Nucleation and Growth-Controlled Morphology Evolution of Cu Nanostructures During High-Pressure Thermal Evaporation

Abstract

The formation of porous material structures has been widely investigated for the development of high-performance energy materials, catalysts, and chemical sensing devices. Various nanoporous structure fabrication methods are based on wet-chemical processes, which require precise control of the process parameters. Physical vapor deposition such as thermal evaporation utilizes high vacuum so that the deposition process is relatively simple, free of contamination, and easily reproduced. However, because of the long mean-free-path of the evaporated atoms in high vacuum, heterogeneous nucleation and the growth of adatoms occurs on the substrate surface, which results in the formation of dense and compact thin films. But by changing the working pressure, various morphologies of porous nanostructures can be obtained. As applied to copper, with increasing pressure the thin film evolves from a dense structure to a coral-like nanoporous structure through a porous columnar structure. All of the porous structures consist of nanoparticle aggregates, where copper nanoparticles are connected to each other, and many nano-gaps are found inside the aggregates. A surface plasmonic effect is expected. The porous copper nanostructured films demonstrated high surfaceenhanced Raman spectroscopy activity.