Radiation-stimulated Diffusion Research Articles

Численное моделирование динамики температурных полей в монокристаллическом кремнии при импульсно-периодической высокоинтенсивной ионной имплантации и энергетическом воздействии пучка на поверхность

Methods to modify surface and near-surface layers of materials and coatings by ion beams are used in many fields of science and technology. The method of high-intensity implantation by high-power density ion beams with submillisecond duration involves significant pulsed heating of the irradiated target’s near-surface layer, followed by its rapid cooling due to heat transfer into the material due to thermal conductivity and the implementation of repetitively-pulsed radiation-enhanced diffusion of atoms to depths exceeding the projective ion range. Using the numerical simulation, this work studies the dynamics of changes in temperature fields into silicon wafer under single-pulse and repetitively-pulsed exposure to submillisecond titanium ion beam with a pulsed power density in the range up to 109 W/m2. The conditions are determined under which the temperature in the ion-doped layer will correspond to the conditions of radiation-stimulated diffusion of the implanted element, and the temperature in the matrix material will not deteriorate its microstructure and properties.

Особенности синтеза карбида кремния методом холодной имплантации атомов отдачи углерода

The Auger electron spectroscopy method confirmed a high concentration of carbon atoms (~ 85 at. % ), introduced into silicon by cold implantation of recoil atoms. Carbon atoms are concentrated in a thin (~ 5 nm) near-surface region of silicon. Annealing of such a structure did not reveal a noticeable diffusion of carbon, which does not allow obtaining a layer of SiC with a thickness of more than a few nm. The solution to this problem was carried out by the use of radiation-stimulated diffusion. This made it possible to control the distribution profiles of carbon atoms in a wide range. Annealing at 1150 oC allowed to obtain layers of amorphous crystalline SiC with a thickness of 50-150 nm. Higher annealing temperatures are required to obtain a single-crystal SiC film.

Effect of Mechanical Activation and Gamma-Irradiation on Structural-Phase State of Ti-Al-C Powder Reagents

The influence of mechanical activation and gamma-irradiation on the structural-phase state of Ti-Al-C powder reagents was studied. The following compositions were used for research: 1) 78% Ti + 14% Al + 8% C; 2) 80% Ti + 12% Al + 8% C; 3) 81% Ti + 10% Al + 9% C. Mechanical activation of these compositions leads to an increase in the diffuse background, a decrease in the intensity of diffraction reflections of mixture components and a broadening of peaks, as well as micro-deformations. Depending on the ratio of components, the structural parameters can either increase in comparison with the initial ones, or decrease. The effect of gamma radiation with a dose rate of 1 Gy/s and accumulated dose of 3·104 Gy on the mechanocomposites of the Ti-Al-C system causes unsystematic change in crystal lattices of elements, which can be explained by radiation-stimulated diffusion. Gamma-irradiation also reduces micro-deformations that occur after mechanical activation, while crystallites of the components remain nanoscale.

Regularities of PLA mechanical property modification under ion implantation conditions

The investigations of the surface physicochemical properties of polylactic acid (PLA) modified by argon, carbon and silver ion implantation to fluences of 1∙1014, 1∙1015 and 1∙1016 cm−2 and energies of 20 keV, 20 keV and 42 keV respectively are described. The projected ion ranges in the polymer matrix are estimated by the computer simulation with the TRIDYN code, as well as energies of electron and nuclear stopping are assessed according to the SRIM modelling. The microhardness and elastic modulus are established to be dependent on the degree of crystallinity of the material. It was found that the microdistortions and strains of the PLA crystal lattice increase after ion implantation due to the structural alteration and defect formation. Long-range effect expressed as bigger depth of modified surface layer than the ion range in the material is suggested as a result of the radiation-stimulated diffusion and thermal restructuring of the material.

Aluminium and titanium alloys surface behaviour under argon and helium ion exposure

Samples of aluminium alloy 2024 and titanium alloy Ti-6Al-4V are irradiated with 2 keV helium (He) and argon (Ar) ion fluxes using FALCON ion source. Cone-like structures are found to be formed on the surface of two Al(2024) samples due to both irradiation conditions: Ar and He ions exposure reaching total fluence 9.75 × 1025 m−2 and total charge 150 Coulomb per sample. Ar ions exposure of Ti-6Al-4V causes cones formation, while exposure for He ions causes only physical sputtering morphology at the same fluence. Chemical composition of grown structures is obtained from energy dispersive spectroscopy (EDS). Surface roughness and roughness profile are investigated with confocal microscope. Hardness of irradiated surfaces is obtained from results of Vickers hardness test. Residual stresses after irradiation and phase composition are measured by X-ray Diffraction spectroscopy (XRD). The mechanisms of cones growth on alloys surface are surface radiation-stimulated diffusion and ion induced collision cascades evolution.

