Posman Manurung
Materials Research Group, Department of Physics, The University of Lampung Jl. S. Brojonegoro No 1, Bandar Lampung 35145
Indonesia

It Meng Low
Materials Research Group, Department of Applied Physics Curtin University of Technology, Perth, WA
Australia

Craig Buckley
Materials Research Group, Department of Applied Physics Curtin University of Technology, Perth, WA
Australia