Bulletin of the American Physical Society
2008 Joint Fall Meeting of the Texas and Four Corners Sections of APS, AAPT, and Zones 13 and 16 of SPS, and the Societies of Hispanic & Black Physicists
Volume 53, Number 11
Friday–Saturday, October 17–18, 2008; El Paso, Texas
Session B2: Condensed Matter: Thin Films |
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Chair: C.A. Quarles, Texas Christian University Room: Union East, 3rd Floor Ray |
Friday, October 17, 2008 10:30AM - 10:54AM |
B2.00001: Bilayer manganites: a playground for magnetoresistance, charge density waves and spin reorientation transitions Invited Speaker: Manganites are perovskite structures that were rediscovered in 1994 with the report of a thousand-fold change in resistance upon the application of a magnetic field. This ``colossal magnetoresistance'' is due to a transition between a paramagnetic insulator phase and a ferromagnetic metallic phase. The complex phase diagram of these pseudocubic compounds results in a plethora of interesting phenomena that have been studied intensively for the last 14 years. A newer class of manganites has a bilayer structure that exhibits more complicated ferromagnetic ground states as a function of the hole doping x, because of the two dimensionality of the system. For example, in single crystals of La$_{2-2x}$Sr$_{1+2x}$Mn$_{2}$O$_{7}$ the spins can arrange themselves ferromagnetically or antiferromagnetically, and with easy axes parallel of perpendicular to the bilayer, as the doping x ranges from 0.30 to 0.50. For x=0.32 this transition occurs as a function of temperature as we have observed directly with magnetic force microscopy. We have also observed a charge density wave in this compound using scanning tunneling microscopy. [Preview Abstract] |
Friday, October 17, 2008 10:54AM - 11:06AM |
B2.00002: Interfacial Barrier Height by Internal Photoemission for Metal/Oxide/Semiconductor Structure Kunal Bhatnagar, Nhan Nguyen Internal Photoemission (IPE) is a powerful technique for investigating electronic properties at solid-solid interfaces and determining band offsets and alignments in MOS (Metal Oxide Semiconductor) structures. In the following research, new metal gate electrodes for MOS structures are investigated - a combinatorial Ni-Ti-Pt ternary thin film library on SiO2 and Si substrate. The zero-field barrier height is determined at the metal and oxide interface for Ni, Pt, Ti, and a compositional mixture of all the three metals using IPE characteristics. The barrier heights are then used to calculate the work function of the different metals to compare to the value obtained using C-V measurements. Interface barrier height at the metal-insulator interface is an important value, as it helps us better understand the structure and functioning of advanced CMOS devices which are a major component of today's computer chips and integrated circuits. [Preview Abstract] |
Friday, October 17, 2008 11:06AM - 11:18AM |
B2.00003: Field dependency of return point memory in exchange bias films Brian Wilcken, Karine Chesnel, Eric Fullerton, Steve Kevan A better understanding of the domain morphology of magnetic thin films is necessary to improvements in the realm of perpendicular magnetic recording technology in computer hard disk drives. The technique of Coherent X-Ray Resonant Magnetic Scattering (XRMS) was used in order to probe the magnetic domain morphologies in CoPt/ IrMn exchange bias thin films. When illuminated by coherent light, the material produces specific speckles patterns, that contain information about the local domain configuration. A cross-correlation approach is used in order to detect statistical variations on domain configuration. A Matlab program was developed for the purpose of analyzing XRMS speckle patterns. A custom built cross-correlation routine handled the comparison between speckle patterns at different levels of magnetization. A comparison between coefficients of correlation and degree of coherence was analyzed for different levels of sample magnetization and at different temperatures. Preliminary results indicate that, at low temperature, the sample shows significant magnetic memory characteristics, when an external magnetic field is applied. In particular, the system exhibits a strong return point memory (RPM), after a complete magnetization cycle. The dependency of this RPM as a function of field will be shown. [Preview Abstract] |
Friday, October 17, 2008 11:18AM - 11:30AM |
