Paata J. Kervalishvili

ISOTOPE EFFECTS IN THE CONDENSED MATTER: SENSORY APPLICATIONS

10 July 2014, Tbilsi

Outline:

Determination of appropriateness and mechanisms of the influence of the isotope effects on the properties of the medium fives new possibilities to pass from the technology of isotope substances pure in the sense of admixtures to the technology of pure isotope substances. Purposeful usage of isotope effects in certain physical phenomena and processes will substantially extend the sphere of utilization and production of stable and unstable isotopes.

Such approach to isotope problem leads us to perspective branches of physics and technology – physics and isotope stimulated phenomena and isotope material science. This relatively new field of solid state physics as well as of molecular physics includes the study of isotope effects of various media. Isotope effect is very effective for nuclear radiation sensors preparation. Today, nuclear radiation detection systems exist utilising a variety of solid state detectors. The solid state detectors are based on semiconductor material such as silicon, germanium, cadmium telluride, zinc oxide, etc. A major advantage of such detection systems is their extremely high energy resolution. Another prospective application of isotope effects is their utilisation in quantum spin based devices. 

The problems concerning an influence of isotope composition upon the number of electrical, physical and chemical properties of condensed systems are being discussed in the scientific world among most important and core issues of modern science and technology.

This great interest is caused by new results of some theoretical and experimental studies, which have shown the existence of sufficiently strong isotope selective effects in contrast to common idea that the isotope effects based on the replacement of some atoms by their isotopes can not be big in principle. It could be explained by the insignificance of separating phenomena in all utilized methods of isotope separation: rectification, chemical exchange, mass-, thermo-, and gas – diffusion, centrifuge methods, etc.

At the same time appeared the scientific works in which isotope selective effects significantly stronger then aforementioned ones could been observed. The property common for new effects is their appearance in processes of response nature and strongly depends upon characteristics of internal freedom degrees of atoms and molecules, interaction between laser radiation and gases, exchange of oscillatory energy of molecules collisions, electron adherence to molecules, ion’s recharging upon its own atom, affinity to an electron in radical solution, dependence of materials’ structure and physical properties on their isotope purity, etc.

At present the studies based on investigation of isotope effects are carried out in the following directions: investigation of mass-transfer and electron spectrum in crystals of various

isotope composition; evaluation of the influence of an isotope composition on a chemical

activity, thermal- and electron transfer in materials; study of an influence of isotope composition on active media upon

generator and spectrum characteristics of gas lasers.

Obtained results bound with determination of the significant influence of the isotope composition of medium on:

- oxidation processes from solid phase,- diffusion and self diffusion,- formation of structure and defect’s conditions,- intensification of processes of energy exchange in nonequilibrium excited

gas media etc.,

 

Isotope Effects in Different Physical and Chemical Processes.

From physical and chemical processes where isotopic effects are distinctly apparent of a high interest are the most simple oxidation ones of elementary substances of various isotope composition.

The selective oxidation of boron-10 and boron-11 isotopes in amorphous boron powders was investigated and reported for the first time by Georgian researchers in early 80s. These experimental works were performed with derivatografic and calorimetric studies of boron samples oxidation with different heating rates. By using a non-isothermal method it was possible correctly evaluate the oxidizing process kinetics. On the basis of the experimental data, the dependence of a (oxidation coefficient) and da/dt (oxidation rate) on the heating rate (b), temperature (T), and time (t) in the process under investigation was calculated.

The comparison was carried out between amorphous and crystalline boron-10 and boron-11 samples. Figure 1 illustrates the curves of the oxidation coefficient dependence on the time for amorphous boron-10 and boron-11 (the heating rate being 2.5 degree/min). The process is developed relatively more intensively in the temperature range 475-5500C. In this case boron-11 oxidation is more intensive. The results of similar thermogravimetric investigation of crystalline boron powder oxidation are illustrated in the figure 2. Relatively high oxidation intensity is displayed by boron-10.

