engleski

Structural relaxation of amorphous Al-W thin films upon heating

The amorphous Al-W thin films exhibit a pronounced variation of electrical resistance due to structural relaxation at temperatures between 100°C and 500°C. The effects of substrate material, deposition temperature, and film thickness upon the magnitude of such variation were examined. Thin amorphous Al78W22 films were prepared by a co-sputtering technique onto alumina ceramic, sapphire, and glass substrates, held at four temperatures: LN2, RT, 200°C, and 400°C, respectively. A measure of structural relaxation was inferred from the variation of electric resistance during a cycle of isochronous heating up to 515°C, isothermal annealing at that temperature for 6 hrs, followed by cooling to room temperature. For the amorphous films deposited onto substrates at LN2 temperature, the degree of structural relaxation decreases in a sequence of alumina ceramic - glass - sapphire substrates, apparently related to the deposition surface roughness. Degree of relaxation also decreases with the increase of temperature at which the substrate was held during deposition. Since the relaxation was more pronounced in aluminum-rich alloys, the role of aluminum constituent was checked: a corresponding investigation on Al-Ti and Cu-Ti amorphous films showed that only the Al-containing alloys exhibit strong structural relaxation. This might be due to specific electronic structure of aluminum. As a conclusion, a reduced irreversible variation of the electric resistance of amorphous Al-W films upon heating up to about 500°C can be achieved only by a careful selection of alloy composition and preparation conditions.

amorphous thin films; Al-W alloys; structural relaxation

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