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This paper focuses on the understanding of the Random Telegraph Signal (RTS) in Single-Photon Avalanche Diodes (SPAD). We studied the RTS of two different SPAD layouts, designed and implemented in a 150-nm CMOS process, after proton irradiation. The two structures are characterized by different junction types: the first structure is constituted by a P+/Nwell junction, while the second is formed by a Pwell/Niso junction. RTS occurrence has been measured in about one thousand SPAD pixels and the differences addressed in two layouts are motivated and discussed. Hypotheses on the RTS origin are drawn by analyzing the RTS time constants and the RTS occurrence evolution as a function of the annealing temperature.

Nanostructured films of carbon and TiO2 nanoparticles have been produced by means of a simple two-step procedure based on flame synthesis and thermophoretic deposition. At first, a granular carbon film is produced on silicon substrates by the self-assembling of thermophoretically sampled carbon nanoparticles (CNPs) with diameters of the order of 15 nm. Then, the composite film is obtained by the subsequent thermophoretic deposition of smaller TiO2 nanoparticles (diameters of the order of 2.5 nm), which deposit on the surface and intercalate between the carbon grains by diffusion within the pores. A bipolar resistive switching behavior is observed in the composite film of CNP-TiO2. A pinched hysteresis loop is measured with SET and RESET between low resistance and high resistance states occurring for the electric field of 1.35 × 104 V/cm and 1.5 × 104 V/cm, respectively. CNP-TiO2 film produced by flame synthesis is initially in the low resistive state and it does not require an electroforming step. The resistance switching phenomenon is attributed to the formation/rupture of conductive filaments through space charge mechanism in the TiO2 nanoparticles, which facilitate/hinder the electrical conduction between carbon grains. Our findings demonstrate that films made of flame-formed CNP-TiO2 nanoparticles are promising candidates for resistive switching components.

Incipient carbon nanoparticles, CNP, formed by incomplete hydrocarbon combustion are composed of polycyclic aromatic hydrocarbons [1,2] and exhibit a quantum dot behavior [3], which make them ideal for a wide range of applications. Flame synthesis offers a continuous and low-cost process for the production of inorganic nanoparticles, such as TiO2, with fine control of cristallinity and phase. Likewise, carbon nanoparticles, CNPs, with tailored size and optical and electronic properties can be produced by optimizing the flame process. The assembly of nanoparticles into a uniform thin film with precise control over chemical and physical properties poses a significant challenge. Thermophoretic sampling relies on the thermophoretic forces driving the particles in the hot flame towards a cold substrate inserted in the flame and can be used to produce nanostructured, self-assembled films that can lead to novel applications. In this work, CNP and CNP/TiO2 nanoparticles have been produced in premixed ethylene-air flames and thin films have been realized by thermophoretic deposition on silicon substrates with gold interdigitated electrodes. Scanning mobility particle sizer furnished the particle size distribution and Raman and optical spectroscopy chemico-physical and structural information. The electrical characterization of the films was conducted by measuring the IV characteristics which shows a good linearity in the interval [-5 V, 5 V] whereas non-linear phenomena appear for wider voltage ranges and hysteresis phenomena are also observed in carbon/TiO2 films. Impedance spectroscopy was used to investigate the films with respect to their microstructure. This method is indeed particularly useful for nanostructured films with inter-grain and grain-edge impedances and capacities. Finally, noise spectral density at low and very low frequency was measured to investigate the electron transport. The main source of noise is of thermal type for the carbon material, whereas carbon/TiO2 film shows a Fliker type, 1/f noise, consistent to a larger amount of localized states responsible for trapping/detrapping processes of charge carriers and charge fluctuations during the conduction process. [1] Schulz, F., Commodo, M., Kaiser, K., De Falco, G., Minutolo, P., Meyer, G., D`Anna, A., Gross, L., "Insights into incipient soot formation by atomic force microscopy" Proc. Combust. Inst. 37: 885-892 (2019). [2] Commodo, M., Kaiser, K., De Falco, G., Minutolo, P., Schulz, F., D`Anna, A., Gross, L., "On the early stages of soot formation: molecular structure elucidation by high-resolution atomic force microscopy" Combust. Flame 205, pp. 154-164. [3] Liu, C, Singh, A.V., Saggese, C., Tang, Q., Chen, D., Wan, K., Vinciguerra, M., Commodo, M., De Falco, G., Minutolo, P., D'Anna, A., Wang H. , Flame-formed carbon nanoparticles exhibit quantum dot behaviors, 2019, DOI:10.1073/pnas.1900205116

Single molecules can be coupled to metallic electrodes when the latter are in the superconducting state. In such emerging hybrid molecular devices, the possibility of the Josephson effect, that is, the dissipation-less transport of Cooper-paired electrons from one electrode to the other, arises. In this theoretical study, we demonstrate that a junction formed by two superconductors linked by an annular molecule, of which benzene (phenylene group) is a prototype, can sustain indeed a supercurrent and work as a “single molecule superconducting field-effect transistor (SMoSFET)”. In this device, Cooper-paired electrons are transmitted via the molecule in the presence of quantum interference. Through the presented model, we show that the resonant nontrivial modulation of the critical current with an external gate voltage may be strongly modified by choosing a paracoupled, a metacoupled, or an orthocoupled molecular ring. These features are directly related to the possibility of obtaining a SMoSFET controlled ...

