Sorgenfrei, N.L. A. N.; Giangrisostomi, E.; Jay, R.M.; Kuehn, D.; Neppl, S.; Ovsyannikov, R.; Sezen, H.; Svensson, S.; Foehlisch, A.: Photodriven Transient Picosecond Top-Layer Semiconductor to Metal Phase-Transition in p-Doped Molybdenum Disulfide. Advanced Materials 33 (2021), p. 2006957/1-8
10.1002/adma.202006957
Open Access Version
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 phasetransition 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.