Papers by Keyword: Interstitial Diffusion

Abstract: Elemental semiconductors play an important role in high-technology equipment used in industry and everyday life. The first transistors were made in the 1950ies of germanium. Later silicon took over because its electronic band-gap is larger. Nowadays, germanium is the base material mainly for γ-radiation detectors. Silicon is the most important semiconductor for the fabrication of solid-state electronic devices (memory chips, processors chips, ...) in computers, cellphones, smartphones. Silicon is also important for photovoltaic devices of energy production.Diffusion is a key process in the fabrication of semiconductor devices. This chapter deals with diffusion and point defects in silicon and germanium. It aims at making the reader familiar with the present understanding rather than painstakingly presenting all diffusion data available a good deal of which may be found in a data collection by Stolwijk and Bracht [1], in the author’s textbook [2], and in recent review papers by Bracht [3, 4]. We mainly review self-diffusion, diffusion of doping elements, oxygen diffusion, and diffusion modes of hybrid foreign elements in elemental semiconductors.Self-diffusion in elemental semiconductors is a very slow process compared to metals. One of the reasons is that the equilibrium concentrations of vacancies and self-interstitials are low. In contrast to metals, point defects in semiconductors exist in neutral and in charged states. The concentrations of charged point defects are therefore affected by doping [2 - 4].

Abstract: In this work we show our result of in-situ nitrocarburizing and nitriding treatments AISI316L specimens. Part of the samples have been depassivated ex-situ and coated with a Ni layer, while other specimens received in-situ depassivation. Processing was carried out in a custom built reaction chamber attached to a Bruker D8 Advance diffractometer. We monitored the 111 peak of both the base material and expanded austenite. From the shrinkage of the base material peak the total thickness of the expanded austenite can be determined. Applying both N and C resulted in a more than 10 times faster growth of the expanded austenite than with N only. The growth is thermally activated. The activation energy for nitrocarburizing is 164 kJ/mol. This is in agreement with the activation energy of the diffusion of interstitials. Detailed analysis of the expanded austenite peak allowed the derivation of a “master curve” for the composition depth profile. This suggest that two interacting process controls the evolution. The width of the reaction zone is limited by the diffusion at low concentration side. The total concentration is determined by the reaction at the interface.

Abstract: The mmolecular dynamics method is applied to investigate carbon interstitial diffusion in austenite at low carbon content. An approximation that carbon atoms can interact with each other only indirectly (via neighbouring iron atoms) is used. Sets of Arrhenius parameters of interstitial carbon jump frequencies identified by the four-frequency model are determined. Comparison of the molecular dynamics results with experimental data analysis in the context of the four-frequency model is performed. It is shown that the four-frequency model may not be adequate to describe the carbon diffusion process. To improve the analytical model the specific role of the transition probabilities during association and dissociation of the first nearest neighbour carbon pairs through the second neighbour sites should be considered. The direct repulsion between the carbon first neighbour positions should be also taken into account in molecular dynamics simulation.

Abstract: Anelastic relaxation measurements have been used in order to obtain information about several aspects of the behavior of solutes in metals, for example, matrix-solute interaction, interstitial diffusion, etc. The diffusion coefficient for interstitial solutes in body centered-cubic metals is accurately determined by anelastic relaxation measurements. The kind of preferential occupation of the interstitial solutes in body centered-cubic metals, such as oxygen and nitrogen in tantalum, is still controversial. Internal friction and frequency measurements as a function of temperature in tantalum sample were performed using a torsion pendulum operating in a frequency oscillation in the hertz bandwidth. These results presented the following phenomenon: the intensity of the internal friction peak decreased between the first run and the other runs. These results were decomposed, by the successive subtraction method, in elementary Debye peaks, for determination of characteristic anelastic relaxation parameters (relaxation strength, peak temperature, activation energy and relaxation time). Interstitial diffusion coefficients for oxygen in tantalum were determined, for different intensities of internal friction peaks, and when compared with literature, these results introduced a better adjustment for the tetrahedral preferential occupation sites of oxygen in tantalum.

Abstract: Metals and alloys containing solute atoms dissolved interstitially often show anelastic behavior due to a process know as stress-induced ordering. The application of mechanical spectroscopy measurements to diffusion studies in body-centered cubic metals has been extensively used in the last decades. However the kind of preferential occupation of interstitial solutes in bodycentered cubic metals is still controversial. The anelastic properties of the Nb and Nb-1 wt% Zr polycrystalline alloys were determined by internal friction and oscillation frequency measurements using a torsion pendulum inverted performed between 300K and 650K, operating in a frequency oscillation in the hertz bandwidth. The interstitial diffusion coefficients of oxygen and nitrogen in Nb and Nb-1 wt% Zr samples were determined at two distinct conditions: (a) for low concentration of oxygen and (b) for high concentration of oxygen.