Experimental study and analytical modeling of the channel length influence on the electrical characteristics of small-molecule thin-film transistors

Bottom-contact p-type small-molecule copper phthalocyanine (CuPc) thin film transistors (TFTs) with different channel lengths have been fabricated by thermal evaporation. The influence of the channel length on the current-voltage characteristics of the fabricated transistors were investigated in the linear and saturation regimes. The devices exhibit excellent p-type operation characteristics. Results show that devices with smaller channel length (L = 2.5 mu m and 5 mu m) present the best electrical performance, in terms of drain current value, field effect mobility and subthreshold slope. Saturation field-effect mobilities of 1.7 x 10(-3) cm(2) V-1 s(-1) and 1 x 10(-3) cm(2) V-1 s(-1) were obtained for TFTs with channel lengths of L = 2.5 mu m and L = 5 mu m, respectively. Transmission line method was used to study the dependence of the contact resistance with the channel length. Contact resistance becomes dominant with respect to the channel resistance only in the case of short channel devices (L = 2.5 mu m and 5 mu m). It was also found that the field effect mobility is extremely dependent on the channel length dimension. Finally, an analytical model has been developed to reproduce the dependence of the transfer characteristics with the channel length and the obtained data are in good agreement with the experimental results for all fabricated devices.Peer ReviewedPostprint (author's final draft

Growth hormone secretory in healthy aged women and men of Tunisian population

With aging, men and women experience multiple hormonal changes, and in particular the activity of the growth hormone (GH)/insulin-like growth factor-I (IGF-I) axis. This perturbation may be involved inaggravations of numerous abnormalities. In 64 healthy elderly, we determined the concentrations of GH in both sexes and its correlation with thyroid-stimulating hormone (TSH), the descriptive data, BMI,electrolytic assessment and some biochemical parameters. Collected data suggest that there was an age-dependent decrease in GH secretion. For TSH, there was a slight increase. The simple regressionanalysis revealed non-significant direct relation between these two hormones. We also found that BMI values were inversely related to the serum concentrations of these hormones. For the lipid metabolism,the positively correlated relation only exists between GH and total-cholesterol, on one hand, and between GH and LDL-cholesterol, on the other. For the other parameters such as glucose and triglycerides as well as HDL-cholesterol, this relation does not exist. For the BMI, this index shows a positively correlated relation with glucose and triglycerides. The electrolytic assessment shows that inmen, phosphorus was positively related to GH. In women, calcium and sodium were positively related to GH. Aging was found to be associated with decreased morning serum GH levels and slightly increased TSH levels in healthy elderly Tunisian population. Reduction of the GH-IGF-I axis in the elderly has important clinical implications. Indeed, this deficiency in GH could contribute to the decline of various functions associated with normal aging

Antibacterial activity of Thymoquinone, an active principle of Nigella sativa and its potency to prevent bacterial biofilm formation

<p>Abstract</p> <p>Background</p> <p>Thymoquinone is an active principle of <it>Nigella sativa </it>seed known as "Habbah Al-Sauda" in Arabic countries and "Sinouj" in Tunisia. Bacterial biofilms tend to exhibit significant tolerance to antimicrobials drugs during infections.</p> <p>Methods</p> <p>The antibacterial activity of Thymoquinone (TQ) and its biofilm inhibition potencies were investigated on 11 human pathogenic bacteria. The growth and development of the biofilm were assessed using the crystal violet (CV) and the 2, 3-bis [2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide (XTT) reduction assay.</p> <p>Results</p> <p>TQ exhibited a significant bactericidal activity against the majority of the tested bacteria (MICs values ranged from 8 to 32 μg/ml) especially Gram positive cocci (<it>Staphylococcus aureus </it>ATCC 25923 and <it>Staphylococcus epidermidis </it>CIP 106510). Crystal violet assay demonstrated that the minimum biofilm inhibition concentration (BIC50) was reached with 22 and 60 μg/ml for <it>Staphylococcus aureus </it>ATCC 25923 and <it>Staphylococcus epidermidis </it>CIP 106510 respectively. In addition our data revealed that cells oxidative activity was influenced by TQ supplementation. In the same way, TQ prevented cell adhesion to glass slides surface.</p> <p>Conclusion</p> <p>The ability of TQ to prevent biofilm formation warrants further investigation to explore its use as bioactive substances with antibiofilm potential.</p

