The extensive research of two-dimensional layered materials has revealed that valleys, as energy extrema in momentum space, could offer a new degree of freedom for carrying information. Based on this concept, researchers have predicted valley-Hall topological insulators that could support valley-polarized edge states at non-trivial domain walls. Recently, several kinds of photonic and sonic crystals have been proposed as classical counterparts of valley-Hall topological insulators. However, direct experimental observation of valley-polarized edge states in photonic crystals has remained difficult until now. Here, we demonstrate a designer surface plasmon crystal comprising metallic patterns deposited on a dielectric substrate, which can become a valley-Hall photonic topological insulator by exploiting the mirror-symmetry-breaking mechanism. Topological edge states with valley-dependent transport are directly visualized in the microwave regime. The observed edge states are confirmed to be fully valley-polarized through spatial Fourier transforms. Topological protection of the edge states at sharp corners is also experimentally demonstrated.

Using polarization dependent scattering spectroscopy, we investigate plasmon propagation on branched silver nanowires. By controlling the polarization of the incident laser light, the wire plasmons can be routed into different wire branches and result in light emission from the corresponding wire ends. This routing behavior is found to be strongly dependent on the wavelength of light. Thus for certain incident polarizations, light of different wavelength will be routed into different branches. The branched nanowire can thus serve as a controllable router and multiplexer in integrated plasmonic circuits.

We study the polarization dependence of surface-enhanced Raman scattering (SERS) in coupled gold nanoparticle-nanowire systems. The coupling between the continuous nanowire plasmons and the localized nanoparticle plasmons results in significant field enhancements and SERS enhancements comparable to those found in nanoparticle dimer junctions. The SERS intensity is maximal when the incident light is polarized across the particle and the wire, and the enhancement is remarkably insensitive to the detailed geometrical structures of the nanoparticles.

Nanowire plasmons can be launched by illumination at one terminus of the nanowire and emission can be detected at the other end of the wire. Using polarization dependent dark-field scattering spectroscopy, we measure how the polarization of the emitted light depends on the polarization of the incident light. We observe that the shape of the nanowire termination plays an important role in determining this polarization change. Depending on termination shape, a nanowire can serve as either a polarization-maintaining waveguide, or as a polarization-rotating, nanoscale half-wave plate. The understanding of how plasmonic waveguiding influence the polarization of the guided light is important for optimizing the structure of integrated plasmonic devices.

In this paper, we report experimentally and theoretically a surface photocatalysis reaction of 4-aminothiophenol (PATP) to p,p 0dimercaptoazobenzene (DMAB) on Au, Ag, and Cu colloids. Surface enhanced Raman scattering (SERS) spectra of PATP on Au and Cu colloids are significantly different from the normal Raman spectrum of PATP powder. Quantum chemical calculations reveal that PATP on Au and Cu colloids is converted to DMAB by a surface photocatalysis reaction, and all the strongly enhanced Raman peaks are the symmetric Ag vibrational mode by surface plasmon. The pH value effects on surface photocatalysis reaction were also investigated experimentally. It is found that plasmon-assisted surface photocatalysis reaction can be efficiently controlled by different pH values. The possibility of protonation of PATP adsorbed on Au and Ag nanoparticles at pH 3 is investigated theoretically. The molecular mechanism is proposed for controlling surface photocatalysis reaction by pH values.

Due to its amazing ability to manipulate light at the nanoscale, plasmonics has become one of the most interesting topics in the field of light-matter interaction. As a promising application of plasmonics, surface-enhanced Raman scattering (SERS) has been widely used in scientific investigations and material analysis. The large enhanced Raman signals are mainly caused by the extremely enhanced electromagnetic field that results from localized surface plasmon polaritons. Recently, a novel SERS technology called remote SERS has been reported, combining both localized surface plasmon polaritons and propagating surface plasmon polaritons (PSPPs, or called plasmonic waveguide), which may be found in prominent applications in special circumstances compared to traditional local SERS. In this article, we review the mechanism of remote SERS and its development since it was first reported in 2009. Various remote metal systems based on plasmonic waveguides, such as nanoparticle-nanowire systems, single nanowire systems, crossed nanowire systems and nanowire dimer systems, are introduced, and recent novel applications, such as sensors, plasmon-driven surface-catalyzed reactions and Raman optical activity, are also presented. Furthermore, studies of remote SERS in dielectric and organic systems based on dielectric waveguides remind us that this useful technology has additional, tremendous application prospects that have not been realized in metal systems.

