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Probing Materials’ Behavior using Fast Electrons
Yimei Zhu
Dept. of Condensed Matter Physics Brookhaven National Laboratory
Long Island, NY 11973
Workshop on Ultrafast Dec 9-12, 2013, Key West, FL
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Ps Ps
1 nm
180o ferroelectric domain wall in multiferroic ErMnO3
Mn Er O
MG. Han /BNL
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Single BN layer
Single Si atom on graphene
red: B; yellow: C; green: N; blue: O
EELS mapping: La0.7Sr0.3MnO3/SrTiO3
Muller et al Science 319, 1073 (2008) Krivanek et al, Nature (2010)
Imaging atoms
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Single BN layer
Single Si atom on graphene
red: B; yellow: C; green: N; blue: O
EELS mapping: La0.7Sr0.3MnO3/SrTiO3
Muller et al Science 319, 1073 (2008) Krivanek et al, Nature (2010)
Imaging atoms
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CaO on MgO
X25000020 nm20 nm
X25000020 nm20 nm
SE
ADF
SrTiO3
5
Atomic surface imaging with secondary electrons
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STEM/ADF
SE
Imaging surface U atoms
e _
Zhu, et al, Nature Materials, 8, 808 (2009)
Atomic surface imaging with secondary electrons
SE ADF
Au
SrTiO3 (111)
SE
ADF
SrO terminated
TiO2 terminated
SrTiO3 (001)
clean sample is a prerequisition
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0 1 2 3 4 5 6
form
fac
tor f x
Cu
core
3d 4s
0.0
0.2
0.4
0.6
0.8
1.0
0 1 2 3 4 5 6
form
fac
tor f x
Cu
core
3d 4s
0.0
0.2
0.4
0.6
0.8
1.0
scattering angle s ( Å - 1 ) scattering angle s ( Å - 1 )
0.00 0.05 0.10 0.15 0.20
10
20
30
40
50
Sinq / l (Å-1)
Cu
Cu+ Cu2+
Electron
X-ray
Ele
ctro
n s
catt
erin
g
Am
pli
tud
e f
e (Å
)
10
20
30
40
50
X-r
ay s
catt
erin
g
Am
pli
tud
e f
x (e
lect
rons)
Electrons interact with electrostatic
potential
( x
2
02
2oe fZ
sinh
em2f
q
l
total
electrons valence
electrons
Bi2Sr2CaCu2O8
384 e /cell
X-rays interact with
electron cloud
Mott formula
Uniqueness of electron scattering
Sensitive to valence electrons at small scattering angles
difficulties for x-ray
suitability criterion 5~1.02
n
V
P. Coppens, (1997), “X-ray charge densities & chemical bonding”
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Ba2Sr2CaCu2O8
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coherent source
n,m
22
gg grHr
i2expF
l
g R = n
004 005 003 002
Accuracy : 0.01 Å
)rr(gi2expf~Feg
eg
Ba2Sr2CaCu2O8
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)rgi2(expF1
)r(g
xg
Valence electron distribution
charge density :
structure factor
rdzrAe
dzzrVCr E
),(),()(
Aharonov-Bohm phase shift of the wave function
Electrostatic and magnetic potential distribution
electrostatic potential V magnetic potential B :
02 V
Imaging electrons, spins, electromagnetic potentials
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Mapping valence electron distribution with quantitative diffraction
CaCu3Ti4O12: PRL 99 037602 (2007)
Experiment : ED + X-ray, 90K DFT, w/o disorder
MgB2: PRL 88 247002 (2002) PRB 69 064501 (2004)
Mg Mg
Mg Mg
B B
-1.59
0.26
0.0
-1.59
0.26
0.0
e/Å3
(a)
(b) -400 -200 000 200 400
inte
nsity
200 -200 400 -400 000
(c)
exp
cal
F - FIAM FFT
)rgi2(expF1
)r(g
xg
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Jang et al Science, 311, 886 (2011)
2-D Electron Gas: SrTiO3/RO/SrTiO3 (R=La, Pr, Nd, Sm, Y)
In collaboration with Prof. C.B Eom
Probing bonding states and charge transfer with EELS
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2-D Electron Gas: SrTiO3/RO/SrTiO3 (R=La, Pr, Nd, Sm, Y)
Probing bonding states and charge transfer with EELS
Ondrej Krivanek
individual Si substitutional atoms on SiC
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BaTiO3 Curie temperature 130C
10nm
10nm
300C
W tip
Vacuum Carbon
BaTiO3
Polking, Han, et al, Nat. Mat., 11 700 (2012)
- RT ferroelectric order can be down to 10-15nm, below 10nm superparaelectric.
