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Ultrathin two-dimensional silica films have been suggested as highly defined conductive models for fundamental studies on silica-supported catalyst particles. Key requirements in this context are closed silica films that isolate the gas phase from the underlying metal substrate and stability under reaction conditions. Here, we present silica bilayer films grown on Pt(111) and Rh(111) and characterize them by scanning tunneling microscopy and X-ray photoelectron spectroscopy. We provide the first report of silica bilayer films on Rh(111) and have further successfully prepared fully closed films on Pt(111). Interestingly, surface and interface silicide phases play a decisive role in both cases: On platinum, closed films can be stabilized only when silicon is deposited in excess, which results in an interfacial silicide or silicate layer. We show that these silica films can also be grown directly from a surface silicide phase. In the case of rhodium, the silica phase is less stable and can be reduced to a silicide in reductive environments. Though similar in appearance to the "silicene" phases that have been controversially discussed on Ag(111), we conclude that an interpretation of the phase as a surface silicide is more consistent with our data. Finally, we show that the silica film on platinum is stable in 0.8 mbar CO but unstable at elevated temperatures. We thus conclude that these systems are only suitable as model catalyst supports to a limited extent.

The processes of formation of a thin film of cobalt disilicide on the silicon surface due to the formation of several nuclei of atomic thickness on the surface of the silicon substrate are presented. To create these structures, the ion implantation method was used. The dependence of the depth of penetration of ions into the substrate during ion implantation on temperature and ion dose was determined. In the case of implantation of Co+ ions into Si at room temperature silicon uniformly combines with Co atoms at a depth of 3.5–4 nm, the Co concentration in these layers is 45–50 at. %. Co has been shown to form chemical bonds with Si atoms in the sample containing 40–45 atomic % of Co. When implanting Co+ into Si at 600 K, it was found that the depth of the same added layer is 2.5–3 nm, and CCo forming bonds with Si atoms increases to 85–90%. [ABSTRACT FROM AUTHOR]

The processes of formation of a thin film of cobalt disilicide on the silicon surface due to the formation of several nuclei of atomic thickness on the surface of the silicon substrate are presented. To create these structures, the ion implantation method was used. The dependence of the depth of penetration of ions into the substrate during ion implantation on temperature and ion dose was determined. In the case of implantation of Co+ ions into Si at room temperature silicon uniformly combines with Co atoms at a depth of 3.5–4 nm, the Co concentration in these layers is 45–50 at. %. Co has been shown to form chemical bonds with Si atoms in the sample containing 40–45 atomic % of Co. When implanting Co+ into Si at 600 K, it was found that the depth of the same added layer is 2.5–3 nm, and CCo forming bonds with Si atoms increases to 85–90%. [ABSTRACT FROM AUTHOR]

The processes of formation of a thin film of cobalt disilicide on the silicon surface due to the formation of several nuclei of atomic thickness on the surface of the silicon substrate are presented. To create these structures, the ion implantation method was used. The dependence of the depth of penetration of ions into the substrate during ion implantation on temperature and ion dose was determined. In the case of implantation of Co+ ions into Si at room temperature silicon uniformly combines with Co atoms at a depth of 3.5–4 nm, the Co concentration in these layers is 45–50 at. %. Co has been shown to form chemical bonds with Si atoms in the sample containing 40–45 atomic % of Co. When implanting Co+ into Si at 600 K, it was found that the depth of the same added layer is 2.5–3 nm, and CCo forming bonds with Si atoms increases to 85–90%. [ABSTRACT FROM AUTHOR]

As a critical material for high-temperature components of aero-engines, the mechanical properties of Ti65 alloy, subjected to high-temperature and long-term thermal exposure, directly affect its service safety. The room-temperature tensile properties of the Ti65 alloy after thermal exposure to temperatures ranging from 450 °C to 650 °C for 100 h were investigated. The results indicate that as the thermal exposure temperature increases, the strength of Ti65 alloy initially increases and then decreases, while ductility exhibits a decreasing trend. The strength of the thermally exposed alloy positively correlates with the size and content of the α2 phase. The ductility of the thermally exposed alloy is comprehensively influenced by the surface oxidation behavior, α2 phase, and silicides. After the prolonged thermal exposure, stress concentration at the crack tips within the oxide layer was enhanced with the increased thickness of the surface TiO2 oxide layer, leading to premature fracture due to reduced alloy ductility. Furthermore, the α2 phase in the matrix promotes the planar slip of dislocations, while silicides at the α/β phase boundaries hinder dislocation motion, causing dislocation pile-ups. Both behaviors facilitate crack nucleation and deteriorate alloy ductility. [ABSTRACT FROM AUTHOR]

The temperature dependences of the thermoelectromotive force of chromium mono and disilicides in the temperature range 200℃÷+600℃ have been studied. For chromium disilicide, the dependence of the thermopower coefficient (α) on temperature (T) has three sections. Chromium monosilicide is characterized by a smooth increase in thermopower with increasing temperatures up to 200℃, and then its constancy. It was revealed that silicides rich in chromium atoms have lower thermopower values than silicides rich in silicon. The maximum thermo-EMF values of 110 μV/K and 190 μV/K were observed for chromium mono- and disilicides, respectively. It was revealed that for chromium silicides the dependence of the dimensionless parameter Q = Z∙T on temperature is linear. The possibility of predicting the technology of synthesis of semiconductor material with optimal thermoelectric properties using the dependence of thermopower on conductivity and the parameter Q on temperature is shown.

