Ti 2p XPS Research Articles

Advanced design of sol-gel derived multilayered cerium titanate films: structural, surface, photoelectrochemical and photocatalytic properties

Crystallization of Ce2Ti2O7 in the mixture of TiO2 and CeO2 was achieved by the three-layered coating of cerium − titanium mixed sol of the 1 : 1 metals molar ratio on a glass substrate at certain temperature regime in air as proven by XRD, SAED and Raman spectroscopy. Anatase and Ce2Ti2O7 crystallization with XRD undetectable crystallites brought to the increase of the specific surface area of the films. The formation of Ti–O–Ce bonds on the surface of the films was proven by the noticeable shift of Ti2p and O1s XPS maxima compared to TiO2 ones. The additional peaks in Ti2p, O1s and Ce3d XPS spectra belonging to the common bonds between the metals ions were identified for the first time. The bandgap energy and band-edge positions of Ce2Ti2O7 were firstly determined by photoelectrochemical measurements. The inactivity of the films in photocatalytic reductive and oxidative processes was caused by the unfavorable position of the valence band of Ce2Ti2O7 causing the recombination of the photo-formed electron−hole pair.

Factors Affecting ORR Activity of Nb-Added TiOx Catalyst Using Carbon Support for PEFC

1. IntroductionCarbon-supported platinum catalysts used for the cathode of present polymer electrolyte fuel cells (PEFCs) have some problems such as a large amount of platinum use and low durability under operation condition. Therefore, we have attempted to develop substitute of platinum based on group 4 and 5 transition metal oxides. We found that stable oxygen vacancies on the surface and lattice distortion of these metal oxides could act as active sites of oxygen reduction reaction (ORR)1). On the other hand, cup-stacked carbon nanotubes (CSCNTs) coated with TiO2 have been investigated as durable supports for a platinum-based catalysts2). We already revealed that Nb-added titanium oxide with lattice distortion showed some ORR activity1). Then, we thought that CSCNTs coated with Nb-added titanium oxide might show definite ORR activity. In this study, we prepared CSCNTs coated with Nb-added TiOx and evaluated their behavior to investigate the factors which affect the ORR activity.2. ExperimentalThe CSCNTs (GSI Creos) without amorphous carbon on the surface was added to 2-propanol and dispersed ultrasonically, then a desired amount of Ti isopropoxide and Nb ethoxide were added with stirring. A sufficient amount of water mixed with 2-propanol were added to proceed hydrolysis and stirred overnight. Suction filtration was performed to obtain a precursor. In this experiment, Nb was added into TiO2 with an atomic% of 10 against Ti, and a loading of oxide was adjusted to 30 wt% of total catalyst. The precursor was heat-treated under an Ar gas containing 4% hydrogen at desired temperature and time to obtain Nb-added TiOx catalysts, designated as Nb-added TiOx/CSCNTs.The Nb-added TiOx/CSCNT was supported on a glassy carbon rod to make a working electrode. Electrochemical measurements were carried out using a three-electrode cell at 30 ± 1 °C in 0.1 M H2SO4. Cyclic voltammetry was performed with 5 mV sec-1 in the potential range from 0.2 to 1.2 V in an oxygen and nitrogen atmosphere to obtain oxygen reduction current. ORR current based on oxides was obtained by subtracting the reduction current of carbon from the reduction current of the entire catalyst. The oxygen reduction current density, iORR, was normalized by the mass of the oxides.3. Results and discussionFigure 1 shows the dependence of iORR at 0.6 V of Nb-added TiOX/CSCNTs on heat treatment temperature. The results of Nb-added TiOx powders prepared without carbon were also plotted. Because the electro-conductivities of the Nb-added TiOx powders were very low, Ketjenblack was mixed as an electro-conductive material to evaluate the ORR activity. The current value of Nb-added TiOx/CSCNT is significantly improved compared to oxide powder. This is because the electron supply increased due to the deposition of oxides on the CSCNT. The highest ORR current density was observed at 800 oC.Figure 2 shows the SEM images of Nb-added TiOX/CSCNTs. Amorphous TiO2 covers with the surface of CSCNTs in the unheated catalyst. At 700 ° C and 800 ° C, the oxide particles of around 10 nanometers were supported with high dispersion. However, at 900 ° C, the particles aggregated to become larger.Figure 3 shows the Ti 2p XPS spectra of Nb-added TiOx/CSCNTs heat-treated at 600-1000 °C. Ti2p peak shifted to the lower binding energy from 600 ° C to 800 ° C and to the higher energy from 800 ° C to 1000 ° C. The proportion of low-valence state Ti3+ increased as the temperature increased from 600 to 800 ° C. The reason why the shift to the higher binding energy occurred above 800 ° C was that the oxide surface prepared at higher heat-treatment temperature was oxidized by exposure of the air.Figure 4 shows the relationship between ratio of Ti3+ / (Ti3+ + Ti4+) and ORR current density at 0.6 V. The ratio of Ti3+ was calculated from the Ti 2p XPS spectra. The iORR at 0.6 V increases as ratio of Ti3+ increases. The ratio of Ti3+ indicates the presence of oxygen vacancies on the surface of the oxide. Therefore, it is considered that the increase of oxygen vacancies on the oxide surface strongly affected the ORR activity.AcknowledgementThe authors wish to thank the supply of the CSCNT from GSI Creos and the support of the New Energy and Industrial Technology Development Organization (NEDO), JSPS grants-in-aid for scientific research, Suzuki Foundation, and Tonen General Sekiyu Research / Development Encouragement & Scholarship FoundationReferences1) A. Ishihara, et. al., Electrochim. Acta, 283,1779 (2018).2) F. Ando, et. al., Electrochim. Acta, 404, 232 (2010) Figure 1

