X-ray Auger Electron Spectroscopy Research Articles

Electron spectroscopy as applied to the layer-by-layer analysis of hydrocarbon coatings produced by ion-plasma deposition

The results of the nondestructive layer-by-layer analysis of hydrocarbon coatings, which is carried out by means of the electron spectroscopy method, are presented. The coating is prepared using the ion-plasma-deposition technique. Analysis of the elemental composition is performed with the help of X-ray photoelectron and Auger electron spectroscopies. The hydrogen concentration is determined via elastic peak electron spectroscopy. The coating structure is investigated by means of electron energy-loss spectroscopy.

Copper substrate as a catalyst for the oxidation of chemical vapor deposition-grown graphene

We report the catalytic effect of copper substrate on graphene–oxygen reaction at high temperature. Previous studies showed that graphene grown on copper are mostly defect-free with strong oxidation resistance. We found that a freshly prepared copper-supported graphene sample can be completely oxidized in trace amount of oxygen (<3ppm) at 600°C within 2h. Both X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) suggest that upon ambient air exposure, oxygen molecules diffuse into the space between graphene and copper, resulting in the formation of copper oxide which acts as catalytic sites for the graphene-oxygen reaction. This result has important implications for the characterization, processing, and storage of copper-supported graphene samples.

Nanoscopic view on the initial stages of corrosion of hot dip galvanized Zn–Mg–Al coatings

The onset and initial progress of atmospheric corrosion of ternary alloyed Zn–Mg–Al coatings induced by an aqueous sodium chloride environment was studied in detail by means of surface sensitive techniques, X-ray photoelectron spectroscopy and Auger electron spectroscopy. Two fundamental processes were found to be involved in the initial corrosion attack: (i) dissolution of the surface layer consisting of MgO and (ii) preferential anodic dissolution of both, binary and ternary eutectic phases constituting the coating, which led to the formation of characteristic cracks/holes and was followed by a predominant deposition of zinc corrosion products around anodic regions.

Effect of Titanium Content on the Sensing and Impedance Characteristics of High-κ TbTixOyElectrolyte–Insulator–Semiconductor pH Sensors

We report the effect of titanium content on the sensing and impedance characteristics of TbTixOy sensing membranes deposited on Si(100) substrates through reactive cosputtering for electrolyte–insulator–semiconductor (EIS) pH sensors. X-ray diffraction (XRD) and Auger electron spectroscopy (AES) were used to investigate the structural and chemical features of these films prepared under different growth conditions (Ti plasma power from 80 to 120 W). The EIS sensor featuring the TbTixOy sensing membrane prepared at the 100 W condition exhibited the best sensing characteristics (pH sensitivity, hysteresis voltage, and drift rate). We attribute this behavior to the optimal titanium content in this sensing film forming a well-crystallized Tb2Ti2O7 structure. In addition, the effect of titanium content on the impedance characteristics of TbTixOy EIS sensors was studied using the capacitance–voltage (C–V) method (frequency-dependent C–V curves). The membrane resistance and capacitance of TbTixOy sensing films we...

Surface modified Ti based metallic glasses for bioactivation by electrochemical treatment technique

The aim of this study is surface modification of Ni-free type Ti based metallic glass (Ti42Hf11Cu11Pd36at.%) for increasing calcification by electrochemical treatment. Ni-free type Ti based metallic glass has excellent mechanical and chemical properties which are comparable with those of Ti based alloys. Surface of Ti based metallic glasses was prepared as follows; one is anodically-oxidized porous layer by potentiostatic control in 5M NaOH solution at 25°C for 2h, and the other is simple hydrothermal treated poros layer by immersion in 5M NaOH solution at 60°C for 24h. The synthesized surface structures were characterized by X-ray diffraction (XRD) identification, SEM observation, energy dispersive X-ray spectroscopy (EDS) analysis and Auger electron spectroscopy (AES) analysis. These surfaces on the modified specimens have nano-mesh laminated structures and are consist of sodium titanate and titanium oxide. In addition, the above two types surfaces with nano-mesh laminated layer were immersed in Hank’s balance salt solution (HBSS) at 37°C for 21days for evaluation of calcification. The apatite-forming ability on these surfaces is observed by SEM observation and EDS analysis. As stated above surface modifications are also discussed about calcification effect by different surface treatment and different formability of porosity in this study.

