COMPUTER-CONTROLLED EXPERIMENTS IN THE SURFACE FORCES APPARATUS WITH A CCD-SPECTROGRAPH

We present a computer-controlled technique to measure the distance-dep endent forces in the surface forces apparatus. The power of our setup is shown by a measurement of the repulsive forces between mica surface s immersed in a 0.01 M NaCl solution. At close distances we find an os cillatory force with a periodicity of 0.30 nm, which roughly correspon ds to the diameter of a water molecule. For the distance determination we use the standard interferometric technique: the interferometer con sists of a medium sandwiched between two mica sheets of equal thicknes s silvered on the backside. The surface separation is measured by comp aring the resonance wavelength to the one obtained from contacting mic a sheets. By substitution of the eye by a CCD-camera we improve the re producibility of the method and we can determine the cavity parameters quantitatively.