Kinds Of Dislocations Research Articles

Atomistic simulation of α‐Al2O3 nanoparticle plastic anisotropy under compression

AbstractAlumina (α‐Al2O3) is one of the major ceramic oxides commonly used for its advanced mechanical properties. Since recently, nanoscale α‐Al2O3 requires more in‐depth characterization related to ceramic powder compaction and sintering as well as for applications in the field of biomedical engineering. In this study, we use classical molecular dynamics simulations with a 2/3‐body interatomic potential to investigate the mechanical response and the elementary deformation processes of α‐Al2O3 nanoparticles under compression. Results show that α‐Al2O3 nanoparticles resist up to particularly elevated critical force before yielding due to a surface nucleation process including various kinds of dislocations and nanotwins strongly sensitive to orientation and temperature. Results are rationalized in terms of stacking‐fault energy and shear stress analysis and are discussed in the light of recent micromechanical tests as well as more fundamental observations performed in the bulk material.

Dense dislocations enable high-performance PbSe thermoelectric at low-medium temperatures

PbSe-based thermoelectric materials exhibit promising ZT values at medium temperature, but its near-room-temperature thermoelectric properties are overlooked, thus restricting its average ZT (ZTave) value at low-medium temperatures. Here, a high ZTave of 0.90 at low temperature (300–573 K) is reported in n-type PbSe-based thermoelectric material (Pb1.02Se0.72Te0.20S0.08−0.3%Cu), resulting in a large ZTave of 0.96 at low-medium temperatures (300–773 K). This high thermoelectric performance stems from its ultralow lattice thermal conductivity caused by dense dislocations through heavy Te/S alloying and Cu interstitial doping. The dislocation density evaluated by modified Williamson-Hall method reaches up to 5.4 × 1016 m−2 in Pb1.02Se0.72Te0.20S0.08−0.3%Cu. Moreover, the microstructure observation further uncloses two kinds of dislocations, namely screw and edge dislocations, with several to hundreds of nanometers scale in length. These dislocations in lattice can strongly intensify phonon scattering to minimize the lattice thermal conductivity and simultaneously maintain high carrier transport. As a result, with the reduced lattice thermal conductivity and optimized power factor in Pb1.02Se0.72Te0.20S0.08−0.3%Cu, its near-room-temperature thermoelectric performance is largely enhanced and exceeds previous PbSe-based thermoelectric materials.

Characterizing armchaired and zigzagged phases: Antimony on oxide layer of Cu(110)

Antimony nanostructures fabricated on metal oxide layers are essential for practical applications in fields of solar cells, electronic and photonic devices. Here the antimony phases were systemically studied on the copper oxide of Cu(110). By high-resolution scanning tunneling microscopy (STM), we revealed that a wrinkled antimony phase was formed on the CuO surface regardless of the initial oxide structure. It exhibited an armchair-like configuration making up of protruded and dipped Sb atoms as confirmed by STM and density functional theory calculations. Further Sb deposition caused the armchair-like phase distorting and subsequently gave rise to formation of a c(2 × 2)-Sb phase. Finally, another kind of wrinkled phase was successfully fabricated. It consisted of two zigzagged antimony chains with protruded and dipped Sb atoms alternately distributing. By analysis of the atomically-resolved STM topographies, several kinds of dislocations have been observed and the corresponding geometric models are addressed. The armchair and zigzag phases both exhibited high stabilities for oxygen exposure. Conductance measurements imply that each phase interacts with the underlying layer. Our results might provide a way for fabricating stable ultrathin materials with a well-defined edge structure on oxide surfaces.

Dislocation and displacement: An analysis of Wang Jiuliang’s Plastic China

This essay uses the concepts of place and space to analyze Wang Jiuliang’s environmental documentary film Plastic China (2016) by examining three kinds of dislocation and displacement: the importation of Western trash to China, Yijie’s migration from Sichuan to Shandong, and Kun’s transformation from an agricultural peasant to an industrial worker in post-socialist China. Building on previous scholarship on dirt, rubbish, and ruins, the essay explores how the film’s focus on trash—“matter out of place”—sustains a critique of global consumerism, capitalism, and eco-colonialism. Cinematic features, such as the spatial imbalance the film constructs between its human subjects and the plastics processing plant where they work, are discussed. Yijie’s longing for home, a preindustrial place untouched by modernization and globalization, is evoked by the use of nondiegetic music. Her desire to go to school, a major narrative theme, is interpreted to indicate her spatialized alienation and non-locatable subjectivity as a migrant child. Although Kun is a native of the town where the processing plant stands, he experiences displacement without moving, as his hometown has been ecologically degraded and thus rendered inhabitable by the intrusion of toxic trash. Both Yijie and Kun, representing millions of Chinese peasants uprooted from the soil, are trapped in a one-way, no-return journey from place to space.

