Fig. 3. (Color online) (a) Scanning electron microscopy images of representative graphene/porous Si. A darker contrast is observed at graphene/porous Si than that of porous Si. (b) I−V curves of graphene/porous Si devices with varying the second step etching times as 20 (green line), 30 (blue line), and 40 seconds (red line). Also, the I−V curve of graphene/Si was obtained (black line).
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