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1
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Nonlinear Many-Staged Diffusion

100%
Janavičius A.
Acta Physica Polonica A
|
1998
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vol. 93
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issue 5-6
731-735
EN
We considered and solved the nonlinear diffusion equation formerly. The more complicated but more useful task of many-staged diffusion is solved in this paper. The obtained solution satisfies the initial distribution of the impurities and can be generalized for many-staged diffusion. Using these solutions we can take into account all the stages of a planary transistor formation.
2
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The Nonlinear Diffusion in the Nonisothermical Case

100%
Janavičius A.
Acta Physica Polonica A
|
1998
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vol. 93
|
issue 3
505-512
EN
We will discuss the properties of the nonlinear equation in the nonisothermical case. In our previous papers the diffusion coefficient directly proportional to the concentration of the impurities was proposed and it was exactly defined. Now the nonlinear diffusion equation is solved for the temperature and for the diffusion coefficient depending on time in a special way. The temperature function T(t) has the singularity at the free chosen time moment t_{0}. The obtained analytical solutions define the diffusion profiles for increasing temperatures and in the case of excited systems when the vacancies and the impurity's atoms are not in the thermal equilibrium with lattice. Considering the connection between temperature function and the population of excited states for atoms surrounding vacancies the possibility of the superdiffusion is shown.
3
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Nonlinear Diffusion Equation with Diffusion Coefficient Directly Proportional to Concentration of Impurities

64%
Janavičius A., Poškus A.
Acta Physica Polonica A
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2005
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vol. 107
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issue 3
519-524
EN
We analyzed a diffusion model based on the assumption that the sufficient condition for the mass flux at point x+L to be different from zero is a nonzero value of the impurity gradient and of impurity concentration at point x. In our model, the length of the jump of diffusing particles from one equilibrium position to another has a defined value L. By describing variation of impurity concentration with time when the frequency of the jumps depends on coordinates and L, the nonlinear diffusion equation was derived. We found that the diffusion coefficient in this nonlinear equation is directly proportional to the concentration of impurities, as it had been proposed in earliest papers. The derived nonlinear diffusion equation was solved numerically for the case of spherical symmetry.
4
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Analytical Solution of Nonlinear Diffusion Equation in Two-Dimensional Surface

64%
Janavičius A., Turskienė S.
Acta Physica Polonica A
|
2005
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vol. 108
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issue 6
979-983
EN
We considered practically important case of nonlinear diffusion in the anisotropic plane where diffusion coefficients for diffusion in x and y axis directions can be different. This equation was transformed using similarity variables. The approximate analytical solution of the transformed equation expressed by power-series expansion for two variables about the zero point including only the first terms. The graphic representations show sufficient accuracy of the obtained analytical solution.
5
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Fast Diffusion of Metastable Vacancies in Surface of Excited Si Crystals

64%
Janavičius A., Turskienė S.
|
EN
We considered the practically interesting, very fast nonlinear diffusion of metastable vacancies in the surface of Si crystal, excited by soft X-rays. Here we used experimentally defined diffusion coefficients of singly and doubly negatively charged very fast vacancies generated by soft X-rays. These high concentration (about 10^{13} cm^{-3}) metastable vacancies at room temperature can diffuse and exist in the crystal for a very long time (about 24 hours for not so fast neutral vacancies) changing electrical conductivity, the Hall mobility of carriers and generating some resonance phenomena in the lattice of Si crystal. We measured superdiffusivity of negatively charged vacancies, generated by the Auger effect in the regions of the sample, where X-rays did not acted. In the paper we modified the formerly obtained analytical solution of nonlinear diffusion equation for calculation of distribution of vacancies in two-dimensional surface.
6
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Modeling of Thermodiffusion Inertia in Metal Films Heated with Ultrashort Laser Pulses

64%
Janavičius A., Turskienė S.
|
EN
Previously, we considered the analytical solution of nonlinear diffusion equation in two-dimensional surface. This allows us to consider the same nonlinear heat conduction equation for metals heated by a picosecond laser. After fast thermalization (within a few femtoseconds) of the laser energy and electron excitation in the conductivity band, electrons ballistically diffuse and transfer their energies to the target atoms and equilibrium electrons from the conductivity band. In this case, we have thermal diffusion of nonequilibrium excited electrons and thermal inertia for thermodiffusion. The relaxation time of excited conductivity electrons is directly connected with thermal inertia and depends on electron-electron collision frequencies. The theoretical temperature surface plots for the thermodiffusion of excited electrons were obtained from analytical solutions of nonlinear thermodiffusion equations.
7
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Analytical Solution of Nonlinear Diffusion Equation Describing Interdiffusion of Gases

64%
Janavičius A., Jurgaitis D.
|
EN
The diffusion is the result of Brownian movement and occurs with a finite velocity. We consider the nonlinear diffusion equation, with diffusion coefficient directly proportional to the impurities concentration. In this case of diffusion from the constant source, the maximum displacements of diffusing particles are proportional to the square root of diffusion time. This result coincides with Brownian movement theory. The obtained analytically solutions were successfully applied for describing the diffusion and superdiffusion experiments' in solids. After theoretical consideration of application of this equation for diffusion in gases, we are investigating here the binary nonlinear diffusion in gases. We obtained the nonlinear interdiffusion equation, for the spherical symmetric case, and presented the approximate analytical solutions.
8
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Nonlinear Diffusion in Excited HgCdTe and Si Crystals

