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Figure 2. (A) (i) Schematic illustration of the chemical reduction method [52] ; (ii) TEM image of hollow sphere Se nanoparticles;
(iii) HRTEM image of a hollow sphere Se nanoparticle; Copyright 2002, Wiley-VCH. (B) Scheme illustration of the solvent-thermal
method [64] ; (i) Large-area HRTEM image and the particle size distribution of Se nanoparticles; (ii) HRTEM image of Se nanoparticles
showing d spacings; Copyright 2021, American Chemical Society. (C) (i) Schematic of the laser-ablation method [65] ; (ii) TEM image of
selenium nanoparticles; Copyright 2019, Springer.

the device application. In contrast, chemical vapor deposition (CVD), which involves chemical reaction,
vapor evaporation, and decomposition, enables the production of defect-free, trigonal Se nanowires. For
example, Chen et al. developed a reliable strategy for Se nanowires synthesis in a selenization furnace with
the aid of plasma [Figure 3B] . Upon reaching its vaporization point at 300 °C, the Se tank emitted Se
[69]
vapor, which flowed towards the plasma coil, creating ionized Se, which is then grown into Se nanowires on
an oxidized silicon substrate [Figure 3B (i)]. As displayed by the SEM and TEM images, a forest of Se
nanowires was synthesized, and high-quality crystallinity was achieved [Figure 3B (ii)].

Although the bottom-up approach allows the massive production of Se nanowires at a low cost and in an
efficient manner, the manipulation of the entangled nanowire mesh and their integration into devices
remains challenging. Very recently, an impressive “top-down” route that exploits the thermal drawing