STM-STS investigation of vacuum annealed ZnO nanoribbons

✍ Scribed by Maffeis, T. G. G. ;Penny, M. W. ;Garbutt, J. D. W. ;Wilks, S. P.

• Publisher: John Wiley and Sons
• Year: 2010
• Tongue: English
• Weight: 329 KB
• Volume: 207
• Category: Article
• ISSN: 0031-8965
• DOI: 10.1002/pssa.200982485

✦ Synopsis

Abstract

We present a scanning tunneling microscopy and spectroscopy (STM–STS) investigation of the effects of ultra high vacuum annealing and oxygen exposure onto ZnO nanoribbons synthesised by chemical vapour deposition. STM imaging revealed a width to height ratio for the nanoribbons between 2:1 and 3:1 and average width and height of 90 and 40 nm, respectively. Imaging before annealing showed the presence of surface contaminants, which were removed after annealing at 800 °C. Analysis of the STS data before annealing shows n‐type behaviour with a band gap of 3.4 eV and an upward band bending of 0.9 eV. Annealing up to 700 °C induced a reduction in surface band bending, towards a near flat band behaviour. After the 800 °C anneal the surface electronic properties were significantly altered, with a large increase of tunnelling current at negative sample bias leading to a narrowing of the apparent surface band gap and a mid gap Fermi level. This change was attributed to a loss of surface lattice oxygen and was found to be reversible upon O~2~ exposure at room temperature. The anneal/O~2~ exposure process could lead to a way of cleaning the ZnO nanoribbons without using ion bombardment techniques.