We discuss the dynamics of a roller coaster cart driven by a constant force along the suspended track of a winding roller coaster. The track is assumed to be arbitrarily long and specially shaped. It is composed of semicircular track portions, in the form of valleys and hills, standing vertically in the same plane. This is a mechanical analog of Josephson junction electrodynamics. To demonstrate the explanatory potential of this analogy, we focus particularly on the conditions of de-trapping of the cart from one of the valleys of the track. This mechanical process has its analog in non-noise-generated premature switching to the finite voltage state of a Josephson junction.

Micro-Raman spectroscopy of FeTe and superconductor Fe(SeTe) films was used to investigate the compression of the lattice which is a typical feature of chalcogenide films. The lattice strain has a strong influence on their electrical, magnetic and superconductor properties. In cases where spin-orbit coupling is non-negligible, an energy split of the 3d orbitals of the Fe atoms that removes the spin energy degeneracy could be generated. This leads to unconventional light scattering mechanisms involving single-magnon excitation. For this reason, we conducted a thorough investigation of FeTe and superconductor Fe(SeTe) films by using visible micro-Raman spectroscopy over a large temperature range. The Raman band at about 1520 cm(-1) featured by the FeS-e(0.5)Te(0.5) films was assigned to the single-magnon scattering, while the Raman response of FeTe films was ascribed to more conventional two-magnon scattering mechanisms. The temperature dependence of the singlemagnon Raman scattering was investigated in the temperature range from 15 K to 295 K, enabling information to be obtained on the influence of spin fluctuations on the magnetic order.

The electronic properties of an infinite row of freestanding, aligned side-by-side, pentacene molecules are derived as a function of the intermolecular overlap integral and the chemical potential shift. We use a semiclassical approximation and a first principles tight binding method to obtain conductance and mobility of this one-dimensional crystal as a function of temperature and gate voltage. For two values of the intermolecular overlap, energy bands show a metallic behavior. For all the other values, a bandgap is present and evolves with the intermolecular overlap following a typical modulation. The magnitude of the scattering parameters estimated by the observed conductivity is coherent with the existing literature values. These findings could be relevant for the implementation of organic-based sensors.

The single-electron transistor (SET) has tremendous importance in the microelectronic industry on account of low-power consumption, an ultrasmall size, and a large integration prospect. The key challenge is to resolve the fabrication issues of a SET to realize a mechanically steady device with reproducible and controllable transport characteristics that operate at room temperature. Herein, we report on the realization of robust and well-controlled SET devices with at least two junctions and multijunctions using an advanced nanochain (NC) architecture of germanium nanoparticles rooted by a germanium oxide ropeway. These two-junction and multitunneling-junction (MTJ) SET devices exhibit an ideal Coulomb staircase behavior of single-electron charge transfer at room temperature and obeyed the theoretical path of increasing threshold voltage with the number of tunnel junctions. This Coulomb transistor prospects magnificent rewards of room-temperature operation, periodic Coulomb oscillations, well-controlled threshold voltage and large on/off ratios and have the potential to modernize the random access memory and digital data storage technologies.

CMOS Single-Photon Avalanche Diodes (SPADs) have been introduced recently in many scientific applications. This paper reports on the performance, in terms of Dark Count Rate (DCR), of a photo-sensor based on CMOS SPADs. The device has been subjected to an accurate investigation, in order to evaluate its behaviour in a radiation environment. Several irradiation tests were conducted, and a complete survey of their effects on the DCR behaviour has been performed. An overall increase in the DCR level has been measured, meaning that new defects have been introduced in the space charge region of the SPADs. Furthermore, for a fraction of the SPADs, DCR measurements show a Random Telegraph Signal (RTS) temporal pattern.

