Stacking faults in pseudomorphic ZnSe-GaAs and latticematched ZnSe-In0.04 Ga0.96 As layers

ABSTRACT We report transmission electron microscopy studies of native extended defects in pseudomorphic ZnSe/GaAs (001) and lattice-matched ZnSe-In0.04 Ga0.96 As (001) heterostructures. The dominant defects present in the layers were identified as Shockley stacking fault pairs lying on (111) and (111) fault planes and single Frank stacking faults lying on (111) or (111) fault planes by comparing experimental images with the predictions obtained with the g b = 0 rule as well as with simulated images.     

Deformation mechanism of long-period TiAl 2

The microstructure of long-period TiAl 2 deformed at room temperature has been studied by means of transmission electron microscopy. Dislocations, stacking faults and twins were found to contribute to the deformation. A screw superdislocation with Burgers vector d 110] dissociates into two ½ d 110] super-partial dislocations associated with an antiphase boundary. The ½; d 110] super-partial dislocation further dissociates into two Shockley partial dislocations associated with a portion of complex intrinsic stacking fault on the closest-packed {111} plane. The propagation of stacking faults on successive {111} planes yields an order twin.     

Plastic behaviour of an AlAs/GaAs superlattice with a short period

Nanoindentation has been used to investigate the plastic behaviour of an AlAs/GaAs superlattice with a short period. The sample was grown on a (001) surface of a GaAs single crystal by metal-organic vapour-phase epitaxy. The mechanical response of the superlattice to nanoindentation testing was compared with that of a (001) surface of bulk GaAs. The indents formed were observed by transmission electron microscopy. The plastic zone size associated with each indent was measured as a function of the maximum load. Finally the arrangement of the dislocations generated by the indenter has been analysed and compared with the arrangement observed in deformed bulk GaAs.     

Investigation of {111} stacking faults and nanotwins in epitaxial BaTiO3 thin films by high-resolution transmission electron microscopy

{111} stacking faults and nanotwins in epitaxial BaTiO₃ thin films on MgO substrates have been investigated by high-resolution transmission electron microscopy. In many cases, the stacking faults and nanotwins were found to be accompanied by partial dislocations. These partial dislocations can be classified as two different types, analogous to the situation in the fcc structure. One is of the Shockley type with the Burgers vector (a/3)<112>. The other is of the Frank type with the Burgers vector (a/3)<111>. The movements of both types of partial can lead to the {111} stacking faults and the {111} twins observed in these films.     

Structural changes induced by low-energy electron irradiation in GaSb

Structural changes in GaSb (001) thin films upon low-energy electron (125?keV) irradiation have been studied by in situ transmission electron microscopy. No structural changes were observed for irradiation at room temperature. However, in a sample irradiated at 473?K domains of {110} variant, rotated 90° from each other, were formed in the matrix. The average diameter of the domains was approximately 18?nm in the sample irradiated to a fluence of 4.8?×?10²⁴?electrons/m². It is considered that the domains are pseudo-{110} planes in the matrix formed by electron-irradiation-induced Shockley partial dislocations.     

Determination of atomic structure of phason planes in the ξ′-Al–Pd–Mn phase

The atomic structures of specific types of linear defects (phason lines) and planar defects (phason planes) in the complex metallic alloy phase ξ′-Al–Pd–Mn have been determined by high-resolution electron microscopy (HREM) and theoretical HREM simulation. The results show that a representational atomic structural model for phason planes can be constructed by introducing a shift between two parts of the perfect crystalline structure using a translation vector of r ?=?(1/2) a ?+?(1/2τ) c . This typical phason plane is normally parallel to the (001) plane of the ξ′-Al–Pd–Mn phase and consists of phason lines, which are arranged side-by-side with their linear direction parallel to the [010] axis. HREM simulations, based on the structural model for both edge-on and inclined types of phason lines, agree well with the experimental results. Taking into account the fact that the structural difference between various curved phason planes arises from the variation in the arrangement of individual phason lines, the atomic structures of the edge-on and inclined phason lines can be used to explain the various curved phason planes frequently observed in the ξ′-Al–Pd–Mn phase.     

