| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016) | |
| Thin Films | Wednesday Sessions |
| Session TF-WeP |
| Session: | Thin Films Posters Session II |
| Presenter: | Premysl Fitl, University of Chemistry and Technology Prague, Czech Republic |
| Authors: | P. Fitl, University of Chemistry and Technology Prague, Czech Republic D. Tomecek, University of Chemistry and Technology Prague, Czech Republic M. Pajkova, University of Chemistry and Technology Prague, Czech Republic J. Vlcek, University of Chemistry and Technology Prague, Czech Republic L. Fiser, University of Chemistry and Technology Prague, Czech Republic E. Maresova, University of Chemistry and Technology Prague, Czech Republic S. Havlova, University of Chemistry and Technology Prague, Czech Republic P. Hozak, University of Chemistry and Technology Prague, Czech Republic M. Vrnata, University of Chemistry and Technology Prague, Czech Republic |
| Correspondent: | Click to Email |
Our work deals with comparison of detection abilities of thin film chemiresistors based on silver phthalocyanine with metallic nanoparticles and ion mobility spectrometry. In our study we focus to the detection of widely used taggant in explosives - 2-nitrotoluene.
The sensing layers of chemiresistors were deposited by vacuum evaporation (AgPc) and DC magnetron sputtering (metallic nanoparticles) on ceramic substrates with platinum interdigital electrodes. We varied type of metallic nanoparticles (Au, Pd and Ag), their amount (equivalent thickness in the range of 1 to 50 nm) and also the deposition sequence of used techniques (bottom AgPc + top nanoparticles vs top AgPc layer - bottom nanoparticles). For underlying metal nanoparticles the substrates were heated during deposition (temperature range of 20 - 600 °C) to investigate and tailor nanoparticle shape and conductivity properties.
Growth of metallic nanoparticles was continuously monitored by in-situ resistance measurements during sputtering and annealing operations. These measurements enable also detection of percolation threshold. The morphology of prepared layers was investigated by electron microscopy.
For as-deposited layers of metal on AgPc it was found that when the amount of metal is relatively low (i.e. less than layer with equivalent thickness of 4 nm for Pd, 5 nm for Au and 8 nm for Ag) metal clusters on organic surface are created. Continuous but incompact layers are formed for slightly greater amounts of sputtered metals. Finally, continuous and compact layers were observed when equivalent thicknesses achieved ≈ 15 nm. When the layers are annealed the percolation threshold is in general shifted to greater amounts of sputtered metal.
Optimized sub-threshold layers containing metallic cluster arrays on chemiresistor substrates were used for detection of 2-nitrotoluene. The taggant vapors were detected in two modes: without or with photoactivation (λ = 266 nm). While the dc-response of AgPc/Au(10 nm) sensor to 189 ppm of non-activated 2-nitrotoluene vapors was negligible, after photoactivation the dc-response rose to 373.
The sensing properties of thin films were compared with sensitivity of commercially available GC-IMS system. The detection limit of our thin film sensors is in range of hundreds of ppb. The ion mobility spectrometer is cable to reach lower detection limits (ppt). Although the ion mobility spectrometry shown the higher sensitivity, the possibility of overexposure and contamination of sampling valve and drift tube may cause fatal ion mobility spectrometer failure. Our phthalocyanine thin film sensors can be used as low cost alternative for detection of 2-nitrotoluene.