Papers by Author: Farhad Akbari Boroumand

Abstract: Poly [2-methoxy, 5-(2¢-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV) is a well known hole-conducting semiconductor utilized in the fabrication of optoelectronic devices because of its interesting electroluminescence. However, both electroluminescence and electrical conduction in this material sharply deteriorate upon exposure to oxygen, necessitating fabrication and hermetic sealing of the MEH-PPV-based devices in oxygen-free environments. Same shortcoming has excluded the material from applications requiring air exposure. We have recently presented a model for the oxidation mechanism of an MEH-PPV layer and have shown that such layers, after oxidation at certain conditions, can support air-stable electrical conduction. Here, we describe the experimental conditions required for the preparation of an oxidized MEHPPV layer, and provide experimental data on the stability of such layers at different conditions. It is shown that the fabricated air-stable oxidized MEH-PPV layers are excellent for a number of chemical sensor applications.

Abstract: Here, we demonstrate the field applicability of the Ag-TiO₂ Schottky diodes for environmental UV level measurements. The device is visible-blind and it is shown that its maximum sensitivity coincides the environmental UV spectrum (UV-A). These features, along with its low voltage and biasing insensitivity of its operation, simplify the electronic circuit required for the fabrication of a hand-held UV monitoring system.

Abstract: A UV-sensitive Schottky diode of Ag-rutile-Ti structure is fabricated on a thermally oxidized titanium chip. The junction is formed by the thermal evaporation of silver in vacuum and a subsequent controlled annealing process. Applying a biasing voltage of-300 mV, the reverse current of the fabricated silver-rutile-titanium structure increases five orders of magnitude under 50 µW/mm2 UV illumination ( λ=355 nm). The device is visible-blind and its operation is described based on the photoelectric mechanism in the carrier-depleted oxide layer. The dominance of the photoelectric, rather than photoconductive, mechanism along with the dense rutile layer are responsible for the fast transient times observed. The response and recovery times of the device are 800 µs and 7 ms, respectively.The device is stable and extremely cost effective.