Foundations of Plasmonics

Plasma physics is a very mature field, studied extensively for well over a century. The cross-disciplinary field of plasmonics (electromagnetics of metallic nanostructures), on the other hand, with its potential for an extraordinary light control through novel class of materials and the resulting applications, has become very fashionable only recently. Inevitably, as a result of this rapid development, the deep connections with the mother discipline, the plasma physics, have sometimes been overlooked. The goal of this work is to review some of these basic connections, which are relevant, and ultimately helpful for researchers in the new field. We focus on the solid-state structured plasmas and address the issue of classical versus quantum treatments. We discuss the little known subtleties of the surface plasmons at metallic surfaces (e.g. multipole plasmons) and their consequences on plasmonics of the textured metallic films. Plasmonics of nanoparticles has been preceded by studies of plasma effects in metallic clusters and semiconducting quantum dots (QDs). In this context, we discuss the little known connection between the Mie resonance in metallic particles and the collective resonance in wide parabolic quantum wells (QWs) and QDs. Researchers dealing with plasmonics of thin films can benefit from earlier studies of plasmons in the semiconductor modulation doped heterojunctions and QWs, with its rich spectrum of intersubband and two-dimensional plasmons. In non-equilibrium plasmonic systems, generation of plasmons can be stimulated, leading to the exciting possibility of the plasmon instability. Extraordinarily complex is the plasmonics of carbon nanotubes and graphene, with its numerous van Hove, one- and three-dimensional plasmons, and we discuss how the plasmonics of metamaterials can benefit from this complexity. Finally, we discuss a few applications, which could directly benefit from plasmonics, including medical and the novel class of solar cells.     

Manipulation of light at the nanoscale for high-performance spectroscopic and optical applications

In this paper, we explore the use of nanostructures for a number of fascinating applications. These applications based on nanostructures include (1) optical sensors, (2) nanopixel printing, (3) improving the resolution of imaging techniques, and (4) lithography. In the sensing field, nanostructures are exploited for advanced sensor performance, namely, the label-free and enhanced sensitivity of (1) the surface plasmon resonance sensor and (2) the extraordinary optical transmission sensor and (3) the high sensitivity and selectivity of surface-enhanced Raman spectroscopy. In addition, research using nanostructures for visual applications was introduced for (1) harnessing nanostructures for full-color pixel printing and (2) exploiting metallic nanostructures to enhance the imaging resolution under diffraction limits based on the plasmonic effect. Finally, we introduce low cost, high accuracy, and fast lithographic methods based on the plasmonic effect by exploiting metallic nanostructures.     

表面等离激元研究新进展

随着理论研究的深入和现代微加工技术的进步,对支持表面等离激元的金属微纳结构体系的研究已形成了一门新兴学科方向,即表面等离激元光子学。由于表面等离激元具有独特的光学特性,在数据存储、超分辨成像、光准直、太阳能电池、生物传感器以及负折射材料等方面有着重要的应用前景,成为当前广受国内外学者重视的热点研究领域之一。本文对表面等离激元的特点、基本现象,以及其带来的新颖效应及其应用研究前景的最新发展进行了介绍。     

Study of electrical field distribution of gold-capped nanoparticle for excitation of localized surface plasmon resonance

The specific optical characteristics which can be observed from noble metal nanostructured materials such as nanoparticles and nanoislands have wide variety of applications such as biosensors, solar cells, and optical circuit. Because, these noble metal nanostructures induce the increment of light absorption efficiency by the enhancing effect of electrical field from localized surface plasmon resonance (LSPR) excitation. However, the enhancing effects of electrical field from LSPR using simple structured noble metal nanostructures for several applications are not satisfactory. To realize the more effective light absorption efficiency by the enhancing effect of electrical field, quite different noble metal nanostructures have been desired for applying to several applications using LSPR. In this study, to obtain the more effective enhancing effect of electrical field, conditions for LSPR excitation using a gold-capped nanoparticle layer substrate are computationally analyzed using finite-difference time-domain (FDTD) method. From the previous research, LSPR excitation using such gold-capped nanoparticle layer substrates has a great potential for application to high-sensitive label-free monitoring of biomolecular interactions. For understanding of detailed LSPR excitation mechanism, LSPR excitation conditions were investigated by analyzing the electrical field distribution using simulation software and comparing the results obtained with experimental results. As a result of computational analysis, LSPR excitation was found to depend on the particle alignment, interparticle distance, and excitation wavelength. Furthermore, the LSPR optical characteristics obtained from the simulation analysis were consistent with experimentally approximated LSPR optical characteristics. Using this gold-capped nanoparticle layer substrate, LSPR can be excited easily more than conventional noble metal nanoparticle-based LSPR excitation without noble metal nanoparticle synthesis. Hence, this structure is detectable a small change of refractive index such as biomolecular interactions for biosensing applications.     

