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The surface reconstruction of electrochemically activated catalysts is an effective way to improve performance. However, there is currently a dearth of study on the surface reconstruction of silicide catalysts for hydrogen evolution reactions (HER). Here, a new HER electrocatalyst, LaRuSi3, is synthesized and electrochemically triggered it to produce Ru clusters on its surface. Experimental data and theoretical simulations reveal that Ru clusters optimize the charge distribution of LaRuSi3, which promotes the adsorption of water by Ru sites and improves the adsorption of hydrogen by Si sites. The conductivity and electrochemical active sites of the catalysts are also enhanced. The catalyst has an overpotential of 45 mV to attain a current density of 10 mA cm−2 in alkaline media, which exceeds the majority of other Ru‐based compounds. This work contributes to the exploration of more efficient novel silicides HER electrocatalysts and broadens the application of surface reconstruction techniques. [ABSTRACT FROM AUTHOR]

Higher manganese silicides (denoted as MnSiγ ) are a prominent class of intermetallic compound for thermoelectric applications that crystallizes into a Nowotny Chimney Ladder (NCL) phase and constitutes a higher concentration of silicon with odd stoichiometry, typically represented by an irrational number. In this work, the genesis of Si odd stoichiometry and secondary phase relations in silicon-rich and silicon-deficient MnSix is presented to clarify the significance of labile (i.e., easily alterable) Si-subsystem in inheriting the modulated lattice structure with characteristic anharmonicity. The transport properties show an interrelation to the presence of a secondary phase, which is driven by the odd stoichiometry, where the thermoelectric figure of merit (zT) is found to be optimal for MnSi1.74. The structural characterization of rapidly solidified melt-spun ribbons and spark plasma sintered bulk specimens reveal a characteristic presence of MnSi and Si as secondary phases in Si-deficient (x ≈ 1.5) and Si-excess (x ≈ 2) compositions of nominal MnSix, respectively, that coexists with the major MnSiγ based NCL phase. This study provides the fundamental basis of phase evolution and the relevance of odd stoichiometry in silicon-rich manganese silicides which exhibit fascinating phonon dynamics in optimal MnSi1.74 stoichiometry. [ABSTRACT FROM AUTHOR]

The oxidation products (MoO3 and V2O5) have low melting points and tend to sublimate at high temperatures despite that MoSi2 and VSi2 may possess good self-lubricating properties. To copewith this challenge, a high-entropy transition metal disilicide was designed in this work in which transition metal elements that could form high melting point oxides were deliberately added. The highentropy (Ti0.2V0.2Nb0.2Mo0.2W0.2)Si2 (HE-MSi2) with hexagonal structure was successfully prepared by SPS using Ti, V, Nb, Mo, W, and Si powders as the initial materials in thiswork. TheHE-MSi2 presents a high hardness (11.8±0.4GPa) and elastic modulus (387.2 ± 46.8 GPa). In particular, its hardness is higher than that of the corresponding disilicides. Noteworthy, HE-MSi2 demonstrated superior wear resistance when compared to Mo-Si-based ceramics (such as MoSi2, Mo5 Si3, and Mo5 SiB2), high-entropy carbides (such as (MoTaWVTi)C, (HfMoNbTaTi)C, and (TiVNbMoW)4.375, and traditional single-phase ceramics (including Sialon, Si3N4, Al2O3, SiC, and ZrO2). Meanwhile, at a high temperature of 600°C, the friction coefficient and wear rate were reduced to 0.64 ± 0.05 and (1.88±0.15)x106 mm³/N•m, respectively. The preferential oxidation of different elements of the HE-MSi2 was validated through systematical characterization of composition evolution, which was dominantly impacted by high temperature and friction induction. [ABSTRACT FROM AUTHOR]

Metal silicides and silicates belong to the silicon‐based non‐oxide and oxide ceramics family with exceptional properties. Silicides face fatal oxidation at low temperatures and intrinsic brittleness, whereas silicates face instability in phase at high temperatures which restricts its usage in vast engineering applications. Hence, the ceramic community introduced the concept of high entropy in metal silicides and silicates. Since 2019, high entropy silicides and silicates, a multicomponent system, have created new avenues for materials discovery and design. High entropy silicides displayed elevated properties than the traditional silicides aiming its applications in microelectronic, high‐temperature oxidation resistance coatings, and structural materials. Similarly, high entropy silicates displayed improved properties than the traditional silicates making them the most promising materials for environmental and thermal barrier coating applications for hot section components in gas turbines. The review focuses on specific case studies to emphasize the latest research and developments in high entropy silicides and silicates. Synthesis approaches employed in developing high entropy silicides and silicates and their structural and microstructural outcomes are addressed. The possible application is predicted based on the overview of the properties explored to date. The review concludes with future possibilities offered by the high entropy silicides and silicates. [ABSTRACT FROM AUTHOR]

In recent years, the rare earth metal silicon‐based materials have attracted much attention. In order to accurately comprehend the application of rare earth silicides, we investigated the physical properties of the tetragonal TM2Si2Ys (TM = Cu, Ir, Os, Pt, Pd, Rh, Ru), orthogonal SiY, hexagonal Si2Y, and Si3Y5 compounds. The structural stability, electronic properties, elastic anisotropy, and optical properties of these silicides are investigated using the first‐principles calculations. The enthalpy of formation and phonon dispersions confirm that the binary and ternary silicides display the structural stability. According to the electronic structure, the stability, and mechanical properties of these silicides can be better understood. Ir2Si2Y has the stronger resistance to deformation and higher hardness. The values of v and G/B ratio confirm that Os2Si2Y, Pd2Si2Y, Pt2Si2Y, Ru2Si2Y, Rh2Si2Y, and Si2Y are the ductile materials. The 3D surface constructions and 2D projections of Young's modulus display the elastic anisotropy properties of the ternary silicides. The optical properties indicate that these silicides can be used as UV shielding materials for optical devices. [ABSTRACT FROM AUTHOR]

The discovery and identification of novel active sites are paramount for deepening the understanding of the catalytic mechanism and driving the development of remarkable electrocatalysts. Here, we reveal that the genuine active sites for the hydrogen evolution reaction (HER) in LaRuSi are Si sites, not the usually assumed Ru sites. Ru in LaRuSi has a peculiar negative valence state, which leads to strong hydrogen binding to Ru sites. Surprisingly, the Si sites have a Gibbs free energy of hydrogen adsorption that is near zero (0.063 eV). The moderate adsorption of hydrogen on Si sites during the HER process is also validated by in situ Raman analysis. Based on it, LaRuSi exhibits an overpotential of 72 mV at 10 mA cm−2 in alkaline media, which is close to the benchmark of Pt/C. This work sheds light on the recognition of real active sites and the exploration of innovative silicide HER electrocatalysts. [ABSTRACT FROM AUTHOR]