51%
Janavičius A., Norgėla Ž., Purlys R.
Acta Physica Polonica A
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2003
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vol. 104
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issue 5
459-467
EN
We discuss the properties of the nonlinear diffusion equation for the case of diffusion in excited systems. The diffusion coefficient is directly proportional to the concentration of impurities and depends on time in a special way. For the description of the excited systems, we used a special temperature function, which defined the time dependent diffusion coefficient and the Boltzmann distribution of the excited vacancies or impurity atoms in solids. This model was used for the approximation of indium concentration profiles in HgCdTe of a rapid diffusion component and very fast diffusion of metastable vacancies irradiated by soft X-rays in an excited Si crystal.
9
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Supercrystallization of NaCl from Solution Irradiated by Soft X-Rays

51%
Janavičius A., Purlys R., Rinkūnas R.
Acta Physica Polonica A
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2013
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vol. 123
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issue 4
777-781
EN
It was found that irradiation of a water solution of NaCl with the diffractometer DRON3-M (Russian device) had a large influence on two-step processes of crystallization. The irradiation in the first stage of crystallization of the solution produces metastable radicals of water and excited seeds, which stimulate a very fast crystallization after switching off irradiation. After the crystals reach a sufficient size, the crystal growth can be explained by creation of vacancy-interstitial pairs in the growing crystal due to irradiation. The increase of linear dimensions of the growing irradiated crystals is proportional to the square root √t of crystallization time because most important place in crystallization takes the ions diffusion by irradiated vacancies.
10
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Investigation of Compound Relaxation Processes in Crystal Lattice Dynamics of Si Irradiated by Soft X-rays

51%
Janavičius A., Purlys R., Norgėla Ž.
Acta Physica Polonica A
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2006
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vol. 109
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issue 2
159-170
EN
We applied soft X-rays for investigation of dynamics of Frenkel point defects in a Si crystal during its saturation with metastable vacancies with neighboring Si atoms in excited states or vacancies with neighboring Si atoms in interstitial states produced in the lattice after ejection of Auger electrons. The irradiated irregularities and defects of the lattice cause a change of Bragg reflection maxima. Several resonance phenomena related to the metastable states introduced into Si crystal by soft X-rays irradiation have been detected.
11
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The Nonlinear Diffusion Equation Describing Spread of Impurities of High Density

51%
Janavičius A., Lūža G., Jurgaitis D.
Acta Physica Polonica A
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2004
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vol. 105
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issue 5
475-483
EN
The nonlinear diffusion equation is derived by taking into account the local variations in the solvent density, within a mechanism of diffusion driven by random particle collisions. Analytical solutions for the case of spherical-symmetric nonlinear diffusion equation for spread of impurities in gas and solids are obtained and discussed. In this case, the solutions of the nonlinear diffusion equation are similar to solutions of Bernoulli equation. We note that the obtained solutions can be used to describe the shapes of impurity gas of high concentration or smoke clouds.
12
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Superdiffusion in Si Crystal Lattice Irradiated by Soft X-Rays

39%
Janavičius A., Balakauskas S., Kazlauskienė V., Mekys A., Purlys R., Storasta J.
Acta Physica Polonica A
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2008
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vol. 114
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issue 4
779-790
EN
We considered the reasons of superdiffusivity and measured profiles of boron and phosphorus in crystalline silicon at room temperature. The superdiffusivity or ultrafast diffusion of metastable vacancies at room temperature in Si crystal irradiated by soft X-rays was obtained experimentally. In this work, we presented experimentally obtained diffusion coefficients of singly and doubly negatively charged long-lived excited vacancies. These high concentration charged metastable vacancies (about 10^{13} cm^{-3}) at room temperature can very fast diffuse changing electrical conductivity and the Hall mobility of carriers. We measured the superdiffusivity of negatively charged vacancies, generated by the Auger effect in the regions of the sample, which were not affected by X-rays. In this paper, we presented the obtained superdiffusion profiles of boron and phosphorus in crystalline silicon measured with secondary-ion mass spectrometer.
13
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Investigation and Generation of Vacancies in Alpha Quartz by Soft X-Rays

39%
Janavičius A., Purlys R., Bulkšas A., Balakauskas S., Mekys A., Šablinskas V.
Acta Physica Polonica A
|
2009
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vol. 116
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issue 6
1076-1080
EN
In this paper we applied the soft-X-ray radiation for generation of point defects, vacancies, and chemical reactions in quartz (SiO_{2}), taking into account our earlier made similar experiments with crystal silicon and importance of quartz for applications in many fields. In this case only radiative Auger's effects with electrons and electric dipole of atoms transitions can generate metastable vacancies, point defects, and induce chemical reactions. Usually, for point defects generation doses of gamma rays are used. We measured values of the Bragg reflections of X-rays and calculated mean square deviations of atoms in crystal lattice for defining the dynamics of irradiated point defects. We accomplished infrared measurements for establishing of generated chemical reactions, and conductivity measurements were also done.
14
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Crystal Lattice and Carriers Hall Mobility Relaxation Processes in Si Crystal Irradiated by Soft X-rays

39%
Janavičius A., Storasta J., Purlys R., Mekys A., Balakauskas S., Norgėla Ž.
Acta Physica Polonica A
|
2007
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vol. 112
|
issue 1
55-68
EN
We applied soft X-rays for investigation of dynamics of the Frenkel point defects in a Si crystal during its saturation with metastable vacancies with neighboring Si atoms in excited states produced in the lattice after ejection of the Auger electrons. The irradiated irregularities and defects of the lattice cause a change of the Bragg reflection maxima. Several resonance phenomena are related to metastable states introduced into Si crystal by soft X-rays irradiation. The resonance of mean square displacements of Si atoms in the lattice and the resonance of the Hall mobility after irradiation are obtained and considered.
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