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.     

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.     

Deep-ultraviolet surface plasmon resonance of Al and Al_(core)/Al_2O_(3shell) nanosphere dimers for surface-enhanced spectroscopy

The localized surface plasmon resonance properties of Al and Alcore/Al2O3 shell nanosphere dimers with Al and Al core nanosphere radii of 20 nm and Al2O3 shell of 2 nm in the deep-ultraviolet region have been studied using the finite difference time domain method. The extinction spectra and the electric field distribution profiles of the two dimers for various gap distances between two individual nanospheres are compared with those of the corresponding monomers to reveal the extent of plasmon coupling. It is found that with the interparticle distance decreasing, a strong plasmon coupling between two Al or Alcore/Al2O3 shell nanospheres is observed accompanied by a significant red shift in the extinction spectra at the parallel polarization direction of the incident light related to the dimer axis, while for the case of the perpendicular polarization direction, a weak plasmon coupling arises characterized by a slight blue shift in the extinction spectra. The electric field distribution profiles show that benefiting from the dielectric Al2O3 shell, the gap distance of Alcore/Al2O3 shell nanosphere dimers can be tailored to < 1 nm scale and results in a very high electric field enhancement. The estimated surface-enhanced Raman scattering enhancement factors suggests that the Alcore/Al2O3 shell nanosphere dimers with the gap of < 1 nm gave rise to an enhancement as high as 8.1 × 107 for interparticle gap = 0.5 nm. Our studies reveal that the Alcore/Al2O3 shell nanosphere dimers may be promising substrates for surface-enhanced spectroscopy in the deep-ultraviolet region.     

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.     

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.     

Influence of roughness on the detection of mechanical characteristics of low-k film by the surface acoustic waves

The surface acoustic wave （SAW） technique is a precise and nondestructive method to detect the mechanical charac- teristics of the thin low dielectric constant （low-k） film by matching the theoretical dispersion curve with the experimental dispersion curve. In this paper, the influence of sample roughness on the precision of SAW mechanical detection is inves- tigated in detail. Random roughness values at the surface of low-k film and at the interface between this low-k film and the substrate are obtained by the Monte Carlo method. The dispersive characteristic of SAW on the layered structure with rough surface and rough interface is modeled by numerical simulation of finite element method. The Young＇s moduli of the Black DiamondTM samples with different roughness values are determined by SAWs in the experiment. The results show that the influence of sample roughness is very small when the root-mean-square （RMS） of roughness is smaller than 50 nm and correlation length is smaller than 20 μm. This study indicates that the SAW technique is reliable and precise in the nondestructive mechanical detection for low-k films.     

Structural,electronic and magnetic properties of the Mn-Ni(110) c(2×2) surface alloy

<正>Using first-principles total energy method,we study the structural,the electronic and the magnetic properties of the MnNi(110) c(2×2) surface alloy.Paramagnetic,ferromagnetic,and antiferromagnetic surfaces in the top layer and the second layer are considered.It turns out that the substitutional alloy in the outermost layer with ferromagnetic surface is the most stable in all cases.The buckling of the Mn-Ni(110) c(2×2) surface alloy in the top layer is as large as 0.26 A(1 A=0.1 nm) and the weak rippling is 0.038 A in the third layer,in excellent agreement with experimental results.It is proved that the magnetism of Mn can stabilize this surface alloy.Electronic structures show a large magnetic splitting for the Mn atom,which is slightly higher than that of Mn-Ni(100) c(2×2) surface alloy(3.41 eV) due to the higher magnetic moment.A large magnetic moment for the Mn atom is predicted to be 3.81μB.We suggest the ferromagnetic order of the Mn moments and the ferromagnetic coupling to the Ni substrate,which confirms the experimental results.The magnetism of Mn is identified as the driving force of the large buckling and the work-function change.The comparison with the other magnetic surface alloys is also presented and some trends are predicted.     

Quantum confinement and surface chemistry of 0.8–1.6 nm hydrosilylated silicon nanocrystals

In the framework of density functional theory(DFT), we have studied the electronic properties of alkene/alkynehydrosilylated silicon nanocrystals(Si NCs) in the size range from 0.8 nm to 1.6 nm. Among the alkenes with all kinds of functional groups considered in this work, only those containing –NH2and –C4H3S lead to significant hydrosilylationinduced changes in the gap between the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) of an Si NC at the ground state. The quantum confinement effect is dominant for all of the alkenehydrosilylated Si NCs at the ground state. At the excited state, the prevailing effect of surface chemistry only occurs at the smallest(0.8 nm) Si NCs hydrosilylated with alkenes containing –NH2and –C4H3S. Although the alkyne hydrosilylation gives rise to a more significant surface chemistry effect than alkene hydrosilylation, the quantum confinement effect remains dominant for alkyne-hydrosilylated Si NCs at the ground state. However, at the excited state, the effect of surface chemistry induced by the hydrosilylation with conjugated alkynes is strong enough to prevail over that of quantum confinement.     

