* Corresponding authors

^a School of Mathematics and Physics, Queen's University Belfast, Belfast, UK
E-mail: a.kumar@qub.ac.uk

^b Microelectronics-Photonics Program and Physics Department, University of Arkansas, Fayetteville, Arkansas 72701, USA

^c Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA

^d Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research, Xi'an Jiaotong University, Xi'an 710049, China

^e Department of Physics, Southern Illinois University, Carbondale, Illinois 62901, USA

^f Ernst Ruska Centre for Microscopy, Forschungszentrum Juelich, Juelich 52428, Germany

^g School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore

^h Center for Materials for Information Technology, University of Alabama, Tuscaloosa, Alabama 35487, USA

ⁱ Center for Nanophase Material Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA