Internal Structure of Diamond Nanocrystals by Modeling and PDF Analysis

2013 ◽  
Vol 1554 ◽  
Author(s):  
S. Stelmakh ◽  
W. Palosz ◽  
S. Gierlotka ◽  
K. Skrobas ◽  
B. Palosz
Keyword(s):  
Crystal Lattice ◽  
Inner Core ◽  
Diamond Crystal ◽  
Perfect Crystal ◽  
Density Waves ◽  
Atomistic Models ◽  
Pdf Analysis ◽  
Density Modulation ◽  
Modulated Waves ◽  
Grain Core

ABSTRACTThe structure of nanocrystalline diamond was approximated by spherical nanograins assuming that the grain core with a perfect crystal lattice is surrounded by a sequence of shells with (essentially) identical atomic architecture but with altered density. We call such a model a nanocrystal with density modulated waves. To examine the effect of density modulation present in nanograins, we built atomistic models of nanodiamond grains and compared the average values of inter-atomic distances calculated for the grains with density waves to those calculated for grains with the perfect, diamond crystal lattice. We show that the atomic structure of nanodiamond can be best described by a model where, between the inner core and the surface layer, three density waves with intermittent compressive and tensile strains exist. The sequence of the density waves is preserved in all examined nanodiamond samples without regard to chemical treatment and vacuum annealing (at up to 1200°C).

Observation of multiple Bragg reflections accompanying forbidden Si(002) reflection in bent-perfect Si crystal

2021 ◽  
pp. 1-6
Author(s):  
P. Mikula ◽  
M. Vrána ◽  
J. Šaroun ◽  
V. Ryukhtin
Keyword(s):  
High Resolution ◽  
Crystal Lattice ◽  
Perfect Crystal ◽  
Monochromatic Beam ◽  
Very High

Strong multiple Bragg reflections (MBRs) which can be realized in a bent-perfect-crystal (BPC) slab provide a monochromatic beam of excellent resolution parameters. For identifying MBR effects in the BPC Si crystal, we used the method of azimuthal rotation of the crystal lattice around the scattering vector of the primary forbidden Si(200) reflection for a fixed chosen wavelength. In this paper, several azimuthal scans searching strong MBR effects with the intention of a possible practical exploitation for very high-resolution diffractometry are presented.

Atomic Model of CdSe QDs Containing Density Waves as Derived from PDF Analysis

2013 ◽  
Vol 1554 ◽  
Author(s):  
B. Palosz ◽  
W. Palosz ◽  
P. Wijewarnasuriya ◽  
S. Gierlotka ◽  
K. Skrobas ◽  
...  
Keyword(s):  
Atomic Structure ◽  
Bulk Crystal ◽  
Atomic Model ◽  
Good Knowledge ◽  
Density Waves ◽  
Cdse Qds ◽  
The Real ◽  
Pdf Analysis ◽  
Grain Surface

ABSTRACTUsing a new methodology of elaboration of PDF data (G(r) function), which is based on the analysis of individual inter-atomic distances (ri), a function describing differences between average inter-atomic distances in CdSe nanograins derived experimentally and those in the parent bulk crystal was determined. Based on that methodology a unique atomic architecture of CdSe QDs is proposed. The results show that a good knowledge about the grain surface of nanocrystals alone may be insufficient for understanding the nanomaterials properties, and that the real atomic structure of the interior of nanograins is of importance as well.

scholarly journals The thermal expansion of gold: point defect concentrations and pre-melting in a face-centred cubic metal

2018 ◽  
Vol 51 (2) ◽  
pp. 470-480 ◽  
Author(s):  
Martha G. Pamato ◽  
Ian G. Wood ◽  
David P. Dobson ◽  
Simon A. Hunt ◽  
Lidunka Vočadlo
Keyword(s):  
Thermal Expansion ◽  
Cell Volume ◽  
Computer Simulations ◽  
Point Defects ◽  
Unit Cell Volume ◽  
Inner Core ◽  
Debye Model ◽  
Perfect Crystal ◽  
Unit Cell ◽  
Real Crystal

