AFM Imaging of Rubbed Polyimide

We use a standard tapping/intermittent contact mode set-up, which is assembled as described in Sect. 3.2.1 (see also hands-on example 31). The operation frequency and amplitude are adjusted to v at 0.85 A0 and 100 nm, respectively. The surface is tracked most accurately by utilizing a high setpoint amplitude ratio (close to 0.9). Care must be taken that the tip does not lose track of the surface when traversing elevated features, therefore the phase (and the amplitude) signal is carefully monitored. Halos in the fast scan direction that are devoid of contrast (i.e. show a constant phase shift or amplitude response), are indicative of absent tip-sample interaction. In this case the setpoint can be lowered slightly. 

The AFM data shows spherically appearing polyimide islands for the pristine film, which are randomly arranged (Fig. 3.85, panel b). No preferred orientation or anisotropy is detected. By contrast, the oriented film (panel c) shows clearly some degree of orientation of the morphological features observed. In (c) two stripes of chained islands, along two slightly different directions (indicated by black arrows), adjacent to patches of random islands (indicated by white arrow) are unveiled. In addition, a marked scratch can be observed in the upper right-hand comer. 

In panel (d) a strikingly different type of defect structure is encountered, the so-called tears. It should be noted that these correspond to much larger defects (compare the scan size). In the work of Russell and coworkers it was found that three types of failure were present in the rubbed polyimide films, namely scratches, tears, and strings of islands, all of which are aligned along the mbbing direction. Local overshearing of the film was held responsible for the observed formation of 

Osswald TA, Menges G (1995) Materials science of polymers for engineers. Hanser-Gardner, Cincinnati 

Balnois E, Stoll S, Wilkinson KJ, Buffle J, Rinaudo M, Milas M (2000) Macromolecules 33 7440-7442 

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