X-ray Photoelectron Spectroscopy Depth Profile Analysis Research Articles

Effect of Bias Potential on the Interface of a Solid Electrolyte and Electrode during XPS Depth Profiling Analysis.

Depth profiling is an essential method to investigate the physical and chemical properties of a solid electrolyte and electrolyte/electrode interface. In conventional depth profiling, various spectroscopic tools such as X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) are utilized to monitor the chemical states along with ion bombardment to etch a sample. Nevertheless, the ion bombardment during depth profiling results in an inevitable systematic error, i.e., the accumulation of mobile ions at the electrolyte/electrode interface, known as the ion pile-up phenomenon. Here, we propose a novel method using bias potential, the substrate-bias method, to prevent the ion pile-up phenomena during depth profiling of a solid electrolyte. When the positive bias potential is applied on the substrate (electrode), the number of accumulating ions at the electrolyte/electrode interface is significantly reduced. The in-depth XPS analysis with the biased electrode reveals not only the suppression of the ion pile-up phenomena but also the altered chemical states at the interfacial region between the electrolyte and electrode depending on the bias. The proposed substrate-bias method can be a good alternative scheme for an efficient yet precise depth profiling technique for a solid electrolyte.

Growth of Carbon Nanotubes on Metallic Substrate: Growth Mechanism and Electrochemical Applications

This work reports the use of carbon nanotubes-modified silver (CNTs-Ag) electrode prepared by chemical vapor deposition (CVD) as indicating system in differential electrolytic potentiometry (DEP) for both redox and precipitation reactions. Characterization of CNTs-Ag electrode by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) showed the formation of aligned CNTs of a good degree of crystallinity and well-graphitized sheets. CNTs-Ag electrode was applied successfully for the determination of ascorbic acid in both pure form and in pharmaceutical and food samples along with in the determination of cyanide too down to quite low concentrations. CNTs-Ag electrode exhibited a fast and stable response and attained equilibrium in a short time. These good characteristics are attributed to the rapid heterogeneous electron transfer and high electrode surface area offered by CNTs. Additionally, modification of the Ag with CNTs grown via CVD method offers adhesion of the CNTs layers to the Ag surface and direct electrical contact better than the external modification methods commonly used such as casting the CNTs or mixing them with Nafion. Moreover, CVD method offers the chance to produce aligned CNTs that have better electrical properties than the randomly distributed ones. This work also proposed a CNTs growth mechanism by XPS depth profiling analysis. Figure 1

Plasma-enhanced atomic layer deposition of amorphous Ga2O3 gate dielectrics

Amorphous gallium oxide (Ga2O3) thin films were investigated as gate dielectrics for electronic device applications using plasma-enhanced atomic layer deposition. The structural and morphological properties as well as the electrical and dielectric behaviors of Ga2O3 thin films were explored. The surface morphology of the amorphous Ga2O3 thin film was highly smooth with root mean square of 0.55 nm and low defect density, which were visible to atomic force microscopy. The grazing incidence X-ray diffraction pattern showed no discernible peak, indicating that the film was amorphous. The X-ray photoelectron spectroscopy depth-profiling analysis showed that the Ga/O ratio was 0.76, slightly more than the optimum 2/3 ratio (0.67). The temperature-dependent current–voltage characteristics of the Au/Ni/Ga2O3/p-Si structure revealed that ideality factor and barrier height values decreased and increased with increasing temperature, respectively, demonstrating their high temperature dependency. Regardless of the applied frequency, Ga2O3 thin films exhibited a good dielectric constant of about ∼9 at zero bias voltage. The comprehensive capacitance–voltage analysis showed low trap densities of about 1012 eV−1 cm−2 at the Ga2O3–p-Si interface.

