Papers

ICMCTF2006 Session B4: Laser Assisted and Ion Beam Coatings and Technologies

Wednesday, May 3, 2006 8:30 AM in Room Royal Palm 1-3

Wednesday Morning

Start	Invited?	Item
8:30 AM		B4-1 Characteristics of ZrC Thin Coatings Grown by Pulsed Laser Deposition J. Woo, K. Siebein, G. Bourne (University of Florida); D. Craciun (National Institute for Laser, Plasma and Radiation Physics, Romania); V. Semet, V.T. Binh (Universite Claude Bernard, France); R.K. Singh, V. Craciun (University of Florida) Refractory compounds, characterized by high melting temperatures, excellent thermal stability, high hardness, and a low work function for electron emission such as ZrC have important applications in vacuum electronics or micromechanics. ZrC also exhibits a lower lattice mismatch and thermal expansion coefficient difference with Si than ZrN, making it an ideal candidate for metallization or diffusion barriers structures for Si-based electronic devices. Although many techniques such as e-beam bombardment, chemical vapor deposition, magnetron sputtering, or laser cladding have been used to deposit ZrC thin coatings, it appears that it has been quite difficult to obtain high crystalline quality materials because of its high melting temperature, low vapor pressures and Zr atoms affinity for oxygen. To overcome these difficulties, ZrC thin coatings were grown on (001)Si, (111)Si and (0001) sapphire substrates by the pulsed laser deposition (PLD) technique. X-ray diffraction, both in symmetrical and grazing incidence geometry, x-ray reflectivity, atomic force microscopy, spectroscopic ellipsometry, transmission electron microscopy, and Auger and x-ray photoelectron spectroscopy investigations were used to characterize the structure, morphology, and composition of the deposited coatings. It has been found that coatings deposited by using a high laser fluence of 10 J/cm² at substrate temperatures higher than 700°C under very low water vapor pressures were highly textured, dense, smooth and with a low oxygen content below 2.5 %. Coatings deposited on (001)Si grew with their (001) axis perpendicular to the substrate, while those deposited on (111)Si and (0001) sapphire grew with their (111) axis perpendicular to the substrate. Pole figures and high-resolution cross-section transmission electron microscopy investigations showed that the coatings were epitaxial, with in plane axis aligned to those of the substrate. Nanoindentation measurements showed higher values of the hardness for higher crystallinity. For the highest crystalline quality, (111) ZrC coatings deposited on sapphire, values over 450GPa for the elastic modulus and 30.4 GPa for the hardness were measured.
9:10 AM		B4-3 Film Growth Phenomena in High-Energetic Room Temperature Pulsed Laser Deposition on Polymer Surfaces J.M. Lackner, W. Waldhauser (JOANNEUM RESEARCH Forschungsgesellschaft GmbH, Austria) Coating of plastics by of inorganic metal-based films requires profound knowledge about the phenomena occurring in connecting materials of very high and very low (visco-)elastic properties. Buckling and delamination are unwanted, stress-release induced effects leading to severe failure. To overcome these problems, higher energetic deposition conditions for strengthening the polymer surface by ion implantation are seen as a chance, but bear the risk of high film stresses and, thus, an increase of buckling. To understand these phenomena in Pulsed Laser Deposition (PLD) with pulsed and within each pulse alternating high- and low-energetic deposition conditions, the current work focuses on topographical, morphological and chemical investigations of polymers, coated with thin films between 5 and 100 nm thickness. Applying this approach enables the understanding of ion implantation during interface growth and stress formation in the growing films. High-resolution transmission electron microscopy and diffraction pattern analysis of some 10 nm thick films lead to a high understanding of stresses and growth influences. The results reveal up to 200 to 300 nm deep implantation of atoms in the polymer surface, hardening the soft polymer surface and increasing the load capacity, which is revealed by nanoindentation measurements. The growing thin films are extremely dense and possess very high elasticity - thus, deformation traces (cracks) after nanoindentation measurements are hardly detectable. Only very low changes of the surface topography after coating (investigated by atomic force microscopy) reveal scarcely influences of the ion bombardment.
9:30 AM		B4-4 Wear Resistance and Tribological Properties of Superhard Ta-C Films Deposited on Various Materials by PLD S. Weissmantel, G. Reisse, D. Rost (University of Applied Sciences Mittweida, Germany) Superhard tetrahedral amorphous carbon (ta-C) films with low internal stress were prepared by a combination of pulsed laser deposition and pulsed laser annealing on tungsten carbide hard metal and a variety of steels. The several µm thick ta-C films were found to have up to 80 to 85 % sp³ bonds and a hardness of up to 60 to 90 GPa. Good adhesion was achieved by optimizing the pre-treatment of the substrate surface prior to deposition and by using adhesion improving layers in the case of steel. It will be shown that various carbides are particularly suited as interlayer material. The critical loads obtained from scratch test measurements performed on 2 µm thick ta-C films were up to 60 N for WC hard metal and up to 30 N for various steels, including nitrided steel. The tribological properties and the wear resistance of such ta-C films deposited on plane WC hard metal and steel substrates as well as drillers will be presented and compared to other hard coatings. Several examples of coated tools and the effect of the films on wear and friction will also be shown.
