Interstitial Agglomerates Research Articles

Point defects, precipitates and the strength anomaly in ordered Fe–Al alloys

AbstractThe strength of B2-ordered Fe60Al40has been investigated with respect to the influence of vacancies and interstitial impurities. Preconditioned states with different ratios of the concentration of vacancies and interstitial impurities have been established, which then were recovered by subsequent annealing treatments. The evolution of the recovered states with temperature has been monitored by measuring the strength (ultra-microhardness) at room temperature as a function of the annealing temperature. The observed dependencies are discussed on the basis of the resistance of vacancies and impurities to dislocation motion, of vacancy – interstitial interactions and also of the possible formation and dissolution of precipitates (primarily perovskites). The yield stress maximum which, independent of the stoichiometry, appears near 800 K is found to be controlled by vacancy migration in combination with strain ageing by interstitial agglomerates and by the formation of precipitates.

Enhanced damage resistance and novel defect structure of CrFeCoNi under in situ electron irradiation

Defect production and growth in CrFeCoNi, a single-phase concentrated solid solution alloy, is characterized using in situ electron irradiation inside a transmission electron microscope operated at 400–1250kV and 400°C. All observed defects are interstitial-type, either elliptical Frank loops or polygonal (mostly rhombus) perfect loops. Both forms of loops in CrFeCoNi exhibit a sublinear power law of growth that is >40 times slower than the linear defect growth in pure Ni. This result shows how compositional complexity impacts the production of Frenkel pairs and the agglomeration of interstitials into loops, and, thus, enhances the radiation tolerance.

The effect of UV Nd:YAG laser radiation on the optical and electrical properties of hydrothermal ZnO crystal

The effect of UV Nd:YAG laser intensity on the conductivity and optical properties of hydrothermal ZnO crystal was studied. Three laser intensities characterizing the change of optical, electrical and morphological properties of the crystal have been revealed. The first is improvement of the crystal quality up to I1=3.2MW/cm2. The second is at laser intensity higher than I2=249.0MW/cm2 when the formation of cracks takes place. The third I3=290.0MW/cm2 leads to the formation of “black ZnO”, which is caused by the emergence of Zn nanoparticles with size around 20nm. At the same time conductivity of ZnO crystal continues to increase and exceeds the initial value by 277 times. The change of ZnO crystal optical and electrical properties is explained by generation, redistribution and agglomeration of Zn interstitials.

In-operando synchronous time-multiplexed O K-edge x-ray absorption spectromicroscopy of functioning tantalum oxide memristors

Memristors are receiving keen interest because of their potential varied applications and promising large-scale information storage capabilities. Tantalum oxide is a memristive material that has shown promise for high-performance nonvolatile computer memory. The microphysics has been elusive because of the small scale and subtle physical changes that accompany conductance switching. In this study, we probed the atomic composition, local chemistry, and electronic structure of functioning tantalum oxide memristors through spatially mapped O K-edge x-ray absorption. We developed a time-multiplexed spectromicroscopy technique to enhance the weak and possibly localized oxide modifications with spatial and spectral resolutions of <30 nm and 70 meV, respectively. During the initial stages of conductance switching of a micrometer sized crosspoint device, the spectral changes were uniform within the spatial resolution of our technique. When the device was further driven with millions of high voltage-pulse cycles, we observed lateral motion and separation of ∼100 nm-scale agglomerates of both oxygen interstitials and vacancies. We also demonstrate a unique capability of this technique by identifying the relaxation behavior in the material during electrical stimuli by identifying electric field driven changes with varying pulse widths. In addition, we show that changes to the material can be localized to a spatial region by modifying its topography or uniformity, as against spatially uniform changes observed here during memristive switching. The goal of this report is to introduce the capability of time-multiplexed x-ray spectromicroscopy in studying weak-signal transitions in inhomogeneous media through the example of the operation and temporal evolution of a memristor.

