53 results on '"Roman E. Boltnev"'
Search Results
2. Experimental evolution of active Brownian grains driven by quantum effects in superfluid helium
- Author
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Oleg F. Petrov, Roman E. Boltnev, and Mikhail M. Vasiliev
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Medicine ,Science - Abstract
Abstract Complex structures, consisting of a large number of interacting subsystems, have the ability to self-organize and evolve, when the scattering of energy coming from the outside ensures the maintenance of stationary ordered structures with an entropy less than the equilibrium entropy. One of the fundamental problems here is the role of quantum phenomena in the evolution of macroscopic objects. We provide experimental evidence for the active Brownian motion and evolution of structures driven by quantum effects for micron-sized grains levitating in superfluid helium. The active Brownian motion of grains was induced by quantum turbulence during the absorption of laser irradiation by grains. The intensity of Brownian motion associated with quantum vortices increased by 6–7 orders of magnitude compared to the values from the Einstein formula. We observed the grain structures in a state far from thermodynamic equilibrium and their evolution to more complex organized structures with lower entropy due to the quantum mechanism of exceedingly high entropy loss in superfluid helium. more...
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- 2022
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3. Dust-Acoustic Nonlinear Waves in a Nanoparticle Fraction of Ultracold (2K) Multicomponent Dusty Plasma
- Author
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Fedor M. Trukhachev, Roman E. Boltnev, Mikhail M. Vasiliev, and Oleg F. Petrov
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ultracold dusty plasma ,nonlinear dusty-acoustic wave ,Debye radius ,Organic chemistry ,QD241-441 - Abstract
The nonlinear dust-acoustic instability in the condensed submicron fraction of dust particles in the low-pressure glow discharge at ultra-low temperatures is experimentally and theoretically investigated. The main discharge parameters are estimated on the basisof the dust-acoustic wave analysis. In particular, the temperature and density of ions, as well as the Debye radius, are determined. It is shown that the ion temperature exceeds the temperature of the neutral gas. The drift characteristics of all plasma fractions are estimated. The reasons for the instability excitation are considered. more...
- Published
- 2021
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4. Impurity Systems in Condensed Helium-4
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I. N. Krushinskaya, I. B. Bykhalo, and Roman E. Boltnev
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Materials science ,Liquid helium ,chemistry.chemical_element ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Nanoclusters ,law.invention ,Helium-4 ,chemistry ,law ,Chemical physics ,Impurity ,Condensed Matter::Superconductivity ,Metastability ,Physics::Atomic and Molecular Clusters ,Particle ,General Materials Science ,Physics::Atomic Physics ,Helium ,Superfluid helium-4 - Abstract
We reviewed systems formed in liquid and solid helium-4 at high concentrations (1016 cm−3 and higher) of impurity particles. A new explanation for the reversible coagulation of fine hydrogen particles into big flakes observed upon the transition of liquid helium into the superfluid phase is proposed. The importance of nanoclusters presence in helium crystals doped with impurity particle for the metastability of icebergs is discussed. more...
- Published
- 2021
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5. Experimental evolution of active Brownian grains driven by quantum effects in superfluid helium
- Author
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Oleg F. Petrov, Roman E. Boltnev, and Mikhail M. Vasiliev
- Subjects
Multidisciplinary - Abstract
Complex structures, consisting of a large number of interacting subsystems, have the ability to self-organize and evolve, when the scattering of energy coming from the outside ensures the maintenance of stationary ordered structures with an entropy less than the equilibrium entropy. One of the fundamental problems here is the role of quantum phenomena in the evolution of macroscopic objects. We provide experimental evidence for the active Brownian motion and evolution of structures driven by quantum effects for micron-sized grains levitating in superfluid helium. The active Brownian motion of grains was induced by quantum turbulence during the absorption of laser irradiation by grains. The intensity of Brownian motion associated with quantum vortices increased by 6–7 orders of magnitude compared to the values from the Einstein formula. We observed the grain structures in a state far from thermodynamic equilibrium and their evolution to more complex organized structures with lower entropy due to the quantum mechanism of exceedingly high entropy loss in superfluid helium. more...
- Published
- 2021
6. Luminescence of molecular nitrogen in cryogenic plasmas
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P. T. McColgan, S. Sheludiakov, David M. Lee, V. V. Khmelenko, A. A. Pelmenev, Roman E. Boltnev, I. B. Bykhalo, and I. N. Krushinskaya
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inorganic chemicals ,Materials science ,genetic structures ,Physics and Astronomy (miscellaneous) ,General Physics and Astronomy ,chemistry.chemical_element ,Cryogenics ,01 natural sciences ,Metastability ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,Molecule ,Physics::Atomic Physics ,Physics::Chemical Physics ,010306 general physics ,Helium ,010302 applied physics ,Plasma ,respiratory system ,Nitrogen ,respiratory tract diseases ,Afterglow ,chemistry ,Chemical physics ,Luminescence ,circulatory and respiratory physiology - Abstract
Great enhancement of molecular nitrogen luminescence in the afterglow of nitrogen-helium gas mixtures was observed at temperatures ≤ 10 K. The effect is explained by the increased efficiency of the recombination of nitrogen atoms and energy transfer from metastable nitrogen molecules and helium atoms to nitrogen molecules in the cold dense helium vapor.Great enhancement of molecular nitrogen luminescence in the afterglow of nitrogen-helium gas mixtures was observed at temperatures ≤ 10 K. The effect is explained by the increased efficiency of the recombination of nitrogen atoms and energy transfer from metastable nitrogen molecules and helium atoms to nitrogen molecules in the cold dense helium vapor. more...
- Published
- 2019
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7. Luminescence of ND radicals during the destruction of molecular nitrogen nanoclusters
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David M. Lee, P. T. McColgan, S. Sheludiakov, Roman E. Boltnev, and V. V. Khmelenko
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010304 chemical physics ,Radical ,General Physics and Astronomy ,chemistry.chemical_element ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Thermoluminescence ,Oxygen ,Nitrogen ,0104 chemical sciences ,Nanoclusters ,chemistry ,Deuterium ,Excited state ,0103 physical sciences ,Physical and Theoretical Chemistry ,Luminescence - Abstract
In this work we studied optical spectra of thermoluminescence accompanying the destruction of collections of molecular nitrogen nanoclusters containing stabilized nitrogen, oxygen, and deuterium atoms. These collections of nanoclusters were formed by the injection of products of a radio-frequency discharge in deuterium-nitrogen-helium gas mixtures into bulk superfluid 4He. In the range from 200 to 1650 nm, the bands at 336 nm, 473 nm along with a new band at 1170 nm as well as the known bands of atomic nitrogen and oxygen, and bands of molecular nitrogen, oxygen, and NO were observed. These three bands were assigned to the emission of the ND radicals formed due to recombinations of nitrogen atoms in excited metastable states and deuterium atoms in the ground state during the destruction of ensembles of molecular nitrogen nanoclusters. more...
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- 2019
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8. An Experimental Setup for Investigation of Cryogenic Helium Plasma and Dusty Plasma Structures within a Wide Temperature Range
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Roman E. Boltnev, Oleg F. Petrov, and Mikhail M. Vasiliev
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010302 applied physics ,Dusty plasma ,Materials science ,0103 physical sciences ,Atmospheric temperature range ,Atomic physics ,01 natural sciences ,Instrumentation ,Helium plasma ,010305 fluids & plasmas ,Electric discharge in gases - Abstract
A new experimental setup for studying various phenomena in both cryogenic helium plasma and dusty plasma structures in a low-pressure gas discharge within the temperature range of 1.6–300 K is described. The setup is equipped with a modern data-acquisition system and high-speed video cameras to observe processes in dusty plasma structures. For the first time, dusty plasma structures were observed and studied at temperatures below 4 К. more...