A novel natural surface-enhanced fluorescence system based on reed leaf as substrate for crystal violet trace detection

The preparation of surface-enhanced fluorescence (SEF) substrates is often influenced by experimental strategies and factors such as the morphology and size of the nanostructures. In this study, using the natural reed leaves (RLs) without any special pretreatment as the substrate, metal silver is modified by magnetron sputtering technology to prepare a stable and efficient SEF system. The abundant “hedgehog-like”protrusions on the RL substrate surface can generate high-density “hot spots”, thus enhancement factor (EF) is enhanced up to 3345 times. The stability and reproducibility are verified in many measurements. The contribution of the intervention of silver nanostructure to the radiation attenuation process of fluorescent molecules is analyzed with the aid of Jablonski diagrams. Three-dimensional (3D) finite difference time domain (FDTD) simulates the spatial electric field and “hot spots”distribution of the substrate. The “hedgehog-like”protrusion structure generates multiple “hot spots”, which produce an excellent local surface plasmon resonance (LSPR) effect and provide higher fluorescence signal. Finally, RL/Ag-35 substrate is used to detect crystal violet (CV), and the detection limit is as low as 10^-13 M. This “hedgehog-like”SEF substrate provides a new strategy for the trace detection of CV, which has a good practical application value.     

Silane decorated metallic nanorods for hydrophobic applications

A novel technique to modify a metallic surface for anti-icing applications is presented. An oblique angle deposition (OAD) technique has been used to fabricate metallic nanorods of Aluminum and Tungsten on a glass substrate. A conformal coating of a silane has been applied using a molecular vapor deposition technique. The resulting surface has shown a static contact angle of 134° with the water droplet. SEM, AFM and XPS have been used to study the surface modification. This is a highly promising approach for anti-icing applications due to its scalability at a very low cost.     

Optical interaction between one-dimensional fiber photonic crystal microcavity and gold nanorod

Localized surface plasmon resonance(LSPR) has demonstrated its promising capability for biochemical sensing and surface-enhanced spectroscopy applications. However, harnessing LSPR for remote sensing and spectroscopy applications remains a challenge due to the difficulty in realizing a configuration compatible with the current optical communication system. Here, we propose and theoretically investigate a hybrid plasmonic-photonic device comprised of a single gold nanorod and an optical fiber-based one-dimensional photonic crystal microcavity, which can be integrated with the optical communication system without insertion loss. The line width of the LSPR, as a crucial indicator that determines the performances for various applications, is narrowed by the cavity-plasmon coupling in our device. Our device provides a promising alternative to exploit the LSPR for high-performance remote sensing and spectroscopy applications.     

在银、金和铂基底上银纳米粒子诱导的单层有机分子的表面增强拉曼散射(英文)

Noble metallic nanostructures exhibit a phenomenon known as surface-enhanced Raman scattering （SERS） in which the scattering cross sections are dramatically enhanced for molecules adsorbed thereon. Thanks to the enormously large enhancement factor on the order of 106～1015, one can readily acquire thevibrational spectra from adsorbates on roughened surfaces of Ag, Au, and Cu. However, SERS has not developed to be as powerful a surface technique as many people had hoped initially because of two specific obstacles.     

Modeling of regular gold nanostructures arrays for SERS applications using a 3D FDTD method

We study the localized surface plasmon resonance (LSPR) and the surface-enhanced Raman scattering (SERS) of arrays of gold cylindrical and ellipsoidal nanoparticles with different diameters or major axes. The LSPR and SERS gains are calculated with the three dimensional Finite-Difference Time-Domain method using the Drude–Lorentz dispersion model. We find that the maximum of the extinction spectrum and the average SERS gain of each investigated nanostructures are shifted whatever their size and their shape. PACS 42.25.Fx; 71.45.Gm; 78.30.-j     

对巯基苯甲酸在电化学沉积金膜表面的SERS研究

SERS技术由于具有高灵敏度的表面效应,能够检测吸附在金属表面的单分子层或亚单分子层的分子,并能给出丰富的分子结构信息,因而己被广泛应用于界面科学以及定性和定量分析科学领域之中。本文在制备电化学沉积金纳米薄膜的基础上,利用扫描电镜观察金纳米薄膜的形貌,通过分析对巯基苯甲酸在电化学沉积金膜表面的SERS光谱,研究对巯基苯甲酸在金纳米薄膜表面的吸附方式。由SERS光谱分析,我们推断出对巯基苯甲酸可能通过羧基和S原子共同作用吸附在金纳米颗粒表面,且苯环平面可能与金薄膜表面成一定倾斜角。     

