Amorphization Of Si Research Articles

Deciphering the Impact of Current, Composition, and Potential on the Lithiation Behavior of Si-Rich Silicon-Graphite Anodes.

Adding silicon (Si) to graphite (Gr) anodes is an effective approach for boosting the energy density of lithium-ion batteries, but it also triggers mechanical instability due to Si volume changes upon (de)lithiation reactions. In this work, component-specific (de)lithiation dynamics on Si-rich (30 and 70wt.% Si) SiGr anodes at various charge/discharge C-rates are unveiled and compared to a graphite-only electrode (100Gr) via operando synchrotron X-ray diffraction coupled with differential capacity plots analysis. Results show preferential lithiation of amorphous Si above ≈200mV and competing lithiation of Gr, amorphous Si, and crystalline Si below ≈200mV. Discharge proceeds via sequential delithiation of Gr and amorphous lithium silicide. Si shifts the interconversion potentials of graphite intercalation compounds, lowering the Gr state of charge compared to 100Gr. In the 30%Si electrode, crystalline Si amorphization at potentials <110mV is found to be kinetically hindered at C-rates higher than C/5, which can be key for enhancing the cycling stability of SiGr anodes. The 70%Si electrode exhibits restricted lithium diffusion in Gr, full Si amorphization, and Li15Si4 formation. These findings related to the potential- and current-dependent dynamic changes on SiGr blends are crucial for designing stable high energy density SiGr anodes.

High Adhesion of Hot-Dip Galvanized Steel and Silicone Adhesive through Si Amorphous Film

High Adhesion of Hot-Dip Galvanized Steel and Silicone Adhesive through Si Amorphous Film

Analysis of Plasmon Loss Peaks of Oxides and Semiconductors with the Energy Loss Function.

This paper highlights the use and applications of the energy loss function (ELF) for materials analysis by using electron energy loss spectroscopy (EELS). The basic Drude-Lindhart theory of the ELF is briefly presented along with reference to reflection electron energy loss (REELS) data for several dielectric materials such as insulating high-k binary oxides and semiconductors. Those data and their use are critically discussed. A comparison is made to the available ab initio calculations of the ELF for these materials. Experimental, high-resolution TEM-EELS data on Si, SiC, and CeO2 obtained using a high-resolution, double-Cs-corrected transmission electron microscope are confronted to calculated spectra on the basis of the ELF theory. Values of plasmon energies of these three dielectric materials are quantitatively analyzed on the basis of the simple Drude's free electron theory. The effects of heavy ion irradiation on the TEM-EELS spectra of Si and SiC are addressed. In particular, the downward shifts of plasmon peaks induced by radiation damage and the subsequent amorphization of Si and SiC are discussed. TEM-EELS data of CeO2 are also analyzed with respect to the ELF data and with comparison to isostructural ZrO2 and PuO2 by using the same background and with reference to ab initio calculations.

Brittle-to-ductile transition in nanoscratching of silicon and gallium arsenide using Berkovich and Conical tips

Determining the brittle-to-ductile transition (BDT) threshold is crucial for developing efficient machining processes for brittle materials. In this study, nanoscratch tests were performed on the (001) face of single-crystal silicon (Si) and gallium arsenide (GaAs) using a sharp Berkovich and a blunt Conical tip. The aim was to understand the effects of tip shape and microstructural variation on their BDT behaviour. The result showed that the critical cutting depth for BDT (dc) was affected by not only material microstructure but also tip shape. The stress distribution within the deformed sublayer varied with tip shape, ultimately impacting the microstructure evolution and thus deformation/removal mechanism. Using the sharp tip, Si had a slightly smaller dc than GaAs due to the ease of cracking along the {111} plane. In contrast, with the blunt tip GaAs had a smaller dc than Si, attributed to its relatively high brittleness index and higher density of crystallite defects. The defects in GaAs caused strain hardening and hence reduced ductility, while the amorphization of Si enhanced its ductility.

Tuning the defects density in additively manufactured fcc aluminium alloy via modifying the cellular structure and post-processing deformation

In this study, using an L-PBF AlSi10Mg alloy with different microstructural properties, the typical structural defects caused by severe plastic deformation are investigated by scanning electron microscopy and high-resolution transmission electron microscopy. Microscopic characterization shows that the deformed L-PBF AlSi10Mg alloy exhibits a heterogeneous microstructure consisting of Al/Si interfaces and a high density of dislocations, stacking faults, and nanotwins. On the basis of experimental data, it is also shown that high stresses build up at the Al/Si interface due to incompatible deformation, enabling the activation of novel deformation modes that control the plastic deformation of the hard Si twin phase and amorphization in the solid state. The revealed synergy and novel deformation modes open a new horizon for the development of next-generation structural materials and provide insights into the atomically resolved structures of dislocations and GBs in nanostructured L-PBF alloys.

