abstractshumberto/documents/track-2...the oxidation state for cerium is mainly tetravalent (+4),...

NSF EPSCoR RII Track 2

Joint Workshops

ABSTRACTS

November 7‐8, 2011 Sheraton Old San Juan Hotel

San Juan, P.R

N E B R A S K A

IDeAI NFP U E R T O R I C O

University of Nebraska

Institution: University of Nebraska ‐ Lincoln

Department: Physics and Astronomy

Title: The effect of BaTiO3 ferroelectric polarization on orbital magnetism and magnetocrystalline anisotropy of Fe thin films with Cu capping layer

Abstract:

Correlations between magnetocrystalline anisotropy energy (MAE), ferroelectric (FE) polarization, and orbital magnetic moment are studied for ferroelectric/ferromagnetic heterostructures consisting of barium titanate (BaTiO3) and thin‐film iron (Fe). Using first‐principles calculations we investigated six different geometries of the BaTiO3/Fe system, in particular with 1, 3, and 5 monolayers of Fe with either a free vacuum surface or Cu as a capping layer. We show that while the presence of Cu effectively removes the difference in MAE for opposite FE polarization directions in BaTiO3, in the case of a vacuum layer (instead of Cu) there is a large MAE change (~20%) upon switching of the polarization sign. This is explained by analyzing the correlation between MAE and orbital magnetic moments for different geometries and opposite polarization directions. We show that the magnetoelectric coupling between MAE and FE polarization is directly linked to the degree of the magnetoelectric coupling between orbital moment and FE polarization.

Author: Pavel Lukashev

Institution: University of Nebraska ‐ Lincoln

Department: Physics and Astronomy

Title: Highly spin‐polarized conducting state at the interface between nonmagnetic band insulators: LaAlO3/FeS2(001)

Abstract:

First‐principles density functional calculations demonstrate that a spin‐polarized two‐dimensional conducting state can be realized at the interface between two non‐magnetic band insulators. The (001) surface of the diamagnetic insulator FeS2 (pyrite) supports a localized surface state deriving from Fe d‐orbitals near the conduction band minimum. The deposition of a few unit cells of the polar perovskite oxide LaAlO3 leads to electron transfer into these surface bands, thereby creating a conducting interface. The occupation of these narrow bands leads to an exchange splitting between the spin sub‐bands, yielding a highly spin‐polarized conducting state distinct from the rest of the non‐magnetic, insulating bulk. Such an interface presents intriguing possibilities for spintronics applications.

Author: J. D. Burton

Institution: University of Nebraska at Omaha

Department: Physics

Title: Effect of Nitrogen doping on electronic and photocatalytic properties of TaON

Abstract:

First principle calculations of electronic structure of TaON as function of nitrogen concentration are performed. TaON is uniquely versatile material, with possible applications as visible‐light responsive photocatalyst, charge capacitors in memory devices, and gate oxides in microelectronic devices.

We find that the position of conduction and valence band can be modified by varying the nitrogen concentration in TaON. The bandgap decreases monotonically with the increase of the nitrogen concentration.

Future studies will include Cs2Nb4O11 and its modifications and include Z‐scheme of photo‐catalysis.

Author: Renat Sabirianov

Institution: University of Nebraska at Omaha

Department: Physics

Title: Giant Electromechanical Response in Graphene Nanoribbons

Abstract:

First principles quantum mechanical calculations have been performed to investigate the effect of twist on the electronic, magnetic and transport properties of a zigzag graphene nanoribbon (ZGNR). We examine the local magnetic moments and the quantum conductance of twisted ZGNR in its ground state (antiferromagnetic) and in case of ferromagnetic spin orientations. We observe electromechanical switch via twisting a ferromagnetic ZGNR in hypothetical ferromagnetic nanoribbons.

Author: Nabil M. Al‐Aqtash

Institution: University of Nebraska Lincoln

Department: chemistry

Title: Structural Transition of Gold Clusters during Soft Landing on TiO2 Surface and its Effect on CO Oxidation

Abstract:

Small gold clusters and nanoparticles being excellent catalysts in many important chemical reactions, such as CO oxidation, hydrogenation, and selective oxidation.The unique catalytic properties of gold clusters are enhanced by many effects: one factor is the structure‐activity relationship (SAR) of gold clusters.â€œSoft landingâ€� technology is used to reduce the momentum of gold cluster dropping on the support can before its landing, in order to avoid the cluster fragmentation during the collision on surface. Even though the collision between gold cluster and the support can still cause deformation and even isomer transition of the gold cluster. In this work, we employed ab intio molecular dynamics simulation method to investigate the collision between gold cluster and TiO2, as well as this deformation affection to the catalytic properties of gold clusters on support. CO oxidation reaction is selected as the probe for the catalysis properties of the gold clusters.

Author: Hui Li

Institution: University of Nebraska‐Lincoln

Department: Chemistry

Title: QM/MM/Continuum Style MP2 Molecular Dynamics Simulation of Excited States

Abstract:

A combined second order MÃ¸ller‐Plesset perturbation theory, polarizable force field and reaction field continuum model (MP2/MM/Continuum) is developed. The code is implemented in our QuanPol program (Quantum Chemistry Polarizable Force Field Program) in the GAMESS package. This method is implemented for closed shell RMP2, spin‐restricted open shell Z‐averaged ZAPT2 and spin‐unrestricted open shell UMP2 methods. Two schemes are used to model the continuum reaction field. One is the conventional surface charge scheme, and one is a novel direct scheme (similar to the image charge method). This method has been applied to study the S0 and T1 states of acetone in solvents.

