Apparent Mobility Research Articles

Translocation of 125I, 75Se and 36Cl to Wheat edible parts following wet foliar contamination under field conditions

Apart from radiocaesium and radiostrontium, there have been few studies on the foliar transfer of radionuclides in plants. Consequently, specific translocation factor (ftr) values for 129I, 79Se and 36Cl are still missing from the IAEA reference databases. The translocation of short – lived isotopes, 125I and 75Se, and of 36Cl to wheat grain were measured under field conditions following acute and chronic wet foliar contamination at various plant growth stages in the absence of leaching caused by rain. The translocation factors ranged from 0.02% to 1.1% for 125I (a value similar to Sr), from 0.1% to 16.5% for 75Se, and from 1% to 14.9% for 36Cl. Both 36Cl and 75Se were as mobile as Cs. The phenomenological analysis showed that each element displayed a specific behavior. Iodide showed the lowest apparent mobility because of its preferential fixation in or on the leaves and a significant amount probably volatilized. Selenite internal transfer was significant and possibly utilized the sulphur metabolic pathway. However bio - methylation of selenite may have led to increased volatilization. Chloride was very mobile and quickly diffused throughout the plant. In addition, the analysis underlined the importance of plant growth responses to annual variations in weather conditions that can affect open field experiments because plant growth stage played a major role in ftr values dispersion. The chronic contamination results suggested that a series of acute contamination events had an additive effect on translocated elements. The highest translocation value obtained for an acute contamination event was shown to be a good conservative assessment of chronic contamination if data on chronic contamination translocation are lacking. The absence of rain leaching during the experiment meant that this investigation avoided potential radionuclide transfer by the roots, which also meant that radionuclide retention on or in the leaves was maximized. This study was therefore able to obtain accurate translocation factors, which are probably among the highest that could be recorded.

Space Charge Trapping and Conduction in Low-Density Polyethylene/Silica Nanocomposite

The high field conduction and space charge distribution were investigated in low-density polyethylene (LDPE) and LDPE/silica nanocomposites filled with various concentrations of nanosilica. The results indicate that nanosilica could effectively suppress space charge accumulation at nanofiller concentrations from 0.1 to 5.0 wt %. However, the conduction current at a high field significantly increases at low concentrations from 0.1 to 0.5 wt % and remarkably reduces at high concentrations from 0.5 to 5.0 wt %. It is shown that the trap depth corresponding to the time from 2 to 3600 s significantly decreases at low nanofiller concentrations from 0.1 to 0.5 wt %. However, the depth of deep traps corresponding to the time from 100 to 3600 s increases with the increase in nanofiller concentration from 0.5 to 5.0 wt %. Moreover, the depth of shallow traps corresponding to the time from 2 to 100 s increases at concentrations from 0.5 to 2.0 wt %, and then it decreases at concentrations from 2.0 to 5.0 wt %. In addition, the apparent mobility varies with the modification of trap depth caused by the introduction of nanofiller. The threshold field EΩ–t for remarkable charge injection and Et–c proportional to the total trap density H are significantly lower in the nanocomposite with a low nanosilica concentration, i.e., 0.1 and 0.5 wt %, while both of them increase at concentrations from 0.5 to 5.0 wt %. It is considered that the impurity effect is greater than the nanofiller effect at a low nanofiller concentration. The deep trap is speculated as the chemical trap in the interface of the nanofiller bonding strongly with the polymer chain, while the shallow trap may be related to the chemical trap in the weakly bonded interface. It is clear that the space charge behavior and conduction are significantly affected by modification of the trap depth and density distribution owing to the introduction of nanofiller.

Ligand Mobility Modulates Immunological Synapse Formation and T Cell Activation

T cell receptor (TCR) engagement induces clustering and recruitment to the plasma membrane of many signaling molecules, including the protein tyrosine kinase zeta-chain associated protein of 70 kDa (ZAP70) and the adaptor SH2 domain-containing leukocyte protein of 76 kDa (SLP76). This molecular rearrangement results in formation of the immunological synapse (IS), a dynamic protein array that modulates T cell activation. The current study investigates the effects of apparent long-range ligand mobility on T cell signaling activity and IS formation. We formed stimulatory lipid bilayers on glass surfaces from binary lipid mixtures with varied composition, and characterized these surfaces with respect to diffusion coefficient and fluid connectivity. Stimulatory ligands coupled to these surfaces with similar density and orientation showed differences in their ability to activate T cells. On less mobile membranes, central supramolecular activation cluster (cSMAC) formation was delayed and the overall accumulation of CD3ζ at the IS was reduced. Analysis of signaling microcluster (MC) dynamics showed that ZAP70 MCs exhibited faster track velocity and longer trajectories as a function of increased ligand mobility, whereas movement of SLP76 MCs was relatively insensitive to this parameter. Actin retrograde flow was observed on all surfaces, but cell spreading and subsequent cytoskeletal contraction were more pronounced on mobile membranes. Finally, increased tyrosine phosphorylation and persistent elevation of intracellular Ca2+ were observed in cells stimulated on fluid membranes. These results point to ligand mobility as an important parameter in modulating T cell responses.

