Heat Treatment In Oxygen Research Articles

Effects of thermal treatment on the electrical behavior of titanium dioxide thin-films

AbstractElectrochemical biosensors made of titanium dioxide have generated significant interest due to their high sensitivity and selectivity for the detection of a variety of diseases. This study focuses on the impact of thermal treatment in an oxygen environment on the electrical properties of titanium dioxide thin films deposited on silicon substrates using pulsed laser deposition; the films were subjected to temperatures of $$\varvec{100\,\,^{\circ }C}$$ 100 ∘ C , $$\varvec{400\,\,^{\circ }C}$$ 400 ∘ C , and $$\varvec{600\,\,^{\circ }C}$$ 600 ∘ C . The primary objective was to explore how thermal processing influences the electrical characteristics of the thin films, with the goal of enhancing their capacitance and thereby improving the performance of sensors developed by functionalizing these films; X-ray photoelectron spectroscopy revealed the presence of Ti$$^{4+}$$ 4 + , Ti$$^{3+}$$ 3 + and TiO$$_x$$ x species in the untreated thin film and in the heat-treated films, with an increase in TiO$$_x$$ x species observed after oxygen heat treatment. Atomic force microscopy demonstrated a decrease in the surface homogeneity of the films at elevated treatment temperatures, which corresponded to a reduction in capacitive behavior; this was further corroborated by Nyquist plots derived from electrochemical capacitance spectroscopy (ECS). The study found that the electrochemical capacitance at lower frequencies decreased significantly from $$\varvec{1.02\,\, \mu Fcm^{-2}}$$ 1.02 μ F c m - 2 to $$\varvec{0.25\,\, \mu Fcm^{-2}}$$ 0.25 μ F c m - 2 when the treatment temperature was increased to $$\varvec{600\,\,^{\circ }C}$$ 600 ∘ C

Analysis of the Response Characteristics of Toluene Gas Sensors with a ZnO Nanorod Structure by a Heat Treatment Process.

The sensing characteristics of toluene gas are monitored by fabricating ZnO nanorod structures. ZnO nanostructured sensor materials are produced on a Zn film via an ultrasonic process in a 0.01 M aqueous solution of C6H12N4 and Zn(NO3)2∙6H2O. The response of the sensors subjected to heat treatment in oxygen and nitrogen atmospheres is improved by 20% and 10%, respectively. The improvement is considered to be correlated with the increase in grain size. The relationship between the heat treatment and sensing characteristics is evaluated.

Short-time heat treatments in oxygen strengthened Ti-Zr α titanium alloys: A simple approach for optimized strength-ductility trade-off

The influence of short-time heat treatments on Ti-4.5Zr alloys (wt%) with respectively low (2000 ppm) and high (6000 ppm) oxygen contents is investigated with the aim of optimizing their strength/ductility trade-off. Starting from a cold-rolled state (85% of total thickness reduction), a high level of ductility is restored in both systems thanks to the recovery process while the resistance drop is limited, thus proving the effectiveness of the approach. This work highlights the potential of reaching a recovered microstructure to obtain optimized mechanical properties in Ti-Zr system.

Effect of Oxygen Flow Rate on Properties of Aluminum-Doped Indium-Saving Indium Tin Oxide (ITO) Thin Films Sputtered on Preheated Glass Substrates

Amorphous aluminum-doped indium tin oxide (ITO) thin films with a reduced indium oxide content of 50 mass% were manufactured by co-sputtering of ITO and Al2O3 targets in a mixed argon–oxygen atmosphere onto glass substrates preheated at 523 K. The oxygen gas flow rate and heat treatment temperature effects on the electrical, optical and structural properties of the films were studied. Thin films were characterized by means of a four-point probe, ultraviolet–visible-infrared (UV–Vis-IR) spectroscopy and X-ray diffraction. Transmittance of films and crystallization temperature increased as a result of doping of the ITO thin films by aluminum. The increase in oxygen flow rate led to an increase in transmittance and hindering of the crystallization of the aluminum-doped indium saving ITO thin films. It has been found that the film sputtered under optimal conditions showed a volume resistivity of 713 µΩ cm, mobility of 30.8 cm2/V·s, carrier concentration of 2.9 × 1020 cm−3 and transmittance of over 90% in the visible range.

