Tuning the optical properties of monolayer WS2 for near-infrared-II photothermal therapy: a first-principles study

Abstract

Photothermal therapy (PTT) is a new therapeutic cancer treatment strategy that offers many advantages over traditional cancer treatments, such as minimal invasiveness, higher specificity, and precise temporal selectivity. Optical imaging in the second near-infrared region (NIR-II, 1000-1350 nm) has prospective applications in PTT and is superior to that in the first near-infrared region (650–1000 nm). However, it proves challenging to find NIR-II materials. To resolve this, several elements were tested via substitutional doping to tune the bandgap of monolayer tungsten disulfide (WS₂). Two-dimensional materials have long been proved to offer various properties, with WS₂ predicted to have ideal adjustable optical properties. Density functional theory calculations revealed the band structure and optical spectra of the differently doped monolayer WS₂. The bandgap of monolayer WS₂ was successfully tailored to activate absorption in the NIR-II region. The results show that zirconium doped WS₂ had a bandgap of 0.04 eV and titanium doped WS₂ had a bandgap of 0.06 eV, which was ideal for NIR-II. Doping with zirconium or titanium exhibits strong absorption in the NIR-II range with absorption coefficients of 18 830 and 13 314 cm⁻¹, respectively, which is very competitive for PTT. This demonstrates the potential of these materials as NIR-II photothermal agents.