Surface analytical methods

In previous chapters a broad variety of methods has been treated which could be easily grouped into spectroscopic methods or techniques employing some sort of interaction between electromagnetic radiation and the electrochemical interface. Various techniques remain which are hard to assign to any of the families of methods presented so far. This is partly caused by the fact, that some of these methods combine optical, i.e. spectroscopic, details with experimental features providing spatial resolution or to the fact, that surface properties like e.g. electrical conductivity are measured which have no direct or obvious relationship to spectroscopic methods. 

The advent of ever smaller electrochemically cells (microcells, capillary cells) which can be placed on selected areas of an electrode surface allows spatially resolved measurements of local properties. Spectroscopic methods modified in such a way like e.g. locally resolved electrochemical mass spectrometry have been treated in previous sections. Optical methods incorporating scanning probes wiU be treated below. Classical electrochemical methods like e.g. impedance measurements employing these miniaturized cells [1] thus providing localized information will not be treated in this book. The same applies to scanning electrodes employed in localized electrochemical impedance measurements (LEIS). 

(2004) The Kinetic Theory of Gases, Dover Publications, Mineola. 

O Hanlon, F. (2003) A User s Guide to Vacuum Technology, ] ohn Wiley Sons, Inc., Hoboken. 

and Kramer, D.A. (1969) Vapor pressure data for the solid and liquid elements. RCA Rev., 30, 285-305. 

---

Each type of mass spectrometer has its associated advantages and disadvantages. Quadrupole-based systems offer a fairly simple ion optics design that provides a certain degree of flexibility with respect to instrument configuration. For example, quadrupole mass filters are often found in hybrid systems, that is, coupled with another surface analytical method, such as electron spectroscopy for chemical analysis or scanning Auger spectroscopy. 

Vapor-phase decomposition and collection (Figs 4.16 to 4.18) is a standardized method of silicon wafer surface analysis [4.11]. The native oxide on wafer surfaces readily reacts with isothermally distilled HF vapor and forms small droplets on the hydrophobic wafer surface at room temperature [4.66]. These small droplets can be collected with a scanning droplet. The scanned, accumulated droplets finally contain all dissolved contamination in the scanning droplet. It must be dried on a concentrated spot (diameter approximately 150 pm) and measured against the blank droplet residue of the scanning solution [4.67-4.69]. VPD-TXRF has been carefully evaluated against standardized surface analytical methods. The user is advised to use reliable reference materials [4.70-4.72]. 

Harrington, D. A. Ultrahigh-Vacuum Surface Analytical Methods in Electrochemical Studies of Single-Crystal Surfaces 28... 

Soriaga, M. P., D. A. Harrington, J. L. Stickney, and A. Wiekowski, Ultrahigh-vacuum surface analytical methods in electrochemical studies of single-crystal surfaces, in Modem Aspects of Electrochemistry, J. O M. Bockris et al., Eds., Vol. 28, Kluwer, New York, 1996, p. 1. 

By today s standards of surface preparation, Will s procedures for surface preparation were crude, the surface structures were not characterized by use of surface analytical instrumentation (Which was neither widely available nor well developed at that time), and he employed extensive potentiodynamic cycling through the "oxide" formation potential region prior to reporting the quasi-steady state voltammetry curve, i.e., the potentiodynamic I-V curve. The studies employing surface analytical methods made a decade or more later were... 

The surface of a solid sample interacts with its environment and can be changed, for instance by oxidation or due to corrosion, but surface changes can occur due to ion implantation, deposition of thick or thin films or epitaxially grown layers.91 There has been a tremendous growth in the application of surface analytical methods in the last decades. Powerful surface analysis procedures are required for the characterization of surface changes, of contamination of sample surfaces, characterization of layers and layered systems, grain boundaries, interfaces and diffusion processes, but also for process control and optimization of several film preparation procedures. 

Pritzkow et al 46 described the application of surface and near-surface analytical methods such as ICP-IDMS (after dilution of layer), Rutherford backscattering spectrometry (RBS) and instrumental... 

As with all surface analytical methods, surface preparation is critical to obtaining reproducible SHG from metallic surfaces and single crystals in particular. For surfaces prepared in UHV and then transferred to an electrochemical cell, sputtering and heating or annealing followed by Auger analysis of impurities should proceed inert transfer. Low energy electron diffraction (LEED) can also be used to check surface order. Metal electrode surfaces, particularly for the rotational anisotropy ex-... 

The "ideal" surface analytical method would produce information that would identify the types and quantities of chemical groups or functionalities and their spatial... 

A number of reviews can be consulted for an introduction to the fundamentals both theoretical and practical covering XPS. These include Riggs and Parker (2) and the book by Carlson (3). Electron spectroscopy is reviewed in alternate years in the Fundamental Reviews issue of Analytical Chemistry. The last literature review was published in 1980 (4) and this and previous reviews can be consulted for a coverage of all aspects of the literature of XPS. A number of recent symposia have been held on applications of surface analytical methods in various aspects of materials science such as the symposium on characterization of molecular structures of polymers by photon, electron, and ion probes at the March 1980 American Chemical Society meetings in Houston ( 5) and the International Symposium on Physiochemical Aspects of Polymer Surfaces at this meeting as well as the symposium on industrial applications of surface analysis of which this article is a part. Review articles on various applications of XPS in materials science are listed in Table I. 

Experiments were performed in Teflon-lined titanium autoclaves, submerged in a thermostated oil bath. The supernatant liquors were analyzed using atomic absorption spectrometry. Solid residues were washed with water, dried and examined by the following surface analytical methods ... 

There has been substantial progress in experimental and theoretical surface analytical methods over the last years. Methods based on X-rays and UV light for diffraction, absorption, or photoelectron spectroscopies benefit from new generation synchrotron light sources. To name a few, surface experimental methods include XPS, AES and SIMS for investigating the surface chemistry A

adsorption energetics and kinetics as well as XPD, RAIRS, HREELS, LEED and STM for molecular and surface structure... 

Self-assembly phenomena on solid substrates are usually studied in ultra-high vacuum (UHV) or at the liquid-solid interface. Surface analytical methods involving electrons require vacuum. But UHV has also the advantage that reactive metal and metal oxide surfaces can be used as substrate since the very low background pressure also guarantees long investigation times on a non-altered sample. 

Table 1 summarizes the most important surface analytical methods working in the UHV, with their characteristics and advantages, which have been applied successfully to the study of passivity and corrosion research as well as the solution of... 

Table 1. Characteristics of some UHV-surface analytical methods...

The analysis of several pure metals and binary alloys yields generally at least a duplex and in some cases a multilayer structure of the passive film, as depicted schematically in Fig. 19. These systems have been examined with surface analytical methods, mainly XPS, but also ISS in some cases. The systematic variation of the electrochemical preparation parameters gives insight to the related changes of layer composition and layer development, and support a reliable interpretation of the results. Usually the lower valent species are found in the inner part and the higher valent species in the outer part of the passive layer. It is a consequence of the applied potential which of the species is dominating. Higher valent species are formed at sufficiently positive potentials only and may suppress the contribution of the lower... 

Fe/Cr alloys have been studied by many groups with electrochemically and surface analytical methods, this owing to their importance for their industrial applications. Cr is the important component that renders the resistance of stainless steel to the... 

---