Combination Of X-ray Photoelectron Spectroscopy Research Articles

Mechanistic Insights into Surface Chemical Interactions between Lithium Polysulfides and Transition Metal Oxides

The design and development of materials for electrochemical energy storage and conversion devices requires fundamental understanding of chemical interactions at electrode/electrolyte interfaces. For Li–S batteries that hold the promise for outperforming the current generation of Li ion batteries, the interactions of lithium polysulfide (LPS) intermediates with the electrode surface strongly influence the efficiency and cycle life of the sulfur cathode. While metal oxides have been demonstrated to be useful in trapping LPS, the actual binding modes of LPS on 3d transition metal oxides and their dependence on the metal element identity across the periodic table remain poorly understood. Here, we investigate the chemical interactions between LPS and oxides of Mn, Fe, Co, and Cu by combining X-ray photoelectron spectroscopy and density functional theory calculations. We find that Li–O interactions dominate LPS binding to the oxides (Mn3O4, Fe2O3, and Co3O4), with increasing strength from Mn to Fe to Co. For C...

Thermally oxidized 2D TaS2 as a high-κ gate dielectric for MoS2 field-effect transistors

We report a new approach to integrating high-κ dielectrics in both bottom- and top-gated MoS2 field-effect transistors (FETs) through thermal oxidation and mechanical assembly of layered two-dimensional (2D) TaS2. Combined x-ray photoelectron spectroscopy (XPS), optical microscopy, atomic force microscopy (AFM), and capacitance–voltage (C–V) measurements confirm that multilayer TaS2 flakes can be uniformly transformed to Ta2O5 with a high dielectric constant of ~15.5 via thermal oxidation, while preserving the geometry and ultra-smooth surfaces of 2D TMDs. Top-gated MoS2 FETs fabricated using the thermally oxidized Ta2O5 as gate dielectric demonstrate a high current on/off ratio approaching 106, a subthreshold swing (SS) down to 61 mV/dec, and a field-effect mobility exceeding 60 cm2 V−1 s−1 at room temperature, indicating high dielectric quality and low interface trap density.

Reaction of formaldehyde over birnessite catalyst: A combined XPS and ToF-SIMS study

Birnessite with very high surface area (>180m2g−1) has been prepared by oxidation of Mn(NO3)2 with H2O2 in KOH solution. The catalytic performance of this free noble metal based material for the formaldehyde (HCHO) selective conversion into CO2 is excellent. Therefore this birnessite material has been selected for X-ray photoelectron spectroscopy (XPS) analysis in combination with time-of-flight secondary ion mass spectroscopy (ToF-SIMS) study to understand the mechanistic interaction between adsorbate and adsorbent. Thermo-desorption of formaldehyde saturated birnessite has been conducted under argon atmosphere, using a catalysis cell allowing the monitoring of the birnessite surface modification. XPS study shows (i) the partial oxidation of formaldehyde at room temperature through the formate species formation and manganese species reduction and (ii) the generation of carbonate species with temperature. ToF-SIMS analyses gave more insight in the kind of cations from birnessite interacting with adsorbed molecules: formate ions interact with manganese and potassium ions while carbonate ions interact only with potassium ions. Formate oxidation takes place on Mn ions to give COx(g) species while formate ions readily decompose on K+ sites at higher temperature.

Imaging XPS and photoemission electron microscopy; surface chemical mapping and blood cell visualization

Combined photoemission electron microscopy (PEEM) and imaging x-ray photoelectron spectroscopy (XPS), i.e., electron spectroscopy for chemical analysis in the nanoregion, has been used for surface characterization of bio-relevant and biological samples. In the first example, the authors prepared a gold patterned silicon substrate, stepwise surface modified by self-assembled monolayers followed by quantum dot (QDot) specific linking and investigated by means of work function mapping and elemental imaging in the submicrometer range. Spatially resolved core level images of C1s, V2p, and Y3d are obtained, which verify the selective thiol adsorption on the gold squares and specific binding of europium doped yttrium vanadate QDots on the self-assembled monolayer. The second example is platelet adhesion to Immunoglobulin G modified silicon surfaces, investigated by means of laterally resolved PEEM. Images of platelets clearly show activated cells with a morphology change including an enlarged surface area and elongated pseudopodia, with a lateral resolution of 140 nm. In the last example, neutrophils were allowed to attach to plain silicon surfaces and investigated by means of PEEM and imaging XPS. Here, the cells show a round shaped morphology, as expected. Threshold imaging with work function contrast is used to localize the area of interest, followed by elemental specific mapping on cells in the submicrometer region. Chemical shifts of C1s in photoemission are used to distinguish vital parts of the cell structure. The strong C1s (C-C) signal is achieved from the region of the cell membrane, i.e., high density of phospholipids, while C1s (C-N) and C1s (C-O) signals are obtained from the core of the cell, in good agreement with the presence of cytoplasm and deoxyribonucleic acid containing cell nucleus. The combination of PEEM and imaging XPS is shown here as a tool to deliver new insight into biological samples, i.e., a rapid sample overview is obtained based on low energy secondary electrons with work function contrast, followed by detailed studies in the narrow mode for elemental compositions based on photoemission. This study illustrates the strength of combined PEEM and XPS in the imaging mode on cell studies.