Experimental and molecular dynamic studies of phase transformation and amorphization in silicon during high-energy ball milling

Nano-sized and amorphous silicon (α-Si) have a wide range of properties and applications, but their atomistic structure and the process of crystal evolution are still unclear. In this study, a combined action is used to present a mechanism for the crystal-to-amorphous solid–solid phase transition in silicon during mechanical alloying (MA) at room temperature. For this purpose, the ball milling of silicon was performed and changes in crystallographic structure and amorphous phase were studied by scanning electron microscopy (SEM), X-ray diffraction patterns (XRD), and energy dispersive X-ray spectroscopy (EDX). The process of changing phase was determined by quantitative phase analysis (MAUD/Rietveld refinement). In the simulation part, a crystal structure of silicon consisting of 64 atoms was created and uniaxial and biaxial external pressures were applied randomly by BIOVIA Materials Studio. The time step and simulation time were 1 and 300 Ps, respectively. Important atomic properties including density, mean square displacement (MSD), angle length and bonds distribution, and the fraction of broken bands were measured after applying per compression. Atomic structure and changes in crystalline phase to nano and amorphous phases were studied and these results had a considerable agreement with the experimental part and well-known previous studies. The diamond cubic structure shows a remarkable toughness during the modeling and so amorphization was performed at an exponential evolution. The Results of the simulations showed that the bond angle and length distribution and MSD, were increased significantly, and in contrast, density was decreased to 1.254 g/cm3. The percentage of the broken Si-Si bonds was 58.12 % and a new definition of Si amorphization based on the fraction of covalent bonds was proposed. The amorphization started from the surface of Si and spread by the partial distribution toward the crystal structure. These findings show that the proposed mechanism based on the fraction of breaking bonds and pressure-induced amorphization could be used for the accurate simulation of the solid–solid phase transformation.

A model for spectroscopic ellipsometry analysis of plasma-activated Si surfaces for direct wafer bonding

In this work, the impact of plasma treatment on Si wafers with native oxide on top was systematically investigated using spectroscopic ellipsometry. A general applicable three-layer optical model structure for ellipsometry data fitting was developed and employed on samples treated with the N2, O2, and N2/O2 mixture plasma. Oxide-growth, amorphization of crystalline Si, and the formation of a transition layer between the SiO2 and the amorphous Si were detected. The estimated thicknesses of produced layers were confirmed by complementary methods, which allow precise ultra-thin layers thicknesses detection, namely, angle-resolved x-ray photoelectron spectroscopy and transmission electron microscopy. The depth-resolved chemical composition and the direct thickness measurements of the produced amorphous structure revealed pronounced elemental gradients and the absence of sharp interfaces. Nitrogen gas used in the plasma process was found to be implanted mainly at the interface of the SiO2/transition layer in the form of Si3N4. However, it was verified that it is feasible to employ one general ellipsometry model consisting of SiO2/transition layer/amorphous Si on crystalline Si for all plasma species due to comparably low Si3N4 concentrations as well as its refractive index n and absorption k similarity to SiO2. Spectroscopic ellipsometry is nondestructive and can be efficiently applied to analyze whole wafers without any sample preparation. It can be concluded that the present approach to ellipsometry model development and verification is well suited for plasma-activated direct wafer bonding processes.

Very-high-cycle fatigue induced growth and amorphization of Si particles in additively manufactured AlSi10Mg alloy: Dependence of applied stress ratio

The microstructural evolution at the fracture surface in response to very-high-cycle fatigue (VHCF) under stress ratios (R) of −1 and 0.5 in an AlSi10Mg alloy produced by Laser Powder Bed Fusion was investigated. The results show that appreciable growth of the Si precipitates at the cellular network boundaries in the as-built microstructure was observed under R = −1. Moreover, significant amorphization of the initial crystalline Si precipitates occurred in the vicinity of the fracture surface under this condition. A layer of fine Al grains was developed in the “fish-eye” region of the fracture surface. These microstructural responses are rationalized by the generation of lattice defects including dislocations and sub-grain boundaries during cyclic pressing of crack surfaces under R = −1, which mediates the Si solute diffusion and re-precipitation in the alloy as well as the amorphization of initial Si crystalline precipitation. In contrast, far fewer dislocations were observed near the crack surfaces under R = 0.5, which is attributed to the absence of cyclic pressing of crack surfaces and severe plastic deformation in this scenario. This work provides insights into the stress ratio dependence of the microstructural evolution in the fatigued Al alloys. The obtained knowledge is useful for future understanding of the fatigue failure in Al alloys produced by additive manufacturing.