9:50 AM		B4-5 Photocatalysis of TiO₂/TiO_2-xN_x Multilayers by Ion-Assisted Electron Beam Evaporation Y.M. Deng, S.F. Shu, T.K. Chen, M.S. Wong (National Dong Hwa University, Taiwan) Titanium oxide and nitrogen-doped titanium oxide (TiO₂/TiO_2-xN_x) multilayers in anatase phase were prepared by ion-assisted electron beam evaporation using rutile TiO₂ powders as source material. Various multilayer structures with distinct top layer or bottom layer were investigated using X-ray diffraction, Raman, and UV/Vis. absorption spectroscopy. The absorption edges of the multilayer films red-shifted from 400 to 470 nm. The multilayers exhibited significant photocatalytic and hydrophilic properties under visible light and UV light irradiation. Multilayer structure with pure TiO₂ top layer and bottom layer exhibited better photocatalytic activity than single-layer TiO₂ film under UV light irradiation.
10:10 AM		B4-6 Relationship Between the Nanostructure and Mechanical Properties of Pulsed Laser Deposited Dichromium Trioxide Thin Films M. Tabbal (Harvard University); T.C. Christidis, S. Kahwaji (American University of Beirut, Lebanon); U. Hangen, W. Stein (Surface, Germany) Dichromium trioxide (Cr₂O₃) is the most stable phase of chromium oxide and, in thin film form, this material has been shown to have very attractive mechanical properties such as high hardness and low friction coefficient with applications as protective coatings, in digital magnetic recording heads. The aim of this work is to investigate the relationship between the nanostructure and mechanical properties of Cr₂O₃ thin films grown on Silicon (100) by KrF excimer laser ablation of a target in oxygen ambient, at temperatures ranging from 20 to 950°C. Compared to other more conventional techniques, pulsed laser deposition induces the growth of dense, non-porous films with uniform grain size and having the stoichiometry of the ablated target. Indeed, for all films, X-ray Diffraction and Rutherford Back-Scattering analyses confirm that Cr₂O₃ is the only phase present, though a significant improvement in the crystalline quality and a reduction of stress in the layers is observed for films deposited above 500°C. These effects are accompanied by an increase in the grain size of the films from about 50 to 200 nm as deposition temperature is raised from 20 to 950°C. Nanoindentation measurements indicate that films with hardness and elastic modulus values as high as 20 and 220 GPa, respectively, can be synthesized at deposition temperatures below 700°C. At higher temperatures, the hardness falls off rapidly to a value of 9 GPa. It was found that the hardness value of the films is linearly correlated to the inverse square root of the grain size thereby suggesting a Hall-Petch relationship. Slight divergence from this behavior is detected for films deposited at low temperature, due to the presence of residual stresses.
10:30 AM		B4-7 Crystalline Films and Nanowires of Lanthanum Monosulfide S. Fairchild (Air Force Research Laboratory); M. Cahay (University of Cincinnati); P. Murray (University of Dayton) Thin films of Lanthanum Monosulfide (LaS) have been successfully deposited on Si and MgO substrates by pulsed laser deposition. Crystalline films were obtained when grown in an H₂S background gas at elevated substrate temperatures as evidenced by x-ray diffraction and transmission electron microscopy. The films are golden yellow in appearance with a mirror-like surface morphology and possess a sheet resistance around 0.1 W/square. The scanning anode field emission microscope (SAFEM) reveals Fowler Nordheim field emission behavior and an effective work function of 0.65 eV. Additionally, LaS nanowires were produced by pulsed laser deposition of LaS on a porous alumina template consisting of a well ordered two dimensional array of 50 nm pores. The wires grow in two modes: one set of wires grows preferentially on the boundary of two regions containing well-regimented arrays of pores, the other set grows inside the pores. Wires in the first set are wide (~ 200 nm diameter) and grow with a density of 109/cm² while those in the other set are thinner (50 nm diameter) and grow with a density > 1010/cm². The current-voltage characteristics of these nanowires are stable and show a Fowler Nordheim behavior.
10:50 AM		B4-8 Plasma Diagnostics of Hybrid Magnetron Sputtering and Pulsed Laser Deposition J.G. Jones, C. Muratore, C.C. Baker, A.A. Voevodin (Air Force Research Laboratory) Magnetron sputtering (MS) combined with Pulsed Laser Deposition (PLD) provides a novel hybrid method of depositing tribological coatings onto low temperature substrates. A variety of plasma diagnostic techniques can be used to monitor optical emissions during a deposition in situ including: an inexpensive fixed wavelength spectrometer having a linear detector, a time of flight system consisting of a filter and photomultiplier tube, a spectrometer having a motorized grating for high resolution, and a time resolved imaging camera (ICCD) that can either be attached to a motorized spectrometer or to an optical assembly for spatially imaging the emissions. A Langmuir probe can also provide complementary diagnostic information about the plume without having an optical line of sight. These optical techniques will be compared with regard to a measured set of thin-film properties measured using surface analysis techniques (XRD, XPS). With in situ sensing of optical emissions, process regulation for the purpose of maintaining atomic composition and structure over long durations becomes possible, even with multiple deposition sources.