Fine structure of the thermal decomposition kinetics of polymethylmethacrylate filled with detonation nanodiamonds

A comparison has been made of the specific features of the fine structure of thermodesorption spectra of polymethylmethacrylate and its composites with nanocarbon fillers: detonation nanodiamonds, fullerene C₆₀, and multiwalled carbon nanotubes. The influence of the fillers on the shape of the thermodesorption spectra has been interpreted as a result of the chemical interaction between functional groups of macromolecules of the polymer matrix and active centers of filler nanoparticles.     

Electron emission properties of detonation nanodiamonds

This paper summarizes the results of systematic studies of field electron emission from detonation nanodiamond coatings corresponding to nanodiamond powders of different modifications. The role of the chemical composition of the surface of detonation nanodiamond particles in field emission mechanisms is discussed. Field emission-related electronic properties of single diamond nanodots are studied using tight-binding calculations and continuum electrostatic simulations.     

Specific features in the observation of electron diffraction

Difficulties in the explanation of the interference pattern produced by electron diffraction are discussed. An important role of exciton drops in the formation of interference pattern is noted.     

Specific features of the electronic structure and optical spectra of nanoparticles with strong electron correlations

Analysis of the experimental optical spectra of CuO nanoparticles with the electronic structure characterized by strong electron correlations has revealed the appearance of unusual states inside the band gap. The intragap states and the specific features of the electronic structure of CuO nanoparticles are discussed in the framework of the generalized tight-binding method previously developed for describing the electronic structure of superconducting cuprates.     

Features of the transformation of detonation nanodiamonds into onion-like carbon nanoparticles

On the basis of the results of investigations carried out by differential scanning calorimetry, X-ray diffraction, nuclear magnetic resonance, high-resolution transmission electron microscopy, and Raman spectroscopy, a scheme for the transformation of detonation nanodiamonds (which are agglomerates of smaller particles) into onion-like carbon nanoparticles during vacuum annealing is verified. At high temperatures, the transition of an individual nanodiamond occurs in a short period of time and may proceed via an amorphous state.     

Specific features in the change of electrical resistivity of carbon nanocomposites based on nanodiamonds under neutron irradiation

The physical properties of bulk composite materials consisting of nanodiamond, pyrolytic carbon, and nanopores were investigated. Samples were irradiated in a channel of the reactor by fast neutrons (E > 0.5MeV) in ampoules with helium and in an aqueous medium. The dependences of the electrical transport properties of materials with different compositions on the dose of irradiation with fast neutrons were studied. A nonmonotonic change in the electrical resistivity with an increase in the neutron fluence was revealed. Possible explanations were offered for the observed dependence of the electrical resistivity on the neutron fluence, in particular, those related to the physical processes occurring in surface states of the three-phase system of the nanocomposite.     

Model of formation of three-dimensional polyurethane films modified by detonation nanodiamonds

The possibility of increasing the strain resistance of three-dimensional polyurethane films modified by detonation nanodiamonds is analyzed. It is found that the physicomechanical characteristics of polyurethane foams modified by nanodiamonds at a content of several thousandths of a weight percent change significantly. Models of the hardening of polyurethane films are proposed.     

Surface structure investigations using noncontact atomic force microscopy

Surfaces of several A_IIIB_V compound semiconductors (InSb, GaAs, InP, InAs) of the (0 0 1) orientation have been studied with noncontact atomic force microscopy (NC-AFM). Obtained atomically resolved patterns have been compared with structural models available in the literature. It is shown that NC-AFM is an efficient tool for imaging complex surface structures in real space. It is also demonstrated that the recent structural models of III-V compound surfaces provide a sound base for interpretation of majority of features present in recorded patterns. However, there are also many new findings revealed by the NC-AFM method that is still new experimental technique in the context of surface structure determination.     

