We studied the ability of Ag/nano-TiO_2 to inhibit Staphylococcus aureus growth on silicone elastomer material. Ag/nano-TiO_2 silicone elastomer was prepared with different concentrations of 0%, 2%, 4%, 6%, 8%, 10%. The antibacterial efficacy of Ag/nano-TiO_2 silicone elastomer was determined by the inhibition zone method and the impregnated culture method. The antibacterial timeliness of Ag/nano-TiO_2 silicone elastomer was tested by direct contact method. The samples were kept through thermal aging process in an accelerated aging chamber. The effect of concentrations of Ag/nano-TiO_2 was insignificant (P < 0.05). There was significant difference between the Ag/nano-TiO_2 silicone elastomer and the blank silicone elastomer (P < 0.5). There was also significant difference among specimen groups whose aging periods were 50°C, 100°C, 150°C, 200°C for 87 h (P < 0.5). The silicone elastomer with different concentrations of Ag/nano-TiO_2 effectively inhibits Staphylococcus aureus growth.
X-ray photoelectron spectroscopy was employed to characterize the surface chemistry and electronic properties of the Zn_{1-x}Cd_{x}O semiconductor systems obtained at the different growth conditions. The effect of the growth conditions on the core and valence band spectra as well as room-temperature photoluminescence of the Zn_{1-x}Cd_{x}O films was investigated and discussed. Behavior of the X-ray photoelectron spectroscopy peaks indicated an increase of the cadmium and a depletion of the oxygen concentrations upon changing the Ar/O_2 gas ratio and dc power.
We present calculation results of multi-color spontaneous emission from quantum-dot-quantum-well semiconductor heteronanocrystals. Our theoretical results explain experimental results of onion-like spherical system similar to: CdSe (core), ZnS (shell), CdSe (shell) spherical quantum dots surrounded by ZnS. We demonstrate influence of shell thickness to exciton localization in distinct layers of heteronanocrystals. Multi-color emission of such heterosystem is determined by l=0, n=1 state localization in CdSe core and by l=0, n=2 state localization in CdSe shell.
We propose a simple model for temperature evolution of magnetic hyperfine field distribution of spherical bcc Fe nanoparticles. We performed mean field approximation calculations of mean spin value in each spherical shell of nanoparticle. Considering magnetic hyperfine field values reported for iron thin films we predicted possible values of hyperfine fields in the internal and surface region of the particles as a function of temperature.
This paper reports our progress towards developing a reproducible and rapid method to prepare triangular silver nanoplates. The methods are all based on a seed-mediated procedure involving the reduction of silver ions with ascorbic acid in aqueous solution and have variously involved polyvinylalcohol, citrate, and polystyrenesulphonate as modifiers. The triangular silver nanoplate sols have well defined local surface plasmon resonances, which can be tuned throughout the visible and near IR. Aspect ratio (the ratio of edge length to thickness) is shown to be a fundamental parameter determining the triangular silver nanoplate sol properties including, the position of their local surface plasmon resonances maxima and suppression of local surface plasmon resonance retardation effects. The high ensemble sensitivities of the triangular silver nanoplate sol local surface plasmon resonance to changes in the surrounding refractive index within the spectral range appropriate for biosensing is attributed to their high aspect ratio. Silver nanoparticles are more challenging to functionalise than the analogous gold systems, as they are prone to oxidation and are susceptible to degradation by chloride ions. Two methods to stabilise triangular silver nanoplates (treating with thiols and coating with gold) and the formation of gold nanoboxes from the triangular silver nanoplates are also described.
