Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R25: Focus Session Chemical Physics Frontiers at Interfaces IFocus
|
Hide Abstracts |
Sponsoring Units: DCP Chair: Robert Baker, Ohio State University Room: 288 |
Thursday, March 16, 2017 8:00AM - 8:36AM |
R25.00001: Ultrafast Excited State Dynamics and Nonlinear Optical Spectroscopy at Interfaces Invited Speaker: Martin Wolf We employ time- and angle-resolved photoemission spectroscopy to obtain a direct momentum resolved view of the ultrafast excited state dynamics and interlayer charge transfer in semiconducting transition metal dichalcogenides (TMDCs). While in bulk TMDCs the overall crystal structure is inversion symmetric, individual layers lack this property and in combination with strong spin-orbit coupling the energy degeneracy of electronic bands of opposite spin polarizations is lifted. Applying circularly polarized light leads to momentum- and spin-selective selective excitation of spin-polarized electrons in the K-valleys of the TMDC band structure. We show that, even in centrosymmetric samples of 2H-WSe$_{\mathrm{2\thinspace }}$we can generate spin-, valley- and layer-polarized excited states in the conduction band which are localized within individual layers at the K points. Subsequent ultrafast scattering populates states at the $\Sigma $-valley with a three-dimensional character facilitating optical control of inter-layer charge transfer. Another important type of interfacial charge transfer processes occurs in electrochemical environment at solid-liquid interfaces. These are difficult to probe by interface specific techniques. Here I will report on our recent progress using nonlinear optical spectroscopy to study the structure of interfacial water and oxide formation on gold electrodes under potential control. [Preview Abstract] |
Thursday, March 16, 2017 8:36AM - 8:48AM |
R25.00002: Probe~LDOS~of~a~single~defect~on~TiO2(110)~surface~under~the~illumination~of~ultrashort~laser~pulses Lihuan Sun, Jianmei Li, Anning Dong, Dong Hao, Yang Guo, Xinyan Shan, Xinghua Lu TiO2 has many applications such as solar energy harvest, photo-catalysis, environment protection, and so on. The functionality of such material is usually determined by the characteristic electronic states within the bandgap as resulted from the dopants or impurities. Here we present a study in modulating the electron of a single OH-O2 defect on TiO2 (110) surface by ultrashort laser pulses. The topographic structure and the electron of the defect are obtained by scanning tunneling microscopy and spectroscopy at a cryogenic temperature of about 20 K. Giant changes in electron are observed under the illumination of ultrashort laser pluses. By increasing the laser power up to about 0.23$\mbox{GW}/\mbox{cm}^{\mbox{2}}$, the observed center energy of the gap state is shifted by 0.2 eV, away from the Fermi level. Meanwhile, the electron intensity of the gap state is increased by a factor of 2. Possible origins of such effect have been considered including optical Stark effect, thermal effect, and photo-induced conductivity. Our observation provides new insights into interactions between photons and localized electronic states in semiconductors at the single defect site scale. [Preview Abstract] |
Thursday, March 16, 2017 8:48AM - 9:00AM |
R25.00003: Quenching of oxygen photodesorption from TiO$_{2}$(110) through co-adsorption Nikolay Petrik, Greg Kimmel, Mingmin Shen, Michael Henderson Fundamental understanding of photochemical reactions on TiO$_{2}$ surfaces is important for many practical applications. We used temperature programmed desorption and photon stimulated desorption (PSD) to show that coadsorbates of varying binding energies (Ar, Kr, Xe, N$_{2}$, CO, CO$_{2}$, CH$_{4}$, N$_{2}$O, acetone, methanol or water) on the rutile TiO$_{2}$(110) surface suppress the hole-mediated photodesorption of adsorbed O$_{2}$. The extent of suppression correlates with the coadsorbate’s gas phase basicity, which in turn determines the strength of the coadsorbate-Ti$^{4+}$ bond. Coadsorbed rare gases inhibited the photodesorption of O$_{2}$ by 10-25\%, whereas strongly bound species (water, methanol and acetone) nearly completely inhibited O$_{2}$ PSD. We suggest that coadsorption of these molecules inhibit the arrival probability of holes to the surface. Band bending effects, which vary with the extent of charge transfer between the coadsorbate and the TiO$_{2}$(110) surface, are not expected to be significant in the cases of the rare gases and physisorbed species. These results indicate that neutral coadsorbates can influence significantly the charge transfer events by altering the interfacial dipole in the vicinity of the target molecule. [Preview Abstract] |
