Papers by Keyword: Antiphase Boundary (APB)

Abstract: Eelectrically active defects in 3C–SiC are investigated by considering the structures and interactions of planar defects. An anti-phase boundary (APB) largely degrades the blocking property of semiconductor devices due to its semimetallic nature. Although APBs can be eliminated by orienting the specific polar face of 3C-SiC along a particular direction, stacking faults (SFs) cannot be eliminated due to Shockley-type partial dislocation glide. SFs with Shockley-type partial dislocations form a trapezoidal plate which expands the Si-terminated surface with increasing 3C-SiC thickness. Although the density of SFs can be reduced by counter termination, specific cross-junctions between a pair of counter SFs forms a forest dislocation, and this is regarded as an electrically active defect. This paper proposes an effective way to suppress the forest dislocations and APBs which nucleate during 3C-SiC growth.

Abstract: In the present study, we describe a comprehensive and consistent physical model for the yield strength change in Allvac^® 718Plus^TM caused by precipitation strengthening. The model incorporates the effect of different shearing and non-shearing mechanisms with respect to atomic continuity between the lattices of precipitates and matrix. We demonstrate that coherency and anti-phase boundary effects are the major strengthening mechanisms in this alloy. The final yield strength of Allvac^® 718Plus^TM during aging is investigated using the thermo-kinetic software MatCalc. The calculated final yield strength evolution is consistent with experimental results.

Abstract: Alloys of Cu-Pt [1] are of interest for research, since the phase transitions "order - disorder" at different concentrations of components form several types of superstructures. In the alloy Cu₃Pt the ordering L1₂ superstructure formed on the basis of fcc lattice. In the ordering of the fcc lattice of the disordered solid solution the equiatomic composition transformed into the L1₁ superstructure with an rhombohedral crystal lattice (a state with an L1₁, whose angles α, β, and γ are other than π/2). A CuPt₃ in an ordered state has an L1₃ superstructure (a state with an L1₃, whose angles α, β, and γ are other than π/2). A possible existence of an ordered phase containing 20 at.% Pt was reported in the literature [2], which corresponds to the composition of Cu₄Pt (type of superstructure was not defined). In other sources, an occurrence of an ordered compound, Cu₇Pt, was predicted, containing 12.5 at.% Pt [3]. Computer experiments performed on the Monte Carlo method, showed that the alloys of the Cu - Pt different composition components undergo phase transformations "disorder - order" from the FCC to the structures of different symmetry [4,11]. This paper presents the results of a study of the structural transformations in the alloys Cu₃Pt, CuPt, CuPt₃ (superstructure L1₂, L1₁, L1₃), containing shear antiphase boundaries (APB) in the planes {111}.

Abstract: The antiphase domain structure in Ni3Al and Al3Ti+Cu intermetallic alloys was recognized by conventional transmission electron microscopy and large angle convergent beam electron diffraction methods. In the case of antiphase boundary the superlattice excess line is split into two lines with equal intensity on bright and dark field LACBED pattern. This splitting can be considered as typical and used to identify APBs. The recognition between perfect structure of the defect-free matrix and the screw deviation around the nanopipes in GaN epilayers was performed with high accuracy using Zone Axis LACBED images.

Abstract: Quantitative efficacies of several methods for stacking fault (SF) reduction are evaluated using Monte Carlo (MC) simulation. SF density on a 3C–SiC {001} surface depends on interactions of adjoining SFs: annihilation between counter pairs of SFs and termination by orthogonal SF pairs. However, SFs are not entirely eliminated when growth occurs on undulant-Si and switch back epitaxy (SBE) due to spontaneous SF collimation that suppresses the annihilation probability of counter SFs. The MC simulation also reveals the efficacy of SF reduction method which includes the growth of 3C–SiC on finite area bounded by side walls. One can theoretically reduce the SF density below 100 cm^-1 on 3C–SiC {001} surface. A practical way for eliminating the SF by termination at side walls is demonstrated, and it clearly exhibits that the SF density can be reduced under 120 cm^-1.

