Papers

ICMCTF2001 Session B6-1: Laser Assisted Deposition

Wednesday, May 2, 2001 8:30 AM in Room Golden West

Wednesday Morning

Start	Invited?	Item
8:30 AM		B6-1-1 Structure and Properties of Novel Functional Diamondlike Carbon Coatings Produced by Laser Ablation Q. Wei (NSF-CAMSS); J. Narayan (North Carolina State University); J Sankar (NSF-CAMSS, NC A&T State University) Diamondlike carbon (DLC) or tetrahedral amorphous carbon (ta-C) is one of the many forms of carbon that mainly consists of sp3 bonded carbon atoms. If properly prepared, DLC can have properties that rival those of crystalline diamond. The beneficial properties of DLC stem from the continuous rigid random networks of sp3 carbon atoms, and the properties can essentially be tailored by the sp3/sp2 ratio. Techniques that have been successfully used to prepare high quality DLC coatings or thin films include pulsed laser ablation (PLA), filtered cathodic vacuum arc (FCVA) deposition and mass selected ion beam (MSIB) deposition. DLC coatings that possess mechanical properties close to diamond in terms of hardness, atomically smoothness, IR transparency, and chemical inertness can be processed easily with these techniques. In the past decade, tremendous progress has been made in experimental and theoretical investigations of hydrogen free DLC. Experimental and commercial applications in microelectronics, micro-tribology, biomedical technologies and so on, have been demonstrated. Potential applications include sensors, flat panel displays (field emitters), photodiode, and so on. In this paper, we report comprehensively the past and recent efforts in the research of functional diamondlike carbon coatings prepared by pulsed laser ablation in our group. In order to alleviate the internal compressive stress problem associated with high quality DLC coatings, we have adopted a novel and ingenuous target design in the growing of DLC films. The films were characterized by Raman spectroscopy, transmission electron microscopy, IR range optical measurements, tribological measurement, and so forth.
9:10 AM		B6-1-3 The Effect of Microstructure on Hardness Enhancements in Ti-Si-C and Ti-W-C Thin Films Deposited by MSPLD J.E. Krzanowski, A.R. Phani (University of New Hampshire); J.J. Nainaparampil (Systran, Inc.) The microstructure of thin-film hard coatings has been proposed as one factor that can influence film hardness, primarily via Hall-Petch grain-size strengthening. One important issue is the influence of the reverse Hall-Petch effect, where reductions in grain size to an ultra-fine scale lead to a decrease in hardness. The objective of our work is to obtain grain size reductions in titanium carbide (TiC) films by additions of a ternary element, either Si or W, and to determine the effect on hardness. Ti-Si-C and Ti-W-C films have been grown by magnetron sputtering/pulsed laser deposition (MSPLD) in the temperature range of 400-600C, and compared to previous results on magnetron sputter deposited samples. In both cases, addition of the ternary element reduced grain size and increased hardness. For example, the hardness of TiC films sputter-deposited in the absence of any substrate bias was typically 13 GPa, while up to 30 GPa was obtained a TiC-50%WC film with a 5 nm grain size. Films of TiC-20%SiC deposited by MSPLD were typically 5-10 GPa harder than films of TiC alone, similar to results obtained in sputter deposited films. Transmission electron microscopy revealed a grain size reduction from 100 to 14 nm due to Si additions. Since no substrate bias was used for these depositions, the residual stress was small. In subsequent experiments, the application of substrate bias was used to improve film density, but also resulted in higher stress levels, both of which can affect hardness. It was found that the proper selection of deposition conditions and film composition can optimize grain structure, and improve the hardness and wear behavior of carbide films deposited at low temperatures by the MSPLD method.
9:30 AM		B6-1-4 Effect of Grain Size of Pb(La,Ti)O₃ Thin Films Grown by Pulsed Laser Deposition for Memory Device S.Y. Lee, C.H Hur (University of Korea) The (Pb1-xLax)TiO₃ (PLT) thin films possessing good ferroelectric properties were successfully obtained by using pulsed laser deposition (PLD) process, followed by post-annealing at 600oC or two-step process. Especially, Dielectric thin films of Pb(La,Ti)O₃ (PLT) for the application of highly integrated memory devices have been deposited on Pt/Ti/SiO₂/Si substrates in situ by pulsed laser deposition(PLD). We have systematically investigated the variation of grain sizes depending on the process condition of post-annealing and the two-step process. The grain sizes of PLT thin films were successfully controlled from 260 to 350 nm by changing annealing process parameters and using two-step deposition process. Electrical properties including dielectric constant, ferroelectric characteristics, crystallization and leakage current of PLT thin films were shown to be strongly influenced by grain size. C-V measurement, ferroelectric properties, leakage current and SEM were performed to investigate the electrical properties and the microstructural properties of Pb(La,Ti)O₃ films.
