The Photoinjection of Electrons Into Liquid Ammonia.
Abstract
The photoinjection of electrons into pure ammonia was successfully studied as a function of temperature, photon energy, and reference potential. A pulsed dye laser was used to inject the electrons from an Ag photocathode into the solvent and the time response of the electrochemical cell was recorded. The photoyield, Y, recovered from the time response data is the net number of charges collected at the counter electrode per incident absorbed photon. Several interesting phenomena have come to light through this investigation. The first observation is a marked dependence of the photoyield on temperature, along with a hysteresis as the temperature was cycled during the experiment. Secondly, the photoyield versus reference potential plots are not simple power laws. There is a photoresponse at all biases between 0.0 and -2.0 Volts (ref Ag) and there seems to be no single function which adequately describes the data for the entire range of biases. Above "threshold" the photoyield undergoes a change in slope in most of the data. This two-slope or two-process change is also signaled in the time response of the photoyield. The photocurrent pulses from which the photyield is obtained have a 100(mu)usec width for the first process. As a second process "threshold" is passed a tail of 1.0 to 10.0 msec duration developes and grows as the photoyield further increases. Only at the more negative reference potentials does the photoyield agree with existing theories. This change in the photoinjection data indicates either a change in the transmission coefficient of the interfacial region or a final density of states in the fluid which includes a band tail comprised of pre-solvated electron trap states along with a conduction band. It is suggested that the injection process first proceeds through the trap states at lower injected electron energies and through the conduction band at higher injected electron energies. Finally, a discrepancy was discovered between the change in the photoyield as the photon energy was changed and the change in the photoyield as the reference potential was changed. Unlike the present theories, these two derivatives were not found to be equivalent.
- Publication:
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Ph.D. Thesis
- Pub Date:
- 1984
- Bibcode:
- 1984PhDT.......167B
- Keywords:
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- Physics: Condensed Matter