Mikhail Yu. Gutkin

Micropipe evolution in silicon carbide

Micropipe bundling and twisting in SiC crystals was revealed using synchrotron x-ray phase sensitive radiography. The computer simulation of micropipe evolution during the crystal growth suggests that the bundled and twisted micropipes arise under the influence of stress fields from other neighboring micropipes. The annihilation of twisted dipoles is attributed to their transformation into semiloops. Reactions of micropipe coalescence lead to the generation of micropipes and/or the annihilation of initial micropipes, resulting in the decrease in their average density.

Rotational Deformation Mechanism in Fine-Grained Materials Prepared by Severe Plastic Deformation

j k h l f m n l o L : G = > A = : ; F H C D > M = C ; 9 9 < J J = 9 : = M p G ; F G M = 9 F A ; B = 9 : G = A > : H : ; > 8 H C M = ? > A D H : ; > 8 D = F G H 8 ; 9 D ; 8 q 8 = \ J A H ; 8 = M D H : = A ; H C 9 ` A = ` H A = M B N 9 = X = A = ` C H 9 : ; F M = ? > A D H : ; > 8 V 7 8 : G = ? A H D = \ p > A ^ > ? : G = D > M = C T : G = A > : H : ; > 8 H C M = ? > A D H : ; > 8 > F F < A 9 X ; H : G = D > : ; > 8 > ? J A H ; 8 B > < 8 M H A N M ; 9 F C ; 8 H : ; > 8 M ; ` > C = 9 T H 9 9 > F ; H : = M p ; : G = D ; 9 9 ; > 8 > ? M ; 9 C > F H : ; > 8 ` H ; A 9 ? A > D J A H ; 8 B > < 8 M H A ; = 9 ; 8 : > : G = H M Q H F = 8 : J A H ; 8 ; 8 : = A ; > A 9 V I 8 = A J = : ; F F G H A H F : = A ; 9 : ; F 9 > ? : G = M ; 9 F C ; 8 H : ; > 8 M ; ` > C = D > \ : ; > 8 H A = F H C F < C H : = M V K H 8 J = 9 > ? ` H A H D = : = A 9 > ? : G = M = ? = F : 9 N 9 : = D H A = A = X = H C = M H : p G ; F G : G = M ; 9 F C ; 8 H : ; > 8 D > : ; > 8 ; 9 = 8 = A J = : ; F H C C N ? H X > < A H B C = V 7 : ; 9 9 G > p 8 : G H : : G = A > : H : ; > 8 H C M = ? > A D H : ; > 8 D = F G H 8 ; 9 D H 9 9 > F ; H : = M p ; : G : G = = D ; 9 9 ; > 8 > ? M ; 9 C > F H : ; > 8 ` H ; A 9 ; 9 F H ` H B C = > ? = 9 9 = 8 : ; H C C N F > 8 \ : A ; B < : ; 8 J : > ` C H 9 : ; F r > p ; 8 q 8 = \ J A H ; 8 = M D H : = A ; H C 9 ` A = ` H A = M B N 9 = X = A = ` C H 9 : ; F M = ? > A D H : ; > 8 V

Modelling of Vacancy Diffusion and Pore Formation during Parabolic Oxide Growth

Vacancy diffusion and the possibility of pore formation during oxide growth by cation diffusion are investigated. For a parabolic time dependence of the oxide thickness growth, the evolution of the vacancy concentration in the metal is analysed by taking into account the annihilation of vacancies at sinks located at the oxide-metal interface and within the metal. By omitting vacancy absorption at growing vacancy agglomerates, upper estimates of the vacancy supersaturation are calculated, from which the nucleation and growth rates of pores are derived. The nucleation rate strongly decreases with increasing oxidation time and temperature whereas the growth rate increases with increasing temperature. The analysis suggests that the appearance of pores is crucially controlled by the strength of vacancy sinks at the oxide-metal interface and by the presence of impurities lowering the surface energy by impurity segregation to the metal surface of vacancy clusters. Possible flaws of the approach which are related to the assumption of parabolic oxide growth are discussed.