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- 2018
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9. Electron Spin Resonance Studies of Nitrogen Atoms Stabilized in Impurity-Helium Condensates
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Roman E. Boltnev, P. T. McColgan, Adil Meraki, V. V. Khmelenko, and David M. Lee
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Condensed Matter::Quantum Gases ,010302 applied physics ,Materials science ,Atoms in molecules ,Matrix isolation ,chemistry.chemical_element ,Condensed Matter Physics ,01 natural sciences ,Molecular physics ,Nitrogen ,Atomic and Molecular Physics, and Optics ,law.invention ,Nanoclusters ,Superfluidity ,chemistry ,law ,Impurity ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,General Materials Science ,Physics::Atomic Physics ,010306 general physics ,Electron paramagnetic resonance ,Helium - Abstract
Impurity-helium condensates (IHCs) created by injection of nitrogen atoms and molecules as well as rare gas (RG) atoms (Ne, Ar, and Kr) into superfluid $$^4$$ He have been studied via electron spin resonance (ESR) techniques. We investigated the influence of addition of rare gas atoms (Ne, Ar, and Kr) into the condensing $$\hbox {N}_2$$ –He gas mixture on the efficiency of stabilization as well as on the local and average concentrations of N atoms attainable in IHCs. Addition of Ar and Kr atoms into the condensing $$\hbox {N}_2$$ –He gas mixture substantially increased the stabilization efficiency of N atoms in nanoclusters forming IHCs. Measurements of the ground-state spectroscopic parameters of nitrogen atoms show that the nanoclusters have a shell structure. Most of the N atoms reside on solid molecular layers of $$\hbox {N}_2$$ . These layers form on the surfaces of RG (Ar or Kr) nanoclusters. more...
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- 2018
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10. Self-Organization Phenomena in a Cryogenic Gas Discharge Plasma: Formation of a Nanoparticle Cloud and Dust–Acoustic Waves
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E. A. Kononov, Oleg F. Petrov, Mikhail M. Vasiliev, and Roman E. Boltnev
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010302 applied physics ,Glow discharge ,Dusty plasma ,Materials science ,General Physics and Astronomy ,Nanoparticle ,chemistry.chemical_element ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Plasma ,Atmospheric temperature range ,01 natural sciences ,Molecular physics ,Electric discharge in gases ,chemistry ,Physics::Plasma Physics ,0103 physical sciences ,010306 general physics ,Helium ,Superfluid helium-4 - Abstract
The dusty plasma structures in a glow discharge of helium in a tube cooled by superfluid helium at a temperature of 1.6 K and higher have been studied experimentally. The bimodal dust plasma formed by clouds of polydisperse cerium dioxide particles and polymer nanoparticles has been analyzed. We have observed wave oscillations in the cloud of polymer nanoparticles (with a size up to 100 nm), which existed in a narrow temperature range from 1.6 to 2.17 K. Vortices have been observed in the dusty plasma structures at helium temperatures. more...
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- 2018
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11. Dust-acoustic waves in weakly coupled (gaseous) cryogenic dusty plasma
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F. M. Trukhachev, Roman E. Boltnev, Oleg F. Petrov, Mikhail M. Vasiliev, and A. A. Alekseevskaya
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Physics ,Dusty plasma ,Glow discharge ,Physics::Plasma Physics ,Astrophysics::Solar and Stellar Astrophysics ,Particle ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Acoustic wave ,Atomic physics ,Condensed Matter Physics ,Radial distribution function - Abstract
Experimental results on dust-acoustic wave study in a weakly coupled cryogenic dusty plasma within the DC glow discharge are discussed. Analysis of dust particle trajectories, their velocity distributions, and the pair correlation function allows us to conclude that the 3D dusty plasma structure studied at T = 83 K was most likely a gaseous structure. more...
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- 2021
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12. Oxygen atoms and nitrogen molecules as spectroscopic probes for the temperature determination in non-equilibrium cryogenic helium plasma jets
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Nelly Bonifaci, I. B. Bykhalo, I. N. Krushinskaya, A. A. Pelmenev, S. Sheludiakov, N. Sadeghi, V. V. Khmelenko, David M. Lee, Roman E. Boltnev, V.M. Atrazhev, LAsers, Molécules et Environnement (LAME-LIPhy ), Laboratoire Interdisciplinaire de Physique [Saint Martin d’Hères] (LIPhy ), and Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA) more...
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010302 applied physics ,[PHYS.PHYS.PHYS-OPTICS]Physics [physics]/Physics [physics]/Optics [physics.optics] ,Materials science ,Analytical chemistry ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Helium plasma ,Nitrogen ,Oxygen atom ,chemistry ,0103 physical sciences ,Molecule ,0210 nano-technology ,ComputingMilieux_MISCELLANEOUS - Abstract
International audience
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- 2021
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13. Formation of solid helical filaments at temperatures of superfluid helium as self-organization phenomena in ultracold dusty plasma
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Roman E. Boltnev, E. A. Kononov, Oleg F. Petrov, and Mikhail M. Vasiliev
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Dusty plasma ,Glow discharge ,Multidisciplinary ,Materials science ,lcsh:R ,lcsh:Medicine ,Plasma ,Dielectric ,Molecular physics ,Article ,Nanoclusters ,Electric discharge in gases ,Protein filament ,lcsh:Q ,lcsh:Science ,Superfluid helium-4 - Abstract
A multimodal dusty plasma formed in a positive column of the direct current glow discharge at superfluid helium temperatures has been studied for the first time. Formation of a liquid-like dusty plasma structure occurred after injection of polydisperse cerium oxide particles in the glow discharge. The coupling parameter ~10 determined for the dusty plasma structure corresponds very well to its liquid-like type. The cloud of nanoparticles and non-linear waves within the cloud were observed at T 6е, levitating in the gas discharge at the temperature ~2 K and pressure 4 Pa have been observed for the first time. Analysis of the experimental conditions and the filament composition allows us to conclude that the filaments and nanoclusters were formed due to ion sputtering of dielectric material during the experiments. more...
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- 2019
14. Argon Nanoclusters with Fivefold Symmetry in Supersonic Gas Jets and Superfluid Helium
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Roman E. Boltnev, David M. Lee, O. P. Konotop, N. V. Krainyukova, O. G. Danylchenko, V. V. Khmelenko, and Valery Kiryukhin
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Diffraction ,Argon ,Materials science ,chemistry.chemical_element ,Electron ,Condensed Matter Physics ,Kinetic energy ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Symmetry (physics) ,010305 fluids & plasmas ,Nanoclusters ,chemistry ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,General Materials Science ,Supersonic speed ,Atomic physics ,010306 general physics ,Superfluid helium-4 - Abstract
In this study argon nanoclusters (800 to $$\sim $$ 6500 atoms) formed in supersonic gas jets are compared to the nanoclusters stabilized in superfluid helium. High-energy electron and X-ray diffraction methods are utilized. Both techniques allow investigation of isolated clusters. It is shown that the theoretical prediction of the so-called multiply twinned particles with fivefold symmetry, such as icosahedra (ico) and decahedra (dec) is valid in the investigated cluster size interval. Around the point of the expected ico-to-dec size-dependent transformation at a cluster size of $$\sim $$ 2000 atoms, hexagonal ico and the statistical distribution of structures with a tendency for dec to replace ico are observed. Kinetic reasons, as well as temperature-related effects, could be responsible for the latter observations. more...
