Si 2p X-ray Photoelectron Spectroscopy Research Articles

Impact of Mn2+-Si4+ co-substitution on the electronic structure of Zn0.3Mn0.7Fe2O4 ferrites studied by X-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (XPS) has been employed to explore the electronic structure of Zn0.3Mn0.7+xSixFe2-2xO4 (x = 0.0–0.3) ferrite series. The Si2p XPS spectra insinuated the presence of Si ions in the +4 valence state. The elemental Si0 and suboxide SiOx are present in the system, the former showing an increase and the latter a decrease in atomic percentage upon Mn–Si substitution. It is also inferred that a fraction of Si0 might be residing at the grain boundaries; however, more studies are required to substantiate this. The Fe2p XPS spectra stipulate that ferrous and ferric ions co-occur in the system. The ferrous ions occupy the octahedral sites while the ferric ions dwell on both the octahedral and the tetrahedral sites. The O1s spectra indicate a remarkable increase in the oxygen defects with increasing Mn–Si substitution (x). The Mn2p XPS data indicate that the Mn+2 states show an overall increasing tendency with increasing Mn–Si concentration. Also, the Mn+4/Mn+3 ratio shows an increment with an increase in Mn–Si substitution.

Surface Contamination with Si and O Impurities for GaN Single-Crystalline Layers Grown by Ultra-High-Vacuum Sputter Epitaxy

Introduction GaN and related alloys have been extensively investigated for their potential applications in optoelectronic and high power electronic devices. The study on surface contamination with Si and O impurities is quite important for device fabrication, especially for Si, because Si is n-type impurity for GaN. In this work, we demonstrate the GaN surface contamination and cleaning technique focused on O and Si based compounds contaminated in air atmosphere. Experiment GaN single-crystalline layers were grown on sapphire (0001) substrates by ultra-high-vacuum radio-frequency sputter epitaxy technique. The thermal desorption spectroscopy (TDS) measurement was carried out for as-grown GaN layers at pressure of 10– 4 Pa, and the chemical etching was also carried out using buffered hydrogen fluoride (BHF) solution. The surface state of the GaN layer was analyzed by X-ray photoelectron spectroscopy (XPS) measurement. Results In the XPS measurements, O1s and Si2p XPS signals were detected from as-grown GaN layer surface. The thermal treatment was then carried out in order to remove these impurities, and the results on XPS measurements indicated the significant decrease of Ga–O bonds on the GaN layer surface. Moreover, from the TDS measurements, the signal of m/z = 70 corresponding to Ga (Figure 1(a)) and the signal of m/z = 32 corresponding to O2 (Figure 1(b)) indicated rapid increase at around 500 °C, which suggests that isolated Ga and O atoms were easily released from the GaN layer surface. On the other hand, the removal of Si compounds by the thermal treatment was quite difficult, because the thermally stable Si–N bonds which would be formed by nitrogen dangling bonds, were terminated with Si atoms during such thermal treatment. The chemical etching was very effective in order to remove the Si contamination, and after the BHF etching treatment the decrease of Si compounds on GaN layer surface was confirmed by the great decrease of Si2p/Ga3d XPS signal intensity ratio. After the chemical etching treatment, the GaN layer was then exposed in air atmosphere. Two kinds of methods were utilized for the air exposure; sample was put in open air (case 1), and also was put at the inside of closed narrow space (case 2) limiting the concentrations of impurities reaching onto the sample surface. Figure 2 shows the Si2p/Ga3d XPS signal intensity ratio depending on an elapsed time in air exposure. At the case 1, the rapid increase of the intensity ratio was observed within initial 120 minutes, and then it indicated the gradual increase. On the other hand, at the case 2, the intensity ratios were always lower than those at the case 1. Therefore, the storage of the sample in air atmosphere is the important factor for Si contamination. It seems that the grade of O contamination depends greatly on temperature and humidity in air atmosphere. The results in GaN layer grown by metal-organic chemical vapor deposition method will be also presented. Acknowledgement A part of this work was conducted at Advanced Characterization Nanotechnology Platform of the University of Tokyo, supported by "Nanotechnology Platform" of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. Figure 1

