Silicide Surface Research Articles

Пассивация MnSi-электрода в сернокислых средах

Several features of the electrode reactions that occur at the surface of transition metal silicide (high strength metal-silicon bond, the effect of chemical reactions and the formation of passivating oxide films) leading to high interest to intermetallic compounds. Anodic behavior of the MnSi electrode in solutions 0.5 M H2SO4 and 0.05 M H2SO4 + 0.45 M Na2SO4 was studied by polarization and impedance measurements. It was concluded that the surface of manganese silicide is coated with an oxide film similar in composition to SiO2. The thickness and resistivity of the oxide film were calculated depending on potential and concentration of sulfuric acid. Generalization and theoretical explanation of the research results may provide a basis for predicting corrosion resistance of metal-silicon alloys in a wide range of corrosive environments.

Fluoroethylene Carbonate Breakdown Mechanisms and Energetics on Two Lithium Silicide Surfaces

Lithium-ion batteries are a leading energy storage technology. One challenge with lithium-ion batteries is the reductive decomposition of electrolyte on the surface, forming a passivating, solid–electrolyte interphase (SEI). The SEI prevents further electrolyte breakdown and consumption, but if not formed properly, may also consume lithium ions and prevent lithium-ion diffusion to the anode. Fluoroethylene carbonate (FEC) is currently one of the best electrolyte additives used to form a more robust SEI on silicon anodes. Herein, we use density functional theory (DFT) to investigate the spontaneous breakdown mechanisms, energies, and charge transfers of FEC on the surface of a silicon anode in a lesser lithiated LiSi and a more lithiated Li15Si4 state. The reductive decomposition of FEC on LiSi and Li15Si4 to F, CO2, and CH2CHO is energetically most favorable on both surfaces, but F, CO, and OCH2CHO can also be formed. The breakdown of FEC via either of the breakdown mechanisms is about 2 times more favora...

Development of anodization technique on zirconium silicide material for reproducing micro/nanosurface structure: Application to nuclear accident tolerant fuel cladding

Zirconium silicide (ZrSi2) surfaces with micro/nanoscale structures were fabricated using an anodization technique with different working solutions. The surface structures evolved depending on the reaction time, and the resulting surface structures were characterized using scanning electron microscopy. For all three solutions, the anodization conditions for producing micro/nano surface structures with the superhydrophilicity were successfully found. The etching rate and thickness were controlled depending on the type of solutions. In the organic bath-based ammonium fluoride (NH4F) solutions, the etching thickness was significantly reduced in comparison to that using a water bath-based hydrofluoric acid (HF) solution. Superior oxidation resistance of ZrSi2 was maintained for all superhydrophilic, anodized ZrSi2 surfaces at 700 °C air oxidation regardless of the type of solution. The superhydrophilic, anodized ZrSi2 surfaces significantly increased the Leidenfrost temperature by inducing liquid-solid contact between the heated surface and coolant. We expect the developed surfaces to be useful in future nuclear fuel cladding material applications for ensuring the safety of nuclear reactors.

Exploration of Properties from Both the Bulk and Surface of Iron Silicides: A Unified Theoretical Study

The properties from both bulk phases (magnetism and thermal stability) and surface (composition, orientation, and stability) of iron silicide model compounds were evaluated by a theoretical study w...

АНОДНОЕ РАСТВОРЕНИЕ И ПАССИВАЦИЯ Mn5Si3-ЭЛЕКТРОДА В КИСЛЫХ И ЩЕЛОЧНЫХ СРЕДАХ

Anodic behavior of Mn5Si3 electrode in sulfuric acid and alkaline solutions was studied by polariza-tion and impedance measurements.It was concluded that the surface of manganese silicide in a sulfate electrolyte is coated with an oxide film similar in composition to SiO2, and in an alkaline electrolyte it is enriched with manganese and its oxidation products. For sulfate electrolyte, the thickness and resis-tivity of the oxide film were calculated depending on the potential and composition of the solution. For an alkaline electrolyte, the change in the thickness of the passivating film was calculated depending on the potential and concentration of NaOH, and the kinetic parameters of the oxygen evolution reaction were determined.

Transition metal silicide surface grafting by multiple functional groups and green optimization by mechanochemistry.

