Eighth Condensed Phase and Interfacial Molecular Science (CPIMS)

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with the most intense electron emission. Similar studies of solid metal nanoparticles using a range of sizes (20 to 120 nm in diameter) are underway. PEEM is a charged particle (photoelectrons) imaging technique and has therefore been applied almost exclusively to conducting materials and in particular metals. We have found, however, that wide-gap semiconductors and even insulating materials, in some cases, yield high quality PEEM images. We have imaged 3 µm diameter polystyrene spheres supported on a thin metal substrate illuminated by 400 nm (~ 3.1 eV) and 800 nm (~ 1.5 eV) femtosecond (fs) laser pulses. Intense photoemission is generated by microspheres even though polystyrene is an insulator and its ionization threshold is well above the photon energies employed. We observe the most intense photoemission from the far side (the side opposite the incident light) of the illuminated microsphere that is attributed to light focusing within the microsphere. The light focused though the microsphere then propagates to the thin film surface where photoemission from the metal substrate can be imaged. For the case of p-polarized, 800 nm fs laser pulses, we observe photoemission exclusively from the far side of the microsphere and additionally resolve sub-50 nm hot spots in the supporting Pt/Pd thin film that are located only within the focal region of the microsphere. We find that the fs PEEM images at both 400 and 800 nm can be modeled using finite difference time domain (FDTD) electrodynamic simulations. The FDTD simulations predict light focusing in the optically transparent microsphere and subsequent focusing of the transmitted field on the supporting metal surface. The ability to obtain high resolution and high contrast PEEM image from an insulator is attributed to photoinduced conductivity of the polystyrene microspheres. Future Directions If exciton-based desorption can be generalized from alkali halides to metal oxides then selective excitation of specific surface sites could lead to controllable surface modification, on an atomic scale, for a general class of technologically important materials. While exciton-based desorption is plausible for MgO and CaO, we note that the higher valence requires a more complex mechanism. With the aid of DFT calculations we have developed such a hyperthermal desorption mechanism that relies on the combination of a surface exciton with a three-coordinated surfacetrapped hole, a so-called “hole plus exciton” mechanism. In every instance we have studied, a hyperthermal O-atom KE distribution can be linked to an electronic surface excited state desorption mechanism. In contrast, a thermal O-atom KE distribution clearly indicates a bulk derived origin for desorption. In analogy to alkali halide thermal desorption, we have considered a bulk-based thermal desorption mechanism involving trapping of two holes at a threecoordinated site (a “two-hole localization” mechanism). Our calculations, however, do not indicate that two-hole localization is likely without invoking a dynamical trapping process. Since extensive calculations have not yielded an enduring theoretical model for thermal desorption we are exploring possible nonthermal mechanisms that yield low kinetic energy particle desorption in the “thermal energy” range. Initial experiments on CsBr thin films suggest intriguing possibilities of near-thermal desorption from surface molecular anion centers (H centers). We will therefore study low energy desorption from thin films of CsBr, CsI, and perhaps RbI grown on insulators and metals. We also plan to grow and study other oxide surfaces in the near term such as ZrO2, BaO, and ZnO. PEEM combined with interferometric time-resolved two-photon photoemission is an experimental method which offers both nanometer spatial and fs time resolution. Using these techniques it should be possible to time-resolve PEEM images of localized surface plasmons for various plasmonics nanostructures such as wires, spheres or particle aggregates. Using PEEM we have directly recorded plasmonic enhancement factors, of core-shell particles, without the presence of a molecular emitter as required using surface enhanced Raman scattering (SERS). 85
