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 !