Corrosion study of nickel-coated copper and chromate-coated aluminum for corrosion-resistant lithium-ion battery lead-tab

The lead tab serves as a terminal that collects charges generated from each electrode inside the battery and transfers it to the outside of the battery. Among the lead tabs used in the electric vehicle industry, a corrosion of aluminum (Al), chromium-coated Al (CCAl), copper (Cu), and nickel-coated Cu(NCCu) during the cycling of lithium-ion batteries is investigated. Cyclic voltammetry (CV) analysis are performed as part of the electrochemical corrosion test during battery cycle life, scanning electron microscope (SEM) for checking lead tab surface, and X-ray photoelectron spectroscopy (XPS) depth profile for a chemical analysis.By the CV results, it was inferred that the Cr and Ni coatings form a layer on the surface, and the morphology was visually confirmed by post CV SEM analysis. Subsequent XPS results confirm the sub-reaction related to LiPF6-carbonate electrolyte. Finally, the composition and distribution of the formed passivation layer were finally confirmed by XPS depth profile analysis. These passivation layers prevent the corrosion of the lead tab and contribute to the extension of battery life by inhibiting the dissolution of Al and Cu metals and the decomposition of the electrolyte during the charge/discharge test of LIB.

XPS Analysis of Oxide Formed on the Surface of Co-28Cr-6Mo-1Si Alloy Oxidized at 550°C

This work investigated the influence of oxidation durations on the formation of oxide on the surface of wrought Co-28Cr-6Mo-1Si alloy. The iso-thermal oxidation was individually performed in air at 550°C for 4, 12 and 24 h. For comparison, the surface of the non-oxidized Co-28Cr-6Mo-1Si alloy was concurrently examined. The chemical compositions of the non-oxidized and oxidized alloys were principally analyzed via X-ray photoelectron spectroscopy (XPS). The XPS results revealed that the surface of the non-oxidized alloy enriched in Cr-oxide. After oxidation treatment, the Co-oxide, existing as Co2+ state was observed coexisting with two Cr-oxide states, Cr3+ and Cr4+. The low concentrations of Mo6+ were also observed on the oxidized alloy surface. With the increase in oxidation durations, the Co-oxide was suppressed by Cr-oxide. The XPS depth profile analysis indicated that the thickness of the oxide film increased with increasing the oxidation duration.

Surface chemistry of TiO2-ZnO thin films doped with Ag. Its role on the photocatalytic degradation of methylene blue

Photocatalytic Ag-loaded (TiO2)0.95-(ZnO)0.05 thin films were synthesized by the sol-gel dip-coating method, with the Ag content varying in the range 1–4 mol%. The films were deposited on glass substrates at room temperature and then annealed at 500 °C. Raman spectroscopy disclosed basically the anatase phase of TiO2. Secondary ion mass spectrometry measurements proved the incorporation of Ag in the films, revealing its diffusion to the film surface as a consequence of thermal treatments. X-ray photoelectron spectroscopy (XPS) was used to study in detail the chemical composition and electronic structure of the samples. The O 1s, Ti 2p, and Zn 2p core level spectra indicated Ti4+ and Zn2+ states associated with TiO2 and ZnO regions. The chemical species identification was confirmed by calculating the modified Auger parameter for O, Ti, and Zn. In addition, an XPS depth profile analysis using an Ar+ ion gun showed the formation of Ti+2 and Ti+3 oxidation states as a consequence of the Ar+ bombardment. The photocatalytic activity under UV irradiation was evaluated by the degradation of methylene blue aqueous solutions, with the best response corresponding to (TiO2)0.95-(ZnO)0.05 thin films doped with 2 mol% Ag.

Atomic-Layer-Deposited MoN x Thin Films on Three-Dimensional Ni Foam as Efficient Catalysts for the Electrochemical Hydrogen Evolution Reaction.

