2p Core Level Research Articles

Local and Symmetry-Resolved Electronic Structure of Liquid Dimethyl Sulfoxide from Resonant Inelastic Soft X-ray Scattering.

Dimethyl sulfoxide (DMSO) is an important polar solvent that derives its unique properties from the lone pair and the strong polar bond at the sulfinyl functional group. To derive the local and symmetry-resolved electronic structure of liquid DMSO, we have used resonant inelastic soft X-ray scattering (RIXS) maps at the S L2,3, C K, and O K edges. The experimental data are compared to calculations of spectra based on density functional theory, which allows a detailed analysis of the molecular orbitals throughout the molecule. In the RIXS maps, we find the signature of molecular-field splitting of the S 2p core levels, vibronic coupling, and ultrafast nuclear dynamics on the time scale of the RIXS process.

XPS Investigation of Co-Ni Oxidized Compounds Surface Using Peak-On-Satellite Ratio. Application to Co20Ni80 Passive Layer Structure and Composition.

XPS data processing for cobalt and nickel core-level peaks can be complicated. This is especially true when analyzing a mixture of oxide/oxyhydroxide/hydroxide compounds of these metals. The objective of this study is to develop a method for decomposing XPS spectra of 2p core levels for nickel and cobalt-oxidized compounds. This methodology was then employed to study the passivation layer of the Co20Ni80 alloy. The analysis of Ni2p and Co2p photo peaks using a homemade code based on core-level peak structure and satellites enables us to determine the chemical composition of the surface layer, knowledge of which is particularly important because it is directly linked to the anticorrosive properties it confers on the surface of the oxidized alloy. The XPS analysis, coupled with sequential ion sputtering, revealed that the passive layer of the Co20Ni80 alloy is heterogeneously covered with either oxidized cobalt compounds or oxidized nickel compounds. The method used also demonstrates that the chemical heterogeneity is associated with the thickness heterogeneity of the passive layer.

Spin asymmetry of O 2p –related states in SrTiO3(001)

Atomically clean SrTiO3(001) is characterized by low energy electron diffraction, core level and valence band photoelectron spectroscopy, the latter also with spin resolution. Samples prepared by a sputtering-annealing procedure exhibited in-gap states in the valence band spectra, Ti3+ components in Ti 2p core level spectra and a noticeable spin asymmetry in the 3–9 eV binding energy range, which corresponds to valence states of mainly O 2p character. Upon annealing in oxygen, the spin asymmetry vanishes, accompanied by the intensity decrease of the contribution of titanium low ionization states and of in-gap states, indicating that these three phenomena are mutually connected. The observed spin asymmetry may be generated by indirect exchange mediated by the in-gap states between O 2p orbitals, or by the partial Ti 3d character of these states, which acquire non-zero spin in case of incomplete oxygen coordination.

Influence of anti-ferromagnetic ordering and electron correlation on the electronic structure of MnTiO3

Electron correlation and long-range magnetic ordering have a significant impact on the electronic structure and physical properties of solids. Here, we investigate the electronic structure of ilmenite MnTiO3 using room temperature photoemission spectroscopy and theoretical approaches within density functional theory (DFT), DFT+ U and DFT+dynamical mean-field theory (DMFT). Mn 2p (Ti 2p) core level photoemission spectra, confirming Mn2+ (Ti4+) oxidation state, exhibit multiple satellites which are very similar to that of MnO (TiO2), suggesting similar strength of various interactions in this system. Valence band spectra collected at different photon energies suggest dominant Mn 3d character in the highest occupied band with a wide insulating gap. DFT(+ U) correctly predicts the experimentally observed anti-ferromagnetic (AFM) insulating ground state for MnTiO3 where the requirement of a large U to reproduce the experimental values of magnetic moment and band gap signifies the importance of electron correlation. Magnetically disordered paramagnetic (PM) phase could be well captured within DFT+DMFT, which provides an excellent agreement for the experimental band gap, paramagnetic moment, valence band spectra as well as dominant Mn 3d character in the highest occupied band. The calculated spectral function remains largely unaffected and exhibits sharper features in the magnetically ordered AFM phase. We show that the electronic structure of MnTiO3 in both the PM and AFM phases can be accurately described within DFT+DMFT.

Deconvoluting XPS Spectra of La-Containing Perovskites from First-Principles.