On the basis ofab initiocomputer simulations, pre-melting phenomena have been suggested to occur in the elastic properties of hexagonal close-packed iron under the conditions of the Earth's inner core just before melting. The extent to which these pre-melting effects might also occur in the physical properties of face-centred cubic metals has been investigated here under more experimentally accessible conditions for gold, allowing for comparison with future computer simulations of this material. The thermal expansion of gold has been determined by X-ray powder diffraction from 40 K up to the melting point (1337 K). For the entire temperature range investigated, the unit-cell volume can be represented in the following way: a second-order Grüneisen approximation to the zero-pressure volumetric equation of state, with the internal energy calculatedviaa Debye model, is used to represent the thermal expansion of the `perfect crystal'. Gold shows a nonlinear increase in thermal expansion that departs from this Grüneisen–Debye model prior to melting, which is probably a result of the generation of point defects over a large range of temperatures, beginning atT/Tm> 0.75 (a similar homologousTto where softening has been observed in the elastic moduli of Au). Therefore, the thermodynamic theory of point defects was used to include the additional volume of the vacancies at high temperatures (`real crystal'), resulting in the following fitted parameters:Q= (V0K0)/γ = 4.04 (1) × 10−18 J,V0= 67.1671 (3) Å3,b= (K0′ − 1)/2 = 3.84 (9), θD= 182 (2) K, (vf/Ω)exp(sf/kB) = 1.8 (23) andhf= 0.9 (2) eV, whereV0is the unit-cell volume at 0 K,K0andK0′ are the isothermal incompressibility and its first derivative with respect to pressure (evaluated at zero pressure), γ is a Grüneisen parameter,θDis the Debye temperature,vf,hfandsfare the vacancy formation volume, enthalpy and entropy, respectively, Ω is the average volume per atom, andkBis Boltzmann's constant.

scholarly journals Сравнительный анализ спектров люминесценции алмазов

2019 ◽  
Vol 127 (9) ◽  
pp. 507
Author(s):  
С.И. Зиенко ◽  
Д.С. Слабковский
Keyword(s):  
Comparative Analysis ◽  
Crystal Lattice ◽  
Diamond Crystal ◽  
Relaxation Frequency ◽  
Luminescence Spectra ◽  
Time Range ◽  
Energy Losses ◽  
Q Factor ◽  
Bandwidth Parameter ◽  
Resonant Radiation

AbstractTo identify the signs that distinguish natural diamonds from artificial diamonds, a comparative analysis of the luminescence spectra with regards to the Q factor, center of gravity, bandwidth parameter, and energy losses in the diamond crystal lattice under conditions of ohmic and dielectric relaxation of luminescence is performed. The phenomenon of resonant luminescence in the femtosecond time range is detected in diamond. It is established that natural and artificial diamonds noticeably differ in the relaxation frequency and in the energy of resonant radiation.

Peierls–Nabarro Model Of Dislocations

2006 ◽  
Author(s):  
Vasily Bulatov ◽  
Wei Cai
Keyword(s):  
Time Scales ◽  
Numerical Solutions ◽  
Continuum Theory ◽  
Perfect Crystal ◽  
Point Of View ◽  
Atomistic Simulations ◽  
Linear Elasticity Theory ◽  
Elastic Fields ◽  
Atomistic Models ◽  
Dislocation Center

Chapter 1 introduced dislocations as dual objects permitting both atomistic and continuum descriptions. The subsequent Chapters 2 through 7 discussed various aspects of atomistic simulations and their application to dislocation modeling. In the rest of the book, from Chapter 8 to Chapter 11, we will be treating dislocations as continuum objects. This is a huge simplification that makes it possible to consider dislocation behavior on length and time scales well beyond reach of the atomistic simulations. The following chapters are organized in the order of increasing length and time scales. This particular chapter deals with the famous Peierls–Nabarro continuum model that is most closely related to the atomistic models discussed earlier. Fundamentally, dislocations are line defects producing distortions in an otherwise perfect crystal lattice. While this point of view is entirely correct, the atomistic models of dislocations can deal with only relatively small material volumes where every atom is individually resolved. Furthermore, having to keep track of all these atoms all the time limits the time horizon of atomistic simulations. On the other hand, when the host crystal is viewed as an elastic continuum, the linear elasticity theory of dislocations offers a variety of useful analytical and numerical solutions that are no longer subject to such constraints. Although quite accurate far away from the dislocation center, where the lattice distortions remain small, continuum theory breaks down near the dislocation center, where lattice discreteness and non-linearity of interatomic interactions become important. To obtain a more efficient description of crystal dislocations, some sort of bridging between the atomistic and continuum models is necessary. For example, it would be very useful to have a hybrid continuum–atomistic approach such that it retains the analytic nature of the continuum theory for the long-range elastic fields but also captures the essential non-linear effects in the atomic core. Bearing the names of Rudolf Peierls [86] and Frank Nabarro [87], the celebrated Peierls–Nabarro (PN) model is one such approach. Possibly the most attractive feature of the PN model is its simplicity.