Interactions Between Topological Defects and Nanoparticles

Liquid Crystal (LC) topological defects have been shown to trap nanoparticles (NPs) in the defect cores. The LC topological defects may thus be used as a matrix for new kinds of NP organizations templated by the defect geometry. We here study composites of LC smectic dislocations and gold NPs. Straight NP chains parallel to the dislocations are obtained leading to highly anisotropic optical absorption of the NPs controlled by light polarization. Combining Grazing Incidence Small Angle X-ray scattering (GISAXS), Rutherford Back Scattering (RBS), Spectrophotometry and the development of a model of interacting NPs, we explore the role of the Np size regarding the dislocation core size. We use NPs of diameter D = 6 nm embedded in an array of different kinds of dislocations. For dislocation core larger than the NP size, stable long chains are obtained but made of poorly interacting NPs. For dislocation core smaller than the NP size, the disorder is induced outside the dislocation cores and the NP chains are not equilibrium structures. However, we show that at least half of these small dislocations can be filled, leading to chains with strongly enhanced electromagnetic coupling between the NPs. These chains are consequently more probably stabilized by the elastic distortions around the defect cores, the distortion being enhanced by the presence of the grain boundary where the dislocations are embedded.

Effect of isotropic stress on dislocation bias factor in bcc iron: an atomistic study

The effect of externally applied stress on the dislocation bias factor (BF) in bcc iron has been studied using a combination of atomistic static calculations and finite element integration. Three kinds of dislocations were considered, namely, a0/2〈1 1 1〉{1 1 0} screw, a0/2〈1 1 1〉{1 1 0} edge and a0〈1 0 0〉{0 0 1} edge dislocations. The computations reveal that the isotropic crystal expansion leads to an increasing or constant dislocation bias, depending on the Burgers vector and type of dislocation. On the other hand, compressive stress reduces the dislocation bias for all the dislocations studied. Variation of the dislocation BF depending on dislocation type and Burgers vector is discussed by analysing the modification of the interaction energy landscape and the capture efficiency values for the vacancy and self-interstitial atom.

{\bb Z}-module defects in crystals.

An analysis is presented of the new types of defects that can appear in crystalline structures where the positions of the atoms and the unit cell belong to the same {\bb Z}-module, i.e. are irrational projections of an N > 3-dimensional (N-D) lattice Λ as in the case of quasicrystals. Beyond coherent irrationally oriented twins already discussed in a previous paper [Quiquandon et al. (2016). Acta Cryst. A72, 55-61], new two-dimensional translational defects are expected, the translation vectors of which, being projections of nodes of Λ, have irrational coordinates with respect to the unit-cell reference frame. Partial dislocations, called here module dislocations, are the linear defects bounding these translation faults. A specific case arises when the Burgers vector B is the projection of a non-zero vector of Λ that is perpendicular to the physical space. This new kind of dislocation is called a scalar dislocation since, because its Burgers vector in physical space is zero, it generates no displacement field and has no interaction with external stress fields and other dislocations.

