The Raman spectrum from a-Si is, then, a measure of the density of vibration states that are modified substantially by small changes in the short-range order . It has been shown that the full width at half maximum (Γ TO), the peak position of the TO phonon mode (ω TO), and the ratio of the intensities of TO (I TO) and TA (I TA) modes, (ITA/ITO), depend almost linearly on the average bond-angle variation (ΔΘ) in an a-Si network : (4) (5) (6) Raman scattering spectra were obtained for the films with x ≥ 0.38, whereas for lower x values the signal was not detected. As Figure 2a shows, the first-order μ-RS spectra consist of two distinct broad
bands peaked at 140 to 160 cm−1 and 460 to 470 cm−1 (curves 1, 2). These spectra are typical for amorphous silicon and can be described as overlapping of four bands Selleckchem Romidepsin related to acoustic and optical Si phonon modes: transverse and longitudinal acoustic (TA and LA) phonons as well as longitudinal and transverse optical (LO and TO) modes. The deconvolution of the spectrum for sample
with x = 0.45 is shown in Figure 2a. It is worth to note that the peak position of TO phonon mode is shifted toward the lower wave numbers (ω ТО ≈ 460 cm−1) with the respect to the peak position of TO phonon observed usually in the spectra of ‘relaxed’ a-Si (ω ТО ≈ 480 cm−1) (Figure 2, curve 2). Figure 2 Micro-Raman spectra of as-deposited, RTA-, and CA-treated Si-rich Al 2 O 3 films. (a) Micro-Raman spectra Protein Tyrosine Kinase of as-deposited Si-rich Al2O3 films with x = 0.68 (1) and x = 0.45 (2). The deconvolution of curve 2 to four Si-phonon bands is also present. The spectra are offset for clarity. (b) Variation of micro-Raman spectra after RTA and CA treatments on the same samples. This ω ТО shift indicates ‘unrelaxed’ microstructure of a-Si in our samples due to either point defects (caused a ΔΘ distortion) or tensile strain field [26, 27]. Based on Eqs. (4) and (5), the ΔΘ value was found
to be ΔΘ ≈ 20° (x = 0.45) and ΔΘ ≈ 18° (x = 0.68) that exceeds significantly the ΔΘ values obtained for ‘relaxed’ a-Si (about ΔΘ = 7° to 11° [26, 27]). This is an evidence of the significant short-range disorder in a-Si phase in our samples, STK38 which can result from numerous point defects or small size of a-Si clusters. At the same time, the ΔΘ values obtained from Eq. (6) are much higher: ΔΘ ≈ 70° (x = 0.45) and ΔΘ ≈ 63° (x = 0.68). This can be explained by significant middle-range disorder that can be caused by the Selleckchem Alvocidib contribution of elastic strains [26, 27]. In our case, they are tensile since the ω ТО shifts to the lower wavenumbers. The observation of Raman spectrum of a-Si in the as-deposited films with x ≥ 0.38 is the evidence of a-Si clusters’ formation during film deposition. Meanwhile, when x < 0.