Oxide Layer Research Articles

Synthesis of tantalum oxide thin films using RF magnetron sputtering for RRAM application

Resistive Random Access Memory (RRAM) is a prominent contender in the realm of emerging non-volatile memory technologies owing to its numerous advantages like simple structure, low power usage, high speed, and exceptional scalability. In the current study, RRAM device was fabricated using tantalum oxide (TaOx) as a resistive switching insulating oxide layer, which was sandwiched between two conducting electrodes, namely Ag and ITO. RF magnetron sputtering was used to deposit the insulating layer of TaOx at room temperature on the ITO substrate. Further, X-ray reflectivity and hard X-ray photoelectron spectroscopy analyses were conducted to find the thickness, roughness, and elemental composition of the deposited TaOx films. Using a semiconductor analyzer, the RRAM cell's first DC switching characteristics were determined. The data acquired exhibited a resistance ratio (R HRS/R LRS) of 120 showing a good distinction between the two-resistance states. Additionally, a thorough investigation was conducted to examine the electrical conduction mechanism occurring inside the fabricated RRAM device.

Investigation of thermal conductivity and mechanical properties in multi-layer of graphene and graphene oxide: a molecular dynamics study

ABSTRACT Multi-layered graphene and graphene oxide have been used as reinforcements in nanodevices and nanocomposites due to their extraordinary mechanical and thermal properties. However, compared to graphene, graphene oxide has a lower Young’s modulus and lower thermal conductivity. Nanodevices and nanocomposites based on multi-layered graphene and graphene oxide require different mechanical properties and thermal conductivity. This study employed molecular dynamics simulation to investigate 10 models of multi-layered graphene and graphene oxide (in the form of different layer arrangements) in single, double, and triple layers. The results showed that an increase in the number of graphene oxide layers leads to irregularities in the nanosheets, resulting in decreased thermal conductivity (by 64.4%) of the nanosheets decreases. Furthermore, the greater number of graphene layers in multi-layer nanosheets resulted in an increase in Young’s modulus (by 79.3%) and tensile strength (by 73.7%). Moreover, the arrangement of graphene and graphene oxide is a crucial factor that can significantly impact the mechanical properties and thermal conductivity of the models. Moreover, an increase in temperature can lead to a decrease in Young’s modulus of multilayered nanosheets. Increasing the number and size of graphene layers enhances both the ultimate tensile strength and the critical energy release rate.

A two-dimensional Aurivillius oxide for enhanced solar energy driven hydrogen evolution and waste water treatment

Bi2WO6 has attracted extensive attention in photocatalysts in recent years as a typical Aurivillius oxide. However, it suffers from severe electron-hole recombination due to the large charge transfer distance from bulk to surface. Unfortunately, strong chemical bonds between the neighboring layers in Aurivillius oxides lead to difficulties in the construction of 2D materials. Here, a facile NaBH4-assisted hydrothermal method is developed to construct 2D Bi2WO6 nanosheets with adjustable thickness from 4.03 to 1.51 nm and O vacancies density (named as BWO-x, x = 15, 30, 45, 60). By balancing the thickness and the O vacancy density in the nanosheets, the charge separation efficiency can be tuned and consequently, the photocatalytic activity can be optimized, leading to over 11 times enhancement in photocatalytic hydrogen evolution. Furthermore, the best performed nanosheets demonstrate universality in dye polluted water treatment. Nearly 100% degradation can be reached after only 5, 50, and 30 min with degradation rate constant of 29.73, 3.21, and 6.62 min−1g−1 for Rhodamine B, methyl orange, and methylene blue, respectively. This work provides a comprehensive approach to produce ultrathin 2D nanosheets of Aurivillius photocatalysts for enhanced charge separation and photocatalytic activity.

