Bulletin of the American Physical Society
2008 Spring Meeting of the Ohio-Region Section of APS
Volume 53, Number 3
Friday–Saturday, March 28–29, 2008; Youngstown, Ohio
Session C2: Condensed Matter/Nanomaterials |
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Chair: Tom Oder, Youngstown State University Room: Moser Hall 2006 |
Saturday, March 29, 2008 8:24AM - 8:36AM |
C2.00001: Scanning Tunneling Microscopy and Spectroscopy on Cu(111) David Gohlke Scanning tunneling microscopy allows us to examine the surface of a material on an atomic scale. Our setup allows us to take detailed atomic-resolution images of the sample, perform tunneling spectroscopy of electronic and magnetic structure, and manipulate single adatoms to build nanostructures with atomic precision. From these nanostructures, we can study cluster physics, seeing how electronic spectroscopy evolves as atoms are added. Our group is also involved in research in Tip-Enhanced Raman Spectroscopy and Spin-Polarized STM, and optical scanning tunneling microscopy. This presentation will examine current work being done by the group as well as preliminary studies of Au on a Cu(111) surface. [Preview Abstract] |
Saturday, March 29, 2008 8:36AM - 8:48AM |
C2.00002: Effects of Temperature, Time, and Solution on Nanoparticle Agglomeration Michael Moulton, Kyung Yu, Laura Braydich-Stolle, John Schlager, Amanda Schrand, Saber Hussain Previous studies from our laboratory have shown that the environment nanomaterials are in can alter nanoproperties. Therefore, prior to nanotoxicity studies, we need to address how different solvents and temperatures can impact nanoparticle behavior. This study examines the effect of increased temperature and time on nanoparticle agglomeration. The nanoparticles used in this study were: SiO2 35nm, 51nm, 110nm, and 420nm, Cu 40nm, 60nm, and 80nm, and Ag 25nm, 55nm, and 80nm. TEM analysis showed that the primary size distributions for the SiO2 nanoparticles were similar to the manufacturer's size. For the Cu nanoparticles, the ranges were Cu 40nm 70.3+/-17.8, Cu 60nm 79.7+/-21.3, and Cu 80nm 110.6+/-26.6. For the Ag nanoparticles the only particle not similar to the manufacturer's range was Ag 80nm with a size of 122.32+/-60.366. The nanoparticles were dispersed in sterile water or exposure media (EM) (media without serum) and stored at 4C or 37C. Using dynamic light scattering, agglomeration was measured at 0, 8, 14, 22, 32, and 48 h to determine if the magnitude of agglomeration was temperature or time dependent. Based on this data, time in solution and temperature appears to impact nanoparticle agglomeration in no predictable or reproducible pattern which should be taken into account in nanotoxicity studies. [Preview Abstract] |
Saturday, March 29, 2008 8:48AM - 9:00AM |
C2.00003: Determining Graphene Sheet Shape in Presolar Graphite Spherules Eric Mandell Presolar graphite spherules are a subset of graphitic stardust exhibiting an intriguing micron-sized nanocrystalline core that is surrounded by concentric graphitic layers, similar to those of a carbon onion. These grains are presolar as indicated by isotopic measurements being significantly different from solar values (i.e. C$^{12}$/C$^{13 }<$ solar = 89). The $r$ and $s$ type nuclear processes required to explain these isotopic ratios suggest grain-forming regions of red giant (AGB) atmospheres as a likely point of origin for these particles. Electron diffraction data has indicated the cores are comprised primarily of unlayered graphene sheets, approximately 2-4[nm] in breadth. Previous diffraction analyses on these grains have focused on examining the differences between the experimental data and a flat, hexagonal graphene diffraction model. Here, improvements in fitting experimental diffraction profiles are realized when altering the shape of the graphene sheet. In addition, curvature of atom-thick sheets or regular relationships between neighboring sheets can introduce coherence effects which manifest in diffraction. Analysis of both diffraction and HRTEM images, and comparisons to simulations, indicates these structural relationships may be present in the core material. [Preview Abstract] |
Saturday, March 29, 2008 9:00AM - 9:12AM |
C2.00004: The Electrical and Physical Properties of Ni and ZrB$_{2}$ Schottky Contacts of n-type 4H-SiC Tom Oder, Ta-Lun Sung, Rani Kummari, Mark Del Fraino We report the electrical and physical properties of Ni and ZrB$_{2}$ Schottky contacts deposited on n-type 4H-SiC. Current-voltage (I-V) and capacitance-voltage (C-V) measurements were used to determine the electrical properties of the Schottky barrier diodes formed. The energy barrier of the diodes formed with the Ni Schottky contacts increased from 1.48 eV for non-annealed contacts to a maximum value of 1.81 eV after a 24 hour annealing in vacuum at 500 $^{o}$C. The physical analysis of this contact determined by the Rutherford backscattering spectroscopy (RBS) revealed a significant formation of nickel silicide. A remarkable improvement of the ZrB$_{2}$/SiC Schottky contact was achieved when the ZrB$_{2}$ contact was deposited on SiC substrates held at temperatures above 400 $^{o}$C. The energy barrier increased with the deposition temperature from an average value of 0.87 eV for contacts deposited at 20 $^{o}$C to 1.07 eV for those deposited at 600 $^{o}$C. The RBS spectra revealed a systematic decrease of oxygen with increase in the deposition temperature, which we believe is a result of oxygen escaping from the interface. [Preview Abstract] |
