Articles de revues : « Atomic defect »

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Chu, Liu, Jiajia Shi, and Eduardo Souza de Cursi. "The Fingerprints of Resonant Frequency for Atomic Vacancy Defect Identification in Graphene." Nanomaterials 11, no. 12 (2021): 3451. http://dx.doi.org/10.3390/nano11123451.

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The identification of atomic vacancy defects in graphene is an important and challenging issue, which involves inhomogeneous spatial randomness and requires high experimental conditions. In this paper, the fingerprints of resonant frequency for atomic vacancy defect identification are provided, based on the database of massive samples. Every possible atomic vacancy defect in the graphene lattice is considered and computed by the finite element model in sequence. Based on the sample database, the histograms of resonant frequency are provided to compare the probability density distributions and interval ranges. Furthermore, the implicit relationship between the locations of the atomic vacancy defects and the resonant frequencies of graphene is established. The fingerprint patterns are depicted by mapping the locations of atomic vacancy defects to the resonant frequency magnitudes. The geometrical characteristics of computed fingerprints are discussed to explore the feasibility of atomic vacancy defects identification. The work in this paper provides meaningful supplementary information for non-destructive defect detection and identification in nanomaterials.

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Sozykin, Sergey Anatolevich, Valeriy Petrovich Beskachko, and G. P. Vyatkin. "Atomic Structure and Mechanical Properties of Defective Carbon Nanotube (7,7)." Materials Science Forum 843 (February 2016): 78–84. http://dx.doi.org/10.4028/www.scientific.net/msf.843.78.

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The article presents the results of first-principle modeling of a defectless (7,7) carbon nanotube and (7,7) nanotubes containing single and double vacancy defects, as well as Stone–Wales defects. These types of defects are often found in real nanotubes and affect their properties. We have established that reliable results can be obtained by using models of more than 1.5 nm in length. It turned out that a single vacancy defect has the least influence on Young modulus, and double n type vacancy defect in the most influential. The elongation at break also depends on the defect type and is 30-60% less than for perfect tubes.

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Schuler, Bruno, Katherine A. Cochrane, Christoph Kastl, et al. "Electrically driven photon emission from individual atomic defects in monolayer WS2." Science Advances 6, no. 38 (2020): eabb5988. http://dx.doi.org/10.1126/sciadv.abb5988.

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Quantum dot–like single-photon sources in transition metal dichalcogenides (TMDs) exhibit appealing quantum optical properties but lack a well-defined atomic structure and are subject to large spectral variability. Here, we demonstrate electrically stimulated photon emission from individual atomic defects in monolayer WS2 and directly correlate the emission with the local atomic and electronic structure. Radiative transitions are locally excited by sequential inelastic electron tunneling from a metallic tip into selected discrete defect states in the WS2 bandgap. Coupling to the optical far field is mediated by tip plasmons, which transduce the excess energy into a single photon. The applied tip-sample voltage determines the transition energy. Atomically resolved emission maps of individual point defects closely resemble electronic defect orbitals, the final states of the optical transitions. Inelastic charge carrier injection into localized defect states of two-dimensional materials provides a powerful platform for electrically driven, broadly tunable, atomic-scale single-photon sources.

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Kim, Honggyu, Yifei Meng, Ji-Hwan Kwon, Jean-Luc Rouviére, and Jian Min Zuo. "Determination of atomic vacancies in InAs/GaSb strained-layer superlattices by atomic strain." IUCrJ 5, no. 1 (2018): 67–72. http://dx.doi.org/10.1107/s2052252517016219.

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Determining vacancy in complex crystals or nanostructures represents an outstanding crystallographic problem that has a large impact on technology, especially for semiconductors, where vacancies introduce defect levels and modify the electronic structure. However, vacancy is hard to locate and its structure is difficult to probe experimentally. Reported here are atomic vacancies in the InAs/GaSb strained-layer superlattice (SLS) determined by atomic-resolution strain mapping at picometre precision. It is shown that cation and anion vacancies in the InAs/GaSb SLS give rise to local lattice relaxations, especially the nearest atoms, which can be detected using a statistical method and confirmed by simulation. The ability to map vacancy defect-induced strain and identify its location represents significant progress in the study of vacancy defects in compound semiconductors.

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Hsu, Julia W. P. "Semiconductor Defect Studies Using Scanning Probes." Microscopy and Microanalysis 6, S2 (2000): 704–5. http://dx.doi.org/10.1017/s1431927600036011.

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Understanding how defects alter physical properties of materials has lead to improvements in materials growth as well as device performance. Transmission electron microscopy (TEM) provides an invaluable tool for structural characterization of defects. Our current knowledge of crystallographic defects, such as dislocations, would not have been possible without TEM. Recently, scanning tunneling microscopy and scanning force microscopy (SFM) have shown the capability of imaging surface defects with atomic or near-atomic resolution in topographic images. What is more important is to gain knowledge on how the presence of a certain type of defects changes the physical properties of materials. For example, how is the carrier lifetime altered near electrically active defects? How does photoresponse vary near grain boundaries? Where are defect levels in the forbidden bandgap? This talk will discuss several examples of how scanning probe microscopies (SPMs) can contribute to this aspect of defect studies in semiconductors.

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Stemmer, S., G. Duscher, E. M. James, M. Ceh, and N. D. Browning. "Atomic Scale Structure-Property Relationships of Defects and Interfaces in Ceramics." Microscopy and Microanalysis 4, S2 (1998): 556–57. http://dx.doi.org/10.1017/s143192760002290x.

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The evaluation of the two dimensional projected atom column positions around a defect or an interface in an electronic ceramic, as it has been performed in numerous examples by (quantitative) conventional high-resolution electron microscopy (HRTEM), is often not sufficient to relate the electronic properties of the material to the structure of the defect. Information about point defects (vacancies, impurity atoms), and chemistry or bonding changes associated with the defect or interface is also required. Such complete characterization is a necessity for atomic scale interfacial or defect engineering to be attained.One instructive example where more than an image is required to understand the structure property relationships, is that of grain boundaries in Fe-doped SrTi03. Here, the different formation energies of point defects cause a charged barrier at the boundary, and a compensating space charge region around it. The sign and magnitude of the barrier depend very sensitively on the atomic scale composition and chemistry of the boundary plane.

