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We investigated surface treatment effects of hexamethyldisilazane (HMDS), poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) and l -cysteine on gold source/drain electrodes in bottom-contact structured pentacene thin-film transistors (TFTs). The treatment methods include spin coating and immersing. We have also researched on two-step treatment based on the combination of each treatment methods. The highest device performance was achieved by treating gold S/D electrodes with l -cysteine first and PEDOT:PSS afterwards, showing field effect mobility up to 0.35 cm 2 /V·s. l -cysteine can reduce the contact resistance between metal and semiconductor layer, and PEDOT:PSS acted as a hole transporting layer while HMDS decreased the surface energy, which enlarged the grain size of pentacene on it. [ABSTRACT FROM AUTHOR]

We report on in situ performance evaluations as a function of layer thickness and substrate temperature for bottom-gate, bottom-gold contact epindolidione organic thin-film transistors on various gate dielectrics. Experiments were carried out under ultra-high vacuum conditions, enabling quasi-simultaneous electrical and surface analysis. Auger electron spectroscopy and thermal desorption spectroscopy (TDS) were applied to characterize the quality of the substrate surface and the thermal stability of the organic films. Ex situ atomic force microscopy (AFM) was used to gain additional information on the layer formation and surface morphology of the hydrogen-bonded organic pigment. The examined gate dielectrics included SiO 2 , in its untreated and sputtered forms, as well as the spin-coated organic capping layers poly(vinyl-cinnamate) (PVCi) and poly((±) endo , exo -bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic acid, diphenylester) (PNDPE, from the class of polynorbornenes). TDS and AFM revealed Volmer-Weber island growth dominated film formation with no evidence of a subjacent wetting layer. This growth mode is responsible for the comparably high coverage required for transistor behavior at 90–95% of a monolayer composed of standing molecules. Surface sputtering and an increased sample temperature during epindolidione deposition augmented the surface diffusion of adsorbing molecules and therefore led to a lower number of better-ordered islands. Consequently, while the onset of charge transport was delayed, higher saturation mobility was obtained. The highest, bottom-contact configuration, mobilities of approximately 2.5 × 10 −3 cm 2 /Vs were found for high coverages (50 nm) on sputtered samples. The coverage dependence of the mobility showed very different characteristics for the different gate dielectrics, while the change of the threshold voltage with coverage was approximately the same for all systems. An apparent decrease of the mobility with increasing coverage on the less polar PNDPE was attributed to a change in molecular orientation from upright standing in the thin-film phase to tilted in the bulk phase. From temperature-dependent mobility measurements we calculated activation barriers for the charge transport between 110 meV and 160 meV, depending on the dielectric configuration. [ABSTRACT FROM AUTHOR]

We fabricated the bottom-contacted ZnO/Pt Schottky diode and investigated the dependence of its photocurrent on the wavelength of illuminated ultraviolet (UV) light source. The bottom-contacted Schottky diode was devised by growing (000 l ) ZnO on (111) Pt, and the fabricated device showed a strong dependence on the UV wavelength for its photo-response characteristics. When longer-wavelength-UV ( e.g. , UV-A) was illuminated on the device, the photo-current was increased by a factor of 200, compared to that under illumination of shorter-wavelength-UV ( e.g. , UV-C). The behavior is attributed to the wavelength-dependent UV penetration depth for ZnO. [ABSTRACT FROM AUTHOR]

Aluminum doped HfO2 (HfAlO) prepared by atomic layer deposition is investigated as gate dielectric for low-voltage organic thin-film transistors (OTFTs). The HfAlO film exhibits a low leakage current density of \(4.92 \times 10^{-8}\) A/cm \(^{2}\) at −3 MV/cm, which is \(\sim 70\) % smaller than its HfO2 counterpart. In addition, copper phthalocyanine (CuPc) OTFT with HfAlO dielectric has an average mobility \(\mu ~(2.58\pm 0.32\times 10^{-3}\) cm \(^{2}\) /Vs) increased by 58%, sub-threshold slope SS (0.9 ± 0.11 V/decade) decreased by 11%, and ON/OFF ratio \(I_{\mathrm{{\scriptstyle ON}}}/I_{\mathrm{{\scriptstyle OFF}}}\) (3.1 ± 1.3 \(\times \) \( 10^{3}\) ) increased by 86% as compared with those with HfO2 as gate dielectric ( \(\mu =1.63\pm 0.27\times 10^{-3}\) cm \(^{2}\) /Vs; \({\rm SS}=1.01\) ±0.1 V/decade; \(I_{\mathrm{{\scriptstyle ON}}}/I_{\mathrm{{\scriptstyle OFF}}}=1.7\pm 0.77\times 10^{3}\) ). All these could be ascribed to the inclusion of Al in the HfO2 film, which increases the conduction band offset and the bandgap and improves the dielectric and interface quality. The temperature effect on the performance of OTFTs is also investigated. [ABSTRACT FROM AUTHOR]

