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3C–SiC epitaxial crystal growth was carried out by repeated cycles of Si MBE deposition at room temperature followed by a carbonization under C2H4 and annealing at 900°C. This was done on a 3×3 reconstructed, well oriented, Si terminated 6H–SiC face. The surface was chemically and crystallographically controlled in situ by photoemission and LEED both during the cleaning procedure and within any growth sequence. By X-ray photoelectron diffraction and by transmission electron microscopy and diffraction, the 16 nm formed epilayer was characterized as a single 3C–SiC phase. A significant part of the cross-section image exhibits moire´ fringes whose periodicity (7.5 A˚) is three time the d1 1 1 reticular distance of the 3C–SiC monocrystal. This is attributed to the superimposition of {1 1 1} twinned domains, a consequence of two equiprobable orientation possibilities for 3C growth onto the hexagonal substrate. The formations of the 15R or the hypothetical 9R polytypes could be ruled out thanks to the electron diffraction patterns. [Copyright &y& Elsevier]

Cerium oxide nanostructured thin films, as well as their variants doped with Gadolinium (Gd), Neodymium (Nd) and Indium (In), were successfully deposited onto both glass and ITO substrates using the spray pyrolysis method. Their structural, morphological, optical, and electrochemical properties were then experimentally studied. X-ray diffraction (XRD) has confirmed the generation of a single-phase polycrystalline cubic fluorite structure of CeO 2. The crystallite size and microstrain of the thin films were found to depend on the type of doping element. Red-shift, peak broadening, and asymmetry in the Raman mode (F 2g), as well as a red-shifted energy gap, were confirmed through Raman spectroscopy and UV–Vis–NIR analyses. SEM images reveal nanograin formation in all the films, while EDS analysis confirms the presence of the elements. The electrochemical measurements indicate that doping CeO 2 with Gd, Nd, and In enhances its electrochemical properties. Furthermore, the doped CeO 2 thin films maintain full transparency during the intercalation and deintercalation of Li + ions. Such pivotal findings broaden the potential applications of this oxide, particularly in supercapacitors and electrochromic devices. [ABSTRACT FROM AUTHOR]

Abstract: Silicon substrates are often used to synthesize polycrystalline diamond films by microwave plasma assisted chemical vapour deposition technique (MPCVD). In the case of highly oriented diamond films, several steps are employed to carefully prepare the silicon surface (pre-treatment steps), to nucleate diamond crystals (nucleation step) and to thick the film (growth step). In this study, we characterize {100} silicon substrates and diamond released from its silicon substrate by electronic microscopies (TEM and SEM), by Atomic Force Microscopy (AFM) and by X-ray photoelectron spectroscopy (XPS), to follow the substrate transformations after each step, particularly the formation and the evolution of the silicon carbide and to characterise the diamond films grown on the carburised silicon. We show that according to the experimental conditions and the level of surface/gas contamination by carbon and silicon species, isolated islands or continuous β-SiC compound are formed over the silicon surface and can generate defects such as voids or strip structures that influence the subsequent diamond nucleation and growth. [Copyright &y& Elsevier]

The Ge growth on SiC(0 0 0 1) follows a Stranski–Krastanov mode for Si-rich (3×3) and (√ of 3×√ of 3)R30° reconstructed surfaces. For Ge deposit in particular temperature conditions, a new (4×4) superstructure takes place and the reflection high energy electron diffraction (RHEED) specular spot intensity presents one oscillation proving a wetting layer formation. An island nucleation is then ascertained by the oscillation vanishing and by the appearance of a k⊥-modulated RHEED pattern. On the other hand, on a (6√ of 3×6√ of 3)R30° C-rich surface, a direct Ge island nucleation is observed from the first growth stage. Indeed, for 1 ML Ge, the RHEED diagram consists in spots and rings, and the atomic force microscopy analysis indicates a high density (∼8×1010 cm-2) of small islands (∅∼30 nm, h∼3 nm). The RHEED spot analysis shows a preferential epitaxial relationship with the substrate Ge(1 1 1)//SiC(0 0 0 1). The Ge–C bonding being energetically unfavourable, Ge tends to form islands immediately rather than wetting the graphite-terminated surface. The Ge growth mode on C-rich surface is thus of Volmer–Weber type. [Copyright &y& Elsevier]

With the aim of comparing initial Ge adsorption and desorption modes on different surface terminations of 4H–SiC(0 0 0 1) faces, 3 × 3, √3×√3R30° (R3) and 6√3×6√3R30° (6R3) reconstructions, of decreasing Si surface richness, have been prepared by standard surface preparation procedures. They are controlled by reflection high energy electron diffraction (RHEED), low energy electron diffraction and photoemission. One monolayer of Ge has been deposited similarly at room temperature on each of these three surfaces, followed by the same set of isochronal heatings at increasing temperatures up to complete Ge desorption. At each step of heating, the structural and chemical status of the Ge ad-layer has been probed. Marked differences between the Si- (3 × 3 and R3) and C-rich (6R3) terminations have been obtained. Ge wetting layers are only obtained up to 400 °C on 3 × 3 and R3 surfaces in the form of a 4 × 4 reconstruction. The wetting is more complete on the R3 surface, whose atomic structure is the closest to an ideally Si-terminated 1 × 1 SiC surface. At higher temperatures, the wetting layer stage transiets in Ge polycrystallites followed by the unexpected appearance on the 3 × 3 surface of a more ordered Si island structure. It denotes a Si clustering of the initial Si 3 × 3 excess, induced by the presence of Ge. A phase separation mechanism between Si and Ge prevails therefore over alloying by Ge supply onto a such Si-terminated 3 × 3 surface. Conversely, no wetting is obtained on the 6R3 surface and island formation of exclusively pure Ge takes place already at low temperature. These islands exhibit a better epitaxial relationship characterized by Ge(1 1 1)//SiC(0 0 0 1) and Ge〈1 1 −2〉//SiC〈1 −1 0 0〉, ascertained by a clear RHEED spot pattern. The absence of any Ge–C bond signature in the X-ray photoelectron spectroscopy Ge core lines indicates a dominant island nucleation on heterogeneous regions of the surface denuded by the 6R3 graphite pavings. Owing to the used annealing cycles, the deposited Ge amount desorbs on the three surfaces at differentiated temperatures ranging from 950 to 1200 °C. These differences probably reflect the varying morphologies formed at lower temperature on the different surfaces. Considering all these results, the use of imperfect 6R3 surfaces appears to be suited to promote the formation of pure and coherent Ge islands on SiC. [Copyright &y& Elsevier]

Abstract: Epitaxial Ge islands on a SiC(0001) substrate have been examined by reflection high-energy electron diffraction (RHEED). These islands have been obtained by depositing three monolayers of Ge at 500°C on a graphitized SiC (6√3×6√3)R30° reconstructed surface. This surface has been chosen for its ability to support epitaxial Ge island growth in a Volmer-Weber mode. The RHEED technique has allowed us to determine the epitaxy relationship and in-plane orientations between relaxed Ge and SiC(0001). Typical transmission electron diffraction patterns indicate that Ge grows according to only one epitaxy relationship Ge{111}||SiC(0001) that corresponds to two in-plane orientations, a preferential one and a minority one rotated by 30° around the growth 〈111〉-Ge (or [0001]-SiC) axis. Double spot RHEED patterns also point out a twinning for each in-plane orientation, a consequence of the three-fold order of the 〈111〉-Ge axis. [Copyright &y& Elsevier]