ICTP 18.2.8 Ultrafast nanophotonics - optical control of coherent electron - Hirofumi Yanagisawa LMU, MPQ
Hirofumi Yanagisawa Japan (Tokyo) Switzerland (Zurich) Germany (Munich) http://roundtripticket.me/world-map-labled.html/best-image-of-diagram-world-map-and-labeled-for-labled
Laser-induced electron emission from a metallic tip
Slow response Phonon system nano-, pico- sec Ultrafast response Electronic system femto-, atto- sec CW laser Pulse Laser (ps) Pulse Laser (fs) 5 Nature series 10 PRL 1973 1987 2006 PRL 30, 1193 Nucl. Instr. And Meth. A 256,191 PRL 96, 077401
Ultrafast nanophotonics? Time Size nm um mm m Size atto-femto Here! pico-nano milli-sec Time
Ultrafast nanophotonics Light Nano structure
http://thescienceofwaves.weebly.com/uploads/2/5/7/8/25786734/1239513_orig.jpg
k Nano-sphere r=100nm ~wavelength (800nm)
10-18 10-15 10-12 10-9 sec Atto Femto Pico Nano Electron Phonon (lattice) 1st 2nd 2nd Plasmonics Tunnelling Rescattering Quiver Sub-cycle Weak field Laser absorption El-El scattering (heating El) El-Ph scattering (heating Ph) Phase transition Coherent phonon Surface Diffusion Melting Strong field El: Electron Ph: Phonon
Sphere Nano-structures Star Tip Adv. Mater. 26, 2353 Bowtie
Laser-induced electron emission from a metallic tip
Reference books - Principles of Nano-Optics Novotny and Hecht - Physics of Surface and Interfaces Harald Ibach - Field Emission and Field Ionization Robert Gomer
We learn today 1. Characeterization of tip apex 2. Beauty of nanophotonics in laser-induced electron emission from tip 3. Optical control of coherent electron wave
Let s learn more about tip and electron emission Why electron source?
1nm = 10-9 m Electron Electron Microscopy Best probe for Nano-object Electron gun Nano-object Detector Atom The TEM picture is taken from http://www.york.ac.uk/res/nanocentre/facilities/fetem.htm
Introduction 2 Electron gun- M. Aeschlimann, Nature 446, 301 (2007) 1fs = 10-15 sec Space 3D Dynamical information New Phenomena Coherence Laser pulse Electron gun ~100nm and ~100fs Tip Time Pulsed laser Brightness lens Tip B. Cho, PRL 92, 246103 (2004) C. Oshima, Nature 396, 557 (1998) ~1fs P. Hommelhoff, PRL 96, 077401 (2006)
How can we get electrons? Surface and work function
Work function Work functions Ionization Energy (surface) (atom) E vac 2-6eV Work function Φ E F Vacuum Metal Change surface to surface
How can we get electrons? 1. Thermal emission 2. Photoemission 3. Field emission 4. Photo-field emission (fs) 5. Optical field emission (as)
How can we get electrons? e -x Thermionic emission Photoemission E vac E vac photon E F E F J T 2 exp(-φ/kt) J I n (n order photon)
Metal Vacuum Field emission Nanometer sharpness Mesh Grid -1~-2kV Tip E F Surface Barrier
How thin barrier has to be? F=3-6V/nm Φ 3-6eV E F Metal Vacuum ~1nm J F 2 exp(-aφ 3/2 /bf)
Photo-field emission photoemission optical fieldemission E F hν hν hν E E x x Weak field Strong field
Various way to characterize tip apex
1 Langmuir 10-6 mbar x 1 second 1.6eV!! Photon and Particle Interactions with Surfaces in Space Volume 37 of the series Astrophysics and Space Science Library pp 323-330 M. Bujor
How to make and keep clean surface? Ar + Ar + 1 Langmuir 10-6 mbar x second Ar + 10-6 mbar -> 1 sec 10-7 mbar -> 10 sec 10-8 mbar -> 2 min 10-9 mbar -> 20 min Heating 10-10 mbar -> 3 hr
Characterization of tip apex First time in history, Erwin Mueller (German physist) A Biographical Memoir Vol 82 by ALLAN J. MELMED 1. Field emission microscopy (FEM) Around 1935 2. Field ion microscopy (FIM) Around 1950 individual atoms and their arrangement. 3. Atom probe field ion microscopy (APFIM)
Field Emission and Field Ionization: Robert Gomer FEM Magnification: x/br b~1.5 10 5-10 6
Field emission pattern with and without laser Intensity high Without laser Field Emission and Field Ionization: Robert Gomer low Tungsten Tip Vtip=-2250V (111) (310)(011)(310) (111) Radius ~ 100nm Side
Various Field emission image from W[011] N 2 Clean Phys. Rev. Lett. 45, 1856 (1980). O 2 FEM pattern change depending on adsorbate
Graphene Simulation, Edited by Jian Ru Gong, ISBN 978-953-307-556-3 Spatial resolution => 1 2nm
Power of FEM FEM View from V tip =-900V Nano-tip?