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- 2016
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15. Optical and Electron Spin Resonance Studies of Destruction of Porous Structures Formed by Nitrogen–Rare Gas Nanoclusters in Bulk Superfluid Helium
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V. V. Khmelenko, David M. Lee, P. T. McColgan, Roman E. Boltnev, and A. Meraki
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Materials science ,genetic structures ,Analytical chemistry ,chemistry.chemical_element ,02 engineering and technology ,01 natural sciences ,Spectral line ,Nanoclusters ,law.invention ,Neon ,law ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,General Materials Science ,010306 general physics ,Electron paramagnetic resonance ,Argon ,Krypton ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Nitrogen ,Atomic and Molecular Physics, and Optics ,chemistry ,Atomic physics ,0210 nano-technology ,Superfluid helium-4 - Abstract
We studied optical and electron spin resonance spectra during destruction of porous structures formed by nitrogen–rare gas (RG) nanoclusters in bulk superfluid helium containing high concentrations of stabilized nitrogen atoms. Samples were created by injecting products of a radio frequency discharge of nitrogen–rare gas–helium gas mixtures into bulk superfluid helium. These samples have a high energy density allowing the study of energy release in chemical processes inside of nanocluster aggregates. The rare gases used in the studies were neon, argon, and krypton. We also studied the effects of changing the relative concentrations between nitrogen and rare gas on thermoluminescence spectra during destruction of the samples. At the beginning of the destructions, $$\alpha $$ -group of nitrogen atoms, Vegard–Kaplan bands of $$\hbox {N}_2$$ molecules, and $$\beta $$ -group of O atoms were observed. The final destruction of the samples were characterized by a series bright flashes. Spectra obtained during these flashes contain M- and $$\beta $$ -bands of NO molecules, the intensities of which depend on the concentration of molecular nitrogen in the gas mixture as well as the type of rare gas present in the gas mixture. more...
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- 2016
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16. Thermoluminescence Dynamics During Destructions of Porous Structures Formed by Nitrogen Nanoclusters in Bulk Superfluid Helium
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Roman E. Boltnev, P. T. McColgan, David M. Lee, A. Meraki, S. Mao, and V. V. Khmelenko
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Materials science ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Thermoluminescence ,Nitrogen ,Atomic and Molecular Physics, and Optics ,Nanoclusters ,Solid nitrogen ,symbols.namesake ,chemistry ,Chemical physics ,Excited state ,0103 physical sciences ,symbols ,Molecule ,General Materials Science ,Atomic physics ,van der Waals force ,010306 general physics ,0210 nano-technology ,Superfluid helium-4 - Abstract
We studied the dynamics of thermoluminescence during destruction of porous structures formed by nanoclusters of nitrogen molecules containing high concentrations of stabilized nitrogen atoms. The porous structures were formed in bulk superfluid helium by injection of the products of discharges in nitrogen–helium gas mixtures through the liquid helium surface. Fast recombination of nitrogen atoms during warming-up led to explosive destruction of the porous structures accompanied by bright flashes. Intense emissions from the $$\alpha $$ -group of nitrogen atoms, the $$\beta $$ -group of oxygen atoms and the Vegard–Kaplan bands of N $$_2$$ molecules were observed at the beginning of destruction. At the end of destruction the M- and $$\beta $$ -bands of NO molecules as well as bands of O $$_2$$ molecules were also observed. Observation of the emissions from NO molecules at the end of destruction was explained by processes of accumulation of NO molecules in the system due to the large van der Waals interaction of NO molecules. For the first time, we observed the emission of the O $$_2$$ molecules at the end of destruction of the porous nitrogen structures as a result of the (NO) $$_2$$ dimer formation in solid nitrogen and subsequent processes leading to the appearance of excited O $$_2$$ molecules. more...
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- 2016
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17. Synthesis of nanoclusters and quasy one-dimensional structures in glow discharge at T ≈ 2 K
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Roman E. Boltnev, E. A. Kononov, M. M. Vasiliev, F. M. Trukhachev, and Oleg F. Petrov
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Glow discharge ,Materials science ,Sputtering ,Self-assembly ,Atomic physics ,Condensed Matter Physics ,Nanoclusters - Published
- 2020
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18. Plasmas and dusty plasmas at temperatures of liquid helium
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O. F. Petrov, Roman E. Boltnev, and M. M. Vasiliev
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History ,Materials science ,Liquid helium ,law ,Plasma ,Atomic physics ,Computer Science Applications ,Education ,law.invention - Abstract
Recent studies of dusty plasma structures formed by polydispersed CeO2 particles in a dc glow discharge at a temperature T > 1.6 K were shown to be the first experiments on dusty plasma in an exotic dark glow discharge mode. The properties of cryogenic helium plasmas at T ~ 1 K are summarized and discussed. more...
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- 2020
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19. Luminescence of Molecular Nitrogen Nanoclusters Containing Stabilized Atoms
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David M. Lee, Adil Meraki, Roman E. Boltnev, P. T. McColgan, and V. V. Khmelenko
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Hydrogen ,Radical ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Nitrogen ,Oxygen ,Nanoclusters ,Chemical energy ,chemistry ,Deuterium ,0103 physical sciences ,Physical and Theoretical Chemistry ,010306 general physics ,0210 nano-technology ,Luminescence - Abstract
We studied the luminescence of molecular nitrogen nanoclusters containing stabilized nitrogen, oxygen, hydrogen, and deuterium atoms. Optical spectra were observed during the destruction of these ensembles of nanoclusters accompanied by a rapid release of chemical energy stored in the samples. Several interesting features were observed including a broad band near λ ≈ 360 nm, which was identified as emission corresponding to 2Ag→1Ag transition of N4(D2h) polymeric nitrogen. Also the sharp lines at λ ∼ 336 and 473 nm were observed, and their assignments to ND radicals are discussed. more...
- Published
- 2017
20. Comparative study of thermo-stimulated luminescence and electron emission of nitrogen nanoclusters and films
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A. A. Pelmenev, Elena V. Savchenko, I. B. Bykhalo, G. B. Gumenchuk, I. V. Khyzhniy, Roman E. Boltnev, I. N. Krushinskaya, Alexey Ponomaryov, David M. Lee, S. A. Uyutnov, Vladimir E. Bondybey, and V. V. Khmelenko more...
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Materials science ,Physics and Astronomy (miscellaneous) ,General Physics and Astronomy ,chemistry.chemical_element ,Ionic bonding ,Electron ,Photochemistry ,Thermoluminescence ,Nanoclusters ,chemistry ,Sublimation (phase transition) ,Atomic physics ,Thin film ,Luminescence ,Helium - Abstract
We have studied thermo-stimulated luminenscence and electron emission of nitrogen films and nanoclusters containing free radicals of atomic nitrogen. Thermo-stimulated electron emission from N2 nanoclusters was observed for the first time. Thermo-stimulated luminescence spectra obtained during the destruction of a N2–He sample are similar to those detected from N2 films pre-irradiated by an electron beam. This similarity reveals common mechanisms of energy transfer and relaxation. The correlation of luminescence intensity and electron current in both systems points to the important role of ionic species in relaxation cascades. Sublimation of solid helium shells isolating nitrogen nanoclusters is a trigger for the initiation of thermo-stimulated luminescence and electron emission in these nitrogen–helium condensates. more...
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- 2013
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21. On charged impurity structures in liquid helium
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I. N. Krushinskaya, Roman E. Boltnev, A. A. Pelmenev, and I. B. Bykhalo
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inorganic chemicals ,Materials science ,Physics and Astronomy (miscellaneous) ,genetic structures ,General Physics and Astronomy ,02 engineering and technology ,Electron ,01 natural sciences ,Molecular physics ,Thermoluminescence ,Nanoclusters ,law.invention ,law ,Impurity ,0103 physical sciences ,Physics::Atomic and Molecular Clusters ,Physics::Atomic Physics ,010306 general physics ,Низкотемпературная физика пластичности и прочности ,Condensed Matter::Quantum Gases ,Liquid helium ,respiratory system ,021001 nanoscience & nanotechnology ,respiratory tract diseases ,Excited state ,Atomic physics ,0210 nano-technology ,Luminescence ,Superfluid helium-4 ,circulatory and respiratory physiology - Abstract
The thermoluminescence spectra of impurity-helium condensates (IHC) submerged in superfluid helium have been observed for the first time. Thermoluminescence of impurity-helium condensates submerged in superfluid helium is explained by neutralization reactions occurring in impurity nanoclusters. Optical spectra of excited products of neutralization reactions between nitrogen cations and thermoactivated electrons were rather different from the spectra observed at higher temperatures, when the luminescence due to nitrogen atom recombination dominates. New results on current detection during the IHC destruction are presented. Two different mechanisms of nanocluster charging are proposed to describe the phenomena observed during preparation and warmup of IHC samples in bulk superfluid helium, and destruction of IHC samples out of liquid helium. more...
