Si Sn Research Articles

Epitaxial SiGeSn grown on Si by ion implantation

We have formed SixGe1−x−ySny compounds on Si substrates by ion implantation and annealing and investigated their concentration profiles, crystallization, and optical properties. Ge and Sn ions were implanted in the range (2.5–10) × 1016 Ge/cm2 at 65 keV, and (1.0–4.0) × 1016 Sn/cm2 at 100 keV, resulting in a peak implant dose at a depth of 50 nm for both species. Epitaxially regrown SixGe1−x−ySny layers (110 nm thick) were produced with Ge and Sn contents that allowed bandgap tuning in the (0.88–1.1) eV range. Shifts in photoelectron binding energies (Si 2p, Ge 3d, and Sn 3d) were consistent with ternary compound formation. Sn segregation was observed for annealing temperatures ≥600 °C. A significant increase in the optical absorption coefficient (×104 cm−1 for λ = (800–1700) nm) was observed for SiGe, SiSn, and SiGeSn alloys, with SiGeSn having coefficients several orders of magnitude higher than for Si. Contributions of segregated Sn to these properties were observed. Metastable SixGe1−x−ySny layers were achieved, which may point to a promising route to mitigate Sn incorporation challenges for near-infrared detectors.

(Invited) Epitaxial Growth Technique for Si1−X Sn x Binary Alloy Thin Films

Silicon tin (Si1−x Sn x ) binary alloys are attractive materials for next-generation Si-based photonics and thermoelectronics. The energy band calculations predicted that the conduction band at the Γ point is more rapidly decreased than the others by the Sn substitution, and direct band gap semiconductors can be realized at more than sufficient Sn content [1], although they varied from 25 to 90% by the calculation methods. The corresponding wavelength range will be matched to the optical communication band, suggesting Si1−x Sn x can be applied to near-infrared light source and detector. Another interest is the dramatic reduction of the thermal conductivity by the Sn substitution owing to the mass-difference phonon scattering. Theoretically [2], the thermal conductivity of bulk Si (145 Wm−1K−1 [3]) can be decreased to ~5 Wm−1K−1 by the 10% Sn substitution; the lowest thermal conductivity (3 Wm−1K−1) is obtained at 50% Sn, which is the lowest value among bulk group-IV alloys. The low thermal conductivity achieves high thermoelectric performance and can help to ensure temperature differences within small thermoelectric generators (TEGs) integrated on Si chips, as is the case of Si nanowire TEGs [4].In contrast to the theoretical studies mentioned above, experimental studies are very limited compared with other group-IV alloys such as silicon germanium and germanium tin. Difficulties of the Si1−x Sn x synthesizing are the extremely low solid solubility of Sn in Si (0.1%), a tenth of that in Ge, and the large (∼20%) mismatch between the Si and α-Sn lattices. Nevertheless, some research groups, including us, showed some possibilities to achieve a high Sn content Si1−x Sn x thin films (x>10%) experimentally; reported the optical properties such as photoluminescence and photo-absorption. However, the technology for freely controlling Sn content is still in its infancy; the Si1−x Sn x ’s thermoelectric properties have not been clarified yet. We will discuss the recent progress on the growth techniques of Si1−x Sn x thin films using solid phase epitaxy/crystallization [5-7], molecular beam epitaxy [8,9], sputtering [10], and the potential in thin-film TEGs application. Acknowledgments This work was partly supported by JSPS KAKENHI (Nos. 19K21971, 20H05188, and 21H01366), PRESTO (No. JPMJPR15R2), and CREST (No. JPMJCR19Q5) from JST, the TEPCO Memorial Foundation, and the Naito Research Grant.

Influence of Si content on thermoelectric properties of Mg2(Sn,Si) films by sputtering

Mg2(Sn,Si) films with different Si content were prepared by magnetron sputtering. The phase composition, surface and cross-sectional morphology, chemical composition and element distribution, carrier concentration, carrier mobility, electrical conductivity, Seebeck coefficient and power factor of the deposited Mg–Sn–Si films were studied. The results show that the deposited films are composed of Mg2(Sn,Si) solid solution phase and a small amount of metal Mg phase. The room temperature carrier concentration decreases and mobility increases with increasing Si content in deposited Mg–Sn–Si films, respectively. The room temperature electrical conductivity and Seebeck coefficient decreases and increases with increasing Si content, respectively. The deposited Mg2(Sn,Si) films with moderate Si content possess the maximum power factor value of 2.76 mW m−1 K−2 at 303 °C and its room temperature figure of merit reaches the highest value of 0.44. The thermal conductivity decreases with increasing Si content, indicating that the lattice distortion caused by Si doping can reduce the thermal conductivity of the deposited films.

