This work is supported by the DST-Nanomission project;
UPOE-II grant from JNU;
DST-Purse grant and MHRD-IMPRINT grant Govt. of India. Authors would like to thanks AIRF-JNU for providing SEM;
TEM and VSM facility. Authors would also like to extend their gratitude to Thermos-fischer Scientific for doing XPS measurements. One of the author (VS) is thankful to University Grant commission;
India for providing financial assistance as SRF;