Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session X24: Conducting Polymers and Devices |
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Sponsoring Units: DPOLY DMP Chair: Pawan Kahol, Missouri State University Room: Colorado Convention Center 201 |
Friday, March 9, 2007 8:00AM - 8:12AM |
X24.00001: Dissipative effects in the electron transport through conducting polymers Natalya Zimbovskaya, Grigory Zimbovskiy Here, we study the effects of stochastic nuclear motions on the electron transport in doped polymer fibers assuming the conducting state of the material. We treat conducting polymers as granular metals and apply the quantum theory of conduction in mesoscopic systems to describe the electron transport between the metalliclike granules. To analyze the effects of nuclear motions we mimic them by the phonon bath, and we include the electron-phonon interactions in consideration. Our results show that the phonon bath plays a crucial part in the intergrain electron transport at moderately low and room temperatures suppressing the original intermediate state for the resonance electron tunneling, and producing new states which support the electron transport. [Preview Abstract] |
Friday, March 9, 2007 8:12AM - 8:24AM |
X24.00002: Tuning the Electrical Conductivity of Polyaniline by Controlling the Molecular Characteristics of the Polymer Acid Template Joung Eun Yoo, Tracy Bucholz, Yueh-Lin Loo We have investigated the electrical conductivity of polyaniline (PANI) that is template synthesized with a polymer acid as a function of the polymer acid molecular characteristics. The polymer acid of choice is poly(2-acrylamino-2-methyl-1-propanesulfonic acid) and it was synthesized by both conventional free-radical polymerization (PAAMPSA) and atom transfer radical polymerization (ATRP); aPAAMPSA. The synthesis of aPAAMPSA is kinetically controlled and thus aPAAMPSA has a narrower molecular weight distribution compared to PAAMPSA. In general, PANI-aPAAMPSA is about twice as conductive as PANI-PAAMPSA of comparable molecular weights. The difference in conductivity is correlated with different crystalline structures observed between PANI-PAAMPSA and PANI-aPAAMPSA. Specifically, the structure of PANI-aPAAMPSA resembles that of PANI doped with AAMPSA, the monomer of PAAMPSA. These results are further corroborated by UV-vis-NIR experiments where the polaron peak becomes broader and is red-shifted with PANI-aPAAMPSA. [Preview Abstract] |
Friday, March 9, 2007 8:24AM - 8:36AM |
X24.00003: Electrical Conductivity Measurements of Nanofibers Electrospun from Polyaniline/Polyethylene Oxide Blends Saima Khan, Aurangzeb Khan, Martin Kordesch Electrically conducting fibers of polyaniline doped with Camphorsulfonic acid PAn.HCSA in the Polyethylene Oxide (PEO) matrix were prepared using the non-mechanical electrospinning technique. The morphology of the fibers was studied using the scanning electron microscope (SEM) and Transmission electron microscope (TEM), showing a uniform thickness along the fiber length. The fibers had a diameter ranging from 800nm to 2$\mu $m. The electrical conductivity of the non-woven fibrous mat and the cast film was measured using the four-point probe method, for different concentrations of Pan.HCSA in the blend. Some possible factors affecting the electrical conductivity of the fibers/films were discussed. [Preview Abstract] |
Friday, March 9, 2007 8:36AM - 8:48AM |
X24.00004: Exciton localization and delocalization in phenyl-cored thiophene dendrimers$^{\ast}$ Muhammet Erkan Kose, Kwiseon Kim, Will J. Mitchell, Nikos Kopidakis, Garry Rumbles, Sean E. Shaheen A group of $\pi $-conjugated dendrimers, which are soluble organic molecules consisting of a core group to which branched arms (dendrons) are attached, were synthesized and characterized$^{1}$. These dendrimers have a phenyl core with 3 or 4 arms, i.e., 3 or 4 thiophene dendrons. It has been shown that these dendrimers present a viable alternative to polymers in organic photovoltaic devices with PCBM as the acceptor$^{2}$. We studied electronic structure of these dendrimers by density functional theory and restricted CI singles methods. Quantum mechanical calculations aimed at predicting the optical properties as well as the spatial location of excitons upon photoexcitation were performed. In particular, correlated electron-hole probability diagrams and transition density plots, to be presented here, reveal the nature of excitonic behavior in the dendrimers. [1] Mitchell, W. J.; Kopidakis, N.; Rumbles, G.; Ginley, D. S.; Shaheen, S. E., \textit{J. Mater. Chem. }\textbf{15}, 4518 (2005). [2] Kopidakis, N.; Mitchell, W. J.; van de Lagemaat, J.; Ginley, D. S.; Rumbles, G.; Shaheen, S. E.; Rance, W. L., \textit{Appl. Phys. Lett. }\textbf{89}, 103524 (2006). *This work was supported by the NREL LDRD program and the Xcel Energy Renewable Development Fund, and done in collaboration with the NREL Chemical and Biosciences Center and NCPV. [Preview Abstract] |
