Optical and Electrical Properties of Vapor Deposited Thin Films of a Sodide and AN Electride.
Abstract
The optical and electrical properties of vapor deposited Na^+C222Na^ - and K^+C222e^ - films were explored. Alkalides and electrides are ionic salts in which the cations are macrocyclic complexed alkali metal cations and the anions are alkali metal anions and trapped electrons, respectively. A vapor deposition apparatus was extensively modified. The accuracy and control of the film temperature and stoichiometry were improved and a fiber optic spectrophotometer was integrated into the deposition system. Electronic circuits were included to allow thin film conductivity measurements. The optical and electrical properties of the best -characterized alkalide, Na^+C222Na ^-, were studied, including a temperature study of the absorbance peak. The temperature dependence of the peak parameters demonstrated thermal broadening effects on the absorbance. The results clarified the previous band-like picture of this sodide. Photobleaching with intense laser pulses showed the presence of new electronic states in absorbance, presumably produced by exciton-exciton interactions. The new absorbers appear to be due to the presence of substantial concentrations of trapped electrons. A conductivity study showed the presence of photoemission, not photoconductivity. The optical and electrical properties of the most conducting electride, K^+C222e ^-, were studied. The shape of the stable optical absorbance spectrum was found to be a broad plasma edge, which decayed irreversibly above {-30 }^circC as the electride film decomposed. Two- and four-probe conductivity studies found apparent band gaps of stable films to be 57 +/- 17 and 62 +/- 20 meV, respectively, slightly lower than previous measurements on powdered samples prepared by crystallization from solution. The combination of the optical and electrical properties indicated that annealing and decomposition mechanisms may introduce defects that lead to increased conductivity prior to massive decomposition above {-30}^circC. Several band-like models are proposed, but apparently defects play a dominant role in the conductivity of K^+ C222e^-.. A potpourri of other compounds was studied briefly in order to characterize new complexing agents such as aza-analogs of crown ethers and large organic globular electron acceptor (LOGEA) precursors. Surprisingly, Na ^- is apparently formed along with radical anions. Their optical and electrical properties are cataloged in the Appendix.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1994
- Bibcode:
- 1994PhDT.......150H
- Keywords:
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- Physics: Condensed Matter; Chemistry: Physical