Direct imaging of ferroelectric order using holography
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Direct observation of the Lithiation process in Li-ion-batteries
Li anode
FeF2/C cathode
electrolyte
Li
Wang et al Nature Comm. 3, 1201 (2012)
55 60 65 70
50 mV
300 mV
600 mV
740 mV
Li4Ti
5O
12
Inte
nsity (
arb
. units)
Energy (eV)
FeF2 + 2Li+ + 2e- 2LiF + Fe
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For BCC Fe NP, the max phase shift is ~50urad, 10-3 of 2/100 Can we image individual spins ?
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www.Jeolusa.com
Zernike phase plate: convert phase contrast to
amplitude contrast
Phase plate for magnetic imaging
May 13, 2013
Pollard, Malac, Belleggia, Kawasaki, Zhu APL 102, 192401 (2013)
Hole free Phase Plate
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2000 nm2000 nm
image
t B map
+ 2 0 +14
Lorentz contrast
500 nm
phase image
in-situ
magnetization vector map
structure V.Volkov and Y. Zhu
PRL. 91 043904(2003)
vortex & antivortex
Imaging magnetic moments
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2um Py square
Pollard et al Nature Comm. 3 1028 (2012)
Direct observations of vortex precession orbit
Vortex dynamics in nanomagnet
Imaging vortex-precession orbit via resonance excitation
175 MHz 170 MHz 165 MHz 160 MHz
J0=7.7x1010A/m2
190 MHz 185 MHz 195 MHz 180 MHz
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Pollard et al Nature Comm. 3 1028 (2012)
Direct observations of vortex precession orbit
190 MHz 185 MHz 195 MHz 180 MHz
200 MHz, CW 180 MHz, CCW 200 MHz, CCW
c
No excitation, CCW
7 8 9 10
70
80
90
100
110
120
130 CW
CCW
CCW (Theory)
CW (Theory)
Ra
diu
s (
nm
)
Current Density (1010
A/m2)
160 180 200 220
0102030405060708090
CCW
CW
CCW (Theory)
CW (Theory)
Tilt
(deg
rees)
Frequency (MHz)
Imaging vortex-precession orbit via resonance excitation
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Challenges:
Coupling electronic-lattice system
→charge, orbital and spin order
One solution: Decouple the subsystems in the time domain and then observe the dynamics of subsystems separately.
Ultrafast ED: better time resolution & simultaneously observe diverse degrees of freedom.
Strong interplay between charge, spins, orbital and lattice → complex phase diagrams, exotic material properties
e(~100 fs)
lattice(ps-ns)
spin(ps)
~1 ps
Our goals: understanding strongly correlated materials
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XJ Wang’s talk Monday morning
- 2-4 MeV electron energy - 100 fs pulse, Hz repetition rate - 106 electrons in a single pulse - energy spread <0.01% - 30urad divergence - beam size on detector 200um - Synchronization of RF & laser <50fs - cryogenic capability - longitudinal coherence length 1-2nm - transverse coherence length ~10nm
Currently optimized at 2.8MeV with 120fs resolution
Ultrafast electron diffraction at BNL
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pump fluence: 1.4 mJ/cm2
0.2ps
1.5ps
SP intensity reduced to ~ 0, without obvious recovery in the following 50 ps
CDW Peak
(3X)
0.4ps quasi-steady state
2H-TaSe2
Coherent phonon: 2.5THz (~ 400fs) P. Zhu et al, APL 2013
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3 2
4 1
2’ 3’
4’
1’
Split of transmitted and diffraction spots due to magnetic domains in permalloy
diffraction
Ultrafast electron diffraction for spin dynamics ?
CO
FM
CO
Bx (x,y)DF T=11K
CO
FM
(a) T=160K (b) (c) (d)
CO
FM
CO
Bx (x,y)DF T=11K
CO
FM
(a) T=160K (b) (c) (d)
2 1
3 4 A
B
1
4
3
2
(000) beam splitting
CO
FM
CO
Bx (x,y)DF T=11K
CO
FM
(a) T=160K (b) (c) (d)
CO
FM
CO
Bx (x,y)DF T=11K
CO
FM
(a) T=160K (b) (c) (d)
orbital-spin ordering La1/4Pr3/8Ca3/8MnO3
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Atomic imaging: D. Su, H. Xin, H. Inada, J. Wall, L. Wu
Electron diffraction: L. Wu, C. Ma, J. Tafto
Holography: MG Han
Magnetic imaging: S. Pollard, V. Volkov, M. Malac
Ultrafast: XJ. Wang, P. Zhu, J. Hill, J. Cao
Supported by US DOE/BES
Acknowledgement
Thank you !