Sensortehnoloogiate labori seminar
Sensors’ seminar will take place in Physicum, room D312, and in Zoom on Thursday, 8th of February at 11:15 (EET):
Martin Siebel
Technical University of Darmstadt
First principle simulation of gas adsorption on graphene / h-BN structures
Master's thesis defence presentation
Reviewers: Prof. Dr Hongbin Zhang and Assoc. Prof. Pavel Rubin
Abstract: This work made density functional theory calculations (using VASP code) for investigating the projected densities of states and adsorption energies of two different graphene / hexagonal boron nitride (h-BN) structures at the adsorption of NO2, NH3 and O3 gas molecules. This was done to investigate the gas-sensing capabilities of those structures. The super-cells of the investigated structures consisted of a base layer with 72 carbon atoms. The difference between the structures was the size of the top layer, which had either 36 boron and 36 nitrogen atoms or 11 boron and 11 nitrogen atoms. In addition, the size of both structures was increased by using periodic boundary conditions. The structures have been relaxed in the first step without the gas molecules and in the second step with all of the different gas molecules. The projected densities of states, Bader charges, and adsorption energies have been calculated.
The results show the theoretical possibility of detecting NO2 using both structures via a shift of graphene's Dirac point within the density of states analyses. In the case of O3, the detectability is given using the complete structure, while the gas dissociated on the reduced structure. In addition, the reduced structure shows promising results for detecting NH3, which acts as a charge acceptor.
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Varasemad
Anna Soosaar
Functionalization of CVD graphene by fs-laser treatment for gas sensing applications
(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.
Burak Baloglu
Graphene in blister-based LIFT
(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.
Dejan Prokop
Preparation of Black Titanium/Titanium Nitride Thin Films by Magnetron Sputtering
Faculty of Mathematics and Physics, Charles University, Prague
Institute of Physics of the Czech Academy of Sciences
Recently, black aluminium (B-Al) films proved to be very useful with their highly structured fractal-like porous surface morphology that is able to effectively trap the incident light. We also proposed some of the applications for it. Motivated by this, we tried to prepare another material – Black Titanium (B-Ti). Compared to aluminium, titanium-based materials are widely used because they possess a combination of useful mechanical, tribological, and chemical properties e.g. TiN has a high hardness, good wear, and corrosion resistance as well as thermal stability. By changing the argon to nitrogen ratio in our magnetron sputtering chamber we can modify the properties of our films. Furthermore, we are trying to implement optical emission spectroscopy to correlate the plasma parameters with resultant films. Even though we are still far from our desired goal, we were able to prepare the films and study the dependence of nitrogen content by optical diffuse reflectance/transmittance measurement and structural properties by X-ray diffraction.
Physical and Chemical Properties of Black Gold Layers
Jan Kejzlar
University of Chemistry and Technology, Prague
Institute of Physics of the Czech Academy of Sciences
This contribution is focused on material characterization of black gold layers compared to a bulk metal. As these layers represent novel approach for gas sensing, broad material characterization is in place. The black gold layer properties are compared to the bulk metal by a high variety of methods. The impact of the nanostructured surface is discussed from the perspective of morphology, crystallography, chemical composition, reflectivity and absorbance.
