Gy. J. Kovács

Phase separation in carbon-nickel films during hyperthermal ion deposition

Microstructure evolution as a function of the substrate temperature and metal content of C:Ni nanocomposite films grown by hyperthermal ion deposition is investigated. The films were grown by pulsed filtered cathodic vacuum arc on thermally oxidized Si substrates held at temperatures in the range from room temperature (RT) to 500 °C and with the metal content ranging from 7 to 40 at. %. The elemental depth profiles and composition were determined by elastic recoil detection analysis. The film morphology and phase structure were studied by means of cross-sectional transmission electron microscopy and selected area electron diffraction. For RT deposition a transition from repeated nucleation dominated toward self-organized growth of alternating carbon and crystalline nickel carbide layers is observed at a Ni threshold content of ∼40 at. %. The surface diffusion increases concomitantly with the growth temperature resulting in the formation of elongated/columnar structures and a complete separation of the fil...

The effect of the carbon matrix on the mechanical properties of nanocomposite films containing nickel nanoparticles

The correlation of structural electronic and mechanical properties of carbon–nickel composite thin films has been investigated. The films were deposited on oxidized silicon substrates by dc magnetron sputtering of Ni and C targets in argon at different temperatures between 25 and 800 °C. Composition variation was achieved by variation of the power of the Ni target with constant power on the C target. Structural investigations were performed by transmission electron microscopy (including high resolution) both in plan view and cross section. The nanocomposite films consisted of metallic nanocrystals embedded in a carbon matrix. The carbon matrix was disordered or graphite-like carbon; the crystalline phase consisted of Ni3C or Ni nanoparticles, depending on the deposition temperature. The temperature coefficient of resistivity measurements at low temperature confirmed the various structures of the carbon matrix. The samples in which the prevailing matrix was disordered carbon show the tunneling effect and samples with graphite-like carbon matrix show metallic behavior. The hardness of the films varies between 2 GPa (hardness of Ni) and 13 GPa depending on the deposition temperature, but is independent of the Ni content. The highest hardness of ~11–13 GPa and modulus of elasticity of ~120 GPa were obtained when the crystalline Ni3C nanoparticles were separated by a 2–3 nm thin carbon matrix consisting of amorphous and graphite-like carbon phases. In these films the hardness to modulus of elasticity ratio (H/E) is ~0.1.

Bulk diffusion induced structural modifications of carbon-transition metal nanocomposite films

The influence of transition metal (TM = V,Co,Cu) type on the bulk diffusion induced structural changes in carbon:TM nanocomposite films is investigated. The TMs have been incorporated into the carbon matrix via ion beam co-sputtering, and subsequently the films have been vacuum annealed in the temperature range of 300 – 700 °C. The structure of both the dispersed metal rich and the carbon matrix phases has been determined by a combination of elastic recoil detection analysis, x-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The as-grown films consist of carbidic (V and Co) and metallic (Cu) nanoparticles dispersed in the carbon matrix. Thermal annealing induces surface segregation of Co and Cu starting at ≥ 500 °C, preceded by the carbide-metal transformation of Co-carbide nanoparticles at ∼ 300 °C. No considerable morphological changes occur in C:V films. In contrast to the surface diffusion dominated regime where all the metals enhance the six-fold ring clustering of C, in th...

Unexpectedly high sputtering yield of carbon at grazing angle of incidence ion bombardment

The relative sputtering yield of amorphous carbon with respect to polycrystalline nickel at Ar-ion bombardment was determined by means of Auger electron spectroscopy depth profiling as a function of the angle of incidence and projectile energy in the ranges of 49°–88° and 0.3–1keV, respectively. It was found that the relative sputtering yield YC∕YNi strongly increases with angle of incidence from 49° to 82°. At around 80° the sputtering yield of C is higher than that of Ni. Above 82° no dependence on the angle of incidence was found. The relative sputtering yield weakly depends on the energy of the projectile. The experimental results will be explained by the help of transport of ion in solid (TRIM) simulations.

Structure and spectroscopic properties of C–Ni and CNx–Ni nanocomposite films

Magnetron-sputtered carbon-nickel and carbon-nitride-nickel thin films were investigated by high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray spectroscopy, electron-energy-loss spectroscopy (EELS), and scanning tunneling microscopy∕spectroscopy (STM∕STS) to clarify the relationship between the structure and the spectroscopic properties. The films were deposited in argon or nitrogen plasma at temperatures from 25to800°C. The microstructures can be described as a nanocomposite, built from Ni or Ni3C nanocrystals in a carbon∕CNx matrix. The nanocomposite shows columnar structure up to 200°C deposition temperature, and above this temperature gradually changes to globular morphology. The C∕CNx matrix also grows thicker as the deposition temperature increases. The matrix is amorphous at high nitrogen content and low deposition temperature and it is ordered into 3–5 layer thick graphitic shells around the Ni3C or Ni crystallites at higher temperatures. The surface roughness of the...

Transformation of database populations and operations from the conceptual to the internal level

Abstract In this paper we describe a framework for the automatic transformation of databases from the conceptual to the internal level. Our approach fits in with the ANSI/SPARC three level architecture for database management systems. The framework consists of three components: structures (database schemata), populations (database contents) and operations (database manipulations). On the conceptual level we describe these components for modelling techniques, such as ER, NIAM and the Binary Relationship Model. On the internal level we focus on (nested) relational models. For each component on the conceptual level a separate transformation is provided to the internal level. The components are integrated by a central notion: the predicator. Further integration is obtained by means of basic population rules.