Enhanced diffusion caused by surface reactions in thin films of Sn–Cu–Mn

This paper describes an investigation of low-temperature diffusion in thin films of Sn/Cu, Cu/Mn and Sn/Cu/Mn. The combination of Rutherford backscattering spectroscopy, grazing incidence X-ray diffraction and Auger electron spectroscopy has been used to provide information about the concentration distribution of components and the depth of the various phases and interfaces. The results show that processes that occur on a free surface of thin films can stimulate diffusion of elements in the bulk. It is shown that the element with higher affinity to oxygen tends to move to the surface in order to oxidize and that this oxidation process provides a driving force for further diffusion. Introduction of a third layer to a bilayer system may lead to changes in the surface topography caused by the reactive diffusion between upper layers and it causes the development of fast, ‘short-circuit’ diffusion paths and so increases the diffusion of elements from the bottom to the top. Reactive diffusion between Sn and Cu in the top layers leads to significant changes at the surface with features of the size of 10 to 20nm appearing. These changes provide shortcuts for the diffusion of Mn atoms from the bottom layer to the free surface. As a consequence of these processes, the sequence of layers of different elements in thin-film structures alters diffusion and results in different sample properties.

Lanthanum Oxide-Modified Cu/SiO2 as a High-Performance Catalyst for Chemoselective Hydrogenation of Dimethyl Oxalate to Ethylene Glycol

Several lanthanum oxide-modified Cu/SiO2 (La-Cu/SiO2) catalysts synthesized by urea-assisted gelation and postimpregnation were used for the vapor-phase chemoselective hydrogenation of dimethyl oxalate (DMO) into ethylene glycol (EG). The 1.0La-Cu/SiO2-u catalyst with 1.0 wt % La loading was found to have the highest activity, whereas the catalyst with higher La loading at 3.0 wt % adversely affected the deterioration of catalytic activity. H2-TPR results revealed that strong interactions between La promoters and Cu species substantially changed catalyst reducibility and made some Cu2+ species on catalyst precursors difficult to be reduced. Several positive variations induced by the introduction of La were confirmed by in situ XRD, N2O chemisorption, H2-TPD, X-ray Auger electron spectroscopy, and in situ FT-IR of chemisorbed CO. These variations included increased Cu metallic dispersion, improved ability for H2 activation, elevated surface concentration of Cu+ species, and enhanced stability of catalyst nanostructure. The formation of unique Cu–O–La bonds between LaOx and cupreous species located at interfacial sites was presumably responsible for the improved catalytic performance and stability of La-Cu/SiO2-u catalyst.

Surface characterization of nanomaterials and nanoparticles: Important needs and challenging opportunities.

This review examines characterization challenges inherently associated with understanding nanomaterials and the roles surface and interface characterization methods can play in meeting some of the challenges. In parts of the research community, there is growing recognition that studies and published reports on the properties and behaviors of nanomaterials often have reported inadequate or incomplete characterization. As a consequence, the true value of the data in these reports is, at best, uncertain. With the increasing importance of nanomaterials in fundamental research and technological applications, it is desirable that researchers from the wide variety of disciplines involved recognize the nature of these often unexpected challenges associated with reproducible synthesis and characterization of nanomaterials, including the difficulties of maintaining desired materials properties during handling and processing due to their dynamic nature. It is equally valuable for researchers to understand how characterization approaches (surface and otherwise) can help to minimize synthesis surprises and to determine how (and how quickly) materials and properties change in different environments. Appropriate application of traditional surface sensitive analysis methods (including x-ray photoelectron and Auger electron spectroscopies, scanning probe microscopy, and secondary ion mass spectroscopy) can provide information that helps address several of the analysis needs. In many circumstances, extensions of traditional data analysis can provide considerably more information than normally obtained from the data collected. Less common or evolving methods with surface selectivity (e.g., some variations of nuclear magnetic resonance, sum frequency generation, and low and medium energy ion scattering) can provide information about surfaces or interfaces in working environments (operando or in situ) or information not provided by more traditional methods. Although these methods may require instrumentation or expertise not generally available, they can be particularly useful in addressing specific questions, and examples of their use in nanomaterial research are presented.

