Bulletin of the American Physical Society
10th Annual Meeting of the Northwest Section of APS
Volume 53, Number 6
Thursday–Saturday, May 15–17, 2008; Portland, Oregon
Session B3: Condensed Matter Physics I |
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Chair: You Qiang, University of Idaho Room: Olin 301 |
Friday, May 16, 2008 2:00PM - 2:36PM |
B3.00001: Characterization and Properties of Nanoparticles Invited Speaker: Nanoparticles and other nanostructured materials are increasingly subject to a wide variety of studies. Although it is often ignored, in many circumstances the character and properties of nano-structured materials vary as a function of time, are altered by coatings and are environmentally dependent. This talk will outline some of the general issues related to characterization of nanoparticles and show measurements of the time and environmentally dependent behaviors of iron metal-core oxide-shell and ceria nanoparticles. Iron nanoparticles are of interest for several reasons including their potential use for medical applications and reduction of environmental contaminants such as chlorinated hydrocarbons or chromates. A study of the changes that occur when iron nanoparticles are exposed to water and the impact of the changes on particle reactivity and reaction pathway will be discussed. For this work, XPS, TEM, BET and XRD have been used to obtain information about the changes that take place in the particles as a function of time. Because of an ability to store and release oxygen, ceria is important for catalytic, fuel cell and possibly health applications. Other researchers have shown that as CeO$_{2}$ particles decrease in size, the Ce valence state changes from a Ce$^{+4}$ to a Ce$^{+3}$. We have found that this transformation is environmentally dependent. Five nm particles can change from +4 to +3 and back to +4, as the environment is altered from oxidizing to reducing conditions and back. These changes can be observed in solution using optical adsorption and may have impacted measurements intended to examine band-gap changes due to particle size. XPS measurements of particles fully corroborate the real time solution measurements. These time and environmentally dependent measurements create important sample and characterization handling challenges. [Preview Abstract] |
Friday, May 16, 2008 2:36PM - 3:12PM |
B3.00002: Structural Fingerprinting of Nanocrystals in the Transmission Electron Microscope Invited Speaker: Two novel strategies for the structurally identification of nanocrystals [1] from either a high resolution (HR) transmission electron microscopy (TEM) image or a precession electron diffractogram (PED) [2] are described (and demonstrated on a mixture of nanocrystalline maghemite and magnetite [3]). The structural information that can be extracted from a HRTEM image is the projected reciprocal lattice geometry, the plane symmetry group, a few structure factor amplitudes and phases. Except for the structure factor phases, the same kind of information can be extracted from a PED, but the information that can be used for structural fingerprinting is in this case not limited to the resolution of the TEM. Searching for this kind of information in (open access) databases (e.g. [4]) and matching it with high figures of merit to that of candidate structures allows for highly discriminatory identifications of nanocrystals. \newline \newline [1] P. Moeck, P. Fraundorf, Z. f\"{u}r Kristallogr. 222 (2007) 634-645; open-access issue at http://www.atypon-link.com/OLD/doi/pdf/10.1524/zkri.2007.222.11.634; expanded version at arXiv:0706.2021 \newline [2] http://www.nanomegas.com \newline [3] P. Moeck, arXiv:0804.0063 \newline [4] http://nanocrystallography.research.pdx.edu/CIF-searchable [Preview Abstract] |
Friday, May 16, 2008 3:12PM - 3:24PM |
