绝缘体中金属离子注入合成纳米颗粒的理论研究

理论上提出了利用离散电子态来计算绝缘体中金属纳米颗粒Fermi能级的方法,给出了金属纳米颗粒的能级结构,并得到了依据金属纳米颗粒等离子体共振峰计算金属纳米颗粒尺寸的新公式.该理论可解释相关现象,通过实验初步验证了该理论的正确性. 关键词： 离子注入 金属纳米颗粒 绝缘体 Fermi能级     

离子注入金红石单晶生成的金属Ni纳米晶的磁学性能研究

研究了能量为64keV、注量1×1017cm-2的Ni离子注入金红石TiO2单晶制备的植入金属纳米晶的微观结构和磁学性能。注入层的结构和磁学性能采用透射电子显微分析（TEM）和超导量子干涉磁强计（SQUID）进行分析。结果表明,金红石单晶中有尺寸为3～18nm的金属Ni纳米晶生成,注入区域基体明显非晶化。10K温度下金属Ni纳米晶的矫顽力约为16.8kA·m-1,比Ni块材的矫顽力大。样品的零场冷却/有场冷却（ZFC/FC）曲线表明,金属Ni纳米晶的截止温度约为85K。     

离子注入金红石单晶生成的金属Ni纳米晶的磁学性能研究

 研究了能量为64keV、注量1×10¹⁷cm^-2的Ni离子注入金红石TiO₂单晶制备的植入金属纳米晶的微观结构和磁学性能。注入层的结构和磁学性能采用透射电子显微分析（TEM）和超导量子干涉磁强计（SQUID）进行分析。结果表明，金红石单晶中有尺寸为3～18nm的金属Ni纳米晶生成，注入区域基体明显非晶化。10K温度下金属Ni纳米晶的矫顽力约为16.8kA·m^-1，比Ni块材的矫顽力大。样品的零场冷却/有场冷却（ZFC/FC）曲线表明，金属Ni纳米晶的截止温度约为85K。     

氨化法制备GaN:Tb纳米颗粒的光学性能

利用简单的氨还原方法制备了GaN:Tb纳米颗粒. X射线衍射结果显示纳米颗粒为六方结构, 根据Scherrer公式, 计算得到了GaN:Tb纳米颗粒的平均晶粒大小为21.2 nm; 透射电子显微镜结果显示为GaN:Tb纳米颗粒尺寸均匀, 尺寸大小约为20 nm; 除正常的GaN Raman振动模式外, 还观察到了251和414 cm^-1 2个额外的Raman散射峰, 前者是表面无序或尺寸限制效应造成的, 而后者则是八面体Ga-N₆振动模式; 最后, 测量了GaN:Tb纳米颗粒的室温光致发光谱, 获得了Tb³⁺离子在可见光区(位于493.9, 551.2, 594.4和630.1 nm)的本征发光.     

Structural and size evolution of indium nanoparticles embedded in aluminum synthesized by ion implantation

The structural and the size evolution of embedded In nanoparticles in Al synthesized by ion implantation and subsequent annealing are experimentally investigated. The average radius r of In nanoparticles is determined as a function of annealing time in a temperature range between 423 K and 453 K. The structural transition of In nanoparticles with the crystallographic orientation In(200)[002] Al(200)[002] is observed to change into In(111)[110] Al(002)[110] with a critical particle radius between 2.3 nm and 2.6 nm. In addition, the growth of In nanoparticles in the annealing process is evidently governed by the diffusion limited Ostwald ripening. By further analyzing the experimental data, values of diffusion coefficient and activation energy are obtained.     

Optical properties of transparent barium titanate nanoparticle/polymer hybrid synthesized from metal alkoxides

A transparent BaTiO₃ particle/polymer hybrid was synthesized from a Ba–Ti double alkoxide modified with an organic ligand and its refractive index and second harmonic generation were studied. BaTiO₃ particles modified with 2-vinyloxyethanol (ethylene glycol monovinyl ether, EGMVE) were polymerized with methyl methacrylate (MMA) yielding the transparent BaTiO₃ particle/poly MMA hybrid. X-ray photoelectron spectra indicated that the formation of chemical bonds between BaTiO₃ nanoparticles and the organic matrix. The refractive indexes of the hybrid films depended on the crystallite size of BaTiO₃ nanoparticles and the volume fractions of BaTiO₃ and polymer phases. The hybrid film synthesized at BaTiO₃/8EGMVE/30H₂O/PMMA revealed a refractive index of 1.65 at 589 nm with an Abbe number of 54. The hybrid film exhibited a second harmonic wave of 532 nm on irradiation with a fundamental wave of 1,064 nm.     

