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Safe storage of grain on Australian farms requires a sealable silo to exclude grain insects and enable effective fumigation to avoid the development of insect resistance to phosphine. A sealable silo must also be fitted with a pressure relief system that allows air to enter the silo rapidly, to avoid damage to the silo fabric, in the event of a sudden temperature drop and subsequent contraction of the internal atmosphere. The most effective pressure relief system allows air into the headspace by a pipe attached to the silo wall, which is connected to an oil bath valve at ground level to facilitate servicing. The oil bath valve prevents grain insects entering and will allow air to bypass when the internal pressure exceeds or falls below 30 – 40 Pascals. The addition of a pipe connecting the headspace pipe to the base of the silo creates a gas recirculation loop. Ambient temperature influences the air within the external pipe and Thermosiphon currents are created, circulating the internal atmosphere. In 2004, a silo manufacturer in Western Australia proposed such a recirculation loop adding an aluminium phosphide (AlP) reaction chamber into the circuit at ground level. A ground-level application system removes the need to climb the silo, making fumigation simpler and safer. Initial experiments in 2005 revealed that the phosphine gas would be extracted from the reaction chamber by Thermosiphon air movement, without building to dangerous concentrations. Seven silo manufacturers across Australia have adopted the Thermosiphon recirculation system linked to a ground level AlP reaction chamber, producing nearly 12,000 transportable silos of 80 – 100t capacity in that period. The development of the recirculation system and effectiveness of Thermosiphon gas distribution is discussed in this paper.

The feasibility of creating top- and bottom-gate pentacene organic field-effect transistors (OTFTs) of comparable performance through the vapor-phase deposition of parylene onto existing pentacene OTFTs on Si/SiO2 is demonstrated. The dependence of the electrical properties on carrier concentration and temperature suggests that, despite differences in interface chemistry and roughness, similar mechanisms are responsible for limiting transport both within the channel and at the metal-organic contacts in both top- and bottom-gate devices.

We describe gated four-probe measurements designed to measure contact resistance in pentacene-based organic thin-film transistors (OTFTs). The devices consisted of metal source and drain electrodes contacting a 300-Å-thick pentacene film thermally deposited on Al2O3 or SiO2 dielectrics with a p-doped Si substrate serving as the gate electrode. Voltage-sensing leads extending into the source-drain channel were used to monitor potentials in the pentacene film while passing current during drain voltage (VD) or gate voltage (VG) sweeps. We investigated the potential profiles as a function of contact metallurgy (Pt, Au, Ag, and Ca), substrate chemistry, VG, and temperature. The contact-corrected linear hole mobilities were as high as 1.75 cm2/V s and the film sheet resistance and specific contact resistance were as low as 600 kΩ/□ and 1.3 kΩ-cm, respectively, at high gate voltages. In the temperature range of 50–200 K, the pentacene OTFTs displayed an activated behavior with activation energies of 15–30 meV. Importantly, the activation energy associated with the contact resistance showed no dependence on contact metal type at high gate voltage. Also, the activation energies of the contact resistance and film resistance were approximately the same. Above approximately 200 K and below 50 K, the mobility was essentially temperature independent. [ABSTRACT FROM AUTHOR]

We report structural and electrical properties in thin films of an n-channel organic semiconductor, N,N′-dipentyl-3,4,9,10-perylene tetracarboxylic dimide (PTCDI–C5). The structure of polycrystalline thin films of PTCDI–C5 was studied using x-ray diffraction and atomic force microscopy. Films order with single crystal-like packing, and the direction of π-π overlap is in the substrate plane. Organic thin film transistors (OTFTs) based on PTCDI–C5 were fabricated on hydrophobic and hydrophilic substrates. OTFTs showed effective mobility as high as 0.1 cm2/V s. Contact resistance of operating OTFTs was studied using resistance versus length plots and a four-probe method for three different contact metals (Au, Ag, Ca). Typical OTFTs had a specific contact resistance of 8×104 Ω cm at high gate voltage. There was no dependence of contact resistance with contact metal. Variable temperature measurements revealed that film resistance in the OTFT was activated in the temperature range 100–300 K, with typical activation energies of 60–80 meV. Contact resistance showed similar activated behavior, implying that the Schottky barrier at the contact is not the limiting resistance for the contact. Film resistance data showed a Meyer–Neldel relationship with characteristic energy EMN=20–25 meV, for various samples. The common TFT instability of threshold voltage shift (TVS) was observed in PTCDI–C5 OTFTs. A model is proposed to explain positive TVS in gate bias stress and oxygen exposure experiments. The model is based on the formation of a metastable complex between PTCDI–C5 and oxygen, which creates a deep acceptor-like trap state. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The structural and electrical characterization of thin films of organic semiconductor molecules consisting of an oligothiophene core capped with electron-withdrawing tricyanovinyl (TCV) groups is reported. The results have shown that the substitution of oligothiophene cores with electron-withdrawing groups is a useful strategy for achieving electron-transporting materials.

The structural and electrical characterization of two new p-channel organic semiconductors from the class of hybrid acene-thiophene materials, 5,5'-bis(2-tetracenyl)-2,2'-bithiophene (1) and 5,5'-bis(2-anthracenyl)-2,2'-bithiophene (2) is reported. The thin-film structures are examined using wide-angle X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXD), and atomic force microscopy (AFM).

Structural and electrical transport properties of a family of pi-stacking soluble organic semiconductors, N,N'-dialkyl-3,4,9,10-perylene tetracarboxylic diimides is reported. Further, the structures of evaporated polycrystalline films are studied using X-ray diffraction and atomic force microscopy.

Complementary organic inverters were fabricated by inkjet patterning of both the metal contacts and the semiconductors. Bottom-gate, bottom-contact organic thin-film transistors with Ta2O5-polymer bilayer dielectrics, inkjet-printed silver electrodes, and inkjet-printed organic semiconductors exhibit hole and electron mobilities as high as ∼10-2 cm2/V s. Complementary inverters based on these transistors operate in ambient and exhibit a gain of -4.4 with supply voltage VDD=+20 V and -3 dB cutoff at 100 kHz with a load of 0.02 pF. The electrical stability of the inverters was evaluated for analog and digital operation, and a noise margin ≥1.1 V at VDD=+15 V was measured with bias-stress effects included. [ABSTRACT FROM AUTHOR]

In this letter we report the use of roughly polished aluminum substrates with spin-coated polymer-smoothing layers for the fabrication of pentacene field-effect transistors. Transistors with spin-coated poly(methylmethacrylate) gate insulator layers were fabricated and showed good performance. On the gate insulator surface, the root-mean-square roughness was found to be 0.18 nm, significantly smaller than the aluminum surface roughness, which is on the scale of tens of nanometers. Field-effect carrier mobilities extracted from the device data reached 0.75 cm2 V-1 s-1; the maximum on/off current ratio was near 5×106. [ABSTRACT FROM AUTHOR]