Low-temperature Diffusion Research Articles

Charge and spin diffusion on the metallic side of the metal-insulator transition: A self-consistent approach

We develop a self-consistent theory describing the spin and spatial electron diffusion in the impurity band of doped semiconductors under the effect of a weak spin-orbit coupling. The resulting low-temperature spin-relaxation time and diffusion coefficient are calculated within different schemes of the self-consistent framework. The simplest of these schemes qualitatively reproduces previous phenomenological developments, while more elaborate calculations provide corrections that approach the values obtained in numerical simulations. The results are universal for zinc-blende semiconductors with electron conductance in the impurity band, and thus they are able to account for the measured spin-relaxation times of materials with very different physical parameters. From a general point of view, our theory opens a new perspective for describing the hopping dynamics in random quantum networks.

The Processing of J-R Nb3Al Superconducting Wires through the Diffusion Method at Low Temperature

Eighteen-core Nb-Al strands have been fabricated by the jelly-roll (J-R) method followed by the thermal diffusion method. The effects of sintering temperature and time on the extent of diffusion and the superconducting properties of the binary Nb-Al system were investigated, with thermal diffusion taking place under isothermal heat treatment at 750 °C-1000 °C. Results showed that the J-R Nb3Al superconducting phase could be obtained by the low-temperature diffusion method, and a higher critical temperature (T c ) was obtained with sintering between 800 °C and 900 °C. On optimizing the sintering temperature and time, it was indicated that the sintering temperature had more significant effects on the superconducting properties than the sintering time. The magnetic analysis showed that the J-R Nb3Al samples were obtained with an optimal T c of about 15.1 K by the low-temperature diffusion method with sintering for 24 h under 900 °C.

Surface analysis of InP and InGaAs after low temperature diffusion of Zinc

In order to develop III–V based devices integrated directly above post-processed silicon wafers, low temperature diffusion of zinc in n-type InP and InGaAs is studied at compatible temperatures, below 425 oC. We particularly focus on the resulting surface degradation. Efficient Zn diffusion is obtained for InGaAs samples, where the surface remains mirror-like after thermal treatment. Conversely, no significant diffusion occurs in InP where the surface is deeply deteriorated. The stability study for InP under thermal annealing in various ambients allows us to rule out thermal dephosphorization as the main cause of the surface degradation. On the basis of experimental observations and thermodynamic considerations, it is suggested that InP degradation is linked to the direct interaction of Zn and P, inducing the formation of parasitic ZnxP2 alloys, which also hinders the efficient diffusion of Zn into the InP substrate.

Chemical synthesis of Cu–Sn powder by tin(II) cementation with copper in aqueous solution

The method of Cu−Sn alloy powder chemical synthesis based on tin(II) cementation with copper powder in aqueous solution has been devised. Tin content was controlled up to 95at.% by the duration of cementation and Sn(II) : Cu molar ratio in the solution. Mechanism and kinetics of complicated reduction-oxidation reactions proceeding during Sn(II) cementation were revealed. The occurrence of overstoichiometric copper corrosion in the presence of thiourea and chloride ions was found. Partial dissolution of the reduced tin and the reduction of the dissolved Cu(I) were disclosed. Bronze powder obtained by cementation in aqueous solution contained crystalline phases of tin, copper and η-Cu6Sn5, δ-Cu41Sn11 and ξ-Cu10Sn3 phases. It was found that intermetallic compounds were formed in the result of copper and tin atoms low temperature diffusion and simultaneous reduction of Sn(II) and Cu(I). The grains in the powder were about 3µm in average size with numerous nanoparticles 40–200nm in diameter on their surface. The powder can be applied for soldering, sintering, it can be pressed in tablets and mixed with liquid fluxes for soldering.

