Iridium Silicide Research Articles

Joining of SiC ceramics by iridium: The interfacial phenomena and joint strength

A methodology for joining SiC ceramic parts using iridium foil was devised. The connecting layer was formed via a solid-state reaction at 1350 °C or via a transient liquid phase (TLP) at temperatures exceeding 1417 °C. The microstructure of the connecting layer formed via solid-state reaction exhibits temporal changes. The overall thickness of the layer remains approximately constant over time; however, the thickness of the carbon-free central part, composed of Ir and iridium silicides, decreases with time. The thicknesses of the porous carbon-containing sublayers located on either side of the central region demonstrate an increase. The greatest average flexural strength value was found to be 110 ± 6 MPa. The flexural strength values decrease with an increase in the holding time. This behavior can be attributed to the growth of a porous carbon-containing layer. The connecting layer, obtained via a transient liquid phase, is composed of IrSi and C. The layers on either side of the central dense IrSi part contain a number of pores and carbon inclusions. The SiC/SiC joints formed at 1425 °C and 1500 °C exhibit bending strengths of 66 ± 4 and 29 ± 4 MPa, respectively. These findings illustrate the potential of iridium to join monolithic SiC ceramic parts at relatively low temperatures.

Microstructural patterning of the reaction zone formed by solid-state interaction between iridium and SiC ceramics

The phenomena occurring within the Ir–SiC couple depending on temperature and time were studied. In the temperature range of 1300–1400°C, when all the components of the Ir–Si–C system are solids, the following sequence of phases is formed between Ir and SiC plates: Ir / Ir3Si / Eutectoid / Ir3Si2 / IrSi / IrSi + C/ SiC. The effect of exposure time on the morphology, phase composition, and thickness of the product layer was studied. The reaction between Ir and SiC was shown to obey the linear law, being indicative of the kinetic control. Iridium atoms diffuse faster across the product layer than silicon atoms do. The product thickness increases mainly due to growth of the IrSi layer with carbon inclusions. A periodic morphology of the IrSi layer composed of carbon-free IrSi layers and IrSi layers with carbon inclusions is observed with increasing exposure time. The thickness of carbon-free IrSi layers and sizes of carbon inclusions increases at greater distances from the reaction front. The process is accompanied by ordering and graphitization of carbon inclusions. The Vickers microhardness for the iridium silicide phases were measured. The microhardness of iridium silicides is ∼ 3 times less than that of SiC that can decrease the brittleness of SiC-based materials.

Investigation of amorphous (Ir,Ru)-Si and (Ir,Ru)-Si-O Schottky contacts to (001) [formula omitted]-Ga[formula omitted]O[formula omitted

In this work we propose a new scheme for Schottky contacts to β-Ga2O3, namely — Ru-Si-O and Ir-Si-O conductive layers, fabricated by means of reactive magnetron sputtering of ruthenium or iridium silicide (Ru-Si, Ir-Si) targets in oxygen containing atmosphere. The influence of oxygen partial pressure during deposition on the microstructure and electrical parameters of layers was investigated. The properties of Ir-Si-O and Ru-Si-O as well as Ir-Si and Ru-Si Schottky contacts to β-Ga2O3 were compared. Work function of Ir-Si-O layers was in range of 4.97–5.08 eV as compared to 5.6–5.65 eV for Ru-Si-O layers. The investigated Schottky contacts show strong positive correlation between homogeneous barrier height and contact work function, roughly following Schottky–Mott relation. Our findings opens new possibilities to produce Schottky contacts to β-Ga2O3 with tailored properties using the M-Si-O (where M is transition metal) material system.

Behavior of Some Refractory Hafnium and Tantalum Compounds in Plasma Flows

By reacting tantalum or hafnium carbide with iridium in the presence of a small amount of silicon, we have prepared refractory hafnium- and tantalum-containing materials consisting of a mixture of phases: the intermetallic compound MIr3, recrystallized tantalum or hafnium carbide, and iridium silicide. We have studied the behavior of the materials during an exposure to a high-speed plasma flow at a sample surface temperature of 2000°C and demonstrated that, owing to their special microstructure, the absence of pores, and the low oxidation rate of the iridium-containing components, they exhibit a good ablation resistance and that the hafnium system withstands a longer exposure.