Thermal Hydrogen Treatment of Electrodes for Performance and Stability Enhancement of Non-Aqueous Redox Flow Batteries

Vanadium acetylacetonate [(V(acac)3] is being used as model redox species for the study of non-aqueous redox flow battery (NAqRFB). The redox species present reversible redox reactions for both V+2/V+3 (i.e. the negolyte ca. -1.75 V vs Ag/Ag+) and V+3/V+4 (i.e. posolyte ca. 0.45 V vs Ag/Ag+). The same discharge state V+3 of this electrolyte can be used on both sides of the half cell. The latter and the fact it dissolves easily in an organic solvent, besides its commercial availability at a fair price makes it a promising candidate for future commercial versions of non-aqueous redox flow batteries.Nonetheless, merits are usually accompanied by some demerits. Vanadium has four valency states starting from V+2 to V+5; for the V-NAqRFB only three oxidations states are desirable V+2, V3+, and V4+ thus the formation of V5+ is unwanted. To avoid this oxidation state, typically the battery open circuit potential is kept below 2.27 V. Another downside of this electrolyte refers to its sensitivity towards a moisture/oxygen-enriched environment. The presence of moisture/oxygen in the environment triggers a non-reversible reaction which leads to the formation of VO(acac)2 at the positive electrode. VO(acac)2 irreversible formation causes rapid battery capacity loss due to its parasitic and increased concentration on the electrolyte. Therefore, the electrolyte must be kept in an inert atmosphere such as dry nitrogen. Nonetheless, it was observed that even by maintaining a strictly controlled saturation of the electrolyte with inert gas, the stability of the batteries was still rather negligible. Components such as the electrodes (carbon felts, CF) could also represent a major source for the oxygen-enriched surface. Many oxidation pre-treatments such as chemical exfoliation (H2SO4) and thermal oxidation under airflow at 450 °C are commonly performed on CFs to increase their wettability and performance in aqueous all vanadium redox flow cells. Nonetheless, these kind of pre-treatments might not be suitable for the system here in the study due to the beforehand mentioned reasons. The latter served as the main motivation for this study.Initially, cyclic voltammetry (CV) was performed using a three-electrode configuration cell and a glassy carbon as the working electrode. The addition of few DI water drop s (0.005% or 50 ppm) and the electrolyte saturation with O2 caused the immediate disappearance of redox species peaks (V2+/V3+ redox couple) and the appearance of additional peaks which indicated a strong influence for the reaction shift towards the formation of parasitic VO(acac)2. V+3/V+4 redox couple was also degraded significantly after 0.05% (500 ppm). Thus, keeping a dry and oxygen-free atmosphere is of utmost importance for maintaining a stable battery operation. Interestingly, it was found that the reversibility of species on top of the WE depends on the exposure time to oxygen. The effect is negligible up to 20 minutes of oxygen saturation but extremely critical over 4 hours as even upon saturating the electrolyte with an inert gas again, the adsorption of the active species was less effective and non-reversible (much lower anodic current peaks and much wider apart oxidation/reduction peaks).The carbon felt electrodes used for the aqueous vanadium redox flow battery, even with no treatment have already oxygen functional groups which serve as the reaction sites for the vanadium redox reaction in the aqueous electrolyte. Hydrogen is known as a powerful reducing agent and so might be employed to remove these oxygen functionalities. Therefore, the impact of different pre-treatments on the carbon felts morphology and performance for the V-NAqRFB was assessed. Mainly, the effect of solely adding a pre-oxygen heat treatment (referred to as PO) to a pristine carbon felt from SGL (4.6GFD), a hydrogen treatment (PH), and a combination of oxygen followed by a hydrogen treatment (POH) to completely remove all previously formed heteroatoms, were tested, each for 10 hours at 400 °C. For comparison purposes, a pristine electrode (P) was also used. Then upon, the electrochemical surface area of each CF was pre-screened by leading CV measurements and the hydrogen treatment followed by an oxygen heat treatment (POH) appeared to be the best solution to increase the number of active sites on the CF structure. Morphological characterization was performed on all electrodes using SEM and FTIR. Later, these CFs were used in NAqRFB-cell for battery cycling, impedance spectroscopy, and polarization measurements. The co-relation of the results highlighted that POH is performing better in the V(acac)3 based non-aqueous electrolyte. Besides, solely conducting a pre-oxygen heat treatment on the CFs condemns the performance of the battery, as expected. The results are shown in the attached figure. Figure 1

Antiferroelectric and Magnetic Performance in La <sub>0.2</sub>Sr <sub>0.7</sub>Fe <sub>12</sub>O <sub>19</sub> System

