Si Sn Research Articles

Phase formation in Mg–Sn–Si and Mg–Sn–Si–Ca alloys

Experimental work is done and combined with the Calphad method to generate a consistent thermodynamic description of the Mg–Ca–Si–Sn quaternary system, validated for Mg-rich alloys. The viability of a procedure for the selection of multicomponent key samples is demonstrated for this multicomponent system. Dedicated thermal analysis with DTA/DSC on sealed samples is performed and the microstructure of slowly solidified alloys is analyzed using SEM/EDX. The thermodynamic description and phase diagram of the ternary Mg–Si–Sn system, developed in detail also in this work, deviates significantly from a previous literature proposal. The phase formation in ternary and quaternary alloys is analyzed using the tool of thermodynamic equilibrium and Scheil calculations for the solidification paths and compared with present experimental data. The significant ternary/quaternary solid solubilities of pertinent intermetallic phases are quantitatively introduced in the quaternary Mg–Ca–Si–Sn phase diagram and validated by experimental data.

Stress-induced Sn Nanowires from Si–Sn Nanocomposite Coatings

The growth of stress-induced tin (Sn) whiskers has been considered responsible for the failure of many electronic devices and many approaches have been developed to mitigate their growth. In this report, however, we describe a simple approach based on the same mechanism to promote the growth of Sn nanowires. The thermal expansion induced stress was utilized as the driving force to initiate the growth of Sn nanowires from Si–Sn phase-separated nanocomposite coatings. The nanostructure of the Si–Sn matrix was the key to controlling the shape and diameter of Sn nanowires. This approach provides additional flexibility for making desirable metallic nanowires with controlled dimensions.

Design of a Si-based lattice-matched room-temperature GeSn/GeSiSn multi-quantum-well mid-infrared laser diode

This paper presents modeling and simulation of a silicon-based group IV semiconductor injection laser diode in which the active region has a multiple quantum well structure formed with Ge(0.9)Sn(0.1) quantum wells separated by Ge(0.75)Si(0.1)Sn(0.15) barriers. These alloy compositions were chosen to satisfy three conditions simultaneously: a direct band gap for Ge(0.9)Sn(0.1), type-I band alignment between Ge(0.9)Sn(0.1) and Ge(0.75)Si(0.1)Sn(0.15,) and a lattice match between wells and barriers. This match ensures that the entire structure can be grown strain free upon a relaxed Ge(0.75)Si(0.1)Sn(0.15) buffer on a silicon substrate - a CMOS compatible process. Detailed analysis is performed for the type I band offsets, carrier lifetime, optical confinement, and modal gain. The carrier lifetime is found to be dominated by the spontaneous radiative process rather than the Auger process. The modal gain has a rather sensitive dependence on the number of quantum wells in the active region. The proposed laser is predicted to operate at 2.3 μm in the mid infrared at room temperature.

Tin induced crystallisation of hydrogenated amorphous silicon thin films

The present article focuses on the effect of annealing temperatures about the Sn induced crystallisation of hydrogenated amorphous Si (a-Si:H) thin films, which are used to fabricate polycrystalline Si (poly-Si) film. The a-Si:H thin films are coated onto Sn metal thin film and subsequently annealed from various temperatures. These are crystallised by annealing for 1 h at 300°C and identified by XRD spectroscopy for the investigation of each phase. Process temperature for crystallisation should not be high because a eutectic temperature of Si–Sn is ∼232°C. Si crystal patterns of the prepared samples showed the tendency of changing from (111) to (002) with increasing temperature. It indicates that the crystal phases depend strongly on the annealing temperature of Sn induced a-Si:H thin films for the preparation of poly-Si film. Semiconducting type of Sn induced poly-Si films were shown in n-type through Hall effect measurement.

Interaction of A-centers with isovalent impurities in silicon

An A-center is an oxygen interstitial atom near a lattice vacancy and is one of the most common impurity-defect pairs in Czochralski-grown silicon crystals. In the present study, density functional theory calculations have been used to predict the binding energies of A-centers that are at nearest neighbor (NN) and next NN sites to isovalent impurities (carbon, germanium, and tin) in silicon. Interestingly, we predict that the A-center is more bound in isovalent-doped and, in particular, tin-doped silicon. We calculate that most of the binding energy of these A-centers originates from the interaction between the isovalent atoms and the vacancies.

