ICMCTF2003 Session B5: Laser Assisted Coatings and Technologies

Wednesday, April 30, 2003 1:30 PM in Room Golden West

Wednesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	B5-1 Synthesis and Laser Processing of Nano and Micro Crystalline CVD Diamond Films V. Konov, V. Kononenko, T. Kononenko, S. Pimenov (General Physics Institute, Russia) Various types of plasma reactors for synthesis of CVD diamond has been developed. They include: 1) 6 kW microwave device with up to 100 mm diameter deposition area; 2) DC arc jet with auxiliary electrical discharge (total electrical power about 11 kW, deposition area about 20 cm² and diamond growth efficiency exceeding 10 carat/kW.h); 3) atmospheric pressure laser plasmatron that allows to deposit diamond without a vacuum chamber. Major emphasis has been made on synthesis of thin ultrasmooth nanocrystalline diamond coatings (thickness 50nm-20µm) and thick (up to 2 mm) thermal, optical and electronic grade diamond plates. Lasers have shown to be an excellent tool in post-growth processing of CVD diamond plates. Major features of short-pulsed laser ablation of diamond via its surface graphitization have been studied. It resulted in the possibility to perform high presision microstructuring of diamond. As an example, excimer KrF laser manufactured high quality CVD diamond IR diffractive optical elements will be presented. The technique of selective laser ablative etching has been successfully applied to polishing (smoothening) of CVD diamond. It is espessially important that application of lasers permits to use contactless optical methods of large area CVD diamond plate thickness control in situ, that is in the process of its polishing. Consiquently, it becomes possible to perform fully automated laser planarization or shaping of CVD diamond. Moreover, by means of such a technique one can also control the rate of CVD diamond ablation in the process of its multi-pulsed irradiation.
2:10 PM		B5-3 The Growth of Transparent Conducting ZnO Films by Pulsed Laser Ablation. S.J. Henley, M.N.R. Ashfold (University of Bristol, United Kingdom) The structure of undoped, Al-doped and Ga-doped ZnO thin films grown on sapphire and NaCl substrates by 193 nm pulsed laser ablation of a ZnO target in a low background pressure of oxygen was investigated using transmission electron microscopy (TEM) and X-ray diffraction (XRD). The films on sapphire grew with the polar (0002) orientation. The samples deposited on NaCl presented a mixture of polar and non-polar orientations, at substrate temperatures above 300°C, as determined by electron diffraction in the TEM. All samples demonstrated improved crystalline quality, as measured by the FWHM of the ZnO (0002) rocking curve, with increasing substrate temperature.. The best crystalline quality was observed for the undoped films. The inclusion of Al or Ga into the lattice degraded the crystallinity of the films but allowed the production of highly conductive films. ZnO:Al and ZnO:Ga film resistivities were measured using a four-point probe method and were found to decrease with increasing deposition temperature. Film thickness was determined using variable angle spectroscopic ellipsometry.
2:30 PM		B5-4 Improved Ferroelectric Properties in Ca Substituted SrBi₂Ta₂O₉ Thin Films Grown by Laser Ablation Technique R.S. Katiyar, R. Das, P. Bhattacharya, W. Perez, P. Dobal (University of Puerto Rico) Fatigue free characteristics of bismuth-layered perovskite SrBi₂Ta₂O₉(SBT), is suitable for the recent non-volatile random access memory (NVRAM) applications. However, the low remanent polarization and higher crystallization temperature are the limiting factors for practical integration of SBT into Si technology. In this study, we have made an effort to improve the remanent polarization of SBT with the incorporation of Ca at Sr-site. Thin films with different concentrations of Ca (0, 0.05, 0.1, 0.15, 0.2) were deposited on Pt/TiO₂/SiO₂/Si substrates using pulsed laser deposition (PLD) technique. Phase purity, crystalline structure and orientation of the films were studied using x-ray diffraction technique. Decrease in lattice parameter with increasing Ca contents in SBT was attributed to the smaller ionic radii of Ca at Sr-site. The change in lattice vibrational frequencies and the transition temperature with the incorporation of Ca in SBT was investigated using Raman spectroscopy. It was found from AFM studies that the grain size and surface roughness of the films were enhanced with the incorporation of Ca in SBT. Films with 20% Ca exhibited remanent polarization (P_r) of 23.5µC/cm²and a coercive field of 175 kV/cm, respectively. The enhanced remanent polarization was attributed to the increased grain size and to increase in the lattice mismatch between TaO₂and SrO planes. The current transport mechanism of the films was studied in metal-ferroelectric-metal configuration. The experimental data was well fitted to the interface dominated Schottky emission theory. The barrier height for SBT was estimated to be 1.27 eV. Detailed results of structural, ferroelectric and conduction mechanism of Ca substituted SBT thin films will be presented, in close correlation with the intrinsic characteristics of Ca-ions. This work was supported in parts by NASA-NCC5-518 and NSF-INT0097018 grants.
2:50 PM		B5-5 Review of Process Control Developments for Pulsed Laser Deposition J.G. Jones, R.R. Biggers, A.A. Voevodin (Air Force Research Laboratory) Process control is currently being applied to pulsed laser deposition (PLD) to improve thin-film quality, as well as to actually grow films that otherwise could not be grown. Hybrid deposition processes that use both magnetron sputtering (MS) and PLD are examples of processes that can require process control to maintain a stoichiometric ratio of plume components with the expectation that the thin-film atomic ratio will remain constant throughout the deposition. Use of recipes, or gain scheduling, allows for a computer to control sequential events to grow multi-layer films in a repeatable manner. When process control is used in conjunction with recipes, multilayer films can be deposited with a high degree of flexibility. Process control methodologies that are being used with PLD to deposit these thin-films will be compared.