Study of iridium silicide monolayers using density functional theory

In this study, we investigated physical and electronic properties of possible two-dimensional structures formed by Si (silicon) and Ir (iridium). To this end, different plausible structures were modeled by using density functional theory and the cohesive energies calculated for the geometry of optimized structures, with the lowest equilibrium lattice constants. Among several candidate structures, we identified three mechanically (via elastic constants and Young's modulus), dynamically (via phonon calculations), and thermodynamically stable iridium silicide monolayer structures. The lowest energy structure has a chemical formula of Ir2Si4 (called r-IrSi2), with a rectangular lattice (Pmmn space group). Its cohesive energy was calculated to be −0.248 eV (per IrSi2 unit) with respect to bulk Ir and bulk Si. The band structure indicates that the Ir2Si4 monolayer exhibits metallic properties. Other stable structures have hexagonal (P-3m1) and tetragonal (P4/nmm) cell structures with 0.12 and 0.20 eV/f.u. higher cohesive energies, respectively. Our calculations showed that Ir-Si monolayers are reactive. Although O2 molecules exothermically dissociate on the surface of the free-standing iridium silicide monolayers with large binding energies, H2O molecules bind to the monolayers with a rather weak interaction.

Iridium–silicide nanowires on Si(110) surface

We studied physical and electronic properties of iridium silicide nanowires grown on the Si(110) surface with the help of scanning tunneling microscopy and spectroscopy. The nanowires grow along the [001] direction with an average length of about 100nm. They have a band gap of ~0.5eV and their electronic properties show similarities with the iridium silicide ring clusters formed on Ir modified Si(111) surface.

Structural stability and elastic properties of IrSi in B31 and B20-phase from first-principles calculations

Abstract A systematic study of the structural stability, elastic properties and electronic structures for iridium silicide (IrSi) in B31 and B20-phase has been carried out with the generalized gradient approximation (GGA) and local density approximation (LDA) in framework of density functional theory (DFT). The obtained formation enthalpies, energy–volume (E–V) curves and enthalpy–pressure (H–P) curves indicate that orthorhombic B31-IrSi is more stable than cubic B20-IrSi at both ambient and pressure conditions. The elastic stiffness constants, bulk moduli, shear moduli, Young’s moduli, Poisson’s coefficients and elastic anisotropy factors of the two phases IrSi are studied for the first time. The small elastic stiffness constant C22 of B31-IrSi induces easily compressibility along the b axis. Moreover, based on the Mulliken overlap population analysis, the hardness Hv of B31-IrSi (Hv = 11.9 GPa) and B20-IrSi (Hv = 13.4 GPa) are evaluated.

Charge storage characteristics of iridium silicide nanocrystals embedded in SiO 2 matrix for nonvolatile memory application

In this work, the nanostructure-assisted “Al/SiO 2/Ir-silicide-NCs/SiO 2/P-Si-sub/Al” stack with iridium silicide nanocrystals (Ir-silicide-NCs) embedded between two SiO 2 layers has been demonstrated in the application of nonvolatile memory for the first time. A significant memory window voltage of 14.2 V at sweeps of +/− 10 V by capacitance–voltage measurement can be reached, when well-distributed Ir-silicide-NCs are observed in cross-sectional TEM examination. In this case, the trap density is estimated to be about 1.06 × 10 13 cm − 2 , indicating a high trapping efficiency stack for nonvolatile memory application.

Kinetics, stoichiometry, morphology, and current drive capabilities of Ir-based silicides

A detailed study of the formation of iridium silicide obtained by ultrahigh vacuum annealing and atmospheric rapid thermal processing is proposed using x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and electrical characterizations. Using XPS analysis, the stoichiometry of each silicide phase (IrSi, IrSi1.6) is identified. A model based on the variation of the measured intensity of the Ir 4f spectra is used to obtain the kinetic coefficients of reaction of Ir silicidation (EA=2.48eV, D0=9cm2∕s). TEM cross sections indicate that the roughness of the silicide∕silicon interface increases with temperature. Lastly, electrical characteristics are used to identify the optimum annealing temperature to obtain an iridium silicide contact with the lowest Schottky barrier height to holes.

Mg3Ir3Si8, a New Magnesium Iridium Silicide with Si4 Tetrahedra and Si12 Truncated Tetrahedra.

