A thin Si nanowire network anode for high volumetric capacity and long-life lithium-ion batteries

Silicon nanowires(Si NWs)have been widely researched as the best alternative to graphite anodes for the next-generation of high-performance lithium-ion batteries(LIBs)owing to their high capacity and low discharge potential.However,growing binder-free Si NW anodes with adequate mass loading and stable capacity is severely limited by the low surface area of planar current collectors(CCs),and is particularly challenging to achieve on standard pure-Cu substrates due to the ubiquitous formation of Li+inactive silicide phases.Here,the growth of densely-interwoven In-seeded Si NWs is facilitated by a thin-film of copper-silicide(CS)network in situ grown on a Cu-foil,allowing for a thin active NW layer(<10μm thick)and high areal loading(≈1.04 mg/cm^(2))binder-free electrode architecture.The electrode exhibits an average Coulombic efficiency(CE)of>99.6%and stable performance for>900 cycles with≈88.7%capacity retention.More significantly,it delivers a volumetric capacity of≈1086.1 m A h/cm^(3)at 5C.The full-cell versus lithium manganese oxide(LMO)cathode delivers a capacity of≈1177.1 m A h/g at 1C with a stable rate capability.This electrode architecture represents significant advances toward the development of binder-free Si NW electrodes for LIB application.

Sub-nano Layers of Li, Be, and Al on the Si(100) Surface: Electronic Structure and Silicide Formation

Within the framework of the density functional theory and the pseudopotential method,the electronic structure calculations of the“metal-Si(100)”systems with Li,Be and Al as metal coverings of one to four monolayers(ML)thickness,were carried out.Calculations showed that band gaps of 1.02 eV,0.98 eV and 0.5 eV,respectively,appear in the densities of electronic states when the thickness of Li,Be and Al coverings is one ML.These gaps disappear with increasing thickness of the metal layers:first in the Li-Si system(for two ML),then in the Al-Si system(for three ML)and then in the Be-Si system(for four ML).This behavior of the band gap can be explained by the passivation of the substrate surface states and the peculiarities of the electronic structure of the adsorbed metals.In common the results can be interpreted as describing the possibility of the formation of a two-dimensional silicide with semiconducting properties in Li-Si(100),Be-Si(100)and Al-Si(100)systems.

Mo SILTCIDE SYNTHISIS BY DUAL ION BEAM DEPOSITION

Mo silicides Mo_5Si_3 with high quality were prepared using ion beamdeposition equipment with two Filter Metal Vacuum Are Deposition (FMEVAD). When the number ofalternant deposition times was 198, total thickness of the coating is 40nm. The coatings withdroplet free can be readily obtained, so the surface is smooth. TEM observation shows that Mo and Sialternant deposition coating is compact structure. The fine Mo silicide grains densely distributedin the coating. The coating adherence on silicon is excellent.

Micro-Mechanism of Disintegration of RE-Silicide Alloy Containing Phosphorus

The microstructure of the RE silicide alloy was studied by SEM. The feature of the phase and the distribution of Ca, P, Al were analyzed, especially the distribution of micro-cracks and its composition were determined. The result demonstrates that only a few phosphides contribute to the spontaneous crumbling of the RE silicide alloy by reacting with water and forming oxide or phosphorus oxide. The phosphorus content is not the critical factor of disintegration in the alloy studied.

Influence of silicide on fracture behavior of a fully lamellar Ti-46Al-0.5W-0.5Si alloy

The fracture behavior of fully lamellar binaryγ-TiAl alloys is extremely anisotropic with respect to the lamellar orientation.For the fully lamellar Ti-46Al-0.5W-0.5Si alloy,the existence of silicide clusters plays a critical role on the fracture behavior.In the present study,tensile test and three point bending test were performed at room temperature with the loading axis parallel and perpendicular to the lamellar orientation,respectively.To investigate the influence of silicide clusters on the initiation and propagation of cracks,the fracture surface and the cracks adjacent to the fracture zone of the specimens have been analyzed.Results show that the fracture process is related to the morphology and distribution of the silicide clusters.Crack preferentially initiates at and propagates along the interface of silicide andα 2 /γlamellar with the loading axis perpendicular to the length direction of silicide.While the silicide can prevent the propagation of cracks from running across with the crack growth direction perpendicular to the length direction of silicide.