Placement of Public Art. Two Examples from Lisbon’s Waterfront

In our contemporary cities, some public spaces seem to have greater ability to host art interventions, like historical centers, urban sprawl areas, gardens and parks, new residential districts, among others. Also in port cities, its waterfronts constitute privileged spaces for the placement of public art. On Lisbon’s riverfront, we can see a relevant number of works and of monuments of strong symbolic nature. In turn, the placement of public art is a way to value the inherently symbolic nature of the waterfronts and to emphasize its monumentality. However, the criteria for the placement of public art on those spaces are not always clear. In some cases, there are some thematic correspondences between the works and the places, namely with the theme of the water, the Discoveries and others like that. Nevertheless, we cannot observe a profound spatial integration, or a design with the context. In some cases, the artistic elements are produced with a logic of isolated work of art and later they are acquired and placed in some public space. In other cases, we assist to an unusual situation: a work is conceived in a strict relation with a place, but then, without any evident justification, it is dislocated to a completely different context. Or simply it is removed, disappearing from the public space. Although it seems a strange situation, such kind of dislocations often occurs in Lisbon. On this framework, this research proposes a discussion about the processes of implementation of public art. We will analyze two cases of public art replacement:1) The monument Primeira Travessia Aérea do Atlântico Sul (First Aerial Crossing of the South Atlantic), by Laranjeira Santos and Rodrigues Fernandes, 1972; and 2) The public sculpture Ribeira das Naus, by Charters de Almeida, 1995. Both works were designed to very specific and important places on Lisbon’s waterfront and both were later replaced to other locations on the inner city, quite far from the river. This kind of “(de)monumentalization” of a space originates the following questions: why is a work removed from a public space and why it is decided to give it another destination? What are the implications of those changes? Is public art removable? Considering public art besides its purely aesthetic significance, this phenomenon seems to reveal that the physical and the social integration with the place are not always important, or, at least, they are only important in some moments. Also, we can see it from another point of view: a removal or a replacement of a work always reveals specific strategies for certain places, in certain moments. We can thus conclude that the processes of implementation of public art are clearly indicators of the policies and of the dynamics of the cities.

Irish Cosmopolitanism: Location and Dislocation in James Joyce, Elizabeth Bowen, and Samuel Beckett by Nels Pearson

<i>Irish Cosmopolitanism: Location and Dislocation in James Joyce, Elizabeth Bowen, and Samuel Beckett</i> by Nels Pearson

The influence of a threading dislocation on (110) interface morphology and growth rate of silicon crystal growth from melt

The crystal growths of Si (110) rough interface have been simulated by molecular dynamics. The morphology transformations of crystal–melt interface influenced by different kinds of dislocations have been investigated. The results showed that the threading dislocation locally changed the morphology of Si (110) interface and then affected the crystal growth rate. A screw threading dislocation induced a type of “V” groove around its outcrop in the Si (110) interface, while an edge threading dislocation formed a triangle cone pit. The influence radius and strain energy of a screw dislocation are bigger than those of an edge dislocation. The growth rate of Si crystal with a screw dislocation is markedly lower than that of an edge dislocation, which is close to that of dislocation-free crystal.

A landscape cannot be a homeland

What is the problem for which landscape is the answer? In this paper, I offer a response to this question, first posed at a meeting of landscape researchers in Brussels in 2011. I argue that the problem can be defined as ontopology, or what I call here homeland thinking, and I propose that a landscape cannot be a homeland. The salience of landscape as a critical term instead involves modes of thinking and feeling that chafe against invocations of homeland as a site of existential inhabitation, as a locus of sentiment and attachment, and a wellspring of identity. The paper explores the connections between ideas of landscape and homeland through discussions of the European Landscape Convention, phenomenology and the term homeland itself. I conclude by arguing that a landscape must be understood as a kind of dislocation or distancing from itself. There are, after all, no original inhabitants.

Anomalous bias factors of dislocations in bcc iron

Dislocation bias factors in bcc Fe have been calculated based on atomistic interaction energy maps on three kinds of dislocations, namely the a0/2〈111〉{110} screw, a0/2〈111〉{110} and a0〈100〉{001} edge dislocations. The results show that the dislocation bias is higher for the a0/2〈111〉 edge dislocation than for the a0〈100〉 edge dislocation, even though the latter possesses a larger Burgers vector. This indicates the importance of the dislocation core contribution. For the a0/2〈111〉{110} screw dislocation, a negative dislocation bias has been obtained, which implies a more efficient absorption of vacancies than of SIAs. The effect of coexistence of both edge- and screw dislocations are assessed by a total bias. A possible complementary mechanism for explaining the long swelling incubation time in bcc metals is suggested and discussed.

