MSEN Seminars Fall 2009

Date	Location	Speaker	Topic
09/25/09	207 ENPH	Dr. David Bahr	Mechanical Deformation in MEMs: Large Strains, Small Structures, and Adhesive Contacts
10/30/09	256 JEB	Dr.Sean McDeavitt	Powder Metallurgy of Uranium Alloy Fuels for Advanced Nuclear Energy System
11/06/09	106 JEB	Dr. Xiaoqing Pan	Effect of Interfacial Structure and Strain on the Properties of Multiferroic BiFeO₃ Thin Films
11/18/09	119B ZACH	Dr. Peter Trefonas	Chemistry and Dissolution Behavior of 193-nm Immersion Photoresist
11/19/09	256 JEB	Dr. Rui Huang	Nonlinear mechanics of monolayer graphene
11/24/09	256 JEB	Dr. Paula Alonso	Applications of computational thermodynamics to metallic alloys
12/04/09	102 MIST	Dr. Daisuke Hojo	Fabrication of the Cerium Oxide Nanocrystal Film with Heterogeneous Ligand Structures

Dr. David Bahr
School of Mechanical and Materials Engineering Washington State University	Time: 4:00 p.m. Date: 10/25/09 Place: 207 ENPH Host: Dr. Xinghang Zhang
Mechanical Deformation in MEMs: Large Strains, Small Structures, and Adhesive Contactss—
For autonomous wireless microsystems, a self-contained source of energy is essential. The finite energy available from conventional batteries make them is insufficient for systems that are expected to have long lifetimes and so there is a critical need for another approach. Energy harvesting systems, in which ambient energy (such as vibrations, thermal gradients, or solar) provide the necessary longevity, but are limited in their available power density, and are vulnerable to fluctuations in the quality of, or even complete absence of, the ambient source of energy. The P3 microengine harvests energy using MEMS technologies. Often MEMS utilize noble metals such as gold and platinum due to their inert behavior in a wide variety of environments, ranging from flexible electrodes for medical implantation to polymer–metal systems for humidity detectors to bottom electrodes for piezoelectric MEMS. Film adhesion can be compromised during both processing and subsequent service. Film fracture, which can occur in strained membranes, is another problematic failure mode in thin films. In response to the poor adhesion of noble metals (gold and platinum) on oxide and polymeric substrates, it is common to utilize thin films of adhesion promoters, such as chromium or titanium, or carry out processing treatments that alter surface chemistry such as plasma etching. This presentation will focus on a variety of thin film and nanostructured materials systems in use or development at WSU for MEMS-based power generation and sensing applications, including piezoelectric thin films and carbon nanotubes for switching applications. Experimental methods to evaluate the elastic, plastic, and fracture performance of these small structures will be described, including bulge testing, nanoindentation, and four point bend testing. These testing methods have led to the development of MEMS structures designed to operate efficiently when stretching as membranes, rather then bending as flexing elements. However, at these high imposed strains structural integrity becomes even more critical in these materials. The effects of near surface chemistry changes, film morphology, grain sizes and underlying substrate compliance on the mechanical response of these materials will be presented. Interfacial toughness will be shown to increase by a factor of five with the addition of adhesion promotion layers. Finally, the behavior of carbon nanotubes used for switching applications in MEMS will be introduced, and the unique deformation structure of these materials in compression will be described. Back to top
Dr. Sean McDeavitt
Department of Nuclear Engineering, Faculty of Materials Science and Engineering Texas A&M University	Time: 4:00 p.m. Date: 10/30/09
Powder Metallurgy of Uranium Alloy Fuels for Advanced Nuclear Energy Systems	Time: 4:00 p.m. Date: 10/30/09
Fast reactors are being evaluated to enable the transmutation of transuranic (TRU) isotopes generated by nuclear energy systems. TRU isotopes have high radiotoxicity and relatively long half-lives, making them unattractive for disposal in a long-term geologic repository. Fast reactors are able to utilize transuranic elements as fuel, thereby destroying them while releasing their valuable residual energy content. An enabling technology is the fabrication metallic fuel containing TRU isotopes using powder metallurgy methods. The performance of U-10 wt. zirconium (Zr) and other uranium (U) alloy fuels was demonstrated at the Experimental Breeder Reactor-II between 1964 and 1994. This fuel was fabricated by injection casting rods from a molten pool of U-Zr alloy. Even though this method is proven and effective, it was accompanied by high material losses due to chemical interactions with quartz casting molds. For the newer TRU-bearing fuel designs, direct melt casting is impractical since americium and, to a lesser extent, neptunium