Synthesis of Amorphous InSb Nanowires and a Study of the Effects of Laser Radiation and Thermal Annealing on Nanowire Crystallinity.

Although various synthesis and characterization strategies have been employed for the synthesis of crystalline nanowires, there is very little work done on development of low-dimensional amorphous semiconductors. This paper presents a simple strategy to grow amorphous (a-) nanowires (NWs) in a chemical vapor deposition (CVD) system. The NWs were grown on substrate coated with indium film and the lack of crystallinity in the as-grown stoichiometric NWs was ascertained by Raman spectroscopy and electron transport measurements. A model proposed to explain the amorphous NW growth mechanism takes into account the fact that NW growth was carried out at the high temperature ramp-up rate of 75 C/min. This high rate is believed to affect the growth kinematics and determine the arrangement of atoms in the growing NW. Raman spectrum of the as-grown sample shows a broad peak around 155 cm, indicative of the presence of high density of homopolar - bonds in the amorphous matrix. It was also found that high intensity laser light induces localized crystallization of the NW, most likely due to radiation-stimulated diffusion of defects in a-. The nonlinear trend of the current-voltage characteristics for individually contacted a- NWs was analyzed to prove that the non-linearity is not induced by Schottky contacts. At high bias fields, space charge limited conduction was the proposed electron transport mechanism. Post-growth annealing of the as-grown a- NWs was found to be very effective in causing the NWs to undergo a phase transition from amorphous to crystalline.

The Effect of γ Irradiation on Phase Transitions in the Polyimide–YBa2Cu3O6 + x System

The effect of γ irradiation on optical properties of films of the polyimide–YBa2Cu3O6.7 system with different concentrations of the filler in the form of the finely crystalline compound YBa2Cu3O6.7 (0.05 wt %, 0.10 wt %, and 0.50 wt %) has been investigated. The properties were studied on an IKS-29 infrared spectrophotometer in a spectral range of 400–4200 cm–1 at room temperature. The samples were irradiated in air under room conditions on an RKhM-γ-20 by doses of 150, 250, and 600 kGy. The power of the exposure dose of the 60Co source was 0.16 rad/s. It has been established that irradiation with a dose of up to 600 kGy of the abovementioned system slightly affects the structure of the polyimide matrix but decreases the number of free radical groups in the film structure with the formation of hydrogen bonds. In the range of 400–4200 cm–1 at D = 150 kGy, the most intense changes in spectra of polymeric composite samples have been revealed. In the range of 2850–3350 cm–1, the wide absorption spectrum band is preserved, which is caused by the presence of Cu, Y, and Ba crystallohydrates. The band is related to deformation vibrations of the Cu–O bond in YBa2- Cu3O6.7 (YBCO) chains due to properties of barium carbonate, formation of oxygen vacancies in the filler, and vibrations of the Cu(I)–O(I) bonds near one or several O(4) vacancies. Irradiation by doses of 250 and 600 kGy for different concentrations of the filler leads to a decrease in the signal intensity in the range of 1800–3600 cm–1 by 20–35% on average. Peaks related to interband transitions (transitions of the Cu(I)–Cu(IY)–Cu(II) system) and bending vibrations O(I)–Cu(I) are not changed by strains of O(IY)–Cu(I) bonds. This testifies to the radiation-stimulated diffusion of oxygen atoms to O(IY) sites determining the orthorhombic phase of YBa2Cu3O6.7 from the occupied positions in the Cu–O sublattice.

Electron-Stimulated Hydrogen Desorption from Nickel and Palladium

New experimental data are presented on the radiation-stimulated diffusion of hydrogen in metals, in particular, nickel and palladium, under the action of a 30-keV accelerated electron beam. Hydrogen desorption rates from nickel and palladium are determined for thermal and electron beam heating; a substantial shift of the thermal gas-desorption peaks to the low-temperature range is detected upon radiationinduced heating. The presence of an internal hydrogen atmosphere is shown to create favorable conditions for the vibrational-translational exchange (V–T exchange), non-equilibrium redistribution, and desorption of hydrogen from a solid upon irradiation. Accelerated hydrogen migration stimulated by electrons with an energy below the defect-formation threshold is explained at a qualitative level. First-principles calculations of the electronic structure of the metal–hydrogen system reveal that plasmons are also an efficient mechanism for radiation-energy dissipation over the whole crystal.

