Force modulation microscopy study of phase separation on blend polymer films

We report force modulation microscopy study of phase separation on blend po lymer films of ether-type phenylene vinylene based copolymer and cyano-subs tituted poly(2,5-didecyloxy-p-phenylene vinylene). Three different tips wit h spring constants of 0.6, 3, and 60 N/m, and various modulation frequencie s between 5 and 10 kHz have been employed. It is found that consistent and correct image contrast can be obtained only with the stiffest tip. Theoreti cal calculation based on Sneddon mechanics also predicts a tip-sample stiff ness close to that of the preferred tip. These results suggest strongly tha t the tip spring constant used in force modulation microscopy should be com parable to (or greater than) the interaction stiffness. (C) 1999 American I nstitute of Physics. [S0003-6951(99)01519-3].