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Magnetometers exploiting interference effect of the superconducting wavefunction are known since the realization of the first SQUID, with several improvements in performance in the following years. In this field, the Superconducting Quantum Interference Proximity Transistor (SQUIPT) offers an interesting alternative to the conventional SQUID thanks to its lower power dissipation that makes it ideal for nanoscale and ultra-low temperature ( $T mK) applications, where very low dissipation is required. Here, a device composed of two facing fully superconducting SQUIPT is proposed. Numerical simulations demonstrate how the interplay between the behaviours of a couple of tunnel junctions in such a design accounts for promising performances as both a flux-to-current and a flux-to-voltage transducer.

The discovery of iron-based superconductors paved the way for advanced possible applications, mostly in high magnetic fields, but also in electronics. Among superconductive devices, nanowire detectors have raised a large interest in recent years, due to their ability to detect a single photon in the visible and infrared (IR) spectral region. Although not yet optimal for single-photon detection, iron-based superconducting nanowire detectors would bring clear advantages due to their high operating temperature, also possibly profiting of other peculiar material properties. However, there are several challenges yet to be overcome, regarding mainly: fabrication of ultra-thin films, appropriate passivation techniques, optimization of nano-patterning, and high-quality electrical contacts. Test nanowire structures, made by ultra-thin films of Co-doped BaFe2As2, have been fabricated and characterized in their transport and intrinsic noise properties. The results on the realized nanostructures show good properties in terms of material resistivity and critical current. Details on the fabrication and low temperature characterization of the realized nanodevices are presented, together with a study of possible degradation phenomena induced by ageing effects.

The quantum Hall effect is the basis for the realisation of the resistance and impedance units in the International System of units since 2019. This paper describes a cryogenic probe that allows to set graphene Hall devices in quantisation conditions in a helium bath (4.2 K) and magnetic fields up to 6 T, to perform precision measurements in the AC regime with impedance bridges. The probe has a full coaxial wiring, isolated from the probe structure, and holds the device in a TO-8 socket. First, characterization experiments are reported on a GaAs device, showing quantisation at 5.5 T. In the AC regime, multiple-series connections will be employed to minimize the residual error, quantified by electrical modelling of the probe.

Electrical characterization of few-layer MoS2 based field effect transistors with Ti/Au electrodes is performed in the vacuum chamber of a scanning electron microscope in order to study the effects of electron beam irradiation on the transport properties of the device. A negative threshold voltage shift and a carrier mobility enhancement is observed and explained in terms of positive charges trapped in the SiO2 gate oxide, during the irradiation. The transistor channel current is increased up to three order of magnitudes after the exposure to an irradiation dose of 100e-/nm2. Finally, a complete field emission characterization of the MoS2 flake, achieving emission stability for several hours and a minimum turn-on field of about 20 V/um with a field enhancement factor of about 500 at anode-cathode distance of 1.5um, demonstrates the suitability of few-layer MoS2 as two-dimensional emitting surface for cold-cathode applications.

Nanowires of Co-doped BaFe 2 As 2 have been realized and characterized. Thin films having thickness of 20 nm were grown on CaF 2 (100) substrates by pulsed laser deposition. The films were then passivated in situ with a thin layer of MgAl 2 O 4 . Using electron beam lithography, several submicron nanowire structures were patterned and electrically contacted to gold pads. The nanostructures have a superconducting critical temperature T of 16 K, for a 500-nm-wide nanowire, and properties, in terms of normal state resistivity (0.3 mΩ·cm) and critical current (1 MA/cm 2 at 3 K), comparable with those of NbN nanowires. Moreover, they show localization effects in the normal state, while the current-voltage characteristics are dominated by flux creep.