Perovskite-based oxides are used in electrochemical CO2 and H2O reduction in electrochemical cells due to their compositional versatility, redox properties, and stability. However, limited knowledge exists on the mechanisms driving these processes. Toward this understanding, herein we probe the core level binding energy shifts of water-derived adspecies (H, O, OH, H2O) as well as the adsorption of CO2 on LaCoO3 and LaNiO3 and correlate the simulated peaks with experimental temperature-programmed X-ray photoelectron spectroscopy (TPXPS) results. We find that the strong adsorption of such chemical species can affect the antiferromagnetic ordering of LaNiO3. The adsorption of such adspecies is further quantified through Bader and differential charge analyses. We find that the higher O 1s core level binding energy peak for both LaCoO3 and LaNiO3 corresponds to adsorption of water-related species and CO2, while the lower energy peak is due to lattice oxygen. We further correlate these density functional theory-based core level O 1s binding energies with the TPXPS measurements to quantify the decrease of the O 1s contribution due to desorption of adsorbates and the apparent increase of the lattice oxygen (both bulk and surface) with temperature. Finally, we quantify the influence of adsorbates on the La 4d, Co 2p, and the Ni 3p core level binding energy shifts. This work demonstrates how theoretically generated XPS data can be utilized to predict species-specific binding energy shifts to assist in deconvolution of the experimental results.

Initial oxidation of low index Mg surfaces investigated by SCLS and DFT

Magnesium (Mg) is a metal having a high structural efficiency and a very high chemical reactivity at the same time. Its potential areas of applications include the automotive industry, biomedicine, and energy storage and generation. Further developments in these very diverse application areas require a more detailed investigation of the behavior of Mg surfaces under oxidative conditions. The basic mechanisms of magnesium reactivity are not yet fully understood and therefore need to be further investigated by a combination of theoretical and experimental studies on representative surfaces with different crystallographic orientations.For this, we measured in situ high-resolution Mg 2p core level spectra at critical low-index Mg(0001), Mg(101¯0), and Mg(112¯0) surfaces to obtain surface core level shifts (SCLSs) at the early stages of Mg oxidation. We also used density functional theory (DFT) to obtain theoretical estimates of the SCLSs for respective surfaces and associated possible reconstructions to guide the analysis of the experimental spectra and to rule out un-reconstructed Mg(112¯0). DFT simulations were also used to reveal the energies of O atom adsorption, and the formation of evolving oxide structures in the Mg surfaces.

X-ray photoelectron spectroscopy, structural, and radiation shielding properties for transparent borosilicate glasses

The current work investigates the impact of SrO content on the structural, physical, and shielding properties of xSrO-10TiO2–10SiO2-(65-x) B2O3, where (15 ≤ x ≤ 30) glasses. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), and radiation shielding features were utilized to investigate the samples’ features. XRD results affirmed the amorphous behavior. The FTIR values presented many peaks attributed to SiO2 and B2O3. The Sr30B50 sample (3.048 g/cm3) showed the highest density, followed by Sr25B55 (2.936 g/cm3), Sr20B60 (2.720 g/cm3) and Sr15B65 (2.679 g/cm3). The XPS analysis of Ti 2p core level spectra reveals that Ti ions exist in both Ti4+ and Ti3+ oxidation states, with the content of Ti4+ increasing with the SrO ratio in the glass sample. The XPS analysis of O 1s core level spectra revealed that the number of non-bridging oxygen atoms is enhanced with an increase in SrO content, indicating the weakening of the glass structure. Furthermore, neutron and photon shielding properties were calculated theoretically using Phy-X software. The gamma shielding properties were enhanced with increasing SrO, while the neutron attenuation was equivalent to water. For example, the fast neutron removal cross-section (FNRCS) values are 0.101, 0.098, 0.102, and 0.101 cm−1 for Sr15B65, Sr20B60, Sr25B55, and Sr30B50, respectively. The findings suggest that the SrO improved radiation shielding properties while decreasing glass stability.

Peculiarities in XPS spectra of Sn/SiO2 layers as an effect of surface charge

X-ray photoelectron spectroscopy based on synchrotron radiation was used to investigate the composition of the observed SnO2-x/Sn:SiO2-x thin layer grown by organometallic chemical vapour deposition on single-crystalline silicon wafer with additional argon ions etching treatment. Due to the formation of a thermodynamic anomaly during in situ layer growth, an efficient oxygen exchange between silicon and tin oxide phases occurs. The present study addresses the effect of localized surface charging and its influence on the obtained XPS core level spectra. We found that due to the high electrical conductivity of metallic tin and the direct coupling of tin particles to the silicon wafer, the XPS Sn 3d5/2 core level spectrum is not affected by the surface charge compared to the highly charged dielectric silicon oxide matrix, as observed for the XPS O 1 s and Si 2p core level spectra. Our results show that the core level spectra of Si 2p and O 1 s are shifted up to 3 eV due to the presence of uncompensated positive charge on the surface of the silica matrix. These results provide insight into the influence of surface charge effects on the analysis of conductor/insulator composite materials and contribute to the application of Sn-based materials in various application concepts related to energy and surface functionalization.