Friday, March 9, 2007 8:48AM - 9:00AM |
X24.00005: Semiconducting molecular crystals: Bulk in-gap states modified by structural and chemical defects S. Haas, C. Krellner, C. Goldmann, K. P. Pernstich, D. J. Gundlach, B. Batlogg Charge transport in organic molecular crystals is strongly influenced by the density of localized in-gap states (traps). Thus, a profound knowledge of the defect states' origin is essential. Temperature-dependent space-charge limited current (TD-SCLC) spectroscopy was used as a powerful tool to quantitatively study the density of states (DOS) in high-quality rubrene and pentacene single crystals. In particular, changes of the DOS due to intentionally induced chemical and structural defects were monitored. For instance, the controlled exposure of pentacene and rubrene to x-ray radiation results in a broad over-all increase of the DOS. Namely, the ionizing radiation induces a variety of both chemical and structural defects. On the other hand, exposure of rubrene to UV-excited oxygen is reflected in a sharp peak in the DOS, whereas in a similar experiment with pentacene oxygen acts as a dopant, and possible defects are metastable on the time-scale of the measurement, thus leaving the extracted DOS virtually unchanged. [Preview Abstract] |
Friday, March 9, 2007 9:00AM - 9:12AM |
X24.00006: Optical Characterization of a Single Cavity in Random Laser Polymer Film Z.Valy Vardeny, Abdullah Tulek Random lasing action with coherent feedback mechanism was previously attributed to inter-particle scattering of light forming close loops. A competing explanation is the formation of natural random cavities in the gain medium. We demonstrate the existence of such random cavities in thin polymer films by optically characterizing some of the lasing key properties such as size, threshold, and azimuthal emission intensity distribution. The optical properties of random cavities are compared with those of a fabricated microdisk having similar size, and the similarities and differences are emphasized. [Preview Abstract] |
Friday, March 9, 2007 9:12AM - 9:24AM |
X24.00007: Unidirectional Emission from Asymmetric Polymer Microcavities Abdullah Tulek, Z.Valy Vardeny Symmetric polymer microcavities that support whispering gallery modes such as microrings and microdisks have been extensively studied due to their ease of fabrication and high quality factors. However an important drawback is their isotropic emission. Two different microcavity configurations; namely a spiral, and a microdisk that contain a linear defect positioned in a specific orientation, have been proposed to overcome this problem. We measured the laser properties of such microcavities with DOO-PPV polymer as gain medium. Using the spiral microcavity we found unidirectional emission with a contrast ratio of about 8 in an angular emission window of $\sim $10$^{0}$. For the `defected' microdisk the observed contrast ratio was $\sim $ 8, and emission window was $\sim $25$^{0}$. Different orientations and the sizes of the defect have been studied thoroughly. [Preview Abstract] |
Friday, March 9, 2007 9:24AM - 9:36AM |
X24.00008: Molecular Spectroscopy Using Slow Surface Plasmon Polaritons Michael Preiner, Ken Shimizu, Nazanin Davani, Jason Fabbri, Nicholas Melosh Surface plasmon polaritons have recently attracted interest for both fundamental science and device applications. In addition to the normal surface plasmon mode, in metal-insulator-metal junctions a slow mode exists that is of particular interest for studying molecular-scale junctions. Accessing the slow mode is of great utility for studying the properties of these junctions, as the field intensity of the slow mode can be thousands of times larger than that of the normal surface mode inside the junction. We have demonstrated the ability to optically couple into the slow modes of molecular junctions using short-period diffraction gratings, and will discuss applications of this technique. [Preview Abstract] |
Friday, March 9, 2007 9:36AM - 9:48AM |
X24.00009: Mechanism for interaction between gases and Phthalocyanine films Amos Sharoni, Corneliu Colesniuc, Jeongwon Park, Forest I. Bohrer, Andrew C. Kummel, William C. Trogler, Ivan K. Schuller Phthalocyanines (Pcs) have been identified as promising candidates for electro-chemical gas sensors. They show potential for chemical selectivity via manipulation of the metal center and substitution of functional groups on the organic ring. However, for a given analyte and Pc, it is not clear which properties define the strength of response. To address this issue, we measured time-dependent current responses, of cobalt and metal free Pc, at constant voltage during exposure to various analyte vapor doses. The current in the device reduces with dosing; the response is linear with concentration and is found to follow first order kinetics. We show that the response is dominated by analyte interactions with the central Pc cavity; coordination strength governs CoPc responses, and hydrogen bonding ability governs H$_{2}$Pc responses. A model for the phthalocyanine electrical response and binding with analytes will be discussed. [Preview Abstract] |
