Ion synthesis and laser annealing of Cu nanoparticles in Al2O3

Al₂O₃ samples with Cu nanoparticles, synthesised by ion implantation at 40 keV with a dose of 1×10¹⁷ ion/cm² and a current density from 2.5 to 12.5 μA/cm², were annealed using ten pulses from a KrF excimer laser with a single pulse fluence of 0.3 J/cm². The copper depth distribution, formation and modification of metal nanoparticles under the ion implantation and laser treatment were studied by Rutherford backscattering (RBS), energy dispersive X-ray (EDX) analysis, atomic force microscopy (AFM) and optical spectroscopy. It was found that laser annealing leads to a reduction in the nanoparticle size without diffusion of metal atoms into the bulk. The change in particle size and the possibility for oxidation of the copper particles are examined in the framework of Mie theory. Calculations presented show that under excimer laser treatment, Cu nanoparticles are more likely to be reduced in size than to undergo oxidation. Received: 19 April 2001 / Accepted: 7 November 2001 / Published online: 23 January 2002     

Influence of ion irradiation on the morphology, structure, and optical properties of gold nanoparticles synthesized in SiO2 and Al2O3 dielectric matrices

Irradiation of fused quartz (SiO₂) and sapphire (Al₂O₃) by Ne⁺ and F⁺ ions with medium energies and their subsequent annealing enables us to control the intensity and frequency of surface plasmon resonance in Au nanoparticles (NPs) synthesized in oxide matrices. The control process can be implemented because NPs dissolve during irradiation and undergo partial reconstruction at annealing. The degree of reconstruction depends on the matrix material and the type and dose of ions. It has been found that the difference in the results obtained by means of irradiation with ions with similar masses is substantially affected by the chemical nature of the ions. The composition, morphology, and structure of the unirradiated and irradiated layers are investigated by transmission electron microscopy, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry.     

冲击压缩下蓝宝石光学性质的晶向效应

本文基于第一性原理计算方法,研究了a向、c向和r向蓝宝石理想晶体和含氧离子空位点缺陷晶体在0-180 GPa冲击压力范围内的光学性质.波长在1550 nm处理想晶体的折射率数据表明,在蓝宝石Corundum、Rh2O3以及CalrO_3相区,其折射率分别表现出强、弱以及强的晶向效应.波长在0-250 nm范围内理想晶体的能量损失谱结果指明,在Corundum和Rh_2O_3结构相区,其晶向效应不明显;在CalrO_3结构相,主峰附近的波段范围内,蓝宝石的能量损失谱有一定的晶向效应:c和r向的主峰强度基本相同,但a向主峰强度明显高于c和r向主峰强度.缺陷晶体数据表明:氧离子空位点缺陷对蓝宝石折射率和能量损失谱晶向效应的影响较微弱.     

Acousto-optic light deflection in an Al2O3 optical waveguide structure

The total deflection of an optical guided wave by a surface acoustic wave (SAW) in a silicon-based SiO₂/AL₂O₃/SiO₂ optical waveguide structure is reported. The SAW is generated by an interdigital transducer with piezoelectric ZnO deposited on top of the optical waveguide structure.     

Acousto-optic light deflection in an Al2O3 optical waveguide structure

The total deflection of an optical guided wave by a surface acoustic wave (SAW) in a silicon-based SiO₂/AL₂O₃/SiO₂ optical waveguide structure is reported. The SAW is generated by an interdigital transducer with piezoelectric ZnO deposited on top of the optical waveguide structure.     

Electronic structure and optical properties of gold nanoparticles

Based on nonempirical calculations of the Au₃₂ cluster, it is found that excited states from which only the quadrupole transition to the ground state is possible arise upon excitation of gold nanoparticles by photons with energies exceeding the minimum energy gap between occupied and vacant states. The possible role of such transitions in lasing of the nanoscale laser called the spaser is discussed.     

Effect of bi-layer ratio in ZnO/Al2O3 multilayers on microstructure and functional properties of ZnO nanocrystals embedded in Al2O3 matrix

Zinc oxide (ZnO) nanocrystals (NCs) embedded in alumina (Al₂O₃) matrix were produced via rapid thermal annealing (RTA) of pulsed laser deposited ZnO/Al₂O₃ multilayered nanostructures. The effect of the thickness ratio (R) between Al₂O₃ and ZnO in one bi-layer on the microstructure and functional properties of NCs has been investigated. Grazing incidence small angle X-ray scattering confirmed the formation of nanocrystals after RTA. Grazing incidence wide angle X-ray scattering studies revealed that ZnO NCs have a high crystalline quality with (100) as preferred orientation. Tensile strain of NCs decreases with increasing R and is correlated to the distribution of NCs. From Raman analysis, it is noticed that the phonon frequency of the E₂ mode, related to the ZnO wurtzite phase, in NCs is shifted towards that of bulk ZnO with increasing R. Photoluminescence studies revealed that the near edge peak position shifts from 382 nm to 371 nm as the ratio R changes from 1.5 to 4 and is attributed to the strain effect. The intensity of emission in the yellow–green region due to defects decreases significantly with increasing R. Current–voltage (I–V) characteristics of Al/ZnO NCs embedded in Al₂O₃/n-Si (100)/Al have shown a hysteresis behavior. The increasing width of the hysteresis with increasing R revealed that the origin of the hysteresis might be due to the existence of polar surface charges on well-separated NCs. The high-resistance and low-resistance states in I–V hysteresis curves seem to be governed by Fowler–Nordheim tunneling and Schottky emission mechanisms, respectively.     