B3.00003: HRTEM of Quantum Dot Nanostructures: The First 15 Years S. Rouvimov, N.N. Ledentsov, P. Moeck, V.A. Shchukin, D. Bimberg The paper reviews the progress in growth and high resolution transmission electron microscopy (HRTEM) characterization of quantum dot (QD) nanostructures for the last 15 years. Understanding of structural properties of QDs resulted in realization of high-performance quantum dot lasers, amplifiers and single photon devices with precisely engineered properties (polarization, fine structure splitting, defect reduction and defect engineering). Furthermore, advanced QD growth including activated phase separation, submonolayer deposition, and combination of the approaches enabled nanostructures with a high density and uniformity of QDs leading to fabrication of vertical cavity surface emitting QD lasers with 20Gb/s operation in a temperature range 25-85$^{\circ}$ C \textit{without current or modulation voltage adjustment}. The paper addresses current developments and challenges of HREM in application to nanostructures of low dimensionality including electron crystallography (``structural fingerprinting''). [Preview Abstract] |
Friday, May 16, 2008 3:24PM - 3:36PM |
B3.00004: Epitaxial BaCuSeF thin films: a new blue LED candidate? Andriy Zakutayev, Robert Kykyneshi, David McIntyre, Heather Platt, Douglas Keszler, Janet Tate BaCuSeF is a wide-gap p-type semiconductor. It belongs to a broader family of layered chalcogenide-fluorides [doi:10.1016/j.tsf.2007.10.073]. This family is isostructural to layered chalcogenide-oxides [doi:10.1016/j.tsf.2005.08.268]. Thin films of BaCuSeF were deposited on MgO substrates using pulsed laser deposition (PLD). BaCuSeF grows epitaxially on MgO, as proven by x-ray diffraction analysis. Resulting thin films have a hole concentration of 10$^{18}$cm$^{-3}$ and mobility of 1.5 cm$^{2}$/Vs, both relatively large for this class of materials. They also exhibit narrow excitonic absorption and emission peaks near 400nm at room temperature. This indicates that the concentration of defects and dislocations in samples is low. These features make epitaxial BaCuSeF films promising candidates for applications in blue light-emitting diodes (LEDs). [Preview Abstract] |
Friday, May 16, 2008 3:36PM - 3:50PM |
B3.00005: BREAK
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Friday, May 16, 2008 3:50PM - 4:26PM |
B3.00006: Enhanced tunneling magnetroresistance and high spin polarization in polystyrene coated Fe$_{3}$O$_{4 }$granular system Invited Speaker: Polystyrene coated Fe$_{3}$O$_{4}$ nanoparticles through surface engineering exhibit intergranular tunneling magnetoresistance (MR) ratio of 22.8{\%} at room temperature and a maximum MR of 40.9{\%} at 110 K. The drastic enhancement of the MR ratio clearly suggests that there is high degree of spin polarization even at room temperature for half metallic Fe$_{3}$O$_{4}$. The derived spin polarization $P$ is about 54{\%} and 83{\%} at room temperature and 110 K, respectively. It is possible that a simple tunnel junction made of Fe$_{3}$O$_{4 }$exhibits large MR in a relatively small field. Fe$_{3}$O$_{4}$ may also be used as an effective spin injector. Knowing that our results provided only a lower limit on the spin polarization of Fe$_{3}$O$_{4,}$ it has the potential to play an important role in spintronic devices. [Preview Abstract] |
Friday, May 16, 2008 4:26PM - 4:38PM |
B3.00007: Electrochemically Prepared Fe/GaAs (110) Sarmita Majumder, Anthony Arrott, Karen Kavanagh Iron has been deposited electrochemically on oriented, n-type GaAs (110) bulk substrates (2x10$^{17}$ Si) at various temperatures in aqueous electrolytes. The film structure, growth kinetics, and residual strain have been investigated via high-resolution x-ray diffraction, and the magnetic properties via SQUID and FMR measurements. The resulting films grow epitaxially with a small tensile strain of 5x10$^{-4}$ {\%} although the lattice mismatch (+1.4{\%}, $a $Fe $> \quad a$ (GaAs)) would predict a compressive strain in the Fe. The preparation of the GaAs surface using ammonium hydroxide, and an initial pulsed constant current power source during deposition, are critical to this result. The thickness versus square root time shows the expected diffusion-limited growth kinetics with an average growth rate of 100-200 nm/minute. The magnetization curves indicate that the film is composed of a single crystalline material with inhomogeneities aligned with the substrate. There is a superimposed uniaxial, anisotropy confirmed by the angular dependence of the FMR resonance field. [Preview Abstract] |
