Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Q32: Focus Session: Optical Properties of Semiconductor and Metal Nanostructures |
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Sponsoring Units: DMP Chair: Rainer Hillenbrand, CIC nanoGUNE, Spain Room: C144 |
Wednesday, March 23, 2011 11:15AM - 11:27AM |
Q32.00001: Application of modified phonon confinement model in Raman characterization of Ge nanowires K. Roodenko, I.A. Goldthorpe, P.C. McIntyre, Y.J. Chabal Raman spectroscopy is an attractive tool for characterization of low-dimensional materials, such as carbon nanotubes, graphene sheets or semiconductor nanowires. Phonon confinement model [1,2] was proposed to interpret Raman signal obtained from low-dimensional materials. Due to the finite-size of the nanostructures, the fundamental q$\sim $0 Raman selection rule is relaxed, allowing the contribution from phonons away from the Brillouin-zone center. In this contribution we address several unresolved issues, such as the factors within the confinement function, incorporation of crystallographic orientation, and the interplay between the temperature and the nanostructure size [3]. Application of the modified model to the interpretation of Raman signal from Ge nanowires will be discussed.\\[4pt] [1] H. Richter, et al., Solid State Commun. 39, 625 (1981).\\[0pt] [2] I. H. Campbell et al., Solid State Commun. 58, 739 (1986).\\[0pt] [3] K. Roodenko et al., Phys. Rev. B 82, 115210 (2010). [Preview Abstract] |
Wednesday, March 23, 2011 11:27AM - 11:39AM |
Q32.00002: Laser-Induced, Local Oxidation of Copper Nanoparticle Films During Raman Measurements Angela R. Hight Walker, Guangjun Cheng, Irene Calizo The optical properties of gold and silver nanoparticles and their films have been thoroughly investigated as surface enhanced Raman scattering (SERS) substrates and chemical reaction promoters. Similar to gold and silver nanoparticles, copper nanoparticles exhibit distinct plasmon absorptions in the visible region. The work on copper nanoparticles and their films is limited due to their oxidization in air. However, their high reactivity actually provides an opportunity to exploit the laser-induced thermal effect and chemical reactions of these nanoparticles. Here, we present our investigation of the local oxidation of a copper nanoparticle film induced by a visible laser source during Raman spectroscopic measurements. The copper nanoparticle film is prepared by drop-casting chemically synthesized copper colloid onto silicon oxide/silicon substrate. The local oxidation induced by visible lasers in Raman spectroscopy is monitored with the distinct scattering peaks for copper oxides. Optical microscopy and scanning electron microscopy have been used to characterize the laser-induced morphological changes in the film. The results of this oxidation process with different excitation wavelengths and different laser powers will be presented. [Preview Abstract] |
Wednesday, March 23, 2011 11:39AM - 11:51AM |
Q32.00003: Observation of UV Surface-Enhanced Raman Spectra using Ga Nanoparticles Yang Yang, John Callahan, Kevin Lantz, John Foreman, Pae Wu, Tong-Ho King, April Brown, Henry Everitt Ultraviolet (UV) surface enhanced Raman spectra (SERS) are observed for the first time using gallium nanoparticles (Ga NPs). Ga NP ensembles were synthesized on sapphire substrates at room temperature by molecular beam epitaxy. In situ spectroscopic ellipsometry was used to tune the UV local surface plasmon resonance (LSPR) wavelengths of the Ga NP ensembles during deposition. Three samples were prepared with LSPR wavelengths of 325, 295, and 260nm. UV Raman spectra using a 325nm HeCd laser were collected from fixed thicknesses of cresyl violet, poly(3-hexylthiopene), or MEH-CN-PPV that were spin cast onto these three samples, each of which had a NP-free region. A sample!`\={ }s enhancement was measured by comparing selected Raman signal intensities from the NP-covered and bare surfaces. Enhancements were found to decrease with increasing detuning between the laser and LSPR wavelengths. Similar behavior was observed from Ga NPs after 3 months of exposure to air, demonstrating the resilience of Ga NPs to oxidation. [Preview Abstract] |
Wednesday, March 23, 2011 11:51AM - 12:03PM |
