CdS:Mn/SiO2复合纳米颗粒的反常的磁学特性

采用反胶束法,合成了硅土包裹的Mn2+掺杂的CdS纳米颗粒。利用高分辨透射电镜(HRTEM)和电子自旋共振谱 (EPR) 对这些纳米颗粒的结构进行了表征。利用超导量子干涉磁力计（SQUID）测量了这些纳米颗粒在低温下的磁学特性。研究结果表明：扩散在硅土基质中的CdS:Mn纳米颗粒的磁滞回线相对于磁场轴有明显的偏移,而有致密包裹层SiO2的CdS:Mn纳米颗粒却使磁滞回线的偏移消失,对于磁性纳米颗粒在磁化过程中出现的这一奇特的现象进行了合理的解释。     

掺杂Mn2+的浓度对CdS纳米颗粒光致发光的影响

采用反胶束法,合成了硅土包裹的掺有不同浓度的Mn2 的CdS纳米颗粒.高分辨电镜表明这些颗粒的直径小于5 nm.仅仅改变Mn2 的掺杂浓度,研究了这些颗粒的光致发光谱和光致发光激发谱,结果表明:Mn2 浓度的大小对掺杂CdS纳米颗粒的发光产生了重要的影响.通过电子顺磁共振谱的测量和分析揭露了Mn2 浓度影响这些掺杂颗粒发光效率的原因.     

温度对CdS纳米颗粒形状和光致发光特性的影响

采用反胶束法,在常温和低温下(接近零度)合成了硅土包裹的CdS纳米颗粒.高分辨电镜表明常温下合成的颗粒呈现直径小于5 nm的球形,而在低温下出现了短棒形和长达微米量级的线形.通过对实验过程的分析表明:不仅合成CdS纳米颗粒溶液的浓度,而且温度对CdS纳米颗粒的形状产生了重要的影响.进一步研究了CdS纳米颗粒的光致发光特性.     

CdS纳米颗粒填充的自支撑多孔硅光致发光特性

为了研究CdS纳米颗粒填充的自支撑多孔硅的光致发光特性,选用电阻率为0.01~0.02Ω·cm的P型硅片,先采用二步阳极氧化法制备自支撑多孔硅,再利用电泳法将CdS纳米颗粒填充入该自支撑多孔硅中.采用扫描电子显微镜、X射线能谱分析、X射线衍射分析、光致发光谱分析对所制备样品的形貌、相结构、组份及发光性能进行研究.实验结果表明:自支撑多孔硅内部成功填充了CdS纳米颗粒,该CdS纳米颗粒衍射峰为(210);CdS纳米颗粒填充的自支撑多孔硅光致发光峰峰位发生红移,且从570nm转移到740nm;电泳时间直接影响CdS纳米颗粒的填充量,导致相关的发光峰强度及发光峰位明显不同.     

核/壳结构ZnS : Mn/CdS纳米粒子的制备及发光

利用溶剂热法制备了Mn离子掺杂的ZnS纳米粒子(ZnS : Mn),利用沉淀法对ZnS ∶ Mn纳米粒子进行了不同厚度的CdS无机壳层包覆。采用X射线衍射(XRD)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)及光致发光(PL)光谱等手段对样品进行了表征。TEM显示粒子为球形,直径大约在14~18 nm之间。由XRD结果可以看出CdS壳层的形成过程受到了ZnS ∶ Mn核的影响,导致其结晶较差。XRD和XPS测量证明了ZnS : Mn/CdS的核壳结构。随着CdS壳层的增厚,样品的发光强度呈现一直减弱的现象。     

尺寸相关的CdS纳米颗粒的拉曼散射特性

采用反胶束法,合成了具有不同尺寸的CdS纳米颗粒。利用透射电镜(TEM)和高分辨透射电镜(HR-TEM)以及紫外-可见光吸收谱(UV/vis)对这些纳米颗粒的结构特性进行了表征和分析。利用拉曼光谱仪测量了这些具有不同尺寸的CdS纳米颗粒的拉曼特性。研究结果表明：当纳米颗粒尺寸小于一定值时,拉曼峰出现了蓝移,大于一定值时出现了红移,这些不同的结果是与纳米颗粒的尺寸效应以及纳米颗粒结构中具有各向异性的电子－声子耦合作用有关。     

