ICMCTF2010 Session B4: Laser and Ion Beam Surface and Coating Engineering

Monday, April 26, 2010 10:00 AM in Room Town & Country
Monday Morning

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Start Invited? Item
10:00 AM Invited B4-1 An Oveerview of Laser Ablation: Thin Films and Nano-Particles
Jyoti Mazumder (University of Michigan)
A laser Ablation technique was used to synthesize nanocrystalline powders and films of intermetallic compounds. Nanocrystalline versions of intermetallic materials offer the prospect of mitigating the brittleness of these materials while retaining their strength and oxidation resistance. To this end, nanocrystalline powders of near-stoichiometric NbAl3and multilayer microlaminates of alternating NbAl3and Al thin film layers have been fabricated using a laser ablation deposition technique. During processing, a laser absorption spectroscopy probe of Nb atoms within the ablation plume provides data regarding plume temperature and density. High purity powders with mean grain sizes of <10 nm were produced. Standard deviation of the particle size distributions were typically 2–6 nm. HRTEM was used to confirm the DO22crystal structure of NbAl3. Multilayer thin films of 15 and 20 layers and individual layer thickness of 80 nm were synthesized on copper and silicon substrates under various processing conditions. Diffusion of elements between layers, observed by STEM-EDS, was minimal. SEM suggests the possibility to tailor microstructure by varying process conditions. Typical grain sizes for crystalline microstructures was 30 nm.
10:40 AM B4-3 Deposition of Nanolaminate Films by Pulsed Laser Deposition from Pre-Synthesized MAX-Phase Targets
Peter Schaaf, Christian Lange (Ilmenau University of Technology, Germany); Marcus Wilke (MFPA Weimar, Germany); Marcus Hopfeld (Ilmenau University of Technology, Germany)

Pulsed laser deposition (PLD) with a Nd:YAG laser was used to grow thin films from a pre-synthesized MAX-phase formulated ablation targets onto oxidized Si(1 0 0), MgO(1 0 0) and stainless steel substrates with and without an 200V Ar or nitrogen ion beam directed at the substrate surface during deposition. The depositions were carried out in a substrate temperature range from room temperature to 650°C.

The properties of the films have been investigated by glow discharge optical emission spectroscopy (GDOES) for film thickness and stoichiometric composition and X-ray diffraction for the crystallinity of the films. X-ray diffraction measurements for all samples show no signs of the MAX phase Ti3SiC2, but only reflections of crystalline TiC. GDOES measurements however showed that silicon is distributed highly inhomogenously through the films. Even in the samples grown without ion beam there is a diffusion like silicon profile in the samples with an increased silicon concentration at the substrate surface. The application of the ion beam enhances this effect. Diffusion length and concentration gradient of these profiles depend on the deposition temperature and the substrate material. Obviously, the silicon shows a much higher mobility during film growth than the two other elements titanium and carbon, which can be explained by a preferred formation of titanium carbide TiC.

These results for deposition from prefabricated MAX-phase targets will be compared with depositions from elemental targets.

The work is supported by the German Research Foundation under grant DFG Scha 632/10.

11:00 AM B4-4 Laser Assisted Deposition of Industrial CAE-PVD TiN Thin Films
Joseba Esparza (Asociación de la Industria Navarra, Spain); Xerman de la Fuente (ICMA-CSIC, Spain)

This work reports on recent advances in Cathodic Arc Evaporation-PVD process assisted by a medium IR fiber laser (1055-1090nm). The main objective of this study is to improve the mechanical properties of titanium nitride (TiN) coatings by the “in-situ” application of laser in the deposition area during the coating growth process. The modification of the characteristic parameters of the laser source (Frequency, power and beam velocity) allows to obtain different effects, both on the final film properties and also on the substrate if the laser treatment is done before the deposition process. All the coatings have been produced in a commercial METAPLAS PVD chamber equipped with 6 arc sources.