The integration of antiferroelectricity and ferromagnetism has been characterized as a novel performance in some special multiferroics, which could be designed for memories and energy storage purposes. Our study demonstrates that La modified M-type strontium hexaferrite (La0.2Sr0.7Fe12O19) has integrated such novel multiferroic features. By substituting 0.3 Sr 2+ ions with 0.2 La3+ ions in pure SrFe12O 19 so as to keep the charge balance, antiferroelectric state is switched on, being evidenced by double P-E hysteresis loops. The polarization saturated at 154 mC/cm 2 while the remnant polarization stays at 38 μC/cm2. The occurrence of antiferroelectrics is related to the the interruption of translational periodic symmetry by occupy of La atoms on Sr sites, which was verified by blue shift of the vibration bands to higher frequency side in Raman spectrum. The substitution lowers the Curie temperature for the phase transition from ferroelectric state to antiferroelectric one down to the vicinity of room temperature. The ferromagnetic hysteresis loop gives the values of remnant magnetic moment at 37.5 emu/g and coercive field at 4737 Oe, implying its strong magnetism. The X-ray photoelectron spectrometry (XPS) reveals the filling of ligating oxygen vacancy sites through oxygen heat-treatment and the enhancement in ferromagnetism is contributed from one additional unpaired 4f 1 electron spin in La 3+ . Therefore, the substitution of La3+ with Sr2+ in SrFe12O19 would not only transform it from ferroelectrics to antiferroelectrics, but could also improve its magnetic performance. This novel multiferroic feature combining antiferroelectrics and ferromagnetism could provide one more additional freedom to store energy by applying magnetic field.

Hydrogen Sensors Based on Flexible Carbon Nanotube-Palladium Composite Sheets Integrated with Ripstop Fabric.

This work describes the design and fabrication of free-standing carbon nanotube-palladium (CNT-Pd) composite sheets for hydrogen gas sensing. The CNT-Pd composites were made by electroplating palladium onto a solvent-densified and oxygen plasma-treated CNT sheet. The latter was prepared using high purity CNTs drawn from a dense, vertically aligned array grown by chemical vapor deposition on silicon substrates. The CNT-Pd sheets were characterized by energy-dispersive spectroscopy, scanning electron microscopy, and X-ray diffraction. The amount of palladium in the composite was 16.5 wt % as measured via thermogravimetric analysis. Thin strips of the CNT-Pd sheets were assembled as chemiresistor sensors and tested for hydrogen gas detection. The sensors demonstrated a limit of detection of 0.1 mol % and displayed signal reversibility without the need for oxygen removal or heat treatment. A decrease in signal reversibility was observed after multiple exposure cycles; however, redensification with ethanol significantly restored the original reversibility. The sensor showed the Freundlich adsorption isotherm behavior when exposed to hydrogen. The material’s potential application toward a wearable, flexible sensor was demonstrated by integrating the chemiresistor onto a fabric material using hot-press processing and testing the composite for hydrogen sensitivity.

Ternary Nb3Sn superconductors with artificial pinning centers and high upper critical fields

In this letter we demonstrate the development of ternary Nb3Sn multifilamentary conductors with artificial pinning centers (APC) which achieve high critical fields. These recently-developed conductors were tested in a 31 T magnet, and the results showed that their upper critical field (Bc2) values at 4.2 K are 27–28 T, and irreversible field (Birr) values are above 26 T, values similar to or higher than those of best rod-restack-process (RRP) conductors. The non-Cu Jc has been brought to nearly 1200 A mm−2 at 16 T and 4.2 K, comparable to RRP, in spite of the fact that the fine-grain Nb3Sn fractions in filaments are still low (20%–30%) and the grain sizes are still not fully refined (70–80 nm) due to conductor designs and heat treatments that are not yet optimized. The Nb3Sn layer Jc at 4.2 K, 16 T is 4710 A mm−2 for the APC wire with 1%Zr, about 2.5 times higher than RRP conductors, in spite of the fact that its grain size is not yet fully refined due to insufficient oxygen and unoptimized heat treatment. An analysis is presented about the non-Cu Jc that can be achieved by further optimizing the APC conductors and their heat treatments.

