Large Differences In Mobility Research Articles

Effect of Substitution on the Hole Mobility of Bis(diarylamino)biphenyl Derivatives Doped in Poly(Styrene)

The effect of substitution on hole mobility in N,N‘-bis(m-tolyl)-N,N‘-diphenyl-1,1‘-biphenyl-4,4‘-diamine (TPD) derivatives doped in polystyrene was studied using the time-of-flight technique. Mobility data were collected as a function of electric field and temperature to yield the energetic and positional disorder parameters defined in the disorder formalism. Substituted derivatives exhibit lower mobilities than regular TPD. This decrease is influenced by the change in dipole moment upon substitution of the molecule. However, the dipolar disorder contribution is found to account only partially for the large differences in mobility.

Dangling bonds with “negative Hubbard U ”: Physical model for degradation of SiO2 gate dielectric under voltage stress

A model proposed to explain the phenomenon of current increase and its fluctuation under voltage stress in a SiO2 gate dielectric is based on the amorphous nature and presence of dangling bonds in SiO2. Dangling bonds D0 are thought to be negative-U centers, where their neutral state is unstable and therefore a spontaneous reaction of charge disproportionation take place: D0+D0→D++D−. As a result, a SiO2 amorphous network has diamagnetic positive D+ and negative D− centers. Due to a large difference in mobility between electrons and holes, hopping current in SiO2 is mainly electron current on D+ centers. Current increase and fluctuation under a voltage stress is due a conversion of D− into D+ centers by the hole component of current through SiO2 gate dielectric. This conversion is an irreversible process accelerated by temperature and electric field.

On-capillary ion-exchange preconcentration of inorganic anions in open-tubular capillary electrochromatogrpahy with elution using transient-isotachophoretic gradient. 2. Characterization of the isotachophoretic gradient.

Diffuse transient-isotachophoretic boundaries can be used as an elution gradient of increasing eluotropic strength to elute inorganic anions that have been preconcentrated on an open-tubular ion-exchange stationary phase prior to electrophoretic separation. The generation and characteristics of these gradients for elution after preconcentration have been investigated. The gradients are generated by placing a low-mobility, weak ion-exchange competing anion in the capillary (weak electrolyte, WE), and a high-mobility, strong ion-exchange competing anion in the electrolyte vials (strong electrolyte, SE). Application of voltage establishes a diffuse boundary with the composition changing from the weak anion to the strong anion. Comparison of elution gradients generated with different electrolyte systems was accomplished by comparing the eluotropic strength (a function of eluent concentration, ion-exchange selectivity coefficient, and charge) and the shape of the profile as it changes from WE to SE. The ion-exchange selectivity coefficient of the SE competing anion is important in establishing a sharp change in elution strength. A large difference in mobility between the WE and SE competing anions gives an SE with a higher final eluotropic strength, but the slope of the gradient is shallower. This results in a reduction in the efficiency of analyte focusing. To ensure maximum focusing efficiency, the WE and SE electrolytes should be selected such that the SE has the highest possible eluotropic strength for a given concentration of WE. The SE competing anion should also have a sufficiently low electrophoretic mobility to ensure focusing for the maximum number of analytes, and the mobility difference between the WE and SE competing anions should be as small as possible.

Stochastic annealing simulation of intracascade defect interactions

Atomic scale computer simulations are used to investigate the intracascade evolution of the defect populations produced in cascades in copper over macroscopic time scales. Starting with cascades generated using molecular dynamics, the diffusive transport and interactions of the defects are followed for hundreds of seconds in stochastic annealing simulations. The temperature dependencies of annihilation, clustering and free defect production are determined for individual cascades, especially including the effects of the subcascade structure of high energy cascades. The subcascade structure is simulated by closely spaced groups of lower energy MD cascades. The simulation results illustrate the strong influence of the defect configuration existing in the primary damage state on subsequent intracascade evolution. Other significant factors affecting the evolution of the defect distribution are the large differences in mobility and stability of vacancy and interstitial defects and the rapid one-dimensional diffusion of small, glissile interstitial clusters produced directly in cascades. Annealing simulations are also performed on high-energy, subcascade-producing cascades generated with the binary collision approximation and calibrated to MD results.

