The elasticity of soft sample,especially biomolecules,is one of the most attractive issues in the field of nano measurement with atomic force microscopy (AFM).However,present results on the compressive elasticity of soft sample,for instance height measurement,are far from the reality due to the inherent limitation of current AFM technology.For example,the measured height of dsDNA by tapping mode AFM (TM AFM) is close to 0.7~0.8nm in air,while the well accepted diameter of dsDNA is about 2 nm by the develo...