Rod-like Defects Research Articles

3D Visualization of Morphological Evolution of Large Defects during Spark Plasma Sintering of Alumina Granules

The mechanical reliability of products must be assured for scaling up and production of complex‐shaped components by spark plasma sintering (SPS) of spray‐dried granules. The evolution of morphologies of pores and defects, which control the mechanical strength, is investigated by using synchrotron X‐ray multiscale tomography during SPS of alumina granules at 1300 °C. While large defects arising from the hierarchical granule packing structure cannot be removed by pressureless sintering, crack‐like defects and branched rodlike defects are almost eliminated by SPS at stresses higher than 30 and 50 MPa, respectively. But, small ellipsoidal porous regions, which may arise from aggregates or dimples of granules, cannot be removed even at a pressure of 50 MPa. A very large defect is also found by using micro‐CT. It is supposed that this defect is formed from a large void in loosely packed granules. The shrinkage of large voids and the elimination of crack‐like defects are explained by the theoretical prediction based on the continuum theory of sintering.

Atomic structures and stability of finite-size extended interstitial defects in silicon: Large-scale molecular simulations with a neural-network potential

The energetics of various extended interstitial (I) defects in crystalline Si is examined by constructing an artificial-neural-network (ANN) potential trained with density-functional-theory (DFT) data, enabling us to perform accurate large-scale simulations and to obtain well-converged formation energies (Ef). By varying the number of interstitials n to around 1,000, Ef is calculated for the compact cluster, I12-like, (001)-plane, (311)-rod-like and Frank-loop defects. For n ≤ 36, the compact cluster or (311)-rod-like defect is found to be most stable, depending on n. This trend strongly depends on simulation cell sizes, suggesting the importance of sufficiently large cells. For 36 < n ≲ 860, the (311)-rod-like defect is most stable whereas the Frank-loop defect becomes most stable for larger n. The ANN potential is demonstrated to outperform empirical potentials in prediction of Ef and defect structures. Furthermore, ANN values of Ef are fitted to analytic functions with the aim of refining macroscopic simulations for device manufacturing processes.

Microstructure Evolution in He-Implanted Si at 600 °C Followed by 1000 °C Annealing.

Si single crystal was implanted with 230 keV He+ ions to a fluence of 5 × 1016/cm2 at 600 °C. The structural defects in Si implanted with He at 600 °C and then annealed at 1000 °C were investigated by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The microstructure of an as-implanted sample is provided for comparison. After annealing, rod-like defects were diminished, while tangled dislocations and large dislocation loops appeared. Dislocation lines trapped by cavities were directly observed. The cavities remained stable except for a transition of shape, from octahedron to tetrakaidecahedron. Stacking-fault tetrahedrons were found simultaneously. Cavity growth was independent of dislocations. The evolution of observed lattice defects is discussed.

Defect structure and properties of Zn diffusion doped Si after swift Xe ion irradiation

The electronic and optical properties of Si doped by Zn diffusion have been studied for a long time. Recently the defect structure and properties of n-Si (111) compensated by Zn during high-temperature diffusion annealing with subsequent quenching were investigated. The large-scale rod-like defects with μ-sizes have been observed. These defects were connected with Zn precipitates or/and dislocations. In the present paper we study the modification of defect structure and properties of Zn diffusion doped Si after swift heavy ion (SHI) irradiation. The SHI irradiation is known to lead to the formation of latent tracks (nanometer-sized disordered regions around ion trajectory) in many semiconductor and oxide crystals. It was established that the craters with a size of about 100nm surrounded by hillocks are fixed on the Si surface. The traces of dislocation group along Xe ion beam direction were revealed on Si surface. The small-angle boundaries and interstitial-type planar defects have appeared. After Xe ion irradiation with a fluence of 5×1012 cm−2 the number of radiating centres in dislocation core increasing so, that increasing the dislocation-related luminescence (DRL) from the lines D1 and D2. When the Xe ion irradiation fluence is increased to a value of 1×1014 cm−2 the DRL in the Si sample is almost extinguished.

