Growth Characteristics of Calcium Silicides Films from the Deposited Ca Films at the Different Sputtering Ar Pressure
Thin Ca films were deposited directly on Si(100) substrates at the different deposition Ar pressure using Radio Frequency (R.F.) magnetron sputtering system (MS) and subsequent annealed at 800°C for 2.5h or 1.5h in a vacuum furnace, respectively. The double-structure Ca2Si films and Ca5Si3 film are grown directly and individually on Si(100) substrates by an interdiffusion process between the deposited Ca atoms and Si bulk crystals, respectively. Experimental results indicated that the selective grown of a single phase calcium silicide in multiple silicide phases in Ca-Si system depends on sputtering condition, annealing temperature and annealing time, especially sputtering condition is the principal factor for the selective grown because it is close contacted with the morphological character, the bombardment defect, the nucleation density of a calcium silicide in a calcium silicides system by bombardment intensity and so on. Besides, 800°C is the adaptive annealing temperature for a single calcium silicide film growth. Keywords-Ca2Si; Ca5Si3; Nucleation; Semiconducting silicides; MS; Annealing
Silicon valence states in calcium silicides: A Si L2,3VV Auger line-shape analysis.
We present a Si ${\mathit{L}}_{2,3}$VV Auger line-shape analysis of the whole set of Ca silicides, ${\mathrm{Ca}}_{2}$Si, CaSi, and ${\mathrm{CaSi}}_{2}$. Measured spectra are compared, after data processing, to theoretical ones, computed within the framework of a one-electron picture. The overall good agreement found in this comparison allows us to understand the observed Si ${\mathit{L}}_{2,3}$VV spectral changes in terms of the Si valence states' evolution across the whole family of Ca silicides. The narrowing of the pp spectral region and the appearance of a distinct sp shoulder observed on going from ${\mathrm{CaSi}}_{2}$ to ${\mathrm{Ca}}_{2}$Si are related, respectively, to the decreased width of the Si 3p band and to the narrowing of the Si 3s states together with their increased energy separation from the Si 3p states. A breakdown of the one-electron picture is observed in ${\mathrm{Ca}}_{2}$Si. We find that this effect is due to the quasiatomic configuration of the Si 3s states in this compound. The introduction of a correlation energy between two sp-like\char21{}final-state holes improves the comparison between theory and experiment, but does not appear to fully account for the Si ${\mathit{L}}_{2,3}$VV spectrum from ${\mathrm{Ca}}_{2}$Si. New theoretical effort is therefore needed to understand this spectrum.
The crystal structure of stilpnomelane. Part II. The full cell
Summary The structural formula of stilpnomelane averaged from 37 representative literature analyses and based on the determined structure is (Ca,Na,K)4(Ti0·1Al2·3Fe35·5Mn0·8Mg9·3)[Si63Al9](O,OH)216·nH2O. Ferrostilpnomelanes have up to 12 R 3+ cations in the octahedral sheet, ferristilpnomelanes commonly have between 24 and 30 R 3+ cations, rarely up to 37. The two groups can be distinguished by accurate X-ray powder diffraction, ferrostilpnomelanes having d 001 less and a greater than have ferristilpnomelanes. The unit cell is triclinic, a = b∼21·8 Å, γ = 120°, d 001∼12·2 Å, P . Hexagonal groups or ‘islands’ of 24 silicon-oxygen tetrahedra co-ordinate to the octahedral sheet, the centres of the ‘islands’ are displaced by 5a/12, 8b/12 on either side of the octahedral sheet as a result of warping of this sheet to permit articulation with the smaller tetrahedral sheet. The 24-tetrahedra ‘islands’ are linked laterally by 6-member rings of inverted tetrahedra, which in turn link at their apices to like rings connecting the next sheet of ‘islands’. Thus a single tetrahedral layer is 4 tetrahedra thick and has symmetry 6/m. The 6-member rings of tetrahedra act as hinges permitting up to 0·5 Å extension or contraction of the tetrahedral sheet to accommodate variations in the octahedral sheet dimensions with varying R 2+/R 3+ ratio.