Future realization of a hydrogen-based economy requires a high-surface-area, low-cost, and robust electrocatalyst for the hydrogen evolution reaction (HER). In this study, the MoN x thin layer is synthesized on to a high-surface-area three-dimensional (3D) nickel foam (NF) substrate using atomic layer deposition (ALD) for HER catalysis. MoN x is grown on NF by the sequential exposure of Mo(CO)6 and NH3 at 225 °C. The thickness of the thin film is controlled by varying the number of ALD cycles to maximize the HER performance of the MoN x/NF composite catalyst. The scanning electron microscopy and transmission electron microscopy (TEM) images of MoN x/NF highlight that ALD facilitates uniform and conformal coating. TEM analysis highlights that the MoN x film is predominantly amorphous with the nanocrystalline MoN grains (4 nm) dispersed throughout it. Moreover, the high-resolution (HR)-TEM analysis shows a rough surface of the MoN x film with an overall composition of Mo0.59N0.41. X-ray photoelectron spectroscopy depth-profile analysis reveals that oxygen contamination is concentrated at the surface because of surface oxidation of the MoN x film under ambient conditions. The HER activity of MoN x is evaluated under acidic (0.5 M H2SO4) and alkaline (0.1 M KOH) conditions. In an acidic electrolyte, the sample prepared with 700 ALD cycles exhibits significant HER activity and a low overpotential (η) of 148 mV at 10 mA cm-2. Under an alkaline condition, it achieves 10 mA cm-2 with η of 125 mV for MoN x/NF (700 cycles). In both electrolytes, the MoN x thin film exhibits enhanced activity and stability because of the uniform and conformal coating on NF. Thus, this study facilitates the development of a large-area 3D freestanding catalyst for efficient electrochemical water-splitting, which may have commercial applicability.

Flotation of coarse and fine pyrochlore using octyl hydroxamic acid and sodium oleate

The flotation of pyrochlore using two common oxide collectors, octyl hydroxamic acid (OHA) and sodium oleate (NaOl), was studied by microflotation tests on high purity pyrochlore sample and batch flotation tests on a pyrochlore ore sample. The high purity pyrochlore sample was screened into different size fractions, −20 µm, −38 + 20 µm, −75 + 38 µm, −125 + 75 µm, and +125 µm and used in separate microflotation tests. The pyrochlore ore sample was floated as a whole in batch flotation but the flotation concentrate as well as the feed were screened into −20 µm, −38 + 20 µm, −75 + 38 µm, and −150 +75 µm to find the grade and recovery in each size fraction. The microflotation showed that under the same pH and collector concentration, OHA floated the −20 µm and −38 + 20 µm pyrochlore more strongly than NaOl. This phenomenon was also observed in batch flotation of the pyrochlore ore sample, where under the same pH and collector dosage either weight based (g/t) or molar based (mol/t), the OHA recovered pyrochlore from the −20 µm size fraction with higher enrichment ratio and higher mass pull than NaOl. The adsorption of NaOl and OHA on the pyrochlore surface was examined by Fourier transform infrared spectroscopy (FTIR), zeta potential and X-ray photoelectron spectroscopy (XPS) analyses. FTIR and zeta potential measurements indicated that both collectors adsorbed on pyrochlore through chemisorption followed by physisorption, and XPS electron binding energy and depth profile analyses showed that the OHA may have a stronger chemical affinity to pyrochlore than NaOl, contributing to the stronger chemisorption. The different adsorption mechanisms were linked to the flotation results, pointing to the role of chemisorption strength on fine particle flotation recovery.

Enhancement in Oxygen Reduction Reaction Activity of Nitrogen‐Doped Carbon Nanostructures in Acidic Media through Chloride‐Ion Exposure