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Weber, William J., Fei Gao, Ram Devanathan, Weilin Jiang, and Y. Zhang. "Defects and Ion-Solid Interactions in Silicon Carbide." Materials Science Forum 475-479 (January 2005): 1345–50. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.1345.

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Atomic-level simulations are used to determine defect production, cascade-overlap effects, and defect migration energies in SiC. Energetic C and Si collision cascades primarily produce single interstitials, mono-vacancies, antisite defects, and small defect clusters, while amorphous clusters are produced within 25% of Au cascades. Cascade overlap results in defect stimulated cluster growth that drives the amorphization process. The good agreement of disordering behavior and changes in volume and elastic modulus obtained computationally and experimentally provides atomic-level interpretation of experimentally observed features. Simulations indicate that close-pair recombination activation energies range from 0.24 to 0.38 eV, and long-range migration energies for interstitials and vacancies are determined.

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Wang, Zhen, Hangwen Guo, Shuai Shao, et al. "Designing antiphase boundaries by atomic control of heterointerfaces." Proceedings of the National Academy of Sciences 115, no. 38 (2018): 9485–90. http://dx.doi.org/10.1073/pnas.1808812115.

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Extended defects are known to have critical influences in achieving desired material performance. However, the nature of extended defect generation is highly elusive due to the presence of multiple nucleation mechanisms with close energetics. A strategy to design extended defects in a simple and clean way is thus highly desirable to advance the understanding of their role, improve material quality, and serve as a unique playground to discover new phenomena. In this work, we report an approach to create planar extended defects—antiphase boundaries (APB) —with well-defined origins via the combination of advanced growth, atomic-resolved electron microscopy, first-principals calculations, and defect theory. In La2/3Sr1/3MnO3 thin film grown on Sr2RuO4 substrate, APBs in the film naturally nucleate at the step on the substrate/film interface. For a single step, the generated APBs tend to be nearly perpendicular to the interface and propragate toward the film surface. Interestingly, when two steps are close to each other, two corresponding APBs communicate and merge together, forming a unique triangle-shaped defect domain boundary. Such behavior has been ascribed, in general, to the minimization of the surface energy of the APB. Atomic-resolved electron microscopy shows that these APBs have an intriguing antipolar structure phase, thus having the potential as a general recipe to achieve ferroelectric-like domain walls for high-density nonvolatile memory.

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Cho, Philip, Aihua Wood, Krishnamurthy Mahalingam, and Kurt Eyink. "Defect Detection in Atomic Resolution Transmission Electron Microscopy Images Using Machine Learning." Mathematics 9, no. 11 (2021): 1209. http://dx.doi.org/10.3390/math9111209.

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Point defects play a fundamental role in the discovery of new materials due to their strong influence on material properties and behavior. At present, imaging techniques based on transmission electron microscopy (TEM) are widely employed for characterizing point defects in materials. However, current methods for defect detection predominantly involve visual inspection of TEM images, which is laborious and poses difficulties in materials where defect related contrast is weak or ambiguous. Recent efforts to develop machine learning methods for the detection of point defects in TEM images have focused on supervised methods that require labeled training data that is generated via simulation. Motivated by a desire for machine learning methods that can be trained on experimental data, we propose two self-supervised machine learning algorithms that are trained solely on images that are defect-free. Our proposed methods use principal components analysis (PCA) and convolutional neural networks (CNN) to analyze a TEM image and predict the location of a defect. Using simulated TEM images, we show that PCA can be used to accurately locate point defects in the case where there is no imaging noise. In the case where there is imaging noise, we show that incorporating a CNN dramatically improves model performance. Our models rely on a novel approach that uses the residual between a TEM image and its PCA reconstruction.

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Ziatdinov, Maxim, Ondrej Dyck, Xin Li, et al. "Building and exploring libraries of atomic defects in graphene: Scanning transmission electron and scanning tunneling microscopy study." Science Advances 5, no. 9 (2019): eaaw8989. http://dx.doi.org/10.1126/sciadv.aaw8989.

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The presence and configurations of defects are primary components determining materials functionality. Their population and distribution are often nonergodic and dependent on synthesis history, and therefore rarely amenable to direct theoretical prediction. Here, dynamic electron beam–induced transformations in Si deposited on a graphene monolayer are used to create libraries of possible Si and carbon vacancy defects. Deep learning networks are developed for automated image analysis and recognition of the defects, creating a library of (meta) stable defect configurations. Density functional theory is used to estimate atomically resolved scanning tunneling microscopy (STM) signatures of the classified defects from the created library, allowing identification of several defect types across imaging platforms. This approach allows automatic creation of defect libraries in solids, exploring the metastable configurations always present in real materials, and correlative studies with other atomically resolved techniques, providing comprehensive insight into defect functionalities.

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Forde, Aaron, Erik Hobbie, and Dmitri Kilin. "Role of Pb2+ Adsorbents on the Opto-Electronic Properties of a CsPbBr3 Nanocrystal: A DFT Study." MRS Advances 4, no. 36 (2019): 1981–88. http://dx.doi.org/10.1557/adv.2019.268.

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ABSTRACTFully inorganic lead halide perovskite nanocrystals (NCs) are of interest for photovoltaic and light emitting devices due to optoelectronic properties. Understanding the surface chemistry of these materials is of importance as surface defects can introduce trap-states which reduce their functionality. Here we use Density Functional Theory (DFT) to model surface defects introduced by Pb2+ on a CsPbBr3 NC atomistic model. Two types of defects are studied: (i) an under-coordinated Pb2+ surface atom and (ii) Pb2+ atomic or molecular adsorbents to the NC surface. From the DFT calculations we compute the density of states (DOS) and absorption spectra of the defect models to the pristine fully-passivated NC model. We observe that for the low surface defect regime explored here that neither (i) or (ii) produce trap-states inside of the bandgap and exhibit bright optical absorption for the lowest energy transition. From the models studied, it was found that the Pb2+ atomic absorbent provides broadening of the conduction band edge, which implies chemisorption of Pb2+ to the NC surface. At higher defect densities it would be expected that Pb2+ atomic absorbents would introduce trap-states and degrade the opto-electronic properties of these materials.

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Matsunaga, Katsuyuki, Teruyasu Mizoguchi, Atsutomo Nakamura, Takahisa Yamamoto, and Yuichi Ikuhara. "First-Principles Calculations of Titanium Dopants in Alumina." Materials Science Forum 475-479 (January 2005): 3095–98. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.3095.

