Synthesis and microstructure of NixAl1-x (0.5 x 1) thin films
Synthesis and Microstructure of NixAh-x (0.5:5x :51) Thin Films
Submitted by Thangaraj Joseph Sahaya Anand
for the degree of Doctor of Philosophy at The University of Hong Kong
in September 2004
Thin films have become important for basic studies in physics and in many other engineering fields. The immense interest in the basic properties of thin films is due to considerable variations in their properties compared to those of bulk materials. Intermetallic aluminides, such as NiAl and NhAl, become candidate thin film materials for their specific high temperature strength and oxidation resistance, and may fmd applications in micro-electronic devices as thin film thermistors. This study attempted to synthesis Ni-Al thin films with stoichiometry of Nio.sAlo.s, Nio.65Alo.35, Nio.sAlo.2 and Nio.9Alo.1 by DC magnetron sputtering technique on both conducting Ni substrates as well as glass microslides.
A substantial amount of oxygen was observed by chemical analysis to exist in the Ni-Al films during deposition at high base pressure conditions (1 x 10-5 mbar). The oxygen content reduced by a certain level at low base pressure conditions (~ 4.0 X 10-6 mbar) and after post-deposition annealing. The structure of these films was revealed by electron microscopy and found to be columnar. An expansion of the lattice by nearly 5% was observed for the Nio.sAlo.5 and the Nio.sAlo.2 films in their low thickness as deposited state. The lattice size reaches the bulk value when the film thickness increases or after vacuum annealing heat-treatment. The Nio.sAlo.2 films have a nanocrystalline structure in which the ordered L h phase appears upon annealing at above 500?.
In the course of assessment of the general physical properties of these alloy thin films a thermal transition was observed in Nio.sAlo.2 stoichiometry. We used two different d.c.-magnetron sputter systems and the results were nearly the same. This proves that the insulator-to-metal transition is characteristic of the NixAll_x alloy system in the thin-film state. The temperature coefficient of resistance (TCR) is negative only to a narrow range ofx from 0.75 to 0.8, and when x 2: 0.9 or x < 0.65, the metallic positive TCR behavior is exhibited. These films are good candidate materials for applications as negative TCR thin film thermistors, with sensitivity tunable by annealing or thickness control.
School:The University of Hong Kong
School Location:China - Hong Kong SAR
Source Type:Master's Thesis
Keywords:nickel aluminum alloys thin films
Date of Publication:01/01/2004