Manipulation of plasmonic wavefront and light–matter interaction in metallic nanostructures: A brief review

The control and application of surface plasmons （SPs）, is introduced with particular emphasis on the manipulation of the plasmonic wavefront and light-matter interaction in metallic nanostructures. We introduce a direct design methodology called the surface wave holography method and show that it can be readily employed for wave-front shaping of near-infrared light through a subwavelength hole, it can also be used for designing holographic plasmonic lenses for SPs with complex wavefronts in the visible band. We also discuss several issues of light-matter interaction in plasmonic nanostructures. We show theoretically that amplification of SPs can be achieved in metal nanoparticles incorporated with gain media, leading to a giant reduction of surface plasmon resonance linewidth and enhancement of local electric field intensity. We present an all-analytical semiclassical theory to evaluate spaser performance in a plasmonic nanocavity incorporated with gain media described by the four-level atomic model. We experimentally demonstrate amplified spontaneous emission of SP polaritons and their amplification at the interface between a silver film and a polymer film doped with dye molecules. We discuss various aspects of microscopic and macroscopic manipulation of fluorescent radiation from gold nanorod hybrid structures in a system of either a single nanoparticle or an aligned group of nanoparticles. The findings reported and reviewed here could help others explore various approaches and schemes to manipulate plasmonic wavefront and light-matter interaction in metallic nanostructures for potential applications, such as optical displays, information integration, and energy harvesting technologies.     

Synthesis of Au nanorods in a low pH solution via seed-media method

The gold(Au) nanorods with various aspect ratios are obtained by a seed-media method in low pH growth solution.Transmission electron microscopy(TEM) and UV-visible spectrophotometry are utilized to characterize the Au nanorods,and the longitudinal absorption peak positions of Au nanorods show different shifting trends of the growth evolutions in various low pH(1～3) solutions. Other influential factors on the shape of Au nanorod are also systematically studied under low pH reaction condition. The positions of longitudinal peak shift between 600 nm and 900 nm, with the aspect ratios of Au nanorods varying from 2 to 5 both in the simulation and experimental results. The simulation results are in agreement with experimental ones.     

Highly sensitive fiber refractive index sensor based on side-core holey structure

We propose a side-core holey fiber （SCHF）-based surface plasmon resonance （SPR） sensor to achieve high refractive index （RI） sensitivity. The SCHF structure can facilitate analyte filling and enhance the overlapping area of the core mode and surface plasmon polariton （SPP） mode. The coupling properties of the sensor are analyzed by numerical simulation. The maximum sensitivity of 5000 nm/RIU in an RI range of 1.33-1.44, and the average sensitivity of 9295 nm/RIU in an RI range from 1.44 to 1.54 can be obtained.     

Investigation on Transmission Properties of Terahertz Wave Through Semiconductor Aperture

The transmission properties of terahertz （THz） wave passing through semiconductor aperture have been investigated. The dispersion relationship for surface plasmon polariton （SPP） at different temperatures has been numerically calculated. The results show that the dispersion relationship increases with the increasing of frequency and the decreasing of temperature, the thickness of slab has to be taken into consideration because of the large skin depth for semiconductor slab. In addition, the propagation constant increases with the increasing of frequency and the decreasing of temperature.     

铝基银纳米阵列制备及其紫外-可见-近红外光吸收特性

基于阳极氧化铝模板,采用真空蒸镀技术,制备了高度有序的周期性银纳米球阵列.阵列几何结构参数调控实验发现,通过控制蒸镀厚度,可实现对阵列中银纳米球尺寸(直径)和间距的有效调控,进而有效实现对紫外-可见-近红外各波段吸收峰位和峰宽的调制.吸收光谱测试显示,该纳米阵列在紫外、可见和近红外波段都具有明显的电磁波吸收特性.时域有限差分理论模拟结合实验分析不同波段光吸收特性的物理机制,紫外超窄强吸收为银、铝介电环境非对称诱发的法诺共振,可见波段吸收源自于银纳米粒子局域表面等离子体共振,近红外波段强吸收为银纳米球阵列表面晶格共振所激发.     

Switching and Fano resonance via exciton–plasmon interaction

We fnrther study theoretically the properties of switching and Fano resonance in a hybrid nanosystem consisting of two quantum dots （QDs） and a metal nanowire via exciton-plasmon interaction. The transmission of the single plasmon can be switched on or off in a wide-frequency region by adjusting the transition frequencies of the QDs and the phase of the propagating plasmon. Specifically, the dynamical mechanism of Fano-type transmission is further revealed and analyzed in detail.     