Precipitation Enhancement of "so Called" Defect-Free Czochralski Silicon Material

Thermal treatments to enhance precipitation like RTA, ramp anneal and argon anneal were performed on low oxygen 300 mm wafers without vacancy or interstitial agglomerates (“so called” defect-free material). Best results were achieved using high temperature argon anneal leading to a homogenous BMD and denuded zone formation. Furthermore the getter efficiency was positively tested by intentional Ni-contamination. Concepts to overcome the slip danger like improved support geometries and nitrogen codoping were also evaluated and are seen to be beneficial.

Comprehensive modeling of ion-implant amorphization in silicon

A physically based model has been developed to simulate the ion-implant induced damage accumulation up to amorphization in silicon. Based on damage structures known as amorphous pockets (AP), which are three-dimensional, irregularly shaped agglomerates of interstitials ( I) and vacancies ( V) surrounded by crystalline silicon, the model is able to reproduce a wide range of experimental observations of damage accumulation and amorphization with interdependent implantation parameters. Instead of recrystallizing the I's and V's instantaneously, the recrystallization rate of an AP containing nI and mV is a function of its effective size, defined as min( n, m), irrespective of its internal spatial configuration. The parameters used in the model were calibrated using the experimental silicon amorphous-crystalline transition temperature as a function of dose rate for C, Si, and Ge. The model is able to show the superlinear damage build-up with dose, the extent of amorphous layer and the superadditivity effect of polyatomic ions.

Ion-implant simulations: The effect of defect spatial correlation on damage accumulation

A predictive damage accumulation model, which takes into account different interdependent implant parameters, has been developed. The model assumes that the recrystallization rate of damage structures known as amorphous pockets (AP) is a function of its effective size, regardless of their spatial configuration. In the model, APs are three-dimensional agglomerates of interstitials (I) and vacancies (V), whose initial coordinates are generated by a binary collision approximation (BCA) code. This work addresses the importance of the spatial correlation of I's and V's in modeling damage accumulation and amorphization, by comparing simulations, whereby the initial coordinates of I and V are generated by BCA or randomly generated from the concentration distribution of an input damage profile. Low temperature implantations were simulated to avoid dynamic annealing in order to compare the initial damage morphology. For the same damage level, simulations by BCA resulted in ion mass dependent APs’ sizes, with lighter implant ions generating smaller APs’ sizes, implying more dilute damage compared with heavier ions. However, the ion mass dependent APs’ size effect was lost by loading the same damage profile and randomly positioning the I's and V's. Consequently, the damage morphology, as well as the annealing behaviour obtained by reading I, V damage profiles is substantially different from those obtained using the much more realistic cascades generated by BCA.

Bimodal distribution of damage morphology generated by ion implantation

A nucleation and evolution model of damage based on amorphous pockets (APs) has recently been developed and implemented in an atomistic kinetic Monte Carlo simulator. In the model, APs are disordered structures (I n V m ), which are agglomerates of interstitials (I) and vacancies (V). This model has been used to study the composition and size distribution of APs during different ion implantations. Depending strongly on the dose rate, ion mass and implant temperature, the APs can evolve to a defect population where the agglomerates have a similar number of I and V ( n ≈ m), or to a defect population with pure I ( m ≈ 0) and pure V ( n ≈ 0) clusters, or a mixture of APs and clusters. This behaviour corresponds to a bimodal (APs/clusters) distribution of damage. As the AP have different thermal stability compared to the I and V clusters, the same damage concentration obtained through different implant conditions has a different damage morphology and, consequently, exhibit a different resistance to subsequent thermal treatments.

Electric-dipole spin-resonance signals related to extended interstitial agglomerates in silicon

Three electric-dipole spin-resonance signals, labeled TU7, TU8, and TU9, were detected after subjecting oxygen-rich silicon samples to two-step annealing procedures at 450 and 650°C for prolonged times. The formation and structural evolution of large interstitial agglomerates, known as rodlike defects, occur in oxygen-rich silicon material during similar annealing procedures. Comparison of parameters and formation peculiarities of the defects, inferred from the investigation of the detected signals, with those previously reported for rodlike defects, allowed the assigning of the TU7, TU8, and TU9 spectra to the line-interstitial defects, the planar defects, and the dislocation dipoles, respectively. Correlations of the spin-resonance signals and peculiarities in the photoluminescence spectra for the samples are reported and analyzed.

