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1.
We study the optical response of strongly coupled metal nanoparticle chains using rigorous multiple scattering calculations. The collective resonant frequency of silver nanosphere chains and the coupling between chains are considered. The coupling between silver nanoparticle chains are understood by the transmission and reflection calculations of 2D periodic arrays of nanospheres. The results are in agreement with recent experiments. The splitting of plasmon resonance modes for different polarizations of the incident light are explored. Our results show that the transverse mode resonant wavelength is very sensitive to the inter-chain distance. Results on the effect of disorder are also presented. 相似文献
2.
Sekika Yamamoto Hiroyuki Yano Tomobumi Mishina Jun’ichiro Nakahara 《Journal of luminescence》2007,126(1):257-262
Time resolved photoluminescence (PL) measurements at low temperature are performed on colloidal ZnO nanocrystals dispersed in t-butanol. Considering the particle size dependence of the decay times we conclude that the luminescence is composed of two trap related emissions one of which undergoes lifetime shortening due to a non-radiative process. Initial fast shift of the spectrum within 30 ps is observed and it is interpreted as a fast hole cooling just after the excitation. 相似文献
3.
We propose a class of graded colloidal crystalline materials which consist of polydisperse metallodielectric nanoshells stacked in layers. We take the Lekner-Lishchuk summation method to treat the graded systems which are not tractable by conventional approach such as Ewald-Kornfeld methods. It is demonstrated that this kind of graded materials exhibit a series of sharp peaks, which merge in a broadened resonant absorption band in the optical region, in contrast to colloidal crystal containing monodisperse nanoshells or nanoparticles. Effects of various gradient profiles of the ratio of the inner/outer radii in the nanoshells and lattice geometries on the optical properties are discussed. These materials are not hard to fabricate by contemporary nanofabrication techniques and they shall be useful in the engineering of optical nanomaterials. 相似文献
4.
This paper reports on the influence of the sintering temperature and atmosphere and transition-metal doping on the magnetic properties of nanocrystalline and bulk In2O3. Undoped nanocrystalline In2O3 is diamagnetic whatever the sintering temperature and atmosphere. All single-phase transition-metal-doped In2O3 samples are paramagnetic, with a paramagnetic effective moment originating from weakly interacting transition metal ions. No trace of ferromagnetism has been detected even with samples sintered under argon, except extrinsic ferromagnetism for samples with magnetic dopant concentrations exceeding the solubility limit. 相似文献
5.
We demonstrate through experiment and simulation that when mono-domain Fe nanoparticles are formed into chains by the application of a magnetic field, the susceptibility of the resulting structure is greatly enhanced (11.4-fold) parallel to the particle chains and is much larger than transverse to the chains. Simulations show that this significant enhancement is expected when the susceptibility of the individual particles approaches 5 in MKS units, and is due to the spontaneous magnetization of individual particle chains, which occurs because of the strong dipolar interactions. This large enhancement is only possible with nanoparticles, because demagnetization fields limit the susceptibility of a spherical multi-domain particle to 3 (MKS). Experimental confirmation of the large susceptibility enhancement is presented, and both the enhancement and the susceptibility anisotropy are found to agree with simulation. The specific susceptibility of the nanocomposite is 54 (MKS), which exceeds the highest value we have obtained for field-structured composites of multi-domain particles by a factor of four. 相似文献
6.
We use Monte Carlo simulations to study the influence of dipolar interaction on the equilibrium magnetic properties of monodisperse single-domain ferromagnetic nanoparticles. Low field magnetizations simulated in zero field cooling (ZFC)/field cooling (FC) procedures and field-dependent magnetization curves above the blocking temperatures show strong dependence on the concentration and the spatial arrangement (cubic or random) of the magnetic particles. The field-dependent magnetizations can not be simply described by the T* model at relative low temperatures due to the interplay between anisotropy and dipolar interactions, as well as the spatial arrangement effect. 相似文献
7.
H.B. Profijt C. Pigot R.M. Grechishkin 《Journal of magnetism and magnetic materials》2009,321(4):259-262
A disc-shaped SmCo magnet with a diameter of 0.85 mm is levitated above a graphite diamagnetic plate at a height of about 14 μm. The magnet is magnetised into a double dipole. The levitation of multipolar magnets above a diamagnetic material was suggested in 1956 by Boerdijk and patented in 1995 by Pelrine, but without any known published experimental results. In this letter, both theoretical and experimental results are presented. 相似文献
8.
For NiO nanorods of 5 nm diameter prepared by sol-gel technique, variations of the magnetization M with temperature T (5-370 K) and magnetic field H up to 55 kOe are reported. Also, temperature variations of the EMR (electron magnetic resonance) parameters (intensity I0, linewidth ΔH and resonance field Hr) of an observed line due to uncompensated spins are followed for The M vs. H and T variations yield a blocking above which the data fits modified Langevin function with magnetic moment μp?1240 μB/particle. For the EMR line, I0 decreases rapidly for T<TB, and the line broadens and shifts to lower H with lowering T, following the lineshift δHr=(ΔH)n with n?2.8. This is close to the value of n=3 expected for randomly oriented particles. 相似文献
9.
