不同制备条件对聚偏氟乙烯纳米线生长的影响

为提高铁电聚合物聚偏氟乙烯(PVDF)的压电性能,利用纳米限域效应,采用模板直接浸润法,将多孔氧化铝(AAO)模板在不同浓度的PVDF的DMF溶液中自然浸润,并添加聚乙烯吡咯烷酮(PVP)作为表面修饰剂,制备了一维材料PVDF纳米线。分别研究了浸润温度、溶液浓度及表面修饰剂等因素对PVDF纳米线生长过程的影响。通过FTIR、SEM、XRD等对样品的形貌结构及性能进行了表征,进一步讨论了AAO模板中PVDF纳米线的生长机制。结果表明:模板法生长的PVDF纳米线形貌主要受溶液浓度的影响,并且当浓度为0.10 g/m L时形貌较优,其平均长度为50μm,平均直径为180 nm,与AAO模板孔径尺寸相当;表面修饰剂PVP可在一定程度上防止纳米线团聚并且优化其尺寸均一性;AAO模板中生长的PVDF纳米线由于纳米限域效应优先向β晶相结晶,并且在生长过程中PVDF并未参与任何化学反应。     

绿色合成银纳米粒子及其在SERS中的应用

采用无毒、绿色的酪氨酸作为还原剂和稳定剂,在碱性条件下还原硝酸银,经60 ℃恒温水浴处理20 min,成功地合成了银纳米粒子。混合溶液颜色由淡黄色变为棕黄色直观地呈现了银纳米粒子的生成。利用紫外可见吸收光谱(UV-Vis)和透射电子显微镜(TEM)对制备样品进行分析和表征。粒子的UV-Vis吸收在412 nm附近。TEM图像显示,银纳米粒子的形状近似球形,粒子直径在15～25 nm。分别以结晶紫(CV)和叶酸(FA)为探测分子,进一步研究了该银纳米粒子的表面增强拉曼散射(SERS)效应。实验结果表明,该合成方法不仅方便、快速、绿色环保,而且合成的银纳米粒子对CV和FA分子有很好的SERS效应。     

AlN纳米线宏观阵列的制备

借助二次模板法成功的合成了AlN纳米线宏观阵列,并进行了表征.主要研究CVD法制备有一定取向,直径均匀的AlN纳米线宏观阵列的过程.通过气相沉积法和利用PS球自组装模板制备了金属纳米颗粒模板;再以模板上的金属纳米颗粒作为催化剂,利用化学气相沉积在模板上合成AlN纳米线宏观阵列.借助SEM,TEM观察所得样品,AlN纳米线阵列面积约为0.3 mm×0.2 mm,直径和长度分布均匀,平均直径约为41 nm,平均长度为1.8 μm左右,分散密度和覆盖率大的六角结构AlN纳米线宏观阵列.得到了可控制备AlN纳米线 关键词： AlN纳米线阵列 模板法 CVD法 SEM     

低温条件下单晶氮化铝纳米线生长机理的研究

在25mL的不锈钢反应釜中，利用无水三氯化铝与叠氮化钠在无溶剂的条件下直接反应，成功地合成出了单晶氮化铝纳米线，反应温度为450℃，有效反应时间为24h.高分辨率透射电子显微镜测试结果显示，纳米线多为长直线状外貌特征，直径在40—60nm范围内，最大长度可达几个微米.高分辨率电子衍射和X射线衍射结果都表明，多数纳米线为六方结构，也有少量呈现面心立方结构.同时，提出了长直线状六方和面心立方单晶氮化铝纳米线的生长机理的假设，并对六方单晶氮化铝纳米线生长方向的人工控制也进行了讨论. 关键词： 六方单晶氮化铝 纳米线 X射线衍射 透射电子显微镜     

表面活性剂辅助固相法合成碘化银纳米线束与光谱表征

卤化银具有光致变色特性,广泛应用于光致变色玻璃,照相感光乳剂等。作为一种光信息载体,具有记录和保存光信息的功能,它还是一类重要的半导体光催化剂,有着广泛的应用。以AgNO3与KI为原料,在非离子表面活性剂聚乙二醇(PEG-400)存在条件下,进行室温固相反应,合成了碘化银纳米线束。采用XRD,TEM和SEM等测试手段对产物结构和形貌进行表征,结果表明,产物为一维碘化银纳米线束,其直径在80～100nm之间,长度约为20μm,长径比>200。表面活性剂PEG-400在碘化银纳米线束的形成过程中起到了软模板剂的作用,诱导产物纳米晶沿着某一特定方向定向有序生长从而生成纳米线束。该方法消除了水对反应过程的影响,操作简单,成本较低,对碘化银纳米线束的制备技术研究具有重要意义。     