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Mg3Ir3Si8, ein neues Magnesium‐Iridium‐Silicid mit Tetraedern und gekappten Tetraedern aus Silicium‐Atomen

AbstractMg3Ir3Si8, a New Magnesium Iridium Silicide with Si4 Tetrahedra and Si12 Truncated TetrahedraThe ternary silicide Mg3Ir3Si8 (cubic, a = 1221.4(1) pm, space group $F{\bar 4}{\rm 3}m$, 8 formula units per unit cell) was prepared by reaction of the elemental components in a sealed molybdenum container (1000 °C, 1 d, cooled with 100 °/h). The crystal structure was determined from single crystal data. Short distances in the three‐dimensional iridium silicon network indicate strong Ir‐Si‐bonding (d(Ir‐Si) = 240.5(2) and 245.6(1) pm). In addition, homonuclear bonding seems to be important, resulting in the formation of Si4‐tetrahedra (d(Si‐Si) = 257(1) pm), and Mg centered Si12‐polyhedra with the shape of truncated tetrahedra (d(Si‐Si) = 241(1) and 261.0(9) pm). Furthermore, Mg4‐tetrahedra with Mg‐Mg‐distances of 355(2) pm are formed. The structure may be derived from the structure of the isotypic compounds Mg5Pd10Si16 and Mg5Pt10Si16 by adding a Mg siteset and subtracting a platinum metal siteset. It can be described by an expanded cubic “close” packing of MgIr6‐octahedra in which Si4‐tetrahedra reside in the octahedral holes while Mg4‐tetrahedra and MgSi12‐units occupy one half of the tetrahedral holes each.

Synthesis, Structure, and Magnetic Properties of the Silicides REIrSi (RE = Ce, Pr, Er, Tm, Lu) and SmIr0.266(8)Si1.734(8)

The equiatomic rare earth metal–iridium–silicides REIrSi (RE=Ce, Pr, Er, Tm, Lu) were prepared by arc-melting of the elements and subsequent annealing. All silicides were characterized through their X-ray powder patterns. The structures of CeIrSi, ErIrSi, and LuIrSi were refined from X-ray single crystal diffractometer data: LaIrSi type, P213, a=629.15(2) pm, wR2=0.1232, 280 F2 values, and 11 variable parameters for CeIrSi; TiNiSi type, Pnma, a=673.4(1), b=416.07(5), c=744.88(9) pm, wR2=0.0705, 339 F2 values, and 20 variable parameters for ErIrSi, and a=664.0(3), b=412.9(1), c=742.6(1) pm, wR2=0.0398, 496 F2 values, and 20 variable parameters for LuIrSi. The iridium and silicon atoms in CeIrSi, ErIrSi, and LuIrSi build three-dimensional [IrSi] networks where the iridium atoms have three (CeIrSi, Ir–Si 229 pm) and four (ErIrSi, Ir–Si 247–258 pm; LuIrSi, Ir–Si 245–256 pm) silicon neighbors. The [IrSi] networks leave larger channels in which the cerium, erbium, and lutetium atoms are located. Temperature dependent susceptibility data for LuIrSi indicate Pauli paramagnetism. CeIrSi shows Curie-Weiss paramagnetism above 100 K with an experimental magnetic moment of 2.56(2) μB/Ce atom. With samarium as rare earth metal component the silicide SmIr0.266(8)Si1.734(8) with α-ThSi2 type structure was obtained: I41/amd, a=409.3(1), c=1397.2(5) pm, wR2=0.0575, 161 F2 values, and 9 variable parameters. Within the three-dimensional [Ir0.266Si1.734] network the Ir/Si–Ir/Si distances range from 230 to 237 pm.

Transmission electron microscopy of iridium silicide contacts for advanced MOSFET structures with Schottky source and drain

The IrSix contacts have been used in Accumulated Low Schottky Barrier MOSFET on SOI. An IrSix layer is formed as a result of reaction between metal and semiconductor during annealing. The process of silicidation in the Ir/Si/SiO2/Si structure has been studied by means of cross-sectional transmission electron microscopy (XTEM). The influence of annealing temperatures (300, 600, 900°C) on silicide formation was analysed. The formation of a thin IrSix layer was observed at a temperature as low as 300°C. In the Ir/Si/SiO2/Si structure annealed at 600°C, the Ir atoms are shown to penetrate across the Si layer, causing disturbance of the Ir/Si interface. After annealing at 900°C large IrSix islands were formed in Si. The expansion of the IrSix grains in the Si layer was observed. TEM results were correlated with XPS and electrical measurements.

Phase composition, orientation, and substructure of iridium silicide films on silicon

The phase composition, orientation, and substructure of iridium silicide films produced by electron-beam evaporation of Ir on (001) and (111) Si at substrate temperatures from 300 to 1000°C were studied by electron microscopy and diffraction. The results demonstrate that the sequence of silicide formation upon Ir deposition onto heated substrates is the same as upon heat treatment of Ir films deposited at room temperature. It is shown that oriented growth of Ir3Si5 and IrSi0.7 is possible. The IrSi3 /Si interface is shown to be, to some extent, coherent, with the lattice mismatch being accommodated by dislocations in some directions and by elastic strain in other directions. The likely mechanism for the formation of a dislocation structure at the IrSi3 /Si interface is discussed.

