Intercalation leads to inverse layer dependence of friction on chemically doped MoS.

We present results of atomic-force-microscopy-based friction measurements on Re-doped molybdenum disulfide (MoS). In stark contrast to the widespread observation of decreasing friction with increasing number of layers on two-dimensional (2D) materials, friction on Re-doped MoSexhibits an anomalous, i.e. inverse, dependence on the number of layers. Raman spectroscopy measurements combined withcalculations reveal signatures of Re intercalation. Calculations suggest an increase in out-of-plane stiffness that inversely correlates with the number of layers as the physical mechanism behind this remarkable observation, revealing a distinctive regime of puckering for 2D materials.