ZnO, Co doped ZnO (ZnO:Co) and CoO thin films were deposited on glass substrates by using the spark discharge technique with Zn-Zn, Zn-Co and Co-Co metal electrodes (tips). The structural and optical properties of the films were characterized by X-ray diffraction, scanning electron microscopy measurements and UV-Vis spectrometry. Cubic phase reflection of CoO (200) was observed in the samples containing Co. The size of nanoparticles had varied between 38 nm and 200 nm in ZnO thin films. When Co electrode was used, spherical structure had deteriorated and clusters of particles, with smaller radii, were observed. In addition, when Co-Co electrode pairs were used, various cavities with different sizes were formed. Especially, it was observed that the optical transmittance had generally increased with the decreasing spark (charge) voltage, while increasing with the number of sparks. The Co-containing samples were green in color and it was observed that the loss of transmission appears in a specific region in the Co-doped ZnO thin films due to characteristic d-d transition of Co²⁺ ions. The thickness of the films had decreased with the increasing number of sparks. In addition, the band gap energy, E_{g}, evaluated by UV-Vis spectroscopy measurements has been shifted to higher wavelengths (red shift) for the ZnO:Co thin films.
Zn_{0.9}Cd_{0.1}O ternary alloys have been grown on the sapphire substrates by using the direct current (dc) magnetron sputtering. X-ray diffraction measurements showed that all samples were highly oriented films along the c-axis perpendicular to the substrate surface. X-ray diffraction confirmed that the crystal quality of Zn_{0.9}Cd_{0.1}O films can be controlled by changing the gas ratio of Ar/O_2. The optical properties of these films have been investigated by means of the optical transmittance and the low-temperature photoluminescence spectra. It was found that the optical band gap of the deposited films can be tuned by growth parameters. The luminescence processes are considered in the terms of alloy fluctuation.
We study a simple theoretical model of multiple exciton generation by a single high-energy photon absorbed in an InAs nanocrystal. We calculate the Coulomb matrix element for the electron-trion coupling in an InAs nanocrystal and show that due to the resulting coupling between single-pair and two-pair states the latter becomes weakly optically active.
Black porous silicon is a new material with low light reflectance and high light absorbance values. Black porous silicon layers are especially useful and important in solar energy conversion. In this work black porous silicon plates were prepared by wet chemical metal-assisted method. Silver and gold nanoparticles were precipitated from colloidal silver nitrate and chloroauric acid solutions. Obtained black porous silicon samples with precipitated nanoparticles were investigated by scanning electron microscope combined with energy dispersive X-ray spectrometer, ultraviolet and visible light spectrometer, the Fourier transformation infrared spectrometer. Scanning electron microscopy and energy dispersive X-ray analysis have revealed the presence of silver and gold nanoparticles on black porous silicon surface. Silver nanoparticles size varied from 30 to 100 nm, gold - from 20 to 70 nm. During UV-VIS analysis significant changes in reflectance of processed black porous silicon samples were obtained. Reflectance of black porous silicon samples was lower than 10%. The Fourier transform infrared analysis has revealed decrease in reflectance in far infrared region. Changes in the Fourier transform infrared spectra in "fingerprint" zone prove modification of the surface of black porous silicon layers after precipitation of metal nanoparticles.
Se-doped ZnO films have been deposited on the sapphire substrates by the radio-frequency magnetron sputtering technique. An influence of the isoelectronic impurity Se on the room-temperature luminescence of the ZnO films is studied. It is revealed that the Se doping leads to an appearance of the intense near-band edge emission spectrum, which consists of three emission bands. The dominant emission band is related to the recombination of the bound excitons. The radiation caused by the band-to-band transitions of free carriers is observed in the high-energy side of the spectrum (ħω > E_{g}).
Structural phase transformations and magnetic properties of mesoporous MCM-41 template modified with iron and nickel salts were studied by nitrogen physisorption, X-ray diffraction, Mössbauer spectroscopy and transmission electron microscopy. The FeNi-oxide or the bimetallic crystal structure is formed for low and high Ni concentrations, respectively. The average size of nanoparticles is about 10 nm. About 70% of particles exist in a superparamagnetic state at room temperature.