The region of the oxidation selectivity being shifted towards higher temperatures: 575-6750C. The activation energies of the oxidizing process in this conditions are as follows: 225 8kJ/mol (boron-10), while 249 9kJ/mol (for boron-11).

Considering the results obtained from the boron oxidation rate dependence on an isotopic content we are coming to notion of vibrational energy for initial and activation states well-known in scientific literature. According to it, oxidation is regarded to the system: activated complex product.Visualizing the activated state as an intermediate structure between the reagent and the product this can be possibly regarded as a basis for boron atomic bonding. Then, the zero levels of the activated complex bonds will not be dependent on the structure of boron (amorphous or crystalline) directly, but will only differ in isotope concentration. As the reagent boron, the difference between the zero levels of the isotopes on the curve of the potential energy in crystalline boron including rigid directed bonds should be higher then in the activated complex. While in amorphous boron, possessing broken bonds, no difference can be assumed between the zero levels. Proceeding from the above, the diagram of the potential energy for boron oxidation can be imagined as shown in the figure 3.

In case of crystalline boron a noticeable difference between the zero energy levels for the bonds B10 – B10 and B11 – B11 as well as their certain difference in the activated state leads to the reduction of the activation energy for B10 oxidation reaction. In the case of amorphous boron, difference in the zero levels of activated complex will be the same as in a crystalline state; the zero level for the light and heavy isotopes should be the same in the initial state. Therefore, the activation energy of boron-11 oxidizing reaction will be lower, the heavy isotope oxidizes more intensively then the light one.

The very interesting results were obtained by calorimetric study of impurity complexes in germanium (Ge) of high purity. The aim of that work was to receive data on the process of formation and decomposition of impurity complexes in germanium monocrystals grown in the atmosphere of hydrogen isotopes - protium and deuterium in 20-9000C temperature range.

It was shown that germanium grown in protium atmosphere is characterized by higher number of endo and exothermal peaks of Ge-H reactions. Germanium grown within the deuterium atmosphere in temperature range up to 9000C has only one endothermal peak at the temperature ~ 5000C. The absence of similarity in observed pictures during that works might be explained by behaviour of protium and deuterium isotopes of hydrogen as well as difference in the formation of quasi-chemical complexes – pairs with acceptors in germanium. Taking into account the not old but already classical model on isotopic effects in radical chemical reactions and on interaction of substances with oxygen and nitrogen, where isotopes with nonidentical number of protons and neutrons (B11, C13) are the more active donors than those with their identical number (B10, C12), we can make the same conclusion for the discussed case for protium and deuterium.

As it was determined the probability of a chemical reaction depends on the super-fine interaction energy, in other words on nuclei spin and their magnetic moments. Therefore, chemical reactions can be used for selecting and enriching magnetic isotopes. For example, when one of radicals participating in a photochemical reaction contains the carbon isotope C13. Radicals pairs containing the magnetic isotope C13 endure the more rapid triplet-singlet conversion than those containing non-magnetic isotope C12. Because of it, pairs with C13 more quickly become singletic and more rapidly recombine into initial molecules than C12 pairs which lag in the triplet-singlet conversion and correspondingly, in the recombination into initial molecules. All this causes the gradual enrichment of the initial substance by the isotope C13. There is observed experimentally the change of the isotope composition in the chemical reaction process that is caused by the difference between rates of singlet-triplet evolution of magnetic and non-magnetic pairs. And this is the magnetic isotope effect due to which the enrichment of magnetic isotopes in chemical reactions takes place.

Superfine interaction with protons in the radical (CH3)CCN is six times grater than in the radical (CD3)2CCN. The thermal decomposition proceeds through singlet radical pairs, therefore, pairs containing protons more quickly are transformed into the triplet state and have a greater probability to dissociate in comparison with pairs containing deuteriumized radicals. Correspondingly, the recombination's probability of protonized pairs is lower than that of deuteriumized ones.

