Silver Nanoparticles Synthesized by Vapor Deposition onto an Ice Matrix

As a strategy for synthesizing metal nanoparticles, thermally evaporated Ag was deposited onto a thin (∼1.2 nm) crystalline ice layer on hafnia (HfO2) at 100 K. The Ag atoms penetrate into the ice matrix but do not reach the underlying HfO2 substrate. After controlled thermal desorption of water by heating to 300 K, atomic force microscopy reveals Ag particle formation. Their lateral dimensions are between 5 and 20 nm and, in many cases, their heights exceed the thickness of the original water layer. Fewer, higher and more regular Ag particles are formed in the presence, as compared to the absence, of ice. This is discussed in terms of two factors – Ag atoms reaching HfO2 are thermally colder when they arrive from the ice matrix and desorption of water involves formation of liquid droplets, a process that concentrates Ag into the volumes occupied by the water droplets.