Microstructural investigation of a rapidly solidified Ti–Zr–Fe–Si–Sn–Nb alloy

A rapidly solidified Ti 45Zr 19Fe 20Si 10Sn 4Nb 2 alloy was prepared by using centrifugal casting and copper mould. Microstructure characterization by using XRD and SEM revealed the formation of refined microstructure on surface layers at surface area with high cooling rate. The refined microstructure shows very high hardness. The current technique of forming “chill zone” of Ti alloy is considered as an alternative to produce novel Ti based alloys with gradient microstructure.

Formation of Ti–Zr–Cu–Ni–Sn–Si bulk metallic glasses with good plasticity

Formation and mechanical properties of Ti–Zr–Cu–Ni–Sn–Si glassy alloys consisting of dissimilar and similar elements are studied. Ti 45.8Zr 6.2Cu 39.9Ni 5.1Sn 2Si 1 glassy alloy can be prepared in a bulk glassy rod form of 4 mm in diameter and exhibits strength of 2100 MPa and a plastic strain of ∼5% prior to failure in compression. The plasticity of the Ti 45.8Zr 6.2Cu 39.9Ni 5.1Sn 2Si 1 bulk metallic glass is attributed to the deformation-induced nanocrystallization in the glassy matrix during compression.

Amorphous In–Sn–Si–O Thin-Film Transistors Having Various Si Compositional Ratios

We investigate the possibility of utilizing a new material, amorphous indium-tin-silicon oxide In10Sn1SixO2x+17 (a-ITSO), for the active layer in oxide-semiconductor TFTs, using a co-sputtering technique with ITO and Si targets. A Si compositional ratio x=1.88 yielded the TFT performance with a field-effect mobility of approximately 5 cm2 V-1 s-1. Spectroscopic investigations confirmed that the diversity of the Si compositional ratio in the a-ITSO films results in significant changes in chemistry and electronic structure, leading to considerable variations in the characteristics of the a-ITSO TFTs.

Influence of tin content on tribological characteristics of spray formed Al–Si alloys

In the present investigation, tribological characteristics of spray formed and hot pressed Al–6.5Si, Al–12.5Si and Al–12.5Si–25Sn alloys have been studied. The alloys were spray formed in an environmental chamber using nitrogen gas at 1.0 MPa gas pressure and a deposition distance of 350 mm. The preforms were vacuum hot pressed, at appropriate temperatures, to achieve its densification, The spray formed alloys showed considerable microstructural refinement with uniform distribution of Si particles in Al–Si alloys and that of Sn and Si particles in the matrix of primary α-Al phase of Al–Si–Sn alloys. Dry sliding wear behaviour of these materials was studied as a function of sliding distance, applied load and sliding velocity. The wear response parameters such as wear rate, seizure pressure and frictional force were measured. A pressure-sliding velocity ( P– V) limit diagram was established from the data obtained. The P– V diagram indicated that the allowable pressure range for wear seizure increased with increasing Si content. A considerable increase in the wear resistance of the alloy and the seizure pressure is observed with Sn addition. The improved wear properties of the alloy containing Sn are discussed in light of the microstructural features of spray formed alloy and the nature of the debris particles.

Pressure-induced diamond toβ-tin transition in bulk silicon: A quantum Monte Carlo study

The pressure-induced structural phase transition from diamond to $\ensuremath{\beta}$ tin in silicon is an excellent test for theoretical total-energy methods. The transition pressure provides a sensitive measure of small relative energy changes between the two phases (one a semiconductor and the other a semimetal). Experimentally, the transition pressure is well characterized. Density-functional results exhibit sensitivity to the particular form of the exchange-correlation functional. Even the generally much more accurate diffusion Monte Carlo method has shown a noticeable fixed-node error. We use the recently developed phaseless auxiliary-field quantum Monte Carlo (AFQMC) method to calculate the relative energy differences in the two phases. In this method, all but the error due to the phaseless constraint can be controlled systematically and driven to zero. In both structural phases we were able to benchmark the error of the phaseless constraint by carrying out exact unconstrained AFQMC calculations for small supercells. Comparison between the two shows that the systematic error in the absolute total energies due to the phaseless constraint is well within $0.5\text{ }\text{m}{E}_{\text{h}}/\text{atom}$. Consistent with these internal benchmarks, the transition pressure obtained by the phaseless AFQMC from large supercells is in very good agreement with experiment.

Macroscopic phase separation and primary FeSi compound growth within undercooled ternary Fe–Sn–Si monotectic alloy

Liquid ternary Fe37Sn32Si31 monotectic alloy in bulk form has been undercooled by 305 K (0.18T L) by the glass fluxing method. Macroscopic phase separation took place and led to the formation of a top Fe-rich zone and a bottom Sn-rich zone. The large degree of undercooling was found to facilitate the evolution of macrosegregation. Dendritic growth was the characteristic of the primary FeSi compound in an Fe-rich zone. The growth velocity was up to 0.42 m/s and the dendrite grains were efficiently refined by an increase in the level of undercooling. The solute trapping of Sn atoms could not occur in the FeSi compound within the undercooling range achieved here, resulting in the suppression of the dendritic growth velocity compared with that in binary Fe50Si50 alloy. The interdendritic microstructures mainly consisted of decomposed Fe5Si3 compound plus some α-Fe phase.