Assessing tungsten-based electrodes coated with W and Ce oxides for pH sensing applications

This study assessed tungsten-based materials with and without dispersed CeO2 for potential use as pH sensors. Specifically, three types of tungsten electrodes were characterized: tungsten electrodes without CeO2 but with native oxide, tungsten electrodes without CeO2 that were oxidized, and a tungsten electrode containing dispersed CeO2 that was oxidized, resulting in a mixture of WO3, CeO2, and Ce2O3. The characterization was performed using SEM/EDAX, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques. The oxide coatings showed higher oxygen contents compared to native tungsten. XPS confirmed the presence of a thick layer of WO3 and cerium oxides. The electrodes exhibited good reproducibility and stability in pH measurements. A linear relationship was found between the open circuit potential and pH, with slopes of 44.9, 40.8, and 46.9 mV pH−1 for native oxide, WO3, and WO3 with CeO2 and Ce2O3, respectively. The latter showed the highest sensitivity and lowest hysteresis. The response times ranged from 14.5–23.5 s and were faster in acidic solutions. Overall, the inexpensive tungsten-based electrodes demonstrated promising capabilities for pH sensing, but in particular ceriated tungsten electrodes.

Surface Morphology of Various Matrixes with Zirconium Oxide Coatings Synthetized by Alternating Pulsing of Zirconium(IV) <i>tert</i>-Butoxide and Water Vapors Treatment of the Surface

Zirconium oxide coatings of various thicknesses were synthesized on the surface of plates of monocrystalline silicon and borosilicate glass by alternating pulsing of zirconium(IV) tert-butoxide and water vapors treatment. The effect of the matrix type and the coating thickness on surface morphology of the samples was investigated using atomic force microscopy. The concentrations of zirconium in the synthesis products were determined by X-ray spectral microanalysis and the growth constant of the zirconium oxide film on silicon was evaluated. Assumptions are made about the influence of the type of the matrix on the structure of the surface of the zirconium oxide layer.

Electrochemical modification of the Ti[sbnd]15Mo alloy surface in solutions containing Ag2O, Ag3PO4 and Ca3(PO4)2 particles

Implants with bioactive coatings are becoming increasingly popular in bioengineering. The incorporation of silver nanoparticles into the oxide layer supports the antibacterial effect. This article describes the surface modification of Ti15Mo alloy subjected to the plasma electrochemical oxidation (PEO) process in baths containing Ag compounds: Ag2O, Ag3PO4, and Ag3PO4+ Ca(PO4)2 to incorporate antibacterial silver particles into the oxide layer on the surface of the tested alloy. Scanning electron microscopy revealed changes in the surface porosity of the obtained oxide layers. Energy dispersive analysis, Raman spectroscopy, and X-ray electron spectroscopy determined the chemical composition and distribution of elements on the sample's surface. The tests showed the presence of embedded silver particles and uniform distribution on the surface. The bioactivity of the obtained layer was tested by adhesion tests of bacteria and fungi: Staphylococcus aureus (ATCC 25923), Escherichia coli (ATCC 25922), and Candida albicans (ATCC 2091).

Long-term ablation behavior of Al4SiC4-YB4 modified Cf/ZrB2-SiC composites at 2600 °C

Long-term ablation behavior of Al4SiC4-YB4 modified Cf/ZrB2-SiC composites was characterized by air plasma torch at 2600 °C for 300 s. The phase composition and the microstructure evolution of the composites were investigated. The addition of YB4 promotes the formation of nano t-Zr0.92Y0.08O1.96 crystals, decreasing the phase transition stress in the oxide layer and reducing the volatilization of the glassy phase. However, the addition of Al4SiC4 reduces the melting point of Zr-based oxides and the viscosity of the oxide layer. Therefore, the air plasma torch blows the oxide layer away, leading to the increase of linear recession rate.

Sensitive detection of histamine utilizing the SERS platform combined with an azo coupling reaction and a composite hydrophobic layer

Herein, the surface-enhanced Raman scattering (SERS) platform was combined with an azo coupling reaction and an aluminum alloy covered with a hydrophobic layer of praseodymium oxide and stearic acid complexes for the detection of histamine. The praseodymium oxide on aluminum alloy was successfully synthesized by the rare-earth-salt-solution boiling bath method and modified by stearic acid. Its surface exhibits a water contact angle (WCA) of 125.0°. Through the azo derivatization reaction with 3-amino-5-mercapto-1,2,4-triazole (AMTA) diazonium salts, histamine can be converted into the derivatization product with higher Raman activity. The mixture of the derivatization product and β-cyclodextrin-modified Ag nanoparticles (β-CD-AgNPs) were dropped onto the surface of an aluminum alloy covered with a hydrophobic layer of praseodymium oxide and stearic acid complexes, and dried for SERS measurement. The intensity ratio between the SERS peaks at 1246 cm−1 and 1104 cm−1 (I1246/I1104) of the derivatization product was used for the quantification of histamine. Under the selected conditions, the limit of detection (LOD) and the limit of quantification (LOQ) for this method were 7.2 nM (S/N = 3) and 24 nM (S/N = 10), respectively. The relative standard deviation (RSD) of this method for the determination of 1 μM histamine was 6.1 % (n = 20). The method was also successfully used for the determination of histamine in fish samples with recoveries ranging from 92 % to 111 %. The present method is simple, sensitive, reliable, and may provide a new approach for preparing the composite hydrophobic layer that can enhance SERS signals through hydrophobic condensation effect. Meanwhile, it may have a promising future in the determination of small molecular compounds containing an imidazole ring.

