Surface analysis methods

It is often desirable to alter the surface properties of a membrane, for example to reduce adsorption or to introduce specific groups that can be used for affinity membranes. Surface modification can also be used as a method of changing the separation properties of a material. 

In composite membranes, the membrane properties are determined by an extremely thin layer, en this layer is applied via a polymerisation reaction, e.g. plasma polymerisation, interfacial polymerisation, or in-situ polymerisation, the chemical nature of this layer is often not known exactly. Hence, it becomes necessary to determine the surface properties by surface analysis. 

Surface analysis methods are based on the concepts outlined schematically in figure IV - 45. 

A solid surface is excited by means of radiation or particles bombardment and the emission products, which provide information about the presence of specific groups, atoms, or bonds, are detected. The following techniques are frequently used [32 - 36]  

ESCA Electron Spectroscopy for Chemical Analysis XPS X-ray Photoelectron Spectroscopy SIMS Secondary Ion Mass Spectrometry AES Auger Electron Spectroscopy 

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Analysis of Surface Elemental Composition. A very important class of surface analysis methods derives from the desire to understand what elements reside at the surface or in the near-surface region of a material. The most common techniques used for deterrnination of elemental composition are the electron spectroscopies in which electrons or x-rays are used to stimulate either electron or x-ray emission from the atoms in the surface (or near-surface region) of the sample. These electrons or x-rays are emitted with energies characteristic of the energy levels of the atoms from which they came, and therefore, contain elemental information about the surface. Only the most important electron spectroscopies will be discussed here, although an array of techniques based on either the excitation of surfaces with or the collection of electrons from the surface have been developed for the elucidation of specific information about surfaces and interfaces. 

Table 8 shows results obtained from the application of various bulk and surface analysis methods to lithium metal at rest or after cyclization experiments, as well as at inert and carbon electrodes after cathodic polarization. The analytical methods include elemental analysis, X-ray photoelectron spectroscopy (XPS or ESCA), energy-dispersive analysis of X-rays (X-ray mi-... 

GDS instruments are viable alternatives to the traditional arc and spark-source spectroscopies for bulk metals analysis. Advantages of GDS over surface analysis methods such as AES, XPS and SIMS are that an ultrahigh vacuum is not needed and the sputtering rate is relatively high. In surface analysis, GD-OES, AES, XPS and SIMS will remain complementary techniques. GD-OES analysis is faster than AES (typically 10 s vs. 15 min). GD-OES is also 100 times more sensitive than... 

Some of the modern surface analysis methods have been used to study the surface chemistry of both plasma etched surfaces and plasma polymerized thin films. Much of this work has involved exposure of these surfaces to air as the samples are transferred from the plasma system to the surface analysis system. However, in a few cases surface analysis has been performed in the plasma system after the plasma gas has been pumped away. This work will be discussed in more detail later in this chapter. 

D. J. Connor, B. A. Sexton, and R. St. C. Smart, eds., Surface Analysis Methods in Materials Science, Springer Series in Surface Sciences, Vol. 23, Springer-Vedag, Berlin, 1992. 

Main features of SIMS as a surface analysis method... 

The main purpose of this Introductory lecture is to set the stage for the detailed papers which follow by indicating broadly the objectives, principles and methods of modern surface analysis. A secondary objective is to provide some perspective on the major developments in modern surface analysis methods during the past decade, and on the prospects for their future development during the coming decade. 

In this symposium emphasis is placed on the first class of methods. Isolated examples of the third class are discussed. Consideration of the second class is omitted entirely. Indeed, the scope of the symposium is perhaps best described as encompassing the more widespread techniques of surface compositional analysis as applied to materials science and electrochemistry oriented problems. Many modern surface analysis methods, e.g., those embodying tip sample geometries (21 22, 3, 34), those based on synchrotron radiation (23, 25), and those dealing with surface structure (15-20) and dynamics ( 3, 21-23), as opposed to surface composition, are not represented in the symposium program even though many of them enjoy "industrial applications" in the areas of electronics, metallurgy and catalytic chemistry. 

It has been shown that energetic ion beams may be utilized to "nondesthuctively" determine the profile of composition vs. depth in a wide variety of near surface situations. The major difficulties and limitations of the method have been delineated with descriptions of alternative methods applicable in difficult cases. The advantages of using these techniques as complementary to other surface analysis methods has also been pointed out. 

