1. Introduction
Metal oxide semiconductors have attracted tremendous
interest due to their wide variety of optoelectronic applica-
tions. Currently, nanostructured metal oxides have
emerged an exceptional material and attracted a great deal
of interest from researchers. Novel physical properties
arising from size reduction are very important for present
and future nano-device applications in electronic, optical
and sensor fields. Low cost, high sensitivity and reliability
of metal oxides are essential in both the fabrication and
application of gas sensors. Morphology and crystallo-
graphic structure of metal oxides have a great effect on
the response of conduct-metric type gas sensors. Nanoscale
structures, such as nanobelts, nanowires, and nanorings,
were found to show high sensitivity as gas sensors due to
the reduction of crystal size [1-5].