- Published
- 2016
22. ESR studies of nitrogen atoms stabilized in aggregates of krypton–nitrogen nanoclusters immersed in superfluid helium
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V. V. Khmelenko, Roman E. Boltnev, S. Mao, and David M. Lee
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inorganic chemicals ,Materials science ,Physics and Astronomy (miscellaneous) ,Krypton ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Nitrogen ,Nanoclusters ,law.invention ,Superfluidity ,chemistry ,Impurity ,law ,Atomic physics ,Electron paramagnetic resonance ,Superfluid helium-4 ,Helium - Abstract
Impurity–helium condensates (IHCs) containing nitrogen and krypton atoms immersed in superfluid 4He have been studied via CW electron spin resonance (ESR). The IHCs are gel-like aggregates of nanoclusters composed of impurity species. It was found that the addition of krypton atoms to the nitrogen–helium gas mixture used for preparation of IHCs increases the efficiency of stabilization of nitrogen atoms. We have achieved high average (5 · 1019 cm−3) and local (2 · 1021 cm−3) concentrations of nitrogen atoms in krypton–nitrogen–helium condensates. The analysis of ESR lines shows that in krypton-nitrogen nanoclusters three different sites exist for stabilization of nitrogen atoms. Nitrogen atoms are stabilized in the krypton core of nanoclusters, in the nitrogen molecular layer that covers the Kr core, and on the surface of the nanoclusters. High concentrations of nitrogen atoms achieved in IHCs provide an important step in the search for magnetic ordering effects at low temperatures. more...
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- 2012
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23. Energy Release Channels During Destruction of Impurity-Helium Condensates
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I. N. Krushinskaya, Roman E. Boltnev, A. A. Pelmenev, V. V. Khmelenko, I. B. Bykhalo, and David M. Lee
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Materials science ,Analytical chemistry ,chemistry.chemical_element ,respiratory system ,Condensed Matter Physics ,Thermoluminescence ,Atomic and Molecular Physics, and Optics ,Spectral line ,Nanoclusters ,Volume (thermodynamics) ,chemistry ,Impurity ,Excited state ,Physics::Atomic and Molecular Clusters ,General Materials Science ,Physics::Atomic Physics ,Atomic physics ,Helium ,Superfluid helium-4 - Abstract
Injection of an impurity-helium gas jet passed through a radiofrequency discharge into a volume of superfluid helium leads to the growth of nanoclusters of impurity species which form impurity-helium condensates (IHCs). IHCs are porous materials with very low impurity density (∼1020 cm−3). High average concentrations of stabilized free radicals can be achieved on the large total surface (∼100 m2/cm3) of impurity nanoclusters. Warming of the IHCs leads to the destruction of the samples and formation of excited atoms and molecules as a consequence of the recombination of stabilized free radicals. We studied the influence of the nitrogen content in neon-helium and krypton-helium gas mixtures on the thermoluminescence spectra accompanying the destruction of the IHC samples, which were formed by using these gas mixtures. The energy release channels in the IHC samples were revealed from analysis of the thermoluminescence spectra. more...
- Published
- 2012
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24. Stabilization of H and D atoms in krypton–helium nanocondensates
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David M. Lee, V. V. Khmelenko, and Roman E. Boltnev
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Condensed Matter::Quantum Gases ,Materials science ,Physics and Astronomy (miscellaneous) ,Isotope ,Hydrogen ,Atoms in molecules ,Krypton ,General Physics and Astronomy ,chemistry.chemical_element ,Nanoclusters ,law.invention ,chemistry ,Impurity ,law ,Physics::Atomic and Molecular Clusters ,Physical chemistry ,Physics::Atomic Physics ,Atomic physics ,Electron paramagnetic resonance ,Helium - Abstract
Impurity–helium condensates formed by krypton nanoclusters containing atoms and molecules of hydrogen isotopes have been studied via an electron spin resonance (ESR) technique. Analysis of the ESR spectra has shown that most of the H and D atoms reside on the surfaces of Kr nanoclusters. Very large average concentrations have been obtained for H atoms (1.2⋅10⋅19cm−3) and D atoms (3.3⋅19cm−3) in these experiments. Line narrowing has been observed for the highest concentration of D atoms stabilized in the Kr–He sample. Exchange tunneling reactions have been studied in Kr–He sample containing H and D atoms. more...
- Published
- 2010
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25. Luminescence of molecular nitrogen nanoclusters containing stabilized nitrogen, oxygen, hydrogen, and deuterium atoms
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David M. Lee, A. Meraki, S. Sheludiakov, P. T. McColgan, V. V. Khmelenko, and Roman E. Boltnev
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History ,Materials science ,Hydrogen ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Oxygen ,Nitrogen ,Computer Science Applications ,Education ,Ion ,Nanoclusters ,chemistry ,Deuterium ,0103 physical sciences ,Molecule ,010306 general physics ,0210 nano-technology ,Luminescence - Abstract
We observed the appearance of a broad feature at 360 nm in spectra obtained during the destruction of ensembles of molecular nitrogen nanoclusters containing stabilized nitrogen, oxygen, hydrogen and deuterium atoms. We attribute this broad feature with a maximum at 360 nm to the N4 polynitrogen molecules which are the product of the neutralization reaction of ions with electrons in solid N2. more...
- Published
- 2018
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26. Stabilization of H and D atoms in Aggregates of Kr Nanoclusters Immersed in Superfluid Helium
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V. V. Khmelenko, David M. Lee, Roman E. Boltnev, I. N. Krushinskaya, E. P. Bernard, and J. Järvinen
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Condensed Matter::Quantum Gases ,Materials science ,Atoms in molecules ,Krypton ,Matrix isolation ,chemistry.chemical_element ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Nanoclusters ,law.invention ,chemistry ,law ,Molecular film ,Physics::Atomic and Molecular Clusters ,Molecule ,General Materials Science ,Physics::Atomic Physics ,Atomic physics ,Electron paramagnetic resonance ,Superfluid helium-4 - Abstract
Impurity–helium condensates containing krypton atoms and also atoms and molecules of hydrogen isotopes have been studied via an electron spin resonance (ESR) technique. Analysis of the ESR spectra shows that most of the H and D atoms reside in molecular layers (H2 or D2) formed on the surfaces of Kr nanoclusters. The thickness of the molecular films was found to determine the rates of recombination of the atoms into molecules, with atoms in the thinner films recombining much more slowly. Very large average concentrations were obtained for H atoms (1019 cm−3) and D atoms (3⋅1019 cm−3) in these experiments. more...
- Published
- 2009
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27. Capture of Superfluid Helium by Porous Structures
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I. N. Krushinskaya, L. P. Mezhov-Deglin, Roman E. Boltnev, I. B. Bykhalo, and S. V. Ivashin
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Condensed Matter::Quantum Gases ,Materials science ,Condensed Matter::Other ,chemistry.chemical_element ,Aerogel ,Atmospheric temperature range ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Nanoclusters ,Condensed Matter::Soft Condensed Matter ,Volume (thermodynamics) ,chemistry ,Impurity ,Physics::Atomic and Molecular Clusters ,General Materials Science ,Physics::Atomic Physics ,Atomic physics ,Porosity ,Superfluid helium-4 ,Helium - Abstract
We have studied superfluid helium capture in a sample of silica aerogel of 98.2% porosity in the temperature range from 1.22 K up to 1.89 K. The high retention of He in the aerogel sample corresponds to a similar phenomenon in impurity-helium condensates, in which very high values of the ratio of helium atoms to impurity atoms (up to 60) have been seen. We have observed that removing the aerogel sample from superfluid helium in a cylindrical glass beaker caused a decrease of the helium level corresponding to the geometrical volume of the sample (≈1 cm3). This observation has allowed us to conclude that superfluid helium is completely captured by the porous sample. Superfluid helium filling aerogel and impurity-helium samples (porous structures) serves as a dispersive medium of gel-like samples which interacts strongly with impurity nanoclusters forming the dispersing system. more...