Effect of CdCl2 heat treatment in (Ar + O2) atmosphere on structural and optical properties of CdTe thin films

Cadmium telluride (CdTe) thin films were deposited by thermal evaporation method under base pressure 2 × 10−5 mbar on corning glass substrate. In this work, we study the effect of cadmium chloride (CdCl2) heat treatment in argon and oxygen (Ar + O2) atmosphere on the structural, morphological and optical properties of CdTe thin films to achieve high quality thin film absorber layer for solar cells applications. The structural characteristics were studied by X-ray diffraction (XRD). The microstructure parameters of the films such as average grain size (Davg), average lattice strain (εavg) and dislocation density (ρD) have been calculated via XRD line broadening analysis. XRD investigation revealed that, the samples show polycrystalline nature pronounced with cubic zinc blende structure with a strong preferentially (1 1 1) texture orientation. It has been found that the crystallinity of the films enhanced during (Ar + O2) annealing and CdCl2 heat treatment. The surface morphology of CdTe thin films was investigated by field emission scanning electron microscope (FE-SEM). XRD and FE-SEM results of CdCl2 treated films showed recrystallization and progressive increase in grain size. The optical properties of all samples were estimated using UV–vis–near-infrared (NIR) spectrophotometer. The Swanepoel envelope method has been employed to evaluate the various optical parameters of CdTe films such as refractive index and film thickness. The as-deposited films have a relatively high value of refractive index of 2.54, in contrast the CdCl2 treated films have a relatively low value of 2.1 in the whole wavelength range. The optical energy gap values slightly decrease from 1.56 eV for as-deposited films up to 1.54 eV for CdCl2 heat treated films. CdCl2 heat treatment in (Ar + O2) atmosphere is found to be a promising method to improve the physical properties of CdTe thin film solar cells.

Characteristics of New Nickel Porous Alloy for Cathode Current Collector in Solid Oxide Fuel Cells

Introduction A Nickel (Ni) porous metal is used for anode current collector in solid oxide fuel cells (SOFCs)[1]. However, it is difficult to be applied as cathode current collector due to its large oxidation resistance at high temperature. In this work, we investigated characteristics and applicability of a new Ni-Sn porous alloy as the cathode current collector for SOFCs. Experimental The Ni porous alloy was prepared by electroplating process. Sn was deposited continuously by electroplating onto the surface of the Ni porous metal. Then, heat treatment was performed under hydrogen atmosphere to obtain the Ni-Sn porous alloy [2]. Figure 1(A) shows a SEM image of three-dimensional structure of the as-prepared sample. Oxidation resistances were evaluated by measuring weight increase due to the heat treatment, and the area-specific resistance at high temperature. The crystalline phases of the specimens before and after heat treatment were identified by XRD. Mechanically polished cross-sections of the specimens were observed via SEM-EPMA. Finally, the prototype SOFCs were fabricated using the Ni-Sn porous alloy as the cathode current collector. Results and Discussion For Ni-Sn porous alloys with various Sn contents, figure 1(B) shows the weight increase due to the heat treatments in air at 800 °C for 1,000 hours and at 600 °C for 3,000 hours. In the case of the heat treatment at 800 °C for 1,000 hours, the weight of Ni-Sn porous alloys increased regardless of the Sn content. And the weight increased more than 1.7 mg/cm2, revealing a noticeable level of oxidation. In contrast, for Ni-Sn porous alloy with Sn content of 5 wt% or more, the oxidation was noticeably retarded in spite of a long-term heat treatment at 600 °C for 3,000 hours. Figure 1(C) shows the distribution of oxygen by using EPMA-EDS to analyze the cross-section area of the Ni-10wt%Sn porous alloy before and after heat treatment at 600 °C in air for 1,000 hours. After heat treatment, one can see a clear existence of oxygen in the depth about 1 μm from the surface, indicating the oxidation of this region. The IV relationship and the power output characteristics of SOFCs with the cathode current collectors made of Pt mesh or the Ni-10wt%Sn porous alloy. Both the behavior of the IV relationship and the output power of the SOFC with the Ni-10wt%Sn porous alloy were almost equivalent to that using the Pt mesh. Conclusions The Ni-Sn porous alloy has relatively low electrical resistance after the heat-treatment in oxygen, and also high electric conductivity at 600 °C. Thus, this new Ni porous alloy has promising perspective to be applied as the cathode current collector for SOFCs operating in an intermediate temperature range. And such demand is expected to grow in near future. [1] W. Guan, et al., Fuel Cells, 12(2012), 1085-1094 [2] K. Okuno, et al., SEI Technical Review, 75(2012), 137-140 Figure 1

