ICMCTF2005 Session H1-3: Nanostructured Coatings and Novel Deposition Strategies

Thursday, May 5, 2005 1:30 PM in Room Royal Palm 4-6

Thursday Afternoon

Start	Invited?	Item
1:30 PM	Invited	H1-3-1 Nanostructured Hardcoatings: Processing, Characteristics and Performance B.H. Kear (Rutgers University); G. Skandan (NEI Corp.) A method has been developed to fabricate thermal sprayed nanostructured WC/Co hardcoatings that display superior abrasive wear properties. A feature of the processing is the use of an aggregated feedstock powder, comprising a mixture of micron-sized WC and nanostructured WC/Co powders. Thus, during thermal spraying, preferably using a high velocity oxy-fuel (HVOF) torch to mitigate decarburization, the nanophase WC/Co undergoes rapid melting, while the WC phase is heated but not significantly melted. A dense coating is formed when the semi-solid or mushy particles impact on the substrate surface. In a wear test, the hard WC dispersed phase resists abrasive wear, whereas the tough WC/Co matrix or binder phase resists undercutting and removal of the hard particles during wear. The characteristics, properties and performance of such "multimodal hardcoatings", relative to conventional hardcoatings, will be discussed, as will the applicability of this materials design concept to other coatings systems, such as Al₂O₃-13TiO₂ and ZrO₂-20Al₂O₃. A feature of the multimodal approach is that composition and structure can be tailored to meet the performance requirements of different applications.
2:10 PM		H1-3-3 Structural Studies of Thin Zno-Poly(styrene-Acrylic Acid) Nanocomposite Films H.A. Ali, A. Iliadis, L. Martinez-Miranda, D. Stratakis (University of Maryland) The study of the structural characteristics of self-assembled ZnO nanoparticles within the poly(styrene-acrylic acid) diblock copolymer, [PS]_m/[PAA]_n , nanocomposite film, with two block repeat unit ratios m/n of 159/63 and 106/17, is reported. The nanocomposite films were formed onto the surfaces of (100)Si, (111)Si, SiO2/Si, (0001)Sapphire and (100)InP, by spincasting, in order to examine the influence of orientation and substrate surface properties on the orientation and self-assembly properties of the nanoparticles in the films. The self-assembly capability of the minority blocks in these diblock copolymers is used to form ZnO nanoparticles by first incorporating the ZnCl2 precursor in the copolymer in liquid phase, then spincasting on the surface and, upon solidification, converting the precursor into ZnO using an ozone based process. The resultant nanocomposite film contains self-assembled ZnO of spherical morphology in copolymer matrix. The conversion dynamics were evaluated by XPS, the morphological properties of the self-assembly were examined by AFM, and the crystallographic properties of the nanostructures were studied by XRD. Analysis of XPS spectra obtained before and after conversion revealed the absence of chlorine in the converted films and a binding energy of the Zn₂p3/2 electrons (1021.7eV) consistent with full conversion into ZnO with minimal losses. AFM images showed smaller and denser particles formed with spherical morphology in the [PS]₁₀₆/[PAA]₁₇ polymer. The size distribution of these particles was found to be 10-60 nm with an average density of 2x10⁸ cm^-2. In crystallographic evaluation, XRD patterns exhibited a dominant (100) diffraction peak for the nanoparticles formed on (100)Si while a dominant (101) peak was observed for those formed on (111)Si. Effects of annealing on size and strain of the nanocrystals will be discussed. Support of NSF grants ECS#9980794 and ECS#0302494 is greatly acknowledged.
2:30 PM		H1-3-4 Sputter Deposition of ZnO Nanorods/Thin Film Structures on Si J.-M. Ting, M.-T. Chen (National Cheng Kung University, Taiwan) Various techniques have been used to grow ZnO nanorods and a common mechanism to explain the growth of ZnO nanorods or nanowires is the vapor-liquid-solid (VLS) mechanism. Different from these processes and the VLS growth mechanism, we have reported in previous papers a new route for the growth of ZnO nanorods using a sputter deposition technique. It was found that the coating of an electroless copper layer on the substrate is critical for the formation of ZnO nanorods. It also appears that the VLS fails to explain the growth mechanism and the growth mechanism is still unclear. Therefore, as a part of the effort to explore the unknown growth mechanism, we have investigated the effect of various copper coatings and ZnO deposition parameters on the formation of ZnO nanorods. The formation of ZnO nanorods is discussed.