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First-principles pseudopotential calculations were performed to investigate atomic and electronic structures of titanium (Ti) dopants in alumina (Al2O3). It was found that a substitutional Ti3+ defect induced an extra level occupied by one electron within the band gap of Al2O3. When two or more substitutional Ti3+ defects were located closely to each other, the defect-induced levels exhibited strong bonding interactions, and their formation energies decreased with increasing numbers of Ti3+ defects. This indicates that association and clustering of substitutional Ti3+ defects in Al2O3 can take place due to the interaction of the defect-induced levels.

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Jones, Jessica Catharine, Ethan Kamphaus, Jeffrey R. Guest, Lei Cheng, and Alex B. F. Martinson. "Targeted Dehydration As a Route to Site-Selective Atomic Layer Deposition at TiO₂ Defects." ECS Meeting Abstracts MA2022-02, no. 31 (2022): 1131. http://dx.doi.org/10.1149/ma2022-02311131mtgabs.

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Crystallographic perfection in epitaxial thin film heterostructures can eliminate interface defects that dilute unique properties and reduce device performance. However, the requirement for epitaxial perfection greatly limits the selection of material candidates and deposition processes. Using selective interface reactions (SIRs), an atomic layer deposition (ALD)-based technique, we target transformation of undesirable defect sites at imperfect surfaces. Defects on the TiO2 surface affect the electronic properties, interfaces, and performance of optoelectronic devices that leverage TiO2 interfaces. We present first principles calculations to predict the difference in hydration/hydroxylation of pristine TiO2 terraces and minority atomic configurations (i.e. “defects”) including step edges and oxygen vacancies. We investigate hydroxylation differences through temperature dependent scanning tunneling microscopy (STM), and ultimately exploit these differences to selectively react ALD precursors at surface defect sites.

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Yudin, Valeriy, and Alexey Taichenachev. "Mass defect effects in atomic clocks." Laser Physics Letters 15, no. 3 (2018): 035703. http://dx.doi.org/10.1088/1612-202x/aa9aa5.

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JIANG, B., J. L. PENG, L. A. BURSILL, and H. WANG. "MICROSTRUCTURE AND PROPERTIES OF FERROELECTRIC Bi4Ti3O12 THIN FILMS." Modern Physics Letters B 13, no. 26 (1999): 933–45. http://dx.doi.org/10.1142/s0217984999001147.

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The film morphology and defect structure of ferroelectric bismuth titanate thin films are studied by high resolution transmission electron microscopy. As-grown and RTA-processed thin films have similar defect structures, consisting of stacking faults and complex intergrowth defect structures. The as-grown specimens prepared at low temperature had smaller particle size with higher density of these defects compared to RTA-processed samples. Detailed atomic structure models for the stacking faults and intergrowth defect structures are proposed and the computer-simulated images are compared with experiment.

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Morifuji, Masato. "Theoretical Study on Effect of Defective Connection to Reservoirs in an Atomic-Scale Conductor." Advances in Condensed Matter Physics 2017 (2017): 1–6. http://dx.doi.org/10.1155/2017/2857393.

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We theoretically investigate the effect of a defect at the interface between a conductor and reservoirs in an atomic-scale device. Since fabrication of atomic-scale contacts is a complex task, there could be defects at the interface between the conductor and reservoirs. Such defective contacts will make it difficult to measure currents properly. In this paper, we calculate current-voltage characteristics in two-dimensional devices with a defective connection to reservoirs by using the nonequilibrium Green’s function method. Results show that the magnitude of resistance change depends on the amplitude of quantized wave functions at the position of the defect.

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Chen, Jun, Gyeonghee Ryu, and Jamie Warner. "Atomic Structure and Dynamics of Defects and Grain Boundaries in 2D Pd2Se3 Monolayers." Microscopy and Microanalysis 26, S2 (2020): 1636–40. http://dx.doi.org/10.1017/s1431927620018802.

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AbstractStructural imperfections of 2D crystals such as point vacancies and grain boundaries (GBs) have considerable impacts on their chemical-physical properties. Here we study the atomic structure and dynamics of defects and GBs in monolayer Pd2Se3 using annular dark field scanning transmission electron microscopy (ADF-STEM). The Pd2Se3 monolayers are reproducibly created by thermally induced phase transformation of few-layered PdSe2 films in an in-situ heating holder in the TEM to promote Se loss. Diverse point vacancies, one-dimensional (1D) defects, GBs and defect ring complexes are directly observed in monolayer Pd2Se3, which show a series of dynamics triggered by electron beam. High mobility of vacancies leads to self-healing of point vacancies by migration to the edge and subsequent edge etching under the beam. Specific defects are stabilized by Se–Se bonds, which shift in a staggered way to buffer strain, forming a wave-like 1D defect. Bond rotations are also observed and play an important role in defect and GB dynamics in Pd2Se3 during vacancy production. The GBs form in a meandering pathway and migrate by a sequence of Se–Se bond rotations without large scale vacancy formation. In the GB corners and tilted GBs, other highly symmetric vacancy defects also occur to adapt to the orientation change. These results give atomic level insights into the defects and GBs in Pd2Se3 2D monolayers.

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ZHANG, S. B. "CATION ANTISITE DEFECTS AND ANTISITE-BASED-DEFECT COMPLEXES IN GaAs." Modern Physics Letters B 04, no. 18 (1990): 1133–36. http://dx.doi.org/10.1142/s0217984990001422.

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Recent theory predicted that the Ga and B antisites in GaAs are bistable. As the Fermi level is lowered towards the valence-band maximum, a structural change from fourfold to threefold coordination will occur. The Ga antisite will undergo an atomic exchange in the presence of an As interstitial.

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Gao, F., and W. J. Weber. "Atomic-scale simulations of multiple ion–solid interactions and structural evolution in silicon carbide." Journal of Materials Research 17, no. 2 (2002): 259–62. http://dx.doi.org/10.1557/jmr.2002.0035.

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Molecular dynamics (MD) were employed in atomic-level simulations of fundamental damage production processes due to multiple ion–solid collision events in cubic SiC. Isolated collision cascades produce single interstitials, vacancies, antisite defects, and small defect clusters. As the number of cascades (or equivalent dose) increases, the concentration of defects increases, and the collision cascades begin to overlap. The coalescence of defects and clusters with increasing dose is an important mechanism leading to amorphization in SiC and is consistent with the homogeneous amorphization process observed experimentally in SiC. The driving force for the crystalline– amorphous (c–a) transition is the accumulation of both interstitials and antisite defects. High-resolution transmission electron microscopy (HRTEM) images of the defect accumulation process and loss of long-range order in the MD simulation cell are consistent with experimental HRTEM images and disorder measurements. Thus, the MD simulations provide atomic-level insights into the interpretation of experimentally observed features associated with multiple ion–solid collision events in SiC.

