We report evidence for surface plasmon excitations in concentric-shell fullerenes. A film of these concentric- shell fullerenes with radii around 5-7 nm produced by carbon bombardment of a silver polycrystalline target and measured by electron-energy-loss spectroscopy (EELS) in reflection geometry. These data were analyzed with the help of a dielectric theory developed for EELS in transmission geometry. Taking into account the concentric-shell-substrate interaction, the spectral shape can be explained as a combination of contributions from sigma-pi* interband transitions (around 13.5 eV), from the surface radial (sigma-pi*) and tangential (sigma-sigma*) plasmons (around 14.5 eV and 16.7 eV, respectively), and from the volume plasmon (24.5 eV). [S0163-1829(99)03107-0].

Growth of CdTe(111)B on Si(100) by molecular beam epitaxy (MBE) was studied with photoelectron spectroscopy using synchrotron radiation. First, a monolayer of Te forms on top of the Si(100) substrate. We suggest that these Te atoms replace the Si dimer atoms and form dimer rows. The surface peak in the Si 2p spectra from clean Si(100) is replaced by four adatom-induced peaks. They are assigned to Si atoms bound to one, two, three and four Te atoms, respectively. Some Te seems to diffuse into the substrate. Finally, CdTe(111)B grows on such Te-terminated Si(100) surfaces, with little effect on the interface electronic structure.

Au/GaN and Pt/GaN contacts have been studied with XPS. According to XPS depth profiling, the N signal is weak in the region below the metal contact and the Pt or Au signal decreases much more slowly than expected for a sharp interface. Next, we have performed in situ studies of the formation of Au contacts on GaN. In contrast to the results from depth profiling, we observe 2D growth and little or no chemical interaction between Au and GaN. This suggests that conventional calculations of sputtering yields and ion-beam-induced mixing cannot be applied to the analysis of noble metal/GaN depth profiles. Heating during or after Au deposition results in strong clustering, observed by both XPS and AFM. The Schottky barrier height measured by XPS is 1.15 eV.

The growth of large-size single crystals of aluminium nitride has been obtained by UHV reactive rf-sputtering at high temperature (1050 degrees C). The growth mode was studied in situ by electron spectroscopy (HREELS, LEED) and by ex-situ High Resolution Transmission Electron Microscopy (HRTEM). The deposition of a buffer layer at lower temperature (700 degrees C) yielded a thick mosaic layer with a very low surface roughness. Electron microscopy has evidenced the presence of a thin interfacial layer composed of small and slightly misoriented domains, suggesting therefore a 3-D growth of the layer before the temperature transition, it has also confirmed the very good crystalline quality of the final thick film. the constituent domains of the film are large (100 nm) and their respective misorientation is less than 0.1 degree. (C) 1997 Elsevier Science Limited.

We present the epitaxial growth by rf reactive sputtering of aluminum nitride on Si(111) at high temperature. The grain size of the obtained films was sufficient to obtain a good low energy electron diffraction (LEED) pattern from which we determined a lattice parameter of 3.1 Å, indicative of fully relaxed films. The surface of the film was examined in situ by Auger electron spectroscopy (AES); no contamination was detected, with the exception of low levels of oxygen. The film and its interface were studied by high resolution electron energy loss spectroscopy (HREELS), x-ray photoelectron spectroscopy (XPS) depth profiling, and transmission electron microscopy (TEM). Again, a low concentration of oxygen and no carbon contamination were detected by XPS. Three different growth methods were applied to the deposition of aluminum nitride at high temperature. The obtained films were studied in order to determine the influence of the methods on the interface, on the ‘bulk structure’ of the film, and on its surface. Each has been shown to have particular characteristics. The first one, performed at a temperature of 1000 °C, and including a cleaning of the surface by exposure to Al flux, was characterized by an interfacial layer with no long-range order and increasing the interaction between the film and the substrate. The second growth consisting of deposition at the same high temperature has shown a good surface quality for very thin layers (<50 Å ) and the absence of an interfacial layer. The last method, based on a first step of growth at low temperature (700 °C), resulted in good quality thick layers which allowed us to determine the infrared dielectric constants of aluminum nitride by HREELS.