The discovery and identification of novel active sites are paramount for deepening the understanding of the catalytic mechanism and driving the development of remarkable electrocatalysts. Here, we reveal that the genuine active sites for the hydrogen evolution reaction (HER) in LaRuSi are Si sites, not the usually assumed Ru sites. Ru in LaRuSi has a peculiar negative valence state, which leads to strong hydrogen binding to Ru sites. Surprisingly, the Si sites have a Gibbs free energy of hydrogen adsorption that is near zero (0.063 eV). The moderate adsorption of hydrogen on Si sites during the HER process is also validated by in situ Raman analysis. Based on it, LaRuSi exhibits an overpotential of 72 mV at 10 mA cm−2 in alkaline media, which is close to the benchmark of Pt/C. This work sheds light on the recognition of real active sites and the exploration of innovative silicide HER electrocatalysts. [ABSTRACT FROM AUTHOR]

Precipitation strengthening of silicides plays an important role in improving the creep resistance of high‐temperature titanium alloys. The oversize and concentrated silicides remarkably reduce the ductility of the alloys, which shorten the serving life of the key components in aerospace engines and gas turbines. To investigate the alloying effect on the stability of Ti5Si3, the enthalpy of solution for IIIB–VIB and IIIA–IVA elements in Ti5Si3, α matrix, and β phase are calculated and compared. It is proposed that Zr and Hf stabilize Ti5Si3 and promote the nucleation and refinement of silicide particles. The β stabilizers and simple metals destabilize Ti5Si3 and would suppress the precipitation of Ti5Si3. [ABSTRACT FROM AUTHOR]

Alloying is a well‐accepted strategy for modulating the electronic structures of catalyst materials. Compared to disordered solid‐solution alloys, intermetallic compounds feature ordered atomic arrangements and provide a unique platform with a rich and diverse resource to study the relationships among chemical composition, atomic structure, electronic structure, and properties. Unfortunately, it is still challenging to synthesize the nanostructures of intermetallic compounds for catalysis research. In this study, a series of intermetallic silicides (PtSi, RhSi, Ru2Si3, IrSi), germanide (Ru2Ge3), and stannides (Ru3Sn7, IrSn2, PdSn3, PdSn2) are rationally designed and constructed through a facile molten‐salt‐assisted route. As an example, the PtSi not only shows highly desirable electrocatalytic properties for the hydrogen evolution reaction (HER) with low overpotentials of 22, 38, and 66 mV at a current density of 10 mA cm‐2 in acidic, alkaline, and neutral media, respectively, but exhibits superior durability, as well as >97% faradic efficiency. The theoretical calculations suggest that the introduction of Si to Pt could weaken the binding energy between Pt and H atoms, which further facilitates the hydrogen generation during the HER process. Further, the findings inspired the authors to develop other kinds of metal‐based carbon‐group intermetallic phases with excellent activity in the HER and beyond. [ABSTRACT FROM AUTHOR]

Iron‐containing PSO precursors (FePSO) were synthesized by modification of polysiloxane with different amounts of ferric acetylacetonate [Fe(acac)3], then porous SiFeCO ceramics were successfully prepared by subsequent pyrolysis. The chemical modification and ceramization process of PFSO precursors were studied by FT‐IR and TGA measurements. XRD patterns imply that the SiC crystalline can be easily observed when PFSO was exposed to 1200℃ in nitrogen atmosphere, while pure PSO exhibited broad diffraction peaks of SiC at 1500℃, meaning that the grain coarsening of SiC was accelerated by adding iron. The crystallization behavior of ferric silicide (FexSiy) is complex due to the variation of iron content in feed and annealing temperature, and FexSiy/SiC@SiOC nanocomposites were produced after annealing. Because of the in‐situ formation of SiC, FexSiy, and carbon strips in nanocomposites, PFSO‐derived ceramics demonstrate enhanced microwave absorption performance. The best effective absorption bandwidth (<−10 dB) and the minimum reflection loss are 2.6 GHz and −38 dB, respectively, which are achieved in the sample PFSO‐3–1300℃. FexSiy/SiC@SiOC nanocomposites synthesized in this work exhibit potential application in the field of electromagnetic interference, the carbon content and the crystallization behavior of FexSiy are the critical factors for the performance optimization. [ABSTRACT FROM AUTHOR]

The reaction between iridium and SiC in the 1000°C–1900°C temperature range was studied in details. The rate of this reaction was found to depend not only on temperature, but also on the grain sizes of the initial reagents, oxygen impurities in SiC, as well as the Ir: SiC ratio. The use of fine‐grained initial reagents accelerates the reaction, whereas oxygen impurities in SiC powders slow it down. For the Ir: SiC ratio = 1:1, the IrSi silicide phase became dominant at 1400°C and remained the main phase at temperatures up to 1900°C. For the 3:1 ratio, Ir2Si was the main phase at 1900°C. It was suggested that stabilization of this phase is due to the quenching effect. No Si‐rich silicide phases were detected in the 1000°C–1900°C temperature range. The coefficients of thermal expansion of silicide phases were determined by high‐temperature X‐ray diffraction analysis. [ABSTRACT FROM AUTHOR]

In this study, silicon oxycarbide (SiOC) is selected as the base polymer to derive a SiOC ceramic (PDC) matrix, and four transition metals M (M = Ni, Mo, Co, and Zr) are individually introduced into the SiOC base to form various SiOC/M systems. SiOC‐Ni, SiOC‐MoCx, and SiOC‐CoSix are obtained by pyrolysis at 1100°C, whereas SiOC‐ZrOx forms upon pyrolysis at 1400°C. The selected SiOC/M systems encompass four different types of phase separation pathways—pure metal, metal carbide, metal silicide, and metal oxide (SiC‐SiO2‐C‐Ni, SiC‐SiO2‐C‐MoCx, SiC‐SiO2‐C‐CoSix, and SiC‐SiO2‐C‐ZrOx). The driving force for crystallization has been analyzed using a Gibbs free energy minimization method and phase fractions of these different PDC systems are calculated based on the lever rule. This work also reveals the energetics related to the quaternary systems and provides guidance to synthesizing metal‐containing PDCs with desired phase contents. In addition, we have examined the broad applicability of the phase content prediction method for a variety of other SiOC/M systems. [ABSTRACT FROM AUTHOR]

