核壳结构纳米复合材料的研究进展

纳米粒子由于具有大量的潜在应用,近年来已引起人们极大的关注.通过制备具有核壳结构的纳米复合材料可以使其获得更多特殊的性质.综述了最近几年制备壳核结构纳米粒子的方法,根据其核、壳的不同材料分了4类,并对其中某些方法进行了比较,同时指出了目前该领域的应用前景、存在的不足和今后的研究发展方向.     

核壳结构纳米复合材料的研究进展

核壳结构纳米复合材料可同时具备核层和壳层材料的性能,能表现出优异于单组份材料的光、电、磁和催化等理化性质。综述了核壳纳米结构材料的制备方法,主要包括溶胶-凝胶法、水热法、自组装法、超声化学法等,介绍了核壳纳米结构材料的性能特点,重点阐述了它们在光子晶体、生物医学、催化等领域的应用,最后展望了核壳结构纳米复合材料未来的发展方向。     

核壳结构纳米颗粒的研究进展

核壳结构纳米颗粒具有不同于核和壳的物理和化学性能，通过调整核和壳的化学组成、尺寸和形貌，可以调控纳米颗粒的性能，扩展纳米颗粒的应用范围。系统总结了近年来制备核壳结构纳米颗粒的研究进展，讨论了核壳结构纳米颗粒对光学特性的影响。     

核壳结构纳米颗粒的研究进展

核壳结构纳米颗粒具有不同于核和壳的物理和化学性能,通过调整核和壳的化学组成、尺寸和形貌,可以调控纳米颗粒的性能,扩展纳米颗粒的应用范围.系统总结了近年来制备核壳结构纳米颗粒的研究进展,讨论了核壳结构纳米颗粒对光学特性的影响.     

核壳结构Co/SiO_2非晶态纳米颗粒的制备和性能

主要研究了核壳结构Co/SiO2非晶态纳米颗粒的制备及性能。正硅酸乙酯水解生成二氧化硅,水溶液中硼氢化钠还原氯化钴生成钴单质,存在硅烷偶联剂APS时,将二者进行结合生成二氧化硅包覆在钴颗粒表面。采用XRD、TEM、FT-IR、VSM等手段对样品进行表征。     

具有核-壳结构的金纳米包覆磁性纳米复合颗粒的研究进展

具有核-壳结构的金纳米包覆的磁性纳米粒子,既具有磁性纳米粒子的特点又增加了金纳米的表面化学性质,近年来受到研究人员的广泛关注。简要综述了近年来国内外制备2类核-壳结构的金包铁磁性纳米复合材料的研究进展及相关应用,并对其应用前景进行了展望。     

核壳型纳米复合材料的研究进展

核壳结构纳米复合材料因其独特的结构而呈现出诸多新奇的物理、化学特性,具有广阔的应用前景.系统地综述了近年来无机/无机、无机/有机、有机/无机3种类型的核壳结构纳米复合材料合成方法的研究进展与形成机理,重点阐述了它们在催化、生物医学、药物控制释放和光子晶体等领域的应用,最后展望了核壳结构纳米复合材料未来的发展方向.     

核壳结构二氧化硅/磁性纳米粒子的制备及应用

核壳结构二氧化硅/磁性纳米粒子作为一种新型功能复合材料在生物医学方面有重要应用前景.综述了核壳结构二氧化硅/磁性纳米粒子的各种制备方法以及国内外在核壳结构二氧化硅/磁性纳米粒子制备方面的研究新进展,并对其在生物医学上的应用作了介绍.     

水热法制备聚苯乙烯/CdS核壳结构纳米复合颗粒

采用水热法合成聚苯乙烯/CdS核壳复合材料,同时引入聚乙烯吡咯烷酮改善CdS纳米粒子与聚合物基体间的亲和性,防止聚苯乙烯团聚;改变水热时间和Cd2+与S2-的摩尔比,对制备条件进行探索优化。利用SEM,TEM,XRD和FT-IR等测试手段对样品的形貌、成分、微观结构和粒度等进行表征。结果表明:水热法制备的聚苯乙烯/CdS复合材料具有明显的核壳结构,颗粒均匀,呈球形,核的平均粒径约260nm,CdS壳层厚度约10~50nm,有良好的可见光催化效能。     

Metastable alloy formation by ion implantation

Implantation into metals at room temperature and at lower temperatures can result in the formation of metastable phases. For low concentrations (not more than about 1 at.%) substitutional and interstitial solutions have been observed for implantation in beryllium, iron, nickel and copper. These results have been explained in terms of modified Hume-Rothery rules and also Miedema coordinates. At higher concentrations (not less than about 10 at.%) both metastable solid solutions and amorphous alloys have been formed in iron, nickel and copper.     

Formation of AlN by nitrogen ion implantation

The phase composition of aluminium after bombardment with doses from 1 × 10¹⁶ to 1 × 10¹⁸ N⁺ ions cm^-2 is investigated by high voltage electron microscopy and selected area diffraction. This implantation always produced polycrystalline aluminium nitride (AlN). A thermal treatment to 600 °C did not yield new crystalline phases. At low temperatures the growth of AlN precipitations takes place mainly coherently as a result of a high vacancy density. Larger AlN precipitations grow similarly to the Ostwald ripening process. In this process incoherent precipitations are associated with a high dislocation density with an anisotropic distribution.     

