Fig. 3: In-situ dynamical process of the highly oriented Mo₆Te₆ NWs formation under electrical bias.

a Optical microscope image shows the geometry of the graphite sandwiched MoTe₂ heterostructure. The top and bottom graphite are marked by red and black outlines, respectively, while the MoTe₂ film in between is marked by a blue outline. Highly oriented growth of NWs was observed in the freestanding hole on the chip indicated by a dashed black circle. b Zoom-in low-magnification HAADF-STEM image taken at the heterostructure region where MoTe₂ is covered by graphite on both sides, within the area indicated by the blue box in (a). Bundle-like structure, namely Mo₆Te₆ NWs, is seen in the region that is fully sandwiched between the graphite sheets (above the red line). Below the red line, absent the graphite sheets, MoTe₂ is converted to amorphous film composed of random size clusters. c, d Schematics of the structural transition from the graphite confined 2H-MoTe₂ to Mo₆Te₆ NWs before and after applying electrical biasing within the area indicated by the green box in (b). The area shaded in grey is the heterojunction region with the graphite edge marked by a red line. The MoTe₂ film that is not sandwiched in graphite sheets in the blue area of (d) is converted into amorphous film composed of clusters. Series of (e) high- and (f) low-magnification HAADF-STEM images that taken during the conversion of 2H-MoTe₂ into Mo₆Te₆ NWs. The MoTe₂ (110) and (100) facets are highlighted by white and yellow dashed line in (e) and (f), and the growth direction of NWs is highlighted by white arrow in (e).