Multiple Modulation and Higher Harmonics Probing Complex Properties

8/7/2019 Multiple Modulation and Higher Harmonics Probing Complex Properties

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Multiple Modulation and Higher

Harmonics Probing Complex Properties

(including Scanning Impedance)

NSF: NIRT, NSEC, MRSEC

Dawn A. Bonnell,S-H. Kim, R. Shao, D. Strachen, C. Staii,

A. T. Johnson

The University of Pennsylvania


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The Ideal Probe

TemperatureChemical environment

Sample stimulationdc + high frequency ac lateral modulationBack gate modulationFrequency dependenceDc + modulated magnetic fieldSingle wavelength optical

Wavelength modulation

Tip Modulationmechanicalelectricaloptical

DetectionHigher order harmonicsMultiple harmonicsFrequency dependenceOptical + electricalOptical + mechanicalWavelength dependence

Van der Waals interactions

V1 + V2 sin(t)surface potential, SIM, NIS

+

++

+

- - -

- --PFM, SCM ,SSRM

electrostatic/mag

netic interactions

Mechanically driven electrostatically driven


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140K

10 nm

Atomic Structure and Ferroelectric

Polarization; BaTiO3

Separating Atomic Lattice and

Charge Lattice: PotassiumMolybdate

Spin and Charge: La

Manganates

CH3-CO-S-Benzen-(Zn-prophyrin)3

STM current image Height =5nm

Diameter =2nm

STM

topography

Biomolecules on Surfaces

Functional Oxide Structure

Not Only Structure .. Also Properties


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Scanning Impedance Microscopyexploiting sample perturbation and frequency dependence

electrons trapped at an interface

band energies in a nanotube

Higher Harmonics

dielectric constant of a thin film

dielectric constant of nanowires

density of states of nanotubes

Higher Harmonics in Tip Scattered Optical Signaldielectric function of porphyrin


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( ) ( ) ( ) ( )[ ] ( ) ( )

++

= tVVVtVVVz

zCzF acsurfdcacsurfdc cos22sin12

1

2

1 22

( )

( )

( )

+

=22

2

1

2

1

acsurfdcdc VVVz

zC

zF

( )( )

( ) acsurfdc

VVVz

zCzF

=

1

( )( ) 2

ac2

V4

1

z

zCzF

=

An Oscillating Electrical Signal


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( )( )

( ) acsurfdc

VVVz

zCzF

=

1

( )( ) 2

ac2

V4

1

z

zCzF

=

Scanning Surface Potential Microscopy/Kelvin Force Microscopy

Scanning Impedance Microscopy

Gated Scanning Impedance



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( )( )

( ) acsurfdc

VVVz

zCzF

=

1

( )( ) 2

ac2

V4

1

z

zCzF

=


New Variants of SSPM/KFM and EFM

Dielectric functionQuantum capacitance

Density of states


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RdR R

V1 V2

V

( )tVVV acdctip += cos

dclat VV =

dctip VV =

( )tVVV acdclat += cos

Scanning Impedance Microscopy: a local probeScanning Impedance Microscopy: a local probe

0 5 10 15

-0.4

-0.2

0 .0

0 .2

0 .4

-0.4

-0.2

0 .0

0 .2

0 .4Amplitude,a.u.

Phase,deg

Dis tance, m

Phase

Amplitude

( )cacssurf tVVV ++= cos

( )20

2tan

=

1 03

1 04

1 05

1 0- 2

1 0- 1

1 00

1 4 8 O h m

5 2 0 O h m

1 . 5 k O h m

4 . 7 k O h m

tan(

gb

)

F r e q u e n c y , H z

R C

CdR R

Rd

1, A1 2, A2

V

Kalinin and Bonnell, Appl. Phys. Lett., 2001, Shao, Kalinin, Bonnell, APL 2003


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1000oC for 15 min in

vacuum: details show up in

surface steps.

