OPTICAL-SPECTRA AND CONDUCTIVITIES OF THIN-FILMS OF THE ELECTRIDE K-)((CRYPTAND[2.2.2])E()

Optical and electrical measurements on vapor co-deposited thin films o f the most conducting electride, K+ (cryptand[2.2.2])e(-), show result s similar to those obtained with polycrystalline pellets and with thin films prepared by solvent evaporation. Initial optical absorbance spe ctra of films deposited below -50 degrees C showed contributions from several species, but these spectra evolved with time (annealed) at low temperatures to yield mostly plasmalike spectra, characteristic of ma rginal metals. Most films deposited at -40 degrees C showed no change in shape with time, indicating that annealing had occurred during depo sition. Four-probe conductivity measurements showed activated temperat ure dependence with an activation energy of about 0.03 eV, while two-p robe conductivity measurements showed similar activation energies, but with a variable resistive barrier at the sample-electrode interfaces. The correlation between conductivities and the decay of the absorbanc e spectra during decomposition was investigated. Thermal decomposition of the electride films leads to complex conductivity behavior. Except when the temperature is increased very slowly, the films become more conducting during the first 40-50% of decomposition, and then the film s rapidly become insulating. The conductivity may be, due to defect ho les that can disappear by annealing or slow decomposition or can be pr oduced during the early stages of rapid decomposition. Alternatively, variable grain-boundary resistance could be responsible. The optical a nd electrical behavior of the films is correlated with the cavity-chan nel geometry of this electride.