Thickness effect of Al2O3 as buffer layer on Alq3 sensitivity for toxic gas

Abstract

Gas sensitivity improved and becomes more stable when a buffer layer (Al2O3) inserted between the active layer (Alq3) and glass substrate. In this paper, we introduce a device (Au/Alq3/Al2O3) exposure to NO2 gas to enhancement the role of Alq3 in organic gas sensor. We employed the pulsed laser deposition technique to grow Al2O3 films with different thicknesses of 50, 75, and 100 nm on glass substrates. The structural and optical properties of the buffer layer were studied. XRD pattern shows that all films are polycrystalline in nature, and the mean crystallite size decreases when buffer layer thickness increase, insert the buffer layer did not change the direction of crystalline growth for the dominant planes of Alq3. The high resolution FE-SEM images for buffer layers indicates that the large crystals collect in the form of nanotubes, and changed into spherical shapes and flakes-like shapes, with increased thickness of Al2O3. The atomic force microscopy technique uncovered the uniform and dense distribution of nano crystallized. The band gap energy is ~3.8 and increased with increase a buffer layer. PL spectra of Alq3/Al2O3 samples exhibits a distinctive green emission at around 535 nm for pure Alq3, and blue shifting occurs toward the low wavelengths with increase thickness of Al2O3. More effect of Al2O3 was appeared when added to Alq3; this is appeared by the effect of shifting energy gap behavior, grain size on the sensor properties. The sensitivity, and response time with increase thickness of buffer layer is improved.