Surface analytical characterization of oxide-free Si(100) wafer surfaces

Summary Wet-chemical cleaning procedures of Si(100) wafers are surface analytically characterized and compared. Hydrophobic surfaces show considerably less native oxides in comparison to hydrophilic surfaces.The growth of the oxide is determined as a function of exposure to air by means of XPS measurements. The chemically shifted Si2p XPS signal is utilized for the quantification of the growth kinetics.One hour after cleaning no chemically shifted Si2p XPS peak is discernible on the hydrophobic surfaces. Assuming homogeneous oxide growth, the detection limit of native oxides is estimated to be below 0.05 nm using an emission angle of 18° with respect to the wafer surface. The calculation of the oxide thickness from the chemically shifted and nonchemically shifted Si2p XPS peak intensities is carried out according to Finster and Schulze [1]. For more than a day after cleaning no surface oxides can be identified on the hydrophobic surfaces. The oxide growth kinetics is logarithmic. The very slow oxidation rate cannot be attributed to fluorine residues since no fluorine is seen by XPS. We explain the slow oxidation rate by a homogeneous hydrogen saturated Si(100) wafer surface.

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Oberflächenanalytische Charakterisierung oxidfreier Si(100)-Waferoberflächen

     

Spectral interference in a binaural detection task

Several investigations suggest that sensitivity to changes in interaural disparities within select spectral regions may be degraded by the presence of energy at other, even remote, spectral regions. This study assessed whether similar degradations would be observed in an MLD paradigm. Detection thresholds were measured for NoSo and NoS pi. The signal, an 800-Hz tone (100-ms), was presented in continuous, broadband noise. Thresholds were also measured in the presence of a 400-Hz tone (the interferer) presented with an interaural phase disparity of 180 degrees and gated simultaneously with the signal or presented continuously. NoS pi thresholds increased by about 7 dB with the gated interferer at 80 dB SPL. Smaller increases were observed with lower levels of the interferer. Presenting the interferer continuously reduced substantially its effect. NoSo thresholds were affected only slightly by the interferer. Reversing the roles of the signal and interferer (400-Hz signal, 800-Hz interferer) led to smaller, but reliable degradations in performance. Diotic interferers had, in general, smaller effects on performance. The possible relation between the mechanisms that produce interference and those that foster an ability to segregate sources of sound is discussed.     

Converged properties of clean metal surfaces by all-electron first-principles calculations

All-electron full-potential linearized augmented plane-wave calculations of the surface energy, work function, and interlayer spacings of close-packed metal surfaces are presented, in particular, for the free-electron-like metal surfaces, Mg(0 0 0 1) and Al(1 1 1), and for the transition metal surfaces, Ti(0 0 0 1), Cu(1 1 1), Pd(1 1 1), and Pt(1 1 1). We investigate the convergence of the surface energy as a function of the number of layers in the slab, using the Cu(1 1 1) surface as an example. The results show that the surface energy, as obtained using total energies of the slab and bulk from separate calculations, converges well with respect to the number of layers in the slab. Obviously, it is necessary that bulk and surface calculations are performed with the same high accuracy. Furthermore, we discuss the performance of the local-density and generalized gradient approximations for the exchange-correlation functional in describing the various surface properties.     

Low-temperature hydride furnace modified for the atomic absorption spectrometric determination of metals with low appearance temperatures

The sample is vaporized from tungsten filament coils (150 W) and transported by an argon stream to the cell of a modified hydride furnace for atomic absorption spectrometry (a.a.s.). The system provides almost the same sensitivity for elements with low appearance temperatures (e.g., Bi, Cd, Pb, Tl, Zn) as graphite-furnace a.a.s. The detection limits are between 0.1 and 5 ng ml^?1, depending on the element.