Abstract
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.