Electron Transport in Vapor-Deposited Naphtlalene Dicarboximide Glasses

Electron mobilities have been measured in vapor-deposited layers of N-(1,2-dimethylpropyl)benzo[k,l]thioxanthene-3,4-dicarboximide-7,7-dioxide (BTDD) and N,N′-bis(1,2-dimethylpropyl)-1,4,5,8-naphthalenetetracarboxylic diimide (NTDI). BTDD is a highly polar acceptor molecule that incorporates both an imide and a sulfone electronegative functionality. NTDI is a weakly polar acceptor molecule that contains two imide functionalities. The results are described by a formalism based on disorder, due to Bässler and coworkers. The formalism is based on the assumption that transport occurs by hopping through a manifold of localized states that are distributed in energy. The key parameter of the formalism is σ, the energy width of the hopping site manifold. The width is described by a model based on dipolar disorder. The model is premised on the argument that the width is comprised of a dipolar component σ d and a van der Waals component σ vdW. Describing the dipolar component by an expression due to Young yields σ d=0.133 eV for BTDD and 0.009 eV for NTDI. The van der Waals component for both molecules is 0.092 eV. The difference in the dipolar component is the principal reason for the large difference in mobility of these molecules.

Comparison of the active-site conformations of bovine alpha-thrombin and meizothrombin(desF1) by electron spin resonance.

The active site of the prothrombin activation intermediate meizothrombin(desF1) was probed using several fluorosulfonylphenyl spin labels specific for the active serine hydroxyl of serine proteases. The mobilities of the thrombin species inhibited with the nitroxide spin labels m-IV [4-(2,2,6,6-tetramethyl-piperidine-1-oxyl) -m-(fluorosulfonyl)benzamide] and m-V [3-(2,2,5,5-tetramethyl-pyrrolidine-1-oxyl) -m-(fluorosulfonyl)benzamide], which are sensitive to differences between alpha- and gamma-thrombin, were quite similar to that of alpha-thrombin. That is, no major conformational differences between meizothrombin(desF1) and alpha-thrombin were observed in this region of the extended active site. On the other hand, p-IV [4-(2,2,6,6-tetramethyl piperidine-1-oxyl)-p-(fluorosulfonyl)benzamide], p-V [3-(2,2,5,5-tetramethylpyrrolidine-1-oxyl) -p-(fluorosulfonyl)benzamide], and m-VII [N-[m- (fluorosulfonyl)phenyl]-4-N-(2,2,6,6-tetramethyl- piperidine-1-oxyl)urea], which probe an apolar binding region of bovine thrombin, exhibited large differences in mobility between alpha-thrombin and meizothrombin(desF1). The conformational consequences of indole binding to spin-labeled thrombin species demonstrated that both species also possess an indole-binding site. However, the nitroxide mobility changes upon indole binding to the spin-labeled protein derivative were somewhat different between the two thrombin species under study. In addition, the effects of the benzamidine binding were quite similar for each labeled protein. Thus is appears that, while both species posses a fully functional active site, the region in meizothrombin(desF1) probed by spin labels p-IV, p-V, and m-VII, which corresponds to the apolar binding region, differs in conformation from alpha-thrombin.

Cascade Defects Beyond the Primary Damage State

AbstractAtomic scale computer simulations are used to investigate the intracascade evolution of the defect distributions of cascades in copper over macroscopic times. Starting with cascades generated using molecular dynamics, the diffusive transport and interactions of the defects are followed for hundreds of seconds in stochastic annealing simulations. The temperature and energy dependencies of annihilation, clustering and free defect production are determined for individual cascades. The simulation results illustrate the strong influence on intracascade evolution of the defect configuration existing in the primary damage state. Other significant factors affecting the evolution of the defect distribution are the large differences in mobility and stability of vacancy and interstitial defects and the rapid one-dimensional diffusion of small, glissile interstitial loops produced directly in cascades. The latter factor introduces a cascade energy dependence of defect evolution that is apparent only beyond the primary damage state, amplifying the need for performing many more cascade simulations at higher energies.