Q32.00004: Electronic origin of photoluminescence from Si nanocrystal embedded in amorphous SiO2 matrix Tianshu Li, Francois Gygi, Giulia Galli Through combining classical molecular dynamics and {\em ab initio} calculation, we have created composite models of Si nano crystal embedded in SiO$_2$ amorphous matrices, with the sizes of Si nanocrystals ranging from 1.3 nm $\sim$ 1.9 nm. Electronic structure calculations showed that the band gap of composite structure increases as the size of Si nanocrystal reduces, however the increase of gap is mainly attributed to the {\em lowering of valence band edge}, with conduction band edge virtually unchanged. It was also found that while the wavefucntions from conduction band edges are extended over the entire Si nanocrystal, those from the valence band edges are mainly distributed near the nanocrystal/matrix interface. Further analysis identified that the valence band edges are dominated by the local distortion of nanocrystal from diamond cubic structure, which increases as both approaching the surface of Si nanocrystal, and decreasing the size of Si nanocrystal. This finding suggests that the local strain induced by surrounding amorphous SiO$_2$ matrix may play a key role in the photoluminescence of Si nanocrystal/SiO$_2$ amorphous matrix composite structures. [Preview Abstract] |
Wednesday, March 23, 2011 12:03PM - 12:15PM |
Q32.00005: Enhanced luminescence in terbium-cerium co-doped tin oxide quantum dots Christie Larochelle, Kelly McCutcheon, Rebecca Sobel SnO$_2$ quantum dots doped with Tb$^{3+}$ exhibit strong luminescence from the Tb$^{3+}$ dopants due to efficient energy transfer from the SnO$_2$ donors to the Tb$^{3+}$ acceptor ions. We report results from a study of the effect of co-doping the SnO$_2$ dots with both Tb$^{3+}$ and Ce$^{3+}$ on the photoluminescence properties of the samples. The dots were synthesized using a sol-gel technique and the Ce$^{3+}$/Tb$^{3+}$ ratio was varied while keeping the total doping level at 1wt$\%$. X-ray diffraction and TEM results confirm the presence of nanocrystals of less than 10 nm in diameter. Photoluminescence results indicate that the Tb$^{3+}$ ions are incorporated in a crystalline environment and that co-doping with Ce$^{3+}$ enhances the energy transfer efficiency and therefore the intensity of the Tb$^{3+}$ luminescence. [Preview Abstract] |
Wednesday, March 23, 2011 12:15PM - 12:27PM |
Q32.00006: Stabilization of fluorescent silver clusters by RNA homopolymers and their DNA analogs: C,G vs A,T(U) Dichotomy Danielle Schultz, Elisabeth Gwinn We show that single-stranded RNA stabilizes fluorescent silver nanoclusters (Ag:RNAs) in aqueous solution, analogous to previously studied Ag:DNAs. To determine whether the different canonical nucleosides play similar roles in stabilizing fluorescent silver species in RNA and DNA hosts, we compare RNA homopolymers of rA,rC,rG and rU to their DNA counterparts, and observe the same base-dependent dichotomy: visible- to IR-emitting silver complexes are stabilized by C and G homopolymers, but not by A or T(U) homopolymers at neutral pH. Shifts in emission wavelengths between Ag:RNA and Ag:DNA analogs show that both base and sugar influence populations of fluorescent species. The data indicate a minimum binding-pocket size of roughly five C or G bases for fluorescent species. These findings open the scope of silver cluster fluorophores to the diversely structured and functional arena of RNA and have implications for rational designs of nucleic acid hosts. Supported by NSF CHE-0848375. [Preview Abstract] |
Wednesday, March 23, 2011 12:27PM - 12:39PM |
Q32.00007: Electronic and Optical Excitations in Perylene Diimide Derived Dye Molecules from First Principles Kopinjol Baishya, Serdar Ogut, Ersen Mete, Oguz Gulseren, Sinasi Ellialtioglu Halogenated perylene diimide dyes, such as Br-PDI (Br$_2$C$_{24} $H$_8$N$_2$O$_4$) and their glycine (BrGly) and aspartine (BrAsp) derivatives are known to absorb and emit light in the visible range with high quantum yields, and have good heat and chemical stability. As such, they are promising alternatives to the expensive (Ru-based) metal-driven dye sensitizers for solar cell applications. In this talk, we present results for the electronic structures, quasiparicle gaps, and the absorption spectra of PDI-derived dye molecules BrPDI, BrGly, and BrAsp, computed within the time-dependent density functional theory as well as many body perturbation techniques such as the GW method and the solution of the Bethe-Salpeter equation. In addition to discussing our results for bare molecules, we also present our preliminary studies for the change in their electronic and optical properties when they are attached to stoichiometric and reduced rutile TiO$_2$ (110) surfaces. [Preview Abstract] |
Wednesday, March 23, 2011 12:39PM - 12:51PM |