Oxidation behavior of Cu–Ag alloy in-situ manufactured via laser powder bed fusion

The oxidation behavior of copper-silver (Cu–Ag) alloy with the structure of triply periodic minimal surfaces (TPMS) processed by laser powder bed fusion (LPBF) was investigated at 300 °C and 600 °C. The lightweight TPMSs increase surface area, boosting measurement sensitivity in oxidation studies. The presence of silver enhances oxidation resistance of Cu–Ag alloy compared to that of pure copper by slowing down the oxidation process and thinning the oxide layer. This suggests that silver in the alloy potentially suppresses the outward diffusion of copper from the substrate to the oxide layer. This effect is evident in the oxidation rate curves, where the introduction of silver changes the oxidation kinetics from a linear rate in Cu to a parabolic rate in Cu–2 wt.% Ag at 300 °C. Moreover, at 600 °C, silver induces a slower parabolic rate in Cu–2 wt.% Ag compared to Cu.

Optical constants and thickness gradients for light intensities in glass substrate layers and for complex electric fields in indium tin oxide (ITO) transparent conductor thin film layer, using Bode and Nyquist wavelength-dependent diagrams

Abstract The optical constants of a thin film layer of transparent conductive indium tin oxide (ITO), deposited on a thick glass substrate (G), were obtained for an ITO-G sample using a multilayer matrix method by fitting the regular transmittance and specular reflectance measurements to the collimated equations of the four-flux model, once the optical constants of the glass substrate layer had previously been obtained from a G sample of a single glass substrate layer. The accuracy of the results was validated using a feedback system called the three-extinction matching requirement, that is, obtaining the same extinction coefficients from the optical constants and from the forward and backward collimated differential equations of the four-flux model. To calculate the extinction coefficients of the glass from optical constants, the compression of the wavelength of the incident light in the glass substrate and in the thin ITO film layer was demonstrated, with a thickness less than the wavelength of incident light. The thickness gradients of the forward and backward collimated light intensities, on the glass substrate of the ITOG sample, were compared with those obtained for the single-layer G sample. Then, the thickness gradients for the complex forward and backward electric fields of the ITO thin film layer were obtained and plotted using spectral magnitude and phase Bode plots and new Nyquist plots, i.e. imaginary versus real parts, dependent on wavelength.

V2O3/VO2@NC@GO ultrathin nanosheets as a high-performance cathode for aqueous zinc-ion batteries

Recently, vanadium oxides have attracted much attention as advanced cathodes for aqueous zinc-ion batteries on account of their high theoretical specific capacity, multi-electron transfer and easy synthesis; however, structural instability and poor conductivity of the materials limit their practical application. Herein, N-doped carbon-coated V2O3/VO2 hybrid nanosheets were encapsulated into graphene oxide (V2O3/VO2@NC@GO) as an advanced cathode for aqueous zinc-ion batteries by the combined process of hydrothermal treatment, high-temperature annealing and freeze drying. The multi-valence of vanadium element activates diverse redox reactions and thus results in high specific capacity, while graphene oxide and N-doped carbon layer derived from polyvinyl pyrrolidone establish an efficient conductive network for electronic transfer and provide a rigid skeleton for enhancing the structural stability of the hybrid nanosheets. Benefiting from the above unique advantages of composition and micromorphology, the V2O3/VO2@NC@GO cathode exhibits excellent reaction dynamics and rapid electron transfer, generating high specific capacities of 493.0 mAh g−1 at 0.5 A g−1 and 411.9 mAh g−1 at 5 A g−1 and outstanding long-term cycling performance with a retention of 92.4 % after 1000 cycles at 5 A g−1. This work offers a viable approach for developing high-performance vanadium oxide-based cathodes for aqueous zinc-ion batteries by enriching the valence states of vanadium and encapsulating active materials into highly conductive carbon materials.

