irradiation with rare-gas ions. In this case, a nanostructure is formed due to silicon self-assembling on the interface between amorphous layer and crystalline substrate. Two bands, at 720 and 930 nm, are found in the photoluminescence spectrum. These bands possibly originate from the quantum confinement effects in nanocrystals and may also be related to the regions of disordered silicon outside the amorphous layer containing nanocrystals. The intensity of the photoluminescence signal is studied as a function of duration of HF etching of samples and their subsequent exposure to atmosphere. The influence of thermal annealing on the photoluminescence spectrum is also studied.
The CMS potential (at LHC) for seeking the production of a charged Higgs boson is investigated for large values of tan β (between 20 and 50) and a relatively light charged Higgs boson MH = 200–400 GeV). A simple parametrization is proposed for the
The mechanisms of energy absorption by metallic alloys with long-range aperiodic lattice order and electronic properties of marginal metals are studied. The heat capacity and linear expansion coefficient of the Al63Cu25Fe12 icosahedral phase in the temperature range 300–1000 K are measured for the first time. Disagreement between the measured heat capacity and predictions made from the Debye model is found and analyzed. It is shown that the excess heat capacity observed at the temperatures of the experiment is fitted by Einstein’s function in the approximation T
The interaction between a quantum well with a large number of equidistant excited electron energy levels and light is investigated. It is shown that nonsinusoidal oscillations occur in the transmitted, reflected, and absorbed energy fluxes under exposure of the quantum well to irradiation with light pulses. For long pulses whose length γl?1 is one order of magnitude longer than the time ?/ΔE (where ΔE is the energy level spacing), the oscillation amplitude is small. In the case of narrow pulses when γl?1≤?/ΔE, the oscillation amplitude is comparable to the flux magnitudes. For very narrow pulses with
, the decaying echo of exciting pulse should be observed at the time intervals 2π?/ΔE. Symmetric and asymmetric pulses are considered. The theory is applicable to narrow quantum wells in a strong magnetic field when the equidistant levels correspond to electron-hole pairs with different Landau quantum numbers.
The solvatochromic 9-hydroxybenzo[b]quinolizinium ion is shown to operate as fluorescent probe for the detection of water in acetonitrile. The dual fluorescence of this photoacid and its dependence on the content of water in the medium enable the ratiometric analysis of the fluorescence data.
Guided-mode coupling in a microresonator generally manifests itself through avoided crossings of the corresponding resonances. This coupling can strongly modify the resonator local effective dispersion by creating two branches that have dispersions of opposite sign in spectral regions that would otherwise be characterized by either positive (normal) or negative (anomalous) dispersion. In this paper, we study, both analytically and computationally, the general properties of nonlinear frequency comb generation at an avoided crossing using the coupled Lugiato-Lefever equation. In particular, we find that bright solitons and broadband frequency combs can be excited when both branches are pumped for a suitable choice of the pump powers and the detuning parameters. A deterministic path for soliton generation is found.
We have studied bound states of the Schrödinger equation for a linear potential together with any finite number (P) of Dirac delta functions. Forx<-0, the potential is given as
High-potential, eco-friendly LiFePO4 cathode materials were synthesized by polyol, hydrothermal, and solid-state reaction methods. The polyol technique was carried out without any special atmosphere and postheat treatment. The synthesized samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectrometry (XPS), and charge-discharge and cyclic voltammetry tests. The LiFePO4 prepared via polyol technique exhibits good electrochemical performance than other method samples do.
The results of molecular dynamics (MD) simulations of CdSe crystals terminated by low-index atomic planes, (100), (110) and (111), are presented. The effect of the crystal termination on the atomic arrangement (interatomic distances) at the surface and underneath the surface is examined. It is shown that the crystal lattice is distorted in lateral and normal directions to the depth of up to about 2 nm from the surface. The exact characteristic of the changes of interatomic distances is specific to the type of the atomic plane terminating the crystal lattice. At some surfaces, the very last monoatomic layer loses the long-range ordering and becomes quasi amorphous. The atoms group into randomly distributed pairs or short linear groups.