In this work the mechanism of current flow during illumination with hν≥Eg in the temperature range of 77÷300 K is considered. It is established that in the PtSi – Si-M structure in the temperature range of 77÷270 K the regime of space charge limited currents (SCLC) is realized. The current-voltage characteristics of the structures show areas of linear and quadratic dependences of current on voltage, as well as areas of a sharp increase in current. These features of the current-voltage characteristic are explained by the presence of deep level structures and sticking levels for charge carriers in the base region. From the temperature dependence of the SCLC, the concentration of adhesion levels was determined to be equal to (1.8÷3) 1015 cm-3 and the adhesion factor to be equal to 6.32·10-2. In the temperature range 77÷115 K at voltages 0.2÷1 V, the current-voltage characteristic obeys the law J ~ Un(n=3÷4), and above U – the law J ~ U6, followed by a transition to the quadratic law.

The electrochemical behavior of manganese silicide-germanides with different ratios of germanium and silicon is studied using the methods of voltammetry and impedance spectroscopy in 0.5 M aqueous sodium sulfate solution. It is shown that the oxidation stability of materials decreases with an increase in the ratio of germanium, which, unlike silicon, is incapable of forming a layer of stable oxides on the material surface. [ABSTRACT FROM AUTHOR]

TC25G alloy was heat treated at 950 °C/3 h, AC + 580 °C/6 h, AC and the bimodal structure with primary α phase + β transition structure was obtained. The creep properties of the alloy were tested in 550–600 °C/150–250 MPa. The results show that the precipitations of silicide and α2 phase is accompanied by the creep process. α2 phase plays a dispersion strengthening role in both the primary and steady-state creep stages. However, in the accelerated creep stage, the mechanism of α2 phase and dislocation changes from cutting mechanism to bypassing mechanism, and the strengthening effect is weakened. Silicide inhibits grain boundary slip mainly in the primary creep stage, and inhibits dislocation slip in the steady-state and accelerated creep stages. At 550 °C, n = 1.6 and Q = 280–371 kJ/mol (150–250 MPa) indicate that the creep of the alloy is a self-diffusion process, and the creep deformation is mainly controlled by dislocation slip. At 570–600 °C, n = 3.2 indicates that the dislocation climb controls the creep deformation. Meanwhile, compared with Q = 274 kJ/mol at low stress (150 MPa), Q = 365 kJ/mol at the high stress (200–250 MPa) indicates that the second phase precipitation enhancement is enhanced. [ABSTRACT FROM AUTHOR]

The microstructural stability and property evolution of high-temperature titanium alloys under long-term high-temperature conditions has been a critical scientific issue in the field of advanced titanium alloys. In this work, we systematically investigated the precipitation behavior of silicides and ordered α2 phase, which are closely related to the microstructural stability of Ti65 high-temperature alloy, during thermal exposure at 650 °C for different periods of time. Furthermore, the effects of thermal exposure on mechanical properties were evaluated using room temperature and high temperature tensile tests, and subsequently, the correlation between the microstructural thermal stability and the mechanical characteristics was discussed. The results reveal that (Ti, Zr)6Si3 silicides initially precipitate within the residual β film and then start to precipitate in the α platelet. A large number of fine spherical α2 precipitates were formed inside the α platelet after a short thermal exposure. The number density of ordered α2 decreased significantly after 1000 h due to Ostwald ripening. The precipitation of silicides and ordered α2 phases during thermal exposure improves the tensile strength but deteriorates the ductility, and the room-temperature ductility is slightly restored due to α2 ripening after long-time thermal exposure. Ti65 high-temperature titanium alloy consistently maintains favorable room-temperature tensile properties throughout long-term thermal exposure. [ABSTRACT FROM AUTHOR]

In this work the mechanism of current flow during illumination with hν≥Eg in the temperature range of 77÷300 K is considered. It is established that in the PtSi - Si-M structure in the temperature range of 77÷270 K the regime of space charge limited currents (SCLC) is realized. The current-voltage characteristics of the structures show areas of linear and quadratic dependences of current on voltage, as well as areas of a sharp increase in current. These features of the current-voltage characteristic are explained by the presence of deep level structures and sticking levels for charge carriers in the base region. From the temperature dependence of the SCLC, the concentration of adhesion levels was determined to be equal to (1.8÷3) 1015 cm-3 and the adhesion factor to be equal to 6.32·10-2. In the temperature range 77÷115 K at voltages 0.2÷1 V, the current-voltage characteristic obeys the law J ~ Un(n=3÷4), and above U - the law J ~ U6, followed by a transition to the quadratic law. [ABSTRACT FROM AUTHOR]

The temperature dependences of the thermoelectromotive force of chromium mono and disilicides in the temperature range 200℃÷+600℃ have been studied. For chromium disilicide, the dependence of the thermopower coefficient (α) on temperature (T) has three sections. Chromium monosilicide is characterized by a smooth increase in thermopower with increasing temperatures up to 200℃, and then its constancy. It was revealed that silicides rich in chromium atoms have lower thermopower values than silicides rich in silicon. The maximum thermo-EMF values of 110 μV/K and 190 μV/K were observed for chromium mono- and disilicides, respectively. It was revealed that for chromium silicides the dependence of the dimensionless parameter Q = Z∙T on temperature is linear. The possibility of predicting the technology of synthesis of semiconductor material with optimal thermoelectric properties using the dependence of thermopower on conductivity and the parameter Q on temperature is shown. [ABSTRACT FROM AUTHOR]

As a critical material for high-temperature components of aero-engines, the mechanical properties of Ti65 alloy, subjected to high-temperature and long-term thermal exposure, directly affect its service safety. The room-temperature tensile properties of the Ti65 alloy after thermal exposure to temperatures ranging from 450 °C to 650 °C for 100 h were investigated. The results indicate that as the thermal exposure temperature increases, the strength of Ti65 alloy initially increases and then decreases, while ductility exhibits a decreasing trend. The strength of the thermally exposed alloy positively correlates with the size and content of the α2 phase. The ductility of the thermally exposed alloy is comprehensively influenced by the surface oxidation behavior, α2 phase, and silicides. After the prolonged thermal exposure, stress concentration at the crack tips within the oxide layer was enhanced with the increased thickness of the surface TiO2 oxide layer, leading to premature fracture due to reduced alloy ductility. Furthermore, the α2 phase in the matrix promotes the planar slip of dislocations, while silicides at the α/β phase boundaries hinder dislocation motion, causing dislocation pile-ups. Both behaviors facilitate crack nucleation and deteriorate alloy ductility.

