Size dependence of complex refractive index function of growing nanoparticles

The evidence of the change of the complex refractive index function E(m) of carbon and iron nanoparticles as a function of their size was found from two-color time-resolved laser-induced incandescence (TiRe-LII) measurements. Growing carbon particles were observed from acetylene pyrolysis behind a shock wave and iron particles were synthesized by pulse Kr–F excimer laser photo-dissociation of Fe(CO)₅. The magnitudes of refractive index function were found through the fitting of two independently measured values of particle heat up temperature, determined by two-color pyrometry and from the known energy of the laser pulse and the E(m) variation. Small carbon particles of about 1–14 nm in diameter had a low value of E(m)∼0.05–0.07, which tends to increase up to a value of 0.2–0.25 during particle growth up to 20 nm. Similar behavior for iron particles resulted in E(m) rise from ∼0.1 for particles 1–3 nm in diameter up to ∼0.2 for particles >12 nm in diameter.     

Burstein–Moss shift and room temperature near-band-edge luminescence in lithium-doped zinc oxide

Nanopowders of pure and lithium-doped semiconducting ZnO (Zn_1−x Li _x O, where x= 0, 0.01, 0.03, 0.06, 0.09 and 0.15 in atomic percent (at.%)) are prepared by PEG-assisted low-temperature hydrothermal method. The average crystallite size is calculated using Debye–Scherrer formula and corrected for strain-induced broadening by Williamson–Hall (W–H) plot. The peak shift in XRD and the lattice constant of ZnO as a function of unit cell composition are predicted by Vegard’s law. The evolution of ZnO nanostructures from rod-shaped to particle nature is observed from TEM images and the influence of dopant on the morphology is investigated. The optical absorption measurement marks an indication that the incorporation of lithium ion into the lattice of ZnO widens the optical band gap energy from ∼2.60 to ∼3.20 eV. The near band edge (NBE) emission peak centered at ∼3.10 eV is considered to be the dominant emission peak in the PL spectra. Blue emission peak is not observed in doped ZnO, thus promoting defect-free nanoparticles. The Burstein–Moss shift serves as a qualitative tool to analyze the widening of the optical band gap and to study the shape of the NBE luminescence in doped ZnO nanopowders. FT-IR spectra are used to identify the strong metal–oxide (Zn–O) interaction.     

Yield of singlet oxygen from optically pumped CCl<Subscript>4</Subscript> solution of fullerenes

Boiling occurs in a solution of oxygen and fullerenes in CCl₄ upon optical pumping of C₆₀ upon the fast appearance of incandescent fullerenes in cold solvent. Upon single-photon absorption, a spherical zone of the critical state of CCl₄ is formed within 5 ns (with a diameter of 22–25 nm, P _cr ∼ 45 atm, and T _cr ∼ 556 K). This spherical zone (gas-bubble nucleus) expands to a diameter of ∼100–400 nm for 2–5 ns. If the external pressure (natural or artificial) is rapidly released, the bubble accelerates and emerges into a vacuum chamber within 0.7–25 μs (the length of the passage is 0.1–5 cm depending on the construction of the singlet oxygen generator). We note that singlet oxygen appears 50 ns after the absorption of a photon by fullerene (i.e., inside of the almost formed gas bubble that only begins to emerge from the liquid to a low-pressure gas region).     

Investigation of scaling laws as applied to the gas discharge in the case of a barrier-discharge-excited Kr/CCl<Subscript>4</Subscript> mixture

The electrical and luminescent characteristics of a barrier-discharge lamp filled with a Kr/CCl₄ (150: 1) mixture are experimentally studied versus the value of pd, which varies in the range (7.6–14) × 10³ Pa cm. When simulating the gas discharge using similarity parameters, the following relationships are fulfilled: for pd = const (p is the pressure, d is the interelectrode distance), the pulse duration and the mean current density are τ _j ∼ 1/p and 〈j〉 ∼ p; the surface charge density on the electrodes, σ ∼ const; the duration of the UV radiation pulse and the efficiency of UV radiation due to a KrCl* (222 nm) exciplex, τ_rad ∼ 1/p and η ∼ p ². The maximal radiation efficiency achieved in the experiments is about 13%. Deviations from the similarity laws for the gas discharge are related to the filamentary form of the observed discharge. Qualitative analysis indicates that similarity laws may be fulfilled for such a form of discharge as well but locally, within a single filament.     