Thin metallic nanowires are highly promising candidates for plasmonic waveguides in photonic and electronic devices. We have observed that light from the end of a silver nanowire, following excitation of plasmons at the other end of the wire, is emitted in a cone of angles peaking at nominally 45-60°from the nanowire axis, with virtually no light emitted along the direction of the nanowire. This surprising characteristic can be explained in a simple picture invoking Fabry-Pérot resonances of the forward-and back-propagating plasmons on the nanowire. This strongly angular-dependent emission is a critical property that must be considered when designing coupled nanowire-based photonic devices and systems.Plasmonic waveguides have significant potential to be used as a key component in miniaturized optical devices at the nanometer scale, and in the integration of photonic circuits with electronics to overcome the limitations of bandwidth and data transmission rates of classical electrical interconnects.1-8 Such an integration of photonics and electronics and the miniaturization of optical devices at the nanometer size are of considerable current interest in nanophotonics. 8 When surface plasmon polaritons (SPPs), 9 the collective motion of free electrons, are excited in the plasmonic waveguides, they can be propagated at distances exceeding tens of micrometers, in nanometer-width geometries such as nanoparticle chains, 10-12 metal stripes, 13 grooves, 14 metal-insulator-metal structures, 7,15 and nanowires. [16][17][18][19][20] While intensive experimental and theoretical efforts have focused on improving the in-coupling efficiency of light 3,19 and on how to reduce the propagation loss, 4,21 relatively little is known about their light-emitting properties.22 This is critically important information for the design and development of SPP waveguides in integrated photonic or electronic devices and systems.In this paper, we measure the spatial distribution of the light emitted from one end of a nanowire following the excitation of SPPs at the other end. Surprisingly, we find that almost no light is emitted in the direction of the nanowire but instead peaked at nominally 45-60°from the direction of the wire. For thin nanowires we observe that the distribution of the emitted light is remarkably insensitive to the diameter and length of the nanowire and the detailed structure of the wire ends.Several different approaches have been developed for the imaging of plasmonic properties of metallic nanostructures. 23,24 In the present work, the SPPs are excited by focusing a laser beam through an objective to one end of the nanowire, which is shown in Figure 1a. The emission from the other end of the nanowire is collected by the same objective and the optical image is recorded by a TE cooled 1392 × 1040 CCD detector mounted on a microscope (Olympus BX51). The intensity of the emission is determined by finding the maximum value in the emission spot from the optical image. The objective itself has an inside iris diaphragm w...

In this study, we attempt to experimentally address the question of whether p,p′-dimercaptoazobisbenzene (DMAB) can be produced from p-aminothiophenol (PATP) by surface photochemistry reaction in the junctions of a Ag nanoparticle-molecule-Ag (or Au) film. First, utilizing surface-enhanced Raman scattering (SERS) spectra, we provide experimental and theoretical evidence that DMAB can be produced from PATP by surface photochemistry reaction in the junctions of a Ag nanoparticle-molecule-Ag film. Second, we investigate the SERS spectra utilizing both experimental and theoretical approaches, ultimately revealing that DMAB cannot be produced from PATP in the junctions of a Ag nanoparticle-molecule-Au film. The electromagnetic enhancements are estimated with three-dimensional finite-difference time domain methods, which are about 9 × 10 5 times in the junctions of Ag nanoparticle-PATP-Ag/Au films.