Sol-flame synthesis of hybrid metal oxide nanowires

Hybrid metal oxide nanowires (NWs), with small characteristic diameter and large aspect ratio, can have unique and yet tunable chemical, optical and electrical properties by independently controlling the chemical compositions and morphologies of the individual components. Such hybrid NWs are promising building blocks in many applications, such as catalysis, sensors, batteries, solar cells and photoelectrochemical devices. However, these applications are hindered by the lack of scalable and economic methods for the synthesis of hybrid NWs. Here, we report a simple, scalable and new sol-flame method to synthesize various hybrid metal oxide NWs, including nanoparticle-shell decorated NWs (NP-shell@NW), NP-chain decorated NW (NP-chain@NW) and doped NWs. The sol-flame process first coats existing NWs with NPs or dopants precursors prepared by the sol–gel process, and then dissociates/oxidizes these precursors in flame. The sol-flame method uniquely combines the merits of the flame process (e.g., high temperature and fast heating rate) with low temperature sol–gel method (e.g., broad material choices and excellent chemical composition control). For both the NP-shell@NW and NP-chain@NW cases, the high temperature flame, compared to furnace, provides much faster heating rate and shorter duration for annealing, which evaporates and burns the precursor solvent rapidly, causing NPs to quickly nucleate around NWs without significant agglomeration. Hence, higher loading density of NPs with smaller sizes is decorated to the NWs, and the formed hybrid NP@NW exhibits significantly higher catalytic activity than that of the furnace-annealed sample. Similarly when using the sol-flame method to dope NWs, the high temperature flame enables rapid dopant diffusion and short annealing duration that maintains the morphology of the original materials and protects the delicate NW substrates from damage. We believe that the new sol-flame method can be applied to synthesize various 1-D hybrid metal oxide nanostructures, thereby impacting diverse application fields.     

Plasmonic nanoparticles and their analytical applications: A review

Plasmonic nanoparticles (NPs) have been reviewed herein for their fascinating optical properties in a wide spectral range and for their various applications. The surface plasmon resonance (SPR) bands of metal NPs can be tuned from visible to near infrared region by varying the shape of the metal NPs. As a result, the tuning of the SPR band over a spectral range is possible by making plasmonic NPs of different shapes. This review emphasizes fundamental studies of plasmonic NPs and nanocomposites with well-defined and controlled shapes that have several analytical applications such as molecular detection and determination in different fields. This review describes how oxidative etching and kinetic control can be utilized to manipulate the shape and optical properties of NPs. This review also describes the specific examples of the sensing applications of the localized surface plasmon resonance studies in which the researchers use both wavelength shift and surface-enhanced Raman scattering sensing to detect the molecules of chemical and biological relevance. The review ends with a perspective of the field, identifying the main challenges to be overcome and suggesting areas where the most promising developments are likely to happen in future.     

Optical Properties of Micro-patterned Silver Nanoparticle Substrates

In this paper, we describe a novel technique for depositing metal nanoparticles (NPs) on a planar substrate whereby the NPs are micro-patterned on the surface by a simple stamp-printing procedure. The method exploits the attractive force between negatively charged colloidal metal NPs and positively-charged polyelectrolyte layers which have been selectively deposited on the surface. Using this technique, large uniform areas of patterned metal NPs, with different plasmonic properties, were achieved by optimisation of the stamping process. We report the observation of unusual fluorescence emission from these structures. The emission was measured using epifluorescence microscopy. Fluorescence lifetime behaviour was also measured. Furthermore, the μ-patterned NPs exhibited blinking behaviour under 469 nm excitation and the fluorescence spectrum was multi-peaked. It has been established that the fluorescence is independent of the plasmon resonance properties of the NPs. As well as optimising the novel NP μ-patterning technique, this work discusses the origin and characteristics of the anomalous fluorescence behaviour in order to characterise and minimise this unwanted background contribution in the use of metal NPs for plasmonic enhancement of fluorescence for optical biochip applications.     