Systematic study on visible light collimation nanostructured slits in the metal surface

We present a systematic experimental investigation on visible light collimation by a nanostructured slit flanked with a pair of periodic array of grooves in gold thin film. A wide variety of aspects are considered, such as the polarization state, the transport path of incident light, the groove-groove spacing, the groove width and depth. Our results clearly show that the relationship between the collimation wavelength and the periodicity of the slit-groove structure accords well with the surface plasmon dispersion model proposed by previous researchers. Furthermore, the surface plasmon wave phase retardation effect induced by the surface structure is also verified via the measurement for samples with different groove widths and depths. These results indicate that the detailed geometry of the groove structure has obvious impacts on the collimation effect and the angular distribution of the diffraction light in the subwavelength plasmonic system.     

Hybrid plasmon waveguides with metamaterial substrate and dielectric substrate:A contrastive study

Hybrid plasmon waveguides, respectively, with metamaterial substrate and dielectric substrate are investigated and analyzed contrastively with a numerical finite element method. Basic properties, including propagation length Lp, effective mode area Aeff, and energy distribution, are obtained and compared with waveguide geometric parameters at 1.55 gin. For the waveguide with metamaterial substrate, propagation length Lp increases to several tens of microns and effective mode area Aeff is reduced by more than 3 times. Moreover, the near field region is expanded, leading to potential applications in nanophotonics. Therefore, it could be very helpful for improving the integration density in optical chips and developing functional components on a nanometer scale for all optical integrated circuits.     

Local field enhancement of pair arrays of silver nanospheres

Local field surface plasmon excitation of pair arrays of silver nanospheres was studied using three-dimensional finite-difference time-domain method. The near-field enhancement was associated with the radius of nanosphere and the incident wavelength, the highest of which always appeared in the penultimate gaps, regardless of the number of the pairs. The surface plasmon resonance could be controlled and tuned by radius of nanosphere and incident wavelength.     

金属表面等离体子振荡

深入浅出地分析了金属表面等离体子振荡形成的机理，利用拉普拉斯方程得到了半无限金属、金属薄膜和球状纳米金属颗粒的表面等离体子振荡频率。     

Nanosphere Templated Metallic Grating Assisted Enhanced Fluorescence

In this paper, enhanced fluorescence from a silver film coated nanosphere templated grating is presented. Initially, numerical simulation was performed to determine the plasmon resonance wavelength by varying the thickness of the silver film on top of a monolayer of 400 nm nanospheres. The simulation results are verified experimentally and tested for enhancing fluorescence from fluorescein isothiocyanate whose excitation wavelength closely matches with the plasmon resonance wavelength of the substrate with 100 nm silver film over nanosphere. The 12 times enhancement in the intensity is attributed to the local field enhancement in addition to the excitation of surface plasmon polaritons along the surface.     

Ag-Al纳米球二聚体的光学性质研究

金属纳米材料因其表面等离子体共振特性而备受关注。异质结构的金属纳米材料的光学特性相比于同质结构因其材料的不同破坏了原有结构的对称性,对称性的破坏将引起光学性质的改变,相邻两个颗粒之间的相互作用会产生Fano共振。Fano共振是由异质纳米结构的表面等离子体共振耦合引起的,通过合理地调控表面等离子体共振的耦合,将进一步调控Fano共振的强度同时促使异质结构的电场增强特性和辐射特性得到进一步优化。受金银等贵金属的带间跃迁影响,金属铝纳米材料成为研究紫外-近紫外光区的表面等离子体共振研究最佳选择。采用有限时域差分方法研究了Ag-Al纳米球二聚体的光学特性。研究了Ag和Al纳米球组成的二聚体的吸收光谱与入射光偏振方向、纳米球半径、颗粒间距和介质折射率等几何结构及物理参数的关系,并深入讨论了二聚体的局域场分布规律;讨论了获取更高效的Fano共振光谱的方法。由于材料的对称性被破坏,异质二聚体的光学性质与同质二聚体明显不同,Ag-Al异质纳米球二聚体呈现出在紫外和可见光区的双Fano共振现象。Ag-Al二聚体表面等离子体互相耦合引起Fano共振从而导致表面等离子体的共振抑制和增强。研究结果对在紫外-可见光区的表面等离子体应用、纳米光学器件的设计与开发及基于表面等离子体共振的表面增强光谱、生物传感和检测研究等有一定参考价值。     

Dynamic investigation of the finite dissolution of silicon particles in aluminum melt with a lower dissolution limit

The finite dissolution model of silicon particles in the aluminum melt is built and calculated by the finite difference method, and the lower dissolution limit of silicon particles in the aluminum melt is proposed and verified by experiments, which could be the origin of microinhomogeneity in aluminum-silicon melts. When the effects of curvature and interface reaction on dissolution are not considered; the dissolution rate first decreases and later increases with time. When the effects of curvature and interface reaction on dissolution are considered, the dissolution rate first decreases and later increases when the interface reaction coefficient （k） is larger than 10 1, and the dissolution rate first decreases and later tends to be constant when k is smaller than 10-3. The dissolution is controlled by both diffusion and interface reaction when k is larger than 10-3, while the dissolution is controlled only by the interface reaction when k is smaller than 10-4.     