Ultrasensitive nanosensors based on localized surface plasmon resonances:From theory to applications

The subwavelength confinement feature of localized surface plasmon resonance(LSPR) allows plasmonic nanostructures to be functionalized as powerful platforms for detecting various molecular analytes as well as weak processes with nanoscale spatial resolution. One of the main goals of this field of research is to lower the absolute limit-of-detection(LOD)of LSPR-based sensors. This involves the improvement of(i) the figure-of-merit associated with structural parameters such as the size, shape and interparticle arrangement and,(ii) the spectral resolution. The latter involves advanced target identification and noise reduction techniques. By highlighting the strategies for improving the LOD, this review introduces the fundamental principles and recent progress of LSPR sensing based on different schemes including 1) refractometric sensing realized by observing target-induced refractive index changes, 2) plasmon rulers based on target-induced relative displacement of coupled plasmonic structures, 3) other relevant LSPR-based sensing schemes including chiral plasmonics,nanoparticle growth, and optomechanics. The ultimate LOD and the future trends of these LSPR-based sensing are also discussed.     

倾斜L形手性结构的制备以及圆二色性

在单层聚苯乙烯小球模板上,制备了大面积倾斜L形手性结构.通过倾斜角沉积技术,在小球的一侧生长二氧化硅,在二氧化硅上面沉积金属层;在垂直方向沉积另一金属层,使两个金属层具有不同高度从而形成倾斜L形手性结构.研究发现,通过控制二氧化硅的厚度,可以实现倾斜L形手性结构的圆二色性的调控.数值模拟结果表明,倾斜L形手性结构的圆二色性机制符合Born-Kuhn模型理论.     

Influence of cavity geometry towards plasmonic gap tolerance and respective near-field in nanoparticle-on-mirror

In this work, we emphasize the importance of cavity geometry along with nanoparticle shape and plasmonic nanogap (based on a nanoparticle on a metallic film (NPOM) design) which plays significant role in understanding the complex plasmonic mode characteristics involving nanoparticle and gap mode resonances. The cross-section imprint of planar cavity on metallic film plays decisive role in near field enhancement properties at similar NP size and plasmonic nanogap conditions for spherical and cubical NPOM systems. By mimicking the NPOM structure to metal-insulator-metal design, we understand the resonant emission differences for the respective plasmonic modes. Influence of dominant and weaker gap mode resonances resulted in an interesting optical behavior (fluctuations in near field enhancement strength) in NP mode in case of cubical nanostructures. By such extensive investigation and interpretation of sub-wavelength complex plasmonic mode characteristics, various practical applications in plasmonics field can be accomplished.     

Plasmonics and SERS activity of post-transition metal nanoparticles

Nanoparticles of the post-transition metals, In, Sn, Pb, and Bi, and of the metalloid Sb were produced by laser ablation synthesis in solution (LASiS) and tested for localized surface plasmon resonances (LSPR) and surface-enhanced Raman scattering (SERS). The nanoparticles were characterized by UV-Vis optical absorption, dynamic light scattering (DLS), and transmission electron microscopy (TEM). Several organic and biological molecules were tested, and SERS activity was demonstrated for all tested nanoparticles and molecules. The Raman enhancement factor for each nanoparticle class and molecule was experimentally determined. The search for new plasmonic nanostructures is important mainly for life sciences-related applications and this study expands the range of SERS active systems.     

Three-dimensional noble-metal nanostructure: A new kind of substrate for sensitive,uniform, and reproducible surface-enhanced Raman scattering

Surface-enhanced Raman spectroscopy(SERS) is a powerful vibrational spectroscopy technique for highly sensitive structural detection of low concentration analyte. The SERS activities largely depend on the topography of the substrate.In this review, we summarize the recent progress in SERS substrate, especially focusing on the three-dimensional(3D)noble-metal substrate with hierarchical nanostructure. Firstly, we introduce the background and general mechanism of3 D hierarchical SERS nanostructures. Then, a systematic overview on the fabrication, growth mechanism, and SERS property of various noble-metal substrates with 3D hierarchical nanostructures is presented. Finally, the applications of 3D hierarchical nanostructures as SERS substrates in many fields are discussed.     