Orientational control of pentacene crystals on SiO2 by graphoepitaxy to improve lateral carrier transport

We controlled the in-plane orientation of pentacene grains by graphoepitaxy using patterned amorphous-SiO2/Si substrates on which periodic grooves with slope edges had been formed. Pentacene crystals exhibited a clear tendency to align their b-axes perpendicular to the groove edges. Organic thin-film transistors were fabricated on the patterned and flat substrates and their transistor characteristics were compared. Although the patterned substrates increased the apparent mobility by only 10–20%, the number of grain boundaries with high potential barriers to carrier transport was reduced to half of that on flat substrates. This improvement is expected to enhance the response speed of pentacene organic thin-film transistors and suppress the sensitivity of their characteristics to the operating temperature.

Correlation between interdomain carrier hopping and apparent mobility in polycrystalline organic transistors as investigated by electron spin resonance

Microscopic charge dynamics inside microcrystal domains and across domain boundaries in polycrystalline organic thin-film transistors (OTFTs) were resolved by angle- and temperature-dependent field-induced electron spin resonance (FI-ESR) spectroscopy. We utilized small-molecule and polymer-based polycrystalline OTFTs, both of which are composed of planar microdomains oriented uniaxially on the substrates. Two types of motional narrowing effect are observed at magnetic fields perpendicular and parallel to the substrate: In the former, we observed the motional narrowing effect due to intradomain transport, while in the latter, we observed another motional narrowing effect due to the carrier hopping across the domain boundaries, which averaged out the variation in $g$ factors between respective microdomains. The analyses revealed that the activation energies for the intradomain transport are between 5 and 21 meV, while those for the interdomain carrier hopping are between 45 and 90 meV. The latter ones coincide with those for the apparent mobility for the respective OTFTs. These results demonstrate that the charge transport is limited by the domain boundaries, which form rate-determining barrier potential both in small-molecule and polymer-based polycrystalline OTFTs.

Effect of hydrophobicity of humic substances on electro-ultrafiltration

One of the critical issues in the application of membrane filtration to drinking water treatment is fouling by natural organic matter (NOM). In order to better understand fouling, Aldrich humic substances (AHSs), a surrogate NOM, were fractionated into hydrophilic fraction (HPIF) and hydrophobic fraction (HPOF) using DAX-8 resin and then fed into an electro-ultrafiltration (EUF) system. The fractionation performance was validated by contact angle measurement. Results showed that the HPIF deposited membrane had a lower contact angle than the HPOF deposited one. The EUF cell was operated in a constant pressure mode for 5 h with and without electric voltage. It was observed that in the absence of an electric field, HPIF caused more severe fouling than HPOF. After applying the electrical voltage, the flux decline decreased due to electrokinetic interactions. In addition, HPOF had a lower flux decline and higher total permeate volume than HPIF, indicating a higher electrophoretic mobility of HPOF. Due to the relatively low apparent electrophoretic mobility (AEM) of HPIF, the flux decline was the highest after applying electricity. Furthermore, the removal efficiency of total organic carbon (TOC) increased by more than 10%, 30% and 13% for the un-fractionated, HPOF, and HIPF, respectively, at 2985 V/m.

Molecular doping effect in bottom-gate, bottom-contact pentacene thin-film transistors

A bottom-gate, bottom-contact (BGBC) organic thin-film transistor (OTFT) with carrier-doped regions over source-drain electrodes was investigated. Device simulation with our originally developed device simulator demonstrates that heavily doped layers (p+ layers) on top of the source-drain contact region can compensate the deficiency of charge carriers at the source-channel interface during transistor operation, leading to the increase of the drain current and the apparent field-effect mobility. The phenomena expected with the device simulation were experimentally confirmed in typical BGBC pentacene thin-film transistors. The 5-nm-thick p+ layers, located 10 nm (or 20 nm) over the source-drain electrodes, were prepared by coevaporation of pentacene and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane as an acceptor dopant. Since the molecular doping in this study can increase the drain current without positive shift of threshold voltage, p+ layers were formed precisely on top of the source-drain regions. This study shows that common inferior characteristics of bottom-contact OTFT devices mainly derive from the supply shortage of charge carriers to the channel region. The importance of reliable molecular doping techniques or heavily doped semiconductor materials for improving OTFT device performance is clearly suggested.

