Investigation of radiation-induced mixed interstitial configurations in a dilute nickel 1 at.% silicon alloy

Abstract

X-ray energy spectra induced by 1 MeV protons and the energy spectra of the backscattered protons have been examined in the <100> and <110> directions of Ni crystals containing 1 at.% Si. The channeling method was used to investigate interactions between the radiation-induced defects and the silicon atoms. From the measured minimum yields and from the shape of the angular scans the fraction of silicon atoms is determined, which are displaced into the <100> and <110> channels due to proton or helium irradiations and subsequent annealing treatments. In undamaged crystals about 98 % of the silicon atoms are on normal lattice sites. After irradiation a dose dependent fraction of the silicon atoms is displaced 0.05 nm away from the substitutional position indicating the formation of a mixed dumbbell consisting of one selfinterstitial atom and one silicon atom. However, the experimental data can also be interpreted by the assumption of a NiSi₂ complex, in which the silicon atoms are displaced 0.08 nm from the lattice site. Subsequent annealing from 50 K to 160 K does not change the configuration and the concentration of the silicon complexes. At room temperature the silicon atoms in the complex are positioned 0.04 nm from the lattice position. The silicon complexes were totally am ihilated at 400 K.     

Relaxation and movement of point defect clusters in copper by molecular dynamics simulation

Abstract

The structures of point defect clusters of both interstitial and vacancy type were examined by computer simulation using molecular dynamics and molecular statics with the DYNAMO code (Daw, Foiles and Baskes [6]). The code implements an isotropic potential of embedded atom method (EAM) developed by Daw and Baskes [5]. Interstitial clusters relax to either the immobile mixture of <100> dumbbell and bcc interstitials or a mobile platelet of parallel <110> interstitials. The latter cluster moves along <110> directions. A tri-vacancy relaxes to an un-collapsed stacking fault tetrahedron (sft) of Damask-Dienes type (3v-sft) containing a central atom that vibrates with a large amplitude. A hexa-vacancy relaxes to a stacking fault tetrahedron the structure of which fluctuates between a sft and void. Larger vacancy clusters are stable as a combination of sft and 3v-sft. In these vacancy clusters, atoms show significant vibration with large amplitude. Voids form only with the inclusion of gas-atoms into vacancy clusters.     

Micro‐Raman depth profiling of silicon amorphization induced by high‐energy ion channeling implantation

In this work, we study the silicon amorphization dependence on the crystal depth induced by 6‐MeV Al²⁺ ions implanted in the <110> and randomly oriented silicon crystal channels, which was not directly experimentally accessible in the previous similar high‐energy ion–crystal implantation cases. Accordingly, the micro‐Raman spectroscopy scanning measurements along the crystal transversal cross section of the ion implanted region were performed. The ion fluence was 10¹⁷ particles/cm². The scanning steps were 0.2 and 0.3 µm, for the channeling and random ion implantations, respectively. The obtained results are compared with the corresponding Rutherford backscattering spectra of 1.2‐MeV protons in the random and channeling orientations measured during the channeling implantation. Additionally, scanning electron microscope picture was taken on the transversal cross section of the implanted region in the channeling implantation case. We show here that the obtained silicon amorphization maxima are in excellent agreement with the corresponding estimated maxima of the aluminum concentration in silicon. This clearly indicates that the used specific micro‐Raman spectroscopy scanning technique can be successfully applied for the depth profiling of the crystal amorphization induced by high‐energy ion implantation. Copyright © 2013 John Wiley & Sons, Ltd.     

The Influence of Interstitial Carbon and Oxygen on Grain Boundary Diffusion in Nickel and Silver

Russian Physics Journal - The paper investigates the influence of interstitial carbon and oxygen atoms on their diffusion along the &lt;111&gt;, &lt;100&gt; and &lt;110&gt;...     

The use of channeling-effect techniques to locate interstitial foreign atoms in silicon

When the channeling-effect technique is used to determine the lattice location of an impurity which is not completely substitutional, quantitative interpretation of the results requires knowledge of the interaction yield between a channeled beam and an interstitial atom. We have investigated this problem for Yb implanted into silicon. Along the <110> direction, a peak of almost a factor of two is observed in backscattering yield from the Yb atoms, using a 1-MeV He beam. The height and angular width of the peak is satisfactorily interpreted in terms of flux-peaking of the channeled beam in the central region of the <110> channels.

The existence of such a large flux-peaking effect seriously complicates quantitative determination of the location of non-substitutional impurities. However, it is still possible to establish rather accurately the lattice position of the impurity, provided the measured minimum yields and angular widths of the <111> and <100> dips are taken into account.     

