Quasi-direct optical transitions in Ge nanocrystals embedded in GeO<Subscript>2</Subscript> matrix

GeO₂ films with germanium nanocrystals (NCs) were deposited from supersaturated GeO vapor with subsequent dissociation on Ge:GeO₂. The films were studied using photoluminescence (PL), Raman scattering, IRspectroscopy techniques. Ge NCs in initial film have sizes about 6–8 nm and have no visible PL signal. The broad green-red PL peak was detected in Ge:GeO₂ films after thermal annealings. According to effective mass approach, maximum of PL signal from such relatively big Ge NCs should be in IR region. The experimentally observed PL signal is presumably originated due to quasi-direct L ₁-L ₃’ optical transitions “folded” in germanium NCs. The article is published in the original.     

Electrohydrodynamic dispersion of metals using electron-beam heating

The generation of metallic nanoparticles using an electrohydrodynamic source is considered; in this process, the surface of a metallic anode tip is melted with an electron beam. At an anode voltage of 11–12 kV and a current of 0.2–0.3 mA, structures that mainly consist of metallic particles 20–30 nm in size form on a substrate. An increase in the current leads to the appearance of larger particles on the substrate. The conditions of nanoparticle formation are analyzed, and nanoparticles are shown to form as a result of the cascade fragmentation of the initial metallic microdrops emitted from the anode surface under the action of an electric field. The fragmentation of the initial drops is caused by the capillary instability that appears due to the recharging of these drops when they fly through an electron beam focused near the anode surface.     

Exact solution in the damped Cummings-Tavis model and entanglement

An exact analytical expression is found for the density matrix of a system composed of a photon mode and two two-level dipole-dipole interacting atoms in a cavity with losses. The behavior of the atom-atom entanglement has been investigated on the basis of the Peres-Horodecki criterion.     

Bispectral Analysis of Gravity Capillary Waves

We perform a laboratory study of the nonlinear phase relation between short gravity waves with wavelengths of the order of 10 cm and their higher harmonics including spurious capillary ripple. The presence of higher harmonics of the basic low-frequency component in the spectrum of gravity capillary waves (GCWs) is confirmed on the basis of the methods of bispectral analysis. To determine the quantitative relations between the contributions of free and forced components in the GCW spectrum, we use the normalized bicoherence function. We show that it is correctly defined for both broadband random processes and polyharmonic random signals. The quantitative relation between the contributions from free and forced waves in the GCW spectrum at the frequency of the second harmonic is obtained.     

Covariant models of energy-information processes induced by the gravitational wave field in open hydro-gasdynamic systems

A covariant approach to the investigation of kinetic subsystems subjected to the action of the hydrodynamic component evolutionizing in the gravitational wave field is formulated. The list of model forces which are a covariant generalization of the well-known classical forces as well as the forces of purely gravitational origin is compiled.V. I. Ul'yanov-Lenin State University, Kazan'. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 79–84, June, 1992.     

Composites Based on Polytetrafluoroethylene and Detonation Nanodiamonds: Filler–Matrix Chemical Interaction and Its Effect on a Composite’s Properties

Specific properties of PTFE composites filled with ultradisperse detonation diamonds (UDDs) with different surface chemistries are studied. It is found for the first time that filler in the form of UDDs affects not only the rate of PTFE thermal decomposition in vacuum pyrolysis, but also the chemical composition of the products of degradation. The wear resistance of UDD/PTFE composites is shown to depend strongly on the UDD surface chemistry. The presence of UDDs in a PTFE composite is found to result in perfluorocarbon telomeres, released as a readily condensable fraction upon composite pyrolysis. The chemical interaction between PTFE and UDDs, characterized by an increase in the rate of gas evolution and a change in the desorbed gas’s composition, is found to occur at temperature as low as 380°C. It is shown that the intensity of this interaction depends on the concentration of oxygen-containing surface groups, the efficiency of UDDs in terms of the composite’s wear resistance being reduced due to the presence of these groups. Based on the experimental data, a conclusion is reached about the chemical interaction between UDDs and a PTFE matrix, its dependence on the nanodiamond surface chemistry, and its effect on a composite’s tribology.     

Statistical Studies of the Electric Breakdown in Nitrogen in the Duration Range of 3 ms–60 min

The statistical characteristics of an electric breakdown in the nitrogen in the spike (cathode)–plane gap in the duration range of (3 × 10^–3)–3600 s at voltages close to a static breakdown have been studied. It has been found that a probability of a gap breakdown is nonmonotonously distributed over time. The presence of maxima in the probability distribution confirms a contribution of some processes that both stimulate and suppress a breakdown. The typical times of the processes are ~30 ms, ~10^–1 s, and ~300 s.