Aerosol-Assisted Synthesis of Sn-Si Composite Oxide Microspheres with the Hollow Mesoporous Structure for Baeyer-Villiger Oxidation

Tetravalent Sn species, such as zeolite or oxide, possess Lewis acidic properties, and thus exhibit prominent catalytic performance in several reactions when they are incorporated into the silica framework. Unfortunately, the synthesis of Sn-based zeolite (Sn–Beta) usually suffers from several drawbacks, including a long crystallization time, limited framework Sn content and complex synthesis steps. Sn-based composite oxides are favored in the industry, due to their simple synthesis steps and easy control of their pore structure, morphology and Sn content. In this work, an aerosol-assisted method is used to prepare Sn–Si composite oxide microspheres, using CTAB as template. The method is based on the formation of aerosol from a solution of Sn, Si precursors and a template (CTAB). The introduction of CTAB causes the surface tension of the atomized droplets to decrease. During the fast drying of the droplets, the Sn–Si composite oxide microspheres with a concave hollow morphology were first formed. After calcination, calibrated mesopores of 2.3 nm were also formed, with a specific surface area of 1260 m2/g and a mesopores ratio of 0.84. Sn species are incorporated in the silica network, mainly in the form of single sites. The resulting material proved to exhibit high catalytic performances in the Baeyer–Villiger oxidation of 2-adamantanone by using H2O2 as green oxidant, which was mainly attributed to the enhancement of the access to the catalytic tin sites through both the continuous hollow and mesopore channels, which have a 52% conversion of 2-adamantanone after 3 h of reaction. This method is simple, convenient, cheap and can be continuously produced, meaning it has broad potential for industrial application.

Sn–Sc microalloying-induced property improvement and micromechanisms of an Al–Mg–Si alloy

Microalloying is of great importance for the property modulation of lightweight high-strength aluminum alloys. Little is known, however, about the properties and micromechanisms of Al–Mg–Si alloys microalloyed with Sn and Sc. In this work, the property changes of Al–0.5Mg–0.4Si (wt%) alloys induced by 0.1Sn and 0.1Sn–0.1Sc (wt%) additions and underlying alloying mechanisms are revealed by atomic-scale transmission electron microscopy and first-principles calculations. The results show that the Sn–Sc coaddition results in a decreased diameter and an increased number density of the Sc-containing constituent particles of Mg2Si and Mg2(Si,Sn), as compared to the sole Sn addition. The featured Si-site columns in β'', B′ and β′ structures can be occupied by Sn and Sc. Substantial peak-aging β'' needles with confined cross-sectional coarsening are observed for the Sn–Sc containing alloy compared to the Sn containing alloy. The modified constituent particles and precipitates improve the plasticity and strength of peak-aging Al–Mg–Si–Sn–Sc alloy. The elevated peak-aging corrosion resistance and over-aging thermal stability of Al–Mg–Si–Sn–Sc alloy are associated with the sparse Sc-containing Mg2(Si,Sn) grain boundary precipitates and low strain filed of Al matrix around the β′ containing Sn/Sc, respectively. The obtained results are hoped to guide the design of high-performance Al alloys.

Developing a high-performance Al–Mg–Si–Sn–Sc alloy for essential room-temperature storage after quenching: aging regime design and micromechanisms

Developing a high-performance Al–Mg–Si–Sn–Sc alloy for essential room-temperature storage after quenching: aging regime design and micromechanisms

Effect of extrusion temperatures on the microstructure, texture, and mechanical properties of Mg–5Sn–1Si–0.6Ca alloy

In this paper, the effect of extrusion temperatures (250 °C, 300 °C and 350 °C) on the microstructure, second phases particle, texture, and mechanical properties of the Mg–5Sn–1Si–0.6Ca alloy were discussed. The results show that after extrusion the second phases in the alloy were broken and distributed along the grain boundary. Decreasing the extrusion temperature is beneficial to dynamic precipitation and grain refinement. During the extrusion process, a large number of Mg2Sn nanoprecipitates are dynamically precipitated from the Mg matrix and their number increased and their size decreased with the decrease of extrusion temperature. The grain size was refined from 5.8 μm to 3.328 μm with the extrusion temperature decreasing from 350 °C to 250 °C. Besides, the texture intensity was also reduced with the decrease in extrusion temperature. The strength and plasticity of the Mg–Sn–Si–Ca alloys are simultaneously improved by the method of “solid solution + low-temperature extrusion”. When the extrusion temperature is 250 °C, the alloy obtains superior engineering mechanical properties with the yield strength of 287 MPa, ultimate tensile strength of 343 MPa and elongation to failure of 23.3%. The high strength is mainly attributed to the combined effect of grain size, weak texture, and high density of precipitation. The good ductility is mainly attributed to the grain refinement and high Schmid factors of basal slip.

