Bulletin of the American Physical Society
45th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 59, Number 8
Monday–Friday, June 2–6, 2014; Madison, Wisconsin
Session T7: Electron Dynamics in Complex Systems |
Hide Abstracts |
Chair: Edward Ackad, Southern Illinois University Edwardsville Room: Hall FI |
Friday, June 6, 2014 8:00AM - 8:12AM |
T7.00001: Electronic dynamics in helium nanodroplets studied via femtosecond XUV pump / UV probe photoelectron imaging Michael Ziemkiewicz, Camila Bacellar, Stephen Leone, Daniel Neumark, Oliver Gessner Superfluid helium nanodroplets consisting of $\sim $ 2 x 10$^{6}$ atoms are examined using femtosecond time-resolved photoelectron imaging. The droplets are excited by a 23.6(2) eV extreme ultraviolet (XUV) pulse in resonance with an electronically excited band associated largely with the 1s3p Rydberg level of free He atoms. Relaxation dynamics are monitored by ionizing transient states with a 3.2~eV probe pulse and measuring the time-dependent photoelectron kinetic energy distributions using velocity map imaging (VMI). A broad, intense signal associated with the initially excited 1s3p band (E$_{\mathrm{kin}}\approx $ 2.5~eV) appears within the experimental time resolution and decays within 190(70) fs. Concomitantly, a second photoelectron feature with kinetic energies ranging from 0 to 0.5 eV appears on a time scale of $\sim $ 200 fs. The new feature is identified as originating from the 1s2p droplet Rydberg band, indicating the direct observation of a previously suggested interband relaxation within the droplet. This feature also decays within $\sim $ 200~fs, likely due to intraband relaxation within the 1s2p/1s2s manifold to states which are too deeply bound to be ionized by the 3.2 eV probe pulse. [Preview Abstract] |
Friday, June 6, 2014 8:12AM - 8:24AM |
T7.00002: X-ray pump / X-ray probe femtosecond coherent diffractive imaging of electron dynamics in pristine and embedded xenon clusters Camila Bacellar, Adam Chatterley, James Cryan, Michael Ziemkiewicz, Oliver Gessner, Charles Bernando, Luis Gomez, Curtis Jones, Rico Tanyag, Andrey Vilesov, Tais Gorkhover, Maria Mueller, Daniela Rupp, Thomas Moeller, John Bozek, Maximilian Bucher, Sebastian Carron, Ken Ferguson, Christoph Bostedt Femtosecond time-resolved coherent diffractive imaging (CDI) experiments on pristine Xe clusters and Xe clusters embedded in superfluid helium nanodroplets have been performed using a new undulator-based X-ray pump/X-ray probe technique at the Linac Coherent Light Source (LCLS). The study aims at elucidating electron dynamics in sub-micron sized clusters induced by irradiation with intense X-ray pulses. A combination of single-shot CDI images in coincidence with single-shot ion mass spectra is employed to obtain a detailed time-resolved picture of ultrafast ionization, nanoplasma formation, charge migration and, ultimately, disintegration of the noble gas clusters. The measurements on Xe clusters embedded in He nanodroplets will be discussed in the light of potential damage control (``tamper'') mechanisms provided by the layer of helium atoms around the Xe core. [Preview Abstract] |
Friday, June 6, 2014 8:24AM - 8:36AM |
T7.00003: The energy of the quasi-free electron in near critical point H$_2$, D$_2$ and O$_2$ Cherice Evans, Kamil Krynski, Zachary Streeter, Gary L. Findley Field enhanced photoemission is used to measure the density ($\rho$) dependent quasi-free electron energy $V_0(\rho)$ in the repulsive fluids H$_2$ and D$_2$, and the attractive fluid O$_2$, for the first time. $V_0(\rho)$ in each of these fluids was obtained from low density to the density of the triple point liquid, at noncritical temperatures and on an isotherm near the critical isotherm. A novel critical point effect is observed in each of the fluids and is accurately explained by the local Wigner-Seitz model with the selection of appropriate intermolecular potentials for each fluid. [Preview Abstract] |
Friday, June 6, 2014 8:36AM - 8:48AM |
T7.00004: Understanding delayed charge injection observed in time-of-flight measurements of hexapentyloxyltriphenylene Nathan Dawson, Michael Patrick, Kenneth Singer, Sanjoy Paul, Brett Ellman, Alexander Semyonov, Robert Twieg Time-of-flight methods are commonly used to measure the mobility in semi-conductors. Features in the transient can be used to identify prominent phenomena in organic semi-conductors such as ion transport, trapping, and recombination. Because of the conditions associated with time-of-flight measurements, low levels of impurities in the bulk are easily observed in time-of-flight measurements that cannot be detected using other techniques. We report on delayed charge injection in hole transport measurements of some purified discogen samples of HAT5. The initial photocurrent appears to follow a stretched-exponential response as a function of time. We model the current response using the continuity equation with a source term at the cathode-material interface. This source term is modeled using a series of trapping states near the interface with the Van de Walle method for describing hydrogen relaxation in amorphous silicon. We give results regarding the accuracy of the model, parameter dependencies on temperature and electric field, and possible mechanisms that influence the degree of these trapping states. [Preview Abstract] |
Friday, June 6, 2014 8:48AM - 9:00AM |
T7.00005: ABSTRACT WITHDRAWN |
Friday, June 6, 2014 9:00AM - 9:12AM |
T7.00006: Electron Dynamics at Dye-Semiconductor Interfaces probed with Picosecond Time-Resolved XPS Stefan Neppl, Andrey Shavorskiy, Ioannis Zegkinoglou, Matthew Fraund, Miquel Salmeron, Jinghua Guo, Hendrik Bluhm, Oliver Gessner Picosecond time-resolved core-level spectroscopy using laser pulses to initiate and short X-ray pulses to probe photo-induced processes have the unique potential to provide electronic state- and atomic site-specific insight into fundamental electron dynamics in complex systems. Up to now, however, most of these experiments have concentrated on the electronic and structural dynamics in isolated or solvated molecules. Here we report preliminary results of a time-resolved X-ray photoelectron spectroscopy (TRXPS) study with the goal to follow the light-driven electron dynamics of N3 dye molecules adsorbed on a nano-structured ZnO semiconductor substrate -- a technologically pertinent system for dye-sensitized solar cells -- on the pico- to nanosecond time scale from the perspective of individual atomic sites at this complex interface. A distinct evolution of the molecular C1s photoemission line shape is observed as a function of time delay between a visible (532 nm) laser pump pulse (resonant with the N3 HOMO-LUMO gap) and the X-ray probe pulses. The observed changes in the C1s TRXPS spectra will be discussed in the context of possible charge recombination and relaxation processes leading to the neutralization of the transiently oxidized dye following ultrafast photo-induced electron injection. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700