Silicide Surface Research Articles

Double-pentagon silicon chains in a quasi-1D Si/Ag(001) surface alloy

Silicon surface alloys and silicide nanolayers are highly important as contact materials in integrated circuit devices. Here we demonstrate that the submonolayer Si/Ag(001) surface reconstruction, reported to exhibit interesting topological properties, comprises a quasi-one-dimensional Si-Ag surface alloy based on chains of planar double-pentagon Si moieties. This geometry is determined using a combination of density functional theory calculations, scanning tunnelling microscopy, and grazing incidence x-ray diffraction simulations, and yields an electronic structure in excellent agreement with photoemission measurements. This work provides further evidence of pentagonal geometries in 2D materials and heterostructures and elucidates the importance of surface alloying in stabilizing their formation.

Thermal stability of gold films on titanium-adhered silicon substrate

In this study, thermally induced changes in the surface of a thin gold film deposited on Si(100) with a 5 nm thick titanium adhesion layer were investigated. The analysis involved X-ray photoelectron spectroscopy, low-energy electron diffraction, and scanning tunnelling microscopy. The sample was subjected to stepwise annealing under ultra-high vacuum conditions at temperatures ranging from 430 to 1330 K. Low-temperature annealing up to 450 K did not alter the morphology but improved the cleanliness of the gold film surface. Annealing between 530 and 930 K resulted in the disintegration of the gold film, along with mixing and interaction between the sample components. Annealing the sample at 980 K led to the emergence of a gold silicide surface on Si(100) exhibiting the (5 × 3.2)R5.7° reconstruction.

Effects of Thermal Exposure Temperature on Room-Temperature Tensile Properties of Ti65 Alloy.

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.

Interface Effects in the Stability of 2D Silica, Silicide, and Silicene on Pt(111) and Rh(111).

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.

Anodic dissolution and passivation of manganese monosilicide in fluoride-containing sulfuric acid solutions

The purpose of this study was to investigate the anode resistance of manganese monosilicide MnSi in fluoride-containing sulfuric acid solutions and the concentration effect of sodium fluoride on the anodic dissolution and passivation of the silicide. The study was carried out on a single-crystal MnSi sample in 0.5 M H2SO4 + (0.0025−0.05) M NaF solutions. The study presents micrographs and elemental composition of the electrode surface after anodic polarization from E corrosion to E = 3.2 V in 0.5 M H2SO4 and 0.5 M H2SO4 + 0.05 M NaF solutions. A stronger etching of the electrode surface was observed in the presence of fluoride ions; elemental analysis showed an increase in the oxygen content in certain areas of the silicide surface associated with the formation of manganese and silicon oxides and their partial removal at high polarization values. The kinetic regularities of the MnSi-electrode anodic dissolution were studied by the methods of polarization, capacitance, and impedance measurements. It was established that the addition of fluoride ions leads to weaker barrier properties of the silicon dioxide surface film, which determines the high silicide resistance in a fluoride-free medium. The order of the reaction was calculated for the MnSi anodic dissolution for NaF depending on the potential. In the region of low anodic potentials (from Ecor to E ≈ –0.2 V), the reaction order ranged from 1.8 to 1.1, which was due to the high influence of silicon in the composition of the silicide and its oxidation products. With an increase in the polarization value (up to E = 0.9 V), the reaction order decreased to 0.5. An increase in the contribution of manganese ionization and oxidation reactions to the kinetics of the anodic dissolution of the silicide was observed. The silicide passivation in a fluoride-containing electrolytewas characterized by higher values of the dissolution current density (10–4−10–3 A/cm2) as compared to a fluoride-free electrolyte (10–6 A/cm2), the reaction order in region of the passive state was ~1.0. Passivation was due to the formation of MnO2 and SiO2 oxides on the surface. In the transpassivation region (E ≥ 2.0 V), there was a weak dependence of the current density on the concentration of fluoride ions. Oxygen release was observed on the surface of the electrode, and the formation of MnO4 – ions was recorded in the near-electrode layer. The article discusses mechanisms and kinetic regularities of anodic processes on an MnSi-electrode in sulfuric acid solution in the presence of fluoride ions

Dissolution-Induced Surface Reconstruction of Ni0.95Pt0.05Si/p-Si Photocathode for Efficient Photoelectrochemical H2 Production.