Water in volcanic glass: From volcanic degassing to secondary hydration

Volcanic glass is deposited with trace amounts (0.1–0.6wt.%) of undegassed magmatic water dissolved in the glass. After deposition, meteoric water penetrates into the glass structure mostly as molecular H2O. Due to the lower δD (‰) values of non-tropical meteoric waters and the ∼30‰ offset between volcanic glass and environmental water during hydration, secondary water imparts lighter hydrogen isotopic values during secondary hydration up to a saturation concentration of 3–4wt.% H2O. We analyzed compositionally and globally diverse volcanic glass from 0 to 10ka for their δD and H2Ot across different climatic zones, and thus different δD of precipitation, on a thermal conversion elemental analyzer (TCEA) furnace attached to a mass spectrometer. We find that tephrachronologically coeval rhyolite glass is hydrated faster than basaltic glass, and in the majority of glasses an increase in age and total water content leads to a decrease in δD (‰), while a few equatorial glasses have little change in δD (‰). We compute a magmatic water correction based on our non-hydrated glasses, and calculate an average 103lnαglass-water for our hydrated felsic glasses of −33‰, which is similar to the 103lnαglass-water determined by Friedman et al. (1993a) of −34‰. We also determine a smaller average 103lnαglass-water for all our mafic glasses of −23‰. We compare the δD values of water extracted from our glasses to local meteoric waters following the inclusion of a −33‰ 103lnαglass-water. We find that, following a correction for residual magmatic water based on an average δD and wt.% H2Ot of recently erupted ashes from our study, the δD value of water extracted from hydrated volcanic glass is, on average, within 4‰ of local meteoric water. To better understand the difference in hydration rates of mafic and felsic glasses, we imaged 6 tephra clasts ranging in age and chemical composition with BSE (by FEI SEM) down to a submicron resolution. Mafic tephra have more bubbles per unit area (25–77mm−2) than felsic tephra (736mm−2) and thicker average bubble walls (0.07mm) than felsic tephra (0.02mm). We use a simplified diffusion model to quantify the hydration rate of vesicular glass as a function of the diffusivity of water and the average bubble wall thickness. Based on fits to our hydration rate data, we estimate the initial low-temperature diffusivity at 0.1wt.% H2Ot in volcanic glass (mafic and felsic) to be on the order of 10−3 to 10−4μm2/year and find that differences in hydration rates between mafic and felsic tephra can be attributed primarily to differences in vesicularity, although slightly slower hydration of basalt cannot be precluded. We also observe no consistent temporal difference in secondary meteoric water uptake in wet versus dry and hot versus cold climates.

Experimental study on a Nb3Al insert coil under high magnetic field

Nb3Al is one of the most promising superconductors to replace Nb3Sn in large scale, high field superconducting magnet. Since the complicated conductor manufacturing process, long and stable Nb3Al conductor is difficult to acquire in a commercial scale. Based on a 70m length of Nb–Al precursor conductor, we designed and fabricated a Nb3Al coil. The coil winding, low temperature diffusion heat treatment and epoxy impregnation are described in detail. The finished Nb3Al coil is tested as an insert in a background magnet. The test is performed at the background field from 7T to 15T. The test results are analyzed and presented in this paper.

Low temperature diffusion bonding of Ti-6Al-4V and duplex stainless steel

The binary phase Ti-6Al-4V alloy was joined with duplex stainless steel (DSS) by the diffusion bonding process in a lower temperature range of 650–800°C. An axial load of 10MPa was applied for 30min to create the joint under vacuum state. Microstructural Characterisation of the bonded interface was analyzed using optical and scanning electron microscopy. The composition of elements presented near the bonded interface was measured using Energy Dispersive Spectroscopy (EDS). The interface layers such as α-Fe+λ, λ+FeTi and β-Ti were identified in diffusion of Ti alloy and DSS at low temperature range. The interlayer growth kinetics and activation energy were evaluated using Arrhenius relationship. The diffusion coefficient of the interface elements under different temperatures were determined by Fick’s law. The quality of the bond was assessed by the mechanical shear test and microhardness. The fractured surfaces were analyzed and fractographs were prepared using XRD for the joint, bonded at 750°C which had more shear strength by hard intermetallic of Fe-Cr-Ti.