New remarks on the magnetic-field regime in the distant geomagnetic tail: Pioneer 8

Summary The emerging overview of the distant tail suggests to interpret some aspects of the magnetic-field observations obtained during January 1968 by Pioneer 8 in the region of expected tail (∼500R _E) in terms of different magnetic-field regimes which might find correspondence in the experimental observations performed at ∼240R _E by ISEE-3. At Pioneer position tail-like fields are typically accompanied by significant values of theB _y component while evidence for a wave activity which mostly perturbs the trasversal magnetic-field components is occasionally detected during tail-like encounters. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

Cumulative and continuous laser vaporization synthesis of single wall carbon nanotubes and nanohorns

The conditions for the scaled synthesis of single wall carbon nanotubes (SWNTs) and single wall carbon nanohorns (SWNHs) by laser vaporization at high temperatures are investigated and compared using in situ diagnostics. An industrial Nd:YAG laser (600 W, 1–500 Hz repetition rate) with tunable pulse widths (0.5–50 ms) is utilized to explore conditions for high-yield production. High-speed videography (50000 frames/s) of the laser plume and pyrometry of the target surface are correlated with ex situ high resolution transmission electron microscopy analysis of the products for pure carbon targets and carbon/catalyst targets to understand the effects of the processing conditions on the resulting nanostructures. Carbon is shown to self-assemble into single-wall nanohorn structures at rates of ∼1 nm/ms, which is comparable to the catalyst-assisted SWNT growth rates. Two regimes of laser ablation, cumulative ablation by multiple pulses and continuous ablation by individual pulses, were explored. Cumulative ablation with spatially overlapping 0.5-ms pulses is favorable for the high yield and production rate of SWNTs at ∼6 g/h while continuous ablation by individual long laser pulses (∼20 ms) at high temperatures results in the highest yield of SWNHs at ∼10 g/h. Adjustment of the laser pulse width is shown to control SWNH morphology.     

Growth mechanism of carbon nanotubes produced by pyrolysis of a composite film of poly (vinyl alcohol) and fly ash

We produced carbon nanotubes (CNTs) by pyrolysis of a composite film of poly (vinyl alcohol) (PVA) with fly ash (FA) at 500°C for 10 min under nitrogen. The composite films were prepared by a suspension of PVA and FA in deionized water and cast onto glass petri dishes. The morphologies of the CNTs were observed in the images of scanning and transmission electron microscopy, showing different types of structures, e.g. whiskers, branches, ropes and graphene sheets. The widths of the CNTs measured varied in the range 18–80 nm. X-ray photoelectron spectroscopy analysis showed five types of carbon binding peaks, C–C/C–H (∼77%), C–O–H (∼9%), –C–O–C (∼5%), C=O (∼5%) and –O–C=O (∼3%). From an image of a broken CNT, a mechanism was proposed for the formation of CNTs. The CNTs grown on FA surfaces have potential for the fabrication of high-strength composite materials with polymer and metal.     

High-frequency study of the orbital ordering resonance in the strongly correlated heavy fermion metal CeB<Subscript>6</Subscript>

A recently discovered magnetic resonance in the orbitally ordered phase of CeB₆ (orbital ordering resonance) is studied in a wide frequency range v = 44–360 GHz. The g-factor for this resonance was found to increase with frequency from g(v = 44 GHz) ∼ 1.55 to g(v > 250 GHz) ∼ 1.7. In addition to the orbital ordering resonance, a new magnetic resonance with a g-factor of 1.2–1.3 was detected for frequencies exceeding 200 GHz. Presented at the 5th Asia-Pasific EPR/ESR Symposium, August 24–27, 2006, Novosibirsk, Russian Federation.     

