Electronic Transport at Low Temperature in Some Sandwiched Films

Abstract

A series of sandwiched films in the configuration, Ni(100 nm)/Al(t)/Ni(100 nm); t = 10 nm, 20 nm,……, 100 nm (labeled as NANI, NAN2,………., NAN10) were produced by thermal and electron beam gun evaporation techniques. The films were deposited onto the glass substrates held at 200°C, under high vacuum conditions in a Hindhivac coating unit. The structure, grain size and interplanar distances were probed by X-Ray Diffraction (XRD). The grain sizes obtained were in the order of few nanometers and decreased with increasing, t. Electrical resistivity in the temperature range from 4 to 300 Khas been measured in an Oxford Instruments make resistivity measurement setup. The resistivity decreased nonlinearly and continuously with increasing temperature for the films NANI, NAN3 and NAN7 similar to that of a semiconductor. Mott’s small polaron hopping and variable range hopping models due to Mott and Greave have been employed to understand resistivity variation with temperature. In the remaining films resistivity decreased up to some temperature and increased thereafter. This indicated a kind of transition occurring in these films from Metallic to Semiconductor (MST). These results are significant as neither of the constituent layers in the present films is semiconducting by nature. The resistivity variation with temperature of some of these films has been analyzed using semi-classical conductivity model of Boltzman which incorporates quantum corrections in to it. It is for the first time that the sandwiched films of the present configuration have been investigated for structure and low temperature resistivity and data analyzed thoroughly. © 2014 Knowledgia Review, Malaysia.