基于等离激元热电子调控的全谱光催化产氢增强（英文）

等离激元效应在光催化体系中的集成为实现广谱光吸收提供了一个新的途径,然而等离激元热电子的较低迁移率和不确定扩散方向使得其光催化效率仍较低.等离激元金属与n型半导体接触后,其界面间会形成肖特基结.在特定波长太阳光照射下,等离激元金属将其表面等离子体能量聚集在表面自由电子上,进而产生热电子.当这些热电子具有的能量高于肖特基势垒时,热电子便可注入到半导体导带上.与此同时,半导体上的电子可以通过肖特基接触发生回流,与金属上的空穴复合,进而降低半导体-等离激元金属复合材料的光催化性能.因此,为了提高光催化效率,如何调控等离激元热电子迁移和充分利用等离激元效应是一个重要挑战.本文尝试将"表面异质结"与肖特基结相结合的复合结构,得以有效地调控等离激元热电子的迁移.在该复合结构中,金纳米颗粒和铂纳米颗粒分别作为等离激元吸光单元和助催化剂,集成在TiO_2纳米片表面.其中"表面异质结"是由TiO_2纳米片的两种不同表面晶面所构成,我们选择由{001}和{101}两组晶面组成的TiO_2纳米片作为半导体衬底.该结构中的{001}晶面导带能级高于{101}导带能级,因而电子由高能级的{001}流向低能级的{101}晶面,可以用来引导等离激元热电子从可见光响应的金纳米颗粒向TiO_2进行高效转移.通过巯基丙酸的桥联作用,将等离激元Au纳米颗粒锚定在TiO_2纳米片的{001}晶面上,获得Au-TiO_2{001}样品.另一方面,利用TiO_2纳米片自身光生电荷导向性光沉积,得到与{101}晶面结合形成的Au-TiO_2{101}样品.我们对两组样品进行光电流和光催化产氢实验对比,确认在"表面异质结"诱导下Au-TiO_2{001}样品中Au产生的光生热电子可以更好地注入到TiO_2纳米片导带上.我们进一步通过光沉积Pt纳米颗粒来判定光生电子所能到达的区域,验证了以上结论.与此同时,肖特基结由铂纳米颗粒与TiO_2纳米片所形成,可以促使电子由TiO_2向铂纳米颗粒进行转移,而避免发生向金纳米颗粒的反向迁移,从而在Au-TiO_2体系中实现高效的单向载流子转移.基于该设计,等离激元光催化剂实现了明显改善的全谱光催化产氢性能.本文为全谱光催化的复合结构理性设计提供了一个新的思路.     

Metal-enhanced Singlet Oxygen Generation: A Consequence of Plasmon Enhanced Triplet Yields

In this Rapid Communication, we report the first observation of Metal-Enhanced singlet oxygen generation (ME¹O₂). Rose Bengal in close proximity to Silver Island Films (SiFs) can generate more singlet oxygen, a three-fold increase observed, as compared to an identical glass control sample but containing no silver. The enhanced absorption of the photo-sensitizer, due to coupling to silver surface plasmons, facilitates enhanced singlet oxygen generation. The singlet oxygen yield can potentially be adjusted by modifying the choice of MEF (Metal-Enhanced Fluorescence) & MEP (Metal Enhance Phosphorescence) parameters, such as distance dependence for plasmon coupling and wavelength emission of the coupling fluorophore. This is a most helpful observation in understanding the interactions between plasmons and lumophores, and this approach may well be of significance for singlet oxygen based clinical therapy.     

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.     

Probing the reaction of membrane proteins via infrared spectroscopies,plasmonics, and electrochemistry

Spectroelectrochemistry, in combination with plasmonic approaches and infrared spectroscopy, has emerged as a powerful tool in the study of membrane protein redox reactions, both for immobilized monolayer samples and those reintroduced into their native environment. Here the use of nanostructured electrodes for surface enhanced spectroelectrochemistry are discussed.     