Author: Dejun Si



Title: QM/MM/Continuum style TDDFT molecular dynamics simulation methods

Abstract:

A combined time‐dependent density functional theory, polarizable force field and reaction field continuum model (TDDFT/MM/Continuum) is developed. The code is implemented in our QuanPol program (Quantum Chemistry Polarizable Force Field Program) in the GAMESS package. The solvatochromic shifts and photodynamics of a variety of organic and biological chromophores in solvents and proteins are studied.

Author: Nandun M. Thellamurege



Title: XAFS Study on Nanostructured Cerium Oxide: the Effect of Activation Temperature on the Microstructure and catalytic activity

Abstract:

Cerium oxide (CeO2) has attracted considerable interests because of its complex electronic structures and wide applications such as heterogeneous catalysis and solid oxide fuel cells. In this talk, we will present our investigation of the effect of activation temperature on the local structure and catalytic activity of nanosized cerium oxide (nanoceria) made by hydrothermal processes. Nanoceria was activated from 200 ÂºC to 1000 ÂºC with an interval of 100 ÂºC. Ce L3 edge was used to investigate the local structure of cerium oxide due to its simplicity and universal applicability. X‐ray absorption near edge spectroscopy (XANES) study showed that the oxidation state for cerium is mainly tetravalent (+4), even if the activation temperature was as low as 200 ÂºC. The crystallinity of the cerium oxide samples were found to increase with an increase in activation temperature. Extended X‐ray absorption fine structures (EXAFS) spectra were fitted with a bulk cerium oxide core shell model by using FEFF 6.0. Coordination number, bond length and Debye‐Waller factor of first three shells were obtained from the EXAFS analysis as a function of activation temperature. The crystals approach the normal coordination at high temperatures. Also, carbon monoxide catalytic oxidation activity of these catalysts was evaluated at various temperatures. The developed procedure for the comparative analysis of structural parameters from the L3 edge spectra of Ce in CeO2 could allow further structural studies of catalytic compounds containing cerium surrounded by oxygen atoms or other types of ligands.

Author: Yunyun Zhou



Title: Developing QuanPol: Parallel computing algorithm of QM/MM using CPU/GPU

Abstract:

We develop and improve computing algorithm of QM/MM methods for Quanpol to perform parallel calculation on CPUs/GPUs. Neighbor list (NL) is commonly used in force field simulations to avoid unnecessary computation time in the calculation of intermolecular inter‐actions. Recently, we develop fast‐list method, which can be used to reduce the update frequency of the neighbor lists at a very low computational cost. Compared to the method that only checks the displacements of individual atoms, the fast‐list method reduces the update frequency by two times at virtually the same cost. We also investigate the adsorption, spectroscopic and excited‐states properties of benzene on metal surface by employing QM/MM methods in Quanpol.

Quanpol (quantum chemistry polarizable force field) program is integrated in the GAMESS package. It is a full‐spectrum and seamless QM/MM program that support all standard QM methods such as HF, DFT, GVB, MCSCF, MP2 and TDDFT and MM methods such as CHARMM, AMBER, OPLS‐AA and user defined force field parameters.

Author: Fengchao Cui


Department: Holland Computing Center

Title: Track2 Activities at HCC

Abstract:

The Track2 co‐funded Linux cluster will be introduced with its hardware configuration and its usage by Track2 researchers.

Author: Jun Wang

Turabo University

Institution: Turabo University

Department: Engneering

Title: Nanoscale Fabrication of the Ferroelectric Polymer Poly(vinylidene Fluoride with Trifluoroethylene) P(VDF‐TrFE) 75:25 Thin Films by Atomic Force Microscope Nanolithography

Abstract:

Thin films of the only organic ferroelectric system, poly(vinylidene fluoride with trifluoroethylene) P(VDF‐TrFE) 75:25 layers have been deposited on Highly Order Pyrolytic Graphite (HOPG) and Silicon Dioxide (SiO2) by the horizontal Schaefer method of Langmuir‐Blodgett (LB) techniques. It is possible to â€œshaveâ€� or mechanically displace small regions of the polymer film by using Atomic Force Microscope Nanolithography techniques such as nanoshaving, leaving swaths of surface area cut to a depth of 4 nm and 12 nm exposing the substrate. The results of fabricating stripes by nanoshaving two holes close to each other, shows a limit in â€œstripesâ€� widths of average 153.29 nm and 177.67 nm that can be produced. Due to the lack of adhesion between the substrates and the polymer film P(VDF‐TrFE) smaller â€œstripesâ€� of P(VDF‐TrFE) cannot be produced, it can be shown by the sequencing of nanoshaved regions, â€œstripesâ€� of thin films can be removed

Author: Omar Vega‐Manzano

Universidad Metropolitana

Institution: Universidad Metropolitana

Department: Science and Technology

Title: PbSe Nanocrystal Excitonic Solar Cells

Abstract:

Colloidal semiconductor nanocrystals (NCs) potentially offer major benefits as photovoltaic materials in next‐generation solar cells. Synthetic adjustments in the NC size, shape, and composition provide control over electronic and optical properties. Photovoltaic devices were fabricated from PbSe NC films sandwiched between layers of ZnO nanoparticles and PEDOT:PSS films. The device I‐V characteristics suggest charge separation mechanisms consistent with signatures of excitonic solar cells. I‐V curves shows an increase of 3.4 % under a 1‐sun power conversion efficiency. This poster will show preliminary results how the particle size can affect solar cell performance.

Author: Mitk'El B. Santiago

University of Puerto Rico

Institution: University of Puero Rico

Department: Physics

Title: Non‐equilibrium coherent potential approximation for electron transport

Abstract:

We generalize the coherent potential approximation (CPA) for non‐equilibrium electron transport. This new approach, based on the non‐equilibrium Green function formalism, does not require summing scattering diagrams to infinite order (vertex corrections) and provides an efficient way to find transport properties of disordered systems. We prove that the proposed approach is equivalent to the standard CPA with vertex corrections to infinite order.