Thursday, March 16, 2017 9:00AM - 9:12AM |
R25.00004: Origin of coverage dependence in photoreactivity of carboxylate on TiO$_{\mathrm{2}}$(110) surface. Igor Lyubinetsky, Zhi-Tao Wang, Michael Henderson Employing scanning tunneling microscopy (STM) and ultraviolet photoelectron spectroscopy (UPS), we have observed a strong nonlinear decay of the reaction rate constant with coverage for the photolysis of trimethyl acetate on TiO$_{\mathrm{2}}$(110). This effect was not linked to intermolecular interactions of TMA but to the accumulation \quad of the coadsorbed bridging hydroxyls (HO$_{\mathrm{b}})$ deposited during (thermal) dissociative adsorption of the parent, trimethylacetic acid (TMAA). Confirmation of the hindering influence of HO$_{\mathrm{b}}$ groups was obtained by the observation that HO$_{\mathrm{b}}$ species originated from H$_{\mathrm{2}}$O dissociation at O-vacancy sites have a similar hindering effect on TMA photochemistry. Though HO$_{\mathrm{b}}$'s are photoinactive on TiO$_{\mathrm{2}}$(110) under ultrahigh vacuum conditions, UPS results show that these sites trap photoexcited electrons, which in turn likely (electrostatically) attract and neutralize photoexcited holes, thus suppressing the hole-mediated photoreactivity of TMA. This negative influence of surface hydroxyls on hole-mediated photochemistry is likely a major factor in other anaerobic photochemical processes on reducible oxide surfaces. [Preview Abstract] |
Thursday, March 16, 2017 9:12AM - 9:24AM |
R25.00005: State-to-State Surface Scattering of Methane Rainer Beck, Maarten E. Van Reijzen, Joern Werdecker We report first results for state-to-state surface scattering experiments for CH$_{\mathrm{4}}$. A molecular beam of CH$_{\mathrm{4}}$, incident on a single crystal Ni(111) surface, is prepared in a single rovibrationally excited quantum state by infrared pumping using a continuous wave optical parametric oscillator. State prepared CH$_{\mathrm{4}}(\nu _{\mathrm{3}}$, J$=$2) collides with the Ni surface with controlled incident energy and angle and the scattered CH$_{\mathrm{4}}$ molecules are detected with quantum state resolution using a cryogenic bolometer in combination with infrared laser tagging. Using this setup, we measured rotational and vibrational state distributions for methane scattered from bare Ni(111), graphene covered Ni(111), and LiF(100)$_{\mathrm{.}}$ The results provide detailed information on the rotational and vibrational energy transfer between the incident CH$_{\mathrm{4}}(\nu _{\mathrm{3}}$, J$=$2) molecules and the target surface. Efficient vibrational energy transfer is observed for incident CH$_{\mathrm{4}}(\nu _{\mathrm{3}})$ leading to scattered CH$_{\mathrm{4}}(\nu _{\mathrm{1}})$ where $\nu_{\mathrm{3}}$ and $\nu_{\mathrm{1}}$ are the anti-symmetric and symmetric C-H stretch normal modes of CH$_{\mathrm{4}}$, respectively. Energy transfer probabilities to other vibrational states of CH$_{\mathrm{4}}$ including the vibrational ground state are currently under investigation and will be reported in this contribution. [Preview Abstract] |
Thursday, March 16, 2017 9:24AM - 10:00AM |
