Towards a uniform and large-scale deposition of MoS₂nanosheets via sulfurization of ultra-thin Mo-based solid films

Abstract

Large-scale integration of MoS2 in electronic devices requires the development of reliable and cost-effective deposition processes, leading to uniform MoS2 layers on a wafer scale. Here we report on the detailed study of the heterogeneous vapor-solid reaction between a pre-deposited molybdenum solid film and sulfur vapor, thus resulting in a controlled growth of MoS2 films onto SiO2/Si substrates with a tunable thickness and cm(2)-scale uniformity. Based on Raman spectroscopy and photoluminescence, we show that the degree of crystallinity in the MoS2 layers is dictated by the deposition temperature and thickness. In particular, the MoS2 structural disorder observed at low temperature (<750 °C) and low thickness (two layers) evolves to a more ordered crystalline structure at high temperature (1000 °C) and high thickness (four layers). From an atomic force microscopy investigation prior to and after sulfurization, this parametrical dependence is associated with the inherent granularity of the MoS2 nanosheet that is inherited by the pristine morphology of the pre-deposited Mo film. This work paves the way to a closer control of the synthesis of wafer-scale and atomically thin MoS2, potentially extendable to other transition metal dichalcogenides and hence targeting massive and high-volume production for electronic device manufacturing.

Atomic Layer Deposition of Crystalline MoS2 Thin Films: New Molybdenum Precursor for Low‐Temperature Film Growth

“…[39,43,44,47] Binding energies of S 2p 3/2 (162.7 eV) and S 2p 1/2 (163.9 eV) seen in Figure 6b are also within the range of values reported for 2H-MoS 2 . [39,40,43,44,[47][48][49]51,52] Additionally, weak doublets at 161.8 and 163.3 eV as well as 163.9 and 165.1 eV were assigned to SnS [80] and CS bonding, respectively. Carbon and oxygen were present in multiple chemical environments, as revealed by their broad peaks ( Figure S2b,c, Supporting Information).…”

“…[46] A four-monolayer MoS 2 film, produced by sulfurization of an MoO x film, yielded E 1 2g FWHM of 6.5 cm −1 at 750 °C, whereas a higher sulfurization temperature of 1000 °C reduced the FWHM to 4.6 cm −1 . [39] In summary, the Raman spectra indicate comparably good crystallinity, especially considering the low deposition temperature of 300 °C.…”

“…The observed binding energies are among those reported for thin 2H-MoS 2 layers and films (231.6 to 233.2 eV for Mo 3d 3/2 ). [39,40,43,44,[47][48][49]51,52] In addition, about 10% of the molybdenum was present as oxidized MoO 3 (Mo 6+ ) with binding energies [79] of 233.4 and 236.6 eV for Mo 3d 5/2 and Mo 3d 3/2 , respectively. This implies that the film surface is at least partially oxidized in air.…”

“…[34,36] Sulfurization of Mo or MoO x films also requires high temperatures, usually 500-1000 °C. [36][37][38][39] Although upscaling of the sulfurization method appears to be easier compared to the MoO 3 -based CVD, sulfurization tends to produce films of lower quality. [34,36,37] Other bottom-up techniques used for the deposition of thin MoS 2 films include sputtering, [40] physical vapor transport, [41] pulsed laser deposition, [42] and atomic layer deposition (ALD).…”

Structural, chemical and optical properties of cerium dioxide film prepared by atomic layer deposition on TiN and Si substrates

“…The instrument resolution is 0.5 eV. The spectra were aligned using C 1s peak (284.6 eV) as reference [32]. The experimental data were fitted with Gaussian-Lorentzian peaks and to obtain the refractive index and the direct and indirect band gaps.…”