Figure 1

The TEM image of CDs (a, inset at top-right: HRTEM image of an individual CD, inset at bottom-left: size distribution of CDs based on 100 counts from the TEM image); the AFM image of CDs (b, inset: height profile measured at the white line), XRD pattern of CDs compared with graphite powder (c), and FTIR spectrum of CDs (d).