Ultra high vacuum spectroscopy

In X-ray photoelectron spectroscopy (XPS), a beam of soft X-rays with energy hv s. focused onto the surface of a solid that is held under an ultra-high vacuum, resulting in the ejection of photoelectrons from core levels of the atoms in the solid [20]. Fig. 15 shows an energy level diagram for an atom and illustrates the processes involved in X-ray-induced photoelectron emission from a solid. 

While electron or ion beam techniques can only be applied under ultra-high vacuum, optical techniques have no specific requirements concerning sample environment and are generally easier to use. The surface information which can be obtained is, however, quite different and mostly does not contain direct chemical information. While with infra-red attenuated total reflection spectroscopy (IR-ATR) a deep surface area with a typical depth of some micrometers is investigated, other techniques like phase-measurement interference microscopy (PMIM) have, due to interference effects, a much better surface sensitivity. PMIM is a very quick technique for surface roughness and homogeneity inspection with subnanometer resolution. 

The physical methods mostly require ultra high vacuum conditions having the disadvantage of not being applicable directly to solvent swollen films, but recent developments of in situ measurements in SIMS X-ray diffraction surface enhanced Raman spectroscopy (SERS) and scanning electrochemical tunneling microscopy... 

Villegas I, Weaver MJ. 1996. Infrared spectroscopy of model electrochemical interfaces in ultra-high vacuum Evidence for coupled cation-anion hydration in the Pt(lll)/K, Cl system. J Phys Chem 100 19502-19511. 

The methodology of surface electrochemistry is at present sufficiently broad to perform molecular-level research as required by the standards of modern surface science (1). While ultra-high vacuum electron, atom, and ion spectroscopies connect electrochemistry and the state-of-the-art gas-phase surface science most directly (1-11), their application is appropriate for systems which can be transferred from solution to the vacuum environment without desorption or rearrangement. That this usually occurs has been verified by several groups (see ref. 11 for the recent discussion of this issue). However, for the characterization of weakly interacting interfacial species, the vacuum methods may not be able to provide information directly relevant to the surface composition of electrodes in contact with the electrolyte phase. In such a case, in situ methods are preferred. Such techniques are also unique for the nonelectro-chemical characterization of interfacial kinetics and for the measurements of surface concentrations of reagents involved in... 

The tools used for the experiments described below have been described in several books and review articles (1-3). Surface structure is determined by low energy electron diffraction (LEED), surface composition by Auger electron spectroscopy (AES), and reaction kinetics and mechanism by temperature programmed reaction spectroscopy (TPRS). Standard ultra-high vacuum technology is used to maintain the surface in a well-defined state. As this article is a consolidation of previously published work, details of the experiments are not discussed here. 

The work function of electrodes emersed from aqueous solutions in ultra high vacuum (UHV) can be measured by means of the ultra-violet photo-electron emission spectroscopy (UPS) [KOtz-Neff-MUller, 1986]. Figure 4-27 shows the work function measured by UPS of the emersed metal electrodes of gold,... 

Surface science experiments and DFT have often been teammates in very successful projects. DFT has been used along with ultra-high-vacuum surface science experiments such as scanning tunneling microscopy (STM), temperature-programmed desorption, X-ray diffraction, and X-ray photoelectron spectroscopy... 

The SEXAFS teehnique is a partieular surface sensitive detection mode applied to an EXAFS measurement, performed in a particular environment, the Ultra High Vacuum, which is needed in order to prepare and protect the atomic-scale eleanliness of surface and interface systems for the whole time length of the experiment. As such the technique borrows equipment and procedures from the surface science spectroscopies, and exploitation procedures of the synchrotron radiation source from the conventional, non vacuum, EXAFS method. The studies described below have been performed at the Laboratoire pour T Utilisation du Rayonnement Electro-magnetique (LURE) exploiting synehrotron radiation from the storage ring DCI... 

Techniques of electron spectroscopies have emerged to become the principal means for investigating electronic structures of solids and surfaces (Rao, 1985 Mason et al, 1986). Most of these techniques involve the analysis of the kinetic energy of the ejected or scattered electrons. Some of the important techniques of electron spectroscopy used to study solids are photoelectron spectroscopy using X-rays (XPS) or UV radiation (UVPS), Auger electron spectroscopy (AES) and electron energy loss spectroscopy, (EELS). All these techniques are surface-sensitive and probe 25 A or less of solids. Cleanliness of the surfaces and ultra-high vacuum ( 10 — 10 " torr) are there-... 

For a better characterization of the catalytic surface, the sample has been transferred through a glove box into an ultra high vacuum device and Auger electron spectroscopy was carried out. 

We begin with the most routine characterization methods—electrochemical methods. We then discuss various instrumental methods of analysis. Such instrumental methods can be divided into two groups ex situ methods and in situ methods. In situ means that the film on the electrode surface can be analyzed while the film is emersed in an electrolyte solution and while electrochemical reactions are occurring on/in the film. Ex situ means that the film-coated electrode must be removed from the electrolyte solution before the analysis. This is because most ex situ methods are ultra-high-vacuum techniques. Examples include x-ray photoelectron spectroscopy [37], secondary-ion mass spectrometry [38,39], and scanning or transmission electron microscopies [40]. Because ex situ methods are now part of the classical electrochemical literature, we review only in situ methods here. 

Only a small amount of research has been published dealing with the reactions of / -diketones with clean metal surfaces.513,514 The interaction of acetylacetone with iron and nickel films under ultra high vacuum conditions has been investigated. X-Ray photoelectron spectroscopy is a particularly useful analytical probe as data on gas phase metal acetylacetonates are available for comparison.515 On iron, dissociative adsorption giving acetylacetonate occurs at 90 K. This decomposes at about 290 K to form surface oxide, chemisorbed oxygen and a species considered to contain Fe—C bonds. 

The X-ray photoelectron spectroscopy (XPS) experiments were performed in an ultra-high vacuum (UHV) chamber coupled to an atmospheric pressure reaction cell. All XPS results were obtained from samples treated in situ in the reaction cell and transferred into UHV without exposure to air. Detailed sample mounting procedures and instrument details are described elsewhere.16 Ar+ bombardment was done with 3 KeV Ar+ ions at a current density of 0.8 pA/cm2 for 1 h in an attempt to remove the carbon overlayer and expose the underlying carbide phase. 

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