Gas Sensing Properties of Single Conducting Polymer Nanowires and the Effect of Temperature

We measured the electronic properties and gas sensing responses of template-grown poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS)-based nanowires. The nanowires have a "striped" structure (gold-PEDOT/PSS-gold), typically 8um long (1um-6um-1um for each section, respectively) and 220 nm in diameter. Single-nanowire devices were contacted by pre-fabricated gold electrodes using dielectrophoretic assembly. A polymer conductivity of 11.5 +/- 0.7 S/cm and a contact resistance of 27.6 +/- 4 kOhm were inferred from measurements of nanowires of varying length and diameter. The nanowire sensors detect a variety of odors, with rapid response and recovery (seconds). The response (R-R0)/R0 varies as a power law with analyte concentration.Comment: 4 figures 8 pages, add 2 reference

Proximity-induced superconductivity in nanowires: Mini-gap state and differential magnetoresistance oscillations

We study proximity-induced superconductivity in gold nanowires as a function of the length of the nanowire, magnetic field, and excitation current. Short nanowires exhibit a sharp superconducting transition, whereas long nanowires show nonzero resistance. At intermediate lengths, however, we observe two sharp transitions; the normal and superconducting regions are separated by what we call the mini-gap phase. Additionally, we detect periodic oscillations in the differential magnetoresistance. We provide a theoretical model for the mini-gap phase as well as the periodic oscillations in terms of the coexistence of proximity-induced superconductivity with a normal region near the center of the wire, created either by temperature or application of a magnetic field.Comment: 11 pages, 4 figure

Dielectrophoretically Assembled Polymer Nanowires for Gas Sensing

We measured the electronic properties and gas sensing response of nanowires containing segments of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) that were synthesized using anodic aluminum oxide (AAO) membranes. The nanowires have a "striped" structure of gold-PEDOT/PSS-gold and are typically 8 um long (1 um-6 um-1 um for each section, respectively) and 220 nm in diameter. Dielectrophoretic assembly was used to position single nanowires on pre-fabricated gold electrodes. A polymer conductivity of 11.5 +/- 0.7 S/cm and a contact resistance of 27.6 +/- 4 kOhm were inferred from resistance measurements of nanowires of varying length and diameter. When used as gas sensors, the wires showed a resistance change of 10.5%, 9%, and 4% at the saturation vapor pressure of acetone, methanol and ethanol, respectively. Sensor response and recovery were rapid (seconds) with excellent reproducibility in time and across devices. "Striped" template-grown nanowires are thus intriguing candidates for use in electronic nose vapor sensing systems.Comment: 18 pages 6 figure

Evidence of local superconductivity in granular Bi nanowires fabricated by electrodeposition

An unusual enhancement of resistance (i.e., superresistivity) below a certain characteristic temperature Tsr was observed in granular Bi nanowires. This superresistive state was found to be dependent on the applied magnetic field (H) as well as the excitation current (I). The suppression of Tsr by magnetic field resembles that of a superconductor. The observed superresistivity appears to be related to the nucleation of local superconductivity inside the granular nanowire without long-range phase coherence. The phenomenon is reminiscent of the Bose-insulator observed previously in ultra thin two-dimensional (2D) superconducting films and 3D percolative superconducting films.Comment: 11 pages, 5 figures. submitted to PR

Thin Film PZT-Based PMUT Arrays for Deterministic Particle Manipulation

Lead zirconate titanate (PZT) based piezoelectric micromachined ultrasonic transducers (PMUTs) for particle manipulation applications were designed, fabricated, characterized and tested. The PMUTs had a diaphragm diameter of 60 lm, a resonant frequency of ∼ 8 MHz and an operational bandwidth of 62.5%. Acoustic pressure output in water was 9.5 kPa at 7.5 mm distance from a PMUT element excited with a unipolar waveform at 5 Vpp. The element consisted of 20 diaphragms connected electrically in parallel. Particle trapping of 4 lm silica beads was shown to be possible with 5 Vpp unipolar excitation. Trapping of multiple beads by a single element and deterministic control of particles via acoustophoresis without the assistance of microfluidic flow were demonstrated. It was found that the particles move towards diaphragm areas of highest pressure, in agreement with literature and simulations. Unique bead patterns were generated at different driving frequencies and were formed at frequencies up to 60 MHz, much higher than the operational bandwidth. Levitation planes were generated above 30 MHz driving frequency

New first order Raman-active modes in few layered transition metal dichalcogenides

Although the main Raman features of semiconducting transition metal dichalcogenides are well known for the monolayer and bulk, there are important differences exhibited by few layered systems which have not been fully addressed. WSe 2 samples were synthesized and ab-initio calculations carried out. We calculated phonon dispersions and Raman-active modes in layered systems: WSe 2 , MoSe 2 , WS 2 and MoS 2 ranging from monolayers to five-layers and the bulk. First, we confirmed that as the number of layers increase, the E9, E0 and E 2g modes shift to lower frequencies, and the A9 1 and A 1g modes shift to higher frequencies. Second, new high frequency first order A9 1 and A 1g modes appear, explaining recently reported experimental data for WSe 2 , MoSe 2 and MoS 2 . Third, splitting of modes around A9 1 and A 1g is found which explains those observed in MoSe 2 . Finally, exterior and interior layers possess different vibrational frequencies. Therefore, it is now possible to precisely identify few-layered STMD. T he field of 2-Dimensional semiconducting transition metal dichalcogenides (STMDs) is growing very fast mainly due to: a) their moderate band gap which can be used for fabricating electronic devices such as field effect transistors (FETs

Basic Research Needs for the Hydrogen Economy. Report of the Basic Energy Sciences Workshop on Hydrogen Production, Storage and Use, May 13-15, 2003

The coupled challenges of a doubling in the world's energy needs by the year 2050 and the increasing demands for ''clean'' energy sources that do not add more carbon dioxide and other pollutants to the environment have resulted in increased attention worldwide to the possibilities of a ''hydrogen economy'' as a long-term solution for a secure energy future