An investigation of electron tunnelling and conduction in Langmuir films
Langmuir films offer the possibility of obtaining unifo:r:m, wellordered, insulating structures of defined and controllable thickness. In this thesis, techniques for the fabrication of these films and the nature of the conduction process in single and multi-layer films of stearic acid/stearate sandwiched between metal electrodes (HIM devices) are discussed. A sophisticated film fabrication system has been designed and implemented and methods necessary for obtaining films of high integrity established. Structural characterisation studies using various techniques demonstrate that the resultant films are unifo:r:m, of predictable composition and substantially free of defects. In single layer MIM devices, detailed observations of the voltage and temperature dependence of the current suggest that the predominant conduction mechanism is direct electron tunnelling between the metal electrodes. This has been confirmed with the aid of additional experiments, including consideration of the role of the oxide film(s) invariably present in the canpleted device and investigation of the inelastic component of the tunnel current. It is argued that the latter provides unequivocal evidence that a significant proportion of all conduction is by electron tunnelling. In multilayer (3-5 layers) MIM devices, the importance of Schottky emission as a mechanism for conduction has been confirmed through a careful examination of the current-voltage relationship and on the basis of the temperature dependence of the current at fixed voltage. Finally, the techniques of Auger and X-ray photoelectron spectroscopy have been employed to provide further insight into the nature of film adhesion and composition. These observations, where possible, have been correlated with the results of electrical measurements.
Thesis from Leicester Polytechnic
- PhD