Single Diffusion Process Research Articles

Experimental Study on Power Consumption in Lifetime Engineered Power Diodes

In this paper, we present a quantitative study of the effects of lifetime engineering treatments on the switching operation of power diodes, with special regards to the whole energy consumption. Not only single platinum diffusion and helium implantation processes, but also the combined effects for both treatments have been analyzed. Results show that care must be taken when choosing the lifetime treatment because univocal rules are difficult to draw.

Growth and Characterization Studies of MnHP Single Crystal in Silica Gel Medium

MnHP (Manganese Hydrogen Phosphate) crystals were grown in silica gel medium using different gel densities, various concentrations of orthophosphoric acid and supernatant solutions in single diffusion process. The gel pH plays an important role in the formation of different HPO4 species in the phosphoric system. The pH range in which HPO42- ions dominates were considered which in turn is necessary for the growth of MnHP crystals. The characterizations of grown crystals were studied by FTIR, SEM, XRD and etching. The results are reported and discussed in detailed manner.

Important Features of Anomalous Single-Dopant Diffusion and Simultaneous Diffusion of Multi-Dopants and Point Defects in Semiconductors

This paper summarizes some of the main results obtained concerning aspects of anomalous single-dopant diffusion and the simultaneous diffusion of multi-diffusion species in semiconductors. Some important explanations of theoretical/practical aspects have been investigated, such as anomalous phenomena, general diffusivity expressions, general non-linear diffusion equations, modified Arrhenius equations and lowered activation energy have been offered in the case of the anomalous fast diffusion for single-dopant diffusion process. Indeed, a single diffusion process is always a complex system involving many interacting factors; conventional diffusion theory could not be applied to its investigation. The author has also investigated a system of multi-diffusion species with mutual interactions between them. More concretely, irreversible thermodynamics theory was used to investigate the simultaneous diffusion of dopants (As, B) and point defects (V, I) in Si semiconductors. Some attempts at theory development were made, such as setting up a system of general diffusion equations for the simultaneous diffusion of multi-diffusion species involving mutual interactions between them, such as the pair association and disassociation mechanisms which predominated during the simultaneous diffusion of dopants and point defects. The paper then gives some primary results of the numerical solution of distributions of dopants (B, As) and point defects (V, I) in Si semiconductor, using irreversible thermodynamics theory. Finally, several applications of simultaneous diffusion to semiconductor technology devices are also offered.

Usage of pattern recognition scheme in kinetic Monte Carlo simulations: Application to cluster diffusion on Cu(1 1 1)

We have invoked a simple pattern recognition scheme in kinetic Monte Carlo simulations of post-deposition evolution of two dimensional islands on fcc(1 1 1) surfaces. On application of the technique to the diffusion of small Cu clusters (8–100 atoms) on Cu(1 1 1) we find that, at room temperature, clusters with certain magic numbers show stick-slip type of motion with striking patterns rather than the random paths followed by the others. At higher temperatures all clusters display random motion. The calculated diffusion coefficients show dependence on size and temperature with an effective barrier ranging between 0.62 eV and 0.84 eV. Small asymmetries in diffusion barriers lead to a large difference in the frequencies of adatom diffusion along the two types of micro-facetted steps on Cu(1 1 1) leading to consequences in their shape evolution. The pattern recognition scheme revealed 49 basic periphery single atom diffusion processes whose activation energy barriers were calculated using the nudged elastic band technique and interatomic potentials from the embedded atom method.

Structure–property relationships in glass‐reinforced polyamide, Part 3: Effects of hydrolysis ageing on the dimensional stability and performance of short glass–fiber‐reinforced polyamide 66

