Insulator-metal transition in a conservative system: An evidence for mobility coalescence in island silver films

TL;DR

This paper provides evidence that mobility coalescence causes aging and an insulator-metal transition in island silver films, with the transition occurring even after deposition stops, indicating a dynamic coalescence process.

Contribution

It demonstrates that mobility coalescence, rather than oxidation, drives aging and the insulator-metal transition in island silver films, supported by microscopy and resistance fluctuation analysis.

Findings

Aging in silver films is mainly due to mobility coalescence, not oxidation.

Insulator-metal transition occurs after deposition stops, indicating ongoing island coalescence.

Resistance fluctuations are linked to percolation path dynamics.

Abstract

Aging, which manifests itself as an irreversible increase in electrical resistance in island metal films is of considerable interest from both academic as well as applications point of view. Aging is attributed to various causes, oxidation of islands and mobility of islands followed by coalescence (mobility coalescence) being the main contenders. The effect of parameters like substrate temperature, substrate cleaning, residual gases in the vacuum chamber, ultrasonic vibration of the substrate, suggest that the mobility coalescence is responsible for the aging in island metal films. Electron microscopy studies show evidence for mobility of islands at high substrate temperatures. The comparison of aging data of island silver films deposited on glass substrates in ultra high vacuum and high vacuum suggests that the oxidation of islands, as being responsible for aging in these films, can be ruled out. Further, under certain conditions of deposition, island silver films exhibit a dramatic and drastic fall in electrical resistance, marking the insulator-metal transition. This interesting transition observed in a conservative system - after the stoppage of deposition of the film- is a clear evidence for mobility coalescence of islands even at room temperature. The sudden fall in resistance is preceded by fluctuations in resistance with time and fluctuations are attributed to the making and breaking of the percolation path in the film.