银纳米线表面等离激元波导的能量损耗

金属纳米结构的表面等离激元可以突破光学衍射极限,为光子器件的微型化和集成光学芯片的实现奠定基础.基于表面等离激元的各种基本光学元件已经研制出来.然而,由于金属结构的固有欧姆损耗以及向衬底的辐射损耗等,表面等离激元的传输能量损耗较大,极大地制约了其在纳米光子器件和回路中的应用.研究能量损耗的影响因素以及如何有效降低能量损耗对未来光子器件的实际应用具有重要意义.本文从纳米线表面等离激元的基本模式出发,介绍了它在不同条件下的场分布和传输特性,在此基础上着重讨论纳米线表面等离激元传输损耗的影响因素和测量方法以及目前常用的降低传输损耗的思路.最后给出总结以及如何进一步降低能量损耗方法的展望.表面等离激元能量损耗的相关研究对于纳米光子器件的设计和集成光子回路的构建有着重要作用.     

Deviating from the nanorod shape: Shape-dependent plasmonic properties of silver nanorice and nanocarrot structures

Noble metallic nanostructures exhibit special optical properties resulting from excitation of surface plasmons. Among the various metallic nanostructures, nanorods have attracted particular attention because of their unique and intriguing shape-dependent plasmonic properties. Nanorods can support transverse and longitudinal plasmon modes, the latter ones depending strongly on the aspect ratio of the nanorod. These modes can be routinely tuned from the visible to the near-infrared spectral regions. Although nanorods have been investigated extensively, there are few studies devoted to nanostructures deviating from the nanorod shape. This review provides an overview of recent progress in the development of two kinds of novel quasi-one-dimensional silver nanostructures, nanorice and nanocarrot, including their syntheses, crystalline characterizations, plasmonic property analyses, and performance in plasmonic sensing applications.     

金属微结构纳米线中等离激元传播和分光特性

本文从理论和实验两方面探讨了具有微结构的金属纳米线系统中表面等离激元传播规律和分光特性. 我们由麦克斯韦方程组出发, 利用严格耦合波近似和有限元差分等方法首先从理论上给出了金属纳米线系统中等离激元的色散关系和能带特征, 然后基于微结构的银纳米线及其等离激元能带结构, 设计并制备出等离激元分光原型器件, 实验展示其将不同频率的光在微小空间分离的特性. 该研究结果是我们前期相关工作的延续和补充, 可应用于构造多功能集成的光子芯片和新型亚波长光电材料和器件.     

Al纳米颗粒表面等离激元对ZnO光致发光增强的研究

基于聚苯乙烯球自组装法,在P型氮化镓(P-GaN)衬底上制备了有序致密的掩模板;采用热蒸发法在该模板上沉积金属Al薄膜,通过甲苯溶液去除聚苯乙烯球,得到了金属Al纳米颗粒阵列;采用原子层沉积法,在Al纳米颗粒阵列表面依次沉积氧化铝(Al_2O_3)和氧化锌(ZnO).通过测试Al纳米颗粒阵列的消光谱以及ZnO薄膜的光致发光谱,研究了Al纳米颗粒表面等离激元与ZnO薄膜激子之间的耦合效应.实验结果表明:引入Al纳米颗粒后,在约380 nm位置附近的ZnO近带边发光峰积分强度增强了1.91倍.对Al纳米颗粒表面等离激元增强ZnO光致发光的机理进行探讨.     

Nanowire plasmonic waveguides,circuits and devices

As typical one‐dimensional nanostructures for waveguiding tightly confined optical fields beyond the diffraction limit, metal nanowires have been used as versatile nanoscale building blocks for functional plasmonic and photonic structures and devices. Metal nanowires, especially those fabricated by bottom‐up synthesis such as Ag and Au nanowires, usually exhibit excellent diameter uniformity and surface smoothness with diameters down to tens of nanometers, which offers great opportunities for plasmonic waveguiding of optical fields with deep‐subwavelength confinement, coherence maintenance and low scattering losses. Based on nanowire plasmonic waveguides, a variety of applications ranging from plasmonic couplers, interferometers, resonators to photon emitters have been reported in recent years. In this article, significant progresses in these nanowire plasmonic waveguides, circuits and devices are reviewed. Future outlook and challenges are also discussed.     