The composition and morphology of these new laser assisted coatings have been studied by FE-SEM and GD-OES, thus changes in the chemical composition profile of the TiN coatings have been observed. The characterization of the films produced includes measurement of the mechanical properties such as film adhesion (scratch test), microhardness and tribology (wear coefficient).

11:20 AM Invited B4-5 Surface Nanostructures Induced by Low Energy Ion Sputtering
Stefan Facsko, Adrian Keller, Mukesh Ranjan, Wolfhard Möller (Forschungszentrum Dresden Rossendorf e.V., Germany)

Under special conditions low energy ion sputtering of solid surfaces leads to the formation of regular nanopatterns. These surfaces represent an interesting example of spontaneous pattern formation in non-equilibrium systems exhibiting different features like wavelength coarsening or a transition to spatiotemporal chaos. Different pattern types are observed for different experimental conditions, i.e. wavelike ripple patterns and hexagonally ordered dot arrays under oblique and normal ion incidence, respectively [1]. These patterns have gained increasing interest in recent years as templates for thin film growth.

According to the model of Bradley and Harper (BH) [2], the regular patterns result from the competition between curvature dependent roughening and smoothing of the surface. Since the local erosion rate is higher in the valleys than on crests, the eroded surface is unstable. In the presence of smoothing mechanisms, however, a wave vector selection occurs and a periodic pattern with one spatial frequency is observed. The pattern formation can be described by continuum equations based on the BH model. Several extensions have been proposed in the last years, with the stochastic Kuramoto-Sivashinsky (KS) equation being the most prominent one [3]. However, although most experimental investigations on ion-induced pattern formation were performed under oblique ion incidence, only few theoretical studies focused on the corresponding anisotropic KS (aKS) equation.

We will also present studies of thin film growth on these patterns. Depending on the interface energy of the metal film with the substrate the films grow in a conformal way reproducing the surface topography or as nanoparticles on the substrate surface. Furthermore, depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanoparticles align parallel to the ripples, eventually coalescing and forming nanowires. Metal thin films grown in this way exhibit distinct optical properties due to their localized surface plasmon resonance. Because of the alignment these nanoparticles exhibit a strongly anisotropic plasmonic resonance [4]. In addition, the magnetic properties of ferromagnetic thin films grown on rippled surfaces are drastically change by the presence of the interface and surface periodic roughness [5].

[1] W. L. Chan and E. Chason, J. Appl. Phys. 101, 121301 (2007)

[2] R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)

[3] R. Cuerno and A.-L. Barabási, Phys. Rev. Lett. 74 4746 (1995)

[4] T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).

[5] M. O. Liedke, B. Liedke, A. Keller, et al., Phys. Rev. B 75, 220407 (2007).

12:00 PM B4-7 Pulsed Laser Deposition of Low Work Function Coatings for Field Emission cathodes
Steve Fairchild (Air Force Research Laboratory); Terry Murray (University of Dayton); Brian Towne (Air Force Research Laboratory); Marc Cahay (University of Cincinnati); Tyson Back (University of Dayton)
Field emission DC cold cathodes continue as an important area of research for uses such as electron microscopy, novel x-ray sources, vacuum electronic THZ sources, and high power microwave sources. Each of these applications typically requires high current densities with a high brightness electron beam. The Air Force Research Laboratory (AFRL) began research on such DC cathodes for use in a THz traveling wave tube (TWT). The TWT requires an electron beam of 100 micron diameter or less which necessitates the need for small diameter cathodes. Various single fiber cathodes have been tested for their field emission properties including those made from graphite and single walled carbon nanotubes (SWNTs). Additionally, low work function coatings have been applied to these fibers to optimize their performance. Pulsed laser deposition (PLD) is initially used to coat planar graphite substrates so that the coating work function can be measured with an in-situ Kelvin Probe. Subsequently the coatings are applied by PLD to single fiber cathodes and their field emission properties are characterized. The fibers are heated during deposition to promote adhesion of the coatings. HfC, ZrC, TiC, and WC have been investigated. Preliminary results with HfC coated graphite fibers show a 3x improvement in emission current.
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