Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session G20: Focus Session: Metamaterials - Nanoparticles and Nanoparticle Arrays |
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Sponsoring Units: DMP Chair: Shun Shang Lo, University of Notre Dame Room: 322 |
Tuesday, March 19, 2013 11:15AM - 11:27AM |
G20.00001: Rare earth doped upconverting particles for different photonic applications Madhab Pokhrel, Ajith Kumar Gangadharan, Dhiraj Kumar Sardar Trivalent rare earth ions especially erbium (Er$^{3+})$ and ytterbium (Yb$^{3+})$ co-doped in various host nanoparticles are known for their extraordinary spectroscopic properties. A thorough optical characterization including the absolute upconversion quantum yield (QY) measurement is of critical importance in evaluating their potential for various photonic applications. In this paper, we will be presenting a measured absolute upconversion QYs for Yb$^{3+}$ and Er$^{3+}$ doped in La$_{2}$O$_{2}$S under 980 and 1550 nm excitation at various power densities. Comparison of absolute QYs for different concentrations of Yb$^{3+}$ and Er$^{3+}$ doped in La$_{2}$O$_{2}$S will be made for all the upconversion emissions with respect to reported most efficient upconverting phosphor NaYF$_{4}$ doped with 20{\%} Yb$^{3+}$ and 2{\%} Er$^{3+}$. Furthermore, applications of these phosphors in different areas such as bio-imaging, solar cell, security, etc. will be explored depending on the measured absolute upconversion quantum yields. In addition, preliminary results on in vitro imaging using upconverting nanoparticles as a contrast agent will be reported. [Preview Abstract] |
Tuesday, March 19, 2013 11:27AM - 11:39AM |
G20.00002: Characterization and light emission from Erbium Oxide Nanoparticles Muhammad Maqbool, Lynda Wilkinson, Iftikhar Ahmad The present work reports light emission from Erbium Oxide nanoparticles. The nanoparticles, with 43 nm diameter, were obtained in the form of nanopowder with 99.9{\%} purity. These nanoparticles were characterized for their light emission under a 532 nm Nd:YAG laser excitation. A Photoluminescence (PL) system was used to detect fluorescence emission from the nanoparticles. The PL system consisted of Pixis brand CCD camera with a range of 300 to 2000 nm. The Erbium Oxide nanoparticles were also mixed in distilled water to obtain spectrum. Two emission peaks were observed at 554 nm and 813 nm. The green emission at 554nm was obtained as a result of $^4$I$_{15/2} \to $ $^4$S$_{3/2}$ transition, and the near infrared emission from $^4$I$_{15/2} \to $ $^4$I$_{13/2}$ transition. The process was also repeated in vacuum and it was found that the green emission enhances tremendously when the nanoparticles are excited in vacuum. This enhanced luminescence from the Erbium Oxide nanoparticles shows their potential importance in the optical devices and Biomedical applications. [Preview Abstract] |
Tuesday, March 19, 2013 11:39AM - 11:51AM |
G20.00003: The Vibrational and Photoluminescence Properties of TiO$_2$ Nanoparticles Reacted with Eu$^{3+}$ Ions under Hydrothermal Conditions L. Farris, H. Yan, P. McCart, R. Mayanovic TiO$_{2}$ has been shown to be an effective material for environmental purification and photocatalysis. The catalytic activity of TiO$_{2}$ nanoparticles (NPs) is enhanced due to the increase in the ratio of surface area to volume at the nano-scale. The enhancement of catalytic activity is further increased by the modification of the surface due to the adsorption of transition-metal ions on TiO$_{2}$ NPs. The reactivity of Eu$^{3+}$ ions with anatase TiO$_{2}$ nanoparticles under various pH and pressure-temperature (P-T) conditions in aqueous fluids has been investigated. A hydrothermal reactor was used to modify the surface of the TiO$_{2}$ nanoparticles with Eu$^{3+}$ ions in aqueous fluids at high P-T conditions. The Eu-reacted and untreated TiO$_{2}$ NPs were examined using XRD, SEM, and Raman and photoluminescence spectroscopy. The modifications of the vibrational and photoluminescence properties of the TiO$_{2}$ NPs due to the surface-adsorption of Eu$^{3+}$ ions are discussed. [Preview Abstract] |
Tuesday, March 19, 2013 11:51AM - 12:27PM |