A simultaneously protonated and functionalized silicide cluster [NHCDippCu(η4‐Si9)H]2− was detected and characterized in liquid ammonia by NMR spectroscopy. Key NMR results were corroborated by theoretical calculations. 1H‐NMR line‐widths at variable temperatures revealed that proton hopping in the metalated complex [NHCDippCu(η4‐Si9)H]2− is less pronounced than in the non‐complexed silicide [HSi9]3−. Besides [HSi9]3− and [NHCDippCu(η4‐Si9)H]2− also the unprotonated analogous cluster [NHCDippCu(η4‐Si9)]3− was detected in solution. In addition, a new 29Si‐NMR signal was obtained in the course of 29Si‐NMR studies that we assigned to [NHCDippCu(η4‐Si9)]3−. The isolation of crystals of (K[2.2.2]‐crypt)2K0.48Rb3.52[NHCDippCu(η4‐Si9)]2 prove the availability of the non‐protonated NHCDippCu(η4‐Si9) fragment in solution. To the best of our knowledge the detection of [NHCDippCu(η4‐Si9)H]2− represents the first case of a protonated and coinage metalated group 14 Zintl cluster in solution so far. [ABSTRACT FROM AUTHOR]

The family of 2D transition metal carbides, carbonitrides, and nitrides (MXenes) has aroused scientific research due to their unique electrical, optical, and chemical properties and their versatile applications. Based on first‐principles calculations, ten transition metal silicide (M2Si, M = Sc, Ti, V, Cr, Mn, Co, Zn, Y, Nb, and Mo) monolayers are studied. Three stable 2D M2Si (M = Mn, Co, and Y) crystals are identified through the investigation of thermodynamic, dynamical, and thermal perspectives. Among them, Y2Si monolayer is a nonmagnetic metal, whereas Mn2Si and Co2Si monolayers are antiferromagnetic metals. The three monolayers are chemically inert to H2 and N2, but highly active to O2, and only Y2Si with its surface functionalized by oxygen exhibits good thermal stability, whose magnetic and electronic properties retain its pristine counterpart. In addition, it is found that the Y2Si shows good electrocatalytic performance in hydrogen evolution reaction (HER). These stable 2D M2Si monolayers have potential in the fields of electronics and electrocatalysis. [ABSTRACT FROM AUTHOR]

The effects of vacancy concentration and Al substitution on the structural, electronic, and elastic properties of Nb5Si3 are studied using first‐principles calculations. The formation energy, elastic modulus, and electronic properties of three different Nb vacancies in Nb5Si3 are discussed in detail. With the increase in vacancy concentration, the obtained shear modulus, Young's modulus, and hardness of Nb vacancy decrease, which are lower than those of pristine Nb5Si3. The bulk modulus/shear modulus (B/G) ratio increases with the increase in Nb vacancy concentration. However, these vacancies result in the transition from brittleness to ductility, and Nb5Si3 with 5% vacancy concentration exhibits ductile behavior. The calculation of electronic structure shows that these Nb vacancies change the local hybridization between Nb and Nb atoms. As the concentration increases, the position of the peak moves toward lower energy. It is predicted that vacancies can improve the ductility behavior of Nb5Si3. [ABSTRACT FROM AUTHOR]

The direct reaction of methyl chloride with magnesium and palladium infused silica substrates to synthesize methyl chlorosilanes is reported. First, high energy ball milling on solid Mg‐SiO2 mixtures produces elemental silicon and MgO. When PdCl2 is infused into the mixture, after additional ball milling and high‐temperature reduction under H2, dipalladium silicide (Pd2Si) is produced. The silicon of the Pd2Si readily reacts with MeCl under Müller–Rochow reaction conditions, to produce methyl chlorosilanes at yield ratios analogous to those of the traditional process. The dominant product is Me2SiCl2 (selectivity > 30%), followed by MeSiCl3 and Me3SiCl, with minor amounts of the remaining chlorosilanes. Silicon conversion exceeds 20% for most of the substrates. The elemental palladium, which remains within the Pd‐Mg‐SiO2 contact mass is re‐converted to Pd2Si at the next H2/high‐temperature treatment and reacts again with MeCl to repeat the methyl chlorosilane production. In principle, the resulting cycle of the mechanochemically induced formation of Pd2Si followed by the reaction with MeCl can be repeated until the starting SiO2 converts completely to methyl chlorosilanes. [ABSTRACT FROM AUTHOR]

Abstract. We report on semi‐metallic cobalt monosilicide (CoSi) as a CMOS‐compatible thermoelectric (TE) material and discuss the effect of n‐ and p‐type dopants on its transport properties. Thin films of CoSi are developed using chemical vapor deposition tools and subsequent rapid thermal processing. Film properties such as microstructure, crystallinity and elemental distribution are studied via electron microscopy, X‐ray diffraction and time‐of‐flight secondary ion mass spectroscopy. Doping silicon with boron prior to silicidation impedes the Co‐Si diffusion process, while phosphorus atoms distribute uniformly in silicides with no voids or agglomerations. CoSi makes a suitable n‐type TE candidate and provides an alternative to Si or SiGe materials. Transport properties of undoped CoSi exhibit a linear dependence within the investigated temperature window, whereas dopants in CoSi increase the number of electron carriers that contribute to charge transport and thereby influence the Seebeck coefficient. Thus, TE characteristics of thin CoSi films can be tuned via (i) the type of dopants used and/or (ii) varying the residual silicon thickness post silicidation. [ABSTRACT FROM AUTHOR]

Herein, the pressure dependence of the structure, electronic properties, mechanical stability, elastic properties, and Debye temperature of (α, β, γ)‐Nb5Si3 is investigated using the GGA‐PW91 functional. The results show that the pressure has a clear effect on the mechanical and electronic properties of (α, β, γ)‐Nb5Si3. The obtained structural and mechanical parameters agree well with the experiments and theoretical values at zero pressure. All these parameters linearly increase with the pressure. In particular, within the range of 25–100 GPa, the ductility of α‐Nb5Si3 increases with the pressure, indicating that the pressure can improve ductility. The anisotropy AU and AT values of Nb5Si3 increase with the increasing pressure, and it is clear that Nb5Si3 is an anisotropic material. The density of states (DOS) shows that the covalent properties of α‐Nb5Si3 are enhanced. The total density of states (TDOS) shape curve shows that the height of this peak decreases with the increasing pressure. The position of the peak shifts to lower energy. The Fermi level moves down with the pressure increases. [ABSTRACT FROM AUTHOR]

Here, structural parameters of various structure reports on RSi2 and R2TSi3 compounds [where R is an alkaline earth metal, a rare earth metal (i.e. an element of the Sc group or a lathanide), or an actinide and T is a transition metal] are summarized. The parameters comprising composition, lattice parameters a and c, ratio c/a, formula unit per unit cell and structure type are tabulated. The relationships between the underlying structure types are presented within a group–subgroup scheme (Bärnighausen diagram). Additionally, unexpectedly missing compounds within the R2TSi3 compounds were examined with density functional theory and compounds that are promising candidates for synthesis are listed. Furthermore, a correlation was detected between the orthorhombic AlB2‐like lattices of, for example, Ca2AgSi3 and the divalence of R and the monovalence of T. Finally, a potential tetragonal structure with ordered Si/T sites is proposed. [ABSTRACT FROM AUTHOR]