阳离子表面活性剂对液相银纳米微粒吸收光谱的影响

粒径为20 nm的黄色银纳米微粒在400 nm处有一吸收峰,当加入阳离子表面活性剂(CS)的浓度较低时,A_{400 nm}减小,波长大于400 nm以上的吸收增大且体系的吸收峰发生红;当CS浓度较高时,波长大于400 nm以上的吸收减小,而在400 nm处的吸收增大,体系的吸收峰发生蓝移。研究表明这是由于CS与带负电荷的银纳米存在较强的疏水和静电作用而导致银纳米微粒形貌的改变所致。     

化学镀制备镍纳米线/管阵列铂钯催化剂载体

以阳极氧化铝作为模板,用化学镀的方法制备了可以用作铂钯复合催化剂载体的镍纳米线和纳米管阵列,利用置换反应将铂钯复合催化剂沉积在镍纳米阵列材料上．SEM图片表明镍纳米线的平均直径 为100 nm,镍纳米管的平均内径为20 nm． EDS扫描的结果表明铂钯元素均匀地分布在阵列材料上．循环伏安研究发现载有铂钯催化剂的镍纳米管阵列对乙醇氧化的电催化活性明显高于载有铂钯催化剂的镍纳米线阵列．     

氧化镁纳米分级结构的合成及生长机理分析

采用气相合成技术合成了MgO三维纳米分级结构.该结构由纳米线、纳米棒、纳米丝3部分组成.高分辨电镜照片显示第一级纳米线的生长方向为[100],纳米棒与纳米丝呈四次对称分布在纳米线的侧面,其生长方向为[110].沉积区的高温和适当的反应物对三维分级纳米结构的形成起了决定性作用,气固生长模式和气液固生长模式共同主导了三维分级纳米结构形成.     

非晶碳氧化硅纳米线的合成与光致发光

利用直流电弧放电合成非晶碳氧化硅(SiCO)纳米线,不使用催化剂和模板,独立的SiCO 纳米线沉积在石墨锅的表面．通过XRD、SEM、TEM、XPS、FTIR等对SiCO纳米线进行了表征．结果表明,纳米线长度为20～100 μm,直径为10～100 nm,Si原子同C原子和氧原子分享成键组成SiCO单元．SiCO纳米线的光致发光谱在454和540 nm呈现了强而稳定的白色发光峰． SiCO纳米线的生长机制为等离子辅助气―固生长机制．     

纳米银胶中PVP和Alq3的荧光猝灭研究

本文通过湿法化学还原法合成了平均粒径为4.42nm、标准差为0.98nm的球形银纳米颗粒,并研究了在不同反应时间后获得的银纳米颗粒对PVP和Alq3的荧光猝灭效应。通过深入研究发现,PVP的荧光猝灭效应主要由于其分子链上的酮基与Ag颗粒之间发生了静电吸附,进而导致处在激发态的PVP分子与银颗粒之间产生电子或者能量转移(即非辐射弛豫),猝灭了PVP的荧光发光;而Alq3的荧光猝灭效应则主要归因于银纳米颗粒的欧姆损耗。通过采用时域有限差分法进行模拟发现,溶液中随机分布的银纳米颗粒,不仅能够吸收激发电磁波,削弱激发场强度,而且能够吸收荧光分子辐射的电磁波,进而猝灭了Alq3分子的荧光效应。这些研究成果将有利于了解金属纳米颗粒与PVP及Alq3分子荧光发光之间的关系,为调控荧光发光提供指导。     

Critical diameters and temperature domains for MBE growth of III–V nanowires on lattice mismatched substrates

We report on the growth properties of InAs, InP and GaAs nanowires (NWs) on different lattice mismatched substrates, in particular, on Si(111), during Au‐assisted molecular beam epitaxy (MBE). We show that the critical diameter for the epitaxial growth of dislocation‐free III–V NWs decreases as the lattice mismatch increases and equals 24 nm for InAs NWs on Si(111), 39 nm for InP NWs on Si(111), 44 nm for InAs NWs on GaAs(111)B, and 110 nm for GaAs NWs on Si(111). When the diameters exceed these critical values, the NWs are dislocated or do not grow at all. The corresponding temperature domains for NW growth extend from 320 °C to 340 °C for InAs NWs on Si(111), 330 °C to 360 °C for InP NWs on Si(111), 370 °C to 420 °C for InAs NWs on GaAs(111)B and 380 °C to 540 °C for GaAs NWs on Si(111). Experimental values for critical diameters are compared to the previous findings and are discussed within the frame of a theoretical model. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and characterization of the transparent nanocomposite mirror film for the infrared region by sol–gel method