Chromium disilicide (CrSi2) particles were synthesized by using an arc melting furnace followed by mechanical milling. XRD and DLS analyses show that aggregates of around 3 μm containing about 10 nm sized crystallites were obtained. These aggregates were functionalized in solution by coupling agents with different anchoring groups (silane, phosphonic acid, alkene and thiol) in order to disperse them into an organic polymer. Dodecene was used to modify the CrSi2 surface during mechano-synthesis in a grinding bowl with quite little solvent quantity and the optimization step allowed the aggregate size to be reduced to 500 nm. A thermoelectric composite was then made of alkene CrSi2 grafted samples and poly(p-phénylène-2,6-benzobisoxazole). This study opens the route for new surface grafting of intermetallic silicides for applications linked to electronics and/or energy.

Peculiarities of the Condensation of Silicon on the Surface of a Tungsten Single Crystal

Using the methods of the field emission microscopy, the condensation of Si on the W surface at various temperatures T of the substrate and numbers n of monatomic layers of the deposited condensate is studied. At low temperatures of T ~ 600 K, a low-temperature Si monolayer with the structure of pure W is formed on the surface, whereas another structure of a high-temperature monolayer, namely, surface silicide, is formed at T ≥ 1000 K. The low-temperature monolayer and surface silicide also differ in their orienting effect when constructing the Si layers. In the case of condensation on a low-temperature monolayer, crystallites of Si are formed starting already from the third monolayer at n ≥ 3, whereas the Si crystallites grow during the condensation on surface silicide starting from n ≥ 300 monolayers.

Formation of graphene-capped cobalt silicides

Intercalation synthesis of graphene-capped cobalt silicides has been studied in situ by core-level photoelectron spectroscopy with synchrotron radiation and low-energy electron diffraction. It is found that at 400 °C the intercalation of graphene/Ni(1 1 1) with cobalt takes place in a wide range of coverage up to 17 ML Co. Graphene is strongly coupled with the upper layer of Co atoms and stabilizes the fcc structure of the intercalated Co(1 1 1) film. Subsequent intercalation of graphene/Co/Ni(1 1 1) with silicon results in the formation of an ordered Co3Si surface phase of the (√3 × √3)R30° structure and then of Co2Si silicide and Co-Si solid solution. Our experimental data and DFT calculations have shown that the coupling between the graphene layer and the surface silicide is rather weak and the properties of quasi-freestanding graphene are preserved.

Impact of nickel silicide on SiGe BiCMOS devices

Nickel silicide (NiSi) can improve the RF performance of SiGe hetero bipolar transistors (HBT) compared to cobalt silicide (Heinemann et al 2016 IEDM Tech. Dig. 51–4). In this paper, the impact of different procedures to form NiSi on HBT and MOS devices of a 0.13 μm BiCMOS cobalt silicide technology is studied. The different NiSi formations are carried out by partly or fully Ni consumption (PC, FC) for low temperature furnace and low pressure anneals. Our investigations indicate, PC results in rough silicide surfaces and substrate interfaces, whereas FC leads to smooth surfaces and interfaces associated with lower resistivities. FC nickel silicidation at 300 °C and 450 °C exhibits an excessive NiSi growth on the STI edges of n doped source drain (N+SD) regions, reducing the breakdown voltage to substrate or p well. An enhanced NiSi growth is found for all investigated silicide schemes on narrow P+SD regions along polysilicon gates. The leakage current of these structures is caused by enlarged lateral silicidation towards the gates. The enhanced lateral NiSi growth could be suppressed by partly Ni silicidation with furnace anneals at 200 °C or 230 °C.

Особенности конденсации кремния на поверхности монокристалла вольфрама

AbstractUsing the methods of the field emission microscopy, the condensation of Si on the W surface at various temperatures T of the substrate and numbers n of monatomic layers of the deposited condensate is studied. At low temperatures of T ~ 600 K, a low-temperature Si monolayer with the structure of pure W is formed on the surface, whereas another structure of a high-temperature monolayer, namely, surface silicide, is formed at T ≥ 1000 K. The low-temperature monolayer and surface silicide also differ in their orienting effect when constructing the Si layers. In the case of condensation on a low-temperature monolayer, crystallites of Si are formed starting already from the third monolayer at n ≥ 3, whereas the Si crystallites grow during the condensation on surface silicide starting from n ≥ 300 monolayers.

АНОДНЫЕ ПРОЦЕССЫ НА МОНОСИЛИЦИДЕ МАРГАНЦА В РАСТВОРАХ ГИДРОКСИДА НАТРИЯ

The anodic behavior of the MnSi electrode in solutions (0.5 - 3.0) M NaOH in the region of potentials from the corrosion potential up to the potential of oxygen evolution inclusive was studied by polarization and impedance measurements. It is concluded that the surface of manganese silicide in the alkaline electrolyte is enriched with the metallic component of the alloy and the products of its oxidation. The kinetic regularities of the anodic behavior of MnSi have been determined, the mechanisms of dissolution and passivation of the silicide have been clarified, the kinetic parameters of oxygen evolution have been determined.

