Радиационно-индуцированные изменения оптических, электрических и механических свойств стекол, диэлектриков и полупроводников тема автореферата и диссертации по физике, 01.04.07 ВАК РФ

K fl oi.gMR - 0 9/9ff

ii:02~f/2rS-0

JOINT INSTITUTE FOR NUCLEAR RESEARCH Flerov Laboratory of Nuclear Reactions

Mohamed Arafat Mohamed Ahmed Adawi

RADIATION INDUCED CHANGES OF OPTICAL, ELECTRICAL AND MECIIf NICAL PROPERTIES OF GLASSES, DIELECTRICS AND SEMICONDUCTORS

Speciality: 01.04.07 - Physics of Condensed Matter

Thesis

Submitted for the Degree Doctor of Physical and Mathematical Science

Президиум ВАК России (решение от"

присудил )~чену10 степень ДОКТОРА

ffi1^ А наук

Начальник уппавАвния ВАК России

Dubna, 2001

4.3. The influence of heavy ion irradiation on the surface phenomena in stainless steel

109

4.3.1 Formation of needle structure 109

4.3.2 The model of behaviour of stainless steel under swift heavy ion irradiation 116

CONCLUSION 127

ACKNOWLEDGMENT 134

REFERENCES 135

1. Introduction.

Although and despite of the great achievements in the releam of radiation physics some central problems are not yet satisfactory solved in this field, at least on the practical level. Among these problems the most challenging one is connected with the radiation effect on materials. As it is commonly known irradiation has different effects on matter and the result of irradiation depends sometimes quite significantly upon both the nature of the irradiated material, the sort of the ionizing radiation used, and the dose and intensity, too. Of great importance are also the conditions of irradiation, firstly the temperature and other outer macroscopic parameter. Besides, different materials react differently on the same radiation and up to now we have not any general theoretical approach to the process, except for some qualitative suggestions to predict, on the practical level, the results of such treating. Consequently we now need to investigate all materials being of interest. Such a task is difficult to carry out as being expensive, very time consuming and necessary effort should be made to investigate materials of strategic or of significant application. Such materials belonging to this class are widely used in nuclear industry, space technology, microelectronics, nano-technology etc. The appearance of the relevant research leads to the development of a new direction of investigation in the field of solid-state physics called solid-state radiation physics. This direction has fundamental scientific, cognitive value as well as wide practical, in particular technological applicafions. The creation of new materials and the modification of materials properties are carried out using different kinds of nuclear radiation: gamma rays, neutrons, light and heavy ions at low and high energies. Besides, a series of materials are broadly applied as radiation detectors. Therefore, it is of great practical meaning to understand what phenomena take place when irradiating the materials in order to predict the final effects and changes of their

properties. As a result of irradiation, the materials experience changes in their physical properties. These changes are caused by the changes in their chemical properties, which, by turn occur due to the change of their chemical structure. Such changes can give the materials the privilege of having modifications as mentioned previously. The results of iterative experimental investigations in that concern helped to compose up new prospective materials, which could fmd applications in the fields of nuclear industry and radiation measurements. The materials, which are supposed to be used in the field of radiation measurements, must have the physical property change, which can be successively evaluated qualitatively and quantitatively in correspondence with the change of the irradiation dose. Such relation can be beneficially used in radiation dose assessment. The detectors, which are based on using these different materials and techniques to determine the irradiation dose, are called passive detectors in the difference with the well-known active detectors. However, the materials, which are suggested to be applied in this respect, must as well fulfill the following requirements:

a) Low fading of the irradiation dose as well as long-term stability of the stored trapped charges at normal temperatures.

b) The distribution of traps must be simple.

c) The material must be resistive to the radiation damage.

d) The environmental effects must be as low as possible.

e) There must be a linear relation between the measured change of the physical parameter and the change of the irradiation dose.

f) The material must possess high TL efficiency besides high TL - sensitivity (this property concerns the luminescent materials where TL is the luminescence intensity).

g) The results of the measurements must be reproducible.

h) There is a possibility of its reuse several times.

i) The material should have a low cost and good quality.