Structure and growth of core–shell nanoprecipitates in Al–Er–Sc–Zr–V–Si high-temperature alloys

Lightweight Sc-containing aluminum alloys exhibit superior mechanical performance at high temperatures due to core–shell, L12-ordered trialuminide nanoprecipitates. In this study, the structure of these nanoprecipitates was studied, using different transmission electron microscopy (TEM) techniques, for an Al–Er–Sc–Zr–V–Si alloy that was subjected to a two-stage overaging heat treatment. Energy-dispersive X-ray spectroscopy of the spherical Al3(Sc, Zr, Er ,V) nanoprecipitates revealed a core–shell structure with an Sc- and Er-enriched core and a Zr-enriched shell, without a clear V outer shell. This structure is stable up to 72% of the absolute melting temperature of Al for extended periods of time. High-angle annular dark-field scanning TEM was used to image the {100} planes of the nanoprecipitates, demonstrating a homogeneous L12-ordered superlattice structure for the entire nanoprecipitates, despite the variations in the concentrations of solute atoms within the unit cells. A possible growth path and compositional trajectory for these nanoprecipitates was proposed using high-resolution TEM observations, where different rod-like structural defects were detected, which are considered to be precursors to the spherical L12-ordered nanoprecipitates. It is also hypothesized that the structural defects could consist of segregated Si; however, this was not possible to verify with HAADF-STEM because of the small differences in Al and Si atomic numbers. The results herein allow a better understanding of how the Al–Sc alloys’ core–shell nanoprecipitates form and evolve temporally, thereby providing a better physical picture for future atomistic structural mappings and simulations.

Transmission electron microscopy and high-resolution electron microscopy studies of structural defects induced in Si single crystals implanted by helium ions at 600 °C

The implantation-induced defects of crystalline silicon implanted with helium ions to a dose of 5 × 1016/cm2 at 600 °C were investigated. The sample was analyzed by transmission electron microscopy and high-resolution electron microscopy. Faceted cavities are observed in the damaged layer. Concurrently the distribution of interstitial-type defect clusters was investigated by conventional electron microscopy in bright and dark field. Many rod-like defects, which belong to {1 1 3}, {1 1 1} and (−2 0 0), are formed in the end of the projected range. In front of the damaged layer, some ribbon-like defects are formed, which belong to 〈2 0 0〉, 〈1 −1 1〉 and 〈1 3 −3〉. The possible reasons of the observed defect clusters are discussed.

Identification of Extended Defect Atomic Configurations in Silicon Through Transmission Electron Microscopy Image Simulation

We used atomistic simulation tools to correlate experimental transmission electron microscopy images of extended defects in crystalline silicon with their structures at an atomic level. Reliable atomic configurations of extended defects were generated using classical molecular dynamics simulations. Simulated high-resolution transmission electron microscopy (HRTEM) images of obtained defects were compared to experimental images reported in the literature. We validated the developed procedure with the configurations proposed in the literature for {113} and {111} rod-like defects. We also proposed from our procedure configurations for {111} and {001} dislocation loops with simulated HRTEM images in excellent agreement with experimental images.

On the origin of dislocation loops in irradiated materials: A point of view from silicon

Numerous dislocation loops are often observed in irradiated and nuclear materials, affecting many physical properties. The understanding of their origin and of their growth mechanism remains unclear rendering all modeling efforts elusive. In this paper, we remind the knowledge which has been gained during the last 20years on the formation and growth of extrinsic dislocations loops in irradiated/implanted silicon. From the compilation of a large number of experimental results, a unified picture describing the thermal evolution of interstitial defects, from the di-interstitial stable at room temperature, to “magic-size” clusters then to rod-like defects and finally to large dislocation loops of two types has emerged. All these defects grow by Ostwald ripening, i.e. by interchanging the interstitial atoms they are composed of, and transform from one to the other driven by the resulting reduction of the defect formation energy. A model has been proposed and is now integrated into process simulators which quantitatively describes the thermal evolution of all these defects, based on pertinent formation energies. The influence of the proximity of free surfaces or other recombining interfaces can be integrated, allowing simulating the possible dissolution of defects.It is suggested that, beyond silicon, the same type of scenario may take place in many materials. Dislocation loops are just one, easily detectable among many, type of defects which forms during the growth of self-interstitials. They do not nucleate but result from the growth and transformation of smaller defects.