We present, for the first time, Low Frequency Noise measurements in Vertical Organic Transistors. Investigated devices are p-type Metal-Base Organic Transistors employing Pentacene and Copper Phthalocyanine as active layers for the Emitter and Collector regions, respectively. The power spectral densities measured at the Base and Collector terminals follow a 1/fγ law, with γ≈1, suggesting that noise is generated, in both cases, by a continuous distribution of traps. Cross-correlation measurements show that Base current noise and Collector current noise are uncorrelated meaning that the physical origin of the noise measured at the Base and Collector terminals is different.

Vertical organic transistors are a promising candidate to overcome the scaling limits of conventional horizontal organic field-effect devices. In this paper, based on the results of direct current (dc) and low-frequency noise (LFN) measurements, we propose a picture for the carrier transport in metal-base organic transistors in which transmission across the base is due to the combined action of both hot-carriers (HCs) and high-conduction paths (pores) in the metal base. Investigated devices employ pentacene and copper phthalocyanine as active layers for the emitter and collector regions, and a bilayer consisting of Au/MoO3 as injecting electrode. The dc analysis highlights that the charge transport in the investigated devices is due to drift diffusion of the emitter-injected carriers in the highest occupied molecular orbital (HOMO) band and is dominated by HC injection, although conduction via pores increases and becomes not negligible at high base–emitter fields. The LFN analysis highlights the presence of two dominant and uncorrelated 1/f current noise sources, one located between base and emitter, due to the fluctuations of the not-transmitted HC current, and a second source located between collector and emitter, due to the fluctuations of the transmitted HC current and/or to the fluctuations of the current through the pores in the metallic base.

In this paper, nanoscale organic two-terminal devices, based on evaporated films of a perylene diimide derivative (PDI8-CN2) and with channel lengths ranging from 1 μm down to 50 nm, have been fabricated by using Focused Ion Beam technique. Devices have been characterized in terms of I–V curves at several temperatures and perylene diimide nanochannels displayed a measurable electrical conduction even at temperatures lower than 50 K. The recorded experimental data stressed the electrical response according to the channel size. Investigation of nanoscale devices allowed us to study the nature of the charge injection and to estimate the energy barrier and the factors influencing it.

In this paper, the metal-semiconductor contacts in n-type bottom-contact bottom-gate Organic Field-Effect Transistors (OFET), based on evaporated films of a perylene diimide derivative (PDI8-CN2), have been investigated by Scanning Kelvin Probe Microscopy (SKPM). OFET were characterized for different thicknesses of the PDI8-CN2 film and in the light of the gold electrode functionalization with an aromatic thiol self-assembled monolayer. SKPM experiments reveal that aromatic thiol functionalization produces a 30% reduction in the contact resistance (Rc), while lowering the organic film thickness, the contact resistance (Rc) phenomenon tends to be magnified. The experimental observation that the voltage drops occurring close the drain electrode are even larger than those taking place at the source contact suggests that it is not possible, for these devices, to explain the overall Rc effects by simply referring to the presence of a reverse-biased Schottky junction limiting the electron injection process into the active channel.

An important step forward for the understanding of high-temperature superconductivity has been the discovery of iron-based superconductors. Among these compounds, iron pnictides could be used for high-field magnet applications, resulting more advantageous over conventional superconductors, due to a high upper critical field as well as its low anisotropy at low temperatures. However, the principal obstacle in fabricating high quality superconducting wires and tapes is given by grain boundaries. In order to study these effects, the dc transport and voltage-noise properties of Co-doped BaFe₂As₂ superconducting films with artificial grain boundary junctions have been investigated. A specific procedure allows the separation of the film noise from that of the junction. While the former shows a standard 1/f behaviour, the latter is characterized by an unconventional temperature-dependent multi-Lorentzian voltage-spectral density. Moreover, below the film superconducting critical temperature, a peculiar noise spectrum is found for the grain boundary junction. Possible theoretical interpretation of these phenomena is proposed.

We study the Josephson effect in S±IS± junctions made by a two band superconductor with s± wave symmetry. We derive the Andreev coefficients for the scattering problem at the junction interface and the temperature dependence of the critical current. We predict various features of the Josephson current for certain values of the second band strengths and tunnel barrier amplitude among which a high temperature π state coupling, and a π to 0 transition as the temperature lowers.