Ultrathin silver‐coated gold nanoparticles as suitable substrate for surface‐enhanced Raman scattering

Surface‐enhanced Raman scattering (SERS) is an extremely powerful tool for the analysis of the composition of bimetallic nanoparticle (BNP) surfaces because of the different adsorption schemes adopted by several molecules on different metals, such as Au and Ag. The preparation of BNPs normally implies a change in the plasmonic properties of the core metal. However, for technological applications it could be interesting to synthesize core–shell structures preserving these original plasmonic properties. In this work, we present a facile method for coating colloidal gold nanoparticles (NPs) in solution with a very thin shell of silver. The resulting bimetallic Au@Ag system maintains the optical properties of gold but shows the chemical surface affinity of silver. The effectiveness of the coating method, as well as the progressive silver enrichment of the outermost part of the Au NPs, has been monitored through the SERS spectra of several species (chloride, luteolin, thiophenol and lucigenin), which show different behaviors on gold and silver surfaces. A growth mechanism of the Ag shell is proposed on the basis of the spectroscopic and microscopic data consisting in the formation and deposit of Ag clusters on the Au NP surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Oblique angle deposition and its applications in plasmonics

Plasmonics based on localized surface plasmon resonance （LSPR） has found many exciting appli- cations recently. Those applications usually require a good morphological and structural control of metallic nanostructures. Oblique angle deposition （OAD） has been demonstrated as a powerful technique for various plasmonic applications due to its advantages in controlling the size, shape, and composition of metallic nanostructures. In this review, we focus on the fabrication of metallic nanostructures by OAD and their applications in plasmonics. After a brief introduction to OAD technique, recent progress of applying OAD in fabricating noble metallic nanostructures for LSPR sensing, surface-enhanced Raman scattering, surface-enhanced infrared absorption, metal-enhanced fluorescence, and metamaterials, and their corresponding properties are reviewed. The future requirements for OAD plasmonics applications are also discussed.     

Synthesis,Morphological Control,and Properties of Silver Nanoparticles in Potential Applications

Nanostructured materials, especially nanoparticles (NPs), of noble metal NPs such as silver (Ag) have been the focus of research in recent decades because of their distinct physical, chemical, and biological properties. These materials have attracted considerable attention because of their potential applications, such as catalysis, biosensing, drug delivery, and nanodevice fabrication. Previous studies on Ag NPs have clearly demonstrated that their electromagnetic, optical, and catalytic properties are strongly influenced by their shape, size, and size distribution, which can be varied by using different synthetic methods, reducing agents, and stabilizers. The valuable optical properties of Ag NPs have allowed for new approaches in sensing and imaging applications, offering a wide range of detection modes, such as colorimetric, scattering, and surface‐enhanced Raman scattering techniques, at extremely low detection limits. Here, an overview of the various chemical, physical, and biological properties of Ag NP fabrication approaches to obtain the various shapes and sizes is presented.     

Tuning the optical properties of Fe-Au core-shell nanoparticles with spherical and spheroidal nanostructures

Present research interest is to highlight on the manufacturing of core-shell nanoparticles because of core activity with unique properties and surface modification by a shell in the diverse fields (e.g. optoelectronic, catalysis and magneto-optics). In addition, the combined optical properties of magnetic-plasmonic core-shell NPs make them ideal candidates for many applications in biomedical fields. The influence of Fe-core and Au-shell for the formation of the core-shell viz. spherical and spheroidal nanostructures is studied using the discrete dipole approximation method. DDA is an approximation method and its accuracy is compared to Mie theory results for spherical core-shell NPs as Mie theory gives the exact solution to spherical targeted NPs. DDA calculations are further extended to spheroidal core-shell nanostructures. It is observed that the localized surface plasmon resonance (LSPR) peak position in considered core-shell nanostructures is enhanced by changing the cores and shell thickness in the core-shell spherical nanostructures and aspect ratio as well as shell thickness in spheroidal core-shell nanostructures. The absorption spectra are found between 363–788 nm wavelength ranges and can be tuned into UV-visible-near-infrared region of the electromagnetic (EM) spectrum in accordance with desired applications. It has been found that the Fe@hollow@Au and prolate core-shell nanostructures show enhancement to LSPR peaks, bandwidth and their corresponding intensities in comparison to other considered spherical and spheroidal core-shell nanostructures. Tunability in core size, shell thickness, aspect ratio, and configuration will open new potential uses of suitable magnetic-plasmonic core-shell nanostructures in cancer therapy, tissue engineering, drug delivery, and many more of biomedical fields.     