Q32.00008: Enhanced light emission via plasmonic and non-plasmonic effects in metal ion-implanted Silicon Akhilesh Singh, Karol Gryczynski, Arkadii Krokhin, Floyd McDaniel, Arup Neogi We have observed enhanced photoluminescence from metal implanted nanoscale Silicon light emitters. Low energy (30 keV) Au and Ag metal ions were implanted in crystalline silicon to achieve non-plasmonic and plasmonic enhancement of light emission over a broad spectral range. The emission in the UV region can be significantly enhanced by the surface plasmon (SP) induced radiative recombination process. The recombination of carriers in Si bound exciton is also influenced by transverse optical phonon due to the polarization of the surface of bound exciton complex. The recombination life time of the electron-hole pair as estimated from the time resolved PL measurement changes from $\sim $ 2 ns to 400 ps in the presence of Ag ion induced SP polaritons. The non-resonant emission can be enhanced by electrostatic-image charge effects. The emission in the visible (570 nm) and UV (370 nm) wavelength range can also be significantly enhanced by electrostatic image charge effects induced by Au nanoparticles [Preview Abstract] |
Wednesday, March 23, 2011 12:51PM - 1:03PM |
Q32.00009: Exciton-plasmon and spin-plasmon interactions in hybrid semiconductor-metal nanostructures Alexander Govorov Coulomb and electromagnetic interactions between excitons and plasmons in nanocrystals cause several effects: energy transfer between nanoparticles, plasmon enhancement, Lamb shifts of exciton lines, Fano interference. In a complex composed of semiconductor quantum dot and metal nanoparticle, plasmons interact with spin-polarized excitons. This interaction leads to the formation of coupled spin-plasmon excitations and to spin-dependent Fano resonances. If an exciton-plasmon system includes chiral elements (chiral molecules or nanocrystals), the exciton-plasmon interaction is able to create new plasmonic lines in circular dichroism spectra. [Preview Abstract] |
Wednesday, March 23, 2011 1:03PM - 1:15PM |
Q32.00010: Generalized Ellipsometry on Ferromagnetic Sculptured Thin Films. Daniel Schmidt, Tino Hofmann, Kah Mok, Heidemarie Schmidt, Ralf Skomski, Eva Schubert, Mathias Schubert We present and discuss generalized ellipsometry and generalized vector-magneto-optic ellipsometry investigations on cobalt nanostructured thin films with slanted, highly-spatially coherent, columnar arrangement. The samples were prepared by glancing angle deposition. The thin films are highly transparent and reveal strong form-induced birefringence. We observe giant Kerr rotation in the visible spectral region, tunable by choice of the nanostructure geometry. Spatial magnetization orientation hysteresis and magnetization magnitude hysteresis properties are studied using a 3-dimensional Helmholtz coil arrangement allowing for arbitrary magnetic field direction at the sample position for field strengths up to 0.4 Tesla. Analysis of data obtained within this novel vector-magneto-optic setup reveals magnetization anisotropy of the Co slanted nanocolumns supported by mean-field theory modeling. [Preview Abstract] |
Wednesday, March 23, 2011 1:15PM - 1:27PM |
Q32.00011: Coupled Quantum Dot-Metal Nanoparticle Systems: Hybrid Behavior and Excitation Transport Ryan Artuso, Garnett Bryant Transmission of information between qubits for quantum communication and quantum computing will require directed nanoscale transmission where the quality of the information can be maintained. One paradigm proposes to achieve directed nanoscale transmission by coupling qubits, for example in quantum dots, to plasmonic nanoantennas or nanoguides made from metallic nanowires and nanoparticles. We study theoretically the response of hybrid nanostructure molecules consisting of multiple semiconductor quantum dots (SQD), and metal nanoparticles (MNP) subject to an applied optical field. We consider the situation where the SQDs interact directly without an MNP and the case in which the interaction is mediated by a MNP. We find modifications to the previously predicted SQD-MNP hybrid response. We also find a new regime of behavior in which breaking the SQD-SQD identical particle symmetry causes the system to no longer reach a steady state and instead oscillate at a beating frequency. Lastly, we identify the effects that MNP size and shape, and the placement of the SQDs have on the SQD-SQD interaction. [Preview Abstract] |
Wednesday, March 23, 2011 1:27PM - 1:39PM |