Enhanced photocatalytic reduction of p-nitrophenol by polyvinylpyrrolidone-modified MOF/porous MgO composite heterostructures

Catalysts derived from Metal-Organic Frameworks (MOF) present a compelling blend of cost-effectiveness and superior performance in reduction reactions. In this study, polymer-decorated MOF-Cobalt (MOF-Co) was deposited onto porous magnesium oxide (MgO) layers, acquired through surface modification of AZ31 Mg alloy via plasma-assisted oxidation, with the aim of fabricating novel catalysts for reduction reactions. Herein, this synthesis involved the utilization of Cobalt-benzene dicarboxylic acid (Co-BDC), where cobalt ions served as metal nodes and 1,4-benzene dicarboxylic acid (H2BDC) functioned as an organic linker, with and without the presence of polyvinylpyrrolidone (PVP) as an active site enhancer. The morphology of the prepared catalysts was affected by several factors such as pH, hydrothermal treatment duration, PVP content, and the presence of a MgO layer. The optimal catalyst, designated as metal-organic frameworks-cobalt at 80 °C temperature and 1 h of hydrothermal treatment at pH 4 (MOF-Co 1.4), was synthesized on the MgO layer using a solution containing 1.7 g of PVP, H2BDC, and Co(NO₃)₂.6H₂O. The paper-like morphology of the MOF-Co 1.4 catalyst facilitated exceptional performance, efficiently degrading p-nitrophenol (p-NP) under visible light irradiation with an impressive 99.74 % efficiency within just 5 min of exposure, while also demonstrating stability over five successive cycles. ·O2− species was found to drive the reduction reaction to p-aminophenol, with harmless compounds as byproducts, while GC-MS analysis identified intermediates in the reduction of p-NP. Density functional theory (DFT) calculations suggested that H2BDC and PVP jointly provided multi-active sites, enabling effective contact with reactants and rapid electron transfer, thus playing a synergistic role in the catalytic reduction process. This study pioneers a novel method for designing efficient bulk catalysts, achieving high efficiency and stability in pollutant degradation with fast, low-energy fabrication.

Over 19% Efficient Inverted Organic Photovoltaics Featuring a Molecularly Doped Metal Oxide Electron-Transporting Layer.

Molecular doping is commonly utilized to tune the charge transport properties of organic semiconductors. However, applying this technique to electrically dope inorganic materials like metal oxide semiconductors is challenging due to the limited availability of molecules with suitable energy levels and processing characteristics. Herein, n-type doping of zinc oxide (ZnO) films is demonstrated using 1,3-dimethylimidazolium-2-carboxylate (CO2-DMI), a thermally activated organic n-type dopant. Adding CO2-DMI into the ZnO precursor solution and processing it atop a predeposited indium oxide (InOx) layer yield InOx/n-ZnO heterojunctions with increased electron field-effect mobility of 32.6 cm2 V-1 s-1 compared to 18.5 cm2 V-1 s-1 for the pristine InOx/ZnO bilayer. The improved electron transport originates from the ZnO's enhanced crystallinity, reduced hydroxyl concentrations, and fewer oxygen vacancy groups upon doping. Applying the optimally doped InOx/n-ZnO heterojunctions as the electron-transporting layers (ETLs) in organic photovoltaics (OPVs) yields cells with improved power conversion efficiency of 19.06%, up from 18.3% for devices with pristine ZnO, and 18.2% for devices featuring the undoped InOx/ZnO ETL. It is shown that the all-around improved OPV performance originates from synergistic effects associated with CO2-DMI doping of the thermally grown ZnO, highlighting its potential as an electronic dopant for ZnO and potentially other metal oxides.

