Showing papers in "Advanced Science Letters in 2010"

Biosynthesis of silver Nanoparticles using Coriandrum Sativum leaf extract and their application in nonlinear optics

Abstract: We present a simple and eco-friendly biosynthesis of silver nanoparticles using Coriandrum sativum leaf extract as reducing agent. The aqueous silver ions when exposed to leaf extract were reduced and resulted in silver nanoparticles whose average size is 26 nm. The silver nanoparticles were characterized by UV-Visible, X-ray diffraction (XRD), Fourier transform infra-red spectroscopy (FT-IR) and transmission electron microscopy (TEM) techniques. Nonlinear optical properties of silver nanoparticles were studied using Z-scan technique with 6 ns pulse duration at 532 nm. The nonlinear refractive index and third-order susceptibility 3 were measured to be ∼ 6 0×10−13 cm2/W and 1 38×10−9 esu, respectively. Silver nanoparticles were found to exhibit strong reverse saturable absorption (RSA). RSA was identified as the main mechanism responsible for optical limiting.

Modulation of size, shape and surface charge of chitosan nanoparticles with reference to antimicrobial activity

Abstract: Chitosan is extensively used in medicine and medical textiles for drug delivery and other applications because of its biocompatibility, biodegradability and inherent antimicrobial properties. In this study, we demonstrated a manipulating route with suitable process conditions to synthesize chitosan nanoparticles which are expected to have the best antibacterial activity for medical application. Ionotropic cross-linking using sodium tripolyphosphate (TPP) was the chosen route for synthesis of chitosan nanoparticles. It was interesting to observe that pH of the chitosan and TPP solution has a significant role in controlling the nanoparticle shape and size and thus can be fine tuned to achieve optimum antimicrobial activity. Solution pH of both chitosan and TPP was demonstrated to be the most critical factor in controlling particle size, surface charge and even shape as revealed by the SEM and TEM micrograph. It was also found that variation in size, shape and surface charge of chitosan nanoparticles resulted in significant variation in their antibacterial activity. The study demonstrated that best antimicrobial activity against bacteria S. aureus was achieved when the chitosan nanoparticles were synthesized at chitosan solution pH fixed at 6.0 and the TPP solution pH at 8.9. These observations can be used to fine tune the synthesis of chitosan nanoparticles for their application as an effective antimicrobial agent in polymers and textiles for their noble use in medical field.

Interpretations of Quantum Mechanics and the measurement problem

Abstract: We present a panoramic view on various attempts to "solve" the problems of quantum measurement and macro-objectivation, i.e. of the transition from a probabilistic quantum mechanic microscopic world to a deterministic classical macroscopic world.

A model of field emission from carbon nanotubes decorated by nanodiamonds

Abstract: Field Emission properties of aligned bundles of SWCNTs decorated by nanodiamond grains have been experimentally studied. Additional information, required to give a physical interpretation to the experimental data, have been acquired by comparing the FE properties of such hybrid materials with those of two types of Single-Walled Carbon Nanotube (SWCNT) samples, constituted by bundles aligned and not aligned along the cathode–anode direction, respectively. For all samples, the characteristics of Field Emission have been described in the frame of the Fowler-Nordheim relationship and analysed following different models. The obtained values of current density from samples formed by SWCNT ensembles suggest that the observations are best accounted by a model based on the mechanism involving field concentration near a nanotube (that is the model generally accepted for SWCNTs and using the factor). Conversely, if nanodiamond grains decorate the SWCNT bundles, one has to invoke a more complex two-factor model, where the factor is coupled to another emission mechanism. Two versions of emission model are here considered: (1) the model coupling the factor to the thermoelectric effect and; (2) the model coupling the factor to a pre-breakdown process.

Nanocrystalline Mg Doped ZnO Dilute Magnetic Semiconductor Prepared by Chemical Route

Abstract: This paper reports on the comparative investigation of ZnO and Mg doped ZnO (MZO) dilute magnetic semiconducting thin films prepared by chemical bath deposition. The films were characterized for their structural properties, optical and morphological studies. The films were polycrystalline in nature with hexagonal phase having (002) preferential orientation. The typical grain size were also estimated and found to be of an average of 200 nm. It was found that Mg doping into ZnO, modulated a shift in optical band gap of the MZO films in the UV region of 3.22 eV. The films exhibit ferromagnetic properties for magnesium doping concentration of 2 at%.

Droplet Epitaxy of InN Quantum Dots on Si(111) by RF Plasma-Assisted Molecular Beam Epitaxy

Abstract: InN quantum dots (QDs) were fabricated on Si(111) substrate by droplet epitaxy using an RF plasma-assisted MBE system. Variation of the growth parameters, such as growth temperature and deposition time, allowed us to control the characteristic size and density of the QDs. As the growth temperature was increased from 100 C to 300 degrees C, an enlargement of QD size and a drop in dot density were observed, which was led by the limitation of surface diffusion of adatoms with the limited thermal energy. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to assess the QDs size and density. The chemical bonding configurations of InN QDs were examined by X-ray photo-electron spectroscopy (XPS). Fourier transform infrared (FTIR) spectrum of the deposited InN QDs shows the presence of In-N bond. Temperature-dependent photoluminescence (PL) measurements showed that the emission peak energies of the InN QDs are sensitive to temperature and show a strong peak emission at 0.79 eV.

Dielectric, Ferroelectric and Relaxor Behavior of BaLaxBi4-xTi4O15 Ceramics

Abstract: Monophasic BaLaxBi4-xTi4O15 (x = 0, 0.2, 0.4, 0.6 and 0.8) ceramics, fabricated from the powders synthesized via the solid-state reaction route exhibited relaxor behavior. Dielectric properties of the well sintered ceramics were measured in a wide frequency range (1 kHz-1 MHz) at different temperatures (300-750 K). The temperature of dielectri maximum (T-m) was found to decrease significantly from 696 K for an undoped sample (x = 0) to 395 K for the sample corresponding to the composition x = 0.8 accompanied by a decrease in the magnitude ofdielectric maximum (epsilon(m)). The temperature variation of the dielectric constant on the high temperature slope of the peak (T > T-m) was analyzed by using the Lorentz-ype quadratic law and the diffuseness of the peak was found to increase with increasing x. Vogel-Fulcher modelling of dielectric relaxation showed a decrease in freezing temperature (T-VF) (from 678 to 340 K) and an increase in the activation energy (5 to 24 meV) for the frequency dispersion with increase in x (La-3 divided by content). Strength of frequency dispersion of the phase transition increased with lanthanum content. Polarization (P)-electric field (E) hysteresis loops recorded at 373 showed a transition from a nearly squarish to slim loop hysteresis behavior with increasing lanthanum content.

Enhanced Conversion Efficiency of GaAs Solar Cells Using Ag Nanoparticles

Abstract: We have studied the enhancement of conversion efficiency in GaAs solar cells using silver nanoparticles with particle average sizes between 11.4 to 17.2 nm. The maximum enhancement of 20.2% in conversion efficiency is achieved for the GaAs solar cells where the Ag nanoparticles have been incorporated. The simulations according to Mie theory suggest that the increased radiative scattering and conversion efficiency is due to a combined effect of the surface plasmon resonance and the interband transition.