Author: Alan Kalitsov

Institution: University of Puerto Rico

Department: Chemical Engineering

Title: Guided Motion of Self‐Propelled Magnetic Colloidal Particles by Brownian Dynamics Simulation

Abstract:

Self‐propulsion of artificial nano‐ and microscale objects by the transformation of chemical energy into motion is one of the most fascinating and exciting challenges currently studied. Intense investigations about this have been developed due to their potential application in diverse areas of nanotechnology. However, it has been shown in recent experiments that autonomous motion of the so‐called â€œcatalyticâ€� motors is hindered by their rotary Brownian motion and thus preventing its potential to be fully realized. On the other hand, such limitation could be relaxed with colloidal particles sensitive to external magnetic fields. The present study investigates the long‐time diffusive behavior of a catalytically driven â€œmagneticâ€� colloidal particle immersed in a dispersion of reactant particles subject to a magnetic field using Brownian dynamics simulations. The strength of the magnetic field is controlled by the Langevin parameter, which physically measures the relative importance of magnetic to Brownian torques, and dictates the spatiotemporal behavior of the particle. The rotational and translational self‐diffusivity is measured for different surface reaction speeds, particle sizes, reactant particle concentrations, magnetic dipole orientations, and Langevin parameters.

Author: Glenn Cooper Vidal‐Urquiza


Department: Physics

Title: Fe‐Anchored Graphene Oxide: A Low‐Cost and Easily Accessible Catalyst for Low‐Temperature CO Oxidation

Abstract:

By means of first‐principles computations, we investigated the catalytic capability of the Fe‐anchored graphene oxide (Fe‐GO) for CO oxidation with O2. The high energy barrier of Fe atom diffusion on GO, and the strong binding strength of Fe anchored on GO exclude the metal clustering problem and enhance the stability of the Fe‐GO system. The Fe‐anchored GO exhibits good catalytic activity for CO oxidation via the favorable Eley‐Rideal (ER) mechanism with a two‐step route, while the Langmuir‐Hinshelwood (LH) mechanism is not kinetically or thermodynamically favorable. The low‐cost Fe‐anchored GO system can be easily synthesized, and serve as a promising green catalyst for low‐temperature CO oxidation.

Author: Fengyu Li


Department: Physics

Title: Observation of direct magnetoelectric effect for Ba0.7Sr0.3TiO3/La0.7Sr0.3MnO3 thin film heterostructures

Abstract:

A robust magnetoelectric (ME) response is essential in multiferroic thin films for the ME based nonvolatile memory elements. We report the ME effect in Ba0.7Sr0.3TiO3/La0.7Sr0.3MnO3 (BST/LSMO) bilayer and (BST/LSMO)n superlattice (SLs) thin films grown by pulsed laser deposition technique. A maximum out‐of‐plane ME voltage coefficient (ï�¡E,33) of 213 was observed for the bilayer whereas SLs structures showed highest in‐plane ME coefficient (ï�¡E,31) ~ 247 mV/cm.Oe for low periodicity and out‐of‐plane ME coefficient (ï�¡E,33) ~ 300 mV/cm.Oe for 24 nm periodicity. Experimental data fitted well with the modified free body Harsheâ€™s model. These ME values show a step forward towards the realization of ME based multistate memories and dual read‐write devices elements.

Keywords: Magnetoelectric, piezoelectric, magnetostrictive, bilayer and superlattice.

Author: Ricardo Martinez‐Valdes


Department: Physics

Title: TRANSPORT PROPERTIES OF DISORDERED GRAPHENE

Abstract:

Due to the electronic properties and flexibility, the crystalline graphene has been wide studied in the past few years from the point of view of different approaches been remarkable the tight‐binding approximation. This model work fine for this material and it is preferred among other by its simplicity. In this poster we present some of the main features for ordered graphene and the methodology that we will be following in order to have some understanding about the changes that impurities introduce in the transport properties of graphene. The Coherent Potential Approximation (CPA) will be the used approach in our study.

Author: Whasington Silvestre‐Alcantara


Department: Physics

Title: Phase transitions of New Room‐Temperature Magnetoelectric Single Phase Material

Abstract:

Mixing 60‐70% lead zirconate

Author: Dilsom A. Sanchez


Department: Physics

Title: Real Time Growth Process Monitoring and Magnetoptic Properties of GaN:Er Thin Films

Abstract:

The rare‐earth (RE) doped GaN semiconducting materials are promising candidates for spintronic and optoelectronic applications. The higher magnetic moment of RE ions compared to the transition metal ions makes RE‐doped GaN as materials of choice for dilute magnetic semiconductor. RE‐doped GaN materials have shown the ability to tune the direct bandgap from the ultraviolet through visible to the near infrared region. GaN:Er thin films are great interest because of their emission in visible regime. The main objective of our work is to make Er‐doping in GaN both magnetically and optically active at room temperature. Here we report, the magnetic and optical properties Er+3 â€“doped GaN epitaxial thin films grown by molecular beam epitaxy (MBE). Thin films of GaN:Er have been grown on Si (1111) and Sapphire (0001) substrates using MBE. The growth process was monitored in situ by reflection high energy electron diffraction (RHEED). The doping concentration and elemental analysis have been calculated from the x‐ray photoelectron spectroscopy (XPS). X‐ray diffraction and atomic force microscopy (AFM) were used to examine the phase purity and smoothness of the films. The concentration and mobility of carriers were calculated from the Hall effect measurements. The magnetic properties of GaN:ErYb thin films were measured using SQUID and magnetotransport measurements. The optical properties of the films were analyzed by photoluminescence (PL) and cathodoluminescence spectroscopy (CL). The magnetic and optical properties of the GaN:Er films will be compared with Yb‐doped GaN films and will be discussed in details.

