Electronic characterization techniques information obtainable

XPS has typically been regarded primarily as a surface characterization technique. Indeed, angle-resolved XPS studies can be very informative in revealing the surface structure of solids, as demonstrated for the oxidation of Hf(Sio.sAso.5)As. However, with proper sample preparation, the electronic structure of the bulk solid can be obtained. A useful adjunct to XPS is X-ray absorption spectroscopy, which probes the bulk of the solid. If trends in the XPS BEs parallel those in absorption energies, then we can be reasonably confident that they represent the intrinsic properties of the solid. Features in XANES spectra such as pre-edge and absorption edge intensities can also provide qualitative information about the occupation of electronic states. 

Scanning electron microscopy is commonly used to study the particle morphology of pharmaceutical materials. Its use is somewhat limited because the information obtained is visual and descriptive, but usually not quantitative. When the scanning electron microscope is used in conjunction with other techniques, however, it becomes a powerful characterization tool for pharmaceutical materials. 

It is true that in some cases, the spectroscopic data on a reactive intermediate are so persuasive that the connection between structure and spectroscopic features is firm. However, in general this will not be the case, and additional spectroscopic or preparative criteria will have to be provided. So we are faced with the question How can we connect the information obtained, for example, from observations in matrices or in solution-phase fast kinetic studies, to molecular structure How do we know that the results of these experiments, using what we hopefully call direct methods, really pertain to the species we are trying to characterize I attempt to deal with this issue in what follows. Since the methods used vary from one class of non-Kekule species to another, specific classes are individually discussed, and special techniques are introduced as needed. Electron spin resonance spectroscopy has played such a pervasive role that it will be useful to give first a brief outline of that method. 

The determination of the photoluminescence parameters (excitation frequency, emission frequency, Stokes shift, fine structure parameter, and lifetime) can lead to information which, at the simplest level, indicates the presence of an electronically excited state of a species, but which can be sufficiently detailed so as to lead to a clear identification and characterization of the photoluminescent sites(J6-44). Moreover, measurements of the variations in the intensity and positions of the bands as a function of time (time-resolved photoluminescence) provide valuable kinetic data representing the reactions occurring at the surface. Although most of the photoluminescence measurements have been carried out at low temperatures for specific reasons (see Section III.C.2), there is much evidence that some of the excited states involved are present even at higher temperatures and that they play an important role in catalytic and photocatalytic reactions. Therefore, it is clear that the information obtained by photoluminescence techniques is useful and important lor the design of new catalysts and photocatalysts. 

Structural information obtained from ET should be complemented with other characterization techniques in view of the intrinsically poor statistics of electron microscopy. 

Different characterization techniques, for example X-ray diffraction,EXAFS, SEELFS, electron diffraction (LEED, RHEED, i SAED, and CBED ), and electron microscopy (HRTEM, WBDF ) give information about crystal structure, lattice distances, or morphology. All these techniques give average information about the shapes and the lattice distances of particle collections and of isolated particles. To obtain information about the particles at the atomic level, HRTEM is necessary. Other information about the surface structure of small particles can be obtained by Most HRTEM studies have been devoted to... 

S. Weber and E. Schleicher on the example of flavoproteins which play a role in both chemically and light-activated electron transfer processes. Chapter 3 on synthetic polymers by D. Hinderberger argues that careful analysis of mundane nitroxide spin label or spin probe CW EPR spectra can reveal a lot of information which is hard to obtain by any other characterization technique. 

The characterization of materials using TEM can give information about their structure and morphology. Allied techniques from TEM, such as EDX, EELS, EFTEM, and electron diffraction (ED), can complement the information obtained for a specific material. Several reviews and compilations of the studies on TEM and related techniques... 

Upon introduction in vivo, the interface between the delivery system and the biological tissue and/or fluid is critically important to the in vivo performance [5]. Accordingly, surface properties including surface chemical composition and surface area must be well characterized. X-ray photoelectron spectroscopy (XPS) is a widely used technique to obtain surface elemental composition, and Branauer, Emmett, and Teller (BET) measurement is used to provide information on surface area. Surface morphology is typically assessed via light, electron, and atomic force microscopy (AFM). The amorphous and crystalline nature of materials can be determined from X-ray diffraction (XRD) and density measurements. 

EC-NMR has made considerable progress during the past few years. It is now possible to investigate in detail metal-liquid interfaces under potential control, to deduce electronic properties of electrodes (platinum) and of adsorbates (CO), and to study the surface diffusion of adsorbates. The method can also provide information on the dispersion of commercial carbon-supported platinum fuel cell electrocatalysts and on electrochem-ically generated sintering effects. Such progress has opened up many new research opportunities since we are now in the position to harness the wealth of electronic, Sp-LDOS as well as dynamic and thermodynamic information that can be obtained from NMR experiments. As such, it is to be expected that EC-NMR will continue to thrive and may eventually become a major characterization technique in the field of interfacial electrochemistry. 

Several techniques have been applied for the characterization of battery materials, but the electronic and structural information has not been properly described yet. NEXAFS can be successfully used to determine the electronic structure of carbonaceous materials that have been synthesized using a unique method described in detail elsewhere. NEXAFS measures the excitation of electrons to partially-filled or unfilled molecular orbitals. The signal obtained by electron-yield detection is surface sensitive, while that obtained by fluorescence yield detection is bulk sensitive. While the electron-yield method is sensitive only to the top few atomic layers, the fluorescence yield method can detect species up to a few thousand A deep into the bulk structure. We employed the electron-yield method in this study. 

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