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Ethanol sensing properties and reduced sensor resistance using porous Nb2O5-TiO2 n-n junction nanofibers
摘要： One-dimensional (1D) and porous Nb2O5-TiO2 n-n junction nanofibers with different Nb molar ratios have been synthesized by a simple electrospinning approach. A decrease in the average grain size and consequently an increase in the specific surface area were observed due to the introduction of Nb2O5 into TiO2 nanofibers. In comparison with pure TiO2 nanofibers, the Nb2O5-TiO2 nanofibers exhibited improved ethanol sensing response and a reduction in electrical resistance. The optimum operation temperature was reduced from 300 °C for pure TiO2 to 250 °C for Nb2O5-TiO2. The best sensing property was found for Nb2O5-TiO2 with 6 mol% Nb2O5, showing the highest response of 21.64–500 ppm ethanol at 250 °C, which was 2.79 times as high as that of pure TiO2 nanofibers at 300 °C. The reduction of Nb2O5-TiO2 based sensor resistance was attributed to the substitution of Ti4+ by Nb5+ ions and the formation of n-n junctions between Nb2O5 nanoparticles and TiO2 nanoparticles. The enhancement sensing mechanism of Nb2O5-TiO2 nanofibers was mainly ascribed to the enhanced resistance modulation owing to the substitution of Ti4+ by Nb5+ ions, formation of n-n junctions, and high surface area as well as small grain size of Nb2O5-TiO2 nanofibers.
关键词： Gas sensor,n-n junctions,Electrospinning,Nb2O5,TiO2
更新于2025-11-14 17:15:25
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Formation and Characterization of Shallow Junctions in GaAs Made by Ion Implantation and ms-Range Flash Lamp Annealing
摘要： With the demand of aggressive scaling in nanoelectronics, further progress can be realized by integration of high mobility semiconductors, such as III–V compound semiconductors, with complementary metal-oxide-semiconductor (CMOS) technology. In this study, the formation of shallow n–p and p–n junctions in GaAs utilizing ion implantation of S and Zn, respectively, followed by millisecond-range flash lamp annealing (FLA) is presented. The distribution of implanted elements obtained by secondary ion mass spectrometry (SIMS) shows that the FLA process can effectively suppress the diffusion of dopants. Simultaneously, the ms-range annealing is sufficient to recrystallize the implanted layer and to activate the dopants. Formation of p–n and n–p junctions is confirmed by current–voltage characteristics. The ratio of reverse to forward current can reach up to 1.7 × 10^7 in the n-GaAs:Zn case.
关键词： GaAs,ion implantation,shallow junctions,flash lamp annealing
更新于2025-09-23 15:23:52
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Electroresistance of Pt/BaTiO<sub>3</sub>/LaNiO<sub>3</sub> ferroelectric tunnel junctions and its dependence on BaTiO<sub>3</sub> thickness
摘要： Recently, ferroelectric tunnel junctions (FTJs) have attracted considerable attention due to their great potential in next generation non-volatile memories. In this work, we report on thickness-dependent tunneling electroresistance (TER) and corresponding evolution of transport behavior in Pt/BaTiO3/LaNiO3 FTJs with various BaTiO3 thicknesses of 2.0, 3.2, and 4.8 nm. The TER effect is observed in the 3.2 nm-thick Pt/BaTiO3/LaNiO3 tunnel junction and an ON/OFF current ratio of ~170 is achieved due to the modulation of barrier height by polarization reversal. When the BaTiO3 is increased to 4.8 nm in thickness, the ferroelectric-modulation of the barrier profile becomes more pronounced and the dominant transport mechanism changes from electron tunneling to thermally-activated thermionic injection. As a result, the OFF state current is significantly reduced due to the suppression of the Fowler-Nordheim tunneling with increased width and height of the BaTiO3 barrier. A greatly improved ON/OFF current ratio of ~12500 is thus achieved in the 4.8 nm-thick Pt/BaTiO3/LaNiO3 FTJ device. These results facilitate deeper understanding of the TER effects from the viewpoint of not only the barrier profile but also the transport mechanism.
关键词： Pulsed laser deposition,Ferroelectric tunnel junctions,Ferroelectric memory,Resistive switching
更新于2025-09-23 15:23:52
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Ion-Implant Isolated Vertical GaN p-n Diodes Fabricated with Epitaxial Lift-Off From GaN Substrates
摘要： Ion-implant isolated vertical GaN p-n junction diodes fabricated with epitaxial lift-off (ELO) from GaN substrates are demonstrated. For the ELO process, a band-gap selective photoelectrochemical (PEC) wet etch with a pseudomorphic InGaN release layer is utilized. Compared with devices isolated using mesa etching, the ion-implant isolated devices exhibit more ideal forward current–voltage characteristics and lower leakage currents. Devices are also compared with and without ELO processing. Devices measured after ELO processing and mounting to metallized carrier substrates show similar electrical performance to GaN-on-GaN control samples without ELO processing. No indication of material quality degradation is found on the ELO devices. The ELO devices exhibit turn-on voltages of 3.15 V (at a current density of 100 A cm?2), with specific on resistance (Ron) of 0.52 mΩ cm2 at 4.8 V and breakdown voltage (Vbr) approximately of 750 V.