Power of FEM Nano-tip? FEM V tip =-900V
Positive bias Positively charged
http://labman.phys.utk.edu/phys222core/modules/m2/conductors_in_electrostatics.htm
Experimental set up Field Emission Microscopy Resistive anode MCP (Chevron) Mesh Grid y Air Vacuum (UHV) Lens : f=15mm Oscillator 800nm, 76MHz, 55fs Laser Polarization θ p Heating φ θ y High voltage Pre amplifier Position computer focus 4μm z x (negative) PC Sample : Tungsten wire
Field emission pattern with and without laser Intensity high Without laser With laser (800nm) low 30nm (111) Radius ~ 100nm Tungsten Tip (310)(011)(310) P L =20mW (111) Side Vtip=-2250V Vtip=-1600V
What is physics behind?
Surface electromagnetic wave Electromagnetic wave couples with surface charge Surface plasmon polariton: Epsilon_R <0 Zenneck wave : Epsilon_R >0, Epsilon_Im >>0 Phys. Rev. B 44, 5855 (1991).
Propagation of surface electromagnetic waves Propagation of Laser E k Photo-field Time average emission Rapex =100nm MaX-1: C. Hafner http://alphard.ethz.ch/ With laser k Max θ p =0 θ p =30 θ p =60 θ p =90 θ p =120 θ p =150 Min
Let s simulate laser-induced field emission images
Simulation of LFEM (photo-field emission model) FEM j exp F DC E vac F=F DC Work function e - E F j exp -j calc =0 Φ MaX-1: C. Hafner Photo-field Field emission
Simulation of LFEM (photo-field emission model) FEM F DC F laser E vac e - F 2 laser hν j exp -j calc =0 Φ, F DC f(e) E F jcalc LFEM Photo-field emission
Simulations : Photo-field emission model PRL 103, 257603 (2009) θ p =0 θ p =30 θ p =60 Exp. Exp. Experiment Simulation Sim. Sim. Exp. θ p =90 θ p =120 θ p =150 Exp. Exp. Sim. Sim. Sim. Top
Q1: Upon laser irradiation, which side of apex will be hotter, laser exposed side or shadow side? Time ave. With laser k
E field Deposited energy J/cm 3 Electron Temp. Phys. Rev. B 86, 035405 (2012)
What s nice? Tip Coherence length ~200nm Spatio-temporal control of coherent electron emission Coherence time ~200fs At 30K Coherence length ~10nm At room temperature B. Cho, Phys. Rev. Lett. 92, 246103 (2004)
Optical control of Young s interference
Without laser With laser (7fs, 40mW) Interference (111) (310) (310) (111)
Polarization dependence of interference pattern Pol=10 Pol=40 C C D A B A Interference Pol=90 Pol=110 A-B C-D B B A
Data analysis: Gaussian fitting Pol=150 2.6 x 105 2.4 Line profile L 2.2 2 1.8 1.6 I S 1.4 1.2 1 L I S 0.8 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 3 x 105 2.5 Gaussian fitting 2 1.5 1 0.5 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
2 2 1 0.002 Polarization dependence of electron 1 intensity 1 0.002 0 0 100 200 0 0 100 200 0 0 100 200 0 0 100 200 0 0 100 200 x 10-3 5 L S I 2*(L*S) 0.5 L+S 0.01 x 10-4 8 x 10-3 8 0.01 7 7 4 0.008 6 6 0.008 3 0.006 5 5 0.006 4 4 2 0.004 3 3 0.004 1 0.002 2 2 0.002 1 1 0 0 100 200 0 0 100 200 0 0 100 200 0 0 100 200 Polarization angle (degree) 0 0 100 200 0 100 0 100 0 100 0 100 0 100 L L S 2*(L*S) 0.5 (A+B) 2 =A 2 +B 2 +2AB I S
Simulations : Interference Far field Potential landscape 2D TDSE (013) (111) Interference peak
Simulations : Energy dependence of interference Scientific Reports 7, 12661 (2017) Energy Dependence
Transmission Probability Q2: Do we need quantum mechanical treatment for transmission probability of photoemission? E F Photo-field emission hν hν hν Photoemission E Photoemission E vac Photon x E F
DeVries, P. L. A First Course in Computational Physics (John Wiley & Sons, Inc., 1994) 9eV Electron 10eV 0eV Surface
Electron 11eV 10eV 0eV Surface
Electron 15eV 10eV 0eV Surface
Time-resolved electron holography k k Delay line
? k A B k Delay line Beam Splitter Such a dense electron source cannot be available.
Summary Introduction of myself Electron emission from a nano-tip How can we get electrons? -work function -various ways to emit electrons How to characterize tip apex: FEM Laser-induced field emission Site-selective technique Optical control of Young s interference
Tomorrow More about electron dynamics