scholarly journals Incorporation of Large Impurity Atoms into the Diamond Crystal Lattice: EPR of Split-Vacancy Defects in Diamond

Crystals ◽  
2017 ◽  
Vol 7 (8) ◽  
pp. 237 ◽  
Author(s):  
Vladimir Nadolinny ◽  
Andrey Komarovskikh ◽  
Yuri Palyanov
Keyword(s):  
Crystal Lattice ◽  
Diamond Crystal ◽  
Vacancy Defects ◽  
Impurity Atoms

Micro Grain Analysis in Plastically Deformed Silicon by 2nd-Order X-Ray Diffraction

MRS Advances ◽  
2018 ◽  
Vol 3 (39) ◽  
pp. 2347-2352 ◽  
Author(s):  
Gabriel Dina ◽  
Ariel Gomez Gonzalez ◽  
Sérgio L. Morelhão ◽  
Stefan Kycia
Keyword(s):  
Crystal Lattice ◽  
Perfect Crystal ◽  
Relative Orientation ◽  
Silicon Single Crystal ◽  
Grain Structure ◽  
X Rays ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Micro Scale

AbstractSecond-order diffraction (SOD) of x-rays refers to all diffraction processes where the photons reaching the detector have been diffracted twice within a crystal lattice. By measuring the two dimensional intensity profile of SOD, it is possible to distinguishing rescattering processes taking place inside each grain (perfect crystal domain) or in between grains. These two SOD regimes, usually called dynamical and kinematical, respectively, are ruled by size and relative orientation of the grains. In this work, we demonstrate how to explore SOD phenomena to understand the micro scale grain structure in plastically deformed silicon single crystal.

Study on Influence of Silicon Crystal Dislocation on Removal in Atmospheric Pressure Plasma Polishing

2016 ◽  
Vol 878 ◽  
pp. 83-88 ◽  
Author(s):  
Guang Lu Jia ◽  
Bing Li ◽  
Ju Fan Zhang
Keyword(s):  
Dislocation Density ◽  
Crystal Lattice ◽  
Dislocation Structure ◽  
Edge Dislocation ◽  
Atmospheric Pressure ◽  
Silicon Crystal ◽  
Atmospheric Pressure Plasma ◽  
Perfect Crystal ◽  
Pressure Plasma ◽  
Quantum Chemistry Simulation

Compared to perfect crystal lattice, typical edge dislocation structure has been modeled by quantum chemistry simulation in order to analyze the influence of crystal structure defects on removal process in atmospheric pressure plasma polishing (APPP). The Partial density of states (PDOS), number of states, average number of bonding electrons and energy have been calculated and analyzed further for these models. The analysis results reveal that silicon crystal with edge dislocation can be etched more easily than that of perfect crystal lattice. It is also found that the removal rate of sample with higher dislocation density is larger than that of lower dislocation density in the same experiment conditions. Thus, theoretical simulation demonstrates that structure dislocation is helpful for raising the etching rate, which accords well with testifying experiments results. But maybe structure dislocation could deteriorate surface roughness to some extent in initial stage of machining, as the dislocation structure is usually etched unevenly, although this is just a transition period.

DIAMOND NANORODS FROM CARBON NANOTUBES BY HYDROGEN PLASMA TREATMENT

2006 ◽  
Vol 05 (02n03) ◽  
pp. 307-313 ◽  
Author(s):  
J. L. GONG ◽  
L. T. SUN ◽  
D. Z. ZHU ◽  
Z. Y. ZHU ◽  
S. X. HE ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Plasma Treatment ◽  
Multiwalled Carbon Nanotubes ◽  
Growth Mechanism ◽  
Amorphous Carbon ◽  
Inner Core ◽  
Diamond Crystal ◽  
Hydrogen Plasma ◽  
Multiwalled Carbon ◽  
Sheath Structure

Single crystalline diamond nanorods with diameters of 4–8 nm and with lengths up to 200 nm have been synthesized by hydrogen plasma post-treatment of multiwalled carbon nanotubes. The diamond nanorods were identified to have a core-sheath structure with inner core being diamond crystal and outer shell being amorphous carbon. A growth mechanism for the diamond nanorods was proposed.

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