Dendritic Pt–Cu nanoparticles were synthesized by a facile one-step method with the help of surfactant Brij58 at room temperature, and we also studied the effects of different Pt–Cu ratios on the morphology and size of nanoparticles. In addition, we further tuned the morphology of the Pt–Cu nanostructures by introducing bromide ions, eventually leading to the appearance of some tripod-like structures. Compared with dendritic Pt–Cu and commercial Pt black, these tripod-like Pt–Cu nanostructures exhibited higher electrocatalytic activity and CO tolerance for catalyzing methanol oxidation.
Nanocomposites with thermo and photo-switchable fluorescent properties were synthesized via mini-emulsion polymerization based on spiropyran and methyl methacrylate monomer. The photophysical behavior of fluorescence nanocomposites was investigated by fluorescence spectrophotometry in different temperature, UV-light and time of exposure. It was found that methyl methacrylate polymer is capable of acting as a protective layer and play a critical role in improving the photostability of colorants. The nanocomposites exhibited excellent fluorescent thermo-switching action with respect to the free spiro molecule.
Addition reaction between C60 and ethylenediamine occurred at room temperature in an ambient condition. C60-ethylenediamine adduct particles were prepared by mixing toluene solutions of C60 and ethyelenediamine. Average diameter of the C60-ethylenediamine adduct particles was changed non-linearly according to the reaction time, which were observed using transmission electron microscopy. Early stage of the reaction, the diameter of the adduct particles was changed from about 250 to about 430 nm. Then, the size of the adduct particles was converged to about 300 nm. During this addition reaction, the crystalline sizes of adduct particles were constant about 2–3 nm, regardless of the sizes of the adduct particles, which were determined by X-ray diffraction measurement.
A series of MZr4(PO4)6:Dy3+ (M = Ca, Sr, Ba) phosphors were prepared by the solid state diffusion method. Confirmation of the phase formation and morphological studies were performed by X-ray powder diffraction (XRD) measurements and scanning electron microscopy, respectively. Photoluminescence (PL) properties of these phosphors were thoroughly analyzed and the characteristic emissions of Dy3+ ions were found to arise from them at an excitation wavelength of 351 nm. The PL emission spectra of the three phosphors were analyzed and compared. The CIE chromaticity coordinates assured that the phosphors produced cool white-light emission and hence, they are potential candidates for UV excited white-LEDs (WLEDs).
High-frequency (HF) conductivity in systems with a dense (with a density of n = 3 × 1011 cm?2) array of self-organized Ge0.7Si0.3 quantum dots in silicon with different boron concentrations nB is determined by acoustic methods. The measurements of the absorption coefficient and the velocity of surface acoustic waves (SAWs) with frequencies of 30–300 MHz that interact with holes localized in quantum dots are carried out in magnetic fields of up to 18 T in the temperature interval from 1 to 20 K. Using one of the samples (nB = 8.2 × 1011 cm?2), it is shown that, at temperatures T ≤ 4 K, the HF conductivity is realized by the hopping of holes between the states localized in different quantum dots and can be explained within a two-site model in the case of
, where ω is the SAW frequency and τ0 is the relaxation time of the populations of the sites (quantum dots). For T > 7 K, the HF conductivity has an activation character associated with the diffusion over the states at the mobility threshold. In the interval 4 K < T < 7 K, the HF conductivity is determined by a combination of the hopping and activation mechanisms. The contributions of these mechanisms are distinguished; it is found that the temperature dependence of the hopping HF conductivity approaches saturation at T* ≈ 4.5 K, which points to a τ0 ≤ 1. A value of τ0(T*) ≈ 5 × 10?9 s is determined from the condition ωτ0(T*) ≈ 1.
