Alcalde Bessia, F., D. Flandre, N. André, J. Irazoqui, M. Pérez, M. Gómez Berisso, and J. Lipovetzky. "Fully-Depleted SOI MOSFET Sensors in Accumulation Mode for Total Dose Measurement." In 2018 IEEE Nuclear Science Symposium and Medical Imaging Conference Proceedings (NSS/MIC), 1–3. 2018 IEEE Nuclear Science Symposium and Medical Imaging Conference Proceedings (NSS/MIC)., 2018.
Abstract: Fully Depleted Silicon-on-Insulator (FD-SOI) transistors fabricated with a custom process in Université Catholique de Louvain (UCL) were irradiated with X-rays using an Elekta Synergy radiotherapy linear accelerator. I-V curves of FD-SOI are sensitive to charges produced in the buried oxide (BOX) by ionizing radiation, so it is possible to use these devices as radiation dosimeters. In this work, we evaluated the use of thick BOX back-gate transistors for Total Ionizing Dose (TID) measurement using different bias conditions and we obtained a maximum sensitivity of 191 mV/Gy for devices operating in accumulation mode.
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Alcalde Bessia, F., M. Pérez, M. Sofo Haro, I. Sidelnik, J. J. Blostein, S. Suárez, P. Pérez, M. Gómez Berisso, and J. Lipovetzky. "Displacement Damage in CMOS Image Sensors After Thermal Neutron Irradiation." IEEE Transactions on Nuclear Science 65, no. 11 (2018): 2793–2801.
Abstract: In this paper, CMOS image sensors were exposed to thermal neutrons observing an increase in the dark signal of many pixels. The effect was found to be similar to the damage caused by alpha particles irradiation. Rutherford backscattering spectroscopy (RBS) and SIMNRA simulation were used to confirm that the sensors contain boron in the insulation layers. The damage produced by thermal neutrons is explained as displacement damage caused by alpha particles and lithium-7 ions in the silicon active volume of the sensors after boron-10 thermal neutron capture.
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ÄŒurlík, I., M. Giovannini, F. Gastaldo, A. M. Strydom, M. Reiffers, and J. G. Sereni. "Crystal structure and physical properties of the two stannides EuPdSn2 and YbPdSn2." Journal of Physics: Condensed Matter 30, no. 49 (2018): 495802.
Abstract: We report on synthesis, crystal structure and physical properties of the isotypic compounds YbPdSn2 and EuPdSn2 crystallizing in the MgCuAl2-type structure. In both stannides a divalent state of respective rare earth element was found from analysis of the magnetic susceptibilities. Whereas in YbPdSn2 only weak paramagnetic behaviour is observed, in EuPdSn2 a long-range magnetic phase transition occurs at 12.5 K with complex magnetic behaviour evidenced by magnetic susceptibity and specific heat measurements. Under the influence of magnetic field, the magnetic behaviour was found to evolve from an antiferromagnetic to a ferromagnetic state as a consequence of a re-arrangement of magnetic moments.
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Bridoux, G., M. Villafuerte, J. M. Ferreyra, J. Guimpel, G. Nieva, C. A. Figueroa, B. Straube, and S. P. Heluani. "Franz-Keldysh effect in epitaxial ZnO thin films." Applied Physics Letters 112, no. 9 (2018).
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Carreras Oropesa, W. G., V. F. Correa, J. G. Sereni, D. J. García, and P. S. Cornaglia. "Landau theory for magnetic and structural transitions in CeCo0.85Fe0.15Si." Journal of Physics: Condensed Matter 30 (2018): 295803.
Abstract: We present a phenomenological analysis of the magnetoelastic properties of CeCo0.85Fe0.15Si
at temperatures close to the Néel transition temperature TN. Using a Landau functional we
provide a qualitative description of the thermal expansion, magnetostriction, magnetization
and specific heat data. We show that the available experimental results (Correa et al 2016 J.
Phys.: Condens. Matter 28 346003) are consistent with the presence of a structural transition
at Ts TN and a strong magnetoelastic coupling. The magnetoelastic coupling presents a
Janus-faced effect: while the structural transition is shifted to higher temperatures as the
magnetic field is increased, the resulting striction at low temperatures decreases. The strong
magnetoelastic coupling and the proximity of the structural transition to the onset temperature
for magnetic fluctuations, suggest that the transition could be an analogue of the tetragonal to
orthorhombic observed in Fe-based pcnictides.