Biased reptation model with electroosmosis for DNA electrophoresis in microchannels with a sub-micron pillar array

A novel biased reptation model with electroosmosis (BRE) is proposed for a long-chain DNA electrophoresis separation mechanism in microchannels with a sub-micron pillar array. The BRE model incorporates effective electroosmosis into the classical biased reptation model (BRM). Initial investigation of the BRM with additional electroosmosis flow was conducted. In order to validate the proposed BRE model, the apparent electrophoretic mobilities of different sizes of long-chain DNA, T4 DNA and lambda DNA at different electric fields were measured in a microfabricated electrophoresis chip with an embedded sub-micron pillar array. The current-monitoring method was used to measure the electroosmotic mobility in the microfabricated electrophoresis chip. The proposed BRE model shows much better agreement with the experimental results compared to the classical BRM and the semi-empirical results based on the biased reptation with fluctuation (BRF). The average standard error between our proposed BRE model and experimental data is 8.13% without any fitting parameters, while the errors are 343.01% for the BRM and 17.54% for the BRF with one fitting parameter, respectively.

Chemical Fractionation of Trace Metals in Sewage Water – Irrigated Soils

The bioavailability of trace metals, their biological uptake and ecotoxiccological effect on soil biota can be better understood in terms of their chemical fractionation. The present study examined the mobility and availability of Cd, Cu, Ni, Pb and Zn in sewage water – irrigated soils using sequential extraction technique as a basis for predicting metal uptake by plants. The residual fraction was the most abundant pool for all the five metals examined. A significant amount (2.7 – 70.2%) of all the five metals was also present in the potentially available fraction: - nonresidual fraction. The result further indicated that the contamination of Cd and Ni in these soils was not as severe as Pb, Cu and Zn. Assuming that mobility and bioavailability of these metals are related to their liability and geochemical forms, and that they decrease in the order of extraction sequence. The apparent mobility and potential bioavailability for these five metals in the soils were: - Pb> Zn> Cu> Ni> Cd.

Evaluation of affinity interaction between drugs and platelet by open tubular capillary electrochromatography

An open tubular capillary electrochromatography (CEC) method was developed for the evaluation of affinity interaction between drugs and platelet. The platelet was attached onto the inner surface of the capillary by physical adsorption, while the coated length was controlled by varying the injection time of platelet suspension. According to the magnitude of the apparent mobility of the analytes and the coated length of platelet, as well as the chromatographic distribution theory of CEC, the equation for calculating of binding constant was deduced. By using the developed method, the binding constants of the anti-platelet aggregation drug aspirin and the negative control pazufloxacin were determined. The results indicated the strong interaction between aspirin and platelet with the binding constant of 0.579 g^-1 L, while the pazufloxacin and platelet showed weak interaction with the binding constant of 0.249 g^-1 L. In the end, affinity extraction has been used for contrast. It can be concluded that the developed method can be used for the determination of affinity interaction of drug with platelet as well as other living cell that can be coated onto the inner surface of capillary.

Transport properties of long straight nano-channels in electrolyte solutions: A systematic approach

The principle of local thermodynamic equilibrium is systematically employed for obtaining various transport properties of long straight nano-channels. The concept of virtual solution is used to describe situations of non-negligible overlap of diffuse parts of electric double layers (EDLs) in nano-channels. Generic expressions for a variety of transport properties of long straight nano-channels are obtained in terms of quasi-equilibrium distribution coefficients of ions and functionals of quasi-equilibrium distribution of electrostatic potential. Further, the Poisson-Boltzmann approach is used to specify these expressions for long straight slit-like nano-channels. In the approximation of non-overlapped diffuse parts of double electric layers in nano-channels, simple analytical expressions are obtained for the apparent electrophoretic mobilities of (trace) analytes of arbitrary charge as well as for the salt reflection coefficient (osmotic pressure), salt diffusion permeability and electro-viscosity (electrokinetic energy conversion). The approximate solutions are compared with the results of rigorous solution of non-linearized Poisson-Boltzmann equation, and the accuracy of approximation is shown to be typically excellent when the nano-channel half-height exceeds ca.3 Debye screening lengths. Due to non-negligible electrostatic adsorption of ions by nano-channels, the apparent electrophoretic mobilities of counter-ionic analytes in nano-channels are smaller than in micro-channels whereas those of co-ionic analytes are larger. This dependence on the charge is useful for the separation of analytes of close electrophoretic mobilities. The osmotic pressure is shown to be positive, negative or pass through maxima as a function of applied salt-concentration difference within a fairly narrow range of ratios of nano-channel height to the Debye screening length. The diffusion permeability of charged nano-channels to single salts is demonstrated (for the first time) to be typically larger than that of neutral nano-channels of the same dimensions due to electrical facilitation of salt diffusion.