This is a significant advantage of PEEM in characterizing novel plasmonic substrates. By adding a time-resolved capability to our PEEM experiments (a Mach-Zhender interferometer is currently under construction) the way opens to a whole new array of applications such as correlating the enhancement factors and dynamics of spatially resolved hotspots formed in the nano-gaps of particle aggregates or in gaps between nanowires. Future plans include femtosecond PEEM to study plasmon resonant photoemission from noble metal nanostructures and pulse-pair PEEM to probe dynamics of oxide nanostructures on surfaces. We will interrogate such metal-insulator systems using a variety of advanced techniques including: x-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) femtosecond 2PPE, PEEM, atomic force microscopy (AFM) and laser desorption. Femtosecond time-resolved PEEM can reveal spatially resolved ultrafast dynamics and is a powerful tool for studying the nearsurface electronic states of nanostructures or plasmonic devices. We will explore the formation of interfacial polarons on a sample of nanoscale insulator (either alkali halides or metal oxides) islands on Cu (111) and possibly other metal substrates. Our goal is to resolve the temporal and spatial evolution of electron emission and the dynamics of small interfacial polarons using the combined PEEM and 2PPE approach. We are also presently developing capabilities to perform energy-resolved two-photon photoemission using a hemispherical analyzer XPS instrument. In combination we expect these two techniques will provide spatially-resolved electronic state dynamics of nanostructured metal-insulator materials. References to publications of DOE BES sponsored research (2009 to present) 1. K.M. Beck, A.G. Joly, and W.P. Hess, “Two-color laser desorption of nanostructured MgO thin films,” Appl. Surf. Sci. 255, 9562 (2009). 2. A.G. Joly, K.M. Beck, and W.P. Hess, “Photodesorption of excited iodine atoms from KI (100),” J. Chem. Phys. 131, 144509 (2009). 3. K.M. Beck, A.G. Joly, and W.P. Hess, "Effect of Surface Charge on Laser-induced Neutral Atom Desorption." Appl. Phys. A, 101, 61 (2010). 4. G. Xiong, R. Shao, S.J. Peppernick, A.G. Joly, K.M. Beck, W.P. Hess, M. Cai, J Duchene, J.Y. Wang W.D. Wei “Materials Applications of Photoelectron Emission Microscopy,” J. Metals, 62, 90 (2010). 5. S.J. Peppernick, A.G. Joly, K.M. Beck, W.P. Hess “Plasmonic Field Enhancement of Individual Nanoparticles by Correlated Scanning and Photoemission Electron Microscopy” J. Chem. Phys. 134, 034507 (2011). 6. P.V. Sushko, A.L. Shluger A.G. Joly, K.M. Beck, and W.P. Hess, “Exciton-driven highlyhyperthermal O-atom desorption from nanostructured CaO” J. Phys. Chem. C. 115, 692 (2011) Cover. 7. S.J. Peppernick, A.G. Joly, K.M. Beck, and W.P. Hess “Near-Field Focused Photoemission from Polystyrene Microspheres Studied with Photoemission Electron Microscopy”, J. Chem. Phys. 137, 014202 (2012). 8. S.J. Peppernick, A.G. Joly, K.M. Beck and W.P. Hess, J. Wang, Y.C. Wang and W.D. Wei, “Two-Photon Photoemission Microscopy of a Plasmonic Silver Nanoparticle Trimer,” Appl. Phys. A (in press). 86
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Eighth Condensed Phase and Interfac
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Potential energy landscape of the (
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Agenda
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Session III Chair: Jay A. LaVerne,
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Table of Contents
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Transition Metal-Molecular Interact
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Ultrafast Electron Transport across
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CPIMS Principal Investigator Abstra
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VUV LDPI image of a polymer photore
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Publications based on DOE support (
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entirely quenched, presumably due t
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Future Plans In addition to the TiO
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The relative path indexes of the ur
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We have recently carried out molecu
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have been obtained with γ-rays sug
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Two novel plasma devices have been
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(Figure 2) can be adsorbed exclusiv
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3. Future Plans Our planned work de
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Figure 1: Snap shots from molecular
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6. Varilly, P., A. J. Patel and D.