Specific heat, enthalpy, and density of undercooled liquid Fe–Si–Sn alloy

The specific heat of liquid Fe90Si6.95Sn3.05 alloy has been investigated by electromagnetic levitation drop calorimetery in the temperature range of 1390–2140 K. The enthalpy of this liquid alloy increases linearly with the rise of temperature. Furthermore, the enthalpy obtained from molecular dynamics calculation shows a similar trend to the experimental results in a broader temperature range of 1000–2200 K. The calculated specific heat is 39.7 J mol−1 K−1, which agrees well with the experimental result of 39.9 J mol−1 K−1. The density of this liquid alloy decreases as a quadratic function of temperature.

The SiSn Chemical Bond: An Integrated Thermochemical and Quantum Mechanical Study of the SiSn Diatomic Molecule and Small Si–Sn Clusters

The silicon-tin chemical bond has been investigated by a study of the SiSn diatomic molecule and a number of new polyatomic Si(x)Sn(y) molecules. These species, formed in the vapor produced from silicon-tin mixtures at high temperature, were experimentally studied by using a Knudsen effusion mass spectrometric technique. The heteronuclear diatomic SiSn, together with the triatomic Si(2)Sn and SiSn(2) and tetratomic Si(3)Sn, Si(2)Sn(2), and SiSn(3) species, were identified in the vapor and studied in the overall temperature range 1474-1944 K. The atomization energy of all the above molecules was determined for the first time (values in kJ mol(-1)): 233.0+/-7.8 (SiSn), 625.6+/-11.6 (Si(2)Sn), 550.2+/-10.7 (SiSn(2)), 1046.1+/-19.9 (Si(3)Sn), 955.2+/-26.8 (Si(2)Sn(2)), and 860.2+/-19.0 (SiSn(3)). In addition, a computational study of the ground and low-lying excited electronic states of the newly identified molecules has been made. These electronic-structure calculations were performed at the DFT-B3LYP/cc-pVTZ and CCSD(T)/cc-pVTZ levels, and allowed the estimation of reliable molecular parameters and hence the thermal functions of the species under study. Computed atomization energies were also derived by taking into account spin-orbit corrections and extrapolation to the complete basis-set limit. A comparison between experimental and theoretical results is presented. Revised values of (716.5+/-16) kJ mol(-1) (Si(3)) and (440+/-20) kJ mol(-1) (Sn(3)) are also proposed for the atomization energies of the Si(3) and Sn(3) molecules.

Bonding agents of low fusing cpTi porcelains: Elemental and morphological characterization

Low fusing porcelains demonstrate great variations in bond strength with cpTi, a result directly associated with the performance of their bonding agents. The aim of this study was to investigate the composition of bonding agents used for the production of Ti-ceramic restorations. The powder or paste components of nine commercially available products were imaged under LV-SEM and their elemental composition was determined by energy-dispersive X-ray microanalysis (X-ray EDS). According to the EDS results five bonding agents (Duceratin, Duceratin Plus, Ti-22, TitanKeramik, and Triceram) were mainly composed of Si Sn and Na oxides. TiKrom contained La and Ba, whereas Initial Ti was based on La, B, and Sr formulations. Backscattered electron images revealed that Titankeramik, Triceram paste, Initial Bonder and Aesthetic Universal Bonder consisted of a single-phase material, while Duceratin, Duceratin Plus, Ti-22, Tikrom, and Triceram powders consisted of two-phase materials. The large differences found in elemental compositions of the bonding agents and the development of completely new formulations imply that the relevant technology has not yet attained a standard and thus is a promising field for further research.

