Spectroscopic techniques tunneling microscopy

We have considered briefly the important macroscopic description of a solid adsorbent, namely, its speciflc surface area, its possible fractal nature, and if porous, its pore size distribution. In addition, it is important to know as much as possible about the microscopic structure of the surface, and contemporary surface spectroscopic and diffraction techniques, discussed in Chapter VIII, provide a good deal of such information (see also Refs. 55 and 56 for short general reviews, and the monograph by Somoijai [57]). Scanning tunneling microscopy (STM) and atomic force microscopy (AFT) are now widely used to obtain the structure of surfaces and of adsorbed layers on a molecular scale (see Chapter VIII, Section XVIII-2B, and Ref. 58). On a less informative and more statistical basis are site energy distributions (Section XVII-14) there is also the somewhat laige-scale type of structure due to surface imperfections and dislocations (Section VII-4D and Fig. XVIII-14). 

Ozensoy et al.127 also used PM-IRAS to study the CO adsorption behavior on Si02-supported Pd clusters. As mentioned above, these crystalline, ultrathin silica films possess the structural and electronic properties of the bulk analogues, but are thin enough to permit the use of vibrational and electronic spectroscopic techniques (and tunneling microscopy) without charging.39 40 As with the... 

Diffraction techniques (low-energy electron diffraction [34, 35], helium diffraction [36, 37] and grazing incidence X-ray diffraction [38]), scanning tunneling microscopy (STM) [36, 39, 40] and atomic force microscopy (AFM) [41] served to solidify the conclusions inferred from the less direct spectroscopic methods and provide additional structural details. The sulfur atoms order epitaxially on the substrate in a (x/3 X V3) R30° structure [36-38, 40, 41]. The angle of the sulfur-carbon bond with respect to the substrate plane is approximately 104° for alkanethiol monolayers [38, 42] and 180° for arylthiol SAMs [42, 43]. Given the agreement between the results obtained from direct structural methods and indirect spectroscopic methods, one... 

Fortunately, the success of surface science, optical and x-ray techniques in the last few decades has provided access for electrochemists to structural information of electrode/electrolyte interfaces. The optical and X-ray spectroscopic techniques have mainly been used in situ, i.e., in the presence of the bulk electrolyte. These techniques include EXAFS (extended x-ray absorption fine structure), SXS (surface x-ray scattering), XSff (x-ray standing wave technique, SERS (surface enhanced Raman scattering), NOM (nonlinear optical methods) IRS (infrared spectroscopy), MS (Mossbauer spectroscopy), RLS (radioactive labelling spectroscopy), STM (scanning tunneling microscopy), and... 

Some of the principal techniques used to characterize microporous catalysts are listed in Table 1. With the exception of electron microscopy and scanning tunneling microscopy, all the techniques integrate information over large portions of the sample volume or surface. As a result, nonuniformities in chemical and structural environments invariably contribute to a broadening of the observed spectroscopic signatures. Since each method provides only one or two elements of information, a combination of techniques can be used to achieve a comprehensive understanding of composition and structure. 

Electrochemical measurements of the type described earlier give indirect evidence about dissolution processes. More direct chemical information can be obtained from in-situ spectroscopies, in particular from IR and Raman methods. Chazalviel and coworkers have showed the power of this approach in studies on silicon and GaAs [73,98,99]. Electrochemical and spectroscopic techniques are macroscopic methods giving a view of the whole electrode surface. To study semiconductor dissolution at the microscopic (atomic) level, one needs techniques such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM). The anodic and chemical dissolution of sihcon has been studied in very elegant work by Allongue and coworkers [100-102]. 

See also Blood and Plasma. Clinical Analysis Glucose. DNA Sequencing. Fluorescence Overview. Forensic Sciences Drug Screening in Sport. Microscopy Techniques Electron Microscopy Scanning Electron Microscopy Atomic Force and Scanning Tunneling Microscopy. Nucleic Acids Spectroscopic Methods. Raman Spectroscopy Instrumentation. Sensors Overview. 

Figure 4.25 General overview of the applicability ranges of some spectroscopic techniques [71]. OM, optical microscopy nS, neutron scattering STM/AFM, sctmning tunnelling microscopy/atom probe ion microscopy...

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