Energy Resolution X-ray Photoelectron Spectroscopy Research Articles

Bulk In2O3 crystals grown by chemical vapour transport: a combination of XPS and DFT studies

High purity In2O3 crystals were synthesized by the chemical vapour transport (CVT) as confirmed by X-ray Photoelectron Spectroscopy (XPS) using survey, core-levels and valence band scans of the samples. Further, high energy resolution XPS spectra revealed perfectly bonded In 3d configuration and excluded the presence of metallic In0, concurrently, the dual band observed for O 1s configuration was interpreted in term of the additional defectiveness in the oxygen sublattice. The valence band as measured by XPS is in agreement with the calculated one using DFT approach, and an insignificant shift of valence band toward Fermi level (about 0.05 eV) caused by the presence of the defects was established. Moreover, the energetics of the primarily defects were calculated and the trends were set in the perspective of XPS measurements. Altogether we make CVT In2O3 crystals ready to be used for the onward studies and technical applications.

Molybdenum Oxides Deposited by Modulated Pulse Power Magnetron Sputtering: Stoichiometry as a Function of Process Parameters

Molybdenum oxide films were deposited using modulated pulse power magnetron sputtering (MPPMS) from a molybdenum target in a reactive environment where the flow rate of oxygen was varied from 0 sccm to 2.00 sccm. By varying the amount of reactive oxygen available during deposition, the composition of the films ranged from metallic Mo to fully stoichiometric MoO3, when the molybdenum target became poisoned, due to the formation of a dielectric surface oxide coating. Film compositions were verified using high energy resolution x-ray photoelectron spectroscopy. Target poisoning occurred at an oxygen flow rate of 1.25 sccm and reversed when the flow rate decreased to about 1.00 sccm. MoO3 films deposited via MPPMS had densities of 3.8 g cm−3, 81% of the density of crystalline α-MoO3 as determined by x-ray reflectivity (XRR). In addition, XRR and atomic force microscopy data showed sub-nanometer surface roughness values. From spectroscopic ellipsometry, the measured refractive index of the MoO3 films at 589 nm was 1.97 with extinction coefficient values <0.02 at wavelengths above the measured absorption edge of 506 nm (2.45 eV).

Soft landing of bare PtRu nanoparticles for electrochemical reduction of oxygen.

Magnetron sputtering of two independent Pt and Ru targets coupled with inert gas aggregation in a modified commercial source has been combined with soft landing of mass-selected ions to prepare bare 4.5 nm diameter PtRu nanoparticles on glassy carbon electrodes with controlled size and morphology for electrochemical reduction of oxygen in solution. Employing atomic force microscopy (AFM) it is shown that the nanoparticles bind randomly to the glassy carbon electrode at a relatively low coverage of 7 × 10(4) ions μm(-2) and that their average height is centered at 4.5 nm. Scanning transmission electron microscopy images obtained in the high-angle annular dark field mode (HAADF-STEM) further confirm that the soft-landed PtRu nanoparticles are uniform in size. Wide-area scans of the electrodes using X-ray photoelectron spectroscopy (XPS) reveal the presence of both Pt and Ru in atomic concentrations of ∼9% and ∼33%, respectively. Deconvolution of the high energy resolution XPS spectra in the Pt 4f and Ru 3d regions indicates the presence of both oxidized Pt and Ru. The substantially higher loading of Ru compared to Pt and enrichment of Pt at the surface of the nanoparticles is confirmed by wide-area analysis of the electrodes using time-of-flight medium energy ion scattering (TOF-MEIS) employing both 80 keV He(+) and O(+) ions. The activity of electrodes containing 7 × 10(4) ions μm(-2) of bare 4.5 nm PtRu nanoparticles toward the electrochemical reduction of oxygen was evaluated employing cyclic voltammetry (CV) in 0.1 M HClO4 and 0.5 M H2SO4 solutions. In both electrolytes a pronounced reduction peak was observed during O2 purging of the solution that was not evident during purging with Ar. Repeated electrochemical cycling of the electrodes revealed little evolution in the shape or position of the voltammograms indicating high stability of the nanoparticles supported on glassy carbon. The reproducibility of the nanoparticle synthesis and deposition was evaluated by employing the same experimental parameters to prepare nanoparticles on glassy carbon electrodes on three occasions separated by several days. Surfaces with almost identical electrochemical behavior were observed with CV, demonstrating the highly reproducible preparation of bare nanoparticles using physical synthesis in the gas-phase combined with soft landing of mass-selected ions.