A detailed characterization of the voltage-noise properties has been performed in FeTe0.5Se0.5 epitaxial thin films and Co-doped BaFe2As2 bilayers, deposited by pulsed laser deposition. In all the samples analyzed, the experimental voltage-spectral density has a 1/f noise component. Different behaviors are observed for the bias current and temperature dependencies of this 1/f noise, and are related to specific structural and electric transport properties of the two materials.

We have fabricated submicron YBa2Cu3O7−x grain boundary junctions using [100] tilt bicrystal substrates. In these substrates, crystal planes are tilted around the b-axis, parallel to the bicrystal line. We have obtained high-quality junctions and fitted experimental data using a recently theory accounting for d-wave symmetry of the order parameter in layered superconductors with arbitrary orientation. In our experiment, sensitive to the amplitude of the pairing state, lobes of different signs do not influence the electrical transport in the junction. Nevertheless, the effects of a non-conventional symmetry are clearly observed on the temperature dependence of the critical current.

A voltage-noise analysis of FeTe0.5Se0.5 thin films has revealed the existence of nonlinear fluctuations above an electric field bias threshold. Below this threshold the fluctuations are standard and compatible with the presence of electron- and hole-type carriers, and it has been possible to evaluate the value of the Hooge noise parameter. Above the electric field bias threshold and at temperatures higher than 70 K, an increased nonlinear 1/f noise is found with a power exponent scaling with the temperature squared. Several possible theoretical interpretations are considered and discussed.

Electric transport and voltage-noise measurements on FeTe0.5Se0.5 epitaxial thin films are reported. The films were grown by pulsed laser ablation deposition on lanthanum aluminate single crystal substrates, and subsequently patterned by ion beam etching. Several configurations, with different voltage contacts distances and different strip widths, have been measured. At low temperature and current bias, the measured low frequency 1/f noise behaves according to the standard resistance fluctuations model. Conversely, an excess unconventional 1/f noise is observed in the high-temperature region (T >; 70 K). The experimental results indicate the existence of an electric field threshold, above which nonlinear fluctuation processes are activated. The results of noise measurements correlate well with the already reported change in sign of the Hall resistance in the same temperature range. Possible correlation between the hole contribution to the electrical transport and nonlinear noise effects observed is discussed.

We have fabricated and analyzed submicron YBa2Cu3O7−x grain boundary Josephson junctions grown on [100] tilt SrTiO3 bicrystal substrates. We present an experiment sensitive to the amplitude of the order parameter. To this aim, we have measured electrical properties of [100] tilt bicrystal YBa2Cu3O7−x grain boundary junctions with nominal widths of 700 nm and 300 nm. Junctions are fabricated so that positive lobes of the d-wave electrodes face one another (d0–d0 junction). We demonstrate that, in such devices, the temperature dependences of the critical current may be accounted for by very high-transparency junction barriers, in which the influence of nodes in the pair potential is an essential element. We based our analysis on a recent theoretical model that, starting from the Bogoliubov–de Gennes equations, takes into account the presence of Andreev bound states in layered superconductors, with Cu–O planes tilted with respect the substrate plane, as is the case of [100] tilt grain boundary junctions.

We present a closed form solution for the self-resonances in a short Josephson tunnel junction. This solution is alternative to the well known textbook result \cite{Barone,Kulik} based on a series expansion. Results are derived for the up-to-date case of a $0 - \pi$ junction., Comment: 14 pages, 3 figures, typos added

We have fabricated and measured high-quality [100] Y-Ba-Cu-O grain boundary junctions in both symmetric and asymmetric configurations. High values of the critical current times normal resistance I/sub c/R/sub n/ products have been systematically observed. The high I/sub c/R/sub n/ values found in these junctions may be of interest for the fabrication of high-sensitive superconducting quantum interference devices.

Recent experimental results on the physics of high temperature superconductivity (HTS) related to coherent phenomena and unconventional pairing symmetry are discussed. Some consequences of the d-wave order parameter symmetry on the phenomenology of HTS junctions of different type are investigated. The attention is focused on recent experiments based on biepitaxial YBa2Cu3O7-delta Josephson structures where junctions with a pi shift in the phase have been reproducibly obtained. Anisotropy measurements confirm the relevance of effects of d-wave order parameter symmetry on the properties of the junctions, and prove that intrinsic d-wave effects can be predominant over extrinsic effects. The possibility to obtain some kind of tunnel-like barriers and to tune d-wave effects through a suitable geometry has been demonstrated opening some perspectives towards novel device concepts within the framework of pi circuitry and "quiet qubit".

