A. Kaduwela

PHOTOELECTRON DIFFRACTION: SPACE, TIME, AND SPIN DEPENDENCE OF SURFACE STRUCTURES

The current status of photoelectron-diffraction studies of surface structures is briefly reviewed, and several recent developments and proposals for future areas of application are then discussed. The application of full-solid-angle diffraction data, together with simultaneous characterization by low-energy electron-diffraction and scanning-tunneling microscopy, to epitaxial growth is considered. Several new avenues that are being opened up by third-generation synchrotron-radiation sources are also considered. These include photoelectron diffraction from surface and interface atoms, the possibility of time-resolved measurements, and circular dichroism in photoelectron angular distributions. The addition of spin to the photoelectron-diffraction measurement is also considered, and can be achieved either through core-level multiplet splittings or by circular-polarized excitation of spin–orbit-split levels. This last development should make it possible to study short-range magnetic order, perhaps even in a holographic fashion.

Electron emission holography of small clusters and surfaces

We consider the three‐dimensional imaging of near‐surface structures by holographic transformations of large‐solid‐angle electron emission data sets. Results are presented for both single and multiple scattering theoretical simulations and experimental data which have been obtained for both the c(2×2) structure of S on Ni(001) and clean Si(111). Although features associated with near‐neighbor atoms are seen in Fourier‐transform images for all of the cases studied, these peaks show shifts of 0.30–1.5 A, as well as broadening and artifacts, that are primarily due to strong forward peaking and phase shifts in the electron‐atom scattering. We further discuss correcting these image aberrations by several methods such as eliminating the forward peaking by a reduction of the data set or multiplication by a suitable Gaussian function, using the scattered‐wave‐included Fourier transform method, and taking a phased summation of several transforms at different energies. All of these correction methods are found to i...

Surface structures for the O/Ni(001) system from c(2×2)O to saturated NiO

The use of x‐ray photoelectron diffraction (XPD) for the structural study of oxide growth on Ni(001) from c(2×2)O up to the saturated oxide of approximately two‐monolayers thickness is described. Some rather unique structural information is obtained from XPD. This includes the site type and position of the c(2×2) overlayer and the geometry and lattice parameters of the saturated oxide. The XPD data are also in excellent agreement with single‐scattering cluster calculations at the spherical wave level.