Structure of the dispersive medium and sedimentation resistance of suspensions of detonation nanodiamonds

The specific features of the stabilization of suspensions formed by detonation nanodiamonds in polar and nonpolar media are investigated. It is demonstrated that the polydispersity of nanodiamond particles in an aqueous medium periodically changes in an ultrasonic field. The conditions are determined under which the optimum dispersity can be maintained for a long time. A technique is devised for chemical modification of the nanodiamond surface through the grafting of organosilyl groups. This technique makes it possible to prepare finely dispersed suspensions of nanodiamonds in nonpolar organic media. A model is proposed for an aggregate that consists of detonation nanodiamond particles and is stabilized through hydrogen bonds formed by functional groups of different types.     

Identification of fly eggs using scanning electron microscopy for forensic investigations

Forensic entomology is the science that studies the role of insects in decomposing corpses and one of the most common uses is to estimate the post-mortem interval (PMI) based on insect activity on a decomposing body. Usually, flies are the first insects to reach a carcass and are able to oviposit on carrion within a few hours after death. Scanning electron microscopy (SEM) gives detailed information about morphological characters helping to identify the immature forms of flies and consequently serves as a tool in crime scene investigations. Sometimes, only eggs and larvae are found in corpses. Some dipteral species are important because their larvae develop in organic matter. The aim of this study is to identify eggs of species of forensic importance, such as Chrysomya megacephala, Chrysomya putoria, Lucilia cuprina, Lucilia eximia and Ophyra aenescens, using scanning electron microscopy (SEM). C. megacephala had no anastomosis or holes at the top of the islands and C. putoria had few anastomoses and no holes, whereas L. eximia and O. aenescens were found to have anastomoses and holes and L. cuprina had only anastomoses. The median area was bifurcated anteriorly in C. megacephala, L. eximia and O. aenescens and rounded in C. putoria and L. cuprina. Also the sculptures observed in the chorionic cells, the length and the way that median area ends up posteriorly are characteristics of great diagnostic value to identify muscoids of forensic importance.     

Comparative structural characterization of the water dispersions of detonation nanodiamonds by small-angle neutron scattering

The structure of nanodiamond water dispersions prepared under different conditions was investigated by small-angle neutron scattering at the scale of 1 to 100 nm. The study of diluted dispersions was regarded as of paramount importance. Similarly to previous studies, strong clustering of particles was revealed in the solutions. The typical size of clusters (40 nm and above) depends on the modification of the dispersions. A common property can be distinguished for different systems: the fractal dimension of the clusters is in the range of 2.3?C2.4, which indicates that there is a common clustering mechanism in such systems. Using contrast variation, the existence of a nondiamond component in the colloidal particles of the dispersions was confirmed; it correlates with the presence of a graphene shell on crystallite surfaces.     

Specific features of electron avalanche in high gas multiplication mode

The results of studying an electron avalanche in narrow-gap wire chambers in the region of avalanche-to-streamer transition are described. The amplitude and temporal characteristics of the chambers in the high gas multiplication mode (≥10⁷) are given. Due to specific features of the electric field distribution in narrow-gap chambers and the application of a CF₄-based working gas, previously unknown processes taking place in a shower and more clearly reflecting the dynamics of avalanche development were discovered—electron velocity distribution, electrostatic oscillations of the avalanche as a whole, decrease in the anode signal duration, increase in the delay time of charge induction on the cathode by the avalanche development time, and, finally, varying shapes of the anode and cathode signal amplitude distributions. The observed processes can be explained if a completed avalanche is represented in the form of a double charged layer. The basis for such a representation is the specific features of a high-current avalanche mentioned above. The model under consideration is simple, provides answers to questions related to streamer formation and growth, and reflects the structure of an ionized channel and its stability mechanism.     

Specific features of the CuI nanocrystal structure in photochromic glasses

Physics of the Solid State - The absorption spectra of CuI nanocrystals with an average radii of 5.3 and 6.2 nm in photochromic glass matrix have been studied in the temperature range 38–300...     

