Surface plasmon tunneling through a touching gold nanocylinder array on a thin gold film

The optical property of a structure composed of a touching gold nanocylinder array on a thin gold film is investigated using finite-difference time-domain (FDTD) method. It is discovered that the transmission behavior can be tuned by tuning the geometry of the structure. As the film thickness increases, the transmission mode associated with the localized surface plasmon resonance blue shifts accompanied with a decrease of magnitude and full width at half maximum, and a second transmission appear due to the interaction of the plasmons on the cylinder with their images induced on the film. The localized waveguide resonance diminishes but the second resonance peak is intensified and broadened noticeably with the separation of the cylinder array and film increase. The cylinder radius size influences the localized surface plasmon resonance mode obviously. These results may be helpful for the design of a novel optical device.     

Surface plasmon sensor with gold film deposited on a two-dimensional colloidal crystal

A sensor based on surface plasmon resonance (SPR) of plasmonic crystals fabricated via a colloidal-crystal-assisted templating method is studied. Plasmonic crystals are prepared by depositing a thin gold (Au) layer onto a two-dimensional array of polystyrene spheres self-assembled on a quartz substrate. The enhanced transmission as a result of the SPR of Au plasmonic crystals, which are immersed in different ambient liquids, are measured and compared with that of polystyrene (PS) microsphere templates of different sizes, both before and after removal of Au nanoprisms formed on the quartz substrate through pores among the spheres. It is found that the measured sensitivities exhibit a linear dependence on the refractive index of the surrounding medium and are linked to coupling effects between SPRs on the corrugated Au film and nanoislands. The feasibility of the SPR system in molecular monolayer detection is further demonstrated through a formation of alkanethiolate self-assembled monolayers on the Au film surface, which causes a 4 nm red-shift of the main SPR. PACS  07.07.Df; 73.20.Mf; 78.66.-w; 81.16.Dn     

A novel plasmonic refractive index sensor based on gold/silicon complementary grating structure

A novel complementary grating structure is proposed for plasmonic refractive index sensing due to its strong resonance at near-infrared wavelength.The reflection spectra and the electric field distributions are obtained via the finite-difference time-domain method.Numerical simulation results show that multiple surface plasmon resonance modes can be excited in this novel structure.Subsequently,one of the resonance modes shows appreciable potential in refractive index sensing due to its wide range of action with the environment of the analyte.After optimizing the grating geometric variables of the structure,the designed structure shows the stable sensing performance with a high refractive index sensitivity of 1642 nm per refractive index unit(nm/RIU)and the figure of merit of 409 RIU^-1.The promising simulation results indicate that such a sensor has a broad application prospect in biochemistry.     

A high figure of merit localized surface plasmon sensor based on a gold nanograting on the top of a gold planar film

We investigate the sensitivity and figure of merit （FOM） of a localized surface plasmon （LSP） sensor with gold nanograting on the top of planar metallic film. The sensitivity of the localized surface plasmon sensor is 317 nm/RIU, and the FOM is predicted to be above 8, which is very high for a localized surface plasmon sensor. By employing the rigorous coupled-wave analysis （RCWA） method, we analyze the distribution of the magnetic field and find that the sensing property of our proposed system is attributed to the interactions between the localized surface plasmon around the gold nanostrips and the surface plasmon polarition on the surface of the gold planar metallic film. These findings are important for developing high FOM localized surface plasmon sensors.     

Fabrication of a highly sensitive sensor electrode using a nano-gapped gold particle film

Controlling a gap between electrodes arranged in nanometer size has a great potential for a highly sensitive detection. We have successfully fabricated a sensor based on a nano-gapped gold particle film consisting of gold nanoparticle–alkylchain–gold nanoparticle repeated sequences in a straightforward manner. Here we report on its application to direct DNA analysis, enabling us to read out a specific complementary DNA through electronic protocols.     

A theoretical and experimental study of the behaviour of a parametric array in a random medium

The fluctuations of a parametric signal in a random medium have been investigated. A theoretical expression for the mean square amplitude and phase fluctuations has been derived, by using the small perturbation method. A simplified version of the theoretical model, which predicts the axial amplitude fluctuations of the difference frequency signal, was computerized. Laboratory experiments were carried out in a heated tank in which the fluctuations of a parametric signal and a linearly generated signal were compared. A similar experiment was also carried out in an estuary. The experimental results obtained were consistent with the theoretical estimates.     

