Diffusion Processes and Pre-Exponential Factors in Homo-Epitaxial Growth on Ag(100)

1997 ◽  
Vol 492 ◽  
Author(s):  
Ulrike Kürpick ◽  
Talat S. Rahman
Keyword(s):  
Crystal Growth ◽  
Diffusion Coefficients ◽  
Diffusion Processes ◽  
Step Edge ◽  
Many Body ◽  
Self Diffusion ◽  
Adatom Diffusion ◽  
Exchange Processes ◽  
Exponential Factors ◽  
Vibrational Density

ABSTRACTWe provide a recipe for the evaluation of pre–factors for various diffusion processes relevant to crystal growth on Ag(100), based on explicit calculations of appropriate vibrational density of states using realistic many-body interaction potentials. Our calculated diffusion coefficients show that while hopping processes are favored for terrace self-diffusion, exchange processes dominate step-edge diffusion. We also find the characteristics of adatom diffusion along the < 100 >-step-edge to be strikingly different from the < 110 >-step-edge with interesting consequences for interlayer transport on this surface.

scholarly journals Theoretical Modelling of Ion Exchange Processes in Glass: Advances and Challenges

2021 ◽  
Vol 11 (11) ◽  
pp. 5070
Author(s):  
Xesús Prieto-Blanco ◽  
Carlos Montero-Orille
Keyword(s):  
Ion Exchange ◽  
Diffusion Coefficients ◽  
Molten Salts ◽  
Theoretical Modelling ◽  
Copper Films ◽  
Theoretical Frameworks ◽  
Self Diffusion ◽  
Exchange Processes ◽  
The One ◽  
Made In

In the last few years, some advances have been made in the theoretical modelling of ion exchange processes in glass. On the one hand, the equations that describe the evolution of the cation concentration were rewritten in a more rigorous manner. This was made into two theoretical frameworks. In the first one, the self-diffusion coefficients were assumed to be constant, whereas, in the second one, a more realistic cation behaviour was considered by taking into account the so-called mixed ion effect. Along with these equations, the boundary conditions for the usual ion exchange processes from molten salts, silver and copper films and metallic cathodes were accordingly established. On the other hand, the modelling of some ion exchange processes that have attracted a great deal of attention in recent years, including glass poling, electro-diffusion of multivalent metals and the formation/dissolution of silver nanoparticles, has been addressed. In such processes, the usual approximations that are made in ion exchange modelling are not always valid. An overview of the progress made and the remaining challenges in the modelling of these unique processes is provided at the end of this review.

Self-Diffusion in Isotopically Controlled Heterostructures of Elemental and Compound Semiconductors

1998 ◽  
Vol 527 ◽  
Author(s):  
H. Bracht ◽  
E. E. Haller ◽  
K. Eberl ◽  
M. Cardona ◽  
R. Clark-Phelps
Keyword(s):  
Temperature Dependence ◽  
Diffusion Coefficients ◽  
Secondary Ion Mass Spectrometry ◽  
Activation Enthalpy ◽  
Exponential Factor ◽  
Self Diffusion ◽  
Diffusion Studies ◽  
Exponential Factors ◽  
Secondary Ion ◽  
Diffusion Profiles

ABSTRACTWe report self-diffusion studies of silicon between 855 and 1388°C in highly enriched epitaxial 28Si layers. Diffusion profiles of 30Si and 29Si are determined with high resolution secondary ion mass spectrometry (SIMS). The temperature dependence of the Si self-diffusion coefficients is accurately described with an activation enthalpy of 4.76 eV and a pre-exponential factor of 560 cm2s-1. The single activation enthalpy indicates that Si self-interstitials dominate self-diffusion over the whole temperature range investigated. Self- and interdiffusion in buried Al71GaAs/Al69GaAs/71GaAs isotope heterostructures with different Al composition is measured between 800 and 1160°C. Ga self-diffusion in AlGaAs and interdiffusion of Al and Ga at the AlGaAs/GaAs interface show that Ga diffusion decreases with increasing Al composition and that the interdiffusion coefficient depends linearly on Al concentration. Furthermore Al is found to diffuse more rapidly into GaAs than Ga diffuses in GaAs. The temperature dependence of Ga and Al diffusion in GaAs and of Ga diffusion in AlGaAs is described by a single activation enthalpy in the range of 3.6±0.1 eV, but by different pre-exponential factors. Differences found for Ga and Al diffusion in GaAs and for Ga diffusion in AlGaAs with different Al concentrations are discussed.

