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The 2D transition metal dichalcogenides attract high research interest due to their electronic properties, and MoS2 is likely the most explored compound of this group. The fabrication of MoS2 thin films by the sulfurization of predeposited MoO3 layers on a c‐plane sapphire substrate by radio frequency magnetron sputtering from stoichiometric MoO3 target is reported. The structure and properties of as‐grown MoO3 and MoS2 layers are characterized by several methods including X‐ray diffraction, grazing‐incidence wide‐angle X‐ray scattering, photoelectron spectroscopy, Raman spectroscopy, and atomic force microscopy. Furthermore, the influence of the crystallographic structure of MoO3 layers on the final MoS2 films is studied. The influence of the crystallographic structure of MoO3 on the resulting MoS2 films is focused. A strong texturation in the c‐axis direction and an indication of a high degree in‐plane orientation of MoS2 thin films on the c‐sapphire substrate is observed. [ABSTRACT FROM AUTHOR]

[Display omitted] • The frictional properties of monolayer and few-layer MoSe 2 flakes are investigated. • The angular dependence of the friction is highly anisotropic for both types of MoSe 2. • The friction force anisotropy decreases with applied normal load. • The anisotropy demonstrates an opposite angular dependence for mono- and few-layer MoSe 2. The frictional properties of two-dimensional (2D) materials are strongly dependent on the crystallographic orientation and number of layers. Although friction anisotropy caused by crystallographic orientations has been reported for various 2D materials, the flexural deformations and different defects complicate the insight into the mechanism of the in-plane friction anisotropy of these materials. Here, the anisotropic friction behavior between an atomic force microscopy tip and monolayer (ML) and few-layer (FL) MoSe 2 flakes grown by CVD was performed by nanofriction measurements at different crystallographic directions, applied loads (F A), and tip scanning velocities. Our results reveal that the angular dependence of the friction forces is highly anisotropic for both types of MoSe 2 flakes, and the anisotropy decreases with F A. Importantly, the anisotropies demonstrate opposite angular dependence for ML and FL MoSe 2 flakes. As confirmed by the friction scanning velocity dependences, this difference seems to originate from different friction mechanisms for ML and FL MoSe 2 flakes. The friction of FL flakes was predominantly influenced by atomic stick–slip motion. In contrast, ML MoSe 2 is characterized by a coexistence of deformation-induced and atomic stick–slip motion. The experimental results presented here extend the understanding of the tribological properties of dry lubricants operating at the nanoscale. [ABSTRACT FROM AUTHOR]

• Crystallographic orientation of MoS 2 influences its nanotribological properties. • Macroscopic coefficient of friction follows the findings on the nanoscale. • The correct growth process for the lubricant layers is crucial for applications. Tribological properties of a surface are controlled by its topography and chemical structure as suggested by theoretical studies. However, the effect of crystallographic orientation on the tribological properties is still controversial. By tuning the heating rate during sulfurization of CVD Mo films, we prepared the few-layer MoS 2 films with similar surface topography but different crystallographic c -axis orientation. This resulted in distinctly different tribological behavior both on the nanoscale and macroscale that can be attributed to different surface chemistry and surface electronic and phonon structures. In particular, horizontally aligned MoS 2 sheets with c -axis oriented along the surface normal favor the weak van der Waals forces which resulted in a twice lower coefficient of friction comparing to the vertically aligned MoS 2 sheets. These results demonstrate the possibility to optimize tribological properties by crystallographic orientation as required for the thin solid-state lubricating layers for extreme conditions. [ABSTRACT FROM AUTHOR]