Aug 14, 2014
Enhancing dielectric growth with two-dimensional materials
Graphene’s hydrophobic nature makes it difficult to deposit dielectrics on its surface. This limits its application in optoelectronics such as field effect transistors (FET). Reporting in Nanotechnology, researchers may have solved this problem. They utilize two-dimensional (2D) dielectric materials, such as single-sided fluorinated graphene (SFG) or hexagonal boron nitride (h-BN), as a seed layer for atomic layer deposition (ALD).
The researchers, from Zhejiang University, China, and the University of Cambridge, UK, have shown that the surface of SFG/graphene or h-BN/graphene heterostructures can be hydrophilic. The typical ALD growth of a metal oxide (e.g. Al2O3 or HfO2) employs water as a precursor, followed by a metal organic source. Due to the polarity of water molecules, the polar surface of the target substrate is essential for physical adsorption. SFG and h-BN are very suitable for this purpose as they display considerably stronger physical adsorption of water molecules than pristine graphene. The electro-negativity between F/C-atom or B/N-atom is also relatively large.
With these facts, first principle simulations are applied to investigate the electron cloud distribution between atoms and the interaction between H2O molecule and substrate. The team demonstrates that electrons tend to surround the F and N atoms, forming covalent bonds with polarity. As a result, the adsorption energy of H2O for the heterostructure is much larger than that for graphene alone.
Moreover, the team demonstrates that h-BN is not only a good candidate for growing dielectrics on graphene, but also preserves the intrinsic electronic properties of graphene. On the other hand, a SFG seed layer may introduce n-doping to graphene.
By choosing 2D materials as a seed layer, it is possible to grow dielectrics on graphene by ALD. The technique may find great potential in future graphene electronics.
More information about the research can be found in the journal Nanotechnology 25 355202.
Studies of defects in boron nitride reveal useful properties for devices (Jan 2014)
Selective electrochemical biosensing using molybdenum disulphide (July 2014)
Hexagonal boron nitride: impurity free for further applications (Mar 2014)
About the author
Hongwei Guo, Yunlong Liu, Yang Xu and Jack Luo in the Department of Information Science and Electronic Engineering at Zhejiang University, China, work on van der Waals 2D heterostructures. The research of Yang Xu’s Group focuses on 2D/3D heterostructures for a variety of applications including electronics and sensing. Tawfique Hasan, in Cambridge Graphene Centre at the University of Cambridge works on 2D material-based applications in the field of (opto)electronics and energy.