Lateral electrical transport, optical properties and photocurrent measurements in two-dimensional arrays of silicon nanocrystals embedded in SiO2

In this study we investigate the electronic transport, the optical properties, and photocurrent in two-dimensional arrays of silicon nanocrystals (Si NCs) embedded in silicon dioxide, grown on quartz and having sizes in the range between less than 2 and 20 nm. Electronic transport is determined by the collective effect of Coulomb blockade gaps in the Si NCs. Absorption spectra show the well-known upshift of the energy bandgap with decreasing NC size. Photocurrent follows the absorption spectra confirming that it is composed of photo-generated carriers within the Si NCs. In films containing Si NCs with sizes less than 2 nm, strong quantum confinement and exciton localization are observed, resulting in light emission and absence of photocurrent. Our results show that Si NCs are useful building blocks of photovoltaic devices for use as better absorbers than bulk Si in the visible and ultraviolet spectral range. However, when strong quantum confinement effects come into play, carrier transport is significantly reduced due to strong exciton localization and Coulomb blockade effects, thus leading to limited photocurrent

The effect of Si impurities on the transport properties and the electron-surface phonon interaction in single layer graphene deposited on polar substrates

We investigated theoretically the effect of introducing Si impurities in a single layer graphene (1LG) that had been deposited on a polar substrate on the transport properties of the graphene layer. We consider in our analysis the scattering effects due to the surface optical (SO) phonons located at the interface of the 1LG with various polar substrates such asSiC, hexagonal BN,SiO2andHfO2. Our results demonstrate a reduction of SO phonon-limited (SOPL) mobility, and SOPL conductivity as well as an increase of the SOPL resistivity and of the scattering rate in the presence of Si impurities in the 1LG. Further, we studied the effect of Si impurities on the electron-surface phonon interaction. For our analysis we used the eigenenergies aquired from the tight-binding Hamiltonian in 1LG. Indeed the presence of the Si impurities induces a decrement in the resonant coupling between the electronic sub-levels and the surface vibration modes in monolayer graphene deposited on polar substrates. Finally, we investigated the effect of Si impurities on the Auger scattering process which affects the carriers relaxation. Our results show an enhancement of the Auger scattering rate in the case of the Si-doped 1LG compared to the undoped 1LG. © 2018 Elsevier B.V

Extracting parameters from the current-voltage characteristics of polycrystalline octithiophene thin film field-effect transistors

Organic field-effect transistors (OFETs) in which the active semiconductor is made of polycrystalline octithiophene (8T) were fabricated and characterized. Several methods have been used to extract the parameters of the polycrystalline (8T) transistors as function of gate voltage at room and at low temperatures. These parameters such as the mobility, the threshold voltage, contact resistance and density of traps are extracted from the current-voltage characteristics of OFETs. The first method consists of deriving the drain current as function of gate voltage (transconductance), leading to the so-colled field effect mobility. It appears that the data must be corrected for the substantial source and drain contact resistance. In the second method, the carrier mobility has been corrected for the contact resistance. It is found to increase quasi linearly with gate voltage. Therefore, the contact resistances have been directly extracted from the experimental channel conductance. In the third method, data are interpreted according the multiple thermal trapping and release model using a power law dependence of the mobility with gate voltage together with a constant resistance. Finally, using a model where charge transport is limited by trapping and thermal release at localized states located at grain boundaries, the barrier height at grain boundaries in polycrystalline octhithiophene FETs has been estimated. It is shown that is gate bias dependent

Characterization and modeling of organic thin-film transistors based pi-conjugated small molecule tetraphenyldibenzoperiflanthene: effects of channel length