Based on the diffusion technology, many scientists and specialists have conducted research on obtaining materials that are fundamentally different in electrical and photo-thermal parameters from the original material by introducing various input atoms into semiconductor materials and creating deep energy levels in their band gap. The electrical, photoelectric, optical, and magnetic properties of these semiconductor materials have been extensively studied with metal group elements, isovalent elements, and rare earth elements added to silicon through the process of growth, ion implantation, or diffusion from the gaseous state. The technology of introducing impurity atoms into silicon by the diffusion method is distinguished from other methods in its simplicity, energy efficiency, and low cost. Up-to-date, the technology of changing the resistivity and conductivity of the initial sample by diffusion of manganese atoms into single-crystal silicon is studied insufficiently. In the article, it was determined that when manganese atoms diffuse into silicon, a high-manganese silicide is formed on its surface and in the near-surface layer. Based on the analysis of the experimental results, the thermal EMF (electromotive force) in Mn4Si7-Si --Mn4Si7 structures in a certain temperature range and under illumination (with monochromatic or integrated light) is explained by the fact that it based on the Pelte effect, observed in semiconductors.The volt-ampere characteristics (VAC) of the obtained structures were measured at various temperatures, in the dark and in the light. Formation of a boundary layer with high resistivity at the boundary of the higher manganese-silicon transition, the transition from higher manganese silicide to the base of the structure due to the effect of ionization of pores during illumination of structures and external influence. The applied field was clarified based on VAC results. The manganese high silicide layer formed on the silicon surface has the properties of a semiconductor, and the formation of a heterojunction upon transition to silicon is shown on the basis of the sphere diagram.

The microstructural stability and property evolution of high-temperature titanium alloys under long-term high-temperature conditions has been a critical scientific issue in the field of advanced titanium alloys. In this work, we systematically investigated the precipitation behavior of silicides and ordered α2 phase, which are closely related to the microstructural stability of Ti65 high-temperature alloy, during thermal exposure at 650 °C for different periods of time. Furthermore, the effects of thermal exposure on mechanical properties were evaluated using room temperature and high temperature tensile tests, and subsequently, the correlation between the microstructural thermal stability and the mechanical characteristics was discussed. The results reveal that (Ti, Zr)6Si3 silicides initially precipitate within the residual β film and then start to precipitate in the α platelet. A large number of fine spherical α2 precipitates were formed inside the α platelet after a short thermal exposure. The number density of ordered α2 decreased significantly after 1000 h due to Ostwald ripening. The precipitation of silicides and ordered α2 phases during thermal exposure improves the tensile strength but deteriorates the ductility, and the room-temperature ductility is slightly restored due to α2 ripening after long-time thermal exposure. Ti65 high-temperature titanium alloy consistently maintains favorable room-temperature tensile properties throughout long-term thermal exposure.

In this study, the effect of the initial phases of the Si-bearing near-α titanium alloy Ti–6Al–2.75Sn–4Zr–0.4Mo–0.45Si (Ti-1100) on Vickers microhardness during aging at 600°C from 5 min to 42 days was investigated by transmission electron microscopy. The initial phases included α′ martensite and α phases. The variation in the hardness of the specimen with the initial α′ martensite phase occurred in the following order: the decrease caused by dislocation recovery, the increase caused by silicide precipitation, the decrease caused by silicide coarsening, and the increase caused by α² precipitation. As for the initial α phase, hardness initially decreased and then increased because of dislocation recovery and silicide/α² precipitation, respectively. The difference in age-hardening behavior resulted from the difference between the dislocation amounts in the two initial phases. Silicide precipitation was promoted by dislocations, whereas α² precipitation occurred via homogeneous nucleation irrespective of the dislocations. [ABSTRACT FROM AUTHOR]

The microstructure and room temperature tensile properties of heat-treated TC25G alloy after thermal exposure were investigated. The results show that the α2 phase dispersed in the α phase, and silicide precipitated firstly at the α/β phase boundary and then at the dislocation of the αp phase and on the β phase. When thermal exposure was 0–10 h at 550 °C and 600 °C, the decrease of alloy strength was mainly due to the dominant effect of dislocations recovery. With the rise and extension of thermal exposure temperature and time, the increasing quantity and size of precipitates played an important role in the improvement of alloy strength. When thermal exposure temperature rose to 650 °C, the strength was always lower than that of heat-treated alloy. However, since the decreasing rate of solid solution strengthening was smaller than the increasing rate of dispersion strengthening, alloy still showed an increasing trend in the range of 5–100 h. When thermal exposure time was 100–500 h, the size of the α2 phase increased from the critical value of 3 nm to 6 nm, and the interaction between the moving dislocations and the α2 phase changed from the cutting mechanism to the by-pass mechanism (Orowan mechanism), and thus alloy strength decreased rapidly. [ABSTRACT FROM AUTHOR]

