Hyper-Rayleigh scattering (HRS) or incoherent second harmonic generation (SHG) technique has been used to investigate the second-order optical nonlinearities of nanoparticles and seems sensitive to nanoparticle surfaces. Here, more direct evidence that shows the importance of surfaces for HRS response of nanoparticles was experimentally obtained. Two CdS nanoparticles of 3 nm average diameter with different surface-capping molecules, CdS/AOT-SO3- (AOT-SO3- is anion of bis (2-ethylhexyl) sulfosuccinate, disodium salt) and CdS/Py/AOT-SO3- (Py represents pyridine molecule), were studied by HRS technique. The "per particle" first-order hyperpolarizability β values were evaluated to be 3.98×10-27 esu for the CdS/AOT-SO3- and 2.63×10-27 esu for the CdS/Py/AOT-SO3- nanoparticles. A reduction in β value is found when AOT-SO3- on CdS nanoparticle surface is replaced by pyridine. Similarly, the reduction of HRS signal intensity of a solution containing the CdS/AOT-SO3- nanoparticles was observed when increasing pyridine concentration in the solution. Furthermore, the dynamic process of the surface-capping molecule exchange was studied by detecting both HRS signal intensity and electroconductivity variations with time. Possible effect mechanism is discussed in terms of a two-level model approximation derived from molecular chromophores, when considering the influence of different surface-capping molecules on the polarity of Cd-S bonds at nanoparticle surfaces.

Magnetite nanoparticles were prepared by coprecipitation of Fe2+ and Fe3+ with NH4OH, and then, amino silane was coated onto the surface of the magnetite nanoparticles. Transmission electronic microscopy shows the average size of 7.5nm in diameter. Powder X-ray diffraction and electronic diffraction measurements show the spinel structure for the magnetite nanoparticles. FT-IR spectra indicate that amino silane molecules have been bound onto the surface of the magnetite nanoparticles by Fe-O-Si chemical bonds. Energy dispersive X-ray spectroscopy (SEM-/EDS) indicates atomic ratio of 96.75:3.25 for Fe:Si, implying a nearly monolayer coating of amino silane on the magnetite particle surface according to a rough calculation. By an enzyme-linked assay, it was proved that the amino silane-coated magnetite nanoparticles could significantly improve the protein immobilization.

This paper describes an improved approach for the coating of superparamagnetic magnetite nanoparticles with shells of amorphous silica. Magnetite (Fe3O4) nanoparticles are prepared by partial reduction coprecipitation method and modified by adding citric acid. The silica coating is conveniently controlled by a dilute silicate solution pretreatment and subsequent Stober process directly in ethanol. Transmission electron microscopy, photon correlation spectroscopy and zeta-potential analysis results show that the attractions between the superparamagnetic nanoparticles are screened by the silica coating. With enough tetraethylorthosilicate added, the stable core-shell colloid was obtained. Vibrating sample magnetometer characterization shows that the magnetic core-shell structure is superparamagntic.

A dynamic chemical etching method based on siphon principle has been developed for controllable fabrication of fiber nano-tips, which could be used in near-field optical microscope and optical nanosensors. Compared with traditional static chemical etching, this method has advantages such as reproducibility, controllability, convenience, less cost, and making tip surface smooth. The overall shape and the tape angle of the tip can be effectively controlled through the speed and direction of water flux. Tips with taper angles from 20

A novel core-shell structured composite, titania (TiO2) coated Mn-Zn ferrite nanoparticle, was prepared byhydrolysis of titanium (Ⅳ) chloride (TiCl4) in the presence of Mn-Zn ferrite nanoparticles synthesized with stearic acid gel method. The obtained samples were characterized by energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results show that spinel structural Mn-Zn ferrite nanoparticles (6 nm average diameter) or their aggregates are coated by TiO2 nanoshell with anatase structure for annealed sample. The magnetic measurements were carried out on a vibrating sample magnetometer (VSM), and the measurement results indicate the reduction of the magnetization of the TiO2 coated Mn-Zn ferrite nanoparticles compared with the uncoated ferrite nanoparticles. High coercivity also shows that the prepared uncoated and coated ferrite nanoparticles are not superparamagnetic.