Hydrogen plasma exposure of In/ITO bilayers as an effective way for dispersing In nanoparticles

TL;DR

This study demonstrates that hydrogen plasma exposure effectively disperses indium nanoparticles from thin films and bilayers, with temperature and exposure time influencing nanoparticle size and formation mechanisms.

Contribution

It reveals the role of hydrogen plasma in releasing In atoms from ITO and details how temperature affects nanoparticle growth and coalescence mechanisms.

Findings

Hydrogen plasma reduces surface oxide and reshapes In films into spheres.

In NPs grow via VW mode at low temperature and coalesce into larger particles at higher temperature.

Large In droplets form through a liquid phase growth process, especially in bilayer structures.

Abstract

We address the production of indium nanoparticles (In NPs) from In thin films thermally evaporated on both c-Si substrates and sputtered indium tin oxide (ITO) as well as from sputtered ITO thin films, exposed to a hydrogen (H2) plasma. On the one hand, we show that evaporated In thin films grow in Volmer-Weber (VW) mode; H2 plasma reduces their surface oxide and substrate annealing reshapes them from flat islands into spheres, without any remarkable surface migration or coalescence. On the other hand, we studied the In NPs formation on the ITO thin films and on In/ITO bilayer structures, by varying the H2 plasma exposure time and the substrate temperature. This led us to postulate that the main role of H2 plasma is to release In atoms from ITO surface. At low substrate temperature (100{\deg}C), In NPs grow on ITO surface via a solid phase VW mode, similar to evaporated In thin films, while at 300{\deg}C, small In droplets preferentially nucleate along the ITO grain boundaries where ITO reduction rate and atomic diffusion coefficient are higher compared with the ITO grain surface. As the droplets grow larger and connect with each other, larger ones (1-2 um microns) are suddenly formed based on a liquid phase growth-connection-coalescence process. This phenomenon is even stronger in the case of In/ITO bilayer where the large In drops resulting from the evaporated In connect with the smaller NPs resulting from ITO reduction and rapidly merge into very large NPs (15 um)