Combinatorial study of a gold nanoparticle infusion process in a polymer film

A novel two-step process is described for infusion of gold nanoparticles (5–20 nm typical diameter) into a polymer film. The technique is demonstrated for the first time in a thermoplastic polyurethane elastomer (TPU). An amine-functional monomer, 2-(diethylamino)ethyl methacrylate, and a free-radical photoinitiator are infused into the surface of the TPU, followed by photopolymerization. An amine-functional semi-interpenetrating network (SIPN) is created within a shallow (~100 μm) surface layer. In the second step, a gold salt, HAuCl₄·3H₂O, is infused into the SIPN from a ternary solvent mixture, and redox reaction with the immobilized amine functional groups produces Au⁰ nanoparticles. Combinatorial processing is conducted to visualize the interdependent effects of two variables, monomer soak time (t ₁) and gold salt solution soak time (t ₂). Combinatorial infusion is accomplished by creating orthogonal gradients in t ₁ and t ₂ in a square TPU plate, allowing examination of sample color, particle size, and polydispersity over a wide range of parameter space. Small angle X-ray scattering (SAXS) is employed as non-invasive means to characterize the Au⁰ particles at three locations in the plate. SAXS measurements are validated by TEM analysis of Au⁰ particle size in a reference sample. A rationale is developed for changing particle size and polydispersity through variation of simple process parameters.     

Tunability and linewidth sharpening of plasmon resonances on a periodic gold nanowire array coupled to a thin textured silver film

We theoretically study the plasmon mode spectrum of a multilayer structure consisting of a periodic gold nanowire array and a spatially separated thin silver film with periodic slits. Results show that the plasmon mode spectrum of the multilayer structure depends sensitively on the relative lateral displacement of the Au nanowire array with respect to the textured silver film. This is due to the interaction between the localized surface plasmon (LSP) of the nanowire array and the plasmon modes, including the horizontal LSP and the antisymmetric short-range surface plasmon polariton (SPP), of the textured thin silver film. The strong coupling between the LSP and the antisymmetric short-range SPP results in a redshifted plasmon resonance with a significantly narrow linewidth and a large electromagnetic field enhancement. Moreover, the lateral displacement also has a great influence on the spacer layer controlled dipole-surface interaction. Therefore, this relative lateral displacement provides an efficient way to tune the optical properties of the multilayer structure, and this kind of highly tunable nanostructure can be used as a tunable plasmonic filter or a substrate for LSPs sensor.     

Electromagnetic field distribution on a rough gold thin film: An experimental study as a function of the gold thickness

The electromagnetic field distribution on an illuminated rough gold surface has been investigated by apertureless scanning near-field optical microscopy. The sample consists of an alumina substrate with a variable gold coverage ranging from 0 to 30 monolayers (ML). For such small thicknesses, the metal layer is not continuous but exhibits a certain roughness. We have studied the influence of this thickness on the electromagnetic field localization on the surface. For a gold coverage smaller than 10 equivalent monolayers, the electromagnetic field is almost uniform on the surface. For 10 and 14 ML, the field becomes inhomogeneous and isolated, localized peaks start to be visible. The width of the peaks is smaller than 50 nm. Above 14 ML, strong variations are apparent everywhere on the sample. Their amplitude tends to saturate beyond 24 ML. A complete statistical study of the sample (standard deviation, Fourier analysis) is performed.     

Experimental and theoretical study of the cracking behavior of sol-gel-derived SiO2 film on InP substrate

In this paper, we study and characterize the cracking behavior of a sol-gel-derived amorphous silica film on a InP substrate. The sol-gel silica films are deposited by spin-coating and rapid thermal processing (RTP). It is observed that the volatility of the III-V semiconductor results in the cracking of the films when the annealing temperature is higher than 450 °C, and that the crack patterns are all parallel or perpendicular to 𘜄¢. The experimental results on the crack patterns in the sol-gel silica films are then theoretically analyzed. In addition, the critical thicknesses of the sol-gel films on InP are compared with those deposited on Si.     