Experiment showed that some luminescent materials, some polymeric materials, some kinds of glasses, some composite materials as well as some compounds are liable to be used in the field of radiation dose assessment The following may through some light on the efforts done in this direction.

The effect of irradiation on the luminescent materials was studied extensively in the last few decades. Many authors investigated the effect of gamma rays and neutron irradiation on the radiophotoluminescence (RPL) [111] and the radiothermolumunescence (RTL) [12-27] spectra of some materials. The results are showing that among those materials there were many compounds based on Li2F, Li2B407, BciAli O3, CaF2 and CaS04. Most of these materials were not applicable due to the high cost and their complicated behaviour under heat treatment [28,29] and radiation damage revealed to high level radiation exposure. So the search for low cost and available alternative luminescent materials, which possess the properties required for the use in irradiation dosimetry, declares about itself

Another kind of available materials, which possesses high degree of sensitivity towards the ionizing irradiation, was found to be some polymeric materials. Polyethylene and polyvinyl alcohol belong to that class of materials.

The effect of irradiation on polyethylene had been reported by many authors [30-35]. In case of polyethylene it is found that the structural modifications which are caused by ionizing radiation strongly affect the electrical properties such as the electric resisitivity of the polymer [36-39]. The possibility of applying the electric resistivity measurement technique to measure the change in the electric resistivity of polyethylene, which is caused by irradiation, may help to find a relation between these two parameters. Such a relation may be used in the process of determining the radiation dose.

Polyvinyl alcohol (PVA) is an example ofhigh polymers. It is required as

a net work matrix of polyethylene within which a hydroxyl group is replacing

the hydrogen atom on each carbon [40]. The addition of certain threshold

concentrations of dopant metallic salts to the PVA matrix improves and

enhances the physical properties as well as the elasticity [41]. Many

investigators [42,43] have reported such viscoelastic behaviour relaxation

process, temperature transitions and density as well as the effect of gamma ray

5 7

irradiation in doses 10 up to 10 Gy on the molecular weight, infrared spectra and electrical properties. Meantime, none of these studies are of easy use and direct performance in the field of processing level. The UV-visible optical abso^tion spectrophotometry is an easy procedure, available in different research laboratories due to its multiuse purposes. This technique can be used for radiation dose assessment.

The experiments on PVA assured that on doping the polymer with certain threshold metallic salts concentration the elasticity of the polymer improves [44]. The irradiation of this polymer causes decrease of the elasticity of the polymer with increasing the irradiation dose. Consequently its microhardness increases with increasing the irradiation dose. So, the microhardness may have 5ome coefficient relation with the irradiation dose. This coefficient relation may эе used beneficially in measuring the irradiation doses.

Ionizing radiation can produce free holes and electrons in glass, which may then become trapped thus forming defect centers. These defect centers :ause an increase in the optical absorption of the visible portion of spectrum eading to darkening of the glass. The use of glasses as a gamma irradiation losimeter as well as neutron detectors [1,45-47] has several advantages that nake them especially attractive for the use in this field. These include rigidity, Asolubility, small size and permanence. The induced radiation damage to the ptical glass, which is revealed as a change in the transmitted visible light, may

be beneficially used in radiation measurements. This needs a glass composition, which produces optical absorption peak whose value is increasing with the increase of the irradiation dose at a definite wavelength. In other words there must be a coefficient relation between these two quantities.

Another important direction is the investigation of the influence of irradiation on the properties of the materials used in building nuclear reactors, nuclear power stations, being developed thermonuclear reactors and accelerators. These units produce powerful neutron beams, gamma irradiation and fission fragments, which by turn, interact with the materials of the nuclear device itself (the first wall of the fusion nuclear reactor and the zirconium rods which contain the nuclear fuel in the fission reactors). Investigation was carried Dut in that direction to explore the effect of the interaction of such species with the structural materials of the reactors. A great deal of work was carried out immediately in this field after noticing great changes in the materials. These changes were of negative effects on the device maintenance period and the idequacy of their working functions. A series of such harmful effects -epresented by swelling, anisotropy growth, radiation brittleness, phase ransformation, radiation stimulated diffusion and other effects appeared among hese harmiul effects [48-73].