- Published
- 2007
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28. Study of the stabilization and recombination of nitrogen atoms in impurity–helium condensates
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Roman E. Boltnev, E. A. Popov, A. A. Pelmenev, I. N. Krushinskaya, D. Yu. Stolyarov, and V. V. Khmelenko
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Condensed Matter::Quantum Gases ,Materials science ,Physics and Astronomy (miscellaneous) ,Condensed Matter::Other ,General Physics and Astronomy ,chemistry.chemical_element ,Atmospheric temperature range ,Thermoluminescence ,Nitrogen ,Molecular physics ,law.invention ,chemistry ,law ,Impurity ,Physics::Atomic and Molecular Clusters ,Specific energy ,Physics::Atomic Physics ,Atomic physics ,Electron paramagnetic resonance ,Helium ,Superfluid helium-4 - Abstract
The stabilization and recombination of nitrogen atoms N(4S) in nitrogen-helium and nitrogen–neon-helium condensates obtained by the injection of impurity particles from a gas discharge into bulk superfluid helium are investigated by the EPR method. It is established that the stabilized nitrogen atoms reside inside and on the surface of impurity clusters forming a porous structure in the bulk superfluid helium. The possibility of increasing the specific energy of impurity–helium condensates by increasing their density through mechanical pressing is investigated. For nitrogen-helium condensates an eightfold increase in the specific energy is achieved. The recombination loss of N(4S) upon heating of impurity–helium condensates in the temperature range 1.7–7 K is detected. This permits verification of the mechanism of thermoluminescence of impurity–helium condensates. more...
- Published
- 2005
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29. Long term stability of H atoms in HD-D2-He solids
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D. M. Lee, E. P. Bernard, Roman E. Boltnev, and V. V. Khmelenko
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Condensed Matter::Quantum Gases ,Materials science ,Hydrogen ,chemistry.chemical_element ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,law.invention ,Nanoclusters ,Superfluidity ,Deuterium ,chemistry ,Impurity ,law ,Physics::Atomic and Molecular Clusters ,Molecule ,General Materials Science ,Physics::Atomic Physics ,Atomic physics ,Electron paramagnetic resonance ,Helium - Abstract
We employed en electron spin resonance (ESR) technique for investigating the long term behavior of hydrogen and deuterium atoms in the HD-D2 impurity helium solids that were created by sending a gas mixture [H2]:[D2]:[He]= 1:4:100 through a radio-frequency electrical discharge into a volume of superfluid 4He at T = 1.5 K. H and D atoms were stabilized inside nanoclusters of impurity molecules. The exchange tunneling reactions D + H2 → HD + H and D + HD→D2 + H proceeded to eliminate D atoms and increase the concentration of H atoms in the HD-D2 impurity-helium solids. Local concentrations of H atoms inside the molecular nanoclusters of order 1020 cm−3 were achieved. The high concentration of H atoms was stable during ∼ 40 hours storage of the sample at T = 1.35 K. These solids are possible candidates for collective quantum phenomena of atomic hydrogen if the Bose-Einstein degeneracy regime can be attained. more...
- Published
- 2005
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30. Paramagnetic Attraction of Impurity-Helium Solids
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Roman E. Boltnev, E. P. Bernard, David M. Lee, and V. V. Khmelenko
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Materials science ,Condensed matter physics ,Hydrogen ,Liquid helium ,Diffusion ,chemistry.chemical_element ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,law.invention ,Paramagnetism ,Deuterium ,chemistry ,Impurity ,law ,Physics::Atomic and Molecular Clusters ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Physics::Atomic Physics ,Atomic physics ,Superfluid helium-4 ,Helium - Abstract
A small permanent magnet was used to attract impurity-helium solid samples composed of hydrogen, deuterium, and nitrogen radicals. The magnetic field gradient was sufficiently strong to lift each of the impurity-helium solids while submerged in superfluid helium, but only strong enough to lift one of four samples through the liquid surface. This suggests ranges of local atomic radical concentrations that partially agree with previous ESR measurements. The attractive paramagnetic force is strong enough to be useful as a trap for the formation of a pure hydrogen impurity-helium solid, for use in radical concentration measurements and for sorting and moving impurity-helium solids. more...
- Published
- 2004
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31. Impurity-Helium Solids: Chemistry and Physics at 1.5 K
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Roman E. Boltnev, V. V. Khmelenko, David M. Lee, Valery Kiryukhin, E. P. Bernard, and S. I. Kiselev
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Hydrogen ,Atoms in molecules ,Krypton ,Analytical chemistry ,chemistry.chemical_element ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Neon ,symbols.namesake ,chemistry ,Impurity ,Condensed Matter::Superconductivity ,Physics::Atomic and Molecular Clusters ,symbols ,Molecule ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science ,Physics::Atomic Physics ,Atomic physics ,van der Waals force ,Helium - Abstract
Impurity-helium solids are porous gel-like materials held together by Van der Waals forces. They consist of impurity atoms, molecules or clusters of atoms and molecules, each surrounded by very thin layers of solid helium. Impurities studied include neon, krypton, and molecular and atomic nitrogen, hydrogen and deuterium. The pore sizes and cluster sizes in impurity-helium solids are determined by ugtrasound attenuation and X-ray diffraction. The ESR technique is employed to study atomic impurities. The tunnelling exchange chemical reactions D+H2→HD+D and D+HD→D2+H are observed. Large concentrations of atomic hydrogen (∼8⋅1017 per cm3) are produced in these reactions. more...
- Published
- 2004
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32. Stabilization of High Concentrations of Nitrogen Atoms in Impurity-Helium Solids
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David M. Lee, Roman E. Boltnev, V. V. Khmelenko, and E. P. Bernard
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inorganic chemicals ,Materials science ,Condensed matter physics ,Liquid helium ,Atoms in molecules ,Analytical chemistry ,chemistry.chemical_element ,respiratory system ,Condensed Matter Physics ,Nitrogen ,Atomic and Molecular Physics, and Optics ,respiratory tract diseases ,law.invention ,Superfluidity ,chemistry ,law ,Impurity ,Physics::Atomic and Molecular Clusters ,General Materials Science ,Physics::Atomic Physics ,Electron paramagnetic resonance ,Helium ,Line (formation) - Abstract
Impurity-helium (Im-He) solids created by injecting gaseous helium with an admixture of nitrogen atoms and molecules into superfluid 4He have been studied via electron spin resonance (ESR). We have studied the efficiency of stabilization of N atoms in Im-He samples prepared from nitrogen-helium gas mixtures with different fractions of nitrogen varying from 0.25% to 4%. Some of the observed ESR spectra of N atoms in the Im-He samples are very broad. The highest local concentration of N atoms determined from dipole-dipole broadening of the ESR line is ∼8×1020 cm−3. The highest average concentrations of N atoms in N-N2-He solids were much lower (of order 1019 cm−3). The samples with high concentrations of N atoms were stable in liquid helium, and remained stable even after draining liquid helium from the sample at T≤3.5 K. more...
- Published
- 2004
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33. [Untitled]
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Evgenii B Gordon, Roman E. Boltnev, E. A. Popov, I. N. Krushinskaya, Giorgio Frossati, and A. Usenko
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Cryostat ,Jet (fluid) ,Materials science ,Liquid helium ,Evaporation ,chemistry.chemical_element ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,law.invention ,chemistry ,law ,Impurity ,General Materials Science ,Atomic physics ,Lambda point refrigerator ,Helium ,Superfluid helium-4 - Abstract
We have introduced guest particles into superfluid helium using a directed helium jet containing traces of species under study. The distinguishing peculiarity of the method consists in that the whole system is sealed from the cryostat main helium bath. This allows: (i) on the account of the absence of evaporating helium upflow to realize a complete capture of the impurities from the jet into liquid helium; (ii) to eliminate the dependence of the process conditions on liquid He level position in the main bath as well as on the amount of liquid He condensed inside a cell; and (iii) this method can be used to introduce impurities into liquid 3He. Two modifications of the technique have been designed—one for an optical cryostat and another for a cryostat with narrow 1” tail typical for use in a very high magnetic field. Optical and X-ray diffraction studies have confirmed the possibility of embedding in superfluid helium samples consisting of submicron D2 particles with a rate of 10mmoles per hour. Such samples are necessary for the achievement of strong D2 nuclear spin polarization by the brute force method. more...
