Formation Of Amorphous Regions Research Articles

Ion Dynamics in Nanocrystalline Li2S‐LiI – on the Influence of Local Disorder on Short‐Range Hopping and Long‐Range Ion Transport

The enormous interest in developing powerful Li‐based batteries leads to a boost in materials research. Though Li–sulfur batteries offer very high energy densities, the nature of Li‐ion dynamics in the final discharge product has not been fully understood yet. While nanocrystalline shows enhanced ion dynamics compared to its coarse‐grained counterpart, the interaction of with another binary such as LiI seems to be rather unexplored. Herein, an equimolar mixture of and LiI is treated in a high‐energy ball mill, and both the overall and local structural changes are studied by X‐ray powder diffraction and nuclear magnetic resonance (NMR), respectively . Besides the formation of amorphous regions, evidences are found for the generation of anion‐mixed sites that give rise to facile Li exchange on the 2D exchange NMR timescale. Compared to a coarse‐grained reference sample, the overall (bulk) ionic conductivity of nanocrystalline ‐LiI increases by two orders of magnitude. Besides the anion‐mixing effect, this increase benefits from nanosize effects that include the formation of defect‐rich interfacial regions. NMR relaxation measurements fully support this result and reveal heterogeneous dynamics with lower activation energies for both the localized hopping processes and long‐range ion transport in nm‐sized ‐LiI.

The role of halloy site on crystallinity, ion conductivity, thermal and mechanical properties of poly(ethylene-oxide)/halloysite nanocomposites

Halloysite nanotubes were applied as an inorganic filler to prepare poly(ethylene-oxide)/halloysite (PEO/halloysite) nanocomposites for the purpose of increasing the ion conductivity of PEO matrix. The resulting PEO/halloysite nanocomposites were characterized by X-ray diffraction (XRD), Fourier Transfer infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), ion conductivity test, thermogravimetry analysis (TG) and mechanical properties test. SEM and TEM micrographs confirmed the good dispersion of halloysite nanotubes in PEO matrix. FTIR spectroscopy showed that the interaction between PEO and halloysite changed the ether oxygen vibrational modes of PEO. XRD and DSC results indicated that the PEO crystallinity gradually decreased with the increment of halloysite concentration. Meanwhile, the reduced PEO crystallinity promoted the improvement of ion conductivity and the maximum value (3.8 × 10−5 S/cm) appeared at a halloysite concentration of 20 wt%. The formation of amorphous region around halloysite is beneficial for the Li+ ion conduction. Furthermore, the tensile strength of PEO/halloysite nanocomposites was enhanced when halloysite was introduced into the polymer matrix with filler loading no more than 10 wt%.

The role of exfoliated kaolinite on crystallinity, ion conductivity, thermal and mechanical properties of poly(ethylene oxide)/kaolinite composites

Kaolinite particles were exfoliated by the intercalation and subsequent deintercalation of urea in the interlayer of kaolinite. The exfoliated kaolinite particles were used to prepare a novel poly(ethylene oxide)/kaolinite (PEO/kaolinite) composite. The resulting exfoliated kaolinite and PEO/kaolinite composites were characterized by X-ray diffraction (XRD), Fourier transfer infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), ion conductivity test, thermogravimetry (TG) analysis and mechanical test. XRD results showed that the 001 diffraction of kaolinite in the XRD pattern almost disappeared after exfoliation treatment. FTIR spectra showed that the inner surface hydroxyls of kaolinite decreased after exfoliating kaolinite layers. SEM micrographs confirmed the exfoliation of kaolinite particles and showed a good dispersion of exfoliated kaolinite in PEO matrix. A gradual decrease in PEO crystallinity in PEO/kaolinite composites was observed with the increment of the exfoliated kaolinite concentration by DSC test. The ion conductivity of the composites gradually increased with exfoliated kaolinite content and reached 6.1 × 10−5 (S/cm) at a filler concentration of 20 wt%. The formation of amorphous region around the exfoliated kaolinite was beneficial for the Li+ ion conduction. Thermogravimetry analysis showed that the decomposition temperature of PEO matrix at weight loss of 10 and 50 wt% was increased when exfoliated kaolinite was introduced into PEO matrix. In addition, the mechanical properties of PEO matrix were also enhanced when exfoliated kaolinite content in PEO matrix was no more than 15 wt%.

