The use of optical techniques, such as interference microscopy and IR micro-imaging, has enabled the direct observation of transient concentration profiles. In a one-dimensional crystal, surface permeabilities on opposing crystal faces are usually equal, so that mass transfer occurs symmetrically and the fluxes through both crystal faces are identical. If the surface permeabilities on opposing crystal faces are different from each other, mass transfer is not symmetrical anymore. We are going to show that the fraction of molecular uptake (or release) through a given host face is inversely proportional to the time constant of uptake/release via this crystal face. This finding permits a straightforward estimate of the influence of asymmetry on overall uptake.

Proton pulsed field gradient (PFG) NMR technique at high magnetic field (17.6 T) and high magnetic field gradients (up to 30 T/m) is applied to study diffusion of the anions and cations in the ionic liquid 1-ethyl-3-methylimidazolium ethylsulfate ([Emim][ETSO4]) with and without water. Excellent NMR spectral resolution attained by this technique allowed high-precision monitoring of the diffusivities of the anions, cations and water in a single experiment. The PFG NMR data show that the anomalous relationship between the ion diffusivities, i.e. larger self-diffusion coefficient of the bulkier [Emim] cation than that of the less bulky [ETSO4] anion, becomes much less pronounced due to addition of water into the ionic liquid. This observation is explained by the distortion of the local structure in the ionic liquid by water molecules leading to a possible loss of the diffusion anisotropy for the cation diffusion. The reported experimental data are in a qualitative agreement with the most recent results of molecular dynamics simulations (see references 9 and 10).

The dissociative mechanism of nickel in silicon has been studied experimentally, assuming the near equilibrium represented by CiCV / Cs = Ci eq C eq / Cs eq , where subscripts i, V, and s represent interstitial nickel atoms, vacancies, and substitutional nickel atoms, respectively, superscript eq represents the thermal equilibrium, and CA is the concentration of component A. However, the assumption of the near equilibrium has not yet been verified experimentally, because it is difficult to measure CV in silicon. In the present work, the simultaneous diffusion equations of the dissociative mechanism of nickel in silicon are solved numerically by double-precision FORTRAN without assuming the near equilibrium under the condition of in-diffusion of nickel into a silicon specimen, and the establishment of the near equilibrium is verified. It is also clarified that the near equilibrium is a transitional process which continues until the thermal equilibrium is reached. After the near equilibrium is reached, the very small difference of two nearly equal terms is an important factor in solving the diffusion equations. In other words, high accuracy is necessary to solve the diffusion equations. Concerning this, it is verified that the accuracy of double-precision FORTRAN is sufficiently high to solve the diffusion equations in the present work.

Besides common implant techniques, dopant diffusion enables steep diffusion profiles in heavily doped deep-source drain and ultra-shallow junctions as required in advanced microelectronic technology. Experimental phosphorus dopant diffusion profiles in silicon are described by a rational function diffusion (RFD) model, based on direct solution of Fick’s equations and suitable for actual work in junction engineering.

A multi-pulsed free-induction NMR experiment is described theoretically for spins diffusing within a cylindrical capillary. The characteristic time for the particles to move on a distance of the capillary diameter is smaller or comparable to the time interval between the applied 90° rf pulses and the relaxation times entering the Bloch equations. In this case the spin diffusion is restricted and the classical solutions of these equations for unbounded media are not applicable. We have calculated the mean magnetization in the cross-section of the capillary after any of the rf pulses and found the induced NMR signal within the Bloch-Torrey-Stejskal theory for spins reflected at boundaries. The problem is extended by considering a possible macroscopic (plug and Poiseuille) flow of the fluid inside a capillary. It is found that with the increase of the rf pulse number, the maxima of the observed signals do not decay to zero but converge to a nonzero value. The proposed theory thus seems to be suitable for the description of experiments on systems rapidly relaxing due to diffusion and flow.

A method using Pulsed Field Gradient Nuclear Magnetic Resonance PFG-NMR for water-incrude oil emulsion droplet size determination has been optimized and compared with optical microscope for validation. The method applies a combination of Pulsed-Field Gradient (PFG) NMR, Stimulated Echo (STE), and Carr-Purcell-Meimboom-Gill (CPMG) sequences for measuring diffusion, resolving oil and water signal and for measuring the attenuation due to a distribution in T2 values. This returns the droplet size distributions of water-in-oil emulsions within a minute. No prior assumption is made on the shape of the droplet size distribution, which enables the method to resolve for instance bimodal distributions. To validate this method, three different crude oils were used in the experiment. The emulsions prepared had water cuts from 10 to 40 %. The correlation between PFG-NMR and optical microscopy was good for the emulsions. Any potential discrepancies between the two techniques are discussed, so are the limitations and advantages of the methods.

Preferential heat and mass transfer induces diffusive thermal instabilities in premixed laminar flames. Such instabilities in hydrocarbon flames are characterized by cellular structure and a tendency to promote flame extinction. We investigate the properties of such instabilities in C4H10-C3H8/air flames. The adiabatic burning velocity of the laminar premixed flame was measured at different equivalence ratios while exhibiting cellular instabilities. Direct photographs have been captured to qualitatively asses the effect of burner plate temperature on the cellular structure of the flame. The present study preliminarily suggests a normal logarithmic correlation to predict the adiabatic burning velocity of diffusive thermal instabilities in laminar premixed C4H10-C3H8/air flames.

Point defects in semiconductors play a decisive role for the functionality of semiconductors. A detailed, quantitative understanding of diffusion and defect reactions of dopants is required for advanced modelling of modern nanometer size electronic devices. With isotope heterostructures which consist of epitaxial layers of isotopically pure and deliberately mixed stable isotopes, we have studied the simultaneous self- and dopant diffusion in several major semiconductors such as silicon and germanium. Detailed analysis of the simultaneous diffusion of self- and dopant atoms in Si and Ge yields information about the ionization levels of native defects and about dopant-defect interactions in Si and Ge. The results of these diffusion studies are highlighted in this work.

The crystal structure of mayenite (ideal composition: Ca12Al14O33) consists of a (disordered) calcium-aluminate framework comprising 32 of the 33 oxygen anions. It contains large open cages, 1/6 of them being filled randomly by the remaining “free” oxygen which is available for diffusion and very high ionic conductivities. This extraframework oxygen could be substituted by nitrogen, opening up possibilities for a pure nitrogen ionic conductor. From high temperature neutron powder diffraction experiments, data analysis employing difference Fourier methods and anharmonic Debye-Waller factors and comparing pure O-mayenite with partly exchanged N/O-mayenite it is concluded that oxygen diffusion proceeds via jump-like processes, intimately coupled to relaxations of Ca and involving exchange of the “free” oxygen with framework oxygen, while nitrogen diffusion appears to proceed via an interstitial process.

The diffusion of Ag in CdTe exhibits anomalous concentration profiles, which essentially reflect the profile of the deviation from stoichiometry. At a diffusion temperature of about 800 K, the Ag dopant atoms are present as charged interstitials. The deviation from stoichiometry at diffusion temperature substantially changes upon an external source of Cd atoms. Such an external source can be represented either by the vapor pressure from metallic Cd or by a Cd layer arising at the interface to an evaporated layer of Cu or Au. Also, the Co diffusion in CdZnTe is shown to be strongly affected by the presence of an external vapor pressure of Cd, but in a substantially different way compared to the Ag diffusion in CdTe.