Electrically-active defects have a significant impact on the performance of electronic devices based on wide band-gap materials such as diamond. This issue is ubiquitous in diamond science and technology, since the presence of charge traps in the active regions of different classes of diamond-based devices (detectors, power diodes, transistors) can significantly affect their performances, due to the formation of space charge, memory effects and the degradation of the electronic response associated with radiation damage. Among the most common defects in diamond, the nitrogen-vacancy (NV) center possesses unique spin properties which enable high-sensitivity field sensing at the nanoscale. Here we demonstrate that NV ensembles can be successfully exploited to perform a direct local mapping of the internal electric field distribution of a graphite-diamond-graphite junction exhibiting electrical properties dominated by trap- and space-charge-related conduction mechanisms. By performing optically-detected magnetic resonance measurements, we performed both punctual readout and spatial mapping of the electric field in the active region at different bias voltages. In this novel "self-diagnostic" approach, defect complexes represent not only the source of detrimental space charge effects, but also a unique tool to directly investigate them, by providing experimental evidences on the conduction mechanisms that in previous studies could only be indirectly inferred on the basis of conventional electrical and optical characterization.

Magnetic Force Microscopy (MFM) has been exploited to develop a technique capable of investigating the field-dependent magnetisation reversal processes in patterned systems, allowing the full reconstruction of a local hysteresis loop. Fe–Si–B dots with a lateral size of 6 μ m and a thickness of 250 nm have been prepared by sputtering and optical lithography. In the as-prepared state, the dots are characterised by a dense stripe domain configuration, clearly visible at the MFM. Subsequently, the dots have been thinned by means of exposition to a focussed ion beam, consisting of Ga+ ions having an energy of 30 keV. The local hysteresis loops have been measured by means of the MFM-derived technique. The progressive thinning of the dots results in the disappearance of the perpendicular anisotropy responsible for the dense stripe domain configuration, with the dominance of the shape anisotropy for thickness values below ≈ 70 nm . The results are consistent with the spin reorientation transition effect studied on similar systems in the form of continuous thin films.

We have realized nanowires using Co-doped BaFe2As2 thin films with 20 nm thickness deposited on CaF2 (100) substrates by pulsed laser deposition. The films were passivated in-situ with a thin layer of MgAl2O4. Subsequently, several submicron nanowire structures were patterned using electron beam lithography, and electrically contacted to gold pads. Electrical characterizations of the realized nanostructures show good properties in terms of material resistivity and critical current, with a Tc of 16 K for a 500 nm wide nanowire.

The self-assembly (SA) of diblock copolymers (DBCs) based on phase separation into different morphologies of small and high-density features is widely investigated as a patterning and nanofabrication technique. The integration of conventional top-down approaches with the bottom-up SA of DBCs enables the possibility to address the gap in nanostructured lateral length standards for nanometrology, consequently supporting miniaturization processes in device fabrication. On this topic, we studied the pattern characteristic dimensions (i.e., center-to-center distance L0 and diameter D) of a cylinder-forming polystyrene-b-poly( methyl methacrylate) PS-b-PMMA (54 kg mol–1, styrene fraction 70%) DBC when confined within periodic SiO2 trenches of different widths (W, ranging between 75 and 600 nm) and fixed length (l, 5.7 μm). The characteristic dimensions of the PMMA cylinder structure in the confined configurations were compared with those obtained on a flat surface (L0 = 27.8 ± 0.5 nm, D = 13.0 ± 1.0 nm). The an...

The control of the charge state of nitrogen-vacancy (NV) centers in diamond is of primary importance for the stabilization of their quantum-optical properties, in applications ranging from quantum sensing to quantum computing. To this purpose, in this work current-injecting micro-electrodes were fabricated in bulk diamond for NV charge state control. Buried (i.e. 3 {\mu}m in depth) graphitic micro-electrodes with spacing of 9 {\mu}m were created in single-crystal diamond substrates by means of a 6 MeV C scanning micro-beam. The high breakdown field of diamond was exploited to electrically control the variation in the relative population of the negative (NV-) and neutral (NV0) charge states of sub-superficial NV centers located in the inter- electrode gap regions, without incurring into current discharges. Photoluminescence spectra acquired from the biased electrodes exhibited an electrically induced increase up to 40% in the NV- population at the expense of the NV0 charge state. The variation in the relative charge state populations showed a linear dependence from the injected current at applied biases smaller than 250 V, and was interpreted as the result of electron trapping at NV sites, consistently with the Space Charge Limited Current interpretation of the abrupt current increase observed at 300 V bias voltage. In correspondence of such trap-filling-induced transition to a high-current regime, a strong electroluminescent emission from the NV0 centers was observed. In the high-current-injection regime, a decrease in the NV- population was observed, in contrast with the results obtained at lower bias voltages. These results disclose new possibilities in the electrical control of the charge state of NV centers located in the diamond bulk, which are characterized by longer spin coherence times., Comment: 28 pages, 8 figures

