Sains Ma1aysiana 26(3&4): 99-107 (1997)                                                               Sains Fizis dan Gunaan/

                                                                                                                                Physical and Applied Sciences

The use of Langmuir-Blodgett Films of Hematin

Mixed with Arachidic Acid to Detect

Carbon Monoxide Gas

Muhamad Mat Salleh, A. S. Belal & Muhamad Yahaya

Department of Physics

Faculty of Physical and Applied Sciences

Universiti Kebangsaan Malaysia

43600 UKM Bangi Selangor D.E. MALAYSIA

ABSTRAK

Terdapat minat yang besar terhadap penderiaan gas terutama bagi gas toksik seperti karbon monoksida. Kertas ini melaporkan penggunaan filem Langmuir-Blodgett (LB) hematin bercampur asid arakidik untuk mengesan gas karbon monoksida dalam gas nitrogen pada suhu bilik. Pengesanan dikaji berasaskan perubahan serapan optik dan pantulan filem yang masing-masing menggunakan spektrofotometer dan satu sistem serat optik. Spektrum serapan bagi 20 lapisan filem LB berkurang apabila filem itu didedahkan kepada 10, 100, 1000 ppm gas CO, dan mempunyai masa pulihan yang pantas apabila aliran gas dihentikan. Satu sistem serat optik yang terdiri daripada satu sumber cahaya diod laser, penduga pantulan, sampel filem nipis di atas satu cermin pemantul dan pengesan cahaya telah dibina. Menggunakan sistem ini didapati keamatan cahaya yang terpantul meningkat selepas filem disempuhlindap selama satu jam pada 100°C. Keputusan ini dijelaskan menggunakan imej mikroskop daya atom (AFM) filem LB yang diambil sebelum dan selepas sempuhlindap.

ABSTRACT

There is great interest in gas sensing especially for toxic gases such as carbon monoxide. This paper reports the use of Langmuir-Blodgett films of hematin mixed with arachidic acid to detect carbon monoxide gas in nitrogen at room temperature. The detection was studied based on changes in the optical absorption and reflection of the film using a spectrophotometer and an optical fiber system, respectively. The absorption spectra of a 20 layers LB film decreased when exposed to 10, 100, 1000 ppm CO gas, and had fast recovery time when the gas flow was stopped. An optical fiber system consists of a laser diode as light source, a fiber reflectance probe, thin film sample on a reflecting mirror and a light detector was setup. Using this system it was found that the intensity of the reflected light increased when the film was exposed to the gas. The sensing sensitivity of the films increased after the films were annealed for one hour at 100°C. The result is explained using the atomic force microscope (AFM) images of the LB films taken before and after annealing.

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