AbstractNitrogen‐doped carbon nanostructures (CNx) are promising cathode materials as catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte membrane (PEM) fuel cells. Incorporation of chlorine into CNx catalysts using a facile methodology can lead to a significant improvement in the ORR activity in acidic media, as confirmed by electrochemical half‐cell measurements. The chlorine‐containing CNx catalyst (CNx−Cl) is synthesized by soaking CNx powder in 0.3 M HCl. The analysis of near‐edge X‐ray absorption fine structure spectra collected in the C K‐edge region and Fourier‐transform infrared spectra confirm the formation of C−Cl bonds in CNx−Cl. X‐ray photoelectron spectroscopy (XPS) results reveal the presence of three distinct chlorine species in the CNx−Cl sample: (i) organic chlorine (C−Cl), (ii) anionic chloride in the positively charged environment of a pyridinium ring (N+Cl−), and (iii) physisorbed ionic chloride. Results from temperature‐programmed desorption studies under inert atmosphere corroborate the conclusions from XPS depth profiling analysis. The improvement in ORR activity after exposure of the CNx catalyst to chloride anions can be attributed to the creation of C−Cl functionalities as additional active sites. The difference in the electronegativity of C and Cl atoms results in a net positive charge on adjacent carbon sites, leading to the side‐on adsorption of oxygen molecules and breakage of the O−O bond during ORR.

Fe3O4-TiO2: Gd nanoparticles with enhanced photocatalytic activity and magnetic recyclability

In this study, photocatalytic Fe3O4-TiO2: Gd berry-like pseudo-core-shell (BL-PCS) nanoparticles with various Gd doping content for wastewater treatment were prepared. Their characteristics were evaluated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), X-ray photoelectron spectroscopy (XPS). The results show that Gd3+ ions are incorporated in the TiO2 lattice. A secondary phase of FeTiO3 was observed for undoped and low Gd doping level, phase which is no longer present for high doping content. By TEM and XPS depth profile analysis it was showed that a BL-PCS structure is formed. All the samples have superparamagnetic behavior. The optimum concentration of Gd dopant which assures the best photocatalytic performance on the RhB degradation under visible light irradiation was obtained. The photocatalytic degradation was examined by varying the operational parameters such as: catalyst amount and irradiation time. The photocatalyst can be easily separated from solution due to its magnetic component and presents a good stability with a minor loss of efficiency after 4 repeated cycles. According to the analysis of the reaction intermediates and final products, a mechanism of photodegradation was proposed. Additionally, electron paramagnetic resonance (EPR) study on the ability of Fe3O4-TiO2: Gd to generate reactive oxygen species was conducted and shows that hydroxyl radical and superoxide anion radical are generated under light irradiation, radicals which are involved in the photocatalytic process.

Chemical Analysis of the Interface in Bulk-Heterojunction Solar Cells by X-ray Photoelectron Spectroscopy Depth Profiling

Despite the wide use of blends combining an organic p-type polymer and molecular fullerene-based electron acceptor, the proper characterization of such bulk heterojunction materials is still challenging. To highlight structure-to-function relations and improve the device performance, advanced tools and strategies need to be developed to characterize composition and interfaces with sufficient accuracy. In this work, high-resolution X-ray photoelectron spectroscopy (XPS) is combined with very low energy argon ion beam sputtering to perform a nondestructive depth profile chemical analysis on full Al/P3HT:PCBM/PEDOT:PSS/ITO (P3HT, poly(3-hexylthiophene); PCBM, [6,6]-phenyl-C61-butyric acid methyl ester; PEDOT, poly(3,4-ethylenedioxythiophene; PSS, polystyrenesulfonate; ITO, indium tin oxide) bulk-heterojunction solar cell device stacks. Key information, such as P3HT and PCBM composition profiles and Al-PCBM chemical bonding, are deduced in this basic device structure. The interface chemical analysis allows us to evidence, with unprecedented accuracy, the inhomogeneous distribution of PCBM, characterized by a strong segregation toward the top metal electrode. The chemical analysis high-resolution spectra allows us to reconstruct P3HT/PCBM ratio through the active layer depth and correlate with the device deposition protocol and performance. Results evidence an inhomogeneous P3HT/PCBM ratio and poorly controllable PCBM migration, which possibly explains the limited light-to-power conversion efficiency in this basic device structure. The work illustrates the high potential of XPS depth profile analysis for studying such organic/inorganic device stacks.

