Comprehensive Characterization of Neat Polymers and Compositional Imaging Heterogeneous Polymer Systems with AFM Based M
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Comprehensive Characterization of Neat Polymers and Compositional Imaging Heterogeneous Polymer Systems with AFM Based Mechanical, Electric and Spectroscopic Methods Marko Surtchev, Sergey Belikov, Ivan Malovichko and Sergei Magonov NT-MDT Development Inc., 7910 S. Kyrene Road, Tempe, AZ 85284, U.S.A. ABSTRACT Comprehensive characterization of materials suggests measuring their different properties for optimal use in technological applications and this task becomes more challenging as size of related structures decreases and their complexity increases. At smaller scales Atomic Force Microscopy (AFM) enables visualization of structures and quantitative measurements of their mechanical and electric properties. So far, several properties such as elastic modulus and work of adhesion, surface potential and dielectric permittivity can be extracted from the results obtained in various AFM modes. More complicated are the AFM experiments and their analysis in case of viscoelastic, piezoelectric and thermoelectric properties. Several examples of quantitative characterization of neat polymers will be given. In many cases the dissimilarity of the components’ properties is employed for their recognition in heterogeneous systems such as polymer blends, block copolymers and metal alloys. The confined geometries, which are common for small-scale structures, might restrict such identification and a combination of AFM with spectral methods such as Raman scattering will be helpful. Achievements and challenges of compositional mapping will be illustrated on several complex materials. INTRODUCTION In last decades AFM applications are developing in the contact and oscillatory modes, which complement each other in high-resolution imaging, where these modes provide visualization of molecular-scale features and measurements of materials properties at scales down to nanometers. The contact mode is used for current, piezoresponse and contact resonance studies, whereas the oscillatory resonant mode – Amplitude Modulation (AM) is applied for local magnetic or electric measurements in single- or multi-frequency methods. In the oscillatory non-resonant mode such as HybriD mode [1] the probe deflection – the attribute of the contact mode - is applied for surface tracking. (Similar modes are used by Nanotec Electronica, JPK Instruments and Bruker.) This happens in every cycle while the probe-sample separation periodically changes from a non-contact to contact state at a frequency much smaller than that of the probe. This mode, in which the tip-sample forces fall in between the most gentle AM operation and stronger forces (particularly, lateral) of the contact mode, is useful for nanomechanical and electric studies. All three modes are successfully applied for quantitative examination of the elastic modulus of various materials and the analysis of the force curves in these modes will be demonstrated on samples of poly(vinyl acetate) (PVAC), polystyrene (PS) and low density polyethylene (LDPE). The different time scale of the tip-sample interactions
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