Fick’s Laws

Diffusion simulation based on atomistic model and mobility determination via Kirkendall experiment for multi-component systems

First principles study of the occurrence of gold in pyrite

Study of diffusion and atomic mobilities for fcc Ag–Cd and Ag–Sn solder alloys

Correlation between estimated diffusion coefficients from different types of diffusion couples in multicomponent system

Diffusion in the Ag-Cd system was investigated at 600°C with vapor-solid and solid-solid diffusion couples in the α-phase for the determination of intrinsic diffusion coefficients, atomic mobilities and interdiffus ion coefficients. Intrinsic diffusion coefficients, DCd and DAg, determined experimentally, were compared with those predicted from the models of Darken, Manning, and Dayananda with the aid of tracer diffusion and thermodynamic data. The experimental coefficients for various alpha alloys were found to be higher than those evaluated from each of the three models. On the other hand, the experimental values of the ratio, DCd/DAg were found to be in good agreement with the models of Manning and Dayananda where the vacancy wind effects on intrinsic diffusion are taken into account. Darken’s relations are considered inadequate to interrelate tracer and intrinsic diffusion coefficients in the Ag-Cd system, since vacancy wind effects are found to be appreciable in this system.

This paper examines how the Forty-Eighters, who came to America in search of freedom after the failure of the 1848 German revolutions, perceived and experienced American liberty, focusing on three main themes. Chapter 2 discusses the stance of the liberal Forty-Eighters on American political institutions and contemporary issues, centered on the 1854 Louisville Platform. Chapter 3 describes the critiques of America by the socialists who were part of the Forty-Eighters and the reaction of American society to them. Finally, it examines the position the Forty-Eighters held on the issue of slavery, which drove America to war in the mid-19th century, and the roles they played in the Civil War, focusing on several key figures. The Forty-Eighters viewed American politics and society as a bundle of contradictions. The American president, a “king in a dress coat,” wielded powerful authority like a German monarch, while the American federal system appeared unstable to those who had yearned for a centralized, unified Germany. However, the guaranteed freedom of the press and the possibility of reform through the ballot were better than in Germany. Their demands for radical reform in American society were specified in the 1854 Louisville Platform, which called for the abolition of slavery, separation of church and state, free distribution of public lands, and the abolition of the presidency. Socialists like Weitling and Willich organized labor movements and engaged in radical journalism. The socialist Forty-Eighters also provoked antagonism in an American society deeply rooted in Lockean liberalism, which held private property as absolute; this sometimes manifested as nativist violence against German immigrants, such as the “Bloody Monday” riot in Louisville in 1855. The issue of slavery was the black hole that absorbed all other political issues in the 1850s. The vast majority of Forty-Eighters strongly supported the abolition of slavery, and the Louisville Platform mentioned this issue first. Furthermore, the Forty-Eighters did not just pay lip service to abolition; when the Civil War broke out, many enlisted as officers in the Union Army, risking their lives to fight for the end of slavery. The Forty-Eighters acted as both external critics and internal reformers of American democracy in the mid-19th century. While America was an alternative and a hope for them after the failure of the revolution, once they arrived, they found it to be an object of reform, just like their German fatherland. The issue of slavery and the Civil War provided an opportunity to show American society that they were not mere dreamers chasing empty ideals detached from reality.

