Monochromatic XPS

Sensitive materials, such as certain metal salts or organometallic compounds used as catalyst precursors, may decompose during XPS analysis, particularly in equipment with standard X-ray sources. Heat and electrons generated by the source are usually responsible for damage to samples. In these cases the monochromatic XPS offers a solution. For example, reliable spectra of the organoplati-num complexes in Figs. 3.4 and 3.5 could only be obtained with a monochromatic source. Under the standard source the Pt(IV) complex indicated in Figs. 3.4 and 3.5 decomposed into the Pt(II) precursor and Cl2 gas. 

The data in the Figs. 9.1,9.2 and 9.4 nicely illustrate the complementarity of XPS and SIMS and the possibilities that thin film oxide supports offer for surface investigations. Owing to the conducting properties of the support, charging is virtually absent and typical single crystal techniques such as monochromatic XPS and static SIMS can be applied to their full potential to answer questions on the preparation of supported catalysts. 

Fundamental XPS Data to assist peak-fitting elements, binary oxides and chemical compounds, from The XI Library of Monochromatic XPS Spectra (Xi Corp., US registered copyright, TX 4-560-881). 

Sensitive materials, such as metal salts or organometallic compounds used as catalyst precursors, may decompose during XPS analysis, particularly when a standard X-ray source is used. Heat and electrons from the source may cause damage to samples. In such cases a monochromatic XPS offers a solution [24]. 

Borg, H. J., Oetelaar, L. C. A. V. D. Niemantsverdriet, J. W. Preparation of a rhodium catalyst from rhodium trichloride on a flat, conducting alumina support studied with static secondary ion mass spectrometry and monochromatic XPS. Catalysis Letters 17, 81-95 (1993). 

XPS is best performed using a monochromatic X-ray source. Monochromatic XPS inflicts the least damage to delicate materials and optimises chemical state sensitivity. A monochromatic X-ray sonrce is an essential requirement to extract the maximum information content from most polymer systems. 

B.V. Crist, Handbook of Monochromatic XPS Spectra. Polymers Polymers Damaged by X-Rays, Wiley-Interscience, New York, NY (2000). 

The material quoted in this chapter is based upon work supported by the National Science Foundation, the Air Force Office of Scientific Research, and NASA. The monochromatic XPS data were recorded on an instrument funded by the National Science Foundation under grant CHE-9421068. The author ac-... 

Crist B.V. (2000) The Handbook if Monochromatic XPS Spectra, Part 2, Polymers and Polymers Damaged by X-rays. John Wiley, Chichester... 

If monochromatic X-rays are used as the ionizing radiation the experimental technique is very similar to that for XPS (Section 8.1.1) except that it is the kinetic energy of the Auger electrons which is to be measured. Alternatively, a monochromatic electron beam may be used to eject an electron. The energy E of an electron in such a beam is given by... 

The photoelectron line of main interest is Cls. Different bonding in the environments of the carbon atoms leads to very small chemical shifts of this line. High-resolution XPS is, therefore, required and monochromatic radiation should be used to prevent overlap with satellite lines. 

Another important characteristic of XPS is that relatively little damage occurs when samples are illuminated with X-rays, especially from a non-monochromatic... 

Other techniques utilize various types of radiation for the investigation of polymer surfaces (Fig. 2). X-ray photoelectron spectroscopy (XPS) has been known in surface analysis for approximately 23 years and is widely applied for the analysis of the chemical composition of polymer surfaces. It is more commonly referred to as electron spectroscopy for chemical analysis (ESCA) [22]. It is a very widespread technique for surface analysis since a wide range of information can be obtained. The surface is exposed to monochromatic X-rays from e.g. a rotating anode generator or a synchrotron source and the energy spectrum of electrons emitted... 

X-ray photoelectron spectroscopy (XPS) is based on the photoelectric effect. When a sample is irradiated with monochromatic X-rays, such as the K lines of Mg (1253.6eV) or Al (1486.6 eV), core-level electrons from the inner shells of atoms in the sample will be ejected from the sample to the surrounding vacuum. The kinetic energy, Er, of the emitted photoelectron is given by... 

Calculation of the mean diameter was done by means of the Scherrer equation [34] and the atomic percentage of gold at the carbon surface was determined by XPS, M-Probe Instrument (SSI) equipped with a monochromatic A1 Ka source (1486.6 eV). 

Here, we demonstrate clear and direct evidence for the modified electronic structures of surface Pt atoms in Pt-Co and Pt-Ru by using EC-XPS [Wakisaka et al., 2006]. The sample electrode was transferred between an XPS chamber and an electrochemical (EC) chamber without exposure to air (to minimize contamination of the surface). All photoelectron spectra, including the valence level region) were taken by using a monochromatic Al Ka (hv = 1486.58 eV). The uncertainty of binding energy measurement was less than + 0.03 eV. 

XPS or ESCA (electron spectroscopy for chemical analysis) is a surface sensitive technique that only probes the outer atomic layers of a sample. It is very useful tool to study polymer surfaces [91]. An XPS spectrum is created by focusing a monochromatic beam of soft (low-energy) X-rays onto a surface. The X-rays cause electrons (photoelectrons) with characteristic energies to be ejected from an electronic core level. XPS, which may have a lateral resolution of ca. 1-10 pm, probes about the top 50 A of a surface. 

Fig. 2 Scheme of a modern XPS instrument with a monochromatic X-ray source... 

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