Effect of Microwave Radiation on the Band Structure and Electronic Parameters of the Heterosystems with Fullerenes

The results of a complex study of C60/Si heterosystems are presented in this work: the crystal structure and composition of the films, internal mechanical stresses, electronic parameters of the film and the film-substrate interface, and the effect of external influences (ultraviolet irradiation, thermal annealing, gamma and microwave irradiation). The advantage of microwave treatment over others is established: the absence of fullerene decomposition, the removal of internal mechanical stresses in the heterosystem, and the improvement of its electronic parameters. Methods for remove the decomposition of C60 molecules under the influence of other treatments have been developed. To eliminate the interaction of fullerenes with oxygen, it was proposed to perform thermal annealing and UV irradiation in vacuum, and in the case of g-irradiation, apply a protective coating on the surface of the film (GeOx or SiOx). In solar cells with C6 films in the polymer matrix on Si, a significant advantage of titanium contacts in comparison with gold is established, especially after microwave treatment. Contact resistance decreased as a result of hybridization of 3d-orbitals of titanium and 2p-orbitals of fullerenes with the formation of ТіхС60 carbides and radiation-stimulated diffusion of metals, which increases the contact area.

Assessment of segregation kinetics in water-moderated reactors pressure vessel steels under long-term operation

In reactor pressure vessel (RPV) bcc-lattice steels temper embrittlement is developed under the influence of both operating temperature of ∼300 °C and neutron irradiation. Segregation processes in the grain boundaries (GB) begin to play a special role in the assessment of the safe operation of the RPV in case of its lifetime extension up to 60 years or more. The most reliable information on the RPV material condition can be obtained by investigating the surveillance specimens (SS) that are exposed to operational factors simultaneously with the RPV itself. In this paper the GB composition in the specimens with different thermal exposure time at the RPV operating temperature as well as irradiated by fast neutrons (E ≥ 0.5 MeV) to different fluences (20–71)·1022 m−2 was studied by means of Auger electron spectroscopy (AES) including both impurity and main alloying elements content. The data obtained allowed to trace the trend of the operating temperature and radiation-stimulated diffusion influence on the overall segregants level in GB. The revealed differences in the concentration levels of GB segregants in different steels, are due to the different chemical composition of the steels and also due to different grain boundary segregation levels in initial (unexposed) state. The data were used to estimate the RPV steels working capacity for 60 years. The estimation was carried out using both the well-known Langmuir-McLean model and the one specially developed for RPV steels, which takes into account the structure and phase composition of VVER-1000 RPV steels, as well as the long-term influence of operational factors.

Coefficient of Radiation-Stimulated Diffusion of Interstitial Atoms in a Flux of Fast Electrons

An expression for the coefficient of radiation-stimulated diffusion of interstitial atoms, which arises in a flux of fast electrons, is obtained on the basis of a solution of Boltzmann’s equation. As a specific example, a relation for approximate evaluation of the coefficient of radiation-stimulated diffusion of interstitial atoms in a flux of fast electrons formed when fast heavy charged particles decelerate in materials is presented and analyzed.

Formation of InAs nanoclusters in silicon by high-dose ion implantation: Experimental data and simulation results

A physicomathematical model and dedicated software are developed for simulating high-dose implantation of two types of atoms to form InAs nanoclusters in a silicon matrix. The model is based on solving a set of convection–diffusion–reaction equations. The synthesis of InAs nanoclusters produced by highdose implantation of As+ and In+ ions into crystalline silicon is numerically simulated. Using the methods of transmission electron microscopy and Raman scattering, it is found that InAs nanoclusters are crystalline and have a mean diameter of 7 nm. After As implantation (170 keV, 3.2 × 1016 cm−2) and In implantation (250 keV, 2.8 × 1016 cm−2) into silicon at 500°C, the nanoclusters are distributed with a density of 2.87 × 1011 cm−2. From experimental data and theoretical results, the coefficients of radiation-stimulated diffusion of In and As in silicon, as well as the fraction of the implant in the bound state (i.e., entering into InAs nanoclusters), are determined. Experimental data are compared with simulation results.