At the end of 80s there was carried out the investigation of characteristics of the carbon dioxide's isotopically selective synthesis process under conditions of electric discharge in the CO + Ar mixture.It is theoretically and experimentally proved that the isotope effect is a result of the oscillating pumping but not of kinetic mass-effect. The dependence of the CO2 synthesis' isotopic selectivity on the specific power-contribution into the discharge, the initial temperature and CO + Ar mixture's partial composition showed that the carbon dioxide's output is monotonously increased with the rise of the power-contribution into the discharge, and by the gas's temperature decrease the growth of the synthesis isotopic selectivity can be obtained. Alongside with that, at low temperatures of gas (Tgas~100K) the isotopic selectivity of the CO2 synthesis 80.

The very important results in the field of isotope material science were obtained researchers from Russian science centre “Kurchatov Institute”, Moscow Engineering-Physics Institute and Institute of Stable Isotopes of Georgia. Among them one of the most interesting is the study of isotopic effect during the boron carbide (B4C) film preparation. As it is well-known B4C is a refractory, high hardness, high abrasion resistive, and chemically inactive semiconductor material famous in nuclear technology. Presently the best results of boron carbide film preparation were obtained by the Laser Plasma Deposition method. LPD method permits to produce films of multi-component compounds without disturbing the stoichiometric composition of the source materials.Availability of high-energy ions in laser plasma allows a considerable decrease in the temperature of crystalline growth of the deposited films as compared with the other methods of film production. Evaporation by pulsed laser was carried out from a hot-pressed sample of boron carbide (target) of natural enrichment (boron-10 content up to 10%) and boron carbide enriched in a boron-10 isotope up to 90 %. The target composition coincided with B4C stoichiometry.

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Investigations of the ion part of the products of boron carbide evaporation which were done by laser mass-spectrometer shown that laser plasma ion components consisted generally of singly charged ionsof boron (B10+ , B11+) and carbon (C12+, C13+) within a wide range of density of laser radiating power (q=4.108 - 5.109 W.cm-2). The composition of boron carbide vapor, when the density of laser radiation power was at the ionization threshold, was also investigated. A diagnostic complex on a basis of a dynamic mass-spectrometer was applied for this purpose. Within the whole range of densities of laser radiating power the boron carbide vapor contains the single atoms B10, B11, C12 and C13. Molecules and fragments of two or more atoms have not been detected in the process of experimental studies. An isotopic ratio B10/B11 in the evaporated products also corresponds to the value of the initial bulk samples. These experiments show that the plasma formed by boron carbide evaporation with laser radiation with the impulse duration 10ns and power density range 8 . 107-5.109 W.cm-2 is comprised mostly of single atoms and the ions of boron and carbon. The vapor stoichiometric composition corresponds to a 4:1 ratio, which is characteristic of a bulk sample of B4C. The probe ion current dependence on time I(t) at various densities of laser radiating power has been registered. The velocity V and the energy E of ion motion was determined by the time t, passed from the moment of evaporation to the arrival to the probe. While the ion concentration in the plasma flow and the function of their distribution were determined by the ion current saturation oscillogram I(t) according to formulas:

where: eZ is the ion charge ratio (in our experiment Z=1), m - ion mass, L – target-probe distance, S- the probe area.

The investigations have shown that the ion energy distribution essentially depends on the density of laser radiating power (fig. 4). When the density of radiating power is near ionization threshold (q=4.1.108 W.cm-2), the majority of the ions have energy in the range 10-300 eV with the mean energy 100eV. As the density of radiating power increases up to 2.6.109 W.cm-2, the amount of high-energy ions considerably rises. The majority of the ions have energy in the range 20-800 eV, the mean energy value being 120eV.

