Nonlinear Transport in Hybrid Polypyrrole–Gold Nanostructures (original) (raw)
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Charge Transport in Polypyrrole Nanotubes
Journal of Nanoscience and Nanotechnology, 2015
True metallic conductivity in conjugated polymers has been major challenge for the last few years. Heeger and co-workers have reported metallic conductivity in bulk polyaniline film, but the problem of metallic transport in their nanophase still remains unexplored. In the recent past, our group had observed metallic conductivity in single nanotube by studying I-V characteristics using Atomic Force Microscopy. In the present work, Polypyrrole (PPy) nanotubes with variable wall thickness have been synthesized by chemical route. Electrical measurements-current-voltage characteristics as well as variation of resistance over the temperature range from 12 K to 300 K for these nanotubes with variable wall thickness, have also been carried out. The conductivity varies widely from semiconductor to metallic as the wall thickness decreases. Transmission Electron Microscopic study, further, confirms that very aligned and ordered polymer chains are formed due to directional growth in thin walled polypyrrole nanotubes, results in true metallic conductivity with a positive temperature coefficient of resistance over the whole temperature range. To the best of our knowledge, there is no such systematic study reported so far which embraces variation of charge transport characteristics with varying wall thickness of conjugated polymer nanotubes involving both I-V and R-T measurements supplementing each other, which being the main focus of this communication.
Journal of Physics D: Applied Physics, 2014
Electric field activated charge transport is studied in the metal/polymer/metal device structure of electropolymerized polypyrrole down to 10 K with varying carrier density and disorder. Disorder induced nonlinear behaviour is observed in polypyrrole devices grown at room temperature which is correlated to delocalization of states. The slope parameter of currentvoltage characteristics (in log-log scale) increases as the temperature decreases, which indicates the onset of stronger field dependence. The field dependence of mobility becomes dominant as the carrier density decreases. The sharp dip in differential conductance indicates the localization of carriers at low temperatures which reduces the effective number of carriers involved in the transport.
Charge transport processes in polypyrrole nanoscale composites
Synthetic Metals, 1996
Polypyrrole molecular composites were prepared by in situ deposition in poly(ethylene oxide) complexes with copper chloride blended with polystyrene. The electrical conductivity of these materials showed some peculiar features such as anisotropy, sharp change with temperature and nonlinear I-V characteristics which were enhanced at a particular composition or certain deposition condition. These various results have been explained on the basis of phase-segregated morphology and a Poole-Frenkel type of conduction process, and are confirmed by detailed studies of the I-V characteristics.
Isotherms of the imaginary part of the permittivity from 10 −2 to 2 10 6 Hz from liquid nitrogen to room temperature for fresh and thermally aged specimens of conducting polypyrrole reveal a dielectric loss peak, which is affected by the reduction of conducting grains with aging. Charge trapping at the interfaces separating the conductive islands seems invalid. Thermal aging indicates that macroscopic conductivity and short range one have different aging evolution. The first dc conductivity is dominated by the tunneling of the carriers between neighboring grains through the intermediate insulating barriers, though the second ac conductivity is due to a backward-forward movement of the carriers and is controlled by the intrachain transport of them and their hopping between the chains.
Solid State Communications, 2010
Polypyrrole was synthesized by the chemical oxidation method in the presence of phosphoric acid by varying oxidant to monomer molar ratio for the optimization of electrical conductivity. The conductivity in doped polypyrrole reached up to a maximum value of 9.18 S/cm. Granular morphology was observed in chemically synthesized polypyrrole. Neutralization of doped polypyrrole was done with aqueous ammonium hydroxide and three orders of reduced conductivity were obtained in neutral polypyrrole. Doped and undoped samples of polypyrrole were then electrically characterized over a wide temperature range of 10-300 K. The measured electrical conductivity rises with the increase in temperature and shows the semiconducting nature of the material. Strong and weak temperature dependence of conductivity was revealed by undoped and doped polypyrrole samples respectively. An effort has been made to explore the electrical transport in doped and undoped polypyrrole by charge transport models. The experimental data obeys Kivelson's hopping model in temperature range of 60-300 K and fluctuation assisted tunneling was the dominant conduction mechanism below 60 K.