Resonant photoemission studies on Fe-Ni alloys

This paper investigates the electronic structure of Fe1−xNix (x = 0.32, 0.36, 0.4, 0.5) alloys employing high resolution photoelectron spectroscopy using synchrotron radiation. The valence bands and the core levels have been recorded at various on-resonance and off-resonance photon energies of Fe and Ni. An anti-resonance dip observed in the valence bands taken at Fe 3p → 3d resonance lies closer to the Fermi level compared to that observed at Ni 3p → 3d resonance, indicating larger density of itinerant Fe 3d electrons. Whereas, Ni 3d states are comparatively less itinerant in these alloys. The hybridization effects increase with increase of Fe content in the alloy system. The intensity of Ni L3M4,5M4,5 Coster-Cronig Auger transition observed with 853 eV (Ni 2p → 3d resonance) photon energy, drops down drastically for the Invar alloy (Fe0.64Ni0.36) as compared to other Fe-Ni alloys due to the existence of Ni in more than one local chemical surroundings as expected for Invar alloy. The electron-electron interaction energy (Udd) of Ni 3d shell is found to decrease with the decrease of Ni concentration. The 3p and 3s core levels of Fe and Ni recorded at 707 eV (Fe 2p → 3d resonance) are overwhelmed by various intense resonant Auger features such as Fe L3M2,3M2,3, Fe L3M2,3M4,5 and Fe L3M1M4,5. The 1S state of Fe L3M2,3M2,3 is greatly enhanced in the Invar alloy as compared to other alloys. The microscopic compositional in-homogeneity present in Invar alloy plays a crucial role in the screening of holes in Ni sites but does not contribute in screening the holes in Fe sites.

Iron oxide nanoparticles produced by the laser ablation technique and analyzed by x-ray photoelectron spectroscopy

The study of iron nanoparticles is one of the most researched areas in recent times due to the potential applications they have and because the study of iron by XPS is one of the most debated elements. In this work, we provide investigation data of iron oxide nanoparticles produced using the laser ablation technique, which were characterized using x-ray photoelectron spectroscopy. Survey spectra, C 1s, O 1s, and Fe 2p core levels spectra were acquired. Results showed the presence of Fe+3 and Fe+2 elements that constitute hematite and magnetite with differences in their concentrations depending on the fitting method. In addition, the presence of adventitious carbon and carbon from impurities was detected.

Cluster Mo2C deposited on graphene nanowalls by x-ray photoelectron spectroscopy

Molybdenum deposited on carbon graphene nanowalls was characterized by x-ray photoelectron spectroscopy with an Al Kα (1486.6 eV) excitation source. The sample was fixed to a stainless-steel sample holder with copper double-sided adhesive tape. Survey spectrum, C 1s, O 1s, Si 2p, and Mo 3d core levels spectra were acquired.

Enhanced photocatalytic performance of ZnO under visible light by co-doping of Ta and C using hydrothermal method.

This study attempted to improve the photocatalytic activity of zinc oxide (ZnO) semiconductors in the visible light region by introducing the co-doping of carbon (C) and tantalum (Ta) to ZnO (ZTC) using a simple hydrothermal method with the respective precursors. The obtained uniform ZTC nanoparticles with an average crystal size of 29.30 nm (according to Scherrer's equation) revealed a redshift with a decrease in bandgap (Eg) from 3.04 eV to 2.88 eV, allowing the obtained photocatalyst to absorb the energy of the visible light for photocatalysis. Furthermore, the Zn 2p and Ta 4f core level spectra confirmed the presence of Zn2+ and Ta5+ in the ZTC sample. In addition, the infrared spectra identified hydrogen-related defects (HRDs), while the O 1s spectra indicated the existence of oxygen vacancies (VO). Electrochemical tests revealed improvement in the electron conductivity and charge separation of the obtained materials. To follow, the photocatalytic performance assessment was conducted by varying the C/Zn2+ ratios (5, 10, and 15 mol%) in ZTC samples, the initial RhB concentration (7, 15, and 30 ppm), and the pH of the RhB solution (3.0-10.0). The photodegradation on ZTC samples showed the most effectiveness for a 7 ppm RhB solution with a C/Zn2+ ratio of 10 mol% in the slightly alkaline medium (pH 9.0). Additionally, ZTC also exhibited commendable durability after being reused several times. The nature of RhB photodegradation was proposed and discussed via a mechanism at the end of this work.

