Direct Writing of Nanoscale Bismuth(III)Selenide from a Single-Source Precursor

Two-dimensional (2D) metal chalcogenides have gained attention in recent years for their exotic optoelectronic properties. Bismuth(III)selenide (Bi 2 Se 3 ) has drawn attention as a topological insulator (TI). Current fabrication methods for Bi 2 Se 3 can be complex, and device integration at the nanoscale is limited. In this work, the direct writing of nanoscale 2D bismuth selenide structures is reported using electron-beam lithography (EBL) using a single-source precursor as a negative-tone resist. The precursor was synthesized from bismuth nitrate and a selenourea ligand under mild conditions. Characterization of the resulting bismuth selenourea complex was performed using elemental analysis, single-crystal X-ray diffraction, NMR spectroscopy, and thermogravimetric analysis (TGA). Annealing the precursor in a 5% H 2 /Ar atmosphere gave Bi 2 Se 3 as polycrystalline nanosheets, confirmed via transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Thin films of the precursor, formed by spin-coating, were patterned with an electron beam, forming polycrystalline Bi 2 Se 3 nanostructures that retain their geometry after annealing in 5% H 2 /Ar. Characterization of the nanostructures with scanning electron microscope (SEM), EDS, and TEM reveals bismuth selenide nanocrystals of less than 100 nm dimension, which can be easily localized based on e-beam pattern design. The versatility of pattern design also means that bismuth selenide nanostructures with varying shapes, sizes, and thicknesses can be precisely positioned, further enabling their functional applications. Direct writing of bismuth selenide by EBL offers a facile synthesis of a TI with the potential for simplistic device integration by on-chip preparation.