Transparent cosputtered ITO–ZnO electrode ohmic contact to n-type ZnO for ZnO/GaN heterojunction light-emitting diode

A transparent cosputtered ITO–ZnO film was used as an ohmic contact electrode to the n-type ZnO layer. The contact resistance of the ITO–ZnO/n-ZnO contact system was optimized by a rapid thermal annealing (RTA) treatment. Through x-ray diffraction and Auger electron spectroscopy depth profile measurements, the achievement on the ohmic contact of the ITO–ZnO/n-ZnO contact system was attributed to the outdiffusion of the oxygen atoms at the n-type ZnO layer surface, which was favourable for the increase of the electron carriers. By contrast, the mechanism responsible for the degradation of the contact resistance was due to the significant outdiffusion of the zinc atoms at the n-type ZnO layer surface, which also resulted in the marked peak shift of the Zn2In2O5 phase. The resulting n-ZnO/p-GaN heterojunction light-emitting diode fabrication, which used the transparent ITO–ZnO/n-ZnO ohmic contact system, exhibited rectifying behaviour and emitted a near-ultraviolet radiation at approximately 410 nm.

Observations of soft x-ray emission and wall ablation in a fast low-energy pulsed capillary discharge

We report on experimental observations of pulsed capillary discharges aimed at soft x-ray production within the water-window range. Through systematical studies of capillary tube characteristics and discharge conditions, radiation emission was analysed. Plasma properties were studied by means of spectrometry, wide-band PIN diode signals and plasma micro-channel plate imaging. Surface and bulk material analyses were performed using scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS) and Auger electron spectroscopy (AES) in order to characterize the capillary inner surface after discharges. We report on hollow cathode effect enhancement by modification of cathode electrode aperture, as well as pressure conditions along the capillary, which were found to have an important effect over plasma and x-ray yields due to the modification of local electrical field and gas density. Capillary tube material and inner diameter also modified the interaction of the plasma channel with the capillary surface, thus modifying the plasma source characteristics. It was found that emission of the NVI line at 28.8 Å can be enhanced within the conditions studied, from no significant emission to sources delivering an average brightness of over 70.0 mW mm−2 per 2π sr. This demonstrates that hollow cathode electrons and plasma–wall interaction and ablation have a direct impact on emission quality.

Carbon dioxide adsorption on MgO(001)–CO2 kinetics and dynamics

Thermal desorption spectroscopy (TDS) and molecular beam scattering were used to characterize the adsorption kinetics and dynamics, respectively, of CO2 on MgO(001). X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy as well as low energy electron diffraction were used for sample characterization. TDS revealed two CO2 desorption peaks at 200K and 260K, consistent with carbonate decomposition. XPS of adsorbed CO2 did reveal one broad C1s structure at 289.4eV which also indicates carbonate formation. Carbonates decompose into CO2, CO, and O2 as evident from multi-mass TDS. CO2 beam scattering indicates non-activated and precursor-mediated adsorption with a low impact energy adsorption probability of 0.74.

The diffusion doping of Cu crystals with 0.1 at.% In at high annealing temperatures for surface segregation measurements

In order to study the segregation of In in polycrystalline Cu crystals the Cu was doped with a low concentration of In. Due to the very low melting point of In the electron evaporated In layer was covered with a Cu layer to prevent the melting of the In layer during the high temperature annealing process in which the Cu was diffusion doped with In. The In/Cu thin layers were characterized with X-ray diffraction (XRD) and Auger electron spectroscopy. The XRD data and the Auger depth profiles illustrated a CuxIny phase formation and segregation of In to the surface of the In/Cu layers during the heat treatments. The formation of a CuxIny phases (with a higher melting points than pure In) in the In/Cu thin layers corresponds to a change in the melting point of the system from that of pure In (156.6°C) to that of the CuxIny phase with a much higher melting point. It was found that the use of phase transition in the In/Cu thin layers is a promising method to dope Cu crystals with In (≈0.1at.%) at higher annealing temperatures without melting the In or CuxIny phases. The method was further verified by doping the Cu crystals with a low concentration of In (≈0.1at.%). It was observed that the In segregated to the surface when the In doped Cu crystal was annealed.