D carrier induced intrinsic room temperature ferromagnetism in Nb:TiO2 film

High crystalline anatase TiO2 and Nb:TiO2 thin films were fabricated on LaAlO3 (100) substrates by pulsed laser deposition. Room temperature ferromagnetism was obtained in Nb:TiO2 but absent in pure TiO2. The Kondo effect and anomalous Hall effect observed in metallic Nb:TiO2 strongly confirmed the existence of exchange interaction between intrinsic local magnetic moments and carriers. High energy resolution x-ray photoelectron spectroscopy studies of the Nb:TiO2 thin film revealed clear signals of Ti3+ and Nb4+ ions, which had one unpaired d electron responsible for the local magnetic moments. This result consisted quite well with the spin polarized first principle calculation.

Self-assembled monolayers of l-cysteine on palladium electrodes

l-cysteine modification of palladium (Pd) electrodes have been characterized using various electrochemical and surface analytical techniques such as cyclic voltammetry (CV), reductive/oxidative desorption, electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and specular reflectance Fourier transform infrared (FT-IR) spectroscopy. The electron transfer reaction of l-cysteine modified Pd electrode was probed by employing Fe ( CN ) 6 3 - / 4 - redox couple using cyclic voltammetry and electrochemical impedance. The CVs results revealed a quasi-reversible voltammograms for the Pd modified electrode, demonstrating that the electron transfer is not blocked due to surface modification. EIS results for the Pd modified electrode showed a decrease in the resistance in comparison with the bare Pd electrode. The surface coverage was 6.4 ± 0.4 × 10 −10 mol/cm 2. The XPS survey study for the l-cysteine modified Pd electrode exhibited the presence of sulfur on the surface. High energy resolution XPS and FT-IR indicated that the l-cysteine molecules are sulfur bonded to the Pd surface. These results suggest the modification of palladium surface by the l-cysteine amino acids.

Surface grafting polymerization of vinyl monomers on poly(tetrafluoroethylene) films by plasma treatment

Poly(tetrafluoroethylene) films were surface modified by argon plasma treatment followed by graft polymerization. Peroxidе groups were introduced on the surface of poly(tetrafluoroethylene) films after plasma treatment and the consequent contact with air when the films were taken out of the reactor. Grafting polymerization initiated by the surface peroxide (hydroxide) groups was performed on the poly(tetrafluoroethylene) film surface by using acrylic acid, 4-vinylpyridine and 1-vinylimidazole as monomers. Copolymers were obtained with grafting yield from 0.436 to 0.457 mg/cm2 for poly(acrylic acid), from 0.299 to 0.390 mg/cm2 for poly(4-vinylpyridine) and from 0.212 to 0.256 mg/cm2 for poly(1-vinylimidazole), respectively. The free surface energies of the copolymers were determined. The chemical structures and the copolymer surfaces were characterized by IR, XPS and SEM analyses. High energy resolution X-ray photoelectron spectroscopy (XPS) confirmed the grafting of acrylic acid, 4-vinylpyridine and 1-vinylimidazole. The surface hydrophilicities of modified polytetrafluoroethylene films were significantly enhanced after plasma treatment and grafting modification. It is worth emphasizing that in this work acrylic acid, 4-vinylpyridine and 1-vinylimidazole were used as the reactive monomers for grafting on the poly(tetrafluoroethylene) film by plasma treatment. We believe that this vinyl monomers may be employable as functional groups, permitting a potentially wide range of applications: as ionomers, membranes, carriers for immobilization of biomolecules, for complex formation with heavy metals as catalysts.

