L. Torsi

Electronic sensing of vapors with organic transistors

We show that organic thin-film transistors have suitable properties for use in gas sensors. Such sensors possess sensitivity and reproducibility in recognizing a range of gaseous analytes. A wealth of opportunities for chemical recognition arise from the variety of mechanisms associated with different semiconductor–analyte interactions, the ability to vary the chemical constitution of the semiconductor end/side groups, and also the nature of the thin-film morphology.

Multi-parameter gas sensors based on organic thin-film-transistors

Abstract In this communication, evidence is provided that an organic thin-film-transistor (OTFT) can be used as a novel gas sensor. When exposed to chemical species at room temperature, four parameters can be measured: the bulk conductivity of the organic thin film, the field-induced conductivity, the transistor threshold voltage and the field effect mobility. Measurements of these parameters may allow for recognition of molecular species.

Intrinsic Transport Properties and Performance Limits of Organic Field-Effect Transistors

The field-effect mobility in thin-film transistors based on α-sexithiophene (α-6T) and related materials displays a temperature dependence that is remarkably nonmonotonic. Above a transition temperature TT (specific to a given material) the transport is thermally activated, whereas below TT there is a very steep enhancement of the mobility. In the activated regime, the results are well described by the theoretical predictions for small polaron motion made by Holstein in 1959. An analysis of the transistor characteristics shows that the hopping transport in these devices is intrinsic. Performance limits for devices based on α-6T and related materials were established; these limits point to the strong possibility that better molecular materials for transistor applications may be designed from first principles.

An analytical model for short‐channel organic thin‐film transistors

An analytical model that describes the operation of α‐hexathienylene (α‐6T) thin‐film‐transistors (TFTs) is presented. The current‐voltage characteristics of TFTs with channel lengths ranging from 1.5 to 25 μm have been calculated after modifying the equations that describe the characteristics of conventional enhancement mode p‐channel metal‐oxide‐semiconductor field‐effect‐transistors. The calculated current‐voltage characteristics are compared with the experimental data. The model takes into account the non‐inversion‐mode operation of α‐6T TFTs as well as short channel effects such as series parasitic resistance, channel length shortening, apparent threshold voltage, and apparent field‐effect mobility. Furthermore, the field‐effect mobility is observed to depend on longitudinal electric fields which are higher than 105 V/cm, and this effect is also included in the model. The highest field‐effect mobility measured is 0.03 cm2/V s. From an analysis of measured data, the carrier mobility of field‐induced p...

Conductivity-type anisotropy in molecular solids

Thin polycrystalline films of perylenetetracarboxylic dianyhydride (PTCDA), an organic molecular solid, exhibits substantial anisotropies in its electronic transport properties. Only electrons transport in the directions along molecular planes, while mainly holes transport in the direction normal to molecular planes. A series of measurements on both field effect transistors with PTCDA active layers and light emitting diodes with PTCDA transport layers documents the anisotropy seen in the electronic transport in thin films of PTCDA.

Organic field-effect bipolar transistors

Organic field‐effect transistors (FETs) which employ two carefully selected active materials can function as n channel, p channel, or both n‐ and p‐channel devices. It is shown that under an appropriate set of bias conditions the channel current in FETs with α‐hexathienylene (α‐6T) and C60 active layers consist of electron and hole components that are injected from the source and drain contacts into the C60 and α‐6T layers, respectively.

NTCDA organic thin-film-transistor as humidity sensor: weaknesses and strengths

Abstract 1,4,5,8-Naphthalene-tetracarboxylic-dianhydride (NTCDA) organic thin-film-transistors employed as humidity sensors exhibit higher performance level compared to NTCDA chemiresitors. In particular, the transistor on-current exhibits higher values and a larger dynamic range as well as a better reversibility, compared to the response of an NTCDA resistor. On the basis of the FT-IR spectra of NTCDA humid and anhydrous thin-films, a model for the NTCDA/H 2 O system is proposed which eventually explains the variation of NTCDA thin-film-transistor parameters, while the device is exposed to changing water vapor atmosphere.

Regioregular polythiophene field-effect transistors employed as chemical sensors

Abstract Soluble alkyl- and alkoxyl-substituted regiochemically defined polyterthiophenes are used as active layers in sensing organic thin films transistors (OTFTs). Such active layers have a polycrystalline morphology and the substituent chains bear different associated dipole moments. Volatile organic compounds carrying moieties that are chemically homologous to the selected polymers’ side chains are used as analytes. Both electrical and quartz crystal microbalance sensor responses are evaluated and a rationale for the sensing mechanisms involving weak polar/polar-type interactions is proposed.

Organic thin film transistors: from active materials to novel applications

Abstract In this paper, a birds eye view of most of the organic materials employed as n-channel and p-channel transistor active layers is given along with the relevant device performances; organic thin film transistors (OTFT) operation regimes are discussed and an interesting perspective application of OTFT as multi-parameter gas sensor is proposed.

Ion-beam sputtered palladium-fluoropolymer nano-composites as active layers for organic vapours sensors

Abstract Ion-beam sputtering deposited palladium-fluoropolymer (Pd-CFx) nano-structured composite films have been investigated as active layers for the detection of organic solvents vapours. The composites sensing properties have been studied and compared to those of homologous Au-CFx films by means of ellipsometric and quartz crystal microbalance (QCM) experiments. Differences have been shown between sensitivity, selectivity and response repeatability of Au-CFx and Pd-CFx sensors exposed to organic solvent vapours. X-ray photoelectron spectroscopy (XPS) analysis has revealed strong similarities between the two materials as to the polymer matrix structure, but higher concentration of metal oxides and fluorides in the case of palladium. The results of the analytical characterisation have been used to discuss the performance level of the sensors.