Kinetics of high-temperature precipitation in dislocation-free silicon single crystals

The defect structure of dislocation-free silicon single crystals has been calculated using the approximate solution of the Fokker-Planck partial differential equations. It has been demonstrated that the precipitation starts to occur near the crystallization front due to the disappearance of excess intrinsic point defects on sinks whose role is played by oxygen and carbon impurities.     

On the recombination of intrinsic point defects in dislocation-free silicon single crystals

The recombination of intrinsic point defects in dislocation-free silicon single crystals is investigated. It is established experimentally and confirmed by thermodynamic calculations that this process in the vicinity of the crystallization front is hindered by the recombination barrier. The recombination parameters (such as the recombination barrier height, the recombination time, and the recombination factor) for the model describing the dynamics of point defects at low and high temperatures are evaluated in terms of the heterogeneous mechanism of nucleation and transformation of grown-in microdefects. It is confirmed that the decomposition of a supersaturated solid solution of point defects can occur according to two mechanisms, namely, the vacancy and interstitial mechanisms. Vacancies and intrinsic interstitial silicon atoms find sinks in the form of oxygen and carbon background impurities. It is demonstrated that the formation of “intrinsic-point-defect-impurity” pairs is a dominant process in the vicinity of the melting temperature.     

Instability of interstitial dislocation loops in electron-irradiated dielectrics

The experiments on electron irradiation of yttrium-stabilized zirconium oxide samples show the formation of strong elastic fields near interstitial dislocation loops. The fields increase with an increase in the loop radius and, when the loop radius reaches a certain critical value, the loops became unstable due to the beginning of plastic deformation and the formation of a dislocation network. The mechanism of the occurrence of this instability is suggested. It is based on the accumulation of charges at dislocation loops due to ionization processes in an electron-irradiated dielectric. It is shown that the accumulation of the electric charge at growing dislocation loops in dielectrics may be responsible for an increase in elastic stresses near dislocation loops and for their instability because of the beginning of plastic deformation near the loops when stresses at growing loops become close to the theoretical yield stress of the material.     

Diffusion and solubility of zinc in dislocation-free and plastically deformed silicon crystals

Floating-zone Si crystals enclosed in quartz ampoules were exposed to Zn vapour released by an elemental diffusion source. Penetration profiles of Zn in Si were recorded using the spreading-resistance technique or neutron activation analysis. Both the erfc-type distributions observed in plastically deformed specimens and the non-erfc profiles determined on dislocationfree wafers are consistently interpreted within the framework of the kick-out model. As an implication, Si self-interstitials generated in excess by interstitial-to-substitutional transitions of in-diffusing Zn atoms annihilate not only at the surface but also at dislocations. On the other hand, dislocation-induced segregation of Zn appears to be rather minor, as revealed by transition electron microscopy. Combining the Zn incorporation rate in dislocation-free Si with solubility data from saturated specimens yields the self-interstitial contribution to the Si self-diffusion coefficient.Dedicated to H.J. Queisser on the occasion of his 60th birthday     

Statistical mechanics of vacancy and interstitial strings in hexagonal columnar crystals

Columnar crystals contain defects in the form of vacancy-interstitial loops or strings of vacancies and interstitials bounded by column "heads" and "tails." These defect strings are oriented by the columnar lattice and can change size and shape by movement of the ends and by forming kinks along the length. Hence an analysis in terms of directed living polymers [S. A. Safran, Statistical Thermodynamics of Surfaces, Interfaces, and Membranes (Addison-Wesley, Reading, MA, 1994), Sec. 8] is appropriate to study their size and shape distribution, volume fraction, etc. If the entropy of transverse fluctuations overcomes the string line tension in the crystalline phase, a string proliferation transition occurs, leading to a supersolid phase [E. Frey, D. R. Nelson, and D. S. Fisher, Phys. Rev. B 49, 9723 (1994); see also J. Prost, Liq. Cryst. 8, 123 (1990)]. We estimate the wandering entropy and examine the behavior in the transition regime. We also calculate numerically the line tension of various species of vacancies and interstitials in a triangular lattice for power-law potentials as well as for a modified Bessel function interaction between columns such as occurs in the case of flux lines in type-II superconductors or long polyelectrolytes in an ionic solution. We find that the centered interstitial is the lowest-energy defect for a very wide range of interactions; the symmetric vacancy is preferred only for extremely short interaction ranges.     

Mechanism of formation of the interlamella dislocation network in polyethylene single crystals

It was found experimentally that bilayered polyethylene single crystals with an orientational misfit angle larger than the critical angle, θ*, show moire pattern and only those with an angle smaller than θ* show the interlamella dislocation network. The intermediate pattern, which could neither be classified into the typical moire pattern nor the typical interlamella dislocation network, was found in the vicinity of θ*. Criteria for discrimination between the moire pattern and the interlamella dislocation network are discussed. The crystal with a misfit angle a little larger than θ* also comes to show the feature of the dislocation network during long storage of the crystal in the mother solution at the crystallization temperature. θ* is, therefore, a function of the time of storage. A mechanism is presented such that crystal lattices near the interfacial boundary are distorted to form the dislocation network by intermolecular force between the overlying crystals when the misfit angle is smaller than θ*.     