Molecular dynamics simulation of the early stages of self-interstitial clustering in silicon

We have studied the early stages of self-interstitial clustering in silicon using molecular dynamics simulation techniques. We have generated silicon samples of over 200,000 atoms where we introduced a 0.5% extra concentration of self-interstitials. Then samples were annealed at several temperatures. During the simulations we observed the formation of interstitial clusters with different atomic structures, ranging from spherical and amorphous-like clusters, to highly ordered extended configurations such as (110) chains, {111} rod-like defects and dislocation loops, and {100} planar defects. This last type of defects, while common in germanium, have not been observed in silicon until very recently, in ultra-fast laser annealing experiments. The particular morphology of formed interstitial clusters is found to be related to the annealing temperature, as it is observed in the experiments. From the molecular dynamics simulations we have analyzed the atomic mechanisms leading to the formation and growth of interstitial clusters, with special attention to the newly found {100} planar defects.

Extended Defects Formation in Nanosecond Laser-Annealed Ion Implanted Silicon

Damage evolution and dopant distribution during nanosecond laser thermal annealing of ion implanted silicon have been investigated by means of transmission electron microscopy, secondary ion mass spectrometry, and atom probe tomography. Different melting front positions were realized and studied: nonmelt, partial melt, and full melt with respect to the as-implanted dopant profile. In both boron and silicon implanted silicon samples, the most stable form among the observed defects is that of dislocation loops lying close to (001) and with Burgers vector parallel to the [001] direction, instead of conventional {111} dislocation loops or {311} rod-like defects, which are known to be more energetically favorable and are typically observed in ion implanted silicon. The observed results are explained in terms of a possible modification of the defect formation energy induced by the compressive stress developed in the nonmelted regions during laser annealing.

Structure and luminescence of silicon irradiated by protons

The temperature dependence of photoluminescence (PL) in the range 8-300 K is studied for sin� gle crystalline silicon irradiated by protons at high temperatures. It is shown that the samples with ptype con� ductivity display intense PL in contrast to the samples with ntype conductivity, which do not display photo� luminescence. Studies using highresolution transmissi on electron microscopy (TEM) have shown that pho� toluminescence exists until crack formation and splitting of the irradiated layer. The rodlike defects {113} formed during irradiation transform into residual fragments of dislocation structures.

Electrical characterisation and predictive simulation of defects induced by keV Si+ implantation in n-type Si

In this work, we focused on the analysis of implantation-induced defects, mainly small interstitial clusters (ICs) and {311} defects introduced in n-type Si after ion implantation using deep level transient spectroscopy (DLTS). Silicon ions (at 160 keV or 190 keV) of fluences ranging from (0.1–8.0) × 1013 cm−2 have been implanted into n-type Si and annealed at temperatures between 500 °C and 800 °C specifically to create small ICs or {311}s rod-like defects. In samples dominated by small ICs, DLTS spectra show prominent deep levels at Ec − 0.24 eV and Ec − 0.54 eV. After increasing the fluence and temperature, i.e., reducing the number of small ICs and forming {311} defects, the peak Ec − 0.54 eV is still dominant while other electron traps Ec − 0.26 eV and Ec − 0.46 eV are introduced. There were no observable deep levels in reference, non-implanted samples. The identity and origin of all these traps are interpreted in conjunction with recently developed predictive defect simulation models.

Characterization of Deep Levels Introduced by RTA and by Subsequent Anneals in n-Type Silicon

In this work, deep levels introduced by RTA and by subsequent anneals in n-type silicon were studied by deep level transient spectroscopy and by photoluminescence. After annealing at 650 {degree sign}C, centers related to rod-like defects appeared. Furthermore, signals related to thermal donors were found in a wide temperature range. New thermal donors were found even after annealing at temperatures above 900 {degree sign}C. The appearance of rod-like defects indicates that during cooling after RTA soak interstitials supersaturate. The appearance of rod-like defects is accompanied by a decrease of the thermal donor concentration

Contrast in transmission X-ray diffraction topographs of growth defects in the core of SrLaGaO4single crystals

Defects in the core of SrLaGaO4single crystals, grown by the Czochralski method using a [001]-oriented seed, were studied by transmission X-ray diffraction projection topography. Topographs were taken with radiation from a laboratory source and with high-energy radiation available at the ESRF beamline ID19 in Grenoble. The contrast of the investigated defect images was analysed for various diffraction vectorsgand for various values of the product μ0t(μ0is the linear absorption coefficient andtthe crystal thickness). This allowed the contrast formation to be studied as a function of absorption. The results of the analysis confirm the model of crystal lattice deformation around rod-like volume defects in SrLaGaO4crystals.

