Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session P16: Focus Session: Optical Resonances and Techniques in Nano-Optics |
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Sponsoring Units: DMP Chair: Henri Lezec, CNRS & Caltech Room: LACC 404A |
Wednesday, March 23, 2005 11:15AM - 11:51AM |
P16.00001: Cavity cooling of a microlever Invited Speaker: Few years ago P. F. Cohadon, A Heidmann, and M. Pinard demonstrated that laser-cooling of the vibrational modes of a mirror can be achieved by subjecting it to a radiation pressure, actively controlled through a servo loop adjusted to oppose its brownian thermal motion. Atoms in an optical trap on the other hand can be laser-cooled passively without such active feedback, because their random motion is intrinsically damped through their interaction with radiation. In very close analogy with laser-cooling of atoms we have developed a simple and direct experimental method for passive optical cooling of a micromechanical resonator. We established that exploiting cavity-light induced forces allow to quench efficiently the brownian vibrational fluctuations of a gold-coated silicon microlever from room temperature down to an effective temperature of 18 K. Extending this method to optical-cavity-induced radiation pressure might enable the quantum limit of the lever vibrational ground state to be reached. [Preview Abstract] |
Wednesday, March 23, 2005 11:51AM - 12:03PM |
P16.00002: Optical forces at Morphology Dependent Resonance Tsz-Fai (Jack) Ng, Zhifang Lin, Che-Ting Chan A strong optical force can be induced on a pair of transparent dielectric microspheres by exciting the morphology dependent resonance (MDR). We investigate such a resonant optical force through rigorous calculations using multiple scattering theory for the electromagnetic field and the Maxwell stress tensor for the electromagnetic force. The bonding and anti-bonding modes of the electric field of the MDR's correspond to strong attractions and repulsions respectively. At resonance, the force can be enhanced by orders of magnitude as compare to the off-resonance case. With a modest incident light intensity, it is showed that the MDR-force can be stronger than thermal fluctuations and the van der Waals forces when the separation between the spheres is more than a few tens of nano-meter, thus achieving the goal of manipulation. It is showed that stable binding of the spheres is possible. The dependence of the force on separation between the spheres, and the role of absorption by the material, and the robustness against sphere size dispersions are also discussed. [Preview Abstract] |
Wednesday, March 23, 2005 12:03PM - 12:15PM |
P16.00003: Single Metal Nanoparticle Optical Interference Sang-Kee Eah, Heinrich M. Jaeger, Norbert F. Scherer, Gary P. Wiederrecht, Xiao-Min Lin Optical interference of plasmon light scattering from a single gold nanoparticle is experimentally observed by placing a plane mirror nearby. The unique interference patterns in both spatial and spectral domians are reproduced by simulations based on the Huygens-Fresnel diffraction theory. The large spectral resonance enables us to determine the distance to the mirror with a 10 nm resolution without scanning the mirror [1]. The image dipole from a spherical mirror's reflection interferes with the real dipole of a single gold nanoparticle attached to an optical fiber tip [2], resulting in enhancement and inhibition of the resonant scattering rate by the modulation in the scattered light intensity collected outside the interference solid angle. [1] S.-K. Eah, H.M. Jaeger, N.F. Scherer, G.P. Wiederrecht, {\&} X.-M. Lin, submitted to Phys. Rev. Lett. (Nov. 2004). [2] S.-K. Eah, H.M. Jaeger, N.F. Scherer, G.P. Wiederrecht, {\&} X.- M. Lin, Appl. Phys. Lett. (in press). [Preview Abstract] |
Wednesday, March 23, 2005 12:15PM - 12:27PM |
