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Ultrafast nanophotonics
- optical control of coherent electron -
ICTP 18.2.8
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
1973 1987 2006
CW
laser
Pulse
Laser (ps)
Pulse
Laser (fs)
Slow response
Phonon system
nano-, pico- sec
Ultrafast response
Electronic system
femto-, atto- sec
PRL 30, 1193
Nucl. Instr. And Meth.
A 256,191
PRL 96, 077401
5 Nature series
10 PRL
Ultrafast nanophotonics? Time Size
Size m um nm mm
Time
milli-sec
pico-nano
atto-femto Here!
Nano structure
Ultrafast nanophotonics
Light
http://thescienceofwaves.weebly.com/uploads/2/5/7/8/25786734/1239513_orig.jpg
k
~wavelength (800nm)
Nano-sphere
r=100nm
10-18
Atto
10-15
Femto
10-12
Pico
10-9
Nano
sec
Phonon (lattice) Electron
Coherent phonon
Melting
Laser absorption
El-Ph scattering (heating Ph)
Phase transition
El-El scattering (heating El)
Tunnelling
Rescattering
Quiver
Sub-cycle
Surface Diffusion
Plasmonics
Strong field El: Electron
Ph: Phonon
1st 2nd
2nd
Weak field
Tip
Sphere
Bowtie
Star
Adv. Mater. 26, 2353
Nano-structures
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
Why electron source?
Let’s learn more about
tip and electron emission
Electron
Best probe for
Nano-object
The TEM picture is taken from
http://www.york.ac.uk/res/nanocentre/facilities/fetem.htm
Electron Microscopy
Nano-object Atom
Dete
cto
r
Electron gun
1nm = 10-9m
Tip Laser
pulse
B. Cho, PRL 92, 246103 (2004)
C. Oshima, Nature 396, 557 (1998)
Brightness
Coherence
Space
Time
Introduction 2 –Electron gun-
P. Hommelhoff, PRL 96, 077401 (2006)
~1fs
M. Aeschlimann, Nature 446, 301 (2007)
~100nm and ~100fs
Electron gun
Pulsed laser
lens
Tip
1fs = 10-15sec 3D Dynamical information
⇒New Phenomena
How can we get electrons?
Surface and work function
Work function
Work functions ⇔ Ionization Energy
(surface) (atom)
Vacuum
EF
Evac
Metal
Work
function Φ
Change
surface to surface
2-6eV
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?
Thermionic
emission Photoemission
photon Evac
EF
Evac
EF
J∝T2exp(-Φ/kT) J∝In (n order photon)
e-x
Mesh Grid
-1~-2kV Tip
Field emission
EF
Metal Vacuum
Nanometer sharpness
Surface
Barrier
EF
Metal Vacuum
How thin barrier has to be?
~1nm
Φ 3-6eV F=3-6V/nm
J∝F2exp(-aΦ3/2/bF)
Photo-field emission
photoemission
hν
hν
hν
x
EF
E
optical fieldemission
x
E
Weak field Strong field
Various way to characterize tip apex
Photon and Particle Interactions with Surfaces in Space
Volume 37 of the series Astrophysics and Space Science Library pp 323-330
M. Bujor
1 Langmuir
10-6mbar x 1 second
1.6eV !!
How to make and keep clean surface?
Heating
Ar+
Ar+
Ar+
10-7mbar -> 10 sec
10-8mbar -> 2 min
10-9mbar -> 20 min
10-10mbar -> 3 hr
10-6mbar -> 1 sec
1 Langmuir
10-6mbar x second
Characterization of tip apex
Erwin Mueller (German physist)
First time in history,
individual atoms and their arrangement.
A Biographical Memoir Vol 82
by ALLAN J. MELMED
1. Field emission microscopy (FEM)
Around 1935
2. Field ion microscopy (FIM)
Around 1950
3. Atom probe field ion microscopy
(APFIM)
Field Emission and Field Ionization: Robert Gomer
Magnification: x/br b~1.5
105-106
FEM
Vtip=-2250V
Without laser
Field emission pattern with and without laser
Radius ~ 100nm
Side
Intensity high
low
Tungsten
Tip
(011)
(111)
(111)
(310) (310)
Field Emission and Field Ionization: Robert Gomer
Various Field emission image from W[011]
N2
O2
Clean
FEM pattern
change depending
on adsorbate
Phys. Rev. Lett. 45,
1856 (1980).
Graphene Simulation, Edited by Jian Ru Gong, ISBN 978-953-307-556-3
Spatial resolution => 1 – 2nm
View from
Nano-tip?