Oxidation and interdiffusion behavior of a germanium-modified silicide coating on an Nb–Si-based alloy

To investigate the interdiffusion behavior of Ge-modified silicide coatings on an Nb–Si-based alloy substrate,the coating was oxidized at 1250°C for 5,10,20,50,or 100 h.The interfacial diffusion between the(Nb,X)(Si,Ge)_2(X = Ti,Cr,Hf) coating and the Nb–Si based alloy was also examined.The transitional layer is composed of(Ti,Nb)_5(Si,Ge)_4 and a small amount of(Nb,X)_5(Si,Ge)_3.With increasing oxidation time,the thickness of the transitional layer increases because of the diffusion of Si from the outer layer to the substrate,which obeys a parabolic rate law.The parabolic growth rate constant of the transitional layer under oxidation conditions is 2.018 μm×h^(-1/2).Moreover,the interdiffusion coefficients of Si in the transitional layer were determined from the interdiffusion fluxes calculated directly from experimental concentration profiles.

FORMATION OF MANGANESE SILICIDE THIN FILMS BY SOLID PHASE REACTION

Manganese silicide MnSi_(2-x) thin films have been prepared on n-type siliconsubstrates through solid phase reaction. The heterostructures were analyzed by X-ray diffraction,Rutherford backscattering spectroscopy, Fourier transform infrared transmittance spectroscopy andthe four-point probe technique. The results show that two manganese silicides have been formedsequentially via the reaction of thin layer Mn with Si substrate at different irradiation annealingstages, i.e., MnSi at 450 deg C and MnSi_(1.73) at 550 deg C. MnSi_(1.73) phase exhibits preferredgrowth after irradiation with infrared. In situ four-point probe measurements of sheet resistanceduring infrared irradiation annealing show that nucleation of MnSi and phase transformation of MnSito MaSi_(1.73) occur at 410 deg C and 530 deg C, respectively; the MnSi phase shows metallicbehavior, while MnSi_(1.73) exhibits semiconducting behavior. Characteristic phonon bands ofMnSi_(2-x) silicides, which can be used for phase identification along with conventional XRDtechniques, have been observed by FTIR spectroscopy.

INTERMETALLIC ALLOYS AND COMPOSITES FOR THE 21ST CENTURY: A BASIC ENERGY SCIENCES PROGRAM OF THE U. S. DEPARTMENT OF ENERGY

Progress has been made in intermetallic alloys over the past decade and a half, but intermetallics remain a relatively unexplored class of materials for energy applications. Hence, they offer considerable opportunities both for scientific research on fundamental structural property processing relationships and for technological development. The Department of Energy supports a program of scientific research on intermetallic alloys such as the nickel and iron aluminides and is establishing new research efforts in silicides and Laves phases through the program of the Division of Materials Sciences, of the Office of Basic Energy Sciences. Areas of research include theory and materials simulation, microalloying, high resolution sudies of structure and composition, mechanical properties, point defects and dislocation mechanics, phase transformations, and processing. Research is conducted through programs at the Department of Energy National Laboratories and through grants to academic and industrial researchers.Research results from Division of Materials Sciences programs have provided the basis and transportation. In addition, a cooperative effort between research groups has been established as a project on intermetallic materials under the Center of Excellence in Synthesis and Processing of Advanced Materials.

EXPLORATION OF Nb-BASED ADVANCED INTERMETALLIC MATERIAL

Since the late 1980's there have been a number of research efforts aimed at exploring and developing the refractory intermetalllic materials for service at temperatures which compete with the nickel-based superalloys in structural applications. These efforts have documented the physical and mechanical properties of a broad set of compositions. However, only in the last three years have these efforts yielded sufficient experimental results on single selected systems to suggest that damage tolerance, creep resistance and oxidation resistance may be obtained and controlled simultaneously. These findings led to alloy development concepts and approaches which are currently under investigation and are expected to lead to research focused on a smaller set of alloys. An overview of selected alloy development strategies and resulting structural properties is presented herein.

Ternary alloying of Mo_5Si_3 with Zr, Ti, Co and V

The Mo 5Si 3 base alloys with a series of transition metal elements were prepared by arc melting, and were annealed at 1?250?℃ in vacuum for 24?h. Ternary alloying effect was investigated by X ray diffractometry (XRD), optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy(EDS). The EDS results show that Zr, Ti, Co and V have certain solubility in homogenized Mo 5Si 3, which are determined to be 2.20±1.42, 15.94±0.18, 3.33±0.76 and 7.43±0.22 (mole fraction, %), respectively. Microstructural characteristics indicate that all studied alloys have a two phase microstructure, i.e., Mo 5Si 3 matrix and the second phase Mo 37 Zr 20 Si 43 , Mo 66 Si 19 Ti 15 , MoCoSi or (Mo, V) 3Si.