Crystal-binary collision simulation of atomic collisions and dynamic damage buildup in crystalline silicon

Abstract

Channeling profiles of 5–200 keVB⁺, 100–500 keV P⁺ and 40–300 keV As⁺ implanted near <100> and <110> axes in crystal silicon are calculated using the binary collision approximation code CRYSTAL. Calculated profiles are compared to carefully chosen experimental ones. Also, high dose phosphorus profiles with damage accumulation are compared to published experimental data.     

Oscillating trajectories in planar channeling studied in a double alignment configuration

The scattering yield of protons measured in a particular configuration of planar double alignment from a thin gold crystal exhibits strong oscillations when the incident energy varies, providing a new method of observation of particle trajectories in planar channeling.     

Polarization and thickness effects in Mössbauer spectroscopy

The lattice sites of positive pions in gold have been determined as a function of temperature by means of π⁺/μ ⁺ channelling experiments. A blocking pattern in the <100> direction at low temperatures indicates that only octahedral interstitial sites are occupied. The vanishing of this pattern and the reduction of muon flux enhancement observed in <110> ifT is raised above the Debye temperature (165 K) may be interpreted in terms of muon dechannelling owing to the thermal vibrations of the lattice atoms. Time-differential π⁺/μ ⁺ channelling studies on α-iron showed between 20 K and 70 K a strong dependence of the channelling profiles on the time the pions spent in the sample. The ‘young’ pions are well localized on O- or T-sites whereas the ‘old’ pions either become delocalized or occupy sites with strongly reduced symmetry. A model accounting for these observations is suggested. It is argued that there is a close relationship to earlierμ ⁺ SR experiments.     

Orientation of the oxygen-induced non-axially symmetric electric field gradient at181Ta in Ta

The interaction of dilute¹⁸¹Ta in Ta with interstitial oxygen has been investigated via the γ-γ TDPAC-technique applied to the 482 keV state in¹⁸¹Ta. The trapping of Oxygen leading to a quadrupole interaction frequency ν_Q=580(5) MHz with an asymmetry parameter of η-0.37 (1) has been observed after melting the radioactive parent isotope¹⁸¹Hf with Ta. The temperature dependence of the quadrupole interaction frequency between 17 K and 293 K was found to be very weak whereas η varied by about 10%. In a single crystal experiment the orientation of the three principal axes of the electric field gradient leading to ν_Q was determined. The V_zz-axis points in <110>, the V_yy-axis in <100> and the V_xx-axis in <110> direction. These results can be understood in the charge cloud model, suggested by Wrede et al. /1/ for a similar situation found in the HfNb system.     

A model for growth directional features in silicon nanowires

Long silicon nanowires (SiNWs) grown by laser ablation or by thermal evaporation of monoxide source materials are primarily oriented in the <112> direction, and some in the <110> direction, but rarely in the <100> or <111> directions. We propose a model to explain these SiNW growth directional features. The model consists of two parts. Part one is concerned with mechanism-based criteria and part two with applying these criteria to explain the experimental results. Four criteria are considered: (i) the stability of a Si atom occupying a surface site; (ii) the Si {111} surface stability in the presence of oxygen; (iii) the stepped Si {111} surface layer lateral growth process; and (iv) the effect of dislocations in providing perpetuating {111} steps to facilitate SiNW growth. Analyses of SiNW growth in accordance with these criteria showed that <112> and <110> are the preferred SiNW growth directions, and that <111> and <100> are not. Received: 12 November 2001 / Accepted: 20 November 2001 / Published online: 23 January 2002     

Growth of iron single crystals in the etched ion tracks of polymer foils

Pulse reverse electrolysis in an ultrasonic field is used to grow iron single crystals of micron size in templates formed by etching the tracks of swift ions in polymer foils. High-grade crystals are produced from high-temperature ferrous chloride baths. The crystals are oriented along their <110>, <100>, and <111> crystallographic axes. Their orientation turns out to depend on supersaturation during the growing process. At low overvoltages of deposition, <110> and <100> orientations are observed. The crystals of <111> orientation appear more frequently at higher cathode pulse current density. The crystals possess prominent resistance to corrosion. Received: 20 February 2001 / Accepted: 21 February 2001 / Published online: 3 May 2001     

Reprint of: Determination of deuteron characteristic channeling parameters by simulation of RBS spectrum along Si <100>

In this paper, the channeling behavior of deuterons in the energy of 1400 keV along the <100> channel of Si was studied by the simulation of the channeling Rutherford spectrum in the backscattering geometry. The simulation was done by taking three considerations into account: (i) a minimum random component of the beam which enters the sample because of the scattering ions from the surface, (ii) the dechanneling starts at the greater penetration depths and (iii) the dechanneling follows a Gompertz type sigmoidal function with the two parameters which present the dechanneling rate and range, respectively. The Levenberg–Marquardt algorithm was used to set the best characteristic channeling parameters, the penetration depth at which the dechanneling starts, the energy loss and the dechanneling rate and range. The energy dependence of the ratio of channeling to random energy loss of deuterons in the energy range 1–2 MeV is investigated by comparing the determined value with the ones obtained in the other references.     

