Principles of surface analysis

In surface studies, one is confronted with the difficulty of detecting a small number of surface atoms in the presence of a large number of bulk atoms a typical solid surface has 10 atoms/cm as compared with 10 atoms/cm in the bulk. In order to be able to probe the properties of solid surfaces using conventional methods, one needs the use of powders with very high surface-to-volume ratio so that surface effects become dominant. However, this technique suffers from the distinct disadvantage of an entirely uncontrolled surface structure and composition which are known to play an important role in surface chemical reactions. It is thus desirable to use specimens with well-defined surfaces which generally means small surface area, of the order of 1 cm, and examine them with tools that are surface sensitive. 

Many such techniques have been developed and used. Low-Energy Electron Diffraction, in which electrons are elastically scattered off a surface, has been the most successful among those for surface crystallography. Inelastically scattered electrons also 

The universal curve for the electron mean free path as a function of electron kinetic energy. Dots show individual measurements 

We now briefly describe the mechanism, capabilities and limitations of the main techniques used in surface analysis classifying them by the nature of the information obtained with them. 

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The principle of surface analysis methods is as follows (Figure 3.13). The surface to be analyzed is irradiated with electrons. X-rays or ions. As a result of collisions of the incident particles with atoms of the solid, electrons, photons or ions are emitted that contain specific chemical information. With a suitable detector one measures their quantity and their energy or mass. 

Then we discuss the principles involved in the measurements of surface-specific physical quantities. Since each of the many techniques of surface analysis is sensitive to a few particular aspects of the surface (such as relative atomic positions, electronic levels, chemical composition, binding energies and vibration frequencies), we classify these techniques according to the surface characteristic that they are most sensitive to. 

This paper is a synopsis of the introductory lecture at the American Chemical Society Symposium on "Industrial Applications of Surface Analysis." Following a review of the objectives of surface analysis, an outline is given of the design principles for measurements to achieve these objectives. Then common techniques for surface analysis are surveyed briefly. An example of the application of these techniques in microelectronics is indicated. The paper concludes with an assessment of the major advances in surface analysis during the past decade and an indication of the major current trends which could lead to comparable advances during the coming decade. 

Markey R, Principles of surface plasmon resonance, in Real-Time Analysis of Biomolecular Interactions—Applications of BIAcore, ed. K. Nagata and H. Handa (Tokyo, Japan Springer-Verlag, 2000) pp. 13-32. 

Principles and Characteristics As polymer surfaces (top 10 A) and microscopic phases (<60 /xm) influence many of today s critical technologies, their detailed quantitative characterisation is crucial. However, the spatially resolved chemical analysis of polymer surfaces and microscopic phases has historically been difficult to obtain. It is clearly the ultimate objective of surface analysis to give a quantitative description of the... 

Thin films are usually prepared from the vapor phase, but they can al.so be obtained from liquid or solid phases by applying physical or chemical driving forces, or various combinations of the latter [1-3). In principle, two types of film may be identified from the point of view of surface analysis one in which the film is deposited on a substrate (workpiece), and the other in which the film is created as a result of the modification of the surface atomic layers of a substrate. In the latter case there is a strong involvement of the constituents of the solid substrate. A brief survey of the most frequently applied deposition and implantation techniques is presented below. 

Fig.1 The basic principles of surface plasmon resonance and analysis in BIAcore experiments. See text for details...

The eddy current method allows to evalute the state of stress in ferromagnetic material. The given method is used for determining own stress as well as that formed in effect of outside load. With regard to physical principles of own stress analysis, the dependence between the magnetic permeability and the distance between atomic surfaces is utilized. 

The common civil engineering seismic testing techniques work on the principles of ultrasonic through transmission (UPV), transient stress wave propagation and reflection (Impact Echo), Ultrasonic Pulse Echo (UPE) and Spectral Analysis of Surface Waves (SASW). 

As on previous occasions, the reader is reminded that no very extensive coverage of the literature is possible in a textbook such as this one and that the emphasis is primarily on principles and their illustration. Several monographs are available for more detailed information (see General References). Useful reviews are on future directions and anunonia synthesis [2], surface analysis [3], surface mechanisms [4], dynamics of surface reactions [5], single-crystal versus actual catalysts [6], oscillatory kinetics [7], fractals [8], surface electrochemistry [9], particle size effects [10], and supported metals [11, 12]. 

Because surface science employs a multitude of teclmiques, it is necessary that any worker in the field be acquainted with at least the basic principles underlying tlie most popular ones. These will be briefly described here. For a more detailed discussion of the physics underlymg the major surface analysis teclmiques, see the appropriate chapter m this encyclopedia, or [49]. 

Surface Area and Permeability or Porosity. Gas or solute adsorption is typicaUy used to evaluate surface area (74,75), and mercury porosimetry is used, ia coajuactioa with at least oae other particle-size analysis, eg, electron microscopy, to assess permeabUity (76). Experimental techniques and theoretical models have been developed to elucidate the nature and quantity of pores (74,77). These iaclude the kinetic approach to gas adsorptioa of Bmaauer, Emmett, and TeUer (78), known as the BET method and which is based on Langmuir s adsorption model (79), the potential theory of Polanyi (25,80) for gas adsorption, the experimental aspects of solute adsorption (25,81), and the principles of mercury porosimetry, based on the Young-Duprn expression (24,25). 

An introduction to the principles behind SPI-SALI, this ankle presents a theoretical discussion of why SPI-SALI is much less fragmenting than MPI-SALI. Examples are shown which describe the additional fragmentation induced by the desorption beam—in this case ESD is compared to ion sputtering. The main focus of the article is the advantages of SPI-SALI for surface analysis of bulk organic polymers. 

Therefore, this book is to give the analyst - whether a newcomer wishing to acquaint themself with new methods or a materials analyst needing to inform themself on methods that are not available in their own laboratory - a clue about the principles, instrumentation, and applications of the methods, techniques, and procedures of surface and thin-film analysis. The first step into this direction was the chapter Surface and Thin Film Analysis of Ullmann s Encyclopedia of Industrial Chemistry (Vol. B6, Wiley-VCH, Weinheim 2002) in which practitioners give briefly outline the methods. 

X-ray photoelectron spectroscopy (XPS), which is synonymous with ESCA (Electron Spectroscopy for Chemical Analysis), is one of the most powerful surface science techniques as it allows not only for qualitative and quantitative analysis of surfaces (more precisely of the top 3-5 monolayers at a surface) but also provides additional information on the chemical environment of species via the observed core level electron shifts. The basic principle is shown schematically in Fig. 5.34. 

The control of materials purity and of environmental conditions requires to implement physico-chemical analysis tools like ESC A, RBS, AUGER, SEM, XTM, SIMS or others. The principle of SIMS (Secondary Ion Mass Spectroscopy) is shown in Eig. 31 an ion gun projects common ions (like 0+, Ar+, Cs+, Ga+,. ..) onto the sample to analyze. In the same time a flood gun projects an electron beam on the sample to neutralize the clusters. The sample surface ejects electrons, which are detected with a scintillator, and secondary ions which are detected by mass spectrometry with a magnetic quadrupole. 

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