Monochromatic X-ray Photoelectron Spectroscopy Research Articles

Surface reaction kinetics of NO on Rh{110}

The reaction of NO with Rh(110) single crystal surfaces was studied by means of various surface analytical tools including static secondary ion mass spectrometry (SSIMS), temperature programmed desorption (TPD), monochromatized x-ray photoelectron spectroscopy (MXPS), and ion scattering spectroscopy (ISS). Molecular NO adsorption was found to occur below 200 K. Higher temperatures caused dissociation of adsorbed NO molecules. Complete dissociation occurred only below a critical coverage, i.e., ΘNO≤0.12. Nitrogen and oxygen molecules were the only desorption products in TPD under these conditions. For higher coverages, thermal desorption of NO occurred and was found to be associated with an activation energy Ed=130±6 kJ/mol and a preexponential νd=10(15.0±0.8) s−1 for the limit of zero NO coverage in a first order process. The dissociation of molecular NOad caused a shift of the N1s core level binding energies from 400.3 to 397.6 eV. SSIMS studies were performed in either real time or in a temperature programmed manner (TPSSIMS) and the calibrated intensities of ionic species were taken to evaluate the dissociation kinetics. Both the activation energy Edis and the preexponential k0dis for dissociation were determined from the TPSSIMS data by assuming first order kinetics in a Polanyi–Wigner ansatz. Values of Edis=15±2 kJ/mol and k0dis=10(1.9±0.5) s−1 were found. These data are compatible with the rate constant kdis=0.18 s−1 obtained in real-time measurements during the ongoing NO adsorption and dissociation at 300 K. In this case, the SSIMS data were evaluated on the basis of consecutive reaction kinetics, including site inhibition by oxygen and Kisliuk’s precursor-mediated adsorption. ISS measurements indicated that oxygen atoms can also partly diffuse into the interior of the Rh(110) crystal.

Combined instrument for the on-line investigation of plasma deposited or etched surfaces by monochromatized x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry

A combined instrument has been developed for the investigation of plasma deposited or etched surfaces which couples a versatile chemical reaction chamber on-line with a surface analytical system. The plasma can be generated either by microwave (2.45 GHz) or radio frequency (13.56 MHz) excitation, with and without magnetic field assistance. The surface analytical part of the instrument is equipped with monochromatized x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry. Auxiliary energy or mass spectroscopic techniques can be applied where necessary. All spectroscopies can be performed while the sample is heated or cooled. We report on the general design and the performance of the instrument, as well as first applications in the fields of polymer analysis and bioengineering.

In situ scanning of surface reaction kinetics: NO dissociation on Rh{110}

Static secondary ion mass spectrometry (SSIMS) was applied in either real-time or temperature programmed (TPSSIMS) mode in order to probe the dissociation kinetics of NO on Rh{110}. The validity of the experimental approach was ensured by detailed calibration measurements using temperature programmed desorption (TPD), ion scattering spectroscopy (ISS) and monochromatized X-ray photoelectron spectroscopy (MXPS). The TPSSIMS data were evaluated to obtain both the activation energy, E dis = 15 ± 2 kJ mol , and the pre-exponential, v dis = 10(1.9±0.5) s −1, assuming first order kinetics in a Polanyi-Wig

High resolution monochromated X-ray photoelectron spectroscopy (XPS) studies on novel biodegradable poly(ortho esters) prepared using N-methyl- and N-phenyldiethanolamine, correlated with binding energies obtained from ab initio molecular orbital methods

High resolution monochromated X-ray photoelectron spectroscopy (XPS) was used to investigate the surface chemical structure of novel poly(ortho esters) prepared from N-methyl and N-phenyldiethanolamine (MDE and PDE), respectively. Good agreement was observed between the theoretical and experimental values for the atomic percentages and also for the carbon environments within the C1s spectra. Ab initio molecular orbital calculations were carried out to investigate the effect of local chemical environment on the C -N binding energy. Excellent agreement was observed between experimental and calculated values, provided that the nitrogen configuration in PDE was assumed to be essentially planar and in MDE was pyramidal. This apparent dependence of calculated binding energy on nitrogen configuration is particularly noteworthy and is the subject of further study.

Preparation of a rhodium catalyst from rhodium trichloride on a flat, conducting alumina support studied with static secondary ion mass spectrometry and monochromatic X-ray photoelectron spectroscopy

A rhodium catalyst has been prepared by electrostatic adsorption of RhCl3-derived species in aqueous solution on a model support, consisting of a 4–5 nm thick layer of aluminum oxide on an aluminum foil. The conversion of the rhodium precursor species into metallic rhodium has been studied by monochromatic XPS and static SIMS. Freshly prepared catalysts contain adsorbed Rh-complexes with only one chloro ligand; this is explained by a mechanism in which chloro ligands of the initially adsorbed complex, of the form [RhCln(OH)4-n(H2O)2]−, are displaced by surface OH groups. Analysis of molecular secondary cluster ions of the type RhCl− shows that the Rh-Cl species decompose at reduction temperatures below 200 °C, whereas reduction temperatures well in excess of 200 °C are needed to remove chlorine from the alumina support.