Synergistic effect of Ni-Ag-rutile TiO2 ternary nanocomposite for efficient visible-light-driven photocatalytic activity.

P25 comprising of mixed anatase and rutile phases is known to be highly photocatalytically active compared to the individual phases. Using a facile wet chemical method, we demonstrate a ternary nanocomposite consisting of Ni and Ag nanoparticles, decorated on the surface of XTiO2 (X: P25, rutile (R)) as an efficient visible-light-driven photocatalyst. Contrary to the current perspective, RTiO2-based Ni–Ag–RTiO2 shows the highest activity with the H2 evolution rate of ∼86 μmol g−1 W−1 h−1@535 nm. Together with quantitative assessment of active Ni, Ag and XTiO2 in these ternary systems using high energy synchrotron X-ray diffraction, transmission electron microscopy coupled energy dispersive spectroscopy mapping evidences the metal to semiconductor contact via Ag. The robust photocatalytic activity is attributed to the improved visible light absorption, as noted by the observed band edge of ∼2.67 eV corroborating well with the occurrence of Ti3+ in Ti 2p XPS. The effective charge separation due to intimate contact between Ni and RTiO2via Ag is further evidenced by the plasmon loss peak in Ag 3d XPS. Moreover, density functional theory calculations revealed enhanced adsorption of H2 on Ti8O16 clusters when both Ag and Ni are simultaneously present, owing to the hybridization of the metal atoms with d orbitals of Ti and p orbitals of O leading to enhanced bonding characteristics, as substantiated by the density of states. Additionally, the variation in the electronegativity in Bader charge analysis indicates the possibility of hydrogen evolution at the Ni sites, in agreement with the experimental observations.