Tailored Transition Metal Oxide Spheres Using Versatile Polymer-Template for Sodium-Ion Battery Cathodes

Transition metal oxides have been studied as positive- and negative-electrode materials for sodium-ion batteries (SIBs). In this study, we report the strategic synthesis methods of tailored cathode materials for high performance SIBs using external-stimuli responsive polymer particles and water-in-oil system. The primary particles consisting of the polymer and metal precursors are fabricated by introduction of various metal ions and polar molecules into the three-dimensional cross-linked polymer spheres in aqueous solution. The assembled secondary metal oxide spheres with tailored structures were prepared by water-in-oil system and heat treatment in high purity oxygen. When tested in an electrochemical Na-half cell, the tailored transition metal oxide spheres exhibit good Na storage capabilities.

Composition-dependent structural and electrical properties of p-type SnOx thin films prepared by reactive DC magnetron sputtering: effects of oxygen pressure and heat treatment

The composition-dependent structural and electrical properties of p-type SnOx films prepared by reactive DC sputtering at various oxygen partial pressures (PO) and post-heat treatment temperatures (TA) were investigated.

Nitric acid oxidation of Si method for improvement of crystalline Si solar cell characteristics by surface passivation effect

We have investigated effects of formation of an ultrathin silicon dioxide (SiO2) layer using the nitric acid oxidation of Si (NAOS) method and the subsequent ammonia (NH3) plasma treatment on single crystalline Si solar cell characteristics and the surface chemical structures, respectively. The NAOS SiO2 layer formed between Si and silicon nitride (SiN) improves the conversion efficiencies from 17.2 to 18.9% for n-Si-based solar cells, and from 16.6 to 17.5% for p-Si-based solar cells. The improvement is attributed to elimination of interface states, but not to fixed charges because the flat band-voltage of the <Al/SiN/Si> MIS diodes isn’t largely changed by formation of a NAOS SiO2 layer at the SiN/Si interface. The minority carrier lifetime of the NAOS SiO2/p-Si structure is greatly improved from 12 to 45μs (or 35μs) by heat treatment in oxygen at 800°C (or 600°C). In the absence of a NAOS SiO2 layer, the NH3 plasma treatment forms an SiN layer of 0.3nm thickness on the Si surface. In the presence of a NAOS SiO2 layer, on the other hand, only 0.1 monolayer of SiN is formed on the surface, and at the Si interface, silicon oxynitride species is produced. It is concluded that the NAOS SiO2 layer prevents direct nitridation of Si substrates, and thus avoids introduction of plasma damage in Si.

Effect of oxygen content and heat treatment on carbide precipitation behavior in PM Ni-base superalloys

The influence of oxygen content and heat treatment on the evolution of carbides in a powder metallurgy (PM) Ni-base superalloy was characterized. The results reveal that oxygen content has little influence on the precipitation of carbides inside the particles. However, under the consolidated state, stable Ti oxides on the particle surface act as nuclei for the precipitation of prior particle boundaries (PPB). Also, oxygen can diffuse internally along grain boundaries under compressive stress, which favors the precipitation of carbides inside the particles. Therefore, a higher amount of carbides will appear with more oxygen content in the case of consolidated alloys. It is also observed that PPB can be disrupted into discontinuous particles at 1200°C, but this carbide network is hard to be eliminated completely. The combined MC-M23C6 morphology approves the nucleation and growth mechanism of carbide evolution.

Rheological behavior and thermal properties of pitch/poly(vinyl chloride) blends

The effect of adding poly(vinyl chloride) (PVC) and coke filler on the rheological behavior and thermal properties of a coal tar pitch was investigated with a view to developing an appropriate viscoelastic binder for the injection molding of graphite components. Dynamic mechanical analysis revealed that the pitch formed compatible blends with PVC featuring a single glass transition temperature (Tg) intermediate to the two parent Tg’s. Adding PVC to the pitch increased melt viscosity substantially and resulted in strong shear thinning behavior at high PVC addition levels. Adding coke powder as filler increased the melt viscosity even further and enhanced shear thinning trends. Pyrolysis conducted in a nitrogen atmosphere revealed interactions between the PVC and pitch degradation pathways: the blends underwent significant thermal decomposition at lower temperatures but showed enhanced carbon yields at high temperatures. Pyrolytic carbon yield at 1000°C was further improved by a heat treatment (temperature scanned to 400°C) in air or oxygen. However, carbon yield decreased with addition of PVC. In addition, the degree of ordering attained following a 1h heat treatment at 2400°C also decreased with increasing PVC content.

