Funding for this research was provided by:
Vietnam Academy of Science and Technology (HĐ 22/AD-VCNMT, VAST. TĐ. NANO.04/15-18)
Received: 7 January 2019
Accepted: 31 May 2019
First Online: 27 June 2019
: The co-author Pau Loke Show declared himself as a member of the editorial board of this journal. Other authors declared that they have no competing interests.