Model of the Early Deformation Stage of bee Metals in Low Temperature

A qualitative and quantitative model of the early deformation stage of bcc metals at low temperatures is proposed. Due to a large difference in mobility of screw and edge dislocations, there is a stress range where only edge-segments are mobile. The force for the edge dislocation mobilization has one component connected with the overcoming of local barriers and another one related to the formation out of screw segments. A rapid creation of hardly mobile screw dislocation dipoles is assumed as the main source of strain hardening. At some critical value of the screw dislocation density and sufficiently high applied stress, some local movement and mutual annihilation of long segments of screws is possible. This last process effectively decreases the strain-hardening rate and leads to a smooth, continuous transient between elastic and plastic deformation. The model is confronted with experimental data and a satisfactory agreement is obtained.

Bipolar Diffusion Charging of Particles in Noble Gases

The bipolar diffusion charging of particles, suspended in argon is investigated. Particle charge is measured as function of particle size and ion concentration. Since rare gases do not attach electrons, free electrons are available in the gas. This leads to a large difference in mobility and attachment coefficients between negative and positive charge carriers and also of the resulting particle charge. Additionally, negatively charged particles have a maximum as function of the ion concentration, before the equilibrium is reached. This can be explained by the existence of two types of negative charge carriers: free electrons and negative ions, formed by attachment of electrons to impurities in the gas.

The effect of water movement on the transport of dicyandiamide, ammonium and urea in unsaturated soils

AbstractA laboratory experiment was conducted to investigate the relative mobility of dicyandiamide (DCD) and jointly applied ammoniacal salts or urea in three different soils of lower Egypt, and to determine the extent to which DCD separates from N‐fertilizer in unsaturated soil undergoing leaching.The experimental results suggest that, under conditions of water flow, DCD is readily separated from NH4+ but parts from urea to a far lesser extent. The large difference in mobility between DCD and NH4+ should severely limit the effectiveness of DCD as a nitrification inhibitor in the three soils considered when applied in conjunction with ammoniacal salts. In two out of three cases, the situation is similarly unfavorable in the case of joint DCD and urea application. However, the observation that DCD, in a low CEC sandy loam, moves within the soil solution at a slightly lower rate than urea suggests that joint application with urea would keep at least part of the DCD in contact with the NH4+ ions and, therefore, would preserve some of the effectiveness of DCD under leaching conditions in this soil.

On the transition from local equilibrium to paraequilibrium during the growth of ferrite in Fe-Mn-C austenite

The concept of paraequilibrium, introduced a long time ago by Hultgren and analyzed thermodynamically by Hillert, has been analyzed in detail by means of a kinetic model. The concept applies to alloy systems where there is a large difference in mobility of the different components, e.g. in steels where substitutional elements diffuse many orders of magnitude slower than interstitial solutes like H, C and N. By definition paraequilibrium means that only the mobile elements are equilibrated while the sluggish ones behave as a single element. In the present work we have applied a phenomenological model that takes into account the diffusion in the matrix in front of a moving phase interface, a finite interface mobility, the effect of surface tension and the sluggishness of diffusion across the phase interface, i.e. the solute drag. We have studied theoretically the edgewise growth of a ferrite platelet in Fe-Mn-C alloys. In particular we have studied how the growth process depends on the Mn content. We have investigated under what conditions paraequilibrium or full thermodynamic equilibrium is established locally at a moving phase interface.

