probing materials’ behavior using fast electrons · 2013. 12. 16. · (x 2 0 2 e o zf h sin 2 m e...
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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
Ps Ps
1 nm
180o ferroelectric domain wall in multiferroic ErMnO3
Mn Er O
MG. Han /BNL
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
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
CaO on MgO
X25000020 nm20 nm
X25000020 nm20 nm
SE
ADF
SrTiO3
5
Atomic surface imaging with secondary electrons
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
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”
Ba2Sr2CaCu2O8
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
)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
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
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
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
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
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
For BCC Fe NP, the max phase shift is ~50urad, 10-3 of 2/100 Can we image individual spins ?
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
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
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
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
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
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
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
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
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 !
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