T. W. H. Oates

Optical properties of silver nanowire arrays with 35 nm periodicity

We present highly ordered Ag nanowire arrays with 35nm periodicity grown on patterned templates. The optical properties measured using generalized ellipsometry exhibit strong anisotropy. Dielectric functions are calculated by fitting the Jones matrix elements with a biaxial layer model, accounting for both metallic behavior and localized surface plasmon resonances. The amplitude and wavelength maximum of the plasmon resonance perpendicular to the wires increase with increasing wire width and thickness. The dielectric coefficients of 10-mm-wide nanowires show a transition behavior from insulating in UV to metallic above 550nm. Their potential application as polarization-dependent plasmonic-scattering transparent conductive electrodes is discussed.

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...

A high-current pulsed cathodic vacuum arc plasma source

Cathodic vacuum arcs (CVAs) are well established as a method for producing metal plasmas for thin film deposition and as a source of metal ions. Fundamental differences exist between direct current (dc) and pulsed CVAs. We present here results of our investigations into the design and construction of a high-current center-triggered pulsed CVA. Power supply design based on electrolytic capacitors is discussed and optimized based on obtaining the most effective utilization of the cathode material. Anode configuration is also discussed with respect to the optimization of the electron collection capability. Type I and II cathode spots are observed and discussed with respect to cathode surface contamination. An unfiltered deposition rate of 1.7 nm per pulse, at a distance of 100 mm from the source, has been demonstrated. Instantaneous plasma densities in excess of 1×1019 m−3 are observed after magnetic filtering. Time averaged densities an order of magnitude greater than common dc arc densities have been demon...

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.

Plasma immersion ion implantation using polymeric substrates with a sacrificial conductive surface layer

Conventional ion beam implantation has been shown to modify the surface properties of polymers, giving an improvement in such qualities as hardness, conductivity and biocompatibility. Plasma immersion ion implantation (PIII) offers an alternative to conventional ion beam implantation, with the advantages of high implantation rates and conformal treatment of three-dimensional surfaces. There are, however, problems inherent to the application of PIII to non-conducting materials, such as the transfer of the high-voltage bias to the polymer and surface charging. To overcome these difficulties, we have developed a technique whereby a thin conductive film is deposited on the substrate prior to implantation. The film is contacted to the high-voltage pulser and ions from the plasma are implanted through the conductive film and into the underlying polymer. If required, the conductive film can be subsequently removed by etching, revealing the modified polymer surface beneath. Cross-sectional TEM results are presented, showing the extent of the implantation. Surface conductivity measurements show an increase with implantation time. The advantages and limitations of the technique are discussed.

Electric probe measurements of high-voltage sheath collapse in cathodic arc plasmas due to surface charging of insulators

High-voltage sheath dynamics near a negatively biased substrate in cathodic arc plasmas are investigated using a biased electrical probe. Since the sheath is devoid of electrons, the sheath boundary can be inferred from the position where a positively biased probe draws no electron current. The extent of the sheath is primarily dependent on the plasma density, the ion velocity and the applied voltage. Using insulating substrates, the sheath boundary eventually retracts due to a dynamic reduction in the applied voltage. This reduction is caused by positive charge accumulation on the insulator surface. The collapse time of the sheath is dependent on the plasma density and the substrate characteristics. We believe this to be the first direct observation of the reduction in the width of the high-voltage sheath when implanting an electrical insulator using plasma-based ion implantation (PBII). This information is important when determining the optimal parameters for plasma-based ion implantation of insulators. Our measurements are compared with theoretical predictions based on the Child-Langmuir equations for high-voltage sheaths. By choosing appropriate values for the secondary electron coefficient the theory could be made to fit the experimental data. A discussion of the validity of the choice of secondary electron coefficients is presented.

Nanoscale precipitation patterns in carbon―nickel nanocomposite thin films: Period and tilt control via ion energy and deposition angle

Periodic precipitation patterns in C:Ni nanocomposites grown by energetic ion codeposition are investigated. Films were grown at room temperature by ionized physical vapor deposition using a pulsed ...

Insulator surface charging and dissipation during plasma immersion ion implantation using a thin conductive surface film

Plasma immersion ion implantation of insulating materials is inherently problematic due to charge accumulation on the insulator surface. Surface charge can be removed by the application of an ultrathin conductive film, which is essentially transparent to the incident ions. The minimum thickness of the film is determined by its capability to effectively conduct away the implanted charge. We present a model for charge accumulation on insulators during plasma immersion ion implantation and use this to study the plasma sheath width and voltage, with and without an ultrathin metal film. Charge accumulation occurs more quickly when the plasma has a directed velocity greater than the Bohm velocity, which is the case for a cathodic arc plasma. We show that for both cases the effectiveness of plasma immersion ion implantation is improved with the application of an ultrathin conductive film.

Determination of the equilibrium ion sheath in the drifting plasma by numerical Simulation

A one-dimensional (1-D) particle-in-cell (PIC) numerical method is developed to determine the equilibrium steady-state sheath width established in a drifting plasma. The simulated and measured steady-state sheath widths are in approximate agreement although the measured width is slightly larger than the simulated. The probe is biased to +90 V and this greatly influences the potential structure within the sheath boundary. The simulation shows that the mean-charge state and mean-atomic-mass approach to dealing with multiple ion species with a range of charge states does not accurately predict the position of the equilibrium sheath when the difference between the charge-to-mass ratios of the ion species is large. A more robust approach is to simulate the steady sheath by a 1-D-PIC method that can handle multiple ion species. In experimental situations where the sample stage is finite in size, the assumption that the equilibrium ion sheath expands from a biased plate of infinite extent may be violated. A two-dimensional PIC numerical method expressed in r-z cylindrical coordinates has been developed to investigate the condition where the 1-D assumption becomes inaccurate. The results confirm that the 1-D-PIC method becomes inaccurate when the steady-state sheath width has dimensions comparable with the sample stage diameter.

Influence of gas flow rate and entry point on ion charge, ion counts and ion energy distribution in a filtered cathodic arc

Abstract We report the results of an investigation in which we measured ion charge, ion counts and ion energy distributions of a titanium cathodic arc operated in a nitrogen atmosphere, using a Hiden mass selected ion energy analyser. Measurements were taken under standardised conditions of arc current and magnetic confinement. Two different gas entry points (over the cathode and in the main chamber close to the Hiden port), three different background gas pressures (2, 4 and 7.5 mtorr) and two different flow rates (23 and 71 sccm) were investigated. Counts were taken at 14, 24, 28, 48 and 62 amu, representing N + or N 2 2+ , Ti 2+ , N 2 + , Ti + and TiN + , respectively. Ion energy was measured up to a maximum of 80 eV relative to vessel wall potential. Multiple data sets were collected for each combination of gas entry, gas pressure and flow rate. Ion counts, ion energy and mean charge all decrease as flow rate increases. For cathode entry, Ti ion counts increase greatly, N ion counts decrease slightly, mean ion energy increases and mean ion charge does not show a clear trend. Similarly, the responses of ion counts, ion energies and mean ionic charges to increases in pressure do not show a single, clear trend. The results of the study are reported and some implications for PBII processing are discussed.