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Iguchi, Hidehiko. "Atomic diffusion mediated by intrinsic point defects in GaAs and AlxGa1−xAs–GaAs superlattices." Journal of Materials Research 6, no. 7 (1991): 1542–52. http://dx.doi.org/10.1557/jmr.1991.1542.

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Point-defect-mediated atomic diffusion in GaAs and AlxGa1−xAs–GaAs superlattices is examined thermodynamically by focusing on activation enthalpy of diffusion. Through a review of available experimental results of impurity diffusion of Si, Zn, and Be, their diffusion phenomena are discussed by taking the characteristics of column-III-site-related point defect, such as Ga vacancy and arsenic-antisite, into consideration. It is suggested that Zn and Be diffusion should be mediated by As-antisite defects. On the other hand, Si diffusion is mediated by either Ga vacancy or As-antisite, depending on the growth method of materials and diffusion conditions. It is argued that As-antisite should be a mediator of diffusion in As-antisite-rich materials and with using As-rich diffusion source under p-type conditions. Cation self-diffusion or interdiffusion is also discussed in the same manner. Impurity-enhanced layer-disordering phenomena are examined by considering the reduction of defect energy of Ga vacancy and As antisite under n-type and p-type conditions, respectively. Beryllium enhanced and suppressed interdiffusion (cation self-diffusion) in MBE-grown AlxGa1−xAs–GaAs superlattices are interpreted in view of point-defect-mediated cation diffusion on the basis of the Fermi-energy dependence of point defect. In order to explain the phenomena, crystal-growth methods and surface-localized point defects which is responsible for Fermi-level stabilization are taken into consideration.

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Zhou, Wu, Mark P. Oxley, Andrew R. Lupini, Ondrej L. Krivanek, Stephen J. Pennycook, and Juan-Carlos Idrobo. "Single Atom Microscopy." Microscopy and Microanalysis 18, no. 6 (2012): 1342–54. http://dx.doi.org/10.1017/s1431927612013335.

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AbstractWe show that aberration-corrected scanning transmission electron microscopy operating at low accelerating voltages is able to analyze, simultaneously and with single atom resolution and sensitivity, the local atomic configuration, chemical identities, and optical response at point defect sites in monolayer graphene. Sequential fast-scan annular dark-field (ADF) imaging provides direct visualization of point defect diffusion within the graphene lattice, with all atoms clearly resolved and identified via quantitative image analysis. Summing multiple ADF frames of stationary defects produce images with minimized statistical noise and reduced distortions of atomic positions. Electron energy-loss spectrum imaging of single atoms allows the delocalization of inelastic scattering to be quantified, and full quantum mechanical calculations are able to describe the delocalization effect with good accuracy. These capabilities open new opportunities to probe the defect structure, defect dynamics, and local optical properties in 2D materials with single atom sensitivity.

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Biborski, Andrzej, L. Zosiak, and Rafal Abdank-Kozubski. "Triple-Defect B2 Binary Intermetallics: Bragg-Williams Solution and Monte Carlo Simulations." Defect and Diffusion Forum 289-292 (April 2009): 361–68. http://dx.doi.org/10.4028/www.scientific.net/ddf.289-292.361.

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Surprisingly low rate of “order-order” kinetics in stoichiometric NiAl intermetallic known of very high vacancy concentration suggested a specific triple-defect mechanism of ordering/disordering in this system [1]. This mechanism implies a correlation between the concentrations of antisite defects and vacancies; the latters being trapped in triple defects and thus, inactive as atomic migration agents. The process was modelled by means of Monte Carlo (MC) simulations recognised as a powerful tool for such tasks [2], but requiring now the implementation of thermal vacancy thermodynamics. Temperature dependence of vacancy concentration in an AB B2 binary system was determined within an Ising-type model solved first in Bragg-Williams approximation [3] and then by means of MC simulation of a Grandcanonical Ensemble. Without any a priori assumptions concerning the formation of particular types of point defects the model yielded temperature domains where the concentrations of antisite defects and vacancies were proportional. The effect associated with the formation of triple defects appeared for specific values of atomic pair-interaction energies. Moreover, non-stoichiometric A-B systems with the same atomic pair-interaction energies showed the existence of constitutional vacancies at low temperatures. Monte Carlo simulations of “order-order” (disordering) kinetics in B2 AB systems modelled with triple-defect-promoting atomic pair-interaction energies were run with temperature-dependent concentra-tion (i.e. number) of vacancies given by the above model. The simulated relaxations showed two stages: (i) rapid formation of triple defects engaging almost all vacancies present in the system, (ii) very slow process of further generation of antisite defects until the equilibrium concentration was reached. The result reproduced very well the experimental observations [1].

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Zhao, Xin-Jing, Hao Hou, Peng-Peng Ding, et al. "Molecular defect-containing bilayer graphene exhibiting brightened luminescence." Science Advances 6, no. 9 (2020): eaay8541. http://dx.doi.org/10.1126/sciadv.aay8541.

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The electronic structure of bilayer graphene can be altered by creating defects in its carbon skeleton. However, the natural defects are generally heterogeneous. On the other hand, rational bottom-up synthesis offers the possibility of building well-defined molecular cutout of defect-containing bilayer graphene, which allows defect-induced modulation with atomic precision. Here, we report the construction of a molecular defect-containing bilayer graphene (MDBG) with an inner cavity by organic synthesis. Single-crystal x-ray diffraction, mass spectrometry, and nuclear magnetic resonance spectroscopy unambiguously characterize the structure of MDBG. Compared with its same-sized, defect-free counterpart, the MDBG exhibits a notable blue shift of optical absorption and emission, as well as a 9.6-fold brightening of its photoluminescence, which demonstrates that a single defect can markedly alter the optical properties of bilayer graphene.

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Wang, Fen Ying, Wei Sun, Yan Feng Dai, Yi Wang Chen, Jian Wei Zhao, and Xiao Lin. "Influence of Atomic Defect on the Deformation Properties of Nanowires Subjected to Uniaxial Tension." Advanced Materials Research 873 (December 2013): 139–46. http://dx.doi.org/10.4028/www.scientific.net/amr.873.139.