Temperature and frequency dependence of the spin-lattice relaxation times of E′1 centers in neutron-irradiated quartz glass

Results are reported for measurements of the spin-lattice relaxation times of E′₁ centers in quartz glass, produced by neutron irradiation, with the measurements made at two frequencies 9.25 and 24.0 GHz over a wide temperature interval 1.5–300 K. The experimental data are interpreted on the basis of interaction mechanisms of the spins with two-level systems with excitation energies ∼6, ∼26, and ∼420 cm⁻¹. A small modification of the existing theory allows us to explain a number of features of the observed temperature and frequency dependence of the relaxation rate. The results are compared with the data available in the literature on spin-lattice relaxation of irradiation centers in crystalline quartz and quartz glass. Fiz. Tverd. Tela (St. Petersburg) 39, 1335–1337 (August 1997)     

Effect of easy-plane anisotropy on the transient process time in magnetic films and plates

The effect of easy-plane anisotropy on the damping of the nonlinear magnetization oscillations that accompany 90° pulsed magnetization of magnetic films and plates is analyzed numerically. It is shown that the magnetization time can be decreased to ∼0.5 ns at an effective anisotropy field H _{K p} ≥ 6 kOe and that magnetization oscillations are fully damped at H _{K p} ≥ 20–40 kOe. The magnetization time can be ∼0.15–0.20 ns at a magnetizing pulse amplitude H _m ∼ 20–40 Oe.     

Structure and properties of the Ti-Si-N nanocrystalline coatings synthesized in vacuum by the electroarc method

Phase composition, defect substructure, and mechanical properties of the Ti-Si-N coating deposited on metal and ceramic-metal substrates by electroarc sputtering of the Ti-Si composite cathode in an ionized nitrogen atmosphere are investigated by the methods of modern materials science. It is established that coatings so formed with a thickness of ∼1–3 μm are superhard (H_v ∼ 50 GPa), and have the nanocrystalline structure (with crystalline sizes D = 7 nm) based on titanium nitride δ-TiN. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 46–51, February, 2007.     

Crystal structure of nanostructured PbS films at temperatures of 293–423 K

The crystal structure of lead sulfide films prepared by the hydrochemical deposition has been studied by X-ray diffraction. The thickness of the films synthesized is ∼100 nm, the size of coherent scattering regions is ∼70 nm, and the value of microstrains is ∼0.20%. It is established, for the first time, that the as-synthesized PbS films and the same films annealed in the temperature range 293–423 K have a cubic crystal structure (space group Fm3m) different from the B1-type structure. In the crystal lattice of the structure revealed, sulfur atoms are located not only in the 4(b) positions but also in the 8(c) positions. The occupancies of the 4(b) and 8(c) positions by the S atoms are ∼0.84 and 0.08, respectively.     

Telecom-grade fiber laser-based difference-frequency generation and ppb-level detection of benzene vapor in air around 3 μm

We report on the development of a field deployable compact laser instrument tunable over ∼232 cm⁻¹ from 3.16 to 3.41 μm (2932.5–3164.5 cm⁻¹) for chemical species monitoring at the ppb-level. The laser instrument is based on widely tunable continuous-wave difference-frequency generation (DFG), pumped by two telecom-grade fiber lasers. DFG power of ∼0.3 mW near 3.3 μm with a spectral purity of ∼3.3 MHz was achieved by using moderate pumping powers: 408 mW at 1062 nm and 636 mW at 1570 nm. Spectroscopic performance of the developed DFG-based instrument was evaluated with direct absorption spectra of ethylene at 3.23 μm (∼3094.31 cm⁻¹). Absorption spectra of vapor-phase benzene near 3.28 μm (∼3043.82 cm⁻¹) were recorded with Doppler-limited resolution. Line intensities of the most intense absorption lines of the ν ₁₂ band near 3043.8 cm⁻¹ were determined to support development of sensitive mid-infrared trace gas detection of benzene vapor in the atmosphere. Detection of benzene vapor in air at different concentration levels has been performed for the first time using multi-pass cell enhanced direct absorption spectroscopy at ∼3.28 μm with a minimum detectable concentration of 50 ppb (1σ).     

