Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session F26: Focus Session: At the Interface of Molecules and Materials I |
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Sponsoring Units: DCP Chair: George Schatz, Northwestern University Room: 204A |
Tuesday, March 3, 2015 8:00AM - 8:36AM |
F26.00001: Tunable and responsive plasmonic properties of metal oxide nanocrystals Invited Speaker: Delia Milliron Degenerately doped metal oxide semiconductors, like ITO, exhibit plasmonic resonance at near and mid-infrared wavelengths tunable by varying their composition. Nanocrystals of many such materials have now been synthesized and applications are emerging that leverage the responsiveness of their localized surface plasmon resonance (LSPR) to electronic charging and discharging. For example, electrochromic glass that can dynamically control heat loads in buildings is under development. In biological systems, plasmonic oxide nanocrystals can act as remote sensors, where changes in their optical absorption indicates biochemical redox has occurred. Nonetheless, significant fundamental questions remain open regarding the nature of the infrared optical response in these doped oxides. Dopant impurities influence the optoelectronic properties beyond simply donating free carriers. For example, the distribution of Sn in ITO was found to dramatically influence the line shape of the LSPR and the effective electron mobility. In addition, by post-synthetically modifying carrier concentrations (through photodoping or electrochemical doping), we have observed that aliovalent doping and electronic doping each modify LSPR spectra, providing access to a broad range of tunable optical properties. Heterogeneous broadening, uncovered by single nanocrystal spectroscopy, also contributes to ensemble line shapes, complicating direct interpretation of LSPR spectra. Finally, the possibility of electric field enhancement by metal oxide LSPRs is critically examined to suggest what future applications might be on the horizon. [Preview Abstract] |
Tuesday, March 3, 2015 8:36AM - 8:48AM |
F26.00002: Tunable Plasmonic Nanoparticles with Catalytically Active High-Index Facets Hao Jing, Nicolas Large, Qinfeng Zhang, Peter Nordlander, Hui Wang Noble metal nanoparticles have been of tremendous interest due to their intriguing size- and shape-dependent plasmonic and catalytic properties. Combining tunable plasmon resonances with superior catalytic activities on the same metallic nanoparticle, however, has long been challenging because nanoplasmonics and nanocatalysis typically require nanoparticles in two drastically different size regimes. Here, we demonstrate that creation of high-index facets on subwavelength metallic nanoparticles provides a unique approach to the integration of desired plasmonic and catalytic properties on the same nanoparticle. Through site-selective surface etching of metallic nanocuboids whose surfaces are dominated by low-index facets, we have controllably fabricated nanorice and nanodumbbell shaped particles, which exhibit drastically enhanced catalytic activities arising from the catalytically active high-index facets abundant on the particle surfaces. The nanorice and nanodumbbell particles also possess appealing tunable plasmonic properties that allow us to gain quantitative insights into nanoparticle-catalyzed reactions with unprecedented sensitivity and detail through time-resolved plasmon-enhanced spectroscopic measurements. [Preview Abstract] |
Tuesday, March 3, 2015 8:48AM - 9:24AM |
F26.00003: Protected Noble-Metal Clusters at the Transition from Molecules to Materials Invited Speaker: Robert L. Whetten Protected noble-metal clusters are found at a molecular level of definite composition and structure up to a size of 145-165 metal atoms. Curiously, this size-range is also where several key signatures of metallic character begin to converge. These substances have been of great interest for many application-areas in the past couple decades, but the understanding of their structure and bonding, remarkable self-selection, electronic structure and optical properties has only recently started to reach a fundamental or molecular level of definition. ~This presentation emphasizes this recent progress and also outlines the prospects for extending the molecular domain of metallurgy well beyond the 200- atom range, thanks to advances in experimental {\&} theoretical methods. [Preview Abstract] |
Tuesday, March 3, 2015 9:24AM - 10:00AM |
F26.00004: ABSTRACT WITHDRAWN |
Tuesday, March 3, 2015 10:00AM - 10:12AM |
F26.00005: Rich Information on Quantum States and Ways to Calculate It in The Absorption Spectra of Au$_{144}$ Gold Cluster Compound Xochitl Lopez-Lozano, Robert L. Whetten, Hans-Christian Weissker In recent decades, the prevalent view has been that noble-metal clusters of intermediate size necessarily have smooth optical absorption spectra of low information content in the near-IR, VIS and near-UV regions. At most, one expects a broad, smooth localized surface plasmon resonance feature. Recently, we demonstrate that, in contradistinction to the commonly held view, the optical absorption of the most widely applied gold cluster, the thiolate-protected Au$_{144}$ cluster, exhibits a rich spectrum of bands that are individually visible over the entire near-IR, VIS and near-UV regions (1.0-4.0 eV), demonstrating high information content related to the quantum size effects which distinguish the nanoparticles from the bulk materials. In the calculation, the result is sensitive to the details of the structure. In the present work, we systematically compare the different structures actually used to date. We studied aspects like symmetry, geometry and type of ligands. In particular, we discuss the effect of their differences on the optical absorption spectra as well as how the theoretical methodology influences the final results. [Preview Abstract] |
Tuesday, March 3, 2015 10:12AM - 10:24AM |