P16.00004: A Simple Route to Tunable Ordered Arrays of Quantum Dots Jessica Pacifico, Daniel Gomez, Paul Mulvaney This work presents an innovative method to grow structurally defined systems of CdSe@ZnS quantum dots (QDs). By firstly utilizing nanosphere lithography (NSL) to generate hexagonally patterned metallic islands, self-assembly of QDs was achieved with the aid of appropriate linker molecules. The ordered arrays were analyzed using AFM imaging and confocal microscopy techniques. The method for building this type of arrays is quite simple and permits the scale-up and scale-down of the size of the arrays. The next step was the construction of a 3D structure by organizing a bi-functionalized chemical linker on the QDs surface, building a structure made of several layers of QDs. Optical properties were studied here. Such arrays may have a large range of applications, as CdSe@ZnS QDs are well-known as the photonic crystals used in waveguides or information storage. Jessica Pacifico, Daniel Gomez and Paul Mulvaney, Advanced Materials, in press, 2004. [Preview Abstract] |
Wednesday, March 23, 2005 12:27PM - 12:39PM |
P16.00005: Optical Studies of a Nanoporous Array in Silicon L. Tian, I. Ahmad, K. Bhargava Ram, L. Menon, M. Holtz We have studied the effects of nanometer-scale texturing on the optical properties of silicon. Surfaces are textured using a non- lithographic template method combined with plasma etching. The process results in an array of cylindrical nanopores 60 nm in diameter and varying in depth up to 1 micron. We observe a significant reduction in near-normal specular optical reflectance from silicon textured this way. This reduction is across a broadband range of photon energies from 2.0 to 6.0 eV, and varies systematically with increasing pore depth. We develop a two-dimension Maxwell-Garnett effective medium approximation to model the specular reflectance. Agreement between the model and data is good provided we take into account the roughness of the nanoporous surface. Micro-Raman scatter is found to depend strongly on the texturing, exhibiting an increase in intensity with pore depth. These results support the notion that both insertion and extraction are enhanced by the nanopore surface treatment. We will summarize the nanotexturing approach, the optical properties, and the effective medium model. [Preview Abstract] |
Wednesday, March 23, 2005 12:39PM - 12:51PM |
P16.00006: Numerical Aperture Increasing Lens Assisted Microscopy and Spectroscopy Anthony N. Vamivakas, Mesut G. Eraslan, M. Selim Unlu, Bennett B. Goldberg A Numerical Aperture Increasing Lens (NAIL) is used for high resolution far-field microscopy and spectroscopy of semiconductor nanostructures. Incorporating NAIL into our low temperature confocal microscope, we have been able to perform high collection efficiency spectroscopy of single, self-assembled InGaAs/GaAs quantum dots. We plan to exploit the measured six-fold collection efficiency increase in our system to enhance the signal-to-noise ratio in a Hanbury-Brown Twiss (HBT) interferometer. In an attempt to quantify the far-field optical resolution of our NAIL assisted thermal microscope, we are using a pulsed UV laser to generate a thermal radiation source in Si with a spatial extent less than .5 micrometers. Previously, we experimentally demonstrated an optical resolution of 1.4 micrometers when imaging semiconductor integrated circuits. [Preview Abstract] |
Wednesday, March 23, 2005 12:51PM - 1:03PM |
P16.00007: Nano-patterning Using an Embedded Particle Monolayer as an Etch Mask Tsutomu Nakanishi, Toshiro Hiraoka, Akira Fujimoto, Koji Asakawa A new nano-fabrication technique using a self-assembled nano-particle monolayer as an etch mask is developed, which forms a homogeneous particle monolayer over a large area. A periodic nano-cone pattern, which acts as an antireflective structure, was fabricated onto the SiO2 substrate by transferring the nano-particles. A trapping layer of thermoplastic resin was formed on the substrate, and then nano-particles were spread to form a multilayer of particles. As it was heated, the particles of the bottom layer were spontaneously embedded in the trapping layer. Excess particles were washed away and the bottom layer remained. The substrate below was etched using the particle monolayer as an etch mask by CF4 reactive ion etching (RIE). As a result, conical nano-cone patterns were transferred over the entire surface of the substrate. Using this method, an antireflective structure with a two-dimensional grating known as a moth-eye surface was fabricated on the SiO2 substrate. Compared with the flat surface, the reflectivity was reduced more than 40{\%}. This can be applied to large flat display. [Preview Abstract] |
Wednesday, March 23, 2005 1:03PM - 1:15PM |