Simulation of Pressure Effects on Self-Diffusion in BCC Metals

2008 ◽  
Vol 277 ◽  
pp. 125-132 ◽  
Author(s):  
Irina Valikova ◽  
Andrei V. Nazarov
Keyword(s):  
Atomic Structure ◽  
Diffusion Processes ◽  
Pressure Effects ◽  
Many Body ◽  
New Approach ◽  
Self Diffusion ◽  
Bcc Metals ◽  
Perfect System ◽  
Bcc Iron ◽  
And Migration

This work is devoted to the study of the point defect diffusion features in metals. In particular, we propose the model, which allows calculating activation volumes that describe the influence of pressure on the diffusion processes in solids. Our model realizes a new approach that makes it possible to self-consistently determine atomic structure near defect and constants characterizing the displacement of atoms in an elastic matrix around computational cell. Also we take into consideration that the energy of perfect system and system with a defect differently depends on the outer pressure, and this gives an addition to the values of migration and formation volumes. This addition can comprise a considerable part of activation volume. Moreover, we take into account that the atomic jump is a momentary process and so we carry out only partial relaxation of the atomic structure in the vicinity of a defect. The formation and migration energies and formation and migration volumes have been calculated for vacancies, di-vacancies and interstitials in bcc iron and tungsten using pair and many-body potentials.

Transport Properties in Ionic Media

2000 ◽  
Vol 651 ◽  
Author(s):  
A.-L. Rollet ◽  
M. Jardat ◽  
J.-F. Dufrêche ◽  
P. Turq ◽  
D. Canet
Keyword(s):  
Elastic Scattering ◽  
Experimental Evidence ◽  
Transport Properties ◽  
Diffusion Coefficients ◽  
Electrical Transport ◽  
Brownian Dynamics ◽  
Diffusion Processes ◽  
Dynamical Processes ◽  
Self Diffusion ◽  
Nafion Membranes

AbstractTransportcoe[ ]cients in charged media exhibit strong variations, according to the conditions of displacement of the particles. Electrical transport, characterized by the simultaneous displacement of positive and negative charges in opposite directions obeys Ohm's law, but its variation with concentration (non-ideality), depends on several types of interactions, whose time of establishment varies from picosecond to nanosecond. Several diffusion processes can occur: mutual diffusion, where ions move simultaneously in the same direction, keeping local elec- troneutrality, and self diffusion where individual ionic particles move separately. The variation of diffusion coefficients with concentration dependson non-ideality factors analogous to those occuring in conductance, and their experimental evidence is facilitated b y the availability of experimental tec hniquesowing different characteristic times of observation. This phenomenon is particularly noticeable for self-diffsuion coefficients, where the dynamical processes can be observed from the picosecond range (neutron quasi-elastic scattering), to millisecond (NMR) and to hour scale (radiactive tracers). The results are especially enhanced for porous charged media like ion exchanging membranes (nafions).Those results are be explained here theoretically in the framework of contin uous solv en t model theories (brownian dynamics) and experimentally in the study of self-diffusion in nafion membranes.

scholarly journals The change of diffusion processes for O+ + N2 → NO+ + N reaction in the ionospheric F region during the solar eclipse over Kharkov