单一晶相氧化锰纳米颗粒的交换偏置效应

本文利用高温油相法制备出尺寸、形状均一的 MnO纳米颗粒, X射线衍射图 (XRD) 和透射电子显微镜 (TEM) 照片清晰表明MnO纳米颗粒为单一的面心立方岩盐晶体结构, 尺寸为15nm, 粒径分布很窄. 通过零场冷却 (ZFC) 和带场冷却 (FC)的磁滞回线发现MnO纳米颗粒具有明显的交换偏置效应, 而且磁滞回线同时表现出横向和纵向偏移. 横向偏移说明纳米颗粒中两相复合的存在, 纵向偏移说明了存在自旋玻璃相或者超顺磁相. 进而通过不同频率下随温度变化的交流磁化率的测定, 根据Mydosh的经验数值确认 MnO纳米颗粒表面层为自旋玻璃相, 并得到 MnO纳米颗粒表面自旋玻璃相的转变温度为T_SG=32K. 关键词： 纳米颗粒 氧化锰 交换偏置 自旋玻璃     

一维Mn2+掺杂CdS纳米晶体的水热合成及其发光性能

用水热方法合成了一维Mn2 掺杂CdS纳米晶体.产品分别用SEM,EDS,XRD,TEM,HRTEM和PL等技术进行了表征.结果表明,掺杂Mn2 完全替代了CdS晶格中Cd2 的位置,产品具有较好的结晶性.荧光光谱中,CdS纳米晶体表面缺陷态的发射峰被完全抑制,只能观察到单一的Mn2 的发射峰.     

溶剂热再结晶合成由纳米颗粒自组装成的一维CdS纳米棒

采用两种不同的溶剂热路径合成出了不同形貌和尺寸的CdS纳米晶, 一种是以无水乙二胺(en) 为溶剂, CdCl₂·2.5H₂O和硫脲(H₂NCSH₂N) 为镉源和硫源, 在不同反应温度(160 ℃-220 ℃ 下制备出了CdS纳米晶, 讨论温度对CdS纳米晶生长的影响; 另一种是以en为溶剂, 将在160 ℃下合成的产物在200 ℃下原位再结晶生长2-8 h, 分析原位生长时间对CdS纳米晶生长的影响. 通过X射线衍射(XRD)、 扫描电子电镜(SEM) 和透射电子电镜(TEM) 等表征产物的物相、 形貌和微结构, 分析可知: 两种路线合成的产物均为六方相CdS; 当温度为160 ℃时, 产物形貌为纳米颗粒状, 当温度高于160 ℃时, 产物为CdS纳米棒状; 同时, 在200 ℃下原位再结晶生长不同时间后发现产物形貌由纳米颗粒转变为纳米棒, 通过场发射扫描电镜(HRTEM) 分析可知: 纳米棒是由零维纳米颗粒自组装而成. 最后, 讨论了影响产物CdS纳米晶形貌转变的因素和纳米棒的生长机理.     

Ag@SiO_2的制备及其SERS活性研究

本文用柠檬酸三钠还原硝酸银的方法制得银纳米粒子,并且通过调节加入正硅酸乙酯(TEOS)的量形成不同包裹厚度的Ag@SiO2。用紫外可见吸收光谱、扫描和透射电子显微镜测试手段对样品进行了分析和表征。获得了比较均匀的银纳米颗粒,加入TEOS后,在银纳米颗粒的周围包裹了一层二氧化硅膜,形成分散性较好的Ag@SiO2纳米颗粒。通过吡啶分子来探测不同SiO2厚度的Ag@SiO2的包裹致密性以及增强效果,选出增强效果最好的Ag@SiO2作为SERS基底,并把它运用于检测农药的残留问题。实验结果表明当加入1!L的TEOS时形成的Ag@SiO2纳米颗粒包裹得均匀致密并且拉曼增强效果很好。     

The influence of the shell on magnetic properties of CdS: Mn/SiO<Subscript>2</Subscript> composite nanoparticles

Silica-coated Mn-doped CdS nanocrystals were synthesized by use of a reverse-micelle method. Transmission electron microscopy, X-ray diffraction and electron paramagnetic resonance were adopted to characterize the samples, and their magnetic properties were studied via superconducting quantum interference device magnetometry. The samples exhibit anomalous ferromagnetic property at low temperature. The CdS: Mn nanocrystals dispersed in a silica matrix exhibit an obvious hysteresis loop shift toward the direction of the magnetic field; by contrast, the nanocrystals coated with compact SiO₂ shell layers display a symmetric hysteresis loop. The shell layers are supposed to be responsible for the distinct magnetic behaviors.     

Preparation of iron oxide nanocrystals by surfactant-free or oleic acid-assisted thermal decomposition of a Fe(III) alkoxide

A new non-hydrolytic, alkoxide-based route was developed to synthesize iron oxide nanocrystals. Surfactant-free thermal decomposition of the iron 2-methoxy-ethoxide precursors results in the formation of uniform iron oxide nanocrystals with an average size of 5.6 nm. Transmission electron microscope study shows that the nanocrystals are protected against aggregation by a repulsive surface layer, probably originating from the alkoxy-alkoxide ligands. Addition of oleic acid resulted in monodisperse nanocrystals with an average size of 4 nm. Mössbauer analysis confirmed that the nanocrystals mainly consisted of maghemite. Analysis of the magnetic hysteresis loop measurements and the zero field and field cooled measurements displayed an excellent fit to established theories for single-domain superparamagnetic nanocrystals and the size of the magnetic domains correlated well to the crystallite size obtained from transmission electron microscope.     