The calculations are carried out by the use of semiempirical methods of molecular orbital local combination of atom orbital. The calculations results show that Zn will deposit more probable on interstitial sites on 1.5 angstroms distances from the substratum surface with 0.3 eV bond energy, and its position is energetically instable. For Ga atoms, beside interstitial sites (r0 equals 0.5 angstroms, E0 equals -2.3 eV) there are NaCl lattice sites and bond center (r0 equals 1.5 angstroms, E0 equals -1.8 eV). The S atoms will trap by the crystalline lattice sites with 5.0 - 5.5 eV bond energy at 2.5 angstroms distance. Moreover, its penetration to monolayer surface through interstitial sites at r0 equals 4 angstroms distance is possible. In spite of Zn at ZnGa2S4 compound sputtering evaporates the most effectively, the probability of its deposition in the first layer on NaCl substratum is low. Ga and S atoms will substitute Zn atoms, which transit inside lattice or to the next monolayers. The Ga2S structure formation with S localization on sites and Ga in interstitial sites of NaCl lattice is expected.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Geometrical modeling of the B2 structure indicates that the tetrahedral interstitial site is always the largest both before and after an a/2〈111〉 translation on {110}, such as occurs during the slip of a partial dislocation in some B2 compounds. The tetrahedral site within the APB which trails a gliding a/2〈111〉 dislocation is larger than in the unslipped lattice, suggesting that interstitial atoms will segregate there. Also, some interstitial sites in a B2 lattice are larger than those in a bcc lattice of the same lattice parameter, suggesting that interstitials may have greater solubility in B2 compounds.

In resistive random access memory devices (RRAM), materials selection plays a critical role in the tuning of properties like switching voltages, retention, and endurance. Aside from choosing between transition metal-oxide matrices like HfOx, TiOx, TaOx, NiOx, and AlOx, doping in the oxide can also be a powerful tool for device optimization. However, only a handful of dopants have been studied in detail [1-3], and it is currently not known which will offer the greatest benefit for device performance. The filamentary switching mechanism in RRAM devices, in which charged oxygen vacancies (VO’s) coalesce into conductive filaments during switching, has been widely documented [4-9]. Dopants have been shown to affect the switching characteristics of RRAM devices by decreasing the formation energy of VO’s and potentially stabilizing conductive filaments [1-3]. In this investigation, first principles modeling is used to characterize 42 possible dopants in HfOx. In addition to quantifying their effects on HfOx devices, trends are extracted which can serve as general guidelines for doping in any transition metal-oxide, and which are applicable to conductive bridge random access memories (CBRAM) as well. This work identifies a critical new metric for predicting dopant behavior in RRAM and CBRAM: the relative favorability of the dopant forming on substitutional or interstitial sites in the oxide lattice. Dopants that form on interstitial sites, such as Ag, Cu, and Ni, also tend to form cation filaments and thus CBRAM devices. Conversely, dopants that strongly prefer to substitute onto the Hf lattice site are unlikely to produce competing cation filaments, leaving the VO-based switching mechanism intact. The relative favorability is also independent of dopant chemical potential, allowing a direct one-to-one comparison of different dopant species in HfOx. In this work, the quantity of relative stability is formulated and quantified over all 42 cation dopants. The results are shown in Fig. 1. The impact of these dopants on VO formation energy is also analyzed, as shown in Fig. 2. The effect of dopants on device properties is strongly dependent upon dopant species, and Fig.’s 2 and 3 clearly show that these effects follow predictable trends. Finally, the trends underlying dopant behavior are explored, and a model is developed to predict dopant behavior in the oxide system. The behavior of the dopant was found to vary predictably as a function of six key quantities: (1) the valence difference between the dopant and Hf, (2) the dopant atomic radius, (3) the dopant oxide enthalpy of formation, (4) the change in dopant coordination from native oxide to HfOx, (5) the magnetization of the doped system, and (6) the perturbation of neighboring ion charge states by the dopant. The derived composite function predicts the relative dopant site favorability with 95% accuracy. Since these quantities can all be calculated for different oxides, it is expected that these trends can be used as guidelines for doping in any transition metal-oxide for both RRAM and CBRAM applications. [1] D. Duncan, B. Magyari-Köpe, and Y. Nishi, Appl. Phys. Lett. 108, 043501, 2016. [2] L. Zhao, S. W. Ryu, A. Hazeghi, D. Duncan, B. Magyari-Köpe, and Y. Nishi, Tech. Digest VLSI Tech. Symp., T106-T107, 2013. [3] D. Ning, P. Hua, and W. Wei, Chin. Phys. B 23(10), 107306, 2014. [4] D. Duncan, B. Magyari-Köpe, and Y. Nishi, Elec. Dev. Lett. 37 (4), 400-403, 2016. [5] B. Magyari-Köpe, S.G. Park, H.-D. Lee, and Y. Nishi, J. Mater. Sci. 47, pp. 7498-7514, 2012. [6] S.G. Park, B. Magyari-Köpe, and Y. Nishi, Phys. Rev. B, 82, 115109, 2010. [7] H.-D. Lee, B. Magyari-Köpe, and Y. Nishi, Phys. Rev. B 81, 193202, 2010. [8] S.G. Park, B. Magyari-Köpe, and Y. Nishi, Tech. Digest VLSI Tech. Symp., 2011. [9] B. Magyari-Köpe, M. Tendulkar, S.G. Park, H.-D. Lee, and Y. Nishi, Nanotechnology 22, 254029, 2011. Figure 1