The Deep Ion Beam Lithography technique has been extensively adopted in recent years for the fabrication of graphitic electrodes in bulk diamond with a wide range of technological applications. Particularly, it has been recently shown that a high current can be driven in devices consisting of micrometer-spaced sub-superficial graphitic electrodes. This effect has been exploited to stimulate electroluminescence from color centers placed in the active region of the device. A deep understanding of the conduction mechanisms governing charge transport in micro-regions of defective diamond comprised between graphitic electrodes is necessary in order to fully exploit the functionality of these opto-electronic devices, as well as to assess the ion-beam-micromachining of diamond as a convenient technique for the fabrication of solid-state micro-devices. In this work, a temperature-dependent characterization of the electrical properties of a sub-superficial graphite-diamond-graphite junction is presented and discussed. The ohmic behavior observed at low bias voltages is ascribed to a donor level with an activation energy of (0.217 ± 0.002) eV, a value compatible with previous reports on nitrogen-related defects. A transition to a high-current regime above a critical voltage VC was also observed, and interpreted in terms of the Space-Charge-Limited Current model. The temperature-dependent measurements allowed to investigate the role of charge trapping in the charge injection mechanism of the junction. By fitting the temperature dependence in the high-current regime it was possible to determine the relevant trap level of the associated Poole-Frenkel mechanism, leading to a value of (0.278 ± 0.001) eV from the conduction band. The Poole-Frenkel conduction model in high-current regime enabled also a preliminary investigation in the effects of ion implantation on the modification of the dc dielectric constant of diamond.

The detection of quantal exocytic events from neurons and neuroendocrine cells is a challenging task in neuroscience. One of the most promising platforms for the development of a new generation of biosensors is diamond, due to its biocompatibility, transparency and chemical inertness. Moreover, the electrical properties of diamond can be turned from a perfect insulator into a conductive material (resistivity Ohm cm) by exploiting the metastable nature of this allotropic form of carbon. A 16 channels MEA (Multi Electrode Array) suitable for cell culture growing has been fabricated by means of ion implantation. A focused 1.2 MeV He+ beam was scanned on a IIa single-crystal diamond sample (4.5x4.5x0.5 mm3) to cause highly damaged sub-superficial structures that were defined with micrometric spatial resolution. After implantation, the sample was annealed. This process provides the conversion of the sub-superficial highly damaged regions to a graphitic phase embedded in a highly insulating diamond matrix. Thanks to a three-dimensional masking technique, the endpoints of the sub-superficial channels emerge in contact with the sample surface, therefore being available as sensing electrodes. Cyclic voltammetry and amperometry measurements of solutions with increasing concentrations of adrenaline were performed to characterize the biosensor sensitivity. The reported results demonstrate that this new type of biosensor is suitable for in vitro detection of catecholamine release., 14 pages, 5 figures

The overdamped Nb/Al-AlOx/Nb superconductor-normal metal-insulator-superconductor SNIS Josephson junctions recently developed at INRIM exhibit high values of critical current density and characteristic voltage, making these devices appealing both for metrology and digital electronics. High current densities could allow reduction of junction size, increasing the integration level. In this work authors present first results concerning the realization of sub-μm SNIS including a nanolithographic technique (Electron Beam Lithography, EBL) into the conventional process, to reduce junction dimensions. Fabrication and electrical parameters have been evaluated considering the scaling of the areas of junctions, furthermore RF and temperature behaviour have been studied.

