Papers

ICMCTF2011 Session B3: Laser and Ion Beam Assisted Coatings and Technologies

Tuesday, May 3, 2011 1:30 PM in Room Golden West

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		B3-1 Growth of Bi₅Fe_0.5Co_0.5Ti ₃O₁₅ Thin Films by Pulsed Laser Deposition Yalin Lu (U.S. Air Force Academy); Gail Brown (Air Force Research Laboratory); Gregory Kozlowski (Air Force Research Laboratory/Wright State University); Kurt Eyink (Air Force Research Laboratory); Larry Grazulis (Air Force Research Laboratory/UDRI); Krishnamurthy Mahalingam (Air Force Research Laboratory) Thin films of Bi₅Fe_0.5Co_0.5Ti₃O₁₅ (BFCTO) with potentially broad application in functional multiferroic devices were fabricated by using pulsed laser deposition (PLD) .In a search of optimal conditions to achieve epitaxially grown BFCTO thin films, different substrate temperatures (600°C, 650°C, 700°C and 760°C) and different partial pressures of oxygen (50 mTorr, 100 mTorr, 150 mTorr and 200 mTorr) in the PLD chamber were used during deposition of BFCTO films on LaAlO₃, LSAT, MgO and STO single crystal substrates with (100) surface orientations. Combination of 100 m Torr of oxygen partial pressure and substrate temperature of 650°C gives the best crystallinity of the thin films. Thorough structural and chemical studies of these BFCTO films were done by using SEM, HRTEM, AFM, XPS and Electron Probe Microanalyser measurements. Optical properties of these films were measured by using ellipsometry and their correlations with structural and chemical properties were established.
1:50 PM		B3-3- Nanoparticle Fabrication by Through Thin Film Ablation Paul Murray, Eunsung Shin, Leanne Petry (University of Dayton) We have developed a process denoted Through Thin Film Ablation (TTFA), which entails ablating, from the backside, a thin film target. The TTFA process results in the deposition of nanoparticles on a substrate with little agglomeration and without the large micrometer-sized particles that are normally formed by standard pulsed laser ablation. The nanoparticles thus formed by TTFA typically have diameters ranging from 1 to 5 nm. We have done extensive characterization of the dynamics of the TTFA process and have determined the mass and speed distributions of the nanoparticles. In this presentation examples will be given for the formation of Fe and Pt nanoparticles.
2:10 PM		B3-4 Laser-Deposition and Characterization of Amorphous Thermoelectric Films Garth Wilks (Air Force Research Laboratory); Terry Murray (University of Dayton); Steven Fairchild, Nicholas Gothard, Jonathan Spowart (Air Force Research Laboratory) From the Efficient Cluster Packing model describing the topology of metallic glasses, it is understood that certain compositions are favored for glass-formability based on the ratio of atomic sizes between constituents. In this regard, the half-Heusler composition Zr_0.5Hf_0.5NiSn is nearly ideal. Although the crystallized form of this material has been widely studied because of its high thermoelectric power factor, it has been suggested that partial vitrification may enhance the thermoelectric figure of merit by preserving the favorable aspects of electronic structure while significantly disrupting thermal transport. Capitalizing on the high quench rates possible during pulsed laser deposition, a spectrum of thin films including amorphous and partially-amorphous duplex microstructures has been grown under various conditions. Transport characteristics relevant to the thermoelectric effect are rationalized in light of accompanying microstructure characterization.
