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Original Research ARTICLE Provisionally accepted The full-text will be published soon. Notify me

Front. Mater. | doi: 10.3389/fmats.2019.00264

Topological Constraint Theory Analysis of Rigidity Transition in Highly Coordinate Amorphous Hydrogenated Boron Carbide

Bradley J. Nordell1,  Thuong D. Nguyen1,  Anthony N. Caruso1, William A. Lanford2, Patrick Henry3, Han Li3, Liza L. Ross3, Sean W. King3 and  Michelle M. Paquette1*
  • 1University of Missouri–Kansas City, United States
  • 2University at Albany, United States
  • 3Intel (United States), United States

Topological constraint theory (TCT) has revealed itself to be a powerful tool in interpreting the behaviors of amorphous solids. The theory predicts a transition between a ‘rigid’ overconstrained network and a ‘floppy’ underconstrained network as a function of connectivity or average coordination number, . The predicted results have been shown experimentally for various glassy materials, the majority of these being based on four-fold-coordinate networks such as chalcogenide and oxide glasses. Here, we demonstrate the broader applicability of topological constraint theory to uniquely coordinated amorphous hydrogenated boron carbide (a-BC:H), based on six-fold-coordinate boron atoms arranged into partially hydrogenated interconnected twelve-vertex icosahedra. We have produced a substantial set of plasma-enhanced chemical vapor deposited a-BC:H films with a large range of densities and network coordination, and demonstrate a clear threshold in Young’s modulus as a function of , ascribed to a rigidity transition. We investigate constraint counting strategies in this material and show that by treating icosahedra as ‘superatoms,’ a rigidity transition is observed within the range of the theoretically predicted c value of 2.4 for covalent solids with bond-stretching and bond-bending forces. This experimental data set for a-BC:H is unique in that it represents a uniform change in connectivity with and demonstrates a distinct rigidity transition with data points both above and below the transition threshold. Finally, we discuss how TCT can be applied to explain and optimize mechanical and dielectric properties in a-BC:H and related materials in the context of microelectronics applications.

Keywords: Boron carbide, Amorphous hydrogenated boron carbide, Amorphous solids, topological constraint theory, Rigidity theory

Received: 20 Jun 2019; Accepted: 10 Oct 2019.

Copyright: © 2019 Nordell, Nguyen, Caruso, Lanford, Henry, Li, Ross, King and Paquette. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Mx. Michelle M. Paquette, University of Missouri–Kansas City, Kansas City, 64112, Missouri, United States,