Ballistic Deposition of Nanoclusters

TL;DR

This study investigates the growth and structure of nanoporous thin-films made from nanoclusters of tungsten disilicide and copper, revealing low-density films formed by ballistic deposition with minimal restructuring.

Contribution

It provides experimental evidence supporting a ballistic deposition model for nanocluster film growth, highlighting the low density and limited merging of clusters.

Findings

Films have about 15% of bulk density.

Growth follows a ballistic deposition mechanism.

Minimal merging or sintering observed.

Abstract

Nanoporous thin-films are an important class of materials, offering a way to observe fundamental surface and bulk processes with particles larger than individual atoms, but small enough to interact significantly with each other through mechanisms such as stress and surface mobility. In-Situ X-ray Reflectivity and Grazing Incidence Small Angle X-Ray Scattering (GISAXS) were used to monitor thin-films grown from Tungsten Disilicide (WSi$_2$) and Copper (Cu) nanoclusters. The nanoclusters ranged in size from 2 nm to 6 nm diameter and were made by high-pressure magnetron sputtering via plasma-gas condensation. X-Ray Reflectivity (XRR) measurements of the film at various stages of growth reveal that the resulting films exhibit very low density, approaching 15% of bulk density. This is consistent with a simple off-lattice ballistic deposition model where particles stick at the point of first contact without further restructuring. Furthermore, there is little merging or sintering of the clusters in these films.