Computing electron energy loss spectra with the Discontinuous Galerkin Time-Domain method

In this work, we demonstrate how to extract electron energy loss spectra of metallic nano-particles from time-domain computations. Specifically, we employ the Discontinuous Galerkin Time-Domain (DGTD) method in order to model the excitation of individual metallic nano-spheres and dimers of spheres by a tightly focussed electron beam. The resulting electromagnetic fields that emanate from the particles act back on the electrons and the accumulated effect determines the electrons’ total energy loss. We validate this approach by comparing with analytical results for single spheres. For dimers, we find that the electron beam allows for an efficient excitation of dark modes that are inaccessible for optical spectroscopy. In addition, our time-domain approach provides a basis for dealing with materials that exhibit a significant nonlinear response.     

Transmission properties of periodically patterned triangular prisms

Transmission properties of plasmonic structure arrays are simulated by finite element method. The array unit is composed of two combined triangular prisms. Results reveal that several resonant modes are found in the transmission spectra, which are due to the resonance of the surface plasmon polariton in the metal slit or to the localized surface plasmon resonance of the combined prisms. The resonant wavelengths can be tuned by changing the structural parameters of the combined prisms. In addition, the resonant modes are sensitive to small refractive index changes of the surrounding media, revealing potential detection applications in nanophotonic systems.     

Enhanced UV/blue fluorescent sensing using metal-dielectric-metal aperture nanoantenna arrays

Subwavelength aperture antenna arrays are designed and fabricated for potential applications in fluorescence sensing in the near UV/blue range. They are designed using finite-difference time-domain (FDTD) simulation, fabricated using focused ion beam etching and characterised using angular Fourier spectroscopy. The aperture arrays are formed in the top layer of an aluminum-silica-aluminum trilayer and produce a maximum simulated field intensity enhancement of 5.8 times at 406 nm and highly directive emission with a beamwidth of 8.3 deg. The normal incidence reflection response has been measured and shows reasonable agreement with modelled results. In addition, to investigate higher field intensity enhancements, bowtie aperture arrays are simulated and the influence of parameters such as dielectric gap, position of dipole source, and aperture shape and size are discussed and show enhancements up to 67 times are possible.     

Highly integrated plasmonic sensor design for the simultaneous detection of multiple analytes

Herein, a highly integrated plasmonic sensor based on a multichannel metal-insulator-metal waveguide scheme for the simultaneous detection of multiple analytes is proposed. The numerical study is conducted via the finite element method based on commercially available software COMSOL. The sensor design is highly sensitive which can detect a minute change in the refractive index of the analyte. In this study, we have used the refractive index values of three different concentrations of ethanol and d-glucose solution to determine the sensor performance. It is observed that the device is highly sensitive as the operational wavelength lies in the deep shortwave infrared region. The numerically calculated sensitivity as high as 1948.67 nm/RIU is obtained for the cavity length of 325 nm which can be further improved by designing the device with large cavities. We believe that the proposed study is beneficial for the realization of the highly integrated plasmonic sensors for the lab-on-chip operations.     

Controlling light with plasmonic multilayers

Recent years have seen a new wave of interest in layered media – namely, plasmonic multilayers – in several emerging applications ranging from transparent metals to hyperbolic metamaterials. In this paper, we review the optical properties of such subwavelength metal–dielectric multilayered metamaterials and describe their use for light manipulation at the nanoscale. While demonstrating the recently emphasized hallmark effect of hyperbolic dispersion, we put special emphasis to the comparison between multilayered hyperbolic metamaterials and more broadly defined plasmonic-multilayer metamaterials A number of fundamental electromagnetic effects unique to the latter are identified and demonstrated. Examples include the evolution of isofrequency contour shape from elliptical to hyperbolic, all-angle negative refraction, and nonlocality-induced optical birefringence. Analysis of the underlying physical causes, which are spatial dispersion and optical nonlocality, is also reviewed. These recent results are extremely promising for a number of applications ranging from nanolithography to optical cloaking.