R25.00006: Ultrafast plasmon-enhanced hot electron process in model heterojunctions: Ag/TiO$_{\mathrm{2}}$ and Ag/graphite Invited Speaker: Hrvoje Petek We study the plasmonically enhanced nonlinear photoemission from Ag nanocluster-decorated graphite and TiO$_{\mathrm{2}}$(110) surfaces by time-resolved two-photon photoemission spectroscopy (TR-2PP). Evaporating Ag atoms on graphite and TiO$_{\mathrm{2}}$ surfaces forms pancake-like Ag clusters with 5 nm diameter and 1-1.5 nm height through self-limiting growth mode. The Ag nanoparticles enhance the two-photon photoemission (2PP) signal by approximately two-orders of magnitude as compared with the bare surfaces for p-polarized excitation. In the case of s-polarization there is essentially no enhancement for graphite, and only about an order-of-magnitude enhancement for TiO$_{\mathrm{2}}$. Wavelength dependent measurements of the enhancement reveal that for Ag/graphite there is a single plasmonic resonance due to the $\bot $-plasmon mode at 3.6 eV. By contrast, for Ag/TiO$_{\mathrm{2}}$ there are $\bot $ and \textbar \textbar -plasmon modes with resonant energies of 3.8 and 3.1 eV, respectively. Apparently the dielectric properties of the substrate have strong influence on the type and frequency of Ag plasmonic modes that can exist on the surfaces. 2PP spectra of the Ag/graphite and Ag/TiO$_{\mathrm{2}}$ surfaces reveal two distinct components that are common to both. The high energy component consists of a coherent 2PP process from an occupied interface state, which only exists in the presence of Ag. We identify this state, as an interface state formed by charge donation from the Ag-5s band to the unoccupied states of the substrates. The low energy component consists of a hot electron signal that is created by plasmon dephasing. TR-2PP measurements are performed on the plasmon-induced electron dynamics to assess their relevance for plasmonically enhanced femtochemistry. [Preview Abstract] |
Thursday, March 16, 2017 10:00AM - 10:12AM |
R25.00007: Ultrafast hot electron process in graphite and at Ag/graphite interface Shijing Tan, Yanan Dai, Jindong Ren, Liming Liu, Jin Zhao, Hrvoje Petek We have investigated multiphoton photoemission from clean and Ag nanocluster decorated graphite surfaces. An unconventional multi-photon induced electronic heating involving up to eight quanta of light has been observed in clean graphite. Nonlinear photoexcitation between the $\pi $ and $\pi $* bands within the Dirac cones in graphite creates the primary anisotropic nonthermal hot electron populations. Ineffective screening enables further hot electron multiplication and energy redistribution through Auger recombination processes. Within 25 fs, the primary hot electron population instantaneously thermalizes through Coulomb scattering and leads to a Boltzmann population with effective electron temperatures exceeding 5000 K. Depositing Ag atoms onto graphite forms nanoclusters and introduces an interface state at 0.2 eV below $E_{F}$. The charge donated by Ag to the graphite near $E_{F}$ enhances the screening of Coulomb potential, and thereby leads to a dramatic suppression of heating of electron gas in graphite. Furthermore, tuning of $h\nu $ around 2.1 eV, a resonant two-photon transition from the interface state to the $\sigma $-interlayer band in graphite is observed. This resonant transition opens a direct channel for the ultrafast interfacial electron transfer from Ag clusters to the graphite substrate. [Preview Abstract] |
Thursday, March 16, 2017 10:12AM - 10:24AM |
R25.00008: Ultrafast time-resolved photoemission of a metallic tip/substrate junction Xiang Meng, Wencan Jin, Hao Yang, Jerry Dadap, Richard Osgood, Nicholas Camillone III The strong near-field enhancement of metallic-tip nanostructures has attracted great interest in scanning microscopy techniques, such as surface-enhanced Raman scattering, near-field scanning optical microscopy and tip-enhanced nonlinear imaging. In this talk, we use a full vectorial 3D-FDTD method to investigate the spatial characteristics of the optical field confinement and localization between a tungsten nanoprobe and an infinite planar silver substrate, with two-color ultrafast laser excitation scheme. The degree of two-color excited field enhancement, geometry dependence, the exact mechanism of optical tip-substrate coupling and tip-substrate plasmon resonances are significant in understanding the electrodynamical responses at tip-substrate junction. The demonstrated measurements with subpicosecond time and subnanometer spatial resolution suggest a new approach to ultrafast time-resolved measurements of surface electron dynamics. [Preview Abstract] |
Thursday, March 16, 2017 10:24AM - 10:36AM |