Friday, May 16, 2008 4:38PM - 4:50PM |
B3.00008: Microstructures of Bi-alloy Metal Films by Dealloying W.J. Yeh, Shilpa Chava, Julia Tilles The objective of this study is to synthesize and characterize different microstructures that are fabricated by dealloying from bi-alloys. With selected chemical etching one element with high etching rate is dissolved and the remaining component may form porous structures. This process is also called as dealloying. The experiments were conducted on three different materials. 6 carat white gold (Au/Ag alloy, 1:3 ratio by weight) leafs that were purchased commercially were etched with 70{\%} HNO$_{3}$ to remove silver. The remaining gold materials congregated to form well connected network structure that was free standing. This Au nanoporous samples had void sizes from a few nanometers to a few hundred nanometers. The second material we studied was the 50/50 solder wire (Pb/Sn alloy). The solder wire was pressed to a thin sheet. The Pb/Sn sheet was etched with 93{\%} H$_{2}$SO$_{4}$. After Sn was dissolved Pb porous structure was formed. In this porous structure, Pb formed crystal-like nanostructures. The third one was Imitation Italian gold leaf (Cu/Zn alloy, 82/18 by wt. {\%}). The leaf was immersed into NaOH solution. By etching out Zn, a free-standing nanoporous Cu film has been formed. [Preview Abstract] |
Friday, May 16, 2008 4:50PM - 5:02PM |
B3.00009: Giant positive magnetoresistance in Co-doped ZnO nanocluster films You Qiang, Yufeng Tian, Shishen Yan, Ryan Souza We studied magnetoresistance of 0.5{\%}, 12{\%} and 30{\%} Co-doped ZnO nanocluster films which are deposited on Si wafer. Microstructure analysis is performed by XPS, TEM and XRD, and shows a uniform mean size of 20 nm with perfect wurtzite ZnO structure. MR increases with Co doping concentration-0.5{\%} with 469{\%} while the other two samples have 744{\%} and 811{\%}. The large magnetoresistance is explained by suppression of spin-dependent hopping paths when localized states with onsite correlation undergo a relatively large Zeeman splitting in a magnetic field due to strong s,p-d interactions. [Preview Abstract] |
Friday, May 16, 2008 5:02PM - 5:14PM |
B3.00010: Photoluminescence and ferromagnetism in nitrogen doped ZnO nanoclusters Yufeng Tian, Ryan Souza, Alan Mcconnaughey, Amit Sharma, Shishen Yan, You Qiang Wide-band-gap semiconductor ZnO has been extensively studied for its potential applications in optoelectronic and spintronics. Nitrogen is supposed to be the most promising p-type dopant. We synthesized nitrogen doped ZnO nanoclusters using a third generation sputtering-gas-aggregation cluster source. High-resolution TEM images show nanoclusters sizes are around 12 nm. XRD patterns are identical to bulk ZnO wurtzite structure with the existence of Zn as a minor phase. PL measurements reveal both ultraviolet and green emission which is respectively attributed to recombination of free excitons and deep defect level emissions from intrinsic defects. Unexpected room temperature ferromagnetism is obtained without any magnetic doping elements. It is believed when the doping nitrogen atom is beside zinc atom, one electron in the completely filled d-orbits of Zn possibly jumps to compensate the dangling bond of nitrogen in order to reduce energy. Net spin is established in the left d-orbits of zinc and long range ferromagnetism can be established as described by a bound magnetic polaron model. *supported by DOE-BES (DE-FG02-07ER46386) and DOE-EPSCoR. [Preview Abstract] |
Friday, May 16, 2008 5:14PM - 5:26PM |
B3.00011: Transparent Conductive Oxide by Pulsed Laser Deposition: Zn$_{2}$In$_{2}$O$_{5}$ Robert Kykyneshi, Janet Tate Zn$_{2}$In$_{2}$O$_{5}$ (ZIO) belongs to the class of transparent conductive oxides, in which wide band-gap and high conductivity coexist. A systematic study on the influence of pulsed laser deposition parameters on the electro-optical properties of ZIO thin films is carried out. Electron mobility up to 40 cm$^{2}$/Vs and conductivity of 2000 S/cm are obtained in textured-crystalline and amorphous films. An indirect band-gap around 3 eV and low absorption in the visible range are characteristic qualities of ZIO films. [Preview Abstract] |