Enhanced photocatalytic performance of nanostructured TiO2 thin films through combined effects of polymer conjugation and Mo-doping

Mo-doped TiO2 [≤ 0.20 wt% Mo; ≤ 0.10 mol% (metal basis)] with conjugated polyvinyl alcohol (TiO2/C-PVA) composite thin films was prepared by sol–gel dip coating on polished fused SiO2 substrates, followed by annealing at 180 °C for 4 h. These conditions were sufficient for solid solubility, despite the unusually low annealing temperature. The annealed thin films consisted of homogeneously distributed individual and slightly agglomerated anatase grains in a continuous C-PVA matrix characterized by the carbon double bond formed upon conjugation. The films exhibited drying shrinkage cracks, which increased consistently in extent with increasing Mo-doping concentration, effectively increasing the number of exposed TiO2 particles. Mo addition enhanced anatase nucleation, recrystallization, and growth at lower doping concentrations (up to ≤ 0.10 wt%), thereby increasing crystallinity. However, increasing doping levels (> 0.10 wt%) appeared to exceed the solubility limit, resulting in supersaturation and significant lattice destabilization. Mo-doping also caused the Ti2p XPS peaks to shift to lower binding energies and the Mo3d peaks to shift to higher binding energies. These data are consistent with thermodynamically unstable Ti4+ → Ti3+ conversion and thermodynamically stable Mo5+ → Mo6+ conversion, which are interpreted in terms of intervalence charge transfer (IVCT), in which charge compensation is achieved through majority Ti4+ → Ti3+ reduction plus Mo5+ → Mo6+ oxidation. Ti3+ concentration also reflects a direct correlation with the Mo-doping concentration and resultant IVCT within the Mo solubility limit and a reverse effect upon supersaturation. There is a correlation with the Eg but this can be attributed to recrystallization rather than a semiconducting effect. No effect of midgap state formation from enhancement of the $$ {\text{V}}_{\text{O}}^{ \cdot \cdot } $$ concentration is expected because IVCT is a redox effect only and dissolution of Mo5+ or Mo6+ would generate Ti vacancies. The methylene blue dye degradation data exhibited the same trend but at a significant level (90.6% degradation), thus indicating that the mechanism dominating the photocatalytic performance is the recrystallization of the anatase and/or the modification of the semiconducting properties induced by Mo-doping, as indicated by the trends in band gap.

Characterization of Au/PbTi0.5Fe0.5O3/Si structure for possible multiferroic based non-volatile memory applications

Magnetoelectric multiferroic PbTi0.5Fe0.5O3 films are deposited on a ⟨100⟩ conducting p-Si substrate without any buffer layer by using pulsed laser deposition and characterized for possible non-volatile memory applications. Their crystalline structure and surface morphology were characterized by using x-ray diffraction and AFM techniques. HRTEM was employed to determine the film–substrate interface. The electronic structure of the film was investigated by XPS, and no signature of metal was found for all the elements. The chemical shift of the Ti 2p XPS peak is attributed to the replacement of Ti with Fe in the PbTiO3 matrix. Piezoelectric force microscopy (PFM) results indicate the 180° phase shift of ferroelectric polarization. The upward self-polarization phenomenon is also observed in the PFM study. Magnetic and magneto-electric coupling measurements were carried out to confirm the magnetic nature and electro-magnetic coupling characteristics. C–V measurements exhibit clock-wise hysteresis loops with a maximum memory window of 1.2 V and a sweep voltage of ±7 V. This study could influence the fabrication of silicon compatible multiple memory device structures.

Solvothermal-assisted synthesis of self-assembling TiO2 nanorods on large graphitic carbon nitride sheets with their anti-recombination in the photocatalytic removal of Cr(vi) and rhodamine B under visible light irradiation.

TiO2-based nanorods (TNRs) were self-assembled on large graphitic carbon nitride (g-C3N4) sheets via the solvothermal-assisted route. The results demonstrated that the effective anchoring of TNRs (a side length of ca. 200-300 nm) was highly dispersed on the surface of whole g-C3N4 sheets. The shift in the Ti 2p XPS core level spectrum indicated an increase in the net positive charge of the Ti ions, ensuring the formation of an interface between TNRs and g-C3N4. The charge transferred from g-C3N4 sheets to TNRs effectively prevented the recombination of excited charges, which is consistent with the significant quenching of PL. The extent of visible-light-sensitive photocatalytic (PC) activity was evaluated by the removal of potassium dichromate (Cr(vi)) or the degradation of rhodamine B (RhB). The photocatalytic removal of Cr(vi) using RhB was effectively improved. The synergistic effect between the removal of Cr(vi) and degradation of RhB was revealed by multiple utilization of TNRs/g-C3N4 for PC activity. The effective suppression of the recombination of photo-induced charges and the absorption of RhB was responsible for the enhancement in the PC activity. An alternate mechanism for enhanced visible-light photocatalytic activity was also considered.