Numerical study of dumbbell-shaped gold nanoparticles using in plasmonic waveguides in near infra-red spectrums

In this paper, we investigated plasmonic waveguides in near infra-red spectrum using dumbbell-shaped gold nanoparticles. It is possible to shift localized surface plasmon resonance (LSPR) to the desired wavelength with proper geometrical properties. 3-D FDTD simulations are used to determine the set of geometrical parameters of nanoparticles to obtain LSPR at 1310 and 1550 nm. Employing different configuration of nanoparticles chains, we not only can design waveguides with better optical characteristics but also achieve the demultiplexing function in V-form arrays. The proposed nanoparticles show sharp resonance peak, 168 FWHM bandwidth for λ?=?1310, and 204 nm for λ?=?1550 nm. Linear chains of particles can transport the electromagnetic energy at λ?=?1310 nm, with transmission losses γ_L?=?3 dB/452 and γ_T?=?3 dB/446 nm and group velocities v_gL?=?0.336C₀ and v_gT?=?0.256C₀ for longitudinal and transverse polarizations, respectively, where C₀ is the speed of light in the vacuum. At λ?=?1550 nm, γ_L?=?3 dB/490, γ_T?=?3 dB/604, v_gL?=?0.382C₀ and v_gT?=?0.260C₀. Moreover, we attained 8.13 as minimum ratio of averaged electric field intensity and 36.8 as minimum ratio of averaged Poynting vector as a function of position between two ports in demultiplexing function.     

A theoretical study on the melting of a finite slab with a pulsed laser

Calculations of the spatial and temporal temperature distributions in the molten layer thickness, the still solid part and in the backward surface of the finite slab were carried out during the irradiation with a pulsed laser. The two-dimensional Laplace integral transform technique has been applied to obtain the mathematical expressions for these temperature distributions and the molten layer thickness as a function of the melting time. The derivations have taken into account the temperature-dependent absorption coefficient of the irradiated surface and the cooling. As an illustrative example, computations were carried out on a finite aluminum (Al) target.     

Effects of different structural parameters and the medium environment on plasmonic lattice resonance formed by Ag nanospheres on SiO_2 nanopillar arrays

The effects of the diameter of SiO2 nanopillars,the diameter of Ag nanospheres,the arrays’period,and the medium environment on the plasmonic lattice resonance(PLR)formed by Ag nanospheres on SiO2 nanopillar arrays are systematically investigated.Larger diameters of SiO2 nanopillars with other parameters kept constant will widen the PLR peak,redshift the PLR wavelength,and weaken the PLR intensity.Larger diameters of Ag nanospheres with other parameters kept constant will widen the PLR peak,redshift the PLR wavelength,and strengthen the PLR intensity.Larger array periods or larger refractive index of medium environment corresponds to larger PLR wavelengths.     

Comparative study of ethanol sensor based on gold nanoparticles: ZnO nanostructure and gold: ZnO nanostructure

Gold colloid:ZnO nanostructures were prepared from Zn powder by using thermal oxidation technique on alumina substrates, then it was impregnated by gold colloid for comparative study. The gold colloid is the solution prepared by chemical reduction technique; it appeared red color for gold nanoparticle solution and yellow color for gold solution. The heating temperature and sintering time of thermal oxidation were 700 °C and 24 h, respectively under oxygen atmosphere. The structural characteristics of gold colloid:ZnO nanostructures and pure ZnO nanostructures were studied using filed emission scanning electron microscope (FE-SEM). From FE-SEM images, the diameter and length of gold colloid:ZnO nanostructures and ZnO nanostructures were in the ranges of 100-500 nm and 2.0-7.0 μm, respectively. The ethanol sensing characteristics of gold colloid:ZnO nanostructures and ZnO nanostructures were observed from the resistance alteration under ethanol vapor atmosphere at concentrations of 50, 100, 200, 500, and 1000 ppm with the operating temperature of 260-360 °C. It was found that the sensitivity of sensor depends on the operating temperature and ethanol vapor concentrations. The sensitivity of gold colloid:ZnO nanostructures were improved with comparative pure ZnO nanostructures, while the optimum operating temperature was 300 °C. The mechanism analysis of sensor revealed that the oxygen species on the surface was O²⁻.     

