Papers

ICMCTF2009 Session B4: Laser and Ion Beam Surface Engineering

Wednesday, April 29, 2009 8:00 AM in Room Golden West

Wednesday Morning

Start	Invited?	Item
8:00 AM		B4-2 Excimer and Femtosecond Laser Microstructuring of Superhard Pulsed Laser Deposited ta-C Films - Effects on Friction and Wear Resistance S. Weissmantel, G. Reisse, M. Nieher, R. Boettcher, A. Engel, K. Guenther (University of Applied Sciences Mittweida, Germany) Recently, we developed a novel method for the preparation of several micrometer thick super-hard tetrahedral amorphous carbon (ta-C) films with low internal stress. The method is a combination of excimer laser ablation for film deposition and excimer laser irradiation of as-deposited sub-layers for the reduction of the high stresses. Film hardness measured by a dynamic indentation method was found to be in the range of 55 to 65 GPa and the Young´s modulus in the range of 700 - 900 GPa. Good film adhesion on hard metal and steel was obtained by using tungsten carbide intermediate layers, which are also deposited by excimer laser ablation immediately prior to the ta-C deposition. The ta-C films have been microstructured using (1) excimer laser pulses of 248 nm wavelength and 30 ns pulse duration and (2) femtosecond laser pulses of 775 nm mean wavelength and 130 fs pulse duration. By using the excimer laser, well defined gratings with the width and depth of the grooves as well as the grating spacing in the range of 1.0 to a few micrometer were produced. By using the femtosecond laser, ripple structures with some 0.5 μm spacing, were produced in the films. The influence of different microstructures on wear resistance and friction coefficient measured by using a commercial tribotester under dry and lubricant conditions will be presented. For example, the friction coefficient measured under dry conditions decreases significantly from some 0.12 – 0.15 for unstructured ta-C down to below 0.05 and in some cases even below 0.01 for microstructured ta-C films.
8:20 AM		B4-3 Control of Femtosecond Pulsed Laser Deposited Thin Films through Plasma Optimization by Temporal Shaping Based on Genetical Algorithm M. Guillermin, C. Liebig, F. Garrelie, R. Stoian, A.S. Loir (Université Jean Monnet, France); S. Valette (Ecole Centrale de Lyon, France); E. Audouard (Université Jean Monnet, France) Time resolved emission spectroscopy of the plasma induced by a Ti:Sapphire laser (150 fs, 800 nm) irradiation coupled to the temporal shaping of the femtosecond laser pulses is carried out on pure aluminum samples (99.9%) in ultra high vacuum (~10-5 Pa). The emission lines ratio of the laser-induced plasma plume are modified by the use of a numerical adaptive loop with a feedback on the spectrally analyzed optical emission of the plasma. A line associated with Al-II ions is enhanced with respect to two transitions of neutral aluminum in a high fluence regime F=5.8 J/cm2 (~ 10 Fth). The result of the optimization is an optimized temporal shape for laser pulses consisting in series of femtosecond pulses separated by ~ 1 ps and distributed on a Gaussian envelop of 6 ps duration. Simplified temporal shapes of the femtosecond laser pulses are extracted from the optimized shape and their corresponding laser induced plasma emissions are discussed. This study is completed by an optimization of same lines with a lower fluence (low F=1.16 J/cm2 ~ 2 Fth) and an other one on the emission of an Al-III transition with respect to the line of Al-II used during the two first optimizations in the high fluence regime. The plasma optical emissions induced by the optimized and initial temporal shapes of the femtosecond pulses are spectrally analyzed and compared, evidencing modification of the ionization degree of the plasma plume. Thin film depositions are realized using the different temporally optimized and femtosecond distribution. Morphological and structural characterizations of the films are reported.
8:40 AM		B4-4 Deposition of Nanocomposite DNA Thin Films by Through Thin Film Ablation S. Fairchild (Air Force Research Laboratory); P. Murray (University of Dayton Research Institute); O. Shenderova (International Technology Center); F. Ouchen (University of Dayton Research Institute) There is increasing need for sensors in applications with lightweight and low power requirements and in thin film transistors with high effective charge carrier mobility for switching and communications. Thin films of biopolymers may be well suited for both applications. We have used a recently-developed, novel form of laser ablation, denoted through thin film ablation (TTFA), to deposit thin films of deoxyribonucleic acid (DNA). In addition, we have incorporated other materials into the ablation process to form nano-composite films. These include nano-diamond, onion like carbon, and metal (Ag, Pt) nanoparticles. We have characterized the films by XPS, Raman spectroscopy, SEM, AFM, and circular dichroism. The capacitance and conductivity of the nano-composite films were also measured. In addition to forming pin-hole free films, TTFA has potential advantages over other more conventional processing techniques such as spin coating. These advantages include controlled depos ition and uniformity of thinner films as well as the ability to create and tailor in-situ DNA-nanoparticle matrices suitable for optimized device properties.