Power of FEM
Vtip=-900V
FEM
Nano-tip? Power of FEM
Vtip=-900V
FEM
Positive
bias
Positively
charged
http://labman.phys.utk.edu/phys222core/modules/m2/conductors_in_electrostatics.htm
Experimental set up Field Emission Microscopy
Pre amplifier
Position computer
Resistive
anode
MCP
(Chevron)
Mesh
Grid
High voltage
(negative)
Heating
φ θ
z
y
x
Lens : f=15mm
y
Vacuum
(UHV)
Sample : Tungsten wire
focus
4μm
Air
Oscillator
800nm, 76MHz, 55fs
θp
Laser Polarization
PC
30nm
PL=20mW
Vtip=-2250V
Without laser With laser (800nm)
Vtip=-1600V
Field emission pattern with and without laser
Radius ~ 100nm
Side
Intensity high
low
Tungsten
Tip
(011)
(111)
(111)
(310) (310)
What is physics behind?
Surface electromagnetic wave
Electromagnetic wave couples with surface charge
Surface plasmon polariton: Epsilon_R 0, Epsilon_Im >>0
⇒Phys. Rev. B 44, 5855 (1991).
Photo-field emission Time average
Rapex
=100nm
Max
Min
MaX-1: C. Hafner
http://alphard.ethz.ch/
θp=0 θp=30 θp=60 θp=90 θp=120 θp=150
Propagation of surface electromagnetic waves
k
With laser
Propagation of
Laser
E k
Let’s simulate
laser-induced field emission images
⇒Φ
jexp-jcalc=0
Evac
EF
Photo-field emission
FEM
e-
Field emission
jexp
FDC F=FDC
Work
function
MaX-1: C. Hafner
Simulation of LFEM (photo-field emission model)
Simulation of LFEM (photo-field emission model)
⇒Φ, FDC
jexp-jcalc=0
Evac
EF
Photo-field emission
FEM
∝F2laser
jcalc ⇒ LFEM
f(E)
Flaser
hν
e-
FDC
Experiment
Simulation
θp=0 θp=30 θp=60
θp=90 θp=120 θp=150
Simulations : Photo-field emission model
Exp.
Sim.
Exp.
Sim.
Exp.
Sim.
Exp.
Sim.
Exp.
Sim.
Top
PRL 103, 257603 (2009)
Time ave.
k
With laser
Q1: Upon laser irradiation, which side of apex will be hotter,
laser exposed side or shadow side?
Phys. Rev. B 86, 035405 (2012)
E field
Deposited energy
J/cm3
Electron
Temp.
At 30K
B. Cho, Phys. Rev. Lett. 92, 246103 (2004)
Coherence length ~200nm
Coherence time ~200fs
Tip
What’s nice?
Coherence length ~10nm
At room temperature
Spatio-temporal
control of
coherent electron
emission
Optical control of
Young’s interference
Without laser With laser (7fs, 40mW)
Interference
(111)
(111)
(310) (310)
Pol=10
Pol=90 Pol=110
Pol=40
C
A
B
C
A
D
B B
A
Polarization dependence of interference pattern
Interference
A-B
C-D
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.8
1
1.2
1.4
1.6
1.8
2
2.2
2.4
2.6x 10
5
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.5
1
1.5
2
2.5
3x 10
5
L
I S
Pol=150 Line profile
L I S
Gaussian
fitting
Data analysis: Gaussian fitting
0 100 2000
1
2
3
4
5x 10
-3 S
0 100 2000
0.002
0.004
0.006
0.008
0.01
L
0 100 2000
1
2
3
4
5x 10
-3
0 100 2000
0.002
0.004
0.006
0.008
0.01
0 100 2000
1
2
3
4
5
6
7
8x 10
-4 I
0 100 2000
1
2
3
4
5
6
7
8x 10
-32*sqrt(S)*sqrt(L)
0 100 2000
1
2
3
4
5
6
7
8x 10
-4
0 100 2000
1
2
3
4
5
6
7
8x 10
-3
0 100 2000
0.002
0.004
0.006
0.008
0.01
S+L
0 100 2000
0.002
0.004
0.006
0.008
0.01
Polarization angle (degree)
(A+B)2=A2+B2+2AB
L S 2*(L*S)0.5
0 0 0 0 0 100 100 100 100 100
L
I S
S L I 2*(L*S)0.5
L+S
Polarization dependence of electron intensity
Potential landscape Simulations : Interference
(111)
(013) Interference
peak
2D TDSE
Far field
Simulations : Energy dependence of interference
Energy
Dependence
Scientific Reports 7, 12661 (2017)
Transmission Probability
Photoemission
Photon Evac
EF
Q2: Do we need quantum mechanical treatment for
transmission probability of photoemission?
Photo-field emission
Photoemission
hν
hν
hν
x
EF
E
10eV
0eV
Surface
9eV
Electron
DeVries, P. L.
A First Course in Computational Physics
(John Wiley & Sons, Inc., 1994)
10eV
0eV
Surface
11eV
Electron
10eV
0eV
Surface
15eV
Electron
k k
Delay
line
Time-resolved electron holography
A k
B k
Delay line
?
Beam Splitter
Such a dense electron source cannot be available.
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
Summary
Tomorrow
More about electron dynamics