The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
John P. Hirth - One of the best experts on this subject based on the ideXlab platform.
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The motion of multiple height Ledges and disconnections in phase transformations
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 1998Co-Authors: John P. Hirth, R. G. Hoagland, Richard J. KurtzAbstract:For phase transformations with well-defined terrace planes, interface motion can occur by the motion of Ledges or disconnections (Ledges with added dislocation character). Symmetry imposes restrictions on the nature of these defects and may lead to the need for multiple height Ledges. The structure of the Ledge riser can also be variable. These possibilities impose constraints that can influence the motion of the defects and hence affect the rate of phase transformation. Examples of these phenomena are presented for interfaces with differing degrees of lattice matching.
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Computer simulation of Ledge migration under elastic interaction
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 1996Co-Authors: Masato Enomoto, John P. HirthAbstract:The diffusional growth of a phase by the motion of disconnections (Ledges which contain transformation or misfit dislocations) was studied by a finite difference computer model. The elastic stress of these dislocations is considered to alter the (local equilibrium) solute concentration at the riser of Ledges and cause a complex diffusion field interaction among Ledges as they migrate. In some cases, however, the Ledges forming a train can migrate all at the same speed in the presence of elastic interaction. The condition under which Ledges overcome the elastic barrier and form a multipleheight Ledge was determined. The model was applied to the migration of Ledges/Shockley partial dislocations at γ′-plate interfaces in Al-Ag alloys.
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The elastic stabilization of multiple-height growth Ledges during diffusional phase transformations
Acta Metallurgica Et Materialia, 1994Co-Authors: S.v. Kamat, John P. HirthAbstract:Abstract In diffusional phase transformations that proceed by the terrace-Ledge-kink mechanism, both atomic-scale, unit-height Ledges and multiple-height Ledges are observed. Both types of Ledges also have dislocation character, thereby making them disconnections. The dislocation interaction is shown to provide a strong stabilizing force for the multiple Ledges and to lead to a capture distance for additional unit Ledges that increases with Ledge height. Implications for the mechanism of phase transformation are discussed.
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INTERFACE DISLOCATIONS AND LedgeS IN OXIDATION AND DIFFUSIONAL PHASE TRANSFORMATIONS
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 1991Co-Authors: John P. HirthAbstract:The origin of Ledge concepts in growth from the vapor is reviewed. The ideas are extended to solid-state phase transformations with the added effects of strain and misorientation. Types of Ledges and dislocations are classified. The concepts are illustrated for the example of oxidation of a metal. Further extensions to diffusional phase transformations are briefly discussed.
Shadi A Dayeh - One of the best experts on this subject based on the ideXlab platform.
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recordings and analysis of atomic Ledge and dislocation movements in ingaas to nickelide nanowire phase transformation
Small, 2017Co-Authors: Renjie Chen, Shadi A DayehAbstract:The formation of low resistance and self-aligned contacts with thermally stable alloyed phases is a prerequisite for realizing reliable functionality in ultrascaled semiconductor transistors. Detailed structural analysis of the phase transformation accompanying contact alloying can facilitate contact engineering as transistor channels approach a few atoms across. Original in situ heating transmission electron microscopy studies are carried out to record and analyze the atomic scale dynamics of contact alloy formation between Ni and In0.53Ga0.47As nanowire channels. It is observed that the nickelide reacts on the In0.53Ga0.47As (111) || Ni2In0.53Ga0.47As (0001) interface with atomic Ledge propagation along the Ni2In0.53Ga0.47As [101¯0] direction. Ledges nucleate as a train of strained single-bilayers and propagate in-plane as double-bilayers that are associated with a misfit dislocation of b→=2c3[0001]. The atomic structure is reconstructed to explain this phase transformation that involves collective gliding of three Shockley partials in In0.53Ga0.47As lattice to cancel out shear stress and the formation of misfit dislocations to compensate the large lattice mismatch in the newly formed nickelide phase and the In0.53Ga0.47As layers. This work demonstrates the applicability of interfacial disconnection (Ledge + dislocation) theory in a nanowire channel during thermally induced phase transformation that is typical in metal/III–V semiconductor reactions.
