Simulation of boronizing kinetics of ASTM A36 steel with the alternative kinetic model and the integral method

In this study, two different mathematical models have been proposed for estimating the diffusivities of boron in the Fe2B layer on ASTM A36 steel in the range of 1173 to 1273 K with exposure times of 2 to 8 h. The boride incubation period required for the formation of such a layer was constant regardless of the boriding conditions. In both approaches, the boron diffusivity in the iron phase was considered in an unsaturated matrix. The first approach was derived from the mass balance equation at the (Fe2B/substrate) interface while the second approach employed the integral diffusion model. The calculated values of boron activation energies for ASTM A36 steel were found to be very comparable for the two approaches (161.65 and 160.96 and kJ mol-1). Afterwards, these values of activation energy were confronted with the results from the literature. Experimental validation of these two approaches has been done by comparing the experimental value of Fe2B layer thickness measured at 1123 K for 2.5 h with the simulated values. Finally, the predicted values of Fe2B layer thickness were in line with the experimental measurement.

Li and B diffusivity in hydrated silicate melts: an experimental study

<p>Magmatic volatiles play a major role in controlling magma dynamics, such as ascent characteristics and eruption style. In order to fully understand their influence in magmatic systems, it is crucial to examine their behaviour within silicate melts. Although numerous studies have been conducted on volatile solubility, exsolution and degassing, some aspects of  magma degassing such as bubble formation, bubble growth and the affect on the distribution of fluid-mobile elements are poorly understood. For instance, magma degassing is likely to affect the abundance and dispersion of fluid-mobile elements, such as Li and B, in the magma. Thus, this study focuses on the diffusivity of Li and B in hydrated silicate melt as a proxy for degassing processes.</p><p>Lithium and boron are particularly suitable as geochemical tracers of degassing processes because they are light elements, present in natural volcanic systems in low concentrations, and have similar characteristics: both elements are fluid-mobile and each has two stable isotopes with different transport behaviours due to their atomic weights, which can lead to isotope fractionation. In order to successfully model their behaviour during magmatic ascent, their diffusivities in silicate melts have to be well constrained.</p><p>Diffusion data in hydrous settings are missing or underrepresented: very little studies have been conducted on boron diffusivity, the literature gives contradictory diffusion coefficients for lithium. In this study, we focus on elemental diffusion and isotopic fractionation of lithium and boron in hydrated silica-rich melts, in order to better understand B diffusivity and solve the discrepancies about Li data.</p><p>Sets of diffusion-couple experiments on synthetic water-bearing rhyolitic glasses have been performed, using an internally heated pressure vessel, at a constant pressure of 300 MPa and temperatures of 700°, 800° and 1000° C, with durations of 0 seconds, 30 minutes, 2 hours and 4 hours. Lithium and boron elemental concentrations have been measured by LA-ICP-MS, resulting in 600 μm long profiles, while isotopic ratios are being evaluated by SIMS analysis.</p><p>The zero-hour experiment indicates that lithium diffuses very rapidly, potentially already at temperatures below 700° C (during the heating process), while boron diffusion is generally slower, hence the necessity of higher temperatures and longer experimental run durations. Overall, our experimental results confirm previous literatue findings that Li diffuses faster in water-bearing melts, and give first constraints on boron diffusivity in hydrated silicate melts, whereas previous studies only considered anhydrous samples. The determination of diffusion coefficients of the two elements gives us a better understanding of the diffusion timescales. This information allows us to interpret additional decompression experiments, simulating a wide range of magma ascent rates, and to correlate the elemental and isotopic behaviour of lithium and boron with decompression-induced bubble formation processes.</p>

Diffusion and Activation of Ultra Shallow Boron Implants in Silicon in Proximity of Voids

We have designed a set of experiments in which a controlled supersaturation of vacancies can be maintained constant during annealing of a boron implant. In presence of voids, a remarkable reduction of boron diffusivity is observed and, for low fluence B implantation, TED can be totally suppressed. We show that the presence of nanovoids in the B implanted region is not a prerequisite condition for the reduction of B diffusivity. Large voids located at more than 100 nm apart from the B profile still show the same effect. Small voids can also be used to increase the activation of boron. All these results are consistent with the hypothesis that, during annealing, vacancies are injected from the voids region towards the Is rich region in the implanted region where they massively recombine. Finally, we show that BICs cannot be simply dissolved by injecting vacancies into the region where they stand.