Metal silicide/Si photoelectrodes have demonstrated significant potential for application in photoelectrochemical (PEC) water splitting to produce H2. To achieve an efficient and economical hydrogen evolution reaction (HER), a paramount consideration lies in attaining exceptional catalytic activity on the metal silicide surface with minimal use of noble metals. Here, this study presents the design and construction of a novel Ni0.95Pt0.05Si/p-Si photocathode. Dopant segregation is used to achieve a Schottky barrier height as high as 1.0eV and a high photovoltage of 420mV. To achieve superior electrocatalytic activity for HER, a dissolution-induced surface reconstruction (SR) strategy is proposed to in situ convert surface Ni0.95Pt0.05Si to highly active Pt2Si. The resulting SR Ni0.95Pt0.05Si/p-Si photocathode exhibits excellent HER performance with an onset potential of 0.45V (vs RHE) and a high maximum photocurrent density of 40.5mAcm-2 and a remarkable applied bias photon-to-current efficiency (ABPE) of 5.3% under simulated AM 1.5 (100mWcm-2) illumination. The anti-corrosion silicide layer effectively protects Si, ensuring excellent stability of the SR Ni0.95Pt0.05Si/p-Si photoelectrode. This study highlights the potential for achieving efficient PEC HER using bimetallic silicide/Si photocathodes with reduced Pt consumption, offering an auspicious perspective for the cost-effective conversion of solar energy to chemical energy.

Oxygen vacancies coupled with surface silicide facilitate CO2 activation at near-room temperature for efficient methane productivity on Ni-oxide supported Pd nanoparticles

A schematic representation of CO2 reduction reaction pathways on the surface of a NiOTPd15-T catalyst.

Vliyanie primesey na adsorbtsiyu kisloroda na poverkhnosti Ti5Si3(0001)

The influence of simple and transition metal impurities, as well as interstitial impurities (B, C, and N), on the oxygen adsorption on the Ti5Si3 titanium silicide surface has been studied using the of projector augmented wave method within the electron density functional theory. It has been shown that titanium-substituting impurities belonging to the latter halves of the 3d–5d periods cause most significant changes in the adsorption energy. In addition, simple metals and interstitial impurities reduce the oxygen–surface interaction. By analyzing local electron densities of states, charge density difference distribution, charge transfer, and the overlap population of oxygen bonds to nearest-neighbor atoms, we have revealed special aspects of impurity influence on chemical bonding between the titanium silicide surface and oxygen. Factors responsible for an increase/decrease in the adsorption energy of oxygen on the doped surface are discussed. A correlation between the change in adsorption energy and the electronegativity of impurities has been found.

Semimetallic Orbital Hybridization by Particular Surface Engineering in Ternary Cobalt Silicide to Accelerate Oxygen Evolution Reaction

The oxygen evolution reaction (OER) plays an important role in efficient energy conversion, but needs excellent catalysts to overcome the sluggish reaction kinetics. The classic reaction kinetics implies that catalytic activity strongly depends on the electronic‐state occupation at surface active sites. Herein, a semimetallic orbital‐hybridization strategy is suggested to optimize the reaction activity of metal site at ternary cobalt silicide surface by particular interlayer electronic‐state coupling, which is completely different from the atomic configuration with double‐layered metal surface. The detailed analysis about electronic structure demonstrates that the semimetallic orbital hybridization is responsible for reducing OER activation barrier, due to a proper bonding strength. Instead, the stronger metallization cannot benefit a fast intermediate dissociation, which requires a higher activation barrier at OER. Herein, a new insight into accelerating OER by a particular surface engineering is provided.

On the influence of Ni(Pt)Si thin film formation on agglomeration threshold temperature and its impact on 3D imaging technology integration

Ni(10 at.% Pt) monosilicide is used as contact in microelectronics but suffers from degradation at relatively low temperatures due to agglomeration. Recent results obtained on 28 nm-FDSOI (Fully Depleted Silicon On Isolator) microelectronics devices have demonstrated severe yield loss after an anneal at 550 °C/2 h linked to Ni(Pt)Si film dewetting. Such agglomeration thermal budget is 100 °C lower than the ones measured on blanket wafers with in-situ or ex-situ four-point probe measurements. In this context, the aim of this paper is to investigate the effect Ni(Pt)Si formation process on the Ni(Pt)Si agglomeration using different approaches as (i) the classical one in which one anneal is applied to form silicide and leads also to agglomeration, (ii) the silicide formation through the standard SALICIDE process, “Self-Aligned Silicide”, and a subsequent anneal to induce agglomeration, and (iii) the standard SALICIDE process for silicide formation followed by an encapsulation of the top silicide surface by a SiN layer as applied in devices, and submitted finally to the agglomeration anneal. Our work demonstrated that the film thermal stability is influenced by the sequencing of the Selective Etch (SE) in the formation process and whether it is formed by a single or a double anneal. For single anneal, the thermal budget needed to agglomerate Ni(Pt)Si film is higher i.e., agglomeration occurs at around 700 °C/30 s in single anneal as compared to double anneal at around 550 °C/30 s. Another conclusion of this work is that four-point probe measurements are not sensitive enough to well estimate the real starting point of agglomeration phenomenon which is detrimental for devices (holes formation at the triple junctions). Some additional characterizations such as tilted Scanning Electron Microscopy (tilted SEM) are deeply needed for an accurate determination of agglomeration thermal budget. This study allows clarifying the main parameters leading to agglomeration: the film thickness and the grain size appear to be the more important ones.