Optical reflection from dielectric layers containing metal particles formed by ion implantation

Dielectric layers with silver nanoparticles, which are synthesized in a soda-silicate glass by implantation of 60-keV ions with a dose of 7.0×10¹⁶ Ag⁺/cm² at an ion current density of 10 μmA/cm², are analyzed. The depth of silver distribution was measured by Rutherford backscattering. Data on optical characteristics of composite layers were obtained from the transmission spectra and from the reflection, which were measured both from the side of an implanted glass surface and from the unimplanted side. To calculate reflection spectra, a multilayer plane-parallel film structure was considered, which was modeled on the basis of the matrix method using complex Fresnel coefficients. Dielectric functions of separate layers were determined using the Maxwell-Garnet theory of an effective medium. A qualitative agreement between the experimental and the model optical spectra was obtained taking into account a nonuniform depth distribution of metal nanoparticles in a composite material.     

聚合物物理属性对离子注入效应的影响

聚合物导电性能差, 表面电荷积聚所产生的电容效应致使其表面电位衰减, 采用等离子体浸没离子注入对其表面改性是非常困难的. 建立了绝缘材料等离子体浸没离子注入过程的粒子模拟(PIC)模型, 实时跟踪离子在等离子体鞘层中的运动形态及特性并进行统计分析. 并基于PIC模型, 将聚合物表面的二次电子发射系数直接与离子注入即时能量建立关联, 研究了聚合物厚度、介电常数和二次电子发射系数等物理量对鞘层演化、离子注入能量和剂量的影响规律. 研究结果表明: 当聚合物厚度小于200 μ m, 相对介电常数大于7, 二次电子发射系数小于0.5时, 离子注入剂量和高能离子所占的份额与导体离子注入情况相当. 通过对聚合物表面离子注入剂量和高能离子所占份额的研究, 为绝缘材料和半导体材料表面等离子体浸没离子注入的实现提供了理论和实验依据.     

Dewetting of polymer films by ion implantation

We report dewetting of thermodynamically stable, thick (∼ 100 nm) polystyrene films by titanium ion implantation. The dynamic dewetting patterns in time evolution are recorded. The dewetting mechanism is determined to be heterogeneous nucleation, where the defects and Ti nanoparticles formed by ion implantation serve as the nuclei. In addition, we observe abundant rims with regular polygonal shapes in dewetting patterns. This is attributed to fingering instability, which results from the balance between the driving force arisen from thermally induced surface tension gradient and the resistive forces from the combination of friction force, Laplace pressure and long-range van der Waals interactions. Finally, a model based on mass conservation is used to qualitatively describe the transition from circular to polygonal shaped rims at a critical diameter for holes.     

离子注入掺杂锐钛矿TiO2薄膜的光学性能

 在玻璃基体上,采用射频磁控溅射方法在不同的基体温度下制备了TiO₂薄膜,然后在薄膜中注入注量分别为5×1016, 1×1017和5×1017/cm2的N离子以制备N掺杂的TiO₂薄膜。X射线衍射结果表明：制备出的TiO₂薄膜为锐钛矿型。X射线光电子能谱研究结果表明：注入的N离子与TiO₂晶粒相互作用,形成了含氮的TiO_xN_2-x化合物,从而改变了TiO₂薄膜的吸收边;随N离子注量增加,吸收边移动更明显;同时,由于氮离子注入产生的辐照缺陷使TiO₂薄膜在紫外和可见光区的吸收也明显增强。     

Optical properties of silicon nanoparticles synthesized via electrical spark discharge in water

In this paper, we report a simple and low-cost technique for fabrication of silicon nanoparticles via electrical spark discharge between two plane silicon electrodes immersed in deionized water (DI). The pulsed spark discharge with the peak current of 60 A and a duration of a single discharge pulse of 60 μs was used in our experiment. The structure, morphology, and average size of the resulting nanoparticles were characterized by means of X-Ray Diffraction (XRD), Raman spectroscopy and transmission electron microscopy (TEM). TEM images illustrated nearly spherical and isolated Si nanoparticles with diameters in the 3–8 nm range. The Raman peaks of the samples were shifted to the lower wave numbers in comparison to this of bulk crystalline silicon indicating the existence of tiny particles. The optical absorption spectrum of the nanoparticles was measured in the violet–visible (UV–Vis) spectral region. By measuring of the band gap we could estimate the average size of the prepared particles. The silicon nanoparticles synthesized exhibited a photoluminescence (PL) band in the violet-blue region with a double peak at around 417 and 439 nm. It can be attributed to oxide-related defects on the surface of silicon nanoparticles, which can act as the radiative centers for the electron-hole pair recombination.     