Interactions in Al2O3 - graphene oxide composite: XPS study

The structure of an aluminum oxide/graphene oxide (GO) composite was studied using X-ray photoelectron spectroscopy (XPS). High-energy resolved XPS measurements of Al 2p-core level spectra revealed the formation of Al–O–C bonds, which indicated the occurrence of interfacial reactions between Al2O3 and GO in the process of composite synthesis. An increase in intensity in the near-edge region of XPS valence band (VB) spectrum was observed with increasing GO concentration, indicating possible contribution of the electronic states of carbon. Filling the electronic states on the edge of VB allows to associate GO doping with the loss of dielectric properties of the original Al2O3 compound. Addition of graphene oxide to Al2O3 ceramics changed conductive properties of the composite due to formation of new chemical bonds.

Evolution of structural phase transition from hexagonal wurtzite ZnO to cubic rocksalt NiO in Ni doped ZnO thin films and their electronic structures

This study thoroughly examines the collective influence of compositional variation and annealing temperature on the electronic structure of sol–gel derived NixZn1−xO (x = 0 to 1) thin films annealed at different temperatures (700 ° C, 800 ° C, and 900 ° C) using x-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy. A gradual structural phase transition from hexagonal wurtzite ZnO to cubic rocksalt NiO with increasing Ni concentration was revealed by x-ray diffraction (XRD). Grain growth was observed from scanning electron microscopy with increasing annealing temperature. Photoluminescence measurements indicate the presence of interstitial oxygen when Ni atoms are incorporated in the film. The Ni L 3,2 absorption edge shows an intensity enhancement in the white-line feature with increasing Ni concentration, evidencing the presence of higher oxidation states. Concurring results were observed by XPS where both Ni2+ and Ni3+ free ion multiplets are present in the Ni 2p core level spectrum for 20% and higher Ni concentration. O K and Zn L 3,2 XAS spectra demonstrated the e g-t 2g sub-band splitting at higher Ni concentration, triggered by band anti-crossing interaction and crystal field splitting. The extended x-ray absorption fine structure (EXAFS) simulation for the Zn K edge revealed a Zn–Zn/Ni bond length change for 60% Ni concentration. The thermal disorder factor increased up to 40% Ni concentration, and beyond that, it decreased due to stable NiO phase dominance in the alloy composite. Ni K edge EXAFS fitting indicated an insignificant change in the Ni-O and Ni–Ni/Zn bond lengths throughout the range of varying Ni concentrations. The thermal disorder factor increases with increasing annealing temperature, indicating a more disordered lattice. Such investigation is essential where the electronic properties of nanometer-sized materials determine the performance of functional devices. The present work critically elucidates the combined impact of compositional variations and annealing temperatures on electronic structures.

Comprehensive structural and surface investigation of Sb2Se3 thin-films

Earth-abundant antimony selenide (Sb2Se3) is a promising material for the thin-film photovoltaic applications due to its desirable optoelectronic properties and suitable band gap. In this work, we present a comprehensive study on the structural and surface properties of Sb2Se3 thin-films for the potential applications in solar cells. The Sb2Se3 samples were grown on Si (100) substrate and at different substrate temperatures using radio frequency (RF) magnetron sputtering. The XRD diffractogram exhibits that Sb2Se3 is the predominant phase in all the samples, whereas the TEM measurements confirm the nanocrystalline nature of the samples. Raman spectroscopy measurements in the range of 30–500 cm−1 displays the Raman shifts at 148, 190 and 206 cm−1, which confirms the presence of the Sb2Se3 phase. The average surface roughness and grain size were obtained via surface topography with the help of the high-resolution AFM images. The EDS spectra revealed the presence of both Se and Sb as constituent elements in all the samples. The deconvolution of XPS spectra of Se 3p and Sb 3d core level disclose the Sb+3 and Se−2 oxidation state and further confirms the presence of Sb2Se3 phase. The XPS and EDS measurements predict that there is loss of Se during the deposition and it could have adverse effects on the performance of Sb2Se3 solar cell devices.

