Thermally activated motion of the contact line of a liquid He-4 meniscus on a cesium substrate

We have measured the contact angle of a liquid helium-4 meniscus on a cesiu m substrate as a function of the velocity of the three phase contact line, at various temperatures. The velocity is found to vary exponentially with t he applied force. We show that the contact line advances through thermally activated jumps. Their area of about 125 nm(2) is probably related to the r oughness of the cesium substrate which is evaporated at low temperature.