Exploration of Nanoscale Electromechanical CouplingsMiller, Nathaniel (2020) Exploration of Nanoscale Electromechanical Couplings. Doctoral Dissertation, University of Pittsburgh. (Unpublished)
AbstractThis dissertation explores the electromechanical properties of organic piezoelectric materials and the measurement systems used to determine their unique properties. The project focus was to gain experimental insight into previously predicted piezoelectric molecules and develop new methods to accurately determine the electromechanical properties of their self-assembled monolayers. Using atomic force microscopy, the nanoscale properties of organic self-assembled monolayers were studied to compare previous computational predictions with experiment. Piezo force microscopy (PFM), was used to quantify the magnitude of sample deformation by an applied electric field across monolayers of a set of macromolecules (peptides and peptoids) to determine their effective piezo coefficient (deff). This resulted in small but differentiable responses been the peptides and peptoids. Through the study of these macromolecular monolayers, conventional PFM methods were found to be lacking sensitivity for these soft-flexible SAMs. These insights lead to the development of a new method leveraging the physics of dual AC resonance tracking PFM (DART-PFM) to simultaneously increase the sensitivity of the measurement system and reduce the sources of error. A new DC-sweep DART-PFM methodology allowed for the accurate determination of piezo response in soft macromolecular monolayers, plus several small molecule and crystalline reference materials. The method adds an additional DC field sweep to the classical AC field sweep DART-PFM to determine the in-situ point where the electrostatic component of the tip response is minimized. This new method should provide accurate determination of the vast library of “soft” piezoactive materials, as well as those with negative piezo coefficients, in which the material compresses under an applied field instead of expanding. The newly developed DC-sweep DART-PFM method was implemented to study piezoactive “buckybowl” organic ferroelectric materials, in which the net polarization of the film can be flipped with a coercive field. The deff of a corannulene derivative was determined and hysteresis loops were observed via scanning Kelvin probe force microscopy, suggesting ferroelectric behavior near room temperature. Share
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