Surface Contamination with Si and O Impurities for GaN Single-Crystalline Layers Grown by Ultra-High-Vacuum Sputter Epitaxy

In this study, we demonstrated a GaN surface contamination and cleaning technique focused on O- and Si-based compounds generated by an exposure to the atmosphere. The GaN single-crystalline layers were grown on sapphire (0001) substrates using the ultra-high-vacuum radio-frequency sputter epitaxy technique. During X-ray photoelectron spectroscopy (XPS) measurements, O1s and Si2p XPS signals were detected on the as-grown GaN layer surface. Thermal treatment was performed in order to remove these impurities, and the results of the XPS measurements indicated a significant decrease in the O–Ga bonds on the GaN layer surface. Following the buffered hydrogen fluoride etching treatment, a decrease in the Si compounds on the GaN layer surface was confirmed by a significant decrease in the Si2p/Ga3d XPS signal intensity ratio.

Structural Characterizations of Aluminosilicates in Two Types of Fly Ash Samples from Shanxi Province, North China

In order to determine the structural characterization of aluminosilicates in two types of fly ashes, two samples from Shanxi Province, China were selected for study. One was from a pulverized coal boiler (FA-1), and the other from a circulating fluidized bed boiler (FA-2). FA-1 had a much higher content of silicon dioxide (SiO2) (70.30%) than FA-2(42.19%), but aluminum oxide (Al2O3) was higher in FA-2 (25.41%) than in FA-1 (17.04%). The characterizations were investigated using various methods including X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), magic angle spinning nuclear magnetic resonance (MAS–NMR) spectrometry, and X-ray photoelectron spectroscopy (XPS). The XRD analysis showed that FA-1 contained aluminosilicate glass, quartz and mullite, while FA-2 contained significant amounts of amorphous aluminosilicate, quartz and gypsum. The FTIR results showed an increased substitution of Al3+ for Si4+ as the band of asymmetric stretching vibrations Si–O(Si) (1100 cm−1) moved to 1090 cm−1 for FA-2, much lower than for FA-1(1097 cm−1). Moreover, the sharpness of the bands in the 1250–1000 cm−1 region for FA-2 indicates that the silicate structure of FA-2 was more ordered than for FA-1. It can be understood from the 29Si MAS–NMR results that Q4(mAl) (Q4 are connected via 4 bridging O atoms to mAl) is the main structural type in FA-1 and FA-2, and that FA-2 contains more Al, which substitutes for Si in the Q4 structure. 27Al MAS–NMR demonstrated that a combination of tetrahedral, pentahedral, and octahedral Al existed in FA-1 and FA-2. The Si 2p XPS spectra suggested that there were three forms of Si, including bridging Si (Si–O2), non–bridging Si (Si–O), and SiO2 gel. The content of Si–O2 for FA-1 was 37.48% higher than Si–O (28.57%), while the content of Si–O2 was 30.21% lower than Si–O (40.15%) for FA-2. The Al 2p XPS spectra showed that octahedral Al was the dominant form for FA-1 with a content of 40.25%, while the main phase was tetrahedral Al for FA-2 with a proportion of 37.36%, which corresponds well with the 27Al MAS–NMR results.

Improving the performance of Li-ion battery carbon anodes by in-situ immobilization of SiOx nanoparticles

A 30% improvement of the capacity of a lithium ion battery was demonstrated by introducing a C/SiOx nanocomposite electrode having a SiOx nanoparticle loading of 15 wt.%. The nanocomposite was tailored from tetraethyl orthosilicate (TEOS) and 3-aminophenol which simultaneously underwent hydrolysis-condensation and polymerization, respectively, to produce a C/SiO2 intermediate when subjected to microwave irradiation. SiO2 was present as nanoparticles on the carbon surface, which allowed for facile reduction. Under a mild reducing agent, concurrent carbonization of the 3-aminophenol polymer and the reduction of SiO2 nanoparticles were performed. The value of x in the synthesized C/SiOx was 1.24 according to the binding energy from the Si 2p x-ray photoelectron spectroscopy spectrum. The synthesized C/SiOx nanocomposite delivered a reversible capacity of 383 mA h/g as a lithium battery anode—a 30% improvement on the carbon-only electrode. Charge-discharge cycling shows 84% capacity retention after 100 cycles.

