The objectives of this project are (1) develop a simple and effective approach for growing large-scale, high-density, and well-patterned conical boron nitride nanorods, (2) Study their structures and understand their growth mechanism, (3) Explore the optical and field-emission properties ofthe nanorods and their potential applications.

Growth and structure of prismatic boron nitride nanorods

H.Z. Zhang, J. D. Fitz Gerald, L. T. Chadderton, J. Yu, Y. Chen

Physical Review B 74(1)(2006) 045407

Growth takes place by rapid surface diffusion of BN molecules, and follows heterogeneous nucleation at catalytic particles of an Fe/Si alloy. Lattice imaging transmission electron microscopy studies reveal a central axial row of rather small truncated pyramidal nanovoids on eachnanorod, surrounded by three basal planar BN domains which, with successive deposition of epitaxial layers adapt to the void geometry bycrystallographic faceting. The bulk strain in the nanorods is taken up by the presence of what appear to be simple nanostacking faults in theexternal, near-surface domains which, like the nanovoids are regularly repetitive along the nanorod length. Growth terminates with a clearcuneiform tip for each nanorod. Lateral nanorod dimensions are essentially determined by the size of the catalytic particle, which remains as afoundation essentially responsible for base growth. Growth, structure, and dominating facets are shown to be consistent with a system which seekslowest bulk and surface energies according to the well-known thermodynamics of the capillarity of solids.

(a) Lattice images of the nanorods (b) Corresponding electrondiffraction pattern (c) the distribution of the apex angles (d) thecomposition of the nanorods: B and N only.

 

PatternedGrowth and Cathodoluminescence of Conical Boron Nitride Nanorods

H.Z. Zhang, M. Phillips, J. Fitz Gerald, J. Yu, Y. Chen,

Appl. Phys. Lett. 88 (2006) 093117

Cathodoluminescence (CL) spectra of the nanorods show two broad emission bands centered at 3.75 and 1.85  eV. Panchromatic CL images reveal clear patterned structure. ©2006 American Institute of Physics

Conical Boron NitrideNanorods Synthesized Via the Ball-Milling and Annealing Method

H.Z. Zhang, J. Fitz Gerald, J. Yu, Y. Chen,

Journal of the American Ceramic Society 89 (2006) 675-679

Nanorods: A boron nitride (BN) nanostructure, conical BN nanorod, has been synthesized in a large quantity on Si substrates for the first time viathe ball-milling and annealing method. Nitridation of milled boron carbide (B4C) powders was performed in nitrogen gas at 1300°C on the surface of thesubstrates to form the BN nanorods. The highly crystallized nanorods consist of conical BN basal layers stacked along the nanorod axis. Ball milling ofthe B4C powders can significantly enhance the nitridation of the powders and thus facilitate the formation of nanorods during the annealing process.(2) Patterned growth:  A catalyst layer of Fe(NO3)3 was patterned on a silicon substrate by using a copper grid as a mask. The nanorods were grownvia annealing milled boron carbide powders at 1300  °C in a flow of nitrogen gas. The as-grown nanorods exhibit uniform morphology and the catalystpattern precisely defines the position of nanorod deposition.

1.Milling-effect:

(a) XRD pattern shows the milled B4C powder having smallcrystallite sizes; (b) Enhanced nitridation of the milled B4C powder

2.Morphology:

 

(a) The BN nanorods are grown on the silicon substrate on alarge sacle. The nanorods have (b) conical tips and (c) bulbousattachment(catalyst particles)