P16.00008: Higher external efficiency of LEDs having nano-structured surface fabricated by self-assembled block-copolymer Akira Fujimoto, Koji Asakawa Recently, the internal quantum efficiency of LED has improved, but the external efficiency remains as low as a few {\%} due to the high refractive index of semiconductors (n=3-3.5). In order to extract more light, a nano-pillar structure on the LED surface was fabricated. This structure has two functions; as an antireflective layer completely transmitting light below a critical angle to the LED surface, and as gratings that diffract the light larger than the critical angle to extract -1st order light. To fabricate this structure on the semiconductor (GaP) surface by dry etching, we employed a periodic dots pattern with self-assembled diblock-copolymer process. The diblock copolymer of polystyrene (PS) - polymethyl methacrylate (PMMA) was used in this study since the PMMA is etched much faster than the PS. The GaP was dry-etched by Cl-based inductively coupled plasma using the remaining PS dots as a mask, and the nano-pillars with a diameter of 100 nm, a period of 150-200 nm, and a height of 400 nm were fabricated. As a result, we improved the external extraction efficiency of the fabricated surface more than 100{\%} compared with the flat one. [Preview Abstract] |
Wednesday, March 23, 2005 1:15PM - 1:27PM |
P16.00009: Ultra-small Ni/NiOx/Ni tunnel junctions for terrahertz and ir applications R.B. Laibowitz, P. Hobbs, F. Libsch, R. Koch, J. Kirtley, G. Keefe, J. Chey We have studied current-voltage, conductance, second derivative and temperature dependence of Ni/NiOx/Ni tunnel junctions having areas less than 0.1 um2. These overlap junctions have very small capacitance and are being studied for use as room temperature, high frequency detectors. The junctions are fabricated using a photolithography derived shadow mask and angular depositions of the Ni. The oxide barrier is formed using a plasma oxidation process. Electron micrographs of the overlap junctions are used to estimate junction area. For RT operation a nonlinear i-v is required and is generally observed. The temperature dependence of the iv characteristics from 100 C to 4 K appears to be that of tunneling although at RT other parallel conduction paths may exist. The nonlinearity of the iv curves at 4 K is much greater than at RT the ratio being about 5 to 1 at 0.1 V applied. Tunneling spectroscopy studies at 4 K reveal scattering mechanisms that can be related to Ni-O excitations. Detailed simulation of both the temperature dependence and the i-v curves shows that the barrier height is about 0.2 eV. [Preview Abstract] |
Wednesday, March 23, 2005 1:27PM - 1:39PM |
P16.00010: An alternative mechanism for surface enhanced spectroscopy: second harmonic surface plasmon resonance Hsia Yu Lin, Yang Fang Chen Strong ultraviolet luminescence having intensity comparable with device quality GaN epifilms has been observed in Au nanoparticles. It is identified that the luminescence involves radiative recombination of electrons in band 6 (sp conduction band) with holes in band 4 (secondary top d band), near the L symmetry point. We show that the strong emission is a consequence of the second harmonic surface plasmon resonance (SHSPR), which is an inherent nature of metallic nanoparticles with high density of surface plasmons. However, for SHSPR we only need a dim pumping source, which is used to trigger the second harmonic absorption of very dense quantum particles, such as surface plasmons in Au nanoclusters. Unlike in the conventional SHG process, the high density quantum particles responsible for the nonlinearity in the SHSPA process preexist in the studied material, which are not due to external perturbation. In addition to Au nanoparticles, we demonstrate that SHSPR provides a very efficient way to enhance the luminescence of a material incorporated with metal nanoparticles. As an example, incorporation of Au nanoparticles into SiO$_{2}$ nanoparticles can enhance the luminescence intensity of the SiO$_{2 }$nanoparticles by a factor as large as 2 orders of magnitude. We thus point out that SHSPR can serve as one of the underlying mechanisms responsible for surface-enhanced nonlinear optical phenomena. [Preview Abstract] |
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