A Nanocolumnar Tantalum Oxide-Guided Mode Resonance Sensor for Volatile Organic Compounds

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.