AFM topography images of the films were recorded in tapping mode using a Multimode NanoScope IIIa (Digital Instruments/Veeco Metrology Group) at a scan rate of 1 Hz and tip velocity of 2 um/sec. Silicon AFM probes were used with approximate characteristics as follows: resonant frequency 300 kHz, spring constant of 40 N/m, and tip radius 10 nm.