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Atomic defects play an important role in the brittle deformation of nanowires at low temperatures. With molecular dynamics simulations, we study the influence of vacancy defects on the deformation and breaking behaviors of [10 oriented single-crystal gold nanowires at 50 and 150 K. The size of the nanowire is 10a × 10a × 30a (a stands for lattice constant, 0.408 nm for gold). It is shown that good crystalline structure appears in the whole deformation process, and it is in a brittle way at low temperature. The nanowire breaking behavior is sensitive to atomic vacancies when the atomic vacancy ratio is 1% in single-layer crystalline plane. Within the limitation of vacancy-induced breaking of the nanowire, the mechanical strengths increase under atomic vacancies. However, it decreases with the defect ratio increasing.

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Jaworske, D., K. de Groh, G. Podojil, T. McCollum, and J. Anzic. "Leveling Coatings for Reducing Atomic Oxygen Defect Density in Graphite Fiber-Epoxy Composites." Journal of the IEST 37, no. 3 (1994): 26–31. http://dx.doi.org/10.17764/jiet.2.37.3.l4133w17742570j2.

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Pinholes or other defect sites in a protective oxide coating provide pathways for atomic oxygen in low-Earth orbit to reach underlying material. Onc concept for enhancing the lifetime of materials in low-Earth orbit is to apply a leveling coating to the material prior to applying any reflective and protective coatings. Using a surface-tension-leveling coating concept, a low-viscosity epoxy was applied to the surface of several composite coupons. A protective layer of 1000 Å of SiO2 was deposited on top of the leveling coating, and the coupons were exposed to an atomic oxygen environment in a plasma asher. Pinhole populations per unit area were estimated by counting the number of undercut sites observed by scanning electron microscopy. Defect density values of 180,000 defects/cm2 were reduced to about 1000 defects/cm2 as a result of the applied leveling coating. These improvements occur at a mass penalty of about 2.5 mg/cm2.

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Dyakonov, Vladimir, Hannes Kraus, V. A. Soltamov, et al. "Atomic-Scale Defects in Silicon Carbide for Quantum Sensing Applications." Materials Science Forum 821-823 (June 2015): 355–58. http://dx.doi.org/10.4028/www.scientific.net/msf.821-823.355.

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Atomic-scale defects in silicon carbide exhibit very attractive quantum properties that can be exploited to provide outstanding performance in various sensing applications. Here we provide the results of our studies of the spin-optical properties of the vacancy related defects in SiC. Our studies show that several spin-3/2 defects in silicon carbide crystal are characterized by nearly temperature independent axial crystal fields, which makes these defects very attractive for vector magnetometry. The zero-field splitting of another defect exhibits on contrast a giant thermal shift of 1.1 MHz/K at room temperature, and can be used for temperature sensing applications.

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PENG, QING, JARED CREAN, ALBERT K. DEARDEN, et al. "DEFECT ENGINEERING OF 2D MONATOMIC-LAYER MATERIALS." Modern Physics Letters B 27, no. 23 (2013): 1330017. http://dx.doi.org/10.1142/s0217984913300172.

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Atomic-thick monolayer two-dimensional materials present advantageous properties compared to their bulk counterparts. The properties and behavior of these monolayers can be modified by introducing defects, namely defect engineering. In this paper, we review a group of common two-dimensional crystals, including graphene, graphyne, graphdiyne, graphn-yne, silicene, germanene, hexagonal boron nitride monolayers and MoS2monolayers, focusing on the effect of the defect engineering on these two-dimensional monolayer materials. Defect engineering leads to the discovery of potentially exotic properties that make the field of two-dimensional crystals fertile for future investigations and emerging technological applications with precisely tailored properties.

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Yu, Sheng, Tikaram Neupane, Bagher Tabibi, Qiliang Li, and Felix Jaetae Seo. "Spin-Resolved Visible Optical Spectra and Electronic Characteristics of Defect-Mediated Hexagonal Boron Nitride Monolayer." Crystals 12, no. 7 (2022): 906. http://dx.doi.org/10.3390/cryst12070906.

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Defect-mediated hexagonal boron nitride (hBN) supercells display visible optical spectra and electronic characteristics. The defects in the hBN supercells included atomic vacancy, antisite, antisite vacancy, and the substitution of a foreign atom for boron or nitrogen. The hBN supercells with VB, CB, and NB-VN were characterized by a high electron density of states across the Fermi level, which indicated high conductive electronic characteristics. The hBNs with defects including atomic vacancy, antisite at atomic vacancy, and substitution of a foreign atom for boron or nitride exhibited distinct spin-resolved optical and electronic characteristics, while defects of boron and nitrogen antisite did not display the spin-resolved optical characteristics. The hBNs with positively charged defects exhibited dominant optical and electronic characteristics in the longer spectral region. Acknowledgment: This work at HU is supported by ARO W911NF-15-1-0535, NSF HRD-1137747, and NASA NNX15AQ03A.

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Nakatomi, Masashi, and Koichi Yamashita. "A THEORETICAL STUDY OF POINT DEFECTS IN ZIRCONIA – SILICON INTERFACES." International Journal of High Speed Electronics and Systems 16, no. 01 (2006): 389–96. http://dx.doi.org/10.1142/s0129156406003710.

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We present a theoretical study on the point defects in ZrO 2–silicon interfaces using molecular dynamics (MD) calculations. A super-cell model that contains 9 atomic layers of silicon and 9 atomic layers of ZrO 2 was used for the simulation. Three atomic layers containing 17 oxygen atoms, eight silicon atoms, and nine Zr atoms were used to simulate the ZrO 2–silicon interface. We then performed density functional theory (DFT) with plane-wave basis to calculate the interface band structure. Results demonstrate that the stretched Zr – O bonds at the interface would produce some defect levels in the band gap. Particularly, the defect levels originated from the interstitial oxygen atoms are located close to the bottom of the ZrO 2 conduction band and hence it will affect the electrical properties of the gate dielectrics.

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Wichert, Th. "Atomic Defect Configurations Identified by Nuclear Techniques." Materials Science Forum 83-87 (January 1992): 1081–96. http://dx.doi.org/10.4028/www.scientific.net/msf.83-87.1081.

