Spin deposition of MoSx thin films

Abstract

Thin films of MoS2 and amorphous MoS3 have been prepared on various glass and stainless steel substrates by thermolysis of spin cast solutions of (NH4)2MoS4 in an organic diamine (ethylenediamine and 1,2-diaminopropane). After deposition the resulting single-source precursor film [(H3NCnH2nNH3)MoS4] was dried at 250°C in air and subsequently heat treated at temperatures between 300 and 800°C under inert nitrogen (N2) atmosphere yielding films of MoSx (2&le;x&le;3) with carbon impurities. The resulting films with thicknesses up to 160 nm (800°C) and 250 nm (300°C) are highly homogeneous with a metallic lustre and appear brown in transmission. While the films are amorphous to X-ray diffraction up to temperatures of 400°C, the crystallinity increases for higher temperatures due to the formation of MoS2 microcrystallites. Furthermore, the composition and the microstructure strongly depend on the used diamine solvent. Both X-ray and electron diffraction reveal a partially preferred orientation of the crystallites with their basal planes parallel to the substrate (c, type II). After heat treatment at 800°C under N2 the MoS2 layer stacks consist of three to four layers with a length of 5-8 nm. The optical characterisation of the thin films shows a strong absorption in the visible part of the spectrum characteristic of MoS2 with an absorption coefficient &alpha;550 of 2x105 cm-1. Tribological measurements up to 5000 cycles against steel reveal the highest wear-life with a friction coefficient &micro;<0.1 for coatings heat treated at 500°C. The highest capacity for reversible electrochemical Li intercalation of 30 mC/cm2 was found in amorphous MoSx coatings (400°C heat treatment). A weak electrochromic effect with a change in transmission of &Delta;T&asymp;0.08 around 800 nm was observed after Li intercalation.