Effect of backfilled stone/brine media on the long‐term free corrosion and electrochemical performance of an aluminum sacrificial anode

AbstractAn Al–Zn–In–Si–Sn–Ti sacrificial anode, utilized to protect steel shells of subsea‐immersed tunnels, works in a backfilled stone (6–10 mm)/brine (40 Ω cm) media (125 Ω cm). This paper investigated its impact on the anode's long‐term free corrosion and electrochemical performance. After prolonged free corrosion, the anode's general corrosion rate is minimal. Although its capacity (Q) and current efficiency (η) increase slightly, it shows a nonuniform dissolution state. Over a long‐term working period, a significant amount of Al(OH)3 deposits and diffuses between the backfilled stone toward the cathode surface, creating distinct stone impressions and a thick product layer. These effects considerably increase the media ρ around the anode and continuously decrease the brine's pH, decreasing Q and η values and output currents. Nonetheless, the current distribution within the media gradually becomes uniform with time, resulting in a homogeneous potential distribution along the cathode.

Si–Sn codoped n-GaN film sputtering grown on an amorphous glass substrate

DC-pulse magnetron sputtering was utilized to deposit a 300 nm-thick n-type GaN thin film that was co-doped with Si–Sn onto an amorphous glass substrate with a ZnO buffer layer. The deposited thin films were then subjected to post-growth thermal annealing at temperatures of 300 °C, 400 °C, or 500 °C to enhance their crystal quality. Hall measurements revealed that the film annealed at 500 °C had the lowest thin-film resistance of 0.82 Ω cm and the highest carrier concentration of 3.84 × 1019 cm−3. The thin film surface was studied using atomic force microscopy; the film annealed at 500 °C had an average grain size and surface roughness of 25.3 and 2.37 nm, respectively. Furthermore, the x-ray diffraction measurements revealed a preferential (002) crystal orientation and hexagonal wurtzite crystal structure at 2θ ≈ 34.5°. The thin film had a full width at half maximum value of 0.387°, it was also found to be very narrow. Compositional analysis of the films was conducted with x-ray photoelectron spectroscopy and verified that both Si and Sn were doped into the GaN film utilizing covalent bonding with N atoms. Finally, the film annealed at 500 °C had a high optical transmittance of 82.9% at 400–800 nm, a high figure of merit factor of 490.3 × 10−3 Ω−1, and low contact resistance of 567 Ω; these excellent optoelectronic properties were attributed to the film’s high electron concentration and indicate that the material is feasible for application in transparent optoelectronic devices.

Phase relations in the Si–Sn–As system

The goal of this work was to study phase relations in the ternary Si–Sn–As system: to establish cross sections, to construct a scheme of phase equilibria, and to identify the temperature of non-variant transformations. Ternary alloys were obtained through direct synthesis from simple substances and subjected to long-term solid-phase annealing. Alloys of four polythermal sections of the Si–Sn–As system were examined using X-ray phase and differential thermal analysis. The results of X-ray powder diffraction allowed establishing that the phase subsolidus demarcations was performed by the SnAs–SiAs2, SnAs–SiAs, Sn4As3–SiAs, and Sn4As3–Si sections. As a result of the experiment, taking into account the theoretical analysis, we suggested a scheme of phase equilibria in the system that involved the implementation of eutectic and four peritectic invariant equilibria, and we used differential thermal analysis to determine the temperature of these four-phase transformations. It was found that extended solid solutions were not formed in the system, and only a substitutional solid solution at least 3 mol % wide was formed based along the SnAs–SiAs2 section based on tin monoarsenide

Tin Metal Improves the Lithiation Kinetics of High-Capacity Silicon Anodes

Si-based anodes present a great promise for high energy density lithium-ion batteries. However, its commercialization is largely hindered by a grand challenge of a rapid capacity fade. Here, we demonstrate excellent cycling stability on a Si–Sn thin film electrode that outperforms pure Si or Sn counterpart under the similar conditions. Combined with the first-principles calculations, in situ transmission electron microscopy studies reveal a reduced volume expansion, increased conductivity, as well as dynamic rearrangement upon lithiation of the Si–Sn film. We attribute the improved lithiation kinetics to the formation of a conductive matrix that comprises a mosaic of nanostructured Sn, LiySn (specifically, Li7Sn2 develops around the lithiation potential of Si), and LixSi. This work provides an important advance in understanding the lithiation mechanism of Si-based anodes for next-generation lithium-ion batteries.

