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ωħ

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Scanning probe microscopy based investigations of carbon nanotubes

and of carbon nanowalls

Annual INPAC MeetingLa Foresta, Vaalbeek, November 29, 2007

WP4

KULeuvenT. Moorkens

KULeuvenC. Van Haesendonck

KULeuvenK. Schouteden

KULeuvenJ. Piot

UNamurJ. B.Nagy

UNamurA. Fonseca

VITOA. Vanhulsel

KULeuven, VITOA. Malesevic

KULeuvenM. PalChowdhuryKULeuvenA. Volodin

Carbon Nanotubes and Nanowalls

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Our multifunctional SPM: AFM, EFM,…

SPM AutoProbe M5Stage:Z - travel range: 35 mmX, Y -travel range: 200 x 200 mmResolution: 1.0 µmMetrology Scanner:x, y 100 µmz 7.5 µmResolution: x, y 1 nm; z 0.1 nm

Vacuum SPMStage:Z - travel range: 25 mmX, Y -travel range: 20 x 20 mmResolution: 2.5 µmScanner:x, y 80 µmz 7.5 µm

LT UHV STM “Omicron”

LT STM stageSpecifications

Lowest temperature at the sample: < 5 KInitial cool down time to 5 K: < 6 hTime between LHe refills: > 15 hCoarse movement: X/Y/Z = 5 x 5 x 10 mmScan range (and offset range) : X/Y/Z = 10x10x1 µm at 300 KX/Y/Z = 1.8x1.8x0.2 µm at 5 KZ-resolution: < 0.01 nmGap Voltage: ± 0.5 mV to ± 10 VTunneling current setpoint: 50 pA... 50 nABakeout temperature: up to 150°CVacuum achievable: 10-11 mbar range

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Carbon nanotube: LT UHV STM image

CNT deposition: Au(111) substrate

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CNT deposition by STM manipulation: InAssubstrate cleaved in UHV

STM tip

CNT-bundle deposited on InAs substrate

180×180 nm2 image 12×12 nm2 image of the CNT-fragment

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Carbon nanotubes: where are the defects?

T = 77 K, 10-11 mbar STM image (2.6 x 2.6 nm2) of carbon nanotube

Carbon nano-walls (CNWs)

5nm

Freestanding CNW grown by means of microwave plasma-enhanced chemical vapor deposition (MW PECVD) in VITO

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CNW deposited on Au(111)/mica: STM imaging

AB

Current-carrying nanostructures: how to measure voltage

cm-range nm-range?

AFM tip

3µm

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Our new set-up for the EFM measurements

Standard AFM

Velectrode

substrate

~

~

nanostructured conductor

Vac

VdcVm

lock-in ωres

ω

Ω

ωres

photodetector

force

AFM tip

Our new set-up for the EFM measurements

Standard AFM

Standard EFMV

electrode

substrate

~

~

nanostructured conductor

Vac

V

V

dc

s

Vm

lock-in ωres

lock-in ωω

Ω

ωres

photodetector

AFM tipV-

0 50 100 150 2000.0

0.3

0.6

0.9

1.2

1.5

Forc

e (n

N)

Distance (nm)

FVdW

Fe

Vs (x,y) – work functionV(x,y) – voltage drop

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Our new set-up for the EFM measurements

Standard AFM

Standard EFM

EFM

Velectrode

substrate

~

~

nanostructured conductor

Vac

V

V

dc

s

Vm

lock-in ωres

lock-in ω

lock-in Ω

ω

Ω

ωres

photodetector

AFM tipV-

V

ϕ

( )( )( ) ( ) ( , ) ( , ) 1 sin( ) sin( )ac sF C z V V x y V x y m t tω ω′′∇ ≈ ⋅ ⋅ − ⋅ + ⋅ Ω ⋅

second derivative of the capacitance of the tip-sample system

modulation coefficient

work function

Our new set-up for the EFM measurements

A. Volodin, et al., Appl. Phys. Lett. 91, 142111 (2007)

Standard AFM

Standard EFM

EFM

Velectrode

substrate

~

~

nanostructured conductor

Vac

V

V

dc

s

Vm

lock-in ωres

lock-in ω

lock-in Ω

ω

Ω

ωres

photodetector

AFM tipV-

V

ϕ

( )( )( ) ( ) ( , ) ( , ) 1 sin( ) sin( )ac sF C z V V x y V x y m t tω ω′′∇ ≈ ⋅ ⋅ − ⋅ + ⋅ Ω ⋅

harmonic detection of the phase shift variations of the AFM cantilever oscillations at the frequency Ω/2π that is used to modulate the current flowing across the sample between the two electrodes

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EFM of contacted nanotubes

AFM EFM

highly conductive CNT part is equipotentialtopo

EFM

100nm100nm

Future plans: contacted CNW

Velectrode

substrate

~

~

nanostructured conductor

Vac

V

V

dc

s

Vm

lock-in ωres

lock-in ω

lock-in Ω

ω

Ω

ωres

photodetector

AFM tipV-

V

ϕ

Transport + EFM study

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Future plans: STM on CNTs with different diameters

1nm

T = 77 K

1nm

T = 77 K

+ defects…

Future plans: EFM + transport; scanning gate microscopy

Thank you!