Adsorption and Decomposition of a Lignin β-O-4 Linkage Model, 2-Phenoxyethanol, on Pt(111): Combination of Experiments and First-Principles Calculations

To sustain the current attempts in valorizing lignin-based derivatives, this study focuses on the decomposition upon a temperature ramp of 2-phenoxyethanol, a model for the β-O-4 linkage in lignin, on a Pt(111) surface. Under ultrahigh-vacuum conditions, benzene, hydrogen, and carbon monoxide are the main desorbing products. Although benzene is the only aromatic desorbed product at low initial molecular coverages, very small amounts of phenol can be detected at higher initial coverage. Combining X-ray photoelectron spectroscopy and temperature-programmed desorption experiments together with density functional theory calculations, a reaction mechanism is suggested, starting with the OH bond scission. Phenoxy, PhO, is proposed as a key surface intermediate that preferentially deoxygenates rather than desorbs as phenol, similarly to the case of anisole. This behavior, typical of ultrahigh-vacuum conditions, is attributed to the reducing properties of carbonaceous surface species that efficiently deoxygenate ...

Interplay Between Chemical and Optoelectronic Properties of III/V-Water Interfaces from Ab Initio Simulations

Photoelectrochemical cells promise sustainable production of hydrogen fuel from water using sunlight, mimicking natural photosynthetic processes. However, finding light-absorbing semiconductor photoelectrode materials that are suitably efficient and also durable under operation has proven challenging. This is largely because electrode durability and efficiency are extremely sensitive to the chemistry at the interface between liquid water and the semiconductor, which is often extraordinarily difficult to probe under operating conditions. In this talk, I will illustrate how ab initio methods have been applied to understand the complex chemistry active at the interface of water with III-V semiconductor photocathodes (GaP, InP, and GaInP2), which offer among the highest solar-to-hydrogen conversion efficiencies but suffer from durability shortcomings. I will show how large-scale ab initio molecular dynamics simulations have assisted in determining the dependence of the available chemical pathways on the surface structure and composition of these materials. I will also show how dynamics simulations can be coupled to many-body perturbation theory to directly probe the link between macroscopic optoelectronic properties and local interfacial chemistry, which is necessary for devising meaningful interface optimization strategies. Finally, I will discuss how combining X-ray photoelectron spectroscopy (XPS) simulations with near-ambient-pressure XPS experiments can identify interfacial chemical speciation under operating conditions. Key differences between InP and GaP will be highlighted, including how different chemistry and mass transport behavior at the interface with water impact relative stability and efficiency. Specific implications for understanding the performance and durability of III-V photocathodes will be discussed, along with some general insights for engineering photoelectrochemical interfaces. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Effect of Isothermal Oxidation and Sol-Gel Thin Film Formation on Corrosion Behaviour of AZ31 and AZ61 Commercial Magnesium Alloys

