Ultrahigh-vacuum techniques

Ultrahigh vacuum techniques have become common, especially in connection with surface spectroscopic and diffraction studies, but also in adsorption on very clean surfaces. The techniques have become rather specialized and the reader is referred to Ref. 8 and citations therein. 

Modern Methods in Surface Kinetics Flash, Desorption, Field Emission Microscopy, and Ultrahigh Vacuum Techniques Gert Ehrlich... 

Application of Spectrophotometry to the Study of Catalytic Systems H. P. LeftinandM. C, Hobson,Jr. Hydrogenation of Pyridines and Quinolines Morris Freifelder Modern Methods in Surface Kinetics Flash, Desorption, Field Emission Microscopy, and Ultrahigh Vacuum Techniques Gert Ehrlich... 

The reflection technique has not been used as extensively as transmission. Its slow development may be attributed to several factors. It is used primarily on highly polished metal surfaces including those involved in fundamental studies of single crystals. The theoretical framework for reflection IR spectra has been developed only recently. Ultrahigh-vacuum techniques are required and modifications are needed for standard IR spectrometers. Since the reflection technique can be used with single crystals of metals, it is a bridge between the more sophisticated surface techniques used in surface science and the IR studies of the more practical catalysts. 

Ultrahigh vacuum techniques (basic pressure xl02 Pa) enable adsorption studies to be made on stringently clean solid surfaces whereas degassing under moderate vacuum conditions, as normally applied in surface area determinations, leave the adsorbent covered with a preadsorbed layer of impurities and/or the adsorbate. On subsequent adsorption (e.g. of N2 or noble gases) completion of the physisorbed monolayer is usually reached at p/pn 0.1 whereas on clean surfaces this state occurs at p/p° values which may be smaller by orders of magnitude. However, as mentioned above, it should be kept in mind that linearity of the BET plot does not in itself provide conclusive evidence for the validity of njj,. 

In the endeavor for a better understanding of the catalytic act and of its relation to the properties of the solid, two lines of approach may be followed. First, with the help of ultrahigh-vacuum techniques, it seems possible to measure the catalytic activity of nearly perfect surface planes (single crystals) and correlate it to some reliable measurements of solid-state surface properties. A few studies of this type have been published [see, for instance, Farnsworth 17)] but no definite correlations between catalytic activities and surface properties have been proposed. 

This tremendous advance has, in large measure, been made possible by the reduction of ultrahigh vacuum techniques to a matter of complete routine. For the first time it has become easy to specify exactly the environment at an interface and to perform meaningful measurements on samples with a surface area of less than a square centimeter. As a consequence, considerable progress has been made in apprehending the relation between surface structure and the elementary rate processes important in adsorption. 

Flash desorption, as well as electron and ion emission microscopy are based on a mastery of ultrahigh vacuum techniques, that is upon the ability to establish and maintain pressures well below 10 mm. In... 

What Langmuir had in mind were clean, well-defined singlecrystal surfaces that can now be prepared and investigated through the introduction of ultrahigh vacuum techniques and the development of a whole arsenal of surface physical methods. 

The ultrahigh vacuum technique of secondary ion mass spectrometry (SIMS) is the most sensitive of all the commonly employed sruface analytical techniques. There are a number of variants of the technique for example, static SIMS is used to examine submonolayer elemental analysis, dynamic SIMS is used to obtain compositional information as a function of depth below the sruface, and imagining SIMS is used for spatially resolved elemental analysis. Specimens commonly examined by SIMS are 2.5 cm in diameter and 1 cm thick. When ceramic materials are examined, sample charging is prevented by flooding the surface of the sample with an electron beam. Dynamic SIMS is of great interest and has been used to study changes in elemental composition from weathered or corroded surfaces of samples into the bulk matrix. 

Schrader, M.E. (1970), Ultrahigh Vacuum Techniques in the Measurement of Contact Angles 11. Water on Gold, J. Phys. Chem. 74. p.2313. 

Clusters on surfaces, or supported clusters, lend themselves to a variety of X-ray and electron spectroscopies, such as extended X-ray absorption fine stmcture (EXAFS), X-ray and ultraviolet photoelecfron spectroscopy (XPS and UPS), and transmission electron microscopy (TEM) to name a few. Most studies of model systems have used sodium chloride or carbon substrates and ultrahigh-vacuum techniques. 

G. Ehrhch, Modern Methods in surface kinetics flash desorption, field emission microscopy, and ultrahigh vacuum techniques. Adv. Catal. 14, 255 27 (1963). doi 10.1016/S0360-0564(08)60341-7... 

Finally it should be noted that ultrahigh vacuum techniques such as photoelectron and ion spectroscopies are being applied in creative ways to the characterization of complex interfaces. In this area examples are too numerous to cite in this brief overview, and the reader is referred to the chapter by Pomerantz and coworkers W the qrplication of two of these techniques, electron energy loss spectroscopy (EELS) and secondary ion mass spectrometry (SIMS), to the study of organic monolayer films. 

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