The effect of supports (Al2O3, Al2O3-CeO2 and Al2O3-CeZrO2) on the nature of gold-species in supported gold catalysts

This work is concerned with the study of Au specimens produced by gold deposition on nanosized mixed oxides (alumina, ceria, zirconia) prepared by the sol-gel method using organometallic precursors. According to X-ray absorption near edge structure, extended X-ray absorption fine structure, transmission electron microscopy data, and ultraviolet-visible and X-ray photoelectron spectroscopy measurements, mixed Al-Ce-Zr oxides are quite effective for stabilization of different gold specimens. The samples pre- treated in hydrogen at 150°C are characterized by the presence of gold Au³⁺ cations located on the surface in slightly disordered octahedral oxygen coordination. Metallic gold nanoparticles with a size of about 2 nm and gold clusters were found in the samples treated in hydrogen at 300°C.     

Au:TiO2和Au:Al2O3纳米颗粒复合膜的线性和非线性光学特性

主要从实验和理论两个方面,探讨了不同Au颗粒尺寸和不同基质对Au：TiO₂和Au：Al₂O₃复合膜线性和非线性光学性质的影响.用吸收光谱研究了Au颗粒尺寸和基质与Au复合膜表面等离子体共振带之间的关系;用皮秒Z扫描技术研究了共振和非共振情况下(激发光波长分别为532nm和1064nm),Au颗粒尺寸和基质与复合膜三阶非线性极化率的关系.基于表面等离子体共振理论和局域场增强理论对复合膜进行了分析,得到了不同Au颗粒大小和不同基质时Au复合膜的 关键词： 金属纳米颗粒 复合膜 三阶非线性 表面等离子体共振     

Diffraction patterns and nonlinear optical properties of gold nanoparticles

Stable gold nanoparticles have been prepared by using soluble starch as both the reducing and stabilizing agents; this reaction was carried out at 40 °C for 5 h. The obtained gold nanoparticles were characterized by UV–Vis absorption spectroscopy, transmission electron microscopy (TEM) and z-scan technique. The size of these nanoparticles was found to be in the range of 12–22 nm as analyzed using transmission electron micrographs. The optical properties of gold nanoparticles have been measured showing the surface plasmon resonance. The second-order nonlinear optical (NLO) properties were investigated by using a continuous-wave (CW) He–Ne laser beam with a wavelength of 632.8 nm at three different incident intensities by means of single beam techniques. The nonlinear refractive indices of gold nanoparticles were obtained from close aperture z-scan in order of 10^?7 cm²/W. Then, they were compared with diffraction patterns observed in far-field. The nonlinear absorption of these nanoparticles was obtained from open aperture z-scan technique. The values of nonlinear absorption coefficient are obtained in order of 10^?1 cm/W.     

Ion beam synthesis and carrier dynamics of ZnO nanoparticles embedded in a SiO2 matrix

Zinc oxide (ZnO) nanostructures have been synthesized by the implantation of ZnO molecular ions into SiO₂ followed by high temperature thermal annealing. 35 keV ZnO^? ions were implanted to a fluence of 5×10¹⁶ ions/cm² into SiO₂ at room temperature (RT). The implanted sample was annealed in an oxygen environment to allow the growth of ZnO precipitates. In the as-implanted sample, Zn nanoparticles up to 4.5 nm in diameter were observed and were distributed throughout the implanted depth in the SiO₂. The highest concentration of Zn from the implantation was at a depth of 25 nm. During annealing, Zn diffused into the substrate and combined with oxygen to form ZnO. ZnO nanostructures thus formed had diameters up to 8 nm, embedded in SiO₂. Donor-bound exciton (D, X), acceptor-bound exciton (A, X), and donor–acceptor-pair (DAP) transitions were observed in low temperature photoluminescence (PL) measurements on an annealed sample. RT-PL measurement showed band-edge emission in the ultraviolet region with a full width at half maximum of 121 meV. Time-resolved PL measurements performed at 4 K revealed an excitonic lifetime of 160 ps.     

