Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session S26: Chemical Physics at the Edges IFocus
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Sponsoring Units: DCP Chair: V. Ara Apkarian, University of California, Irvine Room: 289 |
Thursday, March 16, 2017 11:15AM - 11:51AM |
S26.00001: Atomic-Scale Inelastic Tunneling Probe of Molecular Potentials Invited Speaker: Wilson Ho The spatial distribution of the electrostatic potential of a molecule adsorbed on a solid surface reflects its structure and composition and further defines its chemistry. This potential can be probed by a carbon monoxide (CO) molecule attached to the tip of a scanning tunneling microscope (STM). In the inelastic tunneling probe (itProbe) with the STM, this CO molecule in the tunneling gap lies in an overall potential energy surface defined by its binding to the tip and its interaction with the potential of the adsorbed molecule. As the CO-tip scans over the adsorbed molecule, its vibrations are perturbed in energy, intensity, and line shape by variations in the three-dimensional landscape of the potential energy surface (PES) in which the CO is immersed. Spatial maps of the soft hindered translational mode of the CO reveal different features of the PES, such as the ridges and valleys, as the vibrational energy is related to the curvature of the PES. Thus the itProbe maps the gradient of the force on the CO molecule as it scans over the potential of the adsorbed molecule. These images reveal line features that reflect the skeletal structure of molecules and perturbations in space due to intermolecular interactions. Examples are given to illustrate such effects that illuminate the nature of chemical interactions when atoms are in close proximity of each other, leading to intramolecular interactions, and in the assembly of extended molecular structures involving weaker intermolecular interactions. [Preview Abstract] |
Thursday, March 16, 2017 11:51AM - 12:27PM |
S26.00002: Radical Chemistry and Charge Manipulation with an Atomic Force Microscope Invited Speaker: Leo Gross The fuctionalization of tips by atomic manipulation dramatically increased the resolution of atomic force microscopy (AFM) [1]. The combination of high-resolution AFM with atomic manipulation now offers the unprecedented possibility to custom-design individual molecules by making and breaking bonds with the tip of the microscope and directly characterizing the products on the atomic scale. We recently applied this technique to generate and study reaction intermediates [2] and to investigate chemical reactions trigged by atomic manipulation. We formed diradicals by dissociating halogen atoms and then reversibly triggered ring-opening and -closing reactions via atomic manipulation, allowing us to switch and control the molecule’s reactivity, magnetic and optical properties [3]. Additional information about charge states [4] and charge distributions [5] can be obtained by Kelvin probe force spectroscopy. On multilayer insulating films we investigated single-electron attachment, detachment and transfer between individual molecules [6]. References: [1] L. Gross et al. Science 325, 1110 (2009) [2] N. Pavliček et al. Nature Chem. 7, 623 (2015) [3] B. Schuler et al. Nature Chem. 8, 220 (2016) [4] L. Gross et al. Science 324, 1428 (2009) [5] F. Mohn et al. Nature Nanotech. 7, 227 (2012) [6] W. Steurer et al. Nature Commun. 6, 8353 (2015) [Preview Abstract] |
Thursday, March 16, 2017 12:27PM - 1:03PM |
S26.00003: Scanning probe microscopy with single-molecule sensors and transducers: New ways to visualize molecules and their properties Invited Speaker: Frank Stefan Tautz As nanoscience progresses, it becomes ever more important to ``see'' molecules on surfaces with submolecular resolution. But it is not just the structure of a molecule that is of interest. It is of equal importance to visualize as many of its properties as possible on a submolecular scale. Scanning probe microscopy with single-molecule sensors and transducers offers a framework to approach this challenge [1]. If the junction of a scanning tunneling microscope (STM) is functionalized with a nanoscale particle, images can be obtained