Dense arrays of aligned quasi-1D Bi₄Br₄ topological insulator nanoribbons achieved via lattice-guided oriented epitaxy on WTe₂

Bi₄Br₄, an emerging quasi-1D topological insulator, exhibits rich topological phases and great potential for low-power electronics and topological quantum computing. High-quality, oriented Bi₄Br₄ films are essential for exploring low-dimensional topological physics and developing functional devices. However, the growth of such films is highly challenging due to their sensitivity to growth parameters, and current synthesis techniques can only yield randomly oriented or multidirectional Bi₄Br₄ nanostructures, which impedes the study of intrinsic anisotropy and device integration. Here, we demonstrate a molecular beam epitaxy approach using anisotropic WTe₂ as an epitaxial template to achieve oriented Bi₄Br₄ nanoribbon arrays with controlled thickness. Through systematic optimization of growth temperature, source rate ratio and annealing conditions, we established the optimal window for high-quality nanoribbon synthesis. The resulting nanostructures exhibit well-defined morphologies and sharp edges, with a thickness of 2–9 nm. This work establishes a viable route for the oriented growth of Bi₄Br₄ and provides an ideal platform for investigating topological edge transport, anisotropic phenomena, and the design of topological quantum devices.