Emergence of Oxygen Reduction Activity in Niobium-Doped Titanium Oxides As Non-Platinum Cathode for PEFCs

Development of non-platinum electrocatalysts for oxygen reduction reaction (ORR) is required for wide commercialization of polymer electrolyte fuel cells. We focused on titanium oxide-based electrocatalysts, because of their high chemical stability and much less expensive than platinum. We found that Ti-Nb complex oxide mixed with magneli phase titanium oxide (Ti4O7) had high ORR onset potential and superior durability [1]. However, the ORR current was small because of their large particle size. In this study, we have tried to prepare titanium oxide-based nano particles using multi-walled carbon nano-tubes (CNTs) as support via hydrolysis method. We examined the effect of heat-treatment condition such as temperature and time on the ORR activity. We prepared Nb doped titanium oxide [mass ratio of TiO2:Nb2O5= 8:2] supported CNTs with total oxide mass ratio of 20wt%. These catalysts were heat treated at 600-900 oC for 0-60 min under 4%H2/Ar atmosphere. The catalyst without heat-treatment had poor ORR activity. The heat-treatment under reductive atmosphere enhanced the ORR activity of the catalysts. Figure 1 shows the dependence of the ORR current at 0.6 and 0.7 V of the catalysts prepared at several temperatures for 10 min under 4%H2/Ar in 0.1M H2SO4 at 30 oC. The catalyst prepared at 800 oC showed highest ORR activity. The SEM observation indicated that the sizes of the oxide-based particles were around 20 nm for all catalysts with and without heat treatment. Therefore, the surface area of the oxide-base particles was almost the same. The dependence of the ORR activity was not responsible for the change of the surface area. The XRD patterns revealed that the catalyst without heat treatment was composed of anatase phase of TiO2, and the peaks due to the rutile TiO2 apparently appeared at around 700-800oC. In particular, the peaks due to Rutile TiO2 shifted at lower angular, suggesting that the niobium doped into the TiO2 phase. Thus, the Nb doping into rutile TiO2 could affect the ORR activity. Figure 2 shows the Ti 2p XPS spectra of these catalysts. As shown in Fig.2, the peak at 457.8 eV corresponding to Ti3+ (Ti2O3) as well as the peak at 459.2 eV corresponding to Ti4+ (TiO2) were observed. The peak due to Ti3+ increased from 600 to 800 oC, and decreased at 900oC. This behavior was well corresponded to the ORR activity. Therefore, we concluded that Ti3+ could act as active sites for the ORR. According to the XRD patterns, the Nb doping into rutile TiO2 proceeded with increasing the temperature from 700 to 800oC. The niobium doping generated the Ti3+ via electro-neutral principle. The formation of the Ti3+ in TiO2 rutile phase was considered to be essential for emergence of the ORR. [1] A. Ishihara et al., J. Electrochem. Soc, 163(7), F603 (2016). Figure 1

Thermal Treatment Effects in PbTiO3 Crystals Studied by XPS and Electric Conductivity Tests

The as-grown aged and thermally annealed at 720 K and 820 K PbTiO3 crystals were prepared. The ɛ′(T,f) and σAC(T,f) were measured at radio frequencies. Samples heated at 720 K shown resistive switching to metallic-type σAC(T). The resistivity switching was confirmed by RDC(T) measurement. The samples annealed at 820 K were rejuvenated, exhibited Curie-Weiss dependence above TC = 750 K and semiconductor conductivity. Annealing induced changes in shape of the Pb 4f, Ti 2p, O 1s, and VB XPS lines. We propose a model related to ionic migration toward FE domain walls and to vortices which provide conducting channels.