- Published
- 2002
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34. [Untitled]
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Roman E. Boltnev, David M. Lee, Valery Kiryukhin, Bernhard Keimer, Evgenii B Gordon, V. V. Khmelenko, and S. I. Kiselev
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Diffraction ,Materials science ,Analytical chemistry ,chemistry.chemical_element ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,chemistry ,Nanocrystal ,Agglomerate ,Impurity ,Molecule ,General Materials Science ,Atomic physics ,Porous medium ,Superfluid helium-4 ,Helium - Abstract
We have performed studies of the formation and evolution of samples of Im-Helium (Im=Ne, D2, N2) solids obtained by allowing a mixed beam of helium and impurity molecules to fall onto the surface of superfluid helium. Clusters consisting of single impurity molecules and/or small aggregates of the molecules surrounded by layers of solid helium agglomerate to form porous solids. These solids have been studied by x-ray diffraction techniques. As the solids were heated above their formation temperature of T=1.5 K, the small aggregates or clusters of impurities tended to form larger clusters, which x-ray diffraction revealed to be nanocrystallites ranging in size from 3 to 6 nm. more...
- Published
- 2002
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35. Optical and electron spin resonance studies of xenon-nitrogen-helium condensates containing nitrogen and oxygen atoms
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A. A. Pelmenev, Igor B. Bykhalo, David M. Lee, Irina N. Krushinskaya, A. Meraki, P. T. McColgan, V. V. Khmelenko, Roman E. Boltnev, Scott Wilde, and S. Mao
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Condensed Matter::Quantum Gases ,Chemistry ,chemistry.chemical_element ,Spectral line ,Nanoclusters ,law.invention ,Xenon ,law ,Excited state ,Physics::Atomic and Molecular Clusters ,Molecule ,Physics::Atomic Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Electron paramagnetic resonance ,Helium ,Superfluid helium-4 - Abstract
We present the first observations of excimer XeO* molecules in molecular nitrogen films surrounding xenon cores of nanoclusters. Multishell nanoclusters form upon the fast cooling of a helium jet containing small admixtures of nitrogen and xenon by cold helium vapor (T = 1.5 K). Such nanoclusters injected into superfluid helium aggregate into porous impurity-helium condensates. Passage of helium gas with admixtures through a radio frequency discharge allows the storage of high densities of radicals stabilized in impurity-helium condensates. Intense recombination of the radicals occurs during destruction of such condensates and generates excited species observable because of optical emission. Rich spectra of xenon-oxygen complexes have been detected upon destruction of xenon-nitrogen-helium condensates. A xenon environment quenches metastable N((2)D) atoms but has a much weaker effect on the luminescence of N((2)P) atoms. Electron spin resonance spectra of N((4)S) atoms trapped in xenon-nitrogen-helium condensates have been studied. High local concentrations of nitrogen atoms (up to 10(21) cm(-3)) stabilized in xenon-nitrogen nanoclusters have been revealed. more...
- Published
- 2014
36. Percolation in aggregates of nanoclusters immersed in superfluid helium
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David M. Lee, Roman E. Boltnev, S. Mao, V. V. Khmelenko, and A. Meraki
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Materials science ,Condensed matter physics ,Percolation ,Condensed Matter Physics ,Superfluid helium-4 ,Electronic, Optical and Magnetic Materials ,Nanoclusters - Published
- 2014
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37. The thermoluminescence spectra obtained on the destruction of impurity–helium solid phase samples
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D. Yu. Stolyarov, Roman E. Boltnev, I. N. Krushinskaya, A. A. Pelmenev, and V.V. Khmelenko
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Condensed Matter::Quantum Gases ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Thermoluminescence ,Spectral line ,chemistry ,Impurity ,Phase (matter) ,Physics::Atomic and Molecular Clusters ,Molecule ,Physics::Atomic Physics ,Physical and Theoretical Chemistry ,Atomic physics ,Helium ,Superfluid helium-4 - Abstract
The thermoluminescence spectra during the destruction of impurity–helium solid phase samples of different compounds, containing stabilized N and O atoms, have been obtained. For the samples formed by injection of mainly Ar or Kr atoms into bulk superfluid helium (HeII), M-bands of the NO molecule are observed. The green bands appropriate to the E 1 Σ → B 1 Σ transition of the XeO molecule are observed on the destruction of samples containing Xe atoms. more...
- Published
- 1999
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38. Inert-Gas Solids with Nanoscale Porosity
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Bernhard Keimer, V.V. Khmelenko, Evgenii B Gordon, Roman E. Boltnev, and Valery Kiryukhin
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Materials science ,Krypton ,Atoms in molecules ,Matrix isolation ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Type (model theory) ,Neon ,chemistry ,Impurity ,X-ray crystallography ,Atomic physics ,Helium - Abstract
The structure and thermal properties of novel mesoporous inert-gas solids were studied by synchrotron x-ray diffraction. The materials were prepared by injecting a jet of helium containing dilute amounts of inert atoms and molecules (Ne, Kr, ${\mathrm{N}}_{2}$) into superfluid helium. The characteristic size of the constituent building blocks is $\ensuremath{\sim}60\AA{}$, and the density is $\ensuremath{\gtrsim}{10}^{20}\mathrm{impurity}$ atoms per c${\mathrm{m}}^{3}$. The Kr and ${\mathrm{N}}_{2}$ solids are stable outside of liquid He, up to temperatures above 10 K. These materials may find various applications as a new type of porous medium for fundamental physics, as well as in cluster physics, matrix isolation spectroscopy, and catalysis of low temperature chemical reactions. more...
- Published
- 1997
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39. Analysis of decomposition of impurity–helium solid phase
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E. A. Popov, A. F. Shestakov, Roman E. Boltnev, V. V. Khmelenko, Evgenii B Gordon, A. A. Pelmenev, I. N. Krushinskaya, and M. V. Martynenko
- Subjects
Materials science ,Physics and Astronomy (miscellaneous) ,Liquid helium ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Atmospheric temperature range ,Decomposition ,law.invention ,Superfluidity ,chemistry ,law ,Impurity ,Phase (matter) ,Monolayer ,Physics::Atomic Physics ,Atomic physics ,Helium - Abstract
The elemental composition of the impurity–helium solid phase (IHSP) grown by injecting of a gas jet containing Ne, Ar, Kr, and Xe atoms and N2 molecules into superfluid HeII is studied. The measured stoichiometric ratios S=NHe/NIm are much larger than the values predicted by the model of frozen together monolayer helium clusters. The theoretical possibility of freezing together of two-layered clusters is justified in the continual model of the helium subsystem of IHSP which fills the space between rigid impurity centers. Regularities of decomposition of “dry” samples (extracted from liquid helium) are analyzed in the temperature range 1.5–12 K under pressures from 10 to 500 torr. Two stages of sample decomposition are discovered: a slow stage accompanied by cooling and a rapid stage accompanied by heat release. These results suggest the presence of two types of helium in IHSP, viz., weakly bound and strongly bound helium which can be attributed respectively to the second and first coordination spheres of ... more...
- Published
- 1997
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40. Luminescence of Oxygen Atoms Stimulated by Metastable Helium at Cryogenic Temperatures
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A. A. Pelmenev, A. Meraki, David M. Lee, S. Mao, P. T. McColgan, V. V. Khmelenko, Roman E. Boltnev, and Scott Wilde
- Subjects
Jet (fluid) ,Materials science ,Trace Amounts ,Astrophysics::High Energy Astrophysical Phenomena ,General Physics and Astronomy ,chemistry.chemical_element ,Oxygen ,Afterglow ,chemistry ,Impurity ,Metastability ,Physics::Atomic and Molecular Clusters ,Physics::Atomic Physics ,Physics::Chemical Physics ,Atomic physics ,Luminescence ,Helium - Abstract
We present investigations of the afterglow of oxygen-helium gas mixtures at cryogenic temperatures. The cooling of a helium jet containing trace amounts of oxygen after passing through a radio frequency discharge zone led to the observation of strong emissions from atomic oxygen. The effect results from the increasing efficiency of energy transfer from metastable helium atoms and molecules to oxygen impurities in the cold dense helium vapor. This effect might find an application for the detection of small quantities of the impurities in helium gas. more...