Friday, March 9, 2007 9:48AM - 10:00AM |
X24.00010: The Electronic structure at the copper phthalocyanine to P(VDF-TrFE) copolymer thin films interface Jie Xiao, Carolina Ilie, Peter Dowben Copper phthalocyanine (CuPc) is an organic semiconducting material which has a potential application in organic thin film transistors. We explore the band offsets of CuPc deposited on crystalline polyvinylidene-trifluroethylene P(VDF-TrFE) copolymers through combined photoemission and inverse photoemission studies. Other work indicates that dipole orientation affects the band alignments of adsorbate molecules, so the possibility exists that the band offsets of the adsorbate molecule may be affected by ferroelectric phase transition in the P(VDF-TrFE) copolymer thin film substrate. Alternatively such a change, in the band alignment of CuPc, may be affected by a reversal of dipole orientation in the adjacent P(VDF-TrFE). [Preview Abstract] |
Friday, March 9, 2007 10:00AM - 10:12AM |
X24.00011: Transport properties and non-volatile memory application of self assembled nanoparticle array by microtubules Mei Xue, K.L. Wang, Jing Zhou, Bruce Dunn A method of self-assembly of gold nanoparticles with the diameter of around 1nm is developed by the use of bio species (microtubule) and transport properties of nanoparticle arrays are investigated. Via self-assembly, the attachment sites of gold nanoparticles to the microtubule can be controlled. The density of the gold nanoparticles in our experiments achieved is on the order of 10$^{9 }$cm$^{-2 }$and can be extended to as high as 10$^{13}$ cm$^{-2}$. A transport bi-stability is observed in a sandwich structure of Au/ MT + gold nanoparticle array / P$^{+}$ Si substrate. On the basis of detailed analysis of the temperature and electrical field dependences, a band model incorporating electron-tunneling is suggested to explain the observed bi-stability and other transport characteristics. The retention time is also measured to be larger than 10$^{5}$s. The operation and endurance of this memory device are confirmed. With its simple structure and the compatible fabrication process with conventional MOS, this MT/Au nanoparticle array holds a great potential for memory applications. [Preview Abstract] |
Friday, March 9, 2007 10:12AM - 10:24AM |
X24.00012: ABSTRACT WITHDRAWN |
Friday, March 9, 2007 10:24AM - 10:36AM |
X24.00013: Nondestructive Memory Elements Based on Polymeric Langmuir-Blodgett Thin Films T.J. Reece, S. Ducharme Ferroelectric field effect transistors (FeFETs) have attracted much attention recently because of their low power consumption and fast nondestructive readout. Among the ferroelectric thin films used in FET devices; the ferroelectric copolymer of polyvinylidene fluoride, PVDF (C$_{2}$H$_{2}$F$_{2})$, with trifluoroethylene, TrFE (C$_{2}$HF$_{3})$, has distinct advantages, including low dielectric constant, low processing temperature, low cost and compatibility with organic semiconductors. By employing the Langmuir-Blodgett technique, we are able to deposit films as thin as 1.8 nm. We discuss the characterization, modeling and fabrication of metal-ferroelectric-insulator-semiconductor (MFIS) structures incorporating these films. [Preview Abstract] |
Friday, March 9, 2007 10:36AM - 10:48AM |
X24.00014: Salt-induced phase transitions in charged polymerized membranes Angelo Cacciuto, Erik Luijten We study the behavior of charged, fully polymerized membranes in the presence of multivalent salt by means of molecular dynamics simulations. At moderate salt concentrations the interplay between the electrostatic interactions and the in-plane elasticity of the membrane gives rise to a novel multi-step folding transition pathway that is qualitatively different from the folding induced by generic attractive interactions at low temperatures. Furthermore, the number of folds in the membrane is greatly reduced when the salt concentration exceeds a critical value, indicating a reentrant transition. Both observations can be viewed as the two-dimensional counterpart of the behavior displayed by flexible linear polyelectrolytes in multivalent salt solutions [1]. \newline \newline [1] P.-Y. Hsiao and E. Luijten, Phys. Rev. Lett. 97, 148301 (2006). [Preview Abstract] |
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