Bulletin of the American Physical Society
Spring 2013 Meeting of the APS Ohio-Region Section
Volume 58, Number 2
Friday–Saturday, March 29–30, 2013; Athens, Ohio
Session E3: Condensed Matter Physics II |
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Chair: Eric Stinaff, Ohio University Room: Grover Hall E304 |
Saturday, March 30, 2013 11:00AM - 11:12AM |
E3.00001: Atomistic origin of doping-enhanced ultrafast crystallization in Ag-doped Ge$_{2}$Sb$_{2}$Te$_{5}$ Binay Prasai, Gang Chen, David Drabold We have applied ab-initio molecular dynamics (AIMD) simulations to directly simulate the effects of Ag-doping on the phase change properties of Ge2Sb2Te5. The short range order is preserved, whereas a slight improvement in the chemical order is observed. A slight decrease in the fraction of tetrahedral Ge (sp3 bonding) is reflected in the reduction of the optical band gap and in the increased dielectric constant. Simulations of the amorphous to crystalline phase change cycle revealed the enhanced crystallization speed in Ag0.5Ge2Sb2Te5 as compared to Ge2Sb2Te5. Moreover, the smaller density difference and the larger energy difference between the two phases of Ag0.5Ge2Sb2Te5 (compared to Ge2Sb2Te5) suggest a smaller residual stress in devices due to phase transition and improved thermal stability for Ag0.5Ge2Sb2Te5. The potential viability of this material suggests the need for a wide exploration of alternative phase change memory materials. [Preview Abstract] |
Saturday, March 30, 2013 11:12AM - 11:24AM |
E3.00002: Deformation of mesoporous silica by capillary pressure: an X-ray scattering study Mayur Sundararajan, Gang Chen Capillary pressure originates from surface tension between two immiscible interfaces. In the case of water confined in nanosized pores (i.e. mesopores), the capillary pressure becomes so enormous that it easily deforms solid scaffold of the mesoporous materials. We developed a combined small and wide angle x-ray scattering(S/WAXS) technique to study the deformation of prototypical mesoporous silica (i.e., MCM-41) induced by in situ capillary condensation. ~The capillary strain on the silica scaffold was measured as a function of relative humidity, from which the mechanical properties such as Young's modulus and Poisson's ratio of the mesoporous silica were analyzed. The measurements performed on two samples with different thermal history reveal that thermal annealing has significant impact on the mechanical properties of the mesoporous material. Our study demonstrates a novel X-ray-based technique for analyzing mechanical properties of mesoporous materials. [Preview Abstract] |
Saturday, March 30, 2013 11:24AM - 11:36AM |
E3.00003: Analytic Local and Total Density of States for Hydrogen Adatoms on Graphene Nicholas Pike, David Stroud Spin transport through graphene is strongly influenced by the presence of adatoms with unpaired spins, such as hydrogen adatoms. In this work, we calculate the local density of states (LDOS) for a simple model of hydrogen on graphene using a tight binding model. The model includes nearest neighbor hopping between carbon atoms, the value of the hydrogen energy level, hopping between the carbon and hydrogen atoms, and a Hubbard U-term to account for the on-site Coulomb interaction. When U = 0, we develop an exact analytic equation for the LDOS on the adatom site, and for the total density of states (DOS). When U $\neq 0$, we carry out the same calculation but treat the Hubbard term using mean-field theory. We find that the hydrogen adatom has a net non-integer spin polarization, and that some of the electronic density is transferred from the hydrogen adatom to the graphene host. Possible implications of these results for spin transport through graphene will be discussed. [Preview Abstract] |
Saturday, March 30, 2013 11:36AM - 11:48AM |
E3.00004: Synthesis and Characterization of Sb-Te Phase-change Thin films Chandrasiri Ihalawela, Binay Prasai, Kevin Cooper, David Ingram, Xiao-Min Lin, Gang Chen Phase change memory materials (PCMM) are semiconducting chalcogenides that exhibit rapid phase transition under optical or electric pulse excitation. Among various PCMMs, Sb-Te binary has captured full attention due to their high switching performance and is regarded as one of the prototypical PCMMs. In this study, we focused on binary Sb-Te thin films synthesized by an electrochemical method. The advantage of this method over other techniques lies in its high performance in growing nanowires through templates to fulfill the demand of high-density memory devices. Energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Rutherford backscattering spectroscopy, X-ray diffraction, extended X-ray absorption fine structure, differential scanning calorimetry and four-probe resistance were used to characterize their atomic and electronic structure as well as physical properties. The relations between the structure and properties will be discussed. [Preview Abstract] |
