Photodriven Transient Picosecond Top‐Layer Semiconductor to Metal Phase‐Transition in p‐Doped Molybdenum Disulfide

Abstract

Visible light is shown to create a transient metallic S–Mo–S surface layer on bulk semiconducting p‐doped indirect‐bandgap 2H‐MoS2. Optically created electron–hole pairs separate in the surface band bending region of the p‐doped semiconducting crystal causing a transient accumulation of electrons in the surface region. This triggers a reversible 2H‐semiconductor to 1T‐metal phase‐transition of the surface layer. Electron–phonon coupling of the indirect‐bandgap p‐doped 2H‐MoS2 enables this efficient pathway even at a low density of excited electrons with a distinct optical excitation threshold and saturation behavior. This mechanism needs to be taken into consideration when describing the surface properties of illuminated p‐doped 2H‐MoS2. In particular, light‐induced increased charge mobility and surface activation can cause and enhance the photocatalytic and photoassisted electrochemical hydrogen evolution reaction of water on 2H‐MoS2. Generally, it opens up for a way to control not only the surface of p‐doped 2H‐MoS2 but also related dichalcogenides and layered systems. The findings are based on the sensitivity of time‐resolved electron spectroscopy for chemical analysis with photon‐energy‐tuneable synchrotron radiation.

Photo-induced lattice distortion in 2H-MoTe2 probed by time-resolved core level photoemission

“…This mechanism has been recently observed in 2H-MoS 2 , in which the transition to the 1T metallic phase is reversible. 35 The measurements presented in Fig. 2 characterize the photoexcited system in the microsecond range, therefore they dene the SPV corrected position of the core levels acquired in the sub-nanosecond XPS measurement.…”

“…This mechanism has been recently observed in 2H-MoS 2 , in which the transition to the 1T metallic phase is reversible. 35…”

Pulsed Laser Phosphorus Doping and Nanocomposite Catalysts Deposition in Forming a-MoSx/NP-Mo//n+p-Si Photocathodes for Efficient Solar Hydrogen Production

“…The laser-doped Si wafer surface could not have the same optical properties (low reflection coefficient) as the pyramid-textured surface specifically created by chemical etching. The textured surface problem can be solved in the long term by using other laser treatment modes, for example, by employing lasers with shorter pulse durations [57]. The chosen mode of pulsed laser doping may not be optimal for obtaining a high-quality n + p-junction.…”

“…The Mo 6+ state was realized in molybdenum trioxides; the binding energy for the Mo3d5/2 peak in this compound was 232.75 eV [55]. To decompose the S2p spectra, a traditional approach was used that distinguishes high-and low-binding energies [56,57] The XPS spectrum of the sample with a relatively thin a-MoSx/NP-Mo film showed peaks from the silicon substrate. This was due to the depth of the photoelectron escape from silicon exceeding the thickness of the deposited a-MoSx/NP-Mo film.…”

“…This was due to the depth of the photoelectron escape from silicon exceeding the thickness of the deposited a-MoSx/NP-Mo film. In the Si spectrum, in addition to the Si-Si doublet, there was a weak peak, possibly a product of Si-O To decompose the S2p spectra, a traditional approach was used that distinguishes high-and low-binding energies [56,57]. The high-binding energy doublet with the S2p 3/2 line position at 162.77 eV is associated with the apical S 2− and bridging (S 2 2− ) br ligands in Mo 3 S 13 /Mo 3 S 12 clusters.…”