Interaction of Oxygen with the Stable Ti5Si3 Surface

The atomic structure and surface energies of several low-index surfaces (0001), (11¯00) and (112¯0) of Ti5Si3 in dependence on their termination were calculated by the projector augmented-wave method within the density functional theory. It was revealed that the mixed TiSi-terminated (0001) surface is stable within the wide range of change in the Ti chemical potential. However, the Ti-terminated Ti5Si3(0001) surface is slightly lower in energy in the Ti-rich limit. The oxygen adsorption on the stable Ti5Si3(0001) surface with TiSi termination was also studied. It was shown that the three-fold coordinated F1 position in the center of the triangle formed by surface titanium atoms is the most preferred for oxygen adsorption on the surface. The appearance of silicon as neighbors of oxygen in other considered F-positions leads to a decrease in the adsorption energy. The factors responsible for the increase/decrease in the oxygen adsorption energy in the considered positions on the titanium silicide surface are discussed.

Screening and Understanding Lattice Silicon-Controlled Catalytically Active Site Motifs from a Library of Transition Metal-Silicon Intermetallics.

A joint theoretical and experimental study is reported to systematically explore over a library of transition metal-silicon intermetallics for understanding silicon-controlled active site motifs and discovering hydrogen-evolving electrocatalysts. On the one hand, every low-index surface termination of 115 transition metal (M)-silicon (Si) intermetallics is enumerated, followed by cataloging of stable adsorption sites and prediction of catalytic activities on the main exposed facets. It is theoretically found that silicon atoms in silicon-rich structures (especially MSi2 and MSi) show a strong site-isolating effect, which can eliminate M-M-M hollow and M-M bridge sites with too strong hydrogen-binding ability and thereby provide great opportunities for the exposure of novel highly active sites (e.g., M-top and Si-related sites). On the other hand, solid-state redox reactions are developed to synthesize a set of 24 silicides containing 5 MSi, 13 MSi2 , and 6 others, most of which are phase-pure samples. The experimental studies demonstrate that too rich silicon content in silicides (e.g., MSi2 ) leads to adverse effects, such as the formation of amorphous SiOx layers on the silicide surface, masking the presence of active sites during electrocatalysis. Finally, 5 MSi (M = Rh, Pd, Pt, Ru, Ir) as highly active hydrogen-evolving electrocatalysts are identified.

Коррозионно-электрохимическое поведение дисилицида железа в сернокислом электролите

The corrosion-electrochemical behavior of FeSi2 electrode in 5% H2SO4 and 5% H2SO4 + (0.1–0.5) g/l NaF solutions was studied. It is concluded that in 5% H2SO4 solution with a corrosion potential, an oxide film is formed on the FeSi2 surface, which is similar in composition to SiO2. The oxide film is not reduced at low cathodic polarizations; as a result of anodic polarization, the film grows and is doped with iron oxides. The presence of an oxide film on the silicide surface determines its high chemical resistance. It is shown that the effect of sodium fluoride, which activates the dissolution of FeSi2 electrode in a sulfuric acid solution, is associated with a weakening of the passivating effect of silicon dioxide and iron oxides. With increasing of NaF concentration, the role of iron in the kinetics of electrode processes on silicide increases, while that of silicon decreases. The order of the reaction of FeSi2 dissolution by NaF was calculated depending on the potential.

Surface Silicide Facilitates the Co2 Reduction Performance of Ni Oxide Supported Pd Nano-Islands

Surface Silicide Facilitates the Co2 Reduction Performance of Ni Oxide Supported Pd Nano-Islands

Surface Silicide Facilitates the Co2 Reduction Performance of Ni Oxide Supported Pd Nano-Islands

Surface Silicide Facilitates the Co2 Reduction Performance of Ni Oxide Supported Pd Nano-Islands

ПАССИВАЦИЯ ДИСИЛИЦИДА ХРОМА В КИСЛЫХ СРЕДАХ

The anodic behavior of CrSi2 electrode in 0,5 M H2SO4, 0,5 M HClO4, 0,5 M HNO3 and 0,5 M HCl solutions has been studied by the methods of polarization, capacitance, and impedance measurements. It has been concluded that in the process of anodic oxidation at potentials from corrosion E to transpassivation E inclusive, an oxide film is formed on the surface of chromium disilicide in the studied media, which is close in composition to SiO2 (with a small content of chromium oxides). The presence of this film on the silicide surface determines its high chemical resistance in the studied solutions. The thickness of the oxide film on CrSi2 has been calculated depending on the potential and composition of the electrolyte. The growth constant of the oxide film has been determined.

