X-ray Photoelectron Spectroscopy Chemical Shifts Research Articles

Part 2.N-[m-(3-(trifluoromethyl)diazirine-3-yl)phenyl]-4- (-3-thio(-1-D-galactopyrannosyl)-maleimidyl)butyramide (MAD-Gal) on diamond

Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and x-ray photoelectron spectroscopy (XPS) are used to characterize a newly synthesized glycosylated photoactivatable reagent designed for surface glycoengineering. The glycoaryldiazirine reagent MAD-Gal (N-[m-(3-(trifluoromethyl)diazirine-3-yl)phenyl]-4-(-3-thio(-1-D- galactopyrannosyl)-maleimidyl)butyramide) is immobilized with 350 nm light on diamond surfaces. The XPS atomic constituents and chemical shifts, as well as ToF-SIMS-specific characteristic fragments of the photoimmobilized molecule, are identified. The grafting on oxygen-containing sites previously observed for N-(m-(3-(trifluoromethyl)diazirine-3-yl)phenyl)-4-maleimido-butyramide (MAD) is confirmed. The difference in grafting efficiency for fresh and aged substrates indicates that other still unidentified reaction sites could be involved. The ToF-SIMS imaging is used to exhibit the ability to pattern the surface with the glycosylated aryldiazirine. © 1998 John Wiley & Sons, Ltd.

Surface analysis for the investigation of electrochemical and corrosion systems

The use of the surface analysis in investigating electrochemical and corrosion systems is discussed. In particular x-ray photoelectron spectroscopy (XPS) in both the core and valence band region are described. Examples are given for metallic and carbon fiber electrode systems, and the role of core XPS chemical shifts analyzed by curve fitting is demonstrated. Valence band XPS is shown to have the ability to probe subtle differences in chemical structure, and is more effective in this respect than core XPS. Unfortunately, since all compounds posses valence electrons, the spectra contain features that cannot readily be interpreted without the help of reliable calculations. Examples illustrates how X-alpha cluster and other calculations can be used to interpret such spectra, allowing subtle chemical differences to be detected and thus enabling the approach to be used as a sensitive analytical surface chemistry probe. New X a and ab initio calculations for the valence band of tetragonal ZrO 2 are presented.

An experimental correlation between points of zero charge and X-ray photoelectron spectroscopy chemical shifts of oxides

Measurements are reported of X-ray photoelectron spectroscopy (XPS) investigations, performed under conditions of ultrahigh vacuum, of several metal oxides either produced commercially (high purity) or prepared in the laboratory. The same oxides were also subjected to electrochemical measurements in aqueous solutions for the determination of the point of zero charge (PZC) values and/or the isoelectric points (IEPs). The PZC (IEP) values appear to be linearly correlated with the sum of the metal and oxygen XPS chemical shifts (DM + DO). The higher (more alkaline) the PZC (IEP), the lower the XPS (DM + DO) term and vice versa. The weighting of the different components in the accuracy of the correlation is discussed. It is shown how a cross comparison between experimental XPS and electrochemical data obtained for the same samples can be used as a diagnostic criterion for the occurrence of secondary phenomena at the solid/liquid boundary.

The Ba/Si(100)-2 × 1 interface: I. XPS and XAES studies of silicide formation

In two complementary papers we present the results and analysis of an extended study of the Ba/Si(100)−2 × 1 interface. In this paper, we will discuss X-ray excited Auger electron spectroscopy- and X-ray photoelectron spectroscopy chemical shifts, as well as plasmon losses, which have been studied to answer the question whether silicide formation occurs at this interface. It is found that no silicide formation takes place at room temperature. Two Ba-Si phases are detected as reaction products upon annealing the Ba/Si(100) system at ~ 550 K.

X-ray photoelectron spectroscopy studies of the reaction of N+2 -ion beams with niobium and tantalum metals

I n situ nitrogen-ion implantation of polycrystalline niobium and tantalum was performed and the surface was characterized by x-ray photoelectron spectroscopy (XPS). The XPS chemical shifts indicated the formation of metal nitride. The chemical shift values are calculated theoretically and compared with the experimental values.

Is there a relationship between X-ray photoelectron spectroscopy chemical shifts and Drago'sE andC parameters? Application to the study of acid-base properties of polymers in the solid state

Is there a relationship between X-ray photoelectron spectroscopy chemical shifts and Drago'sE andC parameters? Application to the study of acid-base properties of polymers in the solid state

Correlation between the isoelectric point of solid surfaces of metal oxides and X-ray photoelectron spectroscopy chemical shifts

The isoelectric point of solid surfaces (IEPS) is an important parameter characterizing the acid—base and adhesion behaviour of oxide surfaces. A satisfactory correlation is obtained between the sum of the metal and oxygen X-ray photoelectron spectroscopy chemical shifts and the IEPS for some anhydrous oxide surfaces. This shows that the overall acid—base behaviour of the surface results from the competition between the acidity of the cation and the basicity of oxygen.

