Molecular Capacitor Discharge as a Probe of Film Restructuring at Low Temperatures

Discharge of weakly bound, positive, and negative charges upon annealing of atomic and molecular layers that form a nanocapacitor is demonstrated as a sensitive detection method of low-temperature restructuring of films, such as densification, phase transitions, and desorption. This is detected by employing temperature-programmed contact potential difference (TP-ΔCPD) measurements utilizing a Kelvin probe within an ultrahigh-vacuum environment. Onset temperature for the discharge and its profiles are shown to be dependent on the film growth temperature but independent of the charge identity. The discharge is triggered by the restructuring processes, as demonstrated for very different materials─Kr, CD₃Cl, and amorphous solid water (ASW) films. The discharge phenomenon leads to a deeper and better understanding of the complex low-temperature processes that take place within molecular films, often at temperatures significantly lower than their onset for desorption.