Cathodoluminescence Studies of Single to Penta-wall WS₂ Nanotubes Obtained through Plasma Treatment of WS₂ Multiwall Nanotubes

Wide investigation of multiwall (MW) inorganic nanotubes (INTs) of WS₂ became possible due to the breakthrough in their synthesis, resulting in pure phase and macroscopic amounts. In addition, we have demonstrated that single to penta-wall nanotubes (referred as “daughter” nanotubes - DINT) could be generated by high-energy plasma treatment of MWINTs. For optimization of DINT synthesis, the precursor MWINT were deagglomerated and the parameters of plasma irradiation (plasma power, duration, temperature, argon pressure, etc.) were widely varied. The deagglomeration and following pre-annealing of the INT samples at 350 ^oC, using a bias voltage of 37 V to 70 V and high temperature (up to 600C), had a discerning effect on the quality as well as quantity of the daughter nanotubes.

HRTEM corroborated the formation of such a small nanotubes comprising from single to five layers with dimensions ranging from 3 to12 nm in diameter and up to 200 nm in length. The DINT were mostly visible entrapped within the exfoliated flaky regions in the vicinity of damaged outer layers of “mother” tubes. In order to assess the cathodoluminescence (CL) originating specifically from the daughter nanotubes, they were dispersed on the marked TEM grids. Subsequently, this grid with fixed location of DINT was used as a sample for CL study in HRSEM. Here we report our preliminary results on CL spectra obtained at -140 ᵒC of multiwall nanotube, generated a peak at 660 nm (1.88 eV), while the corresponding peak of the daughter tubes was visible at 630 nm (1.97 eV). The observed blue shift provides direct evidence of the quantum confinement effect, originating from the DINTs, and renders the nanotubes potent to be exploited in telecommunication and electronic devices. Future focus of this work involves study of the CL of DINT vs. their diameter and amount of the layers.