Assessment of the Feasibility of the Use of Conductive Polymers in the Fabrication of Ion Mobility Spectrometers

The development of an ion mobility spectrometer with an injection molded plastic drift tube made from carbon-loaded nylon and the cyclo-olefinpolymer Zeonex is described. Thermogravimetric assessment combined with headspace analysis by ion mobility spectrometry and gas chromatography-mass spectrometry indicated that Zeonex encapsulated carbon-loaded nylon could be used to fabricate a snap-together injection molded stacked ring drift tube, 4.25 cm long that could be substituted for a conventional wire-wound heated ceramic drift tube of the same length into a high temperature ion mobility spectrometer. Temperature stability experiments indicated that such a combination of polymers produced stable water-based reactant ion peaks [(H(2)O)(n)H](+) up to a temperature of approximately 50 °C. Above this temperature, ammonia appeared to outgas, resulting in the production of [(H(2)O)(n)(NH(4))(m)H](+) type species before, at higher temperatures, the release of oligomeric entities suppressed resolved ion responses. Surface charging effects were also observed, and over a period of continuous operation of 4 h, these caused suppression of the signal intensity (1.11-0.954 V) and an apparent mobility shift in the observed responses (K(0) = 1.86-1.90 cm(2) V(-1) s(-1)). Substituting nylon, a polymer with a significantly lower surface resistivity, for the Zeonex demonstrated how surface charging phenomena could be managed though control of surface resistivity in future polymer formulations. The device was challenged successfully with test atmospheres of hexan-1-ol (K(0) = 1.66 cm(2) V(-1) s(-1) (monomer) and 1.32 cm(2) V(-1) s(-1)(dimer)) and dimethylmethyl phosphonate (K(0) = 1.70 cm(2) V(-1) s(-1) (monomer) and 1.44 cm(2) V(-1) s(-1) (dimer)). The potential advantages of developing polymeric systems using more advanced polymer formulations are discussed.

Effects of hole and electron trapping on organic field-effect transistor transfer characteristic

Routine organic field-effect transistor measurements are performed at negative and positive gate voltages leading to the occurrence of both hole and electron trapping. Despite this fact, the big majority of studies have focused either on hole trapping or on electron trapping but not on both at the same time. This paper presents the influences of trapped electron concentration n trap and trapped hole concentration p trap on the transfer characteristic (TC) features: onset voltage, hysteresis and transconductance, i.e. apparent mobility. Some effects are common to both charge types: (1) hysteresis is due to a combination of lower detrapping rate than sweep rate for n trap and p trap , (2) the transconductance is decreased by the super-linear V G dependence of p trap and by n trap detrapping. One effect is opposite to both charge types: p trap ( n trap ) shifts the onset voltage towards negative (positive) value. We consider that the knowledge of trap-induced effects from both charge types is useful for correctly interpreting and understanding TCs.

Influence of chelating ligands on bioavailability and mobility of iron in plant growth media and their effect on radish growth

In this study, the effects of chelating ligands on iron movement in growth medium, iron bioavailability, and growth of radish sprouts ( Raphanus sativus) were investigated. Iron is an important nutrient for plant growth, yet the insoluble state of iron hydroxides in alkaline conditions decreases its bioavailability. Iron chelates increase iron uptake and have been used in agriculture to correct iron chlorosis. While previous studies have reported the effects of chelating ligands on iron solubility and bioavailability, the present study elucidates the pattern of iron movement by chelating ligands in plant growth medium. The apparent mobility of iron in growth medium was calculated using a ‘4-box’ model. Ethylenediaminedisuccinic acid (EDDS) and hydroxy-iminodisuccinic acid (HIDS) produced the highest apparent mobility of iron from the bottom layer of the medium (initially 10 −4 M Fe(III)) to the upper layer (no iron), followed by glutamatediacetic acid (GLDA), ethylenediaminetetraacetic acid (EDTA), methylglycinediacetic acid (MGDA), and iminodisuccinic acid (IDS). Iron movement in the growth medium was influenced by the chelating ligand species, pH, and ligand exposure time. The iron uptake and growth of radish sprouts were related to the iron mobility produced by the chelating ligands. These results suggest that, in alkaline media, chelating ligands dissolve the hardly soluble iron hydroxide species, thus increasing iron mobility, iron uptake, and plant growth. HIDS, which is biodegradable, was one of the most effective ligands studied; therefore, this compound would be a good alternative to other environmentally persistent chelating ligands.