Structured lens formed by a 2D square hole array in a metallic film

A method is proposed to modulate phase using variant square holes in a metallic film based on a fundamental mode approximation model. Phase retardation through square holes in a subwavelength scale in a thin metal film has been analyzed and calculated. Based on the model, a structured lens with a numerical aperture of 0.583 and a focal length of 240 microm formed by a 2D square hole array in a metallic film is designed. Numerical simulation using the finite-difference time-domain method is carried out, and the results agree with the theoretical analysis. A focal spot close to the diffraction limit can be obtained.     

A Method for Preparation of Ordered Porous Silicon Based on a 2D SiO_2 Template

A new method for fabricating ordered porous silicon is reported.A two-dimensional silica nanosphere array is used as a template with a hydrofluoric acid-hydrogen peroxide solution for etching the nanospheres.The initial diameter and distribution of the holes in the resulting porous silicon layer are determined by the size and distribution of the silica nanospheres.The corrosion time can be used to control the depths of the holes.It is found that the presence of a SiO_2 layer,formed by the oxidation of the rough internal surface of the hole,is the primary reason allowing the corrosion to proceed.Ultraviolet reflection and thermal conductivity measurements show that the diameter and distribution of the holes have a great influence on properties of the porous silicon.     

A theoretical model to predict the low-frequency sound absorption of a helmholtz resonator array

A theoretical method based on mutual radiation impedance is proposed to compute the sound absorption performance of a Helmholtz resonator array in the low-frequency range. Any configuration of resonator arrangement can be allowed in the method, while all the resonators may or may not be identical. Comparisons of the theoretical predictions with those done by the past studies or experiments show that the present method can accurately predict the absorption performance in more general cases.     

Superconductivity of bilayer titanium/indium thin film grown on SiO_2/Si(001)

Bilayer superconducting films with tunable transition temperature(Tc) are a critical ingredient to the fabrication of high-performance transition edge sensors. Commonly chosen materials include Mo/Au, Mo/Cu, Ti/Au, and Ti/Al systems. Here in this work, titanium/indium(Ti/In) bilayer superconducting films are successfully fabricated on SiO_2/Si(001)substrates by molecular beam epitaxy(MBE). The success in the epitaxial growth of indium on titanium is achieved by lowering the substrate temperature to-150?C during indium evaporation. We measure the critical temperature under a bias current of 10 μA, and obtain different superconducting transition temperatures ranging from 645 m K to 2.7 K by adjusting the thickness ratio of Ti/In. Our results demonstrate that the transition temperature decreases as the thickness ratio of Ti/In increases.     

Rectified vortex motion in an Nb film with a spacing-graded array of holes

Superconducting Nb thin films with a spacing-graded array of holes were prepared by electron beam lithography. Two films with different hole gradients were fabricated. The ac-driven vortices were investigated in Nb superconductors with a spacing-graded array of holes. The measurements revealed pronounced rectified voltage when the vortex lattice is driven by an ac injected current. The rectified voltage is mainly caused by the strength of the vortex–vortex interaction. The rectified motion of a vortex is affected by the pinning potential of the spacing-graded array and the applied magnetic field. The vortex–vortex interaction strength changes the effective pinning landscape of the vortices and an asymmetric potential is formed. Vortices depin easily from high concentration to low concentration of pinning sites. In both samples, the ac-driven vortices exhibit a variety of dynamical responses and the rectified voltage is tunable with the applied magnetic field.     

A combined experimental and theoretical study on 8-hydroxy-2-quinolinecarboxylic acid

The mid-IR and Raman spectra of 8-hydroxy-2-quinolinecarboxylic acid (8HQC) were recorded. These spectra were interpreted with the help of B3LYP/6–311 ++G(d,p) calculations and potential energy distribution (PED) analysis. As a result of the calculations, seven tautomers were determined among many stable conformations. The experimental spectra were concordant with the theoretical data of one tautomer. In the functional group region overtone and combination bands were detected and assigned. In addition, because of several peaks in the IR spectrum, it was proposed that the 8HQC exhibits dimerization in condensed phase. Possible dimeric forms of 8HQC were evaluated at the same level of theory, and it has been seen that the calculation results confirm the above proposal. ¹H and ¹³C NMR chemical shifts of 8HQC have been calculated, and compared with the experimental data. The frontier molecular orbital properties and the atomic charges were also theoretically obtained and presented.