Structural analysis of high-energy implanted Ni atoms into Si(100) by X-ray absorption fine structure spectroscopy

Ni silicide synthesis by Ni ion beam irradiation into Si attracts attention due to its advantages including the ability of formation of local structures, the controllability of ion beams, the formability of silicide without heat treatment and the high reproducibility of the resulting specimen. In this work, we investigate the local atomic structure of Si implanted with 3.0 MeV Ni+ ions. Analysis of Ni K-edge fluorescent-yield extended X-ray absorption fine structure reveals that Ni atoms have mixed structure of metallic-like face-centered cubic Ni and NiSi2 phases at the initial stage of the irradiation and the formation of NiSi2 promotes significantly with the ion fluence above 1015 ions⋅cm−2. With consideration of the agreement between the ion fluence threshold for the structural transition and the critical Si-amorphization fluence (7.1 × 1014 ions⋅cm−2), it is concluded that the amorphization of Si plays an important role in the synthesis of the NiSi2 phase in Ni+-irradiated Si.

Influence of Covalent Element B and Si Addition on Magnetocaloric Properties of Gd-Co-Fe-(B,Si) Amorphous Alloys

The effect of covalent element addition on the magnetic and magnetocaloric properties of ferrimagnetic Gd60Co20Fe20 amorphous alloy was studied. Particularly, the co-doping of B and Si promoted the magnetocaloric performance (with a larger magnetic entropy change |ΔSM| at higher working temperature) of the initial Gd60Co20Fe20 amorphous alloy. This is possibly ascribed to the modified magnetic transition behavior. Additionally, the broadened magnetocaloric effect with |ΔSM| of 2.25 J kg−1 K−1 at 222.5 K under a magnetic field change of 0–2 T and high relative cooling power of 396.0 J kg−1 were obtained for (Gd0.6Co0.2Fe0.2)95B2Si3. These properties reveal that the material could be a good candidate as a magnetic refrigerant suitable for active magnetic refrigerators.

Nanoporous Pd–Cu–Si Amorphous Thin Films for Electrochemical Hydrogen Storage and Sensing

Increasing the efficiency of hydrogen storage and release using recent generation metallic glass nanofilms (MGNFs) offers green solutions for nanoscale energy applications. Contrary to flat nanofil...

Nano-scale depth-varying recrystallization of oblique Ar+ sputtered Si(111) layers

Silicon, the workhorse of semiconductor industry, is being exploited for various functional applications in numerous fields of nanotechnology. In this paper, we report the fabrication of depth controllable amorphous silicon (a-Si) layers under 80 keV Ar+ ion sputtering at off-normal ion incidences of 30°, 40° and 50° and crystallization of these amorphous Si(111) layers under thermal annealing. We find that the irradiated samples were not fully amorphized even for the lowest oblique incidence of 30°. Sputtering at off-normal incidences induces depth controllable surface amorphization in Si(111). Annealing at temperature of 1,073 K is characterized by formation of depth-varying buried amorphous layer due to defect recrystallization and damage recovery. Some remnant tensile stress has been observed for recrystallized samples even for lowest oblique incidence. The correlation of amorphization and stress due to sputtering induced by oblique incidence has been discussed systematically. The possible mechanism of recrystallization is discussed in terms of vacancies produced in sputtering dominated regime and their migration during annealing treatment. Our results reveal that with appropriate selection of oblique ion beam sputtering parameters, depth controllable surface amorphization and recrystallization may be fine-tuned to achieve co-existing amorphous and crystalline phases, playing a crucial role in fabrication of substrates for IC industry.

