  We show that the static force spectroscopy curve is significantly modified
due to presence of intrinsic cantilever instability. This instability acts in
tandem with such instabilities like water bridge or molecular bond rupture and
makes the static force spectroscopy curve (including "jump-off-contact")
dependent on the step-size of the movement of sample stage. A model has been
proposed to explain the data. This has been further validated by applying an
electric field between tip and substrate which modifies the tip-substrate
interaction.