A very long period of time was needed to test the resistivity to radiation )f materials in a nuclear reactor. Such procedure was done in order to reach ligh fluence of neutrons Fxt, where t-is the time needed to attain the required iamage dose and F- is the beam intensity. The damage dose is xFxt where Td is the damage production cross-section. In turn this time-consuming )rocedure lead to the activation of the materials, which are investigated. After he process of such activation it became difficult to achieve post-irradiation measurements. There appeared the need of using hot cells or keeping the amples aside for long times in order to decrease their induced activity.

The programme of studying the possibility of building new type of energetic i.e. thermonuclear reactors introduced special criteria concerning the structural materials of these piles [73,75]. These materials have to operate in the field of irradiation of 14 MeV neutrons and under the influence of plasma [7678]. The development of the accelerator technique and the creation of the powerful sources of charged particles (electrons, protons, light and heavy ions) provided the possibility of modulating the influence of neutrons by using these charged particles. The use of charged particles got widespread application in modulating the influence of the neutrons not only on the materials, which are already functioning in nuclear energetic complexes but also on those new worked out materials suggested for use in nuclear power and research plants [79-85].

This is firstly connected with the high velocity of defect creation in the materials, which are irradiated with light and heavy ions. In comparison with the case of neutron irradiation the time of irradiating with heavy ions, which is needed to reach the required damage dose is saved in 10A-10A times. Besides the activation of the samples is greatly lower than the activation caused by reactors. \4oreover, the use of charged particle accelerators makes it easy to change and ;o control the irradiation conditions with a great degree of accuracy. One of the most important privileges of such modulation procedure is the possibility of jsing different methods of studying the processes of accumulated radiation lamage in materials directly during their irradiation (on beam measurements), rhese methods include electrical resistivity measurements, determination of the change in mechanical properties, optical methods and a series of other methods 81-87].

The implication of heavy and light ions possessing high specific onization energy loss for studying radiation phenomena in condensed matter illowed the possibility of observing a series of peculiarities in the process of

defect production [88-95]. These peculiarities cannot be explained from the point of view of the traditional approach of using only the mechanism of elastic collision [54,56,57.

The manufacturing of heavy ion accelerators having high intensity ion beams (F) and energy (E/A), higher than 1 MeV/amu helped the developing of the physics of radiation damage, from the point of view of material modification in order to achieve radiation work of stimulated changes of their properties and create new semiconductor technology [96,97]. First of all this is connected with great enlargement of the projective range Rp of the projectile ion in the rradiated material up to 10|Lim and more. This in turn permits the exclusion of he effect of surface accumulation of point defects. In this way such layers are egarded as macroscopic. Moreover, the formation of deep implanted layers with previously given certain configuration in the ion-irradiated nonocrystalline becomes actual (possible). The increase of the ion energy leads O great increase of the specific ionization energy loss (dE/dx)inei compared to he elastic loss (dE/dx)ei (for the ions with energy up to 1 MeV the conditions dE/dx)ei> (dE/dx)inei are fulfilled). This in turn changes the character of the lefect accumulation and their evolution on irradiation especially for dielectric nd semiconductors due to the local heating regions which appear around the rajectories of heavy ions (tracks). The lifetime of these structures (tracks) may e comparatively enough long to permit crystallization and diffusion processes Dtake place [98-102].

The above mentioned formulated statements determine the actuality of le present work and reveal as proof that this direction of investigation is a new nd important in the field of the physics of radiation interaction with condensed latter.