9:00 AM		B4-5 Broad-Area Ion Beam Systems for Materials Processing: An Overview of Technology and Applications L.J. Mahoney, D.E. Siegfried, B.A. Knollenberg, V. Kanarov, A.J. Devasahayam (Veeco Instruments, Inc.) Over the last several decades broad-area ion sources have continued to be used in numerous materials processing applications where tailored ion energy and current flux are required and where material properties and substrate fixturing prohibit the use of other plasma processing techniques. In this presentation we survey existing and emerging ion beam processing applications for both broad-beam gridded ion sources and for gridless end-Hall and anode layer sources (ALS). We first review the use of gridded source systems which provide a well controlled ion energy and ion beam divergence for process substrate widths that range from 5 to 110 cm. These systems are widely used for ion beam milling and deposition of data storage structures and films, patterned LCD devices, mechanically structured optics and well-controlled deposition of high-performance optical filters. Gridless ion sources (end-Hall and ALS) are used when process requirements favor high ion current fluxes and yet allow for relatively broad distributions of ion energy and high ion beam divergence. These systems have been scaled to process widths from 10 to 150 cm wide. Gridless ion source systems are most commonly used in high-rate ion beam assisted deposition of low and high index optical coatings, direct deposition of tribological coatings, surface treatment and nano-texturing for improved adhesion over various materials and growth of anti-reflection coatings.
9:40 AM		B4-7 Ion Beam Irradiation Effects in Polymers Confined at Nanometer Scale and Nanomaterials M. Chipara, K. Lozanon, M.D. Chipara, A. Adhikari, M. Mihut (The University of Texas Pan American) Ion-beam irradiation effects in polymeric materials are rather complex ranging from physical and structural modifications up to chemical modifications. A feature of radiation-induced modifications in polymers and biologic materials is the presence of degradation processes characterized by very long lifetimes (larger than 105 s). This lecture focuses on ion-beam irradiation effects in ultra thin polymeric films and polymeric structures confined at nanometer scale. The lecture includes a brief analysis of the glass transition phenomenon in polymeric materials, an in-depth analysis of the effect of nanometer scale confinement/thickness of the polymeric film, and of the average molecular mass of the polymer on the glass transition temperature. An in-depth discussion aiming to understand from a theoretical standpoint the complex effect of ion beam irradiation on ultrathin polymeric films (with a thickness smaller than 1,000 nm) or confined polymeric structures will conclude the first part of the lecture. Theoretical predictions will be supported by preliminary experimental data reported elsewhere and tentatively connected to additional experimental difficulties (in ion beam lithography) expected to occur when the size of ion beam characteristic features or the thickness of polymeric films are dropped below 102 nm. While there are few theoretical models and experimental data regarding the effect of electron beams on copolymers and or block-copolymers confined at submicron scale (or with a thickness smaller than 1 micron), the lecture will provide a qualitative analysis of the expected radiation-induced modifications in such polymeric nanostructures. The second part of this lecture will critically review the modifications induced in the radiation behavior of materials due to their nanometer-sized confinement, from both theoretical and experimental standpoints. The analysis will include conducting, semiconducting, and magnetic nanostructures. The lecture will end with a brief analysis of some potential applications of such materials confined at submicron scale for microelectronics, spintronics, space missions, and radiation environments (nuclear plant environment).