XPS analysis of W xC y thin films prepared by sputter deposition

W x C y thin films with different compositions were studied in order to correlate their properties with the thin-film composition and chemical bonding of C and W atoms. Three W x C y thin films with C concentrations in the range 40–80 at% were deposited on WC–Co substrates by the plasma beam sputtering technique. The composition of the thin films and chemical states of elements were analysed by X-ray photoelectron spectroscopy (XPS) depth profiling. The C and W concentrations in the films were quantified using XPS intensities from a WC–Co substrate with a known composition. The C1s peaks in the high energy resolution XPS spectra of thin films allowed identification of the WC phase and the amorphous carbon phase as a function of the film composition. The results show that the amorphous carbon a-C phase is present in those films with composition x< y. The measured hardness of the films decreases with a decrease of the WC concentration.

Electrochemical and Surface Characterization of 4-Aminothiophenol Adsorption at Polycrystalline Platinum Electrodes

The formation of a self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) on polycrystalline platinum electrodes has been characterized by surface analysis and electrochemistry techniques. The 4-ATP monolayer was characterized by cyclic voltammetry (CV), linear sweep voltammetry, Raman spectroscopy, reflection-absorption infrared (RAIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). CV was used to study the dependence of the adsorption time and 4-ATP solution concentration on the relative degree of coverage of 4-ATP monolayers on polycrystalline Pt electrodes. The adsorption time range probed was 24-72 h. The optimal concentration of 4-ATP needed to obtain the highest surface at the lowest adsorption time was 10 mM. RAIR and Raman spectroscopy for 4-ATP-modified platinum electrodes showed the characteristic adsorption bands for 4-ATP, such as nuNH, nuCH(arom), and nuCS(arom), indicating the adsorption on the platinum surface. The XPS spectra for the modified Pt surface presented the binding energy peaks of sulfur and nitrogen. High energy resolution XPS studies, RAIR, and Raman spectrum for platinum electrodes modified with 4-ATP indicate that the molecules are sulfur-bonded to the platinum surface. The formation of a S-Pt bond suggests that ATP adsorption leads to an amino-terminated electrode surface. The thickness of the monolayer was evaluated via angle-resolved XPS (AR-XPS) analyses, giving a value of 8 A. As evidence of the terminal amino group on the electrode surface, the chemical derivatization of the 4-ATP SAM was done with 16-Br hexadecanoic acid. This surface reaction was followed by RAIR spectroscopy.

Monitoring Super- and Subsurface Oxygen on Ag(210) by High Energy Resolution X-ray Photoelectron Spectroscopy: Subsurface Diffusion and Segregation

We report on a high energy resolution X-ray photoelectron spectroscopy plus supersonic molecular beam investigation of O/Ag(210). Two components are detected in the O1s spectra upon O2 adsorption, at binding energies EB=527.7 and 529.6 eV. The former peak persists up to 470 K, while the latter one decreases abruptly above 280 K. Comparison with a previous vibrational spectroscopy investigation on the same system (L. Vattuone, et al. Phys. Rev. Lett. 2003, 90, 228302) allows to assign both features to atomic oxygen. The low-energy peak is identified with adatoms, while the other is correlated to O atoms in subsurface sites. A minor contribution at the same binding energy, due to carbonates, is quantified by inspection of the C1s region and shows a different temperature behavior with respect to oxygen. Oxygen segregation into the subsurface region is observed when heating the crystal in the presence of supersurface oxygen.

Hydrophilic modification of polyethersulfone membranes by low temperature plasma-induced graft polymerization

A complete and permanent hydrophilic modification of polyethersulfone (PES) membranes is achieved by argon plasma treatment followed by polyacrylic acid (PAA) grafting in vapor phase. Both Ar plasma treatment alone and post-PAA grafting rendered a complete hydrophilicity to the PES membranes. The hydrophilicity of the membranes treated with only the Ar plasmas is not, however, permanent. In contrast, the PES membranes treated with Ar plasma and subsequent acrylic acid (AA) grafting are permanently hydrophilic. High energy resolution X-ray photoelectron spectroscopy (XPS) confirmed the grafting of PAA to all surfaces of the membrane. Furthermore, water bubble point measurements remain unaffected. The pore sizes of the grafted membranes at higher grafting yield are slightly decreased. The modified membranes are less susceptible to protein fouling than the unmodified membranes and the pure water flux for the modified membranes was tremendously increased by plasma treatment. Furthermore, the modified membranes are easier to clean and required little caustic to recover permeation flux.

