Deformational methods of material nanostructuring: Premises,history, state of the art,and prospects

Brief history of origin and development of methods of deformational nanostructuring of materials (DNM) also referred to as methods of severe plastic deformation (SPD) are presented. Principles and efficiencies of the most widespread DNM methods — torsion under quasi-hydrostatic pressure (THP), equal channel angular pressing (ECAP), and hydrostatic isothermal forging (HIF) — are analyzed. Results of pioneer research of the structure and properties of nanomaterials produced by these methods are given. Prospects for the DNM application in industrial technologies of metal treatment and product manufacturing are indicated. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 47–59, May, 2008.     

Template based growth of nanoscaled films: a brief review

Growth of ultrathin films of metals and inorganic materials using various templates — both solid and liquid has been reviewed. Such nanoscaled films have been found to be effective in fabrication of devices and sensors. Use of crystal nanochannels of some inorganic compounds has been found to induce novel properties to the films grown within them. It is expected the latter approach will lead to the synthesis of materials with hitherto unknown properties.     

High-frequency (94.9 GHz) EPR spectroscopy of paramagnetic centers in a neutron-irradiated sapphire single-crystal fiber

Initial results are reported of an EPR study, conducted at 94.9 GHz, of a thermally annealed, neutron-irradiated white sapphire (α-Al₂O₃) single-crystal fiber. The optical centers produced in sapphire by neutron irradiation and thermal annealing are of interest for optical technologies involving the phenomenon of spectral hole-burning. While these centers have been modeled as consisting of electrons localized at anion vacancies, experimental tests of this model have been very limited. EPR spectroscopy — a choice technique for elucidating structural details of such color centers — reveals signals from numerous paramagnetic centers in this material. The predominant signals, with amplitudes a hundredfold greater than any other signals, derive from three closely related, highspin-multiplicity centers. These centers do not, however, derive from radiation-induced lattice defects: they are readily identified as Cr³⁺ (S = 3/2) and a pair of crystallographically equivalent Fe³⁺ (S=5/2) impurity ions. The advantages of high-frequency-EPR instrumentation in facilitating this identification are presented and discussed in detail. These advantages include enhanced sensitivity for this volume-limited, fiber sample. Moreover, the analysis of the spectra — entailing spectral assignments, evaluation of the spin-Hamiltonian parameters, and spin-counting — is greatly facilitated when the Zeeman interaction is dominant.     

Reflective and photoacoustic infrared spectroscopic techniques in assessment of binding media in paintings

This study proposes a method to estimate the lipid content in binding media in paintings that can be used at any laboratory equipped with an infrared spectrometer. The lipid content estimator, termed greasiness index (GI), is defined as a ratio of lipid ν(C=O) and protein amide I bands at 1743 and 1635 cm⁻¹, respectively. Three Fourier transform infrared (FTIR) sampling techniques were evaluated for GI determination: reflective attenuated total reflection—ATR, specular reflection microscopy—μSR and photoacoustic—PAS. A set of model painting samples containing three tempera binding media (casein, egg, egg + oil), seven pigments and one varnish type were used in the study. Multivariate analysis was used to evaluate the resulting data. A good reproducibility of GI was obtained by ATR and PAS but not with μSR. The discriminative power of the technique is higher for unvarnished samples, but, generally, the GI estimator can be used for the categorisation of binding media in large populations of painting samples analysed with the same FTIR technique (sampling technique, detection, etc.).     

On creating multilayer X-ray focusing mirrors

We review the recent studies and results obtained in the last five years at the Institute for Physics of Microstructures (IPM) in the field of multilayer mirror construction for hard X-ray wavelength range ( 7n = 0.05—0.25 nm), E = 25—5 keV)). Mirrors with cylindrical and spheroidal shapes as well as Kirkpatrick-Baez cross systems are considered.     

Correlation Inequalities for Interacting Particle Systems with Duality

We prove a comparison inequality between a system of independent random walkers and a system of random walkers which either interact by attracting each other—a process which we call here the symmetric inclusion process (SIP)—or repel each other—a generalized version of the well-known symmetric exclusion process. As an application, new correlation inequalities are obtained for the SIP, as well as for some interacting diffusions which are used as models of heat conduction,—the so-called Brownian momentum process, and the Brownian energy process. These inequalities are counterparts of the inequalities (in the opposite direction) for the symmetric exclusion process, showing that the SIP is a natural bosonic analogue of the symmetric exclusion process, which is fermionic. Finally, we consider a boundary driven version of the SIP for which we prove duality and then obtain correlation inequalities.     