Single-photon avalanche diodes (SPADs) in the CMOS technology are very attractive solution for photon detection due to the excellent timing resolution achievable. Unfortunately, such devices suffer from large values of the dark count (DC) pedestals. In this paper, we analyzed a test chip containing SPADs with different layouts, implemented in the 150-nm CMOS technology. The behavior of such devices has been investigated after proton irradiation. It is observed that, after irradiation, the DC rate switches between two or more discrete levels, phenomenon known as random telegraph signal (RTS). The effect is related to the density and distribution of defects in the semiconductor lattice. RTS characteristics have been studied as the function of both temperature and bias voltage. Discussion of results and main hypotheses on defect types responsible for RTS are reported.

In this paper, we report on the fabrication of n-type bottom-gate bottom-contact transistors, based on evaporated films of a perylene diimide derivative (PDI8-CN2), displaying electrical performances comparable to their top-contact counterparts. By combining very thin (20 nm) electrodes and a cleaning process with oxygen plasma, indeed, bottom-contact devices with maximum mobility approaching 0.2 cm2/V s and a contact resistance lower than 35 kΩ cm at low VDS values have been achieved. AFM analyses reveal that the improved electrical responses are accompanied by the optimized PDI8-CN2 film morphology which, very significantly, exhibits similar features on the gold and dielectric (i.e., SiO2) surfaces.

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 by quantum interference.

This paper investigates the Random Telegraph Signal (RTS) in Single Photon Avalanche Diodes (SPADs). The test-chip features SPADs with different architectures implemented in 150 nm CMOS technology. The test-chip has been irradiated with 21 MeV proton beam. RTS occurrence probability has been investigated in two different architectures. RTS measurements allowed to investigate the defect responsible for RTS phenomenon.

We investigated the radiation tolerance of a Single-Photon Avalanche Diode (SPAD) device manufactured using a 150-nm CMOS process. CMOS SPADs have been studied in view of utilization as photo-detectors in future space missions. An irradiation campaign has been carried out on several test chips containing SPAD arrays with different dimensions. Samples have been exposed to different displacement damage dose. The dark count rate (DCR) characterization as a function of the delivered proton fluence has showed a significant increase in mean DCR, providing the limits of operability of such devices in a space environment. Annealing and cooling have been investigated as possible damage mitigation approaches.

Molecular electronics represents the ultimate step of the miniaturization process of the integrated circuits. Including molecules in manmade devices may introduce novel functionalities in nanodevices, such as the possibility to interact with biological environments with tremendous implications in several fields. With these motivations, we present a Bogoliubov-de Gennes description of the transport properties of a Normalmetal/molecule/Superconductor (N/m/S) junction formed by contacting an annular molecule (m) (e.g., a benzene molecule) with a normal (N) and a superconducting electrode (S). Differently from N/m/N junctions, the superconducting correlations in S play a crucial role in determining the transparency of the system. We demonstrate that the zero-bias differential conductance of the device is strongly suppressed in presence of charge accumulation on the molecule, while a resonant transmission with maximum conductance is observed when the charge stored on themolecule is negligible. We explain these findings observing that the space distribution of molecular quantum states is strongly affected by the Andreev mechanism, which represents the dominant scattering process at the m/S interface when the energy of the incident quasi-particle is below the superconducting energy gap. The relevance of these findings is briefly discussed.

We report on recent results on Josephson junctions and dc-SQUIDs made by using Fe(Se,Te) chalcogenide superconductor. Josephson devices have been fabricated on SrTiO3 bicrystal substrates. The ratio of critical current densities of Josephson- like junctions to the critical current density of the bare film decreases for misorientation angles from 0° up to 24°. For larger angles, this ratio stays constant. As expected, the absolute critical current values depend strongly on the thin film quality. As a general occurrence, the reproducibility of electrical parameters is generally low for different thin film fabrications, even if the bare films show the same transition temperature and they are fabricated following the same procedure. Finally, an analysis of vortex creep motion in Fe(Se,Te) nanostrips is presented. The pinning energy of self-generated vortices ha has been derived from experiments in narrow strips. The analysis reveals the -need of including an additional energy term due to the interaction of vortex-antivortex that, with the narrowing of the strip widths, cannot be neglected.

