A model describing the current-voltage characteristics of organic thin-film transistors (TFTs) is presented. The model is based on the trap distribution deduced from temperature-dependent current-voltage measurements on Au/alpha-sexithienyl (α6T)/Au symmetrical structures, which comprises a dominant single shallow trap level located near the valence-band edge. Numerical and approximate analytical derivations of the saturation current density as a function of the gate voltage have been made. From these calculations, the dependence of the threshold voltage on the parameters of the trap level (density and energy) is deduced. It appears that the threshold voltage corresponds to the filling of traps, and is a surface equivalent of the trap-filled limit voltage in bulk space-charge-limited current. The model is in good agreement with experimental data on α6T TFTs. The energy of the trap level compares well with that obtained from the temperature-dependent conductivity. However, the mobility is much lower in the TFT than in a bulk structure. This is tentatively explained by the strong influence of the state of the insulator-semiconductor interface on the characteristics of a TFT.
BackgroundMortality associated with aortic graft infection is considerable. The gold standard for surgical treatment remains explantation of the graft. However, prognostic factors associated with early mortality due to this surgical procedure are not well-known.MethodsRetrospective analysis of patients admitted in our center between January 2006 and October 2011 for aortic graft infection. The primary endpoint was in-hospital mortality. A bivariate analysis of characteristics of patients associated with in-hospital outcome was performed.ResultsTwenty five evaluable patients were studied. All patients were male. Their mean age was 67 ± 8.4 years. Most of them (92%) had severe underlying diseases. An in situ prosthetic graft replacement, mainly using cryopreserved arterial allografts, was performed in all patients, excepted one who underwent extra-anatomic bypass. Causative organisms were identified in 23 patients (92%). The in-hospital mortality rate was 48%. Among pre-operative characteristics, age ≥ 70 years, creatinine ≥ 12 mg/L and C reactive protein ≥ 50 mg/L were significantly associated with in-hospital mortality. Hospital mortality rates increased with the number of risk factor present on ICU admission, and were 0%, 14.3%, 85.7% and 100% for 0, 1, 2 and 3 factors, respectively. The only intra-operative factor associated with prognosis was an associated intestinal procedure due to aorto-enteric fistula. SAPS II, SOFA score and occurrence of medical or surgical complications were postoperative characteristics associated with in-hospital mortality.ConclusionMorbidity and mortality associated with surgical approach of aortic graft infections are considerable. Age and values of creatinine and C Reactive protein on hospital admission appear as the most important determinant of in hospital mortality. They could be taken into account for guiding the surgical strategy.
Electroluminescence (EL) in anthracene single crystals has been known for thirty years.[" In this time, organic lightemitting diodes (OLEDs) have been fabricated with various molecular materials. The major drawbacks of these early organic EL devices were their poor stability and the need for relatively high operating voltages.More recently, considerable interest has focused on OLEDs made of conjugated polymers.[' -71 Light emission of various colors has been demonstrated, with good quantum efficiencies and a reasonable stability. As the generation of light in OLEDs results from the recombination of electrons and holes injected from metallic electrodes, the possibility of injecting both kinds of charges is an important feature in these devices. The use of low work function metals, such as calcium, has been shown to improve considerably the quantum efficiency of conjugated polymer-based OLEDS.[~] Another idea, introduced by Tang and co-workers,['] was the use of multilayer devices, consisting of an emitting layer (EML) sandwiched between a hole transport layer (HTL)[' I Permanent address: Laboratoire de Physique de la Matiire Condensee, [**I We thank Dr. Michel Schott for very fruitful discussions. The work was and an electron transport layer (ETL). Such a concept has recently been applied to conjugated polymer OLEDS,[~I with the realization of a two-layer EL diode made of poly-(phenylene-vinylene) (PPV) and a cyano-substituted polymer. PPV has been shown to be both a good hole-transporting and light-emitting polymer, whereas electron injection is most favored in the second polymer, owing to its higher electron affinity. The quantum efficiency of this two-layer device was claimed to reach 4 %.Conjugated oligomers of well-defined length are actively studied as models of their polymeric counterparts. It has also been shown in this 1aboratory[lo1 and elsewhere[". that thiophene oligomers can advantageously replace polythiophene in organic-based electronic devices such as Schottky diodes and field-effect transistors. The possibility of making OLEDs with oligothiophenes has also been demonstrated 14] but the efficiency of such devices remained poor. However, Uchimaya and co-workers" have reported that the quantum efficiency of sexithiophene base OLEDs could be enhanced by a factor of up to 1000 by using multilayer structures, where a blocking layer made of a shorter thiophene oligomer (quaterthiophene or quinquethiophene) is interposed between the sexithiophene emitting layer and the aluminum cathode.In the present study, we show that the performance of oligothiophene-based OLEDs can be dramatically improved by using two-layer devices made of unsubstituted sexithiophene (6T) and a substituted 6T, with either decyl groups in the side position (2D6T), or with a bulky triisopropylsilyl derivative at the end position (DPSGT), see Figure 1. 6T ClO~Zl Fig. 1. Molecular formulae of sexithiophene (6T), didecyl 6T (2D6T) and bistriisopropylsilyl 6T (DPS6T).We have already shown that 6T/Al diodes exhibit rectifying current-voltag...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.