A residual gas analyzer (Stanford RGA100 model; Stanford Research Institute, Sunnyvale, CA, USA) and sample temperature programmable control unit (Dual Regulated Power Supply OmniVac-PS 120 Model) were used to perform the TDS analysis. During the thermal physical desorption (TPD) cycle, the TDS spectra of selected gases like H2, H2O, O2, and CO2 have been registered. Heating ramp was set at 6°C per minute, in the range of 50 to 350°C. Other experimental details have been described elsewhere [14]. Results and discussion XPS and TDS comparative studies provide interesting information on the surface chemistry, including the behavior of surface contamination, Tipifarnib clinical trial of synthetized SnO2 nanowires.

Figure 1 (lower part) shows the XPS survey spectrum of the VPD-deposited 17-AAG datasheet SnO2 nanowires after their preparation and exposure to air and before the TPD process. The spectrum contains the well-recognized main core level of XPS O1s, double Sn3d, and Sn4d peaks. Moreover, there is an evident contribution from the C1s peak related to strong surface carbon contamination. In turn, there is no contribution of XPS Ag3d double peaks, and this can be explained by the fact that the metal catalyst deposited at Si (100) substrate does not appear at the surface of grown SnO2 nanowires. Figure 1 XPS survey spectra of air-exposed SnO 2 nanowires (before TPD process) and after subsequent TPD process. Quantitative

Megestrol Acetate analyses of surface chemistry (including stoichiometry) of SnO2 nanowires after

air exposure have been performed. It consists in the determination of the relative concentration of the main components (within the escape depth of inelastic mean free path of photoelectrons of approximately 3 nm), based on the area (intensity) of the main core level XPS O1s, Sn3d, and C1s, weighted by the corresponding atomic sensitivity factor (ASF) [16]. The details of this procedure were already described in reference [14]. According to this find more analysis, the relative [O]/[Sn] concentration on the surface of SnO2 nanowires after air exposure, was about 1.55 ± 0.05. It means that these SnO2 nanowires are slightly non-stoichiometric. This is probably related to the presence of oxygen vacancy defects in the surface region of the SnO2 nanowires recently identified by Kar et al. [17–19] for the SnO2 nanowires prepared by vapor-liquid-solid method with rapid thermal annealing from the UV photoluminescence (PL) measurements in combination with XPS, Raman, and transmission electron microscopy (TEM) studies. Probably, these oxygen vacancies can be treated as the surface active center responsible for the strong adsorption of different C species (contaminations) of the air-exposed SnO2 nanowires, what was confirmed by the corresponding relative [C]/[Sn] concentration estimated as 2.30 ± 0.05. This is additionally indicated by the XPS C1s spectrum shown in Figure 2 (lower spectrum).