Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session J21: Focus Session: Imaging and Modifying Materials at the Limits of Space and Time Resolution I |
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Sponsoring Units: DMP GIMS DCP Chair: Arnaud Delcorte, Universite Catholique de Louvain, Belgium Room: D161 |
Tuesday, March 22, 2011 11:15AM - 11:27AM |
J21.00001: Transformation of carbon nanoparticles under laser microirradiation Ninad Ingle, Vijayalakshmi Varadarajan, Ali Koymen, Samarendra Mohanty Functional, mechanical, electrical and thermal properties of carbon nanoparticles (CNP) have been shown to change significantly with change in its shape and structure. Here, we show that shape of the CNPs can be transformed by exposure to tightly focused near-infrared Ti: Sapphire laser beam. The CNPs were prepared using electric plasma discharge generated in an ultrasonic cavitation field of liquid benzene. High resolution TEM image showed nanoparticles with average radius of $\sim $5nm with crystalline structure. A Nanonics Multiview Atomic Force Microscopy (AFM) was integrated on the laser micro-irradiation system to reveal the shape transformation of the CNPs before and after laser irradiation. Since near-IR laser irradiation can lead to significant heat generation in CNP in absence of aqueous solution (sink), the system is far from thermal equilibrium and can curve or bend graphitic layers by introducing topological defects. The photothermally-induced shape transformation can occur below laser power required for complete melting of CNP since surface melting can suffice the observed shape transformation. The results show significant reduction in the volume of irradiated CNP-clusters, which was attributed coalescing of melted CNPs. Raman spectroscopic measurements are being carried out to evaluate possibility of ultrastructural changes. [Preview Abstract] |
Tuesday, March 22, 2011 11:27AM - 11:39AM |
J21.00002: The effect of Au condensation in laser desorption/ionization of organic materials Aneesh Prabhakaran, Arnaud Delcorte Matrix-assisted desorption/ionization (MALDI) mass spectrometry, where the analyte is mixed in a low molecular weight matrix, often constitutes a limitation for the analysis and imaging of real world samples. Herein, we investigate the influence of a thin layer of gold (1-15nm) deposited on the surface of different organic materials, in the laser ablation using 355nm wavelength light. We see a significant effect of the condensed metal nanoparticles in the laser ablation process. Compared to pristine samples, the metallized samples show a significant intensity of characteristic fragments as well as metal cationized molecules. Relatively soft desorption/ionization is indicated by the observation of characteristic molecular ions of the different analytes. The observed effects can be explained by the increased laser absorption by the gold nanoparticles in this wavelength range and the increased ionization by the gold. Hence the metallization improves the surface characterization using lasers and also proves to be a novel technique for chemical imaging of organic surfaces. [Preview Abstract] |
Tuesday, March 22, 2011 11:39AM - 11:51AM |
J21.00003: Atomic-level simulations of structural transformations in layered Au-Cu and Ag-Cu metal targets irradiated by a femtosecond laser pulse Chengping Wu, Derek Thomas, Zhibin Lin, Leonid Zhigilei The structural transformations in Ag/Au film - Cu substrate systems irradiated by femtosecond laser pulses are investigated in simulations performed with a model that couples the molecular dynamics method with a continuum-level description of the laser excitation and subsequent relaxation of the excited electrons. The higher strength of the electron-phonon coupling in Cu compared to Ag and Au results in a preferential sub-surface heating and melting of the Cu substrate. The melting is followed by rapid cooling and resolidification. In the case of Cu-Ag system, the rapid resolidification results in a complex structure of the interfacial region, where the lattice-mismatched interface is separated from the Ag-Cu mixing region by an intermediate pseudomorphic bcc Cu layer that grows epitaxially on the (001) face of the fcc Ag film during the final stage of the resolidification process. The new lattice-mismatched interface consists of a periodic array of stacking fault pyramids outlined by stair-rod partial dislocations. The intermediate bcc layer and the stacking fault pyramid structure of the mismatched interface present a barrier for dislocation propagation, resulting in the effective hardening of the layered structure treated by laser irradiation. [Preview Abstract] |
Tuesday, March 22, 2011 11:51AM - 12:27PM |