Author: Ratnakar Palai


Department: Physics

Title: Electrical characteristics of Lanthanide compound LaGdO3 gated MOS capacitors for logic devices.

Abstract:

Ultra‐thin layers of SiO2 to SiONx (ï�¥r= 3.9 to 7) upheld the down‐scaling of transistors and the resulting advances in integrated circuit technologies had given us computers with powerful processing capabilities due to high‐speed/high‐density memories and processors. In the case of processors, it served well so far as a high quality dielectric layer by sustaining high electric field with low leakage current, to strongly modulate the channel conductance for various technology nodes(â‰¥45nm). However, below 45 nm technology node thickness reduction of SION for further scaling was not considered due to excessive leakage current by tunneling. In this regard, Hf‐based oxides have proven credential and HfSiON with medium dielectric constants ï�¥r(~15) was introduced in current technology node (32nm). In order to achieve the long term goal (22 nm technology node or below), another class of dielectrics with even higher ï�¥r (>20) and lower leakage currents is needed. Rare‐earth based multi‐component oxides in the amorphous state are being considered as the next generation dielectrics after HfSiON and we have selected a new compound LaGdO3 for the present study. Amorphous LaGdO3 (LGO) films were prepared on SiOx/p‐Si(111) substrate using Pulsed Laser Deposition (PLD) technique and its electrical properties have been studied. The equivalent oxide thickness (EOT) and gate leakage current density (Jg) were determined on metal‐oxide‐semiconductor (MOS) structures. Capacitance‐Voltage characteristics showed negligible hysteresis, ~8 mV. Capacitance at accumulation showed a systematic reduction with increase in thickness. The dielectric constant obtained from the slope of the EOT vs. thickness was ~21.6 Â± 1.7, and the interfacial capacity correspond to an EOT of ~1.8 Â± 0.3 nm, matching well with the interfacial SiOx layer thickness. LGO layers with EOT of 3nm had a Jg ~ 3 x 10‐8 A/cm2 at accumulation (Vg=VFB‐1). The estimated interfacial trap density at the flat band voltage as determined by Lehovec method was in the range 1012 eV‐1cm‐2. Leakage current of LGO films were lower than the corresponding SiO2 film for the same EOT. These results show that LGO ultra thin films are promising high‐k gate insulators.

Author: Shojan P. Pavunny


Department: Physics

Title: Photovoltaic effect in a wide‐area semiconductor‐ferroelectric device

Abstract:

Millimeter‐diameter planar devices of glass/ZnO:Al/BiFeO3/La0.67Sr0.33CoO3 (LSCO) heterostructures were fabricated by pulsed laser deposition (PLD) techniques. Diode‐like behavior with high short‐circuit current (Isc ~ 4 microA/cm2) and open‐circuit voltage (Voc ~ 0.22 V) was obtained under the illumination. Impedance spectroscopy revealed that electrode/dielectric interface and grain‐boundary conduction are mainly responsible for the photo‐current. Electrode/dielectric interface, grain boundary impedance, and low‐frequency ac conductivity change by almost three orders of magnitude under weak light. Relaxation time of the photo‐carriers changes from 80 ms to 96 micro second suggesting that with optimal collecting instruments, one should expect currents several orders higher.

Author: Tanaji P. Gujar


Department: Physics

Title: Dependence of the Structural, Dielectric, and Ferroelectric properties with Periodicity and Composition in artificial BaTiO3/ (Ba,Sr)TiO3 superlattices

Abstract:

Artificially fabricated superlattices (SLs) constructed by alternate layers of different polar and non‐polar perovskites oxides BaTiO3 (BT), SrTiO3 (ST), LaAlO3 and PbTiO3 have been popular objects of investigations over the past few years. In addition to novel physics, SLs exhibit superior properties such as low‐loss, high dielectric constant, high polarization, and high Curie temperature that make them attractive for thin‐film device applications. Physical properties different from parent materials can be obtained in the SL structure by modifying the lattice, i.e. change in the unit cell, strain, and the lattice mismatches across the interface between the layers and/or at the film‐substrate interface. Local stress in the epitaxial films can be controlled by several ways: varying the deposition conditions, the substrate, varying the film thickness, varying the thickness, or altering the lattice parameters by doping. Superlattices of BT/ST and BT/Ba(1‐x)SrxTiO3 (BT/BST) with x = (0, 0.3, 0.4, 0.5, 0.6, 0.7, 1) were grown on (001) MgO substrate by pulsed laser deposition techniques. The thin‐film stack was deposited by alternately focusing the beam on stoichiometric BT, ST, and BST targets. The filmsâ€™ modulation period (ï�Œ) in BTï�Œ/2/STï�Œ/2 SL was varied between ~16 Ã…

superlattice structure, folded acoustic phonon doublets was observed in the low‐frequency region of Raman spectra for both sets of SLs. The frequency dependence of the dielectric constant and loss tangent of BT/BST SLs showed almost constant high values of dielectric constant ranging between 1000‐2000 below 10 kHz and relatively low loss tangent (~ 0.1) at frequencies below 10 kHz. All BT/BST SLs showed ferroelectric properties, nevertheless strong polarization switching with well saturated hysteresis was observed in BT/Ba0.3Sr0.7TiO3 (BT/BST3070) and BT/Ba0.7Sr0.3TiO3 (BT/BST7030) at different frequencies. I‐V characteristic show a asymmetric behavior due to effect of the dissimilar top and bottom electrodes (Pt and La0.67Sr0.33MnO3), however the superlattices show very low leakage current density far above its coercive field. Temperature dependence of dielectric and ferroelectric properties of the SLs will be discussed.