Phase-tunable hybrid devices, built upon nanostructures combining normal metal and superconductors, have been the subject of intense studies due to their numerous combinations of different charge and heat transport configurations. They exhibit solid applications in quantum metrology and coherent caloritronics. Here we propose and realize a new kind of hybrid device with potential application in single charge manipulation and quantized current generation. We show that by tuning superconductivity on two proximized nanowires, coupled via a Coulombic normal metal island, we are able to control its charge state configuration. This device supports a one-control-parameter-cycle being actuated by the sole magnetic flux. In a voltage biased regime, the phase-tunable superconducting gaps can act as energy barriers for charge quanta leading to an additional degree of freedom in single electronics. The resulting configuration is fully electrostatic and the current across the device is governed by the quasiparticle populations in the source and drain leads. Notably, the proposed device can be realized using standard nanotechniques opening the possibility to a straightforward coupling with the nowadays well developed superconducting electronics., Comment: 7 pages, 4 figures

We report on the structural modifications induced by a lambda = 532 nm ns-pulsed high-power laser on sub-superficial graphitic layers in single-crystal diamond realized by means of MeV ion implantation. A systematic characterization of the structures obtained under different laser irradiation conditions (power density, number of pulses) and subsequent thermal annealing was performed by different electron microscopy techniques. The main feature observed after laser irradiation is the thickening of the pre-existing graphitic layer. Cross sectional SEM imaging was performed to directly measure the thickness of the modified layers, and subsequent selective etching of the buried layers was employed to both assess their graphitic nature and enhance the SEM imaging contrast. In particular, it was found that for optimal irradiation parameters the laser processing induces a six-fold increase the thickness of sub superficial graphitic layers without inducing mechanical failures in the surrounding crystal. TEM microscopy and EELS spectroscopy allowed a detailed analysis of the internal structure of the laser irradiated layers, highlighting the presence of different nano graphitic and amorphous layers. The obtained results demonstrate the effectiveness and versatility of high-power laser irradiation for an accurate tuning of the geometrical and structural features of graphitic structures embedded in single crystal diamond, and open new opportunities in diamond fabrication., 24 pages, 7 figures

Focused MeV ion beams with micrometric resolution are suitable tools for the direct writing of conductive graphitic channels buried in an insulating diamond bulk, as already demonstrated for different device applications. In this work we apply this fabrication method to the electrical excitation of color centers in diamond, demonstrating the potential of electrical stimulation in diamond-based single-photon sources. Differently from optically-stimulated light emission from color centers in diamond, electroluminescence (EL) requires a high current flowing in the diamond subgap states between the electrodes. With this purpose, buried graphitic electrode pairs, 10 μm spaced, were fabricated in the bulk of a single-crystal diamond sample using a 6 MeV C microbeam. The electrical characterization of the structure showed a significant current injection above an effective voltage threshold of 150 V, which enabled the stimulation of a stable EL emission. The EL imaging allowed to identify the electroluminescent regions and the residual vacancy distribution associated with the fabrication technique. Measurements evidenced isolated electroluminescent spots where non-classical light emission in the 560–700 nm spectral range was observed. The spectral and auto-correlation features of the EL emission were investigated to qualify the non-classical properties of the color centers.

Real-time detection and generation of single microwave photons would be important in many quantum technology applications. For single-microwave-photon sources, much of the groundwork has been done already within the framework of circuit quantum electrodynamics (cQED) in the frequency range 4 GHz - 8 GHz. However, currently there are no detectors that can reliably resolve single microwave photon events, unlike at optical frequencies. In June 2013, we started a joint research project to develop both microwave detectors and sources working at the single-photon level as a final goal. All devices operate at cryogenic temperatures, most of them below 100 mK. We also aim at improving the performance of other cryoelectronic quantum devices by understanding and eliminating the detrimental effects caused by microwave radiation. The work is done in project MICROPHOTON of the European Metrology Research Programme (EMRP). The goals and status of the project will be described in the presentation.