AbstractWe present results on an in‐depth study of the effects of hydrolysis testing on the mechanical performance, weight change, and dimensional stability of injection molded glass–fiber‐reinforced polyamide 66 (PA66) based on two chopped fiber products with different sizing formulations. Composite and resin samples have been characterized both dry as molded and after conditioning at either 120 or 150°C for a range of times up to 1,000 h. The results reveal that hydrothermal ageing in water–glycol mixtures results in significant changes in the mechanical performance, weight, and dimensions of these materials. The negative effects of conditioning could be mitigated to some degree by the appropriate choice of the glass–fiber sizing; however, the sizing effect diminished with increasing conditioning time. All materials showed a weight increase due to conditioning at 120°C that was typical of a single Fickian diffusion process and there was clear evidence of multiple processes involved when conditioning at 150°C. It was not apparent that the glass–fiber sizing affected the dimensional stability of the composites. We show that there is a strong correlation between the swelling of these samples and the level of fluid adsorption. Although the PA66 resin showed reasonably homogeneous swelling, the composites exhibited different levels of swelling depending on direction. These effects were well in line with the known effects of fibers on restriction of the matrix deformation (mechanical, thermal, or moisture swelling) in the fiber direction. These differences correlate well with the average fiber orientation with respect to the various direction axes. Composite tensile strength and unnotched impact resistance appeared to scale inversely with the level of swelling of the material. POLYM. COMPOS. 28:344–354, 2007. © 2007 Society of Plastics Engineers.

How Polymer Surface Diffusion Depends on Surface Coverage

Measurements are presented of how surface diffusion of flexible polymers at the solid−liquid interface is controlled by surface coverage. Surface coverage is varied over the full range from dilute to saturated surface coverage. The method of measurement is fluorescence correlation spectroscopy (FCS), and the systems are poly(ethylene oxide) (PEG) and dextran adsorbed onto methyl-terminated self-assembled monolayers in buffered aqueous solution. A detailed study of PEG (Mw = 10 800 g mol-1) shows nonmonotonic behavior. The translational diffusion coefficient (D) at first increases with increasing surface concentration, presumably because the number of adsorption sites per molecule decreases as chains switch from pancake to loop−train−tail conformation. Excellent fits to behavior characteristic of a single diffusion process argue against aggregation or crystallization in the adsorbed state. In-situ ellipsometry measurements appear to rule out conformation changes to a hypothetical helical structure, as this would introduce birefringence to the adsorbed polymer layer causing deviations from the observed linear growth of apparent layer thickness with increasing surface coverage. For all three samples studied (PEG of Mw = 10 800 and 20 000 g mol-1 and also dextran with Mw = 10 000 g mol-1), D at surface coverages larger than the estimated surface overlap concentration slow by 1 order of magnitude, presumably reflecting crowding and entanglement with neighboring chains.

A Predictor‐Corrector Algorithm for Reaction‐Diffusion Equations Associated with Neural Activity on Branched Structures

In this paper, we present a numerical method for solving reaction‐diffusion equations on one‐dimensional branched structures. The method effectively decouples the many branches at the nodal junctions so that the equations can be solved as a system of smaller problems that are purely tridiagonal. This strategy enables a number of improvements. In particular, difficulties associated with implicit methods for closed loops in the network are eliminated, and spatial adaptivity can be easily implemented. We apply this method to the electrical activity of a neuron. A neuron can be effectively represented as a one‐dimensional branched structure, and the model equations, based on the Hodgkin–Huxley cable equations, are a set of reaction equations coupled to a single diffusion process. Spatially adaptive methods are particularly effective for neuronal simulations as the region of activity is often very localized in space. Since the algorithm scales with activity instead of network size, it will make a substantial reduction in computational cost over existing methods.

Studies of unusual adsorption and diffusion behaviour of benzene in silicalite-1

The adsorption and diffusion properties of benzene in silicalite-1 have been investigated using gravimetric techniques, molecular simulation methods and the frequency response (FR) approach. Two steps at loadings of ca. 4 and 6 molecules per unit cell (m. u.c.−1), respectively, and a hysteresis loop between loadings from 6 to 8 m. u.c.−1 can be found in the isotherms of benzene in silicalite-1. These stepped isotherms could be classified as showing type VI isotherm behaviour but in this system the reasons behind the steps are of a new and novel nature. The anomalous adsorption behaviour has been ascribed to the subtle interplay of increased sorbate–sorbate interactions and decreases in the entropy of sorption due to the energetically heterogeneous surfaces which are present in the adsorbent. The diffusivity of benzene in silicalite-1 also displays an unusual behaviour. At loadings lower than 4 m. u.c.−1, only a pure, single diffusion process can be observed, while at higher loadings, two diffusion processes are found. The former case can be ascribed to the movement of the sorbed benzene molecules mainly down the straight channel direction, whereas the latter case has been associated with diffusion processes involving (a) benzene molecules which are part of clusters and (b) molecules which are not clustered, respectively. It is an entropic driving force which causes the faster diffusivity of the clustered molecules. Both the adsorption and diffusion properties of this system depend on the composition and structure of the silicalite-1 samples.