W. T. Reynolds - One of the best experts on this subject based on the ideXlab platform.
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effects of Ledge density on the morphology and growth kinetics of precipitates in a ni cr alloy
Acta Materialia, 2005Co-Authors: G. Chen, G Spanos, R A Masumura, W. T. ReynoldsAbstract:Abstract Aging a quenched, face-centered cubic, Ni–45wt%Cr alloy at intermediate temperatures produces Cr-rich body-centered cubic precipitates with a lath morphology and two prominent boundary facets. Both the faceted boundaries migrate by a Ledge mechanism. The density of Ledges in these boundaries were measured as a function of time and related to the precipitate’s shape and growth kinetics. A tendency of Ledges to coalesce on one of the facets contributes to differences in the migration behavior of the two boundaries. One boundary has a distinct crystallographic habit, the other does not, and while both boundaries migrate with parabolic kinetics, they have different rate constants. The rate constants are influenced by the formation rate of Ledges on the respective boundaries. Growth models are used in conjunction with the experimental measurements to show that the boundaries and Ledges move at rates controlled by solute diffusion in the matrix.
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The elastic strain energy of growth Ledges on coherent and partially coherent precipitates
Metallurgical and Materials Transactions A, 1994Co-Authors: G. Chen, J. K. Chen, W. T. ReynoldsAbstract:The formation rate of growth Ledges on a faceted precipitate strongly affects the growth kinetics and the shape of the precipitate. An Eshelby-type model is used to compare the strain energy associated with the nucleation of a Ledge on different facet planes of a body-centered cubic (bcc) precipitate in face-centered cubic (fcc) matrix. Ledge nucleation is only likely at facet areas where the interaction energy between the Ledge and the precipitate is negative. The strain energy for Ledge formation is not symmetric on any of the facet planes, but it is symmetric about the center of the precipitate. For coherent precipitates comparable to those observed in the Ni-Cr system, Ledges form with the lowest strain energy on the broad facet of the precipitate implying that precipitate thickening should occur faster than lengthening and widening. A procedure for modifying the Eshelby model is suggested in order to allow strain-energy calculations of partially coherent precipitates. The strain energy for Ledge formation on at least one type of partially coherent lath is lowest for a Ledge located on the facet perpendicular to the crystallographic invariant line (IL). This situation favors precipitate lengthening in the invariant line direction.
Renjie Chen - One of the best experts on this subject based on the ideXlab platform.
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recordings and analysis of atomic Ledge and dislocation movements in ingaas to nickelide nanowire phase transformation
Small, 2017Co-Authors: Renjie Chen, Shadi A DayehAbstract:The formation of low resistance and self-aligned contacts with thermally stable alloyed phases is a prerequisite for realizing reliable functionality in ultrascaled semiconductor transistors. Detailed structural analysis of the phase transformation accompanying contact alloying can facilitate contact engineering as transistor channels approach a few atoms across. Original in situ heating transmission electron microscopy studies are carried out to record and analyze the atomic scale dynamics of contact alloy formation between Ni and In0.53Ga0.47As nanowire channels. It is observed that the nickelide reacts on the In0.53Ga0.47As (111) || Ni2In0.53Ga0.47As (0001) interface with atomic Ledge propagation along the Ni2In0.53Ga0.47As [101¯0] direction. Ledges nucleate as a train of strained single-bilayers and propagate in-plane as double-bilayers that are associated with a misfit dislocation of b→=2c3[0001]. The atomic structure is reconstructed to explain this phase transformation that involves collective gliding of three Shockley partials in In0.53Ga0.47As lattice to cancel out shear stress and the formation of misfit dislocations to compensate the large lattice mismatch in the newly formed nickelide phase and the In0.53Ga0.47As layers. This work demonstrates the applicability of interfacial disconnection (Ledge + dislocation) theory in a nanowire channel during thermally induced phase transformation that is typical in metal/III–V semiconductor reactions.
Xin Huang - One of the best experts on this subject based on the ideXlab platform.
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Ledge: Leveraging Edge Computing for Resilient Access Management of Mobile IoT
IEEE Transactions on Mobile Computing, 1Co-Authors: Di Wu, Xin HuangAbstract:Due to the blooming of Internet of Things (IoT), heterogeneous IoT mobile devices emerge to connect the network infrastructure. Traditional mobile access system faces several challenges arising from these IoT devices: 1) centralized controllers are distant from the end devices, 2) inefficient access control of heterogeneous IoT devices, and 3) insufficient authentication and monitoring for IoT devices. In order to tackle the challenges from IoT devices on mobile access control and scalable access monitoring, we present Ledge, an agile and secured software-defined edge computing system for resilient access management of mobile IoT. In a nutshell, our Ledge is a synergy of an efficient location authentication method to secure communication between each IoT mobile device and access point (AP) pair, an optimal AP assignment scheme to satisfy IoT flow requests, a Personal AP protocol for scalable access, and a deep learning model for anomaly detection. We prototype our system, and realistic testbed experiments demonstrate that Ledge could achieve promising results in mobile IoT.