Fractal characterizations of energetic Si ions irradiated amorphized‐Si surfaces

The fractal characterizations of amorphized‐silicon (a‐Si) surfaces under low‐energy ion irradiations are presented. The crystalline Si surfaces have been irradiated with Si ions having different energy of 35, 50, 75, and 100 keV at a fixed fluence of 2 × 1015 ions‐cm−2. The samples have been characterized by means of using Raman spectroscopy, Channeling‐Rutherford backscattering spectrometry (C‐RBS), and atomic force microscopy (AFM) techniques. The ion irradiation leads to the amorphization of Si near surface and subsurface region, as confirmed by Raman and C‐RBS measurement. The AFM analysis shows that the ion irradiation also leads to the formation of nanodots on the surface and size of the dots increases with increasing of the ion energy. The fractal analysis has been performed using AFM images in order to get the significant evidence about nanodot formations and the correlation inside the surface microstructures. The kinetic roughening and surface smoothening, due to dissipation of kinetic energy of ions through collision cascades of the surface atoms, lead to the formation of dot‐like structures.

Carbon Coated Si-Metal Silicide Composite Anode Materials Prepared by High-Energy Milling and Carburization for Li-Ion Rechargeable Batteries

In this article, we report a novel Si-Metal silicides/Carbon composite anode material for lithium-ion rechargeable batteries. The composite powder comprised of Si, FeSi2 and CrSi2 were synthesized by high-energy mechanical milling and then a primary carbon was formed over the Si-silicide at 900°C. The prepared composite powder was agglomerated and subsequently a thin carbon layer was coated. The X-ray diffraction results revealed that the Si and silicide crystal size decrease with respect to milling time. The critical milling time to achieve the completely nano-scale powders was 5 h. The composite powder exhibits randomly distributed carbon-coated Si-silicide. The TEM microstructure revealed homogeneous distribution of nanocomposite powder consists a very fine nanoparticles of the order of ∼30 nm. The prepared Si-silicide/C composite powders exhibited good capacity retention with an average coulombic efficiency of 99.6%. The composite powders showed good cyclability, 1076 mAh g−1 at 50th cycle and 959 mAh g−1 at 100th cycle. The electrode internal microstructure revealed a shell-like carbon-coated Si-silicide phases, and a complete amorphization of nanocrystalline Si during the initial cycling, while the inactive silicide phase remains unchanged. Consequently, the size reduction of Si-silicide and carbon coating over it greatly enhanced the cycling performance of the electrode.

Oscillatory magnetic behavior in an ion-irradiated Si/Ni/Si sandwich system

We have investigated the evolution of magnetic behavior with ion fluence in ion irradiation of a Si/Ni/Si sandwich system. An oscillatory behavior of the saturation magnetic moment and the coercive field has been observed with increasing ion fluence. As reported earlier, with increasing ion fluence, this system also shows an oscillatory amorphization and recrystallization of the Si substrate on which the Ni layer was grown. Ion beam induced Ni redistribution, associated with the oscillatory behavior of amorphization and recrystallization of Si, appears to be responsible for the oscillatory magnetic behavior in the sandwich structure.

Si amorphization by focused ion beam milling: Point defect model with dynamic BCA simulation and experimental validation

A Ga focused ion beam (FIB) is often used in transmission electron microscopy (TEM) analysis sample preparation. In case of a crystalline Si sample, an amorphous near-surface layer is formed by the FIB process. In order to optimize the FIB recipe by minimizing the amorphization, it is important to predict the amorphous layer thickness from simulation. Molecular Dynamics (MD) simulation has been used to describe the amorphization, however, it is limited by computational power for a realistic FIB process simulation. On the other hand, Binary Collision Approximation (BCA) simulation is able and has been used to simulate ion-solid interaction process at a realistic scale. In this study, a Point Defect Density approach is introduced to a dynamic BCA simulation, considering dynamic ion-solid interactions. We used this method to predict the c-Si amorphization caused by FIB milling on Si. To validate the method, dedicated TEM studies are performed. It shows that the amorphous layer thickness predicted by the numerical simulation is consistent with the experimental data. In summary, the thickness of the near-surface Si amorphization layer caused by FIB milling can be well predicted using the Point Defect Density approach within the dynamic BCA model.

Facile Synthesis and Electrochemistry of Si-Sn-C Nanocomposites for High-Energy Li-Ion Batteries

Si-Sn-C nanocomposites were synthesized via a facile mechanical milling method. Phase composition and morphologies of the as-produced Si-Sn-C nanocomposites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy. Both XRD and Raman studies revealed the amorphization of Si after mechanical milling process, while Sn remained as the crystalline phase in both Si-Sn and Si-Sn-C nanocomposites. Meanwhile, the particle size was significantly reduced, but Si tended to agglomerate during the milling and it was alleviated through the addition of carbon. The galvanostatic charge/discharge measurements were carried out to evaluate the electrochemical performance. Compared to milled Si, Si-Sn nanocomposites, Si-Sn-C nanocomposites exhibited a higher initial capacity of ∼1000 mAh/g, and its capacity was retained at ∼80% after 50 cycles. The possible buffering effect of Sn and carbon at different operating potentials during the lithiation/delithiation process was discussed.

