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