Author: Nora P. Ortega

Institution: University of Puerto Rico ‐ Cayey

Department: Physics

Title: Zinc Oxide aluminum doped as transparent conductive oxide

Abstract:

Zinc oxide doped with aluminum (ZAO) is one of the transparent conductive oxides (TCOs) being studied for energy harvesting applications. Most recent efforts to increase conductivity ~ 104S/cm while maintaining high transparency, for specific layer thickness or other boundary parameters, have been unsuccessful as result of the inability to activate dopants and control crystallinity in order to produce large free carrier concentration and high mobility conditions.In this project it is proposed to synthesize ZAO using electrospinning techniques to study the parameters controlling generation of free carriers by doping, crystallinity and optical transparency. Most published reports on electrospinning deal with the use of specific precursors and post‐fiber treatments to obtain the desired material characteristic‐properties, but little effort has been placed in understanding how precursor solution treatments could affect them. Both, classical and non‐classical crystallization mechanisms depend on reaction conditions present in the precursor solution such as reagent chemistry and concentration, ionic strength and temperature10,11. It is then proposed to use the synthesis of ZnO:AL as a model system to study how to control the nucleation and crystalline growth of the ZnO fibers and the Al doping effect.

Author: Wilfredo Otaño

Institution: University of Puerto Rico ‐ Humacao

Department: Physics and electronics

Title: Electron properties of various nanosystems

Abstract:

Currently, molecular tunnel junctions are recognized as important active elements of various nanodevices. This gives a strong motivation to study physical mechanisms controlling electron transport through molecules. Electron motion through a molecular bridge is always affected by the environment, and the interactions with the environment could change the energy of the travelling electron. Under certain conditions these inelastic effects may significantly modify transport characteristics. In the present work we describe inelastic and dissipative effects in the electron transport occurring due to the molecular bridge vibrations and stochastic thermally activated ion motions.

Author: Natalya A. Zimbovskaya


Department: Physics and Electronics

Title: Photoelectron Spectroscopy Studies in Ferroelectric Organics and Inorganic Materials; An Experimental Approach

Abstract:

Photoelectron spectroscopy is a valuable experimental technique that allows the study of the electronic band structure for different types of materials. Thin films of GdN deposited on a LaAl2O3 substrate and organic Poly(vinylidene fluoride) PVDF/Poly(3‐Hexylthiophene) P3HT Polymer blender were studied using x‐ray and ultraviolet photoemission spectroscopy. Inverse photoemission spectroscopy was also performed providing information on the unoccupied electron states and the electronic band gap of these materials.

Author: Manuel Andres Bonilla


Department: Physics and Electronics

Title: Dipole‐dipole Interaction in Zwitterions On Gold and Graphene Substrates

Abstract:

We have adsorbed zwitterion molecules with large dipoles (about 10 Debyes for each molecule) on two very conducting substrates: gold and graphene. The goal is to ascertain whether the interaction of these strongly dipolar molecules is the same on these otherwise highly conducting substrates.

Author: Godohaldo J. Perez

Institution: University of Puerto Rico ‐ Mayaguez


Title: DFT Study of the Interaction of CO2 and Epoxides with Metal Salen Catalysts

Abstract:

Few chemical processes have proven successful in using CO2 as a feedstock in chemical reactions. While CO2 is abundant and nontoxic, its stability imposes a challenge in finding routes for its effective use. Some transition metal salen complexes can catalyze the coupling reaction of CO2 with epoxides to produce either cyclic carbonates or polycarbonates via two competing reactions. We have used density functional theory calculations to understand how these reactions proceed and to unravel the role of the catalyst on these systems. We have studied the adsorption of CO2 and ethylene oxide onto six metal salen complexes (Co, Cr, Fe, Mn, Zn, Al) using the unrestricted OPBE functional along with the effective core potential LANL2DZ for the basis set. Geometrical optimizations were carried out beginning with a variety of different conformations and frequency calculations were used to verify that structures lie in an energy minimum.

Author: Maria C. Curet‐Arana



Title: Active microrheology of chemically active particles

Abstract:

We consider a long‐time self‐diffusivity of a catalytic particle pushed through a dispersion of reactant particles by an external force. Chemical reaction of the first kind takes place at a surface of contact between the catalytic and a reactant particle.

The long‐time self‐diffusivity as a function of the Peclet number (a measure of an external force) and Damkohler number (a dimensionless reaction rate) is analyzed. Both increase and decrease in the self‐diffusivity are possible depending on the parameter range.

Author: Sergey Shklyaev



Title: Synthesis of ZnO thin film nanostructures for applications in logic and memory devices

Abstract:

The goal of this project is to study the synthesis of ZnO thin film nanostructures for applications in logic and memory devices. The nanostructures are being prepared using sol‐gel and sputtering deposition techniques with the aim of creating a stable room temperature diluted magnetic semiconductor (DMS).The project effort is directed toward distinguishing between structural and compositional effects on carrier concentration and multifunctional response. Sol‐gel and sputtering deposition techniques have great potential in industrial applications because they provide a well established process for coating large areas and the possibility of obtaining films with uniform thickness. The challenge is the synthesis of films with high quality crystallinity using these techniques. The first objective of the proposed work is to investigate the use of processing parameters to increase crystalline perfection. For sputtering deposition these parameters include substrate temperature, flux of reacting materials, and energy and momentum transfer. For sol‐gel deposition, the type of substrate, the pre‐ and post heat treatment and type of solvent used are process parameters that affect the thin film crystallinity. The second objective is to introduce variations in these processing parameters to produce systematic changes in defect density that will shed light on the mechanism responsible for the ferromagnetic behavior. The third objective is to introduce transition metal dopants in the ZnO films with different defect densities to correlate changes in carrier concentration and possible ferromagnetic behavior with doping and crystal quality.