High field conductivity in polypyrrole
Synthetic Metals, 1998
We have measured high electric field conduction properties of polypyrrole films prepared by anodic deposition as a function of temperature. The field dependence is in reasonably good agreement with the model of intergranular tunnelling with Coulomb-like repulsion barriers. The high field results however demonstrate that pure quantum tunnelling probably does not exist at low enough temperatures. The previously observed levelling-off of conductivities as 'temperature T tends to 0' is most likely an artefact produced by the finite magnitude of current flowing in the system. Current filaments remove space charge barriers which otherwise would localize carriers at zero temperature (T= 0). Despite this new observation, we argue that the grain tunnelling model is still a better description than variable range hopping. We show that it is reasonable and consistent within this model to expect grains and interfaces to charge up at low temperatures and to produce energy mismatch which then requires inelastic tunnelling. At very high fields, the current has a Fowler-Nordheim tunnelling characteristic which suggests that the grain barriers are slowly varying near the maximum as one might expect. Dedicated to Professor Dr Josep Castells. height of the barriers separating the grains [2]. The energydependent tunnelling model also leads to the characteristic Mott-type law: exp[ -(To/T)S], s < 1, without the need to introduce the concept of 'variable range hopping' .
Influence of film thickness on charge transport of electrodeposited polypyrrole thin films
2002
We report the investigation of charge transport properties of thin electrodeposited polypyrrole (PPy) films. The charge transport in these films is limited by thermionic injection and an expression for thermionic injection into low mobility materials is used to evaluate the energy barrier between electrodes (tin-oxide, Al and Ni) and PPy. Using the same expression, we estimate the positive charge carrier mobility, demonstrating that its value is higher for thinner films.
Electrochemical evaluation of charge-transport rates in polypyrrole
The Journal of Physical Chemistry, 1988
The theoretical and experimental aspects of a new current-pulse method for electrochemical investigations of charge-transport rates in thin redox active films on electrode surfaces are described. This method yields an apparent diffusion coefficient, Dapp, which is a quantitative measure of the rate of the charge-transport process in the film. This method is ideally suited for solving the myriad problems associated with electrochemical analyses of electronically conductive polymers (e.g. polypyrrole, polyaniline, etc.). When applied to such polymers, the Dap p obtained is a quantitative measure of the rate of the insulator-to-conductor switching reaction. We have used this method to obtain what we believe are the first reliable electrochemically-generated values of Dapp for the polymer polypyrrole.
dc Conduction in electrochemically synthesized polypyrrole films
1998
DC conductivity measurements were performed by modified four-probe rig on electrochemically synthesized polypyrrole films at a temperature range of -30 • C to 120 • C. Conductivity increased with temperature. The temperature dependence of conductivity was very high for lightly doped polymers, decreasing as the doping level increased. The model used to describe the conduction process was the conduction model originally developed for amorphous silicon by Mott and Davis. When applied to conducting polymers, it assumes that electron transport originates from localized or fixed states within the polymer chain. The charge transfer between the chains takes place by hopping, referred to as phonon-assisted hopping, between two localized states. Plots of DC conductivity versus temperature can be parametrized by Mott's Variable Range Hopping conduction model. The DC conductivity of polypyrrole films doped from light to intermediate levels with p-toluene sulphonic acid were measured in the temperature range of 77K to 300K. The localization length of localized electrons was assumed to be 3Å, which is approximately equal to the length of the pyrrole monomer. Mott parameters of polypyrrole films doped with p-TS were evaluated at 300K and 10K. Results were found to be consistent with the Mott's requirement that αR >> 1 . Theoretical values of α and N (EF ) have been determined at approximately 10 8 cm −1 and 10 19 -10 20 cm −3 eV −1 , respectively. Hence according to Mott parameters determined by the experimental data for the p-TS doped polypyrrole samples, Mott parameters are seen to have a better agreement with those expected from disordered systems, particularly for lightly doped samples, indicating the suitability of Mott's model to these samples. The average hopping distance R decreased from 16Åto 4.4Åwith the increase in the doping level from 0.006 M to 0.03 M at 300K, whereas at 10K, R decreased from 37Å to 10Å over the same dopant range.