Surface plasmon band tailoring of plasmonic nanostructure under the effect of water radiolysis by synchrotron radiation

Plasmonic metal nanostructures have a significant impact on a diverse domain of fields, including photocatalysis, antibacterial, drug vector, biosensors, photovoltaic cell, optical and electronic devices. Metal nanoparticles (MNps) are the simplest nanostructure promising ultrahigh stability, ease of manufacturing and tunable optical response. Silver nanoparticles (AgNp) dominate in the class of MNps because of their relatively high abundance, chemical activity and unique physical properties. Although MNps offer the desired physical properties, most of the synthesis and fabrication methods lag at the electronic grade due to an unbidden secondary product as a result of the direct chemical reduction process. In this paper, a facile protocol is presented for fabricating high‐yield in situ plasmonic AgNps under monochromatic X‐rays irradiation, without the use of any chemical reducing agent which prevents the formation of secondary products. The ascendancy of this protocol is to produce high quantitative yield with control over the reaction rate, particle size and localized surface plasmon resonance response, and also to provide the feasibility for in situ characterization. The role of X‐ray energy, beam flux and integrated dose towards the fabrication of plasmonic nanostructures has been studied. This experiment extends plasmonic research and provides avenues for upgrading production technologies of MNps.     

Anti-Reflection Characteristics of Si Nanowires for Enhanced Photoluminescence from CdTe/CdS Quantum Dots

CdTe/CdS quantum dots(QDs) are fabricated on Si nanowires(NWs) substrates with and without Au nanoparticles(NPs). The formation of Au NPs on Si NWs can be certified as shown in scanning electron microscopy images. The optical properties of samples are also investigated. It is interesting to find that the photoluminescence(PL) intensity of Cd Te/Cd S QD films on Si nanowire substrates with Au NPs is significantly increased,which can reach 8-fold higher than that of samples on planar Si without Au NPs. The results of finite-difference time-domain simulation indicate that Au NPs induce stronger localization of electric field and then boost the PL intensity of QDs nearby. Furthermore, the time-resolved luminescence decay curve shows the PL lifetime, which is about 5.5 ns at the emission peaks of QD films on planar, increasing from 1.8 ns of QD films on Si NWs to4.7 ns after introducing Au NPs into Si NWs.     

Immune recognition construct plasmonic dimer for SERS‐based bioassay

We have first time demonstrated the construction of a plasmonic gold dimer model for bioassays based on immune recognition with surface‐enhanced Raman scattering (SERS). To induce a strong plasmonic coupling effect, a dimer of gold nanoparticles (NPs) with a Raman label located between adjacent NPs is assembled through specific recognition in biological systems. One promising application for this model is the provision of a new type of in situ self‐calibrated and reliable SERS platform where biotinylated molecules can selectively be trapped by streptavidin and placed in the gap enhanced plasmonic field, which may enable the development of powerful, biospecific recognition‐based SERS assays. The capabilities of the dimeric constructions for analytical applications were demonstrated through the use of the SERS technique to detect biotin at very low concentrations. Additionally, the spatial SERS radiation for the gold dimer assembled on the silicon slide was simulated using the finite‐difference time‐domain method; this simulation demonstrated the distribution of the electric field as well as the utility of the proposed system, thereby introducing potential uses of bio‐specific recognition as well as opportunities for the construction of plasmonically coupled nanostructures and bioassay applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Au-MoOx nanoparticles for LSPR hydrogen detection prepared by a facile anodizing method

Nowadays, the plasmonic properties of defective transition metal oxides, have attracted great attention in the sensing and catalyst applications. The aim of this paper is to fabricate plasmonic Au-MoO_x nanoparticles (NPs) using a facile anodizing in liquid approach to be used as localized surface plasmon resonance (LSPR) hydrogen sensor. Firstly, dark blue MoO_x nanosheets with a strong NIR (700–800 nm) LSPR band were obtained. The Au-MoO_x NPs (Au size=5–7 nm) were then obtained by adding a gold cation into the blue MoO_x liquid base. Thanks to the catalytic properties of Au NP, this system exhibited LSPR hydrogen sensing ability where the LSPR variations allowed us to detect hydrogen in the 0–3% concentration range with a good linearity and possible many data points.     