Microstructure investigation of bronze/steel brazed joints proposed for HHF components of ITER manufacturing

Brazing is considered as one of the perspective option of high heat flux components of ITER manufacturing. CuCrZr bronze, austenitic steel AISI 321-type and PM-17-type (Ni–Mn–Fe–Si–Sn–B alloy) brazed material were used for the development of brazing technology. Two type of brazing have been studied within the framework of recent investigation: • Hot isostatic pressing (HIP)-assisted brazing. • Furnace-assisted brazing (with uniaxial compression loading). For the hydrostatic pressing (HIP) the brazed components were pressed out for about 175 MPa during 2.5 h at the temperature 1035–1040 °C. For the furnace-assisted brazing all components were inserted into the sealed can, vacuumed and heated up to brazing temperature ∼950 °C. Fast cooling and ageing heat treatment (500 °C and 4 h) were applied to provide high strength of CuCrZr bronze. Microsections of specimens cut from the joints were studied by optical microscopy and by scanning electron microscopy (SEM). The microstructure, distribution of alloying elements of base metals and of brazed material components were studied in the joints. Results of these studies are discussed in this paper. The data shows that there is a potential for using more simple and cheap (in comparison with common HIP) technologies of bronze to steel joining with satisfactory quality.

Analysis of ambient gas influence on silicon layers crystallized by means of LPE

Epitaxial growth of thin layers from the liquid phase can occur with the use of solutions saturated under different ambient gases. Most often this process takes place in a vacuum or gaseous atmosphere of hydrogen or argon. As the experimental data show, the morphology of crystallized layers is determined by the ambient type in which the process occurs.The cohesion energy responsible for epitaxial lateral deposition processes on the substrate surface depends on the surface free energy which is a measure of attraction of the solution atoms by substrate atoms. In the case of crystallization of an epitaxial lateral layer of Si on a substrate partially masked with dielectric, the chemical potentials of atoms in the neighboring phases (determining the interface evolution) are not without influence on the relaxation velocity of the saturated liquid phase, and on the horizontal and vertical growth rate.The aim of the investigation was to analyze experimentally the influence of the ambient gases used during the LPE growth on the cohesion of the Sn–Si solution with substrates applied for the lateral epitaxial growth of Si layers. This work presents comparative temperature analysis of the wetting angle of such surfaces as Si, SiO2 and SiNx by the Sn–Si solution.

An extended morphological stability model for a planar interface incorporating the effect of nonlinear liquidus and solidus

Incorporating the effect of nonlinear liquidus and solidus, an extended morphological stability model for a planar interface was developed under local non-equilibrium conditions both at the solid/liquid interface and in the bulk liquid. The model was adopted to describe the cellular breakdown of the planar interface upon rapid solidification of Si–Sn alloys, and a quantitative agreement was obtained between the model predictions and the experimental results. It has been found that, independent of the effect of non-equilibrium liquid diffusion, two critical interface velocities V min and V max always occur, because of the retrograde characters of the Si–Sn phase diagram. If V min ⩽ V ⩽ V max, the so-called neutral stability curve can be evaluated in terms of the planar interface response function and the marginal stability criterion. Whereas if V > V max or V < V min, the calculation of the maximum solid solubility C S max ( V ) from the planar interface response function is performed. In comparison with the model assuming linear liquidus and solidus, which fails to predict the retrograde characters of the Si–Sn phase diagram both at low ( k → k e) and at high ( k → 1) interface velocities, the effect of nonlinear liquidus and solidus on the cellular breakdown of the planar interface is highlighted.

Thermodynamic Description of the Au—Si—Sn System.

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Thermodynamic modeling of the Mg–Si–Sn system

All available thermodynamic and phase diagram data of the Mg–Si and Mg–Sn binary systems, and the Mg–Si–Sn ternary system have been critically evaluated and all reliable data have been simultaneously optimized to obtain one set of model parameters for the Gibbs energies of the liquid and all solid phases as functions of composition and temperature. The liquid phase was modeled using the Modified Quasichemical Model in order to describe the strong ordering in Mg–Si and Mg–Sn liquids. The Mg 2Si–Mg 2Sn solid solution phase was modeled with consideration of the solid miscibility gap. All calculations were performed using the FactSage thermochemical software.

Syntheses and X-ray Diffraction, Photochemical, and Optical Characterization of Cu2SixSn1-xS3 (0.4 ≤ x ≤ 0.6) for Photovoltaic Applications

The study of the pseudobinary system Cu(2)SnS(3-)Cu(2)SiS(3) shows that a solid solution (Cu(2)Si(x)Sn(1-x)S(3)) exists in the range 0.4 < or = Si/(Sn+Si) < or = 0.6. Based on diffuse reflectance and photoelectrochemical measurements these compounds show potential as absorber materials for photovoltaic devices. The compounds were prepared at 850 degrees C from copper sulfide, silicon, tin, and sulfur and were analyzed with single-crystal (for x approximately 0.40) and powder diffraction techniques. Optical band gaps of 1.25, 1.35, and 1.45 eV were observed for the three compositions x = 0.39, 0.48, and 0.61; cathodic photocurrent occurring is significant.