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Wager, J. F., and J. A. Van Vechten. "Atomic model for theEL2 defect in GaAs." Physical Review B 35, no. 5 (1987): 2330–39. http://dx.doi.org/10.1103/physrevb.35.2330.

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Theodosiou, Constantine E., Mitio Inokuti, and Steven T. Manson. "Quantum defect values for positive atomic ions." Atomic Data and Nuclear Data Tables 35, no. 3 (1986): 473–86. http://dx.doi.org/10.1016/0092-640x(86)90018-5.

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Taichenachev, A. V., and V. I. Yudin. "Effects of mass defect in atomic clocks." Journal of Physics: Conference Series 951 (January 2018): 012026. http://dx.doi.org/10.1088/1742-6596/951/1/012026.

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Patel, Ajay M., Nipun Gosai, and Anand Y. Joshi. "A Review on Defects in Carbon Nanotubes." Applied Mechanics and Materials 813-814 (November 2015): 145–50. http://dx.doi.org/10.4028/www.scientific.net/amm.813-814.145.

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Various defects on the CNT wall have been reported, which are formed during the synthesizing process. CNTs have superior properties compared to the traditional engineering materials. However, these properties hold only for the ideal case of carbon nanotubes, where these are made of perfect hexagonal graphite honeycomb lattice of mono-atomic layer thickness. The advantages or disadvantages of the presence of defects in carbon nanotubes depend on their applications. Structural defects may increase the adhesion of other atoms and molecules to carbon nanotubes. It has also been found that the defects in CNT do cause a change in its resonant frequency as compared to that of a non-defective CNT. The defects that have been considered for the purpose of analysis in this research includes defects in the carbon nanotubes likewise Waviness, Vacancy Defect, Pinhole Defect, Fracture and Stone Wales Defect. It has been observed that with the increase in the number of defects in CNT, a reduction in the fundamental frequency is observed.

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Pang, Haosheng, Hongfa Wang, Minglin Li, and Chenghui Gao. "Atomic-Scale Friction on Monovacancy-Defective Graphene and Single-Layer Molybdenum-Disulfide by Numerical Analysis." Nanomaterials 10, no. 1 (2020): 87. http://dx.doi.org/10.3390/nano10010087.

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Using numerical simulations, we study the atomic-scale frictional behaviors of monovacancy-defective graphene and single-layer molybdenum-disulfide (SLMoS2) based on the classical Prandtl–Tomlinson (PT) model with a modified interaction potential considering the Schwoebel–Ehrlich barrier. Due to the presence of a monovacancy defect on the surface, the frictional forces were significantly enhanced. The effects of the PT model parameters on the frictional properties of monovacancy-defective graphene and SLMoS2 were analyzed, and it showed that the spring constant of the pulling spring cx is the most influential parameter on the stick–slip motion in the vicinity of the vacancy defect. Besides, monovacancy-defective SLMoS2 is found to be more sensitive to the stick–slip motion at the vacancy defect site than monovacancy-defective graphene, which can be attributed to the complicated three-layer-sandwiched atomic structure of SLMoS2. The result suggests that the soft tip with a small spring constant can be an ideal candidate for the observation of stick–slip behaviors of the monovacancy-defective surface. This study can fill the gap in atomic-scale friction experiments and molecular dynamics simulations of 2D materials with vacancy-related defects.

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Zhang, Zhongli, Jinming Zhang, Yushan Ni, Can Wang, Kun Jiang, and Xuedi Ren. "Multiscale Simulation of Surface Defect Influence in Nanoindentation by the Quasi-Continuum Method." Proceedings 2, no. 14 (2018): 1113. http://dx.doi.org/10.3390/iecc_2018-05246.

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Microscopic properties of nanocrystal Aluminum thin film have been simulated using the quasicontinuum method in order to study the surface defect influence in nanoindentation. Various distances between the surface defect and indenter have been taken into account. The results show that as the distance between the pit and indenter increases, the nanohardness increases in a wave pattern associated with a cycle of three atoms, which is closely related to the crystal structure of periodic atoms arrangement on {111} atomic close-packed planes of face-centered cubic metal; when the adjacent distance between the pit and indenter is more than 16 atomic spacing, there is almost no effect on nanohardness. In addition, the theoretical formula for the necessary load for the elastic-to-plastic transition of Al film has been modified with the initial surface defect size, which may contribute to the investigation of material properties with surface defects.

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Černošek, Zdeněk, Marek Liška, Peter Pelikán, Eva Černošková, Marián Valko, and Miloslav Frumar. "Computer Simulation of Electron Spin Resonance Spectra of Ge25S75and Ge30S70 Bulk Glasses." Collection of Czechoslovak Chemical Communications 62, no. 11 (1997): 1721–29. http://dx.doi.org/10.1135/cccc19971721.

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The electron spin resonance (ESR) spectra of bulk glasses of the chemical composition Ge25S75 and Ge30S70 were measured at liquid nitrogen temperature and subjected to computerized separation. The complex ESR spectra of both glasses were found to represent a superposition of three paramagnetic defect spectra, two with orthorhombic tensors g and one with the axial tensor g. The former two paramagnetic centers can be related to a two-atomic defect of the sulfur-sulfur type, the latter to a germanium-sulfur defect. The experimental results are in a good agreement with the non-dangling bond model of paramagnetic defects in Ge-S glasses.

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Stevens Kalceff, M. A. "Detection of Interstitial Molecules in Wide Band Gap Materials Using Cathodoluminescence Microanalysis." Microscopy and Microanalysis 5, S2 (1999): 732–33. http://dx.doi.org/10.1017/s1431927600016986.

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Cathodoluminescence (CL) microanalysis (spectroscopy and microscopy) enables both pre-existing and irradiation induced defects in the bulk and surface defect structure of wide band gap materials (i.e. semiconductors and insulators) to be monitored and characterized with high spatial resolution and sensitivity. The local micro-volume of specimen may be selected for investigation by varying the electron beam parameters. CL micro analytical techniques allow the in situ monitoring of electron irradiation induced defects and the investigation of irradiation induced electromigration of mobile charged defect species. Irradiation can result in the formation of defects and /or the transformation of existing defect precursors. CL emissions from a material are usually associated with native and impurity defects of the host lattice, however in special cases CL microanalysis can provide direct or indirect evidence for the presence of interstitial molecular species in a material. Atomic displacements from the normal bonding (i.e. defect free) sites induced by an electron beam can result from either knock-on, or radiolytic processes, depending on the incident electron beam energy.

