Plasmonic films based on colloidal lithography

This paper reviews recent advances in the field of plasmonic films fabricated by colloidal lithography. Compared with conventional lithography techniques such as electron beam lithography and focused ion beam lithography, the unconventional colloidal lithography technique with advantages of low-cost and high-throughput has made the fabrication process more efficient, and moreover brought out novel films that show remarkable surface plasmon features. These plasmonic films include those with nanohole arrays, nanovoid arrays and nanoshell arrays with precisely controlled shapes, sizes, and spacing. Based on these novel nanostructures, optical and sensing performances can be greatly enhanced. The introduction of colloidal lithography provides not only efficient fabrication processes but also plasmonic films with unique nanostructures, which are difficult to be fabricated by conventional lithography techniques.     

Bimetallic gold–silver nanoplate array as a highly active SERS substrate for detection of streptavidin/biotin assemblies

The silver-modified gold nanoplate arrays as bimetallic surface-enhanced Raman scattering (SERS) substrates were optimized for the surface-enhanced Raman detection of streptavidin/biotin monolayer assemblies. The bimetallic gold–silver nanoplate arrays were fabricated by coating silver nanoparticles uniformly on the gold nanoplate arrays. Depending on silver nanoparticle coating, the localized surface plasmon resonance (LSPR) peak of the bimetallic gold–silver nanoplate arrays blue-shifted and broadened significantly. The common probe molecule, Niel Blue A sulfate (NBA) was used for testing the SERS activity of the bimetallic gold–silver nanoplate arrays. The SERS intensity increased with the silver nanoparticle coating, due to a large number of hot spots and nanoparticle interfaces. The platforms were tested against a monolayer of streptavidin functionalized over the bimetallic gold–silver nanoplate arrays showing that good quality spectra could be acquired with a short acquisition time. The supramolecular interaction between streptavidin (strep) and biotin showed subsequent modification of Raman spectra that implied a change of the secondary structure of the host biomolecule. And the detection concentration for biotin by this method was as low as 1.0 nM. The enhanced SERS performance of such bimetallic gold–silver nanoplate arrays could spur further interest in the integration of highly sensitive biosensors for rapid, nondestructive, and quantitative bioanalysis, particularly in microfluidics.     

Synthesis of silver nanoprisms in formamide

Polygonal (mainly triangular) silver nanoprisms were prepared by reducing silver perchlorate in formamide in the presence of polyethylene glycol (PEG) at room temperature. The reduction of silver ions by formamide leads to the deposition of arrays of triangular shaped silver nanoparticles on the glass walls of the container, accompanied by evolution of CO2 gas. In the presence of poly(N-vinyl-2-pyrrolidone) (PVP) and PEG (1:1), both nanospheres and nanoprisms are formed.     

Mini-pillar Based Multi-channel Electrochemical Platform for Studying the Multifactor Silver Electrodeposition

Here, we demonstrated a mini-pillar based multi-channel electrochemical platform that can efficiently adjust multiple electrochemical deposition parameters in the microdroplet arrays to control and predict the final structures of silver nanomaterials. Each mini-pillar is capable of anchoring microdroplet to form a separate microreactor, and the electrodes are integrated to achieve a multi-channel electrochemical electrodeposition platform. We systematically investigated the multiple deposition parameters of silver nanostructures and summarized the relevant experience of electrochemical silver deposition to guide silver nanostructure preparation. Such the mini-pillar based microdroplet platform provides an approach for further high-throughput and intelligent nanomaterial fabrication.     

银纳米粒子簇的设计、 制备和表面增强拉曼光谱

通过匹配激光光斑直径与胶体微球的尺寸, 设计制备了银纳米粒子的表面增强拉曼散射(SERS)基底, 并将其用于研究单个银纳米粒子簇的表面增强拉曼光谱. 在制备纳米粒子的过程中, 考察了等离子体刻蚀时间与银沉积厚度对“单”银纳米粒子结构与形貌的影响. 将吡啶、 巯基苯和罗丹明R6G作为SERS探针分子, 研究了其SERS效应, 通过荧光共振能量转移(FRET)机理, 实现了染料分子在单银纳米粒子簇上的SERS效应. SERS光谱测试与相关计算结果表明, 单个银纳米粒子簇的拉曼增强因子能够达到约10⁶.     

The optically detected coherent lattice oscillations in silver and gold monolayer periodic nanoprism arrays: the effect of interparticle coupling

Using femtosecond transient spectroscopy, we studied the optically detected laser-induced coherent phonon oscillation of monolayers of periodic arrays of prismatic-shaped silver and gold nanoparticles, assembled by using the technique of nanosphere lithography. In this method, the same size of polystyrene sphere and the same vacuum conditions are used. Under these circumstances, the gold nanoprisms formed are found to have sharper tips than the corresponding silver nanoprisms. For both gold and silver nanoparticles, the surface plasmon absorption maximum is found to depend linearly on size. The coherent lattice oscillation periods are also found to depend linearly on size. However, although the observed dependence for the silver nanoparticle is found to follow the calculated dependence of a single particle on size (based on a one-dimensional standing wave model), the gold nanoparticle deviates from this model, and the deviation is found to increase with the size of the nanoparticles. This deviation can be explained by considering interparticle coupling. A simple interparticle lattice oscillating dipolar coupling model of the dimer is found to qualitatively account for both the sign and the size dependence of the deviation. The absence of this deviation in the silver nanoparticle arrays is blamed on the weak interparticle coupling due to their rounded tips and the possibility of oxidation of their surfaces.     

