New Experimental Constraints on Non-Newtonian Forces below 100 microns
  We have searched for large deviations from Newtonian gravity by means of a microcantilever-based Cavendish-style experiment. Our data eliminate from consideration mechanisms of deviation that posit strengths ~10^4 times Newtonian gravity at length scales of 20 microns. This measurement is 3 orders of magnitude more sensitive than others that provide constraints at similar length scales. 
J. Chiaverini, S. J. Smullin, A. A. Geraci, D. M. Weld, and A.   Kapitulnik