Semiconducting P3HT microstructures: fibres and tubes obtained from macroporous silicon template

Microtubes and microfibres composed of poly(3‐hexylthiophene) (P3HT) were fabricated by melt‐assisted templates using ordered macroporous silicon. We have studied the influence of the pore depth and the template type on the microstructure fabrication, where the templates were membranes or structures opened only at one end. Current– voltage (I–V) measurements demostrated that the resistivity of these P3HT microstructures was in the same order as that of homogeneous films, which allows them to be used in electronic devices. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Radon-induced surface contaminations in low background experiments

In low background experiments the reduction of all possible radioactive contaminants is a crucial point for detector construction. This is also true for the surface contaminants, either those introduced during the production of detector components or those introduced during handling, treatment or storage. One of the most critical issue in this field is the control of the contamination induced by ²²²Rn and its progenies in the environment where the detectors are assembled and stored. Radioactive atoms can stick on detector components and create a net increase of the contaminants present on their surfaces, introducing an additional—often not negligible—source of background. The reduction of this kind of contaminations can become of primary importance in the case of fully sensitive devices, like cryogenic particle detectors. In this paper the analysis on the Rn sticking factor for copper and tellurium dioxide—the two main materials used for the construction of the CUORE detector—is discussed. The diffusion of radioactive atoms inside the detector components is considered in order to evaluate the effective contribution of Rn exposure to the background counting rate of an experiment.     

Locating of Nucleic Acid Intercalators in Yeast Cells by Image Analysis Combined Fluorescence Microscopy

Intracellular distribution in the intact (not fixed) Saccharomyces cerevisiae cells of the nucleic acid intercalators (NAI) was studied using fluorescence microscopy combined with computer image analysis (ImageJ software, NIH, USA). Three NAI—the anthracycline anticancer drug doxorubicin (DR) along with the nucleic acid dyes ethidium (E) and 4′,6-diamidino-2-phenylindole (DAPI)—were used. Staining pattern and ImageJ quantitative analysis data provided evidence that all three NAI were located in the nuclei and in the mitochondria. DR and E, in contrast to DAPI, may be bound to not only DNA, but to the mitochondrial membranes as well. Experiments on the combined application of DR+DAPI and E+DAPI have shown potential competition of DAPI with DR and E for binding sites in the nuclear and mitochondrial DNA. With the approach presented herein, the yeast cells of S. cerevisiae can be used as a model for locating intracellular sites of the fluorescing nucleic acid intercalators. This model may be of help in designing new DNA-targeted drugs and in preliminary studies of their interaction with eukaryotic cells.     

Intersectingp — p′ branes inpp-wave background

Several supergravity solutions corresponding to bothDp, as well asDp—Dp′ systems, inNS-NS andR-R pp-wave background originating fromAdS ₃ xS ³ xR ⁴ are presented. The supersymmetry properties of these solutions are analysed along with a brief outline of the world sheet construction for thep — p′ branes.     

Studies of phase transitions and quantum chaos relationships in extended Casten triangle of IBM-1

A precise solution of the classical energy functional E(N, η, χ; β) minimum problem with respect to deformation parameter β is obtained for the simplified Casten version of the standard interacting boson model (IBM-1) Hamiltonian. The first-order phase transition lines as well as the critical points of X(5), -X(5), and E(5) symmetries are considered. The dynamical criteria of quantum chaos—the basis state fragmentation width and the wave function entropy—are studied for the (η, χ) parameter space of the extended Casten triangle, and the possible relationships between these criteria and phase transition lines are discussed. The text was submitted by the authors in English.     

Green’s functions in quantum chemistry I. The Σ perturbation method

As an improvement over the Hartree-Fock approximation, we investigate a Green’s Function method—theΣ perturbation method—for molecular calculations. The method is applied to hydrogen molecule and to theπ-electron system of ethylene under PPP approximation. When the algebraic approximation is used, the energy obtained is better than that of the HF approach, but is not as good as that of the configuration-interaction method. The main advantage of this procedure is that it is devoid of the most serious defect of HF method, viz. incorrect dissociation limits.     

Eu2+ and Eu3+ based “concentrated phosphors” as converters for UV LED light: two approaches and two new examples

The absolute majority of phosphors are composed of a host lattice and some percentage of an activator. At higher activator concentrations the concentration quenching occurs. However, there are phosphors in which only minor quenching of the emission occurs with increasing of the activator content. Based on the existence of two different valence states of the Eu ion (2+ and 3+), two approaches for the development of “concentrated phosphors”, i.e. light emitting materials in which the activator ion is a main part of the crystal lattice, are discussed. In both approaches, reduced energy migration leading to the luminescence quenching is considered as a main condition to reach a high quantum efficiency of a concentrated phosphor. Two kinds of phosphors—Eu²⁺-doped alumosilicate and Eu³⁺-doped oxyfluoride—are used as an experimental basis for this discussion. Starting from the stoichiometric Ca_1-xEu_x²⁺Al₂Si₂O₈\mathrm{Ca}_{1-x}\mathrm{Eu}_{x}^{2+}\mathrm{Al}_{2}\mathrm{Si}_{2}\mathrm{O}_{8} anorthite and Eu³⁺OF oxyfluorides, the non-stoichiometric powders with Eu²⁺_0.92Al_1.76Si_2.24O₈\mathrm{Eu}^{2+}_{0.92}\mathrm{Al}_{1.76}\mathrm{Si}_{2.24}\mathrm{O}_{8}, Eu³⁺(O, F)_2,35 and Eu³⁺(O, F)_2,16 compositions were synthesized by a solid state reaction and investigated. It was shown that—in spite of the almost 100% Eu concentration—light converters with high quantum efficiency of more than 45% can be realized. A possible application of these materials as UV LED light converters for white light emitting diodes are discussed as well.     

