Submicron-thick films of graphene oxide and polyvinyl alcohol (PVA) were deposited onto the surface of 160 MHz quartz surface acoustic wave (SAW) delay lines, and manufactured devices were used as humidity sensors. Films were obtained by consecutive atomization of 0.35 μl droplets of 0.33 mg/ml graphene oxide water suspension or 5.00 mg/ml PVA water solution using 25 MHz SAW atomizers. During measurements authors did not observe additional attenuation of the surface acoustic wave propagating along the surface of the sensors, which confirms that deposited films have low thickness and good uniformity. It was shown that SAW quartz humidity sensors with graphene oxide films, PVA thin films and uncoated surface have sensitivity of 1.54 kHz/%RH, 0.47 kHz/%RH and 0.13 kHz/%RH respectively. Sensors with graphene oxide thin films showed the best sensitivity and dynamic response. It was concluded that they can be used as sensitive coatings in humidity sensors for industrial environment.
a b s t r a c tSymmetric surface acoustic wave (SAW) atomizer was used to deposit graphene oxide (GO) nanofilms from microdroplets of the aqueous GO dispersion onto the surface of the SAW humidity sensors. The sensors with the deposited GO films were tested in a wide range of relative humidity and showed the amplitude of the response in the range of 1-40 kHz sufficient for the majority of applications. The kinetics of the adsorption of water molecules was modeled using the assumption that two independent first order adsorption processes take place. Saturation amplitudes and rate coefficients for both processes were experimentally evaluated using LSQ fitting of the sensor response in the time domain for the films obtained by different number of depositions. The mechanism of the adsorption of water molecules to the GO flakes is proposed and discussed.
Thin MWCNTs films were obtained by deposition of the atomized single droplet of a suspension of MWCNTs in N-Methylpyrrolidone (NMP) on the silicon substrate. Symmetric focused surface acoustic wave (SAW) atomizers with focal line and focal point were used to atomize the droplet. Atomizers were fabricated on 128 o YXcut of LiNbO 3 . Atomization frequency was 27.4 MHz. Their effectiveness was experimentally estimated and it was found that the atomizers with focal point have the maximum atomization effectiveness. It was experimentally shown that the film thickness is proportional to the number of single droplet atomizations. Using the developed method, we deposited thin uniform MWCNTs films through the small window on the substrate surface, covering an area of just a few square millimeters. This technique can be used in digital chemistry applications, where microliter volumes of reacting substances are used, and for fabrication of nanomaterial-based sensitive films for SAW sensors.
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