Epitaxy Growth of Robust Mono-Oriented Rhombohedral NbSe₂ Ribbons on c-Plane Sapphire

Abstract

Developing two-dimensional (2D) transition metal dichalcogenides (TMDs) that possess uniform crystal orientation and controlled interlayer stacking is essential for next-generation electronic and quantum devices. However, precise control over both lattice alignment and stacking polytype in materials like NbSe₂ remains challenging, primarily due to the small energy difference favoring the hexagonal (H)-stacked phase and the significant lattice mismatch with conventional substrates. Here, we demonstrate the successful growth of mono-oriented rhombohedral-stacked (R-stacked) NbSe₂ ribbons on c-plane sapphire substrates via step-guided epitaxy. This approach utilizes the interaction between atomic steps on the sapphire surface and the NbSe₂ layers: the steps control the orientation and stacking of the NbSe₂ layers. Combined experimental and theoretical analyses reveal that these atomic steps simultaneously guide unidirectional alignment and stabilize the R-stacking configuration. The synthesized NbSe₂ ribbons exhibit promising superconducting properties, with a superconducting transition temperature of 5.6 K and a residual resistance ratio of 4.5. This work paves the way for large-scale integration of single-crystal R-stacked NbSe₂ ribbons, holding immense potential for future applications in superconducting electronics and beyond.

Keywords

c-plane sapphire / CVD / NbSe₂ / orientation alignments / R-stacked

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