Defect‐Rich MoSe₂ 2H/1T Hybrid Nanoparticles Prepared from Femtosecond Laser Ablation in Liquid and Their Enhanced Photothermal Conversion Efficiencies

Abstract

MoSe2 2H/1T hybrid nanoparticles are prepared by femtosecond laser ablation of MoSe2 powder in isopropyl alcohol with different laser powers and ablation times, and their formation mechanisms and photothermal conversion efficiencies (PTCEs) are studied. Two types of spherical nanoparticles are observed. The first type is onion‐structured nanoparticles that are formed by nucleation on the surfaces of melted droplets followed by inward growth of {002} planes of MoSe2. The second type is polycrystalline nanoparticles, formed by coalescence of crystalline nanoclusters fragmented from the powder during the laser ablation. The nanoparticle size in all samples shows a bimodal distribution, corresponding to different fragmentation mechanisms. The 2H‐to‐1T phase transition in the nanoparticles is likely caused by electron doping from the laser‐induced plasma. The PTCEs of the nanoparticles increase with laser power and ablation time; the highest PTCE is around 38%. After examining the bandgaps and the Urbach energies of the nanoparticles, it is found that the high PTCEs are primarily attributed to defects and structural disorder in the laser‐synthesized nanoparticles, which allow absorption of photons with energies smaller than the bandgap energy and facilitate non‐radiative recombination of photoexcited carriers.

PEGylated MoSe2 Nanomaterials with Limited Oxidation via Femtosecond Laser Ablation for Photothermal Therapy

“…Figure illustrates spherical nanoparticles produced by laser ablation with different powers. This is consistent with our previous work that spherical nanoparticles, rather than quantum dots, are produced using short ablation times . The size distributions of the nanoparticles prepared with different laser powers are presented in Figure S4.…”

“…The nanoparticles prepared with 0.15 and 0.3 W laser pulses have mean sizes of 26.3 and 23.5 nm, respectively, while the nanoparticles prepared with 0.6 and 1.5 W laser pulses have smaller mean sizes of 14.7 and 12.6 nm, respectively. According to our previous work, the large spherical nanoparticles produced in low-power laser ablation are primarily formed by thermodynamic equilibrium melting and evaporation of the ablated particles, while the smaller nanoparticles produced in high-power laser ablation are primarily formed by explosive boiling of the ablated particles.…”

“…Given the produced quantum dots display very close sizes (Figure S1), the larger bandgaps of the quantum dots prepared in the PEG solutions with lower concentrations might stem from more significant oxidation (Figure h). The Urbach energies of the quantum dots were measured by the method introduced in our previous work, and the plots used to determine the Urbach energies are presented in Figure S7. A higher Urbach energy suggests higher sub-bandgap absorption of photons because of an increased density of electronic states extending into the forbidden gap (Urbach tails) as a result of increased lattice disorder or defects in materials.…”

“…The absorbance spectra of the nanomaterials were measured with a UV–vis–NIR spectrometer (Lambda 1050, PerkinElmer). The PTCEs of the nanoparticles were evaluated using a custom-built setup, as described in the previous work. ,, The concentration of MoSe 2 in all of the samples was 1.1 mM. 1 mL of each sample was transferred to a quartz cuvette with a path length of 1 cm and then illuminated by an 808 nm continuous-wave laser (BWF1-B&W Tek) for 10 min followed by cooling for 10 min.…”

“…Recently, pulsed laser ablation in liquid (PLAL) was proven to be an efficient, simple, and green method to prepare TMDC nanomaterials including quantum dots and spherical nanoparticles. − PLAL involves irradiating femtosecond-laser or nanosecond-laser beams on bulk targets or powders in various solvents. The nanomaterials are usually fragmented from the ablated materials via photothermal mechanisms such as spallation, thermodynamic equilibrium melting, and vaporization and explosive boiling or direct, intense laser electric field–matter interactions such as Coulomb explosion and photoexfoliation, depending on the intensity and the pulse duration of the laser beam .…”