Scanning electron microscopy image of the PbTe/Pb nanostructure. (a) The representative SEM image of PbTe/Pb nanostructure arrays with a field of view of 30 μm (w) × 20 μm (h). (b) The SEM image of the single PbTe/Pb nanostructure. The upper right insert figure gives the central configuration schematic of the electrochemical cell. The lower left insert figure gives the applied voltage waveform. The applied voltage varies from 0.5 to 0.9 V in a square waveform with 1 Hz frequency.