Investigation of Carrier Generation Mechanism in Fluorine-Doped n+-In–Ga–Zn-O for Self-Aligned Thin-Film Transistors

We investigated the carrier generation mechanism in the stacked film of fluorinated silicon nitride $(\hbox{SiN}_{x}\hbox{:F})$ on InGaZnO $(\hbox{IGZO/SiN}_{x}\hbox{:F})$ through post-annealing and compared its mechanism to that of the $\hbox{SiO}_{x}$ stack $(\hbox{IGZO/SiO}_{x})$ . The resistivity $(\rho)$ and carrier concentration $(n)$ of two types of the stacked films through post-annealing were measured by the Hall measurement. The as-deposited $\hbox{n}^{+}$ a-IGZO film with the $\hbox{SiN}_{x}\\hbox{:F}$ stack showed $\rho$ of 3.3 $\times\hbox{ 10} ^{-3}~\Omega\cdot\hbox{cm}$ and $n$ of 1.0 $\times \hbox{ 10} ^{20}~\hbox{cm}^{-3}$ , which was approximately one order of magnitude higher than that with the $\hbox{SiO}_{x}$ stack. X-ray photoelectron spectroscopy (XPS) analyses indicated that ${\rm V}_{\rm O}$ defect was the main source of free electrons in both of the as-deposited $\hbox{IGZO/SiO}_{x}$ and $\hbox{IGZO/SiN}_{x}\hbox{:F}$ stacks. After post-annealing at 300 $^{\circ}\hbox{C}$ , the carrier generation mechanism in the $\hbox{IGZO/SiN}_{x}\hbox{:F}$ stack changed from defects related to ${\rm V}_{\rm O}$ to the fluorine doping. XPS depth profile analyses also revealed that fluorine in IGZO film passivated ${\rm V}_{\rm O}$ and substituted metal–oxygen to thermally stable metal–fluorine (M-F) bonds simultaneously. As a consequence, the thermal stability of $n$ in the $\hbox{IGZO/SiN}_{x}\hbox{:F}$ stack drastically improved, as compared with that in the $\hbox{IGZO/SiO}_{x}$ stack. Therefore, we consider that this fluorine doping method in IGZO is suitable for achieving self-aligned thin-film transistors to improve operation speed of system-in-display.

Low-temperature growth of stoichiometric aluminum nitride films prepared by magnetic-filtered cathodic arc ion plating

AlN films were prepared on Si(100) and quartz glass substrates with high deposition rate of 30 nm·min−1 at the temperature of below 85 °C by the magnetic-filtered cathodic arc ion plating (FCAIP) method. The as-deposited AlN films show very smooth surface and almost no macrodroplets. The films are in amorphous state, and the formation of AlN is confirmed by N1s and Al2p X-ray photoelectron spectroscopy (XPS). The XPS depth profile analysis shows that oxygen is mainly absorbed on the AlN surface. The AlN film has Al and N concentrations close to the stoichiometric ratio with a small amount of Al2O3. The prepared AlN films are highly transparent over the wavelength range of 210–990 nm. The optical transmission spectrum reveals the bandgap of 6.1 eV. The present technique provides a good approach to prepare large-scale AlN films with controlled structure and good optical properties at low temperature.

Studies of CdS/CdTe interface: Comparison of CdS films deposited by close space sublimation and chemical bath deposition techniques

The CdS layers were deposited by two different methods, close space sublimation (CSS) and chemical bath deposition (CBD) technique. The CdS/CdTe interface properties were investigated by transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). The TEM images showed a large CSS-CdS grain size in the range of 70–80 nm. The interface between CSS-CdS and CdTe were clear and sharp, indicating an abrupt hetero-junction. On the other hand, CBD-CdS layer had much smaller grain size in the 5–10 nm range. The interface between CBD-CdS and CdTe was not as clear as CSS-CdS. With the stepwise coverage of CdTe layer, the XPS core levels of Cd 3d and S 2p in CSS-CdS had a sudden shift to lower binding energies, while those core levels shifted gradually in CBD-CdS. In addition, XPS depth profile analyses indicated a strong diffusion in the interface between CBD-CdS and CdTe. The solar cells prepared using CSS-CdS yielded better device performance than the CBD-CdS layer. The relationships between the solar cell performances and properties of CdS/CdTe interfaces were discussed.

