1. 1Data Storage Institute, A*STAR (Agency for Science, Technology and Research), 138634, Singapore
2. 2University of Pennsylvania, Department of Electrical and Systems Engineering, Pennsylvania, United States
3. 3Centre de Recherche sur l’Hétéro-Epitaxie et ses Application, CNRS, Rue Bernard Gregory, Sophia-Antipolis, 06560 Valbonne, France