Electrical properties of collapsed MoS2 nanotubes†

Molybdenum disulfide (MoS₂) is a promising material for future high-performance and ultra-low-power electronics. Growth from a vapor phase at chemical equilibrium enables the production of crystals possessing a relatively low density of structural defects. Besides thin MoS₂ flakes, MoS₂ nanotubes (NTs) and collapsed NTs in the shape of nanoribbons (NRs) are also synthesized in the same growth process. Here, we present the first study on the structural and electrical properties of the NRs. High resolution electron microscopy revealed a chiral structure of the NRs with no peculiarities at the inner interface where both walls are in contact. In contrast, resonant Raman spectroscopy revealed the presence of bands typical of a few layers thick MoS₂, suggesting that some of the layers of the NR are partially split. Contact current imaging spectroscopy (CCIS) revealed longitudinal wrinkles on the NR surface, with elevated regions found to be more conductive than the depressed areas. The edges of the NR, where molecular layers are strongly curved but not broken, exhibit varying conductivity. While some parts exhibit zero conductivity, others show much higher conductivity than the central part of the NR, suggesting an electron confinement effect. Charge injections strongly altered the NR's work function and induced changes in the NR's topography. The surface wrinkling was intensified, and the NR tended to rotate around its longitudinal axis. This rotation is explained as the reverse piezoelectric effect.