  We present results of atomic-force-microscopy-based friction measurements on
Re-doped molybdenum disulfide (MoS2). In stark contrast to the widespread
observation of decreasing friction with increasing number of layers on
two-dimensional (2D) materials, friction on Re-doped MoS2 exhibits an
anomalous, i.e., inverse dependence on the number of layers. Raman spectroscopy
measurements combined with ab initio calculations 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.