Dust-Lower-Hybrid Surface Waves in Classical and Degenerate Plasmas

The dispersion relation for general dust low frequency electrostatic surface waves propagating on an interface between a magnetized dusty plasma region and a vacuum is derived by using specular reflection boundary conditions both in classical and quantum regimes. The frequency limit ωωci ωce is considered and the dispersion relation for the Dust-Lower-Hybrid Surface Waves(DLHSW's) is derived for both classical and quantum plasma half-space and analyzed numerically. It is shown that the wave behavior changes as the quantum nature of the problem is considered.     

Effects of clouds, sea surface temperature, and its diurnal variation on precipitation efficiency

The effects of clouds, sea surface temperature, and its diurnal variation on precipitation efficiency are investigated using grid-scale data from nine equilibrium sensitivity cloud-resolving model experiments driven without large-scale vertical velocity. The precipitation efficiencies are respectively defined in surface rainfall, cloud, and rain microphysical budgets. We mathematically and physically demonstrate the relationship between these precipitation efficiencies. The 2℃ increases in spatiotemporal invariant sea surface temperature (SST) from 27℃ to 29℃ and from 29℃ to 31℃, and the inclusion of diurnal SST difference 1℃ and the 1℃ increase in diurnal SST difference generate opposite changes in the precipitation efficiency by changing ice cloud-radiation interactions. The radiative and microphysical processes of ice clouds have opposite effects on the precipitation efficiency because of the rainfall increase associated with the reduction in the saturation mixing ratio caused by the exclusion of radiative effects and the decrease in rainfall related to the reduction in net condensation caused by the exclusion of deposition processes. The radiative effects of water clouds on the precipitation efficiency are statistically insensitive to the radiative effects of ice clouds.     

Ferromagnetic-insulators-modulated transport properties on the surface of a topological insulator

Transport properties on the surface of a topological insulator （TI） under the modulation of a two-dimensional （2D） ferromagnet/ferromagnet junction are investigated by the method of wave function matching. The single ferromagnetic barrier modulated transmission probability is expected to be a periodic function of the polarization angle and the planar rotation angle, that decreases with the strength of the magnetic proximity exchange increasing. However, the transmission probability for the double ferromagnetic insulators modulated n-n junction and n-p junction is not a periodic function of polarization angle nor planar rotation angle, owing to the combined effects of the double ferromagnetic insulators and the barrier potential. Since the energy gap between the conduction band and the valence band is narrowed and widened respectively in ranges of 0 ≤ 0 〈π/2 and r/2 〈 0 ≤ π, the transmission probability of the n-n junction first increases rapidly and then decreases slowly with the increase of the magnetic proximity exchange strength. While the transmission probability for the n-p junction demonstrates an opposite trend on the strength of the magnetic proximity exchange because the band gaps contrarily vary. The obtained results may lead to the possible realization of a magnetic/electric switch based on TIs and be useful in further understanding the surface states of TIs.     

Study on incident laser modulation using surface micro-defects on KH2PO4 crystal

KH2PO4 crystal is a crucial optical component of inertial confinement fusion. Modulation of an incident laser by surface micro-defects will induce the growth of surface damage, which largely restricts the enhancement of the laser induced damage threshold. The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method. The results indicate that after the modulation of surface defects, the light intensity distribution inside the crystal is badly distorted, with the light intensity enhanced symmetrically. The relations between modulation properties and defect geometries （e.g., width, morphology, and depth of defects） are quite different for different defects. The modulation action is most obvious when the width of surface defects reaches 1.064 p-m. For defects with smooth morphology, such as spherical pits, the degree of modulation is the smallest and the light intensity distribution seems relatively uniform. The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value. The critical depth is 1.064 μm for cuboid pits and radial cracks, while for ellipsoidal pits the value depends on both the width and the length of the defects.     

Step instability of the surface during Ino.2Gao.sAs （001） annealing

Anisotropic evolution of the step edges on the compressive-strained In0.2Ga0.8As/GaAs（001） surface has been investigated by scanning tunneling microscopy （STM）. The experiments suggest that step edges are indeed sinuous and protrude somewhere a little way along the [110] direction, which is different from the classical waviness predicted by the theoretical model. We consider that the monatomic step edges undergo a morphological instability induced by the anisotropic diffusion of adatoms on the terrace during annealing, and we improve a kinetic model of step edge based on the classical Burton Cabrer-Frank （BCF） model in order to determine the normal velocity of step enlargement. The results show that the normal velocity is proportional to the arc length of the peninsula, which is consistent with the first result of our kinetic model. Additionally, a significant phenomenon is an excess elongation along the [110] direction at the top of the peninsula with a higher aspect ratio, which is attributed to the restriction of diffusion lengths.     

