@article{MTMT:34786414, title = {Road Type Classification Using Time-Frequency Representations of Tire Sensor Signals}, url = {https://m2.mtmt.hu/api/publication/34786414}, author = {Dózsa, Tamás and Jurdana, V and Segota, S B and Volk, János and Radó, János and Soumelidis, Alexandros and Kovács, Péter}, doi = {10.1109/ACCESS.2024.3382931}, journal-iso = {IEEE ACCESS}, journal = {IEEE ACCESS}, unique-id = {34786414}, issn = {2169-3536}, year = {2024}, eissn = {2169-3536}, pages = {1-11}, orcid-numbers = {Volk, János/0000-0003-3633-6190; Soumelidis, Alexandros/0000-0002-0067-7746; Kovács, Péter/0000-0002-0772-9721} } @article{MTMT:34196964, title = {Effect of process parameters on co-sputtered Al(1-x)ScxN layer's properties: Morphology, crystal structure, strain, band gap, and piezoelectricity}, url = {https://m2.mtmt.hu/api/publication/34196964}, author = {Nguyen Quoc, Khánh and Horváth, Zsolt Endre and Zolnai, Zsolt and Petrik, Péter and Pósa, László and Volk, János}, doi = {10.1016/j.mssp.2023.107902}, journal-iso = {MAT SCI SEMICON PROC}, journal = {MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING}, volume = {169}, unique-id = {34196964}, issn = {1369-8001}, abstract = {The effect of pulse direct current (DC) reactive ion co-sputtering parameters on the morphology, crystal structure, residual stress, band gap, and piezoelectric properties of the Al(1-x)ScxN thin film deposited in large target-to-substrate distance (TSD) system has been studied using Scanning Probe Microscopy, X ray Diffractometry, Spectroscopic Ellipsometry, and profilometer, among others. The process pressure was revealed to be the key factor which essentially determines the quality of the film for such system. As low as 0.2 Pa working pressure is needed to achieve smooth nitride layer with good piezoelectric properties. High N2/(Ar + N2) gas ratio also was shown to result in better film properties. Residual stress in nitride film, and thereby the optical band gap can be tuned by variation of process pressure, gas ratio, and Sc fraction in the studied x range (0–0.5). The Al(1-x)ScxN film deposited at low pressure, medium N2 gas ratio with x ∼ 0.41 shows high piezoelectric coefficient, relatively low residual stress, and smooth surface. Top electrode has been applied to eliminate the interfering effect of the restraining force induced by the unexcited matrix materials around tip/sample contact for Piezoresponse Force Microscopic (PFM) measurement of piezoelectric constant of thin nitride film. We have shown by comparing the corrected d33corr data determined with PFM to those obtained from direct piezoelectric method that PFM using proper measurement conditions and correction can be applied as a quantitative method for study of piezoelectric properties of thin film.}, year = {2024}, eissn = {1873-4081}, orcid-numbers = {Nguyen Quoc, Khánh/0000-0001-7032-2919; Horváth, Zsolt Endre/0000-0002-4632-0136; Zolnai, Zsolt/0000-0003-3457-7679; Petrik, Péter/0000-0002-5374-6952; Volk, János/0000-0003-3633-6190} } @article{MTMT:33836337, title = {Novel manufacturing method for highly flexible poly(lactic acid) foams and ferroelectrets}, url = {https://m2.mtmt.hu/api/publication/33836337}, author = {Vadas, Dániel and Bordácsné Bocz, Katalin and Igricz, Tamás and Volk, János and Bordács, Sándor and Madarász, Lajos and Marosi, György}, doi = {10.1016/j.aiepr.2023.03.005}, journal-iso = {ADV INDUST ENGIN POLYMER RES}, journal = {ADVANCED INDUSTRIAL AND ENGINEERING POLYMER RESEARCH}, unique-id = {33836337}, issn = {2542-5048}, abstract = {Poly (lactic acid) (PLA) foams have demonstrated a high variety of functional characteristics, still, the rigidity of this cellular material remains a major limiting factor when it comes to implementation options. In this contribution, PLA foams with outstanding flexibility were created for the first time by a new approach of uniaxial stretching and immediate relaxation