We report the heteroepitaxy of Al(111) on alpha-Al2O3(0001) realized at 470 degrees C by aluminium evaporation and characterized by Auger spectroscopy (AES) and low energy electron diffraction (LEED). This crystalline growth is preceded by suboxide formation due to the superficial oxygens of the sapphire substrate, and the nucleation of aluminium crystallites with a (111) surface randomly oriented around the (0001) axis. Epitaxial growth dominates with the relationship[($) over bar 211](111)Al parallel to(($) over bar 2110)(0001)Al2O3.Aluminium evaporation onto a sapphire crystal held at 720 degrees C generates a uniform etching of the substrate similar to the silicon-beam etching of sapphire, in contrast to what is observed for the re-evaporation of a room-temperature-grown Al layer which leads to a severely damaged surface, Increasing the growth temperature reduces the sticking coefficient of the aluminium on alpha-Al2O3(0001) and does not seem to affect the depth-limited character of the reaction.The results are discussed on the basis of the complex crystallographic structure of sapphire and its surface phase changes induced either by thermal treatments or reactive metal deposition. The sensitivity of Auger spectroscopy towards chemical shifts related to metal reaction is underlined.

The growth by RF reactive sputtering of aluminium nitride (AlN) at the surface of oxidised iron was studied by X-ray photoelectron spectroscopy (XPS). The observation of the substrate lines showed that the top layer of the iron oxide, constituted of Fe2O3 was first reduced into Fe3O4 by the incoming Al atoms to form an aluminium oxide. Moreover, an analysis of the O 1s level has highlighted that the lower iron oxide Fe3O4 is reduced further until a diffusion barrier is formed and stops the diffusion of oxygen from the substrate towards the deposited layer. The study of the nitrogen core level evidenced the existence of oxynitrides at the interface: first the presence of iron oxynitride confirmed the reduction of the Fe3O4 and second, Al oxynitride was only detected in low concentrations located at the near interface. A growth model based on the formation of AlN clusters on top of the aluminium oxide before completion of this oxide layer, was applied to the Al 2p line intensities, and revealed a growth mode intermediary between a high density of small clusters of AlN and layer-by-layer growth of the nitride. The thickness of the oxide layer has been determined to range from 20 to 44 Å.

The growth of aluminium nitride (AlN) thin films on clean and oxidised polycrystalline iron was studied by Auger electron spectroscopy. The films of AlN were deposited by reactive RF sputtering (argon + nitrogen atmosphere). On clean iron, a modelisation of the Auger peak-to-peak intensities evidences a Stranski-Krastanov growth mode (one layer followed by island formation) with an interfacial layer made of iron nitride covered by the AlN. Results on oxidised iron suggested the growth of a two-phase film with stoichiometry gradient of the (AlN)x(Al2O3)1−x form, x increasing with the film thickness. Grains of AlN in the layer were shown to favour the diffusion of oxygen from the substrate to the film until thicknesses of about 80 monolayers are reached. The presence of grains of both phases supports the hypothesis of an island growth mode for this interface.

We have studied by Auger electron spectroscopy (AES) and electron energy loss spectroscopy (EELS) the room temperature growth of aluminium nitride (AlN) at the surface of clean and oxidized polycrystalline iron. The films were deposited by reactive rf-sputtering in an N2-Ar atmosphere. Very low coverages were possible thanks to a precise partial pressure controller based on electron impact emission spectroscopy (EIES).The AlN/Fe interface study has revealed the formation of an iron nitride at the surface of the substrate and of a compound close to AlN as a first monolayer. AlN clusters grow directly on this nitride layer and we did not detect the formation of any alloy between iron and aluminium. A modelization of the AES signal intensities suggests a Stranski-Krastanov growth mode.For the oxidized iron, Auger lines showed an Fe2O3 surface layer on an Fe3O4 film oxide. The former oxide was reduced to Fe3O4 by the incoming aluminium which forms a two-phase film made of Al2O3 and AlN resulting in an (AlN)x(Al2O3)1-x stoichiometry. The concentration of this oxide phase decreases after the diffusion of the oxygen stops. Pure AlN begins to grow on this two-phase film.