The figure 5 shows the dependence of the ion maximum energy Emax and the mean ion energy Emeanon density of laser radiating power. The value of the maximum ion energy linearly depends on q, while the value of the mean ion energy is proportional to q ½. The availability of high-energy ions in laser plasma leads to the appearance of stable defects – a “vacancy” and an “atom in interstitial site” – in a surface layer on the substrate, and conditions a temperature decrease in the beginning of oriented growth at laser plasma deposition. It is explained by the fact that stable nuclei during epitaxial growth are generally formed in the sites of the crystal lattice disturbance. The equilibrium quantity of disturbances is not large, therefore the substrate temperature should be sufficiently high to help adatoms migrating towards growth centres. Creation of short-life artificial growth centers as “vacancy”- type defects, permits the production of crystalline films at lower adatoms migration ratio, i. e. at lower temperatures.produced on the NaCl substrate.

 Results and Conclusions. On the base of analysis of results concerning investigations of physical and chemical processes proceeding with changes of substance's isotopic composition there are proposed last years some interpretations of these phenomena explaining to certain extent obtained experimental data.In works dealing with the study of chemical reactions' kinetics depending on reagents isotopic composition (as, for example, in case of the magnetic isotopic effect and corresponding enrichment of isotopes) the observed effects directly or indirectly are connected with the change of the atoms electron shells' state taking place due to nuclei's mass and spin changes. This viewpoint is endorsed by results of studying the electron affinity N 15 > N14 and C13 > C12 in some chemical reactions as well as by boron atoms' isotope-selective mass transport occurring during the substance's laser sedimentation from the gas phase and the light-produced mass transport .Since the electron affinity is a main parameter characterizing the substance's chemical activity, in general the substances' reaction capability depends on their isotopic composition. On the other hand, in accordance with known theoretical concepts the electron's rotation in atom also is accompanied by the nuclei's rotation with a common frequency around their centre of gravity. Here, the equality of centripetal and Coulomb forces is expressed by the correlation mre2 = Mrn2 , where m and M are respectively electron and nucleus masses; re and rn - electron's and nucleus's orbits radiuses respectively; - cyclic frequency.Taking into consideration the fact that the energy equal to the atom's ionization potential from the basic state (energy of electron's removal from the atom to the infinite distance) generally is

E = - (Z2e4m 2/8)1/3, where Z is an element's number; e - electron's charge it may be written

E = - [Z2e4mM2/8 (m+M)]1/3 = - [Z2e42/8 (1+m/M)]1/3. Therefore, the nucleus mass change results only in an ionization energy's insignificant change. For instance, in case of boron, the substitution of the isotope B10 with the isotope B11 leads to the growth of boron atom's ionization potential up to 0.01 eV.

Taking into account the above mentioned, during the formation of boron atoms' pure ionic bonds (for example, with oxygen) there will be observed the isotopic effect around tens of Joules per mole. It is sufficiently small for providing such a selectivity that is observed in experiments on the isotopic enrichment in oxidation-reduction radical chemical reactions. It seems that during formation of a covalent bond between boron (nitrogen, carbon, etc.) atoms and oxygen the isotopic effect is to be more obvious than during formation of an ionic chemical bond. All this together with electrons' singlet-triplet conversions provides the possibility of an existence of the isotopic effect during the oxidation of light elements many times (10 - 100) more strongly than it might be concluded from assessments obtained on the base of former theoretical concepts. Besides, the selectivity during the interaction is become apparent better than during the excited states of substance's atoms that corresponds to small values of bond's energy. Such an excitement of the electron subsystem can be achieved by forming certain radical chemical compounds, with laser excitement of atoms, in processes of electron and ionic interactions in various crystalline solid state bodies, practically in any photo-stimulated electron processes, etc. The known step increase of the solid state bodies' thermal conductance observed within certain temperature ranges and linked with the growth of their isotopic purity (monoisotopity) last years acquired a new sense due to the possibility of their use in solid state electronics. Though systematic experimental investigations of isotopic effects just are being started they already have shown a very big importance of one of promising direction of modern physics - isotopic phenomena in condensed media.  