following supercritical CO2-assisted extrusion foaming. Instead of improving the resilience of the PLA raw material, structural elasticity of the foam was achieved via altering the deformation mechanism from cell wall collapse or rupture towards reversible and extensive flexural strain. In addition, PLA foams with excellent piezoelectric properties were also achieved via high-voltage corona poling, giving additional function to the lens-like anisotropic foam cells. This foaming technology creates the opportunity to produce PLA piezoelectrets in a way entirely different from the state-of-the-art methods. Correlation between the tensile as well as compression elongations and moduli, cell morphology and longitudinal piezoelectric coefficients (d33) of electretized foam samples were studied. Unprecedented reversible tensile elongations of up to 16% and total elongations of up to 35% were reached, as well as considerable d33 values in the range of 50–320 pC/N were obtained for PLA ferroelectrets.}, year = {2024}, orcid-numbers = {Volk, János/0000-0003-3633-6190; Bordács, Sándor/0000-0003-0420-5997; Marosi, György/0000-0002-4774-2023} } @misc{MTMT:34472720, title = {Tire Deformation Monitoring Sensor for Advanced Driver-Assistance Systems}, url = {https://m2.mtmt.hu/api/publication/34472720}, author = {Bársony, István and Dózsa, Tamás and Radó, János and Nagy, Attila and Braun, Ferenc and Simonyi, Ernő and Battistig, Gábor and Soumelidis, Alexandros and Kovács, Péter and Volk, János}, unique-id = {34472720}, year = {2023}, orcid-numbers = {Bársony, István/0000-0002-3469-9468; Battistig, Gábor/0000-0003-2445-857X; Volk, János/0000-0003-3633-6190} } @inproceedings{MTMT:34145789, title = {Towards intelligent tire development}, url = {https://m2.mtmt.hu/api/publication/34145789}, author = {Dózsa, Tamás and Ámon, Attila and Braun, Ferenc and Simonyi, Ernő and Soumelidis, Alexandros and Volk, János and Kovács, Péter}, booktitle = {XIII. International Conference on Transport Sciences / XIII. Nemzetközi Közlekedéstudományi Konferencia, Győr}, unique-id = {34145789}, year = {2023}, pages = {145-155}, orcid-numbers = {Soumelidis, Alexandros/0000-0002-0067-7746; Volk, János/0000-0003-3633-6190; Kovács, Péter/0000-0002-0772-9721} } @article{MTMT:34053613, title = {Atomic structure and annealing-induced reordering of ε-Ga2O3: a Rutherford Backscattering/Channeling and Spectroscopic Ellipsometry study}, url = {https://m2.mtmt.hu/api/publication/34053613}, author = {Zolnai, Zsolt and Petrik, Péter and Németh, Attila and Volk, János and Bosi, M and Seravalli, L and Fornari, R}, doi = {10.1016/j.apsusc.2023.157869}, journal-iso = {APPL SURF SCI}, journal = {APPLIED SURFACE SCIENCE}, volume = {636}, unique-id = {34053613}, issn = {0169-4332}, abstract = {The crystallographic structure of thin Ga2O3 layers grown by metal-organic vapour phase epitaxy on Al2O3 substrate was analyzed by Rutherford Backscattering Spectrometry/Channeling (RBS/C) angular yield scans performed around the c-axis of as-grown Ga2O3. The measured widths and minimum yields of the scan curves for the Ga and O component were compared to calculations based on the continuum steering potential model. The results obtained are consistent with a crystal structure containing oxygen atoms arranged in a 4H hexagonal closely packed lattice and Ga atoms preferentially occupying octahedral interstitial sites in the 4H cells - a structure closely related to the epsilon-Ga2O3 polymorph. After high-temperature annealing remarkable structural transformation is detected via significant changes in the RBS/C spectra. This effect is related to the hexagonal-monoclinic, i.e., epsilon-beta phase transformation of Ga2O3. Spectroscopic ellipsometry spectra of as-grown and annealed samples can be best fitted using a vertically graded single-layer B-spline model. Significant differences in the dielectric functions were found, showing bandgap reduction for long term annealing. These features are related to the epsilon-beta polymorphic transformation, variation of the preferred crystallographic orientation upon annealing, and differences in residual strain and defect structure determined by the annealing conditions.