Near coalescent submicron polycrystalline diamond films deposited on silicon: hydrogen bonding and thermal enhanced carbide formation

The influence of high temperature annealing up to 1200 °C in vacuum on ∼100 nm nearly continuous thick diamond films consisting of 30-50 nm crystallites, deposited onto silicon substrates is reported. The hydrogen bonding and phase composition of the films were studied with Raman spectroscopy, while the surface microstructure and composition were studied with high resolution scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray photoelectron spectroscopy (XPS), respectively. Annealing to 800-900 °C of ∼100 nm thick films results in a decrease in the intensities of the peaks associated with hydrogen bonding (Raman), as well as changes to the morphological microstructure at the film surface. Heating the films to 1000 °C resulted in the complete disappearance of the Raman peaks associated with hydrogen bonding at grain boundaries, and an increase in the relative intensity of the diamond peak relative to the graphite-related D and G Raman peaks, concomitant with changes to the microstructure (SEM and TEM). Ex situ XP analysis of the films annealed to 800 and 1000 °C provides clear evidence for the formation of SiC on the films surface and near surface region. However a sharp SiC Raman peak at 796 cm-1 appears only after annealing to 1200 °C and it is concomitant with a decrease in the Raman peaks associated with sp2 bonded carbon. Our results suggest that formation of SiC phase preferentially consumes sp2/sp hybridized carbon matrix, produced by thermal desorption of hydrogen atoms at diamond grain boundary and at the diamond film-silicon substrate interface

Bulk and surface thermal stability of ultra nanocrystalline diamond films with 10-30 nm grain size prepared by chemical vapor deposition

The thermal stability of nanocrystalline diamond films with 10-30 nm grain size deposited by microwave enhanced chemical vapor deposition on silicon substrate was investigated as a function of annealing temperature up to 1200&deg;C. The thermal stability of the surface-upper atomic layers was studied with near edge x-ray absorption fine structure (NEXAFS) spectroscopy recorded in the partial electron yield mode. This technique indicated substantial thermally induced graphitization of the film within a close proximity to the surface. While in the bulk region of the film no graphitization was observed with either Raman spectroscopy or NEXAFS spectroscopy recorded in total electron yield mode, even after annealing to 1200&deg;C. Raman spectroscopy did detect the complete disappearance of transpolyacetylene (t-PA)-like 1 and 3 modes following annealing at 1000&deg;C. Secondary ion mass spectroscopy, applied to investigate this relative decrease in hydrogen atom concentration detected only a &sim;30% decrease in the bulk content of hydrogen atoms. This enhanced stability of sp3 hybridized atoms within the bulk region with respect to graphitization is discussed in terms of carbon bond rearrangement due to the thermal decomposition of t-PA-like fragments. <br /

The templated growth of a chiral transition metal chalcogenide

We demonstrate that an intrinsically chiral, high Miller index surface of an achiral metal can be used to template the enantioselective growth of chiral transition metal chalcogenide films. Specifically, Cu(643)R can be used as a template for the enantioselective growth of a chiral copper telluride alloy surface. Beyond a critical alloy thickness the chiral influence of the Cu(643)R surface diminishes and an achiral surface forms. Our work demonstrates a new method of producing chiral transition metal chalcogenide surfaces, with potential applications in the study of structurally chiral topological insulators

Dust in Supernovae and Supernova Remnants II: Processing and survival

Observations have recently shown that supernovae are efficient dust factories, as predicted for a long time by theoretical models. The rapid evolution of their stellar progenitors combined with their efficiency in precipitating refractory elements from the gas phase into dust grains make supernovae the major potential suppliers of dust in the early Universe, where more conventional sources like Asymptotic Giant Branch (AGB) stars did not have time to evolve. However, dust yields inferred from observations of young supernovae or derived from models do not reflect the net amount of supernova-condensed dust able to be expelled from the remnants and reach the interstellar medium. The cavity where the dust is formed and initially resides is crossed by the high velocity reverse shock which is generated by the pressure of the circumstellar material shocked by the expanding supernova blast wave. Depending on grain composition and initial size, processing by the reverse shock may lead to substantial dust erosion and even complete destruction. The goal of this review is to present the state of the art about processing and survival of dust inside supernova remnants, in terms of theoretical modelling and comparison to observations