ChemInform Abstract: Diffusion‐Assisted Synthesis of Co2FeSn Heusler Nanoparticles and Their Magnetic Properties.

AbstractCo2FeSn Heusler nanoparticles (5—12 nm particle size) are prepared by boiling Co2Fe and Sn nanoparticles in tetraethylene glycol (stirring, 230 °C, 24 h) which results in diffusion of molten Sn into Co2Fe nanoparticles.

Low-temperature diffusion of implanted sodium in silicon

We have studied the low-temperature diffusion of sodium atoms implanted (at primary ion energy E = 300 keV to total doses within Φ = 5 × 1014–3 × 1015 cm–2) in single-crystalline silicon grown by the method of float-zone melting (fz-Si) with low oxygen concentration N O and by the Czochralski method in the presence of magnetic field (mCz-n-Si and mCz-p-Si) with N O ≈ 5 × 1017 cm–3. The diffusion was studied at annealing temperatures within T ann = 500–420°C for periods of time t ann = 72–1000 h. It is established that the temperature dependence of the diffusion coefficient D(103/T) of sodium in fz-Si in a broad range of T ann = 900–420°C obeys the Arrhenius law with E fz = 1.28 eV and D 0 = 1.4 × 10–2 cm2/s. The same parameters are valid for the implanted sodium diffusion in mCz-Si in the interval of T ann = 900–700°C. However, at lower temperatures, the values of D in mCz-Si are lower than to those in fz-Si, which is related to the formation of more complicated Na–O n (n > 1) complexes in the former case. Estimation of the diffusion activation energy of these complexes yields ΔE ≈ 2.3 eV.

Low temperature diffusion and its impact on hydrogenation

The impact of a low temperature diffusion (LTD) step at about 650°C after emitter diffusion on the performance of silicon solar cells is investigated. Neighbouring wafers from a silicon ingot with and without LTD were chosen to make the cells using screen printed techniques. The efficiency was measured and detailed photoluminescence images were performed for the cells with and without LTD. It is found that LTD can significantly increase the efficiency of the cells about 2% by a gettering effect. The post-firing hydrogen passivation was then applied to the screen printed cells made with and without LTD. The efficiency and photoluminescence image before and after post-firing hydrogen passivation were measured to examine the impact of hydrogenation on the cells made with and without LTD. It is found that cells with LTD can respond better to hydrogenation.

Bond formation kinetics affects self-assembly directed by ligand-receptor interactions.

In this paper we study aggregation kinetics in systems of particles functionalised by complementary linkers. Most of the coarse-grained models currently employed to study large-scale self-assembly of these systems rely on effective potentials between particles as calculated using equilibrium statistical mechanics. In these approaches the kinetic aspects underlying the formation of inter-particle linkages are neglected. We show how the rate at which supramolecular linkages form drastically changes the self-assembly pathway. In order to do this we develop a method that combines Brownian dynamics simulations with a Gillespie algorithm accounting for the evolution of inter-particle linkages. If compared with dynamics based on effective potentials, an explicit description of inter-particle linkages results in aggregates that in the early stages of self-assembly have a lower valency. Relaxation towards equilibrium is hampered by the time required to break existing linkages within one cluster and to reorient them toward free particles. This effect is more important at low temperature and high particle diffusion constant. Our results highlight the importance of including kinetic rates into coarse-grained descriptions of ligand-receptor systems.

A novel method for development of hard nano crystalline surface through SMAT and mechanical alloying