Focused MeV ion microbeams are suitable tools for the direct writing of conductive graphitic channels buried in an insulating diamond bulk, as demonstrated in previous works with the fabrication of multi-electrode ionizing radiation detectors and cellular biosensors. In this work we investigate the suitability of the fabrication method for the electrical excitation of colour centres in diamond. Differently from photoluminescence, electroluminescence requires an electrical current flowing through the diamond sub-gap states for the excitation of the colour centres. With this purpose, buried graphitic electrodes with a spacing of 10 micrometers were fabricated in the bulk of a detector-grade CVD single-crystal diamond sample using a scanning 1.8 MeV He micro-beam. The current flowing in the gap region between the electrodes upon the application of a 250 V bias voltage was exploited as the excitation pump for the electroluminescence of different types of colour centres localized in the above-mentioned gap. The bright light emission was spatially mapped using a confocal optical microscopy setup. The spectral analysis of electroluminescence revealed the emission from neutrally-charged nitrogen-vacancy centres ($NV^0$, $\lambda_{ZPL}$ = 575 nm), as well as from cluster crystal dislocations (A-band, {\lambda} = 400-500 nm). Moreover, an electroluminescence signal with appealing spectral features (sharp emission at room temperature, low phonon sidebands) from He-related defects was detected ($\lambda_{ZPL}$ = 536.3 nm, $\lambda_{ZPL}$ = 560.5 nm); a low and broad peak around {\lambda} = 740 nm was also observed and tentatively ascribed to Si-V or GR1 centres. These results pose interesting future perspectives for the fabrication of electrically-stimulated single-photon emitters in diamond for applications in quantum optics and quantum cryptography.

The control of emission from localized light sources is an objective of outstanding relevance in nanophotonics. In a recent past, a large number of metallic nanostructures has been proposed to this end, wherein plasmonic modes are exploited as energy carriers on a subwavelength scale. As an interesting alternative, we present here the use of surface modes on patterned dielectric multilayers to deliver electromagnetic power from free-space to localized volumes and vice versa. Thanks to this low-loss energy transfer, proper periodic ring structures are shown to provide a subwavelength focusing of an external radiation onto the multilayer surface. By reciprocity, the radiated power from emitters within the ring center is shown to be efficiently beamed in the free-space, with a well-controlled angular divergence. This mechanism overcomes some important limitations involved in the all-plasmonic approach, while opening new opportunities for hybrid devices in photon management applications such as optical sensing and lighting.

Among Field-Coupled technologies, NanoMagnet Logic (NML) is one of the most promising. Low dynamic power consumption, total absence of static power, remarkable heat and radiations resistance, in association with the possibility of combining memory and logic in the same device, make this technology the ideal candidate for low power, portable applications. However, the necessity of using an external magnetic field to locally control the circuit represents, currently, the weakest point of this technology. The high power losses in the clock generation system adopted up to now wipes out the most important advantages of this technology.

In recent years, magnetic-based technologies, like nanomagnet logic (NML), are gaining increasing interest as possible substitutes of CMOS transistors. The possibility to mix logic and memory in the same device, coupled with a potential low power consumption, opens up completely new ways of developing circuits. The major issue of this technology is the necessity to use an external magnetic field as clock signal to drive the information through the circuit. The power losses due to the magnetic field generation potentially wipe out any advantages of NML. To solve this problem, new clock mechanisms were developed, based on spin transfer torque current and on voltage-controlled multiferroic structures that use magnetoelastic properties of magnetic materials, i.e., exploiting the possibility of influencing magnetization dynamics by means of the elastic tensor. In particular, the latter shows an extremely low power consumption. In this paper, we propose an innovative voltage-controlled magnetoelastic clock system aware of the technological constraints risen by modern fabrication processes. We show how circuits can be fabricated taking into account technological limitations, and we evaluate the performance of the proposed system. Results show that the proposed solution promises remarkable improvements over other NML approaches, even though state-of-the-art ideal multiferroic logic has in theory better performance. Moreover, since the proposed approach is technology-friendly, it gives a substantial contribution toward the fabrication of a full magnetic circuit and represents an optimal tradeoff between performance and feasibility.

In analogy to the well-known plasmonic bull's eye, we introduce here an all-dielectric mutilayered ring structure with high-directivity antenna capabilities. Radiated energy from organic emitters localized within the ring center is resonantly transferred to surface modes on the multilayer and then diffracted in the free space. The structure can be obtained by properly applying the Bragg law to a diffraction pattern defined in the Fourier plane as a superposition of ""caustics"". This approach allows designing diffractive structures producing a surface-mode-assisted beaming of radiation out of the sample with an arbitrary propagation angle in two dimensions. Specifically, we demonstrate that an anisotropically periodic ring structure can beam fluorescence emission with a tilt angle of 11.5 deg from the normal direction. The proposed use of surface modes for manipulating light at a subwavelength scale can represent an interesting alternative to the more conventional all-plasmonic approach.