Annealing-induced evolution in interface stability and electrical performance of sputtering-driven rare-earth-based gate oxides

Annealing temperature-dependent ultrathin Dy2O3 gate dielectric films, grown on Si substrates by reactive sputtering, were characterized in terms of structural, optical and electrical properties using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), UV–Vis transmission spectroscopy and electrical measurements of Dy2O3/Si gate stack. Additionally, the thickness of the interfacial SiO2 layer during the deposition and annealing process has been calculated using the Si 2p XPS spectra to exclude its influence on the electrical parameter of Dy2O3 films. XPS analyses for all the samples have shown the abrupt growth of the Dy-silicate for 700°C-annealed sample, which is identified as the primary reason for the dramatic reduction in its electrical performance. In addition, optimized Dy2O3 sample with annealed temperature at 600 °C exhibits the lowest equivalent oxide thickness of 1.6 nm, the highest dielectric constant 16.8, the lower leakage current density 4.45 × 10−8 A/cm2 and the lower frequency dispersion of 6.21%. Based on the experimental analysis, the optimized annealing temperature has been obtained to achieve Dy2O3 gate dielectric thin films as deposition of high-k with high-quality on Si substrates.

Effects of AC and DC corona on the surface properties of silicone rubber: Characterization by contact angle measurements and XPS high resolution scan

This study utilized a multi-needle corona electrode system to investigate the influence of AC and DC coronas on the surface properties of high temperature vulcanized (HTV) silicone rubber. Contact angle measurements and X-ray photoelectron spectroscopy (XPS) analysis were performed to characterize the chemical structure and hydrophobicity changes in state of the silicone rubber surface after corona exposure. The results indicated that the effects of AC corona were greater than that of DC corona, and the effects of negative DC corona were slightly greater than that of positive DC corona. XPS results showed that the C elemental content on the silicone rubber surface decreased, whereas the O elemental content increased. High-resolution scan on Si 2p XPS spectra proved that surface oxidation occurred during corona exposure and caused the high binding energies of Si atoms and silica-like layer. High-resolution C 1s XPS spectra showed that corona exposure destroyed the Si-CH3 groups on the surface. Some C-O and C=O bonds appeared following the corona exposure. High-resolution O 1s XPS spectra confirmed the formation of Si-OH groups and chemically absorbed water, which was ignored in the past research. Chemically absorbed water was detected as one of the essential factors that caused the loss of hydrophobicity of silicone rubber after corona exposure, together with Si-OH groups and silica-like layer.

Investigation of nanoparticulate silicon as printed layers using scanning electron microscopy, transmission electron microscopy, X-ray absorption spectroscopy and X-ray photoelectron spectroscopy.

The presence of native oxide on the surface of silicon nanoparticles is known to inhibit charge transport on the surfaces. Scanning electron microscopy (SEM) studies reveal that the particles in the printed silicon network have a wide range of sizes and shapes. High-resolution transmission electron microscopy reveals that the particle surfaces have mainly the (111)- and (100)-oriented planes which stabilizes against further oxidation of the particles. X-ray absorption spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS) measurements at the O 1s-edge have been utilized to study the oxidation and local atomic structure of printed layers of silicon nanoparticles which were milled for different times. XANES results reveal the presence of the +4 (SiO2) oxidation state which tends towards the +2 (SiO) state for higher milling times. Si 2p XPS results indicate that the surfaces of the silicon nanoparticles in the printed layers are only partially oxidized and that all three sub-oxide, +1 (Si2O), +2 (SiO) and +3 (Si2O3), states are present. The analysis of the change in the sub-oxide peaks of the silicon nanoparticles shows the dominance of the +4 state only for lower milling times.