Research on the feature extraction of DC space charge behavior of oil-paper insulation

As the ultra high DC voltage grid comes into an important stage in the ‘Twelfth Five-year Plan’ of China, the requirement on the operation safety of power equipment needs to be improved. Oil-paper insulation plays a significant role as the main insulation material of many key power equipments. The space charge behaviors of oil-paper insulation not only affect the dielectric strength, but also relate to the stability and security of power transmission facilities. Until now, the research on the space charge behaviors of oil-paper insulation remains on the stage of objective description and phenomenon explanation, thus it is very urgent to make some feature extractions on the test results in order to further investigate the DC space charge behaviors of oil-paper insulation. In this paper, based on the large numbers of test data in the first stage, data mining and feature extractions were performed on the DC space charge behavior of oil-paper insulation. The variation laws of some key characteristic parameters obtained in different experiment conditions such as the total charge injection amount, apparent charge mobility, and trap energy distribution were analyzed. In addition, the distribution of trapping level inside oil-paper was calculated by using the PEA test results based on the mechanism of the isothermal decay current, which realized the approximate calculation of trap depth by charge decay characteristics. What’s more, the exponential injection and decay equations of DC space charge changing with time were acquired for the first time, and the physical meanings of related parameters were defined. This has laid a foundation for the prediction and simulation of space charge in the oil-paper insulation.

Simultaneous Analysis of Amino Acids and Carboxylic Acids by Capillary Electrophoresis−Mass Spectrometry Using an Acidic Electrolyte and Uncoated Fused-Silica Capillary

A simple, low-cost capillary electrophoresis-mass spectrometry (CE-MS) method is demonstrated for the simultaneous analysis of amino acids and small carboxylic acids (glycerate, lactate, fumarate, succinate, malate, tartrate, citrate, iso-citrate, cis-aconitate, and shikimate). All CE-MS experiments were performed using a single uncoated fused-silica capillary and with a single separation electrolyte, formic acid. For CE polarity, the CE inlet was set as the anode, and the MS side was set as the cathode. By using high-speed sheath gas flow, the apparent mobilities of all compounds were sped up; thus, the migration times of the carboxylic acids were reduced. In positive ion mode ESI-MS detection, small carboxylic acids were detected faintly as m/z = [M + 18](+) or [M + 23](+), after protonated molecule detection (m/z = [M + 1](+)) of the amino acids. In negative ion mode, all of these small carboxylic acids were detected clearly as deprotonated molecules (m/z = [M - 1](-)), after detection of the amino acids. By changing the polarity of the MS during CE separation, both amino acids and small carboxylic acids were detectable in a single electrophoresis analysis run. With this method, the diurnal metabolic changes of pineapple leaves were observed as reflecting Crassulacean acid metabolism.

A Closed Form for Fluorescence Correlation Spectroscopy Experiments in Submicrometer Structures

Fluorescence correlation spectroscopy (FCS) is a powerful technique for measuring low concentrations of fluorescent molecules and their diffusion coefficients in an open detection volume. However, in several practical cases, when FCS measurements are carried out in small compartments like microchannels, neglecting boundary effects could lead to erroneous results. Here, a close form solution is proposed to explicitly account for the presence of walls located at a distance comparable with the characteristic detection volume lengths. We derive a one-dimensional diffusion constrained model and then generalize the solution to the two- and the three-dimensional constrained cases. We further indicate within which limits the standard autocorrelation function (ACF) model gives reliable results in microconfinement. Our model relies just on the assumption of elastic hits at the system walls and succeeds in describing the ACF of fluorescent probes confined along one direction. Through the analysis of FCS experimental data, we are able to predict the correct shape of the ACF in channels of micrometric and submicrometric width and measure the extent of lateral confinement. In addition, it permits the investigation of microstructured material features such as cages and cavities having dimensions on the micrometric range. On the basis of the proposed model, we also show in which conditions confinement could generate an apparent time dependent probe mobility, thus allowing a proper interpretation of the transport process taking place in submicrometric compartments.