Role of lattice defects and crystallite morphology in the UV and visible-light-induced photo-catalytic properties of combustion-prepared TiO 2

The physico-chemical, photo-physical and micro-structural properties responsible for the strikingly different photocatalytic behavior of combustion-prepared TiO 2 (c.TiO 2) and Degussa P25 (d.TiO 2) samples are elucidated in this study. Electron microscopy and selected area electron diffraction micrographs revealed that the two samples exhibited different morphologies. The grains of c.TiO 2 were spherical and comprised of 5–6 nm size primary particle. On the other hand, d.TiO 2 consisted of large (0.5–3.0 μm) size and irregular shape aggregates having primary particles of 15–40 nm cross-sectional diameter. The ESR study revealed that the presence of certain defect states in c.TiO 2 helped in stabilization of O − and Ti 3+–OH type species during room-temperature UV-irradiation. No such paramagnetic species were however formed over d.TiO 2 under similar conditions. C1s and Ti 2p XPS spectra provide evidence for the presence of some lattice vacancies in c.TiO 2 and also for the bulk Ti 4+ → Ti 3+ conversion during its UV-irradiation. Compared to d.TiO 2, c.TiO 2 displayed considerably higher activity for discoloration of methyl orange but very poor activity for splitting of water, both under UV and visible light radiations. This is attributed to enhanced surface adsorption of dye molecules over c.TiO 2, because of its textural features and also the presence of photo-active ion-radicals. On the other hand, the poor activity of c.TiO 2 for water splitting is related to certain defect-induced inter-band charge trapping states in the close vicinity of valence and conduction bands of c.TiO 2, as revealed by thermoluminescence spectroscopy. Further, the dispersion of nanosize gold particles gave rise to augmented activity of both the catalysts, particularly for water splitting. This is explained by the promotional role of Au 0 or Au 0/TiO 2 interfacial sites in the adsorption and charge–adsorbate interaction processes.

Lepidocrocite-like structure of the TiO2 monolayer grown on Ag(100)

Titanium oxide ultrathin films were grown on Ag(100) by evaporation of titanium in an O(2) atmosphere. The growth of the oxide films was monitored by means of XPS. The Ti2p XPS spectra indicate the formation of films with a TiO(2) stoichiometry in the whole range of coverages studied here. The STM results show that titania films appear to grow as islands of uniform thickness up to the completion of the first layer. Up to the formation of one complete monolayer, a (5 × 1) LEED pattern is observed. This pattern can be interpreted as a coincidence mesh and the lattice parameters of the oxide layer are very close to those of TiO(2) films with a lepidocrocite-like structure. However, the STM images show a long-range coincidence between the periodicity of the oxide film and that of the substrate along the short side of the oxide unit cell revealing that this lattice parameter is not exactly equal to that of the substrate. Above the monolayer coverage, additional spots become visible in the LEED pattern which can be interpreted in terms of the unit cell of rutile (110). The structural determination was carried out for the monolayer of titania by means of XPD and LEED intensity analysis. The results of these investigations demonstrate that the titania monolayer has a lepidocrocite-like structure. The DFT calculations carried out for the titania monolayer show the higher stability of the lepidocrocite structure with respect to other structures derived from crystallographic planes of bulk TiO(2) phases. Moreover, these calculations allow us to determine the oxide-substrate interface energy as well as to clarify the effect of the strain on the stability of the oxide layer.

