Neljapäeval, 1. juunil kell 11:15 toimub ruumis D312 Sensortehnoloogiate labori seminar:
Sensors’ seminar will take place in room D312 on Thursday, 1st of June at 11:15:
(materials of BSc thesis, 10 min)
Graphene and related 2D materials can be used to construct very sensitive gas sensors. In order to achieve high selectivity for detecting different gases, it is necessary to functionalize these materials. In this work, the functionalization is carried out by femtosecond laser treatment. A new fs-laser treatment set-up at the Institute of Physics was tested, and different laser-processed chemiresistive gas sensor chips were studied. The analysis by Raman spectroscopy revealed that the laser-induced defects were created by a two-photon mechanism. The sensitivity of laser-treated sensor chips made on Si/SiO2 substrates increased up to 10 times to 150 ppb of NO2 gas exposure in the air.
(materials of MSc thesis, 15 min)
Laser-induced forward transfer (LIFT) can provide a clean (non-contact and solvent-free) technique for the high-resolution printing of two-dimensional materials, a significant technological step for their integration into microdevices. The blister-based (BB) version of LIFT allows the transfer of ultra-thin layers without damaging the materials on the receiving substrate with intense laser light. This work investigated single-layer graphene in different roles as a donor, acceptor and release material in BB-LIFT. The transfer of graphene and ultrathin oxide (ZrO2) layers was confirmed and characterised through optical microscopy, Raman spectroscopy and scanning electron microscopy (SEM). The crucial role of the graphene interlayer in ZrO2 transfer was revealed. The immediate motivation for the work was the improvement of graphene-based gas sensors by transferring ultrathin oxides as gas sensor receptor layers on the CVD graphene as a transducer layer. It was found that the sensitivity of sensors to trace level NO2 gas did not practically increase after BB-LIFT of ultrathin (0.5-50 nm) ZrO2 layers. This was interpreted as a lack of strong interactions of the transferred oxide flakes (and a small contact area) with the graphene layer of the sensor substrate. In order to increase the interaction, the sensors were annealed at a higher temperature (up to 500 ℃ in a vacuum), which significantly accelerated the gas response. The work highlights the finding that the oxide layer can be transferred only when graphene is inserted between the blister and oxide layers. This is a novel application for graphene, considerably widening the scope of materials transferable by BB-LIFT.