AFM OBSERVATION OF MONATOMIC STEP MOVEMENTS ON NACL(001) WITH THE HELP OF ADSORBED WATER

AFM observation of cleaved NaCl(001) surface in air at room temperatur e revealed spontaneous motion of monatomic steps, depending on relativ e humidity, to minimize one-dimensional surface free energy. While ste p motion was recognized only at the parts having large positive curvat ure at 52% humidity, even straight steps moved at 57%, The motion was accelerated toward higher humidity. It is suggested that adsorbed wate r having 2-dimensional nature transports ions at the surface. By holdi ng the AFM tip at one place, salt solution was collected beneath the t ip by capillary action. Upon removal of the tip, the solution droplet turned into a bell-shaped hillock of salt as high as 78 nm. Although t he hillocks gradually flattened spontaneously, the method has potentia l application in pattern formation.