9:50 AM		B6-1-5 Influence of Deposition Pressure on the Composition and Structure of Carbon Nitride Films by Direct Current Plasma Assisted Pulse Laser Deposition C, Yuhang (Nanyang Technological University, Singapore); X.L. Qiao (Huazhong University of Science and Technology, PR China) Carbon nitride films were deposited by pulse laser ablation of graphite target under nitrogen atmosphere at room temperature.A direct current discharge apparatus was used to supply active nitrogen species during the deposition of carbon nitride films. FTIR and XPS were used to characterize the composition and bonding structure of the deposited films. The influence of deposition pressure in the range 1-20Pa on the composition and bonding structure of carbon nitride films were studied. The composition and structure are strongly depended on the deposition pressure. The ratio of N/C in the deposited films increases linearly with increasing deposition pressure of 10Pa, further increase of the deposition pressure results in the slightly increase of N/C ratio. FTIR spectra indicate the existence of C-N, C=N, and CÂºN bonds. Increasing deposition pressure results in the increase of the C=C and C=N bonds fraction and the decrease of the C-N bonds fraction in the deposited films. XPS results is consistent with FTIR results, which indicate that increasing deposition pressure leads to the increase of N atoms fraction bonded to sp2C and sp2C atoms fraction bonded to N atoms, and the decrease of N atoms fraction bonded to sp3 C and sp3 C atoms fraction bonded to N atoms.
10:30 AM		B6-1-7 New Developments and Applications in Laser Build-Up Welding A. Techel, N. Steffen, E. Beyer (Fraunhofer-Institute for Material and Beam Technlogy Dresden, Germany)
11:10 AM		B6-1-9 Characterization of Plume Fluence for Laser Ablation of YSZ in Mixed Oxygen and Argon Environments J.G. Jones, A.A. Voevodin, Jeffrey S. Zabinski (Air Force Research Laboratory) Pulsed-laser-deposition (PLD) produces a highly energetic plume that has characteristics that are highly dependent on the chemical identity and partial pressure of gases in the background. Low pressure oxygen is the most common choice for the deposition of highly oriented yttria stabilized zirconia (YSZ) films. The goal of this research was to deposit highly oriented YSZ films at low temperature using PLD. Intensity measurements of YSZ plumes were made using four different narrow band filters in conjunction with a high-speed photomultiplier tube and digital phosphorous oscilloscope. For each filter selection, experiments were performed with five background gas compositions containing oxygen and argon, at seven different pressures ranging from 2 - 200 mTorr. The data suggests that as the pressure of the gases increases to 100 - 200 mTorr, especially with oxygen, that there are multiple components, which are clearly visible in the measured oscilloscope waveforms. One of the main plasma components was positive zirconium ions. At lower pressures, 50 mTorr and below, the time of peak intensity, from the measured oscilloscope waveforms, occurs relatively consistently in comparison to higher pressures. YSZ films were grown at low pressure, each with distinct background gas compositions containing oxygen and argon, with and without a negative substrate bias for zirconium ion acceleration. Using a substrate bias voltage, the crystal size was dramatically increased from 10-20 nm to 150-200 nm as measured by AFM. Films grown with the substrate bias had a crystal lattice that was much more cubic, as measured by XRD.
11:30 AM		B6-1-10 Optical Properties of ZnO Thin Films Fabricated by Pulsed Laser Deposition E.S. Shim, S.H. Bae, J.H. Kim (Yonsei University, Korea); S.Y. Lee (University of Korea) ZnO thin films on (001) sapphire and (100) p-type silicon substrates have been deposited by pulsed laser deposition technique using a Nd:YAG laser with the wavelength of 355 nm at the oxygen ambient. Substrate temperatures were varied in the range of 200° C to 600° C. According to XRD, (002) textured ZnO films of high crystalline quality have been obtained by pulsed laser deposition technique. After oxygen post-annealing treatment, the stoichiometry of ZnO has been enhanced. We have investigated the structural and optical properties of ZnO thin films using X-ray diffraction (XRD), photoluminescence (PL), and Rutherford Backscattering Spectrometry (RBS).
11:50 AM		B6-1-11 Surface Modifications Using Advanced Precursor Technology K.D. Parks (Applied Research Laboratory- Pennsylvania State University) A new, patented series of high tech precursors and application techniques are under investigation as a method to modify surface chemistry of metal or ceramic substrates using lasers and other suitable high-energy sources. Successful alteration of metallic substrates is possible when a thin layer of precursor precedes irradiation. Preliminary test results have shown that modified surfaces possess beneficial physical and chemical properties, including smooth finish, increased hardness, wear and corrosion/oxidation or erosion resistance. Use of these precursors offers cost reduction, versatility, and greater metallurgical compatibility with base metal substrates than some conventional alloying and cladding methods. The process can be used to accomplish out-of-position surface modification. Possible applications include Cr plate replacement, in situ repair and/or refurbishment of degraded surfaces, along with creation of unique surface chemistries.