F26.00006: Surface Plasmons in Quantum-Sized Noble-Metal Clusters: Quantum Calculations and the Classical Picture of Charge Oscillations Hans-Christian Weissker, X\'ochitl L\'opez-Lozano The localized surface-plasmon resonance (LSPR) in metal clusters corresponds to a collective charge oscillation of quasi-free electrons of the metal. We use the real-time formulation [1] of time-dependent density-functional theory (TDDFT) with pseudopotentials to study the correspondence and differences of the quantum calculations with the classical picture. By means of animations, we discuss the real-time evolution of the electronic density for different geometries. While there is a clear correspondence between the overall picture of a charge oscillation and the actual dynamics in quantum-sized clusters, the situation is much more intricate owing to quantum effects and the atomistic inhomogeneity of the cluster. A fine pattern is present over the volume of the cluster even at moments of zero overall polarization. The difference between Ag and Au is clearly visible. Finally, we discuss the question of collective vs. molecular-like transitions; even for single transitions, the dynamics of the total density can be similar to the picture of a charge oscillation.\\[4pt] [1] Yabana, K.; Bertsch, G. F., Phys. Rev. B 54, 4484 (1996).\\[0pt] [2] Weissker, H.-Ch., Whetten, R.L., and L\'opez-Lozano, X.; PCCP 16, 12495 (2014).\\[0pt] [3] L\'opez-Lozano, X.; Barron, H.; Mottet, C.; Weissker, [Preview Abstract] |
Tuesday, March 3, 2015 10:24AM - 10:36AM |
F26.00007: Plasmon induced electric current in a molecular junction Partha Pal, Nan Jiang, Matthew Sonntag, Naihao Chiang, Edward Foley, Richard Van Duyne, Tamar Seideman We report light-triggered, plasmon-enhanced charge transport in a tip-molecule-surface molecular junction. Experimentally, enhancement of tunneling current is recorded when a chopped laser beam illuminates the junction. The enhancement is quenched when the sample is devoid of molecules and its amplitude increases steeply when the focus of the beam moves closer to the space between the tip and the mono layered sample. Finite difference time domain calculations indicate that maximum electromagnetic field enhancements due to plasmonic activity, occurs in the space between the tip and the sample which is also the region where the tunneling current perturbation peaks. The perturbation in the transport characteristics at the tip-sample junction is theoretically estimated utilizing a recent formulation for describing the transient electronic distribution due to plasmon decoherences. We find the enhancement in the electronic current to be directly proportional to the plasmon excitations only in the presence of a molecular linker which is in excellent agreement with the experimental results. Further analysis reveals that the nascent distribution allows injection of electrons through additional molecular resonances which were previously inaccessible, thus leading to an increased current. [Preview Abstract] |
Tuesday, March 3, 2015 10:36AM - 10:48AM |
F26.00008: Long-range structural correlations in amorphous ternary In-based oxides Rabi Khanal, Julia Medvedeva In recent years, there is an increasing shift towards the use of oxide semiconductor materials in their amorphous form owing to several technological advantages and the fact that amorphous oxides exhibit similar or even superior properties than their crystalline counterparts. In this work we have systemically investigated the effect of chemical composition and oxygen stoichiometry on the local and long-range structure of ternary amorphous oxides, namely In-X-O with X$=$Sn, Zn, Ga, Cd, Ge, Sc, Y, or La, by means of ab-initio molecular dynamics. The results reveal that the local MO structure remains nearly intact upon amorphization and exhibit weak dependence on the composition. In marked contrast, the structural characteristics of the metal-metal shell, namely, the M-M distances and M-O-M angles that determine how MO polyhedra are connected into a network, are affected by the presence of X. Complex interplay between several factors such as the cation ionic size, metal-oxygen bond strength, as well as the natural preference for edge, corner, or face-sharing between the MO polyhedra, leads to a correlated behavior in the long-range structure. These findings highlight the mechanisms of the amorphous structure formation as well as the species of the carrier transport in these oxides. [Preview Abstract] |
Tuesday, March 3, 2015 10:48AM - 11:00AM |
F26.00009: TMAA surface-molecule photon interactions on Au-supported TiO$_{2}$ nanocrystals Richard Osgood, Denis Potapenko, Zhisheng Li Nanostructured titanium dioxide is a versatile photocatalytic material. While its photocatalytic properties have been extensively studied in liquid/gas-phase environments, studies of the physics of photoinduced dynamics and reactions on bare well characterized titania nanoparticles using surface science tools have been lacking. Here we explore these photoinduced properties of TMAA-dosed TiO$_{2}$ nanocrystals prepared in situ on Au(111) substrate with Scanning Tunneling Microscopy (STM) and Temperature Programmed Desorption (TPD). Photodesorption of trimethyl acetic acid was chosen as a model for light-driven reaction dynamics since it is easily imaged with STM and since this system has been the subject of many earlier studies. For comparison, we explored dynamics of TMAA on TiO$_{\mathrm{2}}$ rutile(110) by exposing it to monochromatized UV light and by injecting charges from the STM tip. We then demonstrated that 1--3 nm high and 10--25 nm wide nanocrystals of TiO$_{\mathrm{2}}$ grown on Au(111) surface also exhibit photoreaction activity for TMAA when illumined with UV light. TPD results, which provided surface-averaged information, agree well with STM data and demonstrate TMAA desorption on a single-molecule basis. [Preview Abstract] |
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