Machinability improvement of titanium alloy in face grinding by ultrasonic assisted jet plasma oxidation

A novel machining technology, namely ultrasonic assisted jet plasma oxidation modification face grinding (UAJPMG), was proposed to improve the machinability of the titanium alloy, in which the titanium alloy materials are modified by plasma oxidation followed by face grinding. This paper introduced the processing principle of UAJPMG and the design of an ultrasonic jet nozzle to promote plasma oxidation. Using the ultrasonic jet nozzle produced in-house, the effect of the ultrasonic vibration on the plasma intensity was experimentally investigated. The results revealed that the application of ultrasonic vibration can diminish the thickness of the gas film by elevating the jet flow rate, thereby reducing the generation delay time and enhancing the plasma intensity. Subsequently, a scratch test was performed to assess the difference in the mechanical strength between the plasma oxide layer and the titanium alloy substrate. It was found that the plasma oxide layer with a reduced mechanical strength exhibited a deeper scratch depth under the same normal load. Based on these, the machining performance under different conditions was examined considering the removed material of the abrasive grains. Compared with the removed material was Ti-6Al-4V substrate in conventional face grinding, the ultrasonic assisted plasma oxidized material can inhibit the chip adhesion on the wheel working surface, resulting in a reduction of the grinding force and the surface roughness and an improvement of the groove shape accuracy. The novel machining technology, i.e., UAJPMG, proposed in this paper might provide a new approach for the precision machining of critical components made from titanium alloy.

Performance evaluation and stability analysis of super-junction IGBTs in high-temperature environments

Abstract This paper aims to evaluate and analyze the performance and stability of super-junction IGBTs (Insulated Gate Bipolar Transistors) in high-temperature environments. The study begins with an overview of the significance of IGBTs in the field of power electronics. It provides a comprehensive discussion of the advantages of super-junction technology and the challenges posed by high temperatures on the performance of IGBTs. Through a series of experiments on various commercial super-junction IGBT models, this research thoroughly assesses the devices’ saturated current, threshold voltage, leakage current, switching time, and switching losses at different temperature points (25°C, 75°C, 125°C, and 175°C). The experimental results demonstrate a significant impact of high temperatures on the performance of IGBTs, particularly in terms of changes in saturated current and threshold voltage. Additionally, the study predicts the lifespan of super-junction IGBTs through High-Temperature Operating Life (HTOL) testing and analyzes the failure modes in high-temperature environments. The results indicate that the expected lifespan of the devices significantly decreases with increasing temperature, with primary failure modes including degradation of the gate oxide layer, an increase in interface traps, and disruption in conductive pathways. The paper also compares experimental results with existing literature, emphasizing the potential and importance of optimized design for super-junction IGBTs in high-temperature environments. The study suggests that improvements in materials, structural design, manufacturing processes, and innovative cooling technologies can further enhance the performance and stability of IGBTs in high-temperature applications. Finally, this research provides new insights into the development of super-junction IGBTs in high-temperature power applications and offers valuable references for professionals in related fields.

Tribo-mechanical performance of Al-nano TiC composites processed by microwave-assisted powder metallurgy

This study aims to investigate the microstructural, mechanical, and tribological characteristics of Al-nano TiC composites. The microwave-sintered nanocomposites were analyzed using optical and scanning electron microscopes, providing valuable insights into the spatial distribution and interaction of TiC within the matrix material. Microstructure characterization confirmed the uniform dispersion of nano TiC particles throughout the Al. Furthermore, the microwave-sintered nanocomposite samples displayed greater hardness than pure aluminum, indicating the strengthening impact of nano-TiC. Al-6 wt.% nanocomposites fabricated using microwave-sintered powder metallurgy showcased an impressive hardness rating of 51 VHN. The assessment of tribological properties revealed that a higher TiC concentration reduced wear rate, showcasing improved surface protection. However, it was observed that the friction coefficient rise with the addition of nano-TiC particles, implying changes in the bonding between the composite and the interacting surface. The thorough examination of worn surfaces yielded insights into the wear mechanisms present in the nanocomposite materials. Detailed examination of worn surfaces highlighted the formation of protective oxide layers, contributing to the improved wear resistance. This research contributes to our understanding of the complex interactions occurring during tribological processes by clarifying the morphological features of worn surfaces.

