Temperature Dependence of Competitive Reaction of Iodine Ions on H-Terminated Si(111) Surface in a Concentrated HI Solution

Abstract

The surface reactions of iodine ions on nearly atomically flat, H-terminated Si(111) surfaces, when immersed in 7.6 M HI in a temperature range of −20 to 63 °C, were investigated by atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy, and core-level shift spectra. It was revealed that the following two reactions simultaneously occurred, which were competitive with each other: (1) substitution reaction of Si−H bonds with Si−I bonds and (2) cluster formation by the condensation of SiHxI4−x or their oligomer species, which were generated by surface etching reaction. The ratio of those competitive reactions was strongly dependent on the temperature of the HI solution. At the high temperature, the former reaction was enhanced, whereas the latter reaction was suppressed. Inversely, at the low temperature, the latter reaction was relatively enhanced, resulting in that the ordered rodlike clusters were formed on the Si(111) surface. These results were explained by the fact that the former and latter reactions were mainly enhanced by the H2O and dissolved oxygen, respectively, and the concentration of dissolved oxygen was drastically decreased in the HI solution at high temperature, compared with that at low temperature. It was also revealed that the order and shape of the clusters formed by the condensation of SiHxI4−x or their oligomer species produced by etching reaction were strongly dependent on the temperature of the HI solution.