2:30 PM		B3-5 Multi-Beam, Multi-Target Pulsed Laser Deposition: Beyond Single Film Deposition Robert Eason (University of Southampton, UK) Many labs are currently using Pulsed Laser Deposition for rapid growth of a range of materials that would naturally includes metals, dielectrics, semiconductors, functional materials such as ferroelectrics or piezoelectrics, biomaterials, and more. Each PLD set-up will also have been designed around a particular interest or application area which might be the basic growth process itself, involving a range of on-line diagnostics, or the optimisation of a particular material, in terms of film quality, properties, thickness or size. However, while some labs may use multiple targets, via carrousels or specialist composite sector targets, one factor which is common to most facilities is that a single laser is used to ablate these targets and films are grown from a single laser plume/substrate interaction process. We have chosen to extend the basic single beam/single target geometry to a new 3 laser/ 3 target deposition set-up, and we believe this offers unique new capabilities within PLD research. Three independent laser plumes allow either a sequential or coincident deposition capability. If sequential deposition is implemented, there is the added flexibility of adjusting the temporal delay so that plume-plume interactions can be either utilised or avoided. Use of multiple plumes means that oxide films for example can now be grown from their separate constituents, and dopants can be added to a growing film in a gradual or graded manner, for applications in lasing planar waveguides. Combinatorial growth can be explored in a manner equivalent to the RGB three colour palette. Films that incorporate lateral or horizontal variation such as donut structures can be fabricated and new materials such as quaternary or penternary oxide crystals can be grown from ternary targets. Finally, multilayers, superlattices and mixed films are readily grown, by rapid shuttering of the individual plumes or incident lasers. Our work to date using multiple targets and laser beams will be described, for end applications that require low loss, single crystal films for lasing and amplifying end applications. I will describe what we now consider as routinely achievable and also our wish list for truly exotic fabrication strategies involving both horizontal and vertically integrated growth.
3:10 PM		B3-7 Capacitive Properties of x BaTiO₃-(1-x) BiScO₃ Thin Films Fabricated by Pulsed Laser Deposition Charles Stutz (Air Force Research Laboratory); Gregory Kozlowski (Wright State University); Steven Smith (Air Force Research Laboratory/UDRI); A Baker, C Randall (Penn State); Susan Trolier-McKinstry (Pennsylvania State University); Gerald Landis (Air Force Research Laboratory/UDRI); John Jones (Air Force Research Laboratory); Tyson Back (Air Force Research Laboratory/UTC) Thin films of x BaTiO₃-(1-x) BiScO₃ (BTBS) showing a high permittivity are useful both in capacitor applications and in piezoelectrics. BTBS thin films and SrRuO₃(SRO) or La_0.5Sr_0.5CoO₃(LSCO) conductive bottom electrodes were prepared by using pulsed laser deposition on <100> La_0.3Sr_0.7Al_0.65Ta_0.35O₃ (LSAT) single crystal substrates.In a search of optimal conditions to achieve epitaxially grown BTBS, SRO or LSCO thin films, different substrate temperatures (600°C, 650°C and 750°C) and different partial pressures of oxygen (100 mTorr, 200 mTorr and 300 mTorr) in the chamber were used during deposition on LSAT substrates. The best epitaxial films of BTBS strongly depend on composition (value of x). An example is if x is equal to 0.8, we have achieved the best quality film under 100 mT of oxygen partial pressure with a substrate temperature of 650°C. XRD diffraction pattern measurements show the high quality of these films. Also, a conductive buffer layer of SRO film requires 300 mT of oxygen partial pressure and substrate temperature of 750°C. The thorough structural and chemical studies of these BTBS films were done by using SEM, HRTEM, AFM and XPS measurements. The capacitance properties of these films were measured and their correlations with structural and chemical properties were established.