We report the results of a comparative investigation of graphene films prepared on Si(100) and fused silica (SiO2) combining pulsed laser deposition and rapid thermal annealing using Ni catalyst. The effect of modifying the substrate and/or growth temperature (600–1,000°C) of graphene synthesis was investigated by Raman microspectroscopy mapping. Graphene grown on Si(100) was multilayered, and various nickel silicide phases had formed underneath, revealing dependence on the growth temperature. Films prepared on SiO2 mainly comprised bilayered and trilayered graphene, with no traces of nickel silicide. Analysis of Raman D, G, and 2D peak intensities and positions showed that modifying the growth temperature had different effects when a Si(100) or a SiO2 substrate is used. These findings advance our understanding of how different combinations of substrate and thermal processing parameters affect graphene synthesis from solid carbon source using nickel as a catalyst. This knowledge will enable better control of the properties of graphene film (defects, number of layers, etc.) and will have a high potential impact on the design of graphene‐based devices for scientific or industrial applications. [ABSTRACT FROM AUTHOR]

Phase composition of AZ61‐SiC composite with 5 wt.% of nanosized silicon carbide reinforcement was analysed and failure mechanism by in situ tensile test in scanning electron microscope was observed. Microstructure of the experimental materials was heterogeneous with grain size of 15 μm. Based on the quantitative analysis of composite, besides, silicon carbide strengthened particles added externally into the matrix magnesium silicide, magnesium oxide, and aluminium/manganese particles formed in situ were found in the matrix. In situ tensile test in scanning electron microscope has shown that reinforcing particles substantially influenced failure mechanism. Large, brittle magnesium silicide particles (size of 40 μm–50 μm) cracked during tensile deformation and at the same time, as a result of different physical properties, decohesion of the matrix and smaller aluminium/manganese, silicon carbide and magnesium oxide particles (size of 5 μm–10 μm, 10 μm and 50 nm respectively) occurred. Reinforcing particles and brittle secondary phases driven micro voids and their coalescence was found as a major cause of large cracks formation. Subsequently the increase of stress caused the cracks propagation by the coalescence of fractured particles and decohesively release smaller dispersed particles. The fracture propagated at approximately 90° angle to the direction of the tensile load direction. Fracture surface had feature of transcrystalline and intercrystalline failure. [ABSTRACT FROM AUTHOR]

The existence of [μ‐HSi4]3− in liquid ammonia solutions is confirmed by 1H and 29Si NMR experiments. Both NMR and quantum chemical calculations reveal that the H atom bridges two Si atoms of the [Si4]4− cluster, contrary to the expectation that it is located at one vertex Si of the tetrahedron. The calculations also indicate that in the formation of [μ‐HSi4]3−, protonation is driven by a high charge density and an increase of electron delocalization compared to [Si4]4−. Additionally, [Si5]2− was detected for the first time and characterized by NMR. Calculations show that it is resistant to protonation, owing to a strong charge delocalization, which is significantly reduced upon protonation. Thus, our methods reveal three silicides in liquid ammonia: unprotonated [Si5]2−, terminally protonated [HSi9]3−, and bridge‐protonated [μ‐HSi4]3−. The protonation trend can be roughly predicted by the difference in charge delocalization between the parent compound and the product, which can be finely tuned by the presence of counter ions in solution. Long ago Zintlsized and now analyzed: 29Si and 1H NMR experiments confirm the existence of Zintl ions [μ‐HSi4]3− and [Si5]2− in liquid ammonia. For [μ‐HSi4]3−, NMR and theoretical calculations reveal a bridging hydrogen atom forming a 3c‐2e‐bond. Additionally, [Si5]2−, only known from solvate crystal structures so far, was characterized by 29Si NMR. Here, NBO analysis indicates the formation of three localized 3c‐2e‐bonds. [ABSTRACT FROM AUTHOR]

Intermetallic compounds SrNi2Si and BaNi2Si were prepared by arc‐melting of stoichiometric mixture of the elements and subsequent annealing in welded niobium ampoules. Both compounds were investigated by X‐ray diffraction on powder as well as single crystal methods. The title compounds both crystallize in the BaNi2Ge structure type (space group Pmmn, Z = 2), a ternary ordered variant of TiCu3: a = 4.0296(9) Å, b = 6.5121(14) Å, c = 5.6839(21) Å, R1 = 0.040 for SrNi2Si and a = 4.0681(9) Å, b = 6.580(4) Å, c = 5.976(5) Å, R1 = 0.031 for BaNi2Si. The structure contains corrugated polyanionic [Ni2Si]2– layers, stacked according to the primitive sequence AA along the c axis. Six‐membered Ni rings adopt a boat conformation, silicon atoms are in the plane with nickel, and the alkaline earth cations sit between the layers. These two compounds extend the family AeNi2X (Ae = Ca, Sr, Ba; X = Si, Ge), where up to date CaNi2Si, SrNi2Ge, and BaNi2Ge are known. LMTO band structure calculations, including DOS, COHP, and ELF were performed to gain more insight into the electronic situation of SrNi2Si and BaNi2Si. [ABSTRACT FROM AUTHOR]

Abstract: We report on the first unambiguous detection of the elusive [HSi9]3− anion in solutions of liquid ammonia by various 29Si and 1H NMR experiments including chemical exchange saturation transfer (CEST). The characteristic multiplicity patterns of both the 29Si and 1H resonances together with CEST and a partially reduced 1H,29Si coupling constant indicate the presence of a highly dynamic Si8 entity and a Si−H moiety with slow proton hopping. Theoretical calculations corroborate both reorganization of Si8 on the picosecond timescale via low vibrational modes and proton hopping. In addition, in a single‐crystal X‐ray study of (K(DB[18]crown‐6))(K([2.2.2]crypt))2[HSi9]⋅8.5 NH3, the H atom was unequivocally localized at one vertex of the basal square of the monocapped square‐antiprismatic cluster. Thus experimental studies and theoretical considerations provide unprecedented insight into both the structure and the dynamic behavior of these cluster anions, which hitherto had been considered to be rigid. [ABSTRACT FROM AUTHOR]

The silicide family of thermoelectrics includes more than 15 compounds, among them are semimetals and semiconductors with band gaps ranging from 0.1 to 2.3 eV. The silicides have obvious attractive features as the materials for thermoelectric energy converters. Many of the constituting elements are abundant, have low price, the compounds have good high temperature stability. Another feature of silicides, much less recognized by thermoelectric community, is their compatibility with silicon‐based microelectronic technology. It opens a door for development of integrated thermoelectric power sources (energy harvesters) for electronic circuitry of wireless sensors and actuators. Considerable efforts have been undertaken, especially in the past 10 years, in order to develop efficient silicide‐based thermoelectric materials. Currently the most efficient silicide thermoelectrics are based on Mg2(Si‐Sn) alloys, MnSi1.75 and ReSi1.75. This article is a review of the current status of the research on the silicide‐based thermoelectric materials. Most of the non‐transition metal silicides were intentionally excluded from this review. On the other hand more attention is paid to the silicide materials, which have been not in the research focus; to compounds with topologically non‐trivial electronic structure, such as CoSi and SrSi2. [ABSTRACT FROM AUTHOR]