Radiation from 39 and 45 MeV electrons channeled in Lithium Niobate

Abstract

Channeling radiation from 39 and 45 MeV electrons channeled along the <0001> axis, the (0110) plane and the (1210) plane of a 30 μm thick LiNbO ₃ crystal has been measured. Calculations of the planar crystal potentials were performed by means of the many-beam formalism. Good agreement between theory and experiment is obtained for the planar channeling radiation. Associated with channeling additional radiation lines have been observed, which may be explained by a periodic perturbation of the continuum potential.     

Further evidence against a channeling effect in the optical excitation of ion beams transmitted through single crystals of gold

The intensity and polarisation of light emitted by He⁺ ions excited by transmission through a single crystal gold film have been studied for the case when the He⁺ ions are incident close to a <111 > channel. No evidence for a channeling effect was observed.     

Study of the paraelectric behavior of OH− ions in alkali halides with optical and caloric methods-I. Statics of dipole alignment

The electric field induced alignment of substitutional OH^? ions in a variety of alkali halide crystals was studied, using electro-optical and electro-caloric techniques. As basis for the electro-optical studies, the u.v. absorption of OH^? in various crystals was thoroughly investigated at different temperatures, and in several cases oscillator strength values were determined. The energy position of the u.v. absorption of OH^? in 13 alkali halides follows closely an Ivery-relation, which is discussed in terms of a charge-transfer model. The observed electric field induced zero-moment changes of the u.v. absorption, which depend strongly on light polarization, field direction and temperature, can be quantitatively accounted for by a paraelectric alignment model of permanent dipoles with moment p. The anisotropy of the OH^? electro-dichroism reveals <100> dipole orientation in NaCl, KCl, KBr, RBCl, RbBr and RbI, <110> orientation in KI, and <111> orientation in CsBr. The determined dipole moment values p show little variation with the host material, which excludes sizeable contributions to p from off-center shifts of the OH^? ion. The observed saturation of the electro-dichroism indicates a peculiar ‘mixed’ polarization behavior of the optical transition, which will be discussed. Reversible electro-caloric measurements, performed on several OH^? systems, reveal a field dependence and anisotropy in the high field range, which yield dipole orientation and dipole moment values in agreement with the electrooptical results.     

Self-interstitial in germanium

Low-temperature radiation damage in n- and p-type Ge is strikingly different, reflecting the charge-dependent properties of vacancies and self-interstitials. We find, using density functional theory, that in Ge the interstitial is bistable, preferring a split configuration when neutral and an open cage configuration when positively charged. The split configuration is inert while the cage configuration acts as a double donor. We evaluate the migration energies of the defects and show that the theory is able to explain the principal results of low-temperature electron-irradiation experiments.     

The theoretical study of the cationic conductivity of AgBr

AgCl and AgBr are a special type of superionic conductor, whose superionic phase transition does not accompany any first-order structural phase transition. In the paper, the ionic conductivity of AgBr is investigated by the first principles calculations with VASP code. The calculated results show that the isolated charged interstitial or vacancy is always more stable than the neutral one whether the system is doped or not; the interstitial hops along <001> direction, and the potential barrier is 0.29 eV; the vacancy hop mainly along <111> direction, and the barrier is 0.16 eV; the migration barrier of vacancy is obviously lower than that of interstitial, and then the ionic conductivity is mainly due to the diffusions of vacancies.     

The excitonic molecule emission in the uniaxially stressed Si with the different electron valley degeneracy

The excitonic molecule emission spectra in Si uniaxially stressed along <100> and <110> directions have been investigated. The binding energy of the excitonic molecules is found to be weakly dependent of space orientation of the electron valleys.     

Orientation and Rate Dependence of Wave Propagation in Shocked Beta-SiC from Atomistic Simulations

The orientation dependence of planar wave propagation in beta-SiC is studied via the molecular dynamics （MD） method. Simulations are implemented under impact loadings in four main crystal directions, i.e., （lO0）, （llO）, 〈111〉, and 〈112}. The dispersion of stress states in different directions increases with rising impact velocity, which implies the anisotropic characteristic of shock wave propagation for beta-SiC materials. We also obtain the Hugoniot relations between the shock wave velocity and the impact velocity, and find that the shock velocity falls into a plateau above a threshold of impact velocity. The shock velocity of the plateaux is dependent on the shock directions, while 〈111} and 〈112/ can be regarded as equivalent directions as they almost reach the same plateau. A comparison between the atomic stress from MD and the stress from Rankine-Hugoniot jump conditions is also made, and it is found that they agree with each other very well.