Effect of thermal annealing on electrical and structural properties of Ni/Au/n-GaN Schottky contacts

The effects of thermal annealing on the electrical and structural properties of Ni/Au Schottky contacts to n-type GaN were investigated by current–voltage (I–V) and capacitance–voltage (C–V) characteristics, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) depth profile analysis. The metallization patterns on GaN grown by metal organic chemical vapor deposition (MOCVD) on a (0001) sapphire substrate were formed using the photolithography and lift-off techniques. The Schottky barrier height (SBH) for these contacts was obtained from I–V and C–V measurements. The value of SBH of the as-deposited contacts was found to be 0.560±0.004eV (from I–V) and 0.622±0.018eV (from C–V) with an ideality factor of 1.856±0.085. The values of SBH obtained from the C–V measurements were found to be higher than that of obtained from the I–V measurements. This case was attributed to the presence of the lateral inhomogeneities of the barrier height. However, the values of SBH slightly increase after the annealing temperatures at 100, 200, 300, 400 and 500°C. The SBH of the Ni/Au Schottky contact for the other annealing temperature of 600°C was 0.617±0.005eV. The highest value of SBH for Ni/Au Schottky contact was obtained after annealing at 700°C and the value was 0.910±0.019eV. The variations in the chemical composition of the contacts with the annealing process were examined by XPS depth profile analysis.

Highly flexible titanium dioxide-based resistive switching memory with simple fabrication

We demonstrate a flexible resistive switching random access memory (ReRAM), which is a promising next-generation memory on a flexible substrate. The proposed method enables us to fabricate an Al/TiO2/Al structure on a polyimide substrate, which has highly flexible and durable characteristics, rather than a Si-based substrate by a simple fabrication process. To understand the role of oxygen vacancies in TiO2, our devices was analyzed by X-ray photoelectron spectroscopy (XPS) and XPS depth profile analyses. Moreover, severe bending of the device did not affect the memory performance owing to its small channel length and the high ductility of the electrode. The results presented here can provide a new approach to the fabrication of nonvolatile memories for flexible electronic devices.

Compositional Study of Surface, Film, and Interface of Photoresist-Free Patternable SnO2Thin Film on Si Substrate Prepared by Photochemical Metal-Organic Deposition

The direct-patternable <TEX>$SnO_2$</TEX> thin film was successfully fabricated by photochemical metal-organic deposition. The composition and chemical bonding state of <TEX>$SnO_2$</TEX> thin film were analyzed by using X-ray photoelectron spectroscopy (XPS) from the surface to the interface with Si substrate. XPS depth profiling analysis allowed the determination of the atomic composition in <TEX>$SnO_2$</TEX> film as a function of depth through the evolution of four elements of C 1s, Si 2p, Sn 3d, and O 1s core level peaks. At the top surface, nearly stoichiometric <TEX>$SnO_2$</TEX> composition (O/Sn ratio is 1.92.) was observed due to surface oxidation but deficiency of oxygen was increased to the interface of patterned <TEX>$SnO_2/Si$</TEX> substrate where the O/Sn ratio was about 1.73~1.75 at the films. This O deficient state of the film may act as an n-type semiconductor and allow <TEX>$SnO_2$</TEX> to be applied as a transparent electrode in optoelectronic applications.