Superhydrophilicity and XPS study of boron-doped TiO 2

This study examines the superhydrophilicity and chemical state of boron-doped TiO 2 prepared by the ion implantation method and explores the effect of annealing on them. XRD measurements show that the implanted sample forms a polycrystalline structure of anatase with no trace of rutile. Their water-contact angles are significantly reduced upon irradiation with ultraviolet light. The Ti 2p XPS spectra of the oxide exhibit a shoulder peak at the lower binding energy side of the main peak, whereas no shoulder is observed in single-crystal and annealed TiO 2. This suggests that the titanium ions with lower valences are produced by boron doping and they disappear on subsequent annealing. The SIMS depth profile of boron in the as-implanted TiO 2 exhibits a peak at a depth of 15–20 nm, whereas this peak disappears upon annealing. The water-contact angles increased on annealing under ultraviolet light illumination. It is concluded that the improvement in the superhydrophilicity by boron doping is due to the reduction of titanium, and the deterioration of superhydrophilicity with the subsequent annealing is due to the oxidation of reduced titanium and the inward diffusion of boron.

Fabrication and structural characterization of TiO nanoparticle soft-landed on substrate by the magnetron sputtering-gas aggregation method

We have succeeded to fabricate the thin film mainly or entirely consisting of nano-crystallites TiO on a substrate at room temperature by using the magnetron sputtering combined with the gas aggregation method which has the capability to deposit grown small particles and/or clusters of the desired compound material on the substrate in soft-landed mode. The important experimental parameters to control the growth of TiO particles are identified as partial pressure of additional oxygen gas, growth-reaction distance Ltd, and LN2 cooling of growth chamber. The smallest averaged diameter of TiO nano-particles is 5.62 nm and size distribution being from 2 to 8 nm under 50 mm of Ltd. The compositional uniformity is confirmed by EDS and EELS. The chemical state of the film observed by Ti 2P XPS peak confirms the primarily growth of TiO and indicates the formation of minor content of amorphous Ti1-xOx and/or Ti1-xCx particularly at the surface of the film.

Polarized X-ray absorption spectroscopy and XPS of TiS3: S K- and Ti L-edge XANES and S and Ti 2p XPS

Sulfur and Ti 2p XPS and polarized S K- and L2,3- and Ti L2,3-edge XANES spectra have been obtained from oriented ribbon-like crystals of TiS3 grown by vapor transport. The S 2p XPS spectrum for (001) crystal faces has line widths of 0.53eV and is completely accounted for by partially overlapped 2p3/2/2p1/2 doublets for sulfide (S2−) and disulfide (S22-) species, which are separate and independent entities in TiS3. Evidence of unsaturated surface states is lacking, consistent with a surface monolayer for the (001) growth face of disulfide atoms oriented with their charge-neutral sides outward. The S K-edge XANES spectra show pronounced anisotropy in the (001) plane of TiS3 crystals, associated with the photoelectron transition channel S 1s→3pxσu∗ with the electric vector (E) parallel the a-axis (and the S–S bond of the disulfide group), and transitions to unoccupied antibonding orbitals of S–Ti bonds with E parallel to the b-axis (the direction of the well-known quasi-one-dimensional character of TiS3). The XPS and ultrasoft and soft X-ray region XANES spectra confirm the surface and near-surface structural integrity of TiS3.

Elastic electron backscattering from Ti: grain size effect

AbstractMeasurements of elastic electron backscattering probabilities may provide the electron inelastic mean free paths (IMFP). This technique is known as elastic peak electron spectroscopy (EPES). The IMFPs in Ti can be determined from optical data by Tanuma et al., Gries or the TPP‐2M predictive formulae. Studies on Si and Ni show a weak influence of surface roughness, but a stronger influence of atomic composition, density, texture, average grain size and surface excitations on the IMFPs. In the present work, the elastic electron backscattering probability and IMFPs are determined for Ti exposed to sputtering and annealing. The atomic composition of Ti is determined by XPS and texture and grain size is determined by x‐ray diffraction (XRD). Ti samples exhibit no texture and grain size from 1 µm to 100 µm. For annealed samples the titanium hydride phase can be observed from the binding energy shift of Ti 2p XPS spectra. Scatter in the resulting IMFPs due to density and composition change (O and C contamination, and H from vacuum background) is negligible in comparison to scatter due to the grain size and standard used (Al and Cu). The IMFPs in Ti of grain size 1–10 µm are smaller than IMFPs in Ti of grain size 100 µm. These differences are explained by effects not accounted for in the calculations, i.e. the inelastic losses on the grain boundaries which are more pronounced in Ti of small grain size, and surface excitations which differ for Ti, Al and Cu. Copyright © 2004 John Wiley & Sons, Ltd.