MnSi1.7 nanosheet bundles with an improved homogeneous composition were synthesized by annealing from CaSi2 crystal powders with MnCl2 in molten salt. The MnSi and Si phases were formed at the initial stage of the synthesis with an inhomogeneous Mn distribution within the nanosheet bundles. Subsequently, the phases were transformed into MnSi1.7 with an improved homogeneous Mn distribution within them for 10 h annealing in the molten salt. The formation of multiple Mn-silicide phases and remarkable improvement in the structural homogeneity of the MnSi1.7 nanosheet bundles were discussed in terms of the reactions of Mn or Si with chloride compounds, decomposition of chlorides at elevated temperatures, phase selection of multiple silicide phases, shrinkage of the volume from Si to MnSi1.7, and dominant diffusion species. Multiple growth variants of the MnSi1.7 domains were stacked in the nanosheets. For comparison, the growth in a deliquescent environment realized by NH4Cl addition was examined. [ABSTRACT FROM AUTHOR]

The volumetric thermal expansion coefficient α V is discussed in relation to the bulk modulus B 0 for transition-metal disilicides (TrSi2), alkaline-Earth metal disilicides (AeSi2), Mg2Si, and Si clathrates. For this purpose, the α V of CoSi2 at 300 K is determined to be 3.1 × 10−5 K−1 using powder X-ray diffraction measurements at temperatures ranging from 300 to 835 K. AeSi2 and Mg2Si have B 0 values ranging from 27.9 to 52.9 GPa, while the values for α V range from 3.2 × 10−5 to 4.8 × 10−5 K−1. TrSi2 including CoSi2 has larger B 0 values ranging from 148.9 to 243 GPa and smaller α V values ranging from 2.3 × 10−5 to 3.3 × 10−5 K−1 than AeSi2. Si clathrates have intermediate values of α V and B 0, which are in between those of TrSi2 and AeSi2. Thus, the silicides with small B 0 values tend to have large α V values. [ABSTRACT FROM AUTHOR]

Auger electron spectroscopy, high-speed electron diffraction, and light-absorption spectroscopy are used to study the composition, size, and electronic and crystal structures of NiSi2 nanoparticles and layers formed in the surface region of Si(111). Nanocrystalline structures are obtained by implanting Ni+ ions into Si(111) with an energy of E0 = 25 keV by varying the ion dose within the range from 1014 to 1017 cm—2. Prior to ion implantation, Si samples are degassed under ultrahigh vacuum conditions (10—6 Pa) first at Т ≈ 1200 K for 3–4 h and then at Т ≈ 1500 K for 10 min. It is shown that at doses of Ni+ ions of D ≤ 5 × 1015 cm–2, after heating, crystalline particles up to 10 nm in size are formed, and at D ≈ 6 × 1016 cm–2, a continuous nanolayer is formed. An analysis of the spectra obtained using Auger electron spectroscopy in combination with complete etching showed that, at doses less than D ≈ 1015 cm–2, the NiSi2 nanocrystalline phases are formed as spheres, at D > 1015 cm–2 they transform into a shape close to an ellipsoid, and at D = DS a continuous homogeneous NiSi2 layer is formed. An analysis of high-energy electron diffraction patterns shows that the Si films formed on the surface of the Si/NiSi2/Si(111) system are single crystal and have a structure with a cubic lattice. Due to the fact that the value of the lattice constant of NiSi2 (a ≈ 5.42 Å) barely differs from a of pure Si (5.41 Å), very narrow (d ≤ 3–5 nm) transition layers are formed at the Si/NiSi2 and NiSi2/Si(111) interfaces. A relationship is established between the size and band-gap width of the surface nanocrystalline phases of NiSi2. The sizes of nanophases, at which quantum-size effects begin to appear, are determined. [ABSTRACT FROM AUTHOR]

This paper reports on a facile bottom-up method for the direct integration of a silicon (Si)-magnesium silicide (Mg2Si) heterojunction solar cell (HSC) with a textured rear reflector made of stainless steel (SS). Modified wet chemical etching and post processing of SS substrates resulted in the formation of both a rough surface texture and diffusion barrier layer, consisting of magnetite (Fe3O4) with reduced optical reflection. Then, Si, Mg2Si and CaSi2 layers were stepwise thermally evaporated onto the textured SS surface. No traces of Fe and Cr silicide phases were detected by Raman spectroscopy, confirming effective suppression of impurity diffusion from the SS to the upper layers at least at temperatures required for Si deposition, as well as Mg2Si and CaSi2 formation. The obtained black-SS/Fe3O4/Si/Mg2Si/CaSi2 sample preserved, to some extent, its underlying textured morphology and demonstrated an averaged reflection of 15% over the spectral range of 200–1800 nm, while its prototype HSC possessed a wideband photoresponse with a photoelectric conversion efficiency of 7.5% under AM1.5 illumination. Moreover, Si layers deposited alone onto a black-SS substrate demonstrated competitive antireflection properties compared with black Si (b-Si) obtained by traditional top-down etching approaches, and hybrid b-Si/textured-SS structures with a glue-bonded interlayer. [ABSTRACT FROM AUTHOR]

In order to solve the challenge of recyclability of tantalum substrates in high temperature oxidation environments, a novel MoSi 2 -WSi 2 -HfSi 2 -TiSi 2 composite ceramic coating containing an Nb interlayer was prepared on the surface of tantalum substrate by a three-step method. The mix ceramic silicide coating exhibited superior performance and effective protection for 10.2 h at 1800 °C, possibly due to the formation of an outer SiO 2 -HfO 2 -HfSiO 4 composite oxide film with low oxygen permeability, moderate viscosity and thermal expansion coefficient, as well as good self-healing ability. Furthermore, the coating successfully passed 537 thermal cycles from room temperature to 1800 °C. The presence of Nb interlayer significantly mitigated the thermal mismatch between the ceramic coating and the tantalum substrate, and the bidirectional diffusion of Nb element during the high temperature oxidation and thermal shock process further reduced the tendency of the coating to crack. [ABSTRACT FROM AUTHOR]

The formation of nanosized films of silicides on the surface of Si (111) and Si (100) was studied by the method of low-energy ion implantation. The optimal technological modes of ion implantation and subsequent annealing for the formation of thin nanoscale films of silicides were determined. It is shown that the appearance of new surface superstructures is additional confirmation of the formation of thin silicide films with a single crystal structure.