Nanosphere dispersion on a large glass substrate by low dose ion implantation for localized surface plasmon resonance

Dispersing nanospheres on a large glass substrate is the key to fabricate noble metal nanostructures for localized surface plasmon resonance through dispersed nanosphere lithography. This article reports that by modifying the glass surface with low dose ion implantation and successively dip coating the surface with poly(diallyldimethyl ammonium chloride) (PDDA), polystyrene or silica nanospheres can be dispersed on a large glass substrate. Investigation shows that several kinds of ions, such as silicon, boron, argon, and arsenic, can improve the nanosphere dispersion on glass, attributed to the ion bombardment-caused silicon increment. Ion implantation imposes no surface roughness or optical loss to the glass substrate, thus this method is suitable for localized surface plasmon resonance application. Experiments show silicon ion implantation can best disperse the nanospheres. For the gold nanostructures obtained by obliquely evaporating 30 nm of gold film onto the polystyrene nanospheres, which are dispersed on a silicon ion implanted glass substrate, a localized surface plasmon resonance sensitivity of 242 nm/RIU is achieved.     

有序金纳米颗粒阵列的制备及光吸收特性研究

采用纳米球刻蚀技术中漂移法在玻璃基片上制备较大 面积不同直径的聚苯乙烯小球掩模板, 采用磁控溅射技术在掩模板上沉积不同厚度的金薄膜, 去除聚苯乙烯小球后, 通过扫描电子显微镜观察到周期排列的三角状金纳米颗粒点阵. 通过紫外-可见分光光度计测试所制备样品的光吸收特性, 发现表面等离子体共振峰随粒径增大发生红移, 随金纳米颗粒高度增加发生蓝移. 基于Mie理论, 利用Matlab软件编程对不同粒径的金阵列光吸收特性进行理论模拟, 并与实验结果进行对比. 关键词： 纳米球刻蚀 金纳米颗粒阵列 表面等离子体共振     

Performance of La203/InA1N/GaN metal-oxide-semiconductor high electron mobility transistors

We report on the performance of La203/InA1N/GaN metal-oxide-semiconductor high electron mobility transistors （MOSHEMTs） and InA1N/GaN high electron mobility transistors （HEMTs）. The MOSHEMT presents a maximum drain current of 961 mA/mm at Vgs = 4 V and a maximum transconductance of 130 mS/mm compared with 710 mA/mm at Vgs = 1 V and 131 mS/mm for the HEMT device, while the gate leakage current in the reverse direction could be reduced by four orders of magnitude. Compared with the HEMT device of a similar geometry, MOSHEMT presents a large gate voltage swing and negligible current collapse.     

Effect of ultrathin GeO_x interfacial layer formed by thermal oxidation on Al_2O_3 capped Ge

We propose a modified thermal oxidation method in which an Al2O3 capping layer is used as an oxygen blocking layer （OBL） to form an ultrathin GeOx interracial layer, and obtain a superior Al2O3/GeOx/Ge gate stack. The GeOx interfacial layer is formed in oxidation reaction by oxygen passing through the Al2O3 OBL, in which theAl2O3 layer could restrain the oxygen diffusion and suppress the GeO desorption during thermal treatment. The thickness of the GeOx interfacial layer would dramatically decrease as the thickness of Al2O3 OBL increases, which is beneficial to achieving an ultrathin GeOx interfacial layer to satisfy the demand for small equivalent oxide thickness （EOT）. In addition, the thickness of the GeOx interfacial layer has little influence on the passivation effect of the Al2O3/Ge interface. Ge （100） p-channel metal- oxide-semiconductor field-effect transistors （pMOSFETs） using the Al2O3/GeOx/Ge gate stacks exhibit excellent electrical characteristics; that is, a drain current on-off （Ionloft） ratio of above 1 104, a subthreshold slope of - 120 mV/dec, and a peak hole mobility of 265 cm2/V.s are achieved.     

Resonant surface plasmons of a metal nanosphere treated as propagating surface plasmons

On the assumption that the resonant surface plasmons on a spherical nanoparticle are formed by standing waves of two counter-propagating surface plasmon waves along the surface, by using Mie theory simulation, we find that the dispersions of surface plasmon resonant modes supported by silver nanospheres match with those of the surface plasmons on a semiinfinite medium-silver interface very well. This suggests that the resonant surface plasmons of a metal nanosphere can be treated as a propagating surface plasmon wave.     

Laser-induced forces in metallic nanosystems: the role of plasmon resonances

We present calculations of the laser-induced force between metallic nanospheres, similar and dissimilar in character, and that between a metallic nanosphere and a planar surface. When the separation between these objects is in the 0.5-2 nm range, we find very strong resonances in the laser-induced force associated with excitation of plasmon resonances. Measurement of such forces will provide direct access to the plasmon enhancements of laser fields so critical to optical spectroscopy in the nanoenvironment.