Mg15Ir5Si2, a Magnesium Iridium Silicide with Isolated Ir5Si2 Building Groups.

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Electron spectroscopic studies of iron and iridium silicides

AbstractThe formation of iron and iridium silicides was studied by means of highly resolved photoelectron spectroscopy of core and valence levels as well as by means of low‐energy electron diffraction (LEED). The experiments were carried out at BESSY II in Berlin using synchrotron radiation for the photoemission studies. After evaporation of seven monolayers of Fe on Si(111) at room temperature and annealing to 410 K for 420 s, an ordering of the surface structure and the formation of an (1 × 1) LEED pattern is observed. Upon further heating to 500 K a strong change in both UPS and XPS spectra occurs. This behaviour is attributed to the formation of FeSix (1 ≤ x ≤ 2). After annealing of a thin Ir layer on Si(100) to 1130 K, a p(2 × 2) LEED pattern with respect to the silicon substrate is observed, which indicates the formation of a well‐ordered surface compound. Comparison with the literature shows that the formation of an IrSi species is well known, but only an amorphous and a polycrystalline modification have been described upto now. Copyright © 2002 John Wiley & Sons, Ltd.

The role of the Si 3s3d states in the bonding of iridium silicides (IrSi, Ir3Si5 and IrSi3)

Si L2,3 soft-x-ray emission spectra of IrSi,Ir3Si5 and IrSi3 compounds have been takenand the valence band densities of states associated with themhave been analysed as functions of the concentration of Siatoms, the coordination number of Si-Ir in the iridiumsilicide compounds and the average distances of the Si-Si bondsin those compounds. The role of silicon 3s3d states in thebonding of the different iridium silicides is discussed. Allthe spectra show two regions, one associated with thelow-energy Si 3s states and another one associated withhigh-energy Si 3s3d states. The effects of the interaction between the Si and Ir atoms in the silicides are: (a) thedistribution of silicon states, even those associated with theleast energetic s electrons, are modified, suggesting that thes electrons play a role in the formation of the iridiumsilicides; (b) the energy bandwidth corresponding to the Si 3s3dstates increases up to 2.5 eV as the number of Si atoms thatinteract with the Ir atoms increases; and (c) there is asignificant contribution from the d electrons, the fraction ofthe states associated with them being at least 20% of thetotal of states associated with the 3s3d states.

Micro-Raman study of iridium silicides

The micro-Raman spectra of three iridium silicides, IrSi, IrSi1.75 and IrSi3, were obtained. The silicides were prepared by rapid thermal annealing of iridium films deposited on Si substrates. The three phases were identified by Rutherford backscattering spectrometry. The main bands observed in the micro-Raman spectra are described in order to provide a simple characterization method for these silicides with high spatial resolution. The three silicides present phonon bands around 165 and 200 cm−1. Some additional broad bands between 240 and 500 cm−1 were also observed. Copyright © 2002 John Wiley & Sons, Ltd.

Micro‐Raman study of iridium silicides

AbstractThe micro‐Raman spectra of three iridium silicides, IrSi, IrSi1.75 and IrSi3, were obtained. The silicides were prepared by rapid thermal annealing of iridium films deposited on Si substrates. The three phases were identified by Rutherford backscattering spectrometry. The main bands observed in the micro‐Raman spectra are described in order to provide a simple characterization method for these silicides with high spatial resolution. The three silicides present phonon bands around 165 and 200 cm−1. Some additional broad bands between 240 and 500 cm−1 were also observed. Copyright © 2002 John Wiley & Sons, Ltd.

Structure and thermoelectric properties of binary and Fe-doped iridium silicide thin films

The structure-formation process and thermoelectric properties of binary and Fe-doped IrxSi1−x (0.30 ≤ x ≤ 0.41) thin films were investigated. The films were prepared by means of physical vapor deposition techniques, in particular by magnetron co-sputtering and electron beam co-evaporation. The amount of Fe dopant varied between 0 and 5 at.%. The phase-formation process depends on the volume fractions of the major components Ir and Si, whereas the small concentrations of dopant did not change the sequence of the crystalline phases formed. On the other hand, the thermoelectric transport properties correlate strongly with both the structure-formation process and the chemical composition of the films. Fe-doped iridium silicide films with useful thermoelectric power factors were successfully obtained by both magnetron co-sputtering and electron beam co-evaporation. A maximum thermoelectric power factor of 8.5 μW/(K2 cm) at 1200 K was observed for evaporated layers with thechemical composition Ir0.35Si0.63Fe0.02.