Alteration of Ti 2p XPS spectrum for titanium oxide by low‐energy Ar ion bombardment

AbstractAlteration of Ti 2p XPS spectra for TiO2 single crystal was measured during Ar ion sputtering. The acceleration voltage of Ar ion bombardment ranged from 10 V to 2 kV.Components of Ti2+ and Ti3+ as reduced states have appeared, in addition to the Ti4+ state, after ion bombardment at 2 kV. However, although a small amount of Ti3+ has been observed in the case of 10 V bombardment, the Ti2+ component has not appeared. The intensities of the reduced states (Ti2+ and/or Ti3+) that have appeared at each acceleration voltage reach constant values after a long sputtering time. This saturation shows that the surface reaches an equilibrium state between the sputtered atoms and implanted ions. Moreover, the intensities of the reduced states increase with increasing accelerating voltage of the primary ions. The alteration by 10 V ion bombardment suggests that there is a critical energy for reduction to the Ti2+ state. Copyright © 2002 John Wiley & Sons, Ltd.

Alternation of Ti 2p XPS Spectrum for TiO2 by Ar Ion Bombardment

Angle resolved XPS measurements were performed for a reduced TiO2 single crystal after Ar ion sputtering with 500 V in order to examine the depth profile of the reduced states. Comparing this angle resolved XPS measurement with the calculation, the component of Ti2+ has a gaussian like depth distribution. The component of Ti3+ is a localized near surface and smoothly distributed inner layer. Ar ion bombardment with low angle incidence was performed in order to decrease the thickness of the reduced layer. The intensities of the reduced states decreased with lowering incident angle of Ar ion. Moreover, ion bombardment with the low angle incidence has revealed that most of the reduced states are decreased and the intensities of the undamaged Ti4+ components are increased. These results prove that suitable conditions for the Ar ion sputtering will give a correct depth profile of the chemical states for the compounds which are altered by the ion bombardment.

XPS and ionic conductivity studies on Li 2O–Al 2O 3–(TiO 2 or GeO 2)–P 2O 5 glass–ceramics

Lithium ion conducting glass–ceramics composed of the crystalline conducting phase LiM 2(PO 4) 3 (M=Ti and Ge) in which the M 4+ ions are partially substituted by Al 3+ ions (Li-analogue of NASICON) have been synthesized by heat-treatment of Li 2O–Al 2O 3–MO 2–P 2O 5 (M=Ti and Ge) glasses. The as-prepared and annealed glasses and glass–ceramics have been characterized by XRD, DSC, XPS and conductivity techniques. The glass transition temperature, T g of the annealed glasses was found to be 601°C and 474°C for the M=Ti and Ge glass systems whereas the crystallization temperature, T c of the annealed glasses are 644°C and 578°C respectively. XPS studies show that the O 1s spectra for all the glasses and glass–ceramics could be deconvoluted into two peaks corresponding to the non-bridging (NBO) and bridging oxygen (BO) atoms. The binding energies (BE) of Li, Ti, Ge, Al and P have also been listed. In the Li 2O–Al 2O 3–TiO 2–P 2O 5 system, the deconvoluted Ti 2p XPS spectra indicate the existence of two oxidation states of titanium, 3+ and 4+. The Ti 2p and Ge 3d core levels are characterized by high BEs, suggesting that Ti 4+–O and Ge 4+–O bonds are highly ionic in character. The glass–ceramics show fast ion conduction ( σ 303 K=6.53×10 −4 (M=Ti) and 3.99×10 −4 S cm −1 (M=Ge)) and low E a value (0.31 eV). These σ values are slightly higher than the corresponding crystalline Li 1+ x M 2− x Al x P 3O 12 (M=Ti and Ge) phases and four to five orders of magnitude higher than the respective glassy phases. Plausible explanation for the enhancement of σ in glass–ceramics is given. It is suggested that the M=Ge glass–ceramics can be used as a solid electrolyte in the all-solid state Li-ion rechargeable battery.