Polymers in anisotropic environment with extended defects

The conformational properties of flexible polymers in d dimensions in environments with extended defects are analyzed both analytically and numerically. We consider the case, when structural defects are correlated in \varepsilon_d dimensions and randomly distributed in the remaining d-\varepsilon_d. Within the lattice model of self-avoiding random walks (SAW), we apply the pruned enriched Rosenbluth method (PERM) and find the estimates for scaling exponents and universal shape parameters of polymers in environment with parallel rod-like defects (\varepsilon_d=1). An analytical description of the model is developed within the des Cloizeaux direct polymer renormalization scheme.

Characterization of Deep Levels Introduced by RTA and by Subsequent Anneals in n-Type Silicon

In this work, deep levels introduced by RTA and by subsequent anneals in n-type silicon were studied by deep level transient spectroscopy and by photoluminescence. After annealing at 650°C, centers related to rod-like defects appeared. Furthermore, signals related to thermal donors were found in a wide temperature range. New thermal donors were found even after annealing at temperatures above 900°C. The appearance of rod-like defects indicates that during cooling after RTA soak interstitials supersaturate. The appearance of rod-like defects is accompanied by a decrease of the thermal donor concentration.

Direct correlation of R-line luminescence with rod-like defect evolution in ion-implanted and annealed silicon

Abstract

Detailed microscopic analysis of self-interstitial aggregation in silicon. I. Direct molecular dynamics simulations of aggregation

A comprehensive atomistic study of self-interstitial aggregation in crystalline silicon is presented. Here, large-scale parallel molecular dynamics simulations are used to generate time-dependent views into the self-interstitial clustering process, which is important during post-implant damage annealing. The effects of temperature and pressure on the aggregation process are studied in detail and found to generate a variety of qualitatively different interstitial cluster morphologies and growth behavior. In particular, it is found that the self-interstitial aggregation process is strongly affected by hydrostatic pressure. {111}-oriented planar defects are found to be dominant under stress-free or compressive conditions while {113} rodlike and planar defects are preferred under tensile conditions. Moreover, the aggregation pathways for forming the different types of planar defect structures are found to be qualitatively different. In each case, the various cluster morphologies generated in the simulations are found to be in excellent agreement with structures previously predicted from electronic-structure calculations and observed experimentally by electron microscopy. Multiple empirical interatomic potential models were employed and found to generally provide similar results leading to a fairly consistent picture of self-interstitial aggregation. In a companion article, a detailed thermodynamic analysis of various cluster configurations is employed to probe the mechanistic origins of these observations.

An electric-field-active 1377-nm narrow-line Si light-emitting diode at 150 K

A new class of silicon-based light-emitting diode is demonstrated using InSb-quantum-dot-embedded Si containing the emissive {311} rod-like defects (RLDs). A narrow peak centered at 1377 nm (900 meV) characteristic of the {311} RLDs was found to develop out of an otherwise broad background electroluminescence (EL) upon the application of electric fields in the growth direction. Such electric-field-active EL was observed up to 150 K with a slight downward shift of the peak energies, accompanied by an anomaly in the thermal roll-off of the EL intensity. Spectral variations with temperature and electric field indicate a switching of dominance between the closely correlated defect states that are responsible for the EL emission.

Relative stability of extended interstitial defects in silicon: First-principles calculations

Interstitials stored in {311} or {111} habit planes form rows of interstitial chains elongated in $⟨011⟩$ direction. Exploiting the large aspect ratio to treat chains as infinite, first-principles calculations of large computation supercells reveal a unique formation energy trend for each defect, which is closely correlated with its distinct shape. The most energetically favorable structure changes from {311} rodlike defects to Frank loops as the number of interstitials in the defect increases. These results are consistent with transmission electron microscopy studies.