Activity coefficients and diffusion coefficients of dilute aqueous solutions of lithium, sodium, and potassium hydroxides

A simplified version of Harned's conductimetric technique has been used to measure binary diffusion coefficients of aqueous lithium, sodium, and potassium hydroxides at 25°C from 0.002 to 0.14 mol-dm−3. Because of the large difference in mobility between OH− and the cations, the electrophoretic effect tends to reduce the rate of diffusion of the alkali metal hydroxides; the largest effect is observed for LiOH solutions. The measured diffusion coefficients are in excellent agreement with predictions of the Onsager-Fuoss theory of ion transport. Precise activity coefficients determined from the diffusion measurements are compared with activity coefficients obtained previously by emf methods.

Kinetics of slow diffusing species in ion exchangers

Abstract The slow diffusion of plutonyl nitrate into a weak-base anion exchange resin has been investigated by sectioning and autoradiograping single ion exchange beads. There is clear evidence of a shell progressive diffusional effect in the early stages of the reaction, but more conventional diffusion is apparent after 336 hours of reaction. This could also be explained by Nernst-Planck diffusion of counterions with a large difference in mobility. The rate of uranium sorption by an aminophosphonic acid resin is controlled by diffusion within the ion exchange bead and the mechanism can be fitted to mathematical treatments of homogeneous diffusion and shell progressive or ash layer diffusion. The sorption of caesium by potassium copper(II) cyanoferrate is controlled by diffusion within the ion exchanger and the rate is virtually independent of particle size. Chemical reaction rate control at a moving boundary layer is the most satisfactory mathematical model and this is supported by a measured activation energy of 17.88 kcal/mol.

Hole Transport in MOS Oxides

Hole and electron transport are reported for three different kinds of MOS oxides: wet, dry, and ion-implanted. The electron-hole pairs are generated in the bulk of the oxide by a 3 ns x-ray pulse and the separation of the electron and hole photocurrents is made possible by the large difference in mobility. The electrons are so mobile that they are swept from the oxide (or trapped in a heavily ion-implanted region) during the x-ray pulse. The holes, on the other hand, have much lower mobilities which depend strongly on the preparation of the oxide. In the dry oxide the nominal mobility at room temperature is several orders of magnitude higher than in the wet oxide. The mobility is strongly activated by temperature in the oxides, and at liquid N$sub 2$ temperature no hole motion could be detected even though the electrons are still swept out. The low temperature charging of oxides can be understood in terms of the bulk trapped holes, but room temperature charging seems to be dominated by trapping close to the Si/SiO$sub 2$ interface rather than the transport of the holes from the bulk to the interface. Ion implantation provides electron traps which seem to be associatedmore » with the lattice damage rather than the ion. The electron traps can be successfully annealed out at 900$sup 0$C in 20 minutes. (auth)« less

Dislocation velocities in indium antimonide

Velocities of individual dislocations in InSb were measured by the double etch technique. A large mobility difference between In-type and Sb-type dislocations was observed. The velocities of both types depend on temperature as exp ( −Q kT ) but with different activation energies Q. For the faster, In-type dislocation, a lower Q was measured. Hence, the mobility difference is concluded to be due to different Peierls barriers. A linear stress dependence of velocity was found.

Simplified calculation of electrophoretic mobility of non-spherical particles when the electrical double layer is very extended

Experiments in our laboratories (1) have shown tha t some dispersions in nonpolar solvents exhibit very large differences in mobility (sometimes as much as an order of magnitude) from particle to particle. Naturally, the question arises as to why this is so. Generally, since the ion concentration is low in these liquids, the diffuse part of the electrical double layer is very extended and does not contribute appreciably to the (i.e., the electrophoretic drag and relaxation effect (2) are negligible). Therefore, to calculate the mobility of a particle of charge Q, one may simply balance the force EQ, due to the applied electric field E, against the opposing force due to ordinary hydrodynamic drag. Using this approximation, which greatly simplifies the calculations, we can investigate whether the observed large variations in mobility can be caused by variations in shape. The answer is no, as is shown by the following calculations for el]ipsoidal particles}