Electronic states and electrical conductivity of the Si(111) native oxide surface adsorbed with electron donor tetrakis(dimethylamino)ethylene

Electronic states and electrical conductivity of the native oxide Si(111) surface adsorbed with an electron donor tetrakis(dimethylamino)ethylene (TDAE) were investigated using ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy (XPS), and independently driven four-probe conductivity measurements. The formation of positively charged TDAE species is confirmed by the downward shift of the vacuum level by 1.45 eV, the absence of HOMO level in the valence band, and observation of the positively charged state in the N 1s XPS spectra. Si 2p XPS spectra and four-probe conductivity measurements revealed that TDAE adsorption induces an increase in downward band bending and a reduction in electrical resistance of the surface, respectively. The sheet conductivity and the electron density of the surface are 1.1 μS/◻ and 4.6 × 109 cm−2, respectively, after TDAE adsorption, and they are as high as 350% of the original surface. These results demonstrate that the electron density of the semiconductor surface is successfully controlled by the electron donor molecule TDAE.

Crystal growth, experimental and theoretical studies on the electronic structure of CNGS and Nd:CNGS

Ca3NbGa3Si2O14 (CNGS) and Nd:Ca3NbGa3Si2O14 (Nd:CNGS) single crystals were grown using the Czochralski technique, and the dielectric, elastic and piezoelectric properties of the Nd:CNGS crystals were evaluated at room temperature by the impedance method. It is proved that the Nd:CNGS crystals have larger dielectric constants, piezoelectric constants and elastic compliance as compared with the CNGS crystals. The electronic structure and chemical composition of the crystals were analyzed using X-ray photoelectron spectroscopy (XPS). Constituent element representative core levels and auger lines in this complex langasite crystal have been measured. The Ca 2p, Ca 3p, Ga 3p, Ga 3d, Si 2p XPS spectra show a shift toward higher binding energies while the O 1s level moves in the lower binding energy direction with increasing Nd content and can be interpreted as a doping induced change in the chemical potential. Furthermore, it was confirmed by the X-ray photoelectron spectra that Ca–O, Ga–O, and Si–O bonds in Nd:CNGS have stronger ionicity compared with the CNGS crystal. On the basis of the density functional theory (DFT), first-principles calculations have been employed to study the electronic structure of CNGS successfully. The calculated results are essentially consistent with the corresponding experimental results, which indicate that the contributions of the Nb–O groups are dominant in the CNGS crystal for producing optical properties.

Surface Cleaning of SiGe(100) and Passivation of Ge(100) with Aqeuous Ammonium Sulfide