Novel applications of Moessbauer spectroscopy

SIGLEAvailable from British Library Document Supply Centre- DSC:DX88885 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Normal-incidence x-ray standing-wave determination of the adsorption geometry of PTCDA on Ag(111): Comparison of the ordered room-temperature and disordered low-temperature phases

Normal incidence x-ray standing wave (NIXSW) experiments have been performed for monolayers of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) adsorbed on the Ag(111) surface. Two phases were analyzed: the low-temperature phase (LT phase), which is disordered and obtained for deposition at substrate temperatures below 150 K, and the ordered phase, which is obtained for deposition at room temperature (RT phase). From the NIXSW analysis the vertical bonding distances to the Ag surface were obtained for the averaged carbon atoms and the two types of chemically different oxygen atoms in the terminal anhydride groups. For the LT phase, we find about 2% (0.05 A degrees) and 8% (0.21 A degrees) smaller averaged bonding distances for the C and O atoms, respectively, compared to the RT phase. In both phases, the planar geometry of the free molecule is distorted; in particular, the carboxylic O atoms are closer to the surface by 0.20 A degrees (RT) and 0.31 A degrees (LT) with respect to the averaged C distance. The difference between the vertical bonding distances of the carboxylic and anhydride O atoms is found to be 0.32 (RT) and 0.33 A degrees (LT). These structural parameters of the two phases are compared to those of PTCDA monolayers adsorbed on Au(111) and Cu(111) surfaces and are discussed in the frame of current bonding models

A taxonomy of spatial units in a mixed 2D and 3D cadastral database

The aim of this paper is to define the range of objects that may need to be accommodated in the development of a practical cadastral database, to also accommodate 3D spatial units, and permit a range of encodings to coexist. The level of geometric encoding as defined in the ISO19152 LADM provides a framework of categorization of spatial units recorded in a cadastre, whether formal or informal, historic, current or planned. The levels of encoding range from simple “text based” spatial unit to the “topology based” encoding (in both 2D and 3D). In our proposed categorization, there are two more aspects, in addition to the levels of encoding, which we identify: 1. types of real world spatial unit (according to law/ regulations) and 2. types of geometric descriptions. The existence of real-world examples of various combinations of 2D and 3D spatial units provide guidelines in the development of a 3D cadastral system. These include, amongst others, spatial units with: open or closed volumes (unspecified top / bottom), faces restricted or not to horizontal or vertical orientation, fixed or moving face(s) (ambulatory), faces (partly) related to physical constructions or not, 3D spatial unit within single surface parcel or crossing many surface parcels (legal space for pipeline), etc. These are characterizations of the real-world spatial unit, but there are also issues that may become important by virtue of choices made in the database implementation, such as the presence or not of “caves” (dents, holes and trough holes), non 2-manifold boundaries allowed or not, volumes with contiguous or not interiors, boundaries described by planar (flat) or curved primitives, etc. All three classification aspects, encoding level, real-world spatial unit type, geometric representation are more or less orthogonal (in theory all combinations are possible), but in practice also very much related. In developing any database, it is vital to have a complete picture of the range of possible objects that need to be modeled, if “surprises” are to be avoided in the implementation and acceptance testing. This paper provides a discussion on the type of classification that is useful for a cadastral jurisdiction and the validation requirements of these classes of objects.OTBArchitecture and The Built Environmen

Low Temperature Growth of Graphene on a Semiconductor

The industrial realization of graphene has so far been limited by challenges related to the quality, reproducibility, and high process temperatures required to manufacture graphene on suitable substrates. We demonstrate that epitaxial graphene can be grown on transition-metal-treated 6H-SiC(0001) surfaces, with an onset of graphitization starting around 450–500 °C. From the chemical reaction between SiC and thin films of Fe or Ru, sp3 carbon is liberated from the SiC crystal and converted to sp2 carbon at the surface. The quality of the graphene is demonstrated by using angle-resolved photoemission spectroscopy and low-energy electron diffraction. Furthermore, the orientation and placement of the graphene layers relative to the SiC substrate are verified by using angle-resolved absorption spectroscopy and energy-dependent photoelectron spectroscopy, respectively. With subsequent thermal treatments to higher temperatures, a steerable diffusion of the metal layers into the bulk SiC is achieved. The result is graphene supported on magnetic silicide or optionally, directly on semiconductor, at temperatures ideal for further large-scale processing into graphene-based device structures