Hydrogen photosensitization, photochromism, and surface-enhanced infrared absorption in AgI thin films

Abstract

Atomic photochemical hydrogen was produced by two methods: either employing a special hydrogen generator (a $\mathrm{W}{\mathrm{O}}_{3}$ thin film) or directly via a photochemical reaction on the surface of AgI films, with the atomic hydrogen being detached under the action of light from especially selected hydrogen-donor molecules previously adsorbed on the halide surface. The aim was to organize doping of the AgI film surface by atomic hydrogen, which yielded hydrogen sensitization simultaneous to illumination. Photochromism was achieved in the AgI evaporated films, which has been never observed before. Being an excellent reducing agent, the atomic hydrogen triggers formation of sensitization centers at the AgI surface, which provides, in turn, growth of nanosized silver clusters and colloids under the action of light. In fact, a composite material was created consisting of AgI, Ag, and hydrogen-donor molecules adsorbed on the AgI film surface and over the silver particles. The surface-enhanced infrared absorption (SEIRA) for the absorption bands attributed to vibrations of the hydrogen-donor molecules was observed in this composite, with the silver colloids of $\ensuremath{\sim}20\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ in diameter being formed in the AgI films under illumination, which are the best substrates to observe SEIRA. SEIRA, in turn, appears to be a very helpful method in the investigation of the hydrogen abstraction reaction yielding other evidences of the photoinitiated detachment of hydrogen atoms from the hydrogen-donor molecules. This paper will be of interest for many scientists in various branches of solid-state physics, materials physics, and nanoscience.