Atomic layer deposition and high-resolution electron microscopy characterization of nickel nanoparticles for catalyst applications

Abstract Ni nanoparticles (diameter 2 ) and H 2 O as precursors. In the second step, the NiO films are reduced in H 2 atmosphere at 400–800 °C. The size of the resulting Ni nanoparticles is controlled by the temperature. The largest particles with a diameter of about 7 nm are obtained at 800 °C. NiO film and Ni nanoparticles deposited on Si substrates are characterized by high-resolution electron microscopy. It was found that the Ni(MeCp) 2 precursor reacts with the substrate, leading to the formation of NiSi 2 precipitates beneath the surface of the Si wafer and amorphization of the surrounding area, resulting in a 10 nm thick top layer of the Si wafer. After reductive annealing, NiSi 2 precipitates are preserved but Si recrystallizes and the amorphous NiO film transforms into crystalline Ni nanoparticles well distributed on the wafer surface. Process parameters were optimized for Si substrates and transfer of the process to ceramic LST/YSZ substrates is possible in principle. However, a much higher number of ALD cycles (1200 compared to 100 for Si) are necessary to obtain Ni nanoparticles of similar size and the number density of particles is lower than observed for Si substrates.

Investigating 64Zn+ ion-doped silicon under conditions of hot implantation

The results from visualizing the structure and identifying the composition of surface and the nearsurface layers of CZ n-Si (100) implanted by 64Zn+ ions with dose of 5 × 1016 cm–2 and energy of 50 keV under conditions of a substrate heated to 350°C are presented. It is found that there is no Si amorphization after Zn implantation, and only one layer 200 nm thick forms and is damaged because of radiation-induced defects. Zn nanoparticles 10–100 nm in size are found on a sample’s surface and in its near-surface layer. Computer analysis and mapping of the elemental and phase composition of FIB crater walls and the surface show that the main elements (54%) in the sample near-surface layer are Si, O, and Zn. The presence of ZnO phase is recorded to a depth of 20 nm in the sample.

Ordered arrays of Au catalysts by FIB assisted heterogeneous dewetting

Synthesizing Au0.8Si0.2 nanocatalysts that are homogeneous in size and have controlled position is becoming a challenging and crucial prequisite for the fabrication of ordered semiconductor nanowires. In this study, Au0.8Si0.2 nanocatalysts are synthesized via dewetting of Au layers on Si(111) during thermal annealing in an ultra-high vacuum. In the first part of the paper, the mechanism of homogeneous dewetting is analyzed as a function of the Au-deposited thickness (hAu). We distinguish three different dewetting regimes: (I) for a low thickness (), a submonolyer coverage of Au is stabilized and there is no dewetting. (II) For an intermediate thickness (), there is both dewetting and Au0.8Si0.2 phase formation. The size and density of the Au0.8Si0.2 clusters are directly related to hAu. When cooling down to room temperature, the clusters decompose and reject the Si at the Au/Si substrate interface. (III) For a large thickness (), only dewetting takes place, without forming AuSi clusters. In this regime, the dewetting is kinetically controlled by the self-diffusion of Au (activation energy ∼0.43 eV) without evidence of an Si-alloying effect. As a practical consequence, when relying solely on the homogeneous dewetting of Au/Si(111) to form the Au0.8Si0.2 catalysts (without a supply of Si atoms from vapor), regime II should be used to obtain good size and density control. In the second part of the paper, a process for ordering the catalysts using focused ion beam-(FIB) assisted dewetting (heterogeneous dewetting) is developed. We show that no matter what the FIB milling conditions and the Au nominal thickness are, dewetting is promoted by ion beam irradiation and is accompanied by the formation of Au0.8Si0.2 droplets. The droplets preferentially form on the patterned areas, while in similar annealing conditions, they do not form on the unpatterned areas. This behavior is attributed to the larger Au-Si interdiffusion in the patterned areas, which results from the Si amorphization induced by the FIB. A systematic analysis of the position of the nanodroplets shows their preferential nucleation inside the patterns, while thicker platelets of almost pure Au are observed between the patterns. The evolutions of the size homogeneity and the occupancy rate of the patterns are quantified as a function of the FIB dose and annealing temperature. Nice arrays of perfectly ordered AuSi catalysts are obtained after optimizing the FIB and dewetting conditions.