Electronic structure of iridium silicides

We present a detailed ultraviolet and x-ray photoelectron spectroscopy investigation of the electronic structure of three bulk iridium silicide compounds, IrSi, ${\mathrm{IrSi}}_{\mathrm{x}}$ (x≃1.6), and ${\mathrm{IrSi}}_3$. We observed a narrowing of the iridium d band and a concomitant broadening of the Si 2p band in the silicides which indicate that the bonding in these compounds is caused by a hybridization of the Ir d states and the Si sp hybrids. This is consistent with bonding models proposed for 3d and 4d transition-metal silicides. However, a d-band shift was not observed as reported in other transition-metal silicides. Also, we found that IrSi and ${\mathrm{IrSi}}_3$ are metallic. However, we observed that ${\mathrm{IrSi}}_{\mathrm{x}}$ (x≃1.6) is a semiconductor, in agreement with earlier work. We discuss this difference in terms of chemical trends in the bonding of iridium silicide compounds.