Formation of the nanostructure in amorphous alloys of the Al-Ni-Y system

The formation of the amorphous-nanocrystalline structure during the crystallization of metallic glasses of the Al-Ni-Y system has been investigated by X-ray diffractometry, differential scanning calorimetry, and transmission electron microscopy. It has been shown that the crystallization onset temperature depends on the chemical composition of the alloy, and the crystallization is accompanied by changes in the structure of the amorphous phase, such as the phase separation and the formation of amorphous regions of various compositions with different short-range orders. The nanocrystals nucleate in the amorphous phase by the heterogeneous mechanism. It has been found that the size of precipitated aluminum nanocrystals depends on the alloy composition. The amorphous-nanocrystalline structure formed during the thermal treatment is stable and remains unchanged during the isothermal annealing at 150°C for 500 h.

Classical molecular dynamic simulation of (111) Si and Al surface sputtering under bombardment by polyatomic clusters

The self-sputtering processes of (111) Si and Al surfaces under bombardment by SiN and AlN ions and clusters (N = 1−60) with the same energy per particle-projectile atom (1 keV/atom) are studied in this paper. The nonlinear effects produced in the target during the development stage of an atomic-collision cascade and during the postcascade stage are analyzed, and a correlation between these effects and secondary emission characteristics is found. The study has been carried out in the framework of classical molecular dynamics. As a result, a number of features of (111) Si and Al surface sputtering and erosion have been revealed. Thus, it has been established that the sputtering yield increases nonadditively as the size N of the implanted cluster increases at N > 10, which is related to the appearance of nonlinear cascades and the postcascade heat spike, and is accompanied by microcrater formation. It is shown that the implantation of clusters into the Si target leads to the formation of amorphous regions.

Simulation of doping and primary radiation damage to the SiC(111) surface under bombardment by Si N atomic and cluster ions (N = 1, 5, and 60) using classical molecular dynamics

The features of the cascade of atomic collisions, the spatial distribution of dopes, and primary radiation damage in a near-surface region of cubic silicon carbide under bombardment by SiN ions and clusters (N = 1, 5, and 60) in the case of the same energy per one atom of the particle-projectile (200 and 1000 eV/atom) are studied in this paper. The study is carried out using classical molecular dynamics. As a result, several features of the low-energy implantation of polyatomic clusters in SiC(111) are revealed, namely, a relatively weak effect of the size of the implanted cluster on the distribution of ranges of incorporated atoms, a low degree of nonlinear effects at the cascade and postcascade stages, and formation of amorphous regions in the target during cluster implantation.

Disorder-Recrystallization Effects in Low-Energy Beam-Solid Interactions

It is widely believed that high-kinetic-energy (>1 keV) recoils in crystalline Si result in the formation of amorphous regions, whereas low-kinetic-energy recoils lead directly to isolated point defects. Here we study the response of a Si crystal using dynamical density-functional calculations and show that recoils of much less than 1 keV result in highly disordered regions that persist for hundreds of femtoseconds. Therefore, beam-induced defect formation is controlled by recrystallization processes during dynamic annealing even following low-energy ion implantation.

The Effect of Implanted Gallium on the Recrystallization of Amorphous Layers formed during FIB Milling of Silicon

The focused ion beam (FIB) miller allows preparation of site-specific transmission electron microscopy (TEM) specimens from a wide range of materials in both cross-sectional and planar configurations [1,2]. However, radiation damage during exposure to the high-energy gallium beam may result in the formation of amorphous regions on thin film specimens. The thickness of such damage layers, on both sides of a TEM specimen, is comparable with the thickness required for lattice imaging. For example, the thickness of an amorphous layer in Si after 30 kV Ga+FIB processing has been reported in the range from 15 [3] to 28 nm [4]. This problem limits the capabilities of FIB sample fabrication.The aim of this study was to investigate, in detail, the structure, composition and the thickness of the damage layers in Si specimens after milling with a gallium ion beam. Using a FEI xP200 FIB system, with 30 kV Ga+ions, a row of trenches on a silicon sample was milled under different beam currents ranging from 150 to 6600 pA. The average size of such trenches was 15×10 μm wide and 1 μm deep. The trenches were then removed from the FIB and sputter coated with a thick Au film to preserve the trench surfaces from further damage during subsequent TEM specimen preparation steps. Cross-sectional TEM specimens of the trench walls were then prepared using standard FIB procedures [5]. Observations were made using a Philips CM 200 Field Emission Gun TEM operating at an accelerating voltage of 200 kV.