The change in the electrical properties of the Si(111) and Si(100) surfaces during ion implantation and subsequent annealing was studied. The possibilities of controlling of the electrophysical properties of the Si(111) and Si(100) surface layers by the implantation of ions of alkaline and alkaline-earth elements are analyzed. Some electrophysical properties of semiconductors containing p- and n-structures and the possibilities of their application in electronics are discussed.

The microstructure and room temperature tensile properties of heat-treated TC25G alloy after thermal exposure were investigated. The results show that the α2 phase dispersed in the α phase, and silicide precipitated firstly at the α/β phase boundary and then at the dislocation of the αp phase and on the β phase. When thermal exposure was 0–10 h at 550 °C and 600 °C, the decrease of alloy strength was mainly due to the dominant effect of dislocations recovery. With the rise and extension of thermal exposure temperature and time, the increasing quantity and size of precipitates played an important role in the improvement of alloy strength. When thermal exposure temperature rose to 650 °C, the strength was always lower than that of heat-treated alloy. However, since the decreasing rate of solid solution strengthening was smaller than the increasing rate of dispersion strengthening, alloy still showed an increasing trend in the range of 5–100 h. When thermal exposure time was 100–500 h, the size of the α2 phase increased from the critical value of 3 nm to 6 nm, and the interaction between the moving dislocations and the α2 phase changed from the cutting mechanism to the by-pass mechanism (Orowan mechanism), and thus alloy strength decreased rapidly.

Polymer infiltration and pyrolysis (PIP) has a limitation in increasing the relative density of SiC ceramics above 90 %. This is due to the blockage of open pore channels. In this study, a new process that incorporates Ni and graphite nanoparticles into SiC preceramic precursor is examined. Ni nanoparticles react with the SiC precursor to form low melting point nickel silicide phases which infiltrate into pores of the bulk without a blockage problem. In later infiltration cycles, graphite nanoparticles are added to convert the nickel silicide to nickel carbide and silicon carbide, which may prevent the deterioration of mechanical strength at high temperature. The relative density of SiC ceramics in this study increases to 92 % and above, which is higher than that of SiC ceramics prepared by the traditional PIP. The results of this study show a pathway to process high density SiC ceramics at relatively low sintering temperatures. [ABSTRACT FROM AUTHOR]

Because of the ease of formation, and good lattice match with Si, metal silicides often form high-quality epitaxial layers and have established themselves over the years as important technological materials with industrial applications. For the fabrication of silicon-based devices, the contact between metal electrodes and Si is a key issue. The properties of thin films on silicon substrates are strongly dependent on their microstructure and local chemistry. However, a concrete understanding of the influence of a silver layer on different transition metal/silicon interfaces is not currently available. We propose, for the first time, a new model called molecular-incident reaction effect (MoIRE) model that successfully explains the different chemical reactions for Co/Si and Ni/Si interfaces by the introduction of a 3×3R30o-Ag layer. The interaction transfer of silicon atoms forms a Co silicide for Co/3×3R30o-Ag/Si(111) with a thickness of a few nanometers, thus greatly reducing the temperature needed for the formation of a layered CoSi2 silicide compared to that for typical CoSi2 silicide formation at a Co/Si interface. Based on the MoIRE mechanism, the introduction of the 3×3R30o-Ag layer as an intermediate layer permits the silicidation temperature needed to produce a NiSi layer to be reduced to 400 K from typically above 600 K. This approach is advantageous for the formation of a silicide at the Ni/Si interface at low temperature. Based on the MoIRE model for silicide formation at Ni/3×3R30o-Ag/Si(111), we propose a technique for the synthesis Ni silicide layers at lower temperatures with simpler fabrication steps due to the difference in the properties between Co and Ni. This mechanism of low-temperature fabrication includes the formation of (1) a 3×3R30o-Ag and (2) a NiSi layer. The findings presented herein will be useful for more efficiently forming salicides in integrated circuit fabrication, as well as for developing superconducting circuits and quantum bits for quantum computing.