Effects of thickness and atmospheric annealing on structural, electrical and optical properties of GZO thin films by spray pyrolysis

Gallium doped zinc oxide (GZO) films have been prepared on glass substrates by the spray pyrolysis (SP) technique. The effects of thickness and annealing in air and oxygen on structural, electrical and optical properties of GZO thin films were investigated. As-deposited films were found polycrystalline with hexagonal structure that showed compressive stress along the c-axis. The compressive stress was found to decrease by thickness and by annealing in air or oxygen. The best characteristics have been obtained after heat treatment in oxygen, where the highest carrier concentrations have been achieved and with visible transmittance of 85–70% and resistivity of 4.21–2.25×10−3Ωcm with increasing thickness. The band gaps of oxygen annealed samples are found to have low values in comparison to air annealed and as deposited samples. The band gap dependence on the film thickness and annealing atmosphere is correlated to the shrinkage effect. Photoluminescence (PL) study was confirmed that broad visible emission in GZO films due to both the intrinsic traps and deep level vacancies.

Influence of oxygen dose and heat treatment conditions on the formation of ion synthesized borosilicate layers

The results from investigating buried silicate layers formed by implantation in silicon with both oxygen and boron ions are presented. The properties of the synthesized layers were studied by means of infrared spectrometry, Auger spectrometry, and SIMS. It is shown a buried layer of silicate glass is formed in the system if the dose of molecular oxygen is 44017 cm2. Our results confirm the possibility of creating nanocluster systems in a buried layer in a silicon matrix.

Evolution of deep electronic states in ZnO during heat treatment in oxygen- and zinc-rich ambients

Hydrothermally grown ZnO samples have been annealed in Ar, Zn-rich, and O-rich ambients and investigated by deep level transient spectroscopy (DLTS). The DLTS measurements reveal up to 6 different defect levels in the band gap after different annealing conditions. A clear correlation has been found between the annealing treatment and the formation/suppression of two deep defect levels at ∼0.2 and ∼0.5 eV below the conduction band edge (Ec). As a result, the Ec-0.5eV level is assigned to a Zn-rich defect while the Ec-0.2eV level is due to a O-rich defect, where the latter shows donor behavior as revealed by a distinct Poole-Frenkel effect.

A facile synthesis method of hierarchically porous NiO nanosheets

In this study, highly hierarchically porous NiO nanosheet arrays were synthesized on glass by a hydrothermal growth method. The effects of temperature and the reactant concentrations on the morphology of the nanosheets were examined. SEM revealed uniform and hierarchical porous NiO nanosheets at 50 mM of a nickel nitrate hexahydrate solution at 90 °C in 2 h. After heat treatment in oxygen at 450 °C for 1 h, the resistivity of the annealed NiO nanosheet samples was five orders of magnitude lower than the as-prepared samples. In addition, the resistivity of the nanosheet arrays decreased significantly with increasing reactant concentration. The hierarchically porous nanosheets synthesized under optimal conditions were 200–400 nm in thickness and 6–8 μm in height. These nanosheets might have potential electrochromic applications.

Surface and Bulk Oxygen Vacancy Defect States near the Fermi Level in 125 nm WO3−δ/TiO2(110) Films: A Resonant Valence Band Photoemission Spectroscopy Study

An approximately 125 nm thick pulsed laser deposited blue, nonstoichiometric WO3−δ film grows on TiO2 (110) in the [220] direction. Oxidative treatment at 400 °C turns the film color from blue to yellow and improves the film quality considerably, as shown by improvement of the Kiessig oscillations in the X-ray reflectometry curves. Detailed analysis of resonant valence band photoemission spectra of the as-deposited nonstoichiometric blue film and oxidized yellow film suggests that a transition near the Fermi energy originates from the nonstoichiometry, i.e., oxygen deficiency, and insofar poses electronic defect states that partially can be eliminated by heat treatment in oxygen. The defects of the as-deposited blue film seem to be located throughout the film, except for the top surface due to exposure to oxygen in ambient air. Thermal after-treatment under oxygen heals the defects in the bulk, whereas residual defect states appear to remain near the film–substrate interface. Potential strain at the substrate–film interface due to lattice mismatch may be one origin for the remanence of the defect states in the bulk.