Author: Nelson Granda


Department: Physics

Title: Modeling electron transport properties of nanostructures

Abstract:

In this poster, we present our work on modeling electron transport properties of nanostructures, including theoretical investigation of modeling dynamic transport, wave‐packet dynamics in graphene, and computational simulation of electric and magnetic properties of graphene few layers.

Author: Junqiang Lu


Department: Physics

Title: Effect of Vanadium Ions on the Functional Properties of Nanocrystalline Zinc Oxide

Abstract:

Transition metal ion‐doped ZnO, also known as diluted magnetic semiconductor, may exhibit a ferromagnetic behavior due to the effective incorporation of dopant species in the host oxide structure and the subsequent exchange interactions between available spins. This ferromagnetic functionality will enable the application of this material in data storage and spintronics‐based devices. On this basis, a systematic study was carried out to determine the effect of composition and crystal size on the structural, optical and magnetic properties of pure and Vanadium‐doped ZnO nanocrystalline powders and films in the 0.0 at%‐1.0 V‐at% range. Powders and films were synthesized via a sol‐gel approach, where ethanolamine was used to increase the viscosity of the precursor solutions and promote the adhesion of resulting films on quartz or Silicon substrates. TGA‐DTA measurements suggested the complete formation of the oxide structure at temperatures above 350ÂºC in air. X‐ray diffractometry verified the development of the ZnO host structure after annealing of the precursors in air. The average crystallite size in thin films varied from 11nm to 23nm when the samples were annealed fin air or one‐hour in the temperature range between 450ÂºC and 550ÂºC. UV‐vis and photoluminescence, PL, measurements confirmed the formation of the host oxide with a PL intensity that was strongly dependent on the contents of the Vanadium dopant. Room‐temperature magnetic measurements, carried out in a squid system, evidenced the ferromagnetic behavior in the samples depending on the Vanadium concentration and annealing temperature.

Author: Marco A. Gálvez‐Saldaña


Department: Physics

Title: Annular wave packets at Dirac points in graphene

Abstract:

Wave packets in graphene whose central wave vector is at Dirac points are investigated by numerical calculations. Starting from an initial Gaussian function, these wave packets form into annular peaks that propagate to all directions like ripple‐rings on water surface. At the beginning, electronic probability alternates between the central peak and the ripple‐rings and transient oscillation occurs at the center. As time increases, the ripple‐rings propagate at the fixed Fermi speed, and their widths remain unchanged. The axial symmetry of the energy dispersion leads to the circular symmetry of the wave packets. The fixed speed and widths, however, are attributed to the linearity of the energy dispersion. Interference between states that respectively belong to two branches of the energy dispersion leads to multiple ripple‐rings and the probability‐density oscillation. In a magnetic field, annular wave packets become confined and no longer propagate to infinity. If the initial Gaussian width differs greatly from the magnetic length, expanding and shrinking ripple‐rings form and disappear alternatively in a limited spread, and the wave packet resumes the Gaussian form frequently. The probability thus oscillates persistently between the central peak and the ripple‐rings. If the initial Gaussian width is close to the magnetic length, the wave packet retains the Gaussian form and its height and width oscillate with a period determined by the first Landau energy. The wave‐packet evolution is determined jointly by the initial state and the magnetic field, through the electronic structure of graphene in a magnetic field.

Author: Ji Luo


Department: Physics

Title: Effect of finite coverage on electronic transport property of a graphene monolayer

Abstract:

We investigate electronic transport property of a graphene monolayer covered by another layer with infinite or finite size. We demonstrate that electronic transport property of a graphene monolayer can be changed considerably if the other layer is a nanoribbon with finite width; while the change is more insignificant if the other layer is infinite or even semi‐infinite large. We show that the different effects from infinite and finite coverage are attributed to antiresonance in electronic transmission due to interlayer interference between the wavefunctions.

Author: Daniel Valencia

Institution: University of Puerto Rico ‐ Rio Piedras


Title: Triangular copper(II) based pyrazolate based metal organic frameworks

Abstract:

Metal Organic Frameworks (MOFs) are 3‐dimensional porous materials constructed by connecting metal complexes with organic/inorganic linkers. Because of their high surface area and pore volume, MOFs have often been used for applications like gas storage and separation, catalysis, etc. The pores can also be desirably functionalized pre‐ or post‐ synthetically. MOFs possessing polynuclear metal complexes as secondary building units (SBUs) can be of functional importance, as the properties of the metal complex can be transformed to the MOF. In this study, we describe the synthesis, characterization and gas sorption properties of MOFs based on CuII3‐pyrazolate SBUs, focusing mainly on CO2. Cu‐pyrazolate MOFs with linear 4,4â€™‐bipyridyl linkers crystallize as highly interpenetrated structures, and the extent of interpenetration varying with substituents on the pyrazole.

Author: Logesh Mathivathanan



Title: A Combined First‐Principles Molecular Dynamics/Density‐Functional Theory Study of Ammonia Oxidation on Pt(100) Electrode

Abstract:

We conduct a combined density‐functional theory (DFT)/molecular dynamics (MD) study on the electrochemical oxidation of ammonia on the most catalytically active low‐index single‐crystal Pt(100) electrode surface. The NH3/NHx (x=1,2) oxidation processes, nature of the adsorbed intermediates NHx(ads) and N2Hx+y(ads) (x+y=2‐4), and the potential dependence of the oxidation processes on the single‐crystal Pt(100) electrode will be studied to gain a thorough atomic‐level understanding of these catalytic processes at the metal/alkaline solution interface. Because of the complexity of such an electrochemical system, there is a lack of understanding of the atomistic details governing such processes. The study will provide insight into the mechanism for ammonia oxidation processes and nature of the adsorbed intermediates as a function of electrode potential.