Second harmonic excitation spectroscopy of silver nanoparticle arrays

Frequency-scanned excitation profiles of coherent second harmonic generation (SHG) were measured for silver nanoparticle arrays prepared by nanosphere lithography. The frequency of the fundamental beam did not coincide with the localized surface plasmon resonance (LSPR) of the nanoparticles and was tuned so that the coherent second harmonic (SH) emission was in the region of the LSPR at 720-750 nm. The SH emission from the arrays was compared with a smooth silver film to identify an enhancement of SH emission efficiency that peaks near approximately 650 nm for nanoparticles 50 nm in height. The polarization and orientation dependence of this enhancement suggests that it is related to a dipolar LSPR mode polarized normal to the plane of the substrate. Linear extinction spectra are dominated by in-plane dipoles and do not show this weak out-of-plane LSPR mode. The nanoparticle arrays are truncated tetrahedrons symmetrically oriented by nanosphere lithography to cancel SH from in-plane dipoles which allows observation of the weak out-of-plane component.     

Fabrication of superhydrophobic polymer films with hierarchical silver microbowl array structures

Flexible superhydrophobic polyvinyl alcohol (PVA) films with silver bowl-like array structure are fabricated based on the thermal evaporation with sphere monolayer as templates and the modification of 1H, 1H, 2H, 2H-perfluorodecanethiol on silver surface. The silver microbowl arrays were composed of silver nanoparticles with an average diameter size of ca. 10 nm. The polymer films exhibit excellent stability and remarkable superhydrophobicity with a high water contact angle (CA) of about 163° and a low sliding angle (SA) of less than 3°.     

SiO2-TiO2中空型界面光催化剂的制备及性能

采用十八烷基三乙氧基硅烷对TiO2和核壳中空型纳米粒子SiO2-TiO2进行了壳表面疏水烷基化修饰,制备出新型界面光催化剂,并用IR和XRD进行表征.在紫外光照射下,考察了两种界面光催化剂的光稳定性,并以弱酸性黄G溶液的界面光降解为模型反应,考察了催化剂的光催化活性.结果表明,长链烷基成功接枝在了两种纳米粒子表面,且改性前后晶型无变化.与TiO2界面光催化剂相比,SiO2-TiO2界面光催化剂不仅具有优异的界面光稳定性,同时在无搅拌状态下对弱酸性黄G溶液也有良好的光催化活性.     

利用去湿现象制备具有SERS活性的银纳米粒子图案

构建了具有表面增强拉曼散射(SERS)活性的二维有序环状与盘状的银纳米粒子结构, 利用CTAB包覆银纳米粒子的氯仿溶液直接在图案化的金基底上进行去湿, 当改变银纳米粒子的浓度时可以得到不同的图案. 利用原子力显微镜(AFM)对其结构进行了表征, 以4-巯基吡啶作为探针分子, 采用表面增强拉曼成像技术研究了这种基底的SERS活性, 这将为SERS的研究开拓新的领域.     

Redox-induced synthesis and encapsulation of metal nanoparticles in shell-cross-linked organometallic nanotubes

A new approach to encapsulate silver nanoparticles inside block copolymer nanotubes is reported and involves an in situ redox reaction between a polyferrocenylsilane (PFS) inner wall and silver ions. Partial preoxidation of the PFS domains was found to be a key step for the efficient formation of one-dimensional arrays of silver nanoparticles confined within the nanotubes.     

Electromagnetic interactions in plasmonic nanoparticle arrays

Single two-dimensional planar silver arrays and one-dimensional linear gold chains of nanoparticles were investigated by dark-field surface plasmon spectroscopy and studied as a function of interparticle distance, particle size, and number of particles. In agreement with recent theoretical predictions, a red shift of the surface plasmon resonance occurring in two-dimensional arrays was found for lattice spacings below 200 nm. This red shift is associated with a significant broadening of the resonance and is attributed to the onset of near-field interactions. We found that the relative contributions of the long-range and short-range interactions in two-dimensional arrays of particles are fundamentally different to those occurring in individual linear chains.     

Hierarchical self-assembly of silver nanocluster arrays on triblock copolymer templates

Poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer templates which present in-plane cylinders of polystyrene (PS) aligned parallel to the plane of the substrate have been prepared by a solvent-induced order-disorder phase transition method. Silver nanoclusters have been obliquely deposited onto the SBS copolymer templates at low coverage, utilizing the directed low-energy cluster beam deposition (LECBD) method. The morphology of the samples has been characterized by a tapping-mode AFM. It is shown that the silver nanoclusters form ordered linear arrays and the intercluster distance within each individual linear array is comparable to the cluster size. Optical absorption spectra indicate that the surface plasmon resonance (SPR) of the silver nanocluster linear arrays occurs at about 444.5 nm, manifesting a red shift of approximately 21.4 nm compared to the SPR absorption of silver nanoclusters deposited on a fused quartz substrate. This is attributed mainly to the near-field electrodynamic interactions between the silver nanoclusters. This hierarchical approach to create ordered nanostructures transcends the spatial limits of lithography and provides a promising route to achieve well-ordered cluster-based nanostructures.     

