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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
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
• Investigate; optical, electrical measurements
• Special conditions; high fields, low temperatures
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
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
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]
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]
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
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).
Electric scanned probe imaging
Local gating by AFM tip,
revealing potential
modulations
in semiconducting nanotube
[Tans et al]
9 kΩ/µm
Electrostatic Force
Microscopy (EFM) measures
potential drop along nanotube
[Bachtold et al]
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:
Also:
AFM lithography 11/9, Transmission Electron Microscopy 18/9,
and ”why?” (scientific issues) in following sections of the course
Fysik 714 – Nanophysics
Fysik 715 – Experimental X-ray physics