Investigation of Magnetic Dead Layer on Iron Silicide Surfaces

Investigation of Magnetic Dead Layer on Iron Silicide Surfaces

Surface Sensitivity of Fluoroethylene Carbonate Breakdown on Lithium Silicide Surfaces

Silicon anodes are a promising material for lithium ion batteries due to their large theoretical capacity for storing lithium. When the battery is charging, the anode works by alloying lithium ions with the silicon anode where the lithium ions are reduced. In addition to the lithium ions being reduced, unwanted side reduction reactions of the electrolyte also occur. When the electrolyte reductively decomposes at the anode surface, a solid-electrolyte interphase (SEI) is formed. Fluoroethylene carbonate (FEC) is added to the electrolyte to make a more robust SEI which prevents further electrolyte decomposition. From FEC reductive decomposition, the primary reduction products are CO2, CH2CHO, and F-. While the decomposition products have been discovered, the lowest energy surface facet which promotes the breakdown of FEC into those products is still unknown. Here FEC and its reduction products are being studied on different lithium silicide surfaces using density functional theory. The lithium silicide phases under consideration are the crystalline LiSi phase with a low lithium concentration and the crystalline Li15Si4 phase with a higher lithium concentration. All unique low index surface facets are considered for each lithium silicide phase. The interactions of FEC and its dissociation products are analyzed on the different anode surface facets to determine the surface sensitivity of FEC breakdown. From the binding energies of the FEC reactant and the CO2, CH2CHO, and F- products on the lithium silicide surface facets, FEC dissociation reaction energies are calculated. The facet on which SEI formation begins to form is determined from the reaction energies for both the low and high concentration lithium silicide anodes. This material is based upon work supported by the U. S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE. ORISE is managed by ORAU under contract number DE-SC0014664. Use of the Center for Nanoscale Materials, an Office of Science user facility, is supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC02-06CH11357.

The (2×2) reconstructions on the surface of cobalt silicides: Atomic configuration at the annealed Co/Si(111) interface

We have used scanning tunneling microscopy (STM) and ab initio total-energy calculations to characterize surface and interfacial structure of Co-Si(111) system. It has been found experimentally that two different types of the (2×2) surface structures occur. The coexistence of two phases is demonstrated by the example of STM image of the surface formed at the early stages of cobalt silicide formation under moderate annealing temperatures (500°C). The measured height difference between the adjacent (2×2) reconstructed patches equal to about 1.0Å (as determined from the filled-state STM images). In addition, the shift of the atomic rows by half of the row spacing is observed. Two adatom models of the (2×2) surface structures are developed. According to our data, these structures are assigned to CaF2-type CoSi2 and CsCl-type CoSi with a (2×2) array of Si adatoms on their surfaces. If the latter is the case, it has а coherent double interface CoSi/CoSi2/Si(111) with a two-layer CoSi2. Both of these interfaces are characterized by the eightfold cobalt coordination and incorporate a grown-in stacking fault.

Initial surface silicidation on Ni(110)

Initial silicide formation on a Ni(110) surface was studied by scanning tunneling microscopy (STM) in an ultrahigh vacuum. Less than 0.5ML of Si deposition initiated a Si-Ni mixed layer by displacing substrate Ni, and dark sites were formed in the STM images. A 0.5ML-Si deposited surface showed that Si and Ni were alternately aligned in a close-packed [11¯0] row whereas Si pairs aligned along the [001] direction forming p(1×2), obliquely aligned forming c(2×2), or even straightly-and-obliquely aligned forming c(4×2) superstructures. A first-principles total energy calculation showed that the p(1×2) and c(4×2) structures had almost the same energy while the c(2×2) structure gave 13meV/1×1 higher energy. Because a Si-Si bond in the close-packed [11¯0] row is energetically unfavorable, Si deposition of more than 0.5ML did not further replace the substrate Ni, but silicide islands were nucleated along with a trench structure.

Intercalation synthesis of cobalt silicide under a graphene layer

The silicon intercalation under single-layer graphene formed on the surface of an epitaxial Co(0001) film was investigated. The experiments were performed under conditions of ultra-high vacuum. The thickness of silicon films was varied within the range of up to 1 nm, and the temperature of their annealing was 500°C. The characterization of the samples was carried out in situ by the methods of low-energy electron diffraction, high-energy-resolution photoelectron spectroscopy using synchrotron radiation, and magnetic linear dichroism in photoemission of Co 3p electrons. New data were obtained on the evolution of the atomic and electronic structure, as well as on the magnetic properties of the system with an increase in the amount of intercalated silicon. It was shown that the intercalation under a graphene layer is accompanied by the synthesis of surface silicide Co2Si and a solid solution of silicon in cobalt.

