L. Ryves

Deposition of epitaxial Ti2AlC thin films by pulsed cathodic arc

A multicathode high current pulsed cathodic arc has been used to deposit Ti2AlC thin films belonging to the group of nanolaminate ternary compounds of composition M(n+1)AX(n). The required stoichio ...

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...

Dielectric functions of a growing silver film determined using dynamic in situ spectroscopic ellipsometry.

The dielectric functions of plasma deposited silver on SiO2 through all stages of Volmer-Weber growth at room temperature and 150 degrees C were determined unambiguously by applying a model-independent inversion method to dynamic in situ spectroscopic ellipsometric data. The results show large differences in the localized plasmon resonance and the percolation threshold at the two temperatures. Using these model-independent dielectric functions we assess the effectiveness of modelling the plasmon resonance by fitting a Lorentz oscillator. The methods show agreement for the position of the plasmon resonance below the percolation threshold and for the effective film thickness up to 5.6 nm at room temperature and 11.5 nm at 150 degrees C, however the line shape of the resonance is described by the Lorentzian only in the early stages of film growth.

Dynamic spectroscopic ellipsometry determination of nanostructural changes in plasmonic silver films

Dynamic in situ spectroscopic ellipsometry is used to probe post-deposition nano-structural changes in silver films at room temperature in the pre- and post-coalescence stages of Volmer-Weber growth. In the island growth phase the Maxwell-Garnett theory is used to determine structural changes in the island film. Changes in the plasmon resonance frequency indicate an increased distance between islands which explain pre-coalescence resistivity changes. Post-coalescence changes in the resistivity are determined to be due to grain growth. A reduction in film thickness of 0.2 - 0.3 nm is also observed. The results are used to evaluate recent competing theories based on in situ stress measurements.

Relationship Between Microstructure, Stress and Hardness in Multilayer Coatings.

The need to synthesize advanced materials which exhibit superior mechanical properties has increased over the past decade with the insurgence of machining and bio-medical devices into the global market. These applications including silicon-based semiconductor devices, Micro-ElectroMechanical Systems (MEMS), tool steel coatings and artificial organs require materials with a variety of properties including enhanced surface hardness and wear resistance, and reduced crack propagation and delamination. Significant advances in Physical Vapor Deposition (PVD), mainly Pulsed Filtered Cathodic Arc, have allowed accurate control of thin film properties enabling specifically tailored coatings to be engineered.

Oriented graphite layer formation in Ti/C and TiC/C multilayers deposited by high current pulsed cathodic arc

Ti/C and TiC/C multilayers with periods ranging from 2 to 18 nm were grown by filtered high current pulsed cathodic arc. The growth was monitored in situ by ellipsometry and cantilever stress measurements. The ellipsometry results reveal that the optical properties of the carbon vary as a function of thickness. Correspondingly, the stress in each carbon layer as measured in situ exhibits two well defined values: initially the stress is low and then takes on a higher value for the remainder of the layer. Transmission electron microscopy shows that the initial growth of carbon on Ti or TiC layer is oriented with graphitic basal planes aligned parallel to the interface. After 2–4 nm of growth, the graphitic structure transforms to amorphous carbon. Electron energy loss spectroscopy shows that the carbon layer simultaneously undergoes a transition from sp2 rich to sp3 rich material.