Van der Waals Nanowires with Continuously Variable Interlayer Twist and Twist Homojunctions

Abstract

Moiré patterns at van der Waals interfaces between twisted 2D crystals give rise to distinct optoelectronic excitations, as well as, narrowly dispersive bands responsible for correlated electron phenomena. Contrasting with the conventional, mechanically stacked planar twist moirés, recent work shows twisted van der Waals interfaces spontaneously formed in nanowires of layered crystals, where Eshelby twist due to axial screw dislocations stabilizes a chiral structure with small interlayer rotation. Here, the realization of tunable twist in germanium(II) sulfide (GeS) van der Waals nanowires is reported. Tapered nanowires host continuously variable interlayer twist. Homojunctions between dislocated (chiral) and defect‐free (achiral) segments are obtained by triggering the emission of axial dislocations during growth. Measurements across such junctions, implemented here using local absorption and luminescence spectroscopy, provide a convenient tool for detecting twist effects. The results identify a versatile system for 3D twistronics, probing moiré physics, and for realizing moiré architectures without equivalent in planar systems.

Ultrathin Twisted Germanium Sulfide van der Waals Nanowires by Bismuth Catalyzed Vapor–Liquid–Solid Growth

“…The nanowires show lattice fringes with a separation of 0.53 nm, consistent with the spacing of (002) planes in bulk GeS. [38] Bi-catalyzed GeS vdWs nanowires down to diameters of ≈15 nm show the same stacking and orientations as the thicker nanowires synthesized over Au catalysts, [1,15,17] that is, GeS c-axis aligned along the symmetry axis of the wires (longitudinal layering, see also Figures S1-S3, Supporting Information). Compared to GeS nanowires grown under similar conditions over Au catalysts, the Bi-catalyzed vdWs nanowires show i) reduced taper over large distances, [17] ii) absence of GeS plates along their length, [19,39] and iii) no residual catalyst nanoparticles decorating the wire surface.…”

“…[38] Bi-catalyzed GeS vdWs nanowires down to diameters of ≈15 nm show the same stacking and orientations as the thicker nanowires synthesized over Au catalysts, [1,15,17] that is, GeS c-axis aligned along the symmetry axis of the wires (longitudinal layering, see also Figures S1-S3, Supporting Information). Compared to GeS nanowires grown under similar conditions over Au catalysts, the Bi-catalyzed vdWs nanowires show i) reduced taper over large distances, [17] ii) absence of GeS plates along their length, [19,39] and iii) no residual catalyst nanoparticles decorating the wire surface. [1] Analysis of the nanowire diameter distribution also shows that Bi-catalyzed GeS nanowires have significantly smaller diameters compared to Au-catalyzed nanowires (see Figures 5a,b) grown under identical conditions.…”

“…The wire retains a constant diameter even upon ejection of the dislocation, in contrast to growth on Au where the ejection is usually associated with thickness change. [17] Thus, with suitable thermal protocols [17] Bi should be a suitable catalyst for the realization of junctions between dislocated (chiral) and non-dislocated sections of GeS nanowires.…”

“…Prior work using VLS growth over Au catalyst particles showed single-crystalline GeS nanowires with layering along the wire axis, typical diameters in the 50-120 nm range, and length exceeding 10 µm. [1,15,17] Replacing Au by Bi results in the synthesis of high-quality crystalline GeS nanowires with the same layer orientation, but with diameters as small as 15 nm. Other unique attributes include exceptionally smooth surfaces without any catalyst residues, and suppressed tapering along the wires.…”

“…The underlying twist moiré, realized here on a helicoid surface rather than a planar vdWs interface (IF) as in the conventional twisted homo-and heterostructures, [16] can modulate the bandgap and the local optoelectronic properties. [17] vdWs nanowires have been synthesized with high crystal quality using vapor-liquid-solid (VLS) growth, in which a liquid catalyst drop at the tip of the growing wire transports material from the vapor phase to the nanowire growth front. As in the growth of conventional 3D-crystalline (e.g., Si, Ge) nanowires, [18] the catalyst thus defines the positioning on the substrate and the diameter of the growing nanowire.…”