2:50 PM		H1-3-5 Plasma-Based Techniques to Reduce Particle Contamination in Sputtering Systems D. Ruzic, H.-J. Shin, B. Jurczyk, D. Alman (University of Illinois Urbana-Champaign) Particle contamination during the deposition of Si/Mo multi-layer mirrors for EUV can create significant distortions and loss of reflectivity and must be avoided. Particles larger than 50 nm are problematic. They can be generated from agglomeration of Si and Mo atoms of clusters in the gas phase, the ion source components itself in an ion-beam sputtering apparatus), flaking from the high-stress films deposited on the surfaces of the chamber, and micro-arcs across non-conducting films built up on the surface of the target. Several plasma-based techniques are under investigation aiming to reduce particle contamination during the deposition process. The preliminary experiment simulates the particle contamination of mirror samples by introducing external insulating nano-particles of 200 nm size. A RF antenna is used to create a weak plasma which simulates the ion beam sputtering environment near the substrate. It will charge the particles and suspend them from landing on the nearby surfaces. Bare Si wafers are used as substrate in a vacuum chamber with an 8” substrate holder that is electrically isolated. The particle deposition is simulated by switching the plasma off and a baseline for particle contamination levels is determined. A pulsed negative voltage on the substrate is timed to coincide with the cessation of the plasma and then test the effectiveness of the scheme in preventing particle contamination. Data from pulsed plasma schemes to remove particle contamination will also be shown. Inert gas flows are also added and their effectiveness on particle reduction is measured as well. Metrology for these experiments is performed with a Tencor Surfscan 7600 Wafer Inspection system which allows for detection of particles as small as 150 nm, has a sensitivity of 0.4 ppm and has a count accuracy of +/- 1.5%.
3:10 PM		H1-3-6 Relation of Hardness and Oxygen Flow of γ-Al₂O₃ Coatings Deposited by Bipolar Pulsed Magnetron Sputtering L. Lugscheider, K. Bobzin, M. Maes, C. Piñero (Aachen University, Germany) Aluminum oxide thin films are widely used because of their excellent properties, especially in terms of chemical, thermal, abrasive and corrosive resistance. Different applications and environments demand different kind of properties in thin films. The properties of aluminum oxide films are strongly deposition parameters dependent. The most common aluminum oxide form deposited by PVD-technology is the amorphous form. However, crystalline Al₂O₃ offers higher density and hardness than the amorphous form, as well as, higher chemical and thermal resistance. At high temperatures is possible the deposition of γ and ? Symbol -k alumina by CVD processes, but they cause high tensile stresses in coating and also limit the substrate material repertory. In this work, nanostructured Al₂O₃-films consisting of γ-Al₂O₃ grains imbedded in amorphous-Al₂O₃ were deposited by means of pulsed magnetron sputter ion plating technology. The influence of the most important parameters for the deposition of γ-Al₂O₃, i.e. power density at the target, duty cycle, puls-frequency, temperature, and O₂-partial pressure, were analyzed. The deposited Al₂O₃-films were then characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Hardness and Young's modulus were determined by nanoindentation. Surface energy of the coated samples was also measured.
3:30 PM		H1-3-7 Dynamics, Strength and Vibration Damping Properties of Nanoscale-Reinforced Composite Materials and Coatings M.V. Kireitseu (University of New Orleans) Enhanced vibration damping can be provided by materials reinforced with nanoparticles. Carbon nanotubes (CNT) are promising cost-decreasing materials as reinforcement in damping materials. Since the dynamics, strength and damping behaviour of novel carbon-nanotube-reinforced materials and systems is largely unknown, much of the focus in this paper is directed toward to measuring these characteristics, its correlation with technological parameters and checking if they are consistent with present theories and fundamentals. One part of research is development, approbation, optimization and checkout of manufacturing technology and design concept for nanoscale-reinforced polymer structures for vibra-tion damping systems, with application in fun blades of Rolls-Royce aero-engine. Another part of the paper is development and validation of the computational tools and algorithms required to estimate and validate performance and damp-ing characteristics of the materials (metrology at nanoscale), and then making these computational tools useful. Experimental test program will cover few CNT-based polymer materials. Thus, the research will reveal the best possible effect of nano-scale reinforcement in such materials. The major advantages should be the fundamentality of the concept and reliable database to avoid unnecessary speculations. The outcome of the paper is expected to have wide-ranging technical benefits with direct relevance to industry in areas of transportation (aerospace, automotive, rail), civil development, and other applications.
