  Systematic displacement measurements of freestanding graphene as a function
of applied bias voltage and tunneling current setpoint using scanning tunneling
microscopy (STM) are presented. When the bias voltage is increased the graphene
approaches the STM tip, while, on the other hand, when the tunneling current is
increased the graphene contracts from the STM tip. To understand the role of
the bias voltage, we quantitatively model the attractive force between the tip
and the sample using electrostatics. For the tunneling current, we
qualitatively model the contraction of the graphene using entropic concepts.
These complementary results enhance the understanding of each other and
highlight peculiarities of the system.
