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INTRO TO NANOTOOLS
at the NanoScience Center
University of Copenhagen
Jesper Nygård
(experimental physics)
Plan: MBE, CVD, TEM, SEM, EBL, SPM, AFM, MFM…
”This is experimental physics”
…and that’s just the detector…
Tools for nanoscience - the top-down
approach
1-100 nm
Typical menu:
• Materials; chemical synthesis, crystal growth
• Characterization; electron microscopy, x-ray,
scanning probe microscopy
• Fabricate your ”nano-lab”; lithography
• Interface to macro world; electrical leads, tubes…
• Investigate; optical, electrical measurements
• Special conditions; high fields, low temperatures
wet, …
I. MATERIALS FOR NANOELECTRONICS
Growing on top of single crystals,
preserving the crystal structure
3D, 2D
Molecular Beam Epitaxy (MBE)
Sources
UHV
III-V Nanolab, GaAlAs
•Layer-by-layer (if lattice matching)
•Perfect crystals, very few impurities
•Heterostructures, 2D
•Optical and electronic applications
1D
Molecular Beam Epitaxy (MBE)
GaAs nanowires
Diameter: 30-100 nm
Length: 1 µm
III-V Nanolab, GaAlAs
Claus B. Sørensen, NBI
1D
Chemical Vapour Deposition (CVD) of
nanotubes
30,000 kr
- Substrate with catalyst nanoparticles
- Heat to 900°C
- Flow methane gas CH4
- Adsorption, decomposition, solution, saturation,
precipitation of nanotubes (root growth)
AFM image
H. Dai et al, NanoLetters 2002
Hybrid structure: Nanotube grown
expitaxially into a semiconductor crystal
- Epitaxial overgrowth by MBE (single crystal)
- Nanotubes survive being buried
- Hybrid electronics from molecular and
solid state elements
NanoLetters 4, 349 (2004)
II. IMAGING
NB: Can map the topography,
surface potential, magnetic
fields, surface chemistry …
Magnetic force microscopy (MFM)
(tip with magnetic coating)
Tracks on harddisk surface
Domain structures in thin film
micromagnets [D. Weiss et al]
Electrostatic force microscopy (EFM)
on carbon nanotubes
Q ~ -3000 e
September 2005 issue
Transmission Electron Microscope (TEM)
Optical
- Å resolution
- Transmission,
ie only thin slices
TEM
”Fullerene peapods”
10 nm
Transmission Electron Micrograph
Scanning Electron Microscope (SEM)
- imaging of 3D structures
Au electrodes on
SiO2 substrate
Silicon nitride bridge
III. LITHOGRAPHY
- two examples
Electron beam lithography (EBL)
I. Metallize
II. Etch
Resolution tens of nm
- limited by scattering of electrons
(not spot size or wave length)
Electron beam lithography (EBL)
- examples
Side gated quantum point contact
etched into two-dimensional electron
gas (GaAs/GaAlAs) [P. Utko]
Electrodes for contacting individual
carbon nanotubes [Nygard et al]
Technicality:
AFM and alignment marks; EFM
Atomic Force
Microscopy (AFM)
Electrostatic
Force Microscopy (EFM)
EFM
AFM
Bockrath et al, NanoLetters (2002)
Jespersen et al, NanoLetters (2005)
12 µm
0.1 mm
SWNTs
Henrik I. Jørgensen, NBI
Poster
V
AFM lithography
Eg. by local oxidation of surface with biased AFM tip, line width ~10 nm
Quantum point contact in
2DEG (GaAs/GaAlAs) [M. Aagesen]
”Quantum ring” in 2DEG
[Enslin et al, ETH]
Tools for nanoscience - hands on
Typical menu:
9 Materials; chemical synthesis, crystal growth
9Characterization; electron microscopy,
scanning probe microscopy
9 Fabricate your ”nano-lab”; lithography
9 Interface to macro world; electrical leads
• Investigate; optical, electrical measurements
• Special conditions; high fields, low temperatures
IV. Electron transport
measurements
Electrical measurements on
individual nanotube molecules
sour
drain
ce
Au
SiO2
p++ Si gate
Vg
I
V
Low temperature transport
Dilution refrigerator
20 mK
sample
T ~ 300 mK
sour
2
G (e /h)
Current
I (nA)
0.3
drain
ce
Au
0.2
SiO2
p++ Si gate
0.1
0.0
-7.5
-7.0
-6.5
Vg (V)
-6.0
-5.5
Gate voltage Vg (V)
Vg
I
Cost for adding one more electron:
charging energy: Q2/C ~ e2/C ~ 10 meV
>> thermal energy kT = 0.1 meV at 1K
Consequence: current is blocked (Coulomb blockade)
charging by one electron at a time!
V
Gold nanoparticle single-electron
transistor with carbon nanotube leads
i.
ii.
iii.
iv.
SiO2
CVD grown nanotubes (Cph)
EBL (electron beam lithography) (Cph)
AFM imaging and manipulation (Lund)
low temperature transport measurements (Lund)
Au
SiO2
7 nm gold particle (e2/C~60 meV)
C. Thelander et al,
APL 79, 2106 (2001).
Nanoscience - a food chain of ”tools”
I.
II.
III.
IV.
Materials; crystal growth MBE, CVD
Characterization; electron microscopy TEM, SEM
scanning probe AFM, EFM, MFM, …
Lithography EBL, AFM
Measurements; electrical, optical, etc
New phenomena, improve understanding,
or functionality (ie a new tool)
- Hands on experiments, usually not M$ instruments
- Very versatile, eg.
- SEM for imaging and lithography
- AFM for imaging (topography, electrical and
magnetic fields, …), lithography, manipulation
More to come:
8/9: Lithography, Transmission Electron Microscopy
15/9: Scanning probe microscopy (AFM, STM)
and ”why?” (scientific issues) in following sections of the course
10/11: Nanotube electronics
Acknowledgements
• Nanophysics group, Niels Bohr Institute
2000
2004