P-type organic thin film transistors (OTFTs) with different channel lengths have been fabricated and characterized by thermal evaporation using the small tetraphenyldibenzoperiflanthene (DBP) as an active material on Si/SiO2 substrate. The influence of the channel length on the electrical performance of DBP based organic thin film transistors (DBP-TFTs) prepared with bottom gate-bottom contact in the linear and saturation regimes was systematically examined in this work. All devices showed a significant increase in the output and transfer drain current as the channel lengths were decreased in the linear and saturation regimes. We have reported the variation of the electrical parameters such as transconductance (g(m)), field effect mobility (mu(lin) and mu(sat)), contacts and total resistances (R-C and R-T), threshold voltage (V-th), total trap density (N-trap), subthreshold slope (SS), the interface trap density (D-it), turn-on voltage (V-on) and the ratio current (I-on/I-off) by channel length variation which are extracted from the experimental electrical data current-voltage of DBP-TFTs. We found that the field effect mobility is extremely dependent on the channel length dimensions. We also show that for smaller channel length, it results in a good mobility and a good ratio current of the DBP-TFTs with a short channel length (good saturation mobility and current ratio mu(sat.max) = 3 x 10(-2) cm(2) V-1 s(-1),1.6 x 10(4), respectively, for L = 2.5 mu m). The developed model shows a good agreement with the measured data for all values of channel lengths (L).Peer Reviewe

Temperature dependence of the electrical properties of organic thin-film transistors based on tetraphenyldibenzoperiflanthene deposited at different substrate temperatures: Experiment and modeling

A series of inverted-staggered (top contact) p-channel organic thin film transistors based on small molecule tetraphenyldibenzoperiflanthene (DBP) as an active layer have been fabricated by thermal evaporation at different substrate temperatures (300, 330, 360 and 390 K). In this work, these devices have been electrically characterized at different temperatures from 300 K to 370 K in steps of 10 K under vacuum. The influences of the temperature on the electrical performance of DBP-TFTs have been investigated in saturation regime. We found that the p-channel DBP-TFTs deposited at a substrate temperature (Tsub = 390 K) exhibited a better performance under a measurement temperature of 370 K, where µFET, Vth and the ratio current were approximately 8.5 × 10- 4 cm2 V- 1 s- 1, - 0.33 V and 3 × 106, respectively. The field effect mobility of these types of devices is strongly dependent on temperature and follows the simple Arrhenius law. Additionally, the temperature-dependent electrical measurements performed on these devices reveal a thermally-activated behavior for each substrate temperature. This suggests that the charge transport in the examined devices occurs via hopping between localized states. The obtained results demonstrate well that the deposition conditions of organic active layer can improve well the device performance. Finally, an analytical model has been developed to reproduce the dependence of the total resistance and the current-voltage characteristics with the temperature and to understand the charge transport in the DBP-TFTs. The obtained data are in good agreement with the experimental results for all fabricated devices.Peer Reviewe

Experimental study and analytical modeling of the channel length influence on the electrical characteristics of small-molecule thin-film transistors

Bottom-contact p-type small-molecule copper phthalocyanine (CuPc) thin film transistors (TFTs) with different channel lengths have been fabricated by thermal evaporation. The influence of the channel length on the current-voltage characteristics of the fabricated transistors were investigated in the linear and saturation regimes. The devices exhibit excellent p-type operation characteristics. Results show that devices with smaller channel length (L = 2.5 mu m and 5 mu m) present the best electrical performance, in terms of drain current value, field effect mobility and subthreshold slope. Saturation field-effect mobilities of 1.7 x 10(-3) cm(2) V-1 s(-1) and 1 x 10(-3) cm(2) V-1 s(-1) were obtained for TFTs with channel lengths of L = 2.5 mu m and L = 5 mu m, respectively. Transmission line method was used to study the dependence of the contact resistance with the channel length. Contact resistance becomes dominant with respect to the channel resistance only in the case of short channel devices (L = 2.5 mu m and 5 mu m). It was also found that the field effect mobility is extremely dependent on the channel length dimension. Finally, an analytical model has been developed to reproduce the dependence of the transfer characteristics with the channel length and the obtained data are in good agreement with the experimental results for all fabricated devices.Peer Reviewe