Fig. 1. (Color online) Schematic showing the growth of Mo₂C pyramids on liquid Cu substrate.

Fig. 2. (Color online) Growth and characterization of Mo₂C pyramids. (a) Crystal and (b, c) electronic structure of Mo₂C from first-principles calculations. (d) Optical images of grown Mo₂C pyramids structures on liquid Cu surface. (e, f) XPS spectra of Mo₂C flake, indicating existence of Mo and C, respectively. (g–i), AFM images of three typical layered pyramids structures.

Fig. 3. (Color online) Further characterization and proposed model of Mo₂C pyramid structures. (a) Optical images of grown layered Mo₂C structures on liquid Cu surface and SiO₂/Si substrate. (b) Raman spectrum of Mo₂C flake, having characterized peak at around 650 cm^–1. (c, d) Optical image of broken layered Mo₂C structure, with bare hexagonal profile of Cu left.

Fig. 4. (Color online) Growth of novel Mo₂C pyramid structures. (a) Optical images of the large-area as-grown Mo₂C structures on liquid Cu surface and transferred onto SiO₂/Si substrate, respectively. (b) AFM image of the single structure, displaying clear layered feature. The inset shows height profile of the structure, showing step feature across the whole flake reflected in thickness. (c–f) Optical images of the growth process of Mo₂C structures, showing the time-dependent feature. (g) Schematic diagram illustrates the growth of novel layered Mo₂C structures, corresponding to the observations in (c–f).

Fig. 5. (Color online) STEM characterization of Mo₂C pyramid. (a) STEM-ADF image of a typical edge region in the Mo₂C pyramids structures. (b) Strain field mapping based on the image shown in (a).