B2.00004: From exchange bias to magnetic memory Karine Chesnel, Steve Kevan, Eric Fullerton, Jeff Kortright, Olav Hellwig, Brian Wilcken, Joe Nelson Magnetic memory, the ability of a material to remember its magnetic domains spatial configuration throughout magnetization cycling, is a key feature in ferromagnetic materials and offers potential technological interest for the data storage industry. One way to quantify the magnetic memory is to use Coherent X-ray Resonant Magnetic Scattering (XRMS) tools, at synchrotron facilities. The light is tuned to the resonant edge of the magnetic element to optimize the magneto-optical contrast. When illuminated by the coherent beam the sample produces speckle patterns that are collected on two dimensional detectors. Our approach is to cross-correlate patterns recorded at different field values throughout the magnetization cycle, and at different temperatures. We are particularly interested in the return point memory (RPM) and the conjugate point memory (CPM) that characterize the memory after a full, or half cycle respectively. We will give here an overview of different type of memory behaviors, first showing disorder induced memory in thin CoPt films and the influence of the film roughness, then demonstrating the ability to control the magnetic memory by inducing exchange bias. We will see how the local exchange couplings pin the magnetic domain in the ferromagnetic layer and lead the large memory enhancement. [Preview Abstract] |
Friday, October 17, 2008 11:30AM - 11:42AM |
B2.00005: Low Temperature Bonding of Si to Silicates using Langmuir-Blodgett molecular films as precursors for a bonding SilOxSi interphase Murdock Hart, Shawn Whaley, James Bradley, David Sell, Nicole Herbots, Robert Culbertson, Vasudeva Atluri Low temperature (25\r{ }C-200\r{ }C) bonding between Si(100) and oxide wafers, either made of Silica or oxidized Si (100) is achieved through a dual wet chemical process which terminates the stabilized ordered (1x1) Si$<$100$>$wafer surface in air at room temperature with 2-D Langmuir-Blodgett film consisting of ordered arrays of O-H silanol group. The parallel wet chemical processing of the oxide surfaces renders the SiO2 subsotichiometric in oxygen and therefore hydrophilic surface polarization. When put into contact the Si and oxide surfaces are attracted to one another and consequently form a bond at room temperature. Cross-Bonding via chemical oxidation of the surfaces in contact requires the two surfaces to be brought within nano-meter separation distances to allow cross-bridging during reoxidation of both surfaces and the formation of a new interphase between the two. The application of uniform mechanical compression to overcome the Coulomb force and decrease large-scale surface geometry warping in the wafer is critical. A 24 hour 180\r{ }C anneal in controlled ambient air is used to activate the silanol molecular film on the (1x1)Si(100) surface and the oxidation process by which molecular bonds between the (1x1)Si(100) and SiO2 wafers are created. [Preview Abstract] |
Friday, October 17, 2008 11:42AM - 11:54AM |
B2.00006: Use of a non-contact synthesis method in selective area porous silicon thin film formation Daniel Taylor, Toni Sauncy Porous silicon (p-Si) is a unique form crystalline silicon (c-Si), composed of a matrix of thin-walled c-Si surrounding numerous voids. Interest in the study of this structure was initially spurred by the observation of visible luminescence the well-known indirect band gap material. For pore formation, we utilized stain etching, a non-contact method of synthesizing p-Si. A 20-mW He-Ne (632.8nm) laser is used to produce a local electric field on the c-Si surface while the sample is immersed in hydrofluoric acid; this laser generated field is in lieu of the traditional applied voltage used in the standard contact technique. Our objective with this study was to investigate the efficacy of beam manipulation to produce selective patterned regions of p-Si thin film on the crystalline surface. Variation in patterning techniques, processing time and dopant type, along with optical and electrical characterization of the processed samples will be discussed. [Preview Abstract] |
Friday, October 17, 2008 11:54AM - 12:06PM |
B2.00007: Doped mesoporous silica thin films for chemical vapor detection John Como, Jacob Ajimo, Louisa Hope-Weeks, Juyang Huang, Kwan Cheng Highly luminescent lanthanide-ligand complex (LLC) doped mesoporous silica thins films were fabricated for the use in trace chemical vapor detection. Different silicate precursors were made using the sol-gel process and spin-coated onto a substrate. Under UV excitation, the sensitizing ligands exhibited efficient energy transfer to the lanthanide to produce a detectable luminescence in the visible spectrum. Fluorescence quenching of the LCC by direct exposure of the films to fluorophosphate vapor was observed. Sensitivity to the chemical vapor was evaluated as a function of the sol-gel pore size, surface roughness, and thickness. [Preview Abstract] |
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