Spectroscopy in the X-ray Range

Instrumentation. In both cases, a near field probe is employed—either a metal-coated fiber (aperture-based) or a metal tip (apertureless). Distance regulation, as used with scanning probe methods (see Sect. 7.2), controls the probe-surface gap it may also be used to obtain a topographic mapping of the studied surface. Scattered light is collected and guided to a Raman spectrometer. In a (non-electrochemical) study, dye-labeled DNA that had adsorbed onto evaporated silver layers on FIFE nanospheres was observed [531]. Special surface sites with particularly high enhancement could be identified. 

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Photons as probes may also cause the emission of electrons from the sample, and the kinetic energy distribution of these photoelectrons can be recorded and analysed. This technique is called photoelectron spectroscopy (PES) in general, but if the photons are in the ultraviolet range, UPS, or in the X-ray range, XPS. Photoelectron spectroscopy permits direct examination of electronic orbitals of atoms by providing information about the electrons in both the valence bands and the core levels of the constituent elements of solids. Under suitable conditions the electronic states of bulk and surface atoms can be distinguished. 

X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are the two main techniques based on electron spectroscopy. In XPS, a source of photons in the X-ray energy range is used to irradiate the sample. 

ZSM-5 zeolites modified by conventional and solid-state ion-exchange were characterized by X-ray diffraction, BET measurements, derivatography, IR spectroscopy in the framework vibration range and acidity measurements with pyridine as probe. NO adsorption and transformation on Cu-, Co-, Ni- and FeZSM-5 zeolites were followed by IR spectroscopy. Mono- and dinitrosyl surface species, adsorbed NjO and NO were detected in different concentrations on the tested catalysts. Differences in adsorption behaviour were observed for samples exchanged by the conventional and solid-state procedures. 

For many problems in atomic, molecular, and solid-state physics intense sources of mnable X-rays are required. Examples are inner-shell excitation of atoms and molecules or spectroscopy of multiply charged ions. Until now, these demands could only partly be met by X-ray tobes or by synchrotron radiation. The development of lasers in the spectral range below 100 nm is therefore of great interest. Besides the free electton laser, which represents the most powerful but expensive X-ray laser, there are other possibilities which can realize much less expensive table top lasers in the X-ray region. They are based on different excitation mechanisms ... 

The task of an X-ray absorption spectrometer is the precise and accurate measurement of the linear X-ray absorption coefficient of a substance. A principal use of such spectrometers is the measurement of X-ray absorption fine structure (XAFS) spectra of solids, liquids, and molecular gases. XAFS consists of modulations in the X-ray absorption coefficient in the vicinity of an X-ray absorption edge, which may extend more than one KeV beyond the edge. Applications and theory of X-ray Absorption Spectroscopy are covered elsewhere in this volume. This article is directed primarily to instrumental requirements for X-ray absorption spectroscopy over the energy range from several KeV X-ray photon energy to approximately 100 KeV, with emphasis on synchrotron radiation based instruments. 

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