Q32.00012: Plasmon Behavior in Gold Nano-dot Media N. Limberopoulos, J. Derov, A. Drehman, E. Crisman We present correlations between the plasmon resonance of a gold nano-dots medium suspended in Al$_{2}$O$_{3}$ and the plasmon resonance of a single layer film of solid gold. We also present the effective medium properties of multi-layered, dot-film media. The gold dots were fabricated on Al$_{2}$O$_{3}$ substrates by sputter-depositing the gold and then annealing the resultant films. The median dot size ranged from 70 to 250 nm depending on the processing. Successive Au-dot layers were made by depositing Al$_{2}$O$_{3}$ over the previous dot pattern followed by depositing another gold film, followed by re-annealing. We used attenuated-total-reflection to couple transverse-magnetic optical waves to the plasmon resonance and controlled the degree of coupling by varying the spacing between the dot medium and the coupling prism. The plasmon resonances for the dot media had asymmetric line shapes compared to that for the continuous gold film. We were able to show correlations between that asymmetry and the spatial parameters of the dot/Al$_{2}$O$_{3}$ media construction. Effective media parameters and the dispersion characteristics for nano-dot/Al$_{2}$O$_{3}$ bi-layer were determined. [Preview Abstract] |
Wednesday, March 23, 2011 1:39PM - 1:51PM |
Q32.00013: Surface Plasmon Generation by Excitons in Carbon Nanotubes Igor Bondarev, Todor Antonijevic Optical properties of semiconducting carbon nanotubes (CNs) originate from excitons and may be tuned by either electrostatic doping [1], or via the quantum confined Stark effect (QCSE) by means of an electrostatic field applied perpendicular to the CN axis[2]. In both cases exciton properties are mediated by surface plasmon excitations [2,3]. We have shown recently that the QCSE allows one to control the exciton-interband-plasmon coupling in individual CNs and their optical absorption, accordingly [2]. Here, we extend our studies to demonstrate the possibility of low-energy localized surface plasmon generation by optically excited excitons in small-diameter ($\sim $1nm) CNs. The stimulated character of such an energy transfer causes the buildup of the macroscopic population numbers of coherent localized surface plasmons and, as a consequence, high-intensity coherent optical-frequency fields localized at nanoscale, which can be used for various applications, such as near-field nonlinear-optical probing, sensing, or materials nanoscale modification. [1] M.Steiner, et al., NL9,3477. [2] I.V.Bondarev, et al., PRB80,085407. [3] C.D.Spataru and F.Leonard, PRL104,177402. [Preview Abstract] |
Wednesday, March 23, 2011 1:51PM - 2:03PM |
Q32.00014: Nanocrystal optoelectronic devices by plasmon-based optical trapping Kenneth Evans, Daniel Ward, Gautam Kini, Michael Wong, Douglas Natelson Optical trapping is an important tool for studying and manipulating nanoscale objects. In conventional laser trapping, the trapping volume is diffraction limited. Recent experiments have shown that subwavelength control of nanoparticles can be achieved by using plasmonic nanostructures, rather than using the laser directly, to generate the electric fields necessary for trapping. We present a numerical model describing the trapping forces on an individual semiconducting nanocrystal in a nanoscale metallic junction, and discuss initial experimental results. Calculations of the fields are performed in COMSOL, a commercial finite element solver package, and the trapping forces are computed using the full Maxwell stress tensor formalism. We propose the use of plasmonic optical trapping in this geometry as a method to fabricate electrically driven, single nanocrystal light-emitting devices. [Preview Abstract] |
Wednesday, March 23, 2011 2:03PM - 2:15PM |
Q32.00015: The Morphology and Evolution of Bipyramidal Gold Nanoparticles for Plasmon-assisted Nanosheet Biosensor Nicholas Geitner, Amos Deopke, Melodie Fickenscher, Jan Yarrison-Rice, William Heineman, Howard Jackson, Leigh Smith We examine the growth and evolution bipyramidal gold nanoparticles. These particles are then characterized based on their longitudinal LSPR peak and their physical dimensions. Bipyramidal particles are grown using a seed-mediated growth process, and variations in the particles are produced by varying silver nitrate concentration and growth time. While each growth's physical dimensions were well defined and consistent with previous results, two different distinct modes of temporal evolution are observed after the primary growth period. We also observe a distinct linear relationship between tip radius of curvature and wavelength of longitudinal LSPR peak, in agreement with numerical calculations. These particles are to be functionalized and dispersed onto CdS nanosheets for biosensor applications. [Preview Abstract] |
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