The electron transfer processes in thin-film diode structures of Ta–Ta2O5–Au have been studied. The structures were prepared by electron beam evaporation of tantalum at 10−6 Torr followed by plasma oxidation of the tantalum film to the desired thickness. The counterelectrode metal was then evaporated without breaking the vacuum. Current—voltage—temperature characteristics of these structures were studied. Tunnel emission was observed when the tantalum electrode was biased positively and Schottky emission was observed for the tantalum electrode biased negatively. Trapezoidal energy barrier models have been used by many authors to explain electron injection and transfer through extremely thin insulating films. Such a model is proposed here for the tantalum—tantalum-oxide system, and as is shown, it provides a self-consistent framework for describing both Schottky and tunnel emission electron transfer processes in these structures. Using this model, it was found that the barrier height at the parent tantalum oxide interface is 1.1 eV and the built-in voltage with a gold counterelectrode is 0.5 eV.
This article relates to the construction of a portable, low cost, thermal-regulating light-emitting diode (LED)-based, handheld fluorometer. This regulated fluorometer is based on both a low thermal mass infrared heater, and an orthogonal geometry LED-based filter fluorometer. Power is supplied through an external power supply and data is collected in real time through standard serial interfaces of personal computers or personal digital assistants. Thermal regulation is automatically maintained using temperature sensor feedback control. Optical excitation relies on LED light source(s) and optical detection is made through an adjustable integrating photodetector. With such a handheld system, applications requiring temperature sensitive photometric measurements for real-time analyte detection can be more easily performed in the field.
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