2021 ◽  
Vol 25 (Spec. issue 1) ◽  
pp. 51-56
Author(s):  
Mehmet Yasar
Keyword(s):  
Solar Eclipse ◽  
Experimental Measurement ◽  
Diffusion Coefficients ◽  
Diffusion Processes ◽  
Medium Scale ◽  
Self Diffusion ◽  
F Region ◽  
Solar Eclipses ◽  
The Relationship

Research on solar eclipses has been a very importance in detecting short and medium-scale changes in the ionosphere. In this paper, the relationship between the changes in self-diffusion coefficients (SDC) of the O+ + N2 ? NO+ + N reaction with the solar eclipse of March 29th, 2006 in Kharkov (49.6? N and 36.3? E) was investigated for 202, 252 and 303 km. The results of the research showed that self-diffusion coefficients increases with the increase of ionospheric altitude in each three days and the maximum diffusion value is reached at 303 km on 29th of March. It can be said that results of effects of solar eclipse in Turkey on ionosphere, results of the study of the experimental measurement and obtaining results of our study are consistent with one another.

scholarly journals Self-Diffusion Coefficients, Aggregation Numbers and the Range of Existence of Spherical Micelles of Oxyethylated Alkylphenols

2021 ◽  
Author(s):  
Victor P. Arkhipov ◽  
Natalia A. Kuzina ◽  
Andrei Filippov
Keyword(s):  
Aqueous Solutions ◽  
Diffusion Coefficients ◽  
The Self ◽  
Self Diffusion ◽  
Aggregation Numbers ◽  
Temperature Ranges ◽  
Spherical Micelles ◽  
Limiting Values

AbstractAggregation numbers were calculated based on measurements of the self-diffusion coefficients, the effective hydrodynamic radii of micelles and aggregates of oxyethylated alkylphenols in aqueous solutions. On the assumption that the radii of spherical micelles are equal to the lengths of fully extended neonol molecules, the limiting values of aggregation numbers corresponding to spherically shaped neonol micelles were calculated. The concentration and temperature ranges under which spherical micelles of neonols are formed were determined.

scholarly journals Effect of Modification on the Fluid Diffusion Coefficient in Silica Nanochannels

Molecules ◽  
2021 ◽  
Vol 26 (13) ◽  
pp. 4030
Author(s):  
Gengbiao Chen ◽  
Zhiwen Liu
Keyword(s):  
Diffusion Coefficient ◽  
Diffusion Coefficients ◽  
Surface Effect ◽  
Bulk Water ◽  
Self Diffusion ◽  
Average Diffusion Coefficient ◽  
Average Diffusion ◽  
Chain Lengths ◽  
Fluid Diffusion ◽  
Self Diffusion Coefficient

The diffusion behavior of fluid water in nanochannels with hydroxylation of silica gel and silanization of different modified chain lengths was simulated by the equilibrium molecular dynamics method. The diffusion coefficient of fluid water was calculated by the Einstein method and the Green–Kubo method, so as to analyze the change rule between the modification degree of nanochannels and the diffusion coefficient of fluid water. The results showed that the diffusion coefficient of fluid water increased with the length of the modified chain. The average diffusion coefficient of fluid water in the hydroxylated nanochannels was 8.01% of the bulk water diffusion coefficient, and the diffusion coefficients of fluid water in the –(CH2)3CH3, –(CH2)7CH3, and –(CH2)11CH3 nanochannels were 44.10%, 49.72%, and 53.80% of the diffusion coefficients of bulk water, respectively. In the above four wall characteristic models, the diffusion coefficients in the z direction were smaller than those in the other directions. However, with an increase in the silylation degree, the increased self-diffusion coefficient due to the surface effect could basically offset the decreased self-diffusion coefficient owing to the scale effect. In the four nanochannels, when the local diffusion coefficient of fluid water was in the range of 8 Å close to the wall, Dz was greater than Dxy, and beyond the range of 8 Å of the wall, the Dz was smaller than Dxy.

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