have especially high vapor pressures and cannot be contained in a molten alloy pool at 1,200 to 1,500°C. The research described in this seminar is developing powder metallurgical fabrication technologies to produce U-Zr-TRU alloys at relatively low processing temperatures (500ºC to 600ºC) using a combination of hot extrusion and/or “alpha-phase” sintering. The fundamental aspects of both processing methods will be quantified. Surrogate metals are used to simulate the TRU elements. For example, magnesium is used since it melts at a similar temperature to plutonium and it’s vapor pressure properties are comparable to americium. If successful, this process will produce novel solutions to some of the nagging issues related to metallic fuels such as fuel-cladding chemical interactions, and fuel swelling, volatility losses during casting, and casting mold material losses. Two candidate processing pathways are being investigated: (1) hot extrusion between 500°C and 650°C, and (2) sintering of alpha uranium with liquid phase enhancements at ~650°C. Back to top
Dr. Xiaoqing Pan
Department of Materials Science and Engineering Program The University of Michigan	Time: 4:00 p.m.. Date: 11/06/09 Place: 256 JEB Host: Dr. Haiyan Wang
Effect of Interfacial Structure and Strain on the Properties of Multiferroic BiFeO₃ Thin Films
BiFeO₃ has attracted great interest owing to their room temperature multiferroic nature with potential applications in spintronic devices and memories. The characterization and control of domain structures are critical issues for the fabrication of epitaxial BiFeO₃ thin films desirable for devices. It has been shown that the ferroelectric domain structure of BiFeO3 films is strongly influenced by strain and the atomic structure of the substrate surface. In this talk I will present the effects of electrical and mechanicals boundary conditions on the domain structure and ferroelectric properties ial BiFeO3 thin filmsof epitax grown on different substrates including SrTiO₃ (cubic), TbScO₃(orthorhombic), and Si single crystal substrates. Both high-resolution x-ray diffraction reciprocal space mapping (RSM) and atomic resolution transmission electron microscopy (TEM) reveal that the domain configurations and domain wall structures strongly depend on film/substrate misfit, substrate surface structure and symmetry, and electrical charges at interfaces. It will be shown that epitaxial BiFeO₃ thin films with desirable domain patterns can be fabricated with controlled electrical and mechanical boundary conditions. The experimental results are compared with phase-field simulations. Back to top
TBA
TBA Back to top
Dr. Peter Trefonas
Dow Electronics Materials, Marlborough, Massachusettes	Time: 4:00 p.m. Date: 11/18/09 Place: TBA Host: Dr. Jaime Grunlan
Chemistry and Dissolution Behavior of 193-nm Immersion Photoresist
A brief history of photomicrolithography, and the development of 193-nm sensitive photoresists which are capable of sub-40 nm resolution. He will then discuss the concepts for incorporating chemically amplified photospeed, improving dissolution contrast, and designing in the ability to resolve features as small as 20% of the image wavelength. The discussion will then move into the new area of double-pattern photolithography, which enables the ability to print images on top of each other to allow for frequency multiplication and print even smaller regular patterns. Back to top
Dr. Rui Huang
The University of Texas at Austin Aerospace Engineering and Engineering Mechanics	Time: 4:00–5:00 p.m. Date: 11/19/09 Place: 256 JEB Faculty host: Dr. Xinghang Zhang
Nonlinear mechanics of monolayer graphene
The unique two-dimensional lattice structure of graphene offers a rich spectrum of physical properties and potential applications. By combining continuum and atomistic approaches, we develop a theoretical framework that describes the nonlinear mechanical properties of monolayer graphene sheets under both in-plane and bending conditions. This talk will present two parts of our work on graphene. For the first part, the nonlinear elastic properties and the fracture strength of graphene nanoribbons are predicted theoretically by atomistic simulations based on a reactive empirical bond-order potential. It is found that the free edges (zigzag or armchair) have a profound effect on the deformation and mechanical properties of graphene nanoribbons. Under an infinitesimal strain, the edge force is nearly constant and compressive for both zigzag and armchair edges. Under a large strain, the uniaxial stress-strain behavior for a graphene nanoribbon becomes highly nonlinear and anisotropic. A failure criterion is proposed for brittle fracture of the graphene at low temperatures, taking into account the strain-dependent edge forces. For the second part, we consider graphene monolayer supported on an oxide substrate. The typically nanoscale surface roughness of the substrate and process-induced mismatch strain can cause morphological corrugation of the supported graphene, which in turn impacts the electric and thermal transport properties. We theoretically analyze the stability of a graphene monolayer on an oxide substrate, subject to van der Waals interactions and mismatch strains. A transition from conformal to non-conformal morphology is predicted, and the effect of surface roughness on the interfacial adhesion energy is analyzed. With these theoretical results, we suggest possible means to control the morphology of graphene monolayer on oxide substrates by surface patterning and strain engineering. Back to top
