Atomic Scale Coupling of Electromagnetic Radiation to Single Molecules Wilson Ho University of California, Irvine
Surface Photochemistry
Direct Adsorbate Excitation
Photoelectron Mechanism
Objective How to achieve atomic scale resolution in probing matter with electromagnetic radiation? Spectroscopy Optical Phenomena
Resolution of Optical Spectroscopy
Tip-Induced Plasmon Modes ε t Plasmon ε s Plasmon size : dr
Combination of Electromagnetic Radiation With Spatial Resolution of the STM
Molecules in Double Barrier Junctions The oxide film spacer increases the lifetime of the transient charged molecular state created after electron injection/withdrawal.
Single Molecule Electroluminescence
Photon Emission from Single Molecules: Zn-Etioporphyrin on Partially Oxidized NiAl(110) Oxide NiAl(110) Zn-Etioporphyrin
Zn(II) Etioporphyrin on Al 2 O 3 & NiAl(110)
Mechanism of STM-induced Electroluminescence : Step 1
Mechanism of STM-induced Electroluminescence : Step 2
Mechanism of STM-induced Electroluminescence : Step 3
Light collection setup (electroluminescence) Focusing Lens Mirror 2 Collection Lens Sample Spectrometer & hv CCD Camera Mirror 1 Viewport STM Tip Collection Efficiency: 1% UHV chamber
Photon Emission From Molecules on Oxide Films
800 600 400 200 2.072 0 1.912 Ag tip Ag tip Photon Energy (ev) 1.776 1.657 1.554 1.462 1.381 400 0 600 650 700 750 800 850 900 Wavelength (nm) 300 200 100 TIF Ag vs. W Tips 1 2 3 4 5 6 1.7 1.6 1.5 Peak Sequence W tip Ag tip Ag tip W tip Photon Count (arb. unit) Peak Energy (ev)
Tunneling Electron Induced Single Molecule Fluorescence: Zn-Etioporphyrin
Spatial Dependence of Single Molecule Fluorescence
Tunneling Electron Induced Single Molecule Fluorescence
LUMO & LUMO + 1: MgP
TIF Mechanism 2.0 Energy (ev) 0.0-2.0 Tip evbias -4.0 NiAl Vacuum Oxide
RF Induced Rectification Current
STM Apparatus Low temperature (10 K) ultrahigh vacuum STM
Origin of Rectification Current ) cos( 2 t V V V J B ω + = +L + + = ) ( cos ) cos( 2 ) ( ) ( 2 2 2 2 0 t V dv I d t V dv di V I V I J V J V B B B ω ω +K + + + = 2 ) cos(2 1 ) cos( 2 ) ( ) ( 2 2 2 0 t V dv I d t V dv di V I V I J V J V B B B ω ω + L + = + = V B J B J B R B J B dc dv I d V V I V V I V I V V I 2 2 2 0 0 2 1 ) ( ), ( ) ( ), ( V B J J B R dv I d V V V I 2 2 2 2 1 ), (
Spatial Localization of RF Field
Double Modulation Vibrational Rectification
Vibrational Rectification Current: C 2 D 2 and C 2 H 2 on Cu(001)
Vibrational Rectification Microscopy: C 2 D 2 and C 2 H 2 on Cu(001)
Rectification of Single Mn Atom
Photon Induced Tunneling
Single Molecule Electron Transfer
Mechanism of Photon-Induced Electron Transfer to a Single Molecule
Photon-Induced Electron Transfer Threshold
Photon Induced Tunneling
Spatial Variations of Electron Transfer within a Single Molecule
Ultrafast Optical Spectroscopy with Spatial Resolution of the STM Femtosecond Lasers: Chemistry at the Temporal Limit Scanning Tunneling Microscopes: Chemistry at the Spatial Limit
Acknowledgment Past Present Xi Chen Chi Chen Jennifer Gaudioso Ungdon Ham Jae Ryang Hahn Kiyeo Kim Martin Janson Markus Lackinger Lincoln Lauhon Gary Mikaelian Hyojune Lee George Nazin Joonhee Lee Freddy Toledo Ning Liu Xiuwen Tu Niklas Nilius Shiwei Wu Naoki Ogawa Nilay Pradhan Xiaohui Qiu Mohammad Rezaei Christophe Silien Barry Stipe Mitch Wallis Nicolas Lorente Shiwu Gao Mats Persson
Prospects Instrumentation Development Electron Spin - microwave-rf excitation - T sub-k, B 10 Tesla Zeeman spectroscopy - spin interactions: Kondo, nanomagnetism Laser-STM - simultaneous spatial + temporal limits 1 Å 10 fs - sub-molecular photochemistry, non-linear optics Non-Vacuum Environment - biological systems
< 1 K, 9 Tesla UHV STM
Mn Chains: 1 to 16 Atoms
Spin-Dependent Tunneling
Acknowledgment Past Present Jennifer Gaudioso Chi Chen Jae Ryang Hahn Xi Chen Lincoln Lauhon Ungdon Ham Hyojune Lee Martin Janson Joonhee Lee John Karnes Ning Liu Kiyeo Kim Niklas Nilius Markus Lackinger Nilay Pradhan Gary Mikaelian Xiaohui Qiu George Nazin Mohammad Rezaei Naoki Ogawa Christophe Silien Xiuwen Tu Barry Stipe Shiwei Wu Mitch Wallis Nicolas Lorente Shiwu Gao Mats Persson
Atomic Scale Photochemistry Wilson Ho University of California, Irvine
Photon Emission from molecules on metal surfaces Photon Count (arb. unit) 400 Ag tip/nial Ag tip/znetioi/nial 300 200 100 Metal Molecule 0 700 750 800 850 900 950 1000 Wavelength (nm)
Tunneling Electron Induced Single Molecule Fluorescence
IET vs. Single Molecule Fluorescence: Inelastic Electron Tunneling Fluorescence
Inelastic Electron Tunneling Spectroscopy (STM-IETS)
Frequency Dependence of RF Voltage Across Junction
RF Voltage Across STM Junction: VJ
Monitoring Photon-Induced Electron Transfer in a Single Molecule
Single Molecule Photon Induced Electron Transfer with Sub-Molecular Spatial Resolution
Mg-Porphine Orbitals
Single Molecule Vibronic States: MgP
Neutral and Charged States: MgP
Experimental Setup Focusing Lens Mirror 2 Collection Lens Sample Spectrometer & hv CCD Camera Mirror 1 Viewport STM Tip Collection Efficiency: 0.1% UHV chamber
Plasmon modes in the STM junction
Double Modulation Spectroscopy Modulate RF Signal at ω c f ( t) = 4 1 sin( nωct) π n (Square Wave 1 to +1 at ω c ) n= 1,3,5... f ( t) 2 1 1 = sin( n ω t C ) + π n 2 (Square Wave 0 to +1 at ω c ) n= 1,3,5... 2 = + 1 1 I( t) I0( VB ) I R sin( nωct) + π n= 1,3,5L n 2 (Modulated Current) 2 I1( t) = I R sin( ωct) π (First Harmonic Signal) 2 1 X 1 ( RMS) = I R π 2 (First Harmonic rms Amplitude) = π 1 (Absolute Rectification Current) I R X 2 Lock-in Sensitivity: 1 na/1 V I R 1 pa I 0 (V B ) 1 na
Vibrational Rectification: Single 12 C 16 O & 13 C 18 O
Single Molecule Photon Induced Electron Transfer
Single Molecule Photon Induced Electron Transfer with Sub-Molecular Spatial Resolution
Monitoring Photon-Induced Electron Transfer in a Single Molecule
Single Molecule Electron Transfer