The nanosuperconducting quantum interference device (nanoSQUID) is a powerful tool for nanoscience investigations. In this paper, the main features of niobium nanoSQUID based on deep submicron Josephson tunnel junctions have been investigated. The superconductive nanosensor has a rectangular loop of (1 × 0.4 μm 2) interrupted by two square Josephson junctions having a side length of 0.3 μm. The crucial steps of the fabrication process have been performed using focusing ion beam (FIB) nanosculpting technique. A full characterization of the nanosensor has been performed including the measurement of the voltage swing, the voltage responsivity, the spectral density of the magnetic flux and spin noise and the investigation of the main characteristics as a function of the temperature. Due to a very high responsivity (2.9 mV/ Φ0), the nanodevice exhibited, at T= 4.2 K, an intrinsic spectral density of the magnetic flux as low as 600 n Φ0/Hz 1/2, corresponding to a magnetic moment noise of 9 μB/Hz 1/2. For temperature less than 4.0 K, the nanodevice shows hysteretic current-voltage characteristics. However, the high critical current modulation depths ensure a suitable sensitivity for nanoscale applications.

In June 2013, we started a joint research project MICROPHOTON, 'Measurement and Control of Single-Photon Microwave Radiation on a Chip', as a part of the European Metrology Research Programme (EMRP). The objectives of the project include the development of novel microwave detectors and sources that would ultimately operate at the single-photon level, and the improvement in the performance of cryoelectronic quantum devices by understanding and eliminating the detrimental effects caused by microwave radiation coming from the electromagnetic environment. This paper describes the goals and plans of the project.

A three dimensional nano-SQUID (Superconducting Quantum Interference Device) has been realized in a vertical configuration (with the loop in the same plane of Josephson Tunneling Junctions, JTJs). The loop area is 0.25 μm2 corresponding to a modulation period of about 5 mT, the square JTJs have a side length of 0.3 μm. Josephson junction's fabrication is carried out combining optical lithography to pattern trilayer and three dimensional (3D) Focused Ion Beam (FIB) sculpting technique to define the junctions' and the loop's areas. Two different ion etching processes were performed, perpendicular and parallel to the multilayer, resulting in a precise 3D structure. Finally, a standard anodization was performed to eliminate the unstructured surface material generated by the high energetic ion beam assuring high quality junctions. Electric transport characteristics of the nanodevice measured at T = 4.2 K are reported, in particular the current-voltage characteristics and critical current vs external magnetic field. The high modulation depth of the critical current (up to 70% of the Ic at zero magnetic flux) and the device reliability are very encouraging in view of nanoscience applications.

The use of linear and circular subwavelength gratings for improving the fluorescence extraction from organic dyes spotted on the surface of a one-dimensional photonic crystal is demonstrated. The one-dimensional photonic crystal hosting the gratings allows Bloch surface waves (BSWs) to be coupled in the visible range. We provide experimental evidence for the distributed diffraction of BSW-coupled fluorescence that is locally excited using a microscope-based setup. By diffracting the BSW-coupled fluorescence, a significant improvement in the total fluorescence collection is obtained as compared to a flat one-dimensional photonic crystal.

In this work we introduce the use of a patterned polymer-based surface functionalization of a one-dimensional photonic crystal (1DPC) for controlling the emission direction of fluorescent proteins (ptA) via coupling to a set of two Bloch Surface Waves (BSW). Each BSW dispersion branch relates to a micrometric region on the patterned 1DPC, characterized by a well defined chemical characteristic. We report on the enhanced and spatially selective excitation of fluorescent ptA, and on the spatially-resolved detection of polarized emitted radiation coupled to specific BSW modes. As a result, we provide an optical multiplexing technique for the angular separation of fluorescence radiated from micrometric regions having different surface properties, even in the case the emitting labels are spectrally identical. This working principle can be advantageously extended to a multi-step nanometric relief structure for self-referencing biosensing or frequency-multiplexed fluorescence detection.