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hypothesis that delocalized charges
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Efforts will be made to observe ele
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Photochemistry and Solvation Dynami
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complementary to work we have carri
Page 49 and 50: The Co3O4 films for the optical pum
Page 51 and 52: chamber will allow us to heat the s
Page 53 and 54: calculations. Additional PMF calcul
Page 55 and 56: the gas solute first needs to cross
Page 57 and 58: laser system, which is an infrared
Page 59 and 60: Publications (10/1/2009-present) fo
Page 61 and 62: interest are: (i) What is the diffu
Page 63 and 64: and anilino groups attached to the
Page 65 and 66: had been formed. This coincides wit
Page 67 and 68: Figure 1. (A) Simplified bR photocy
Page 69 and 70: Figure 4. Photocurrent density of b
Page 71 and 72: single-file diffusion and cannot ca
Page 73 and 74: PUBLICATIONS SUPPORTED BY USDOE CHE
Page 75 and 76: arrangement. However, the hydrogen
Page 77 and 78: (5) “Water Dynamics in Salt Solut
Page 79 and 80: from high- energy x-ray diffraction
Page 81 and 82: concentrated aqueous solutions. The
Page 83 and 84: molecule’s center of mass, or alt
Page 85 and 86: Moreover, SHG studies by Saykally
Page 87 and 88: The effective fragment potential (E
Page 89 and 90: 10. D.D. Kemp, J. Rintelman, M.S. G
Page 91 and 92: temperature dependent, equilibrium
Page 93 and 94: mimicking real organic photovoltaic
Page 95 and 96: 100 kHz amplifier, SE-FSRS was succ
Page 97 and 98: photovoltaics will be explored via
Page 99: for laser surface reactions to thes
Page 103 and 104: the STM, which might underlie the u
Page 105 and 106: Future Plans: Figure 3. One and two
Page 107 and 108: methane molecule and a lattice atom
Page 109 and 110: eactive than the Ni, experiment sug
Page 111 and 112: Fig. 1. PE spectra of M3Oy � (M =
Page 113 and 114: each of the intermediates obtained
Page 115 and 116: a regime where each solvent molecul
Page 117 and 118: observables that arise from subtle
Page 119 and 120: total potentials. One can see from
Page 121 and 122: Our calculations have shown that ch
Page 123 and 124: our understanding of structure and
Page 125 and 126: viscosity, η, are inversely relate
Page 127 and 128: photodissociation of the metal - NO
Page 129 and 130: from a Ru 2p3/2 orbital to an orbit
Page 131 and 132: Integrated O 2 PSD (ML) Integrated
Page 133 and 134: anisotropy in the structure of the
Page 135 and 136: XPS studies have been performed on
Page 137 and 138: Publications with BES support since
Page 139 and 140: MLCT (metal to ligand charge transf
Page 141 and 142: molecule-metal interface without a
Page 143 and 144: observe the predicted effects, whic
Page 145 and 146: (4*) Lymar, S. V.; Schwarz, H. A. J
Page 147 and 148: (τ .820 ns), but we have not been
Page 149 and 150: B. Photodissociation spectroscopy o
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oth BLYP and PBE. Our results have
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Publications from BES support (2010
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understanding of factors that contr
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Our talk will discussion our initia
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Figure 1 shows the band structure o
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likely to also occur in low coordin
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These results are promising indicat
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This page is intentionally left bla
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method recently developed by Prende
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and coordination regions. A differe
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two ions I - [3] and IO3 - [7]. One
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"Probing the Hydration Structure of
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world-wide scientific user base sup
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10) C. Zhang, M.E. Grass, A.H. McDa
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produce the nanoparticles needed fo
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step as a symmetry-breaking templat
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work provides what we believe in th
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Selected publications acknowledging
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2. Optical Stark study of PtF (Acce
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Figure 4. The Q(3.5) line of the [1
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In marked contrast to the selective
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y depositing cobalt onto copper sin
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Carlo calculations, we have carried
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approach on a model phenol-amine pr
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We performed pump-probe experiments
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15. “A phenomenological approach
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may be initially produced in a non-
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4. Inelastic scattering of hydrogen
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Using QM/MM free energy methods we
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gas phase using electrospray ioniza
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order of Li + > Na + > K + for comp
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2. MM Meyer, XB Wang, CA Reed, LS W
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Technical Approach and Progress to
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Ionic liquid synthesis and characte
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Studies of structure and reaction d
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structure theory that include elect
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9. S. Pandelov, J. C. Werhahn, B. M
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pulse duration is a few times longe
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Figure 1 (Left) The HOMO and LUMO e
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slightly preferable in energy, the
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Participant List Dr. Musahid Ahmed
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Professor Kenneth Eisenthal Columbi
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Dr. Ireneusz Janik Notre Dame Radia
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Professor Eric Potma University of
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Dr. James Wishart Brookhaven Nation
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Eighth Condensed Phase and Interfacial Molecular Science (CPIMS)

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