A hard Nano crystalline surface was produced by simultaneous surface mechanical attrition treatment (SMAT) and mechanical alloying (MA) with activated carbon, followed by low temperature annealing below 500°C. The thermal stability of surface Nano crystals produced by SMAT and low temperature diffusion of carbon into Nano crystals were also investigated by annealing 200°C to500°C for 1h. Ni-Cr-Mo casehardening steel was used in the present study. The formation of Nano crystals and surface alloying with activated carbon by SMAT, microstructural changes during annealing, thermal stability of the Nano crystals and the surface hardness were been investigated by using Optical microscope, SEM, XRD and microvicker’s hardness tester. Experimental results had showed 20-50 nm crystals by SMAT operation by enhancing 0.19C to 0.4C. Enhanced diffusion kinetics of Nano crystals observed during the annealing process even at 200°C. The simultaneous SMAT and MA with carbon increased the surface hardness from 1.5 to 3.0 GPa in 20 minutes and subsequent annealing further increased the hardness steadily up to 450°C. A maximum hardness of 4.5 GPa was achieved by annealing treatment. The hardness decreased considerably at 500°C indicating grain growth at thistemperature. The results had clearly demonstrated that the surface Nano crystals formed by SMAT were found stable up to 450°C.

Low-Temperature Diffusion at Ni/SiC Interface with the Aid of Femtosecond Laser-Induced Strain

Low-Temperature Diffusion at Ni/SiC Interface with the Aid of Femtosecond Laser-Induced Strain

Diffusion-assisted Synthesis of Co2FeSn Heusler Nanoparticles and Their Magnetic Properties

Abstract Co2FeSn Heusler nanoparticles with the particle size of 5–12 nm were synthesized by using pre-synthesized Co2Fe and Sn nanoparticles in high boiling-point solvents, wherein the molten Sn diffused into Co2Fe nanoparticles to form Co2FeSn nanoparticles. The obtained Co2FeSn nanoparticles show a high magnetic moment of 5.2 μB at 5 K, which is comparable with that of most of the bulk Co2YZ Heusler compounds. This low-temperature diffusion method is believed to have potential applications in synthesizing other Heusler nanoparticles.

Correct determination of low-temperature free-exciton diffusion profiles in GaAs

We report on low-temperature spatially resolved photoluminescence (SRPL) experiments to study the diffusion of free excitons in a $1.5\text{\ensuremath{-}}\ensuremath{\mu}\mathrm{m}$-thick layer of high-purity epitaxial GaAs. Extending previous SRPL experiments, we analyze the stationary diffusion profiles detected on the second LO-phonon replica of the free exciton. This allows us to circumvent the inherent interpretation ambiguities of the free-exciton zero-phonon line. Moreover, a spatially resolved line shape analysis of the $(FX)\ensuremath{-}2\ensuremath{\hbar}{\mathrm{\ensuremath{\Omega}}}_{\text{LO}}$ replica provides direct experimental access to the pump-induced exciton temperature profile. We demonstrate that only resonant optical excitation prevents the buildup of a temperature gradient in the carrier system, which otherwise severely distorts the stationary and time-resolved free-exciton diffusion profiles.

Joining of Silver Nanomaterials at Low Temperatures: Processes, Properties, and Applications.

A review is provided, which first considers low-temperature diffusion bonding with silver nanomaterials as filler materials via thermal sintering for microelectronic applications, and then other recent innovations in low-temperature joining are discussed. The theoretical background and transition of applications from micro to nanoparticle (NP) pastes based on joining using silver filler materials and nanojoining mechanisms are elucidated. The mechanical and electrical properties of sintered silver nanomaterial joints at low temperatures are discussed in terms of the key influencing factors, such as porosity and coverage of substrates, parameters for the sintering processes, and the size and shape of nanomaterials. Further, the use of sintered silver nanomaterials for printable electronics and as robust surface-enhanced Raman spectroscopy substrates by exploiting their optical properties is also considered. Other low-temperature nanojoining strategies such as optical welding of silver nanowires (NWs) through a plasmonic heating effect by visible light irradiation, ultrafast laser nanojoining, and ion-activated joining of silver NPs using ionic solvents are also summarized. In addition, pressure-driven joining of silver NWs with large plastic deformation and self-joining of gold or silver NWs via oriented attachment of clean and activated surfaces are summarized. Finally, at the end of this review, the future outlook for joining applications with silver nanomaterials is explored.