Constricted hysteresis loops in Fe and Ni single crystals

Magnetic hysteresis loops reflect the variety of magnetic domain structures and have been considered to have normal rectangular or leaf-like shapes in standard ferromagnets such as Fe and Ni metals. We report on observations of constricted hysteresis loops in Fe and Ni single crystals with very low defect densities. The constricted loops were observed below T=150 K and in a medium temperature range from 150 to 430 K in Fe and Ni single crystals, respectively. These constricted loops disappear by weak plastic deformation for both single crystals. The origin of constricted hysteresis loops was explained by eddy current effects under less domain wall pinning due to dislocations.     

Computer simulation of the vacancy defects interaction with shuffle dislocation in silicon

The interactions between the 60^° shuffle dislocation and two different types of vacancy defects in silicon are separately studied via the molecular dynamics simulation method. The Stillinger–Weber potential is used to describe the atomic interactions. The results show that the dislocation slip velocity will decrease due to the interaction with the vacancy cluster (V ₆). The simulation also reveals that the divacancy will be absorbed by the dislocation. Meanwhile, a climbing of the dislocation occurs during their interactions. However, the divacancy has little effect on the dislocation slip velocity. Based on the above results, the decrease in threading dislocation density in SiGe/Si heterostructures with the use of low-temperature Si buffer layer may be explained.     

Magnetoplasticity and diffusion in silicon single crystals

The effect of static magnetic fields on the dynamics of surface dislocation segments, as well as the diffusion mobility of a dopant in silicon single crystals, has been analyzed. It has been experimentally found that the preliminary treatment of p-type silicon plates (the dopant is boron with a concentration of 10¹⁶ cm⁻³) in the static magnetic field (B = 1 T, a treatment time of 30 min) leads to an increase in the mobility of surface dislocation segments. The characteristic times of observed changes (about 80 h) and the threshold dopant concentration (10₁₅ cm⁻³) below which the magneto-optical effect in silicon is not fixed have been determined. It has been found that diffusion processes in dislocation-free silicon are magnetically sensitive: the phosphorus diffusion depth in p-type silicon that is preliminarily aged in the static magnetic field increases (by approximately 20%) compared to the reference samples.     

Laser grown single crystals of silicon

Single crystal rods of silicon have been grown by laser-induced chemical vapor deposition (LCVD) using visible light. We believe these to be the first reported single crystals of any material grown by LCVD.     

Slip band formation and mobile dislocation density generation in high rate deformation of single fcc crystals

The mechanisms for the nucleation, thickening, and growth of crystallographic slip bands from the sub-nanoscale to the microscale are studied using three-dimensional dislocation dynamics. In the simulations, a single fcc crystal is strained along the [111] direction at three different high strain rates: 10⁴, 10⁵, and 10⁶?s^??1. Dislocation inertia and drag are included and the simulations were conducted with and without cross-slip. With cross-slip, slip bands form parallel to active (111) planes as a result of double cross-slip onto fresh glide planes within localized regions of the crystal. In this manner, fine nanoscale slip bands nucleate throughout the crystal, and, with further straining, build up to larger bands by a proposed self-replicating mechanism. It is shown that slip bands are regions of concentrated glide, high dislocation multiplication rates, and high dislocation velocities. Cross-slip increases in activity proportionally with the product of the total dislocation density and the square root of the applied stress. Effects of cross-slip on work hardening are attributed to the role of cross-slip on mobile dislocation generation, rather than slip band formation. A new dislocation density evolution law is presented for high rates, which introduces the mobile density, a state variable that is missing in most constitutive laws.     

Magnetoresonant hardening of silicon single crystals

JETP Letters - A microwave magnetic field crossed with a static field was found to exert a resonance effect on the dislocation mobility in single crystals of p-type silicon. The frequency of...     

The activation energy of single vacancy formation in platinum

The formation energy of single vacancies in platinum (purity 5 N) has been measured resistometrically in thin wires, quenched exponentially from temperatures 650 ÷ 1150 °C. Attention has been paid to the establishment of the effective temperature, corresponding to the total concentration of vacancies. In pure samples, the influence of this correction on E^F is rather small, whereas the uneven distribution of temperature along the specimen length is of greater importance. The size-effect correction partially improves the curvature of the Arrhenius plot at low temperatures. The quenching rate in helium gas was high enough to retain almost all vacancies present in the solid solution. For evalution of experimental data the method of least squares was used, taking into account the changing scale of the Arrhenius plot. The most probable value of formation energyE ^F is 1·31±0·05 eV; it is compared with results of other authors and the reason of large spread of experimentally found formation energies is discussed.     