As scaling of microelectronic devices continues, germanium and silicon-germanium are promising materials for integration into silicon-based technology. Germanium and silicon-germanium based field-effect transistors can reduce leakage current and consume less power by means of improved carrier mobility and a narrower band gap, as opposed to traditional electronics. However, silicon-germanium surfaces are more challenging to work with because the topmost surface layer is comprised of germanium oxides that complicate cleaning and passivation processes. Here we seek to obtain a smooth, oxide free SiGe surface and hope to garner an understanding of the best conditions to effectively remove surface oxides. Additionally, we hope to further our understanding of aqueous ammonium sulfide passivation processes on Ge surfaces that will prevent re-oxidation of the surface for applications towards modern field-effect transistors (FETs). The first portion of this work focuses on the removal of oxides from the SiGe surface with 50 and 75% Ge molar ratios using a variety of aqueous processes. These processes include SC-1, HCl, HF, and HCl/HF mixtures. The SiGe surface was characterized using X-ray photoelectron Spectroscopy (XPS) after each chemical treatment. Film thicknesses were measured using spectroscopic ellipsometry. Immersion in HCl showed similar results to as shipped samples and was ineffective in removing surface oxides. Aqueous HF, however, removed both surface oxides and carbon contamination. SC-1 treatments selectively reduced the Ge in the SiGe film and left the surface enriched in Si, which oxidized as confirmed by XPS. If the Ge could be completely removed from the top-most layer, the SiO2 layer that forms could be used to passivate the SiGe surface and avoid problematic Ge oxides. Ellipsometry results showed that SC-1 solutions (NH4OH:H2O2:H2O, 1:1:100 v/v) etched 1 nm of the SiGe film, which was then oxidized. Ge 2p to Si 2p XPS peak ratios confirmed that increasing concentrations of SC-1 depleted the Ge content on the surface from 0.8 to 0.4, confirming the enrichment of the surface in Si. Ge to Si peak area ratios as a function of the SC-1 dilution factor showed a non-linear trend for SiGe 50% surfaces. Passivation of Ge with aqueous (NH4)2S was also studied. Because Ge oxides are unstable and water soluble, it is advantageous to remove them and deposit a sulfur layer to prevent further oxidation when exposed to air. Surface passivation was studied as a function of deposition time, solution concentration and the addition of H2O2. Passivation of the surface was ineffective at times below 20 min. Changing the concentration of (NH4)2S also had no noticeable effect on the surface based on XPS. Furthermore, at high ammonium sulfide concentrations the addition of H2O2 did not affect the passivation process. The addition of H2O2 to dilute (NH4)2S showed poor passivation due to oxidation of the surface by H2O2.

Influence of MgO precursors on mechanically activated forsterite synthesis

Brucite-fumed silica and hydromagnesite-fumed silica mixtures were used to investigate the influence of MgO precursors on mechanically activated forsterite synthesis. The changes in morphology, chemical bond and phase composition of the ground and calcined mixtures were examined with scanning electron microscopy (SEM), Si 2p X-ray photoelectron spectroscopy (XPS) and 29Si magic angle spinning nuclear magnetic resonance (MAS-NMR), and X-ray diffraction (XRD), respectively. The XPS and MAS-NMR analyses show that high-energy milling generates more Mg–O–Si chemical bonds in the brucite-fumed silica mixture than in the hydromagnesite-fumed silica sample. This is because brucite has a higher concentration of Mg–OH bonds than hydromagnesite. However, single-phase forsterite forms at a higher temperature of 1000°C in the milled brucite-fumed silica mixture than that of 800°C in the ground hydromagnesite-fumed silica sample after the same grinding. The different forsterite completion temperature is probably due to the longer Mg2+ and Si4+ diffusion distance of over 500nm in the former milled mixture than that of less than 300nm in the latter ground sample.

Quantitative analysis of chemical interaction and doping of the Si(111) native oxide surface with tetrafluorotetracyanoquinodimethane

The charge-transfer states and the carrier concentration of the native oxide Si(111) surface adsorbed with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) were investigated by X-ray photoelectron spectroscopy (XPS) and independently driven four-probe electrical conductivity measurements. The XPS results show that F4-TCNQ molecules are involved in charge transfer with the SiO2/Si(111) surface. The Si 2p XPS spectra and the surface photovoltage shift provide the evidences of (i) change in the oxidation states at the SiO2-Si(111) interface region and (ii) formation of a p-type space charge layer (SCL) with a hole concentration of 1.7 × 1010 cm−2, respectively. The four-probe I–V measurements also support the formation of the p-type SCL, and the estimated hole concentration of 2.0 × 1010 cm−2 agrees well with the XPS results. The estimated SCL hole concentrations were much smaller than the excess charge density in the F4-TCNQ layer, of the order of 1013 cm−2, suggesting that most of charges were localized as the oxidation states at the SiO2-Si(111) interface region. The present quantitative methods ensure precise determination of the doping concentration near the surface region.