Isotopic equilibration reaction of dinitrogen over raney ruthenium: Importance of the structural factor

The isotopic equilibration reaction of dinitrogen ( 28N 2 + 30N 2 = 2 29N 2) was studied over three Ru catalysts: stabilized Raney Ru, AlRu alloy, and Ru powder. The turnover frequency (TOF) at 588 K ranges from 10 −6 to 10 −6 and depends on the Al/Ru ratio and the microcrystal size of Ru. The highest TOFs are obtained over samples leached at 373 K from alloys having an atomic percent of Ru from 6 to 33. These samples have a smaller average Ru crystal size and a lower Al content, ranging from 8 to 18 mol% as measured by X-ray photoelectron spectroscopy (XPS). We also suggest that the high activity is related to strongly adsorbed nitrogen, the uptake of which exceeds hydrogen adsorption. Almost no XPS chemical shift is observed for any leached Raney Ru, whereas the Ru 3 d binding energy in AlRu alloys is about 1 eV lower than that in Ru metal powder. In spite of the pronounced chemical shift, the TOF on AlRu alloy is quite low. Results suggest that structural factors are most important in this system, rather than the electronic factor that has been emphasized for supported Ru catalysts.

Supported uranium oxides as oxidation catalysts: I. Synthesis and characterization of uranium oxides on A 2O 3, SiO 2, TiO 2, and MgO supports

Supported uranium oxides were prepared on commercial SiO 2, TiO 2, Al 2O 3, and MgO carriers, and characterized by a variety of physicochemical techniques. Simultaneous thermoanalytical techniques (TG, DTA, DTG) allowed a mechanism to be proposed explaining the formation and stabilization of these catalysts. Combined X-ray Photoelectron Spectroscopy (XPS), Energy Dispersive X-Ray Analysis (EDX), and analytical electron microscopy were used to probe the dispersion of the active phase on each support, as a function of the calcination temperature. Encapsulation phenomena of the active phase (UO x ) by the support were observed in the case of SiO 2-and TiO 2-based catalysts calcined at 900 °C. Strong oxide-oxide interaction was postulated to explain the corresponding XPS chemical shift of the uranium level. Segregation of UO x species probably occurs on the more refractory supports, e.g., Al 2O 3 and MgO.

Chemical information from XPS—applications to the analysis of electrode surfaces

Some of the difficulties in using x‐ray photoelectron spectroscopy (XPS) for the chemical characterization of surfaces are considered. XPS chemical shifts are often quite small, compared to spectral line widths and to the accuracy of the reference data. Moreover, subtle differences in peak shape are often degraded by inadequate counting statistics. However, progress toward better chemical characterization is being made by using rigorous peak‐fitting routines and correlating chemical shift information from several photoelectron and Auger electron lines. This paper describes two examples of these procedures in the study of electrode processes: (1) the use of multiple line shifts to follow the evolution and growth of different copper oxide phases during anodic polarization of a copper–metal electrode; (2) the use of peak‐fitting routines to determine stoichiometric changes on a UO2 electrode surface with good precision.

XPS study of the initial growth of oxide films on Inconel 600 alloy

The gas phase oxidation of Inconel 600 alloy has been studied under very mild oxidation conditions. Depth-composition profiles of thin oxide films formed on the alloy have been studied using X-ray photoelectron spectroscopy (XPS) and ion bombardment. The oxide and metal phases within the surface film are reproducibly differentiated using the XPS chemical shift. The film composition and structure were studied as a function of oxidation time, temperature, oxygen concentration and surface topography. Oxidation at 100°C results in formation of a duplex NiO-Cr 2O 3 layer. At 280°C a duplex layer also forms consisting of a NiFe 2O 4 spinel, near the surface, and Cr 2O 3 near the metal interface. Iron diffusion is found to be strongly affected by the method of preparation; chromium diffusion is not. Oxygen concentration affects the relative concentration of nickel oxide produced during oxidation. The chromium oxide phase, however, is unaffected by oxygen concentration at this temperature, suggesting that growth of this protective layer is severely limited by the low outward diffusion rate of chromium ion. The initial oxide film is more enriched in chromium at 500°C than at 300°C, and some evidence of internal oxidation is seen. Oxidation of the nickel phase occurs after a limiting thickness of Cr 2O 3 is established. At 700°C, a surface oxide phase of CrO 2 is established initially. The optimum conditions for formation of a pure chromium oxide layer on Inconel 600 are high temperature, annealed alloy surfaces and a low oxidant concentration.