The fabrication of nickel silicide ohmic contacts to n-type 6H-silicon carbide

This paper reports that the nickel silicide ohmic contacts to n-type 6H-SiC have been fabricated. Transfer length method test patterns with NiSi/SiC and NiSi2/SiC structure axe formed on N-wells created by N^＋ ion implantation into Si-faced p-type 6H-SiC epilayer respectively. NiSi and NiSi2 films are prepared by annealing the Ni and Si films separately deposited. A two-step annealing technology is performed for decreasing of oxidation problems occurred during high temperature processes. The specific contact resistance Pc of NiSi contact to n-type 6H-SiC as low as 1.78× 10^-6Ωcm^2 is achieved after a two-step annealing at 350 ℃for 20 min and 950℃ for 3 min in N2. And 3.84×10-6Ωcm^2 for NiSi2 contact is achieved. The result for sheet resistance Rsh of the N＋ implanted layers is about 1210Ω/□. X-ray diffraction analysis shows the formation of nickel silicide phases at the metal/n-SiC interface after thermal annealing. The surfaces of the nickel silicide after thermal annealing are analysed by scanning electron microscope.

Evolution laws of microstructures and mechanical properties during heat treatments for near-αhigh-temperature titanium alloys

Evolution laws of microstructures,mechanical properties,and fractographs after different solution temperatures were investigated through various analysis methods.With the increasing solution temperatures,contents of the primaryαphase decreased,and contents of transformedβstructures increased.Lamellarαgrains dominated the characteristics of transformedβstructures,and widths of secondaryαlamellas increased monotonously.For as-forged alloy,large silicides with equiaxed and rod-like morphologies,and nano-scale silicides were found.Silicides with large sizes might be(Ti,Zr,Nb)_(5)Si_(3) and(Ti,Zr,Nb)_(6)Si_(3).Rod-like silicides with small sizes precipitated in retainedβphase,exhibiting near 45°angles withα/βboundaries.Retainedβphases in as-heat treated alloys were incontinuous.980STA exhibited an excellent combination of room temperature(RT)and 650°C mechanical properties.Characteristics of fracture surfaces largely depended on the evolutions of microstructures.Meanwhile,silicides promoted the formation of mico-voids.

Evaluation and modification of inclusion characteristics in HK40 heatresistant cast steel

Specifications of inclusions such as the type, morphology, number, composition, size, and place of inclusions in HK40 heat-resistant casting steel were studied by optical microscopy and scanning electron microscopy equipped with an energy-dispersive spectroscopy system. The effects of calcium silicide （CaSi） addition on these characteristics were evaluated at two pouring temperatures of 1420℃ and 1470℃. It was found that most of the appeared inclusions were in the type of chromium oxide. CaSi addition had a significant effect on the morphological modification, size and distribution of inclusions as well as changing the composition to oxide-sulfide compounds.

Investigation on laser cladding of MoSi_2 powder on steel

The feasibility of the fabrication of coatings for elevated-temperature structural applications by laser cladding MoSi2 pow- der on steel was investigated. A dense and crack-free fine coating, well-bonded with the substrate has been obtained by this technique This coating consists of FeMoSi, Fe2Si and a small amount of MosSi3 due to dilution of the substrate in the coating. The microstructure of the coating is characterized of typical fine dendrites, The dendrites are composed of FeMoSi primary phase, and the interdendritic areas are two eutectic phases of FeMoSi and Fe2Si. The hardness of the coating reaches 845 Hv0.5, 3.7 times larger than that of the steel substrate （180 Hv05）.

Suppression of oxygen and carbon impurity deposition in the thermal system of Czochralski monocrystalline silicon

When preparing large monocrystalline silicon materials,severe carbon etching and silicide deposition often occur to the thermal system.Therefore,a suppression method that optimizes the upper insulation structure has been proposed.Assisted by the finite element method,we calculated temperature distribution and carbon deposition of heater and heat shield,made the rule of silicide and temperature distributing in the system,and we explained the formation of impurity deposition.Our results show that the optimized thermal system reduces carbon etching loss on heat components.The lowered pressure of the furnace brings a rapid decrease of silicide deposition.The increase of the argon flow rate effectively inhibits CO and back diffusion.The simulated results agree well with the experiment observations,validating the effectiveness of the proposed method.