Low-temperature thermal conductivity of highly enriched and natural germanium

Experimental data on the thermal conductivity K(T) of crystals of natural and highly enriched germanium (99.99%) ⁷⁰Ge with lapped and polished surfaces are analyzed in the temperature range ∼1.5–8 K. In all the samples in the temperature range ∼1.5–4 K the standard boundary mechanism of scattering dominates. As the temperature is raised, an isotopic scattering mechanism is observed in the natural samples. In the highly enriched samples the theoretical values of K(T) turn out to be much smaller than the experimental ones. It is conjectured that a Poiseuille viscous flow regime of the phonon gas emerges in this case. Zh. éksp. Teor. Fiz. 114, 1757–1764 (November 1998)     

Luminescent properties of Bi-doped boro-alumino-phosphate glasses

A new Bi-doped boro-alumino-phosphate glass (BAP) composition was developed. Absorption and emission spectra and luminescence decay kinetics were investigated. The emission spectrum consists of two wide bands in the visible (0.6–0.8 μm) and near-infrared (∼1.0–1.5 μm) ranges. The luminescence decay curve investigation has revealed a complicated behavior dependent on both excitation and registration wavelengths. In contrast to earlier investigated Bi-doped glasses, Bi:BAP has good technological properties and can be easily scaled. This makes the developed glass composition interesting for broadband tunable (∼1.0–1.5 μm) lasers and amplifiers. PACS 32.70.Cs; 78.20.-e; 78.55.Qr     

New nuclear charge radii database

Several large relational databases (DBs) containing various atomic nucleus parameters and nuclear reaction features were produced at the Centre for Photonuclear Experiments Data (Centr Dannyh Fotoyadernykh Eksperimentov (CDFE)) of the Skobeltsyn Institute of Nuclear Physics, Moscow State University). The sources are numerical data founds maintained by International Nuclear Data Centers Network of the International Atomic Energy Agency (IAEA) and produced by CDFE. The original CDFE product is the electronic “Chart of Quadrupole Nuclear Deformations” which includes ∼2000 sets of data on nuclei quadrupole moments Q and quadrupole deformation parameters β₂ for ∼1500 nuclei. At last time, in the frame of joint research with the Joint Institute for Nuclear Research (JINR) that electronic Chart was supplemented with the data on nuclear mean-root-square (MRS) charge radii (∼900 isotopes of 90 elements (Z = 1–96, N = 0–152)) and therefore transformed into the “Chart of Nucleus Shape and Size Parameters”—complete collection of data under discussion. New Chart allows one to investigate the isotopic and isotonic behavior of nuclei quadrupole moments, parameters of quadrupole deformation and charge radii, and study the R(Z, N) surface structure and R(A) dependence of the fine structure. Original Russian Text ? I.N. Boboshin, V.V. Varlamov, Yu.P. Gangrsky, B.S. Ishkhanov, S.Yu. Komarov, K.P. Marinova, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 6, pp. 857–862.     

Nanocrystalline ruthenium oxide and ruthenium in sensing applications – an experimental and theoretical study

In this project, we have explored RuO₂ and Ru nanoparticles (∼ ∼10 and ∼ ∼5 nm, respectively, estimated from XRD data) to be used as gate material in field effect sensor devices. The particles were synthesized by wet chemical procedure. The capacitance versus voltage characteristics of the studied capacitance shifts to a lower voltage while exposed to reducing gases. The main objectives are to improve the selectivity of the FET sensors by tailoring the dimension and surface chemistry of the nanoparticles and to improve the high temperature stability. The sensors were characterized using capacitance versus voltage measurements, at different frequencies, 500 Hz to 1 MHz, and temperatures at 100–400°C. The sensor response patterns have been found to depend on operating temperature. X-ray photoelectron spectroscopy (XPS) analyses were performed to investigate the oxidation state due to gas exposure. Quantum-chemical computations suggest that heterolytic dissociative adsorption is favored and preliminary computations regarding water formation from adsorbed hydrogen and oxygen was also performed.     