Radioluminescence of color centers in LiF crystals

Abstract Luminescence of color centers in the near-infrared region under cathode beam excitation is revealed for the first time in as-grown pure LiF and LiF:Mg,O crystals. Emission efficiency of F 2 + , F 3 − and F 2 − centers is higher for the samples enriched by oxygen and magnesium than for ultrapure crystals. The intensity of the NIR luminescence remains practically constant with the increase of the electron beam density. In contrast, visible emission typical for F 3 + and F2 centers is suppressed due to the induced absorption bands. It is assumed that the high-density electronic irradiation leads to the strongly pronounced thermal- and radiation-stimulated diffusion in a relatively thin layer. It causes the association of point radiation defects with the formation of various complex centers and aggregates. Results obtained suggest that LiF crystals can be used for in-situ detection of ionizing radiation.

Radiation-stimulated diffusion in single memory cells

A model of radiation-stimulated diffusion (RSD) of phosphorus (P) in Si is proposed to interpret the results of the high-dose γ-irradiation of complementary metal-oxide-semiconductor (CMOS) memory transistors. The devices are irradiated with doses≥1 Mrad. A degradation of the parameters of memory transistors is explained on the basis of a model of RSD of impurities in the n–p junctions and a spreading of the impurity profiles. The RSD of P in Si occurs as a result of the ionization-induced decrease in potential barriers of diffusion hopping. A possible increase in the diffusion coefficient caused by the irradiation is estimated. An approach for the prediction of the exploitation resource of devices in extreme conditions is considered. In this case, the method of the similarity conversion is used. The approach is illustrated by a numerical example.

Ionizing radiation-stimulated diffusion and desorption of hydrogen from metals

The processes of hydrogen diffusion from a sample depth activated by electrons with an energy of tens of keV are studied. The difference from the known models of electron-stimulated desorption, which consider as a rule electron energies from 0.5 to several keV, is noted. The proposed model is shown to correspond to at least two established experimental facts: the nonlinear dependence of hydrogen isotope desorption on the electron beam current density affecting the sample and the dependence of hydrogen desorption on the irradiation time of the sample.

Radiation-stimulated diffusion induced by high-current density nitrogen ion beam processing of steels

A model of an activated surface layer induced by radiation stimulated diffusion is considered for the case of high-current-density nitrogen ion implantation and generalized to take into account the time dependence of the activated layer width. Experimental data to confirm the developed model are presented.

Radiation-stimulated diffusion in Al–Si alloys

A di-vacancy low-temperature diffusion is proposed to explain diffusion-controlled processes in Al–Si alloys responsible for neutron-induced silicon precipitation. Ab initio calculations of potential barriers for Si atom hopping in aluminium lattice showed that in the case of di-vacancy diffusion, they are small compared with that of mono-vacancy diffusion. The low temperature diffusivity of mono-vacancies is too small to account for the measured Si diffusivities in aluminium. The dependencies of radiation-stimulated diffusion on the neutron flux and on the temperature are obtained and can be used for the experimental verification of the developed model.

Electron-beam boriding of low-carbon steel

Structural transformations happening in the surface layers of boriding steel during the irradiation by high-energy electron beam were analyzed by means of depth-selective conversion Mössbauer spectroscopy in parallel with metallography of the sample transversal sections and microhardness measurements. It was revealed that the high-energy electron irradiation during 10s of a borided sample results in a sharp modification of subsurface phase composition: the recrystallization of the crystalline phases derivated in the solid-phase boriding process for the benefit of Fe2B phase take place. As a result of boron radiation-stimulated diffusion processes, the thickness of boriding coating is increased.

High dose low temperature Ti and Al implantation in metals

This article presents the results of investigation of Ti and Al ion implantation into copper and uranium. Titanium and aluminium are selected as implanted ions because these materials are the main candidates to the production of corrosion resistant protective coatings. Special features of near-surface transient layers formation at high dose low energy implantation are investigated. The temperature dependencies of Al concentration in near-surface layers of Cu are plotted. The time and energy dependence of Al and Ti concentration curves on the irradiation energy in the range 1.0–4.0 keV is studied. The calculations of the impurity radiation-stimulated diffusion at the high dose implantation are carried out.

Diffusion of As ions and self-diffusion in silicon during implantation

Experimental concentration profiles of As ions in a silicon substrate at temperatures of 20, 600, and 1050°C and ion current of 40 µA/cm2, as well as at 1050°C and 10 µA/cm2, are presented. On the basis of our and previously published experimental data, the process of radiation-stimulated ionic diffusion and self-diffusion in silicon is simulated. A number of interesting dependences, which are discussed in the conclusion of this study, are obtained.