Surface Modification of Cured Cement Pastes by Silane Coupling Agents

X-ray photoelectron spectroscopy (XPS) and static contact angle measurements were used to study the interaction between silane coupling agents and cured cement paste. Three different silane coupling agents were investigated: aminopropyltriethoxy silane (APTES), 3-glycidyloxypropyltrimethoxy silane (GPTMS), and methoxy-terminated polydimethxyl siloxane (PDMS). These silanes have different end groups, so the change in surface energy after undergoing a successful reaction between the silane and hydroxyls on the surface of the cement paste was demonstrated by a change in contact angle. Relative to untreated samples, APTES samples decreased the contact angle, PDMS samples increased the contact angle, and GPTMS did not show a significant change in contact angle. Samples with a water-to-cement ratio (w/c) of 0.5 showed a larger change in contact angle than 0.4 w/c ratio samples, because of a greater number of hydroxyl groups at the surface. Deconvolution of the O 1s and Si 2p XPS peaks were performed to determine contributions from bridging and nonbridging atoms. An increase in bridging silicon and oxygen atoms relative to untreated samples indicated successful silane condensation and that a covalent bond was formed between the cement paste and silanes.

Well-isolated L1 FePt–SiNx–C nanocomposite films with large coercivity and small grain size

FePt–SiNx–C films on TiN/CrRu/glass substrate with large coercivity, (001) texture, and small isolated grains were obtained by co-sputtering FePt, Si3N4, and C targets at 380 °C. It was found that when C was doped into the FePt–SiNx films, the out-of-plane coercivity increased while the small in-plane coercivity remained unchanged. Grain size decreased and grain size distribution became more uniform with increasing the C doping concentration. The x-ray photoelectron spectroscopy (XPS) depth profile showed a uniform depth distribution of Si in the FePt layer. The Si2p XPS spectrum implied the existence of Fe–Si bonds, indicating that SiNx was located at the FePt grain boundaries and was stable against diffusion to the surface, thus favoring grain isolation. Well-isolated FePt (001) granular films with coercivity higher than 21.5 kOe and an average grain size of 5.6 nm were obtained by doping 40 vol. % of SiNx and 20 vol. % of C.

X-ray photoelectron spectroscopic studies of black silicon for solar cell

The black silicon has been produced by plasma immersion ion implantation (PIII) process. The microstructure and optical reflectance are characterized by field emission scanning electron microscope and spectrophotometer. Results show that the black silicon appears porous or needle-like microstructure with the average reflectance of 4.87% and 2.12%, respectively. The surface state is investigated by X-ray photoelectron spectroscopy (XPS) technique. The surface of the black silicon is composed of silicon, carbon, oxygen and fluorine element. The formation of Si x O y F z in the surface of black silicon can be proved clearly by the O 1s, F 1s and Si 2p XPS spectra. The formation mechanism of the black silicon produced by PIII process can be obtained from XPS results. The porous or needle-like structure of the black silicon will be formed under the competition of SF x + ( x ≤ 5) and F + ions etching effect, Si x O y F z passivation and ion bombardment.

High resolution X-ray Photoelectron Spectroscopy (XPS) study of K2O–SiO2 glasses: Evidence for three types of O and at least two types of Si

High resolution O 1s, K 2p and Si 2p XPS Spectra were collected for a series of potassium silicate glasses ranging in composition from 10mol% to 35mol% K2O. The mole fraction of bridging oxygen (BO) has been accurately evaluated from the O 1s spectra. BO mole fractions of K-silicate glasses were calculated from Q-species distributions previously reported by 29Si MAS NMR data. The mole fractions of BO are identical for the two techniques (within experimental error) in glasses containing 13mol% to 25mol% K2O but in the compositional range between 25mol% and 35mol% BO mole fractions obtained by XPS are slightly greater than values derived from NMR data. The slight discrepancies between the two techniques at higher K2O content have not been resolved. The experimental data between 13mol% and 25mol% K2O indicate the presence of a third type of oxygen, O2−, in these glasses. A thermodynamic analysis indicates O2− is present at a few mol% in the glasses of low K2O content, but increases monotonically with increased K2O content.The O 1s XPS line widths for the BO peaks are highly variable. The variation in line widths may result from two types of BO contributing to the BO peak. As in the Na2O–SiO2 glass system, one type probably bridges two Si atoms (SiOSi) and the second type is O bonded to two Si atoms and one K atom.The Si 2p XPS spectra are distinctly non-symmetric, with low binding energy shoulders commonly present on the major peak, suggesting two contributions to the Si 2p signal. There is a strong correlation of Si 2p XPS peak and shoulder intensities with the abundances of the Q4 and Q3 species in glasses of the same composition suggesting that, with additional resolution, XPS may be capable of resolving individual Q-species in this system.