An alternative method to plasmon techniques for the enhancement, control and detection of fluorescence is proposed. The role of the metallic layer is played by a silicon-based one-dimensional photonic crystal that can sustain Bloch surface waves (BSWs), which can be regarded as the dielectric analogue of surface plasmon polaritons (SPPs) for metals. Throughout the paper we explore the route that leads to an enhanced, directionally-controlled and selfreferencing fluorescence-detection scheme. We first consider a 1DPC that is functionalized with a thin, flat and homogeneous polymeric layer decorated with a fluorescent dye. The enhancement of the BSW-coupled fluorescence emission is studied against a similar scheme that uses a common thin glass coveslip. An enhancement as large as 560 is found. We further investigate the BSW coupling of the illuminating laser light into 30-nm thin polymeric waveguides. Imaging the BSW-coupled emitted fluorescence through the leakage radiation microscopy is used for the purpose. The possibility of coupling BSWs into nanometric guiding ridges makes feasible the design of a spatially-resolved and multiplexing fluorescence-detection scheme, which can be most useful for self-referencing in the biosensing field. We conclude the paper by investigating the effects on the fluorescence emission of a multistack that consists of a dielectric multilayer and a thin metallic layer deposited on top. The implications of using a metallo-dielectric structure for the coupling of the emitted fluorescence with BSW and SPP modes is discussed.

Since the original paper from Josephson on tunnel phenomena occurring in superconducting junctions (Josephson, 1962), superconductors have been widely studied by metrologists, because of the quantistic origin of most effects observed in such class of materials. There is, in fact, an intimate relationship between the definition of more accurate and stable standards and Quantum Mechanics. Indeed, the Josephson Voltage Standard (JVS) is believed to be a fundamental quantum physical effect, which is the same everywhere, and at all times. Tunnel effect has, however, several other implications, one of them being the possibility of localizing a single electron in space. An electric current can flow through the conductor because some electrons are free to move through the lattice of atomic nuclei. The charge transferred through the conductor determines the current. This transferred charge can have practically any value, in particular, a fractional charge value as a consequence of the displacement of the electron cloud against the lattice of atoms. This shift can be changed continuously and thus the transferred charge is a continuous quantity, not quantized at all! If a discontinuity in space is introduced, e.g. by means of a tunnel junction, electric charge will move through the system by both continuous and discrete processes. Since, from a semi-classical point of view, only discrete electrons can tunnel through junctions, charge will accumulate at the surface of the electrode against the isolating layer, until a high enough bias has built up across the tunnel junction, and one electron will be transferred. This argument, which will be substantiated in a purely quantistic view in the following, led K. Likharev (Likharev, 1988) to coin the term `dripping tap' as an analogy of this process. In other words, if a constant current I is forced to pass through a single tunnel junction, the so called Coulomb oscillations will appear with frequency f = I/e where e is the charge of an electron. The current biased tunnel junction is a very simple circuit able to show the controlled transfer of electrons. Differently from the JVS, devices capable to control the electron transfer one-by-one are still far to reach the accuracy level necessary for metrological applications. Controlling and counting electrons one-by-one in an electrical circuit will give the possibility of realizing a quantum standard for electrical current. It is important to remember that in the SI system, the base electrical unit is the ampere, but, nowadays, the primary electrical standards are the

Array of dots have been designed by assembling a monolayer of polystyrene nanospheres (PN) on sputtered thin films having Ni80Fe20 and Co composition with different thickness, ranging in the interval 20 ÷ 80 nm. Subsequently the films are nanopatterned using the nanospheres as a mask during sputter etching with Ar+ ions. A Reactive Ion Etching (RIE) process before sputter etching is used to control the final diameter of the magnetic dots that thus can be tailored as desired (typically ranging in the interval 250 ÷ 400 nm depending on the PN starting diameter). In addition, electron beam lithography has been exploited to obtain arrays of dots in Ni80Fe20 thin films having approximately the same mean size and dot distance as in self-assembled samples. All films have been routinely characterized by SEM and AFM microscopy to evaluate the microstructure. Magnetic domain patterns at magnetic remanence and in the demagnetised state have been imaged by MFM microscopy technique. Room-temperature hysteresis properties have been measured by an alternating gradient force magnetometer. In general, the magnetization process in all patterned films has been observed to have features typical of a vortex whose nucleation field depends on sample thickness and mean dot dimension. A comparison between magnetic arrays of Ni80Fe20 dots prepared by self-assembling of polystyrene nanospheres and electron beam lithography is presented to rule out the role of microstructure (i.e., order, size, and mutual distance of the magnetic dots) on magnetic properties.

