Synchrotron radiation surface electronic structure

Pi TW, Liu Ch, Hwang J (2006) Surface electronic structure of Ca-deposited tris (8-hydroxyquinolato) aluminum studied by synchrotron radiation photoemission. J Appl Phys 99 123712... 

From the perspective of this symposium, analysis of the atomic dynamics and electronic structure of surfaces constitutes an even more exotic topic than surface atomic geometry. In both cases attention has been focused on a small number of model systems, e.g., single crystal transition metal and semiconductor surfaces, using rather specialized experimental facilities. General reviews have appeared for both atomic surface dynamics (21) and spectroscopic measurements of the electronic structure of single-crystal surfaces (, 22). An important emerging trend in the latter area is the use of synchrotron radiation for studying surface electronic structure via photoemission spectroscopy ( 23) Moreover, the use of the very intense synchrotron radiation sources also will enable major improvements in the application of core-level photoemission for surface chemical analysis (13). 

The boranes nido-B and m do-BioHi4 and carbaboranes n/do-2,3-Et2C2B4H6 and c/oro-l,2-C2BioHi2 have been used as precursors for boron and boron carbide thin films. ISEELS has been used to characterise the molecular precursws at solid surfaces a comparison has been made between the bond lengths determined for the molecular clusters by MNDO calculations and results from X-ray or electron diffraction and from extended EELS fine structure. A study of the deposition of boron carbide films on Si(lll) surfaces from the synchrotron radiation induced decomposition of nido-2,3-diethyldicarbahexaborane has been described. The dissociation of the cluster is the rate determining step in the process. As with the deposition of boron from nido-BioHi4, it is found that thoe is an activation barrier to the dissociation of the boron carbide precursor on Si(l 11) surfaces.43... 

The availability of high-intensity, tunable X-rays produced by synchrotron radiation has resulted in the development of new techniques to study both bulk and surface materials properties. XAS methods have been applied both in situ and ex situ to determine electronic and structural characteristics of electrodes and electrode materials [58, 59], XAS combined with electron-yield techniques can be used to distinguish between surface and bulk properties, In the latter procedure X-rays are used to produce high energy Auger electrons [60] which, because of their limited escape depth ( 150-200 A), can provide information regarding near surface composition. 

In this symposium emphasis is placed on the first class of methods. Isolated examples of the third class are discussed. Consideration of the second class is omitted entirely. Indeed, the scope of the symposium is perhaps best described as encompassing the more widespread techniques of surface compositional analysis as applied to materials science and electrochemistry oriented problems. Many modern surface analysis methods, e.g., those embodying tip sample geometries (21 22, 3, 34), those based on synchrotron radiation (23, 25), and those dealing with surface structure (15-20) and dynamics ( 3, 21-23), as opposed to surface composition, are not represented in the symposium program even though many of them enjoy "industrial applications" in the areas of electronics, metallurgy and catalytic chemistry. 

Surface analytical techniques such as Auger electron spectroscopy (27), X-ray photoelectron spectroscopy (28), and secondary-ion mass spectrometry (29) have been used to study LB films. Synchrotron radiation is a particularly powerful probe enabling X-ray near-edge structure and extended X-ray absorption fine structure to be measured. Angle-resolved photoemission studies (30) confirmed the existence of a one-dimensional energy band along the (CH2)jc chain in a fatty acid salt film. 

The electronic structure of the Cu 100 -c(2x2)-Pd, Au and Mn systems have been probed by ARUPS. Wang et al. [16] have compared valence band photo-emission spectra using synchrotron radiation from the Cu 100 -c(2x2)-Au surface alloy with a CusAullOO bulk alloy terminated by a mixed c(2x2) CuAu monolayer. A surface-induced Au d-band narrowing of 0.45 eV was foimd for the Cu 100 -c(2x2)-Au surface alloy, despite the smaller lattice... 

This chapter elaborates on the methods and incentives for using nanomaterials as precursors to electrocatalysts. This precursor method facilitates tailoring of precursors with controlled structures and control of the interface between two metals. By use of this method homogeneous alloys, segregated alloys, layered bimetallics, and decorated paticles are all readily accessible. The incentive for the use of this concept is that we can preprepare and thoroughly characterize the active components of electrocatalysts with the application of modern analytical techniques, including synchrotron radiation, electron microscopy. X-ray diffraction, and electrochemical examination of the surface. 

It then became clear that largely because of transition probabilities but also because of escape-depth effects (surface sensitivity) the multiplet structure of 4/ electrons is indeed best studied with soft X-ray photons. Studies using synchrotron radiation in the range 0—80 eV on RE sulfides (13) fully confirmed this expectation. Only at photon energies greater than 70 eV did the 4/ signal become dominant, but... 

Synchrotron radiation began to be applied to problems in geochemistry beginning in the early 1980 s, introducing techniques that are completely impractical on laboratory X-ray sources. These include spectroscopy, microprobe and surface scattering, methods that reveal chemical, atomic and electronic structure of materials. 

C.S. Fadley. The Study of Surface Structures by Photoelectron Diffraction and Auger Electron Diffraction. In R.Z. Bachrach, editor. Synchrotron Radiation Research. Advances in Surface and Interface Science, Volume I Techniques. Plenum Press, New York, 1992. 

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