Ultra-high vacuum technique

Surface defects (Section VII-4C) are also influenced by the history of the sample. Such imperfections may to some extent be reversibly affected by processes such as adsorption so that it is not safe to regard even a refractory solid as having fixed surface actions. Finally, solid surfaces are very easily contaminated detection of contamination is aided by ultra-high-vacuum techniques and associated cleaning protocols [24]. 

Soriaga M P 1992 Ultra-high vacuum techniques in the study of single-crystal electrode surfaces Prog. Surf. Sc/. 39 325... 

Some elements, such as the rare eartlrs and the refractory metals, have a high afflnity for oxygen, so vaporization of tlrese elements in a irormaT vacuum of about 10 " Pa, would lead to the formation of at least a surface layer of oxide on a deposited flhrr. The evaporation of these elements therefore requires the use of ultra-high vacuum techniques, which can produce a pressure of 10 Pa. 

The field emission microscope was invented by E. W. Muller in 1937 and developed by him in the years following (1). For various reasons the device failed to attract general attention until the end of World War II. Its potentialities are now being recognized the field and ion microscopes, in conjunction with recently developed ultra high vacuum techniques, are rapidly becoming important tools for the study of physical and chemical surface phenomena. 

Vacimm Technique. There is a growing literature on ultra high vacuum technique by conventional methods (22). It will suffice to say that vacua of the order of 10 to 10 mm. Hg can be obtained readily with the use of either oil or mercury diffusion pumps. The crucial points are ... 

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. 

Ultra-High Vacuum Techniques of Surface Characterization... 

For measurements of ultraviolet light from a quartz mercury arc passes through a quartz monochromator, silica lens, and window, and is focused onto the crystal at an angle of incidence of about 45°. The saturated photocurrent is collected by the surrounding metal drum to determine ip by the Fowler method (4). A vacuum thermopile measures the light intensity. Photoelectric and diffraction currents are measured by a vibrating reed electrometer. Ultra-high-vacuum techniques are employed, which result in residual pressures of less than 10-9 mm. of Hg. 

The emergence in the 1960s of ultra-high-vacuum techniques, structural studies through LEED and surface sensitive spectroscopies became recognised as the surface science approach to catalysis, answering many of the issues raised in Taylor s paper. It was, however, the last paragraph of his paper that made a particular impression on me ... 

As noted in Section 2.1.2, measurement of the kinetics of chemisorption on clean metal surfaces generally requires ultra high vacuum techniques, in order to accomplish the experiment in a reasonable period of time. The variant of the classical adsorption method known as the flash-filament technique has been developed by several groups of workers and recently summarised by Ehrlich . 

Schrader, M.E. (1980). Ultra-high vacuum techniques in the measurement of contact angles. 5. LEED study of the effect of structure on the wettability of graphite. J. Phys. Chem., 84, 2774-9. 

In summary, to produce a useful probe of subnanometer size, a high-brightness gun is essential together with optimised use of the probe-forming aperture to limit the aberration effects. Among the choice of the various electron sources, the field emission gun stands out. The penalty to be paid for a field emission source is the necessity to use ultra-high vacuum techniques. Such instruments were usually restricted to the dedicated STEM , but nowadays field emission sources are also popular in analytical TEMs. The improvement in the latter has blurred the distinction between dedicated STEM and TEM-STEM . 

Smith, E.F., Rutten, F.J.M., Wlar-Garcia, I.J., Briggs, D. and Licence, P., Ionic liquids in vacuo Analysis of liquid surfaces using ultra-high-vacuum techniques, Langmuir 22, 9386-9392 (2006). 

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