Transparent mirror coated, SiO₂–Ag/PV P nanocomposites were prepared on the Pyrex glass slides by dip-coating technique. Embedding of the silver (Ag) nanoparticles on silica modified polyvinyl pyrrolidone (PVP) was performed by the sol–gel method. As prepared transparent mirror coated SiO₂–Ag/PV P nanocomposite films were finally characterized for surface morphology, chemistry, and nano size dimensions using various advanced analytical techniques including, UV visible, Fourier transform, infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), dispersive x-ray analaysis (EDAX) and transmission electron microscopy (TEM) analysis. It was found that all the prepared samples were almost uniform particles of Ag nanospheres of 7–8 nm diameters arranged as double paralleled nanowires with an average length of 200–450 nm and diameters of around 20–25 nm.     

Preparation and characterization of Ag nanoparticle-embedded polymer electrospun nanofibers

Poly (vinyl alcohol) (PVA) and poly (vinyl pyrrolidone) (PVP) nanofibers embedding Ag nanoparticles (5–18 nm) have been prepared successfully by electrospinning at room temperature. Scanning electron microscope (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier transform IR spectra (FTIR), and Raman scattering were used to characterize the structure and properties of Ag nanoparticle-embedded PVA and PVP nanofibers before and after heat treatment at different temperature. The antibacterial activity of Ag nanoparticle-embedded PVP nanofibers after heat treatment was also tested, which indicated that the biological activity of yeast cells was effectively inhibited by these Ag nanoparticle-embedded PVP nanofibers.     

The synthesis of Ag/polypyrrole coaxial nanocables via ion adsorption method using different oxidants

Ag/polypyrrole (PPy) coaxial nanocables (NCs) were synthesized by an ion adsorption method. In this method, the pre-made Ag nanowires (NWs) were dispersed in the aqueous solution of copper acetate (Cu(Ac)₂), and the Cu²⁺ ions adsorbed onto the surface of Ag NWs can oxidize pyrrole monomers to polymerize into uniform PPy sheath outside Ag NWs after the Cu(Ac)₂-treated Ag NWs were re-dispersed in the aqueous solution of pyrrole. The morphology of NCs was characterized by transmission electron microscope (TEM) and scanning electron microscope (SEM). The relationship between the thickness of polymer sheath and the concentration of Cu(Ac)₂ was established. As Cu(Ac)₂ which served as the oxidant can also be replaced by AgNO₃ in this synthesis, the differences on the structure of polymer sheath caused by different oxidants were studied by surface-enhanced Raman scattering (SERS), high-resolution transmission electron microscope (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Comparing with the characterization results of Ag/PPy NCs synthesized using AgNO₃ as the oxidant which indicates the random arrangement of PPy chains at the interface between polymer sheath and Ag NWs, PPy chain oxidized by Cu²⁺ tends to show a relatively ordered conformation at the interface with the pyrrole rings identically taking the plane vertical to the surface of Ag NWs. In addition, although the main part of the polymer sheath was composed of PPy whatever kind of oxidant was used, the sheath of the NCs oxidized by Cu²⁺ is typical for the existence of Cu(I)–pyrrole coordinate structures with strong Cu(I)–N bond signal shown in XPS characterization.     

Arrays of ordered Ag nanowires with different diameters in different areas embedded in one piece of anodic alumina membrane

Nanochannel arrays with the same nanochannel density but different nanochannel diameters in different areas in one piece of anodic alumina membrane had been created. SEM observations on one piece of this type of anodic alumina membrane show that the nanochannel diameters radially decrease from 80 nm to 60 nm and to 40 nm along the radial direction. Therefore, using this type of membrane as a template, ordered Ag nanowire arrays with the same nanowire density but with diameters decreasing radially were obtained by electrodeposition. SEM and TEM images taken of different areas of the Ag nanowire arrays show that we can control the growth of aligned Ag nanowires with different diameters in a single process at the same time. Using this type of template in combination with other fabrication techniques, nanometer-scale fibrils, rods, wires, and tubules of metal, semiconductors, carbon, and other materials with same density but different diameters in different areas can be fabricated. The simultaneous integration of ordered nanowire structures with different diameters embedded in a single anodic alumina membrane could be useful in nanodevice manufacture as well as electronics, optoelectronics and magnetics. PACS 81.05.Bx; 82.80.Fk; 85.30.Vw     

Size-dependent transformation from Ag templates to Au–Ag nanoshells via galvanic replacement reaction in organic medium