The authors review their recent research work in an endeavour to interpret the influence of native oxide films on the corrosion behaviour of commercial AZ31 and AZ61 magnesium alloys and the oxidation kinetics of these alloys in air at 200ºC. The tendency of some of these thin films to be sufficiently protective in mild or weak corrosive environments was examined. For obtaining oxide films with different protective properties, some of the specimens were tested with the surface in the as-received condition, while others were tested immediately after mechanical polishing. The techniques applied to characterise thin oxide films of a thickness of just a few nanometres present on the surface of alloys has mainly been XPS (X-ray photoelectron spectroscopy) in combination with ion sputtering. Oxidation resistance of the alloys was quantified by thermogravimetric (TG) curves. Their corrosion rate was evaluated by Electrochemical Impedance Spectroscopy (EIS) and hydrogen evolution measurement in chloride solutions with different concentrations. Emphasis was placed on the possible effects of: (a) the different thickness of the native oxide films formed on the polished surfaces on the corrosion behaviour of the alloys; and (b) the different film homogeneity and uniformity on the oxidation results [1-5]. In parallel studies, an attempt was made to learn more about the influence of the native oxide films that covers the substrate on the subsequent growth and protective behaviour of the sol-gel coatings. In this way, the influence of heat treatment of magnesium alloy substrates on corrosion resistance of a sol-gel coating has been assessed during immersion tests in 0.6M NaCl aqueous solution. Relative differences in the chemical nature of the layers were quantified by scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDX). Long-term immersion testing showed that the sol-gel/heat treated AZ61 substrate exhibited a superior anti-corrosion property in comparison with the sol-gel/non-heated substrate. In contrast, no significant changes have been observed between the heated and non-heated samples in the case of the sol-gel coated AZ31 substrates. A link was found between lower O/Si atomic ratios observed by EDX analysis on the sol-gel coatings after the preparation process and reduced corrosion upon the coated substrates. The thermal treatment increases the protective properties of the passive film on the surface of the AZ61 substrate and hence inhibited magnesium dissolution and hydrophilic groups formation during coating preparation [5-7]. Finally, some preliminary results are shown on our studies in progress about the modification of these sol-gel coatings with different inhibitor (L-cysteine, benzotriazole and 8-hydroxyquinoline) in an attempt to improve the corrosion performance of the AZ31 and AZ61 magnesium alloys. Acknowledges: This work was supported by the Ministry of Economy and Competitiveness of Spain (Project MAT2015-65445-C2-1-R). References Feliu Jr., S., Maffiotte, C., Samaniego, A., Galván, J.C., Barranco, V., Effect of naturally formed oxide films and other variables in the early stages of Mg-alloy corrosion in NaCl solution, Electrochimica Acta, 56 (12), pp. 4554-4565 (2011).Feliu Jr., S., Maffiotte, C., Samaniego, A., Galván, J.C., Barranco, V., Effect of the chemistry and structure of the native oxide surface film on the corrosion properties of commercial AZ31 and AZ61 alloys, Applied Surface Science, 257 (20), pp. 8558-8568 (2011).Feliu, S., Maffiotte, C., Galván, J.C., Barranco, V., Atmospheric corrosion of magnesium alloys AZ31 and AZ61 under continuous condensation conditions, Corrosion Science, 53 (5), pp. 1865-1872 (2011). Feliu S. Jr, Samaniego A., Barranco V., El- Hadad A.A., LLorente I., Serra C., Galván J.C., A study on the relationships between corrosion properties and chemistry of thermally oxidised surface films formed on polished commercial magnesium alloys AZ31 and AZ61, Applied Surface Science, 295, pp 219-230 (2014).Feliu S. Jr., El hadad A.A, Barranco V., Llorente I., García-Galván F.R., Jiménez-Morales A., Galván J.C., Native Oxide Films on AZ31 and AZ61 Commercial Magnesium Alloys: Corrosion Behaviour Resistance, Effect on Conversion Coating Growth and Sol-gel Thin Film Formation. In “New Trends in Alloy Development, Characterization and Applications”. Editor: Zaki Ahmad. Publisher: InTechOpen, September 2015.El hadad A.A., Barranco V., Samaniego A., Llorente I., García-Galván F.R., Jiménez-Morales A., Galván J.C., Feliu Jr. S., Influence of substrate composition on corrosion protection of sol-gel thin films on magnesium alloys in 0.6 M NaCl aqueous solution, Progress in Organic Coatings 77 (11) 1642–1652 (2014).Diaz, L., García-Galván, F.R., Llorente, I., Jiménez-Morales, A., Galván, J.C., Feliu Jr, S., Effect of heat treatment of magnesium alloy substrates on corrosion resistance of a hybrid organic-inorganic sol-gel film, RSC Adv., 5, 105735-105746 (2015).