Intercalation of graphene formed on silicon carbide with iron, cobalt and silicon atoms

Intercalation of graphene formed on silicon carbide surface with iron, cobalt and silicon has been used to form the graphene/silicides/SiC interfaces. The experiments were carried out in situ in ultrahigh vacuum conditions. The elemental composition and chemical state of the sample surfaces, as well as their atomic structure, were controlled by high-energy-resolution photoelectron spectroscopy and low-energy electron diffraction. The nominal thicknesses of the deposited iron, cobalt and silicon layers varied in the range of 2-20 Å, and the temperature of the sample annealing was changed from room temperature to 600°C. It is shown, that the intercalation of graphene/Fe/SiC with Si leads to the formation of Fe-Si solid solution layer covered with surface silicide Fe3Si, while intercalation of graphene/Co/SiC with Si results in the formation of a Co-Si solid solution and CoSi silicide covered with Co3Si surface phase. The obtained silicide layers are reliably protected by graphene, making it compatible for nanoscale applications at ambient conditions.

Formation of Iron Silicides Under Graphene Grown on the Silicon Carbide Surface

The formation of iron silicide thin films under graphene grown on the silicon carbide surface is investigated. The thin films are synthesized by consecutive intercalation of iron and silicon atoms into the graphene. Experiments are carried out in situ in ultrahigh vacuum. The elemental composition and chemical state of the surface of prepared samples and their atomic structure are determined by low-energy electron diffraction and high-resolution X-ray photoelectron spectroscopy using synchrotron radiation. The thickness of deposited iron and silicon layers varies in the range of 0.1–2 nm, and the sample annealing temperature is varied from room temperature to 600°C. We show that intercalation of silicon into the graphene/Fe/SiC system leads to the formation of a layer of Fe–Si solid solution coated with the surface silicide Fe3Si. The films are effectively protected by graphene from exposure to ambient environment, which opens possibilities for their practical application.

Corrosion behavior of titanium silicide surface with hydrogen peroxide: Formation of sub-μm TiOx- based spheres, nanocomposite TiOx/SiOx phases, and mesoporous TiOx/SiOx network

So far unexplored corrosion of titanium silicide (Ti5Si3) surface with acidified hydrogen peroxide is of interest due to its potential use in improving osseointegration of titanium implants coated by titanium silicides. Detailed examination of corrosion products by FTIR, Raman and XP spectroscopy, electron microscopy, XRD, BET and light scattering techniques allows recognition of hydrated nanocomposite TiOx/SiOx (x ≤ 2) phases composed of segregated amorphous SiOx species and TiOx–based networks containing Ti-O-Si and -O-O- bonds. The appearance of the TiOx networks depends on the extent of peroxidation. A less progressed peroxidation yields sub-μm-sized TiOx-based spheres which upon annealing develop anatase nanograins withstanding 800° C. A more progressed peroxidation produces larger mesoporous TiOx-based bodies which disintegrate upon sonication into micrometer-sized entities. The proposed mechanism of surface corrosion is based on the complementary use of analytical techniques. The one-step production of bioactive (hydrated TiOx and SiOx) species deserves to be explored in osseointegration studies of slightly corroded Ti5Si3-coated titanium implants.

Several Specifics of Silicon Atom Condensation on the Surface of a Tungsten Single Crystal

Field emission microscopy was used to study Si condensation on a W surface by varying substrate temperature T and number n of monoatomic layers of the precipitated condensate. A low-temperature Si monolayer with a pure W structure formed at lower temperatures of T ~ 600 K, while another structure of a high-temperature surface silicide monolayer formed at T ≥ 1000 K. The orienting effect additionally differed between the low-temperature monolayer and surface silicide during further growth of Si layers. Pure Si crystallites formed starting from the third monolayer (n ≥ 3) in the case of condensation on the low-temperature monolayer and starting from n ≥ 300 monolayers in the case of condensation on surface silicide. Estimates were obtained for the activation energy Qdif of Si diffusion into the W lattice and the desorption energy Qdes of Si atoms from the W surface.