}, year = {2023}, eissn = {1873-5584}, orcid-numbers = {Zolnai, Zsolt/0000-0003-3457-7679; Petrik, Péter/0000-0002-5374-6952; Volk, János/0000-0003-3633-6190} } @article{MTMT:33879666, title = {Interplay of Thermal and Electronic Effects in the Mott Transition of Nanosized VO2 Phase Change Memory Devices}, url = {https://m2.mtmt.hu/api/publication/33879666}, author = {Pósa, László and Hornung, Péter and Török, Tímea Nóra and Schmid, Sebastian Werner and Arjmandabasi, Sadaf and Molnár, György and Baji, Zsófia and Dražić, Goran and Halbritter, András Ernő and Volk, János}, doi = {10.1021/acsanm.3c00150}, journal-iso = {ACS APPL NANO MATER}, journal = {ACS APPLIED NANO MATERIALS}, volume = {6}, unique-id = {33879666}, abstract = {Volatile memory devices relying on the Mott-type insulator-to-metaltransition of vanadium oxide (VO2) are widely utilizedin the field of neuromorphic computing. Such devices, however, arerealized in a nanoscale geometry, where the switching relies on theself-heating of an ultrasmall spot as well as the presence of extremelyhigh electric fields in the active region. In this paper, we investigatethe interplay of such nanoscale thermal and nonlinear electronic phenomenaby investigating the temperature and voltage dependent conductionproperties of our custom-designed VO2 devices, where aV-shaped electrode focuses the switching to an ultrasmall single-spotactive region. This simplified spatial structure of the active volumefacilitates the device modeling and the identification of physicalmechanisms behind the phase transition. We find that purely thermalor electronic effects fail to describe the device operation, however,according to our finite element simulations, a combined electronicand thermal model provides a precise description of the device characteristics.These results facilitate the understanding as well as the thermaland electronic design of novel VO2-based neuronal devices.}, year = {2023}, eissn = {2574-0970}, pages = {9137-9147}, orcid-numbers = {Molnár, György/0000-0002-4792-5516; Baji, Zsófia/0000-0001-5051-3128; Halbritter, András Ernő/0000-0003-4837-9745; Volk, János/0000-0003-3633-6190} } @article{MTMT:33836342, title = {AlGaN/GaN heterostructure based 3-dimensional force sensors}, url = {https://m2.mtmt.hu/api/publication/33836342}, author = {Neumann, Péter Lajos and Radó, János and Bozorádi, János Márk and Volk, János}, doi = {10.1016/j.mne.2023.100198}, journal-iso = {MICRO NANO ENG}, journal = {MICRO AND NANO ENGINEERING}, volume = {19}, unique-id = {33836342}, abstract = {Tactile sensing is an essential physical-electrical gateway in sensing technology. Creating such sensors is a complex challenge if the goal is to reproduce human-like sensation. Classical MEMS tactile sensor solutions in typical environmental conditions exist few types, but harsh conditions such as space technology or high-temperature range are not solved yet. One proposed material complex is the GaN/AlGaN system. In this study, we present an AlGaN/GaN MEMS force sensor for external force and load direction sensing in the mN range. The demonstrated sensor showed a sensitivity of 100 mV/N/V, which is an order of magnitude higher than the Si-based sensor with the same geometry. The sensing mechanism is based on the interface discontinuity between compound alloy layers, where two-dimensional electron gas (2DEG) is created and in which the carrier concentration can be linearly modulated by the internal crystal stress. The location of the sensing element was optimized by FEM simulation. The maximum load force of the samples varies with direction, which information allows the sensor to be used without fatigue and to obtain safety an electrical response signal under different external tensions. In addition to the advantage of this design for harsh environments, it is also possible to monolithically integrate active elements adjacent to the sensor for local acquisition and processing of the measured signal.