Rod‐like defects in CZ‐Si investigated by spin resonance and photoluminescence spectroscopies

The atomic structure of large agglomerates of interstitials in silicon crystals, i.e. rod-like defects (RLD), was extensively investigated previously using transmission electron microscopy (TEM) methods. Much less is known about electronic properties of these defects. The electric-dipole spin resonance (EDSR) signals and photoluminescence (PL) spectra from Si samples with RLDs allow investigation of electronic properties and formation-evolution peculiarities of these defects. Obtained results clearly show qualitative evolution of the EDSR signals from RLDs with annealing time. Namely, new signals with modified symmetry are formed upon annealing and that detected at earlier stages of annealing – disappear. Comparison of the EDSR results with published TEM data allows determination of atomic structures related to distinct EDSR signals. Correlations of the EDSR signals and peculiarities in the PL spectra for the similar samples are reported. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ESR signature of tetra-interstitial defect in silicon

The electron spin resonance spectra Si-B3 and NL51 were detected in hydrogen-doped float-zone-grown silicon (Si) samples after electron-irradiation and annealing for the first time. Recently, the Si-B3 spectra were attributed to tetra-self-interstitial (I 4) agglomerates in positive charge-state, however an origin of the NL51 spectra was not yet established. Results obtained in this study suggest that the NL51 originate from an excitonic state of neutral I 4 agglomerate in Si. Therefore, detection of interstitial agglomerates in Si at early stages of their formation becomes possible.

Influence of Hydrogen on the Formation of Interstitial Agglomerates in Silicon

Influence of Hydrogen on the Formation of Interstitial Agglomerates in Silicon

Point defects, precipitates and the strength anomaly in ordered Fe–Al alloys

Abstract The strength of B2-ordered Fe60Al40 has been investigated with respect to the influence of vacancies and interstitial impurities. Preconditioned states with different ratios of the concentration of vacancies and interstitial impurities have been established, which then were recovered by subsequent annealing treatments. The evolution of the recovered states with temperature has been monitored by measuring the strength (ultra-microhardness) at room temperature as a function of the annealing temperature. The observed dependencies are discussed on the basis of the resistance of vacancies and impurities to dislocation motion, of vacancy–interstitial interactions and also of the possible formation and dissolution of precipitates (primarily perovskites). The yield stress maximum which, independent of the stoichiometry, appears near 800 K is found to be controlled by vacancy migration in combination with strain ageing by interstitial agglomerates and by the formation of precipitates.

In Situ HREM Irradiation Study of an Intrinsic Point Defects Clustering in FZ-Si

Various extended defects produced by in situ electron irradiation in a high resolution electron microscope (JEOL 4000EX ) at room temperature on {113} and {111} habit planes are reviewed on the base of the results recently obtained. It was observed that both interstitials and vacancies tend to aggregate in the shape of -oriented chain-like defects on {113}, in addition to well-known rod-like defect of interstitial type. These defects are characterized by a different magnitude and opposite type of lattice relaxation introduced in surrounding. -oriented interstitial chains are also formed by agglomeration of interstitials to the core of vacancy or interstitial Frank partial dislocations to provide a relaxation of the strongly deformed crystal areas.

The engineering of intrinsic point defects in silicon wafers and crystals

Using new techniques which manage intrinsic point defect concentrations during the growth of silicon crystals and subsequent processing of silicon wafers, it is possible to achieve two highly desirable results. First, using techniques which maintain crystals sufficiently close to equilibrium during growth such that it is possible to grow large diameter CZ silicon crystals which are completely free of agglomerates of vacancies (voids) or self interstitials (dislocation loops). Secondly, through the control of quenched-in vacancy concentration profiles in thin silicon wafers during rapid thermal annealing processes, it is possible to obtain ideal oxygen precipitation behavior in silicon wafers. Such vacancy concentration engineered wafers are effectively programmed to produce robust defect distributions suitable for internal gettering (IG) applications. The performance of such wafers is independent of all parameters previously important to engineering of IG structures: oxygen concentration, crystal growth method and even the application in which the wafer is used. These two new types of material represent important simplifications to the successful defect engineering of silicon wafers in advanced IC applications. It is shown that, taken together, results from both crystal growth and wafer processing studies place a large number of constraints on the parameter set used to describe the properties of the vacancies and self interstitials in silicon. A model for the oxygen precipitation enhancement in the MDZ process is given.