The direct measurement of the electronic density of states of graphene using metastable induced electron spectroscopy

Graphene single and multilayers were investigated for the first time with metastable induced electron spectroscopy (MIES). MIES is only sensitive to the electronic structure of the outermost layer and thus the substrate does not contribute to the spectra. It has been shown that the electronic structure of graphene changes with the number of layers and can be correlated to the band structure calculations. Angle resolved x-ray photoelectron spectroscopy in combination with Raman spectroscopy were employed to determine the thickness and the structure of the graphene samples and their defect density. We demonstrate that MIES can be used to measure directly the electronic density of states in graphene samples, which correlates to their structural characteristics such as number of layers and presence of defects.

Comparative characterization of graphene grown by chemical vapor deposition, transferred to nonconductive substrate, and subjected to Ar ion bombardment using X-ray photoelectron and Raman spectroscopies

Graphene specimens grown by chemical vapor deposition on copper and graphene transferred to Si/SiO2 substrate were subjected to an Ar+ ion treatment. A combination of X-ray photoelectron spectroscopy and Raman spectroscopy was used for the characterization graphene in as-grown, air exposed, transferred to Si/SiO2, and subjected to Ar+ bombardment states. We paid attention to make the analysis of the same spot of the sample. It is shown, that the bombardment of graphene on Cu substrate leads to edge etching and decrease of graphene crystallites size. The samples on Si/SiO2 appear less susceptible to etching, however, the defect concentrations reach up the value two orders of magnitude higher than that in graphene on Cu. It is explained by an interaction of carbon on the defect sites introduced under the bombardment with carbon-oxygen radicals generated due to decomposition of organic groups adsorbed on graphene surface.

Elucidating the process of hydrogen generation from the reaction of sodium hydroxide solution and ferrosilicon

For the first time, the process of hydrogen evolution from ferrosilicon 75 using sodium hydroxide solution has been investigated as a function of temperature using a combination of X-ray photoelectron spectroscopy, X-ray diffraction and physical measurements. Ferrosilicon 75, a mixture of silicon (~50wt.%) and iron disilicide (~50wt.%), has been shown to produce hydrogen by the action of sodium hydroxide solution on the silicon only, with the iron disilicide acting in the role of spectator/protector species for the silicon. Neither iron disilicide alone nor ferrosilicon 45, which does not contain a pure metallic silicon phase, was found to generate hydrogen under similar reaction conditions, further indicating that the presence of a pure metallic silicon phase is essential for hydrogen generation. As the iron disilicide acts as a diluent for the active silicon, it is hypothesized that this would result in a slower release of hydrogen than that which would be obtained from the reaction of silicon alone, which may be useful for applications which require a long-term, sustained release of hydrogen. A hydrogen yield of 462.5mL/g and a maximum hydrogen generation rate of 83mL/min g were obtained within 10min of reaction with 40wt.% NaOH at 348K.

Dissolution and Sorption Processes on the Surface of Calcite in the Presence of High Co2+ Concentration

The interaction of the calcite surface with Co2+-rich aqueous solutions ([Co2+aq]initial = 1000 ppm, i.e., ca. 17 mM) was investigated by means of macroscopic experiments and surface spectroscopic techniques. In the case of the macroscopic experiments, calcite powder and monocrystals were immersed into solutions for different time periods (from 1 min to one month). The Ca concentrations in the filtrates was measured by means of atomic absorption spectrometry (AAS) while the interacted solids were studied using a combination of X-ray photoelectron spectroscopy (XPS) and 12C-rutherford backscattering spectrometry (12C-RBS). The macroscopic data showed a characteristic surface dissolution process, in parallel to the surface sorption processes. Adsorption and co-precipitation were seen for almost the entire immersion period for both calcite powder and monocrystals. The surface study by XPS (analyzed at a depth of approximately 12 nm) suggested that adsorption takes place in the first hour of the interaction, followed by incorporation of Co2+ into calcite surface layers, leading to the formation of a Co2+-bearing surface (co)precipitate, which occurs over a period of hours and days. The 12C-RBS measurements on calcite { 10 1 ¯ 4 } indicated that the thickness of this surface co-precipitate was 270 nm after one day and then stabilized at 320 nm after more than a week.