Thin-film multilayers with dielectric and semiconductor nanolayers of 200-10 nm thicknesses have been deposited by thermal evaporation onto irradiation-resistive substrates using pure crystals as evaporated targets. Some multilayers were γ-irradiated in air at room temperature with dose of 83 kGy. X-ray diffraction and microscopy studies reveal that the multilayers consist of nanometer-sized crystals with cubic structure and defined size. Film structures were oriented along the (1 1 1) plane. Absorption spectra of non-irradiated LiF nanocrystals of 100 nm size and those of initial crystals give evidence of metal colloids presence. Photoluminescence spectra of γ-irradiated nanostructures with various LiF content show the enhancement of F3+-colour centres excitation in the region of metal colloids absorption and the increase is observed between emission intensities of F3+ and F2 centers with respect to initial crystals γ-coloured in identical conditions. Emission intensities of both centers under excitation in the M band correlate with LiF content. These effects, which are related to high-quality nanocrystals, but at the same time depend strongly on the defect content, especially as far as their 1-2 ps nonlinearities are concerned, could depend on nanocrystal purity and metal excess collection in their boundaries regions. 相似文献
10.
The effect of solution temperature on crystallite size and magnetic properties of Zn substituted Co ferrite nanoparticles 总被引:1,自引:0,他引:1
M. Mozaffari S. Manouchehri J. Amighian 《Journal of magnetism and magnetic materials》2010,322(4):383-143
In this work zinc substituted cobalt ferrite nanoparticles (Co0.5Zn0.5Fe2O4) have been synthesized by the coprecipitation method, using stable ferric, zinc and cobalt salts with sodium hydroxide, at different solution temperatures, from room temperature to 363 K. The cobalt-zinc ferrite crystalline phase, the particle size and the morphology of the resulting nanoparticles were studied by X-ray diffraction and transmission electron microscopy. The average crystallite size of each sample was calculated from the broadening of the most intense peak (3 1 1), using Scherrer's formula and the results show crystallite sizes increased from 6 to 8 nm by increasing the solution temperature from room temperature to 363 K respectively. Room temperature VSM measurements show that the prepared nanoparticles have superparamagnetic behavior and did not saturate at maximum field of 800 kA/m. The variation of AC-susceptibility of the samples with respect to temperature was measured and it was found that the blocking temperature increased from 198 to 270 K by increasing the solution temperature from room temperature to 363 K respectively. FTIR spectra of the samples have been analyzed in the frequency range 400-4000 cm−1, which also confirms the results of XRD. 相似文献
11.
CdTe nanocrystals were grown from commercially available RG850 Schott filter glass by two-step heat-treatment process which almost doubles the particle to matrix volume fraction. A calculation shows that a quantized-state effective mass model in the strong confinement regime might be used to deduce the average radius for the nanocrystals larger than 2 nm in radius from the energetic position of the first exciton peak in optical absorption spectrum. Size-induced shift of ∼360 meV in the first exciton peak position was observed. The steady state photoluminescence spectra exhibit a broad band red shifted relative to the first exciton band, which indicates the existence of shallow trap states. The non-linear optical properties of CdTe nanocrystals were studied by room temperature resonant photoabsorption spectroscopy. The differential absorption spectra had three-lobed structure whose size-dependent evolution was explained by bleaching of the absorption, red shift and broadening in the Gaussian absorption band used to fit the first exciton peak. A maximum red shift of 2.32 meV for the average nanocrystal radius of 4.65 nm was estimated by fitting the photomodulation spectra with a combination of first and second derivative Gaussian absorption bands. We presume that the red shift is induced by the electric field of trapped charges in surface states. Internal electric field strengths of 23 and 65 kV/cm were predicted for the average nanocrystal radii of 3.95 and 4.65 nm, respectively, with the help of second-order perturbation theory in the strong confinement limit. 相似文献
12.
Hongxue Liu Baobao Cao Charles J. O’Connor 《Journal of magnetism and magnetic materials》2010,322(7):790-793
Undoped and Co-doped BaTiO3 nanoparticles were synthesized by a one-step sol-precipitation method. For all the samples, X-ray diffraction showed characteristic diffraction lines for BaTiO3 without the indication of secondary phases. High-resolution transition electron microscopy images showed that BaTiO3 nanoparticles exhibit the nature of single-crystal. Magnetometry revealed that all the Co-doped BaTiO3 samples show paramagnetic behaviors and Co ions in BaTiO3 are present as isolated paramagnetic centers. This is contrasted to several reported cases of ferromagnetism in Co-doped BaTiO3. 相似文献
13.
Feng Luo 《Solid State Communications》2004,132(9):595-599
CeVO3 nanocrystals were fabricated by sintering CeVO4 precursors in flowing hydrogen. Under an applied field of 20 Oe, a G-type orbital ordering transition, corresponding to the cooperative Jahn-Teller distortion, was enhanced and observed from the magnetization curve of CeVO3 nanorods, different from that of the nanocrystallites. This enhancement of the orbital ordering transition depended on the giant magnetocrystalline anisotropy induced by strong crystallographic anisotropy. Furthermore, a stronger applied field decreased the anisotropy of electronic state induced by spatial shapes of orbitals and confined the cooperative Jahn-Teller distortion by lifting the orbital degeneracy, leading to the suppression of the orbital ordering transition. 相似文献
14.