On the Agglomeration of Interstitials during Irradiation with High-energy Particles

On the Agglomeration of Interstitials during Irradiation with High-energy Particles

Interstitial-type defects away from the projected ion range in high energy ion implanted and annealed silicon

Defects in high energy ion implanted silicon have been investigated, especially in the depth range around half of the projected ion range RP/2 after annealing at temperatures between 700 and 1000 °C. Preferable trapping of metals just in this depth range proves the existence of defects there. No vacancy-like defects could be detected by variable energy positron annihilation spectroscopy after annealing at temperatures T>800 °C. Instead, interstitial-type defects were observed in the RP/2 region using cross section transmission electron microscopy of a specimen prepared under special conditions. The results indicate the presence of small interstitial agglomerates at RP/2 which remain after high temperature annealing.

Diffusion Process of Interstitial Atoms in an Electron Irradiated InP Studied by Transmission Electron Microscopy

Growth of interstitial agglomerates, that are formed in InP by post-annealing above 700 K following 200 keV electron irradiation, has been systematically examined by transmission electron microscopy to understand the migration of point defects in InP. The nucleation and growth of the agglomerates stopped at an early stage of post-annealing. The number density of interstitial atoms in agglomerates, estimated after the growth of all agglomerates stops, did not depend on annealing temperature but on electron dose, and it increased quadratically with electron dose up to 2.5×1022 cm-2. These results were well explained by a model in which the agglomerates were formed through the migration of Ini–Pi interstitial-pairs. The migration energy for the pairs was estimated as 1.52 eV.

Nucleation-limited amorphization of GaAs at elevated temperatures

By a detailed correlation of damage profiles from Rutherford backscattering and channeling with cross-sectional transmission electron microscopy images, we have identified an intriguing nucleation-limited amorphization regime in GaAs irradiated with ions at elevated temperatures. When the rate of dynamic annealing during irradiation exceeds the damage production rate, amorphization can take place at depths significantly different from the maximum in the energy deposition density. This process results from the incomplete annihilation of mobile irradiation-induced defects and occurs either at the surface or at a dislocation band, formed by the agglomeration of interstitials. Once formed, such amorphous layers grow by a layer-by-layer process.

Physical mechanisms of transient enhanced dopant diffusion in ion-implanted silicon

Implanted B and P dopants in Si exhibit transient enhanced diffusion (TED) during annealing which arises from the excess interstitials generated by the implant. In order to study the mechanisms of TED, transmission electron microscopy measurements of implantation damage were combined with B diffusion experiments using doping marker structures grown by molecular-beam epitaxy (MBE). Damage from nonamorphizing Si implants at doses ranging from 5×1012 to 1×1014/cm2 evolves into a distribution of {311} interstitial agglomerates during the initial annealing stages at 670–815 °C. The excess interstitial concentration contained in these defects roughly equals the implanted ion dose, an observation that is corroborated by atomistic Monte Carlo simulations of implantation and annealing processes. The injection of interstitials from the damage region involves the dissolution of {311} defects during Ostwald ripening with an activation energy of 3.8±0.2 eV. The excess interstitials drive substitutional B into electrically inactive, metastable clusters of presumably two or three B atoms at concentrations below the solid solubility, thus explaining the generally observed immobile B peak during TED of ion-implanted B. Injected interstitials undergo retarded diffusion in the MBE-grown Si with an effective migration energy of ∼3.5 eV, which arises from trapping at substitutional C. The concept of trap-limited diffusion provides a stepping stone for understanding the enormous disparity among published values for the interstitial diffusivity in Si. The population of excess interstitials is strongly reduced by incorporating substitutional C in Si to levels of ∼1019/cm3 prior to ion implantation. This provides a promising method for suppressing TED, thus enabling shallow junction formation in future Si devices through dopant implantation. The present insights have been implemented into a process simulator, allowing for a significant improvement of the predictive modeling of TED.