Soft X-ray Photoelectron Spectroscopy (SX-XPS, 0.15~2 keV)
Soft X-ray Photoelectron Spectroscopy (SX-XPS) is an advanced analytical method utilized for probing the electronic structure and surface properties of various materials with exceptional precision. Operating within the soft X-ray energy range of 0.15 to 2 keV, SX-XPS offers valuable insights into the material composition and bonding states at the atomic level. The mechanism of SX-XPS involves irradiating the sample surface with soft X-rays, which have energy levels sufficient to eject core-level electrons from atoms within the material. These photoelectrons, emitted from the sample surface, carry information about the elemental composition and chemical environment of the material.
By analyzing the kinetic energy and intensity of these photoelectrons using sophisticated detection systems, SX-XPS researchers can identify specific elements present in the material, determine their chemical states, and map out the spatial distribution of surface species. This powerful analytical technique finds wide-ranging applications in fields such as surface science, catalysis, and nanotechnology, providing invaluable insights for understanding material behavior and optimizing material properties for various technological applications.
The advantage of the synchrotron radiation light source is that the X-ray energy incident on the sample can be adjusted very conveniently. According to the diagram on the left of the electron kinetic energy and mean free path, the effective depth of the sample detected will also change with different X-ray energies.
XPS depth analysis in traditional laboratories must be combined with ion beam processing to remove surface materials in order to measure deeper signals. However, this also destroys the sample structure and may affect the characteristics of the sample.
Synchrotron radiation XPS can use continuous energy adjustment to detect sample signals at different depths without destroying the surface structure of the sample, thereby ensuring the integrity of the sample structure and the authenticity of the signal.
Photoelectrocatalytic
XPS of the NTG photoanode was conducted to determine its chemical analysis environment. The wide scan spectra (Figure 2a) identified C 1s, O 1s, Ti 2p, and N 1s. The XPS O 1s spectrum (Figure 2b) exhibited contributions at 530.35 eV (Ti-O bound) and 532.85 eV (C=O on the NTG film surface). The high-resolution XPS C 1s spectrum (Figure 2c) indicated the presence of residual carbon at 289.5 eV and C-O-C bond. Additionally, the high-resolution N 1s spectrum of the NTG film (Figure 2e) revealed contributions at 399.7 eV and 407.4 eV, linked to substitutional and interstitial nitrogen in N-Ti-N and NO-Ti type structures. XPS spectra indicated the N-doping of TiO2 with the presence of nitrogen in the TiO2 lattice.
Reference:
MI Carreño-Lizcano, Andrés F. Gualdrón-Reyes, V. Rodríguez-González, JA Pedraza-Avella, ME Niño-Gómez. Photoelectrocatalytic phenol oxidation employing nitrogen-doped TiO2-rGO films as photoanodes. Catalysis Today 2020, 341, 96-103.
https://www.sciencedirect.com/science/article/abs/pii/S0920586119300495
Chemistry
XPS was utilized to gain a structural understanding of two types of dimensionally controllable 2D-WS2 colloidal nanoflakes (NFLs) synthesized through a surfactant-assisted non-hydrolytic route. The XPS analysis of NFLs sample B (blue) revealed the presence of both 2H and 1T/1T’ forms of WS2, with 1T’-WS2 being the predominant form (56.8 ± 5.4%), as depicted in Figure 3a. Evidence of partial oxidation was observed in signals corresponding to WOx species. In Figure 3b, the S 2p region displayed three components, indicating the presence of S2− ions in WS2 and two types of sulfur ions (S22− and S2−) associated with WOxSy formation. The ratio between the doublet peaks of S 2p species at higher binding energy exceeded the theoretical value, possibly due to minor contributions from other sulfur species. The atomic ratio between S 2p and W 4f aligned with the stoichiometric ratio. Similar chemical composition and structure were noted in WS2 NFLs sample A (green), suggesting that alkylamines influenced reactivity and lateral size but not atomic structure. The effectiveness of the XPS technique was evident in providing information on both chemical speciation and the existence of two crystal phases, 1T/1T’ and 2H.
Reference:
Scarfiello R., Mazzotta E., Altamura D., Nobile C., Mastria R., Rella S., Giannini C., Cozzoli P.D., Rizzo A., Malitesta C. An Insight into Chemistry and Structure of Colloidal 2D-WS2 Nanoflakes: Combined XPS and XRD Study. Nanomaterials 2021, 11, 1969.
https:// doi.org/10.3390/nano11081969
Corrosion Studies
The study focused on the corrosion reaction characteristics, employing XPS depth profiling to understand the elemental composition changes in corroded FeSiAl alloy (FSA). Figure 4a shows a survey spectrum of identified surface elements (Fe, Si, Al, O, C, Cl). Elemental concentrations were calculated with Ar ion beam dissection of the FSA at various sputtering times (0-390s) as shown in Fig. 4b. Fe, O, and C dominated the after-corroded surface, showing the prevalence of Fe-based matter. Deep-level XPS analysis explored Fe and C composition and oxidation states. Fe 2p3/2 spectra indicated a shift in Fe concentration with increased sputtering time (Fig. 4c). Fe transitions (Fe0 → Fe2+ → Fe3+) were observed, with identified compounds such as FeCl3, Fe2O3, FeO, and Fe3O4. Deeper regions revealed varied compositions, showcasing the complexity of corrosion layers. High-resolution C1s spectra analysis displayed C–O, C= O C=C/C–C, and C–C bonds (Fig. 4j). The presence of oxygen-containing groups and molecular COx indicated the involvement of CO2 in the corrosion process. Chemical composition changes during sputtering time demonstrated the transformation process from Fe0 → Fe2+ → Fe3+. The study provided detailed insights into the corrosion behavior and composition evolution of FSA, crucial for understanding corrosion mechanisms in materials.
Reference:
Guo, Yang; Ali, Rashad; Zhang, Xingzhong; Tian, Wei; Zhang, Li; Lu, Haipeng; Jian, Xian; Xie, Jianliang; Deng, Longjiang (2020). Raman and XPS depth profiling technique to investigate the Corrosion behavior of FeSiAl alloy in a salt spray environment. Journal of Alloys and Compounds, 834(), 155075.
https://www.sciencedirect.com/science/article/abs/pii/S0925838820314389