In situ anion diffusion experiments using radiotracers

Diffusion experiments in compacted bentonite have been carried out in situ using the borehole laboratory CHEMLAB. The “ordinary” anion iodide and the redox-sensitive pertechnetate ion have been investigated. In spite of strongly reducing groundwater conditions, technetium was found to diffuse mostly unreduced as TcO 4 −, although in some spots in the compacted clay, the activity was significantly higher, which may be explained by reduction of some TcO 4 − by iron-containing minerals in the bentonite. The measured concentration profiles in the clay cannot be accommodated by assuming one single diffusion process. The experimental data are modeled assuming two diffusion paths, intralamellar diffusion and diffusion in external water. The apparent diffusivity for the intralamellar diffusion was found to be 8.6×10 −11 m 2 s −1 for iodide with a capacity factor of 0.1, while the apparent diffusivity for the diffusion in external water was found to be 5×10 −14 m 2 s −1 with α=2.26. The corresponding values for Tc were found to be D a=6×10 −11 m 2 s −1, α=0.1 and D a=1×10 −13 m 2 s −1, α=0.46, respectively. The diffusion constants and capacity factors obtained in this study are in accordance with data from laboratory experiments.

ATR-FTIR spectroscopic investigations on the effect of solvents on the permeation of benzoic acid and salicylic acid through silicone membranes

The effect of a series of alcohols on the permeation of salicylic acid (SA) and benzoic acid (BA) through silicone membrane was evaluated, using Franz-type diffusion cells. Although permeants were applied at the same thermodynamic activity in all vehicles, the resulting fluxes were found to differ significantly. This was a consequence of the interactions between the vehicles and the membrane. The interactions between the vehicles and the membrane were further investigated using ATR-FTIR spectroscopy. With this technique, it was possible to identify two different diffusion processes when the membrane was pre-treated with buffer, whereas one single diffusion process was observed when the membrane was pre-soaked with the vehicle. The technique was successfully used to deconvolute the relative magnitude of partition and diffusion in the permeation process. It was shown that the permeation of both acids was affected by the effect of the vehicles on the diffusion coefficient and the partition coefficient in the silicone membrane. The solubility of the drug in the impregnated membrane was found to be proportional to the saturated solubility in the vehicle used to treat the membrane. The solubility of BA in the impregnated silicone membrane was twice that of SA.

Adsorption and diffusion of cyclic hydrocarbon in MFI-type zeolites studied by gravimetric and frequency-response techniques

The adsorption and diffusion of benzene, toluene, ethylbenzene, p-xylene, cyclohexane and cis-1,4-dimethylcyclohexane in MFI zeolites have been investigated using a gravimetric balance and the frequency-response (FR) technique respectively. Distinct steps were observed in the isotherms of benzene and toluene in silicalite-1 at loadings of greater than four molecules per unit cell (m./u.c.), which were reversible, whereas a hysteresis loop was found in the isotherms of p-xylene in silicalite-1 but not in the isotherms of p-xylene in ZSM-5. In contrast with some explanations in the literature, the heterogeneous sorption sites of the MFI topology for these sorbates and sorbate–sorbate interactions have been invoked to explain these results. The mass transfer of benzene and cyclohexane molecules in MFI zeolites is controlled by a pure micropore diffusion process. The diffusivities of ethylbenzene and cis-1,4-dimethylcyclohexane in the sorbents may be influenced by the rotation of the methyl groups in these molecules. The transport properties of toluene and p-xylene inside the pores of MFI are dependent on loading. At loadings ≲1 m./u.c. and ≳4 m./u.c. only a single diffusion process can be detected by the FR measurements, whereas at intermediate loadings a bimodal FR behaviour is found. The diffusivities of the four aromatics decrease in the order of p-xylene>toluene>benzene>ethylbenzene, and the diffusion coefficients of the two cyclic alkanes are at least one order of magnitude smaller than the values for benzene, i.e. <10 −15 m 2 s −1. The activation energies of the aromatics in silicalite-1 have also been measured in this study.

