Fig. 1: Vicinal van der Waals epitaxy towards grain-boundary-free textures.
a, Schematic of the c-cut sapphire substrates with diverse vicinal angles of 0° (top), 2° (middle) and 15° (bottom) towards the A axis. b,c, Optical images (b) and schematic (c) of MoS2 ML facet crystals grown on the vicinal substrates (0° – A, 2° – A, 10° – A and 15° – A). Two crystallographic variants of the MoS2 facets are represented by blue and red colours. The terrace width is defined as the distance between the adjacent atomic steps. d, Statistical distribution of the two MoS2 variants (blue and red facets in c) on different vicinal angle substrates. e, Anisotropic geometry of a MoS2 facet on a vicinal sapphire substrate: La denotes the bottom length of the trapezoidal grain, which is parallel to the atomic steps, and Lb denotes the side length, perpendicular to the atomic steps. f, Variation in La and Lb with growth time on sapphire substrates of different vicinal angles. Shaded circles, squares, upward triangles and downward triangles denote La values at 0° – A, 2° – A, 10° – A and 15° – A, respectively, whereas the corresponding unshaded symbols denote Lb values for each substrate. Data were obtained from 20 crystals and are presented as mean ± standard deviation (s.d.). Error bars represent the s.d. (n = 20). g, Growth rates in the parallel (Va) and perpendicular (Vb) directions. The aspect ratios (Lb/La) of the facet grains on different vicinal angle substrates are also plotted. Upward triangles, downward triangles and squares denote Va and Vb and the aspect ratio, respectively. Data are presented as mean ± s.d. Error bars represent the s.d. (n = 20).
