Physical evaporation of SiO and SiO(2) under ultra-high vacuum conditions was monitored in situ with infrared spectroscopy at frequencies between 450 cm(-1) and 5000 cm(-1). The measured vibrational spectra of the condensed films are identical in both cases, for SiO and SiO(2) evaporation, and can be described with four Brendel oscillators located at 380 cm(-1), 713 cm(-1), 982 cm(-1), and 1101 cm(-1), corresponding to typical vibration modes in SiO.

The formation of self-assembled Pb nanorods on a vicinal Si(335)/Au surface at 305K was monitored in situ with polarization dependent infrared spectroscopy. The rods have formed from Pb evaporated on a single domain Au-stabilized Si(335) surface under ultrahigh vacuum conditions and reached lengths of about 1μm. As the rods are aligned almost parallel, a large optical anisotropy of the transmitted infrared light was detected. A plasmonic antennalike resonance appeared in the spectra. Since such resonance frequencies are mainly determined by the length of the rods, the growth process was directly monitored via the shift of the resonance frequency. The estimated extinction cross section at resonance frequency indicates field enhancement similar to that observed for gold nanorods.

Context. Silicate minerals belong to the most abundant solids that form in cosmic environments. Their formation requires that a sufficient number of oxygen atoms per silicon atom are freely available. For the standard cosmic element mixture this can usually be taken for granted, but it becomes a problem at the transition from the oxygen-rich chemistry of M-stars to the carbon-rich chemistry of C-stars. In the intermediate type S-stars, most of the oxygen and carbon is consumed by formation of CO and SiO molecules, and left-over oxygen to build SiO 4 -tetrahedrons in solids becomes scarce. Under such conditions SiO molecules from the gas phase may condense into solid SiO. The infrared absorption spectrum of solid SiO differs from that of normal silicates by the absence of Si-O-Si bending modes around 18 μm whereas the absorption band due to Si-O bond stretching modes at about 10 μm is present. Observations show that exactly this particular characteristic can be found in some S-star spectra. Aims. We demonstrate that this observation may be explained by the formation of solid SiO as a major dust component at C/O abundance ratios close to unity. Methods. The infrared absorption properties of solid SiO are determined by laboratory transmission measurements of thin films of SiO produced by vapour deposition on a Si(111) wafer in the range between 100 cm −1 and 5000 cm −1 (2 μm and 100 μm). From the measured spectra the dielectric function of SiO is derived by using a Brendel-oscillator model, particularly suited to the representation of optical properties of amorphous materials. The results are used in model calculations of radiative transfer in circumstellar dust shells with solid SiO dust in order to determine the spectral features due to SiO dust. Results. Comparison of synthetic and observed spectra shows that reasonable agreement is obtained between the main spectral characteristics of emission bands due to solid silicon monoxide and an emission band centred on 10 μm, but without the accompanying 18μm band, observed in some S-stars. We propose that solid SiO is the carrier material of this 10 μm spectral feature.

The growth of ultrathin SiO layers on clean Si(111) was observed by in situ infrared spectroscopy under ultra-high vacuum conditions. SiO was deposited by thermal evaporation of SiO powder from a Knudsen cell. A large shift of the SiO main vibrational line, from about 864 cm À1 for sub-monolayer coverage up to the bulk value of SiO at about 982 cm À1 for thicknesses above 10 Å , was observed. The extraordinary low vibrational frequencies for species at the SiO-Si interface corroborate recently published theoretical results for SiO adsorption on Si and for the SiO 2 -Si interface.

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