Intercalation synthesis of graphene-capped iron silicide atop Ni(111): Evolution of electronic structure and ferromagnetic ordering

A new method for synthesis of graphene-protected iron silicides has been tested, which consists in formation of graphene on Ni(111) followed by two-step intercalation of the system with Fe and Si. Characterization of the samples was performed in situ by low-energy electron diffraction, angular-resolved photoelectron spectroscopy, core-level photoelectron spectroscopy with synchrotron radiation and magnetic linear dichroism in photoemission of Fe 3p electrons. It is shown, that at 400°C the intercalation of graphene/Ni(111) with iron occurs in a range up to 14ML. The graphene layer strongly interacts with the topmost Fe atoms and stabilizes the fcc structure of the film. The in-plane ferromagnetic ordering of the film has a threshold nature and arises after the intercalation of 5ML Fe due to the thickness-driven spin reorientation transition. Subsequent intercalation of graphene/Fe/Ni(111) with Si leads to the formation of the inhomogeneous system consisted of intercalated and nonintercalated areas. The intercalated islands coalesce at 2ML Si when a Fe-Si solid solution covered with the Fe3Si surface silicide is formed. The Fe3Si silicide is ferromagnetic and has an ordered (√3×√3)R30° structure. The graphene layer is weakly electronically coupled to the silicide phase keeping its remarkable properties ready for use.

Chlorosilane Interactions with Iron at High Temperatures

Chlorosilane species are commonly used at high temperatures in the manufacture and refinement of ultra-high purity silicon and silicon materials. They are highly corrosive in these processes, necessitating the use of high cost alloys for the construction of reactors, pipes, and vessels required to handle and produce them. In this study, iron, the primary alloying component of low cost metals, was exposed to a variety of silicon tetrachloride-hydrogen-hydrogen chloride vapor streams at industrially-relevant times (0-100 hours), temperatures (500-700°C), and compositions. Post exposure analyses including FE-SEM, EDS, XRD, and gravimetric analysis revealed formation and growth of stratified silicide and chloride surface layers, which vary as a function of time, temperature and gas composition. Additionally, there was evidence for various regimes of diffusion-limited and reaction-limited surface layer growth. Speculated mechanisms to explain these observations were supported by thermodynamic equilibrium simulations of experimental conditions. This study furthers the understanding of metals in chlorosilane environments, which is critically important for manufacturing the high purity silicon required for silicon-based electronic and photovoltaic devices.

Evaluating Work-Function and Composition of ErSix on Various Surface Orientation of Silicon

The work function of ErSiX on different surface orientation of Si was evaluated. ErSiX was formed by suppressing of the oxidation during the Si surface cleaning, Er sputtering, and silicidation annealing. Almost ideal Schottky diode properties are obtained on every surface orientation. The work function of ErSiX depends on the surface orientation and deposited Er thickness. The work function of ErSiX on Si(100) decreases and that on Si(551) increases with the increasing Er thickness. In addition, the work function ErSiX on Si(111) for the thickness less than 5 nm is constant and very low value of about 0.25 eV. These work function values depend on Si concentration in ErSiX, and it is considered that the concentration difference is caused by the lattice mismatch between ErSi2 and Si surface.

High-Temperature (550–700°C) Chlorosilane Interactions with Iron

Chlorosilane species are commonly used at high temperatures in the manufacture and refinement of ultra-high purity silicon and silicon materials. The chlorosilane species are often highly corrosive in these processes, necessitating the use of expensive, corrosion resistant alloys for the construction of reactors, pipes, and vessels required to handle and produce them. In this study, iron, the primary alloying component of low cost metals, was exposed to a silicon tetrachloride-hydrogen vapor stream at industrially-relevant times (0–100 hours), temperatures (550–700°C), and vapor stream compositions. Post exposure analyses including FE-SEM, EDS, XRD, and gravimetric analysis revealed formation and growth of stratified iron silicide surface layers, which vary as a function of time and temperature. The most common stratification after exposure was a thin FeSi layer on the surface followed by a thick stoichiometric Fe3Si layer, a silicon activity gradient in an iron lattice, and finally, unreacted iron. Speculated mechanisms to explain these observations were supported by thermodynamic equilibrium simulations of experimental conditions. This study furthers the understanding of metals in chlorosilane environments, which is critically important for manufacturing the high purity silicon required for silicon-based electronic and photovoltaic devices.