Investigation of the properties of boron nanostructures with respect to the use in the nanotechnology

• Applicants: Dr. Jens Kunstmann; Professor Dr. Mark H. Rümmeli
• Subject Area: Synthesis and Properties of Functional Materials ; Theoretical Condensed Matter Physics
• Term: from 2009 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 160384604

• Final Report Year: 2016

Final Report Abstract

The objective of this project was to fabricate boron nanostructure and to explore their properties by combining theoretical and experimental techniques. By theoretical investigations it was found that free-standing, single-wall boron nanotubes (BNTs) with diameters larger than 0.6 nm are thermally stable at the experimentally reported synthesis temperatures. The walls of thermally stable BNTs were found to have a variety of different mixed triangular-hexagonal morphologies which are different from the structural patterns found in bulk structures. Furthermore, the intrinsic conductance of ideal single-wall nanotubes with large diameters (D≈10 nm) was determined and it was found that all considered boron nanotubes are highly conductive, irrespective of their lattice structures and chiralities, and they have higher conductivities than carbon nanotubes. In order to further understand the transport properties of BNTs, the effects of wall curvature, structural defects and electrical contacts were investigated. Curvature effects were found to generally have a pronounced effect on the ballistic currents through a nanotube. We then studied how the BNT geometry and the position of structural defects affect the conductance and found that, in the dilute limit, the reduction of the conductance by defects depends only on the number of defects in the system but not on their relative position or on the defect type. The contact structure of Ag-BNT was established and studied, and found to form structurally stable and strongly bound interfaces. A set of different Ag-BNT systems was found to form transparent, Ohmic contacts. This further indicates that BNTs are excellent materials to carry high current densities and they are thus very promising for applications in nanoelectronics. The influence of several functional groups and adatoms on the boron α-sheet were also examined. The results indicate for the first time the chemical properties of 2D boron and the related BNTs. Furthermore, the structure, non-stoichiometry, and geometrical frustration of α-tetragonal boron was studied in detail. Our results offer theoretical evidence that the α-tetragonal phase can exist as a pure and thermodynamically stable phase and thus resolve a long-standing scientific debate. By experimental investigations it was found that amorphous materials embedded with catalyst particles and sometimes without serve as excellent precursors for the room temperature growth of both amorphous and crystalline nanowires inside a TEM. The reactions are driven entirely by the imaging electron beam and has now triggered a new synthesis approach for nanowires and nanotubes. The in situ work demonstrates very nicely how radiolysis reactions can decompose material in a useful manner such the decomposition species can in effect serve as precursor materials for the fabrication of nano materials. Moreover, the decomposition species can be effective as volatile species and/or diffusing species over surfaces. This work paves the way for in situ TEM based nanolaboratories. Indeed, our in-situ growth method was reported to be a “revolutionary technique to prepare nanowires” by nanowerk.com on 4 Feb 2014.

Publications

• Highly conductive boron nanotubes: transport properties, work functions, and structural stabilities. ACS Nano 5, 4997–5005 (2011)
  Bezugly, V. et al.
  
• Defect assisted thermal synthesis of crystalline aluminum borate nanowires. J. Appl. Phys. 112, 024308 (2012)
  Gonzalez-Martinez, I. et al.
  
• SCC-DFTB Parametrization for Boron and Boranes. J. Chem. Theory Comput. 8, 1153–1163 (2012)
  Grundkötter-Stock, B. et al.
  
• Quantification of curvature effects in boron and carbon nanotubes: Band structures and ballistic current. Phys. Rev. B 87, 245409 (2013)
  Bezugly, V. et al.
  
• Approaches to mitigate polymer-core loss in plastic optical fibers: a review. Mater. Res. Express 1, 032002 (2014)
  Ioannides, N. et al.
  
• Localization of metallicity and magnetic properties of graphene and of graphene nanoribbons doped with boron clusters. Philos. Mag. 94, 1841–1858 (2014)
  Özdoğan, C., Kunstmann, J. & Quandt, A.
  
• Room Temperature in Situ Growth of B/BOx Nanowires and BOx Nanotubes. Nano Lett. 14, 799–805 (2014)
  Gonzalez-Martinez, I. G. et al.
  
• Unveiling the Atomic Structure of Single-Wall Boron Nanotubes. Adv. Funct. Mater. 24, 4127–4134 (2014)
  Kunstmann, J., Bezugly, V., Rabbel, H., Rümmeli, M. H. & Cuniberti, G.
  
• Low Voltage Transmission Electron Microscopy of Graphene. Small 11, 515–542 (2015)
  Bachmatiuk, A. et al.