wp4 scanning probe microscopy based investigations of carbon … annual 07/volodi… · a. volodin,...
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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!