Lubricant-surface interactions of polymer-coated engine journal bearings

This work provides the methodology for the improved understanding of tribocontacts with tribolayers formed from the interactions of an engine oil and the surface of a journal bearing under boundary lubricating conditions. In particular, advanced surface characterisation combining X-ray photoelectron spectroscopy (XPS) and high resolution mass spectroscopy (MS) contributed to integrated knowledge on tribochemical and tribomechanical processes in the tribocontact studied. An engine connecting rod bearing lubricated with commercial 0W-20 GF5 engine oil was evaluated as part of the tribosystem. Bearing material was a recently developed polymer-based overlay which increased in popularity in the automotive market owing to the durability and superior tribological properties. After engine bench tests and fatigue experiments, conventional oil analyses showed only minor changes regarding oil chemistry whereas MS revealed significant additive degradation, e.g., formation of organic phosphates from ZDDP and depletion of tris(2,4-di-tert-butylphenyl)phosphite additive. Regarding the fatigue experiments, surface analysis by XPS showed the formation of tribofilms with a thickness only in the range of a few nanometers and composed of P, S and Zn, i.e., mainly elements in ZDDP. This publication reports for the first time on surface characterisation by laser desorption ionisation MS applied to engine journal bearings: the presence of an organic phosphorus compound the origin of which is assumed from ZDDP could be revealed by this approach.

Processing and charge state engineering of MoOx

The effects of wet chemical processing employed in device fabrication standards are studied on molybdenum oxide (MoOx) ultra-thin films. We have combined x-ray photoelectron spectroscopy (XPS), angle resolved XPS and x-ray reflectivity to gain insight into the changes in composition, structure and electronic states upon treatment of films with different initial stoichiometry prepared by reactive sputtering. Our results show significant reduction effects associated with the development of gap states in MoOx, as well as changes in the composition and structure of the films, systematically correlated with the initial oxidation state of Mo.

Single-layer ZnS supported on Au(111): A combined XPS, LEED, STM and DFT study

Single-layer of ZnS, consisting of one atomic layer of ZnS(111) plane, has been grown on Au(111) and characterized using X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). While the LEED measurement indicates a coincidence structure of ZnS-(3×3)/Au(111)-(4×4), high resolution STM images reveal hexagonal unit cells of 6.7×6.7Å2 and 11.6×11.6Å2, corresponding to √3 and 3 times the unit cell of the ideal zincblende ZnS-(1×1), respectively, depending on the tunneling conditions. Calculations based on density functional theory (DFT) indicate a significantly reconstructed non-planar structure of ZnS single-layer on Au(111) with 2/3 of the S anions being located nearly in the plane of the Zn cations and the rest 1/3 of the S anions protruding above the Zn plane. The calculated STM image shows similar characteristics to those of the experimental STM image. Additionally, the DFT calculations reveal the different bonding nature of the S anions in ZnS single-layer supported on Au(111).

Surface chemical-bonds analysis of silicon particles from diamond-wire cutting of crystalline silicon

The recycling of the Si powder resulting from the kerf loss during silicon ingot cutting into wafers for photovoltaic application shows both significant and achievable economic and environmental benefits. A combined x-ray photoelectron spectroscopy (XPS), attenuated total reflection (ATR)-Fourier transform infrared (FTIR) and micro-Raman spectral analyses were applied to kerf-loss Si powders reclaimed from the diamond wire cutting using different cutting fluids. These spectroscopies performed in suitable configurations for the analysis of particles, yield detailed insights on the surface chemical properties of the powders demonstrating the key role of the cutting fluid nature. A combined XPS core peak, plasmon loss, and valence band study allow assessing a qualitative and quantitative chemical, structural change of the kerf-loss Si powders. The relative contribution of the LO and TO stretching modes to the Si-O-Si absorption band in the ATR-FTIR spectra provide a consistent estimation of the effective oxidation level of the Si powders. The change in the cutting media from deionized water to city water, induces a different silicon oxide layer thickness at the surface of the final kerf-loss Si, depending on the powder reactivity to the media. The surfactant addition induces an enhanced carbon contamination in the form of grafted carbonated species on the surface of the particles. The thickness of the modified surface, depending on the cutting media, was estimated based on a simple model derived from the combined XPS core level and plasmon peak intensities. The effective nature of these carbonated species, sensitive to the water quality, was evidenced based on coupled XPS core peak and valence band study. The present work paves the way to a controlled process to reclaim the kerf-loss Si powder without heavy chemical etching steps.