Abstract: As a promising thermoelectric material, higher manganese silicides are composed of earth‐abundant and eco‐friendly elements, and have attracted extensive attention for future commercialization. In this review, the authors first summarize the crystal structure, band structure, synthesis method, and pristine thermoelectric performance of different higher manganese silicides. After that, the strategies for enhancing electrical performance and reducing lattice thermal conductivity of higher manganese silicides as well as their synergism are highlighted. The application potentials including the chemical and mechanical stability of higher manganese silicides and their energy conversion efficiency of the assembled thermoelectric modules are also summarized. By analyzing the current advances in higher manganese silicides, this review proposes that potential methods of further enhancing zT of higher manganese silicides, lie in enhancing electrical performance while simultaneously reducing lattice thermal conductivity via reducing effective mass, optimizing carrier concentration, and nanostructure engineering. [ABSTRACT FROM AUTHOR]

Abstract: To improve the oxidation resistance of SiC composites at high temperature, the feasibility of using Ti3SiC2 coated via electrophoretic deposition (EPD) as a SiC fiber reinforced SiC composite interphase material was studied. Through fiber pullout, Ti3SiC2, due to its lamellar structure, has the possibility of improving the fracture toughness of SiCf/SiC composites. In this study, Ti3SiC2 coating was produced by EPD on SiC fiber; using Ti3SiC2‐coated SiC fabric, SiCf/SiC composite was fabricated by hot pressing. Platelet Ti3SiC2 powder pulverized into nanoparticles through high‐energy wet ball milling was uniformly coated on the SiC fiber in a direction in which the basal plane of the particles was parallel to the fiber. In a 3‐point bending test of the SiCf/SiC composite using Ti3SiC2‐coated SiC fabric, the SiCf/SiC composite exhibited brittle fracture behavior, but an abrupt slope change in the strength‐displacement curve was observed during loading due to the Ti3SiC2 interphase. On the fracture surface, delamination between each layer of SiC fabric was observed. [ABSTRACT FROM AUTHOR]

Yttrium silicide (YSi2) nanoparticles in SiGe are reported to enhance the thermoelectric figure‐of‐merit (ZT) to the recorded value (≈1.81). However, the thermoelectric properties of bulk YSi2 has never been reported. In this work, the thermoelectric properties of YSi2 is studied for the first time. The bulk YSi2 is fabricated by arc melting highly pure Si and Y raw materials. The ingot is crushed to powder and compacted to form a highly dense pellet by spark plasma sintering. By optimizing the processing parameters, the single phase with the AlB2‐type structure (P6/mmm) is formed. The Hall measurements show that YSi2 exhibit a metallic‐like behavior with a very high electron concentration. This result in the thermoelectric properties with a very large electrical conductivity (≈18 × 105 Ω−1 m−1) but a small Seebeck coefficient (−26 µV K−1) at room temperature, and decrease with temperature. The thermal conductivity is around 14–19 W m−1 K−1 for all temperature range. The maximum ZT value is 0.026 at 423 K. [ABSTRACT FROM AUTHOR]

Searching for layered MAX phase-like materials with properties of both ceramics and metals is a topic in its infancy. Herein, through a combination of crystal structure, electronic structure, chemical bonding, and elastic property investigations, we report two MAX phase-like layered materials Rh2YSi and Ir2YSi. Rh2YSi and Ir2YSi have bulk modulus B of 150 and 185 GPa, respectively, which are comparable to the typical MAX phases like Ti2AlC, Ti3AlC2, and Ti3SiC2, but much lower shear modulus G (82 and 97 GPa for Rh2YSi and Ir2YSi, respectively) than MAX phases. The high stiffness is due to the presence of rigid Si2-M-Si3-M (M = Ir, Rh) units, while the low shear deformation resistance is due to the presence of metallic bonds and the weak bonds that link the rigid Si2-M-Si3-M (M = Ir, Rh) units. Based on the low shear deformation resistance and low Pugh's ratio, Rh2YSi and Ir2YSi are predicted as damage-tolerant silicides and promising water vapor-resistant interphase materials for SiCf/SiC composites if yttria or yttrium silicates are formed to protect the SiC fibers in oxygen containing environments. The possible slip systems are {0001} < [ABSTRACT FROM AUTHOR]

A comparative study of reactive melt infiltration using Si and Si-Y alloys is presented to provide insight into the governing processes that control the effectiveness of the melt interaction with a carbonaceous preform and the temperature capability of the SiC matrix for ceramic matrix composites. Through experiments on two substantially different scales of capillaries in porous graphite tubes using Si and Si-Y alloys, the current study has characterized the phenomena that play a role in the infiltration of the melt and its reaction with the preform. It is shown that (i) the interface reaction controls wetting in both large and small capillaries and the climb rate is enhanced by the presence of Y; (ii) reaction choking occurs at critical throats within the pore network, usually behind the infiltration front; and (iii) different residual silicides can form during reaction and upon cooling. A potential mechanism for SiC growth is described, and the implications for the interplay between SiC growth and infiltration are discussed. [ABSTRACT FROM AUTHOR]

Within the framework of a thermodynamic model, the phonon anharmonicity associated with both acoustic and optical vibrations of the crystal lattice is investigated. On this basis we have performed self-consistent simulations of thermal and elastic properties of FeSi and CoSi compounds and their solid solutions Fe1- xCo xSi ( x = 0.1, 0.3, 0.5), which are promising spintronic materials. The non-lattice contributions to the heat capacity and coefficient of thermal expansion of the considered systems have been established. It is shown that the Invar effect observed in Fe0.7Co0.3Si and Fe0.5Co0.5Si is associated with anomalies of their electronic and magnetic subsystems. [ABSTRACT FROM AUTHOR]

Metal silicides are the preferred contact materials for metal-oxide semiconductor (MOS) structures. With further technology development, the materials changed within the last decades toward lower resistivity and lower thermal budget. Currently NiSi partly further stabilized with Pt or Pd is the material of choice. The understanding of phase transformation processes and structural features is of great importance for production process optimization. Here we present a fast laboratory-based in situ X-ray diffraction method with two different experimental arrangements (Bragg-Brentano and grazing incidence) optimized concerning the materials texture. Its application is demonstrated for the transformation of Ni to different Ni silicide phases starting with a 46 nm thick Ni layer sputtered on a Si(001) substrate and covered with TiN. Activation energies for the Ni to Ni2Si (1.55 ± 0.13) eV and the Ni2Si to NiSi transition (1.30 ± 0.15) eV are measured by repeating fast diffraction scans over a limited angular range under isothermal conditions and analyzing the diffraction peak height versus time. [ABSTRACT FROM AUTHOR]