34nm

24o

{100}

Grain Boundary Structure

0 50 100 1500

1

2

3

X[nm]

Z[nm]

Aberration corrected STEM image of a SrTiO3

bicrystal and calculated charge density

0.5n

m

Sr

O

Ti


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34nm

24o

{100}

Fine Structure at the Grain Boundary

2nm


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103

104

105

10-2

10-1

100

148 Ohm

520 Ohm

1.5 kOhm

4.7 kOhm

tan(

gb

)

Frequency, Hz

R

C

Temperature Dependent SIM Identifies an Interface Induced Ferroelectric

Phase Transition in SrTiO3

Shao, Duscher, Chisholm, Bonnell, PRL (2005)

Scanning surface potentiometry

50 1001502002503003500.0

3.0x104

6.0x104

9.0x104

1.2x105

1.5x1051.8x10

5

R,

T,K

50 100 150 200 250 3006

9

12

C-1,m

2/F

T, K

Curie-Weiss Law: Cgb TTC 1 and TC=40K


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Direct Imaging of the Boundary PotentialDirect Imaging of the Boundary Potential

2 0 0 n m

0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0- 1 0 0

-5 0

0

5 0

1 0 0

SurfacePotentia

l,mV

La te ra l d is tance ,nm

V120mV

VGB-40mV

0 200 400 600 800 1000

-8 0

-4 0

0

40

80

Lateral d istance,nm

SurfacePot

ential,mV

200nm

VGB-100mV

0 500 1000-80

-40

0

40

Surface

Potential,m

V

Lateral distance,nm

30K98K

293K


13/32Shao, Duscher, Chisholm, Bonnell, PRL (2005)

Temperature Dependent Transport Reveals Collapse of theTemperature Dependent Transport Reveals Collapse of the

Interface Potential Barrier in SrTiOInterface Potential Barrier in SrTiO33

0 50 100 150 200 250 300

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

RGrain

(m2)

RGB

(

m2)

24o

36.8o

T(K)

grain

0 500 1000

-80

-40

0

40

Surface

Potential,mV

Lateral distance,nm

30K98K

293K


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Field Induced Dipole Alignment

Boundary charge=0.06C/m2

That is 0.3 electron/unit cell

That is 0.8 electrons/Ti unit

Interface charge determined from first principles calculations aInterface charge determined from first principles calculations and transportnd transport

measurements are in good agreementmeasurements are in good agreement

0.5nm

Sr

O

Ti

Aberration corrected Z

contrast TEM

DFT calculations



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Temperature Dependent Transport Reveals Collapse of theTemperature Dependent Transport Reveals Collapse of the

Interface Potential Barrier in SrTiOInterface Potential Barrier in SrTiO33

0 50 100 150 200 250 300

10-9

10-8

10-7

10-6

10-5

10-4

10-3

10-2

RGrain

(m2)

RGB

(

m2)

24o

36.8o

T(K)

grain

0 500 1000

-80

-40

0

40

Surface

Potential,mV

Lateral distance,nm

30K98K

293K

I t f h d t i d f fi t i i l l l tiI t f h d t i d f fi t i i l l l ti d t td t t


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Field Induced Dipole Alignment

Boundary charge=0.06C/m2

That is 0.3 electron/unit cell

That is 0.8 electrons/Ti unit

Interface charge determined from first principles calculations aInterface charge determined from first principles calculations and transportnd transport

measurements are in good agreementmeasurements are in good agreement

0.5nm

Sr

O

Ti

Aberration corrected Z

contrast TEM

DFT calculations


Nanoimpedance Spectroscopy


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Detecto

r

Tip

Laser AFM

Controller

Impedance

AnalyzerHP4294A

Z(), ()

Topo

Nanoimpedance Spectroscopy

Single-terminal measurements

Two-terminal measurements

-Zim

-ZreR1+R2R1

( ) 111

CR

( ) 122

CR

Shao, et al, APL 2003

ieZZ =

0 100 200 300 400

0

50

100

150

200

-Z

im(k

)

Zre(k )

(c)

12

3

|Z|

(c)

12

3

|Z|

14M

19M

(e)

12

3

(e)

12

3

-

90o

-20o

(d)

1

3

|Z|

2

(d)

1

3

|Z|

2

6.1M

18M

(f)

1 2

3

(f)

1 2

3

-

90o

-

10o


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Scanning Impedance on


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SamplesfromCraighead &MacDiarmidGroups