G20.00004: Optical Spectroscopy of Single Gold Nanoparticles Invited Speaker: Michel Orrit Compared to electron microscopy or to scanning probe microscopy, the optical selection of individual nanoparticles in a far-field microscope provides non-invasive probing of deep layers and commands a wide range of time-resolved and frequency-resolved techniques. Optical signals provide unique insights into the dynamics of nano-objects and of their surroundings [1]. I shall illustrate applications of single-nanoparticle optics with recent topics from our group. i) We study single gold nanoparticles by photothermal and pump-probe microscopy [2]. These experiments can be done in an optical trap, where a single nanorod orients along the trapping polarization, and studied the acoustic damping of gold nanoparticles. ii) Photothermal microscopy opens the study of non-fluorescent absorbers, down to single-molecule sensitivity [3]. Combining photothermal contrast with photoluminescence, we can measure the luminescence quantum yield on a single-particle basis. Moreover, the high signal-to-noise ratio opens up uses of individual gold nanoparticles for local plasmonic and chemical probing, down to single-protein level [4]. iii) Gold nanorods generate strong field enhancements near their tips. By matching the rod's aspect ratio to a dye's fluorescence and excitation spectra, we could observe thousand-fold enhancements for the fluorescence of single Crystal Violet molecules [5]. Gold nanorods can produce local fields as high as those of bow-tie antennas, thanks to their narrow plasmon resonance, but they are much easier to synthesize, functionalize and disperse in solution than lithographically made nanostructures. Acknowledgement : The work presented was done over the last 7 years by F. Kulzer, M. Lippitz, A. Tchebotareva, A. Gaiduk, P. Zijlstra, S. Khatua, M. A. van Dijk, P. V. Ruijgrok, M. Yorulmaz, HF. Yuan, and N. Verhart in the author's group.\\[4pt] [1] F. Kulzer et al., Angew. Chem. \textbf{49} (2010) 854.\\[0pt] [2] A. L. Tchebotareva et al., Laser Photon. Rev. \textbf{4} (2010) 581-597.\\[0pt] [3] A. Gaiduk et al. Science \textbf{330} (2010) 353\\[0pt] [4] P. Zijlstra et al., Nature Nanotech. \textbf{7} (2012) 379.\\[0pt] [5] HF. Yuan et al., Angew. Chem., in press (2013). [Preview Abstract] |
Tuesday, March 19, 2013 12:27PM - 12:39PM |
G20.00005: Physical property control of nanoparticles for effective light-energy use Sungsook Ahn, Sung Yong Jung, Sang Joon Lee Up-to-now only limited materials are useful for solar energy harvesting, which makes the expansion of available photoactive materials important. In this point of view, physical property control is one of the reasonable solutions rather than creation of new materials. In this study, as a representative light-responsive metal nanoparticle (NP), gold NPs of a fixed size (average diameter of 20 nm) are surface-activated in pH-controlled aqueous solutions or chemically cross-linked, followed by electron-beam treatment. Chemical-interlinking of NPs behaves like a polymerization, generating characteristic structures (Fractal dimension). The absorbance at UV-vis and THz regions are significantly modified depending on the surface-modification and controlled cluster structures of NPs. Electron beams of different doses are applied to change the surface energy of NPs forming a specific surface layer (proximity length) and the structural modification of NP clusters. This changes the absorption energy band toward shorter-wavelength UV-vis light, benefiting solar energy harvesting. This study contributes to fundamental understanding on nanoparticle technology and provides general information for new metamaterial design for effective light energy use. [Preview Abstract] |
Tuesday, March 19, 2013 12:39PM - 12:51PM |
G20.00006: Size and shape dependence of electronic and optical excitations in TiO$_2$ nanocrystals Kopinjol Baishya, Serdar Ogut We present results for the electronic structures, quasi-particle gaps, and the absorption spectra of TiO$_2$ nanocrystals of both rutile and anatase phases with various shapes, sizes, and surfaces exposed. We study the size and shape dependences of these electronic and optical properties, computed both within time-dependent density functional theory and many-body perturbation methods such as the GW-BSE, using appropriately passivated nanocrystals to mimic bulk termination. Surface effects are examined by using nanocrystals of various sizes with particular surfaces, such as (110) in rutile and (101) in anatase phases, exposed. We interpret the resulting optical absorption spectra of these nanocrystals in terms of the bulk spectra and compare them with predictions from classical Mie-Gans theory. [Preview Abstract] |
Tuesday, March 19, 2013 12:51PM - 1:03PM |