Atomistic Modeling of Amorphization in Silicon

ABSTRACTWe discuss atomistic simulations of ion implantation and annealing of Si over a wide range of ion dose and substrate temperatures. The DADOS Monte Carlo model has been extended to include the formation of amorphous regions, and this allows simulations of dopant diffusion at high doses. As the dose of ions increases, a continuous amorphous layer may be formed. In that case, most of the excess interstitials generated by the implantation may be swept to the surface as the amorphous layer regrows, instead of diffusing through the crystalline region. This process reduces the amount of transient enhanced diffusion during annealing. This model also reproduces the dynamic annealing during high temperature implants.

Properties of high-strength polyethylene fibre undergoing radiochemical modification

Irradiation of ultrahigh-molecular-weight polyethylene (UMWPE) with low doses of γ-quanta in a polymerization-active gas (ethylene, acetylene) increases its thermostability. Minimal loss of the mechanical characteristics of the fibre is observed in irradiation in acetylene with doses up to 0.5 Mrad. The increase in the thermostability of the irradiated fibre is due to the formation of amorphous regions of cross-linked structure which are partially preserved in isothermal heating to 180°C.

B+, P+, AS+ and Si+ Ion Implantation Induced Defects in Silicon Studied by a Variable-Energy Positron Beam

ABSTRACTVacancy type defects introduced by As+, P+, Si+ and B+ ion implantations into Si (100) single crystals were studied by a variable-energy positron beam. Depth distributions of the defects were obtained from measurements of Doppler broadening profiles of the positron annihilation as a function of incident positron energy. The results showed that this technique is sensitive not only to a vacancy type defect but to formation of amorphous regions. The defects introduced by lower doses were identified as vacancy clusters from isochronal annealing experiments. By higher doses such as 5×1014 /cm2, amorphous layers were formed for 150KeV As+, 150KeV P+, and 200KeV Si+ ions, and it was not formed for 80KeV B+ by the dose of 5×1015 /cm2. These results are consistent with the calculated critical doses. In the case of B+, pre-amorphous formation was observed with higher ion beam current over 5mA and a dose of 5×1015 /cm2.

TEM characterization of phosphorus-implanted silicon

Implantation of dopant-species into silicon can result in the formation of amorphous regions, interfaces and extended defects (in the silicon). The presence of these defects can cause modification of dopant distributions, and the rise of leakage currents in p-n junctions. An understanding of the behavior of implant-induced defects and their effect on dopant-distributions is therefore relevant. Such understanding could lead to better defect and dopant control and therefore to more reliable device performance. In this study, a correlation between dopant distributions and damage in implanted silicon, is investigated.The samples investigated were p-type (14-20 Ω-cm) silicon (100) wafers implanted with phosphorous at 180 kev to a dose of 1x1016 cm-2. The implants were performed at room temperature. Post-implant annealing was performed (by rapid-thermal annealing “RTA“) at 800°C for 15 seconds. SIMS (secondaryion mass-spectrometry) and XTEM (cross-section TEM) analysis were performed on as-implanted and annealed samples. Cross-section TEM specimens were made in the 110 geometry. TEM investigation was performed using a JEOL JEM 200CX transmission electron microscope operating at 200 kV. SIMS analysis was performed using an Atomika A-DIDA quadropole instrument with 8 keV O2+ primary ions.

Atomic structure of ion implantation damage and process of amorphization in semiconductors

Atomic structure of ion implantation damage and the process of amorphization in silicon have been investigated using high-resolution electron microscopy techniques. The specific damage energy density for crystalline to amorphous transition has been determined to be 6.0×1023 eV/cm3 or 12 eV/atom at 4 K with no annealing. The amorphous regions are produced when the damage energy deposited by the ions exceeds this critical value. Since the damage energy deposited by the ions is a strong function of ion implantation and substrate variables, the formation of amorphous regions and the process of amorphization are strong functions of these variables. The details of atomic structures of amorphous silicon containing microcrystallites and that of amorphous-crystalline interfaces are presented. The calculations of the mean-free path between collisions and the energy deposited per atom are found to be consistent with experimental observations on amorphization of silicon. Some results on the projected ranges of low-energy recoils, which are primarily responsible for the production of amorphous cascades, are presented. The solid-phase crystallization phenomena and the role of microcrystallites during the crystallization process are discussed.