Electronic Transport at Low Temperature in Ni/Al/Ni Films

Abstract

A series of sandwiched films in the configuration, Ni(100nm)/Al(t)/Ni(100nm); t = 10nm, 20nm,……, 100nm (labeled as NAN1, NAN2, ………, NAN10) were deposited by thermal and electron beam gun evaporation techniques. The films were deposited onto the glass substrates held at 473K, under high vacuum conditions. The structure, grain size and interplanar distances were probed by X-ray diffraction (XRD). The grains were of few nanometers in dimension and their size decreased with increasing, t. Electrical resistivity in the temperature range from 4.2K to 300K has been measured. The resistivity decreased nonlinearly and continuously with increasing temperature for the films NAN1, 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 these three films. Remaining seven films exhibited metallic to semiconductor (MST) transition. These results are significant as neither of the constituent layers in the present films is semiconducting by nature. The resistivity data of NAN4 and NAN5 films has been analyzed using semi-classical conductivity model of Boltzman which incorporates quantum corrections in to it.  The data belonging to the metallic region of the remaining five films has been analyzed using the conventional Matheissen’s rule, as these films produced only small amount of data in the semiconducting region. 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.