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Zhang, Zhongli, Yushan Ni, Jinming Zhang, Can Wang, Kun Jiang, and Xuedi Ren. "Multiscale Simulation of Surface Defects Influence Nanoindentation by a Quasi-Continuum Method." Crystals 8, no. 7 (2018): 291. http://dx.doi.org/10.3390/cryst8070291.

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Microscopic properties of nanocrystal aluminum thin film have been investigated using the quasicontinuum method in order to study the influence of surface defects in nanoindentation. Various distances between the surface defect and indenter have been taken into account. The results show that as the distance between the pit and indenter increases, the nanohardness increases in a wave pattern associated with a cycle of three atoms, which is closely related to the crystal structure of periodic atoms arrangement on {1 1 1} atomic close-packed planes of face-centered cubic metal; when the adjacent distance between the pit and indenter is more than 16 atomic spacing, there is almost no effect on nanohardness. In addition, the theoretical formula for the necessary load for elastic-to-plastic transition of Al film has been modified with the initial surface defect size, which may contribute to the investigation of material property with surface defects.

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Vancsó, Péter, Alexandre Mayer, Péter Nemes-Incze, and Géza István Márk. "Wave Packet Dynamical Simulation of Quasiparticle Interferences in 2D Materials." Applied Sciences 11, no. 11 (2021): 4730. http://dx.doi.org/10.3390/app11114730.

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Materials consisting of single- or a few atomic layers have extraordinary physical properties, which are influenced by the structural defects. We present two calculation methods based on wave packet (WP) dynamics, where we compute the scattering of quasiparticle WPs on localized defects. The methods are tested on a graphene sheet: (1) We describe the perfect crystal lattice and the electronic structure by a local atomic pseudopotential, then calculate the Bloch eigenstates and build a localized WP from these states. The defect is represented by a local potential, then we compute the scattering by the time development of the WP. (2) We describe the perfect crystal entirely by the kinetic energy operator, then we calculate the scattering on the local defect described by the potential energy operator. The kinetic energy operator is derived from the dispersion relation, which can be obtained from any electronic structure calculation. We also verify the method by calculating Fourier transform images and comparing them with experimental FFT-LDOS images from STM measurements. These calculation methods make it possible to study the quasiparticle interferences, inter- and intra-valley scattering, anisotropic scattering, etc., caused by defect sites for any 2D material.

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Mirzade, F. Kh. "On the Propagation of Waves in an Anisotropic Solid with Laser-Induced Atomic Defects." Advances in Condensed Matter Physics 2015 (2015): 1–11. http://dx.doi.org/10.1155/2015/547521.

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The behavior of plane waves in a linear, elastic anisotropic laser-excited solid has been investigated taking into account the effects of atomic defect generation. It is found that there are four types of dispersive waves in these crystals, namely, a quasilongitudinal (QL-mode), two quasitransverse (QT-mode), and a quasidefect concentration (N-mode) wave. The complex secular equations for cubic and transversely isotropic crystals are reduced as special cases. It is demonstrated that when waves propagate in one of the planes of transversely isotropic solid having defect concentration field, only one purely quasitransverse wave decouples from the rest of the motion and is not influenced by defect concentration changes. The other waves are coupled and get modified due to presence of defects. When waves propagate along the axis of the solid, only QT- and N-mode are coupled, whereas the two QT-modes get decoupled from the rest of the motion. The phase velocities and attenuation factors of waves have been obtained. Significant effect of defects and anisotropy on wave characteristics is observed in certain ranges of frequency. It is also shown that there is an appreciable variation in case of QL-mode as compared with QT- and N-mode.

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Warner, Jamie, and Alex Robertson. "The atomic structure of defects in graphene." Acta Crystallographica Section A Foundations and Advances 70, a1 (2014): C514. http://dx.doi.org/10.1107/s2053273314094856.

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Defects in graphene influence its electronic, magnetic, chemical and mechanical properties. It is therefore important to have a detailed understanding of their exact atomic structure in order to accurately predict their behaviour. In this talk I will present a summary of research on resolving the atomic structure of vacancy defects in graphene, single atom dopants covalently bonded in the lattice, and their transition dynamics. By using aberration-corrected transmission electron microscopy, combined with monochromation of the electron source to reduce chromatic aberration effects, sub-Angstrom spatial resolution at a low accelerating voltage of 80 kV is achieved. Methods have been developed to introduce defects into the lattice of graphene with 10 nm spatial accuracy within the electron microscope using a controlled focussed beam. This enables the study of defect structures with unprecedented clarity and accuracy whilst in a low-pressure vacuum environment. Atomic models determined from TEM imaging are compared with DFT calculated atomic models to gain deeper insights into the C-C bond lengths and the relationship between electronic charge density distribution and bond lengths.

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Bundhoo, Fayik. "Evidence of Atomic Dislocation Loops Crystal Lattice Flaws Causing EOS/ESD Damage in 〈100〉 Silicon." International Journal of High Speed Electronics and Systems 23, no. 01n02 (2014): 1420007. http://dx.doi.org/10.1142/s0129156414200079.

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Crystalline lattice point defects in integrated circuit can lay hidden below the silicon surface exist in the atomic lattice point structure or as interstitials. Initially they may not necessary represent an electrical failure but can act as seeds for electrical degradation in a time period. This paper study one category of Silicon defect “Dislocation loops” that initially were dormant then propagated under the silicon surface in the crystal lattice structure causing catastrophic EOS damage. This is particularly true if the crystalline defect exists near or at the boundary of PN junctions. This paper present evidence of dormant crystalline lattice defects in the form of crystalline dislocation loops degrading to EOS. Over a period of time under normal operation life of the part these dislocation loops can trigger EOS/ESD events.

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He, Jizhong. "A Correlative Defect Analyzer Combining Glide Test with Atomic Force Microscope." Advances in Tribology 2013 (2013): 1–8. http://dx.doi.org/10.1155/2013/657363.

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We have developed a novel instrument combining a glide tester with an Atomic Force Microscope (AFM) for hard disk drive (HDD) media defect test and analysis. The sample stays on the same test spindle during both glide test and AFM imaging without losing the relevant coordinates. This enables an in situ evaluation with the high-resolution AFM of the defects detected by the glide test. The ability for the immediate follow-on AFM analysis solves the problem of relocating the defects quickly and accurately in the current workflow. The tool is furnished with other functions such as scribing, optical imaging, and head burnishing. Typical data generated from the tool are shown at the end of the paper. It is further demonstrated that novel experiments can be carried out on the platform by taking advantage of the correlative capabilities of the tool.