Abstract We study the current-voltage characteristics of Fe(Se,Te) thin films deposited on CaF2 substrates in form of nanostrips (width w ~ λ, λ the London penetration length). In view of a possible application of these materials to superconductive electronics and micro-electronics we focus on transport properties in small magnetic field, the one generated by the bias current. From the characteristics taken at different temperatures we derive estimates for the pinning potential U and the pinning potential range δ for the magnetic flux lines (vortices). Since the sample lines are very narrow, the classical creep flow model provides a sufficiently accurate interpretation of the data only when the attractive interaction between magnetic flux lines of opposite sign is taken into account. The observed voltages and the induced depression of the critical current of the nanostrips are compatible with the presence of a low number ( $$\lesssim 10$$ < ˜ 10 ) magnetic field lines at the equilibrium, a strongly inhomogeneous current density distribution at the two ends of the strips and a reduced Bean Livingston barrier. In particular, we argue that the sharp corners defining the bridge geometry represent points of easy magnetic flux lines injection. The results are relevant for creep flow analysis in superconducting Fe(Se,Te) nanostrips.

The Josephson effect in a molecular structure mimicking a benzene molecule (C6H6) placed between two nanometric superconducting electrodes is theoretically studied. In the tight binding model, the Bogoliubov-de Gennes equations are solved to derive the Andreev reflection coefficient and hence the dc Josephson current. Two effects are pointed out: the quantum interference effect on the supercurrent due to the presence of two branches in the molecule and a on-resonance off-resonance state operation in the presence of an applied gate voltage. The results provide an insight on the molecular electronics devices in the case of superconducting nano-electrodes

We have fabricated and analyzed bicrystal grain boundary superconducting quantum interference devices made by Fe(Se,Te) superconductors, grown on [001] tilt SrTiO3 bicrystal substrates. We have realized several devices using the so-called hole-type geometry, with different loop inductances and different junction widths. Modulations of the voltage under an external applied magnetic field have been observed for three samples. Voltage amplitudes of the order of few microvolt have been measured. The maximum magnetic flux-to-voltage transfer parameter value that we have observed has been V-Phi= 9.4 mu V/Phi(0) . The experimental data are analyzed in the famework of existing theoretical models.

We have fabricated and characterized single junctions, dc Superconducting Quantum Interference Devices (SQUIDs), and nanostrips made by Fe(Te, Se) superconductive thin films. SrTiO 3 bicrystal substrates with different misorientation angles have been used for the fabrication of Josephson junctions and SQUIDs. Nanostrips have been realized growing thin films on CaF 2 substrates. The interaction between fluxons and antifluxons has been taken into account for the evaluation of the pinning energy values.

•The magnetic diffraction pattern depends on the geometry of the junction tunnel barrier.•Circular annular tunnel barrier junction have a well known magnetic diffraction pattern.•The well known result for circular annular junctions applies untouched to the elliptic case.

We report an experimental investigation that shows how magnetic vortices are generated and cross a current carrying superconducting strip when illuminated by a bright (similar to MeV) and fast (<500 ps duration) infrared light pulse. The work has been carried out using a strike-and-probe electro-optic technique on a device consisting of a parallel superconducting strip configuration, with wide spacing between the strips to allow the interaction of the photons with a single strip. We find that photons hitting one strip induce a collective current redistribution in the parallel strips, which we can quantitatively account for in the framework of the London model by including the effect of generated and trapped magnetic vortices in the superconducting loops formed by the two adjacent slots. The amount of trapped vorticity and its dependence on increasing current density flowing in the illuminated strip is in good agreement with the photon-assisted unbinding of vortex-antivortex pairs. This work allows us to gain a deeper understanding of the interaction between photons and current carrying superconducting strips.