Low temperature aging in a molecular glass: the case of <i>cis</i>-methyl formate

Cassidy, Andrew; Jørgensen, Mads Ry Vogel; Glavic, Artur; Lauter, Valeria; Plekan, Oksana; Field, D.

doi:10.1039/d1cp01332g

Cited by 2 publications

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“…The example of cis -methyl formate is shown in Figure a. This behavior has pioneered a new technique for the study of relaxation by molecular rotation in supercooled molecular glasses. , Neutron scattering has been used to quantify molecular translational diffusion and to differentiate it from rotation, in these materials . Layering isotopically labeled spontelectric films generates a sample with multiple interfaces.…”

Section: The Spontelectric Effect As a Probe Of Dynamics In Glassesmentioning

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: The Spontelectric Effect As a Probe Of Dynamics In Glassesmentioning

confidence: 99%

“…The dashed vertical lines indicate the barriers to rotation derived from panel (a) and show that rotations of approximately 50° from the resting position are required. Adapted with permission from ref . Copyright 2021 Royal Sociey of Chemistry.…”

Section: The Spontelectric Effect As a Probe Of Dynamics In Glassesmentioning

confidence: 99%

A Spontaneously Electrical State of Matter

2023

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Hidden singularities in spontaneously polarized molecular solids

Cassidy

Pijpers

Field

2023

The Journal of Chemical Physics

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Films of dipolar molecules formed by physical vapor deposition are, in general, spontaneously polarized, with implications ranging from electron transfer in molecular optoelectronic devices to the properties of astrochemical ices in the interstellar medium. Polarization arises from dipole orientation, which should intuitively decrease with increasing deposition temperature, T. However, it is experimentally found that minimum or maximum values in polarization vs T may be observed for cis-methyl formate, 1-propanol, and ammonia. A continuous analytic form of polarization vs T is developed, which has the property that it is not differentiable at all T. The minima and maxima in polarization vs T are marked by singularities in the differential of this analytic form. This exotic behavior is presently unique to films of dipolar species and has not been reported, for example, in the related magnetic phases of spin glasses.

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Low temperature aging in a molecular glass: the case of cis-methyl formate

Abstract: The spontaneously generated electric field in a molecular glass, decays with time at deeply supercooled temperatures. Here, we fit the rate of decay with a model to extract the activation barrier to molecular rotation, as the glass ages.

Cited by 2 publications

References 32 publications

A Spontaneously Electrical State of Matter

A Spontaneously Electrical State of Matter

Hidden singularities in spontaneously polarized molecular solids

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