CdSe/CdS/SiO2 core/shell/shell nanoparticles

Quantum dots (QD) of a CdSe-ZnS core-shell structure are coated with silica spheres to improve their stability in biological buffers and biocompatibility in fluorescence imaging. We found that it was critical to transfer quantum dots from organic phase to aqueous phase before the silica shell growth process. As a result, high quality CdSe-ZnS-SiO2 core-shell-shell nanoparticles were prepared in high yields and their size and distribution are characterized with transmission electron microscopy and dynamic light scattering, which yielded uniform sizes and narrow polydispersity. Single particle fluorescence spectroscopy on the silica-protected quantum dots showed they were stronger emitters with consistent fluorescence intensity and "on-off" behaviors than bare CdSe-ZnS nanocrystals.     

Preparation and tunable luminescent characteristics of SiO2 coated ZnO:LiAc nanoparticles

ZnO:LiAc nanopaticles were successfully synthesized though a colloidal-sol technique in nonaqueous solution under ultrasonic irradiation. The luminescent characteristics from blue to red can be tunable by varying [Li]/[Zn] ratios. The possible reason of tunable luminescent characteristics can be attributed to the increase of density of oxygen vacancies caused by Li+ adsorbed in the surface of magic-sized ZnO nanocrystals based on XRD, zeta potential and XPS results. What's more, it is found that SiO2 shell coated on ZnO:LiAc nanoparticles can improve the surface property of ZnO nanoparticles and enhance the PL emission intensity and optical stability. Due to its excellent luminescent characteristic and optical stability, as-prepared SiO2 coated ZnO:LiAc nanoparticles may be a promising candidate for some applications in high-efficiency low-voltage phosphor, solar cells and biological luminescent labels.     

UV-durable superhydrophobic textiles with UV-shielding properties by coating fibers with ZnO/SiO2 core/shell particles

ZnO/SiO(2) core/shell particles were fabricated by successive coating of multilayer polyelectrolytes and then a SiO(2) shell onto ZnO particles. The as-prepared ZnO/SiO(2) core/shell particles were coated on poly(ethylene terephthalate) (PET) textiles, followed by hydrophobization with hexadecyltrimethoxysilane, to fabricate superhydrophobic surfaces with UV-shielding properties. Transmission electron microscopy and ζ potential analysis were employed to evidence the fabrication of ZnO/SiO(2) core/shell particles. Scanning electron microscopy and thermal gravimetric analysis were conducted to investigate the surface morphologies of the textile and the coating of the fibers. Ultraviolet-visible spectrophotometry and contact angle measurement indicated that the incorporation of ZnO onto fibers imparted UV-blocking properties to the textile surface, while the coating of SiO(2) shell on ZnO prohibited the photocatalytic degradation of hexadecyltrimethoxysilane by ZnO, making the as-treated PET textile surface show stable superhydrophobicity with good UV-shielding properties.     

Preparation,characterization and application of Fe3O4/ZnO core/shell magnetic nanoparticles

Fe₃O₄ magnetic nanoparticles (MNPs) were synthesized by a co-precipitation method. The phase purity was confirmed by X-ray powder diffraction (XRD) analysis. The crystal size was found to be 10 nm from transmission electron microscopy (TEM). It is evidenced that the surface of Fe₃O₄ MNPs was modified by sodium citrate. The Fe₃O₄/ZnO core/shell MNPs were obtained by coating the MNPs with direct precipitation using zinc acetate and ammonium carbonate. The precursor was firstly dried and then calcined at 350 °C. The antioxidation tests indicated that the core/shell MNPs give better antioxidation than that of the Fe₃O₄ MNPs. The photocatalytic degradation of methyl orange revealed that the core/shell MNPs have higher photocatalytic activity than that of the ZnO nanoparticles. Separation of the core/shell MNPs from the aqueous suspension using a magnet provides an easy way to recycle the core/shell MNPs. After four-time recycling, the photocatalytic degradation percentage of the core/shell MNPs is about 70%.     

Ni-silicide growth kinetics in Si and Si/SiO2 core/shell nanowires

A systematic study of the kinetics of axial Ni silicidation of as-grown and oxidized Si nanowires (SiNWs) with different crystallographic orientations and core diameters ranging from ～ 10 to 100 nm is presented. For temperatures between 300 and 440?°C the length of the total axial silicide intrusion varies with the square root of time, which provides clear evidence that the rate limiting step is diffusion of Ni through the growing silicide phase(s). A retardation of Ni-silicide formation for oxidized SiNWs is found, indicative of a stress induced lowering of the diffusion coefficients. Extrapolated growth constants indicate that the Ni flux through the silicided NW is dominated by surface diffusion, which is consistent with an inverse square root dependence of the silicide length on the NW diameter as observed for (111) orientated SiNWs. In situ TEM silicidation experiments show that NiSi(2) is the first forming phase for as-grown and oxidized SiNWs. The silicide-SiNW interface is thereby atomically abrupt and typically planar. Ni-rich silicide phases subsequently nucleate close to the Ni reservoir, which for as-grown SiNWs can lead to a complete channel break-off for prolonged silicidation due to significant volume expansion and morphological changes.     

