Preparation Of Granulartin Films And Charactization Of Its Morphology And Gas-sensitivity

Granular metals are composite materials of metals and insulators, while granular tin films belong to another form of granular metals, which is formed during the initial stage of depositing thin metal films, consisting of metallic grains coated by a highly resistive oxide. As a result of the unique film structure, the eletronic conduction of granular tin films is extremely inhomogeneous on an atomic length scale. Besides, superconductivity, optical, electrical and structure property has triggered a great deal of interest, becoming the studying object of scientific researchers. HV( high vacuum) evaporation system is used to prepare granular tin films with the presence of oxygen at room temperature or higher temperature. Morphology and gas-sensitive properties of granular tin films are explored.To obtain the specific conditions of the formation of granular films and the influence of substrate temperature, oxygen pressure and evaporation power on the morphology, granular tin films were prepared at room temperature and at higher temperature with the help of homemade evaporation source. It was found that, at room temperatue spherical granules can be obtained on condition that the oxygen pressure reach a certain value(≥1.0×10-2Pa); while at higher temperature, the presence of oxygen helps to form regular granules but remote the growth of Sn clusters, resulting an increase in granule sizes.Investigations on the relevant factors influencing the morphology shows that, there was no substantial effect of the evaporation power on the evolution of the morphology. However, the surface morphology of granular tin films is strongly dependent on the oxygen pressure and the substrate temperature. As oxygen pressure raises, the grain size of tin granules decreases,while the shape becomes regular; with increasing substrate temperature, the grain size of tin granules increases up to a certain value and then declines, and the shape becomes regular.A homemade gas-sensing measurement platform was set up. Sheet resistances at 200℃and 300℃with the presence of oxygen were measured by Keithley 2400 Digital SourceMeter. In consequence, at 200℃sheet resistance increases in a parabolic way as the oxygen pressure raises, with the increasing speed from fast to slow while at 300℃in a linear way.