Dr. Paula Alonso
Unidad de Actividad Materiales, Centro Atómico Constituyentes, Departo Materiales, Buenos Airoes, Argentina	Time: 4:00–5:00 p.m. Date: 11/24/09 Place: 256 JEB host: Dr. Perla Balbuena
Applications of computational thermodynamics to metallic alloys
During the last decades first-principles calculations have become a common tool in materials science for predicting systems behavior and for designing alloys composition and structure according to desired properties. Experimental work has now a profiting collaboration with computational techniques based either on fully theoretical ab-initio methods or on semiempirical methods. I will summarize in this talk our efforts that involve mostly computational work but also experimental measurements. The first examples use first principles calculated total energies in a cluster expansion method for the thermodynamic functions: The role of bonding energy between atoms in the decomposition of the metastable BCC γ(U,Mo) phase and the solubility of third elements in U-Mo alloy. Ordering and phase separation in the ternary BCC alloy Ti-Al-Mo around the compositionTi₅₀Al₂₅Mo₂₅ Hardening by coherent precipitation in iron rich Fe-Al-X (X=Ti,V,Nb). Finally, I will discuss a diffusional phase transformation problem that was studied through semiempirical methods to establish phase equilibria and to simulate phase growth: li>UAl₄ intermetallic compound as an undesired phase in the interphase surrounding U-Mo alloy dispersed fuel in aluminum matrix Back to top
Dr. Daisuke Hojo
Advanced Institute for Materials Research, Tohoku University	Time: 11:30–12:20 p.m. Date: 12/04/09 Place: 102 MIST Host: Dr. Winfried Teizer
Fabrication of the Cerium Oxide Nanocrystal Film with Heterogeneous Ligand Structures
The assembling of a highly crystalline metal oxide nanoparticle layer at room temperature has attracted considerable attention. Generally, high crystalline metal oxide films are only obtained through high temperature treatments. If the high crystalline metal oxide nanoparticles are formed elsewhere in advance at high temperature and can be aligned densely on the surface at room temperature, high crystalline film layer can be fabricated even on a heat-sensitive substrate by this method. For this study, the hybrid ceria nanocrystals modified with decanoic acid were covalently adsorbed to the pretreated Si surface to self-assemble mono-layered nanocrystal system. The monolayer of 3-aminopropyltriethoxysilane molecules was formed on the hydroxylated Si surfaces to produce an NH2 terminated surface. 3, 4-dihydroxyhydrocinamic acid (DHCA) was then condensed with NH2 group. On the other hand, DHCA is prone to be exchanged with decanoic acid on the surface of the modified nanocrystals because of equilibriums as found in Fourier transform infrared spectroscopy. Therefore, the bottom surface of the adsorbed nanocrystals is locally modified with DHCA in exchange of decanoic acid and chemical bonds are established between nanocrystals and the substrate. To evaluate these nanostructures dispersed two dimensionally on the surface, scanning electron microscopy (SEM) and spectroscopic ellipsometry (SE) were used. After rinsed with cyclohexane, only mono-layered nanoparticles were left on the surface washed away all of physically adsorbed nanocrystals on the nanocrystals chemically attached to the surface. Two-dimensional structures of the nanocrystals were regarded as a continuous thin film from SE; the defects, with a size of ~10 nm, were sufficiently smaller than the wavelength of probe light. The thickness of layered nanocrystals was evaluated to be ~ 10.6 nm from SE; this value is almost the same as the size of nanocrystals. The refractive index of this film was 1.73 at a wavelength of 633 nm. Comparing to the refractive index of cerium oxide thin films obtained by other techniques such as electron beam evaporation at room temperature, this value was found to be sufficiently high. Since the coverage of nanocrystals was estimated to be ~80% from the SEM image, if the surface was completely covered, the refractive index could increase up to ~1.9 theoretically. The fabrication of two-dimensionally aligned nanoparticle systems will be a key technology for layer-by-layer assembly or precisely controlled colloidal superlattices. Back to top