The effect of annealing ambient during rapid thermal processing on thermal stability of NiSi has been investigated. Nickel films deposited onto Si(100) were annealed in vacuum, Ar and N2 at pressures up to 40 Torr. Rapid thermal annealing in vacuum or in Ar at 750 °C resulted in the formation of NiSi2 with concomitant increase in sheet resistance and surface roughness. However, annealing in N2 increases the NiSi2 nucleation temperature and thus the thermal stability of NiSi. Higher the N2 pressure, higher was the annealing temperature required to initiate NiSi2 nucleation. Experimental results were analyzed using a simple thermodynamic model. It suggests dissolved nitrogen impurities lower the chemical potential and increase thermal stability of NiSi phase. Phase stability observed experimentally was in agreement with that predicted by the model. Threshold nitrogen pressure exists for stabilization of nickel monosilicide during rapid thermal annealing. [ABSTRACT FROM AUTHOR]

Metal silicide (Pd2Si, Ni2Si, CoSi, Fe xSi, and Cu6.69Si) catalysts supported by SBA-15 have been prepared by a chemical vapor deposition method under a H2 atmosphere using (CH3)2SiCl2 as the Si source. Of the SBA-15-supported metal silicide catalysts, Ni2Si/SBA-15 presented a modest activity, notable selectivity to styrene (>90 %), and high stability with respect to the selective hydrogenation of phenylacetylene, which is attributed to the active-site isolation and electron transfer in the silicide. Furthermore, Ni2Si/SBA-15 also has a high selectivity to diphenylacetylene and 1,4-butynediol, which demonstrates that Ni2Si/SBA-15 is a promising, low-cost catalyst alternative to noble-metal catalysts as a selective hydrogenation catalyst. [ABSTRACT FROM AUTHOR]

We have specified the synthetic conditions to obtain one-directionally ordered CaSi2 microwall arrays vertically grown on a Si substrate. Our basic concept is based on the utilization of the Kirkendall effect for reactive deposition epitaxy (RDE). We found for the first time that: 1) a much larger Ca vapor supply on the Si substrate than the conventional RDE, 2) the adoption of a two-step heating process, and 3) the selection of the crystal axis of the Si surface are the keys to control the microstructures of CaSi2 on the Si substrate. The CaSi phase was first formed on Si, then the CaSi2 phase was formed at the CaSi/Si interface. Based on the Kirkendall effect, the interdiffusion of Ca and Si was enhanced in the vertical direction rather than in the parallel direction to the Si surface. CaSi2 tends to grow along four equivalent Si{111} planes, however, the specific orientation of the Si surface resulted in CaSi2 microwalls grown along its Si(11 [ABSTRACT FROM AUTHOR]

We investigate material conversion of compound semiconductor GaAs nanowires to extend their functions. By heating the GaAs nanowires in indium melt, the indium was introduced into the GaAs nanowire, converting the nanowires to be InGaAs compounds. The further heating treatment in N2 ambient progresses the diffusion of Si element from the substrate, eventually forming the indium-silicide compound nanowires. The results suggest the conversion technique possibly extend the functions of the nanowire system by the exchange, introduction, or integrations of various materials. [ABSTRACT FROM AUTHOR]

We report the first solvate structure of the silicide anion Si44-, which provides circumstantial evidence of the stability of the highly charged anion in liquid ammonia solutions. The solvate Rb1.2K2.8Si4 ·7NH3 crystallized from a mixture of the ternary compound K6Rb6Si17 with the transition metal complex [(C6H5)3P]2Ni(CO)2 [bis(triphenylphosphine)dicarbonylnickel] in the presence of the chelating agents 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) and [2.2.2]cryptand (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) in liquid ammonia. Single X-ray diffraction analysis confirms the presence of the Si44- anion in the crystal structure of Rb1.2K2.8Si4 ·7NH3, which represents the first solvate compound of the naked tetrasilicide tetraanion. All five crystallographically independent cation positions show mixed occupancy by Rb+ and K+. [ABSTRACT FROM AUTHOR]

3D sequential integration is a promising alternative to conventional scaling down approach: by stacking transistors level on top of each other, benefits on device density and performance are achieved. However, although the thermal processing of top transistors is currently restricted in order to avoid bottom CMOS degradation, it has been highlighted that Ni0.80Pt0.10 silicide source/drain (S&D) contact remains the most sensitive element to the thermal budget, especially on raised Si0.7Ge0.3:B S&D for pMOS transistors. In this context, a complete and systematic study on self-aligned silicide (SALICIDE) process has been proposed: alternative metallization as well as source and drain surface pre-treatments have been carried out. Indeed, a novel Ni-based silicide, the Ni0.9Co0.1 provides a better stability on unpatterned 300 mm wafers. This stability has been further improved when combined with epitaxial silicon capping layer (Si-Cap) and Si0.7Ge0.3:B S&D preamorphization implant (PAI) using Ge beam. For the first time, a successful Ni0.9Co0.1 SALICIDE implementation has been demonstrated on pMOS planar FDSOI transistor with both PAI and Si-Cap. Moreover, the presence of Si-Cap contributes to reduce silicide roughness and limits Ge partition that damage Si0.7Ge0.3:B S&D. [ABSTRACT FROM AUTHOR]

SUMMARY The silicide phase formation is examined in the Ni/Si system. The multiphase of NiSi and NiSi2 is confirmed in a specimen, in which a 30-mm-thick Ni film is sputter-deposited on Si(100) at 350 °C and subsequently annealed at 400 °C for 1 h. This is interpreted that the NiSi and NiSi2 phases nucleate from the amorphous alloys, as a super-cooled melt, at a composition corresponding to those of eutectic points in different composition, which appear in the intermixed Ni-Si alloy layer with a Ni concentration gradient owing to intermixing between Ni and Si at the interface. To confirm this idea, we performed Ni deposition on a 350 °C-heated Si substrate with a thin SiO2 layer. The results show the direct formation of NiSi2 in a nonuniform fashion. This is because the thin SiO2 layer suppresses Ni diffusion into Si, resulting in the formation of a Ni-Si alloy with a Si-rich composition, from which NiSi2 nucleates at a low temperature. We can demonstrate that the high-temperature phase of NiSi2 nucleates under kinetic constraints from an amorphous alloy with a suitable composition. [ABSTRACT FROM AUTHOR]

