Ultra-high vacuum Photoelectron 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. 

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... 

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-... 

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. 

In situ methods permit the examination of the surface in its electrolytic environment with application of the electrode potential of choice. Usually they are favored for the study of surface layers. Spectroscopic methods working in the ultra high vacuum (UHV) are a valuable alternative. Their detailed information about the chemical composition of surface films makes them an almost inevitable tool for electrochemical research and corrosion studies. Methods like X-ray Photoelectron Spectroscopy (XPS), UV Photoelectron Spectroscopy (UPS), Auger Electron Spectroscopy (AES) and the Ion Spectroscopies as Ion Scattering Spectroscopy (ISS) and Rutherford Backscattering (RBS) have been applied to metal surfaces to study corrosion and passivity. 

Surface chemical composition is controlled by Time-of-Flight Secondary Ion Mass Analysis (ToF-SIMS) and X-ray Photoelectron Spectroscopy (XPS).1 The analysis under ultra-high vacuum (UHV) conditions allows characterization... 

X-ray photoelectron spectroscopy (XPS), with a defunct "propaganda" name of electron spectroscopy for chemical analysis (ESCA), was developed by Siegbahn186 in 1954 it measures the elemental composition and valence state of elements in solids (atomic number Z = 3 to Z = 92) to within about 5 to 10 nm of their surface by impinging X-rays, typically monochromatized A1 Ka (Ex = 1.4867 keV and lx = 0.83386 nm) in a beam of 0.02- to 0.2-mm diameter, onto a sample surface in ultra-high vacuum and measures to within 0.25 eV... 

The experiments were performed in two different ultra high vacuum (UHV) chambers using two different Pt(lll) single crystals. The X-ray photoelectron spectra were obtained in a chamber with a base pressure of lxlO" Torr. The system has been described in detail elsewhere. In brief, the UHV chamber is equipped with low energy electron diffraction (LEED), an X-ray photoelectron spectrometer (XPS), a quadrupole mass spectrometer (QMS) for temperature programmed desorption (TPD), and a Fourier transform infrared spectrometer (FTIR) for reflection absorption infrared spectroscopy (RAIRS). All RAIRS and TPD experiments were performed in a second chamber with a base pressure of 2 X 10 ° Torr. The system has been described in detail elsewhere. In brief, the UHV chamber is equipped for LEED, Auger electron spectroscopy (AES) and TPD experiments with a QMS. The chamber is coupled to a commercial FTIR spectrometer, a Bruker IFS 66v/S. To achieve maximum sensitivity, an... 

UH UPS UV-vis ultra-high vacuum ultraviolet photoelectron spectroscopy ultraviolet-visible ... 

Surface EXAFS (SEXAFS) uses Auger or photo-electrons to detect the EXAFS signal. This ensures that this technique has a much higher surface sensitivity than EXAFS acquired using the total electron yield method. SEXAFS requires ultra-high vacuum and the detection instrumentation normally associated with Auger electron spectroscopy (AES) or X-ray photoelectron spectroscopy (XPS) techniques. 

Experimental studies of the electronic structure in conjugated molecules during metallization with Al and Ca has recently been performed by means of photoelectron spectroscopy chemically pure (oxygen free) thin films of a model molecule for t ra Ji s-polyacetylene shown in Figure 6, a,ai-diphenyltetradecaheptaene (hereafter denoted DPT), were prepared under ultra-high vacuum conditions. The evolution of the valence leotronlo levels in this molecule could than be monitored in situ by ultraviolet photoelectron spectroscopy (OPS) upon vapour deposition, basically in monolayer steps of Al or Ca. 

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