Observation of planar stacking faults in a Ti-rich two-phase Ti-Al alloy after deformation at elevated temperatures

It is a common observation that in two-phase Ti-Al-based binary alloys, deformation of the gamma phase occurs by 1/2<110]-type ordinary dis-location activity and twinning associated with 1/6<112] type partials. In the present study the microstructure of a new Ti-Al-based alloy (Ti-47at.% Al-2at.%Mn-2at.%Nb+ 0.8 vol.% TiB₂) with a duplex microstructure consisting of primary equiaxed gamma grains and lamellar alpha₂+ gamma colonies was studied by transmission electron microscopy (TEM) after deformation at elevated temperatures. Planar stacking faults were found in the gamma laths. A detailed contrast analysis by TEM shows that these planar stacking faults lying on {111} planes are bound by all the fcc variants of the Shockley partial dislocations of type 1/6<121>, in contrast with the observations in stoichiometric binary TiAl alloys, where only 1/6<112]-type Shockley partials are found to be associated with the true twins. It is proposed that the addition of ternary and quaternary elements such as Mn and Nb promotes the other variants of the fcc-like dissociations (not common in L1₀structure) in the present alloy.     

Transmission electron microscopy observations of low-load indents in GaAs

Nanoindentations have been made on (001) surfaces of GaAs single crystals at room temperature and the indents observed by transmission electron microscopy. The permanent deformation, generated by a Berkovitch indentor submitted to maximum loads ranging between 600 to 1700 muN, was analysed and interpreted as a function of the loading curves. The plastic zone size was measured as a function of the maximum load to determine the yield strength of GaAs at room temperature. Finally, the fine structure of the dislocations generated by the indenter has been analysed and this is compared with previously reported structures for higher indenting loads.     

Non-dissociation of Lomer–Cottrell dislocations and 〈110〉{001} slip in silicon

Abstract

Two unexpected features have been revealed by transmission electron microscopy investigations of deformed silicon bicrystals: (a) slip of a/2 〈110〉 dislocations on {001} planes and (b) non-dissociation of Lomer–Cottrell dislocations formed by intersecting slip dislocations.     

Dislocations in indented Ga0·7 Al0·3As

Abstract

Transmission electron microscope observations have been made of dislocations in Ga_0·7Al_0·3As after indentation of (001) surfaces at room temperature. Using two-beam imaging, in bright-field and weak-beam imaging, dissociated dislocations with extended stacking faults were observed both in the [110] and [110] directions. This is different from GaAs in which dissociated dislocations are seen in only one of these directions. These results are compared with published work on indented GaAs and considered in the light of possible mechanisms.     

Plasticity of GaAs(011) at room temperature under concentrated load

Indentations have been made on a (011) surface of GaAs single crystal at room temperature. The loading-unloading curves were compared with those obtained under the same experimental conditions on (001) surfaces. The indents formed were observed by transmission electron microscopy in plan view as well as in cross-sectional view in samples prepared by the focused-ion-beam technique. The gliding systems could be identified, providing a better understanding of the plastic flow under the indenter. The arrangements of dislocations generated by the indenter have been analysed and compared with results previously reported by Ning et al.     

Planar dissociations and recombination energy of [110] superdislocations in Ni3Al: Generalized Peierls model in combination with ab initioelectron theory

Planar dissociation configurations of the [110] superdislocation in stoichiometric Ni₃Al are investigated by the generalized Peierls model using the {111} γ-surface energies calculated by the ab initio electron theory. The dissociation into four Shockley partials with the formation of an antiphase boundary and two complex stacking fault (CSF) ribbons turned out to be the energetically most favourable configuration. For the edge superdislocation the obtained dissociation widths should be large enough to be resolved in a weakbeam image, whereas for the corresponding configuration of the screw superdislocation the CSF ribbon has a rather small width which may be beyond the limit of the resolution. A twofold dissociation involving a superlattice intrinsic stacking fault is energetically less favourable. The recombination energy of the two Shockley partials in one superpartial is found to be 0.24eV/b.     

HREM examination of [101] screw dislocations in Ni3Al

Abstract

The dissociation of [101] screw dislocations in Ni³Al has been examined using high-resolution electron microscopy. [101] superdislocations are found to be dissociated into (a/2)[101] superpartial dislocations on the (010) cube cross-slip plane. These superpartials in turn dissociate into complex stacking faults on the (111) or (111) which are bounded by Shockley partials in agreement with theoretical predictions. The degree of antiphase boundary spreading on (010) was found to increase with deformation temperature while the superpartial core dissociations remain unchanged.     