Electronic transport properties of porous Si nanowires either with embedded Si quantum dots or with a percolative crystalline path are studied as a function of the temperature for the first time. We show that unlike bulk porous Si, the predesigned structure of the wires results in a single distinct conduction mechanism such as tunneling in the former case and variable range hopping in the latter case. We demonstrate that the geometry of the systems with a large internal surface area and high density of the Si quantum dots have a significant conduction enhancement compared to bulk porous silicon. These results can also improve the understanding of the basis of the different electronic transport mechanisms reported in bulk porous silicon.

Single-photon sources represent a key enabling technology in quantum optics, and single colour centres in diamond are a promising platform to serve this purpose, due to their high quantum efficiency and photostability at room temperature. The widely studied nitrogen vacancy centres are characterized by several limitations, thus other defects have recently been considered, with a specific focus of centres emitting in the Near Infra-Red. In the present work, we report on the coupling of native near-infrared-emitting centres in high-quality single crystal diamond with Solid Immersion Lens structures fabricated by Focused Ion Beam lithography. The reported improvements in terms of light collection efficiency make the proposed system an ideal platform for the development of single-photon emitters with appealing photophysical and spectral properties., Comment: 17 pages, 5 figures

The growing interest in the development of nano-superconducting quantum interference devices (nanoSQUIDs) and their applications in nanoscience demands a deep study of these ultra-high-sensitivity nanodevices.In this paper, the main features of niobium planar nanointerferometers as a function of the temperature have been investigated. In particular, two types of nanodevices have been realized and studied: one based on nanobridges and the other on sub-micron Josephson tunnel junctions (JTJs).The nanobridge-based nanointerferometer, fabricated by electron beam lithography (EBL), consists of a sub-micrometric loop (effective area of 0.5 μm2), interrupted by two Dayem nanobridges having a width and length of 50 and 80 nm respectively. The JTJs-based nanointerferometer has two Nb/Al-AlOx/Nb SNIS (superconductor/normal-insulator/superconductor) junctions with an area of 0.09 μm2, connected by a rectangular loop (1 μm × 0.2 μm), and realized by the three-dimensional focused ion beam (3D FIB) sculpting technique. For both nanodevices, measurements of current–voltage characteristics and critical current versus external magnetic flux have been performed at operating temperatures ranging from 4.2 to 1.2 K. The critical current modulation depths, magnetic flux to current transfer factor (current responsivity) and magnetic flux resolution as a function of the temperature have been evaluated for both nanosensors. Furthermore, measurements of the voltage–magnetic flux characteristics and the spectral density of magnetic flux noise have been performed at T = 4.2 K.

Overdamped Josephson junctions based on a Nb/Al-AlOx/Nb superconductor-normal metal-insulator-superconductor structure were realized at the submicrometer scale by using focused ion beam nano-sculpting technique. This approach represents an alternative solution to the classical electron beam lithography and allows for an accurate control of the junction dimensions. Superconductor-normal metal-insulator-superconductor structured junctions were downscaled to about 300 × 300 nm2 and electrically measured at 4.2 K. The simple fabrication process, leading to high current density, Jc, and characteristic voltage, Vc, values and good uniformity, makes these junctions promising as elementary cell in complex circuits for rapid single flux quantum and ac voltage standard applications.

The lateral confinement of Bloch surface waves on a patterned multilayer is investigated by means of leakage radiation microscopy (LRM). Arrays of nanometric polymeric waveguides are fabricated on a proper silicon-nitride/silicon-oxide multilayer grown on a standard glass coverslip. By exploiting the functional properties of the polymer, fluorescent proteins are grafted onto the waveguides. A fluorescence LRM analysis of both the direct and the Fourier image plane reveals that a substantial amount of emitted radiation couples into a guided mode and then propagates into the nanometric waveguide. The observations of the mode are supported by numerical simulations.