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del Corro, P. G., M. Imboden, D. J. Pérez, D. J. Bishop, and H. Pastoriza. "Single ended capacitive self-sensing system for comb drives driven XY nanopositioners." Sensors and Actuators A: Physical 271 (2018): 409–417.
Abstract: This paper presents the implementation of a system to capacitively self-sense the position of a comb drive based MEMS XY nanopositioner from a single common node. The nanopositioner was fabricated using the multi-users PolyMUMPs process, on which comb capacitors fringe fields are large and out of plane forces cause considerable deflection. An extensive analysis of the comb-drive capacitance including the levitation effects and its correlation to the measurements is presented. Each axis is independently measured using frequency division multiplexing (FDM) techniques. Taking advantage of the symmetry of the nanopositioner itself, the sensitivity is doubled while eliminating the intrinsic capacitance of the device. The electrical measured noise is 2.5aF/Hz, for a sensing voltage Vsen=3Vrms and fsen=150kHz, which is equivalent to 1.1nm/Hz lateral displacement noise. This scheme can also be extended to N-degree of freedom nanopositioners.
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Encina, S., P. Pedrazzini, J. G. Sereni, and C. Geibel. "Low temperature thermopower and magnetoresistance of Sc-rich CeSc1-xTixGe." Physica B: Condensed Matter 536 (2018): 133–136.
Abstract: In CeSc1-xTixGe, Ti-alloying reduces the record-high antiferromagnetic (AFM) ordering temperature found in CeScGe at TN=46K and induces ferromagnetism for x≥0.5. In this work we focus on the AFM side, i.e. Sc-rich samples, and study their thermopower S(T) and magnetoresistance Ï(H,T). The measured S(T) is small in comparison with the thermopower of other Ce-systems and shows some features that are compatible with a weak hybridization between the 4f and band states. This is a further hint pointing to the local character of magnetism in this alloy. Magnetic fields up to 16T have a minor effect on the electrical resistivity of stoichiometric CeScGe. On the other hand, for x=0.65, we find that fields above 4T suppress the hump in Ï(T). Furthermore, the 4.2K magnetoresistance displays a strong decrease in the same field range, also in coincidence with magnetization results from the literature. Our results indicate that Ï(T,H) is a proper tool to assess the H−T phase diagram of this system.
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Fasano, Y., P. Szabó, J. KaÄmarÄík, Z. Pribulová, P. Pedrazzini, P. Samuely, and V. F. Correa. "Unconventional superconductivity in the strong-coupling limit for the heavy fermion system CeCoIn5." Physica B: Condensed Matter 536 (2018): 798–802.
Abstract: We present scanning tunneling spectroscopy measurements of the local quasiparticles' excitation spectra of the heavy fermion CeCoIn5 between 440mK and 3K in samples with a bulk Tc=2.25K. The spectral shape of our low-temperature tunneling data, quite textbook nodal-Δ conductance, allow us to confidently fit the spectra with a d-wave density of states considering also a shortening of quasiparticles' lifetime term Γ. The Δ(0) value obtained from the fits yields a BCS ratio 2Δ/kTc=7.73 suggesting that CeCoIn5 is an unconventional superconductor in the strong coupling limit. The fits also reveal that the height of coherence peaks in CeCoIn5 is reduced with respect to a pure BCS spectra and therefore the coupling of quasiparticles with spin excitations should play a relevant role. The tunneling conductance shows a depletion at energies smaller than Δ for temperatures larger than the bulk Tc, giving further support to the existence of a pseudogap phase that in our samples span up to T*∼1.2Tc. The phenomenological scaling of the pseudogap temperature observed in various families of cuprates, 2Δ/kT*∼4.3, is not fulfilled in our measurements. This suggests that in CeCoIn5 the strong magnetic fluctuations might conspire to close the local superconducting gap at a smaller pesudogap temperature-scale than in cuprates.
