Mar 14, 2014
Hexagonal boron nitride: impurity free for further applications
Hexagonal boron nitride (h-BN), often known as “white graphene”, has excellent mechanical and electrical properties. Thanks to these, h-BN has a variety of potential applications including dielectric layers, deep ultraviolet (UV) optoelectronic devices and protective transparent substrates. For these applications to be achievable, the h-BN needs to be impurity free, which is often not possible using the standard synthesis methods. Now, researchers from Yonsei University in Korea have synthesized h-BN free of undesirable by-products by employing a simple filtering system in the synthesis process.
Hexagonal boron nitride (h-BN) is a two-dimensional (2D) insulating material having a large direct bandgap up to 6 eV with its mechanical, electrical and chemical stability similar or superior to graphene. Consequently, h-BN has a multitude of its own potential applications but can also aid its carbon-based counterpart. The ultra-flat and charge impurity-free surface of h-BN is an ideal substrate to maintain the electrical properties of 2D materials such as graphene. A simplified process to synthesizing h-BN free from these impurities is needed, and reporting in Nanotechnology, researchers may have achieved just that.
The problem with CVD
The chemical vapour deposition (CVD) method has been widely used with ammonia borane as a precursor because it is difficult to achieve controllable and massive fabrication of monolayer h-BN with other methods. However, by-products from ammonia borane are polymeric aminoborane nanoparticles that are white non-crystalline BN nanoparticles of 50–100 nm in diameter. The presence of these BN nanoparticles following the synthesis has been hampering the implementation of h-BN to various applications.
A simple solution
The researchers adopt a rather simple filtering system with an entangled open-mesh structure in the CVD process. BN nanoparticles preferentially nucleate on the filter strands with higher surface energy, preventing the introduction of monomeric aminoborane on to a Cu substrate. Using this method, the researchers synthesized wafer-scale high-quality single-layer h-BN without BN nanoparticles. They confirm this using spherical aberration (CS)-corrected high-resolution transmission electron microscopy (HRTEM). These results may lead to the wider application of 2D h-BN.
More information can be found in the journal Nanotechnology 25 145604.
Growing boron nitride the easy way (July 2012)
Hexagonal boron nitride monolayers could make perfect coatings (Dec 2013)
Studies of defects in boron nitride reveal useful properties for devices (Jan 2014)
About the author
Jaehyun Han is a PhD candidate in Jong-Souk Yeo’s group at Yonsei University in the School of Integrated Technology and Yonsei Institute of Convergence Technology. The group carries out various research investigating nanoscale materials and fabrication, and their applications to nano convergence systems.