ZnO nanoparticles embedded in sapphire fabricated by ion implantation and annealing

ZnO nanoparticles were fabricated in sapphire (α-Al(2)O(3) single crystal) by Zn ion implantation (48?keV) at an ion fluence of 1 × 10(17)?cm(-2) and subsequent thermal annealing in a flowing oxygen atmosphere. Transmission electron microscopy (TEM) analysis revealed that metallic Zn nanoparticles of 3-10?nm in dimensions formed in the as-implanted sample and that ZnO nanoparticles of 10-12?nm in dimensions formed after annealing at 600?°C. A broad absorption band, peaked at 280?nm, appeared in the as-implanted crystal, due to surface plasma resonance (SPR) absorption of metallic Zn nanoparticles. After annealing at 600?°C, ZnO nanoparticles resulted in an exciton absorption peak at 360?nm. The photoluminescence (PL) of the as-implanted sample was very weak when using a He-Cd 325?nm line as the excitation source. However, two emission peaks appeared in the PL spectrum of ZnO nanopraticles, i.e., one ultraviolet (UV) peak at 370?nm and the other a green peak at 500?nm. The emission at 500?nm is stronger and has potential applications in green/blue light-emitting devices.     

Formation of aligned silver nanoparticles by ion implantation

Synthesis of metal nanoparticles by ion implantation has a number of advantages. Nevertheless, certain remaining difficulties must be overcome in order to optimize the characteristics of ion-implanted nanocomposites. The principle among these are the lack of control over the size distribution and position of the precipitates within the implanted layer. Two-dimensionally ordered arrangements of Ag nanoparticles are formed in Ag-implanted silica glass by post-implanted Cu ions. The spherical Ag nanoparticles are formed to align at the same deep depth in the silica. Cross-sectional transmission electron microscopy revealed that the Ag nanoparticles are a size of 35-48 nm in diameter. The evolution of nanoparticles is characterized by transmission electron microscopy.     

Nanocavities and germanium nanocrystals produced by Ge ion implantation in fused silica

High-resolution SEM images of germanium nanocrystals (Ge-nc) synthesized by ion implantation in fused silica samples annealed at temperatures below and above the melting point of Ge show a strong size-selective depth-distribution of nanostructures, as evidenced by the correlation between the dimension of the observed objects and the local concentration of implanted Ge measured by Rutherford backscattering spectroscopy (RBS). Whereas the Ge-nc nucleation seems to obey the Ostwald ripening process in samples annealed below 900?°C, Ge desorption effects, non-uniform in depth, in conjunction with the formation of large and spherical nanocavities, become dominant for annealing performed above the solid-liquid phase transition of Ge. Measurements for different annealing times at 1050?°C show two distinct processes in the Ge desorption dynamics: the first is related to direct Ge outgassing effects during the nucleation of Ge-nc, which occurs within the first minutes of the thermal annealing, while the second is due to the release of Ge from Ge-nc, associated with the formation of nanocavities. The formation rate of these nanocavities is more efficient at greater depth than in the vicinity of the sample surface. It appears to be strongly dependent on the local concentration of defects, responsible for the reduction of the Ge diffusion, and to be related to the breaking of Ge-O and Si-Ge bonds at the Ge-nc/SiO(2) interface.     

Formation of a-C thin films by plasma-based ion implantation

Carbon films were prepared on a Si wafer substrate by using a plasma-based ion implantation (PBII) technique. The homogeneity of the carbon films formed on the three-dimensional object and the influence of the duty ratio of the pulse bias to the target on the property of the carbon films were investigated. The homogeneity of the carbon films formed on a convex face and that formed on a concave face by the incidence of the microwave to the target with a low angle of about −30° was almost a constant. The application of the ECR plasma source, with a mirror field, to the PBII system was efficient enough to improve the homogeneity, even though the plasma density was not very high. Diamond-like carbon films with a flat surface and a low friction coefficient can be formed by applying negative high-voltage pulses to a substrate with a low duty ratio of 1%.     

Formation of a-C thin films by plasma-based ion implantation

Carbon films were prepared on a Si wafer substrate by using a plasma-based ion implantation (PBII) technique. The homogeneity of the carbon films formed on the three-dimensional object and the influence of the duty ratio of the pulse bias tothe target on the property of the carbon films were investigated. The homogeneity of the carbon films formed on a convex face and that formed on a concave face by the incidence of the microwave to the target with a low angle of about — 30° wasalmost a constant. The application of the ECR plasma source, with a mirror field, to the PBII system was efficient enoughtoimprove the homogeneity, even though the plasma density was not very high. Diamond-like carbon films with a flat surface and a low friction coefficient can be formed by applying negative high-voltage pulses to a substrate with a low duty ratio of 1%.     

Formation of uniaxially strained SiGe by selective ion implantation technique

Uniaxially strained SiGe layers were fabricated with a newly developed selective-ion-implantation technique. The SiGe layer was grown on the Si substrate, into which laterally selective ion-implantation with stripe pattern was carried out prior to the SiGe growth. A strain-relaxation of the SiGe layer was largely enhanced due to ion-implantation-induced defects selectively in the ion-implanted area while it was hardly enhanced in the neighboring unimplanted area. However, micro-Raman mapping and X-ray diffraction reciprocal space mapping measurements obviously revealed that the relaxed SiGe in the implanted area remarkably influenced a strain state of the neighboring strained SiGe in the unimplanted area, that is, the strain along the stripe line direction was highly relieved due to the stress caused by the neighboring relaxed SiGe while the strain in the direction perpendicular to the line was well maintained. As a result, highly asymmetric strain state, that is, uniaxial strain was realized, where 4 times different relaxation ratios in the two directions were observed. These results indicate that the selective-ion-implantation technique developed in this study has a high potential to realize uniaxially strained Si/Ge channel devices with high mobility.     

Formation of hexagonal 9R silicon polytype by ion implantation

Technical Physics Letters - Transmission electron-microscopy examination revealed the appearance of a hexagonal silicon (9R polytype) inclusions in the subsrface silicon layer upon ion implantation...