In this paper, a comparative study of C-, N- and Xe-based pre-amorphization implantation (PAI) processes is proposed. The impact of the use of such processes on the agglomeration resistance and physical properties of the final Ni(Pt)Si layer, as well as the formation mechanisms via solid-state reactions and electrical performances via the transfer length measurement (TLM) method, is evaluated. It is shown that although all species are able to increase the agglomeration temperature of Ni(Pt)Si layers (up to more than 100 °C), the underlying mechanisms are different. For C- and N-based PAI processes a strong chemical effect is observed, while for Xe-based processes the amorphization depth plays an important role. Consequently, the beneficial effect of stabilizing Ni(Pt)Si layers at high temperatures using C- and N-based PAI processes has to be balanced with an increased layer resistivity (up to 30%) combined with a strong deterioration of the associated specific contact resistivity (which is multiplied by almost a factor 10). In this sense, Xe-based PAI processes seem to be a better option as they could allow to combine both requirements. [Display omitted] • Ni(Pt)Si layer resistance to agglomeration is improved using either C, N or Xe-based PAI processes. • The phase sequence and final Ni(Pt)Si layer properties vary depending on the implanted species. • The underlying mechanisms depend on the implanted species type. • Using TLM structures, lower ρ c values are obtained for Xe-implanted samples compared to C-implanted ones. [ABSTRACT FROM AUTHOR]

This study demonstrates the crucial trade-off between strength and ductility in titanium alloys. High strength-ductility synergy is achieved through severe plastic deformation (SPD) at a relatively lower temperature, resulting in ultrafine grains and well-dispersed (Ti, Zr) 6 Si 3 nano-precipitates. The samples SPD-processed at 800 °C demonstrate excellent room-temperature properties with a tensile strength of 1558.9 MPa and 7.2 % ductility. The findings highlight the impact of SPD temperature and alloying elements on silicide precipitation, revealing two different precipitation mechanisms depending on the SPD processing temperature: single diffusion-controlled nucleation at a higher SPD temperature while a coupled diffusion and dislocation-assisted nucleation at a lower SPD temperature. Lower-temperature SPD is critical to achieving superior strength-ductility synergy. [Display omitted] [ABSTRACT FROM AUTHOR]

Understanding the structure and its relations with the transport properties is important for designing a good thermoelectric (TE) material. In this work, we investigate the relationship between those properties of the low-cost and eco-friendly materials, β-Fe 1- x Mn x Si 2 (0≤ x ≤0.10), prepared by direct arc melting and heat treatment process. The metallic phases (tetragonal α-Fe 2 Si 5 and cubic ε-FeSi) are transformed into the semiconductor phase (orthorhombic β-FeSi 2) through heat treatment. The amount of β-FeSi 2 significantly decreases at x ≥ 0.09. Mn atoms act as an acceptor and improve the carrier density (n H of holes) but decrease the mobility (μ H). By substituting Mn to β-FeSi 2 , the Seebeck coefficient (S) is more uniform at high temperatures and the electrical resistivity (ρ) effectively decreases, leading to an improvement in the power factor. The thermal conductivity (κ) slightly increases with Mn doping. However, with increasing Mn content, the formation of secondary phases increases, resulting in the reduction of solid solution of Mn in β-phase; therefore, the electrical transport deteriorates. As a result, the optimum doping level for improving TE performance is obtained at x = 0.05 sample, verifying with crystal structure analysis that the optimum doping level is in the range of 0 ≤ x ≤ 0.08 because the amount of semiconducting β-FeSi 2 drastically drops at x ≥ 0.09. Our study reveals that by judging the variation of the crystal structures, we could achieve the optimum doping level for improving TE transport properties. [Display omitted] • Structural relations with transport properties of Mn-doped β-FeSi2 are established. • Metallic structures (ε-FeSi and α-Fe2Si5) increase with Mn doping. • The formation of the metallic phase decreases the solubility of Mn in β-FeSi2. • The optimum Mn doping for enhancing the transport properties ranges from 5% to 8%. [ABSTRACT FROM AUTHOR]

• Vanadium disilicide grown on silicon with a specific crystal orientation is strained. • Due to this strain, the islands become elongated as they grow beyond a critical size. • Competing strain relaxation and edge formation energy can explain this transition. We investigated the growth and shape of vanadium silicide clusters on Si(111) using scanning tunneling microscopy, atomic force microscopy and scanning electron microscopy. The deposition of 8 monolayers of vanadium on Si(111) and subsequent annealing at 1200 K leads to the formation of large elongated VSi 2 clusters. This is in marked contrast to the deposition of submonolayer amounts of V where the VSi 2 islands have a compact shape. The shape transition can be explained by a competition between edge formation and strain relaxation energy terms. The VSi 2 clusters, which are aligned along the three high symmetry directions of the Si(111) surface and surrounded by a denuded zone, form a two-dimensional network. [ABSTRACT FROM AUTHOR]

This study explored how MoSi 2 -TaSi 2 ratios in silicide alloys influence the oxygen resistance of ZrB 2 -MoSi 2 -TaSi 2 coatings, using self-propagating high-temperature synthesis and spark plasma sintering. The oxidative self-separation effect of TaSi 2 and MoSi 2 enhances nanoscale Zr and Ta oxide particle dispersion, forming a Zr-B-Ta-Si-O glass with optimal oxygen-blocking in the 50ZrB 2 -(MoSi 2 -10TaSi 2) coating (ZMT10). Compared to ZrB 2 -MoSi 2 , ZMT10 showed 28.87 % and 48.21 % reductions in weight gain and oxygen penetration, increasing protection to 99.71 %. Excessive TaSi 2 leads to Ta5+ dissolution, oxide aggregation, and a dendritic structure, facilitating oxygen diffusion and oxidation, raising the oxygen penetration in 50ZrB 2 -(MoSi 2 -30TaSi 2) to 0.73 %, lowering protection to 99.18 %. • MoSi 2 -TaSi 2 double silicide powders by SHS method to enhance the oxygen barrier of ZrB 2 coatings. • Co-strengthening effect of MoSi 2 -TaSi 2 double silicides reduced the oxidation activity of the coatings. • The low-content TaSi 2 resulted in a 48.21 % reduction in oxygen permeability. • Diffusion of Zr/Ta oxides in glass films formed stable Zr-B-Ta-Si-O complex glass film. • Excessive addition of TaSi 2 exacerbated oxide aggregation and formed a loose dendritic structure. [ABSTRACT FROM AUTHOR]

