(i) Synthesis & Characterization of Boron and Metal Boride Nanostructures (ii) Novel High-aspect Ratio Platelets and Their Use in Composites (iii) Mechanics of Nanotubes and Nanowires
Prof. Rod Ruoff, Northwestern University, USA
Abstract: (i) Crystalline or amorphous boron and (low density) metal boride nanowires (nanotubes) should be very high specific stiffness and strength components which, based at least on bulk properties, might also have superb electronic properties including at high temperature. But all is "not as it seems" with the element boron in solid form, or with metal borides such as calcium hexaboride. For example, it has been believed for over 50 years that CaB6 is intrinsically a metal. Now, it appears that CaB6 has a band gap of ~1 eV [1,2]! It is also known (from crystallographic studies spurred on by the theoretical treatment made also about 50 years ago by Longuet-Higgins) that bulk a-tetragonal boron is actually not pure boron; but what about our boron and metal boride nanostructures? We’ve synthesized and characterized boron nanoribbons , CaB6 nanowires , and hybrid B nanotube/nanowire structures , and talk about these nanostructures in the context of what is now known of the bulk materials. (ii) We then turn to a different topic, namely pseudo 2D nanostructures: platelets of graphite  and our work underway on both the individual platelets themselves, and on polymer composites that have them as filler material. The beautiful morphologies exhibited by such thin platelets in polymer composites and the physical properties of such composites will be discussed. (iii) Time permitting, we discuss our recent measurements of the tensile loading response of B nanowires supplied to us by the Buhro group at Washington University-St. Louis [7,8], as well as re-visiting the issue of the fracture strength of carbon nanotubes as compared to our earlier work published in Science in 2000 .
Support of our research by the NSF, NASA, and ONR is appreciated.
 The effect of boron purity on electric and magnetic properties of CaB6, Jong-Soo Rhyee and B. K. Cho, J. Appl. Phys., 95(11), 6675 (2004); Formation of midgap states and ferromagnetism in semiconducting CaB6, B. K. Cho, Jong-Soo Rhyee, B. H. Oh, M. H. Jung, H. C. Kim, Y. K. Yoon, Jae Hoon Kim, and T. Ekino, Physical Review B 69, 113202 (2005).
. Electronic Band Structure and Fermi Surface of CaB6 Studied by Angle-Resolved Photoemission Spectroscopy, Physical Review Letters 90(2), 027202 (2003).
. Crystalline Boron Nanoribbons: Synthesis and Characterization,Terry T. Xu, Jian-Guo Zheng, Nianqiang Wu, Alan W. Nicholls, John R. Roth, Dmitriy A. Dikin, and Rodney S. Ruoff, Nano Letters, 2004; 4(5); 963-968.
. Single-Crystal Calcium Hexaboride Nanowires: Synthesis and Characterization, Terry T. Xu, Jian-Guo Zheng, Alan W. Nicholls, Sasha Stankovich, Richard D. Piner, and Rodney S. Ruoff, Nano Letters, 4(10), 2051-2055 (2004).
. Boron nanowires and novel tube-catalyst particle-wire hybrid boron nanostructures, Terry T. Xu, Alan W. Nicholls and Rodney S. Ruoff, NANO, in press.
. Top down approaches, e.g., are: Patterning of highly oriented pyrolytic graphite by oxygen plasma etching, Lu XK, Huang H, Nemchuk N, and Ruoff RS, Appl. Phys. Lett., 75, 193-195 (1999). Tailoring graphite with the goal of achieving single sheets, Lu XK, Yu MF, Huang H, and Ruoff RS, Nanotechnology, 10, 269-272 (1999).
. Crystalline Boron Nanowires, Otten, Carolyn Jones; Lourie, Oleg R.; Yu, Min-Feng; Cowley, John M.; Dyer, Mark J.; Ruoff, Rodney S.; Buhro, William E., J. Am. Chem. Soc. (2002), 124(17),4564-4565.
. Mechanics of Crystalline Boron Nanowires, Weiqiang Ding, Lorenzo Calabri, Xinqi Chen, Kevin M. Kohlhaas, Rodney S. Ruoff; we acknowledge Buhro group synthesis (C. Otten) of these structures. Composites Science and Technology 66 (2006) 1109-1121.
. Weiqiang Ding, Lorenzo Calabri, Kevin M. Kohlhaas, and Rodney S. Ruoff, Experimental Mechanics, accepted.
Rodney S. Ruoff is the John Evans Professor in the Department of Mechanical Engineering at Northwestern University, where he serves also as the Director of the Biologically Inspired Materials Center (BIMat Center, a NASA URETI Center). He is the Distinguished Chair Visiting Professor at SAINT-Sung Kyun Kwan University in South Korea. He received his B.S. in Chemistry (1981; high honors) from the University of Texas – Austin and his Ph.D. in Chemical Physics (1988) from the University of Illinois – Urbana/Champaign. From 1988-1989, he was a Fulbright Fellow at the Max-Planck-Institut fuer Stroemungsfoerschung in Göttingen, Germany. From 1989-1990, he was a Postdoctoral Fellow at the IBM T. J. Watson Research Center in Yorktown Heights, New York. Prior to joining the faculty at Northwestern University in 2000, he was a Staff Scientist at the Molecular Physics Laboratory of SRI International from 1991-1996 and an Associate Professor in the Department of Physics at Washington University – St. Louis from 1996-2000. His research interests and activities include synthesis and physical and chemical properties of nanostructures, nanocomposites, nanorobotics, NEMS, and new tools for biomedical research (among others). He played a central role in the development of the Fullerenes Division of the Electrochemical Society by serving for 7 years as Chairman of the Fullerenes Group. He has developed, with colleagues, several new tools/instruments that have led to important and novel science investigations into the mechanics of nanostructures. Professor Ruoff has published ~140 refereed journal articles in the fields of chemistry, physics, mechanics, and materials science.
July 11, 2006, 10:40, FENS G035