The aim of the present work is the creation of materials for working out Dsimeter detectors having quite accurate and reproducible metrical

characteristics for use in dosimetric measurements of different kinds of radiation (neutrons and gamma rays). The other part of the work is achieved in order to receive experimental data about the interaction of the high-energy heavy ions with condensed matter, the study of radiation defect creation, and the change in microscopic properties and microstructure of metals and alloys as well as the investigation of defect evolution process in case of post-irradiation annealing and to reach the formation of thermal and mechanical stable electrically conducting layers at the far depth of the semiconductor single crystal. Moreover, it is intended to develop a model for describing the micro structural changes, which take place in the materials as a result of bombardment with high-energy heavy ions

It was necessary to carry out the following experimental investigation in 3rder to reach a solution of the given problem:

- investigating the optical transmission spectra of alkali silicate glasses, containing different K2O and Na20 impurity concentrations and polyvinyl ilcohol containing different concentrations of a series of metallic salts (C0CI2, "ai804, CuSo4 and Cu(CH3COO)2) before and after irradiation with neutrons and ^amma rays.

- investigating the induced changes, which is caused by neutron and ^amma rays irradiation on the radiothermolumunescence and the radiophoto-uminescence of borosilicate glasses containing UGO8 different impurity concentrations, Pb203/ polytetraftouroethylene composite as well as ;ermanium-sulphur alloys.

- the investigation of micro-hardness of polyvinyl alcohol containing ifferent impurity concentrations before and after irradiation with gamma rays.

- the study of the effect of neutron and gamma rays irradiation on the lectrical properties of polyethylene at post irradiation different temperatures.

- the investigation of the micro-structural changes of the surface of diamond semiconductor, metallic alloys including stainless steel and to study the defect production and their evolution in silicon after irradiation with high-energy heavy ions having energy of about 1 MeV/amu.

A laboratory was based and equipped with high temperature furnace and platinum crossbills for preparing glass samples, the chemicals, which are required for preparing other composites, and the installations, which are required for measuring the parameters characterizing the materials (micro-hardness, electric resistivity, optical absorption spectra, and luminescence spectra). This part of the experimental investigations was achieved at the nuclear research center, Cairo, while the other part (which is connected with high energy heavy ion irradiation) was achieved at the laboratory of nuclear reactions of the JINR, Dubna. The scientific novelty is:

For the first time detailed investigations were achieved in order to study the influence of hard electromagnetic radiation and neutrons on the basic properties of a series of materials (glasses, polyvinyl alcohol, polyethylene, PbiOs and GeS alloys), which are of great practical interest. The conditions of applying the investigated materials as radiation detectors under the influence of different outer circumstances are defined.

The irradiation effect on polycrystalline and monocrystalline (silicon) materials, dielectric (natural and synthetic diamond), and structural metallic lUoys (chromium-nickel steel) with high fluences of high-energy heavy ions (B, \r, Kr, Xe and Ne) with energy E ~ l MeV/amu is investigated.

For the first time the Kr, Xe ion tracks were observed in diamond lemiconductor by (direct observation) and the diameter of the track was neasured by using the scanning transmission microscope.

The possibihty of creating electrically conducting layers at the far depth of semiconductor materials along the projective range of the bombarding ion [on implanting electrically active impurities such as boron ions with energy 1 MeV/amu) was realized. These layers are thermally stable and can be used to form a multi-structure getter layers.

So a great part of the received results of the present thesis could be used as basis to work out devices for the use in the field of nuclear technology 'dosimetry and microelectronics).

The present thesis consists of the introduction, four chapters and the conclusion. The introduction contains a review about the history of the problem 3f interaction of radiation with matter. A hint about the possibility of using beneficially the changes in the properties of materials, which result on rradiation is given. There is also mentioned the basic requirements, which must 3e fulfilled for a material intended to be used in radiation detection. Different echniques and methods, which are applied to determine the irradiation doses ising passive detectors, are also cited. Using high-energy heavy ions lluminates the problem of material modification by using high-energy heavy ons. The applicability of the results in the field of nuclear technology is mderlined. The aim of the present work is formulated together with its duty. The scientific novelity is presented.