Introduction: Vaporization of materials due to shock-wave compression and the following isentropic release from extreme pressures [1,2] is important in several planetary contexts. For instance, vaporization of mantle silicates [3] and even metallic planetary cores [4] in giant impacts seems to be a typical process in final stages of terrestrial planet formation. Furthermore, terrestrial impact spherules layers [5] as well as chemically reduced phases [6,7] and glasses of exotic, complementary composition [8] in the lunar regolith have been interpreted as impact vapor condensates. Despite its significance, knowledge about impact vaporization is, however, limited because physical remnants of impact-generated vapors are scarce [8,9] and a condensate origin can be difficult to prove as impact melting or in-situ reduction in impact melts might also explain their existence. In addition, as the states of impact vaporization lie in a region of phase space that is difficult to reach experimentally for most planetary materials (i.e., in the warm dense matter regime along the liquid-vapor phase boundary and up to the critical point), only a few dynamic-compression studies were focused on vaporization and expanded states [2,10]. Here we report on FeNi silicides and Si-rich, amorphous rims surround target clasts contained in the black impact glasses of the Wabar craters that we interpret as mixtures of impact-vapor condensates and condensates resulting from ablation of the impactor during atmospheric entry. Materials and Methods: We studied samples of black Wabar impact glass [11] using electron microprobe analysis (EMPA) and transmission electron microscopy (TEM). To test whether vaporization of the Wabar IIIAB FeNi metal projectile and quartz sand target occurred, atmospheric entry of the impactor and crater formation was modeled using the SOVA 3D hydrocode [12] and analytical equations of state for iron [13] and quartz [1]. HSC Chemistry 10 was used to predict phase compositions in a simplified N-O-Si-Fe-Ni system between 1,000 and 6,000 K at 1 bar. Results and Discussion: We found several occurrences of FeNi silicides and Si-rich, amorphous domains that were previously undescribed from black Wabar impact glass. FeNi silicide spherules with diameters between <10 nm and ~5 µm occur in rare, ~2-30 µm wide, continuous rims of Si-rich, amorphous matrix surrounding partially melted target (sand/sandstone) clasts. Such clasts are common in the black Wabar impact glasses [11], yet only few of them have FeNi silicide spherules lining their exterior surfaces. Similar spherules occasionally line surfaces of vesicles disseminated in the impact glass. Compositions (EMPA) of larger spherules are consistent with suessite (Fe,Ni)3Si, hapkeite Fe2Si, and xifengite Fe5Si3. The Si-rich, amorphous rims contain between 7 and 45 wt% Fe + Ni, often have higher Si abundances (up to ~58 wt%) than silica (46.74 wt%), and plot onto mixing lines spanned between SiO and either Fe or FeO. TEM imaging and electron diffraction furthermore revealed the presence of linzhiite FeSi2, Fe5Ni3Si2, and Fe1.94Ni5.81Si3 as well as of spherules of cubic cristobalite and likely silicon metal in the Si-rich, amorphous rims. We did not find evidence of reducing agents such as carbon-bearing phases. Overall, the FeNi silicide spherules are much less abundant than Wabar FeNi metal spherules, which are chemically fractionated impact melts of the projectile disseminated in the silicate impact glasses [11]. The hydrocode models suggest that while peak pressures were high enough to vaporize the quartz sand target, only less than 1% of the projectile vaporized upon impact. However, they suggest that depending on impact angle, substantial amounts (27-37%) of the projectile were melted and vaporized during atmospheric entry. Since the final velocity was high, ablation continued until impact, thus opening the possibility that vaporized FeNi metal interacted with SiO and/or Si (formed from breakdown of SiO2; [1]) of the target-derived vapor phase. This is consistent with a thermodynamic model of vapor-phase chemistry and has also been predicted from studies of lunar iron silicides [7]. The resulting mixture of FeNi silicides and SiO condensed onto relatively cold (<2,100 K) target clasts that were ejected from the transient crater and which were subsequently incorporated into larger impact-melt ejecta. Quenching of the melts preserved the highly reduced nature of the FeNi silicides, while the amorphous SiO likely decomposed into sub-nanometer-size SiO2 and Si domains (cf. [14]). [ABSTRACT FROM AUTHOR]

Depth analysis of the surface oxide layer on a Mg2Si crystal was performed with X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). In XPS, X-rays from synchrotron radiation with the energies between 2100 and 3300 eV were used as the excitation sources for depth analysis. The Si 1s and Mg 1s XPS spectra show the formation of a thinner SiO2-X layer at outermost surface and a thicker MgO layer at lower surface on the Mg2Si. In XAS, total electron yield and partial electron yield (PEY) acquisition modes were used for the measurement of Si K-edge. The PEY spectrum was obtained by detecting electrons with a fixed kinetic energy of 5, 10, 20, 30, 40, or 50 eV. Although the PEY spectrum with electrons of 5 eV shows similar features with the total electron yield spectrum, detection of electrons with 50 eV gives an increase in the ratio of a peak at 1843.7 eV to the peak assigned to Mg2Si. The peak at 1843.7 eV can be assigned to the formation of SiO2-X on the Mg2Si. From XPS and XAS results, it is indicated that a thinner SiO2-X layer at outermost surface and a thicker MgO layer at lower surface are formed at initial oxidation of the Mg2Si. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We elucidate here the structure-property relationship in a novel composite system consisting of hydroxyapatite ( HA) and titanium disilicide that addresses the challenge of low electrical conductivity and fracture toughness of hydroxyapatite. Theoretical considerations indicated that the addition of 20 wt.% titanium disilicide (σ ~ 106 S/m) favorably contributed to the increase in electrical conductivity (σ ~ 105 S/m) of the HA-titanium disilicide system. As compared to theoretical value, a lower value of electrical conductivity of HA-20 wt.%TiSi2 composite (σ ~ 67.117 ± 3.57 S/m) was observed in experimental measurement using four probe method. However, this electrical conductivity of HA-20 wt.%TiSi2 composite was significantly higher than the HA, because no current was recorded in case of HA in the sensitivity range of the instrument. During spark plasma sintering, to raise per unit temperature, higher magnitude of current was utilized in case of HA-20TiSi2 than HA. This resulted in higher densification of HA-20TiSi2 during initial stage of sintering. Also, a significant improvement in fracture toughness was observed on the addition of TiSi2 to HA from 0.6 MPa.m1/2 in HA to 1.2 MPa.m1/2 in HA-20TiSi2. The mechanism of increase in fracture toughness involved crack deflection, friction bridging, wake debonding, and elastic bridging. [ABSTRACT FROM AUTHOR]

