- Chemical reaction and metallic cluster formation by annealing-temperature control in ZrO2 gate dielectrics on Si
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Thermal stability of the Zr O2 Zr-silicateSi structure and the Zr-silicide formation were investigated by photoemission spectroscopy depending on the annealing temperature in ultrahigh vacuum. By the annealing below 860 °C, the interfacial layer thickness of the Zr-silicate decreased although the Zr O2 top layer was not affected. The annealing at 860 °C caused the interfacial Zr-silicate layer to disappear. By the annealing above 860 °C, the metallic Zr components appeared and the metallic clusters were formed. High-resolution photoemission spectra have revealed that the clusters consist of a Zr Si2 layer. Valence-band spectra depending on the annealing temperature provide us with the information about the crystallization in the Zr O2 layer.
- Okabayashi,Toyoda,Kumigashira,Oshima,Usuda,Niwa,Liu
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- Sintering mechanisms of zirconium and hafnium carbides doped with MoSi 2
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The microstructure of two pressureless-sintered ultra-high-temperature ceramics, namely ZrC+20 vol% MoSi2 and HfC+20 vol% MoSi2, was characterized by scanning and transmission electron microscopy. With regard to the ZrC-MoSi2/s
- Silvestroni, Laura,Sciti, Diletta,Kling, Jens,Lauterbach, Stefan,Kleebe, Hans-Joachim
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- Annealing of thin Zr films on Si1-xGex(0 ≤ x ≤ 1): X-ray diffraction and Raman studies
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X-ray diffraction experiments have been combined with Raman scattering and transmission electron microscopy data to analyze the result of rapid thermal annealing (RTA) applied to Zr films, 16 or 80 nm thick, sputtered on Si1-xGex epilayers (0 ≤ x ≤ 1). The C49 Zr(Si1-xGex)2 is the unique phase obtained after complete reaction. ZrSi1-xGex is formed as an intermediate phase. The C49 formation temperature Tf is lowered by the addition of Ge in the structure. Above a critical Ge composition close to x = 0.33, a film microstructure change was observed. Films annealed at temperatures close to Tf are continuous and relaxed. Annealing at T > Tf leads to discontinuous films: surface roughening resulting from SiGe diffusion at film grain boundaries occurred. Grains are ultimately partially embedded in a SiGe matrix. A reduction in the lattice parameters as well as a shift of Raman lines are observed as T exceeds Tf. Both Ge non-stoichiometry and residual stress have been considered as possible origins for these changes. However, as Ge segregation has never been detected, even by using very efficient techniques, it is thought that the changes originate merely from residual stress. The C49 grains are expected to be strained under the SiGe matrix effect and shift of the Raman lines would indicate the stress is compressive. Some simple evaluations of the stress values indicate that it varies between -0.3 and -3.5 GPa for 0 ≤ x ≤ 1 which corresponds to a strain in the range (-0.11, -1.15%). X-ray and Raman determinations are in good agreement.
- Chaix-Pluchery,Chenevier,Aubry-Fortuna,Matko
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- A novel preparation of Zr-Si intermetallics by electrochemical reduction of ZrSiO4 in molten salts
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A method of controllably preparing Zr-Si intermetallics by the electrochemical reduction of ZrSiO4 and ZrSiO4-SiO2 mixed powders in molten CaCl2-NaCl at 800°C is developed. The final product composition can be controlled by adjusting the molar ratio of Si to Zr in the starting material, and ZrSi, ZrSi2 and their mixture were obtained by this process. The reduction pathway of ZrSiO4 and SiO2 to Zr-Si intermetallics involves several calcium-containing intermediate phases, such as CaSiO3, Ca2SiO4, and calcia-stabilized zirconia (CSZ).
- Liu, Hongxia,Cai, Yanqing,Xu, Qian,Song, Qiushi,Liu, Huijun
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- New criteria for the applicability of combustion synthesis: The investigation of thermodynamic and kinetic processes for binary Chemical Reactions
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Combustion synthesis is a novel technique that utilizes the exothermic heat of a chemical reaction to maintain the reaction and to rapidly prepare materials. But, hitherto, none of unified criterion for the validation of combustion synthesis has been proposed. Herein, we proposed the conditions need to be met. In terms of kinetics, at the adiabatic temperature (Tad), the diffusion distance of atoms (lTad) within 0.1 s should be larger than the particle size of the reactants(d), that is, lTad≥d. For systems that satisfy Tad/Tm,L≥1(where Tm,L is the melting point of the low-melting point component of the reactants), the presence of a liquid phase significantly increases the atomic diffusion distance from nanometers to tens of microns, making the criterion lTad≥d simplified to Tad/Tm,L≥1 in most situations. In terms of thermodynamics, the system needs to ensure that the reaction components are in an activated state, that is, Tad/Tm,H ≥0.7, where Tm,H is the melting point of the high-melting point component. The criteria for the SHS reactions proposed in this study further improve the theoretical understanding of SHS reactions, and provide guidance for exploring the ultra-fast synthesis of binary and multicomponent compounds.
- Tan, Xiaoming,Su, Xianli,Yan, Yonggao,Uher, Ctirad,Zhang, Qingjie,Tang, Xinfeng
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supporting information
(2021/01/07)
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- High-temperature chemistry and oxidation of ZrB2 ceramics containing SiC, Si3N4, Ta5Si3, and TaSi2
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The effect of Si3N4, Ta5Si3, and TaSi2 additions on the oxidation behavior of ZrB2 was characterized at 1200°-1500°C and compared with both ZrB2 and ZrB2/SiC. Significantly improved oxidation resistance of all Si-containing compositions relative to ZrB2 was a result of the formation of a protective layer of borosilicate glass during exposure to the oxidizing environment. Oxidation resistance of the Si3N 4-modified ceramics increased with increasing Si3N 4 content and was further improved by the addition of Cr and Ta diborides. Chromium and tantalum oxides induced phase separation in the borosilicate glass, which lead to an increase in liquidus temperature and viscosity and to a decrease in oxygen diffusivity and of boria evaporation from the glass. All tantalum silicide-containing compositions demonstrated phase separation in the borosilicate glass and higher oxidation resistance than pure ZrB2, with the effect increasing with temperature. The most oxidation-resistant ceramics contained 15 vol% Ta5Si3, 30 vol% TaSi2, 35 vol% Si3N4, or 20 vol% Si 3N4 with 10 mol% CrB2. These materials exceeded the oxidation resistance of the ZrB2/SiC ceramics below 1300°-1400°C. However, the ZrB2/SiC ceramics showed slightly superior oxidation resistance at 1500°C.
- Talmy, Inna G.,Zaykoski, James A.,Opeka, Mark M.
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p. 2250 - 2257
(2009/09/30)
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- SYNTHESIS OF METAL SILICIDE POWDERS BY THERMOLYSIS OF METAL CHLORIDESI WITH MAGNESIUM SILICIDE
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Thermolysis (850 deg C) of a mixture of Mg2Si and MCln (M= Y,Gd,Dy,Ho,Ti,Zr,Hf,Nb,Ta, Mo,W,Fe,Pt; n=3,4,5) produces metal silicides MxSiy, as microcrystalline powders.The reactions give a useful insight into mechanisms working in this type of reaction. Key words: Metal silicide, metal chlorides, magnesium silicide, powder diffraction, thermolysis.
- Fitzmaurice, Jonathan C.,Hector, Andrew L.,Parkin, Ivan P.,Rowley , Adrian T.
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