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Galimberti, C. L., F. Alcalde Bessia, M. Perez, M. Gómez Berisso, M. Sofo Haro, I. Sidelnik, J. J. Blostein, H. Asorey, and J. Lipovetzky. "A Low Cost Environmental Ionizing Radiation Detector Based on COTS CMOS Image Sensors." In 2018 IEEE Biennial Congress of Argentina (ARGENCON), 1–6. 2018 IEEE Biennial Congress of Argentina (ARGENCON)., 2018.
Abstract: We present the development of a system for the detection of ionizing radiation based on the Omnivision OV5647 Commercial Off The Shelf image sensor. The data is read and processed in real-time using a Raspberry Pi 3 computer. The amount of charge and geometrical characteristics of the cluster of pixels exited when a particle interacts with the sensor is recorded and used to identify the type of incoming particle, distinguishing between alpha particles and X-ray or gamma photons. The software was programmed in C using the OpenCV library. The system was tested with 137Cs and 241Am radiation sources.
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Haberkorn, N., S. Bengio, S. Suárez, P. D. Pérez, M. Sirena, and J. Guimpel. "Effect of the nitrogen-argon gas mixtures on the superconductivity properties of reactively sputtered molybdenum nitride thin films." Materials Letters 215 (2018): 15–18.
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Haberkorn, N., S. Bengio, H. Troiani, S. Suárez, P. D. Pérez, P. Granell, F. Golmar, M. Sirena, and J. Guimpel. "Thickness dependence of the superconducting properties of γ- Mo<inf>2</inf>N thin films on Si (001) grown by DC sputtering at room temperature." Materials Chemistry and Physics 204 (2018): 48–57.
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Martinelli, A., M. Giovannini, J. G. Sereni, and C. Ritter. "Suppression of ferromagnetic order by Ag-doping: a neutron scattering investigation on Ce2(Pd1−x Ag x )2In (x  =  0.20, 0.50)." Journal of Physics: Condensed Matter 30, no. 26 (2018): 265601.
Abstract: The ground state magnetic behaviour of Ce2(Pd0.8Ag0.2)2In and Ce2(Pd0.5Ag0.5)2In, found in the ferromagnetic branch of Ce2Pd2In, has been investigated by neutron powder diffraction at low temperature. Ce2(Pd0.8Ag0.2)2In is characterized by a ferromagnetic structure with the Ce moments aligned along the c-axis and values of 0.96(2) µB. The compound retains the P4/mbm throughout the magnetic transition, although the magnetic ordering is accompanied by a significant decrease of the lattice strain along [0 0 l], suggesting a magnetostructural contribution. The magnetic behaviour of Ce2(Pd0.5Ag0.5)2In is very different; this compound exhibits an extremely reduced magnetic scattering contribution in the diffraction pattern, that can be ascribed to a different kind of ferromagnetic ordering, with extremely reduced magnetic moments (~0.1 µ
B) aligned along [0 l 0]. These results point to a competition between different types of magnetic correlations induced by Ag-substitution, giving rise to a magnetically frustrated scenario in Ce2(Pd0.5Ag0.5)2In.
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N. Haberkorn, S. Bengio, H. Troiani, S. Suárez, P. D. Pérez, M. Sirena, J. Guimpel. "Synthesis of nanocrystalline delta-MoN by thermal annealing of amorphous thins films grown on (100) Si by reactive DC sputtering at room temperature." Thin Solid Films 660 (2018): 242–246.
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N. Haberkorn, Silu Huang, R. Jin. "Anomalous reduction in the long-time flux creep relaxation in superconducting Ca10(Pt4As8)((Fe1−xPtx)2As2)5 (x = 0.05) single crystals." Supercond. Sci. Technol. 31 (2018): 065010.
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Navarro, H., M. Sirena, J. González Sutter, H. E. Troiani, P. G. del Corro, P. Granell, F. Golmar, and N. Haberkorn. "Electrical transport across nanometric SrTiO3 and BaTiO3 barriers in conducting/insulator/conducting junctions." Materials Research Express 5, no. 1 (2018): 016408.