Binder-Free Cu–In Alloy Nanoparticles Precursor and Their Phase Transformation to Chalcogenides for Solar Cell Applications

A low-cost, nonvacuum fabrication route for CuInSe2 and CuInS2 thin films is presented. To produce these films, binder-free colloidal precursors were prepared using Cu–In intermetallic nanoparticles that were synthesized via a chemical reduction method. The Cu–In alloy precursor films were transformed to CuInSe2 and CuInS2 by reactive annealing in chalcogen-containing atmospheres at atmospheric pressure. The as-synthesized nanoparticles and the annealed films were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, electron probe X-ray microanalysis, Raman spectroscopy, and Auger electron spectroscopy depth profile measurements to elucidate the phase evolution pathway and the densification mechanism of the Cu–In–Se–S system. Solar cell devices made with CuInSe2 and CuInS2 absorbing layers exhibited power conversion efficiencies of 3.92% and 2.28%, respectively. A comparison of the devices suggested that the microstructur...

Reduction of charge fluctuation energies in ultrathin NiO films on Ag(001)

As the film becomes atomically thin, the on-site Coulomb interaction energy between two 3p holes of the NiO films on Ag(001) U (Ni 3p) significantly decreases as revealed by both X-ray photoelectron and Auger electron spectroscopies. The reduction of U (Ni 3p) for the ultrathin films is well accounted for by varied image potentials and polarization energies in the films from their bulk values. The present results confirm a previous model predicting the reduction of charge fluctuation energies in ultrathin oxide films on highly polarizable substrates due to the extra-atomic relaxations.

Cation Size Mismatch and Charge Interactions Drive Dopant Segregation at the Surfaces of Manganite Perovskites

Cation segregation on perovskite oxide surfaces affects vastly the oxygen reduction activity and stability of solid oxide fuel cell (SOFC) cathodes. A unified theory that explains the physical origins of this phenomenon is therefore needed for designing cathode materials with optimal surface chemistry. We quantitatively assessed the elastic and electrostatic interactions of the dopant with the surrounding lattice as the key driving forces for segregation on model perovskite compounds, LnMnO3 (host cation Ln = La, Sm). Our approach combines surface chemical analysis with X-ray photoelectron and Auger electron spectroscopy on model dense thin films and computational analysis with density functional theory (DFT) calculations and analytical models. Elastic energy differences were systematically induced in the system by varying the radius of the selected dopants (Ca, Sr, Ba) with respect to the host cations (La, Sm) while retaining the same charge state. Electrostatic energy differences were introduced by varying the distribution of charged oxygen and cation vacancies in our models. Varying the oxygen chemical potential in our experiments induced changes in both the elastic energy and electrostatic interactions. Our results quantitatively demonstrate that the mechanism of dopant segregation on perovskite oxides includes both the elastic and electrostatic energy contributions. A smaller size mismatch between the host and dopant cations and a chemically expanded lattice were found to reduce the segregation level of the dopant and to enable more stable cathode surfaces. Ca-doped LaMnO3 was found to have the most stable surface composition with the least cation segregation among the compositions surveyed. The diffusion kinetics of the larger dopants, Ba and Sr, was found to be slower and can kinetically trap the segregation at reduced temperatures despite the larger elastic energy driving force. Lastly, scanning probe image contrast showed that the surface chemical heterogeneities made of dopant oxides upon segregation were electronically insulating. The consistency between the results obtained from experiments, DFT calculations, and analytical theory in this work provides a predictive capability to tailor the cathode surface compositions for high-performance SOFCs.

Non-volatile switching characteristics in wet-deposited Ag2Se/GeSe double layers for resistive random access memory applications

The resistance switching characteristics of resistive random access memory (ReRAM) based on amorphous GeSe thin films have been demonstrated by using Al/Ag2Se/GeSe/Pt structure. The Ag2Se layer that serves as the metal ionic source of GeSe switching medium was formed by a very simple wet-deposition process in AgNO3 solution. The X-ray diffraction and Auger electron spectroscopy analysis revealed the existence of the Ag2Se layer. As a result, an extremely low-voltage set/reset operation of less than 0.2 V, a high on-off resistance ratio larger than 103, good endurance characteristics, and excellent long-term reliability were achieved by the proposed Ag2Se/GeSe bilayered ReRAMs using the wet-deposition process.