The optical properties of the CdO and Pt doped CdO thin films synthesized by sol-gel technique were investigated. The lowest grain size value (81.34 nm) was found to be for CdO thin film. The Pt doped CdO films are transformed to clusters with nanoparticles. The transparency properties of the CdO thin film is changed with Pt doping. The plots of refractive index indicate abnormal and normal dispersion regions. The refractive index values of the CdO thin film are changed with Pt doping. The direct optical band gap values of the films were changed with doping of Pt. The film of 0.5% Pt doped CdO indicates the lowest optical band gap value (2.421 eV). The imaginary parts of the optical conductivity of the CdO and Pt doped CdO thin films are higher than that of the real parts of the optical conductivity.
Iron-molybdenum silica mesoporous materials were obtained by the application of direct hydrothermal method. The influence of high temperature samples reduction in the H_2 flow on their structural and magnetic properties was studied. Four samples with different metal contents relative to silica were investigated. The study was carried out by means of X-ray diffraction, ^{57}Fe Mössbauer spectroscopy and the temperature programmed reduction method. With an increasing metals content, primary pores of MCM-41 transformed into the bottle-like pores, and then into the slit-like ones. Reduction and heat treatment caused the α-Fe, Fe_2Mo, and Fe-Mo alloy formation. Iron and molybdenum atoms after being released into the silica matrix, where they were embedded, create clusters or crystallites. It was observed that the high temperature reduction caused partial transformation of highly dispersed Fe-Mo oxides species initially embedded in silica walls into crystallites big enough to give magnetic sextet component in the Mössbauer spectra.
Hybrid molecules formed by coupling semiconductor quantum dots to metal nanoparticle nanoantennas provide a new paradigm for directed nanoscale transfer of quantum information. To assess this possibility, we study theoretically the response of these hybrid molecules to applied optical fields. Quantum-coherent time-evolution of the semiconductor quantum dots in the hybrid molecule is found by solving the semiconductor quantum dot density matrix equations. We study hybrid molecules in the weak and strong coupling regimes. In strongly driven, strongly dipole-coupled semiconductor quantum dot-metal nanoparticle hybrids with spherical metal nanoparticles, interference, dispersion near resonance and self interaction define the metal nanoparticle/semiconductor quantum dot coupling and lead to the Fano resonances, exciton induced transparency, suppressed semiconductor quantum dot response and bistability. More complicated response can be tailored by using metal nanoparticle shape and the placement of semiconductor quantum dots to control the local near-fields that couple the metal nanoparticles and semiconductor quantum dots. We describe how coupling to metal nanoparticle dark modes and higher order multipolar modes impact interference and self-interaction effects. The physics of the metal nanoparticle/semiconductor quantum dot coupling is outlined.
This paper presents the combustion synthesis and characterization of one-dimensional silicon carbide nanostructures (nanowires of 3C-SiC polytype with zincblend structure) by means of cathodoluminescence technique. Cathodoluminescence spectra of nano-SiC samples and, as a reference, of a commercially available SiC micropowder are compared. It is shown that the emission band at 1.97 eV which is slightly evidenced in the spectrum of the commercial SiC under 10 keV electron beam irradiation becomes the prevailing band in CL of the purified silicon carbide nanowires.
Novel zinc tetranitro-phthalocyanine (ZnTNPc) supported by multi-walled carbon nanotubes hybrid composites were facilely prepared by a method of ultrasonic impregnation and their photocatalysis behavior was studied. The as-prepared ZnTNPc-MWCNTs composites were characterized by scanning electron microscopy, X-ray diffraction, diffuse reflectance spectra, transmission electron microscopy, thermogravimetric analysis, and the Fourier transform infrared spectra. The results showed that the ZnTNPc was not only grown on the multi-walled carbon nanotubes but also uniformly disturbed without aggregation. Compared with pure ZnTNPc and MWCNTs, ZnTNPc-MWCNTs nanocomposites presented a significantly enhanced photocatalytic activity for the degradation of rhodamine B under visible-light irradiation. Furthermore, a possible mechanism for the photodegradation of rhodamine B was also proposed.