First Structures of an Active Bacterial Tyrosinase Reveal Copper Plasticity

Tyrosinase is a member of the type 3 copper enzyme family that is involved in the production of melanin in a wide range of organisms. The crystal structures of a tyrosinase from Bacillus megaterium were determined at a resolution of 2.0–2.3 Å. The enzyme crystallized as a dimer in the asymmetric unit and was shown to be active in crystal. The overall monomeric structure is similar to that of the monomer of the previously determined tyrosinase from Streptomyces castaneoglobisporus, but it does not contain an accessory Cu-binding “caddie” protein. Two Cu(II) ions, serving as the major cofactors within the active site, are coordinated by six conserved histidine residues. However, determination of structures under different conditions shows varying occupancies and positions of the copper ions. This apparent mobility in copper binding modes indicates that there is a pathway by which copper is accumulated or lost by the enzyme. Additionally, we suggest that residues R209 and V218, situated in a second shell of residues surrounding the active site, play a role in substrate binding orientation based on their flexibility and position. The determination of a structure with the inhibitor kojic acid, the first tyrosinase structure with a bound ligand, revealed additional residues involved in the positioning of substrates in the active site. Comparison of wild-type structures with the structure of the site-specific variant R209H, which possesses a higher monophenolase/diphenolase activity ratio, lends further support to a previously suggested mechanism by which monophenolic substrates dock mainly to CuA.

Air‐Operable, High‐Mobility Organic Transistors with Semifluorinated Side Chains and Unsubstituted Naphthalenetetracarboxylic Diimide Cores: High Mobility and Environmental and Bias Stress Stability from the Perfluorooctylpropyl Side Chain

AbstractN,N′‐bis(3‐(perfluoroctyl)propyl)‐1,4,5,8‐naphthalenetetracarboxylic acid diimide (8–3‐NTCDI) was newly synthesized, as were related fluorooctylalkyl‐NTCDIs and alkyl‐NTCDIs. The 8–3‐NTCDI‐based organic thin‐film transistor (OTFT) on an octadecyltrimethoxysilane (OTS)‐treated Si/SiO2 substrate shows apparent electron mobility approaching 0.7 cm2 V‐1s‐1 in air. The fluorooctylethyl‐NTCDI (8–2‐NTCDI) and fluorooctylbutyl‐NTCDI (8–4‐NTCDI) had significantly inferior properties even though their chemical structures are only slightly different, and nonfluorinated decyl and undecyl NTCDIs did not operate predictably in air. From atomic force microscopy, the 8–3‐NTCDI active layer deposited with the substrate at 120 °C forms a polycrystalline film with grain sizes >4μm. Mobilities were stable in air for one week. After 100 days in air, the average mobility of three OTFTs decreased from 0.62 to 0.12 cm2 V‐1s‐1, but stabilized thereafter. The threshold voltage (VT) increased by 15 V in air, but only by 3 V under nitrogen, after one week. On/off ratios were stable in air throughout. We also investigated transistor stability to gate bias stress. The transistor on hexamethlydisilazane (HMDS) is more stable than that on OTS with mobility comparable to amorphous Si TFTs. VT shifts caused by ON (30 V) and OFF (–20 V) gate bias stress for the HMDS samples for 1 hour were 1.79 V and 1.27 V under N2, respectively, and relaxation times of 106 and 107 s were obtained using the stretched exponential model. These performances are promising for use in transparent display backplanes.

Organic Thin-Film Transistors: The Passivation of the Dielectric-Pentacene Interface by Dipolar Self-Assembled Monolayers

In organic thin-film transistors (OTFTs), the conducting channel is located near the interface between the organic semiconductor and the oxide dielectric; this interface is crucial for transistor performance. Self-assembled monolayers (SAMs) on the interface reduce the negative influences of the oxide dielectric surface by decreasing the coupling of the carriers at the gate and the role of the active surface defects on transfer. In this paper, we show that SAMs carrying a dipole moment determine the OTFT performance by controlling the charge transfer between the oxide dielectric and the semiconductor. The charges introduced into the semiconductor by this transfer (i.e., residual carriers) lead to a threshold shift to positive values, as well as a decrease in the contact resistance and an increase in the apparent mobility. In this study, other effects of the SAMs, such as the gate potential shift in the channel or a direct reaction between semiconductor and SAM molecules, can be excluded as dominant processes.