TiO<Subscript>2</Subscript> microstructures by inversion of macroporous silicon using atomic layer deposition

An approach is presented which is capable of fabricating arbitrarily shaped three-dimensional microstructures. Two methods—namely, macroporous silicon and atomic layer deposition—are combined to realize structures in the micrometer and submicrometer range. Using TiO₂ as an example, the fabrication of single hollow objects as well as complex network structures is shown. The scalability and the wide range of applicable materials are the key points of this method for future applications.     

Bi-large neutrino mixings by radiative magnification

Starting with the unification hypothesis of mixings of quarks and leptons and small quark-like mixings at the see-saw scale, we find that two large mixings for ν_e —νx03BC; andv _μ—v _τ at the weak scale are obtained as a result of renormalization group evolution and radiative magnification if the three neutrinos are quasi degenerate in masses and possess the same CP parity. We also find thatU _e3 remains small and well within the CHOOZ-Palo Verde bound since the correspondingV _ub for CKM mixing is very small. Several testable pedictions are pointed out.     

Electrochemical fabrication of arrayed alumina nanowires showing strong blue emission

Arrayed alumina nanowires having controlled uniform diameters of 30–90 nm and lengths of 2–10 μm have been fabricated electrochemically with a high yield using two-step anodized aluminum oxide membranes as templates. The observed photoluminescence of the arrayed alumina nanowires arising from the emission of F⁺ and F centers is strong and blue-shifted compared with that of porous alumina membranes due to the structural difference of Al₂O₃. Our synthesized alumina nanowires are also found to be chemically more stable than the templates.     

Light absorption in undoped congruent and magnesium-doped lithium niobate crystals in the visible wavelength range

Light absorption measurements of nominally undoped congruent lithium niobate crystals (CLN) as well as 5 mol% magnesium-oxide-doped lithium niobate (MgO:LN) crystals were performed in the light wavelength range of 350 to 800 nm. Absorption spectra reveal that—besides iron (Fe) impurities—chromium (Cr) impurities of less than 0.5 wt. ppm concentration contribute significantly to the total optical absorption in the CLN crystals with a maximum of 0.035 cm⁻¹ around 500 nm. The axial distribution of Cr within a CLN boule is examined, revealing that the bottom part of the boule contains less Cr and therefore light absorption is reduced as well. In the case of the MgO:LN crystals, Cr impurities also contribute significantly to the total optical absorption, which is on the order of 0.025 cm⁻¹ for ordinarily polarized light and 0.015 cm⁻¹ for extraordinarily polarized light around 500 nm.     

Structure and magnetic properties of colossal magnetoresistance compound Tb0.5Sr0.5CoO3

The structure and the magnetic properties of the doped rare earth cobaltite systems are of recent interest owing to the CMR phenomenon that occur in them. In this paper, we investigate the structure and magnetic properties of Tb_0.5Sr_0.5CoO₃ solid solution, for the first time, using neutron powder diffraction technique. The sample Tb_0.5Sr_0.5CoO₃ is found to crystallize in orthorhombic (Pbnm) symmetry. The unit cell volume and Co—O bond length reduce with temperature. The calculatede _g bandwidth obtained from structural parameters turns out to be 0.989 eV. Low temperature neutron diffraction profiles exhibit a magnetic contribution to the fundamental Bragg peaks indicating a ferromagnetic ordering belowT _c. The results are compared with Co—O—Co bond angles and Co—O bond length of La_0.5Sr_0.5CoO₃, highlighting the ionic size effects on substitution of Tb ion for La in the compound.     

On the (Non)Existence of States on Orthogonally Closed Subspaces in an Inner Product Space

Suppose that S is an incomplete inner product space. In (Dvurečenskij, 1992, Gleason's Theorem and Its Applications, Ister Science Press, Bratislava, Kluwer Academic Publishers, Dordrecht), A. Dvurečenskij shows that there are no finitely additive states on orthogonally closed subspaces, F(S), of S that are regular with respect to finitely dimensional spaces. In this note we show that the most important special case of the former result—the case of the evaluations given by vectors in the “Gleason manner”—allows for a relatively simple proof. This result further reinforces the conjecture that there are no finitely additive states on F(S) at all.     

Study of the electronic structure of the quasicrystalline Ti—Zr—Ni system

Photoelectron spectra and optical absorption spectra for clean surfaces of quasicrystalline samples of the Ti—Zr—Ni system are measured. The resonant photoelectron spectra are also measured in the range of photon energies corresponding to Ni 2p and Zr 3d absorption thresholds. The change in the intensities of the spectrum of the valence band near the Zr 3d threshold is insignificant. The emission of Auger electrons increases near the Ni 2p threshold in a resonance way. Our studies make it possible to reveal certain specific features of the electronic structure of quasicrystals, which can be used to construct models of actual electronic structures of quasi-crystalline materials.