Toward White Light Random Lasing Emission Based on Strained Nano Polygermanium Doped with Tin via Metal-Induced Crystallization (MIC)

Solubility of Sn in Ge network gives it a preference for photonic applications, because of the direct transition in GeSn alloy. Here, we employed the metal-induced crystallization (MIC) process of amorphous Ge and Si via Sn as a novel mechanism to incorporate Sn inside Ge and Si networks. (Al/Si/Sn/Ge/Sn) and (Al/Ge/Sn/Ge/Sn) multilayers are deposited by thermal vacuum evaporation on different substrates. The devices are annealed under low vacuum at 500 °C to incorporate the oxygen for band-gap tuning. The structure of Ge-doped nanocrystals is investigated. The direct transition and band-gap values have been estimated using diffuse reflectance spectroscopy and photoluminescence (PL) measurements. PL indicated that the junctions have emissions from visible to NIR regions that make them promising as optically pumped white-light sources as well as waveguide applications, and the impact of the base substrate on enhancing the emission has been investigated via PL measurements. Electroluminescence measurements show that the prepared heterostructures on fluorine-doped tin oxide (FTO) substrate have sharp random lasing spikes over the range of PL samples spectra as the sample can lase randomly by light scattering through the Ge-doped nanocrystalline materials. The charge carrier lifetime measurements show high lifetime for the prepared sample. These give them the chance to be a candidate for white-light random laser diode applications.

Structural transitions on Si(1 1 1) surface during Sn adsorption, electromigration, and desorption studied by in situ UHV REM

Using in situ ultrahigh vacuum reflection electron microscopy, we have studied structural transitions on the Si(111) surface induced by Sn deposition up to 2 ML coverage (1 ML = 7.8∙1014 cm−2) and by Sn desorption at substrate temperatures T = 200–860 °C. We have shown that Si–Sn intermixing in the adsorption layer during Sn deposition onto the Si(111)-(7 × 7) surface at T > 650 °C leads to the shift of the monatomic steps in the step-up direction, and there is formed a mosaic (√3×√3)-Sn phase. The electromigration of Sn adatoms induced by DC resistive heating has been shown to redistribute adsorbed Sn layer and to cause local (√3×√3)-Sn ⇔ “1 × 1”-Sn structural transitions on the surface. We have estimated the lower bound of the Sn adatom positive effective charge on the Si(111) surface qeffSn ≥ 0.001∙e. During AC annealing, the rate of desorption-induced “1 × 1”-Sn domain area shrinkage has been measured as a function of substrate temperature, and the activation energy of Sn adatom desorption has been estimated to be 2.5 ± 0.1 eV.

Designer Cathode Additive for Stable Interphases on High-Energy Anodes.

Rechargeable lithium-based batteries built with high-energy anode materials (e.g., silicon-based and silicon-derivative materials) are considered a feasible solution to satisfy the stringent requirements imposed by emerging markets, including electric vehicles and grid storage, due to their higher energy density compared to contemporary lithium-ion batteries. The robustness of the solid electrolyte interphase (SEI) layer on high-energy anodes is critical to achieve long-term and stable cycling performances of the batteries. Herein, we propose a new type of designer cathode additive (DCA), i.e., an ultrathin coating layer of elemental sulfur on the cathode, for the in situ formation of a thin and robust SEI layer on various types of high-energy anodes. The DCA elemental sulfur undergoes simultaneous oxidation and reduction paths, forming lithium alkyl sulfate (R-OSO2OLi) and poly(ethylene oxide) (PEO)-like polymers on the anode surface. The as-formed R-OSO2OLi/PEO-modified SEI layer has good lithium cation (Li+) permeability to facilitate fast ion transportation across the interphases and superior elasticity to adapt to large volume changes, which is particularly effective for improving the cycling efficiency of high-energy anodes (e.g., ca. 14-35% increase in capacity retention for the silicon-carbon composite (SiC) or silicon-tin alloy (Si-Sn)||LiFePO4 cells). The present work opens a new avenue toward the practical deployment of high-energy rechargeable lithium-based batteries.