Abstract: Low-voltage, n-type organic field effect transistors (OFETs) with simultaneously modified bottom-contact (BC) electrodes and dielectric were compared to their top-contact (TC) counterparts. The devices modified with 6-phenoxyhexylphosphonic acid (Ph6PA) self-assembled monolayer (SAM) showed similar performance, morphology, and contact resistance. Electron mobility of C60 devices were 0.212 and 0.320cm2 V−1 s−1 and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) devices were 0.04 and 0.06cm2 V−1 s−1 for TC and BC devices, respectively. Low contact resistance between 11 and 45kΩcm was found regardless of device architecture or n-type semiconductor used. This work shows it is possible to fabricate solution processable low-voltage bottom-contact devices with performance that is similar or better than their top-contact counterparts without the addition of complex and time-consuming processing steps. [Copyright &y& Elsevier]

Abstract: The effects of sea-state induced vessel motion on the physical performance of the Northeast Fisheries Science Center Yankee 36 survey bottom trawl, rigged with a roller footrope, were investigated. The trawl was instrumented with an acoustic net mensuration system to measure horizontal spread, a head rope mounted acoustic current meter to measure flow at the trawl-mouth, and five sled-mounted inclinometer sensors attached to the wings, quarters and center of the footrope to measure bottom-contact. A vessel motion sensor fixed at the center of the vessel measured roll and pitch. Trawl performance was observed over wave heights of 1–4m. Vessel motion caused by waves at the sea-surface had a strong effect on trawl motion on the seabed. Vessel heading in relation to wave direction is an influential factor dictating the specific vessel motions occurring in a given sea-state. Of the measured components of vessel motion, pitch had the greatest affect on trawl performance. The speed of vertical stern motion, derived from pitch angles, rather than the magnitude of vertical stern displacement, was the most influential factor controlling variations observed in the footrope bottom-contact data and forward trawl velocity component measured by the current meter. Vertical stern motion speeds of 48cm/s and greater caused the survey trawl to surge forward and exacerbated the loss of footrope bottom-contact. Since sea-surface conditions had a strong influence on net behavior, it may alter the catch efficiency of a survey trawl, we recommend fish behavior in response to trawl motion be investigated further. [Copyright &y& Elsevier]

The electrical contact resistance at metal-graphene interfaces can significantly degrade the properties of graphene devices and is currently hindering the full exploitation of graphene's potential. Therefore, the influence of environmental factors, such as humidity, on the metal-graphene contact resistance is of interest for all graphene devices that operate without hermetic packaging. We experimentally studied the influence of humidity on bottom-contacted chemical-vapor-deposited (CVD) graphene-gold contacts, by extracting the contact resistance from transmission line model (TLM) test structures. Our results indicate that the contact resistance is not significantly affected by changes in relative humidity (RH). This behavior is in contrast to the measured humidity sensitivity [Formula: see text] of graphene's sheet resistance. In addition, we employ density functional theory (DFT) simulations to support our experimental observations. Our DFT simulation results demonstrate that the electronic structure of the graphene sheet on top of silica is much more sensitive to adsorbed water molecules than the charge density at the interface between gold and graphene. Thus, we predict no degradation of device performance by alterations in contact resistance when such contacts are exposed to humidity. This knowledge underlines that bottom-contacting of graphene is a viable approach for a variety of graphene devices and the back end of the line integration on top of conventional integrated circuits.