smaller period of corrugations used here required the use of a precise stepper motor and piezocontrolled imprinting technique. The imprinting procedure was done as follows. At first, the second sphere was brought in contact with the grating using a micromanipulator. Then a hard flat stylus (see Fig. 1) was moved in 10 µ m steps using a stepper motor until it comes into contact with the other side of the sphere which is now sandwiched against the grating. Next the imprinting was done by applying a voltage to the z piezo to gently press the sphere between the grating and the hard flat stylus. To obtain deeper imprints while preserving sphericity some additional pressure was put on the sphere using the stepper motor. Special care was needed at this step. If the applied pressure from the hard flat stylus was too much, the resulting rotation of the second sphere will cause the cantilever to break. There is less concern on the preservation of sphericity as polystyrene spheres are elastic. Then the voltage on the z -piezo is reversed to remove the pressure on the sphere. With the help of the same stepper motor the hard flat stylus was gently removed and the sphere was then translated horizontally by around 200 µ m to a different position on the grating. The last operation is necessary because the part of the grating used to imprint corrugations on the sphere might have changed its local amplitude during the imprinting process. This translation was performed preserving the orientation of the cantilever. The same imprinting procedure, but with application of larger pressure by means of the stepper motor, was done with a similar sphere in the second set of our measurements. After the imprint process was done, the system was left in vacuum for more than 2 hours to reach a stable equilibrium. The corrugations on the grating and on both spheres were examined using an AFM and found to be rather homogeneous. This was done after the completion of the experiment. An AFM scan of the Au-coated corrugations of the vertical template grating is shown in Fig. 2(a). The value of the amplitude of these corrugations A$_{1}$ , also measured using the AFM, is indicated above. The variance of the stochastic roughness on the grating was estimated in the following way. The topography of the groove from an AFM scan [see Fig. 2(a)] was fitted to a sine function. Note that the top and bottom of corrugations are symmetric as expected for a sine. This is illustrated in Fig. 2(b) where a typical section of Fig. 2(a) along a y = const plane is shown. Then the difference of heights between the groove topography and the sine function was calculated at a sufficient number of intermediate points. The variance was found using these differences as the root-mean-square deviation between the two curves. A total 30 grooves were used to evaluate the average value of the variance 8