- Published
- 2013
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41. Observation of the fcc-to-hcp Transition in Ensembles of Argon Nanoclusters
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Roman E. Boltnev, Valery Kiryukhin, V. V. Khmelenko, E. P. Bernard, N. V. Krainyukova, and David M. Lee
- Subjects
Diffraction ,Fusion ,Materials science ,Argon ,Close-packing of equal spheres ,General Physics and Astronomy ,chemistry.chemical_element ,Nanoclusters ,chemistry ,Low vacuum ,Chemical physics ,Physics::Atomic and Molecular Clusters ,Cluster size ,Orthorhombic crystal system - Abstract
Macroscopic ensembles of weakly interacting argon nanoclusters are studied using x-ray diffraction in low vacuum. As the clusters grow by fusion with increasing temperature, their structure transforms from essentially face-centered cubic (fcc) to hexagonal close packed as the cluster size approaches $\ensuremath{\sim}{10}^{5}$ atoms. The transformation involves intermediate orthorhombic phases. These data confirm extant theoretical predictions. They also indicate that growth kinetics and spatial constraints might play an important role in the formation of the fcc structure of bulk rare-gas solids, which still remains puzzling. more...
- Published
- 2012
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42. Luminescence of nitrogen and neon atoms isolated in solid helium
- Author
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A. A. Pelmenev, Roman E. Boltnev, V.V. Khmelenko, Evgenii B Gordon, M. V. Martynenko, A. F. Shestakov, I. N. Krushinskaya, and E. A. Popov
- Subjects
Neon ,chemistry ,Impurity ,Metastability ,General Physics and Astronomy ,chemistry.chemical_element ,Physical and Theoretical Chemistry ,Atomic physics ,Luminescence ,Thermoluminescence ,Helium ,Spectral line ,Afterglow - Abstract
Investigations of metastable N( 2 D) and Ne( 3 P 2 ) atoms isolated in solid helium have been carried out for the first time. The luminescence spectra and kinetics in the impurity helium solid phase (IHSP), with impurity centers N 2 , Ne, Ar, and Kr, show the sensitizing influence of a neighboring heavy particle on the forbidden N( 2 D- 4 S) transition. The extremely long-lived (τ≈10 4 s) hyperbolically decaying afterglow and thermoluminescence of this transition have been observed in the IHSP. Thermoluminescence studies allowed the determination of the energy barrier for pair fusion of neighboring centers. In agreement with calculations the energy barrier of this process which determines the IHSP stability turns out to be E 1 = 40 ± 4 K. The activation energy of the long-lived afterglow stage was found to be E 2 ≈ 7 K, close to the energy of vacancy formation in solid helium. By using laser-induced fluorescence, Ne( 3 P 2 ) atoms have been detected in superfluid helium and in the IHSP for the first time. Within an experimental accuracy of 0.18 A their spectral lines were unshifted and unbroadened with respect to the gas-phase values. more...
- Published
- 1994
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43. On the Efficiency of Infrared Filters in Optical Cryostats
- Author
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Laurent Guyon, Mathieu Melich, Roman E. Boltnev, Pierre-Etienne Wolf, Fabien Bonnet, Hélium : du fondamental aux applications (HELFA), Institut Néel (NEEL), Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF), Institute of Energy Problems of Chemical Physics, Russian Academy of Sciences [Moscow] (RAS), and ANR-06-BLAN-0098,HEVEPOR,Un système modèle pour les transitions de phase en milieu désordonné : l'adsorption de l'hélium dans les aérogels(2006) more...
- Subjects
Cryostat ,Materials science ,Infrared ,chemistry.chemical_element ,02 engineering and technology ,Optical cryostat ,01 natural sciences ,Upper and lower bounds ,Optics ,PACS numbers: 07.20.Mc, 44.40.+a, 07.57.-c ,Thermal radiation ,0103 physical sciences ,General Materials Science ,[PHYS.PHYS.PHYS-INS-DET]Physics [physics]/Physics [physics]/Instrumentation and Detectors [physics.ins-det] ,[PHYS.COND.CM-DS-NN]Physics [physics]/Condensed Matter [cond-mat]/Disordered Systems and Neural Networks [cond-mat.dis-nn] ,010306 general physics ,Helium ,Infrared cut-off filter ,[PHYS.PHYS.PHYS-OPTICS]Physics [physics]/Physics [physics]/Optics [physics.optics] ,business.industry ,Condensation ,Aerogels ,Aerogel ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Low temperature shutters ,chemistry ,Optoelectronics ,Infrared filters ,0210 nano-technology ,business - Abstract
8 pages; International audience; In an optical cryostat, the sample temperature is limited by the 300 K ther- mal radiation transmitted through the observation windows. As discussed in this pa- per, the corresponding heat load should be brought much below the μW level by using suitable cold IR filters. However, there are situations where one wants to di- rectly check the absence of IR heating by running the same experiment with the cold observation windows either open or totally blocked. We describe a particular example which is the study of helium condensation in a silica aerogel. On this aim, we devel- oped a simple and compact magnetic system able to move metallic shutters inside our optical cryostat. This allows us to set an upper bound of 1 μW for the effect of 300 K thermal radiation on our sample. We discuss the relevance of this result to the operation of optical dilution refrigerators. more...
- Published
- 2011
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44. Stabilization of hydrogen atoms in aggregates of krypton nanoclusters immersed in superfluid helium
- Author
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David M. Lee, Roman E. Boltnev, J. Järvinen, E. P. Bernard, and V. V. Khmelenko
- Subjects
Physics ,education.field_of_study ,Hydrogen ,Population ,Krypton ,chemistry.chemical_element ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Nanoclusters ,Superfluidity ,chemistry ,Atomic physics ,education ,Quantum ,Superfluid helium-4 ,Line (formation) - Abstract
Impurity-helium condensates (IHCs) containing krypton and hydrogen atoms immersed in superfluid $^{4}\text{H}\text{e}$ have been studied via cw electron-spin-resonance (ESR) techniques. The IHCs are gel-like aggregates of nanoclusters composed of krypton and hydrogen atoms. We have found that very high average $(\ensuremath{\sim}{10}^{19}\text{ }{\text{cm}}^{\ensuremath{-}3})$ and local $(\ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }{\text{cm}}^{\ensuremath{-}3})$ concentrations of hydrogen atoms can be stabilized in these samples. The analysis of ESR line positions and shapes shows that most of the H atom population resides in solid ${\text{H}}_{2}$ layers on the krypton nanocluster surfaces. High concentrations of atomic hydrogen achieved in IHCs provide an important step in the search for collective magnetic and quantum statistical phenomena at lower temperatures. more...
- Published
- 2009
- Full Text
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45. Noble-Gas Nanoclusters with Fivefold Symmetry Stabilized in Superfluid Helium
- Author
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V. V. Khmelenko, N. V. Krainyukova, Roman E. Boltnev, E. P. Bernard, Valery Kiryukhin, and David M. Lee
- Subjects
Diffraction ,Physics ,Nanostructure ,General Physics and Astronomy ,Noble gas ,chemistry.chemical_element ,Nanoclusters ,Superfluidity ,chemistry ,X-ray crystallography ,Physics::Atomic and Molecular Clusters ,Atomic physics ,Superfluid helium-4 ,Helium - Abstract
Macroscopic samples (volume approximately cm(3), atomic density approximately 10(19) -10(20) cm(-3)) of noble-gas nanoclusters (size approximately 5-6 nm) were produced in superfluid helium by an impurity-helium gas injection technique. X-ray diffraction measurements show that the samples consist of weakly interacting nanoclusters with fivefold symmetry, such as icosahedra and decahedra. These results open new opportunities for fundamental research of nanoclusters of noble gases and other materials in well-controlled environments using experimental techniques requiring bulk samples. more...