Microstructure of hot-pressed α-Sic after creep experiments at high temperature

Abstract

Transmission electron microscopy analyses of hot-pressed α-Sic deformed at 1600°C have shown the activation of the basal plane with glide dislocations dissociated into Shockley partials. Loop nucleations have been frequently observed along the dislocation lines and a climb mechanism is proposed to explain, the experimental analyses.     

Onset of plasticity in a Σ = 5 GaAs compliant structure

Compliant structures have been fabricated in which a thin GaAs layer (thickness between 10 and 20nm) was bonded on top of a GaAs substrate with a large twist angle (about 37). This twist angle value was chosen so that the energy of the boundary (coincident boundary of type =5 (001)) was minimized. The structure of the interface was characterized and the onset of plasticity in such a compliant substructure was investigated using nanoindentation that allowed the low-load deformation regime to be observed. The results are compared with those obtained under the same conditions on a GaAs bulk substrate alone. No plastic zone was observed by transmission electron microscopy in the compliant structure under loads below 0.25mN while, under the same loads, plastic deformation was observed in the bulk substrate. For higher loads (2mN), plastic-flow enhancement was observed in the compliant structure. The results are discussed in the light of the arrangement of dislocations observed in the plastic zones.     

On the dislocation mechanism of amorphization of Si by indentation

The formation of an amorphous phase underneath a Vickers indentation produced on a Si(001) surface at room temperature has been observed by cross-sectional transmission electron microscopy. Two types of location are observed for the amorphous phase. One is formed just underneath the image of the indentation and the other is parallel to the slip planes of Si. It is concluded that the latter type, at least, is formed as a result of activation of dislocations which is induced by an external shear stress combined with a hydrostatic pressure.     

Structural characterization of double stacking faults induced by cantilever bending in nitrogen-doped 4H-SiC

Defects in highly nitrogen-doped 4H-SiC deformed by cantilever bending at 550°C have been identified by weak-beam and high-resolution transmission electron microscopy techniques. The induced-defects consist of double stacking faults (DSFs) whose expansion produces a local 4H?→?3C phase transformation. Each DSF is bound by two identical 30° Si(g) partial dislocations which glide on two adjacent basal planes. The DSFs belong to three different populations which differ by their extension as a function of the applied-stress and the 30° Si(g) characteristics (line direction L , Burgers vector b , glide planes and glide direction). The external mechanical stresses are the main driving forces involved in the DSF expansion. However, extra driving forces such as thermodynamic or electronic forces are also likely to be involved.     

Dislocation dissociation and stacking-fault energies in Ge1-xSix alloys

Dislocations in deformed Ge_1-xSi_x alloys in the whole range 0 < x < 1 have been investigated by means of weak-beam transmission electron microscopy. They are dissociated into Shockley partial dislocations bounding intrinsic stacking-faults. The intrinsic stacking-fault energy in the alloys decreases from 61 +/- 10 to 55 +/- 10 mJm^-2 with increasing Si content.     

Influence of Guinier-Preston zones on deformation in Ti-rich Ti-Ni thin films

The deformed microstructure of a Ti-48.9at.%Ni thin film has been investigated by transmission electron microscopy. It was found that Guinier-Preston (GP) zones exist in the thin film and the martensite has (001) compound twins as substructure. The microstructure of the martensite shows that the GP zones do not stop both the shear deformation of martensitic transformation and the twinning shear of (001) deformation twin in the martensite phase. These results give a microstructural explanation for the previous result that Ti-rich Ti-Ni thin films with GP zones show a large transformation strain despite the presence of the GP zones.     

Stress-corrosion cracking in YBa2Cu3O7−x ceramic superconductor

Abstract

Thin-foil transmission electron microscopy specimens of orthorhombic YBa²Cu³O^7?x subjected to residual elastic strains have shown slow crack growth in an atmosphere with low moisture content. Microcracks, initiated by amorphization at the strained edges, propagate alternately along (110) twin boundaries and (001) stacking faults, where strain energy is accumulated locally. The formation of carbon-rich amorphous layers along the strained lattice planes, followed by residual stress-assisted crack propagation, resembles stress-corrosion cracking in this ceramic superconductor.