Thin films of hafnium oxide have been grown by high pressure reactive sputtering on transparent quartz substrates (UV-grade silica) and silicon wafers. Deposition conditions were adjusted to obtain polycrystalline as well as amorphous films. Optical properties of the films deposited on the silica substrates were investigated by transmittance and reflectance spectroscopy in the ultraviolet, visible and near infrared range (UV-VIS-NIR). A numerical analysis method that takes into account the different surface roughness of the polycrystalline and amorphous films was applied to calculate the optical constants (refractive index and absorption coefficient). Amorphous films were found to have a higher refractive index and a lower transparency than polycrystalline films. This is attributed to a higher density of the amorphous samples, which was confirmed by atomic density measurements performed by heavy-ion elastic recoil detection analysis (ERDA). The absorption coefficient gave an excellent fit to the Tauc law (indirect gap), which allowed to obtain a band gap value of 5.54 eV. The structure of the films (amorphous or polycrystalline) was found to have no significant influence on the nature of the band gap. The Tauc plots also give information about the structure of the films, because the slope of the plot (the Tauc parameter) is related to the degree of order in the bond network. The amorphous samples had a larger value of the Tauc parameter, i.e., more order than the polycrystalline samples. This is indicative of a uniform bond network with percolation of the bond chains, in contrast to the randomly oriented polycrystalline grains separated by grain boundaries.2

Zirconium / Hafnium / Thorium / Rutherfordium / Fluoride complexation / Anion and cation exchange chromatography Summary. The fluoride complexation of the group-4 elements Zr, Hf and Rf, and of the pseudo-homolog Th, has been investigated in mixed HNO 3 /HF solutions by studying K d values on both cation exchange resins (CIX) and anion exchange resins (AIX) using the automated rapid chemistry apparatus ARCA. On the CIX, the four elements are strongly retained as cations below 10 Ϫ3 M HF. For Zr and Hf, the decrease of the K d values due to the formation of fluoride complexes occurs between 10 Ϫ3 M HF and 10 Ϫ2 M HF. For Rf and Th, this decrease is observed at one order of magnitude higher HF concentrations. On the AIX, for Zr and Hf, a rise of the K d values due to the formation of anionic fluoride complexes is observed between 10 Ϫ3 M HF and 10 Ϫ2 M HF, i.e. in the same range of HF concentrations where the decrease of the K d values on the CIX is observed, yielding a consistent picture. For Rf and Th, on the AIX, no rise of the K d values is observed even if the HF concentration is increased up to 1 M. By varying the concentration of the counter ion NO 3 Ϫ which is competing for the binding sites on the AIX resin, it could be shown, nevertheless, that Rf does form anionic fluoride complexes. Apparently, there is a more specific competition of NO 3 Ϫ with respect to [RfF x ] (xϪ4)Ϫ than with [ZrF y ] (yϪ4)Ϫ and [HfF z ] (zϪ4)Ϫ .

The optical and vibrational properties of the quaternary chalcopyrite semiconductor alloy Ag x Cu 1x GaS 2

The evolution of the coating stoichiometry with pressure, target-substrate distance, and angle was analyzed for dc sputtering of TixB (x=0.5, 1, 1.6) compound targets by elastic recoil detection analysis. For an investigation of the underlying fundamental processes primarily Ar was used as sputter gas. Additionally, the effect of a reactive gas (N2) as well as bias voltage (floating up to −200 V) was briefly cross-checked. For deposition along the target normal (90°) a pronounced Ti-deficiency of up to 20% is detected. Increasing the pressure or distance from 0.5 to 2 Pa and from 5 to 20 cm, respectively, leads to an almost equivalent linear increase in Ti/B ratio surpassing even the target composition. Off-axis depositions at lower angles (30° and 60°) on the other hand result in a higher Ti/B ratio. This is consistent with results obtained from Monte Carlo simulations combining the respective emission characteristics from the sputter process as well as the gas-phase transport. Hence, the pressure, distance, and sample position induced changes in chemical film composition can be understood by considering gas scattering and the angular distribution of the sputtered flux. The theoretically determined transition from a directional flux to thermal diffusion was experimentally verified by mass-energy analysis of the film-forming atoms.

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