Chapter one contains brief description of the effect of gamma rays, neutron md heavy ion interaction with matter. The effects, which take place as a result )f radiation on material is described for each type of radiation alone. The basic aws goveming these interactions are cited. Concretely, three types of titeraction of gamma rays with matter are considered. Theses are Compton ffect, photo-effect and the effect of pair creation. Besides, the basic aspects of tie influence neutrons on matter are cited. For this case, the process of neutron cattering on the atoms of material takes place. This leads to the production of

point defects. The processes, which take place on irradiating materials with liigh-energy heavy ions, are also described. The process of producing the cascade shift and the elastic and inelastic ion energy loss is cited. At the end of :his chapter a short review about the sputtering process which takes place under effect of inelastic energy loss of high energy heavy ion bombardment on the surface of material. This extremely important process leads to the change of the nicrostructure of the surface.

Chapter two is mainly concerned with the experimental techniques and nethod, which were used to carry out this work. It includes a short description )f the different irradiation facilities such as the U-400 and IC-100 accelerators, ACo gammacell-200 and different neutron sources (Am-Be, Pu-Be and AAACf). Besides, the different methods for studying the properties of materials "in situ" md post-irradiation are described. This includes the method of investigating the )ptical properties (UV/visible spectrophotometry), the electrical properties (DC dectric resistivity measurement), the mechanical properties (Vickers nicrohardness measurement) and the luminescence measurements Radiothermoluminescence and Radiophotoluminescence). The technology of ample preparation is described in this chapter too.

Chapter three contains the results of investigating the neutron and gamma ays interaction with some selected materials. These materials are proposed for AAorking out radiation dosimeters.

The results of measuring the change in the electrical resistivity of olyethylene samples irradiated with different doses of gamma rays and neutron luences at different temperatures are presented. The possibility of using the elation between the irradiation dose and the DC electric resistivity in dose leasurements is checked. The effect of fading of the DC electric resistivity of olyethylene is described.

The results, which are connected with the optical properties of alkalisilicate glass samples Li20-K20 and Li20-Na20 containing 16.6 mol.% Na20 or 16.6mol% K2O are also given. The relation between the radiation induced change of the optical density parameter and the irradiation dose is determined. The possibility of using theses glasses in measuring gamma radiation doses is presented.

The results of measuring the radiothermoluminescence spectra of Dorosilicate glasses (containing different concentrations of UsOg impurity) before and after irradiation with different doses of gamma rays and neutron luences are given in this chapter also. The relation between the RTL-output •espouse and the gamma dose was determined for different samples. Samples containing 4% U3O8 having linear RTL-output dose response are suggested to )e used in gamma radiation dose assessment while U3O8 free samples could be ised for neutron radiation detection.

The radiophotoluminescence spectra of borosilicate glass (containing lifferent concentrations of U3O8 impurity) were measured before and after rradiation with different doses of gamma rays and neutron fluenees. Samples containing 0.3% U3O8 gave linear RPL-output response to gamma doses on a vide range of radiation doses. The possibility of using such samples in adiation dosimetry is checked.

The results of measuring the gamma radiation-induced change of the optical iensity of polyvinyl alcohol samples doped with different concentrations (5%-0% by weight) of metallic salts (C0CI2, №2804 and CUSO4) are presented, luch result could be considered positive from the point of view of radiation OSes assessment and these samples could be used in dosimetry. The possillity f using these samles to work out gamma radiation detectors is regarded.

In the same chapter the results of investigating the change of mechanical roperties of polyvinyl alcohol that is caused by irradiation (containing the

previously mentioned impurity concentrations) are given. The relation between the Vickers microhardness and the irradiation dose was regarded for these samples to be beneficially used in the field of radiation process measurements.

Other results of optical density measurement for polyvinyl alcohol samples doped with copper acetate Cu(CH3C00)2 concentration 5%, 10% and 15%) irradiated with gamma rays and neutrons were obtained. The received relation between the optical density and the irradiation dose was regarded for these samples to be used in neutron detection dosimetry.