J21.00004: Optical Antennas for Enhanced Light Absorption and Emission Invited Speaker: Lukas Novotny The absence of optical antennas in technological applications is primarily associated with their small scale. Antennas have characteristic dimensions on the order of a wavelength, demanding fabrication accuracies better than 10nm for the optical frequency regime. The advent of nanoscience and nanotechnology provides access to this length scale but material challenges associated with optical antennas remain. For example, the penetration of radiation into metals can no longer be neglected. The electromagnetic response is then dictated by collective electron oscillations (plasmons) characteristic of a strongly coupled plasma. These collective excitations make a direct downscaling of traditional antenna designs impossible and demand the careful study of plasmon resonances in metal nanostructures. The introduction of the antenna concept into the optical, infrared and terahertz frequency regime holds promise for a wide range of novel technological applications. Optical antennas can be employed to enhance the efficiency of photovoltaics, to release energy from nanoscale light-emitting devices, and to boost the efficiency of photochemical or photophysical detectors. In this presentation, I will outline the physical properties of optical antennas, review relevant history and recent work. [Preview Abstract] |
Tuesday, March 22, 2011 12:27PM - 12:39PM |
J21.00005: In Situ 3D Coherent X-ray Diffraction Imaging of Shock Experiments: Possible? John Barber In traditional coherent X-ray diffraction imaging (CXDI), a 2D or quasi-2D object is illuminated by a beam of coherent X-rays to produce a diffraction pattern, which is then manipulated via a process known as iterative phase retrieval to reconstruct an image of the original 2D sample. Recently, there have been dramatic advances in methods for performing fully 3D CXDI of a sample from a single diffraction pattern [Raines et al, Nature 463 214-7 (2010)], and these methods have been used to image samples tens of microns in size using soft X-rays. In this work, I explore the theoretical possibility of applying 3D CXDI techniques to the in situ imaging of the interaction between a shock front and a polycrystal, a far more stringent problem. A delicate trade-off is required between photon energy, spot size, imaging resolution, and the dimensions of the experimental setup. In this talk, I will outline the experimental and computational requirements for performing such an experiment, and I will present images and movies from simulations of one such hypothetical experiment, including both the time-resolved X-ray diffraction patterns and the time-resolved sample imagery. [Preview Abstract] |
Tuesday, March 22, 2011 12:39PM - 12:51PM |
J21.00006: Lattice dynamics of laser excited self-assembly gold nanocrystals by time resolved X-ray diffraction Kouhei Ichiyanagi, Hiroshi Sekiguchi, Shunsuke Nozawa, Tokushi Sato, Shin-ichi Adachi, Yuji C. Sasaki The self-assembled gold nanoparticle has attracted considerable interest from researchers as the new nanodevices and bio-sensors. Functional groups such as thiols and amines have assembled on the gold nanoparticles in solution. For using the functional optical nanomaterial, it is necessary to reveal the mechanism of interaction between the laser and the functional nanomaterial. In the present work, we observed the effect of photo-excited process of self-assembled gold nanocrystal in ethanol solution using picosecond time-resolved X-ray diffraction. Gold nanocrystals deposited on the NaCl (100) substrate. After isolation of gold nanocrystals from the substrate, these nanocrystals were assembled with 10-Carboxydecyl disulfide molecules in ethanol. The nanocrystals size was the diameter of about 60 -- 120 nm. The X-ray energy, pulse width and repetition rate for probing the gold nanocrystals were 15 keV, 100 ps and 945 Hz, respectively. The excitation wavelength and the pulse width were 400 nm and 150 fs. The detailed results of the lattice dynamics inside gold nanocrystals will be presented in the presentation. [Preview Abstract] |
Tuesday, March 22, 2011 12:51PM - 1:03PM |
J21.00007: Ultrafast Laser Matter Interaction and Pump-probe Imaging of Transient Electric Fields Jian-Min Zuo, Hyuk Park Ultrafast electron diffraction and microscopy use pulsed laser as pump to initiate dynamic processes in solids. Under irradiation of pulsed laser beam of picoseconds or less, electrons inside a solid can be heated to high temperatures for a short period of time (several picoseconds). A part of hot electrons can be emitted from the surface in a similar way of thermionic emission. The emitted electrons, travel at speeds, produce transient electric fields (TEFs) together with the positively charged surface [1]. However, the effect of photoemitted electrons and their electric fields on ultrafast electron diffraction and microscopy has been a subject of debate [2]. Here we report direct measurement of TEFs using time-resolved electron beam imaging techniques based on the pump-probe approach. Results obtained from Pt thin films, Cu and ZnO nanowires will be shown. We demonstrate that TEFs produced by ultrafast laser irradiation can lead to large beam deflections that depend on the electron beam distance to sample surface, laser fluence and laser wavelength. The work shows that there is clearly a critical need for better understanding of TEFs in the field of ultrafast electron microscopy. The work is supported by DOE DEFG02-01ER4592, DEFG02-91-ER45439 and DOE DEFG02-07ER46453. [1] H. Park and J. M. Zuo, Applied Physics Letters 94, 251103 (2009). [2] H. Park and J. M. Zuo, Physical Review Letters 105, 059603 (2010). [Preview Abstract] |
Tuesday, March 22, 2011 1:03PM - 1:39PM |