3:30 PM		B3-8 Attempt to Synthesize a Ti₃SiC₂ Coating by Pulsed Laser Deposition of a Ti-Si-C Multilayer Structure Marcus Hopfeld, Thomas Kups, Elvira Remdt, Marcus Wilke, Peter Schaaf (TU Ilmenau, Institut für Werkstofftechnik, Germany) The ternary compound Ti₃SiC₂ has a nanolaminated structure and belongs to the M_n+1AX_n phases. In the last 20 years there were several attempts to reduce the formation temperature of MAX phases by different sputtering techniques. Eklund et al. mentioned that thin film processing and the growth of 312 MAX-phases like Ti₃SiC₂, Ti₃GeC₂ and Ti₃AlC₂ require high synthesis temperatures in the range from 800°C to 1000°C regarding the diffusion length of large unit cells [1]. In this work the pulsed laser deposition of Ti-, Si- and C multilayers and the formation of the MAX phase Ti₃SiC₂ are investigated in detail. The incoming ions and particles, generated by the Nd:YAG laser (λ = 1064 nm, τ = 6 ns) ablation, form dislocations and lattice vacancies in each layer at the substrate. These defects support the diffusion of the A element (Si) between the layers. First results from as-deposited films showed the formation of the TiC_0.95phaseat a substrate temperature of 25°C. With respect to the formation process of Ti₃SiC₂, the diffusion of the A element could be supported by increasing the substrate temperature. Thus, different sample-sets were prepared with a varied thickness of each layer at different substrate temperatures from 20°C to 800°C onto amorphous Si₃N₄ substrates. The thicknesses of the layers were calculated by “SRIM” software concerning the kinetic energy of the incoming ions and the recoiled atom distributions. Afterwards, the diffusion profiles and elemental distributions of the as-deposited thin films were analyzed by glow discharge optical emission spectroscopy and electron energy loss spectroscopy. The structure and the phase formation of the as-deposited films were determined by X-ray diffraction using the Gracing Incidence method and transmission electron microscopy. Electrical properties as electrical conductivity were investigated by 4-point-probe. The indentation modulus and the Martens hardness were determined by nanoindentation. [1] Eklund P, Beckers M, Jansson U, Hogberg H, Hultman L. The M(n+1)AX(n) phases: Materials science and thin-film processing. Thin Solid Films 2010;518:1851.
3:50 PM		B3-9 Pusled Laser Deposition of Csl, TiC, and HfC Coatings for Field Emission Cathodes Tyson Back (Air Force Research Laboratory/UTC); Marc Cahay (University of Cincinnati); Terry Murray (University of Dayton); Steven Fairchild, John Boeckl (Air Force Research Laboratory) Field emission cold cathodes continue to be an important area of research for uses such as electron microscopy, novel x-ray sources, vacuum electronic THZ sources, and high power microwave sources. Each of these applications typically requires high current densities with a high brightness electron beam. Fibers made from single walled carbon nanotubes (SWNTs) have demonstrated considerable promise as field emission cathodes. To further exploit the field emission properties of these fibers, uniform low work function coatings were applied to the SWNT fiber surface by pulsed laser deposition (PLD) and thermal evaporation. Low work function coatings have the potential for lowering the turn-on voltage required for emission as well as potentially protecting the fiber cathode from ion back bombardment from the anode. Cesium is commonly used in cathode coatings due to its low work function. For this study, CsI was used as starting material for both laser deposited and thermally evaporated thin films. XPS showed that CsI films deposited by PLD are cesium rich as compared to the thermally evaporated films and have a Cs:I ratio of 2:1. This result agreed well with UPS and in-situ Kelvin probe measurements which yielded work function values more typical of cesium, 2.0-2.4 eV. Carbide coatings were also studied since Cs is susceptible to depletion from the cathode surface which shortens the lifetime of the cathode and increases down time for repair. Hafnium carbide (HfC) and titanium carbide (TiC) were chosen due to their robust nature and stability at high temperatures. Although not as low as Cs, they still have the ability to lower the surface work function of the cathode by greater than 1eV. X-ray photoelectron (XPS) and Auger electron (AES) spectroscopy were used to characterize the chemistry of these coatings. Ultraviolet photoelectron spectroscopy (UPS) and in-situ Kelvin probe measurements were used to determine work functions. In-situ XPS, AES, and UPS were used to optimize the deposition process.
