Mossbauer Investigation into the Reactions of Laser-evaporated Iron with Solid Oxygen at Low Temperatures

Laser-ablation has been studied extensively and has been applied to many fields including the surface treatment of solids and the formation of thin films. Laser-evaporation is a very useful method for vaporizing various kinds of materials without causing radiant heating of surrounding materials. This makes it a convenient method for vaporizing materials near a cold head in a cryostat in order to study low-temperature reactions. We have previously reported reactions of laser-evaporated iron atoms with various reactant gases using a low temperature matrix isolation technique and Mossbauer spectroscopy. 1-4 The reactions of laser-evaporated iron atoms with oxygen produced FeO, Fe(O2), FeO3, (O2)FeO2, and OFeO which are reaction products of the gas phase and are trapped in a low temperature Ar matrix. 5 We have also reported laserdeposition of Fe metal onto Al or Si substrates at various temperatures, 6 and the formation of Fe-Al alloy or Fe-Si compounds was observed at the boundary between the Fe-films and the Al or Si substrate. Laser-deposition of hematite or magnetite onto Al substrates produced iron oxide films whose composition varied depending on the substrate temperature. 7 Thereby laser-deposition has the possibility of producing functional films whose chemical compositions and physical properties can be controlled. Here, we report the reactions of laser-evaporated Fe with solid oxygen at 20 K. While the experimental setup is very similar to that employed in our previous matrix-isolation studies, 5 in this study the Fe atoms and O2 gas are introduced alternately to the cold substrate in order to investigate the reaction of Fe with solid oxygen rather than the gas-phase reactions. This study is also a useful cross reference for the 57 Mn in-beam Mossbauer study of solid oxygen, 8 although the densities of 57 Fe and 57 Mn atoms are very different. Furthermore the reac