Atomic-scale modelling of crystal defects, self-diffusion and deformation processes

2017 ◽  
pp. 215-253
Author(s):  
S. Jahn ◽  
X.-Y. Sun
Keyword(s):  
Crystal Defects ◽  
Atomic Scale ◽  
Self Diffusion ◽  
Scale Modelling ◽  
Deformation Processes

High-Temperature Synthesis of CdSe-Based Core/Shell, Core/Shell/Shell, and Core/Graded-Shell Nanoplatelets for Stable and Efficient Narrowband Emitters

2019 ◽  
Author(s):  
Aurelio A. Rossinelli ◽  
Henar Rojo ◽  
Aniket S. Mule ◽  
Marianne Aellen ◽  
Ario Cocina ◽  
...  
Keyword(s):  
Quantum Dots ◽  
High Temperature ◽  
Equilibrium Shape ◽  
Size Variation ◽  
Crystal Defects ◽  
Atomic Scale ◽  
Quantum Yields ◽  
Core Shell ◽  
Compositional Gradient ◽  
High Quality

<div>Colloidal semiconductor nanoplatelets exhibit exceptionally narrow photoluminescence spectra. This occurs because samples can be synthesized in which all nanoplatelets share the same atomic-scale thickness. As this dimension sets the emission wavelength, inhomogeneous linewidth broadening due to size variation, which is always present in samples of quasi-spherical nanocrystals (quantum dots), is essentially eliminated. Nanoplatelets thus offer improved, spectrally pure emitters for various applications. Unfortunately, due to their non-equilibrium shape, nanoplatelets also suffer from low photo-, chemical, and thermal stability, which limits their use. Moreover, their poor stability hampers the development of efficient synthesis protocols for adding high-quality protective inorganic shells, which are well known to improve the performance of quantum dots. <br></div><div>Herein, we report a general synthesis approach to highly emissive and stable core/shell nanoplatelets with various shell compositions, including CdSe/ZnS, CdSe/CdS/ZnS, CdSe/Cd<sub>x</sub>Zn<sub>1–x</sub>S, and CdSe/ZnSe. Motivated by previous work on quantum dots, we find that slow, high-temperature growth of shells containing a compositional gradient reduces strain-induced crystal defects and minimizes the emission linewidth while maintaining good surface passivation and nanocrystal uniformity. Indeed, our best core/shell nanoplatelets (CdSe/Cd<sub>x</sub>Zn<sub>1–x</sub>S) show photoluminescence quantum yields of 90% with linewidths as low as 56 meV (19.5 nm at 655 nm). To confirm the high quality of our different core/shell nanoplatelets for a specific application, we demonstrate their use as gain media in low-threshold ring lasers. More generally, the ability of our synthesis protocol to engineer high-quality shells can help further improve nanoplatelets for optoelectronic devices.</div>

Fluid inclusion hardening: Nanoscale evidence from naturally deformed pyrite

2021 ◽  
Author(s):  
Anna Rogowitz ◽  
Renelle Dubosq ◽  
David Schneider ◽  
Kevin Schweinar ◽  
Baptiste Gault
Keyword(s):  
Trace Elements ◽  
Fluid Inclusions ◽  
Electron Backscatter Diffraction ◽  
Analytical Techniques ◽  
Atom Probe ◽  
Crystal Defects ◽  
Atomic Scale ◽  
Ductile Deformation ◽  
Temperature Deformation ◽  
Contrast Imaging