G20.00007: Pattern curvature to control pore shape and its ordering Guiduk Yu, Kyusoon Shin Triangular pore in inverse-hexagonal packing was fabricated by anodizing Al with convex pattern in hexagonal packing. The convexly patterned Al was prepared \textit{via} replication of the concave structure formed in self-assembled anodized aluminum oxide (AAO). Self-assembled AAO without pre-patterning produces hexagonal packing circular pores. Exploitation of the inversed structure was found to create well-defined triangular pores in inverse-hexagonal packing. Anisotropic pore feature was discussed to come from the alternating distance between the pits and the curvature of the pattern. Also, by controlling the topography of the convex pattern around pits, we investigated the effect of pattern topography on pore initiation. [Preview Abstract] |
Tuesday, March 19, 2013 1:03PM - 1:15PM |
G20.00008: Patterning of GaAs and Si substrates using self-organized Al$_{2}$O$_{3}$ templates and epitaxial growth of GaAs nanostructures Archana Kumari, John Hatch, Jaesuk Kwon, Xin Zhang, Everett Fraser, Chae Hyun Kim, Hao Zeng, Hong Luo Reactive ion etching is used with Al$_{2}$O$_{3}$ templates to pattern SiO$_{2}$ films deposited on GaAs and Si substrates. The technique allows nanopatterning of substrates without photo or e-beam lithography. The SiO$_{2}$ film pattern consists of holes of about 80 nm diameter with a pitch of about 100 nm. GaAs nanostructures are grown on the patterned substrates by molecular beam epitaxy. The observed arrays of nanostructures closely follow the patterns on SiO$_{2}$. Several types of structures are observed depending on the growth conditions, including pillars with flat hexagonal tops and pyramidal triangular tops. Characterization of the structures will be discussed. This work was supported by NSF DMR1006286. [Preview Abstract] |
Tuesday, March 19, 2013 1:15PM - 1:27PM |
G20.00009: Nanostructures Using Anodic Aluminum Oxide Ilya Valmianski, Carlos M. Monton, Juan Pereiro, Ali C. Basaran, Ivan K. Schuller We present two fabrication methods for asymmetric mesoscopic dot arrays over macroscopic areas using anodic aluminum oxide templates. In the first approach, metal is deposited at 45$^{\mathrm{o}}$~to the template axis to partially close the pores and produce an elliptical shadow-mask. In the second approach, now underway, nanoimprint lithography on a polymer intermediary layer is followed by reactive ion etching to generate asymmetric pore seeds. Both these techniques are quantified by an analysis of the lateral morphology and lattice of the pores or dots using scanning electron microscopy and a newly developed MATLAB based code (available for free download at http://ischuller.ucsd.edu). The code automatically provides a segmentation of the measured area and the statistics of morphological properties such as area, diameter, and eccentricity, as well as the lattice properties such as number of nearest neighbors, and unbiased angular and radial two point correlation functions. Furthermore, novel user defined statistics can be easily obtained. We will additionally present several applications of these methods to superconducting, ferromagnetic, and organic nanostructures. [Preview Abstract] |
Tuesday, March 19, 2013 1:27PM - 1:39PM |
G20.00010: Spectroscopic ellipsometric studies of randomly distributed plasmonic Gallium nanoparticles Yang Yang, Tong-Ho Kim, Neset Akozbek, April Brown, Henry Everitt Ultraviolet surfaced-enhanced Raman scattering (UV-SERS) was recently observed using randomly distributed Gallium nanoparticles (Ga NPs) deposited on sapphire by molecular beam expitaxy at room temperature. Atomic force and scanning electron microscopies revealed that the radii of the hemispheroid NPs follow unimodal or bimodal pseudo Gaussian distributions whose mean diameters increase with increasing Ga dosage (i.e. growth time). Variable angle spectroscopic ellipsometric measurements were then performed on Ga NP ensembles to explore the correlation between the polarimetric optical response and the local morphology. An effective medium composed of single or double Lorentzian oscillators was found to reproduce the optical response of Ga NP ensembles with resonance frequencies that decrease monotonically with increasing NP size. In addition, a strong depolarization response was observed for near-normal incidence. Interestingly, the sample for which the depolarization peak was closest to the 325nm laser excitation wavelength was the sample with the highest SERS enhancement factor. [Preview Abstract] |