The transformation from Ag templates to Au?CAg nanoshells via galvanic replacement reaction with HAuCl₄ was systematically studied in an organic medium in the presence of oleylamine. Decahedral (~43?nm in size) and triangular prism (~53?nm in edge length) Ag templates transformed into equiaxed and triangular prismatic Au?CAg nanoshells, respectively. The first step involved structural and morphological changes from Ag templates to Au?CAg nanoshells with an interior cavity. In the second step, the growth of the shells continued through the deposition of Au. The shell thickness increased from ~5 to ~10?nm for the equiaxed Au?CAg nanoshells (~39-nm interior cavity) and ~5 to ~8?nm for the triangular prismatic Au?CAg nanoshells (~52-nm interior edge length). Oleylamine not only served as a surfactant but also removed AgCl precipitates and reduced HAuCl₄. For the nanoshells derived from the ~20-nm Ag decahedrons, further reaction in excess HAuCl₄ collapsed the nanoshells into Au-rich solid fragments. However, the nanoshells derived from the ~43-nm Ag decahedrons, the nanoshell structure not only persisted in excess HAuCl₄, but its shell thickness also increased. The size-dependent transformation of these nanoshells is discussed.     

Tuning the growth of ZnO nanowires

ZnO nanowires (NWs) with different diameters were obtained by controlling the particles of ZnO sub-layer (SL) exploring hydrothermal method; the diameter of the epitaxial NWs could be tuned from 60 to 146 nm when using SL with a thickness of 70 nm. The thickness of the SL would influence the orientation of the NWs. The top agglomerate NWs could be formed on the SL with a thickness of 10 nm, and the NWs with better orientation were obtained using SL with a thickness of 70 nm. Well aligned ZnO NWs grew perpendicular to the completely stress released SL. The diameter of the NWs was also greatly influenced by the solution concentration; thus ultra fine (diameter∼11 nm) ZnO NWs were obtained through adjusting the solution concentration to 0.001 mol/L. Through our research, we also found that the growth rate of the NWs could also be influenced by the different polarity surface of the SL. In other words, the size of the ZnO NWs could be tuned exactly under optimal conditions.     

Observation of nonlinear saturable and reverse-saturable absorption in silver nanowires and their silica gel glass composite

Silver nanowires (Ag NWs) and their silica gel glass composite were produced. Their nonlinear optical (NLO) properties, mainly saturable absorption (SA) and reverse-saturable absorption (RSA), were investigated at 532 and 1064 nm, using the open aperture z-scan technique and a nanosecond-pulsed laser. We found that Ag NWs demonstrate rather different NLO behaviors in liquid and solid-state matrices. The Ag NWs suspension exhibited only RSA, whereas a transformation from SA to RSA occurred in the silica gel glass composite. The underlying mechanism was proposed from the viewpoint of different environments and electronic dynamics of Ag NWs in the liquid and solid-state matrices.     

基于聚合物的橄榄球形光学微谐振器

利用苯二甲酸丙二醇酯(PTT)聚合物微米线从生物相容性聚合物材料聚乙烯吡咯烷酮(PVP)水溶液中提拉制备得到直径为10～300μm的橄榄球形光学微谐振器。将波长为532nm的绿光和波长为671nm的红光分别耦合到最大直径为94.7μm和68.3μm的橄榄球形微谐振器,观察了其谐振特性。利用1549～1552nm的连续光源对直径为94.7μm的橄榄球形微谐振器进行了光学性能测试,测量了其吸收光谱。观察到明显的回音壁模式吸收峰,测得其品质因子为1.05×105。     

Electron microscopy investigations of the organization of cerium oxide nanocrystallites and polymers developed in polyvinylpyrrolidone-assisted polyol synthesis process

The microstructures and the organization mechanism of cerium oxide (ceria) nanospheres were investigated by transmission electron microscopy. The ceria nanospheres with the diameter of 50–150 nm were produced by the polyol synthesis method with cerium nitrate precursor and with polyvinylpyrrolidone (PVP) used as a protecting agent. Dose-limited observations performed by energy-filtering transmission electron microscopy revealed that the ceria nanospheres were the aggregated products consisting of ceria nanocrystallites ~3 nm in size and PVP-derived polymer products. It was found that the ceria nanocrystallites were oriented within the nanospheres by high-resolution transmission electron microscopy and selected-area electron diffraction. Selective adsorption of PVP on the crystal facets of the ceria nanocrystallites was suggested, and the aggregation of the PVP-adsorbed ceria through cross-linking reaction of PVP causes the crystal orientation.