Since ionization loss spectroscopy (ILS) and disappearance potential spectroscopy (DAPS) may respond in different ways to the changing chemical environment if Coulomb correlation effects are not negligibly small, we chose strongly correlated materials La, Ce and narrow band-materials Cr, Ti and followed their oxidation processes by ILS and DAPS. It was found that generally with DAPS the changes in peak energies were greater than with ILS during oxidation, especiaUy for La, Ce and Cr. Further analyses showed that the difference of the peak positions of DAPS and ILS contained three items of Coulomb correlation energies. The data for this difference versus oxygen exposure could be consistently interpreted for La and Ce in terms of the previous X-ray photoelectron spectroscopy- Bremsstrahlung isochromat spectroscopy (XPS-BIS) results.

Electronic excitation and unoccupied eiectron states at one monolayer Gd, Er, Eu and Pr-Si (lll) interfaces are studied in a quest for 2D silicides. The Er results are compared with those of other techniques that have established a 2D silicide, while Pr is shown to develop a homogeneous but not wholly ordered 2D phase. Gd-Si (111) annealed at 400-600℃ has a distinctive ordered monolayer phase with a different inverse photoemission spectrum from the 3D bulk silicide and low reactivity with oxygen in contrast to the monolayer Eu interface that remains highly reactive and disordered. Further investigations required to confirm the existence of a 2D Gd silicide are discussed.

Nanopatterning of Sis (110) surface by the normal incident Ar+ ion sputtering has been conducted as a function of sample temperature (room temperature-800℃) and ion energy (1-5 keV) with the ion flux of 20μA/cm2. The surface morphology was characterized by an atomic force microscope. For ion energy of 1.5keV, the sputtered surface morphology changes from a dim dot/hole pattern to a distinct dot one with the increasing temperature. On the other hand, at the temperature of 800℃, the nanodot shape of the dot pattern evolves from being circular→elliptical→circular→elliptical with the increasing ion energy in general. A dynamic continuum model is adopted to describe the experimental results, which includes both the Bradley Harper sBHd mechanism good for the amorphous surface under ion sputtering and the Ehrlich CSchwoebel sESd one for the crystalline surface. By adjusting the effective surface tension following its temperature-orion energy-dependence relationship in the BH or ES mechanism-relevant regime, the processes of surface morphology evolution have been simulated, which agrees with the experimental ones.

Photoluminescence (PL) from SiOx (0<x<2) thin films, prepared by evaporation of SiO powder onto the Si (100) substrate followed by thermal annealing, was investigated for various film thickness and annealing temperatures. For the film thickness ranging from 120 to 700nm and annealing at 1100℃ for 30min in nitrogen, the Si nanocrystals (nc-Si) embedded in SiO2 matrix were formed due to the phase separation process, and the PL of nc-Si exhibited a continuous red-shift with increasing film thickness in an exponential decay manner. This thickness dependence was explained by a model modified from that of Zacharias and Streitenberger (2000 Phys. Rev. B 62 8391) regarding the nucleation barrier for Si clusters versus their distances away from the substrate. Further, for the film thickness of 270nm and annealing temperature ranging from 700 to 1100℃, it was found that a green/yellow PL structure developed at elevated annealing temperatures, which reached the maximum in intensity at 900℃, and then dropped down for higher annealing temperatures. This PL emission was identified as due to the structural defects mainly consisting of oxygen vacancies in SiO2 matrix.

Radiation-enhanced diffusion, or RED, has been conventionally studied under the conditions of steady state and homogeneous background of excess defects. Hence MeV ion irradiation and diffusion annealing were conducted simultaneously and the temporal and spatial dependences of the diffusing parameters were ignored. This review covers a new type of RED, i.e. nonsteady-state radiation-enhanced diffusion or NSRED. The sequence of steps in NSRED are (i) keV ion irradiation of the substrate to create defects, (ii) evaporation of the diffusing materials onto the surface, followed by (iii) diffusion annealing. Using such a sequence, the diffusion region directly overlaps with the central region of the ion implantation profile. Ti diffusion in ion pre-irradiated MgO(100) was selected as a model diffusion system, ions of Ar+, Ne+, Kr+, Cl+ and Cr+ were used for irradiation and diffusion was conducted in an inert atmosphere. Secondary ion mass spectroscopy (SIMS) was used to depth-profile the diffusing materials. A phenomenological model based on the concept of depth-dependent diffusion coefficients was developed to quantify the NSRED results. Monte Carlo (TRIM) simulations were used to model the implantation. Compared to conventional RED, vacancy clusters, rather than excess mono-vacancies, are the dominant contributors to NSRED, resulting in two unique observations. The first is a postirradiation annealing effect, i.e. annealing a pre-irradiated substrate enhances the subsequent diffusion. This is due to the key roles of vacancy clusters in the diffusion enhancement. The second is a chemical effect, i.e. the enhanced diffusion does not only depend on the ballistic behaviours of the irradiating ions, as in conventional RED, but on the chemical properties of the ions as well. This effect is consistent with a modified vacancy-clustering model. The results indicate that NSRED is a promising technique for modification of the optical and mechanical roperties of oxides through manipulation of doping ion diffusion behaviours in a well-controlled manner.