Novel sp2-Bonded Materials and Related Nanostructures

Alex Zettl, Program Leader
Marvin Cohen, Steven Louie, Michael Crommie, Alessandra Lanzara, co-P.I.s

This program studies sp2-bonded structures including carbon nanotubes, graphene, nanowires, onions, fullerenes, nanocrystals, hybrid structures, and non-carbon nanomaterials such as BN, BC2N, and BC3 nanotubes and nanococoons, whose dimensions fall in the range of 1-100 nm.  Both theoretical and experimental activities are conducted.  The program consists of three major thrusts:  1)  Fundamentals, including theoretical predictions of new stable structures, and theoretical and experimental examinations of intrinsic electronic, magnetic, and mechanical responses.  Transport measurements such as electrical resistivity and thermal conductivity are pursued, including suitable isotope effects.  The mechanical properties such as Young's modulus and tensile strength are determined;  2)  Functionalized nanosystems, where two or more distinct nanostructures are brought together and allowed to interact; and  3)  Directed growth of nanostructures, where novel synthesis methods are explored for non-equilibrium growth of sp2 -based and other nanoscale materials.    Also,  4) specialized synthesis/characterization instrumentation is developed, including in situ SEM and TEM capabilities, some of which employs novel probes or substrates.

The functionalized nanostructures thrust (2) combines key elements of physics, chemistry, biophysics, and biology methodologies to exploit the properties of integrated nanosystems comprised of nanotubes and other nanoparticles interfaced with complementary nanostructures.  Such systems are formed using new atom-by-atom or molecule-by-molecule assembly techniques using STM and TEM-based nanomanipulators, along with suitable chemistry and biochemistry methods for functionalization.  State-of-the-art theoretical modeling, often using ab-initio methods, supports these efforts.  New nanostructures displaying novel physics, and having interesting new electronic, optical, magnetic, mechanical, and chemical responses are being produced.

The directed growth thrust (3) addresses synthesis via controlled formation of ordered nanostructures, including tailored carbon nanotubes, extended length nanotubes and nanothreads, and the deposition and patterning of molecular reactants for the creation of nanostructures by processes such as thermolysis.  Alternate approaches are taken to understanding and defining growth methods, including the use of structured precursors with catalysts, patterning the reaction volumes to less than a micron in size and studying with STM and AFM the decomposition of the reactants after thermolysis.

CURRENT PROJECTS

• Mechanical, structural and electronic properties of graphene layers and graphene edges;  effects of substrates, adsorbates and a wide range of functionalizations on those properties     (Zettl, Crommie)

• Further development of the nanoscale cell injector, injection technology and injector applications    (Zettl, Bertozzi)

• Methods for preparation of large quantities of pure BN and BxCyNz nanotubes and nanoparticles, as well as other theoretically predicted compositions, and very long, defect-free multiwall carbon nanotubes

• Detailed investigation of the physical, electronic, catalytic and magnetic properties of BN monolayers and multilayers, BN and BxCyNz nanotubes and nanoparticles, and such structures upon exposure to different nanoscale environments. (Zettl)

• Prepare and characterize heterostructures of BCN and carbon layers, tubes and nanostructures (Zettl)

• Continued theoretical investigations of the structural, electronic, vibrational, bonding  and transport properties of sp2-bonded materials, doped materials and nanostructures. A variety of methods are employed to understand/predict bound excitons, electron-phonon interactions, charge carrier dynamics, interface behavior and optical responses in various systems. (Cohen, Louie)

• Temperature and pressure dependence of the band gap Eg(T) of semiconducting carbon nanotubes (Zettl)

• Growth, characterization and theoretical studies of nanotube arrays.

• Functionalize nanotubes in a variety of ways to provide photonic, optical, complex magnetic or biocompatibility properties for numerous specific applications  (Zettl, Bertozzi)

• Development of nano-assembly tools  (Crommie, Zettl)

• Characterization and manipulation of the local adsorbate, electrode and substrate dependent behavior of functionalized carbon nanotubes

• Electronic structure and self energy effects on a large variety of properly engineered sp2 materials in the form of few atom thick sheets (such as BN, MgB2, graphene) and in the form of functionalized membranes; The novel physics of these systems, with properties that often fall beyond the Landau Fermi liquid picture, can be uniquely probed by the Lanzara group’s expertise in performing state of the art angle resolved photoemission spectroscopy experiments (ARPES) with spin, time and nano resolution (Lanzara)