Facultatea de Fizică şi Inginerie / Faculty of Physics and Engineering
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Item Portable electronic nodes for a sensor network [Articol](Editura USM, 2024) Maslova, Tatiana; Bîrnaz, Adrian; Lupan, OlegTo capitalize on the research on metal oxide-based sensors that is being intensively studied by our research team, there is a need to connect these sensors into devices capable of receiving, storing and, if necessary, transmitting measured data. We are also investigating the mechanics of sensor detection using chemistry and applied physics. To achieve this goal, there are some impediments that must be overcome, such as the method of data acquisition, the power consumed by the device, the stability over time with a subsequent correction, the distance to which measured data will be transmitted and others. Another aspect is the size and portability of these devices with built-in sensors. This paper presents some concepts that provide solutions to the problems presented. These devices are important for monitoring environmental parameters with application in agriculture, cellars, production halls. Another possible use is to incorporate them into drones, which will potentially increase their mobility and detection range.Item Composition and surface optical properties of GaSe: Eu crystals before and after heat treatment [Articol](2024) Sprincean, Veaceslav; Haoyi, Qiu; Tjardts, Tim; Lupan, Oleg; Untila, Dumitru; Aktas, Oral Cenk; Adelung, Rainer; Leontie, Liviu; Cârlescu, Aurelian; Gurlui, Silviu; Caraman, MihailThis work studies the technological preparation conditions, morphology, structural char- acteristics and elemental composition, and optical and photoluminescent properties of GaSe single crystals and Eu-doped β–Ga2O3 nanoformations on ε–GaSe:Eu single crystal substrate, obtained by heat treatment at 750–900 ◦C, with a duration from 30 min to 12 h, in water vapor-enriched atmosphere, of GaSe plates doped with 0.02–3.00 at. % Eu. The defects on the (0001) surface of GaSe:Eu plates serve as nucleation centers of β–Ga2O3:Eu crystallites. For 0.02 at. % Eu doping, the fundamental absorption edge of GaSe:Eu crystals at room temperature is formed by n = 1 direct excitons, while at 3.00 at. % doping, Eu completely shields the electron–hole bonds. The band gap of nanostructured β–Ga2O3:Eu layer, determined from diffuse reflectance spectra, depends on the dopant concentration and ranges from 4.64 eV to 4.87 eV, for 3.00 and 0.05 at. % doping, respectively. At 0.02 at. % doping level, the PL spectrum of ε–GaSe:Eu single crystals consists of the n = 1 exciton band, together with the impurity band with a maximum intensity at 800 nm. Fabry–Perrot cavities with a width of 9.3 μm are formed in these single crystals, which determine the interference structure of the impurity PL band. At 1.00–3.00 at. % Eu concentrations, the PL spectra of GaSe:Eu single crystals and β–Ga2O3:Eu nanowire/nanolamellae layers are determined by electronic transitions of Eu2+ and Eu3+ ions.Item Synthesis and properties of β-Ga2O3 nanowires and nanosheets on doped GaS:Mn substrates [Articol](2024) Sprincean, Veaceslav; Haoyi, Qiu; Lupan, Oleg; Tjardts, Tim; Petersen, Deik; Veziroglu, Salih; Adelung, Rainer; Caraman, MihailIn this work, the synthesis, morphology, optical and luminescence properties of Mn-doped β-Ga2O3 (Ga2O3:Mn) nanowires/nanosheets on Mn-doped GaS (GaS:Mn) substrate are studied. The aim was to obtain structures of semiconductors with layers of nanoformations (nanowires, nanosheets) from a wide energy band semiconductor such as β-Ga2O3 and to determine their characteristic properties. For the base material, Mn-doped GaS lamellae were chosen, which are optically transparent in the spectral region where the optical properties of Mn2+ and Mn3+ ions are manifested. Through thermal annealing, single-crystalline β-GaS plates doped with 1.3 atomic percent (at.%) of manganese (Mn) are exposed to an atmosphere enriched with H2O vapor at a temperature of 800 ◦C for 6 h. As a result, the surface of these plates is covered with a composite layer consisting of crystallites of α-Ga2S3:Mn and β-GaS:Mn planar junctions. This composite exhibits a direct band gap of 2.88 eV and an indirect band gap of 2.55 eV corresponding to the β-GaS:Mn crystallites. Upon further increasing the temperature during thermal annealing to 850 ◦ C and 920 ◦C, the surface of the β-GaS:Mn samples transform into a layer of β-Ga2O3: Mn nanowires/nanosheets with a band gap of 4.5 eV. Its intense green-orange photoluminescence is caused by electronic transitions within the Mn2+ ion.Item Preparation, chemical composition, and optical properties of (β–Ga2O3 composite thin films)/(GaSxSe1−x lamellar solid solutions) nanostructures [Articol](2023) Sprincean, Veaceslav; Leontie, Liviu; Caraman, Iuliana; Lupan, Oleg; Adeling, Rainer; Gurlui, Silviu; Cârlescu, Aurelian; Doroftei, Corneliu; Caraman, MihailGaSxSe1−x solid solutions are layered semiconductors with a band gap between 2.0 and 2.6 eV. Their single crystals are formed by planar packings of S/Se-Ga-Ga-S/Se type, with weak polarization bonds between them, which allows obtaining, by splitting, plan-parallel lamellae with atomically smooth surfaces. By heat treatment in a normal or water vapor-enriched atmosphere, their plates are covered with a layer consisting of β–Ga2O3 nanowires/nanoribbons. In this work, the elemental and chemical composition, surface morphology, as well as optical, photoluminescent, and photoelectric properties of β–Ga2O3 layer formed on GaSxSe1−x (0 ≤ x ≤ 1) solid solutions (as substrate) are studied. The correlation is made between the composition (x) of the primary material, technological preparation conditions of the oxide-semiconducting layer, and the optical, photoelectric, and photoluminescent properties of β–Ga2O3 (nanosized layers)/GaSxSe1−x structures. From the analysis of the fundamental absorption edge, photoluminescence, and photoconductivity, the character of the optical transitions and the optical band gap in the range of 4.5–4.8 eV were determined, as well as the mechanisms behind blue-green photoluminescence and photoconduc- tivity in the fundamental absorption band region. The photoluminescence bands in the blue-green region are characteristic of β–Ga2O3 nanowires/nanolamellae structures. The photoconductivity of β–Ga2O3 structures on GaSxSe1−x solid solution substrate is determined by their strong fundamental absorption. As synthesized structures hold promise for potential applications in UV receivers, UV-C sources, gas sensors, as well as photocatalytic decomposition of water and organic pollutants.