Spontaneous polarization of vapor-deposited 1-butanol films and its dependence on temperature

Abstract

Films of 1-butanol were vapor deposited under vacuum conditions at cryogenic temperatures on a polycrystalline platinum foil. Kelvin probe measurements showed the generation of a large negative voltage on the vacuum side of the film relative to its back side in contact with the platinum foil. Voltages across vapor deposited films, which are known to require molecules with an electric dipole moment, were confirmed to be proportional to the amount of gas deposited at a given temperature. Voltages of several hundreds of volts were recorded for films that were a few thousand monolayers thick. As deposition temperature was reduced from 120 K, the film voltage was found to increase almost linearly from 0 V until a little below 38 K, where the trend was reversed. Ramping up the sample temperature after deposition at 15 K/min exhibited an initial increase in absolute magnitude and then a gradual elimination of the voltage as the temperature of 120 K was reached. Both the initial increase and the subsequent decrease were found to be irreversible and indicate structural changes in the amorphous film. The elimination of the film voltage is associated with small rearrangements of the deposited molecules which are facilitated by the gradual increase of the temperature and the cumulative electric field of the surrounding molecules.

Assigning a structural motif using spontaneous molecular dipole orientation in thin films

“…Within the framework presented by Field and co-workers to explain the origin of spontelectric behaviour [3 -5], this can be interpreted as meaning that either the molecular dipoles are completely randomly oriented in an amorphous solid phase, or alternatively, that 90 K represents a phase transition point and the crystalline solid phase prepared by deposition above 90 K presents a lattice motif in which the molecular dipoles are in a centrosymmetric structure. Table 3 summarises our assignment of the IR spectrum of cis-MF in comparison to the reported work in references [14] and [15]. A sharpening of the C=O line profile at around 1720 cm -1 , and of those of the other vibrational modes, is observed between 90 and 100 K.…”

“…In Table 3: Comparison of the vibrational assignment of the IR spectrum of solid cis-MF from this work and from that of Palumbo and co-workers [14] and Brown and co-workers [15].…”

A review of recent progress in understanding the spontelectric state of matter

“…In addition, there is further indirect evidence from neutron scattering data [2] which show structural changes associated with changes in the spontelectric nature of solid N2O. Very recently the spontelectric effect has also been identified in 1-butanol using the Kelvin probe technique [8].…”

Self-Assembled Electret for Vibration-Based Power Generator

“…In general, the potential of the resulting film is considered to be linearly proportional to its thickness and is observed to be stable with time over a period of hours 23 . Surprisingly, in case of 1-butanol, the potential of the film easily exceeds 100 V 19 . These characteristics strongly imply that this phenomenon can be applied to the fabrication of the charged films without using a charging process.…”

“…In fact, spontaneous polarisation has been reported in thin films for some types of molecules. For example, small polar molecules impinging on a cold surface from the gas phase have been observed to be capable of sticking onto a substrate, forming a charged film without a charging process [19][20][21][22][23] . After almost 50 years of research 24,25 , this vital phenomenon has been considered to originate from a partial orientation of the permanent dipoles of the molecules.…”