Abstract: We report the electrical transport properties of conducting/insulator/conducting heterostructures by studying current–voltage IV curves at room temperature. The measurements were obtained on tunnel junctions with different areas (900, 400 and 100 μ m 2 ) using a conducting atomic force microscope. Trilayers with GdBa 2 Cu 3 O 7 (GBCO) as the bottom electrode, SrTiO 3 or BaTiO 3 (thicknesses between 1.6 and 4 nm) as the insulator barrier, and GBCO or Nb as the top electrode were grown by DC sputtering on (100) SrTiO 3 substrates For SrTiO 3 and BaTiO 3 barriers, asymmetric IV curves at positive and negative polarization can be obtained using electrodes with different work function. In addition, hysteretic IV curves are obtained for BaTiO 3 barriers, which can be ascribed to a combined effect of the FE reversal switching polarization and an oxygen vacancy migration. For GBCO/BaTiO 3 /GBCO heterostructures, the IV curves correspond to that expected for asymmetric interfaces, which indicates that the disorder affects differently the properties at the bottom and top interfaces. Our results show the role of the interface disorder on the electrical transport of conducting/insulator/conduction heterostructures, which is relevant for different applications, going from resistive switching memories (at room temperature) to Josephson junctions (at low temperatures).
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Pérez, M., J. J. Blostein, F. A. Bessia, A. Tartaglione, I. Sidelnik, M. S. Haro, S. Suárez, M. L. Gimenez, M. G. Berisso, and J. Lipovetzky. "Thermal neutron detector based on COTS CMOS imagers and a conversion layer containing Gadolinium." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 893 (2018): 157–163.
Abstract: In this work we will introduce a novel low cost position sensitive thermal neutron detection technique, based on a Commercial Off The Shelf CMOS image sensor covered with a Gadolinium containing conversion layer. The feasibility of the neutron detection technique implemented in this work has been experimentally demonstrated. A thermal neutron detection efficiency of 11.3% has been experimentally obtained with a conversion layer of 11.6 μm. It was experimentally verified that the thermal neutron detection efficiency of this technique is independent on the intensity of the incident thermal neutron flux, which was confirmed for conversion layers of different thicknesses. Based on the experimental results, a spatial resolution better than 25 μm is expected. This spatial resolution makes the proposed technique specially useful for neutron beam characterization, neutron beam dosimetry, high resolution neutron imaging, and several neutron scattering techniques.
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Sereni, J. G. "Role of entropy in the ground state formation of frustrated systems." Physica B: Condensed Matter 536 (2018): 397–400.
Abstract: The absence of magnetic order in Rare Earth-based frustrated compounds allows to recognize the action of the third law of thermodynamics in the low temperature behavior of those systems. One of the most relevant findings is the appearance of a coincident specific heat Cm/T|T→0≈7J/molK2 ‘plateau’ in six Yb systems. This characteristic feature occurs after a systematic modification of the thermal trajectory of their entropies Sm(T) in the range of a few hundred milikelvin degrees. Such behavior is explained by the formation of an entropy-bottleneck imposed by the third law constraint (Sm|T→0≥0), that drives the system into alternative ground states. Based in these finding, three possible approaches to the Sm|T→0 limit observed in real systems are analyzed in terms of the ∂2Sm/∂T2 dependencies.
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Sereni, J. G., I. ÄŒurlík, M. Giovannini, A. Strydom, and M. Reiffers. "Physical properties of the magnetically frustrated very-heavy-fermion compound YbCu4Ni." Physical Review B 98, no. 9 (2018): 094420.
Abstract: The physical properties of the very-heavy-fermion compound YbCu4Ni were characterized through structural, magnetic, thermal, and transport studies along nearly four decades of temperature ranging between 50 mK and 300 K. At high temperature, the crystal electric field level splitting was determined with Δ1(Γ6)=85K and Δ2(Γ8)≈200K, the latter being a quartet in this cubic symmetry. An effective magnetic moment μeff≈3μB is evaluated for the Γ7 ground state, while at high temperature the value for a Yb3+ ion is observed. At low temperature this compound shows the typical behavior of a magnetically frustrated system undergoing a change of regime at a characteristic temperature T∗≈200mK into of Fermi-liquid-type “plateau†of the specific heat: Cm/T|T→0 = const. The change in the temperature dependence of the specific heat coincides with a maximum and a discontinuity in respective inductive and dissipative components of the ac susceptibility. More details about the nature of this ground state are revealed by the specific heat behavior under applied magnetic field.
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