4:10 PM		B3-10 Growth and Characterization of SBN60:Ce Thin Films Steven Buller, Dean Evans (Air Force Research Laboratory); Gary Cook (Air Force Research Laboratory/Azimuth); Sergey Basun (Air Force Research Laboratory/UTC); Gregory Kozlowski (Air Force Research Laboratory/Wright State University) Hybrid cell structures comprising a liquid crystal layer in between two photorefractive crystalline windows have been used for two beam coupling applications. They have shown absorption losses due to the thickness of the windows. Photorefractive thin films, that can replace the windows to minimize absorption loss. The Photorefractive thin films have been grown using Pulsed Laser Deposition (PLD) on substrates such as Lanthanum Aluminum Oxide (LAO), Magnesium Oxide (MgO), and undoped Strontium Barium Niobate (SBN). This method has been shown to grow very uniform films from 200 nm-1 µm of Strontium Barium Niobate doped with Cerium (SBN:Ce). Although these films are usually grown epitaxially with the c-axis normal to the surface, the growth of c-axis in the plane has been investigated. The direction of the c-axis is important for creating a space charge field on the surface of the film, which is used to control the liquid crystal layer. X-Ray Diffraction (XRD) has been used to study the lattice structure of the films. It was determined that films grown at 760°C and oxygen pressures of 200 mT give films with the c-axis normal to the surface independent of the substrate type and crystallographic orientation used. Results from the investigation of annealing and poling under electric fields to control the c-axis orientation will be discussed.
4:30 PM		B3-11 Structural and Compositional Control of BCN Films in PLD-Based Deposition Processes Matthew Lange (AFRL/RXBT and UTC); Amber Reed, Chris Muratore (Air Force Research Laboratory); Jianjun Hu (Air Force Research Laboratory/UDRI); Jamie Gengler (Air Force Research Laboratory/Spectral Energies); John Bultman (Air Force Research Laboratory/UDRI); John Jones, Andrey Voevodin (Air Force Research Laboratory) Carbon-based structures are well-known for pushing the limits of materials properties for important technological applications, such as thermal & electrical conductivity, mechanical elasticity, and strength. Sharing some similar physical and chemical properties of useful carbon-based structures, but with enhanced thermal stability, is boron carbon nitride, (BCN), which may be of interest for a range of advanced aerospace applications. BCN films have been grown using pulsed laser deposition, (PLD) in conjunction with other PVD techniques including magnetron sputtering with a choice of power coupling schemes (i.e., dc and HIPIMS). By selecting appropriate plasma sources, the flux of material at the substrate maybe changed which in turn allows manipulation of film structure and composition. For example, films with strong (100) orientations have been grown with pulsed laser deposition of a segmented boron nitride and graphite target in vacuum, as characterized with x-ray diffraction, while films with mixed (002)/(100) orientations have been grown using hybrid PLD/HIPIMS processes with a boron nitride PLD target, and graphite target on a HIPIMS magnetron. Using these PLD-based hybrid techniques, a broad range of compositions (measured by XPS) and structures (characterized with XRD, Raman spectroscopy and electron microscopy) have been explored, and correlated to thermal and mechanical properties, measured with time-domain thermoreflectance and nanoindentation techniques, respectively. Additionally, optical and electrostatic plasma characterization techniques have been used to correlate relative fluxes and characteristic energies of plasma species to the growth mechanisms of BCN films.
4:50 PM		B3-12 Bonding Structures, Mechanical Properties and Biological Behaviors of CN_x Films Prepared by Ion Beam Assisted Deposition and Laser Induced Arc Deposition Tianmin Shao, Songbo Wei, Liang Yin (The State Key Lab. of Tribology at Tsinghua University, China) We report some recent progresses in preparation and characterization of carbon nitride (CN_x) films. CNx films with different N contents were prepared by using laser induced arc deposition and ion beam assisted deposition, respectively. Bonding structures of the CN_x films were characterized by using X-ray photoelectron spectroscopy and Raman spectroscopy. Mechanical properties of the CN_x films were studied by using nanoindentation tester and tribo-tester. Influence of N content on the properties of CN_x films was investigated. Adsorption behavior of fibrinogen to the CN_x flms with different N content was investigated and comparison was made with the results of Ti and TiN films. The results show that CN_x film with adequate N content exhibited smallest fibrinogen absorption among the films tested. Frictional behavior of CN_x films deposited on stainless steel, under the lubrication of artificial saliva, was studied on a standard tribo-tester and a home made apparatus which simulates the friction between archwire and bracket in orthodontic application. Corrosion test was also performed for the CN_x films. The results show that both frictional behavior and corrosion resistance of the arch wire (stainless steel) were evidently improved after deposited with CN_x film.