arXiv subjects

Andrey A. Shiryaev

Publications and source records attributed to Andrey A. Shiryaev.

7 recordsLinked to original sources

arXiv2021

Behavior of implanted Xe, Kr and Ar in nanodiamond and thin graphene stacks: experiment and modeling

Implantation and subsequent behaviour of heavy noble gases (Ar, Kr, Xe) in few-layer graphene sheets and in nanodiamonds is studied both using computational methods and experimentally using X-ray absorption spectroscopy. X-ray absorption spectroscopy provides substantial support for the Xe-vacancy (Xe-V) defect as a main site for Xe in nanodiamond. It is shown that noble gases in thin graphene stacks distort the layers, forming bulges. The energy of an ion placed in between flat graphene sheets is notably lower than in domains with high curvature. However, if the ion is trapped in the curved domain, considerable additional energy is required to displace it.

cond-mat.mes-hall↗

arXiv2021

Molecular dynamics approach for predicting release temperatures of noble gases in pre-solar nanodiamonds

Pre-solar meteoritic nanodiamond grains carry an array of isotopically distinct noble gas components and provide information on the history of nucleosynthesis, galactic mixing and the formation of the Solar system. In this paper, we develop a molecular dynamics approach to predict thermal release pattern of implanted noble gases (He and Xe) in nanodiamonds. We provide atomistic details of the unimodal temperature release distribution for He and a bimodal behavior for Xe. Intriguingly, our model shows that the thermal release process of noble gases is highly sensitive to the impact and annealing parameters as well as to position of the implanted ion in crystal lattice and morphology of the nanograin. In addition, the model elegantly explains the unimodal and bimodal patterns of noble gas release via the interstitial and substutional types of defects formed. In summary, our simulations confirm that low-energy ion-implantation is a viable way for the incorporation of noble gases into nanodiamonds and we provide explanation of experimentally observed peculiarities of gas release.

physics.comp-ph↗

arXiv2021

Shift of CO2-I absorption bands in diamond: a pressure or compositional effect? A FTIR mapping study

Infra-red maps and profiles with high spatial resolution were obtained for two single crystal diamonds with pronounced CO2 IR absorption peaks. Detailed examination allows unambiguous assignment of the spectral features to solid CO2-I phase. It is shown that the distribution of IR band positions, intensities and widths in the sample follows regular patterns and is not chaotic as was suggested in previous works where spectra of a few individual spots were analysed. Consequently, pressure effects alone fail to explain all observed features and shifts of the CO2 bands. Experimental data can be explained by presence of impurities (such as water, N2, etc.) in the trapped CO2. This implies that spectroscopic barometry of CO2 microinclusions in diamond may be subject to poorly controlled bias. However, barometry is still possible if Davydov splitting of the CO2-I ν2 band is unequivocally observed, as this indicates high purity of the CO2 ice.

cond-mat.mtrl-sci↗

arXiv2020

Inelastic neutron scattering: A novel approach towards determination of equilibrium isotopic fractionation factors. Size effects on heat capacity and beta-factor of diamond

A new experimental method of determination of equilibrium isotopic properties of substances based on Inelastic Neutron Scattering (INS) is proposed. We present mathematical formalism allowing calculation of beta-factor of single-element solids based on INS-derived Phonon Density of States (PDOS). PDOS data for nanodiamonds of widely different sizes and of macroscopic diamond were determined from Inelastic Neutron Scattering experiment. This allowed determination of heat capacities and, for the first time, \b{eta}-factors for the diamond nanoparticles. We demonstrate considerable size-dependent increase of the heat capacities and decrease of the beta-factors for nanodiamonds relative to bulk diamond. Contributions of surface impurities/phases and phonon confinement to the size effects are evaluated. Applications to formation of diamond nanoparticles in nature are briefly discussed.

cond-mat.mtrl-sci↗

arXiv2019

Modification of Nanodiamonds by Xenon Implantation: A Molecular Dynamics Study

Xenon implantation into nanodiamonds is studied using molecular dynamics. The nanodiamonds range in size from 2-10 nm and the primary knock-on (PKA) energy extends up to 40 keV. For small nanodiamonds an energy-window effect occurs in which PKA energies of around 6 keV destroy the nanodiamond, while in larger nanodiamonds the radiation cascade is increasingly similar to those in bulk material. Destruction of the small nanodiamonds occurs due to thermal annealing associated with the small size of the particles and the absence of a heat-loss path. Simulations are also performed for a range of impact parameters, and for a series of double-nanodiamond systems in which a heat-loss path is present. The latter show that the thermal shock caused by the impact occurs on the timescale of a few picoseconds. These findings are relevant to ion-beam modification of nanoparticles by noble gases as well as meteoritic studies where implantation is proposed as the mechanism for xenon incorporation in pre-solar nanodiamonds.

cond-mat.mtrl-sci↗

arXiv2018

Ion implantation in nanodiamonds: size effect and energy dependence

Nanoparticles are ubiquitous in nature and are increasingly important for technology. They are subject to bombardment by ionizing radiation in a diverse range of environments. In particular, nanodiamonds represent a variety of nanoparticles of significant fundamental and applied interest. Here we present a combined experimental and computational study of the behaviour of nanodiamonds under irradiation by xenon ions. Unexpectedly, we observed a pronounced size effect on the radiation resistance of the nanodiamonds: particles larger than 8 nm behave similarly to macroscopic diamond (i.e. characterized by high radiation resistance) whereas smaller particles can be completely destroyed by a single impact from an ion in a defined energy range. This latter observation is explained by extreme heating of the nanodiamonds by the penetrating ion. The obtained results are not limited to nanodiamonds, making them of interest for several fields, putting constraints on processes for the controlled modification of nanodiamonds, on the survival of dust in astrophysical environments, and on the behaviour of actinides released from nuclear waste into the environment.

cond-mat.mtrl-sci↗

arXiv2012

Extended defects in natural diamonds: Atomic Force Microscopy investigation

Surfaces of natural diamonds etched in high-pressure experiments in H2O, CO2 and H2O-NaCl fluids were investigated using Atomic Force Microscopy. Partial dissolution of the crystals produced several types of surface features including the well-known trigons and hillocks and revealed several new types of defects. Besides well-known trigons and dissolution hillocks several new types of defects are observed. The most remarkable ones are assigned to anelastic twins of several types. The observation of abundant microtwins, ordering of hillocks and presence of defects presumably related to knots of branched dislocations suggests importance of post-growth deformation events on formation of diamond microstructure. This work confirms previous reports of ordering of extended defects in some deformed diamonds. In addition, the current work shows that natural diamonds deform not only by dislocation mechanism and slip, but also but mechanical twinning. The dominant mechanism should depend on pressure-temperature-stress conditions during diamond transport from the formation domain to the Earth surface.

cond-mat.mtrl-sci↗