Two powder samples: nanocrystalline titanium carbide (TiC) and titanium nitride (TiN) dispersed in a carbon matrix were synthesized by a nonhydrolytic sol-gel process. Both samples were characterized by the X-ray diffraction and transmission electron microscopy. The transmission electron microscopy examination of the TiC and TiN nanoparticles showed that their average crystalline size was about 20 nm. The temperature dependence of the EPR spectra for both samples was measured in 10 K to 200 K temperature range. A similar very narrow (about 0.2 mT) EPR line centered at g≈2 (at room temperature) was recorded in both samples. The EPR line observed in both samples is arising from electron conductivity centers dispersed in the carbon matrix and it was fitted by Dysonian line shape. The temperature dependence of the EPR spectrum showed different behavior of these two samples. It is suggested that in the sample TiC/C multiwall carbon nanotubes are formed while in the sample TiN/C the graphite structure dominates.
Synthetic opals composed of 300 nm silica spheres are impregnated with a Bi₁₂SiO₂₀ melt at 1190 K. Structure and properties of the as-prepared samples are studied by employing the scanning electron microscopy, X-ray diffraction, and optical spectroscopy and direct current conductivity techniques. The nanocomposites are found to be multi-phase systems composed of Bi₁₂SiO₂₀, Bi₄Si₃O₁₂ and SiO₂ crystallites with an average linear size not less than 20 nm. Formation of Bi₄Si₃O₁₂ crystallites becomes possible as a result of changing in the Bi₂O₃-SiO₂ molar ratio due to the melting of silica spheres. The Raman intensity redistribution observed by surface scanning may be caused by both composition inhomogeneity and concentration of the exciting radiation field at composite defects. The "red" shift of photoluminescence band is observed. Activation energy of direct current conductivity is estimated as 1.1 eV.
In this study, Fe and Pt nanoparticles are first synthesized by decomposition of iron(II) chloride tetrahydrate and reduction of platinum(II) acetylacetonate. Then, FePt nanoparticles are similarly fabricated by adding LiBEt3H to the phenyl ether solution in the presence of oleic acid, oleylamine surfactant at 100°C, followed by refluxing at 255°C. The samples were characterized by transmission electron microscopy and energy dispersive spectroscopy analyses after heat treatments. Transmission electron microscopy images show that self-assembled 8 nm Fe nanoparticles are formed as polygon shape, whereas Pt nanoparticles have broad size distribution. On the other hand, 4.5 nm FePt nanoparticles have standard division about 9%. The results of energy dispersive spectroscopy analysis reveal that the composition of Pt, Fe and FePt nanoparticles gives Fe_{56}Pt_{44} stoichiometry.
Oxide nanoparticles embedded in a polymer matrix produce nanocomposites which are useful for optics and electronic applications. Yttrium oxide nanoparticles have received much attention due to their various properties and are significantly used in fundamental and application oriented fields. The present paper reports the influence of annealing temperature on the Y_2O_3:SiO_2 nanocomposite prepared by sol-gel process. Y(NO_3)_3 ·4H_2O and tetraethoxysilane were used as precursors and obtained powdered form of Y_2O_3:SiO_2 composite. The powder sample was annealed at 500C and 900C for 6 h which were characterized by X-ray diffraction, Fourier transform infrared and transmission electron microscope. X-ray diffraction data described that the broadening of peaks decreases with increase in annealing temperature which may be due to the increase in particle size. Sample analyzed by Fourier transform infrared and transmission electron microscopy confirmed the grain size dependence on annealing temperature. Cubic phase of yttrium oxide crystal structure was obtained within the silica matrix. The nanocrystallites size has been calculated using Debye-Scherrer formula, Williamson-Hall plot and transmission electron micrographs and compared at two different temperatures (a) 500C and (b) 900C.
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