Wedge disclination dipole in an embedded nanowire within the surface/interface elasticity

Abstract The elastic behavior of an arbitrary oriented wedge disclination dipole located inside a nanowire, which in turn is embedded in an infinite matrix, is studied within the surface/interface theory of elasticity. The corresponding boundary value problem is provided using complex potential functions. The potential functions are defined through modeling the wedge disclination in terms of an equivalent distribution of edge dislocations. The interface effects on the stress field and strain energy of the disclination dipole and image forces acting on it, the influence of relative shear moduli of the nanowire and the matrix, as well as the different characteristics of the interface are studied thoroughly. It is shown that the positive interface modulus leads to increased strain energy and extra repulsive forces on the disclination dipole. The noticeable effect of the negative interface modulus is the non-classical oscillations in the stress field of the disclination dipole and an extra attractive image force on it.

INTERFACIAL PROPERTIES OF SILICON STRUCTURES FABRICATED BY VACUUM GROOVED SURFACE BONDING TECHNOLOGY

The paper presents a novel modification of a direct bonding technology. A presented innovation is aimed at fabricating void free interfaces with a low defect density. For this purpose the bonding boundaries are manufactured as grooved, and the bonding annealing is performed under vacuum conditions. It has been found that the grooves act as dislocation traps. A trapped gas escapes through the grooves which facilitates the void removal. By X-ray and electron diffraction techniques the grooves have been observed to flatten rapidly. The electrical properties of the grooved interfaces are as good as those of diffusion p-n junctions.

Fraction-exponential representation of the viscoelastic properties of dentin

We propose the fraction-exponential description of the viscoelastic properties of dentin. Creep tests are performed on specimens cut from the molar coronal part. Four parameters determining instantaneous and long term Youngs moduli as well as the relaxation time are extracted from the experimental data. The same procedure is repeated using the experimental measurements of Jantarat et al (2002) for the specimens cut from the root part of incisor. Physical meaning of the parameters and the difference between them for different sets of specimens are discussed.

Structural Transformation of Dislocated Micropipes in Silicon Carbide

The interaction of super screw -dislocations, or micropipes, in PVT grown SiC crystals has been studied by Synchrotron Radiation radiography. The reduction in micropipe density via reactions of coalescence, annihilation and transformation of micropipes has been observed. The reactions have been described quantitatively based on the micromechanics of these defects.

Yield Stress of Nanocrystalline Materials

Most mechanical properties of nanocrystalline materials (NCMs) are essentially different from those of conventional coarse-grained polycrystals. NCMs exhibit extremely high strength and good fatigue resistance [224–226], as desired for numerous applications. Most NCMs show low tensile ductility which limits their practical utility. At the same time, several examples of substantial ductility and even superplasticity have been reported. In particular, nanocrystalline ceramics commonly exhibit superplasticity at lower temperatures and faster strain rates than their coarse-grained counterparts [227, 228].

Synchrotron X-Ray Study on Crack Prevention in AlN Crystals Grown on Gradually Decomposing SiC Substrates

We report on the growth method and the structural characterization of freestanding AlN crystals. An AlN layer is grown on a gradually decomposing SiC substrate yielding a freestanding crack free 2H single crystal with dislocation density 5×104 cm–2 and without grain boundaries as confirmed by synchrotron radiation phase contrast imaging and topography data. Wafers of 600–1000 μm thick and up to 15 mm in diameter are obtained. The thermal stress distribution in a conventional AlN/SiC structure is discussed. Theoretical estimates show that cracking of AlN layers is a natural result of their growth on undecomposed SiC substrates.

Micropipes in crystals: experimental characterization, theoretical modeling and computer simulation

We give an overview of experimental investigations and theoretical modeling of elastic interaction and transformations of dislocated micropipes in growing crystals. We consider elastic interaction of pair of micropipes, split of a micropipe into smaller dislocated micropipes and/or full-core screw dislocations, elastic interaction of micropipe steps, micropipe grouping and twisting. The models reviewed explain the experimental observations of ramified, twisted and grouped micropipes in silicon carbide.