离子注入合成β-FeSi2薄膜的显微结构

采用MEVVA源(Metal Vapor Vacuum Arc Ion Source)离子注入合成β-FeSi2薄膜,用常规透射电镜和高分辨电镜研究了不同制备参数下β-FeSi2薄膜的显微结构变化. 研究结果表明:调整注入能量和剂量,可以得到厚度不同的β-FeSi2表面层和埋入层. 制备过程中生成的α,β,γ和CsCl型FeSi2相的相变顺序为γ-FeSi2→β-FeSi2→α-FeSi2,CsCl-FeSi2→β-FeSi2→α-FeSi2或β-FeSi2→α-FeSi2. 当注入参数增加到60kV,4×1017ions/cm2,就会导致非晶的形成,非晶在退火后会晶化为β-FeSi2相,相变顺序就变为非晶→β-FeSi2→α-FeSi2. 随退火温度逐渐升高硅化物颗粒逐渐长大,并向基体内部生长,在一定的退火温度下硅化物层会收缩断裂为一个个小岛状,使得硅化物/硅界面平整度下降. 另外,对于β-FeSi2/Si界面取向关系的研究表明,在Si基体上难以形成高质量β-FeSi2薄膜的原因在于多种非共格取向关系的并存、孪晶的形成以及由此导致的界面缺陷的形成.     

TEM characterization of yttrium silicide layers synthesized by ion implantation

The structure of Si implanted with high doses of yttrium has been investigated by varying implantation doses and energies. As implantation doses increase into the low 10¹⁷ cm^–2 range, silicide precipitates form. The precipitates are thin and long and lie parallel to {111} planes in the Si matrix. As dopant concentrations increase, the precipitates themselves become more equiaxed, aspect ratios decrease, and precipitates densities increase until the precipitates coalesce to form a continuous buried layer of yttrium silicide within the Si matrix. The layer thickness is relatively uneven. As implant doses increase to 4×10¹⁷ cm^–2, the layer thicknesses become more uniform although there are still defects present. As the implant doses increase further, the precipitate bands on either side of the continuous layer decrease due to gettering of yttrium to the layer. As the energy of the implant is increased, the appearance of the sample is similar to that of the lower energy implants except that the layer is buried deeper in the Si matrix. Observations of the silicide are consistent with its having the AlB₂ structure with ordered vacancies on the Si sublattice.Address from July 1, 1992: Arizona State University, Tempe, AZ     

Optical and mechanical properties of alumina films fabricated on Kapton polymer by plasma immersion ion implantation and deposition using different biases

Alumina films are fabricated on Kapton polymer by aluminum plasma immersion ion implantation and deposition in an oxidizing ambient and the effects of the bias voltage on the film properties are investigated. Rutherford backscattering spectrometry (RBS) reveals successful deposition of alumina films on the polymer surface and that the O to Al ratio is higher than that of stoichiometric Al₂O₃. The thickness of the modified layers decreases from 200 to 120 nm when the bias voltage is increased from 5 to 20 kV. Our results indicate that higher bombardment energy may lead to higher crack resistance and better film adhesion. However, a higher sample bias degrades the optical properties of the films as indicated by the higher absorbance and lower energy band gap. Therefore, the processing voltage must be optimized to yield a protective layer with the appropriate thickness, superior optical properties, as well as high crack resistance.     

Optical waveguides in LiNbO3 formed by ion implantation

Abstract

Ion implantation in LiNbO₃ can be used to modify the refractive index. The change in indices, n ₀ n _e results from the damage formed by energy deposited by the (dE/dx)_nuclear collisions between the ions and the lattice and is independent of the ion species. A saturation change in index of some ?7% occurs after a deposition of 10²³ keV cm^?3 at 300K, greater changes of ?9 % occur with implants at 77K. Annealing studies indicate the optical absorption formed during irradiation is removed below 200°C whereas the index changes exist up to 400°C. For optical waveguide production a negative change in the index is not ideal as the damaged layer cannot directly act as the region of optical confinement. However the (dE/dx)_electronic term is unimportant and so we have been able to form optical waveguides by ion implantation with light energetic ions (e.g. MeV He⁺ ions) because the damaged layer is then formed beneath an unchanged high index surface layer. This retains the desirable electrooptic properties of the single crystal LiNbO₃. The experimentally observed waveguide modes are in accord with our theoretical predictions of the refractive index profiles.     