&lt;p&gt;The interaction of trace elements, fluids and crystal defects plays a vital role in a crystalline material&amp;#8217;s response to an applied stress. For example, dislocations can be arrested by the strain field of immobile defects (i.e., particles or precipitates) or by the accumulation of mobile solutes in their cores, which can lead to strain hardening. The rheology of minerals is also strongly influenced by interactions with fluids, which are typically known to facilitate ductile deformation in geomaterials (i.e., hydrolytic weakening, dissolution creep). Investigation of these nanometer scale processes however, requires a correlative approach combining high-spatial resolution analytical techniques. In recent years, increasing developments in microscopy and microanalysis have allowed for the compositional measurements and spatial imaging of materials at the near-atomic scale. Herein, we have combined electron backscatter diffraction (EBSD) mapping, electron channeling contrast imaging (ECCI), scanning transmission electron microscopy (STEM) and atom probe tomography (APT) on a naturally deformed polycrystalline pyrite aggregate from the Abitibi Subprovince in Canada to investigate the role of fluid inclusions on mineral rheology. The combined EBSD and ECCI data reveal minor crystal misorientation and low-angle grain boundary development in the vicinity and at the tip of microfractures indicating a dominantly brittle regime with minor strain accommodation via crystal-plasticity where dislocations are mostly emitted by the propagating fracture. These interpretations are consistent with the peak temperature conditions of the sample estimated at 302 &amp;#177; 27&amp;#176;C, which falls within the lower range of the brittle to crystal-plastic behaviour of pyrite (260&amp;#8211;450&amp;#176;C). Nanoscale structural and chemical data reveal nanoscale fluid inclusions enriched in As, O, Na and K that are linked by As-enriched dislocations. Based on these results, we propose a model of fluid hardening whereby dislocations get pinned at fluid inclusions during crystal-plastic deformation, initiating pipe diffusion of trace elements from the fluid inclusions into dislocations that leads to their stabilization and local hardening. Although additional experiments are required on other mineral phases, our initial efforts advance the understanding of the interplay between nanostructures and impurities and its impact on the rheology of geomaterials during relatively low temperature deformation.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Isotope Fractionation due to Sedimentation of Atoms in Centrifuged Indium-Lead Alloy

2009 ◽  
Vol 289-292 ◽  
pp. 63-68 ◽  
Author(s):  
Masao Ono ◽  
Yusuke Iguchi ◽  
Satoru Okayasu ◽  
Fumitaka Esaka ◽  
Katsura Kobayashi ◽  
...  
Keyword(s):  
Gravitational Field ◽  
Centrifugal Force ◽  
Isotope Ratio ◽  
Isotope Fractionation ◽  
Mass Difference ◽  
Atomic Scale ◽  
Self Diffusion ◽  
Isotope Abundance ◽  
Secondary Ion ◽  
Negative Gradient

The atomic-scale graded structure of In-Pb alloy was formed by an ultracentrifuge under a gravitational field of 0.81 x 106 g for 100 hours at 150 °C in solid state. The isotope ratio measurements were performed on the centrifuged sample with secondary ion mass spectrometer (SIMS, CAMECA IMS-6f). 206Pb/208Pb and 207Pb/208Pb isotope ratio changed with negative gradient in the direction of centrifugal force approximately 1.5% and 0.8%, respectively. There was a tendency that the heavy 208Pb isotope abundance increased and the light 206Pb isotope abundance decreased in the direction of centrifugal force. Three-isotope diagram of 206Pb/208Pb versus 207Pb/208Pb proved that the isotope fractionation depends on the isotopic mass difference. These results showed that a strong gravitational field not only affected the inter-diffusion but also the self-diffusion in this alloy by causing isotope fractionation effect, which was dependent on the mass-difference.

Electron microscopic interfacial analysis of diamond film grown on silicon substrate

1996 ◽  
Vol 11 (7) ◽  
pp. 1783-1786 ◽  
Author(s):  
N. Jiang ◽  
A. Hatta ◽  
T. Ito ◽  
Z. Zhang ◽  
T. Sasaki ◽  
...  
Keyword(s):  
Chemical Vapor ◽  
Amorphous Solid ◽  
High Resolution Electron Microscopy ◽  
Crystal Defects ◽  
Atomic Scale ◽  
Recrystallization Process ◽  
Electron Microscopic ◽  
Precursor Phase ◽  
Resolution Electron ◽  
Hot Filament

We have investigated the near-interface characterization of diamond films grown on Si(100) substrates by means of a hot-filament chemical-vapor-deposition (HFCVD) method using high-resolution-electron microscopy (HREM). Atomic scale study of the diamond/Si interface reveals that on the top of the amorphous intermediate layer, there exists a precursor phase which seems to be a diamond-like structure, which provides a suitable site for subsequent diamond nucleation. High density crystal defects directly originate from the precursor phase. HREM images also reveal that during the deposition Si recrystallizes in some damaged areas left by pretreatment, such as scratching grooves. In the recrystallization process twins and microtwins can be formed, and amorphous solid is left in the Si crystals.