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Sdoeung, Sayleap, Kohei Sasaki, Katsumi Kawasaki, Jun Hirabayashi, Akito Kuramata та Makoto Kasu. "Probe-induced surface defects: Origin of leakage current in halide vapor-phase epitaxial (001) β-Ga₂O₃ Schottky barrier diodes". Applied Physics Letters 120, № 9 (2022): 092101. http://dx.doi.org/10.1063/5.0085057.

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The elimination of killer defects, which are responsible for the reverse leakage current and breakdown at low voltage in β-gallium oxide (β-Ga2O3) Schottky barrier diodes (SBDs), is crucial for the commercialization of the power devices. We found probe-induced surface defects, which act as a reverse leakage current path in β-Ga2O3 SBDs. Each defect corresponds to a reverse leakage current of −0.725 [Formula: see text]A at a reverse bias of −140 V. These defects are wrinkle shaped, which consists of a pair of the convex and concave structures, as observed by atomic force microscopy. The residual strain around the defects was observed as bright contrasts in the x-ray topography image. The surface defect comprised an 83 nm high convex and a 26 nm deep concave structure. A probe attachment at the pressure of 0.206 GPa induced the surface defect along with a reverse leakage current of −3.75 nA at a reverse voltage of −140 V.

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Chen, Gong, Shuai Wu, Chong Qian, and Xiaoming Dou. "Application of the sparse decomposition algorithm in the film defect denoising." Modern Physics Letters B 32, no. 34n36 (2018): 1840117. http://dx.doi.org/10.1142/s0217984918401176.

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This paper aims to extract the exact defect characteristics of the thin film surface of the lithium battery by sparse decomposition algorithm. An appropriate atomic function was selected and the sparse decomposition iteration was conducted on the defect images in the overcomplete dictionary. This value from observation method was taken as the empirical value and applied as the iteration termination condition of the sparse decomposition. Then, the denoised defect images were obtained. The results reveal that the sparse decomposition has a far superior denoising performance to that of the median filtering technique, and can better restore the thin film defects of the lithium battery.

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Al-Zubi, Ali, Gustav Bihlmayer, and Stefan Blügel. "Electronic Structure of Oxygen-Deficient SrTiO3 and Sr2TiO4." Crystals 9, no. 11 (2019): 580. http://dx.doi.org/10.3390/cryst9110580.

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The conductive behavior of the perovskite SrTiO 3 is strongly influenced by the presence of oxygen vacancies in this material, therefore the identification of such defects with spectroscopic methods is of high importance. We use density functional theory to characterize the defect-induced states in SrTiO 3 and Sr 2 TiO 4 . Their signatures at the surface, the visibility for scanning tunneling spectroscopy and locally conductive atomic force microscopy, and the core-level shifts observed on Ti atoms in the vicinity of the defect are studied. In particular, we find that the exact location of the defect state (e.g., in SrO or TiO 2 planes relative to the surface) are decisive for their visibility for scanning-probe methods. Moreover, the usual distinction between Ti 3 + and Ti 2 + species, which can occur near defects or their aggregates, cannot be directly translated in characteristic shifts of the core levels. The width of the defect-induced in-gap states is found to depend critically on the arrangement of the defects. This also has consequences for the spectroscopic signatures observed in so-called resistive switching phenomena.

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Németh, Péter, István Dódony, Mihály Pósfai, and Peter R. Buseck. "Complex Defect in Pyrite and Its Structure Model Derived from Geometric Phase Analysis." Microscopy and Microanalysis 19, no. 5 (2013): 1303–7. http://dx.doi.org/10.1017/s1431927613001839.

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AbstractNew methods for defect analysis can lead to improved interpretation of experimental data and thus better understanding of material properties. Although transmission electron microscopy (TEM) has been used to study defects for many decades, interpretive ambiguities can arise for cases that seem simple or even trivial. Using geometric phase analysis (GPA), an image processing procedure, we show that an apparent simple line defect in pyrite has an entirely different character. It appears to be a b = ½[100] edge dislocation as viewed in a [001] high-resolution TEM (HRTEM) image, but the measured ux and uy displacements are asymmetric, which is inconsistent with a simple line dislocation. Instead, the defect is best understood as a terminating {101} marcasite slab in pyrite. The simulated HRTEM image based on this model reproduces the defect contrast and illustrates the power of GPA analysis for (1) avoiding potential pitfalls of misinterpreting apparently simple defects in HRTEM images, (2) detecting differences in elastic properties at the atomic scale, and (3) providing data for the positions of atom columns, thereby facilitating the construction of structure models for complex defects.

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Cooke, Jacqueline, Praneeth Ranga, Arkka Bhattacharyya та ін. "Sympetalous defects in metalorganic vapor phase epitaxy (MOVPE)-grown homoepitaxial β-Ga₂O₃ films". Journal of Vacuum Science & Technology A 41, № 1 (2023): 013406. http://dx.doi.org/10.1116/6.0002303.

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We report a new type of structural defect in β-Ga2O3 homoepitaxial thin films grown by metalorganic vapor phase epitaxy, which we have dubbed as “sympetalous defects.” These consist of a line defect (for example, a nanotube defect) in the underlying substrate combined with a multi-faceted inverted polycrystalline pyramid in the epitaxial film, which may also be decorated with twinned polycrystalline grains. In plan-view atomic force, scanning electron, or optical microscopies, the sympetalous defects appear similar in shape to polygonal etch pits observed for single crystals. Photoluminescence microscopy exposed spots of polarization-dependent luminescence at these defects, different from the single crystal films' luminescence. Furthermore, some of the defects exhibited circular dichroism in their luminescence that we correlated with partial helices formed within the pits by the arrangement of linearly dichroic polycrystalline grains. Finally, the density of sympetalous defects agrees with the etch pit densities of the substrates. Understanding and controlling these defects will be of importance as they modify the local properties of films, affect fabricated device yields, and influence characterization experiments.

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Gao *, F., and W. J. Weber. "Atomic-level computer simulation of SiC: defect accumulation, mechanical properties and defect recovery." Philosophical Magazine 85, no. 4-7 (2005): 509–18. http://dx.doi.org/10.1080/02678370412331320170.

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