Modeling and Experiments of Boron Diffusion During Sub-Millisecond Non-Melt Laser Annealing in Silicon

Boron diffusion and defect evolution during sub-millisecond (ms) laser annealing with partial SPER are investigated using secondary ion mass spectrometry and transmission electron microscopy. Boron diffusivity enhancement in amorphous-Si is observed during partial SPER at 550 °C. It is shown that boron diffusion during the laser annealing process is a 2-step diffusion (SPER + Laser). The depth of the amorphous layer affects the dopant activation behavior. During sub-ms laser annealing, end-of-range defects are formed and show an evolution behavior. {311} defects cannot completely transfer to dislocation loops after 1300 °C laser annealing. It is considered that the thermal budget of sub-ms laser is too small for full defect evolution. Atomistic diffusion modeling using a kinetic Monte Carlo method can explain the defect behavior during laser annealing.

Defects Induced by Helium Implantation: Impact on Boron Diffusivity

High dose helium implantation followed by a suitable thermal treatment induces defects such as cavities and dislocations. Gettering efficiency of this technique for metallic impurities has been widely proved. Nevertheless, dopants, as well as point defects, interact with this defect layer. Due to the presence of vacancy type defects after helium implantation, boron diffusion can be largely influenced by such a buried layer. In this paper, we study the influence of helium induced defects on boron diffusion. The boron diffusion in presence of these defects has been analyzed as a function of different parameters such as distance between boron profile and defect layer and defect density. Our results demonstrate that the major impact known as boron enhanced diffusion can be partially or completely suppressed depending on parameters of experiments. Moreover, these results clarify the interaction of boron with extended He-induced defects.

Dopant diffusion in amorphous silicon

ABSTRACTIn this work we investigate the diffusion of high-concentration ultrashallow boron, fluorine, phosphorus, and arsenic profiles in amorphous silicon. We demonstrate that boron diffuses at high concentrations in amorphous silicon during low-temperature thermal annealing. Isothermal and isochronal anneal sequences indicate that there is an initial transient enhancement of diffusion. We have observed this transient diffusion characteristic both in amorphous silicon preamorphized by germanium ion implantation and also in amorphous silicon preamorphized by silicon ion implantation. We also show that the boron diffusivity in the amorphous region is similar with and without fluorine, and that the lack of diffusion for low-concentration boron profiles indicates that boron diffusion in amorphous silicon is driven by high concentrations. Ultrashallow high-concentration fluorine profiles diffuse quite rapidly in amorphous silicon, and like boron, undergo a definite transient enhancement. In contrast, ultrashallow high- concentration phosphorus and arsenic profiles did not significantly diffuse in our experiments.

Diffusion of Boron in Germanium and Si1-xGex (x>50%) alloys Suresh Uppal

Boron diffusion in germanium and relaxed Si1-xGex alloys with Ge content x>50% is reported. Relaxed SiGe layers were grown by LEPECVD and boron was introduced using ion implantation. Samples were given equal thermal budgets using furnace annealing. Diffusivity values of boron have been extracted. The results confirm that diffusion of boron in germanium is indeed slower than that reported in literature. The diffusivity of boron was found to increase gradually for x>50% at 900°C but the increase is not substantial. We found that pairing model is not sufficient to explain boron diffusivity behavior in SiGe alloys over the entire range of germanium content. The results suggest that an interstitial mediation of boron diffusion in germanium should be considered.