X-ray photoelectron spectroscopy depth-profiling analysis of surface films formed on Cu–Ni (90/10) alloy in seawater in the absence and presence of 1,2,3-benzotriazole

X-ray photoelectron spectroscopy (XPS) depth-profiling analysis was performed to investigate the chemical composition of the film formed on Cu–Ni (90/10) alloy in seawater and sulphide-polluted seawater in the absence and presence of an inhibitor, 1,2,3-benzotraizole (BTAH). The chemical composition of the film is found to vary at different depths of the film. In seawater environment, the outermost layer is found to consist of CuO, Cu(OH)2 and Cu2O. After sputtering for 12min, the major constituent of the film is Cu2O. In seawater polluted with sulphide also the outermost layer is found to consist of CuO, Cu(OH)2 and Cu2O without any Cu2S or CuS. After 4min of sputtering only, the peaks due to Cu2S and CuS are detected and the major constituent of the film is still Cu2O. The sulphides of copper are absent after 8min of sputtering. In the presence of BTAH, the XPS of the film showed peaks due to carbon and nitrogen up to 4min of sputtering. This result reveals the presence of the [Cu(I)BTA]n complex on the alloy surface in both seawater and sulphide-polluted seawater. The percentage of Cu2O is found to be much less than that found in the absence of inhibitor. In both the stated environments, in the absence of BTAH, the oxygen concentration is reduced to a small value only after 20min of sputtering. Whereas, in the presence of BTAH, the concentration of oxygen is reduced to a very small value after sputtering for 12min. These results infer the protective ability of the BTAH film on Cu–Ni (90/10) alloy in both seawater and sulphide-polluted seawater even after 30days of immersion.

Studies on CdTe solar cell front contact properties using X-ray photoelectron spectroscopy

The chemical changes between transparent conducting oxide (TCO) and cadmium sulphide (CdS) layers were analyzed using X-ray photoelectron spectroscopy (XPS). Commercially available indium tin oxide (ITO) and ITO/SnO2 were used as substrates. The CdS layers were deposited in vacuum (~10−2Pa) at two different (low and high) substrate temperatures by close spaced sublimation technique. During the growth of CdS layer, the substrate temperature was increased from 25 to 250°C for low temperature layer and from 490 to 550°C for high temperature CdS layer due to the high crucible temperature. Similar to CdTe solar cell device process steps, the samples (TCO/CdS) were annealed in vacuum (10−2Pa) at 520°C and in air at 375°C with and without CdCl2. The XPS depth profile analysis shows that annealing ITO/CdS sample in vacuum induces diffusion of indium into the CdS layer from ITO. The most of the diffused indium atoms are found on top of the CdS layer. No indium diffusion into the CdS layer was observed for the TCO with SnO2 buffer layer between ITO and CdS. However, at SnO2/CdS interface Cd atoms diffuse into the SnO2 buffer layer after CdCl2 activation. The change in chemical and electronic properties of the ITO/CdS and ITO/SnO2/CdS interfaces is discussed in detail.

Comprehensive X-ray Photoelectron Spectroscopy Study of the Conversion Reaction Mechanism of CuO in Lithiated Thin Film Electrodes

The course of the conversion reaction during the electrochemical insertion/deinsertion of lithium in CuO thin film electrodes was surveyed by cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). The electrochemical processes were studied through the comprehensive acquisition and interpretation of XPS and Auger spectra (Cu 2p, O 1s, Cu LMM) recorded at different stages of the first cycle of a Li/CuO cell. The reduction process consisting of three main steps leads successively to Cu+ and Cu0 and involves a Li2O2 peroxide type phase as an intermediate, whereas Li2O is the main lithiated oxide at the end of the discharge. Only the two last steps appear reversible in charge. No evidence of Cu2+ was found at the end of the charge at 3.5 V/Li+/Li, showing the irreversibility of the first step in our experimental conditions. Complementary XPS depth profile analyses were performed to check the evolution of the active material composition over the thickness of the electrode.