Activation energies for the formation and evaporation of vacancy clusters in silicon

The thermal evolution of vacancy-type defects in Czochralski (Cz-) and epitaxially grown (epi-) silicon has been investigated using variable-energy positron annihilation spectroscopy. Heating at 300-500 degrees C caused rapid migration of divacancies and clustering of the resulting defects with activation energies of 2.1(2) and 2.7(7) eV in epi- and Cz-Si. Clustering occurred more rapidly in Cz-Si, attributed to the seeding effect of impurities. Heating at 500-640 degrees C annealed the clusters with activation energies of 3.9(3) and 3.6(3) eV in epi- and Cz-Si, linked to the vacancy-cluster binding energy.     

Diffuse x-ray scattering study of the formation of microdefects in heat-treated dislocation-free large-diameter silicon wafers

Diffuse x-ray scattering (DXS) is used to study the formation of microdefects (MDs) in heat-treated dislocation-free large-diameter silicon wafers with vacancies. The DXS method is shown to be efficient for investigating MDs in silicon single crystals. Specific defects, such as impurity clouds, are found to form in the silicon wafers during low-temperature annealing at 450°C. These defects are oxygen-rich regions in the solid solution with diffuse coherent interfaces. In the following stages of decomposition of the supersaturated solid solution, oxide precipitates form inside these regions and the impurity clouds disappear. As a result of the decomposition of the supersaturated solid solution of oxygen, interstitial MDs form in the silicon wafers during multistep heat treatment. These MDs lie in the {110} planes and have nonspherical displacement fields. The volume density and size of MDs forming in the silicon wafers at various stages of the decomposition are determined.     

Magnetic properties of oxides and silicon single crystals

The magnetic properties of single crystals Si, SrTiO₃, LaAlO₃, MgO, and (La,Sr)(Al,Ta)O₃ were investigated systematically. Three origins of the magnetizations of these crystals, namely, an intrinsic diamagnetic, a paramagnetic, and a ferromagnetic contribution, have been found to influence the magnetic signals measured on the crystals, in some important application scenarios such crystals being served as substrates with the magnetic thin film epitaxially grown on. Quantitative analyses methodologies were developed and thorough investigations were performed on the crystals with the intrinsic materials parameters thus revealed, especially that the intrinsic diamagnetic susceptibility differential dχ_dia/dT were identified quantitatively for the first time in SrTiO₃, LaAlO₃, MgO, and (La,Sr)(Al,Ta)O₃. The paramagnetic contribution is found to be the key in terms of the magnetic properties of the crystals, which in turn is in fact a consequence of the 3d impurities doping inside the crystal. All the intrinsic materials parameters are given in this paper as datasets, the datasets are openly available at https://www.doi.org/10.57760/sciencedb.j00113.00028.     

Post-yielding dislocation retraction of nano-lamellar TiAl single crystals

The perfect single crystal has ultra-high strength but is often accompanied by catastrophic failures after yielding. This study reveals that nano-lamellar TiAl single crystals alleviate the catastrophic failure due to a post-yielding dislocation retraction through atomistic simulations and theoretical analyses. This dislocation retraction leads to a retained post-yielding strength of1.03 to 2.33 GPa(about 50% of the yielding strength). It is shown that this dislocation retraction is caused by local stress relaxation and interface-mediated image force. The local stress relaxation is due to successive dislocation nucleation in different slip systems, and the interface-mediated image force is caused by the heterogeneous interface. Based on dislocation theory, this study demonstrates that the size effect also plays a vital role in dislocation retraction. Theoretical modeling shows that the dislocation retraction occurs when the lamellar thickness is less than approximately 12 nm. Additionally, the post-yielding dislocation retraction is more pronounced at higher temperatures, making it more effective in alleviating catastrophic failures.These findings demonstrate a viable option for avoiding catastrophic failure of single crystals through nanoscale-lamellar design.     

Domain structure of silicon iron single crystals

The model of a new domain structure arising after the magnetization of silicon iron single crystals in planes of the (110) type at an angle of 0°<Θ<-55° to the axis of easy magnetization is considered. Using this model the angular dependence of the domain-structure characteristics is established; it agrees closely with direct observations. On magnetizing a single crystal in the angular range 55° <Θ≤ 90° to the easy axis, layers with a uniform resultant magnetization parallel to the [001] direction are formed.     

Shallow thermal donors in nitrogen-doped silicon single crystals

Czochralski-grown nitrogen-doped silicon crystals contain shallow thermal donors (STD) which are not present in reference crystals. In the course of annealing at 600 or 650°C, the STD concentration reaches saturation and this concentration scales with nitrogen content N as N^1/2. This implies that an STD includes only one nitrogen atom and that the most likely model of the STD defect is the NO_m complex of an interstitial nitrogen atom with m oxygen atoms. The number m is estimated as, on the average, m=3 from data on the temperature dependence of the equilibrium constant for the complex formation reaction