Magnetic fields acting on muons in textured and single crystalline holmium

A THEORY OF DIFFUSION IN THE L12 STRUCTURE II: TRACER AND CHEMICAL DIFFUSION

Chapter Twenty One - Oxygen and Bulk Microdefects in Silicon

In order to clarify the mechanisms of hydrogen diffusion in the cubic (C15) and hexagonal (C14) modifications of Laves phase ZrCr2, we have performed high-resolution quasielastic neutron scattering measurements on C15-ZrCr2H0.45 and C14-ZrCr2H0.5 over the temperature range 10-340 K. It is found that in both systems the diffusive motion of hydrogen can be described in terms of two jump processes: the fast localized H motion within the hexagons formed by interstitial (ZrCr2) sites and the slower hopping from one hexagon to the other. The experimental results are analysed to determine the hydrogen hopping rates and the tracer diffusion coefficients as functions of temperature. The motional parameters of hydrogen in the C15- and C14-type samples are found to be close to each other. Comparison of the motional parameters of hydrogen in ZrCr2Hx and in the related C15-type TaV2Hx shows that the localized H motion in ZrCr2 is slower, whereas the long-range H diffusion is much faster than in TaV2. These features are consistent with the difference between intersite distances in the hydrogen sublattices of ZrCr2Hx and TaV2Hx.

U 2-centers in alkali halides are neutral hydrogen atoms in interstitial lattice sites, as has been shown by EPR measurements. The hyperfine interactions with the proton and with the four nearest halogen nuclei are resolved in the EPR spectrum. In order to resolve hyperfine interactions with further nuclei of the surrounding lattice ENDOR measurements have been performed onU 2-centers in KCl at 77 °K. The analysis of the ENDOR spectra gave precise values for the hyperfine and quadrupole interaction constants of the nearest neighbour chlorine and potassium nuclei. The isotropic hyperfine constant of the chlorine neighbours is 24 times larger than that of the potassium neighbours although both nuclei are on equivalent first shell lattice positions. The hyperfine interactions of second shell potassium nuclei [(1/2, 1/2, 3/2)-position] show an unexpectedly large isotropic hyperfine constant. One expects a pure magnetic dipole-dipole interaction for the outer shell nuclei because of the concentrated hydrogen wave function. Two further chlorine shells could be approximately analysed. A theoretical estimate of the hyperfine and quadrupole interaction constants was made by orthogonalizing the 1s hydrogen wave function to the cores of the surrounding ions. If one takes into account the mutual overlap of neighbouring potassium and chlorine ions, one gets the right order of magnitude of the measured constants and a value of 10.4∶1 for the ratio of the isotropic hyperfine constants of the first shell chlorine and potassium nuclei. The relatively large isotropic constant of the second shell potassium nuclei can also be explained on this basis.

Substitution and electrical activation of carbon in C- and C+P-implanted InP