Presentation Title

Croconic Acid : Surface and Electric Field Influence on Deposition

Faculty Mentor

Dr. Kimberley Cousins

Start Date

17-11-2018 10:15 AM

End Date

17-11-2018 10:30 AM

Location

C327

Session

Oral 2

Type of Presentation

Oral Talk

Subject Area

physical_mathematical_sciences

Abstract

Croconic Acid (CA) deposition into a thin-film has been of recent interest since single crystal CA is a known organic ferroelectric. In our studies of croconic acid on silica (SiO2) and gold (Au) surfaces, we developed models to explain the fundamental differences in deposition properties on such surfaces with and without an applied electric field. In particular, needle-like structures of CA form when an electric field is not applied, while an ordered thin film forms with a strong electric field. We used plane wave density functional theory (DFT) within the VASP program to calculate surface structures and dynamics. These methods from DFT, computationally allow us to model the fundamental behaviors in deposition which can be used to predict behaviors a molecule can have on an array of surfaces. Optimal surface structures were first determined before the addition of CA in the calculations could be inputted for analysis. The surfaces were chosen from the experimental work where they chose gold as the preferred surface since it serves at an electrode, which is needed to shift the polarization of the film. Silicon dioxide was also modeled to support the experimental findings. Each of the surfaces showed a unique influence in CA deposition. A pure alpha silica surface showed strong interactions where CA chemisorbed to the surface and a covalent bond was generated. A gold (111) surface showed little interactions, where a single CA molecule always orientates itself close to the surface and interacts more preferably with another CA on the surface as a dimer system. In a dimer system on a gold surface, when a 0.1 eV/Å electric field perpendicular to the surface is applied, the preferred pleaded motif of CA crystal structure is favored. This pleaded orientation is analogous to the idealized crystal that should give the best ferroelectric response.

Summary of research results to be presented

On a gold surface, a dimer system has showed us that the presence of an electric field promotes the desired pleaded motif, or “zig zag” motif, of CA’s optimal crystal structure along one of its axes. Although this pleaded motif is not the most energetically favored position, the presence of an external electric field allows for it and at a lower energy than if there was no field present. On the other hand, on a silica surface we have seen the strong interactions between the surface and a single CA molecule. In a capped silica surface, a CA molecule has covalently bonded to one of the silicon atoms in the substrate. With this chemisorbed molecule, an electric field analysis showed that the preferred canted position was greatly achieved under the applied field than without. For practical reasons, a hydrogenated SiO2 surface was then used in our calculations. A damping feature was used in the calculation that prevented the molecule from reaching extremely high energies and ultimately exploding. Unfortunately, this led to very little movement of the system in a Molecular Dynamics simulation since the damping feature prevents too much energy from being inputted to the system, to prevent it from exploding, and energy is what allows for movement. Molecular Dynamics simulations are computational calculations that take potential energies and interactions between atoms and solve Newton’s equations of motion to determine the physical movement of those atoms with analogous energies.

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Nov 17th, 10:15 AM Nov 17th, 10:30 AM

Croconic Acid : Surface and Electric Field Influence on Deposition

C327

Croconic Acid (CA) deposition into a thin-film has been of recent interest since single crystal CA is a known organic ferroelectric. In our studies of croconic acid on silica (SiO2) and gold (Au) surfaces, we developed models to explain the fundamental differences in deposition properties on such surfaces with and without an applied electric field. In particular, needle-like structures of CA form when an electric field is not applied, while an ordered thin film forms with a strong electric field. We used plane wave density functional theory (DFT) within the VASP program to calculate surface structures and dynamics. These methods from DFT, computationally allow us to model the fundamental behaviors in deposition which can be used to predict behaviors a molecule can have on an array of surfaces. Optimal surface structures were first determined before the addition of CA in the calculations could be inputted for analysis. The surfaces were chosen from the experimental work where they chose gold as the preferred surface since it serves at an electrode, which is needed to shift the polarization of the film. Silicon dioxide was also modeled to support the experimental findings. Each of the surfaces showed a unique influence in CA deposition. A pure alpha silica surface showed strong interactions where CA chemisorbed to the surface and a covalent bond was generated. A gold (111) surface showed little interactions, where a single CA molecule always orientates itself close to the surface and interacts more preferably with another CA on the surface as a dimer system. In a dimer system on a gold surface, when a 0.1 eV/Å electric field perpendicular to the surface is applied, the preferred pleaded motif of CA crystal structure is favored. This pleaded orientation is analogous to the idealized crystal that should give the best ferroelectric response.