Thermal aging characteristics of CrNxOy solar selective absorber coating for flat plate solar thermal collector applications

A solar selective absorber coating of CrNxOy/SiO2 was prepared on Cu (Si) substrate using DC reactive magnetron sputtering technique. The coating exhibits a high absorptivity (α) of 0.947 and a low emissivity (ε) of 0.05 at 80°C. The spectral selectivity (α/ε) of the coating on Cu substrate is stable (0.930/0.073) even after heat-treatment at 278°C in air for 300h, but decreased (0.904/0.135) at 278°C for 600h. The determinants to govern the thermal stability were investigated by micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements, which reveal that the element diffusion whether throughout all the stacked layers or near the interface region, the chemical interactions adjacent to the interface, and the interface width broadening are the Achilles' heel for the solar thermal coatings to sustain high thermal stability.

Surface characterisation of fine inert gas and water atomised stainless steel 316L powders: formation of thermodynamically unstable surface oxide phases

New insights are presented on the speciation of surface oxide phases on fine inert gas atomised (GA, <45 and <4 μm) and water atomised (WA, <45 μm) stainless steel AISI 316L powders. X-ray photoelectron and Auger electron spectroscopy, scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry were applied for the characterisation. Oxidised manganese was strongly enriched in the outermost surface oxide of the GA powders (13 and 47 wt-%), an effect increasing with reduced particle size. Manganese and sulphur were enriched in oxide nanoparticles on the surface. Oxidised silicon (59 wt-%) was enriched on the WA powder surface. Tri- or tetravalent manganese oxides were observed on the GA particles in addition to α-Fe2O3, and Cr2O3. The oxide of the WA powder revealed in addition the likely presence of a silicate rich phase, mainly consisting of tetravalent Si, di- and/or trivalent Fe, and hexavalent Cr, which was confirmed not present as chromate.

Surface failure and wear of cemented carbide rock drill buttons—The importance of sample preparation and optimized microscopy settings

The combination of suitable mechanical properties and wear resistance makes cemented carbide one of the most interesting engineering composite materials for tribological applications, such as in rock drilling. Despite the fact that cemented carbide buttons have been used in rock drilling applications for a long time the detailed understanding of the prevailing wear mechanisms is far from complete and wear and breakage of rock drill buttons are still one of the lifetime-limiting factors for rock drill bits. Consequently, further research in this area, including detailed characterization of worn drill button surfaces and sub-surface regions, is needed in order to support the future development of new cemented carbide grades with improved failure and wear resistance. In the present paper, high resolution scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Auger electron spectroscopy (AES) have been used to characterize the wear and failure mechanisms of worn drill buttons and samples exposed to well controlled impact and scratch tests performed in the laboratory. The most important mechanisms of surface failure and wear were found to be severe plastic deformation, cracking, crushing of individual WC grains and mechanical/tribochemical degradation of the Co binder phase including Co depletion. Fracture cross-sectioning under tensile stress-state was found to be the best method for achieving large and reliable sub-surface cross-sections within a short time and to a low cost. The importance of optimized microscopy and spectroscopy settings for enhanced surface sensitivity for the examination of small-scale tribological phenomena is illuminated and discussed.

A possible origin of core-level shift in SiO2/Si stacks

Band alignments of SiO2/Si stacks with different SiO2 thicknesses are re-examined by X-ray photoelectron spectroscopy (XPS) and X-ray Auger electron spectroscopy. The energy difference between core-levels of SiO2 and Si is found to decrease with thicker SiO2. A possible explanation based on surface gap states (SGS) and charge neutrality level (CNL) is proposed to elucidate band alignment of SiO2/Si. Due to lower CNL of SiO2 SGS than Fermi level of Si, electrons transfer from Si to SiO2 SGS. With thicker SiO2 fewer electrons transfer from Si to SiO2, resulting in larger potential drop across SiO2 and XPS results.