Preparation of β-SiAlON/SiC composite ceramic foam filters and their oxidation resistance

In this study, ceramic foam filters with high porosity, strength, and oxidation resistance are produced at low temperatures by preparing porous β-SiAlON/SiC composite ceramic foams using the foam impregnation method with Si, Si, α-Al2O3, AlN, and SiC as the raw materials. The presence of SiC inhibits the growth of β-SiAlON grains, which reduces the amount of β-SiAlON produced. As the proportion of β-SiAlON increases, the porosity of the β-SiAlON/SiC composite ceramic foam decreases, whereas the bulk density and compressive strength increase. Non-isothermal oxidation experiments show that β-SiAlON/SiC composite ceramic foams exhibit high oxidation resistance and their macroscopic morphology does not change significantly after oxidation. As the proportion of β-SiAlON increases, the smooth SiO2 oxide layer on the surface of the ceramic foam gradually changes to acicular and columnar mullite crystals, and the oxidation resistance increases. Therefore, β-SiAlON acts as a high-temperature binder when it is added to SiC. Hence, the prepared β-SiAlON/SiC composite ceramic foams can be used as ceramic filters in the field of molten metal filtration.

Functionally multilayered Yb‐silicate EBCs fabricated using slurry spraying‐reactive sintering technique

AbstractFunctionally multilayered environmental barrier coatings (EBCs) with the desired layer sequence of Yb2O3/Yb2SiO5/Yb2Si2O7/SiO2/Si were obtained using an unconventional yet simple technique of reactive sintering. Yb2O3 slurry was sprayed on polycrystalline silicon (used as a bond coat for SiCf/SiC composites) and reactive sintered to generate graded layers that provide a combination of mitigated thermal expansion mismatch as well as silica activity. The Yb2O3‐terpineol slurry produced a uniform deposit of the Yb2O3 topcoat. Reactive sintering of exploratory coatings (t ∼ 10–20 µm) was carried out in air by varying the temperature (1100–1400°C) and time (2–24 h). X‐ray diffraction and scanning electron microscopy‐energy‐dispersive spectroscopy technique confirmed the in situ formation of X2‐Yb2SiO5 and β‐Yb2Si2O7. Rietveld refinement was performed to know the volume fractions of the respective phases. The set of process parameters identified from the preliminary work was employed to fabricate EBCs with thickness ∼ 250 µm. The X2‐Yb2SiO5 and β‐Yb2Si2O7 phases formed next to the Si/SiO2 interface as two separate layers. Post‐sintering heat treatments in air at 1300, 1350, and 1400°C for 3–50 h elucidated the growth characteristics of the oxide layers to be a function of both temperature and time. The theoretical considerations of diffusional reactive phase formation of the EBC multilayer growth rates are discussed.

Formation mechanism of high-temperature oxidation film on WE43 magnesium alloy and its effect on corrosion performance

The oxidation behavior of WE43 magnesium alloy in dry air at three temperatures (225, 440 and 525 °C) and the corresponding corrosion performance of samples attached to oxide film in 3.5 wt% NaCl solution was investigated. The results show that the oxide films formed at all three temperatures are a complex MgO∙RE2O3∙ZrO film with different compositions. The film formed at 225 °C is flat and dense, whose components are 3.2MgO∙1.8RE2O3∙1ZrO. The oxidation ridges begin to form, and then gradually grow into nodular oxides and form a loose and porous oxide layer as the temperature increases to 525 °C. The oxide films formed at all three temperatures improve the corrosion resistance of the alloy due to the MgO∙RE2O3∙ZrO, with the protective properties of oxide films following the order of 225 °C > 440 °C > 525 °C, because the dense MgO∙RE2O3∙ZrO film formed at 225 °C can provide better protection to the substrate than the loose oxide film formed at higher temperatures.

X-ray photoelectron spectroscopy surface oxidation study of remote plasma-enhanced chemical vapor deposition-grown Ge1−xSnx/Si alloys

Recent progress in the remote plasma-enhanced chemical vapor deposition of Ge1−xSnx grown directly on Si substrates has improved crystal structure quality. To understand the impact of postgrowth storage, we study oxidation states of Ge1−xSnx alloys, for x values of 7.5%, 8.8%, 12.5%, and 19.3%. A surface oxidation layer formed naturally at room temperature over five months is quantified using angle-resolved x-ray photoelectron spectroscopy. The GeSn alloys exhibit a high surface oxide concentration with a minimum of 77% in Sn 3d peak analysis. Ge is less susceptible to oxidation than Sn, with oxidation percentages ranging from 25% to 86%. The Sn dopant enhances the oxidation features associated with the Ge 3p peak, aiding surface oxidation and penetrating further into the film. It is feasible that the 4+ state Sn from the precursor readily oxidizes postgrowth resulting in an oxide-rich surface layer.