Isotope effect is very effective for nuclear radiation sensors preparation. Today, nuclear radiation detection systems exist utilising a variety of solid state detectors. The solid state detectors are based on semiconductor material such as silicon, germanium, cadmium telluride, zinc oxide, etc. A major advantage of such detection systems is their extremely high energy resolution. That is, they are very good at determining exactly what the energy of the incident radiation is. A disadvantage is cost: the detectors are quite expensive as are their required electronics.

During the Cold War era, there were two major competitive research groups making gamma and neutron radiation detectors (sensors): Lawrence Berkeley National Laboratory Semiconductor Detector Group and the USSR’s Middle Machinery Ministry (comprising Kurchatov Institute of Atomic Energy, Giredmet Institute of Radioisotope Sevices, etc). Both competitors were focused on the development of semiconductor-based radiation detectors and their applications. The best sensor material for gamma radiation sensors was, and still is, ultra pure Ge and Si or Ge doped by Ga impurities with acceptor concentration up to 1016 cm-3. For neutron radiation measurement the B isotopes contained Si was developed.

Boron and Carbon isotope effects in nanostructured thin solid films for sensory applications

Recently, GTU researchers have started a project to develop a novel boron-based nanosensor element for temperature and neutron sensors that can operate in harsh environments (corrosive media, nuclear radiation, etc.) Boron is a wide-range high temperature semiconductor with a prohibited energy zone of about 1,6 eV. Boron carbide (B4C) and some other boron rich compounds

have a similar forbidden energy gap, which defines their electrical resistance. High mechanical and chemical strength in various corrosive media, and the possibility to change the isotope content from 11B to 10B in almost every concentration range, allows to improve the radiation resistance of boron based sensors nanosystems. One more advantage of boron and its compounds is the possibility to create sensor elements from ceramic, thin films and melting technologies, which make it possible to obtain different material properties and element sensitivities.

References • Buchachenko A. Enrichment of magnetic isotopes – new method of research the mechanisms of chemical reactions.

Journal of Physical Chemistry of USSR, v.51 1977, N 10, p. 2461-2473.• Andrushchenko V., Baiadze K., Baranov V. et all. On nature of isotopic effects in reaction between the nitrogen and

oxygen within the electrical discharge. Journal of Chemical Physics of USSR, v.8, N8, 1989, p.1092-1099. • Kervalishvili P. About isotopic effect at interaction of substances with oxygen. Journal of Atomic Energy, v.68, N1,

1990, p.36-41. • Bairamashvili I., Jandieri T., Kervalishvili P. Elementary boron oxidation. Proceedings of the Academy of Sciences of

USSR, Inorganic Materials, v.20, N7, 1984, p. 1117-1120.• Shemliar M., Perier J. Isotope Separation. Moskva, Atomizdat, 1980, p.215.• Cohen K. The Theory of Isotope Separation, Mc Graw Hill ,1951, p.196.• O’Donnel K., Mhec K., Watkins G. Origin of the 0,97 eV Luminescence in Irradiated Silicon. Proceedings of 12 th

International Conference of Defects in Semiconductors, Amsterdam, Ed. by A. Ammerlaan, 1982, p. 672-677. • Kervalishvili P. Isotope effects and isotope material science for microsystems application. Nexus Research News, v. 1,

1999, p. 23-24.• Jandieri T., Kervalishvili P. Oxidation of the crystalline boron. Proceedings of the Academy of Sciences of USSR,

Inorganic Materials, v.22, N7, 1986, p.1115-1118.• Kervalishvili P., Kalandadze G. Calorimetric Study of Hydrogen-Containing Complexes in Germanium of High

Purity. Proceedings of 20th International Conference on the Physics of Semiconductors, Thessaloniki, Greece, World Scientific, v. 1, 1990, p.799-805.

• Stevenson G., Espe., Reiter C., Demonished solution electron affinities of C-13 and deiterium substituted anion radical precursors allow isotopic enrichment. Journal of Amer. Chem. Soc., v.108, N1, 1986, p.532-555.

