Structural and electrical characterization of hybrid metal-polypyrrole nanowires

Abstract

We present here the synthesis and structural characterization of hybrid Au-polypyrrole-Au and Ptpolypyrrole-Au nanowires together with a study of their electrical properties from room-temperature down to very low temperature. A careful characterization of the metal-polymer interfaces by transmission electron microscopy revealed that the structure and mechanical strength of bottom and upper interfaces are very different. Variable temperature electrical transport measurements were performed on both multiple nanowires -contained within the polycarbonate template -and single nanowires. Our data show that the three-dimensional Mott variable-range-hopping model provides a complete framework for the understanding of transport in PPy nanowires, including non-linear current-voltage characteristics and magnetotransport at low temperatures. † Research associate of the FNRS. ometry of the devices. Despite these experimental efforts, the electrical transport at nanoscale in conjugated polymers is still matter of debate. Until now, very few studies [4,9] focused on the synthesis and electrical characterization of hybrid conjugated polymer-metal nanowires. Moreover, none of them reported on the structural characterization of the metal-polymer interfaces, which could play an important role on the electrical properties of the nanodevices. We present here the synthesis and structural characterization of hybrid metal(Au or Pt)-polypyrrole(PPy)-metal(Au) nanowires together with a study of their electrical properties from roomtemperature down to very low temperature (T ≈ 0.5 K). Metallic segments, few microns long, serving as contacting electrodes are electrochemically synthetized within polycarbonate (PC) templates, before and after the PPy nanowire growth. Interestingly, the resulting metal-PPymetal hybrid nanowires have two morphologically different PPy-metal interfaces (see Fig. 1). In terms of mechanical robustness the PPy-onto-metal interface is smoother and more fragile than the metal-onto-PPy interface. By using Pt instead of Au for the first grown segment, much more robust nanowires have been fabricated. The present all-electrochemical technique allows controlled optimization of the mechanical strength arXiv:1112.4656v1 [cond-mat.mes-hall]

Core level photoemission studies on conducting polypyrrole polymer nanotubes showing switching transitions

“…All spectra could be fitted with three components corresponding to amine-like N (-NH-) atoms, imine-like N (¼N-) atoms, and positively charged aminelike N (-N þ ) atoms, typical of the polypyrrole spectrum. 8,21 For PPY nanotubes, a pronounced shoulder is observed at lower binding energy around 397.7 eV corresponding to (¼N-), which is larger compared to that in AuPPY. For 50 nm diameter nanotubes, the area of the (¼N-) component is found to reduce from 2.4% of the total N 1s spectrum of PPY nanotubes to 1% for AuPPY nanotubes, while for 200 nm diameter it reduces from 4.3% for PPY to 2.1%.…”

“…6(b)). This may be expected in this system, 8 where charge transport is governed by Variable Range Hopping (VRH) model 24 at low temperatures while at higher temperatures thermally activated transport dominates. For the PPY nanotubes, the VRH behaviour is found to prevail up to 28 K and 95 K for 200 nm and 50 nm nanotubes, respectively, while for corresponding diameter AuPPy nanotubes this exists up to 35 K and 199 K, respectively.…”

“…This clearly indicates that the localization length decreases as the diameter of nanotubes decreases, while it increases on incorporation of gold for a given diameter of the nanotube. The localization length is directly related to the amount of disorder in the nanotubes 8 and decreases with the increase of disorder. Thus, the disorder increases as the diameter of nanotubes decreases, while it decreases on incorporation of gold for a given nanotube diameter, which is also obtained from the C1s photoemission data.…”

“…It is therefore crucial to study the electronic structure of these composite nanotubes in order to understand their different transport properties as compared to noncomposite nanotubes, which will thus pave way for incorporating this material in real world devices. Although some brief supplementary X-ray photoemission (XPS) data on gold-PPY multi-segmented nanotubes 8 and on gold nanoparticles reduced by pyrrole 9 can be found in literature, there exists no electronic structure study using XPS for goldpolypyrrole composite nanotubes.…”

“…5 PPY is one of the most widely used active component in various chemical 6 and biological sensors. 7 Electrical transport in PPY nanotubes has been a subject of intensive research, 3,8,11 as it not only provides a model system for testing non-Fermi liquid behaviour in conducting polymers 3,12 but also holds huge potential in device application, 13 owing to its ease of preparation, robust environmental stability, and high electrical conductivity. It has been found that PPY nanotubes show a novel resistance switching transition to a high conducting state from a low conducting state.…”