The results of luminescence spectra measurement of the Pb203/ polymer composite (having the proportion 1:085 by weight) are discussed. These samples were irradiated with different gamma ray doses. The received linear •elation between the change of the RTL intensity for these samples and the ^amma irradiation dose is suggested to be used for evaluating the gamma adiation absorbed dose.

The results of investigating the germanium (GeS) sulphur amorphous alloys having the proportions 1:1, 1:2 and 1:3 Ge to S by atomic weight) by using the hermoluminescence method are given at the end of this chapter. The induced hanges of the RTL intensity, for both gamma rays and neutron irradiation, are leasured. The possibility of using such amorphous semiconductor samples having linear RTL intensity-dose relation) in gamma radiation and neutron etection is checked. This amorphous alloy was found to be very sensitive in eutron detection.

Chapter four is concerned with the influence of heavy ion irradiation on laterials. It includes the investigation of the effect of irradiating dielectric laterial; single crystal semiconductor and stainless steel alloy with high-energy eavy ions.

The surface of boron-doped synthetic and natural diamonds have been vestigated by using the scanning tunneling (STM) and the scanning electronic

(SEM) microscope before and after irradiating the samples with high energy heavy ions having the energy ~lMeV/amu. Samples of natural diamond were irradiated with ,AAXe and ,,AAAr, while the synthetic diamond was irradiated with A,AKr ions. The obtained data are discussed. Direct measurements of the track -adius and depth were achieved using the STM and SEM. The craters were observed on the surface of diamond semiconductor at the position of ion impact. \ physical model of a track formation was developed on the basis of the experimental data. The phenomenological criteria of crater formation on the surface of diamond have been introduced on the basis of that model. The expectation of structuring synthetic diamond films to be used in nanoscale dectronic devices with high mechanical and thermal stability is supported.

The problems, which are connected with the influence of heavy ions on emiconductor single crystals, are discussed in this chapter too. The damage brmation in silicon single crystal, which is formed as a result of heavy ion rradiation, is investigated. Using the optical reflection method, the spreading esistance and the x-ray diffraction method carried out the investigation of the iroperties of the irradiated samples. The results characterizing the change of the lectrical resistance (superficial and spreading), the change in the optical Aflection coefficient and the change in the lattice constant of silicon are iscussed. The microstructure of the ion-implanted layers in silicon is studied, 'he space distribution of the amorphous centers in silicon (resulting from -radiation with boron and argon ions) is obtained from the optical reflection leasurements. The effect of annealing the defects is studied. The possibility of arming thermal and mechanical stable electrically conducting layers along the rojective range at the far depth of the samples by implanting silicon with lectrically active impurities like boron is checked.

The effect produced by heavy ion irradiation on the microstructure of the irface of chromium-nickel steel is investigated and the results are cited in this

chapter. The scanning electron microscope was used to examine the surface of CrlSNilOTi chromium-nickel austenitic steel irradiated with 124 MeV 'AAXe ions in the temperature range 400-650 "C. The formation of structures the surface was studied. The elemental composition of the irradiated surface structure was examined and compared with the elemental composition of the lon-irradiated surface. The inelastic energy loss of " "Xe ions with energy 124 VleV in CrlSNilOTi stainless steel was determined. The track radius and the ;emperature were determined and the functional relation between the track emperature, the radius of the track and the track depth is demonstrated. A comparison between the influence of heavy ion irradiation in diamond and in jtainless steel is done.

The conclusion contains the results and the basic statements, which are submitted to defense.

The set of the results, which are presented in this work solve a series of )robIems in the field of radiation modification of material properties. These nodified materials are found to be applied in the field of radiafion dosimetry for letecting neutrons and gamma radiation. The other part of results, which concerns the heavy ion irradiation of materials, solves some problems of )ractical applications in the field of nuclear technology