Effect of interfacial properties on polymer-nanocrystal thermoelectric transport.

The electrical behavior of a conducting-polymer/inorganic-nanowire composite is explained with a model in which carrier transport occurs predominantly through a highly conductive volume of polymer that exists at the polymer-nanowire interface. This result highlights the importance of controlling nanoscale interfaces for thermoelectric materials, and provides a general route for improving carrier transport in organic/inorganic composites.

Water-processable polymer-nanocrystal hybrids for thermoelectrics.

We report the synthesis and thermoelectric characterization of composite nanocrystals composed of a tellurium core functionalized with the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). Solution processed nanocrystal films electronically out perform both PEDOT:PSS and unfunctionalized Te nanorods while retaining a polymeric thermal conductivity, resulting in a room temperature ZT ∼ 0.1. This combination of electronic and thermal transport indicates the potential for tailored transport in nanoscale organic/inorganic heterostructures.

Chemical and physical sensing by organic field-effect transistors and related devices.

Organic semiconductor films are susceptible to noncovalent interactions, trapping and doping, photoexcitation, and dimensional deformation. While these effects can be detrimental to the performance of conventional circuits, they can be harnessed, especially in field-effect architectures, to detect chemical and physical stimuli. This Review summarizes recent advances in the use of organic electronic materials for the detection of environmental chemicals, pressure, and light. The material features that are responsible for the transduction of the input signals to electronic information are discussed in detail.

Solution-deposited sodium beta-alumina gate dielectrics for low-voltage and transparent field-effect transistors.

Sodium beta-alumina (SBA) has high two-dimensional conductivity, owing to mobile sodium ions in lattice planes, between which are insulating AlO(x) layers. SBA can provide high capacitance perpendicular to the planes, while causing negligible leakage current owing to the lack of electron carriers and limited mobility of sodium ions through the aluminium oxide layers. Here, we describe sol-gel-beta-alumina films as transistor gate dielectrics with solution-deposited zinc-oxide-based semiconductors and indium tin oxide (ITO) gate electrodes. The transistors operate in air with a few volts input. The highest electron mobility, 28.0 cm2 V(-1) s(-1), was from zinc tin oxide (ZTO), with an on/off ratio of 2 x 10(4). ZTO over a lower-temperature, amorphous dielectric, had a mobility of 10 cm2 V(-1) s(-1). We also used silicon wafer and flexible polyimide-aluminium foil substrates for solution-processed n-type oxide and organic transistors. Using poly(3,4-ethylenedioxythiophene) poly(styrenesulphonate) conducting polymer electrodes, we prepared an all-solution-processed, low-voltage transparent oxide transistor on an ITO glass substrate.

Improved morphology and performance from surface treatments of naphthalenetetracarboxylic diimide bottom contact field-effect transistors.

We report bottom contact organic field-effect transistors (OFETs) with various surface treatments based on n-channel materials, specifically, 1,4,5,8-naphthalene-teracarboxylic diimides (NTCDIs) with three different fluorinated N-substituents, systematically studied with a particular emphasis on the interplay between the morphology of the organic semiconductor films and the electrical device properties. The morphological origins of the improvements were directly and dramatically visualized at the semiconductor-contact interface. As a result of a series of treatments, a large range of performances of bottom contact side-chain-fluorinated NTCDI OFETs (mobility from 1 x 10(-6) to 8 x 10(-2) cm(2)/(V s), on/off ratio from 1 x 10(2) to 1 x 10(5)) were obtained. The surface treatments enabled systems that had shown essentially no OFET activity without electrode modification activity to perform nearly as well as top contact devices made from the same materials. In addition, for the fresh bottom contact NTCDI device, the effect of gate bias stress on the tens-of-minutes time scale, during which the threshold voltage (V(t)) shifted and relaxed with similar time constants, was observed.

Modeling interband transitions in silver nanoparticle-fluoropolymer composites.

The interband transition contributions to the optical properties of silver nanoparticles in fluoropolymer matrices are investigated. For the materials in this study, nanoparticle synthesis within the existing polymer matrix is accomplished using an infusion process that consists of diffusing an organometallic precursor gas into the free volume of the fluoropolymer and decomposing the precursor followed by metal nanoparticle nucleation and growth. The resulting polymer matrix nanocomposite has optical properties that are dominated by the response of the nanoparticles owing to the broadbanded transparency of the fluoropolymer matrix. The optical properties of these composites are compared to Maxwell-Garnett and Mie theory with results indicating that interband transitions excited in the silver nanoparticles affect the optical absorption over a range of frequencies including the surface plasmon resonance. It is shown that calculations of the optical absorption spectrum using published data for the silver dielectric function do not accurately describe the measured material response and that a classical model for bound and free electron behavior can best be used to represent the dielectric function of silver.