Passivation of InGaAs/InP heterostructures

ABSTRACTIn this study we report different surface treatments and device designs that can be used to improve the performance of InGaAs/InP heterostructure devices. The surface properties of InGaAs (100) after sulfur or UV-ozone passivation were investigated by photoluminescence and high energy-resolution X-ray photoelectron spectroscopy. The base leakage current and the dc current gain of InGaAs/InP heterostructure bipolar transistors (HBTs) have been used to evaluate the efficiency of the passivation treatments. Although these treatments successfully passivated large area HBTs, the improved device characteristics degraded after a dielectric was deposited by plasma enhanced chemical vapor deposition (PECVD) or even just with time. Nevertheless, we found a combined surface treatment that is successful even under PECVD deposition – a UV-ozone treatment that produces a sacrificial oxide that is then removed by HF. This approach will be contrasted with a different method based on an optimized HBT layer structure with a thin InP emitter. In this case, the thin layer of depleted InP from the emitter left on the extrinsic base passivates the surface, and no treatment is required.

A study of HMDSO/O 2 plasma deposits using a high-sensitivity and -energy resolution XPS instrument: curve fitting of the Si 2p core level

A quantitative X-ray Photoelectron Spectroscopy (XPS) analysis of deposits formed from a microwave sustained hexamethyl disiloxane (HMDSO) plasma is undertaken. Curve fitting of the Si 2p core level has been achieved using component peak binding energies determined from standard compounds. The pure HMDSO plasma deposit was dominated by Si(–O) 2 (44%) environments indicating a large proportion of siloxane bond formation in the plasma environment. The introduction of 200 sccm (standard cubic centimetres per minute) of oxygen to the plasma produced a deposit in which half the silicon atoms were co-ordinated with four oxygen atoms while the majority of the remaining silicon was co-ordinated to three.

An ex situ study of electrodeposited lead on platinum (111): I. Examination of the surface redox behavior of lead and dynamic emersion

Electrochemical deposition of lead onto a Pt(111) electrode was studied ex situ by means of a combined electrochemical and ultrahigh vacuum system. The Pb/Pt(111) system was examined with cyclic voltammetry in the electrochemical cell and Auger spectroscopy, high energy resolution X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry, thermal desorp- tion spectroscopy, and low energy electron diffraction in the vacuum system. Electrodeposition of Pb from 0.1 M HClO 4 involves both classical electrodeposition (i.e., underpotential deposition) and a surface redox reaction. X-ray photoelectron spectra show two distinct types of adsorbed lead, Pb 0 and Pb 2+, in amounts that vary with emersion potential. The standard reduction potential for the reaction Pb 2+ ab + 2 e − Pb 0 ab, as determined by XPS, is E 0 = 0.65 ± 0.05 V RHE, in excellent agreement with reversible peaks at 0.63 V in the cyclic voltammogram. A consequence of the surface redox reaction is that emersion is a dynamic process; discharge of the double layer after emersion results in a final emersed potential close to E 0, regardless of the emersion potential. XPS measurements of the shifts of adsorbate binding energies as a function of emersion potential show that the double layer fully collapses upon emersion at potentials of −0.3 to 0.55 V RHE whereas a partially intact double layer remains after emersion at other potentials. We propose a model of the Pb surface redox process in which the oxidized species Pb 2+ ab must be accompanied by some form of oxygen-containing species, such as O ad or OH ad.

High energy resolution x-ray photoelectron spectroscopy studies of tetracyanoquinodimethane charge transfer complexes with copper, nickel, and lithium

High energy resolution x-ray photoelectron spectroscopy studies of tetracyanoquinodimethane charge transfer complexes with copper, nickel, and lithium