Structural, elastic, and electronic properties of recently discovered ternary silicide superconductor Li_2IrSi_3: An ab-initio study

The structural, elastic, and electronic properties of the very recently discovered ternary silicide superconductor, Li2IrSi3, are calculated using an ab-initio technique. We adopt the plane-wave pseudopotential approach within the frame- work of the first-principles density functional theory （DFT） implemented by the CASTEP code. The calculated structural parameters show reasonable agreement with the experimental results. The elastic moduli of this interesting material are calculated for the first time. The electronic band structure and electronic energy density of states indicate the strong cova- lent Ir-Si and Si-Si bonding, which leads to the formation of the rigid structure of Li2IrSi3. Strong covalency gives rise to a high Debye temperature in this system. We discuss the theoretical results in detail in this paper.

AMORPHIZATION TRANSFORMATION BY MECHANICAL ALLOYING IN THE Mo-Si SYSTEM

Starting from elemental powders, complete MoSi2 powder forms abruptly between 3.5and 4 h during mechanical alloying (MA) of the Mo-66 at.% Si powders. Continuous milling of this MoSi2 Phase leads to a nanocrystalline powder and amorphizationtransformation takes place after 100 h milling. Howeven MA of the Mo-37.5 at.%Si powders does not result in the formation of the Mo5Si3 crystalline phase, but the formation of a Mo(Si) supersaturated solid solution (SSS) and a completely amorphots phase after 5 h and 70 h milling, respectively. The free energy of the Mo-Sisystem has been calculated and it has been found that there is no driving force for the amorphization reaction under normal conditions. The amorphization by MA of the Mo-Si system is attributed to a solid-state amorphization reaction in which defects and a very fine grain size induced during milling process may raise the free energy of the crystalline intermetallic phase (for MoSi2) or the Mo(Si) supersaturated solid solution (for Mo5Si3) above that of the amorphous phase.

Selective Heating of Transition Metal Usings Hydrogen Plasma and Its Application to Formation of Nickel Silicide Electrodes for Silicon Ultralarge-Scale Integration Devices

We developed an apparatus for producing high-density hydrogen plasma. The atomic hydrogen density was 3.1 × 1021 m?3 at a pressure of 30 Pa, a microwave power of 1000 W, and a hydrogen gas flow rate of 10 sccm. We confirmed that the temperatures of transition-metal films increased to above 800。C within 5 s when they were exposed to hydrogen plasma formed using the apparatus. We applied this phenomenon to the selective heat treatment of nickel films deposited on silicon wafers and formed nickel silicide electrodes. We found that this heat phenomenon automatically stopped after the nickel slicidation reaction finished. To utilize this method, we can perform the nickel silicidation process without heating the other areas such as channel regions and improve the reliability of silicon ultralarge-scale integration devices.

Effect of Annealing Temperature on the Formation of Silicides and the Surface Morphologies of PtSi Films

The effect of annealing temperature on the formation of the PtSi phase. distribution of silicides and the surface morphologies of silicides films is investigated by XPS. AFM. It is shown that the phase sequences of the films change from Pt-Pt2Si-PtSi-Si to Pt+Pt2Si+PtSi-PtSi-Si or Pt+Pt2Si+PtSi-PtSi-st with an increase of annealing temperature and the reason for the formation of mixed layers is discussed.

Atomic diffusion in annealed Cu/SiO_2/Si(100) system prepared by magnetron sputtering

Cu thin films are deposited on p-type Si （100） substrates by magnetron sputtering at room temperature. The interface reaction and atomic diffusion of Cu/SiO2/Si （100） systems are studied by x-ray diffraction （XRD） and Rutherford backscattering spectrometry （RBS）. Some significant results can be obtained. The onset temperature of interdiffusion for Cu/SiO2/Si（100） is 350~℃. With the annealing temperature increasing, the interdiffusion becomes more apparent. The calculated diffusion activation energy is about 0.91 eV. For the Cu/SiO2/Si （100） systems copper silicides are not formed below an annealing temperature of 350~℃. The formation of the copper silicides phase is observed when the annealing temperature arrives at 450~℃.