Nikiforov, Liu, Bellan, Craighead, BonnellNano Letters 2005


Reduced Dimension Structures



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Vi

+

+ -

Ev

Ec

EF

Vi

+

+ -

Ev

Ec

EF


Reduced Dimension Structures


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Electronic Structure of Individual Defects


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Tip

Tube

Gate

C1

C2

surf

q

tube VCCC

C

++= 211

Cq - quantum capacitance

C1, C2 geometric capacitances

S. Lyrui, Appl. Phys. Lett. 52, 501 (1988),

M. Freitag, S.V. Kalinin, A.T. Johnson, D.A. Bonnell, PRL (2002)

Onset of depletion

itube V =

Quantum electrostatics

C1

C2 Cq

SIM Determines the Electronic Structure of Individual Defects in


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SGMSGM(current through the nanotube)(current through the nanotube)

SIM amplitudeSIM amplitude(local potential amplitude)(local potential amplitude)

Freitag, Johnson, Kalinin, Bonnell, Phys Rev Lett (2002)

Molecular Wires and Nanotubes

Spot diameter :1* +

=

R

V

VD

i

tip

i

33.1~_spherefree

surfacetip

C

C =

9.32=SiO

nmR 20~radiusTip=

where:

Defect contrast is related to the local electronic structure


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SGM

SIM

Defect contrast is related to the local electronic structure

Increasing tip bias

Defect Slope [nm/V] Vi [mV] Vi* [meV]

1 83.6 3.6 65 20

2 39.1 0.4 139 403 26.4 1.1 206 55

4 53.0 1.2 102 30

M. Freitag, S.V. Kalinin, A.T. Johnson, D.A. Bonnell, PRL (2002)

0 2 4 6 80

100

200

300

400

500

600 Defect 1

Defect 2

Defect 3

Defect 4

Spotdia

meter(nm)

Tip bias (V)



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( )( ) ( ) acsurfdc VVVz

zCzF

=1 ( )

( ) 2ac2 V

4

1

z

zCzF

=

g g

New Variants of SSPM/KFM and EFM

Dielectric functionQuantum capacitanceDensity of states

Simultaneous topographic signal, 1st harmonic and 2nd harmonic detection


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2

Differentialcapacitance

Simultaneous topographic signal, 1 harmonic and 2 harmonic detectionImplemented on custom designed Omicron VT AFM/STM

Effectively 2 lock-in signalsAdditional filters on the frequency demodulator signal

Simultaneous imaging of topography, surface potential (1), and

diff ti l it (2 ) f hi h k id fil (2 HfO Si)


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differential capacitance (2) of high-k oxide film (2nm HfO2 on Si).

topography

1 2

0.002 (Df)

topography

1 2

Omicron UHV VT-AFM/STM

Low dimensional systems exhibit discontinuities in the


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y

density of states

[ ]),(2

2

22

tiptotaltip

F VzCz

Vk

Q

)(zCtt

LzC )(0

),(tipQ

VzC

EtipQDeLC

2=

tipV

ED

tipV

*J. Heo and M. Bockrath, APL 5, 853 (2005).**D. Gekhtman et al. Physical Review Letters82, 3887 (1999).

Combine EFM Feedback Detection with low


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tVVV

tVVtVVV

tip

sin

sin)()(2

1sin)()(

00

22

00000

+=

++

Lock-in

AFM computer

In Ref InV tsin

)2(

Combine EFM Feedback Detection with lowamplitude electric signal detection

Real Time 2nd harmonic of carbon nanotubes


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tube

bare substrate


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There is much information in the long range


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There is much information in the long range

interactions; it is not simple to extract it!!

Combining multiple modulations of tip signals and sample perturbations

yields new information

Scanning Impedance Microscopy

Nano Impedance Spectroscopytrap state time constants

dielectric anomalies

Accessing higher harmonics with multiple signals yields complex propertiesSurface Potential vs Dielectric Constant

polarizability !!!

Exploiting boundary conditions related to sample configuration can yieldfundamental information.

Quantum Capacitance Defect electronic structure

Density of States Quantization at Interfaces

Multiple Modulation and Higher Harmonics Probing Complex Properties

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