Spectroscopy surface reconstruction

Kolb and Franke have demonstrated how surface reconstruction phenomena can be studied in situ with the help of potential-induced surface states using electroreflectance (ER) spectroscopy.449,488,543,544 The optical properties of reconstructed and unreconstructed Au(100) have been found to be remarkably different. In recent model calculations it was shown that the accumulation of negative charges at a metal surface favors surface reconstruction because the increased sp-electron density at the surface gives rise to an increased compressive stress between surface atoms, forcing them into a densely packed structure.532... 

In the first study of its kind, second harmonic generation has been used to study potential induced reconstruction on Au(lll) and Au(100) by Kolb and coworkers [156]. These surfaces have been known to reconstruct in UHY when they are clean [153, 157], Surface reconstruction occurs when the surface atoms of a solid rearrange themselves in a structure different from that expected from simple termination of the bulk lattice. Various studies by cyclic voltammetry, electroreflectance spectroscopy and ex situ electron diffraction have suggested that flame-treated crystals form stable reconstructions in solution. Unfortunately, due to the lack of in situ probes, very little direct evidence for this reconstruction has been available. 

Keywords Surface reconstructions surface states angular resolved photoemission scanning tunneling spectroscopy spin polarized spectroscopy self-organized nucleation. 

Excitation spectroscopy Monitoring of the surface emission allows one to discriminate the upper excited surface states and their relaxation dynamics. Problems such as surface reconstruction, or quantum percolation of surface excitons upon thermal and static disorder, are connected with high accuracy to changes of the exciton spectra.61118,119,121... 

Correlations of in situ and ex situ observations. The characterization methods of surface science have already been established within an electrochemical context, because they can provide structural definition of fine distance scales as well as atomic composition of a surface and, sometimes, vibrational spectroscopy of adsorbates. These ex situ methods normally involve transfer of an electrode from the electrochemical environment to ultrahigh vacuum, and the degree to which they provide accurate information about structure and composition in situ is continuously debated. Additional work is needed to clarify the effect of emersion of samples and their transfer to ex situ measurement environments. The most appropriate experimental course requires observations by techniques that can be employed in both environments. Vibrational spectroscopy, ellipsometry, radiochemical measurements, and x-ray methods seem appropriate to the task. Once techniques suited to this problem are established, emphasis should be placed on the refinement of transfer methods so that the possibilities for surface reconstruction and other alterations in interfacial character are minimized. 

Structure of Alloy Type Sn-Pt/Si02 Catalysts used in Low Temperature CO Oxidation. Both Mossbauer and FTIR spectroscopy provided sufficient proof of surface reconstruction during the low temperature CO oxidation. However, the above reconstruction appeared to be reversible as the reversible interconversion of PtSn Sn -I- Pt was demonstrated by both spectroscopic techniques. This reversibility can only be achieved if the segregation described above is within the supported nanoparticle, i.e., when surface reactions involved in CO oxidation do not result in formation of separate Pt and tin-oxide phases on the silica support. 

The tremendous advances that have occurred in the spectroscopic analysis of the electrode/electrolyte interface have begun to provide a fundamental understanding of the elementary processes and the influence of process conditions. Surface-sensitive spectroscopic and microscopic analyses such as surface-enhanced Raman scattering (SERS) [1], potential-difference infrared spectroscopy (PDIRS) [2], surface-enhanced infrared spectroscopy (SEIRS) [3], sum frequency generation (SFG) [4], and scanning tunneling microscopy (STM) [5,6] have enabled the direct observation of potential-dependent changes in molecular structure [2,7] chemisorption [8,9], reactivity [10], and surface reconstruction [11]. 

Chen et al. [95], very recently, prepared Au thin-film electrodes made by electroless deposition for in situ electrochemical attenuated total-reflection surface-enhanced infrared adsorption spectroscopy (ATR-SEIRAS) which consisted of 46 nm Au nanoparticles deposited on a Si infrared window. Very interestingly, they observed that a square-wave treatment of the Au film led to a much enhanced ORR activity (02-saturated 0.1 M HCIO4) as a consequence of the surface reconstruction of the nanoparticle film. Thus, whereas the ORR activity of the initial Au... 

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