Nanoscale diffusion in Pt/56Fe/57Fe thin-film system

Low-temperature diffusion of Fe in Pt/56Fe/57Fe thin films (grown on MgO (100) substrate) was investigated between 703K and 813K using secondary neutral mass spectrometry. The activation energy of the effective interdiffusion coefficients, evaluated by the “centre-gradient” method, is 1.53±0.25eV reflecting a strong contribution from grain boundaries. This is also supported by the observed deep penetrations of Pt into the 56Fe layer, from which the grain boundary diffusion coefficients for Pt in Fe were also estimated and 1.45±0.25eV activation energy was obtained. A simple model, including the effect of grain boundaries to the overall intermixing at the original sharp interfaces in nanocrystalline films, is developed. This predicts that at short annealing times the grain boundary diffusion dominates, and bulk diffusion coefficients can be determined only in long time limit. At intermediate annealing times, when the grain boundaries are saturated but the bulk diffusion is still negligible, there are no changes in the composition profiles. This yields good qualitative agreement with the experimental data and offers explanation for the time and temperature dependence of the interdiffusion coefficients obtained in similar systems.

Duplex ceramic coating produced by low temperature thermo-reactive deposition and diffusion on the cold work tool steel substrate: Thermodynamics, kinetics and modeling

Specimens of DIN 100MnCrW4 steel (type O1 tool steel) have been cut and prepared for performing a duplex surface treatment involving nitriding and low temperature vanadium thermo-reactive deposition and diffusion (TRD) technique. The TRD process was performed in a molten salt bath at different temperatures of 575, 650 and 725°C for 1–30h. The treatment formed a vanadium carbonitride coating with the thickness up to 10.5μm on a hardened diffusion zone. Characterizations by means of an optical microscope (OM), scanning electron microscope equipped with energy dispersive X-ray spectrometer (SEM–EDS) and X-ray diffraction analysis (XRD) indicated that the compact and dense coating mainly consisted of V(C,N) and V2(C,N) phases. All the growth processes of the formed vanadium carbonitride layer obtained by TRD followed a parabolic kinetics while the calculated activation energy (Q) for the treatment was 181.1kJ/mol. An artificial neural network (ANN) based model for predicting the layer thickness of ceramic coatings was presented. Constructing the model, training, validating and testing of experimental results from 72 different specimens were conducted. The data used as inputs in the proposed model were arranged in a format of five parameters that comprised of “pre-nitriding time”, “ferro-vanadium particle size”, “ferro-vanadium weight percent”, “salt bath temperature” and “coating time”. Accordingly, the thickness of duplex coating in each specimen was estimated accurately. Finally, the proposed ANN-based model showed a strong potential for predicting the layer thickness of duplex ceramic coating performed by the TRD technique on the substrate of cold work tool steel.

Low-temperature diffused p–n junction with nano/microrelief interface for solar cell applications

The investigation is aimed at elaboration of technology for submicron p+-GaAs layer formation on micro/nanotextured n-GaAs substrates by using low-temperature (550°C) diffusion of zinc to take the advantage of optical and recombination properties of textured interface for solar cells. Process duration, surface microrelief morphology (dendrite or quasi-grating (grating-like)) and the substrate doping impurity concentration were varied. Optical, photoelectric and electrical properties of p+–n junction were studied to optimize the process conditions. The highest efficiency was obtained in structures with a quasi-grating surface microrelief, substrate doping close to Nd≃1017cm−3 and process duration about 45min.

Application of femtosecond laser irradiation to low-temperature diffusion at the Ni/SiC interface

We discovered low-temperature diffusion caused by femtosecond (fs) laser irradiation at the Ni/SiC interface. Before annealing, strained layers were introduced into the near-interface region in the SiC substrate by fs laser irradiation. Transmission electron microscopy unveiled Ni diffusion into SiC, occurring preferentially along strained layers, associated with the diffusion of Si and C into the Ni film, resulting in the formation of an interdiffusion layer. The strained layers acted as a sink for absorbing the Kirkendall voids close to the interface. These results indicate the potential application of fs laser irradiation for low-temperature fabrication of contacts at the Ni/SiC interface.