Atomic Scale Modelling of Supported and Assembled Nanoparticles

2000 ◽  
Vol 634 ◽  
Author(s):  
E. Zhurkin ◽  
M. Hou ◽  
H.Van Swygenhoven ◽  
B. Pauwels ◽  
M. Yandouzi ◽  
...  
Keyword(s):  
Lattice Mismatch ◽  
Gold Cluster ◽  
Lattice Relaxation ◽  
Nanostructured Material ◽  
Al Alloys ◽  
Atomic Scale ◽  
Metropolis Monte Carlo ◽  
Scale Modelling ◽  
Positron Lifetime Spectroscopy ◽  
Positron Lifetimes

ABSTRACTThe properties of elemental and bimetallic free, supported and assembled nanoclusters are modeled at the atomic scale and the models are discussed on the basis of experimental observations. This way, the memory of some free cluster properties in nanostructured materials may be evaluated.The combination of molecular statics with High Resolution Transmission Electron Microscopy (HRTEM) allows to predict fine detail of the lattice relaxation of a truncated octahedral gold cluster deposited on MgO. Metropolis Monte Carlo (MC) predicts that a lattice mismatch may contribute to disordering in deposited Cu3Au nanoclusters. In both Cu-Au and Ni-Al free clusters, offset of equilibrium stoichiometry may result in segregation of Au or Al at the cluster surface. An ordered stoichiometric core is surrounded by a disordered mantle where the excess species resides. Different modeling methods predict different nanometer scale textures.Therefore, cluster assembled Ni3Al alloys formed by condensation and pressing are modeled in two different ways. Both make use of a combination of Molecular Dynamics and MC. Whatever the model nanostructure, the segregation properties of free clusters remain in the nanostructured material. This segregation is one possible cause that can inhibit the formation of a metastable martensitic phase as observed in bulk Ni-Al alloys.The occurrence of vacancy clusters and voids is hardly identified by HRTEM. On the other hand, their distribution and sizes are sensitive to the nanostructure modeling. Therefore, a new characterization method is developed, which combines positron lifetime spectroscopy with the calculation of positron lifetimes from selected areas of the model samples.

Magnetic properties of Exchange-spring DyFe2/YFe2 Superlattices by Monte Carlo Simulations

2012 ◽  
Vol 1471 ◽  
Author(s):  
Pierre-Emmanuel Berche ◽  
Saoussen Djedai ◽  
Etienne Talbot
Keyword(s):  
Monte Carlo ◽  
Magnetic Properties ◽  
Monte Carlo Simulations ◽  
Field Dependence ◽  
Hysteresis Loops ◽  
Atomic Scale ◽  
Exchange Spring ◽  
Scale Modelling ◽  
Different Temperatures

ABSTRACTMonte Carlo simulations are used to perform an atomic scale modelling of the magnetic properties of epitaxial exchange-coupled DyFe2/YFe2 superlattices. These samples, extremely well-researched experimentally, are constituted by a hard ferrimagnet DyFe2 and a soft ferrimagnet YFe2 antiferromagnetically coupled. Depending on the layers and on the temperature, the field dependence of the magnetization depth profile is complex. In this work, we reproduce by Monte Carlo simulations hysteresis loops for the net and compound-specific magnetizations at different temperatures, and assess the quality of the results by a direct comparison to experimental hysteresis loops.

Smoothening by Self-Diffusion of Silicon during Annealing in a Rapid Processing Chamber

2013 ◽  
Vol 205-206 ◽  
pp. 364-369
Author(s):  
Pablo Eduardo Acosta-Alba ◽  
Christophe Gourdel ◽  
Oleg Kononchuk
Keyword(s):  
Atomic Scale ◽  
Crystal Surfaces ◽  
Surface Evolution ◽  
Origin And Evolution ◽  
Self Diffusion ◽  
Diffusion Parameters ◽  
Power Spectral ◽  
Rapid Processing ◽  
And Diffusion ◽  
Good Agreement

Atomic-scale mechanisms of thermal activated self-diffusion on crystal surfaces are investigated through AFM images. Surface evolution is studied by means of the Power Spectral Density (PSD) function over a large spatial bandwidth. We propose a parametric model based on the Mullins-Herring (MH) diffusion equation by adding two stochastic terms. Then, surface evolution during high temperature annealing in reducing ambient can be predicted. Very good agreement between experimental and theoretical roughness and diffusion parameters was observed. Origin and evolution of the stochastic terms, describing conservative and non-conservative noises, are discussed.

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