Space-selective co-precipitation of silver and gold nanoparticles in femtosecond laser pulses irradiated Ag, Au co-doped silicate glass

We report on space-selective co-precipitation of silver and gold nanoparticles in Ag⁺, Au³⁺ co-doped silicate glasses by irradiation of femtosecond laser pulses and subsequent annealing at high temperatures. The color of the irradiated area in the glass sample changed from yellow to red with the increase of the annealing temperature. The effects of average laser power and annealing temperature on precipitation of the nanoparticles were investigated. A reasonable mechanism was proposed to explain the observed phenomena.     

Temperature dependence of photoluminescence in amorphous Si1-xCx:H films

We have investigated the temperature dependence of photoluminescence in hydrogenated amorphous silicon-carbon alloys a-Si_1-xC_x:H prepared by glow discharge in the low-power regime. The radiative recombination process, due to photocarriers trapped on band-edge states, is in competition with the thermal escape of the photocarriers into the mobility bands. The model gives a quantitative fit with experiment, without any adjustable parameter, provided the width of the band-edge distribution of states is taken as the width of the conduction band only (measured by “photo-induced infra-red spectroscopy”) and not as the Urbach energy, as it is usually assumed.     

Conceptual design of a phase-shifting telescope-interferometer

This paper deals with the theoretical principle and optical design of a phase-shifting telescope-interferometer. What is called a “telescope-interferometer” (T-I) is indeed a novel, recently proposed wavefront error (WFE) sensing technique, whose basic idea consists in combining the main pupil of a telescope with a second, off-axis reference arm. Then a weak modulation of the point spread function (PSF) is generated at the focal plane, allowing for direct phase measurements. We propose a notable improvement of the method, inspired from classical principles of phase-shifting interferometry. Herein are presented the alternative principle and its achievable measurement accuracy. The technique shows high performance excepted on narrow areas located near the pupil boundary. It is applicable to both ground or space telescopes and is suitable for the co-phasing of segmented mirrors, which is of prime importance in view of future giant telescope projects.     

The diffusion coefficient of a polymer in an array of obstacles is a non-monotonic function of the degree of disorder in the medium

Using Monte Carlo simulations, we have found that there is a surprising non-monotonic dependence of a polymer's diffusion coefficient upon the degree of disorder of the surrounding environment. Starting with a two-dimensional periodic lattice of obstacles, we randomly displace obstacles to create a quenched gel system with a tunable degree of disorder. Very small displacements increase the diffusion coefficient of polymers since they increase the width of the tube through which the polymer chains reptate. As we displace the obstacles further, however, entropic trapping is observed and the diffusion coefficient of the polymer decreases dramatically. This is a striking example of the delicate balance between entropic and frictional effects for a polymer diffusing in a dense system.     

Fabrication and magnetic properties of ordered Fe60Pb40 nanowire arrays electrodeposited in AAO templates

Ordered ferromagnetic-nonmagnetic heterogeneous Fe₆₀Pb₄₀ nanowire arrays were successfully fabricated by alternating current (AC) electrodeposition into nanoporous alumina templates. Transmission electron microscopy (TEM) image and selected-area diffraction (SAED) pattern analysis showed that the Fe₆₀Pb₄₀ nanowires are polycrystalline with an average diameter of 22 nm and lengths up to several micrometers. X-ray diffraction (XRD) observations indicated that α-Fe and fcc Pb phase coexist and do not form metastable alloy phase. The as-deposited samples were annealed at 200, 300, 400 and 500 ^°C, respectively. Magnetic measurements showed that nanowires have high magnetic anisotropy with their easy axis parallel to the nanowire arrays, and the coercivity of the samples increased with the annealing temperature up to 400 ^°C and reached a maximum (2650 Oe). The change of magnetic properties associated with the microstructure was discussed.     

On photoluminescence properties of a-Si:H-based structures

Non-Gaussian photoluminescence peaks observed in a-Si:H-based structures at 6 K are interpreted as a consequence of the presence of different phases in material. Thin films of amorphous silicon deposited on glass substrate have been analyzed.The main aims of the contribution are (i) analysis of numerical data obtained by fitting procedure and (ii) formulation of corresponding conclusions in terms of structural properties of sample. Spectrum of a-Si:H-based samples can be interpreted as superposition of photoluminescence signals arising from two domains with different degrees of structural disordering. By our knowledge this result corresponds to real situation from view of structural properties of amorphous hydrogenated silicon. Under certain circumstances, decomposition of photoluminescence spectrum can give information of geometrical structure of sample.     

Hybrid Deconvolution of Adaptive Optics Retinal Images from Wavefront Sensing

Adaptive optics can be used to compensate for the wave aberration of the human eyes to achieve high-resolution imaging in real time. However the correction ＆ partial due to the limitation of hardware. We propose a kind of hybrid image post-processing method, which uses the blind deconvolution combined with the residual data in wavefront sensor to restore the partially adaptive optics corrected retinal image. This method is applied in the image restoration of the vivid human retinal images. The results show that it is effective to improve the retinal image quality.     

Thermodynamic model for the size-dependent melting of prism-shaped nanoparticles

We report on the size-dependent melting of prism-shaped nanoparticles based on thermodynamic model and applied to understand the melting of prism-shaped indium nanoparticles. It is shown here that the bulk melting temperature cannot be extrapolated from the nanoscale and the extrapolated value will always be lower than the bulk melting temperature as has been observed experimentally.     

Low-temperature specific heat spectra considering nonextensive long-range correlated quasiperiodic DNA molecules

We consider the low-temperature specific heat spectra of long-range correlated quasiperiodic DNA molecules using a q-gaussian distribution, and compare them with those considering the Boltzmann-Gibbs distribution. The energy spectra are calculated using the one-dimensional Schrödinger equation in a tight-binding approximation with the on-site energy exhibiting long-range disorder and non-random hopping amplitudes. We focus our attention at the low temperature region, where the specific heat spectra presents a logarithmic-periodic oscillations as a function of the temperature T around a mean value given by a characteristic dimension of the energy spectrum.     

Functionalization and bioactivity in vitro of mesoporous bioactive glasses

Amino and carboxylic groups functionalized mesoporous bioactive glasses (denoted as N-MBGs and C-MBGs, respectively) were successfully synthesized through a post-grafting process and characterized by XRD, N₂ sorption, TEM, FT-IR and TG techniques. Their in vitro bioactivity and degradation behavior were investigated in simulated body fluid and examined by various techniques. The results demonstrate that the bioactivity of all the samples and the morphology of carbonated hydroxyapatite were affected remarkably by the introduction of functional groups. Spherical carbonated hydroxyapatite particles were observed grown on the N-MBGs surfaces after soaking in simulated body fluid for 8 h, which is different from the rod-like carbonated hydroxyapatite grown on conventional mesoporous bioactive glasses. While for C-MBGs, the nucleation and growth rate of carbonated hydroxyapatite was decreased at increased contents of carboxylic groups.