Author: Dmitry Skachkov



Title: Towards Carbon Neutral Energy via Computations

Abstract:

We will present our most recent efforts in the computational design of novel nanomaterials for (1) nanoelectronics, (2) hydrogen purification membrane, and (3) nanocatalysts for CO oxidation and syngas‐ethanol conversion.

Author: Zhongfang Chen


Department: Computer Science

Title: High Performance Computing facility, University of Puerto Rico

Abstract:

The UPR High Performance Computing facility is a shared resource for computational science. It serves researchers across the entire island of Puerto Rico, with computational resources, advanced networking and technical support. We breifly describe the resources and services available at the HPCf.

Author: Humberto G. Ortiz‐Zuazaga


Department: Physics

Title: Development and understanding of multifunctional nanostructured magnetoelectric and spintronic materials

Abstract:

Development of CMOS compatible high‐k gate oxides to meet the present demand of miniaturization of Si based technology and magnetoelectric (ME) multiferroics and spintronics for the next generation memory technology beyond Si, are the goals of our project. Spintronics combine standard microelectronics with spin‐dependent effects that arise from interactions between electrons and magnetic field. The spin dependent phenomena become challenging at the nanoscale where new physical effects emerge affecting the spin injection, transport, and switching times. Therefore, the fundamental science and understanding is needed to develop such materials that have the potential to form the basis of a new generation of energy efficient nanoscale electronic devices that are fast responding, have low power consumption and high integration density.

We designed and fabricated composite bilayers and superlattices (nano‐capacitor) of ferroelectric PbZr0.52Ti0.48O3(PZT) and half‐metallic oxide La0.67Sr0.33MnO3(LSMO) with different stacking periodicity. High remnant polarization (12‐54 Î¼C/cm2), dielectric constant (400‐1700), and well saturated magnetization were observed showing giant frequency‐dependent dielectric anomaly in the vicinity of the ferromagnetic‐phase transition. Magnetic control of ferroelectric interface was also observed in bilayers. As the field H is increased, the hysteresis loop broadens (becomes lossy) and then disappears at ca. H=0.34T and ambient temperatures the process was reversible. This phenomena was explained due to collapse of colossal magneto‐resistance of LSMO with suitable H, causing short circuiting of the PZT polarization due to high electric field across it.

The PLD grown LaGdO3 (LGO) high‐k dielectric thin films showed effective dielectric constant (k) ~21.6 Â± 1.7, flatband voltage ~1012 eV‐1cm‐2, conduction (Î”Ec 2.73Â±0.12eV) and valence (Î”Ev 1.86Â±0.12eV) band offset. Long n‐channel LGO metal‐oxide‐semiconductor field effect transistors (MOSFET) with 7.5Î¼m channel length and a channel width of 15 Î¼m were fabricated and electrically characterized.

ZnO based dilute magnetic semiconductors (DMS) for the novel magneto electronic devices were screened with various doping levels. The ZnCuO films showed nearly single crystalline phase (â‰¤ 3% Cu doping) with ferromagnetic behavior (Ms ~ 0.76 Î¼B/Cu) that reduced on further increase in Cu doping. The high‐Tc ferromagnetic property in Co‐doped ZnO (ZCO), mediated by donor impurity band was tested by the controlled introduction of shallow donors (Al) in the Zn0.9‐xCo0.1O:Alx (x = 0.005 and 0.01) thin films. The saturation magnetization for the 10% Co‐doped ZnO was 4emu/cc at 300 K that reduced (~ 0.8 emu/cc)

due to Al co‐doping and the resistivity dropped abruptly, from ~ 103 â„¦‐cm for the ZCO film to 0.033 and 0.02 â„¦cm for the 0.5% and 1.0% Al doped ZCO samples respectively. The optical band gap in the Mn‐doped (1‐10%) ZnO was found to increase (3.27 eV to 3.41 eV) due to Mn doping. We synthesized Antimony (Sb 3% and 5%) doped p‐type ZnO films that exhibited high hole concentration of 6.25Ã—1018 cmâˆ’3, mobility of 57.44 cm2/Vs, and low resistivity (Î©â€‰cmâ€‚0.017) in the 5% Sb‐doped ZnO thin film.

Author: Ram S. Katiyar


Department: Physics

Title: Spontaneously detached self‐supported graphene‐diamond hybrid films

Abstract:

Free standing graphene‐diamond hybrid films have been fabricated using saturated hydrocarbon polymers as seeding material by hot filament chemical vapor deposition technique. The films are characterized with X‐ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). The XRD shows the characteristic diffraction peaks of both diamond and graphene. The Raman spectrum shows the characteristic band of diamond at 1332 cm‐1 and D, G, and 2D bands of graphene at 1349, 1592, and 2687 cm‐1, respectively. Both SEM and TEM depict the presence of diamond and graphene in the films. The EELS recorded in the carbon K‐edge region also shows the signature peaks of diamond and graphene. The free standing hybrid films exhibit a remarkably low turn‐on field of about 2.4 V/Âµm and a high emission current density of 0.1 mA/cm2. Furthermore, emission currents are stable over the period of 7 days. The superior field emission characteristics of the free standing graphene‐diamond hybrid films are attributed to the heat sink capability of diamond and high electrical conductivity of graphene.

