Surface data analysis

X-ray absorption spectroscopy is an important part of the armory of techniques for examining pure and applied problems in surface physics and chemistry. The basic physical principles are well understood, and the experimental methods and data analysis have advanced to sophisticated levels, allowing difficult problems to be solved. For some scientists the inconvenience of having to visit synchrotron radia-... 

Chapter 7 (by H. Ishida and A Ishitani) review microscopic and surface analytical techniques. Chapter 8 (by D. M. Haaland) reviews developments in statistical chemometrics for data analysis. 

All LEED data analysis must, however, rely on prior assumptions and model distributions and is, therefore, not really direct. Microscopic methods have the advantage of delivering directly the shape of the surface (domains, terraces, etc.) without any assumptions being made. 

Recent developments in Raman equipment has led to a considerable increase in sensitivity. This has enabled the monitoring of reactions of organic monolayers on glassy carbon [4.292] and diamond surfaces and analysis of the structure of Lang-muir-Blodgett monolayers without any enhancement effects. Although this unenhanced surface-Raman spectroscopy is expected to be applicable to a variety of technically or scientifically important surfaces and interfaces, it nevertheless requires careful optimization of the apparatus, data treatment, and sample preparation. 

In this review we put less emphasis on the physics and chemistry of surface processes, for which we refer the reader to recent reviews of adsorption-desorption kinetics which are contained in two books [2,3] with chapters by the present authors where further references to earher work can be found. These articles also discuss relevant experimental techniques employed in the study of surface kinetics and appropriate methods of data analysis. Here we give details of how to set up models under basically two different kinetic conditions, namely (/) when the adsorbate remains in quasi-equihbrium during the relevant processes, in which case nonequilibrium thermodynamics provides the needed framework, and (n) when surface nonequilibrium effects become important and nonequilibrium statistical mechanics becomes the appropriate vehicle. For both approaches we will restrict ourselves to systems for which appropriate lattice gas models can be set up. Further associated theoretical reviews are by Lombardo and Bell [4] with emphasis on Monte Carlo simulations, by Brivio and Grimley [5] on dynamics, and by Persson [6] on the lattice gas model. 

Solid-surface room-temperature phosphorescence (RTF) is a relatively new technique which has been used for organic trace analysis in several fields. However, the fundamental interactions needed for RTF are only partly understood. To clarify some of the interactions required for strong RTF, organic compounds adsorbed on several surfaces are being studied. Fluorescence quantum yield values, phosphorescence quantum yield values, and phosphorescence lifetime values were obtained for model compounds adsorbed on sodiiun acetate-sodium chloride mixtures and on a-cyclodextrin-sodium chloride mixtures. With the data obtained, the triplet formation efficiency and some of the rate constants related to the luminescence processes were calculated. This information clarified several of the interactions responsible for RTF from organic compounds adsorbed on sodium acetate-sodium chloride and a-cyclodextrin-sodium chloride mixtures. Work with silica gel chromatoplates has involved studying the effects of moisture, gases, and various solvents on the fluorescence and phosphorescence intensities. The net result of the study has been to improve the experimental conditions for enhanced sensitivity and selectivity in solid-surface luminescence analysis. 

XPS Analysis. The ultrahigh vacuum (OHV) catalyst treatment-surface analysis system employed to characterize and treat the cobalt catalysts has been described previously ( 1, 2 The catalyst treatment and data analysis procedures have also been described (JJ. Briefly, the samples were treated in quartz reactors and then transferred under UHV into a modified Hewlett-Packard 5950A BSCA spectrometer for emalysis. Peak areas were normalized with theoretical cross-sections (Z) to obtain relative atomic compositions. 

In the laser flash method, the heat is put in by laser flash instead of electric current in the stepwise heating method mentioned above. Thus this method may be classified as a stepwise heating method. A two-layered laser flash method was developed by Tada et al. " The experimental method and the data analysis, including a case involving radiative heat flow, are described in detail in the review article by Waseda and Ohta. A thin metal plate is placed at the surface of a melt. A laser pulse is irradiated onto a metal plate of thickness / having high thermal conductivity. The sample liquid under the metal plate and the inert gas above the plate are designated as the third and first layers, respectively. The temperature of the second layer becomes uniform in a short time" and the response thereafter is expressed by... 

Most recently, we have been able to obtain the in situ surface EXAFS spectrum of a half-monolayer of underpotentially deposited copper on a bulk Pt(lll) single crystal pretreated with iodine. The spectrum shown in Fig. 23 is a bit noisy (due to limited number of scans) but at least five well-defined oscillations can be observed. Preliminary data analysis indicates that the copper adatoms sit on threefold hollow sites with copper neighbors at 2.80 0.03 A. This distance is very close to the Pt—Pt distance in the (111) direction and indicates the presence of a commensurate... 

Figure 1 shows a sharp decrease of low-pressure hysteresis loop when introducing copper in S-l, pointing to the formation of (CuO)n nanoclusters into the S-l intracrystalline channels and supermicropores. The adsorption data analysis (see Table 1) shows a decrease of both the total (BET) surface area and micropore volume of the CuS-1 sample with respect to the S-l matrix. 

Fatigue data analysis, 13 494-495 Fatigue failures, 13 481, 486-487 Fatigue loads, 13 481 Fatigue performance, sample size and surface finish in, 13.486 487 Fatigue properties... 

Figure 3.1 Schematic diagram of an AAS spectrometer. A is the light source (hollow cathode lamp), B is the beam chopper (see Fig. 3.2), C is the burner, D the monochromator, E the photomultiplier detector, and F the computer for data analysis. In the single beam instrument, the beam from the lamp is modulated by the beam chopper (to reduce noise) and passes directly through the flame (solid light path). In a double beam instrument the beam chopper is angled and the rear surface reflective, so that part of the beam is passed along the reference beam path (dashed line), and is then recombined with the sample beam by a half-silvered mirror.

Numerous examples of applications of nonlinear least squares to kinetic-data analysis have been presented (K7, K8, L3, L4, M7, P2) an exhaustive tabulation of references would, at this point, approach 100 entries. Typical results of a nonlinear estimation and comparison to linear estimates are shown in Table I and discussed in Section III,A,2. Many estimation problems exist, however, as typified in part by Fig. 7. This is the sum-of-squares surface obtained at fixed values of Ks and Ku in the rate equation used for the catalytic hydrogenation of mixed isooctenes (M7)... 

G. C. Nenninger, M. Piliarik and J. Homola, Data analysis for optical sensors based on spectroscopy of surface plasmons, Meas. Sci. Technol. 13 2038-2046 (2002). 

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