Surface chemistry of catalyst preparation studied by using flat alumina model supports

Rhodium on alumina model catalysts have been made by using a flat, electrically conducting support consisting of a thin film of aluminum oxide on an aluminum foil. Rhodium was applied in the same way as is usual in the preparation of powder catalysts, by adsorption from an aqueous solution of rhodium (III) chloride. The catalysts were studied with monochromatic x-ray photoelectron spectroscopy (XPS), static secondary ion mass spectrometry (SIMS), and Rutherford backscattering spectrometry (RBS). Because the systems have electrical conductivity, XPS spectra of high resolution are obtained while informative molecular clusters of the type RhCl− and RhO−n appear in static SIMS. Angle-dependent XPS spectra of Rh and Al yield an effective layer thickness of Rh, as well as the extent to which the support is covered. RBS indicates that the Rh concentration is in the order of 1015 atoms/cm2.

High resolution monochromated X-ray photoelectron spectroscopy of organic polymers: A comparison between solid state data for organic polymers and gas phase data for small molecules

With the new generation of high energy resolution and high intensity XPS spectrometers now commercially available, several novel aspects of the XPS of organic polymers have become apparent. These include observations on the symmetry and width of core line components, effects resulting from the overlap of shake-up and inelastic scattering regions, the effect of shake-up on nonstoichiometry in the core line envelope, and the observation of surface specific states. We report on these effects and show how a comparison of spectra for a solid phase polymer and the corresponding small molecule in the gas phase can assist interpretation of the polymer data. The implications for analytical and curve fitting work on polymers are discussed.

Oxidation state of platinum in oxidative-addition reactions and .eta.1-iodine products from dihalogen reactions with organoplatinum(II) complexes, as inferred from monochromatic x-ray photoelectron spectroscopy

XPS indicates that the organometallic compd. [PtI[C6H3(CH2NMe2)2-2,6](h1-I2)], (I), representing an end-on coordinated dihalogen intermediate in the oxidative addn. reaction of dihalogen to d8 metal centers, contains platinum in a divalent oxidn. state. The use of a monochromatized x-ray source, short measurement times, and a cooled sample are essential to avoid sample degrdn. [on SciFinder (R)]

Study of Thermal Oxide Solid-State Reaction on GaAs Surfaces

ABSTRACTIn this paper, we will present a study of the thermal reaction of AsjOs with GaAs at temperatures below 550°C using monochromatic X-ray photoelectron spectroscopy (MXPS). A solid-state interface reaction of 4GaAs + 3AS2O5 → 2Ga2O3 + 3AS2O3 + 4As, which includes the usual native oxide thermal reaction: 2GaAs + AS2O3 → Ga2O3 + 4As, as well as a decomposition reaction AS2O5 → AS2O3 + O2 is responsible for the thermal reaction in this temperature range.

NEW METHOD OF CHARGE COMPENSATION IN MONOCHROMATIZED X-RAY PHOTOELECTRON SPECTROSCOPY

A new charge-compensation method in monochromatized X-ray photoelectron spectroscopy has been successfully applied to the surface analysis of nonconductive materials such as ETFE and PET films, In this method unmonochromatized Mg X-rays are used effectively as an electron source for neutrallizing the sample chrging. Continuity of secondary electron energies produced by Bremsstrahlung radiations may play an important role in charge-neutralization process.

Pressure dependence of the charging effect in monochromatized small spot X-ray photoelectron spectroscopy

The pressure dependence of the charging effect, a new parameter influencing the charge-up of insulating samples in monochromatized small spot X-ray photoelectron Spectroscopy (XPS) experiments, is reported. The nature and the extent of the pressure effect differ widely from sample to sample. For a typical insulator such as poly(tetrafluoroethylene) (PTFE) the main function of an increased pressure in the analysis chamber seems to be a buffer of differential charging on the surface of the sample. Argon, an inert gas conventionally used for ion sputtering, is an ideal candidate for the control of pressure. For mono XPS measurements of insulators, the reasonableness of the ultrahigh vacuum (UHV) condition (10 −9 Torr or less) is questionable.

XPS as a tool for the investigation of polymers irradiated by energetic ions

Monochromatized X-ray photoelectron spectroscopy (XPS) has been used to investigate the physical and chemical modifications induced in PVDF (polyvinyledene fluoride) surfaces by high energy oxygen ions. The use of monochromatic X-radiation provides artefact-free analysis, improved signal to background ratio and removal of X-ray satellites. In addition, higher energy resolution enables accurate peak assignments to be made in conjunction with an efficient peak synthesis algorithm.

Magnetic and electronic properties of M-Ba–Cu–O (M = Y, Er, Eu)

Various high-Tc superconductors of the La–(Ba,Sr)–Cu–O and the M–Ba–Cu–O systems with M = Y, Er, and Eu have been prepared by the solid-state reaction method. Single-phase samples with no additional diffraction peaks as verified by x-ray diffraction (XRD) measurements have been obtained. Measurements of the electrical resistivity and of the magnetization showed sharp superconducting transitions with a width of 1 K. The measurements of the magnetic susceptibility have been extended above room temperature up to 770 K. There is clear evidence for the formation of a magnetic moment in all M–Ba–Cu–O samples. Monochromated x-ray photoelectron spectroscopy (MXPS) valence band and x-ray photoelectron spectroscopy (XPS) core level spectra have been measured on various samples at room temperature and at liquid nitrogen temperature.