• Shalamberidze S., Kervalishvili P., et all. Isotopic effect during Boron Carbide film production by a laser plasma deposition method. Journal of Material Processing and Manufacturing Science. v.6, N4, 1998, p.321-328.

• Stevenson G., Espe M., Reiter C., Lovett D. Isotopic enrichment by electron exchange. Nature, v.323, N10, 1986 p. 522-523.

• Gordyets B., Mamedov Sh. On isotope separation in chemical reactions of oscillatory excited molecules. Journal of Quantum Electronics of the USSR, v.2, N9, 1975, p. 1992-1997.

• Abdushelishvili G., Bakhtadze A., Kervalishvili P. Laser deposition of substances from gas phases and mass transfer by the light. Journal of Physics and Chemistry of Materials of USSR, N3, 1987, p.77-85.

• Abdushelishvili G., Abzianidze T., Kervalishvili P. et all. Boron particles production in nonequilibrium laser-chemical radical reactions during the IR multiphoton dissociation of HCIC=CBCCl2 molecules. Journal of Laser Chemistry, v.10, 1989, p.81-95.

• Shalamberidze S., Kervalishvili P., et all. Peculiarities of isotope-modified crystalline and amorphous elementary boron oxidation. Journal of Materials Processing and Manufacturing Science. v. 6, N7, 1998, p.307-310.

• Jobava J., Kalandadze G., Kervalishvili P., Petrov V., Makarov V. Oxidation kinetics peculiarities of isotope-modified amorphous boron. Journal of Highly Pure Materials, N5, 1990, p.137-145.

• Rusanov. V., Fridman A., Shelin G. Physics of chemically active plasma and nonequilibrium oscillatory excited molecules. Journal of Success in Physical Sciences of USSR, v.134, N2, 1981, p.185-235.

• P. Kervalishvili. Some Neutron Absorbing Elements and Devices for Fast Nuclear Reactors Regulation, Systems. Nuclear Power and Energy Security, NATO Science Series – B Physics and Biophysics, v. 147, Springer Science + Business Media, 2010, pp. 147-155.

• P. Kervalishvili, S. Shalamberidze, G. Esadze, P.Porta, Semiconductor Material Film Production by Laser Plasma Deposition, Le Vide, les Couches Minces, N.267, 1993, pp.189-198.

• P. Kervalishvili, G. Karumidze, G. Kalandadze, S. Shalamberidze, Semiconductor Sensor for Neutrons, Sensors and Actuators, A., N.36,1993, pp.43-47.

• P.Kervalishvili, K.Oganezov, M. Tabutsidze, hydrogen, nitrogen and oxygen behaviour in boron, Journal Material Research, vol 7, N.7, 1992, pp.1822-1828.

• P. Kervalishvili, G. Gavrilov. Германий для декторов ядерных излучений достижения и проблемы (Rus.). Proceedings of the SU Conference “Novel Physical Principles of Analitical Devices Fabrication” Kiev, KPI Press, 1980, pp. 14-49.

• P. Kervalishvili, G. Kalandadze, G. Karumidze. К вопросу примесного фона в детекторном герамании (Rus.). Physics and Technics of Semiconductors, N-12 1978. pp. 1145-1153.

• P. Kervalishvili. Распределение мелких доноров в детекторном германии (Rus.) Scientific Proceedings of GIREDMET. GIREDMET Press, Moscow. 1978, pp. 49-54.

   

Quantum computation and information systems (sensors) based on nuclear spin qubits

Outline:

Quantum computation quantum bit (qubit) and entanglement problems in experimental realization of QC

Spin-based QC nuclear spin and electron spin in semiconductors as qubits neutron-transmutation-doped Si and SiGe structures as a material for QC 31P nuclear spin qubits in a 28Si nanowire: a scalable unit for quantum computation

Isotopicaly modified Si and Ge

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