}, keywords = {MEMS; Extreme environment; tactile sensing; 2DEG; 3D force sensor; Strain transduction; High-temperature sensor}, year = {2023}, eissn = {2590-0072}, orcid-numbers = {Neumann, Péter Lajos/0000-0002-2881-5733; Volk, János/0000-0003-3633-6190} } @article{MTMT:33836334, title = {VO2 layers with high resistive switching ratio by atomic layer deposition}, url = {https://m2.mtmt.hu/api/publication/33836334}, author = {Baji, Zsófia and Pósa, László and Molnár, György and Szabó, Zoltán and Volom, M. and Surca, A.K. and Drazic, G. and Volk, János}, doi = {10.1016/j.mssp.2023.107483}, journal-iso = {MAT SCI SEMICON PROC}, journal = {MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING}, volume = {162}, unique-id = {33836334}, issn = {1369-8001}, abstract = {The present work explores the atomic layer deposition (ALD) of VO2 layers for resistive switching applications. Tetrakis (ethylmethylamino)vanadium (TEMAV) precursor was used combined with different oxidants, deposition temperatures, and annealing procedures, and the structural and electrical properties of the layers were analysed. All the as-deposited layers were amorphous, but an annealing in oxygen containing atmosphere at temperatures exceeding 400 degrees C yielded pure and crystalline VO2 layers. The thus prepared films are compact with crystallite sizes between 50 and 100 nm, displaying excellent electrical switching properties, with their resistivity decreasing 3 orders of magnitude at 68 degrees C.}, year = {2023}, eissn = {1873-4081}, orcid-numbers = {Baji, Zsófia/0000-0001-5051-3128; Molnár, György/0000-0002-4792-5516; Szabó, Zoltán/0000-0002-2150-1459; Volk, János/0000-0003-3633-6190} } @article{MTMT:33267730, title = {Mechanical Characterization of Two-Segment Free-Standing ZnO Nanowires Using Lateral Force Microscopy}, url = {https://m2.mtmt.hu/api/publication/33267730}, author = {Volk, János and Radó, János and Baji, Zsófia and Erdélyi, Róbert}, doi = {10.3390/nano12234120}, journal-iso = {NANOMATERIALS-BASEL}, journal = {NANOMATERIALS}, volume = {12}, unique-id = {33267730}, abstract = {Mechanical characterization of quasi one-dimensional nanostructures is essential for the design of novel nanoelectromechanical systems. However, the results obtained on basic mechanical quantities, such as Young’s modulus and fracture strength, show significant standard deviation in the literature. This is partly because of diversity in the quality of the nanowire, and partly because of inappropriately performed mechanical tests and simplified mechanical models. Here we present orientation-controlled bending and fracture studies on wet chemically grown vertical ZnO nanowires, using lateral force microscopy. The lateral force signal of the atomic force microscope was calibrated by a diamagnetic levitation spring system. By acquiring the bending curves of 14 nanowires, and applying a two-segment mechanical model, an average bending modulus of 108 ± 17 GPa was obtained, which was 23% lower than the Young’s modulus of bulk ZnO in the [0001] direction. It was also found that the average fracture strain and stress inside the nanowire was above 3.1 ± 0.3 % and 3.3 ± 0.3 GPa, respectively. However, the fracture of the nanowires was governed by the quality of the nanowire/substrate interface. The demonstrated technique is a relatively simple and productive way for the accurate mechanical characterization of vertical nanowire arrays.}, year = {2022}, eissn = {2079-4991}, orcid-numbers = {Volk, János/0000-0003-3633-6190; Baji, Zsófia/0000-0001-5051-3128; Erdélyi, Róbert/0000-0003-0202-4084} }