Phase field crystal study on grain boundary evolution and its micro-mechanism under various symmetry

Phase field crystal method is used to investigate the deformation process and mechanism of twined structure of a trigonal phase under uniaxial tensile deformation, and the evolution and corresponding micro-mechanism of low-angle symmetric and asymmetric grain boundaries (GB) as well as high-angle symmetric and asymmetric GB during deformation process are analyzed in detail. The deformation is performed under the condition that the direction of applied stress is parallel to that of initial GB. Results show that low-angle symmetric GB is composed of two kinds of edge dislocations with the angle made by Burgers vectors being around 60 During deformation, two kinds of dislocations in low-angle symmetric GB move along two opposite directions, then meet with the same kind of dislocation emitted from another GB leading to the annihilation of partial dislocations. As to the low-angle asymmetric GB, its only one kind of dislocation first climbs and moves along the horizontal direction of the applied stress, then each dislocation will break down into two dislocations with their Burgers vectors making an angle about 120, finally a perfect single crystal is formed via the movement and annihilation of dislocations. High-angle GBs first keep horizontal shape under the applied stress, then become serrated, and the dislocations are emitted from the cusps in GBs. Finally, the high-angle asymmetric GB will decompose with the movement and annihilation of dislocation, while the shape of high-angle symmetric GB becomes horizontal again. It can be seen that the high-angle symmetric GB is more stable than the high-angle asymmetric GB; this is in agreement with the results of experiments and molecular dynamics.

Influence of Threading Dislocations on Lifetime of Gate Thermal Oxide

The reliability of gate oxides is a fundamental issue for realizing SiC MOSFETs. Many reports said that crystal defects shorten the lifetime of the gate oxide. And, epi defects, the basal plane dislocations and threading screw dislocations (TSD) are considered killer defects. However, because of the high TSD density of commercial SiC wafers, the exact relationship between other kinds of dislocations with lifetime has not been revealed. On the other hand, RAF wafers that we developed have low TSD density, so it is easy to evaluate the relationship between other kinds of dislocations and lifetime. By using RAF wafers, in this study, we clarified the relationship between the lifetime of the gate oxide and crystal defects. We fabricated MOS diodes and measured their lifetimes by TDDB (Time Dependent Dielectric Breakdown) measurement. The breakdown points were defined by the photo-emission method. Finally, we classified the defects by TEM (Transmission Electron Microscopy). As the results, it was clarified that threading edge dislocation (TED) decreases the lifetime as does TSD, which earlier reports said. The lifetime of the gate oxide area, in which a TED is included, was shorter by one order of magnitude than a wear-out breakdown. And, the TSD was two orders.

Study on the Perfect Dislocation in Cd&lt;sub&gt;0.9&lt;/sub&gt;Zn&lt;sub&gt;0.1&lt;/sub&gt;Te Single Crystals by HRTEM

Two types of 60° perfect dislocation in Cd0.9Zn0.1Te single crystals were observed by HRTEM. The Burger’s vector of the two dislocation were and respectively. With reasonable premise, the possible dissociation mechanisms of the two kinds of dislocations were supposed to be and . There are two kinds of the formation mechanisms, the first one is the accumulation of the point defects and the other kind of dislocation is the lattice gliding caused by the thermal stress.

Dislocations in Bi 0.4Ca 0.6MnO 3 epitaxial film grown on (110) SrTiO 3 substrate

Bi 0.4Ca 0.6MnO 3 (BCMO) film with a thickness of 110 nm was epitaxially grown on a (110) SrTiO 3 (STO) substrate using pulsed laser ablation technique. The microstructure of the epitaxial films was investigated by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) in details. Two different kinds of dislocations, one being perpendicular to the BCMO/STO interface, the other being parallel to the interface, have been commonly observed. The formation mechanism for these dislocations has been discussed. All the dislocations are thought to relieve the local strain in the epitaxial film.

