University of Maryland Mechanical Engineering Department Structures ‘at the bottom’: Carbon nanotubes (CNT) few nm diameter  m length (avg human hair is 70  m wide) already available commercially (5 manufacturers) Already being applied in commercial products

University of Maryland Mechanical Engineering Department 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 epitaxy AFM Tips AFM Tips CNT CNT Probe Si Substrate

University of Maryland Mechanical Engineering Department Carbon nanotube shaft with benzene ring gears [Jie Han et al] max rpm in vacuum w/o slipping: 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

University of Maryland Mechanical Engineering Department MEMS gear trains have been driven upto 250,000 RPM Comparison with Larger Scales: MEMS

University of Maryland Mechanical Engineering Department SWNT Twisting SWNT Axial Comp. SWNT Bending MWNT Bending Molecular Simulations of CNT Deformation

University of Maryland Mechanical Engineering Department Molecular models based on Interatomic Potential Functions: Morse Born-Oppenheimer Lennard-Jones Tersoff-Brenner Costly and Size-limited: requires simultaneous integration of 6N DEs; limited to ~10 5 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