Diffusion Behavior of Ca2+ Ions in Compacted Na-Montmorillonite

ABSTRACTDiffusion behavior of Ca2+ ions in water-saturated, compacted Na-montmorillonite was studied for the safety assessment of geological disposal of high-level radioactive waste. The diffusion coefficients of Ca2+ ions in compacted Na-montmorillonite obtained in this study were from 1.7×10-11 to 6.0×10-12 m2 s-1 with increasing dry density of 1.0 to 1.8 Mg m-3. These values were approximately a quarter those of Na+ ions at each dry density. This suggests that the diffusion of Ca2+ ions could be the rate-determining mechanism for the alteration of Na-montmorillonite into Ca-montmorillonite. The activation energy for diffusion of Ca2+ ions was almost equal to that in free water (17.3 kJ mol-1) at dry densities of 1.0 to 1.6 Mg m-3. However, the activation energy suddenly increased to 25.1 kJmol-1 at a dry density of 1.8 Mg m-3. This increase cannot be explained using a single-diffusion process model, such as the pore-water diffusion model. Diffusion behavior of Ca2+ ions in compacted montmorillonite along with the experimental data on the basal spacing and water content of montmorillonite, and the activation energy for diffusion of Ca2+ and several other ions are discussed.

Moisture conditions in coated exterior wood Part 4: Theoretical basis for observed behaviour. A computer modelling study

A theoretical investigation of moisture movement in pine sapwood was undertaken using two different models of behaviour. Firstly a model was developed using a single diffusion process; this model predicted levels of water absorption and moisture content which were in broad agreement with experimental results. However, this approach proved to be over-simplistic, and predicted a more rapid penetration of moisture than was observed in practice. The model also failed to predict the deceleration in absorption which was recorded in laboratory tests. Consequently, the predictions of the model were of a more uniform moisture distribution than was consistent with experience. A development of the model, to include flow mechanisms appropriate for the level of moisture content, gave more realistic predictions. The improved model is based on different flow mechanisms in three distinct regions of moisture content. Below fibre saturation point (FSP), a diffusion mechanism is assumed for the calculation of moisture flow. Between FSP and a threshold, termed the irreducible saturation point (ISP), flow takes place through the cell wall material. Above the ISP, a continuous path is established for moisture movement from cell to cell through the bordered pits. The improved model proved capable of predicting levels of moisture uptake and moisture content, and of predicting the moisture gradients observed in practice. It also provided an explanation of some of the observed patterns of wood moisture movement reported in earlier parts of this series of papers. In particular it explained why, when water is absorbed by coated timber, the rise in surface moisture content appears not to exceed FSP. Additionally it provided an understanding of the continuing penetration of moisture in depth during the early stages of drying. This is a significant conclusion, because it imposes a limitation, in principle, on the performance of high permeability wood coatings.

RHEED investigations of MBE-growth kinetics of Si on Si(111) and SiC on SiC(100)

Reflection high-energy electron diffraction has been used to study the molecular beam epitaxy-growth kinetics of Si on Si(111) and of SiC on SiC(100). By means of a simple kinematic scattering theory we have estimated diffusion barrier energy values for adatom migration and nucleation energies. Results clearly show that growth kinetics are different at low and high temperatures for both systems. At lower temperatures the nucleation can be explained by a single adatom diffusion process, whereas at higher temperatures much higher activation energies may be attributed to an island coarsening process.

Fiber-Optic-Dynamic-Light-Scattering and Two-Color-Cross-Correlation Studies of Turbid, Concentrated, Sterically Stabilized Polystyrene Latex

Concentrated turbid colloidal suspensions were investigated by means of dynamic light scattering. The results of two different techniques, i.e., fiber-optic quasi-elastic light scattering (FOQELS) and two-color cross-correlation (TCC) were compared. Both techniques allow one to observe correlation functions of singly scattered light. FOQELS determines backscattered light only, whereas measurements at various scattering angles can be performed with TCC. At concentrations up to about 10% (w/w) only a single diffusion process is observed that can be attributed to the collective diffusion. At higher concentrations an additional slow mode occurs which can be identified as long time self-diffusion of the latex spheres. The results of both techniques agree very well and can be understood in the framework of the theories of interacting hard spheres. They demonstrate the capabilities which both methods offer to study dynamic properties of strongly scattering colloidal suspensions.

