The optical absorption spectra of spontaneously electrical solids: the case of nitrous oxide

Cassidy, Andrew; James, Rachel; Dawes, Anita; Lasne, Jérôme and Field, David (2019). The optical absorption spectra of spontaneously electrical solids: the case of nitrous oxide. Physical Chemistry Chemical Physics, 21(3) pp. 1190–1197.

DOI: https://doi.org/10.1039/c8cp05746j

Abstract

Absorption spectra of films of N2O, in the range 115–160 nm, are presented for deposition temperatures between 33 K and 64 K. Observed shifts in the absorption energy vs. deposition temperature are analysed in terms of the temperature-dependent spontaneously electrical (‘spontelectric’) fields present in the films. Using a simple electrostatic theory, we suggest that (i) spectra are associated with Wannier–Mott excitons, (ii) the action of the electric field upon the excitons suffers a blockade at ≤54 K for the C-state and ≤52 K for the D-state of N2O, (iii) the blockade may be attributed to structural defects, which trap excitons, limiting their size and (iv) films form with defect-free regions containing 324 ± 3, 168 ± 46 and 95 ± 1 molecules of N2O at 54 K, 52 K and 50 K respectively, yielding an experimental indication of the scale size of regular periodicity associated with Wannier–Mott excitons. Results demonstrate how the spontelectric effect can be used as a tool for exploring the structure of solids and give a graphic image of the structural changes that take place close to the known phase change at 47 K/48 K.

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