R. G. Agostino

Texture control of PbTiO3 and Pb(Zr,Ti)O3 thin films with TiO2 seeding

The nature and the role of 1 to 5 nm thick TiO2 seed layers for the growth of textured PbTiO3 and Pb(Zr, Ti)O-3 thin films on textured Pt(111) thin film substrates have been studied. Under otherwise identical in situ sputter deposition process conditions, the PbTiO3 texture could be turned from (100) to (111) orientation by adding the seed layer. This is demonstrated by patterning the TiO2 film. Auger electron spectroscopy and x-ray photoemission spectroscopy showed that the seed layer was a continuous TiO2 film. X-ray photoelectron diffraction measurements revealed epitaxial ordering in the seed layer. As there is no azimutal order among the Pt grains, the reduced information of azimutally averaged polar cuts is obtained. These give strong evidence for a strained rutile (110) structure. Various deposition experiments indicated that the TiO2 is effective only when it is ordered before the PbTiO3 nucleation starts. The epitaxial relationship between PbTiO3(111) and Pt(111) is thus mediated by the intermediate, epitaxial TiO2 film, which is dissolved of transformed to PbTiO3 afterwards. The observed growth behavior is discussed in terms of surface and interface energies

X-ray photoelectron and Auger electron diffraction study of diamond and graphite surfaces

Abstract Natural diamond (001) and (111) surfaces as well as highly oriented pyrolithic graphite (HOPG) (0001) have been analyzed by X-ray induced photoelectron diffraction (XPD). The measured 2π patterns of C Is emission (964 and 1450 eV) and of KVV Auger emission (260 eV) are compared to single scattering cluster (SCC calculations, and excellent agreement is found. The comparisons show that photoelectron forward focusing is much less prominent in carbon solids than in all previously studied, heavier elements, and a direct interpretation of the data is therefore more difficult. The highly textured nature of HOPG presents itself as a circular pattern with concentric rings centered at the surface normal (c-axis). The aim of this work is to show the advantage of the XPD technique as a diagnostic tool for the investigation of epitaxial diamond growth with monolayer sensitivity.

Angle-scanned photoemission: Fermi surface mapping and structural determination

Abstract A brief survey of the angle-scanned photoemission technique is given. It incorporates two complementary methods in one: 1. Mapping of X-ray excited photoelectron intensities over virtually the complete hemisphere above the sample surface results in extended data sets where important surface-geometrical structure information is extracted and even “fingerprinting” is possible. This method is known as the very powerful angle-scanned X-ray photoelectron diffraction. 2. Mapping ultraviolet-excited photoelectron intensities as a function of emission angles gives the possibility to do band mapping as well as to study the Fermi surface of single crystals very directly. Therefore, by switching between X-rays and ultraviolet-photons, it is possible to study the geometrical and electronic structure within the same experiment.

Real space mapping of the surface atomic environment via low energy scattering spectroscopy

Abstract Low-energy ion scattering spectroscopy is used to obtain real space surface imaging of the atomic surroundings of different fcc metal surfaces. Scattered He + ions were mapped over a large solid angle sector. By using an universal shadow cone expression, it is possible to invert the angular maps into two-dimensional real space maps. The inversion procedure is tested on Pt(111), Cu(001) and Al(111) surfaces getting nearest neighbour atoms up to a distance of 4 A. Furthermore, for known surfaces the maps also allow to extract information on the scattering mechanism itself.

A chemical state resolved x‐ray photoelectron diffraction study: Initial stages in diamondlike carbon film deposition

The structural sensitivity of x‐ray photoelectron diffraction is greatly enhanced by the acquisition of a full hemispherical diffraction pattern of chemically shifted core levels. Complex systems can be studied resolving the local order per element and per chemical environment. This technique is applied to study the earliest stages of hydrogenated diamondlike carbon film deposition on Si(001). Effects of the sample temperature and ion dose on the structure of deposited layers are discussed.

Structural characterization of submonolayer C/Al(111)

We report on the adsorption of atomic C in submonolayer coverages on the Al(111) surface. The local order at the surface is studied for different thermal treatments by means of full-heimispherical X-ray photoelectron diffraction. Deposition at room temperature results in disordered C adsorption while an ordering process takes place after annealing above 475 K. We depict the structure of the annealed C-rich phase. The C1s diffraction patterns are interpreted by comparison with single scattering cluster calculations. The results are discussed with respect to both previous theoretical and experimental work.