(a)

(b)

(c)

(d)

Figure 4: TEM images and ED patterns of recovered samples treated at 15 GPa and 1000°C (a), at 15 GPa and 1800°C (b), and 15 GPa and 2300°C (c). A TEM image of nanopolycrystalline diamond synthesized from polycrystalline graphite at the same P, T condition is also shown in (d) as a comparison.