Sign flipping of spontaneous polarization in vapour-deposited films of small polar organic molecules

Tourlakis, Georgios M.; Adamopoulos, Sotirios Alexandros T.; Gavra, Irini K.; Milpanis, Alexandros A.; Tsagri, Liveria F.; Pachygianni, Aikaterini Sofia G.; Chatzikokolis, Stylianos S.; Tsekouras, Athanasios A.

doi:10.1039/d1cp01584b

Cited by 3 publications

(3 citation statements)

References 79 publications

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“…Recent studies have shown that various polar organic molecules spontaneously form highly polar films upon their condensation under UHV conditions at cryogenic temperatures. 7,9,11 Subsequent annealing results in nonreversible depolarization profiles that are remarkably similar to the TP-ΔCPD profiles presented here. In order to explore to what extent the charging effects are general among different molecular films, we have extended our study to the behavior of nonpolar molecular films (V film = 0) composed of dipolar molecules that do not form hydrogen bonding.…”

Section: Charging Of Asw Filmssupporting

confidence: 76%

“…TP-ΔCPD measurements were shown to be beneficial in the study of dielectric properties of thick molecular films (ices), with focus on crystalline and amorphous solid water (ASW), either neutral or charged. − In the latter case, the possible effect of the nature of the charging (positive or negative) has not been addressed so far.…”

Section: Introductionmentioning

confidence: 99%

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

Sagi,

Akerman,

Tamburu

et al. 2023

J. Phys. Chem. C

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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, CD 3 Cl, 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.

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Section: Charging Of Asw Filmssupporting

confidence: 76%

Section: Introductionmentioning

confidence: 99%

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

Sagi,

Akerman,

Tamburu

et al. 2023

J. Phys. Chem. C

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“…In recent years, researchers have started to focus their attention on fundamental studies of the molecular structure of liquids, amorphous semiconductors, polymer solutions, liquid metals (because of their optical and electrical properties), glassy states of substances, metal vapors, and many other systems. − Despite the complexity of studying disordered systems at the microscopic level, so far, significant progress has been achieved in this field. General patterns for a wide class of objects have been identified, and the methods for the theoretical analysis of disordered systems have been improved. − …”

Section: Introductionmentioning

confidence: 99%

Analysis of Vibrational Spectra of Tetrafluoroethane Glasses Deposited by Physical Vapor Deposition

et al. 2023

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This paper presents the results obtained in the study of structural phase transitions in thin films of R134A. The samples were condensed on a substrate by physical deposition of R134A molecules from the gas phase. Structural phase transformations in samples were investigated by observing the changes in characteristic frequencies of Freon molecules in the mid-infrared range with the help of Fourier-transform infrared spectroscopy. The experiments were carried out in the temperature range from 12 to 90 K. A number of structural phase states, including glassy forms, were detected. The changes in thermogram curves at fixed frequencies of half-widths of absorption bands of R134A molecules were revealed. These changes indicate a large bathochromic shift of these bands at frequencies of ν = 842 cm–1, ν = 965 cm–1, and ν = 958 cm–1 and a hypsochromic shift of the bands at frequencies of ν = 1055 cm–1, ν = 1170 cm–1, and ν = 1280 cm–1 at temperatures from T = 80 K to T = 84 K. These shifts are related to the structural phase transformations in the samples.

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Surface equilibration mechanism controls the molecular packing of glassy molecular semiconductors at organic interfaces

Fiori

Bagchi

Toney

et al. 2021

Proc. Natl. Acad. Sci. U.S.A.

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Glasses prepared by physical vapor deposition (PVD) are anisotropic, and the average molecular orientation can be varied significantly by controlling the deposition conditions. While previous work has characterized the average structure of thick PVD glasses, most experiments are not sensitive to the structure near an underlying substrate or interface. Given the profound influence of the substrate on the growth of crystalline or liquid crystalline materials, an underlying substrate might be expected to substantially alter the structure of a PVD glass, and this near-interface structure is important for the function of organic electronic devices prepared by PVD, such as organic light-emitting diodes. To study molecular packing near buried organic–organic interfaces, we prepare superlattice structures (stacks of 5- or 10-nm layers) of organic semiconductors, Alq3 (Tris-(8-hydroxyquinoline)aluminum) and DSA-Ph (1,4-di-[4-(N,N-diphenyl)amino]styrylbenzene), using PVD. Superlattice structures significantly increase the fraction of the films near buried interfaces, thereby allowing for quantitative characterization of interfacial packing. Remarkably, both X-ray scattering and spectroscopic ellipsometry indicate that the substrate exerts a negligible influence on PVD glass structure. Thus, the surface equilibration mechanism previously advanced for thick films can successfully describe PVD glass structure even within the first monolayer of deposition on an organic substrate.

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Sign flipping of spontaneous polarization in vapour-deposited films of small polar organic molecules

Abstract: Films of polar molecules vapour-deposited on sufficiently cold substrates are not only amorphous, but also exhibit charge polarization across their thickness. This is an effect known for 50 years, but...

Cited by 3 publications

References 79 publications

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

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

Analysis of Vibrational Spectra of Tetrafluoroethane Glasses Deposited by Physical Vapor Deposition

Surface equilibration mechanism controls the molecular packing of glassy molecular semiconductors at organic interfaces

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