Tuesday, March 19, 2013 1:39PM - 1:51PM |
G20.00011: Optical Properties of Focused Ion Beam-Induced Plasmonic Ga Nanoparticle Arrays on Compound Semiconductor Surfaces Myungkoo Kang, Jia-Hung Wu, Timothy Saucer, Ali Al-Heji, Jieun Lee, Vanessa Sih, Rachel Goldman Recently, metallic nanoparticles (NPs) on semiconductor surfaces have enabled the generation of surface plasmon resonances (SPR) which are promising for enhanced light emission, highly-efficient solar cell, ultra-sensitive biosensors, and negative refractive index metamaterials. Ion sputtering-induced surface pattern formation has the potential to become a cost-effective method for achieving metallic NP arrays. Here, we report optical properties of focused ion beam (FIB)-induced plasmonic Ga NP arrays on compound semiconductor surfaces. To date, we have examined SPR energy of FIB-induced Ga NP arrays. The SPR energies increase with decreasing NP or chain diameter, due to particle diameter-dependent dipole interactions within the metallic NPs. We have utilized SPR of FIB-induced Ga NPs for the enhancement of GaAs photoluminescence (PL) efficiency. The maximum PL enhancement occurs for the Ga NP diameter predicted to exhibit a SPR energy corresponding to the GaAs donor-acceptor pair emission energy. When the SPR energy matches the energy of the free carriers in GaAs, it is transferred to the Ga NPs, inducing an enhancement of the spontaneous emission rate. These results suggest that FIB-induced Ga NPs can be a promising alternative plasmonic material. [Preview Abstract] |
Tuesday, March 19, 2013 1:51PM - 2:03PM |
G20.00012: Engineering structured light with Vogel spiral arrays of nanoparticles Nate Lawrence, Jacob Trevino, Luca Dal Negro We present a general analytical model for light scattering by arbitrary Vogel spiral arrays of circular apertures uniformly illuminated at normal incidence. This model suffices to unveil the fundamental mathematical structure of their complex Fraunhofer diffraction patterns and enables the engineering of optical beams carrying multiple values of orbital angular momentum (OAM). By performing analytical Fourier-Hankel decomposition of spiral arrays and far field patterns, we rigorously demonstrate the ability to encode specific numerical sequences onto the OAM values of diffracted optical beams. In particular, we show that these OAM values are determined by the rational approximations of the continued fraction expansions of the irrational angles utilized to generate Vogel spirals. Finally, we experimentally demonstrate structured light carrying multiple values of OAM in the far-field scattering region of Vogel spiral arrays of metallic nanoparticles. Using Fourier-Hankel mode decomposition analysis and interferometric reconstruction of the complex amplitude of scattered waves, we show the ability to encode well-defined numerical sequences, determined by the aperiodic spiral geometry, into azimuthal OAM values, in excellent agreement with analytical scattering theory. The generation of sequences of OAM values by light scattering from engineered aperiodic surfaces is relevant to a number of device applications for secure optical communication, classical and quantum cryptography. [Preview Abstract] |
Tuesday, March 19, 2013 2:03PM - 2:15PM |
G20.00013: Bandgap analysis and emission enhancement from Aperiodic Vogel Spiral Arrays of dielectric nanopillars Jacob Trevino, Gary Walsh, Luca Dal Negro We report on an experimental and theoretical investigation of the structural and photonic mode properties of Vogel spiral arrays of dielectric cylinders in air. We have designed and fabricated hydrogenated amorphous silicon (aSi:H) golden angle spiral nanopillar arrays with localized bandedge modes at the emission wavelength of a commercial near-infrared (NIR) laser dye. Variable-angle reflectance measurements are utilized to experimentally investigate the photon dispersion diagram of spiral arrays and to locate photonic bandgaps. Experimental results are found to be in good agreement with rigorous coupled-wave analysis (RCWA) calculations. These findings offer the opportunity to create novel photonic devices that leverage radially localized and isotropic bandedge modes to enhance light-matter coupling, such as optical sensors, light sources, concentrators, and broadband optical couplers. [Preview Abstract] |
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