Narrow plasmonic/photonic extinction and scattering line shapes for one and two dimensional silver nanoparticle arrays

The interaction of light with silver nanoparticle arrays can in some cases produce mixed plasmonic/photonic bands that have extremely narrow (<1 meV) line shapes in extinction and scattering. In this paper we extend computational electrodynamics results of a recent communication [S. Zou, N. Janel, and G. C. Schatz, J. Chem. Phys. 120, 10871 (2004)] where this effect was first described to study how these narrow bands are influenced by a number of structural factors, and to determine how useful these arrays might be for sensing applications. Included are studies of the effect of disorder in the array structure on plasmon intensity and width, of the effect of orientation of the array relative to the polarization and propagation direction of the incident light, and of the effect of particle shape (comparing results for silver spheres and cylindrical disks). Our results show that the narrow lines are remarkably robust to array disorder, but vacancy defects can easily destroy the effect. The narrowest lines are associated with one dimensional arrays in which both polarization and wave vectors are perpendicular to the array axis. For two dimensional arrays, the narrowest lines are associated with the wave vector perpendicular to the plane of the array and polarization in the plane. Arrays composed of oblate cylinders generate more intense and more redshifted plasmon/photonic peaks than do prolate or spherical particles under comparable conditions. Finally, for sensing applications in which analyte binding is determined by the plasmon wavelength shift associated with change in the surface refractive index, we show that the arrays have greater sensitivity than isolated nanoparticles.     

Surface-enhanced Raman scattering from helical silver nanorod arrays

Helical silver nanorod arrays with different arm numbers are designed by oblique angle deposition and their surface-enhanced Raman scattering properties are characterized. Assuming that the hot spots are located at the bends between the arms, and considering the optical absorbance of different layers, the SERS behavior can be predicted qualitatively.     

Silver nanoparticles capped by oleylamine: formation, growth, and self-organization

Nearly monodisperse silver nanoparticles have been prepared in a simple oleylamine-liquid paraffin system. Intensive study has found that the formation process of silver nanoparticles could be divided into three stages: growth, incubation, and Ostwald ripening stages. Ultraviolet-visible spectroscopy, transmission electron microscopy (TEM), and high-resolution TEM have all demonstrated the occurrence of Ostwald ripening, which could result in better control over the size and size distribution of silver nanoparticles. SAXS (small-angle X-ray scattering) results show that the as-obtained silver nanoparticles can self-assemble into ordered arrays. The possible reduction mechanism of silver ions by oleylamine is related to the Ag+-mediated conversion of primary amines to nitriles.     

Growth of ordered silver nanoparticles in silica film mesostructured with a triblock copolymer PEO-PPO-PEO

Elaboration of mesostructured silica films with a triblock copolymer polyethylene oxide-polypropylene oxide-polyethylene oxide, (PEO-PPO-PEO) and controlled growth of silver nanoparticles in the mesostructure are described. The films are characterized using UV-visible optical absorption spectroscopy, TEM, AFM, SEM, X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS). Organized arrays of spherical silver nanoparticles with diameter between 5 and 8 nm have been obtained by NaBH₄ reduction. The size and the repartition of silver nanoparticles are controlled by the film mesostructure. The localization of silver nanoparticles exclusively in the upper-side part of the silica-block copolymer film is evidenced by RBS experiment. On the other hand, by using a thermal method, 40 nm long silver sticks can be obtained, by diffusion and coalescence of spherical particles in the silica-block copolymer layer. In this case, migration of silver particles toward the glass substrate-film interface is shown by the RBS experiment.     

Smart oligopeptide gels: in situ formation and stabilization of gold and silver nanoparticles within supramolecular organogel networks

Tripeptide with redox active chemical entities based smart organogels have been used for in situ formation and stabilization of gold and silver nanoparticles within the supramolecular gel networks and the gold nanoparticles are aligned in arrays along the gel nanofibers of peptide 1-toluene gels.     

高透光性有序银网阵列的制备

以水珠为模板制备了聚己内酯(PCL)有序多孔膜. 利用水珠在冷的高分子溶液表面凝结形成有序阵列, 溶剂蒸发后, 高分子材料按照水珠排列的形貌形成了有序多孔膜. 改变蒸发溶液的体积可得到具有透光性的有序贯通膜, 对该膜喷金后在银溶液中置换得到了有序银网阵列膜. 这种银网阵列不仅能够导电, 而且比聚己内酯阵列膜具有更高的透光性和柔韧性.     

Fabrication of optically active flexible polymer films with embedded chain-like arrays of silver nanoparticles

We report a straightforward method for preparation of freestanding transparent polymer film containing 2D silver nanoparticle arrays and possessing polarization-sensitive optical properties.