A non-platinum counter electrode, MnNx/C, for dye-sensitized solar cell applications

A non-platinum metal catalyst, MnNx/C was synthesized via the high-pressure pyrolysis route. The combination of X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) studies indicated the presence of Mn in +2 oxidation state surrounded by four N atoms. The peak-to-peak separation (ΔEp) of the more negative peak pair observed for I3−/I− redox couple over MnNx/C catalyst was 20mV lower than that of the Pt catalyst, indicating high reversibility of the redox couple over MnNx/C catalyst. The charge transfer resistance of the MnNx/C electrode, as measured by the impedance spectroscopy, is∼2Ω higher than that of Pt, which resulted slightly lower short circuit current (Jsc) value for MnNx/C over Pt, however the fill factor (FF) and power conversion efficiency (PCE) values of MnNx/C was slightly higher and comparable to that of Pt respectively. Hence; replacing Pt with MnNx/C would decrease the cost of DSSCs.

Heteroepitaxy of Fe3O4/Muscovite: A New Perspective for Flexible Spintronics.

Spintronics has captured a lot of attention since it was proposed. It has been triggering numerous research groups to make their efforts on pursuing spin-related electronic devices. Recently, flexible and wearable devices are in a high demand due to their outstanding potential in practical applications. In order to introduce spintronics into the realm of flexible devices, we demonstrate that it is feasible to grow epitaxial Fe3O4 film, a promising candidate for realizing spintronic devices based on tunneling magnetoresistance, on flexible muscovite. In this study, the heteroepitaxy of Fe3O4/muscovite is characterized by X-ray diffraction, high-resolution transmission electron microscopy, and Raman spectroscopy. The chemical composition and magnetic feature are investigated by a combination of X-ray photoelectron spectroscopy and X-ray magnetic circular dichroism. The electrical and magnetic properties are examined to show the preservation of the primitive properties of Fe3O4. Furthermore, various bending tests are performed to show the tunability of functionalities and to confirm that the heterostructures retain the physical properties under repeated cycles. These results illustrate that the Fe3O4/muscovite heterostructure can be a potential candidate for the applications in flexible spintronics.

Complex XPS and Raman Study of Graphene on Copper and Si/SiO<sub>2</sub> Subjected to Ar Ion Treatment

Graphene grown by chemical vapor deposition on copper and the one transferred to Si/SiO2 substrate were subjected to Ar ion treatment. A combination of X-ray photoelectron spectroscopy and Raman spectroscopy were used for characterization. According to XPS data sample on Si/SiO2 appears less susceptible to sputtering under bombardment. However, the defect concentrations introduced to the transferred graphene reach up the value two orders of magnitude higher than that in as grown graphene on Cu. We attribute this difference to the influence of the non-compensated charge formed on the insulating SiO2 layer under bombardment.

Chromium functionalized diglyme plasma polymer coating enhances enzyme-linked immunosorbent assay performance.

Ensuring the optimum orientation, conformation, and density of substrate-bound antibodies is critical for the success of sandwich enzyme-linked immunosorbent assays (ELISAs). In this work, the authors utilize a diethylene glycol dimethyl ether plasma polymer (DGpp) coating, functionalized with chromium within a 96 well plate for the enhanced immobilization of a capture antibody. For an equivalent amount of bound antibody, a tenfold improvement in the ELISA signal intensity is obtained on the DGpp after incubation with chromium, indicative of improved orientation on this surface. Time-of-flight secondary-ion-mass-spectrometry (ToF-SIMS) and principal component analysis were used to probe the molecular species at the surface and showed ion fragments related to lysine, methionine, histidine, and arginine coupled to chromium indicating candidate antibody binding sites. A combined x-ray photoelectron spectroscopy and ToF-SIMS analysis provided a surface molecular characterization that demonstrates antibody binding via the chromium complex. The DGpp+Cr surface treatment holds great promise for improving the efficacy of ELISAs.

Investigation of the thermal stability of Mo-In0.45Ga0.47As for applications as source/drain contacts

The electrical and chemical stability of Mo-InGaAs films for source-drain applications in transistor structures has been investigated. It was found that for 5 nm thick Mo films, the sheet resistance remains approximately constant with increasing anneal temperatures up to 500 °C. A combined hard x-ray photoelectron spectroscopy and x-ray absorption spectroscopy analysis of the chemical structure of the Mo-InGaAs alloy system as a function of annealing temperature showed that the interface is chemically abrupt with no evidence of inter-diffusion between the Mo and InGaAs layers. These results indicate the suitability of Mo as a thermally stable, low resistance source-drain contact metal for InGaAs-channel devices.