Force-distance curves were traced using AFM on different types of polymers, prepared and thermal treated in various conditions. Comparative assessment of their elasticity and adhesion was made by this method and correlations with polymer types and obtaining conditions could be established. Time-dependent effects (viscoelasticity and creep) in the mechanical response of polymers were studied using variable loading rates.

For polymeric materials, which are prone to elastic and viscous deformations during AFM scanning, the interference of mechanical properties in AFM morphological images is generally more important than for than rigid materials. This research allowed us to identify of several types of effects of the mechanical properties of studied polymers on their AFM images (height artifacts due to compression or adhesion of surface features, resolution decrease, scanning rate artifacts due to viscoelastic properties) and to estimate their relative magnitude in practical applications and also provided keys to minimize these effects in AFM images of topography.

Submicronic tribological properties of PMMA were investigated using Lateral Force Microscopy. In the peculiar conditions of our experiments the friction forces associated to PMMA and AFM tip follow a generalized form of Amonton-Coulomb macroscopic law, where the adhesive interface force must be considered too.

Behaviour of friction force (a.u.) versus applied force  for a thin PMMA film.

Project:  National basic funding Project MINASIST +, 2006-2008
Contact person: Phys. Raluca Gavrila  e-mail: raluca.gavrila@imt.ro

Special EFM test structure was designed and fabricated using EBL and lift-off  procedures for assessing the functionality of EFM modes

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EFM test structure with various pitch interdigitated finger electrodes -  overview a) and detail b). Simultaneously acquired topography (c) and KPFM images  (d). For electrode pairs put to different bias, adjacent electrodes have the same height (c) but differ in the surface potential (d)

Electrostatic Force Microscopy (EFM) modes have been used in several applicative studies to simultaneously gain insight into morphological and electronic properties of various thin film materials. In particular, KPFM technique has been applied to directly visualize the photovoltaic activity of an organic photovoltaic material - P(3HT- co-3ATH), thus allowing to acquire quantitative information regarding the correlation between nanoscale architecture and function.

KPFM images of  a sample area (9 mm x 2.5 mm) of a P(3HT- co-3ATH) thin film recorded (a) in dark and (b) under white light illumination. Fig (c) illustrates the photovoltaic activity occurring in this polymer by the histogram distributions of the surface potential in the dark and under illumination.
Reduced graphene oxide – P3HT blend studied by Kelvin Probe Force Microscopy. Surface potential distribution is overlaid on top of the rendered topography
Application of EFM to vizualize subsurface details. Morphology (left), and surface potential (right) for a P3HT/PCBM blend used in photovoltaic applications. KPFM image (right) reveals the subsurface nanoscale fibrilar structure attributed to P3HT, masked  by an oxidized and/or amorphous layer at the surface

High resolution – low voltage FEG- SEM imaging