tailieunhanh - Báo cáo hóa học: " Photoinduced oxygen release and persistent photoconductivity in ZnO nanowires"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Photoinduced oxygen release and persistent photoconductivity in ZnO nanowires | Bao et al. Nanoscale Research Letters 2011 6 404 http content 6 1 404 o Nanoscale Research Letters a SpringerOpen Journal NANO EXPRESS Open Access Photoinduced oxygen release and persistent photoconductivity in ZnO nanowires Jiming Bao1 Ilan Shalish2 Zhihua Su1 Ron Gurwitz2 Federico Capasso3 Xiaowei Wang4 and Zhifeng Ren4 Abstract Photoconductivity is studied in individual ZnO nanowires. Under ultraviolet UV illumination the induced photocurrents are observed to persist both in air and in vacuum. Their dependence on UV intensity in air is explained by means of photoinduced surface depletion depth decrease caused by oxygen desorption induced by photogenerated holes. The observed photoresponse is much greater in vacuum and proceeds beyond the air photoresponse at a much slower rate of increase. After reaching a maximum it typically persists indefinitely as long as good vacuum is maintained. Once vacuum is broken and air is let in the photocurrent quickly decays down to the typical air-photoresponse values. The extra photoconductivity in vacuum is explained by desorption of adsorbed surface oxygen which is readily pumped out followed by a further slower desorption of lattice oxygen resulting in a Zn-rich surface of increased conductivity. The adsorption-desorption balance is fully recovered after the ZnO surface is exposed to air which suggests that under UV illumination the ZnO surface is actively breathing oxygen a process that is further enhanced in nanowires by their high surface to volume ratio. Background Semiconductor nanowires provide a natural ready-made structure in applications where small dimensions are required 1-3 . Their small diameter 100 nm implies that a host of surface effects can influence their electrical and optical properties which is important for the functionality and performance of nanowire-based devices 4-6 . Some observations such as enhanced gas sensitivity and photoconductivity nowadays reconfirmed in ZnO .