Hidden singularities in spontaneously polarized molecular solids

Cassidy, Andrew; Pijpers, F. P.; Field, D.

doi:10.1063/5.0138642

Cited by 1 publication

(2 citation statements)

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“…Examples also exist of a maximum in m versus T, for example, for 1-pentanol, 9 where the differential is positive on the low T side and negative on the high T side. 51 The outstanding current problem is that we do not have insight into how the system becomes caught in the spontelectric state or, further, how the behavior in Figure 4 can arise. In earlier work, we made a qualitative suggestion that librational fluctuations were an underlying cause of the spontelectric effect, as supported by recent large scale simulations of cis-methyl formate films.…”

Section: A Physical Model For the Spontelectric Statementioning

confidence: 99%

“…The region of the minimum in m versus T is in fact characterized by the differential becoming infinite, negative to the low T side and positive to the high T side, in this case. Examples also exist of a maximum in m versus T , for example, for 1-pentanol, where the differential is positive on the low T side and negative on the high T side …”

Section: A Physical Model For the Spontelectric Statementioning

confidence: 99%

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A Spontaneously Electrical State of Matter

2023

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Metrics & MoreArticle Recommendations CONSPECTUS: Molecular deposition on solid surfaces forms crystalline or amorphous/glassy thin solid films. Intermolecular interactions govern the packing and dynamics of these films. The connection between molecular structure and intermolecular interactions is based on understanding electrostatic forces, dispersion forces and hydrogen bonding. Recently, an entire class of dipolar molecular species have demonstrated counterintuitive self-organization such that the dipole moments of individual molecules are oriented in thin films. This leads to the spontaneous generation of polarized molecular films manifesting a polarization charge equivalent to tens to hundreds of volts in strength at the film-vacuum interface, relative to the film-substrate interface. These voltages, and the corresponding electric fields present in such films, result from a collective and spontaneous orientation of molecular dipoles throughout the film during film growth and represent a metastable state of polarized material. The existence of these materials should encourage reconsideration of the importance of solid-state intermolecular electrostatic interactions. This account will detail observations of the spontaneous electric fields in molecular solids, provide insights into the dynamics and structure of molecular materials that the emergence of these electric fields can facilitate, and present a dipole-alignment based meanfield model that reproduces the temperature dependence of the electric field strength. Species as diverse as carbon monoxide, nitrous oxide, freons, simple alcohols, and cis-methyl formate have been demonstrated to spontaneously generate electric fields. We have reported electric fields more than 10 8 V m −1 , have shown how field strength varies with the film deposition temperature, and have reported temperature-dependent Stark shifts observable in both infrared and ultraviolet absorption spectra. The latter has led to the reporting of large Wannier−Mott excitons in wide band gap molecular materials, such as solid carbon monoxide and ammonia. Changes in the field strength with time, at specific temperatures, can be related to the structural dynamics of glassy molecular solids. Measurement of surface potentials is a very sensitive technique by which to observe the rotation and translation of molecular species buried in thin films. This is particularly true for polarized, supercooled molecular glasses, where surface potentials have been used to report on secondary relaxation processes that have hitherto been hidden from measurement.Characterizing spontaneously electric molecular films, and understanding their behavior, requires the inclusion of nonlocal and nonlinear effects. The mean-field model that we present describes the data by connecting the energy of interaction of an average dipole with the mean effective field in the film, where this field is itself a function of the degree of polarization. This feedback loop produces a smooth function with a nonintuitive, discontinuous differ...

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Section: A Physical Model For the Spontelectric Statementioning

confidence: 99%

Section: A Physical Model For the Spontelectric Statementioning

confidence: 99%