Abstract: Pseudoelasticity of Fe₃Ga polycrystals doped with third elements (Ti, V, Cr, Mn, Co, Ni, Si, Ge) was examined. Fe₃Ga polycrystals with the appropriate heat treatment were found to exhibit large pseudoelasticity based on reversible motion of dislocation dragging an antiphase boundary (APB). In Fe₃Ga crystals with the D0₃ superlattice structure, paired 1/4<111> superpartial dislocations mainly moved dragging the next-nearest-neighbor APB during loading. During unloading, the APB pulled back the superpartial dislocations resulting in the pseudoelasticity. The D0₃ ordered phase also developed in Fe₃Ga polycrystals with 2at% of the third elements. However, the strain recovery of Fe₃Ga polycrystals depended strongly on third element. Fe₃Ga polycrystals doped with 2at% of Mn, Cr and Co demonstrated large pseudoelasticity. In contrast, the other doped elements decreased the amount of strain recovery. The frictional stress of 1/4<111> superpartial dislocations and the back stress due to the APB, acting on the dislocations, changed by doping the third elements, which was closely related to the pseudoelastic behavior. It is also noted that there was a good correlation between the APB back stress and the ordering temperature from the B2 to D0₃ phase.

Abstract: We performed magnetic imaging of Ni-based ferromagnetic shape memory alloys. The magnetic microstructure was revealed by Lorentz microscopy and electron holography, which are powerful tools based on transmission electron microscopy. Observations of Ni51Fe22Ga27 and Ni50Mn25Al12.5Ga12.5 alloys, both of which have an L21-ordered structure in the parent phase, demonstrated that the antiphase boundaries (i.e., a type of planer defects) caused significant changes in the magnetization distribution due to depression of the atomic order—actually, the magnetization in these alloys depends upon the degree of chemical order. We propose a method which estimates the important magnetic parameters (the magnetocrystalline anisotropy constant and exchange stiffness constant) based on transmission electron microscopy observations. This method should be useful in magnetic measurements of nanometer-scale areas, for which conventional techniques cannot be applied.

Abstract: In 3C-SiC MOSFETs, planar defects like anti-phase boundaries (APBs) and stacking-faults (SFs) reduce the breakdown voltage and induce leakage current. Although the planar defect density can be reduced by growing 3C-SiC on undulant-Si substrate, specific type of SFs, which expose the Si-face, remains on the (001) surface. Those SFs increase the leakage current in devices made with 3C-SiC. In order to eliminate the residual SFs, an advanced SF reduction method involving polarity conversion and homo-epitaxial growth was developed. This method is called switch-back epitaxy (SBE) and consists of the conversion of the SF surface polarity from Si-face to C-face and following homo-epitaxial growth. The reduction of the SF density in SBE 3C-SiC results in a tremendous improvement of the device performance. The combination of the achieved blocking voltage with the demonstrated high current capability indicates the potential of 3C-SiC vertical MOSFETs for high and medium power electronic applications such as electric and hybrid electric vehicle (EV/HEV) motor drives.

Abstract: Long-range ordered intermetallic alloys with L12 (Ni3Al, Cu3Au) and B2 (FeAl) structures were deformed by high-pressure torsion at room temperature up to high grades of deformation. Transmission electron microscopy shows that disordering caused by the deformation occurs on a very local scale within coarse grains along glide planes (Cu3Au, Ni3Al) and in the form of well defined local regions (Ni3Al, FeAl). The latter leads to a duplex structure consisting of an ordered coarse-grained structure and a disordered nanocrystalline structure. The different mechanisms that can lead to disordering during severe plastic deformation are discussed on the basis of the different ordering energies and on the basis of antiphase boundaries associated with gliding dislocations. The results indicate that in intermetallic alloys the formation of a nanocrystalline structure by severe plastic deformation is facilitated by the loss of order.

Abstract: The pseudoelastic behavior of Fe3Al single crystals doped with an extra element (e.g. Ti, V, Cr, Mn, Co, Ni, Si, Ga, Ge) was investigated. In binary Fe-23.0at.%Al crystals with the D03 structure, 1/4[111] superpartial dislocations moved independently dragging the nearest-neighbor anti-phase boundaries (NNAPB) during loading. During unloading, the NNAPB pulled back the superpartials decreasing its energy resulting in a giant pseudoelasticity of which the recoverable strain is about 5 %. Addition of a third element significantly affected the pseudoelastic behavior of Fe3Al single crystals. Mn- or Ga-doped crystal demonstrated a giant pseudoelasticity. In particular, Ga-doping was found to be effective in the enhancement of the pseudoelasticity. On the other hand, the amount of strain recovery decreased upon doping of the other elements. The frictional stress of the superpartials, the back stress of the NNAPB and ordered domain structure in the crystals changed upon doping, which was closely related to the pseudoelastic behavior.