Determination of surface-defect concentration and distribution with He diffraction

AbstractLow energy electron diffraction is a surface sensitive tool which is most widely used for the determination of surface symmetries and equilibrium atomic positions. Experimental and theoretical advances made in the past five years make it possible now to use LEED also for the characterization of a wide variety of surface defect structures. In this paper a variety of experimental results involving analysis of diffracted electron beam shapes as a function of primary electron beam energy, adsorbate coverage, crystal tem-perature and ordering time are presented. These experimental results coupled with kinematic theory, allow the determination of step density, size and shape of reconstruction domains and overlayer islands, island size distribution in an overlayer during growth, and the mode of growth.

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Defect concentration and Δn change in light- and elevated temperature- induced degradation

Journal of Physics D Applied Physics ◽

10.1088/1361-6463/ac34a8 ◽

2021 ◽

Author(s):

Moonyong Kim ◽

Matthew Wright ◽

Daniel Chen ◽

Catherine Chan ◽

Alison Ciesla ◽

...

Keyword(s):

Surface Passivation ◽

Defect Density ◽

Accurate Determination ◽

Defect Concentration ◽

Doping Density ◽

Lifetime Analysis ◽

Materials Used ◽

New Formulation ◽

The Impact

Abstract The wide variety of silicon materials used by various groups to investigate LeTID make it difficult to directly compare the defect concentrations (Nt) using the typical normalised defect density (NDD) metric. Here, we propose a new formulation for a relative defect concentration (β) as a correction for NDD that allows flexibility to perform lifetime analysis at arbitrary injection levels (Δn), away from the required ratio between Δn and the background doping density (Ndop) for NDD of Δn/N dop = 0.1. As such, β allows for a meaningful comparison of the maximum degradation extent between different samples in different studies and also gives a more accurate representative value to estimate the defect concentration. It also allows an extraction at the cross-over point in the undesirable presence of iron, or flexibility to reduce the impact of modulation in surface passivation. Although the accurate determination of β at a given Δn requires knowledge of the capture cross-section ratio (k), the injection-independent property of the β formulation allows a self-consistent determination of k. Experimental verification is also demonstrated for boron-oxygen related defects and LeTID defects, yielding k-values of 10.6 ± 3.2 and 30.7 ± 4.0, respectively, which are within the ranges reported in the literature. With this, when extracting the defect density at different Δn ranging between 1014 /cm3 to 1015 /cm3 with Ndop = 9.1 ×1015 /cm3, the error is less than 12% using β, allowing for a greatly improved understanding of the defect concentration in a material.

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Theory of Doping in Studies of Defect Concentration and Transport Properties of Transition Metal Oxides and Sulphides

High Temperature Materials and Processes ◽

10.1515/htmp-2014-0104 ◽

2015 ◽

Vol 34 (5) ◽

Author(s):

Zbigniew Grzesik

Keyword(s):

Transition Metal ◽

Metal Oxides ◽

Transition Metal Oxides ◽

Oxidation Kinetics ◽

Defect Formation ◽

Defect Concentration ◽

Defect Mobility ◽

Enthalpy And Entropy ◽

Kinetics Of

AbstractIn the present paper the theoretical basis and experimental verification of a method, enabling the calculation of defect concentration and their mobility in transition metal oxides and sulphides have been described. The idea of proposed method consists in determination of both these parameters in indirect way, i.e. in studying the influence of aliovalent metallic additions on the oxidation kinetics of a given metal (doping effect). It has been shown that from the results of oxidation kinetics of binary alloys, the enthalpy and entropy of defect formation and their migration can be calculated. These data, in turn, can be used for the calculation of defect concentration and defect mobility in pure, undoped oxides. Such a possibility has been illustrated on the example of nonstoichiometric nickel oxide, Ni

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Local and Global Reference Stress for Circumferential Irregular-Shaped Defects in Pipes

Journal of Pressure Vessel Technology ◽

10.1115/1.4028680 ◽

2015 ◽

Vol 137 (4) ◽

Cited By ~ 1

Author(s):

Igor Orynyak ◽

Sergii Ageiev ◽

Sergii Radchenko

Keyword(s):

Global Solution ◽

Surface Defect ◽

Surface Defects ◽

Bending Moment ◽

Reference Stress ◽

Local Modeling ◽

Unified Algorithm ◽

Circumferential Defects ◽

Global And Local

Numerical procedures for calculation of reference stresses for pipelines with circumferential defects, based on simulation of global and local ultimate plastic states, are proposed. There are some peculiarities of proposed procedures. First, the schematic analysis of the deformation process of pipe with surface defects is suggested, based on which two critical cases have been specified: Global (the net-section-collapse (NSC) criterion) and local, which are applicable for a very wide surface defect and for a sharp crack, respectively. The global solution also describes behavior of through-wall defects. Second, within the framework of the available NSC criterion the unified algorithm for determination of reference stresses (global solution) for irregular-shaped circumferential defects under multifactor loading (internal pressure, axial force, bending moment) is proposed. Third, according to the local modeling, the restricted capability to resist plastic deformations is takes into account by inserting of artificial symmetrical defect. The unified procedure for calculation of reference stresses (local solution) for pipe with irregular-shaped circumferential defects under multifactor loading is developed. Finally, the results obtained from the proposed solutions are compared with the ones from full-scale burst tests.

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Local and Global Reference Stress for Circumferential Irregular-Shaped Defects in Pipes

Volume 3: Design and Analysis ◽

10.1115/pvp2014-28670 ◽

2014 ◽

Author(s):

Sergii Ageiev ◽

Igor Orynyak ◽

Sergii Radchenko

Keyword(s):

Global Solution ◽

Surface Defect ◽

Surface Defects ◽

Bending Moment ◽

Reference Stress ◽

Sharp Crack ◽

Unified Algorithm ◽

Circumferential Defects ◽

Global And Local

Numerical procedures for calculation of reference stresses for pipelines with circumferential defects, based on simulation of global and local ultimate plastic states are proposed. There are some peculiarities of proposed procedures. First, the schematic analysis of the deformation process of pipe with surface defects is suggested, based on which two critical cases have been specified: global (the Net-Section-Collapse (NSC) criterion) and local, which are applicable for a very wide surface defect and for a sharp crack, respectively. The global solution also describes behaviour of through wall defects. Second, within the framework of the available Net-Section-Collapse criterion the unified algorithm for determination of reference stresses (global solution) for irregular-shaped circumferential defects under multifactor loading (internal pressure, axial force, bending moment) is proposed. Third, according to the local modelling, the restricted capability to resist plastic deformations is takes into account by inserting of artificial symmetrical defect. The unified procedure for calculation of reference stresses (local solution) for pipe with irregular-shaped circumferential defects under multifactor loading is developed. Forth, an analysis of proposed procedure by comparing with results of full-scale burst tests.

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