Author: Deepak Varshney


Department: Physics

Title: Electric Field Induced Reduction of Graphene Oxide: A Direct Evidence form In Situ Raman Study

Abstract:

Graphene consists of a single layer carbon atoms which exhibits very unique physical properties such as very high unusual electrical and thermal conductivities, quantum Hall effect, etc. Since its discovery conventional mechanical exploitation of highly oriented pyrolitic graphite remains a potential method of obtaining high quality graphene. However, this method fails to produce mass scale production of graphene which is required for its large scale applications. The modified Hamorrâ€™s process has emerged as a potential method of producing large quantity graphene oxide by the chemical oxidation of graphite. Graphene oxide shares similar single and few atomic layer structure of carbon as molayer or fewlayer graphene, respectively. However, unlike graphene (which has high electrical conductivity), the presence of hydroxide, epoxy groups in GO makes it highly electrical resistive. This is undesired for any electronic applications. In the present study, we have demonstrated that graphene oxide can be reduced under the application of electric field and thereby the electrical conductivity can be tuned systematically. By varying the applied electrical potential across graphene oxide sheet, the in situ Raman studies were carried out to understand the exact nature of the reduction process; thermal or electrical. Both the G and D Raman band shows a systematic change with applied potential. The detailed analysis of the Raman spectra confirm the reduction process to be purely electrical. The electrical reduction of graphene oxide is found to be a clean and controlled way of tailoring the electrical properties of graphene. The reduced graphene oxide was used as electrode in dye sensitized solar cell which results in increase in the efficiency.

Author: Satyaprakash Sahoo


Department: Physics

Title: Fabrication of graphene using Ni and saturated hydrocarbon polymers

Abstract:

Graphene has been the subject of research in the recent years because of its unique electrical, optical and mechanical properties. These properties make it an ideal material for many applications in electronics, such as a transparent electrode for photovoltaic devices. We fabricated monolayer graphene on Ni‐coated SiO2 substrate and on UNCD films by thermal annealing using saturated hydrocarbon polymers. The materials were characterized by Raman spectroscopy, electron microscopy, and electron energy loss spectroscopy. They show the presence of monolayer sheets of graphene having size of the order of 15‐20 Âµm.

Author: Deepak Varshney


Department: Physics

Title: Fabrication of graphene using Ni and saturated hydrocarbon polymers

Abstract:

Graphene has been the subject of research in the recent years because of its unique electrical, optical and mechanical properties. These properties make it an ideal material for many applications in electronics, such as a transparent electrode for photovoltaic devices. We fabricated monolayer graphene on Ni‐coated SiO2 substrate by thermal annealing using saturated hydrocarbon polymers. The materials were characterized by Raman spectroscopy, electron microscopy, and electron energy loss spectroscopy. They show the presence of monolayer sheets of graphene.

Author: Gerardo Morell


Department: Physics

Title: Dynamic dielectric and impedance anomalies near magnetic phase transitions in multiferroics heterostructures

Abstract:

Magnetoelectric (ME) Multiferroics (MF) are attractive class of multifunctional materials that simultaneously exhibit more than two ferroic orders (i.e ferroelectric (FE), ferromagnetic (FM) and/or ferroelastic) and the additional coupling between them are of interest owing to their potential applications in devices, such as novel memory elements and magnetic‐ field sensors. Artificially designed Nanocapacitor superlattices were formed with 5nm/1nm and 7nm/1nm periodicity of ferroelectric (piezoelectric) PbZr0.52Ti0.48O3 (PZT) and half‐metallic ferromagnetic La0.67Sr0.33MnO3 (LSMO) deposited onto 100‐LaAlO3 (LAO) and (LSAT) substrates by pulsed laser deposition. Î¸‐2Î¸ x‐ray scan and Ð¤ scan revealed epitaxial growth of nanocapacitors. At room temperature, the dielectric tunability was ~35 % at high frequencies with well saturated polarization whereas the local piezo force microscopy (PFM) measurements revealed switching of polarization under the external bias field. To gain further understanding of the electrical properties of the nanocapacitors, impedance spectroscopy, dielectric permittivity and ac conductivity were investigated. We observed dynamic magneto‐resistive and magneto‐dielectric effects near the LSMO metal‐insulator and ferromagnetic phase transition temperature.

Author: Sandra Dussan


Department: Physics

Title: Time‐Dependent Non‐Equilibrium Electron Transport

Abstract:

We consider a mesoscopic region coupled by two leads under the influence of external time‐dependent perturbation in which the leads are assume to be non‐ interacting. The tine‐dependence is coupled to source and drain contact. We present a theoretical study of time‐dependent transport using the single‐band tight‐binding model and the non‐equilibrium Keldysh formalism and provide an analysis of the effect of time‐dependent bias on ac tunneling current. We study several limiting cases such as wide‐band limit and relaxation time limit.

Author: Jose R. Alvarez


Department: Physics

Title: FABRICATION OF TRANSITION METAL SILICIDE AND OXIDES NANO‐ AND MICRO S

Abstract:

We report the fabrication of novel micro and nano structures of chromium silicide. The nano‐ rods and tubes have been grown on a n‐type Si wafer. We synthesise this nanostructure s using a cylindrical quartz tube reactor. We maintain the temperature near 1000 oC for 30minutes. We also report the thermo electric, thermal and electrical measurements of CrSi2 and silcon carbide as a funtion of temperature. The characterization of the nano‐ and microtubes included: HRTEM spectrum an mapping, electron diffraction, X‐ray fluorescence spectroscopies. Details of the morphology and composition of the structures will be presented. We also present the thermo electric response of several nanostructures and its therma conductivity

Author: Luis A. Valentin

abstractshumberto/documents/track-2...the oxidation state for cerium is mainly tetravalent (+4),...

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