Effect of Na–Sn Flux on the Growth of Type I Na8Si46 Clathrate Crystals

In the crystal growth of Na–Si clathrate (type I, Na8Si46) during Na evaporation from a Na–Si–Sn solution at 723 K, the composition of a Na–Sn flux in the starting material strongly influences the morphology and size of the formed clathrate crystals. In this study, the crystals obtained using this flux were larger than the crystals prepared without a flux, and some of them had faceted surfaces. At the Na4Si4 (precursor):4Na–Sn (flux) = 1:4 ratio, multiple dents were observed on crystal surfaces, indicating that the precipitation of a Na9Sn4 solid phase prevented the growth of Na–Si clathrate crystals. In addition, synthesis conditions, under which type I crystals could be obtained by conventional thermal decomposition in vacuum, were established. The results of this work suggest that type I Na–Si clathrate crystals are stable even at temperatures as high as 723 K due to the suppressed evaporation of Na.

Separation mechanism of bulk Si from Si–Sn melt via upwards directional solidification based on the density difference

There is no systematic study on the separation mechanism of bulk Si from Si–Sn melt by directional solidification, although the system has many outstanding advantages. In this work, the influence of alloy composition and cooling rate on the quality of grown bulk Si were studied. The length of the mushy zone increased with the composition, and the stable convex interface only occurred at the composition of Si higher than 50 at.%; As for the composition of Si–12.5 at.% Sn, the convex interface became flatter. The separation effect deteriorated rapidly with the cooling rate. The evolution of the crystal growth process and the transfer of the interface were simulated, which predicts the shape of the interface and explains the residual Sn trapped in bulk Si.

4D microstructural evolution in a heavily deformed ferritic alloy: A new perspective in recrystallisation studies

We present a multiscale study on the recovery and recrystallisation of a heavily deformed (85% reduction in size) Fe–Si–Sn alloy using a combination of dark field X-ray microscopy (DFXM), synchrotron X-ray diffraction (SXRD) and electron backscatter diffraction (EBSD). By utilizing DFXM, we focus on a grain within the high stored energy (HSE) regions, and track it through consecutive isothermal annealing steps. The intra-granular structure of the as-deformed grain reveals deformation bands separated by ≈3–5∘ misorientation. During the early stages of annealing, cells with 2–5∘ misorientation form while new nuclei appear. The recrystallized grains nucleate near prior grain boundaries, having a typical internal angular spread of <0.05∘. The SXRD results suggest no significant macroscopic texture change after annealing for 1400s at 610∘C in the HSE regions. All results indicate that higher misorientation zones such as grain boundaries or junction points of deformation bands are preferential nucleation regions.

Construction of Heterostructured Sn/TiO2 /Si Photocathode for Efficient Photoelectrochemical CO2 Reduction.

Using renewable energy to convert CO2 into liquid products, as a sustainable way to produce fuels and chemicals, has attracted intense attention. Herein, a novel heterostructured photocathode composed of Si wafer, TiO2 layer, and Sn metal particles has been successfully fabricated by combining of a facile hydrothermal and electrodeposition method. The obtained Sn/TiO2 /Si photocathode shows enhanced light absorption performance by the surface plasmon resonance effect of Sn metal. Especially, the Sn/TiO2 /Si photocathode together with rich oxygen vacancy defects jointly promote photoelectrochemical CO2 reduction, harvesting a high faradaic efficiency of HCOOH and a desirable average current density (-4.72 mA cm-2 ) at -1.0 V vs. reversible hydrogen electrode. Significantly, the photocathode Sn/TiO2 /Si also shows good stability due to the design of protecting layer TiO2 . This study provides a facile strategy of constructing an efficient photocathode to improve the light absorption performance and the electron transfer efficiency, exhibiting great potential in the CO2 reduction.

Stable and fast Si−M−C ternary anodes enabled by interfacial engineering

For lithium storage, the co-hybridization of silicon with metal and carbon matrices is a promising strategy to mitigate the intrinsic challenges of silicon anodes. However, current Si–M–C ternary materials often suffer from nonuniform distribution of triple components, and Si is physically combined to M/C dual matrices with weak interactions. Herein, we propose an interpenetrating hydrogel-enabled methodology for the formation of chemical-bonded and uniform-distributed Si−M−C ternary materials. As a proof-of-concept illustration, commercial Si particles have been in situ immobilized within Sn nanorod-filled graphene gel framework, and are covalently bonded with Sn/G dual matrices via interfacial Si–O–Sn and Si–O–C bondings. Thanks to the rationally designed composition and structure, the Si–Sn@G gel framework anode manifests long cycling life (983 mA h g−1 in the 100th cycle at 0.5 A g−1) and good rate capability (717 and 514 mA h g−1 at 5 and 10 A g−1, respectively).

Evolution Mechanism of Solid–Liquid Interface of Large-Sized Bulk Polysilicon via Si–Sn Solution Growth

Evolution Mechanism of Solid–Liquid Interface of Large-Sized Bulk Polysilicon via Si–Sn Solution Growth