▎ 摘　　要

A new approach to characterise the defect density in graphene oxide (GO) is presented in this work. Fluorescence microscopy is employed to directly observe changes in defect density on the graphene oxide surface at the macroscopic level. The area under scan becomes darker as the electrical bias is increased from 0.5 V to 3 V. Gray level conversion of the fluorescence images is used to quantify our results. The reduction of graphene oxide as observed under fluorescence microscopy images is also verified using Raman microscopy where I-D/I(G)ratio decreases as the voltage stress is increased. However, defect density increases for the samples from 0 V to 0.5 V range and is maintained till 1 V, which shows that this range may not be suitable for electronic applications when graphene oxide is employed as its electronic properties are poor in this range. Thus, this in-situ measurement of defect density on the graphene oxide for large area graphene samples can help in identifying the uniformity of the defect density on graphene oxide as well as its defect density changes under electrical bias condition, an information crucial for its electronic applications.