With the support from the Solid State and Materials Chemistry program, the research team will work on an interdisciplinary project in design-directed material synthesis that calls for close interactions with colleagues in the Physics department. The project aims to prepare and characterize a so far unknown class of dielectric materials based on artificial dipolar molecular rotors arranged in a 2-dimensional grid. Such materials do not occur in nature and would be useful for signal processing and specifically for minituarization of analog components in electronic circuitry such as that found in cellular telephones. A post-doctoral student and several undergraduates will receive interdisciplinary training (organic synthesis, a variety of spectroscopic and other physical techniques, and underlying materials theory). The project will attract undergraduate students, K-12 students, and under-represented minorities to nanoscience.
The new 2-dimensional materials are to be assembled on a Langmuir-Blodgett (LB) trough and transferred to a lithographically patterned solid substrate. The specifically synthesized rod-like rotor molecules carry a dipolar rotator between two triptycene units on an axle normal to the surface, and a carboxylic group at one end (the term molecular rotor is used for a molecule with a rotatable part, which is called the rotator). Initial grazing-incidence X-ray scattering and other data demonstrate that molecules of this type self-assemble into a Langmuir monolayer on an aqueous subphase. The structure of the assembly is characterized by an interlocking of the triptycene units into a double-decker trigonal pattern, with almost freely rotatable dipoles between the decks. The distance between the dipoles and their magnitude are such that as long as sufficiently large 2-dimensional single-crystal domains can be prepared, in the first approximation the ground state should be ferroelectric, with a Curie temperature above ambient. Rotator dynamics in the transferred monolayers (and multilayers) are to be studied by electric dichroism in the infrared part of the spectrum in the Michl laboratory and by dielectric spectroscopy in the Rogers laboratory. Theory predicts the existence of ferroelectric ordering with unusually low velocity polar sound waves when long-range dipolar interactions dominate local steric barriers to rotation.