Growth of undoped and Fe doped TiO2 nanostructures and their optical and photocatalytic properties

Undoped and Fe-doped TiO₂ nanostructures have been successfully grown on Pt-coated quartz and Si (100) substrates using vapor-liquid-solid (VLS) growth method. The scanning electron microscopy (SEM) image showed that TiO₂ grew in nanowires (NWs) with diameters of 200–400 nm and lengths greater than 12 μm. However, the morphology of Fe-doped TiO₂ consists of chunk shaped nanoparticles (NPs). The X-ray diffraction analysis for undoped TiO₂ NWs clearly showed the formation of tetragonal rutile TiO₂, whereas for the Fe-doped TiO₂ NPs it showed orthorhombic TiO₂ phase and there are no crystalline peaks for iron or iron oxide. The refractive index and extinction coefficient values of undoped and Fe-doped TiO₂ nanostructures were derived from the ellipsometric measurements. Enhanced photocatalytic activities were obtained for undoped and Fe-doped TiO₂ nanostructures. The obtained results may find potential applications in optical devices and degradation of organic wastes.     

Metal Nanoparticle Photocatalysts: Synthesis,Characterization, and Application

Metal nanoparticles (NPs) have emerged as a kind of new photocatalyst to drive various chemical reactions by visible‐light irradiation. A distinct advantage of metal NP photocatalysts is that their light absorption is not limited to a certain wavelength but instead they are able to utilize a broad range of wavelengths, constituting a large fraction of the solar spectrum. Metal NPs like gold, silver, and copper NPs can strongly absorb visible light due to the localized surface plasmon resonance (LSPR) effect. Recent developments have shown that the light absorption properties strongly depend on the shape, size, and particle–particle interactions of NPs, which directly influence their photocatalytic activities. In this review, an overview of the preparation of metal NPs photocatalysts with various morphologies is given along with a brief discussion of the relationship between the morphology/composition and optical properties. The latest photocatalytic applications of these morphologies are also presented, and some of the challenges for the development of metal NPs photocatalysts are provided.     

Plasmas meet plasmonics

The term ‘plasmon’ was first coined in 1956 to describe collective electronic oscillations in solids which were very similar to electronic oscillations/surface waves in a plasma discharge (effectively the same formulae can be used to describe the frequencies of these physical phenomena). Surface waves originating in a plasma were initially considered to be just a tool for basic research, until they were successfully used for the generation of large-area plasmas for nanoscale materials synthesis and processing. To demonstrate the synergies between ‘plasmons’ and ‘plasmas’, these large-area plasmas can be used to make plasmonic nanostructures which functionally enhance a range of emerging devices. The incorporation of plasma-fabricated metal-based nanostructures into plasmonic devices is the missing link needed to bridge not only surface waves from traditional plasma physics and surface plasmons from optics, but also, more topically, macroscopic gaseous and nanoscale metal plasmas. This article first presents a brief review of surface waves and surface plasmons, then describe how these areas of research may be linked through Plasma Nanoscience showing, by closely looking at the essential physics as well as current and future applications, how everything old, is new, once again.     

十字形银纳米结构的表面等离子体光子学性质

本文应用离散偶极子近似方法计算了十字形银纳米结构的消光光谱及其近场电场强度分布. 研究表明相比于单根纳米棒, 十字形纳米结构能够提供更强的表面电场; 由于相邻凸起间的电场耦合作用, 当入射光的偏振方向改变时, 在十字形纳米结构的侧表面总能激发出较强的电场.另外, 本文还系统地研究了十字形纳米结构的形貌参数对其表面等离子体共振峰的影响. 这些结果将会指导十字形纳米结构的制备, 以满足其在表面增强拉曼散射中的应用.