关键词： ion-implant isolation,epitaxial lift-off,GaN p-n junctions,p-GaN ohmic contact
更新于2025-09-23 15:22:29
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Detection of metal-molecule-metal junction formation by surface enhanced Raman spectroscopy
摘要： Vibrational modes play a key role in characterizing metal-molecule-metal junctions, but their detection currently either requires single-molecule sensitivity or the generation of defect-free large-scale junctions. Here we demonstrate that surface-enhanced Raman scattering (SERS) on non-ideal surfaces can provide a significant amount of information despite many defects in the layer. We determine the vibrational signature of the molecular electronic junction for palladium ions complexed and reduced on 4-mercaptopyridine adsorbed on rough gold and gold nanoparticles using SERS and density functional theory (DFT). We show that these non-ideal surfaces can be used to probe kinetics of metal ion complexation and establish the success of electrochemical metallization. SERS on non-ideal surfaces is thus revealed as a useful tool to rapidly establish the key process parameters in making molecular electronic junctions before embarking on more detailed studies on single molecules or single crystal surfaces.
关键词： gold,4-mercaptopyridine,Metal-molecule-metal junctions,surface-enhanced Raman spectroscopy
更新于2025-09-23 15:22:29
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Fabrication and characterization of physically-linked large-scale josephson junction test arrays
摘要： The efforts of National Institute of Metrology (NIM) towards large scale Nb/ NbxSi1-x /Nb Josephson junction arrays for the quantum voltage standards are presented in this paper. Physically-linked arrays with 10,000 and 20,000 junctions (corresponding to 1 and 2 junctions vertically) are fabricated. DC I-V characteristics of different stacked arrays are measured and experimental results are discussed. Focusing ion beam (FIB) together with scanning electron microscope (SEM) are used to examine the cross-section of three types of junction stacks which vertically contains 2, 3, and 4 junctions respectively. It is shown that grain boundary defects in the niobium wiring layer exist for all of these junction stacks. A method which potentially could solve this problem is proposed.
关键词： superconducting device fabrication,Josephson junctions,quantum voltage,superconducting
更新于2025-09-23 15:22:29
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[IEEE 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Paris (2018.7.8-2018.7.13)] 2018 Conference on Precision Electromagnetic Measurements (CPEM 2018) - Study on the phase shifter in josephson junctions embedded microwave circuits
摘要： In a programmable Josephson voltage standard device which contains multiple branches of Josephson junction (JJ) array, the microwave reflection in arrays may result in a decrease in the Shapiro step margin. According to most of the previous designs, 90° phase shifter is used to cancel microwave reflection from branches to improve the performance of the device. This paper reports our study of the phase shifter in JJ array device with a 2-stage Wilkinson power divider. At first we designed and fabricated JJ array circuits with the phase shifters. Measurement results indicate that unequal powers have been reached to arrays. We then deleted the phase shifters in another design. Identical Shapiro step margins for 4 JJ array branches are achieved.
关键词： phase shifter,Josephson junctions,quantum voltage,superconducting
更新于2025-09-23 15:22:29
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Supercurrent and Multiple Andreev Reflections in InSb Nanosheet SNS Junctions
摘要： In this study, the realization of mesoscopic Josephson junctions based on free-standing InSb nanosheet grown by molecular-beam epitaxy is reported. Below the critical temperature of superconducting aluminium electrodes ((cid:1)1.1 K), the high transparency of the contacts gives rise to proximity-induced superconductivity. A dissipationless supercurrent which can be modulated by a gate voltage acting on the electron density in the nanosheet flows through the superconducting weak links. At finite bias voltage, subharmonic energy-gap structures (SGS) originating from multiple Andreev reflections (MARs) are observed, indicating a highly transparent InSb nanosheet–superconductor interface. At last, a superconducting hybrid device with niobium electrodes is shown, suitable for further higher temperature and magnetic field transport measurements.
关键词： supercurrent,InSb nanosheets,Josephson junctions,multiple Andreev reflections
更新于2025-09-23 15:22:29
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Ultrathin Molecular Layer Junctions Based on Cyclometalated Ruthenium Complexes
摘要： A cyclometalated ruthenium complex has been designed to be immobilized on a surface by diazonium electroreduction. Modified surfaces have been obtained and fully characterized by XPS, electrochemistry and AFM. Molecular junctions consisting of Ru(bpy)2(ppy) oligomer using direct top-coat evaporation are presented.
关键词： XPS,diazonium electroreduction,molecular junctions,AFM,cyclometalated ruthenium complexes,electrochemistry
更新于2025-09-23 15:21:21
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Magnetic field compatible circuit quantum electrodynamics with graphene Josephson junctions
摘要： Circuit quantum electrodynamics has proven to be a powerful tool to probe mesoscopic effects in hybrid systems and is used in several quantum computing (QC) proposals that require a transmon qubit able to operate in strong magnetic fields. To address this we integrate monolayer graphene Josephson junctions into microwave frequency superconducting circuits to create graphene based transmons. Using dispersive microwave spectroscopy we resolve graphene’s characteristic band dispersion and observe coherent electronic interference effects confirming the ballistic nature of our graphene Josephson junctions. We show that the monoatomic thickness of graphene renders the device insensitive to an applied magnetic field, allowing us to perform energy level spectroscopy of the circuit in a parallel magnetic field of 1 T, an order of magnitude higher than previous studies. These results establish graphene based superconducting circuits as a promising platform for QC and the study of mesoscopic quantum effects that appear in strong magnetic fields.
关键词： transmon qubit,magnetic field resilience,quantum computing,Circuit quantum electrodynamics,graphene Josephson junctions
更新于2025-09-23 15:21:01