R25.00009: Adsorption of thiophene derivatives on gold: an experimental and theoretical investigation Walter Malone, Tingming Jiang, Yongfeng Tong, Diana Dragoe, Azzedine Bendounan, Abdelkader Kara, Vladimir Esaulov We investigate using Density Functional Theory (DFT) and Core Level measurements the adsorption of several thiophene derivatives including thiophene(C$_{\mathrm{4}}$H$_{\mathrm{4}}$S), bithiophene (C$_{\mathrm{6}}$H$_{\mathrm{6}}$S), and terthiophene (C$_{\mathrm{12}}$H$_{\mathrm{8}}$S) on an Au(111) surface. Specifically, we look at the change in the 2$p$ core level of the sulfur, and any geometric changes that may occur upon adsorption. We explore several adsorption configurations with the plane of the molecule perpendicular or parallel to the surface. We also investigated the possibility of broken C-S bond and its implications on the adsorption characteristics. The calculations were performed using the Vienna Ab initio Simulation Package (VASP) using a van der Waals force inclusive (vdW) functional, optB88-vdW. The XPS and NEXAFS experiments were done at the French synchrotron SOLEIL and on an in-house high resolution XPS setup on both Au(111) crystal surface and on gold on mica substrates. Comparisons between experimental and computational results will be presented. [Preview Abstract] |
Thursday, March 16, 2017 10:36AM - 10:48AM |
R25.00010: Adsorption of Bromine on Gold Nanoclusters Christopher Salvo, Josiah Keagy, Jory Yarmoff Small metal nanoclusters are extremely effective as catalysts, with rates that rival those of enzymes in biological systems. The first step in a catalytic reaction is the adsorption of a precursor molecule. The neutralization of alkali projectiles during low energy ion scattering (LEIS), which is acutely sensitive to the local electrostatic potential a few {\AA}'s above the surface, is used here to probe Au nanoclusters grown on SiO$_{\mathrm{2}}$ as they are reacted with Br$_{\mathrm{2}}$. Previous work had demonstrated very efficient neutralization in scattering from small catalytically active Au clusters, which was interpreted as an indication that the bare clusters are negatively charged. X-ray photoelectron spectroscopy and LEIS show little or no Br signal after exposing SiO$_{\mathrm{2}}$ and Au foil to Br$_{\mathrm{2}}$, suggesting that adsorption does not occur because the Br-Br bond does not break. Dissociative adsorption occurs rapidly, however, when small Au nanoclusters are reacted with Br$_{\mathrm{2}}$. 1.5 keV Na$^{\mathrm{+}}$ ions scattered from the Au clusters show a decrease in the neutralization probability as Br is reacted, indicating that adsorption results in charge being transferred from the cluster to the Br adatom. [Preview Abstract] |
Thursday, March 16, 2017 10:48AM - 11:00AM |
R25.00011: The reaction of arsine (AsH$_3$) with the silicon (001) surface. Similar to phosphine (PH$_3$), or completely different? Oliver Warschkow, Steven Schofield, Nigel Marks, David McKenzie, Neil Curson The AsH$_3$/Si(001) chemisorption system is of potential utility to the fabrication of atomic-scale Si:As devices using scanning tunneling microscopy hydrogen lithography techniques. This follows from the notion that AsH$_3$ is chemically analogous to phosphine (PH$_3$) for which the corresponding Si:P lithography techniques are becoming well established (see e.g. Ref. 1). This talk uses density functional theory to explore the initial adsorption reaction of an AsH$_3$ molecule, and its stepwise breakdown into AsH$_2$+H, AsH+2H, and As+3H surface species. Comparison with earlier PH$_3$/Si(001) calculations [2] reveals that the relative stability of phosphine and arsine species is qualitatively the same. There are, however, some differences in the activation energies between these two systems that affect in significant ways the rate of dissociation and the preferred path taken. We relate these findings to available experimental observations. [1] M. Fuechsle, J.A. Miwa, S. Mahapatra, H. Ryu, S. Lee, O. Warschkow, L.C.L. Hollenberg, G. Klimeck, and M.Y. Simmons, Nature Nanotechnology 7, 242–246 (2012). [2] O. Warschkow, N.J. Curson, S.R. Schofield, N.A. Marks, H.F. Wilson, M.W. Radny, P.V. Smith, T.C.G. Reusch, D.R. McKenzie, and M.Y. Simmons, J. Chem. Phys. 144 (2016) 014705. [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