Sci-Math Seminar: (i) Boron and Metal Boride Nanostructures (ii) High-aspect Ratio Platelets (iii) Nanotubes and Nanowires

Speaker: Prof. Rod Ruoff, Northwestern University, USA
r-ruoff@northwestern.edu
http://bucky-central.mech.northwestern.edu

Title: (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


Date: Mon 10 July, 2006
Time: 11:00
Place: Science Building, Room Z42

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 [3], CaB6 nanowires [4], and hybrid B nanotube/nanowire 
structures [5], 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 [6] 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 [9].

Support of our research by the NSF, NASA, and ONR is appreciated. 

[1] 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). 
[2]. Electronic Band Structure and Fermi Surface of CaB6 Studied by Angle-Resolved Photoemission Spectroscopy, 
Physical Review Letters 90(2), 027202 (2003). 
[3]. 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.
[4]. 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).
[5]. Boron nanowires and novel tube-catalyst particle-wire hybrid boron nanostructures, Terry T. Xu, Alan W. Nicholls 
and Rodney S. Ruoff, NANO, in press. 
[6]. 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). 
[7]. 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.   
[8]. 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. 
[9]. Weiqiang Ding, Lorenzo Calabri, Kevin M. Kohlhaas, and Rodney S. Ruoff, Experimental Mechanics, accepted. 



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