Superparamagnetic γ-Fe2O3 nanocrystallites have been prepared by γ-irradiating ferrocene in the presence of isopropyl alcohol to get Fe nanoparticles in nitrogen atmosphere and at room temperature, followed by oxidization in air to obtain γ-Fe2O3. The final black powder was characterized with X-ray powder diffraction (XRD), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). From XRD pattern and XPS spectrum, we can confirm to get γ-Fe2O3. The particle size is several nanometers as shown in TEM image. Magnetic hysteresis loop measurements exhibited that the γ-Fe2O3 nanoparticles display superparamagnetism. However, a trace black powder was obtained in kerosene oil using the same method. A possible formation mechanism of the γ-Fe2O3 nanoparticles was suggested. 相似文献
15.
Aurélien Cuche Orestis Faklaris Jean-Paul Boudou Jean-François Roch Serge Huant 《Journal of luminescence》2009,129(12):1475-22226
We present results showing the potential of diamond nanoparticles with size <50 nm as photoluminescent nanoprobes for serving as stable point-like emitters attached at the tip apex of a near-field optical microscope to achieve enhanced spatial resolution. 相似文献
16.
Gallium nitride (GaN) doped by Eu3+ and Tb3+ ions have been synthesized using powder technology. The emission and absorption spectra have been obtained by using photoluminesence technique and correlated with the local structural environments. The room temperature yellow emission from GaN grains as well as from Eu3+ and Tb3+ ions has been observed for nano- as well as for microGaN grains. Additionally, for GaN:1%Eu3 micrograins the blue emission from GaN nanocrystals has been observed. 相似文献
17.
In this work, silicon nanocrystals (Si-nc) embedded in a silicon-rich silicon oxide (SRSO) matrix doped with Er3+ ions for different erbium and silicon concentrations have been deposited by electron-cyclotron resonance plasma-enhanced chemical-vapor-deposition (ECR-PECVD) technique. Their optical properties have been investigated by photoluminescence (PL) and reflectance spectroscopy.Room temperature emission bands centered at ∼1.54 and at 0.75 μm have been obtained for all samples. The most intense emission band at ∼1.54 μm was obtained for samples with concentrations of 0.45% and 39% for erbium and silicon, respectively. Moreover, it has been found that the broad emission band centered at ∼0.75 μm for all samples shows a very strong interference pattern related to the a specific sample structure and a high sample quality. 相似文献
18.
Chih-Ling Huang Jiunn-Der Liao Yi-Te Wu Chou-Ching K. Lin 《Applied Surface Science》2008,255(2):301-303
By applying dynamic contact module and particular measurement of phase angles, harmonic contact stiffness (S) along with the measured displacement (D) of different self-assembled monolayers (SAMs) adsorbed on Au can be distinguished. The relatively ordered and hydrophobic ODT and DDT molecules adsorbed on Au form high contact stiffness, which are presumably unfavorable substrates for a cell to adhere upon. Short-chain MUA molecules adsorbed on Au provides a hydrophilic characteristic with a relatively low contact stiffness, which may significantly promote cell adhesion. It is, therefore, estimated that the behavior of a cell adhered on SAMs/Au is correlated not only with their outermost chemical species but also with a proper dS/dD matrix acting as a cushion. 相似文献
19.
SiO2 layer structures with a middle layer containing Ge nanocrystals were prepared by sputtering on n- and p-type Si substrates, and by consecutive annealing. Ge content in the middle layer was varied in the range of 40-100%. Most of the structures exhibited low breakdown voltages. The current through the structures became Schottky-like after breakdown. However, some p-type samples showed a considerable memory effect. It was obtained by spectroscopic ellipsometry that the middle layer contains amorphous Ge phase as well. The results also suggest intermixing of the layers during the sputtering and/or the annealing process. 相似文献
20.
Tingyin Ning Hong Shen Heng Lu Zhihui Sun Lingzhu Cao Dongyi Guan Dongxiang Zhang Guozhen Yang 《Applied Surface Science》2008,254(7):1900-1903
The triangular-shaped Au/ZnO nanoparticle arrays were fabricated on fused quartz substrate using nanosphere lithography. The structural characterization of the Au/ZnO nanoparticle arrays was investigated by atomic force microscopy. The absorption peak due to the surface plasmon resonance of Au particles at the wavelength of about 570 nm was observed. The nonlinear optical properties of the nanoparticle arrays were measured using the z-scan method at a wavelength of 532 nm with pulse duration of 10 ns. The real and imaginary part of third-order nonlinear optical susceptibility, Re χ(3) and Im χ(3), were determined to be 1.15 × 10−6 and −5.36 × 10−7 esu, respectively. The results show that the Au/ZnO nanoparticle arrays have great potential for future optical devices. 相似文献