Mechano-chemical synthesis and optical properties of ZnS nanoparticles

In the present work, we report the synthesis and optical properties of ZnS nanoparticles produced by the mechano-chemical route. We used zinc acetate and sodium sulphide as source materials in a high energy planetary ball mill at rotation speed of 300 rpm and vial rotation speed of 600 rpm with ball to powder (BPR or charge ratio CR) 5:1 for 30 and 90 min. The milled powders were washed with methanol to remove impurity and dried at 300 °C for 1 h. The prepared nanoparticles have been characterized using X-ray diffraction (XRD), Field emission scanning electron microscope (FESEM), UV–vis–NIR spectrophotometer and Fluorescence spectroscopy. The crystallite size of the synthesized ZnS nanoparticles is found to be in the range 7–8 nm which was calculated using Debye–Scherer's formula. The value of optical band gap has been found to be in the range 3.80–4.15 eV. Room temperature photoluminescence (PL) spectrum of ZnS samples exhibit a blue emission peaked at 466 nm under UV excitation.     

Linear and nonlinear optical properties of highly concentrated gold nanoparticles

Linear and nonlinear (NL) optical properties of composite materials containing high concentration of gold nanoparticles (NPs) were studied using the Maxwell–Garnett model and the degenerated electron gas model. High values of the linear refraction index of the composite, NL shift of the plasmon resonance peak and reversal sign of the real and imaginary parts of the NL third-order susceptibility were observed. Figures of merit for photonic devices were calculated and fulfilled depending of the filling factor and NPs size.     

Ion secondary electron emission from Al2O3 and MgO films

Coefficients of ion induced secondary electron emission (ISEE) γ from thin films of Al₂O₃ and MgO have been measured for argon ions in the energy range between 0–3 keV. Dionne's equation for secondary electron emission, which consists of production and emission terms has been modified to explain the kinetic emission of ISEE. The production term for ion induced secondary electrons has been separately formulated, taking account of the energy loss of primary ions, while the process of emission is considered to remain the same as in SEE. The escape depth λ_S and emission probability B were obtained from the SEE data and were used, along the range value of incident ions, to calculate the emission term in ISEE. The modified form of the equation was used to evaluate theoretically expected ISEE yield energy curves. Fairly good correlation is observed in theoretical and experimental curves which supports the validity of the proposed theoretical model.     

Magnetoresistive properties of Fe3O4 nanoparticles embedded in a Cu matrix

We studied ordered arrays of magnetic nanoparticles (NPs) in a nonmagnetic matrix. The influence of annealing temperature and measurement geometry (varying angle between sample surface and external magnetic field direction) on magnetoresistance and coercive field values was established. Measurements were done on the Au(2 nm)/Cu(20 nm)/Fe₃O₄(NPs)/SiO₂/Si system.     

Radiation stability of powders in mixtures with Al2O3 nanoparticles

A comparative research was conducted to investigate the absorption spectra of barium titanate powders mixtures with aluminum oxide micro- or nanopowders irradiated by electrons. It was established that the addition of aluminum oxide nanopowder enhances the radiation stability of mixtures, which increases with the concentration of nanoparticles. Stability augmentation of mixtures under irradiation is caused by the decrease in the concentration of radiation defects in the anion sublattice of barium titanate.     

Interfacial structure of sub-micron Al2O3 particles in aluminum matrix

The surfaces of ellipsoidal Al₂O₃ particles with average size of 0.15 μm and the interfaces between the Al₂O₃ particles and 1070Al were investigated by transmission electron microscopy (TEM) and high resolution electron microscopy (HREM).The results show that the surfaces of Al₂O₃ particles appear to be polyhedrons consisting of crystal planes with small angle, while every plane of the polyhedrons could be considered as a stepped structure composed of close-packed planes along the close-packed direction. The interfaces of the 0.15 μm Al₂O₃p/1070Al composite bond well, without any interfacial reaction products. It is proposed that there are several kinds of crystallographic orientation relationships between the aluminum matrix and Al₂O₃particles due to the polyhedral structure. In our study, such orientation relationships are found to be {110} _Al ||{1100} _Al2O3 and ?110? _Al ||?1126? _Al2O3 .     

Cathodoluminescent properties of an Am3+ ion in a matrix of yttrium-aluminum garnet Y3Al5O12

The luminescent properties of an americium ion are studied. Luminescence spectra of americium in yttrium-aluminum garnet are recorded for the first time. The luminescence bands are identified, and the levels responsible for the observed optical transitions are determined.     

Self-assembly of gold nanoparticles into chain-like structures and their optical properties

Au nanoparticles with diameters of ca. 15 nm were synthesized according to the well-developed citrate reduction method. It was found that the nanoparticles tended to attach and fuse into each other to form chain-like structures with the removal of the stabilizing agents. UV–Vis absorption and HRTEM characterizations provided solid evidence for the fused features. On the basis of the HRTEM observations, we believed the decreased surface energy as well as the dipole–dipole interaction is responsible for the formation of the chain-like structures. SERS activity investigation indicated that the intensities of the b2-type bands have close relation with the concentration of the probing molecules, which further confirmed the chemical effect character of the b2-type scatterings.