Mechanism of lithium storage in Si–O–C composite anodes

A Si–O–C composite material is prepared by pyrolyzing a copolymer of phenyl-substituted polysiloxane and divinylbenzene at 800 °C under a hydrogen atmosphere. The material has a high delithiation capacity about 965.3 mA h g −1 in the first cycle and retains 660 mA h g −1 after 40 cycles at 50 mA g −1. The differential capacity curves of the anode show that there are several reduction peaks between 0.2 and 0.6 V existing all the time during repeated cycles. By comparing 29Si nuclear magnetic resonance ( 29Si MAS NMR), Si (2p) X-ray photoelectron spectroscopy (XPS) of the anode in the original, fully lithiated, and fully delithiated state, the reduction peaks are related to lithium reversible insertion into SiO 2C 2, SiO 3C, and SiO 4 units, respectively. The corresponding 29Si MAS NMR resonances shift to high field and their binding energies of the Si (2p) XPS peak increase in the fully lithiated state, and then both turn to the opposite direction in the fully delithiated state. The SiO 4 units decrease during repeated cycles. The remaining ones can reversibly transform to Li–silicate (Li 2SiO 3) when lithium is inserted, while the lost ones irreversibly transform to Li–silicate (Li 4SiO 4). However, the SiOC 3 units of the material are totally irreversible with lithium because they nearly disappear in the first discharge process, and lead to the formation SiC 4 units.

XANES and XPS investigations of (TiO2)x(SiO2)1−x: the contribution of final-state relaxation to shifts in absorption and binding energies

The (TiO2)x(SiO2)1−x system (0 ≤ x ≤ 0.33) was synthesized by the sol–gel method and investigated by X-ray absorption near-edge spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS). The use of both hard (Ti K-edge) and soft (Ti L-edge) X-rays provides a useful way to monitor changes in the bulk and surface, respectively, of these amorphous materials. The average CN of both bulk-Ti and surface-Ti increases with greater x in the chemical formula, due to the larger ionic radius of Ti. Comparison of Ti K- and L-edge spectra of annealed samples revealed that Ti atoms at the surface have a higher average CN than in the bulk, likely due to the presence of surface hydroxide and water groups that can coordinate to the Ti centres. The O K-edge, Ti L-edge, and Si L-edge XANES absorption energies showed little to no change with Ti content, while the O 1s, Ti 2p, and Si 2p XPS BEs were found to decrease with increasing Ti content due to nearest-neighbour and next-nearest-neighbour effects, which lead to increased final-state relaxation. The degree of final-state relaxation is more significant than previously believed for these amorphous powders.

Immediate Product after Exposing Si(111)-7×7 Surface to O2 at 300 K

Using real-time O 1s X-ray photoelectron spectroscopy together with Si 2p X-ray photoelectron spectroscopy, the oxygen bonding configurations of oxides shortly after exposing the Si(111)-7×7 surface to O2 at 300 K are revealed. It is found that the ins structure firstly forms where one oxygen atom sits in the backbond of the silicon adatom. It is confirmed that the chemisorbed molecular oxygen, the so-called paul oxygen, is the adsorbate on top of the ins structure. It is also clarified that the ad–ins structure and the ins–tri structure, where ad means an oxygen atom adsorbed onto top of the silicon adatom and tri means the interstitial oxygen atom, appear after a short time. The results implying the presence of mobile O2 on the surface were obtained.