Optical properties of nanocomposites based on polymers and metal nanoparticles

The optical properties of nanocomposites of metal nanoparticles and polymers of two types have been studied. Gold and silver nanoparticles were obtained by laser ablation of corresponding metal targets in acetone and chloroform. The thus formed colloidal solutions were used to prepare nanocomposites of these nanoparticles in polymer matrices of polymethylmethacrylate (PMMA) and fluorine-containing polymer LF-32. The polymer matrix is found to promote aggregation of the metal nanoparticles under study into elongated chains. In turn, metal nanoparticles affect the polymer matrix. In the case of PMMA, suppression of the vibrational peaks of polymer in the low-frequency region of its Raman spectrum occurs. In the case of LF-32, gold and silver nanoparticles amplify the Raman signal of the polymer matrix. In addition, the Raman spectra of nanocomposites indicate aggregation of disordered carbon around the nanoparticles obtained by laser ablation in organic solvents. The possibilities of studying the ultrafast (about 1 ps) optical response of the nanocomposites obtained in order to use it in photonics elements are discussed.     

Structure and composition of silicon carbide films synthesized by ion implantation

The mathematical decomposition of the IR absorption spectrum obtained from a Si layer after the C⁺ ion implantation with an energy of 10 or 40 keV or from a homogeneous SiC_0.7 film has demonstrated that fractions of weak elongated Si-C bonds in the amorphous phase, strong shortened Si-C bonds on the surface of small nanocrystals, and tetrahedral Si-C bonds in the crystalline phase (degree of crystallinity) after high-temperature annealing (1250–1400°C) of the layers are equal to 29/29/42, 22/7/71, and 21/31/48%, respectively. A system of SiC_2.0, SiO₂, SiC_0.8, and SiC_0.6 layers in the film on the Si substrate has been identified using X-ray reflectometry and the simulation with the Release software. The reflectometry data on fluctuations of the intensity of X-ray reflections in the region of the main maximum have been interpreted in terms of variations in the density over the depth of the layer with a Gaussian distribution of carbon atoms from 2.55 and 2.90 g/cm³ for the SiC_0.25 and SiC_0.65 layers, respectively, to 3.29 g/cm³ for the SiC_1.36 layer.     

Spectral and luminescent properties of coumarins in nanoparticles from metal ion complexes

We have studied the absorption spectra of complexes of trivalent ions Y, La, Lu, and Sc with p-phenylbenzoyltrifluoroacetone that were introduced into a solution of 90% H₂O + 10% iso-C₃H₇OH in the absence and presence of either 1,10-phenanthroline or coumarins 6, 7, or 30. We have shown that these coumarins, as well as phenanthroline, are synergistic bidentate ligands that are incorporated into complexes up to concentrations comparable with concentrations of complexes and that stabilize them in the solution. We have studied the dependences of the fluorescence (cofluorescence) intensity (I _cofl) of the coumarins on their concentration in nanoparticles from the complexes mentioned above. We have shown that, in nanoparticles from complexes of Y(III), Ln(III), and Sc(III), I _cofl of coumarin 30 at high concentrations is higher than I _cofl of coumarins 6 and 7. In addition, up to concentrations of coumarin 30 comparable with the concentration of complexes in nanoparticles, there is no concentration quenching of its fluorescence. For coumarins 6 and 7, which are prone to association in the solution under study, the process of incorporating coumarins into complexes competes with their association, which leads to concentration quenching and changes in the shape of their cofluorescence spectra.     

离子注入掺杂锐钛矿TiO2薄膜的光学性能

在玻璃基体上,采用射频磁控溅射方法在不同的基体温度下制备了TiO2薄膜,然后在薄膜中注入注量分别为5×1016, 1×1017和5×1017/cm2的N离子以制备N掺杂的TiO2薄膜。X射线衍射结果表明：制备出的TiO2薄膜为锐钛矿型。X射线光电子能谱研究结果表明：注入的N离子与TiO2晶粒相互作用,形成了含氮的TiOxN2-x化合物,从而改变了TiO2薄膜的吸收边;随N离子注量增加,吸收边移动更明显;同时,由于氮离子注入产生的辐照缺陷使TiO2薄膜在紫外和可见光区的吸收也明显增强。