In
this work, a nanocolumnar tantalum oxide waveguide is introduced
in a guided-mode resonance-based sensor for volatile organic compound
detection. The presence of a nanocolumnar structure where optical
resonance is localized allows for molecular diffusion and adsorption
and hence the enhancement of the sensor’s sensitivity. Here,
the nanocolumnar tantalum oxide film is fabricated using a pulsed
direct current reactive magnetron sputtering system at low kinetic
energy deposition. By optimizing the operation pressure, both the
size and density of the nanocolumnar film can be controlled. The results
show that the tantalum oxide film deposited at a higher pressure (30
mTorr) forms a more discrete nanocolumnar structure (refractive index
of 1.93 and 20.7% porosity). As a result, the sensor’s sensitivity
is remarkably increased up to 15-fold in comparison to the deposition
at a lower pressure (10 mTorr, higher refractive index, n = 2.1, and 6.4% porosity). The sensor exhibits good stability and
reusability over 25 measurements of isopropanol vapor within a duration
of 60 days with 6.4% coefficient of variance at a lower concentration
(5%). The selectivity experiment shows good potential of using the
proposed sensor for toluene and formaldehyde detection.
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