Carbon-Nanotube-Based (Gecko-Inspired) Adhesives
Bryan SchubertMarch 3, 2008
Gecko Adhesion
• Notable features– Strength: 10 N/cm2 from
van der Waals forces– Reusable: 30 days
between molts– Directional– Adheres to most
surfaces; smooth or rugged
– Self-cleaning
1. K. Autumn et al., J. Exper. Biol. 209, 3569 (2006).
Gecko Adhesion
50 μm 5 μm
1 μm
1. K. Autumn et al., J. Exper. Biol. 209, 3569 (2006).
• Basic principle of operation – Contact splitting– Density of contacts scales by contact radius as N ~ R-2
– Force per contact scales as F ~ R-1 (JKR: F = 3πRW) – Force per unit area scales as FN ~ R-1
R
Carbon Nanotube Adhesives - Fabrication
• Vertically-aligned multi-walled carbon nanotubes (VA-MWNTs)– Chemical vapor deposition (CVD) on silicon substrate using thin film
iron as catalyst layer and aluminum film as adhesion layer2,3.
2. L. Delzeit et al., J. Phys. Chem. B 106, 5629 (2002).
3. L. Delzeit et al., J. Phys. Chem. B 106, 5629 (2002).
1 μm
Oxygen plasma etch
5 μm
Top view
Diameter: 20-30 nmLength: 5-100 μmDensity: 1010-1011 cm-2
Carbon Nanotube Adhesives - Fabrication
• Vertically-aligned single-walled carbon nanotubes (VA-SWNTs)– Plasma-enhanced CVD on SiO2/Si wafer with iron layer as catalyst and
pre-coated aluminum adhesion layer. Fast heating4 was used to minimize catalytic particle aggregation, creating single-walled carbon nanotubes.
Nanotube diameter: 2-3 nmBundle diameter: 20-30 nmLength: 5-100 μmBundle density: 1011 cm-2
4. Y. Q. Xu et al., J. Am. Chem. Soc. 128, 6560 (2006).
Carbon Nanotube Adhesives - Performance
• VA-MWNTs
Attachment Cycle
Adh
esio
n St
reng
th (N
/cm
2 )
5. Y. Zhao et al., J. Vac. Sci. Technol. B 24, 331 (2006).
glass 4 mm2
glass 6 mm2
Au 4 mm2
parylene 7 mm2
Si 5 mm2
GaAs 7.8 mm2
Carbon Nanotube Adhesives - Performance
• VA-SWNTs– Normal Adhesion: 12-29 N/cm2
– Shear Adhesion: 4-16 N/cm2
– Performance decreases with use
6. L. Qu and L. Dai, Adv. Mater. 19, 3844 (2007).
4 mm x 4 mm
Before use After use
Carbon Nanotube Adhesives - Performance
• VA-SWNTs– Mostly semi-conducting nanotubes
6. L. Qu and L. Dai, Adv. Mater. 19, 3844 (2007).
4 mm x 4 mm
4.70 N
0.01 N
ComparisonMaterial Gecko VA-MWNTs VA-SWNTs
Maximum Adhesion
10 N/cm2 12 N/cm2 29 N/cm2
Surfaces Any Smooth (glass) Smooth (glass)
Reusable Yes Yes but degrades Yes but degrades
Self-cleaning Yes Maybe (uses Lotus effect)7 Maybe (using Lotus effect)
Directional Yes Probably not Probably not
Electrically Conductive
No Yes Yes
Thermally Conductive
No Yes Yes
7. S. Sethi et al., Nano Lett., 10.1021/nl0727765 (2008).