Zn/ZnO core/shell nanoparticles synthesized by laser ablation in aqueous environment: Optical and structural characterizations

Zn/ZnO core/shell nanoparticles are synthesized by pulsed laser ablation (PLA) of Zn metal plate in the aqueous environment of sodium dodacyl sulfate (SDS). Solution of nanoparticles is found stable in the colloidal form for a long time, and is characterized by UV-visible absorption, transmission electron microscopy (TEM), photoluminescence (PL) and Raman spectroscopic techniques. UV-visible absorption spectrum has four peaks at 231, 275, 356, and 520 nm, which provides primary information about the synthesis of core-shell and elongated nanoparticles. TEM micrographs reveal that synthesized nanoparticles are monodispersed with three different average sizes and size distributions. Colloidal solution of nanoparticles has significant absorption in the green region, therefore, it absorbs 514·7 nm light of Ar⁺ laser and emits in the blue region centred at 350 and 375 nm, violet at 457 nm and green at 550 nm regions. Raman shift is observed at 300 cm⁻¹ with PL spectrum, which corresponds to ³E_2N and E_3L mode of vibrations of ZnO shell layer. Synthesis mechanism of Zn/ZnO core/shell nanoparticles is discussed.     

CdS/ZnO核壳结构纳米微粒的合成及其发射光谱研究

采用单分子前驱体热分解的方法合成了单分散CdS纳米晶,以CdS纳米晶作为核,在CTAB辅助下,对其表面进行修饰,荧光光谱表明CdS/ZnO核壳结构被成功合成。考查了温度对包覆的影响,结果表明,随着温度的升高晶体结晶越好,包覆越来越完全,ZnO包覆在CdS纳米晶的表面而掩盖了CdS纳米晶的缺陷,使得缺陷发光减弱而带隙发光增强。     

Iridium-complex-functionalized Fe3O4/SiO2 core/shell nanoparticles: a facile three-in-one system in magnetic resonance imaging, luminescence imaging, and photodynamic therapy

Highly uniform Fe3O4/SiO2 core/shell nanoparticles functionalized by phosphorescent iridium complexes (Ir) have been strategically designed and synthesized. The Fe3O4/SiO2(Ir) nanocomposite demonstrates its versatility in various applications: the magnetic core provides the capability for magnetic resonance imaging and the great enhancement of the spin-orbit coupling in the iridium complex makes it well suited for phosphorescent labeling and simultaneous singlet oxygen generation to induce apoptosis.     

Facile electrochemical characterization of core/shell nanoparticles. Ag core/Ag(2)O shell structures

We report in this paper a facile approach for the formation and electrochemical characterization of silver-silver oxide core-shell nanoparticles (NPs). Thus, thermal treatment at temperatures between 200 and 360 degrees C of Ag NP, in the gas phase or in an organic solvent, has been used to achieve the formation Ag@Ag2O NP. The evidence of formation of such a core-shell structure was obtained by cyclic voltammetry using a Nafion modified electrode (where Nafion containing carbon particles is used as the matrix to encapsulate the core-shell NP). Initial positive scans measure free Ag. Initial negative scans measure Ag2O, with the following positive scan, compared to the initial one, providing a measure of "trapped" or core Ag. The results presented demonstrate the utility of this approach in characterizing core-shell structures, like Ag@Ag2O, which could be extended to other core-shell forms, such as bimetallic core-shell NP.     

SiC/SiO_2包覆Fe-Ni合金纳米粒子的制备及应用

采用电弧放电法,在15%CH4+10%SiH4+75%Ar的混合气氛中制备了SiC/SiO2包覆Fe-Ni合金纳米粒子,并用制备的SiC/SiO2包覆Fe-Ni合金纳米粒子作为磁性粒子,油酸为表面活性剂,机油为基液制备了磁性润滑油。用XRD、TEM、XPS、红外光谱和氧含量分析等手段研究了SiC/SiO2包覆Fe-Ni合金纳米粒子的相结构、形貌、粒度、表面组成和氧化特性。用粘度计和VSM研究了制备的磁性润滑油的粘度和饱和磁化强度。     

Synthesis and upconversion luminescence of NaYF4:Yb, Tm/TiO2 core/shell nanoparticles with controllable shell thickness

NaYF4:Yb, Tm/TiO2 core/shell nanoparticles were synthesized by a two-step method. First, the NaYF4:Yb, Tm nanocrystals were prepared using solvothermal technology; then, TiO2 shells were deposited on the nanocrystals by the hydrolysis of titanium ethoxide (TEOT) to form core/shell structures. By controlling the reaction time, we can adjust the thickness of TiO2 shell and thereby the weight percentage of TiO2 in the core/shell nanoparticles. The effect of shell thickness on the upconversion fluorescence of NaYF4:Yb, Tm nanocrystals was investigated in detail.     