Saturday, March 29, 2008 9:12AM - 9:24AM |
C2.00005: Performing Many Simultaneous Measurements---Combinatorial Hall and Resistivity Studies on Oxide Films Jeffrey Clayhold, Oshri Pelleg, Anthony Bollinger, Gennady Logvenov, Ivan Bozovic Recent reports of sharp changes of transport properties with small variations of stoichiometry in cuprate superconductors have motivated us to look for similar behavior in optimally- and over-doped La$_{\rm 2-x}$Sr$_{\rm x}$CuO$_{\rm 4+\delta}$, using a recently completed system for creating and measuring samples with ultrafine stoichiometry resolution. The system can measure 31 different Hall effect signals simultaneously as well as 30 different resistance signals. The data are from MBE films grown with a linear stoichiometry gradient. We will show new data for $x$ ranging from 0.15 to 0.30 which show systematic gradations in physical properties such as carrier density, resistance, and the superconducting transition temperature. [Preview Abstract] |
Saturday, March 29, 2008 9:24AM - 9:36AM |
C2.00006: Ensemble Approach to Vicinal Crystal Surfaces Howard L. Richards, Ryan P. Jacob Recent studies of the Step Position Distribution (SPD) have made it clear that there exists a characteristic length $L_W$ (along the $y$-axis, parallel to the average step direction) at which the variance of the SPD is correctly predicted by the Pairwise Einstein Model. We extend this to the case when neighboring steps have different stiffnesses, in particular to the limiting case in which one set of steps has infinite stiffness. A similar characteristic length along $y$ must be introduced to calculate average properties from an ensemble of Gruber-Mullins models, subject to the constraint that the variance of the Terrace Width Distribution (TWD) is as given by the Pairwise Einstein Model. We discuss the relationship between these length scales for a range of step interactions, using TWDs calculated for the restricted terrace-step-kink model using numerical transfer matrix techniques. [Preview Abstract] |
Saturday, March 29, 2008 9:36AM - 9:48AM |
C2.00007: Structural Physics of Bee Honeycomb Forrest Kaatz, Adhemar Bultheel, Takeshi Egami Honeybee combs have aroused interest in the ability of honeybees to form regular hexagonal geometric constructs since ancient times. Here we use a real space technique based on the pair distribution function (PDF) and radial distribution function (RDF), and a reciprocal space method utilizing the Debye-Waller Factor (DWF) to quantify the order for a range of honeycombs made by \textit{Apis mellifera}. The PDFs and RDFs are fit with a series of Gaussian curves. We characterize the order in the honeycomb using a real space order parameter, OP$_{3}$, to describe the order in the combs and a two-dimensional Fourier transform from which a Debye-Waller order parameter, \textbf{\textit{u}}, is derived. Both OP$_{3}$ and \textbf{\textit{u}} take values from [0, 1] where the value one represents perfect order. The analyzed combs have values of OP$_{3}$ from 0.33 to 0.60 and values of \textbf{\textit{u}} from 0.83 to 0.98. RDF fits of honeycomb histograms show that naturally made comb can be crystalline in a 2D ordered structural sense, yet is more `liquid-like' than cells made on `foundation' wax. We show that with the assistance of man-made foundation wax, honeybees can manufacture highly ordered arrays of hexagonal cells. [Preview Abstract] |
Saturday, March 29, 2008 9:48AM - 10:00AM |
C2.00008: Low-Energy Electron Diffraction investigation of the clean, stepped Cu(511) surface Christopher Lemon, Mellita Caragiu, Renee Diehl, Kelly Hanna, Hsin Li, Rundong Wan Results of a Low-Energy Electron Diffraction (LEED) investigation of the clean, stepped Cu(511) surface are reported for two different sets of experimental data. The results show a good match between experimental and theoretical beams for one experimental set, but not so good in the case of the second set, in which case the results presented are only preliminary. The origin of the disparity is attributed to the angle of incidence of the electron beam probing the Cu(511) surface. Ideally, the electron beam would hit the surface under normal incidence, a situation hard to control due to the existence of only one symmetry plane of the real structure, which, in turn, gets translated into only one symmetry plane in the reciprocal space. The uncertainty in the angle of incidence together with computational problems arose by the very small interlayer spacing of the stepped sample [K. Pussi, M. Caragiu, M. Lindroos, R.D. Diehl, Surf. Sci. 544 (2003), 35], make the investigation of this particular surface challenging. [Preview Abstract] |
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