A single-phase Si-modified β-NiAl coating was formed by direct irradiation of Al-Si plasma in vacuum, which is distinctively different from that of the conventional AlSi slurry-diffusion process that normally generates silicides precipitation. A large amount of nanocavities was observed in the plasma-irradiated coating, which might relate to the formation of the single phase. Oxidation of the two coatings at 1000 ℃ shows that the single-phase coating formed an intact and uniform alumina scale whereas the conventional one formed a void-containing and rumpling scale, indicating the uniquely beneficial effects by forming the single-phase Si-modified β-NiAl coating. • Single-phase Si-modified β-NiAl coating was formed by irradiation of Al-Si plasma. • Nanocavities were observed in the single-phase coating. • Plasma irradiation greatly improved the oxidation resistance of Si-modified β-NiAl. [ABSTRACT FROM AUTHOR]

CaSi nanowires were synthesized on a Si substrate by a reactive deposition technique. A large amount of Ca vapor reacted with the surface of the cleaned Si substrate, and CaSi nanowires were grown on the as-synthesized CaSi film. The diameter of the nanowires reached a minimum value of about 25 nm. The CaSi nanowires were self-oriented along the 〈001〉 direction. We can control the length of the nanowires, to a maximum of 4 μ m, by adjusting the experimental parameter settings, such as the amount of Ca source, duration and temperature. The mechanism of formation of Ca silicides on a Si substrate is discussed in detail. Raman spectroscopy confirmed the nanosized character of the CaSi phase. These results give us greater expectations for the application of CaSi, not only in hydrogen storage but also as a new inorganic semiconductor. [ABSTRACT FROM AUTHOR]

BaSi2 homojunction diodes on Nb-doped TiO2 (TiO2:Nb) coated glass substrates were fabricated using aluminum-induced crystallization (AIC) and a two-step evaporation method. From Raman scattering spectra, the growth of BaSi2 on TiO2:Nb was confirmed when the thickness of poly-Si grown by AIC (AIC-Si) was more than 150 nm. The partial formation of BaSi2 diodes was confirmed from the samples prepared at temperature during AIC T AIC = 475 °C–525 °C. The long-wavelength edge of photoresponsivity of the diodes was located around 950 nm, which corresponds to the bandgap of BaSi2 of 1.3 eV, suggesting that this photocurrent is derived from BaSi2 thin films. At T AIC = 500 °C, the maximum value of photoresponsivity was obtained. Since the largest grains in AIC-Si were also obtained at T AIC = 500 °C, these results suggest that larger grain of AIC-Si leads to the improvement of the quality of BaSi2 thin films themselves and the performance of BaSi2 diodes. [ABSTRACT FROM AUTHOR]

In this paper, the fabrication and electrical performance optimization of a four-levels vertically stacked Si0.7Ge0.3 channel nanowires gate-all-around transistor are explored in detail. First, a high crystalline quality and uniform stacked Si0.7Ge0.3/Si film is achieved by optimizing the epitaxial growth process and a vertical profile of stacked Si0.7Ge0.3/Si fin is attained by further optimizing the etching process under the HBr/He/O2 plasma. Moreover, a novel ACT@SG-201 solution without any dilution at the temperature of 40 °C is chosen as the optimal etching solution for the release process of Si0.7Ge0.3 channel. As a result, the selectivity of Si to Si0.7Ge0.3 can reach 32.84 with a signature of "rectangular" Si0.7Ge0.3 extremities after channel release. Based on these newly developed processes, a 4-levels vertically stacked Si0.7Ge0.3 nanowires gate-all-around device is prepared successfully. An excellent subthreshold slope of 77 mV/dec, drain induced barrier-lowering of 19 mV/V, Ion/Ioff ratio of 9 × 105 and maximum of transconductance of ~83.35 μS/μm are demonstrated. However, its driven current is only ~38.6 μA/μm under VDS = VGS = −0.8 V due to its large resistance of source and drain (9.2 × 105 Ω). Therefore, a source and drain silicide process is implemented and its driven current can increase to 258.6 μA/μm (about 6.7 times) due to the decrease of resistance of source and drain to 6.4 × 104 Ω. Meanwhile, it is found that a slight increase of leakage after the silicide process online results in a slight deterioration of the subthreshold slope and Ion/Ioff ratio. Its leakage performance needs to be further improved through the co-optimization of source and drain implantation and silicide process in the future. [ABSTRACT FROM AUTHOR]

The isothermal oxidation behavior of 56Nb-16Si-(20-x)Ti–3Cr–3Al-2Hf-xZr (x ​= ​0, 2, 5, 10 ​at. %) alloys was investigated at 800 ​°C and 1250 ​°C, respectively. The results show that increasing the Zr content evidently increased the oxidation rates at 800 ​°C, accompanied by the obvious occurrence of pesting oxidation. The alloys showed alike linear oxidation kinetics at 1250 ​°C. With the increase of Zr content, the adherence and integrity of oxide scales were improved, but the overall oxidation resistance was slightly deteriorated. The observed oxidation behavior may be attributed to the composition variation of Zr and Ti in the alloys. The oxidation mechanism associated with the composition variation is discussed in this study. [Display omitted] • Increasing Zr in 56Nb-16Si-(20-x)Ti-3Cr-3Al-2Hf-xZr (x = 0, 2, 5, 10 at. %) alloys decreases the oxidation resistance. • The adherence and integrity of oxide scales are improved with the increase of Zr. • The oxidation behaviour of the Nb-Si alloys is affected by both Zr and Ti synergically. [ABSTRACT FROM AUTHOR]