A Study of Surfactant-Induced Growth of Ag on Ag （111）

A new growth model is introduced to describe surfactant-induced growth of Ag on Ag （111） with realistic physical parameters. In this model, the A-S exchange mechanism is considered for the first time. Using the Monte Carlo simulations, the influence of exchange mechanism, surface temperature T, the exchange barrier Eεx, and the coverage of surfactant θM on the growth mode and morphology during multilayer film growth of Ag/Ag （111） are studied in detail Both the referenced value of surfactant coverage and the method to obtain perfect layer-by-layer film in surfactantinduced Ag/Ag （111） system are provided. Our simulation results are consistent with many experimental observations for surfactant-induced growth of Ag on Ag （111）.     

Pulsed ion beam-assisted carburizing of titanium in methane discharge

The carburizing of titanium (Ti) is accomplished by utilizing energetic ion pulses of a 1.5 kJ Mather type dense plasma focus (DPF) device operated in methane discharge. X-ray diffraction (XRD) analysis confirms the deposition of polycrystalline titanium carbide (TiC). The samples carburized at lower axial and angular positions show an improved texture for a typical (200)TiC plane. The Williamson-Hall method is employed to estimate average crystallite size and microstrains in the carburized Ti surface. Crystallite size is found to vary from ～ 50 to 100 nm, depending on the deposition parameters. Microstrains vary with the sample position and hence ion flux, and are converted from tensile to compressive by increasing the flux. The carburizing of Ti is confirmed by two major doublets extending from 300 to 390 cm-1 and from 560 to 620 cm-1 corresponding to acoustic and optical active modes in Raman spectra, respectively. Analyses by scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDS) have provided qualitative and quantitative profiles of the carburized surface. The Vickers microhardness of Ti is significantly improved after carburizing.     

Dynamic surface wettability of three-dimensional graphene foam

In this work, three-dimensional graphene foams （GFs） are synthesized and characterized by scanning electron micro- scope （SEM） and Raman spectroscopy. The SEM images indicate that after the growth of graphene, the graphene covers the surface of nickel （Ni） foam uniformly. Raman spectra show that the percentages of monolayer, bilayer, trilayer, and multilayer graphenes are - 58%, - 32%, - 8%, and ,.o 2%, respectively. The contact angle （CA） （-- 12°） of water droplet （3 p-L） on GF is found to be larger than that on Ni foam （,- 107°）, indicating that graphenes have changed the surface wettability of the Ni foam. Meanwhile, the dynamic characteristics of CA of water droplet on GF are different from those on Ni foam. The mechanisms for different behaviors are discussed, which are attributed to volatilization and seepage of water droplets.     

Germanium nanoislands grown by radio frequency magnetron sputtering： Annealing time dependent surface morphology and photoluminescence

Structural and optical properties of ～ 20 nm Ge nanoislands grown on Si(100) by radio frequency (rf) magnetron sputtering under varying annealing conditions are reported. Rapid thermal annealing at a temperature of 600℃ for 30 s, 90 s, and 120 s are performed to examine the influence of annealing time on the surface morphology and photoluminescence properties. X-ray diffraction spectra reveal prominent Ge and GeO 2 peaks highly sensitive to the annealing time. Atomic force microscope micrographs of the as-grown sample show pyramidal nanoislands with relatively high-density (～ 10 11 cm-2 ). The nanoislands become dome-shaped upon annealing through a coarsening process mediated by Oswald ripening. The room temperature photoluminescence peaks for both as-grown (～ 3.29 eV) and annealed (～ 3.19 eV) samples consist of high intensity and broad emission, attributed to the effect of quantum confinement. The red shift (～ 0.10 eV) of the emission peak is attributed to the change in the size of the Ge nanoislands caused by annealing. Our easy fabrication method may contribute to the development of Ge nanostructure-based optoelectronics.     

Curved surface effect and emission on silicon nanostructures

The curved surface （CS） effect on nanosilicon plays a main role in the activation for emission and photonic manipulation. The CS effect breaks the symmetrical shape of nanosilicon on which some bonds can produce localized electron states in the band gap. The investigation in calculation and experiment demonstrates that the different curvatures can form the characteristic electron states for some special bonding on the nanosilicon surface, which are related to a series of peaks in photoluminecience （PL）, such as LN, LNO, Lo1, and Lo2 lines in PL spectra due to Si-N, Si-NO, Si=O, and Si-O-Si bonds on curved surface, respectively. Si-Yb bond on curved surface of Si nanostructures can provide the localized states in the band gap deeply and manipulate the emission wavelength into the window of optical communication by the CS effect, which is marked as the Lyb line of electroluminescence （EL） emission.