Rapid growth of magnetite nanoplates by ultrasonic irradiation at low temperature

Two-dimensional plate-like Fe(3)O(4) nanocrystals were synthesized by a facile method using ultrasonic irradiation in aqueous solution at low temperature without protection from oxygen. The crystals were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier Transform infrared spectroscopy. The products subjected to ultrasound showed a two-dimensional morphology. The results obtained indicate that the morphologies of the magnetite crystals depend more on the ultrasonic irradiation than on the growth temperature. The thickness and width of the crystals increased with increasing temperature of the reaction medium. In addition, the magnetic hysteresis loop of the magnetite nanoplates was obtained at room temperature.     

Size effects upon phase transitions in vanadium oxide nanocomposites

A phenomenological model has been proposed for the formation of the major thermal hysteresis loop of optical parameters upon the semiconductor-metal phase transition in vanadium oxide nanocomposites. It has been demonstrated that the effects associated with the influence of nanocrystallite sizes on the phase transition temperature in an individual nanocrystallite, which is determined by the width of the elementary hysteresis loop and the position of the phase equilibrium temperature on the temperature scale, manifest themselves in the form of pronounced features in the loop shape. In particular, the size effects for VO₂ polycrystalline films are observed in the formation of a trapezoidal shape of the optical thermal hysteresis loop with a wide lower base, whereas these effects for nanocomposites based on porous glasses with VO₂ nanocrystals are revealed in the form of the optical hysteresis loop with a narrow lower base (wide upper base). The proposed model also explains the symmetric shape of the major hysteresis loop for vanadium oxide nanocomposites based on opals. The size effects in opal nanocomposites with strictly fixed sizes of pores and, therefore, nanocrystallite sizes manifest themselves in the form of well-defined steps in the heating and cooling branches of the major hysteresis loop.     

磁性纳米级Fe3O4的氧气诱导、空气氧化液相合成与表征

氧气诱导、空气氧化液相合成出了粒径为20nm左右的磁性粉体Fe3O4。由X-ray衍射，红外光谱(IR)、透射电镜(TEM)及磁滞回线方法表征了粒子的结构组成。     

Preparation of water-soluble magnetite nanocrystals through hydrothermal approach

Water-soluble Fe₃O₄ nanocrystals have been prepared through hydrothermal approach. These nanocrystals capped with C₆H₆O₆ (the oxidation state of ascorbic acid) could be readily dispersed in hydrated aqueous systems. The final product was characterized with X-ray powder diffraction (XRD), transmission electron microscope (TEM), Fourier Transform Infrared and X-ray photoelectron spectroscopy. From XRD patterns, we confirm the product to be Fe₃O₄. The nanoparticles several nanometers long were well dispersed as shown in TEM image. Magnetic hysteresis loop measurements showed that the Fe₃O₄ nanocrystals display superparamagnetism. A possible formation mechanism of the Fe₃O₄ nanocrystals was suggested.     

Large melting-point hysteresis of Ge nanocrystals embedded in SiO2

The melting behavior of Ge nanocrystals embedded within SiO2 is evaluated using in situ transmission electron microscopy. The observed melting-point hysteresis is large (+/-17%) and nearly symmetric about the bulk melting point. This hysteresis is modeled successfully using classical nucleation theory without the need to invoke epitaxy.     

热分解法制备MnFe2O4纳米粒子及其超顺磁性

采用热分解法制备了单相的锰铁氧纳米颗粒,X射线衍射以及透射电镜测量显示其颗粒大小约为20 nm.磁滞回线测量显示室温超顺磁性.零场和非零场磁测量显示制备的MnFe2O4纳米粒子平均截止温度为84.3 K,样品中最大颗粒的截止温度为230 K,且平均截止温度与外场H2/3存在线性关系.     

Structural,magnetic, and dielectric properties of Ni–Zn ferrite and Bi_2O_3 nanocomposites prepared by the sol-gel method

Ni–Zn ferrite and Bi_2O_3 composites were developed by the sol-gel method. The structural, magnetic, and dielectric properties were studied for all the prepared samples. X-ray diffraction(XRD) was performed to study the crystal structure.The results of field emission scanning electron microscopy(FE-SEM) showed that the addition of Bi_2O_3 can increase the grain size of the Ni–Zn ferrite. Magnetic properties were analyzed by a hysteresis loop test and it was found that the saturation magnetization and coercivity decreased with the increase of Bi_2O_3 ratio. In addition, the dielectric properties of the Ni–Zn ferrite were also improved with the addition of Bi_2O_3.