Superparamagnetic maghemite/polyrhodanine core/shell nanoparticles: Synthesis and characterization

Maghemite nanoparticles (MNPs) with a thin layer of polyrhodanine (PRd) at the surface were synthesized via chemical oxidative polymerization of rhodanine monomer at the MNPs surface in the presence of ferric chloride as oxidant. X-ray diffraction (XRD) pattern gave direct evidence that the synthesized nanoparticles are crystalline maghemite of about 8 nm in size. Magnetization of the particles versus an applied magnetic field exhibited no hysteresis loop, indicated superparamagnetic behavior in the particles. Transmission electron microscopy (TEM) together with Fourier-transform infrared (FT-IR) spectroscopy were used to determine the morphology and the chemical structure of the magnetic core and the polymeric shell. Through the microscopy analysis the shell thickness was estimated to be about 1.5 nm, whereas through thermogravimetric analysis (TGA) it was estimated to be about 0.6 nm. Moreover inductively coupled plasma optical emission spectroscopy (ICP-OES) measurements revealed that the oxidant residue in the polymer backbone is ca. 4 wt.%.     

Crystalline core/shell Si/SiO2 nanotubes formed via interfacial stress imbalance

Crystalline core/shell Si/SiO2 nanotubes (NTs) with outer diameters of 130-220 nm and lengths of approximately 1 microm have been synthesized using thermal evaporation. High resolution scanning electron microscopy reveals that the NT formation stems from the intrinsic interfacial stress imbalance in the strained Si/SiO2 bilayered film, consequently leading to NTs with different orifice levels. The NT diameters depend strongly on the bilayer film thicknesses and crystal orientations of the Si and SiO2 layers. A modified Timoshenko formula is derived to calculate the dependence of the tube diameter on the bilayer film thickness. The obtained results are consistent well with experimental data.     

Three-layer core/shell structure in Au-Pd bimetallic nanoparticles

This paper describes the internal structure of Au-Pd nanoparticles exhibiting newly discovered three-layer core/shell morphology, which is composed of an evenly alloyed inner core, an Au-rich intermediate layer, and a Pd-rich outer shell. By exploitation of spatially resolved imaging and spectroscopic and diffraction modes of transmission electron microscopy (TEM), insights were gained on the composition of each one of the observed three layers, indicating a significant extent of intimate alloy among the monometallic elements.     

CuO/Ta2O5 core/shell nanoparticles produced by arc-discharge in water

The formation of novel nanoparticles, i.e. CuO/Ta₂O₅ core/shell, via anodic arc-discharge in water is reported. Typical core diameters and shell thicknesses are about 20 and 5 nm, respectively. Both core and shell are crystalline. The resulting core/shell-structured nanopowder exhibits dielectric behavior.     

Exchange bias phenomenology and models of core/shell nanoparticles

Some of the main experimental observations related to the occurrence of exchange bias in magnetic systems are reviewed, focusing the attention on the peculiar phenomenology associated to nanoparticles with core/shell structure as compared to thin film bilayers. The main open questions posed by the experimental observations are presented and contrasted to existing theories and models for exchange bias formulated up to date. We also present results of simulations based on a simple model of a core/shell nanoparticle in which the values of microscopic parameters such as anisotropy and exchange constants can be tuned in the core, shell and at the interfacial regions, offering new insight on the microscopic origin of the experimental phenomenology. A detailed study of the magnetic order of the interfacial spins shows compelling evidence that most of the experimentally observed effects can be qualitatively accounted within the context of this model and allows also to quantify the magnitude of the loop shifts in striking agreement with the macroscopic observed values.     

SiO2包覆Fe2O3纳米粒子的制备和性能

在近球形α-Fe2O3颗粒的悬浮液中,以正硅酸乙酯(TEOS)为硅源,氨水和尿素为催化剂,合成了Fe2O3-SiO2核-壳粒子.应用TEM.XRD对Fe2O3-SiO2核-壳粒子结构进行了测定.研究了TEOS.氨水的浓度对核-壳粒子结构的影响.UV-Vis吸收光谱表明,SiO2壳层消除了Fe2O3纳米粒子的表面悬挂键,产生增强的激子发射,使得核-壳粒子的吸收峰发生蓝移.根据带边吸收峰的波长计算出核-壳粒子中Fe2O3的禁带宽度为2.25 eV.