NAVARRO KAREN
Congresos y reuniones científicas
Título:
Horizontal to Vertical Transition of MoS2 grown by CVD on Mo studied by Spectroscopic Ellipsometry
Autor/es:
PATRITO, E. M; KAREN NAVARRO; CARLOS MONZON; JUAN DE PAOLI
Lugar:
Dresden
Reunión:
Congreso; 8th edition of the largest European Conference & Exhibition in Graphene and 2D Materials. Graphene 2018.; 2018
Institución organizadora:
Phantoms Foundation
Resumen:
The control in the orientation of MoS2 layers with respect to the growing substrate is of upmost importance in MoS2 applications.
Horizontally aligned MoS2 layers are preferred for microelectronic devices, whereas vertically aligned MoS2 layers are much useful for the hydrogen evolution reaction and energy storage. Fast sulfurization of metal-seeded substrates has been used to grow vertically standing MoS2
nanosheets [1]. The layers grow until the thin Mo film (5-25 nm) is consumed. However, the growth of MoS2 films on thicker Mo foils
has not been investigated yet.
In this work we investigate structural transitions as a function of temperature for CVD grown MoS2 on specular polished molybdenum surfaces exposed to sulphur gas. Figure 1a show that the thickness of
the MoS2 films obtained from the elllipsometric spectra (inset) have an
abrupt transition around 800oC in agreement with the topography of SEM
images which show a change from smooth films (Fig. 1b) to structures with vertically aligned layers.
The E12g and the A1g Raman modes were used to track the MoS2 film growth as well as changes in crystallinity. The variation of peak areas with temperature shows a different pattern as that of ellipsometric thicknesses. This is interpreted as due to changes in the density of the films associated to horizontal to vertical transitions. At the lower temperatures broader peaks are observed (Fig. 2a) and they become thinner as the temperature increases.The FWHM of the E12g and the A1g peaks shows acontinuous decrease with temperature (Fig.2c) reaching the lowest value of 6.2 cm-1 at 950 oC, thus indicating an increase in the crystallinity of the films.
Horizontally aligned MoS2 layers are preferred for microelectronic devices, whereas vertically aligned MoS2 layers are much useful for the hydrogen evolution reaction and energy storage. Fast sulfurization of metal-seeded substrates has been used to grow vertically standing MoS2
nanosheets [1]. The layers grow until the thin Mo film (5-25 nm) is consumed. However, the growth of MoS2 films on thicker Mo foils
has not been investigated yet.
In this work we investigate structural transitions as a function of temperature for CVD grown MoS2 on specular polished molybdenum surfaces exposed to sulphur gas. Figure 1a show that the thickness of
the MoS2 films obtained from the elllipsometric spectra (inset) have an
abrupt transition around 800oC in agreement with the topography of SEM
images which show a change from smooth films (Fig. 1b) to structures with vertically aligned layers.
The E12g and the A1g Raman modes were used to track the MoS2 film growth as well as changes in crystallinity. The variation of peak areas with temperature shows a different pattern as that of ellipsometric thicknesses. This is interpreted as due to changes in the density of the films associated to horizontal to vertical transitions. At the lower temperatures broader peaks are observed (Fig. 2a) and they become thinner as the temperature increases.The FWHM of the E12g and the A1g peaks shows acontinuous decrease with temperature (Fig.2c) reaching the lowest value of 6.2 cm-1 at 950 oC, thus indicating an increase in the crystallinity of the films.
