Extended Data Fig. 7: Twisted GeS nanostructure in an intermediate twisting state.

a, Low-magnification STEM image of a nanostructure growing horizontally on a substrate. The nanowire had an approximate radial size of 200 nm and height of 150 nm with a twisting morphology that can be clearly observed by SEM imaging. We note that this nanostructure is the thin part of the sample shown in Extended Data Fig. 6. In contrast to free-standing nanowires (Fig. 3d) that have only a screw dislocation, the nanowire was segmented with the presence of both transverse boundaries and a dislocation line in the middle. b, HRTEM view of a boundary. The white arrow shows the boundary. c, d, FFT pattern of the two crystals across the boundary. The HRTEM imaging and the corresponding FFT patterns confirm that the crystals across the boundary have almost  the same orientation and thus the boundary takes on a very small twist angle. e, HRTEM image of the screw dislocation. f, g, Burgers vector analysis, based on the g ∙ b contrast. To perform the analysis, the nanowire was first tilted to the [100] zone axis. Next, the sample was further tilted to create two-beam conditions for different diffraction spots in the diffraction pattern. Dark-field images of the dislocation were taken for g = (002) (f) and g = (020) (g). The insets show the excitation of reflections for the dark-field imaging in which the selected reflections are marked with red circles. For g = (002), high contrast of the dislocation is observed in the dark-field image (f), whereas for g = (020), the dislocation becomes invisible in the image (g). We have therefore determined the Burgers vector of the dislocation to be along the [001] direction, which is the same as for the dislocated nanowires that were grown vertical and free-standing. h, Low-magnification cross-sectional TEM image of the nanowire. i, j, CBED patterns for the [210] and [100] zone axes are collected at locations marked by circles in a, which were separated by 970 nm. This suggests a twist of 23° about the c axis within this length, amounting to a twist rate of 0.4 rad mm⁻¹, which is comparable to the twist rate of mesoscale crystals. k, A series of dark-field TEM images showing that the [020] diffraction band progressively shifts when the sample is continuously rotated about its twist axis by tilting the TEM holder; this dark-field imaging verifies that the crystallographic twist of the nanowire is almost continuous. As such, the nanostructure has both twist boundaries with very small twist angles and an almost continuous twisting profile, exemplifying an intermediate twisting state at the onset of formation of the twist boundary.