Evolution of Molybdenum Disulfide on Metal Surfaces

Abstract

Molybdenum disulfide (MoS2) has attracted tremendous attention over the past decade due to their exciting mechanical, electronic and frictional properties. Heterostructures of semiconductors and metals are the fundamental components of modern electronics. The atomically thin MoS2 sheets, offer unique opportunities for heterostructure devices since they are chemically homogenous, but illustrate electronically distinct semiconducting (1H phase) and metallic (1T phase) characteristics with matched lattices. Here, Au substrates were used to introduce phase transition inside single layer MoS2. The formation of 1T-MoS2 phase could be initiated by the charge transfer and the built-in strain from Au substrates. Because the unavoidable aging and degradation of MoS2, significantly affected the desired performance in semiconductors, catalysts and tribological applications, the structural and chemical evolution of MoS2 under accelerated aging conditions was investigated under UV-ozone condition. We found that, the aging varied strongly with the layer thickness of MoS2 sample. To systematically tune the electronic properties of MoS2, diacetylenethiolate-based molecules could be implemented to dope MoS2 via defect engineering since the thiol groups could bond to sulfur vacancies and the diacetylene thiols could form relatively stable polymers on MoS2 surfaces through UV-induced crosslinking. The mechanical and electronic properties of diacetylene and poly-diacetylene monolayers on Au(111) were fully investigated. The monolayers were found to exhibit higher friction following polymerization due to structural changes in the films. Electronically, size-dependent differences in the electronic properties were found to arise for polydiacetylene islands of around 10 nm when embedded into a dodecanethiolate matrix, which could be attributed to the Coulomb blockade. The knowledge revealed here will guide future designs and applications of MoS2-based electronic devices and tribological systems.