university of maryland mechanical engineering department structures ‘at the bottom’: carbon...
Post on 15-Jan-2016
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Mechanical Engineering Department
University of Maryland
Structures ‘at the bottom’:Carbon nanotubes (CNT)• few nm diameter•10-100 m length(avg human hair is 70 m wide)
•already available commercially (5 manufacturers)•Already being applied in commercial products
Mechanical Engineering Department
University of Maryland
How do we Arrange Stuff into this ‘Space at the Bottom’ ?(Nanoscale Fabrication: Molecular Manipulation)
• Machine-phase synthesis• AFM, MFM, STM, nanotweezers• Self-assembly (e.g., DNA moletronics)• Atomic layer epitaxyAFM
Tips
AFMTips
CNT
CNT Probe
Si Substrate
Mechanical Engineering Department
University of Maryland
Carbon nanotube shaft with benzene ring gears [Jie Han et al]• max rpm in vacuum w/o slipping: 50-100 GHz• fabrication is done by STM (IBM has recently used STM to move organic
molecules 1.5 nm dia, consisting of 173 atoms)• molecular dynamics simulation shows
chatter/chaos
Mechanical Engineering Department
University of Maryland
MEMS gear trains have been driven upto 250,000 RPM
Comparison with Larger Scales: MEMS
Mechanical Engineering Department
University of Maryland
SWNT Twisting
SWNT Axial Comp.
SWNT Bending
MWNT Bending
Molecular Simulations of CNT Deformation
Mechanical Engineering Department
University of Maryland
Molecular models based onInteratomic Potential Functions:• Morse• Born-Oppenheimer• Lennard-Jones• Tersoff-Brenner
• Costly and Size-limited: requires simultaneous integration of 6N DEs; limited to ~105 atoms today
• Dynamic inaccuracies (wrong nonlinear behavior)
• Difficult to address nonlinearities
• Difficult to address realistic boundary conditions
• Continuum models miss some molecular conformations
Molecular Models