A thick silicon-enriched layer was formed on the surface of Fe and Fe-15 mass% Cr alloys by Si electrodeposition using a molten salt as the medium. This surface-treated sample was embedded in the molten salt and the high-temperature corrosion behavior was investigated. For comparison, the high-temperature corrosion behavior of untreated samples was also investigated. The effect of the surface Si conversion by the molten salt electrodeposition treatment on the high-temperature corrosion resistance of the Fe and Fe-15 mass% Cr alloys was then evaluated. As a result, the surface Si electrodeposition-treated Fe did not improve the corrosion resistance as compared to the untreated sample. However, for the Fe-15 mass% Cr alloy, the untreated corrosion weight loss sharply increased and the corrosion rate increased. On the other hand, the corrosion rate was lower on the surface of the Si-treated sample. After the high-temperature corrosion test, a cross section of the sample to which the molten salt was attached was observed and analyzed by SEM and EPMA. As a result, in the untreated sample of Fe, the elemental metal dissolved in the molten salt. In the Si electrodeposition-treated Fe, cracks were generated at the Fe interface between the electrodeposition layer and the substrate, and corrosion proceeded from there. On the other hand, for the Fe-15 mass% Cr alloy, it was confirmed that the surface Si-treated sample formed a continuous SiO2 layer on the surface. It is considered that this SiO2 improved the corrosion resistance. [ABSTRACT FROM AUTHOR]

In this study, the efficient fabrication of nickel silicide (NiSix) Schottky barrier thin-film transistors (SB-TFTs) via microwave annealing (MWA) technology is proposed, and complementary metal-oxide-semiconductor (CMOS) inverters are implemented in a simplified process using ambipolar transistor properties. To validate the efficacy of the NiSix formation process by MWA, NiSix is also prepared via the conventional rapid thermal annealing (RTA) process. The Rs of the MWA NiSix decreases with increasing microwave power, and becomes saturated at 600 W, thus showing lower resistance than the 500 °C RTA NiSix. Further, SB-diodes formed on n-type and p-type bulk silicon are found to have optimal rectification characteristics at 600 W microwave power, and exhibit superior characteristics to the RTA SB-diodes. Evaluation of the electrical properties of NiSix SB-TFTs on excimer-laser-annealed (ELA) poly-Si substrates indicates that the MWA NiSix junction exhibits better ambipolar operation and transistor performance, along with improved stability. Furthermore, CMOS inverters, constructed using the ambipolar SB-TFTs, exhibit better voltage transfer characteristics, voltage gains, and dynamic inverting behavior by incorporating the MWA NiSix source-and-drain (S/D) junctions. Therefore, MWA is an effective process for silicide formation, and ambipolar SB-TFTs using MWA NiSix junctions provide a promising future for CMOS technology. [ABSTRACT FROM AUTHOR]

For the first time, a novel analytical model of contact resistance (${R}_{\text{contact}}$) in vertically stacked nanosheet FETs (NSHFETs) with a silicide/Si (100) contact for a sub-3-nm node is presented. Generally, ${R}_{\text{contact}}$ consists of the interface resistance (${R}_{\text{interface}}$) and spreading resistance (${R}_{\text{spread}}$). Herein, a new model of ${R}_{\text{interface}}$ of silicide/Si (100) contact, which simultaneously considers the source/drain (S/D) doping concentration (${N}_{\text{si}}$), Schottky barrier height (SBH), and SBH lowering, is demonstrated simultaneously. In addition, a new model of ${R}_{\text{spread}}$ that divides S/D into multiple resistance components for vertically stacked NSHFETs is suggested. In vertically stacked NSHFET with 3-nm node, for TiSi2/n-Si (100) and NiPtSi2/p-Si (100) contacts, ${R}_{\text{spread}}$ shows more than ~50.0% higher values compared to ${R}_{\text{interface}}$. On the other hand, 3-nm node FinFET with TiSi2/n-Si (100) and NiPtSi2/p-Si (100) contacts, ${R}_{\text{spread}}$ shows more than ~53.7% lower values compared to ${R}_{\text{contact}}$. The results show that ${R}_{\text{spread}}$ becomes dominant in ${R}_{\text{contact}}$ compared to ${R}_{\text{interface}}$ when using NSHFETs, in contrast to the conventional FinFETs in which ${R}_{\text{interface}}$ is dominant in ${R}_{\text{contact}}$. The high ${R}_{\text{spread}}$ of the NSHFET is mainly caused by the low nanosheet thickness and vertical pitch between the nanosheets. This study provides critical insights into the design of the source/drain of NSHFET for sub-3-nm CMOS technology. [ABSTRACT FROM AUTHOR]

Ion implantation with recoil ions or ion mixing based on the introduction of the required impurity from the surface layers during the transfer of the kinetic energy of the primary beam to them have great prospects for obtaining structures and compounds with desired properties. In the process of ranging of very large scale integrated circuits, the parasitic resistance of interconnections and the non-ohmic nature of contacts are the limiting factors. Refractory metal silicides are promising materials for use in metallization systems. In this work a study was carried out on the introduction of phosphorus ions into molybdenum-silicon systems. The results obtained demonstrate the possibility of the molybdenum silicide formation at a low temperature using implantation of ions that cause ionic mixing. The developed technology makes it possible to achieve a homogeneous interface between the silicide and silicon with the necessary electrophysical characteristics of metalization and ohmic contacts. Due to the deepening of the interface into the bulk of the semiconductor, the effect of the silicon surface state on parameters of ohmic contacts decreases. As a result their necessary stability and reproducibility are ensured.