This book provides an overview of the industrial applications of surface analysis. The range of its uses is so broad that we have not attempted to provide comprehensive coverage. Instead, we have presented some of the topics significant to the industrial sectors and to the energy technologies to illustrate the range of surface analysis methods and their relative utility in solving surface and interface problems. 

Studies of molecular adsorption from solution at well-defined solid surfaces is yielding important results. Well-defined surfaces have a simplifying effect on such studies by eliminating many of the structural imperfections which would otherwise complicate the results with a mixutre of adsorption states. Surface analysis methods such as LEED, Auger spectroscopy, EELS, XPS and voltammetry are very well suited to the characterization of surface molecular structure, composition, and bonding. As a result, clear correlations between adsorbed state and surface chemical or electrochemical reactivity are beginning to emerge. 

Ellipsometry is probably the only easy-to-use surface analysis method which can be operated in situ and in real time. On the contrary, multiple internal reflection Fourier transform infrared spectroscopy is a very powerful technique [38] but it is rather tricky to implement. Ellipsometry allows real time studies of the surface modification during exposure to the plasma, and after the treatment. Figure 10 shows for example the variation of and A ellipsometry angles upon fluorination of Si in fluorine-based plasmas as a function of pressure and gas mixture [39], thus demonstrating the sensitivity of the technique. Infrared ellipsometry has also been used with success to investigate reaction layer composition and formation on Si in CF4-based plasmas [40,41], or to monitor patterning [42]. 

To combine optical SFG spectroscopy with the more traditional surface analysis methods (e.g., LEED, AES, TPD, XPS), the basic requirement is to simply add IR-transparent windows (e.g., CaF2 or BaF2) to a UHV chamber. However, if SFG spectroscopy is to be carried out at high pressure or during catalytic reactions, instruments combining a EIHV surface analysis system with an SFG-compatible... 

Beam Effects, Surface Topography, and Depth Profiling in Surface Analysis (Methods of Surface Characterization), Czanderna, A. W Madey, T. E. Powell, C. J. eds.. Plenum Press New York,... 

Surface Analysis Methods in Materials Science, D.J. O Connor. B.A. Sexton and R.C. Smart, Eds., Springer (1992). (Guide describing major techniques, plus applications in materials science.)... 

Consider a size distribution obtained by a surface analysis method, e.g. photosedimentation, where the measured diameter is the Stokes diameter (r/y,) and the surface fraction between two diameters centered on is Sr-... 

DJ O Connor, BA Sexton, RSC Smart, eds. Surface Analysis Methods in Material Science. Berlin Springer-Verlag, 1992. 

In this section the most important surface analysis methods which are effective to a depth of 50 A are mentioned. They are based either on the interaction of ions with surface layers, the ejection and analysis of electrons from the surface, or the investigation of secondary ions. 

On the other hand, optical microscopy, confocal microscopy, ellipsometry, scanning electron microscopy (SEM), scanning tunneling microscopy (STM), atomic force microscopy (AFM) and total internal reflection fluorescence (TIRF) are the main microscopic methods for imaging the surface structure. There are many good books and reviews on spectroscopic and chemical surface analysis methods and microscopy of surfaces description of the principles and application details of these advanced instrumental methods is beyond the scope of this book. 

The operation and maintenance of ESCA equipment and interpretation of its data are quite complex. Samples intended for ESCA and other surface analysis methods should be handled carefully because minute contamination can mask the surface structure... 

The development of new methods for studying surfaces is progressing rapidly, precipitated by the phenomenal growth and interest in surface physics and chemistry which was stimulated, in part, by the need for clean, well-characterized surfaces for microelectronic and other high-technology applications. The biomaterials field should be able to capitalize upon this plethora of new methods which have appeared primarily in the past 15 years. In particular, many of the new techniques measure surface chemistry directly, in contrast to older methods which often required indirect or thermodynamic data. At the present stage of development in the field of surface analysis, a picture of a surface must be built up by using a variety of methods. Combinations of the classic surface analysis methods (e.g., con-... 

A. Joshi, L.E. Davis, and P.W. Palmberg. Auger Electron Spectroscopy. In A.W. Czandema, editor. Methods of Surface Analysis. Methods and Phenomena Their Applications in Science and Technology, Volume 1. Elsevier, New York, 1975. 

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