J21.00008: Femtosecond Nanocrystallography with X-ray Free-Electron Lasers Invited Speaker: The ultrafast pulses from X-ray free-electron lasers have opened up a new form of protein nanocrystallography. The X-ray pulses are of high enough intensity and of sufficiently short duration that individual single-shot diffraction patterns can be obtained from a sample before significant damage occurs. This ``diffraction before destruction'' method may enable the determination of structures of proteins that cannot be grown into large enough crystals or are too radiation sensitive for high- resolution crystallography. Ultrafast pump-probe studies of photoinduced dynamics can also be studied. We have carried out experiments in coherent diffraction from protein nanocrystals, including Photosystem I membrane protein, at the Linac Coherent Light Source (LCLS) at SLAC. The crystals are filtered to sizes less than 2 micron, and are delivered to the pulsed X-ray beam in a continuously flowing liquid jet. Millions of diffraction patterns were recorded at the LCLS repetition rate of 60 Hz. Tens of thousands of the single-shot diffraction patterns have been indexed, and combined into a single crystal diffraction pattern, which can be phased for structure determination and analysed for the effects of pulse duration and fluence. Experimental data collection was carried out as part of a large collaboration involving CFEL DESY, Arizona State University, Max Planck Institute for Medical Research, University of Uppsala, SLAC, LBNL, LLNL, using the CAMP apparatus which was designed and built by the Max Planck Advanced Study Group at CFEL. [Preview Abstract] |
Tuesday, March 22, 2011 1:39PM - 1:51PM |
J21.00009: Plans for an Upgrade of the Advanced Photon Source Dennis Mills We are presently developing plans for an upgrade of the Advanced Photon Source facility. Science has formally issued Critical Decision 0 and approved the Mission Need Statement in April of 2010, authorizing the APS to develop a conceptual design for the APS Upgrade (APS-U) project. The proposed upgrade will include enhancements to the accelerator, beamlines, and facility infrastructure. The high brilliance x-ray beams at high photon energy (e.g. $>$ 25 keV) provided by the APS Upgrade will have strong impact on research in energy, the environment, new or improved materials, and biological studies. High-energy x-rays can penetrate into a wide range of realistic and/or extreme environments and allow imaging of structures and processes in unprecedented detail on picosecond time scales and nanometer length scales. The presentation will include some of the essential goals of the APS-U and proposed strategies to attain those goals. [Preview Abstract] |
Tuesday, March 22, 2011 1:51PM - 2:03PM |
J21.00010: The Jefferson Lab VUV-FEL at 10 eV and above Gwyn Williams We will present details of the vacuum ultraviolet performance of the Jefferson Lab Free Electron Laser. The JLab FEL is oscillator-based [1] and uses a superconducting energy recovered linac for CW RF operation at up to 75 MHz. Lasing at a fundamental wavelength of 372 nm, the third harmonic is at 124 nm, corresponding to a photon energy of 10 eV. The energy per pulse in the fundamental is 20 microJoules, which at 9 MHz yields an average power of 180 Watts. The pulses have a FWHM of order 300 fs, which essentially determines the optical bandwidth. The third harmonic, which is a 0.1 - 1\% fraction of this, is considerably brighter than any other source in the region. Further, being an FEL, there is a wide range of tunability in the 1 eV to 15 eV range. Additional reach is possible with increased electron beam energy, and some options will be discussed in the talk.\\[4pt] [1] S. Benson et al. Nucl. Instrum. Methods A582, 14-17 (2007). [Preview Abstract] |
Tuesday, March 22, 2011 2:03PM - 2:15PM |
J21.00011: Ultrafast optical fiber microbeam for in-depth fabrication, trapping and fluorescence excitation Mervyn Pinto, Yogeshwar Mishra, Ninad Ingle, Samarendra Mohanty Micro-focused laser beam is finding widespread application in two-photon polymerization (TPP), microsurgery, two-photon fluorescence microscopy and optical trapping of microscale objects. However, limited by short working distance of the microscope objective, it is essential to develop fiber based laser microbeam for in-depth applications. While fiber-optic two-photon fluorescence excitation (TPE) has been explored in past for endoscopic imaging, only recently we demonstrated optical trapping and microsurgery using single fiber optical microbeam. Here, we present use of ultrafast laser coupled to microfabricated single mode optical fiber for in-depth fabrication of microstructures by TPP as well as TPE and manipulation of microscopic objects by fiber optical microbeam tweezers. The microfabrication of fiber optic axicon tip was optimized so as to perform all the four functions, namely fabrication, excitation, manipulation and collection of fluorescence from the trapped object. Owing to the propagation distance of Bessel-like beam emerging from the axicon-fiber tip, relatively longer streak of fluorescence was observed along the microsphere length. Stable trapping of the fluorescent objects was observed due to reduced scattering force as compared to axial gradient force. These results using multifunctional optical fiber will be presented. [Preview Abstract] |
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