- Published
- 2007
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46. Deuterium atoms and molecules in nanoclusters of molecular deuterium
- Author
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Roman E. Boltnev, Valery Kiryukhin, S. I. Kiselev, E. P. Bernard, V. V. Khmelenko, and David M. Lee
- Subjects
Materials science ,Thin layers ,Atoms in molecules ,Relaxation (NMR) ,Analytical chemistry ,chemistry.chemical_element ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Nanoclusters ,Deuterium ,chemistry ,Molecule ,Crystallite ,Atomic physics ,Helium - Abstract
Impurity-helium solids created by injecting deuterium atoms and molecules into superfluid 4 He have been studied via x-ray-diffraction and electron-spin-resonance (ESR) techniques. X-ray-diffraction measurements show thatthese solids are highly porous gel-like structures consisting of D 2 clusters with the characteristic cluster size of 90′ 30 A. The densities of D 2 molecules in the samples are 7 × 10 2 0 -3 × 10 2 1 cm - 3 . Each of the D 2 clusters are either partially or totally surrounded by thin layers of adsorbed helium which may play an important role in preventing the coalescence of the clusters into larger crystallites of solid D 2 . Using ESR, we find that average concentrations of D atoms of order I × 10 1 8 cm - 3 can be achieved in our samples. Measurements of the ground-state spectroscopic parameters and relaxation times of atomic deuterium show that the D atoms reside in the D 2 clusters. The combined x-ray and ESR data show that local concentrations of D atoms as large as 2 × 10 1 9 cm - 3 are obtained in our experiments. The highly porous deuterium nanostructures studied in this work are promising for the production of high concentrations of ultracold neutrons and for significant nuclear polarization of D 2 molecules by the "brute force method" at low temperatures. more...
- Published
- 2004
- Full Text
- View/download PDF
47. Erratum to: Energy Release Channels During Destruction of Impurity-Helium Condensates
- Author
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I. N. Krushinskaya, David M. Lee, Roman E. Boltnev, V. V. Khmelenko, A. A. Pelmenev, and I. B. Bykhalo
- Subjects
Physics ,Section (category theory) ,chemistry ,Impurity ,chemistry.chemical_element ,General Materials Science ,Atomic physics ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Molecular electronic transition ,Excitation ,Helium ,Line (formation) - Abstract
1. Section 2.1, second paragraph, fifth line. Sentence is correct as follows: The α′-group corresponds to the electronic transition N(2D → 4S) accompanied by a simultaneous vibrational excitation v = 0 → v = 1 in the neighbouring N2(X1Σ+ g ) molecule. 2. Section 2.2, line 12: a-group and g-line are corrected as α-group and γ -line. 3. Section 3, second paragraph, line 6: W3 −u (v′′ = 4) → A3Σ+ u (v′ = 0–4) is corrected to W3 u(v′′ = 4) → A3Σ+ u (v′ = 0–4) 4. Section 3, second paragraph, line 16: W3 −u is corrected to W3 u 5. Updated Ref. 2 is as follows: V.V. Khmelenko, I.N. Krushinskaya, R.E. Boltnev, I.B. Bykhalo, A.A. Pelmenev, D.M. Lee, Low Temp. Phys. 38, 871 (2012). more...
- Published
- 2012
- Full Text
- View/download PDF
48. Application of cold beam of atoms and molecules for studying luminescence of oxygen atoms stimulated by metastable helium
- Author
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Scott Wilde, Roman E. Boltnev, S. Mao, David M. Lee, V. V. Khmelenko, P. T. McColgan, A. Meraki, and A. A. Pelmenev
- Subjects
Condensed Matter::Quantum Gases ,History ,Atoms in molecules ,chemistry.chemical_element ,Oxygen ,Computer Science Applications ,Education ,Afterglow ,chemistry ,Impurity ,Metastability ,Physics::Atomic and Molecular Clusters ,Physics::Atomic Physics ,Atomic physics ,Luminescence ,Beam (structure) ,Helium - Abstract
We describe a method for creating a high flux beam of cold atoms and molecules. By using this beam method, spectroscopic studies of the afterglow of oxygen-helium gas mixtures at cryogenic temperatures were performed. The cooling by helium vapor of a helium jet containing trace amounts of oxygen after passing through a radiofrequency discharge zone led to the observation of strong emissions from atomic oxygen. The effect results from the increased efficiency of energy transfer from metastable helium atoms and molecules to the atomic oxygen in the cold dense helium vapor. The effect might find application for the detection of small quantities of impurities in helium gas as well as possible laser action. more...
- Published
- 2014
- Full Text
- View/download PDF
49. Structural studies of impurity-helium solids
- Author
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Evgenii B Gordon, Bernhard Keimer, V. V. Khmelenko, S. I. Kiselev, Valery Kiryukhin, Roman E. Boltnev, and David M. Lee
- Subjects
Diffraction ,Superfluidity ,Materials science ,Nuclear magnetic resonance ,chemistry ,Scattering ,Impurity ,Analytical chemistry ,Matrix isolation ,chemistry.chemical_element ,Order (ring theory) ,Spectroscopy ,Helium - Abstract
We have used x-ray diffraction and ultrasound techniques to study the structure of mesoporous impurity--helium solids created after the injection of impurity particles $({\mathrm{D}}_{2},$ Ne, ${\mathrm{N}}_{2},$ Kr) into a volume of superfluid ${}^{4}\mathrm{He}.$ Clusters of impurities with size of order $50\ifmmode\pm\else\textpm\fi{}20 \AA{}$ and density $\ensuremath{\sim}{10}^{20} \mathrm{impurities}/{\mathrm{cm}}^{3}$ were observed by x-ray diffraction. The presence of a wide distribution of pore sizes in Im--He solids was revealed by ultrasound (80 to $8600 \AA{})$ and by small-angle x-ray scattering (80 to $g400 \AA{}).$ Both x-ray and ultrasound methods detected irreversible structural changes when samples were warmed above ${T}_{\ensuremath{\lambda}}=2.17 \mathrm{K}.$ This is ascribed to the aggregation of small clusters caused by thermally activated diffusion. In addition to being of fundamental interest, the properties of the unique porous media studied in this work may be relevant to investigations of low temperature chemical reactions, storage of free radicals, matrix isolation spectroscopy, and superfluid ${}^{4}\mathrm{He}$ contained in the pores of an extremely compliant medium. more...
- Published
- 2001
- Full Text
- View/download PDF
50. CW ESR studies of impurity-helium condensates containing krypton and hydrogen atoms
- Author
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V. V. Khmelenko, E. P. Bernard, J. Järvinen, Roman E. Boltnev, and David M. Lee
- Subjects
inorganic chemicals ,Condensed Matter::Quantum Gases ,History ,Hydrogen ,Krypton ,Analytical chemistry ,chemistry.chemical_element ,Computer Science Applications ,Education ,Nanoclusters ,Superfluidity ,chemistry ,Impurity ,Physics::Atomic and Molecular Clusters ,Cluster (physics) ,Physics::Atomic Physics ,Atomic physics ,Absorption (chemistry) ,Helium - Abstract
Impurity-Helium condensates (IHCs) containing krypton and hydrogen atoms have been studied in superfluid helium-4 via CW ESR techniques. The IHCs studied in this work are gel-like aggregates of nanoclusters composed of krypton and hydrogen atoms. We have found that such samples contain very high average concentrations of hydrogen atoms (~1018cm-3) as obtained by integration of the microwave absorption signal. Local concentrations (~1019cm-3) of H atoms were calculated from the ESR line width. Detailed studies of the ESR line shapes lead to the conclusion that a large fraction of the H atoms lies on the krypton cluster surfaces. more...
- Published
- 2009
- Full Text
- View/download PDF
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