Midgap state-based YBa2Cu3O7−x π-junctions have been fabricated by a focused ion-beam system using 45° symmetric [001] tilt SrTiO3 bicrystal substrates. Measurements, performed by inserting the junctions in a superconducting loop (as a double-phase sensitive test), show both an unconventional nonmonotonic temperature dependence of the Josephson current, with a local minimum at a crossover temperature T* and, around T*, a half flux quantum shift in the critical current versus magnetic field modulations, clear signs of a 0–π crossover with temperature. Such results demonstrate that conventional 45° symmetric grain boundary junctions may have potential for applications, from digital circuits to quantum computing.

YBa 2 C 3 O 7− δ artificial grain boundary Josephson junctions have been fabricated by a recently implemented biepitaxial technique, employing MgO and CeO 2 as seed layers. The Josephson properties of asymmetric grain boundaries (GBs) characterised by a misalignment of the c -axis (45° c -axis tilt or twist) are presented. A comparison with GBs characterised by 45° c -axis tilt or twist and by an additional rotation of 45° of the a – b planes of one electrode has been also performed. The differences observed in the transport properties have been interpreted in terms of d x 2 − y 2 wave symmetry of the order parameter and faceting of the grain boundary.

The effects of the order parameter symmetry and the interface grain boundary orientation on the transport properties of YBa/sub 2/Cu/sub 3/O/sub 7-x/ biepitaxial grain boundary junctions have been investigated. 45/spl deg/ [100] tilt and twist junctions on SrTiO/sub 3/ [110] and MgO [110] substrates by employing respectively MgO and SrTiO/sub 3/ as seed layers have been fabricated. More complex junctions by using CeO as seed layers have also been fabricated and analyzed. The analysis of experimental data points towards a predominant d-wave symmetry of the superconductive order parameter.

We have numerically studied the static and dynamic behavior of a three terminal vortex-flow transistor based on a parallel array of Josephson junctions. We explicitly show advantages and disadvantages for different device geometric configurations, systematically changing the symmetry of the bias-current distribution. Using parameters typical of high-temperature superconducting junctions at 77K, we have analysed for each configuration the dependence of the critical current on the control current, and the voltage-current curves. We have calculated gain and transresistance for different bias conditions, and explained the numerical results in terms of the vortex dynamics in the array. This study allows us to establish limits for the operating regime of these devices when used as high-frequency amplifiers.

YBa2Cu3O7-x artificial grain boundary Josephson junctions have been fabricated, employing a recently implemented biepitaxial technique. The grain boundaries can be obtained by controlling the orientation of the MgO seed layer and are characterized by a misalignment of the c-axes (45 degrees a-axis tilt or 45 degrees a-axis twist). These types of grain boundaries are still mostly unexplored. We carried out a complete characterization of their transport properties and microstructure. Junctions and de SQUIDs associated with these grain boundaries exhibit an excellent Josephson phenomenology and high values of the ICRN product and of the magnetic flux-to-voltage transfer parameter respectively. Remarkable differences in the transport parameters of tilt and twist junctions have been observed, which can be of interest for several applications. A maximum speed of Josephson vortices as calculated from the voltage step values of the order of 2 x 10(6) m s(-1) is obtained. These devices could also have some impact on experiments designed to study the symmetry of the order parameter, exploiting their microstructure and anisotropic properties. High-resolution electron microscopy showed the presence of perfect basal plane faced boundaries in the cross sections of tilt boundaries.

An analysis of YBa1Cu3O7-delta bicrystal dc-SQUIDs is reported. The devices have been fabricated by de cylindrical magnetron sputtering from a single target. SQUIDs operating at the liquid nitrogen temperature have been obtained employing high-quality films fabricated insitu exhibiting a critical temperature as high as 89-90 K. Two different geometrical configurations for the loop inductance have been investigated. A good control of the transport parameters of the junctions, together with a reasonable correlation between the calculated inductance and the voltage response to an applied magnetic field, have been achieved. A study of the voltage response vs. the applied magnetic field as a function of both temperature and bias current has been carried out. SQUIDs working at temperatures as high as 87 K have been characterized.

The effect of the magnetic field on the current distribution in one-dimensional long Josephson tunnel junctions is investigated. Overlap and mixed overlap/in-line configurations are considered. The latter geometry corresponds to an experimental situation, since it takes into account nonuniformities of the bias current. A simple method to investigate the dependence of the Josephson critical current on the external magnetic field for any junction length is developed. The predictions, based on the phase space analysis, are compared with experimental results obtained on long junctions of different lengths. The possibility of using this method to evaluate relevant junction parameters from the experimental measurements is discussed.

The static configurations of the phase in a long Josephson junction are investigated by studying the phase space associated with the Static Perturbed Sine-Gordon Equation (SPSGE). Mixed overlap/in-line long Josephson junctions are considered. Analytical results concerning the dependence of the zero-field critical current on the junction length are reported.