Detecting nanoparticles by “listening”

In the macroscopic world, we can obtain some important information through the vibration of objects, that is, listening to the sound. Likewise, we can also get some information of the nanoparticles that we want to know by the means of “listening” in the microscopic world. In this review, we will introduce two sensing methods (cavity optomechanical sensing and surface-enhanced Raman scattering sensing) which can be used to detect the nanoparticles. The cavity optomechanical systems are mainly used to detect sub-gigahertz nano particle or cavity vibrations, while surface-enhanced Raman scattering is a well-known technique to detect molecular vibrations whose frequency generally exceeds terahertz. Therefore, the vibrational information of nanoparticles from low-frequency to high-frequency could be obtained by these two methods. The size of the viruses is at the nanoscale and we can regard it as a kind of nanoparticles. Rapid and ultrasensitive detection of the viruses is the key strategies to break the spread of the viruses in the community. Cavity optomechanical sensing enables rapid, ultrasensitive detection of nanoparticles through the interaction of light and mechanical oscillators and surface-enhanced Raman scattering is an attractive qualitatively analytical technique for chemical sensing and biomedical applications, which has been used to detect the SARS-CoV-2 infected. Hence, investigation in these two fields is of vital importance in preventing the spread of the virus from affecting human’s life and health.     

Design and fabrication of structural color by local surface plasmonic meta-molecules

In this paper, we propose a new form of nanostructures with Al film deposited on a patterned dielectric material for generating structural color, which is induced by local surface plasmonic resonant(LSPR) absorption in sub-wavelengthindented hole/ring arrays. Unlike other reported results obtained by using focus ion beam(FIB) to create metallic nanostructures, the nano-sized hole/ring arrays in Al film in this work are replicated by high resolution electron beam lithography(EBL) combined with self-aligned metallization. Clear structural color is observed and systematically studied by numerical simulations as well as optical characterizations. The central color is strongly related to the geometric size, which provides us with good opportunities to dye the colorless Al surface by controlling the hole/ring dimensions(both diameter and radius), and to open up broad applications in display, jewelry decoration, green production of packing papers, security code,and counterfeits prevention.     

Controllable optical activity of non-spherical Ag and Co SERS substrate with different magnetic field

We experimentally fabricate a non-spherical Ag and Co surface-enhanced Raman scattering(SERS) substrate, which not only retains the metallic plasmon resonant effect, but also possesses the magnetic field controllable characteristics.Raman detections are carried out with the test crystal violet(CV) and rhodamine 6G(R6G) molecules with the initiation of different magnitudes of external magnetic field. Experimental results indicate that our prepared substrate shows a higher SERS activity and magnetic controllability, where non-spherical Ag nanoparticles are driven to aggregate effectively by the magnetized Co and plenty of hot-spots are built around the metallic Ag nanoparticles, thereby leading to the enhancement of local electromagnetic field. Moreover, when the external magnetic field is increased, our prepared substrate demonstrates excellent SERS enhancement. With the 2500 Gs and 3500 Gs(1 Gs = 10~(-4)T) magnetic fields, SERS signal can also be obtained with the detection limit lowering down to 10~(-9)M. These results indicate that our proposed magnetic field controlled substrate enables us to freely achieve the enhanced and controllable SERS effect, which can be widely used in the optical sensing, single molecule detection and bio-medical applications.     

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.     

Ultrashort laser pulse–matter interaction: Implications for high energy materials

The interaction of ultrashort [nanosecond (ns)/picosecond (ps)/femtosecond (fs)] pulses with materials is an exhaustive area of research with underlying, and often extremely rich, physics along with a plethora of applications evolving from it. High-energy materials (HEMs) are chemical compounds or mixture of compounds which, under suitable initiation, undergoes a very rapid exothermic and self-propagating decomposition. Herein, we describe the interaction of laser pulses with materials and its implications for studies on HEMs in four parts: (a) ns and fs laser-induced breakdown spectroscopic (LIBS) studies of HEMs towards understanding the molecular dynamics and discrimination, (b) ps/fs pulses interaction with metallic solids towards the production of nanoparticles, nanostructures and their utility in identifying explosive molecules using surface-enhanced Raman scattering studies, (c) interaction of laser pulses with the bulk and surface of glasses and polymers producing micro- and nanostructures for microfluidic/lab-on-a-chip applications, and (d) ultrafast spectroscopic studies for comprehending the excited state dynamics towards elucidation of vibrational dynamics in HEMs. Several applications resulting from these interactions will be discussed in detail.