Kinetics of macrosteps under diffusion and thermal interactions in stagnant media

The step motions considered are those in which crystallization is controlled by a single diffusion process, either the diffusing substance for growth from solution or the flow of latent heat from the step for growth from melt. Quasi-static diffusion near two parallel steps and near a train of parallel steps is considered. Terraces and step risers are assumed to be flat with arbitrary angles between them. The flux of the crystallizing substance to the crystal or the heat sources on the crystal surface are nonvanishing on the step risers only. The kinematics of the steps under the diffusion interaction are investigated when the velocities of the steps are controlled by the supersaturation at the feet of the steps. For solution growth, it is shown that an equidistant train of steady-state steps is unstable against doubling of the period, i.e. neighbouring steps are attracted when the angle of the riser is more than π3. The diffusion interaction stabilizes the train of gently sloping steps. For melt growth, at equal thermal conductivities of the crystal and of the melt, the thermal interaction stabilizes the train of steps without overhanging when the riser angle is less than π2. If the heat transfers through the crystals, then the equidistant train is stable at all riser angles. The evaluations show that this instability can be observed under the real conditions of solution growth of the KDP crystals.

Incipient vortex size-dependent evolution of tropical disturbances Part II — Some governing processes

Recently it was shown (Goswami and Rao 1993) that the process of intensification of tropical disturbances depends on the size of the incipient vortex in a rather nonlinear fashion. Among vortices of size ranging from 100 to 450 km (radius), embedded in the same large scale condition, it is the vortex with size about 250 km that intensifies to the most severe system. These results also showed a strong correspondence between the maximum intensity reached and the initial (3–6 hour) low level convergence field near the centre. The purpose of the present work is to identify the process(es) responsible for this scale selective intensification of tropical disturbances. It is proposed that diffusion is likely to play a crucial role in bringing about this selective intensification. In the present work a series of experiments with an axisymmetric numerical model of tropical cyclone (Wada’s model) is carried out to determine the relative roles of horizontal diffusion of momentum, moisture, heat and vertical diffusion. The results show that diffusion significantly affects the process of intensification and scale selection. While moderate diffusion does not alter the magnitude of intensification significantly, the scale selection is quite sensitive to the strength of diffusion. Interestingly, these diffusion processes, of momentum, moisture, heat and vertical do not affect the scale selection in the same fashion. The scale selection process turns out to be a result of a combined effect of these diffusion processes. However, no single diffusion process alone can give rise to a sharp selection of scale at the size of 250 km.

Diffusion of methyl esters of higher fatty acid in polypropylene

AbstractDiffusion coefficients of several methyl esters of linear higher fatty acid (C10˜C18) into polypropylene (PP) were determined, over the temperature range of 50 to 110°C, using a mass uptake technique. The relations between an amount of mass uptake and t1/2 were linear within 10 min, indicating Fickian diffusion. The diffusion coefficients were in the range of 4.6×10−8 to 6.2×10−12 cm2 sec−1, increased with temperature, and decreased with increasing n‐alkyl chain length of fatty acid. The plots of In D vs. the molecular weight of methyl esters were approximately linear. The temperature dependence of diffusion followed an Arrhenius relationship, and the activation energies were in the range of 133 ˜ 147 KJ mol−1 and increased with an increase in n‐alkyl chain length of corresponding fatty acid. The diffusion coefficients were discussed with the interaction between methyl esters of higher fatty acid and PP. The diffusion coefficients of methyl esters, at the simultaneous diffusion process, were always higher than that derived from the single diffusion process, except for methyl decanoate with lower molecular weight. The difference in diffusion coefficients in single and simultaneous diffusion was discussed thermodynamically. © 1994 John Wiley &amp; Sons, Inc.

Single chain diffusion process and proton magnetic relaxation in polymer melts

Single chain diffusion process and proton magnetic relaxation in polymer melts

Efficient p -type Si IMPATT diodes for V -band frequencies

p-type single-drift IMPATT diodes for V-band frequencies were fabricated by a single diffusion process. The diodes were packaged on a copper heatsink using quartz standoffs and investigated in a resonant cap waveguide structure. The maximum CW output power is 0.5 at 68 GHz with an efficiency of 8.7%