Synchrotron investigations of the specific features in the electron energy spectrum of silicon nanostructures

The Si L _{2, 3} x-ray absorption near-edge structure (XANES) spectra of porous silicon nanomaterials and nanostructures with epitaxial silicon layers doped by erbium or containing germanium quantum dots are measured using synchrotron radiation for the first time. A model of photoluminescence in porous silicon is proposed on the basis of the results obtained. According to this model, the photoluminescence is caused by interband transitions between the energy levels of the crystalline phase and oxide phases covering silicon nanocrystals. The stresses generated in surface silicon nanolayers by Ge quantum dots or clusters with incorporated Er atoms are responsible for the fine structure of the spectra in the energy range of the conduction band edge and can stimulate luminescence in these nanostructures.     

Femtosecond laser pulse irradiation of Sb-rich AgInSbTe films: Scanning electron microscopy and atomic force microscopy investigations

The single-layer and multilayer Sb-rich AgInSbTe films were irradiated by a single femtosecond laser pulse with the duration of 120 fs. The morphological feature resulting from the laser irradiation have been investigated by scanning electron microscopy and atom force microscopy. For the single-layer film, the center of the irradiated spot is a dark depression and the border is a bright protrusion; however, for the multilayer film, the center morphology changes from a depression to a protrusion as the energy increases. The crystallization threshold fluence of the single-layer and the multilayer films is 46.36 mJ/cm², 63.74 mJ/cm², respectively. PACS 79.20.Ds; 78.55.Qr; 78.66.Jg; 68.37.Ef; 68.37.Ps     

Optical and microscopy investigations of soot structure alterations by laser-induced incandescence

2 at 1064 nm, vaporization/fragmentation of soot primary particles and aggregates occurs. Optical measurements are performed using a second laser pulse to probe the effects of these changes upon the LII signal. With the exception of very low fluences, the structural changes induced in the soot lead to a decreased LII intensity produced by the second laser pulse. These two-pulse experiments also show that these changes do not alter the LII signal on timescales less than 1 μs for fluences below the vaporization threshold. Received: 20 October 1997/Revised version: 16 February 1998     

Electron paramagnetic resonance detection of the giant concentration of nitrogen vacancy defects in sintered detonation nanodiamonds

A giant concentration of nitrogen vacancy defects has been revealed by the electron paramagnetic resonance (EPR) method in a detonation nanodiamond sintered at high pressure and temperature. A high coherence of the electron spins at room temperature has been observed and the angular dependences of the EPR spectra indicate the complete orientation of the diamond system.     

Specific features of the space-time structure of acoustic signals in multimode waveguides

The effect of the diffraction focusing of an acoustic field on the space-time intensity distribution of narrow-band pulsed signals in multimode oceanic waveguides is analytically and numerically studied. The laws governing this effect and its specific features are illustrated by the results of calculations based on the standard ray approximation and the mode theory for the acoustic field in an isovelocity waveguide.     

Specific features of low-energy electron scattering by thin films of cubic crystals

The specific features of the electron states in thin films of cubic crystals are considered in the energy range above the vacuum zero of the crystal potential. It is demonstrated that bands of bound states embedded in the energy continuum can exist along particular directions of the two-dimensional Brillouin zone. These bands can substantially affect the intensity of low-energy electron scattering.     

Specific features of speckle structure formed by dispersed laser beams

The geometry of statistical average of intensity speckles formed by a broadband dispersed laser beam spatially coherent in initial plane z = 0 is studied theoretically. A computer simulation was used to obtain two-dimensional distributions of random intensity that provide a clear picture of the transformations experienced by the speckle structure upon laser beam propagation. Correlation functions and power spectra of random intensity are calculated in order to determine the characteristic size and shape of speckles as a function of longitudinal coordinate z, the width and shape of the frequency spectrum, and the degree of dispersion of the light beam. Analytical expressions that describe an increase in the speckle size along the beam axis and in the direction of beam dispersion as a function of distance from the initial plane are obtained. The ultimate (at z → ∞) width of speckles in the direction of beam dispersion is calculated.