The distributed Bragg reflectors (DBRs) consisting of alternating layers of ZnO and heavy doped amorphous silicon (a-Si) have been fabricated by magnetron sputtering. It is novel to find that the optical absorptions exist in the stopband of the DBRs, and that many discrete strong optical absorption peaks exist in the wavelength range of visible to near-infrared. The calculated results by FDTD show that the absorptions in the stopband mainly exist in the first a-Si layer, and that the light absorbed by other a-Si layers inside contributes to the two absorption peaks in near-infrared range. The strong absorptions ranged from visible to infrared open new possibilities to the enhancement of the performance of amorphous silicon solar cells.
In this work, the Stöber process was applied to produce uniform silica nanoparticles (SNPs) in the meso-scale size range. The novel aspect of this work was to control the produced silica particle size by only varying the volume of the solvent ethanol used, whilst fixing the other reaction conditions. Using this one-step Stöber-based solvent varying (SV) method, seven batches of SNPs with target diameters ranging from 70 to 400 nm were repeatedly reproduced, and the size distribution in terms of the polydispersity index (PDI) was well maintained (within 0.1). An exponential equation was used to fit the relationship between the particle diameter and ethanol volume. This equation allows the prediction of the amount of ethanol required in order to produce particles of any target diameter within this size range. In addition, it was found that the reaction was completed in approximately 2 h for all batches regardless of the volume of ethanol. Structurally coloured artificial opal photonic crystals (PCs) were fabricated from the prepared SNPs by self-assembly under gravity sedimentation.
Our present investigation aims at the synthesis and application of new, symmetric bridged bis-pyrazolone based acid dyes. The bis-pyrazolone compounds were accomplished from bis- hydrazine of 4,4′-Diaminostilbene-2,2′-disulfonic acid and ethyl acetoacetate. The bis-pyrazolones have been coupled with diazonium salts of o-hydroxyl aromatic amines which resulted in ligand dyes. The intermediate ligand dyes were treated with 3d transition metals to achieve the targeted metal complex acid dyes. The structures of investigated compounds were confirmed with the help of spectroscopic techniques. Dyes were applied on leather and their application parameters including their light fastness, wash fastness and rubbing fastness were determined.
A new efficient chemosensor 1 was prepared, for the detection of Fe3+ in solutions as a colorimetric and fluorescent sensor. The visual and fluorescent behaviors of the receptor toward various metal ions were also explored. The receptor shows exclusive response toward Fe3+ ions and also distinguishes Fe3+ from other cations by color change and fluorescence enhancement in hydroalcoholic solution (MeOH/H2O = 9/1, v/v). Thus, the receptor can be used as a colorometric and fluorescent sensor for the determination of Fe3+ ion. The fluorescence microscopy experiments showed that the chemosensor is efficient for detection of Fe3+ in vitro, developing a good image of the biological organelles.
We report a novel method for formation of self-organized single-standing carbon nanotubes by customizing a plasma-based process. The growth of carbon nanotubes by plasma-enhanced chemical vapor deposition provides suitable grounds to utilize plasma–solid interactions for nanopatterning. The bulk plasma is utilized to fabricate carbon nanotubes on the prepatterned Ni catalyst which in turn can confine the plasma to the growth region. The plasma localization leads to a dielectrophoretic force exerted on Ni atoms and can be engineered in order to grow a specific pattern of self-organized single-standing carbon nanotubes. Numerical simulations based on the plasma localization and dielectrophoretic force confirmed the experimental results. This method provides a simple and cost-effective approach to obtain nanopatterned arrays of carbon nanotubes which can be used for fabrication of photonic and phononic crystals, self-gated field emission-based transistors and displays.
The effect of interaction of low-index atomic planes, (100), (110), and (111) terminating CdSe platelet nanocrystals is examined using molecular dynamics (MD) simulations. Asymmetry of the environment of atoms at the end surface layers leads to anisotropic deformation of the cubic lattice and to a relative shift of Cd and Se sub-lattices. Interference of distortions of the crystal lattice originating at the terminal surfaces leads to changes of symmetry of the CdSe lattice in the whole sample volume. In the models, 2–3 nm thick, for all types of surfaces under examination, the initial cubic lattice symmetry gets lost in the whole sample volume.
