Humidity modulated surface pattering of large-scale molecular ferroelectric thin films based on natural alkaloids

Abstract

Molecular ferroelectrics with low power consumption offer environmental and economic advantages over conventional ferroelectrics and could lead to next-generation microelectronic devices. To this end, it is of great importance to understand the conditions under which molecules can be engineered to form large-area, highly oriented thin films, as their electrical properties depend on orientation. In the research field of molecular ferroelectrics, homochiral multifunctional organic molecules are often used to induce the self-assembly of molecules through non-covalent interactions to form polar crystal packings and consequently ferroelectric properties. Here, molecular ferroelectric thin films based on the natural Cinchona alkaloid, cinchoninium cation and chlorocobaltate(II) anion were prepared by a dip-coating technique without post-thermal treatment and assisted stabilization process. The deposition parameters (relative humidity, temperature, concentration and withdrawal speed) were modified to produce either completely dense or fully patterned films with randomly distributed holes on the surfaces. While non-covalent interactions are the main factor in determining the structure of cinchoninium-trichloro-cobalt(II) thin films, relative humidity is a key parameter in the simultaneous self-organization happening at the mesoscale, acting as a dewetting agent. Dense cinchoninium-trichloro-cobalt(II) films exhibit a stable ferroelectric switching at a low operating voltage, and patterned films were tested as resistive methanol sensors.