Removal of inelastic scattering part from Ti2p XPS spectrum of TiO2 by deconvolution method using O1s as response function

Abstract Ti2p and O1s XPS spectra of a clean surface of single crystal TiO 2 fractured in situ were taken to study the removal of the inelastic scattering part from the Ti2p spectrum. The features of inelastic scattering peaks in EELS were more influenced by surface than O1s XPS. It indicates that O1s XPS is proper as the response function to deconvolute a Ti2p spectrum. FWHM of the non-energy loss peak of Ti2p 3/2 is smaller than that of O1s. When the raw O1s spectrum is used as the response function, the deconvoluted spectrum has negative intensity values in some regions and beat waves. The replacement of the non-energy loss peak of O1s with narrower Gaussian peak takes off the beat waves. Peak separation of the deconvoluted spectrum reveals that it has six peaks. Two of them are main peaks of Ti2p 3/2 and 2p 1/2 . The others are classified into two kinds of satellite peaks, whose energy separation from the main peaks are 3 and 13 eV. Although the latter satellites have been discussed by many authors, the former satellites are first reported here.

A synchrotron XPS study of the vanadia–titania system as a model for monolayer oxide catalysts

Abstract The deposition of vanadium metal onto stoichiometric TiO 2 (110) has been studied with photoelectron spectroscopy from low to high coverages of vanadium. A synchrotron source was employed in XPS experiments for the study of submonolayer coverages of vanadium in order to determine the oxidation state of the vanadia species formed at submonolayer coverages. The exposure of the titania surface to vanadium metal results in charge-transfer from vanadium to titania at the interface. At low doses of the metal vigorous interaction between the metal and titania surface yields reduction of the Ti 4+ species to Ti 3+ at the interface, as evidenced by both changes in the lineshape of the Ti 2p XPS spectra and Ti LIII-edge spectra. Concurrent with this surface reduction vanadium metal is oxidized. At higher vanadium doses the vanadium 2p binding energy indicates the formation of metallic vanadium. When metallic vanadium deposition is followed by exposure of the surface to oxygen, only one vanadium species remains on the surface, the binding energy of which corresponds to that of the oxide present initially at low doses of vanadium metal. By comparison of the V 2p binding energies to those of bulk oxides, it appears that the oxidation state of the vanadium in the oxide species is +3, suggesting the formation of V 2 O 3 on the surface. Vanadium LIII-edge data also suggest that V 2 O 5 is not formed by the oxidation of predosed vanadium metal.

An NEXAFS investigation of the reduction and reoxidation of TiO 2(001)

The near-edge X-ray absorption fine structure (NEXAFS) technique was applied to characterize the oxidation states of titanium cations on TiO 2(001) surfaces reduced by argon-ion bombardment and reoxidized by thermal treatment. Although many characterization studies of reduced TiO 2 have been performed, none of these has applied both surface-sensitive (electron yield) and bulk-sensitive (fluorescence yield) NEXAFS to characterize reduced TiO 2(001) single-crystal surfaces. The fluorescence yield NEXAFS of polycrystalline samples of the suboxides TiO and Ti 2O 3 were used as standards to fingerprint reduced cations on the TiO 2(001) surface. NEXAFS has allowed us to estimate the concentration of oxygen and titanium in the near-surface region of reduced and reoxidized samples. The results of this study demonstrate that oxygen is preferentially removed during ion bombardment, that the depth of the altered layer is comparable to the ion penetration depth, and that the electronic environment of cations in the altered layer is comparable to that of cations in titanium suboxides. The extents of reduction calculated from NEXAFS results for reduced and reoxidized surfaces as a function of annealing temperature compare favorably with those previously determined by analysis of Ti 2p XPS data.