Critical evolution of the local order parameters related to the nanopolar domains in Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> ceramics

In the present paper, Pb(Mg_1/3Nb_2/3)O₃ (PMN) ceramics prepared by the columbite method were investigated. The dielectric study indicates typical relaxor properties, with a frequency dispersion in the range of 200–350 K. The relaxor-to-paraelectric phase transition was evidenced by the continuous decrease of the local order parameter derived from the permittivity-temperature data. As a result of the critical behavior, the main Raman modes show anomalies at: (i) ∼150 K; (ii) ∼220 K (i.e. close to the critical temperature reported for the field-induced ferroelectric state in PMN single crystal); (iii) ∼260 K (i.e. the temperature of the permittivity maximum); (iv) ∼350 K (the temperature for initiation of the cluster freezing process T ^*); (v) ∼620 K (Burns temperature). The frequency split of the doublet at ∼605 and ∼500 cm⁻¹ presents a critical behavior related to the local symmetry lowering and to the structure ordering due to a phase transformation which takes place below T ^*. The tunability in the paraelectric state was interpreted in terms of reorientation of the non-interacting nanopolar clusters in a double-well potential. The temperature dependence of the nanopolar domain size also shows anomalies in the range of T ^*. The size and dynamics of the polar nanodomains is essential in determining the functional properties of the Pb(Mg_1/3Nb_2/3)O₃ relaxor.     

Magnetoelectric effect in laminates of polymer-based pseudo-1–3 (Tb0.3Dy0.7)0.5Pr0.5Fe1.55 composite and?0.3Pb(Mg1/3Nb2/3)O3–0.7PbTiO3 single crystal

We report an extrinsic magnetoelectric effect in composite laminates made by sandwiching one thickness-polarized 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN–PT) piezoelectric single crystal plate between two length-magnetized, polymer-based pseudo-1–3 (Tb_0.3Dy_0.7)_0.5Pr_0.5Fe_1.55 magnetostrictive composite plates. The laminates exhibit large magnetoelectric voltage coefficients (α _V ) of ∼0.17 V/Oe with a flat response for frequencies in excess of 40 kHz and of ∼2.97 V/Oe at the natural resonance frequency of ∼65 kHz. The distinct advantages of the laminates include high magnetic field sensitivity, low Joule heating loss, wide operating bandwidth, and low cost.     

Thermal conductivity of crystalline fullerite C60 in the simple cubic phase

The behavior of the thermal conductivity k(T) of bulk faceted fullerite C₆₀ crystals is investigated at temperatures T=8–220 K. The samples are prepared by the gas-transport method from pure C₆₀, containing less than 0.01% impurities. It is found that as the temperature decreases, the thermal conductivity of the crystal increases, reaches a maximum at T=15–20 K, and drops by a factor of ∼2, proportional to the change in the specific heat, on cooling to 8 K. The effective phonon mean free path λ _p, estimated from the thermal conductivity and known from the published values of the specific heat of fullerite, is comparable to the lattice constant of the crystal λ _p∼d=1.4 nm at temperatures T>200 K and reaches values λ_p∼50d at T<15 K, i.e., the maximum phonon ranges are limited by scattering on defects in the volume of the sample in the simple cubic phase. In the range T=25−75 K the observed temperature dependence k(T) can be described by the expression k(T)∼exp(Θ/bT), characteristic for the behavior of the thermal conductivity of perfect nonconducting crystals at temperatures below the Debye temperature Θ (Θ=80 K in fullerite), where umklapp phonon-phonon scattering processes predominate in the volume of the sample. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 8, 651–656 (25 April 1997)