and semiconducting property. However, there are still some problems using TMDs as the reactive layer. For example, it is inevitable to take a long time for detachment, resulting in a poor reproducibility of the electrical results. Besides, so far, the limit of detection for TMDs base sensor is about ppm level. In this work, we use hybrid WO3/WSe2 film as the reactive layer for the NO gas detection. The film is formed through a partial selenization. This hybrid WO3/WSe2 film exhibit ultra-high performance as a gas sensor application. The limit of detection can be largely decreased to 25 ppb. We infer that the reason for such a high sensitivity is that there are more edge sites on the surface. Moreover, the gas detachment time is much faster than that of a pure TMDs case under UV illumination. The detachment time can be reduced from tenths of minutes to only 250s. The result implies that the hybrid WSe2/WO3 can overcome the problem of reproducibility in TMDs based gas sensor. More significant, the hybrid film displays ultra-high sensitivity for NO gas.

並列關鍵字

hybrid WSe2 WO3 ； plasma selenization ； gas sensor

參考文獻

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