Defects in a-GaN grown on r-sapphire by hydride vapor phase epitaxy

Non-polar a-GaN films grown on r-sapphire by hydride vapor phase epitaxy (HVPE) are studied using transmission electron microscopy (TEM). Despite the small lattice mismatch in a-GaN ( [ 1 0 1 ¯ 0 ] ∼ 1.1 % and [0 0 0 1] ∼ 16 % ), high dislocation and basal stacking fault densities are observed. Epitaxial lateral overgrowth (ELO) technique is implemented in order to reduce the defect density. ELO reduces both densities by two orders of magnitude: the dislocation density is reduced from 1 × 10 10 to 3 × 10 8 cm − 2 and the stacking fault density is reduced from 1 × 10 6 to 4 × 10 4 cm − 1 . Threading dislocations (TDs) are observed in the ELO mask openings with screw and mixed characters which have Burgers vectors b ⇒ = 1 3 [ 1 1 2 ¯ 0 ] and b ⇒ = 1 3 [ 1 1 2 ¯ 3 ] respectively. In the ELO areas, three kind of dislocations are observed: screw dislocations with b ⇒ = 1 3 [ 1 1 2 ¯ 0 ] , edge dislocations with b ⇒ = 1 3 [ 2 ¯ 1 1 0 ] and partial dislocations (PDs) with b ⇒ = 1 3 [ 1 0 1 ¯ 0 ] and b ⇒ = 1 6 [ 2 0 2 ¯ 3 ] . Basal stacking faults (BSFs) of the type I 1 ( R ⇒ = 1 6 [ 2 0 2 ¯ 3 ] ) and I 2 ( R ⇒ = 1 3 [ 1 0 1 ¯ 0 ] ), and prismatic stacking faults (PSFs) with a R ⇒ = 1 2 [ 1 1 ¯ 0 1 ] are also observed. Cathodoluminescence, spectra and imaging, has shown that TDs are non-radiative recombination centers contrary to BSFs.

Dislocation structures in a { $$ \bar{1} $$ 104}/〈11 $$ \bar{2} $$ 0〉 low-angle tilt grain boundary of alumina (α-Al2O3)

An alumina (α-Al2O3) bicrystal with a ( $$ \bar{1} $$ 104)/[11 $$ \bar{2} $$ 0] 2o low-angle tilt grain boundary was fabricated by diffusion bonding at 1500 °C in air, and the grain boundary was observed by transmission electron microscopy (TEM). High-resolution TEM observations revealed that the grain boundary consists of at least two kinds of dislocations. One is a perfect dislocation which has a Burgers vector of 1/3[ $$ \bar{1} $$ 2 $$ \bar{1} $$ 0]. The other is dissociated into two partial dislocations with a stacking fault on the (0001) plane, and each partial dislocation has a 1/6[ $$ \bar{1} $$ 101] edge component. It is suggested from structural considerations that the dissociated-dislocation pair originates from a b = 1/3[02 $$ \bar{2} $$ 1] perfect dislocation (i.e., 1/3[02 $$ \bar{2} $$ 1] → 1/6[02 $$ \bar{2} $$ 1] + 1/6[02 $$ \bar{2} $$ 1]). This dissociation produces a stacking fault in the anion sublattice. The stacking fault energy is estimated to be roughly 1.3 Jm−2 based on the elastic theory. The authors discuss the dislocation structures and the stacking fault formed on the (0001) plane in detail.

Characterisation of Dislocations in ZnO by X –Ray Imaging

Transmission X-Ray topography (X-ray imaging) was used to characterize the density and type of the native dislocations in ZnO substrates. C-oriented ZnO bulk materials from different origins were compared, either high purity Chemical Vapor Transport (CVT) grown or commercial, hydrothermally grown wafers. Elongated dislocations lying within the substrate were found in hydrothermal substrates. In CVT crystals, the density of dislocations was found to be too high for X-ray determination of their Burgers vector. However, in hydrothermal crystals, the density of dislocations were found to be in the range < 104 / cm2 and extend mainly within the substrate. Whereas complete Burgers vector identification is not achieved, two kinds of dislocations have been evidenced : grown-in, swirled dislocations ("high" temperature) and linear, gliding dislocations, most probably developped during the cooling steps in (0 1–1 0) glide planes.

Dislocations in Si nanocrystals embedded inSiO2

Si nanocrystals (Si nc) were formed by the implantation ofSi+ into aSiO2 filmon (100) Si, followed by high-temperature annealing. High-resolution transmission electron microscopyhas been used to investigate the dislocations in the Si nc produced by a high-dose (ion fluence of3 × 1017 cm−2) implantation. Three different kinds of dislocations, namely perfect, extended andmismatch dislocations, have been observed in some Si nc. The possible formationmechanism for these dislocations has been discussed. The dislocations in the Si nc areexpected to have a great influence on the photoluminescence from Si nc embedded inSiO2.