Friday, May 16, 2008 5:26PM - 5:38PM |
B3.00012: Hydrophobic Interactions in Multiple Scales Using Density-Functional Theory Dennis Jackson, David Roundy We present a classical density functional for water that represents the short-range repulsive interaction using a fundamental-measure-theory (FMT) hard-sphere functional, in addition to a functional that represents the attractive interaction between molecules. The parameters of these functionals are chosen to reproduce the experimental liquid density, bulk modulus and surface tension of water, and to ensure coexistance of liquid and vapor phases. The functional inherits from the FMT functional its accurate description of reduced-dimensionality configurations. We will present computations of the hydrophobic hydration energy of hard-sphere solutes, demonstrating an accurate description at both large and small length scales. [Preview Abstract] |
Friday, May 16, 2008 5:38PM - 5:50PM |
B3.00013: Site Determination of Zn and Mn Doping into Protein Encapsulated Fe$_{3}$O$_{4}$ Nanoparticles V. Pool, M. Klem, J. Holroyd, T. Harris, R. Szilagyi, T. Douglas, M. Young, Y.U. Idzerda In this study, particles grown inside ferritin protein cages with 10{\%}, 15{\%}, 20{\%} and 33{\%} zinc or manganese doped into Fe$_{3}$O$_{4}$ were measured by XAS and XMCD. These spectra were compared to standards and molecular-orbital calculations to determine where in the Fe$_{3}$O$_{4}$ spinel structure the dopant is substituting. Doping into the various Fe-sites of the Fe$_{3}$O$_{4}$ spinel structure suggests that there will be a significantly different magnetic moment per iron lattice position depending on whether the A-site or B-site is favored. For Zn-doping, our results support Zn in the +2 valance state and preferentially substituting in the B-site octahedral site. For Mn-doping, we find Mn also prefers the B-site octahedral site, but may cause a structural transition to the $\gamma$-phase Fe$_{2}$O$_{3}$. [Preview Abstract] |
Friday, May 16, 2008 5:50PM - 6:02PM |
B3.00014: Gas Sensing Properties of ZnO Nanowires at Room Temperature Sirisha Chava, Daqing Zhang, Chris Berven We report the electrical properties of a gas sensor constructed from mats of ZnO nanowires grown on sapphire substrate that shows a reversible response which is unique to CO exposure. The sensor is a two terminal design, where the terminals consist of two 25 $\mu$m diameter gold wires laid parallel on the nanowire mat. The individual nanowires have an average diameter of 50 nm with lengths of about 10 $\mu$m. The nanowire mat is about 20 $\mu $m thick and extends over an area of about 1 cm$^{2}$. When exposed to Ar, CO$_{2}$ or H$_{2}$ no significant changes in the current-voltage behavior of the mat are observed. CO exposure results in approximately a three-fold increase in current. The response is reversible after evacuation. Typical currents when exposed to pure CO under room temperature without prior introduction to any other gas are in the range of 40 nA compared to non-exposed 15 nA. Growth technique of nanowires and comparative work will be discussed. [Preview Abstract] |
Friday, May 16, 2008 6:02PM - 6:14PM |
B3.00015: Island formation and dynamics of gold clusters on amorphous carbon films Guenter Schneider A growing number of potential applications in electronics and catalysis has led to continued experimental and theoretical interest in the dynamics of metal nanoclusters. Experiments of Au clusters deposited on amorphous carbon films showed the formation of Au islands at room temperature. Monte Carlo simulations at multiple length scales give a consistent picture of the complex dynamics in this system. The Au-Au interaction is described by an empirical many-body Gupta potential while the Au-substrate interaction has been determined from ab initio density functional calculations. [Preview Abstract] |
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