Saturday, March 30, 2013 11:48AM - 12:00PM |
E3.00005: Synthesis and luminescence properties of Erbium doped Aluminum Nitride Nanoparticles Sneha Pandya, Martin Kordesch Wide band semiconductor nitrides have been a found to be good hosts for rare earth elements and have potential applications such as optical amplifiers, light emitting sources, detectors, and for optical communications. Erbium doped Aluminum Nitride (AlN:Er) nanoparticles were synthesized using Inert Gas Condensation technique (IGC). AlN:Er particles were imaged using TEM and SEM and were observed to be of the order of 50-150nm. They were found to have two distinct structures. In one case, closed particles made up of several smaller particles with distinct grains were found, in the other case particles were brush-like structures made from hundreds of smaller crystallites. Their Photoluminescence and Cathodoluminescence properties were studied. The emission peaks of Er$+$3 ions lie in the visible region and are observed to be broadened as compared to AlN:Er thin films. This broadening of the peak is attributed to the reduced dimension. The effect of heating on the luminescence of the particles was also studied and it was found that the optical spectra of the heated particles are comparatively sharp with well-resolved peaks. [Preview Abstract] |
Saturday, March 30, 2013 12:00PM - 12:12PM |
E3.00006: Radiation field for a many-body system Mingliang Zhang, David Drabold Semi-classical radiation theory is used to derive possible radiation fields for a group of charged particles obeying quantum mechanics. One of these fields can only be produced by a system with two or more than two charged particles. The polarization of this field is determined by the vector potential of external driving field and the curl of velocity field. We show that the semi-classical results are the zero-order approximation of the non-relativistic quantum electrodynamics in the reaction of radiation fields. A classical analogue is suggested which clearly illustrates the origins of the sources of fields. [Preview Abstract] |
Saturday, March 30, 2013 12:12PM - 12:24PM |
E3.00007: Symmetry Breaking and Low-energy Vibrations in Amorphous Graphene Yuting Li, David Drabold Crystalline graphene is one of the hottest topics in condensed matter science. Recent experiments revealed the existence of amorphous graphene introduced by electron radiation. Here we explore computationally the electronic, structural and vibrational properties of amorphous graphene using the Wooten-Weaire-Winer models due to Kumar and Thorpe. These models are flat and contain both even and odd-member rings. A density functional study shows the odd-member rings changes the electronic structure near the Fermi level. And carbon pentagons induce local curvature, thus breaking the planar symmetry in analogous with fullerenes [1]. Systematically exploring the inherent structures shows the puckered states are more stable and occupy deeper basins on the potential energy landscape. The vibrational modes and spectra provide evidence that one might detect the presence of amorphous graphene from a vibrational signature. We also discuss the imaginary modes indicating the evolution from flat to puckered states and very low energy conformational fluctuations reminiscent of floppy modes [2]. \\[4pt] [1] Y. Li, F. Inam, A. Kumar, M. Thorpe, and D. A. Drabold, Phys. Status Solidi B 248, 2082 (2011)\\[0pt] [2] Y. Li, D. A. Drabold, Phys. Status Solidi B. doi:~10.1002/pssb.201248481(2012). [Preview Abstract] |
Saturday, March 30, 2013 12:24PM - 12:36PM |
E3.00008: p-type and n-type amorphous thin films for solar cells Pratheesh Jakkala The presentation is about making and characterizing the p-type and n-type amorphous semiconductor thin films suitable for solar cells. Indium Gallium Nitride(InGaN), copper oxide thin films of different thickness are deposited on glass substrate using rf sputtering method at different temperatures. p-type nature of copper oxide and n-type nature of InGaN is verified using Hall effect measurement system, resistivity and conductivity values, I-V curves has been recorded. Band gap values has been measured using UV spectro photometer. Experimental values are very close to theoretical values. Composition of InGaN has been found using EDX measurement. [Preview Abstract] |
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