HAXPES reference spectra of bulk W and WSe2 with Cr Kα excitation

Monochromatic Cr Kα radiation (5414.8 eV) was used to acquire high-energy photoelectron spectroscopy data on pure W and bulk WSe2 compound. The reported spectra include a survey scan and high-resolution W 3p1/2, W 3p3/2, W 3d3/2, W 3d5/2, W 4s, W 4p1/2, W 4p3/2, W 4d, W 4f, Se 2s, Se 2p1/2, Se 2p3/2, Se 3s, and Se 3p core-levels. The data will be useful as reference core-level spectra for HAXPES studies on tungsten and its compounds.

Interfacial reactivity in the Co/CuO samples as investigated by x-ray photoelectron spectroscopy

The interfacial reactivity at the Co/CuO interfaces has been investigated in situ by the technique of x-ray photoelectron spectroscopy. Thin films of cobalt were evaporated on the CuO substrates by the technique of e-beam. The depositions were undertaken by maintaining the substrates at ambient temperature. Significant differences have been observed in the Cu 2p core level spectra recorded for these samples and that for pure CuO. The Co 2p core level spectrum also shows differences upon comparison with the spectrum for elemental cobalt. These differences arise from chemical interaction occurring at the Co/CuO interface. The curve fitting technique has been utilized to estimate the relative percentages of the constituents at the interface. The interface width has been determined from the relative percentage of the unoxidized cobalt present in the overlayer. The dependence of the interface width has also been explored as a function of annealing temperature. The interface width is much less for the room temperature deposited sample as compared to that for annealed samples. The spectral data also indicate increase in the diffusion of copper oxide through the cobalt overlayer with increasing temperature.

Paracetamol tablet analyzed by XPS

Paracetamol tablet was analyzed by x-ray photoelectron spectroscopy (XPS). Sample was fixed to a stainless-steel sample holder with a copper double-sided adhesive tape. Survey spectra, C 1s, O 1s, N 1s, Si 2p, Mg 2s, Mg KLL, and Mg 1s core levels spectra were acquired. Results showed the presence of carbon, oxygen, and nitrogen, elements that constitute the chemical structure of paracetamol; however, these can also be part of the excipients. In addition, silicon and magnesium were detected, which are related to excipients.

Electronic properties of MnO(110) film grown on Cu (111)

In this study, we investigated MnO thin films grown on Cu(111) using a soft x-ray and UV based spectroscopy, low energy electron diffraction (LEED), scanning tunneling (STM) and scanning transmission electron microscopy (STEM). MnO thin film assumes (110) preferential plane orientation organized in different spatial domains to better adapt to Cu(111) surface and an in-plane/out-of-plane lattice parameter variation up to 11% with respect to bulk counterpart originating a sizeable XLD signal at Mn L2,3 edges. The formation of oxidized Cu region during the MnO thin film growth is not avoidable due to the copper reactivity to oxygen and at the interface the coexistence of MnO islands alternated with Cu2O regions was observed by STM. Mn 2p and Mn 3s core level photoemission line shapes present a slight change in multiplet peak relative intensity with respect bulk MnO counterpart due to the role of Cu substrate in the core level relaxation process. The photon energy dependent photoemission spectra of valence band discriminate the MnO states and indicate a weak influence of the substrate once the film thickness is reduced to 1 nm. These findings open new route in the tuning oxide thin film properties.

CoS2:Ni17S18:Al2S3 thin film as supercapacitor electrode for astounding energy storage and explicit photocatalyst for pollutants degradation

The ternary metal sulfide CoS2:Ni17S18:Al2S3 thin films were created in the presence of diethyldithiocarbamate as a sulfur source, pursued by physical vapour deposition. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV-visible spectrophotometer, and Fourier transform infrared spectroscopy were used to identify and characterize the synthesised substances. The ternary metal sulfide had a mean crystallite size of 37.8 nm on the nanoscale. SEM revealed spherical particles with rounded edges particles. XPS presented Al 2p, Co 2p, Ni 2p and S 2p core level peaks of the elements. The ternary metal sulfide had a band gap energy of 3.49 eV. The phenomenal storage technology potential of the thin film was evaluated using cyclic voltammetry that revealed an astounding supercapacitance of 515 F g−1, demonstrating the material’s effectiveness. Voltammetric findings show the cycling stability of the nanoparticle thin film. Moreover, the photocatalytic degradation of contaminants such as methylene blue dye, pesticide zoxamide, and phenol was probed, with such a spectacular degradation rate constant of 4.11 × 10−2 min−1 with 91.5% degradation achieved for pesticide.