The fabrication of peripheral CMOS devices for DRAM memories requires specific optimization with respect to a standard logic flow, imposed by the additional constraints linked to the memory element fabrication. Several process tunings are needed to keep pace with the request for low leakage and low cost devices combined with the needs of highly performant and resilient circuits. In this article, we summarize the most significant developments achieved in recent years focusing on HKMG Gate stack, junction tuning, silicide optimization for DRAM peripheral transistors. Three different solutions with different fabrication complexity and performance for HKMG, optimized junction, and thermally stable NiPt silicide fabrication, all compatible with the DRAM requirements, are discussed. [ABSTRACT FROM AUTHOR]

We report the Raman analysis of both as-deposited and annealed amorphous silicon ruthenium thin films embedded with nanocrystals. In the Raman spectra of as-deposited films, variations of TO peak indicate a short-range disorder of a-Si network with an increase of Ru concentration. The substitutional Ru atoms lower the concentration of Si-Si bonds and suppress the intensity of TO peak, but have less effect on TA, LA and LO peaks. In the Raman spectra of annealed films, characteristic parameters confirm the upgrade of a-Si network at a low annealing temperature and the emergence of both ruthenium silicide and silicon nanocrystals at 700 °C. Although ruthenium silicide nanocrystals present no Raman peaks in the Raman spectra of as-deposited samples, the non-linear variations of intensity ratios ILA + LO/ ITO and ITA/ ITO still suggest their existence, and these nanocrystals are subsequently verified by high-resolution transmission electron microscopy. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The germanides Ca3Ir4Ge4, Sr3Ir4Ge4, Eu3Ir4Ge4, Ba2Ir4Ge5, and Ba2MgIr4Ge4 were obtained from mixtures of the elements at 1200 °C. The crystal structures were solved and refined from single crystal diffraction data. With the Na3Pt4Ge4 type structure (space group I $\bar{4}$3 m, Z = 2) crystallize: Ca3Ir4Ge4 [ a = 7.5824(2) Å], Sr3Ir4Ge4 [ a = 7.6972(1) Å], and Eu3Ir4Ge4 [ a = 7.6580(3) Å]. The K2Zn5As4 structure type (space group Cmcm, Z = 4) is adopted by the compounds Ba2Ir4Ge5 [ a = 11.3297(4) Å, b = 6.7614(2) Å, c = 11.5930(5) Å] and Ba2MgIr4Ge4 [ a = 11.0953(5) Å, b = 7.1305(5) Å, c = 11.5685(5) Å]. Both structure types are characterized by stellae quadrangulae Ir4Ge4. In Ca3Ir4Ge4, Sr3Ir4Ge4, and Eu3Ir4Ge4 these are connected to eight others by Ir-Ge bonds. In the structure of Ba2Ir4Ge5 the number of neighboring Ir4Ge4 units linked by direct bonds is reduced to six, whereas two others are connected by additional Ge atoms. In the quaternary compound these Ge atoms are substituted by Mg atoms. [ABSTRACT FROM AUTHOR]

The two compounds AuNi3Si6 and Au2Ni4Si7 were prepared from the elements by arc melting and subsequent annealing at 500 °C. They were investigated by X-ray diffraction (powder and single-crystal methods) and by scanning-electron microscopy which was used for the independent determination of the phase compositions. Both compounds show only minor homogeneity ranges. Single-crystal XRD was used for structure determination. Both title compounds crystallize in new structure types; AuNi3Si6 (Pearson symbol hR30, space group R $\bar{3}$ m) and Au2Ni4Si7 (Pearson symbol mC26, space group C2/ m). The new crystal structures are related to that of NiSi2 (CaF2-type); AuNi3Si6 may be derived from this structure by a shear operation, while Au2Ni4Si7 may be regarded as intergrowth structure of the CaF2 and Hg2Pt-type. [ABSTRACT FROM AUTHOR]

A ternary hexaerbium triacontacobalt enneakaidecasilicide, ErCo5Si3.17, crystallizes as a combination of disordered variants of the hexagonal UCo5Si3 ( P63/ m) and Yb6Co30P19 ( P) structure types and is closely related to the Sc6Co30Si19 and Ce6Rh30Si19 types. The Er, Co and three of the Si atoms occupy sites of m.. symmetry and a fourth Si atom occupies a site of .. symmetry. The environment of the Er atom is a 21-vertex pseudo-Frank-Kasper polyhedron. Trigonal prismatic coordination is observed for the Si atoms. The Co atoms are enclosed in heavily deformed cuboctahedra and 11-vertex polyhedra. Crystallochemistry analysis and the data from electronic structure calculations (TB-LMTO-ASA) suggest that the Er atoms form positively charged cations which compensate the negative charge of the [Co12Si9] m− polyanions. [ABSTRACT FROM AUTHOR]

Cu2ZnSi(S,Se)4 and Cu2Si(S,Se)3 are potential materials to obtain cost effective high band gap absorbers for tandem thin film solar cell devices. A method to synthesize Cu2SiS3, Cu2SiSe3and Cu2ZnSiSe4thin film absorbers is proposed. This method is based on a multistep process, using sequential deposition and annealing processes. X-ray diffraction analysis performed on the final thin films have confirmed the presence of the Cu2Si(S,Se)3 and Cu2ZnSiSe4phases. Scanning electron microscopy images revealed the formation of polycrystalline layers with grains size up to 1 µm. The band gap of the ternary Cu2SiSe3 and Cu2SiS3, and quaternary Cu2ZnSiSe4 based thin films as determined from optical and photoluminescence measurements are found to be close to their theoretical values. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Er-germanosilicide [Er(Si1− zGe z)2− y] films were formed on strained Si1− xGe x layers with different Ge contents ( x = 0.14 and 0.28), and their dependency of formation kinetics on the Ge concentrations was investigated while minimizing the oxygen-incorporation effect using a TaN capping layer. When a ~30 nm-thick Er film was used, uniform Er(Si1− zGe z)2− y films were obtained at an annealing temperature of around 600 °C without their agglomeration and also the strain relaxation of the remaining Si1− xGe x layer. The increase in the Ge concentration of the reacting Si1− xGe x layer enhanced the formation of the crystalline Er(Si1− zGe z)2− y film. Furthermore, some enrichment of the Ge content within the Er(Si1− zGe z)2− y film occurred in comparison with that in the initial and remaining Si1− xGe x layers. [ABSTRACT FROM AUTHOR]

A portable ultrahigh-vacuum system optimized for in situ variable-temperature X-ray scattering and spectroscopy experiments at synchrotron radiation beamlines was constructed and brought into operation at the synchrotron radiation facility ANKA of the Karlsruhe Institute of Technology, Germany. Here the main features of the new instrument are described and its capabilities demonstrated. The surface morphology, structure and stoichiometry of EuSi2 nano-islands are determined by in situ grazing-incidence small-angle X-ray scattering and X-ray absorption spectroscopy. A size reduction of about a factor of two of the nano-islands due to silicide decomposition and Eu desorption is observed after sample annealing at 1270 K for 30 min. [ABSTRACT FROM AUTHOR]