Hot‐wire vapor deposition of amorphous MoS₂ thin films

Abstract

Amorphous, as shown by X‐ray diffraction measurements, MoS2 films (a‐MoS2) were deposited by heating a molybdenum wire at temperatures between 500 and 700 °C in H2S at 1 Torr. As shown by Scanning Electron Microscopy measurements, the morphology of samples depends significantly on the filament temperature; at low temperature samples are homogeneous and smooth, at intermediate temperatures they exhibit a granular microstructure and at high temperatures a columnar one. X‐ray photoelectron spectroscopy measurements have shown S/Mo ratios in films varying between 2.5 and 1.5 dependent on filament temperature. Films also contain oxygen at atomic contents of 8 to 12%. As shown by XPS and Raman spectroscopy, at a filament temperature of 600 °C films are mainly composed of MoS2 also containing oxygen at an atomic ratio of 8%. Spectroscopic ellipsometry measurements made on a‐MoS2 films have shown that their band gap is of the order of 1.4 eV, slightly higher than that for the bulk crystalline material. Photoluminescence spectroscopy measurements have shown that samples exhibit a doublet of peaks at 2.8 and 3 eV blue shifted relatively to MoS2 samples composed of one or two mono‐layers. The above indicate that the electronic structure of crystalline atomic‐layer thick MoS2 is preserved in a‐MoS2 films. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Growth, structure and stability of sputter-deposited MoS2 thin films

“…In keeping with this, energy dispersive X-ray spectroscopy (EDX) analysis of the films in general gave slightly S-enriched Mo/S ratios of 1:2.1. Furthermore, also argon or residual oxygen might have been incorporated into the films [ 37 – 38 ]. This suggests that possibly S atoms (and/or other ad-atoms such as Ar, or residual co-sputtered contaminants such as metals or oxygen from the PVD system) may have been placed in between the MoS 2 layers, resulting in the observed increased interlayer spacing and reduced mass density, whereas the in-plane ordering remains unaffected.…”

“…Intercalation [ 21 , 48 ], substitution [ 49 – 50 ] or adsorption [ 51 ] of add-atoms in/on MoS 2 are known to affect the electrical transport properties of MoS 2 in a variety of ways, including change from n-type to p-type behaviour, changes in carrier numbers or changes in local structure from 2H (semiconducting) to 1T (metallic). Previous work for instance reported significant oxygen and carbon incorporation during typical PVD conditions, where substitutional doping of MoS 2 with oxygen recently was shown to drastically alter its electronic structure [ 37 – 38 50 ]. Also key effects of, e.g., Nb or Na contamination on electronic properties was previously reported [ 29 , 49 ].…”

Electrical characteristics of vapor deposited amorphous MoS2 two‐terminal structures and back gate thin film transistors with Al, Au, Cu and Ni‐Au contacts

“…3 Results and discussion 3.1 MoS 2 film characteristics The deposited aMoS 2 films contain some oxygen (thus, they are in actuality represented by the molecular formula MoS x O y ), the proportion of which is minimized at the filament temperature of 600 o C used [18]. However, while at lower filament temperature the films are smoother, in this case they have a grainy surface with small bumps, as observed in the SEM picture shown in Fig.…”

Gas Sensing Investigation of Porous Hot-wire Molybdenum Disulphide Thin Films

“…The deposition of the hot-wire MoS2 films profits from the vapours formed from the reaction of the native oxide on the surface of the Mo filament and the H2S, according to the following reaction: 2MoO3 + 4H2S → 2MoS2 + 4H2O + O2 The above reaction is extensively used for the hydrodesulfurization of oil [28,29] and has been studied with various experimental methods [30,31]. The structure of MoO3 consists of MoO3 octahedra that are linked together forming bi-layers, due to van der Waals forces [32,33].…”