3:50 PM		H1-3-8 Fabrication of Yttria Stabilised Zirconia Coatings by a Novel Slurry Method X. Wang, P. Xiao (University of Manchester, United Kingdom) By adopting a "bricks and mortar" approach, ceramic coatings were produced on metal substrates using a novel slurry method. The slurry contained large preformed particles, as the "bricks", and concentrated nano-slurry, as the "mortar". Green coatings were prepared by spreading the slurry on substrates. Then sintering at 1200°C was carried out to produce coatings with nano-crystalline structure. The microstructure of the coatings can also be modified by infiltration of the nano-particle suspensions. By using different preformed particles, different micro-architectures were obtained and a reduced thermal diffusivity was achieved.
4:10 PM		H1-3-9 Nanocrystalline Growth and Grain Size Effects in Au-Cu Electro Deposits A.F. Jankowski (Lawrence Livermore National Laboratory) High strength and stability are required in smooth coatings deposited for the novel use of inertial-confinement-fusion capsules. The relationship of processing-structure-property is first explored as free standing foils of the gold-copper alloy system are prepared and characterized to assess the affect of nanocrystalline grain size on the mechanical properties, including strength and hardness. The 5 to 30 micron thick foils are fabricated by electrodeposition using a potassium cyanide solution formed from copper and gold salts. The as-deposited foils are found to have an equiaxed nanocrystalline structure as revealed by transmission electron microscopy and x-ray diffraction. The crystallite size is quantified using the Debye-Scherrer formulation for analyzing peak-broadening of the Bragg reflections found in the x-ray diffraction scans. The composition of the gold-copper foils is determined by the atomic number-absorption-flourescence analysis of energy dispersive x-ray spectra. The electrodeposition process parameters of current-pulse mode and cathode potential affect the grain size and composition of the foils. A decrease in the current density and cathode voltage favor deposition of the more noble metal species whereas millisecond-current pulse durations favor nanocrystalline grain sizes. The Vickers microhardness of gold-5 wt.% copper foils is measured from samples prepared in cross-section using a load force of 5 gm or less. A Hall-Petch variation of microhardness with nanocrystalline grain size is measured from a rule-of-mixtures value of 0.8 GPa to a maximum of 2.9 GPa as the grain size decreases down to 6 nm. This work was performed under the auspices of the U. S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-7405-Eng-48.
4:30 PM		H1-3-11 Photocatalytic Properties of Nanocrystalline TiO₂ Thin Film with Ag Additions C.C. Chang, C.K. Lin, C.C. Chan, C.S. Hsu (Feng Chia University, Taiwan) Anatase-phase TiO₂ with its excellent photocatalytic properties has attracted extensive attentions during the last decades. However, TiO₂ exhibits a relative high energy band (~3.2 eV) and can only be excited by high energy UV irradiation with a wavelength shorter than 387.5 nm. Efforts have been attempted to extend light absorption of the TiO₂-based photocatalysts from the UV toward the visible light range. In the present study, nanocrystalline TiO₂ thin films with or without various percentages of Ag, Ni, or Pd ionic additions were prepared by spin or dip coating technique. The as-obtained films were then exposed under UV light to reduce the corresponding metal ions. Thus nanocrystalline TiO₂ composite thin films with various metal additions can be prepared successfully. The as-prepared TiO₂, TiO₂/Ag, TiO₂/Ni, and TiO₂/Pd thin films were characterized by X-ray diffraction, scanning electron microscopy, and UV/Visible spectroscopy techniques to reveal the structural and topological differences. In addition, photocatalytic properties of these thin films were investigated by degradation of methylene blue under UV and/or visible light irradiation.