that reveal the geometric structure the sample [2]. The particle (H2, CO, Xe) acts as a force sensor, sensing forces and transducing them into a conductance signal [3,4] that can be calibrated [5]. Indications of intermolecular bonding can also be seen [6,7]. Even the local curvature of the potential can be measured [8]. More recently, we introduced scanning quantum dot microscopy (SQDM). It images electrostatic potentials with sub-nm and sub-meV resolution [9,10]. An aromatic molecule is attached to the tip of an AFM. Single electron charging events of this molecular quantum dot are detected in the dynamic response of the AFM. SQDM, an example of the sensor/transducer approach, can measure electrostatic fields of neutral atoms or molecules as far as 7 nm away from the surface, providing quantitative 3D imaging of electric fields of a wide variety of nanostructures. [1] Temirov {\&} Tautz, in: Noncontact Atomic Force Microscopy Volume 3, Eds. Morita et al. Springer 2015 [2] New Journal of Physics 2008, 10, 053012 [3] PRL 2010, 105, 086103 [4] PRB 2014, 90, 085421 [5] PRB 2013, 87, 081408(R) [6] JACS 2010, 132, 11864 [7] JACS 2011, 133, 16847 [8] PRL 2014, 113, 226101 [9] PRL 2015, 115, 026101 [10] Japanese Journal of Applied Physics 2016, 55, 08NA04 [Preview Abstract] |
Thursday, March 16, 2017 1:03PM - 1:15PM |
S26.00004: Probing Photochemisty at the Space-Time Limit using a Scanning Tunneling Microscope Calvin Patel, Christian Kim, Wilson Ho Laser induced phenomena can be probed with sub-angstrom resolution using the scanning tunneling microscope. Here we demonstrate the ability to probe photo-induced chemical processes with sub-Angstrom spatial resolution using femtosecond laser pulse pairs. These studies increase our understanding of chemical dynamics at the single molecule level. [Preview Abstract] |
Thursday, March 16, 2017 1:15PM - 1:27PM |
S26.00005: Single Molecule Chemistry with Time Resolved Scanning Tunneling Microscope Shaowei Li, Siyu Chen, Wilson Ho The combination of a low temperature scanning tunneling microscope and a femtosecond laser enables the possibility to achieve femtosecond temporal resolution simultaneously with sub-Ångström spatial resolution. Here we demonstrate the atomic-scale coupling of femtosecond laser pulses to single molecules adsorbed on metal surfaces. The induction of electron tunneling by light makes it possible to obtain atomic scale spatial resolution, while the time delay between pairs of laser pulses provides the femtosecond time resolution. Possible single molecule chemistry induced by femtosecond lasers includes molecular motions and bond dissociation on metal surfaces. [Preview Abstract] |
Thursday, March 16, 2017 1:27PM - 1:39PM |
S26.00006: Scanning tunneling microscopy study of Cu2O surface facets for molecular adsorption Rui Zhang, Liang Li, Maria K. Chan, Jeffrey R. Guest Cu£« ions on cuprous oxide (Cu2O) crystalline facets play important roles in the catalytic reactions, such as CO oxidation and methanol synthesis. Unfortunately, the active sites for the chemical reactions on the surface, are still unclear due to the lack of knowledge on the chemisorption and dissociation of reactant molecules on Cu2O surfaces. Studies mainly focused on defining the surface structures and adsorption of molecules have been performed by first principles density functional theory (DFT) calculations, low-energy electron diffraction (LEED), and ultrahigh-vacuum scanning tunneling microscopy (STM). However, apart from the Cu2O(100) surface, other crystalline surfaces, such as (111) and (110), which have been suggested as more chemically active for catalysis, have been scarcely investigated. Herein we discuss a combined STM-DFT study of Cu2O(111) and (110) surfaces to determine the stable structure under either oxygen-poor or oxygen-rich condition. The combined approach allows us to also determine the structure of surface defects. Active sites that are possible for dissociative adsorption on the Cu2O crystalline surface are also investigated by direct imaging of the surface adsorption with CO2 molecules and corresponding DFT calculations. [Preview Abstract] |
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