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The growing interest in quantum technologies, from fundamental physics experiments to quantum computing, demands for extremely performing electronics only adding the minimum amount of noise admitted by quantum mechanics to the input signal (i.e. quantum-limited electronics). Superconducting microwave amplifiers, due to their dissipationless nature, exhibit outstanding performances in terms of noise (quantum limited), and gain. However, bandwidth and saturation power still show space for substantial improvement. Within the DARTWARS* collaboration, we are developing state-of-the-art microwave superconducting amplifiers based on Josephson junction arrays and on distributed kinetic inductance transmission lines. Here we report the realization of a setup for the characterization of the performances of Josephson Traveling-Wave Parametric Amplifiers (JTWPA) at a temperature of 300 mK. Although in the final experimental setup these amplifiers will operate at a base temperature of about 20 mK, their characterization at 300 mK allows to evidence the main aspects of their performances, but the ultimate noise level. This represents a quick and relatively inexpensive way to test these superconductive devices that can be of help to improve their design and fabrication. IEEE

The recent developments in quantum technologies, as well as advanced detection experiments, have raised the need to detect extremely weak signals in the microwave frequency spectrum. To this aim, the Josephson travelling wave parametric amplifier, a device capable of reaching the quantum noise limit while providing a wide bandwidth, has been proposed as a suitable cryogenic front-end amplifier. This work deals with the numerical study of a Josephson travelling wave parametric amplifier, without approximations regarding the nonlinearity of the key elements. In particular, we focus on the investigation of the system of coupled nonlinear differential equations representing all the cells of the Josephson travelling wave parametric amplifier, with proper input and output signals at the boundaries. The investigation of the output signals generated by the parametric amplification process explores the phase-space and the Fourier spectral analysis of the output voltage, as a function of the parameters describing the pump and signal tones that excite the device. Beside the expected behavior, i.e., the signal amplification, we show that, depending on the system operation, unwanted effects (such as pump tone harmonics, incommensurate frequency generation, and noise rise), which are not accounted for in simple linearized approaches, can be generated in the whole nonlinear system. IEEE

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.

This article compares two instruments for the traceable measurement of dc low currents, a custom capacitance–voltage ( $C\text{-} V$ ) source and the ultrastable low-current amplifier (ULCA), a commercial precision transresistance amplifier. The instruments are calibrated through independent traceability routes. The comparison base relative accuracy is in the $10^{-6}\!-\!10^{-5}$ range. Differences between the two instrument readings, in the $10^{-5}$ range, are interpreted as an effect of the frequency dependence of the capacitor employed in the $C\text{-} V$ source. Such frequency dependence can also affect primary metrology experiments in other fields.

The presence of Persian sources in Nietzsche’sThus Spoke Zarathustrahas been a topic of debate for decades. This paper summarizes the main results of a comparative study of Nietzsche and the ancient Persian scriptureAvestā. In addition to several secondary sources Nietzsche repeatedly encountered, there is strong evidence that he read Johann Friedrich Kleuker’s German translation of theAvestātexts reconstructed by Abraham Hyacinthe Anquetil-Duperron. Analyzing Nietzsche’s diverse sources of Zoroastrianism as well as his knowledge of this religion, this paper shows that many metaphors, references and claims in bothThus Spoke Zarathustraand in Nietzsche’s notebooks can be traced back to Zoroastrianism. Taking these sources into consideration contributes significantly to our understanding of one of Nietzsche’s major works.

In this paper, we propose a novel kind of Josephson-Energy Suppression Pump (JESP) controlled by a fully magnetic flux drive. The device presented here is composed of two superconducting loops interrupted at one side by superconducting nanowires which are joined together by a superconducting island. The phase difference developed at the edges of the nanowires by means of the magnetic flux threading the loops can collapse their Cooper condensates, leading to complete suppression of the Josephson energies. This mechanism allows to greatly reduce the leakage current when performing Cooper pair pumping by a pure magnetic pumping cycle without involving any gate modulation. The pumping capability of the JESP is studied through a master equation approach in the non-adiabatic case.

We report on a comparison experiment between a low dc current source based on the capacitance-voltage method, and an ultrastable-low noise current amplifier (ULCA). The two instruments can be calibrated independently using different methods and traceability paths. The agreement is of a few parts in 105 for currents close to 10 pA and 100 pA; the residual deviation might be related to the frequency dependence of the capacitance employed in the source.

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.

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.

In the last few years, several groups have proposed and developed their own platforms demonstrating quantum-limited linear parametric amplification, with evident applications in quantum information and computation, electrical and optical metrology, radio astronomy and basic physics concerning axion detection. Here we propose a short review on the physics behind parametric amplification via metamaterials composed by coplanar wave-guides embedding several Josephson junctions. We present and compare different schemes that exploit the nonlinearity of the Josephson current-phase relation to mix the so-called signal, idler and pump tones. The chapter then presents and compares three different theoretical models, developed in the last few years, to predict the dynamics of these nonlinear systems in the particular case of a 4-Wave Mixing process and under the degenerate undepleted pump assumption. We will demonstrate that, under the same assumption, all the results are comparable in terms of amplification of the output fields.

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.

The investigation of materials under extreme pressure conditions requires high-performance cells whose design invariably involves trade-offs between the maximum achievable pressure, the allowed sample volume, and the possibility of real-time pressure monitoring. With a newly conceived hybrid piston-clamped anvil cell, we offer a relatively simple and versatile system, suitable for nuclear magnetic resonance experiments up to 4.4 GPa. Finite-element models, taking into account mechanical and thermal conditions, were used to optimize and validate the design prior to the realization of the device. Cell body and gaskets were made of beryllium-copper alloy and the pistons and pusher were made of tungsten carbide, while the anvils consist of zirconium dioxide. The low-temperature pressure cell performance was tested by monitoring in situ the pressure-dependent 63Cu nuclear-quadrupole-resonance signal of Cu2O.

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...

Quantitative nano-imaging of metal traces in a solid is a recent capability arising from the construction of hard X-ray nanoprobes dedicated to X-ray Fluorescence (XRF) imaging on upgraded third generation synchrotrons. Micrometer sample preparation valid for trace analysis is a fundamental part of the required developments to capitalize on the reduced Minimum Detection Limits. Practical guidelines lead us to propose a customized use of Focused Ion Beams (FIB) backed by state of the art Monte Carlo XRF modeling to initiate preparations of new samples and certified standards. The usefulness of these developments is illustrated by the first detection of Ni traces (4.57E+07 ± 3.2E+06 (7.1%) at μm −3 ) in a 3.35 Ga old microstructure of putative microbial origin from Barberton (South Africa). A list of feasibility checks provides a way of getting below 5 ppm MDLs for acquisition-times of 10 s with an analytical precision better than 10%.

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.

In the present work, we report on the monolithic fabrication by means of ion beam lithography of hollow micro-channels within a diamond substrate, to be employed for microfluidic applications. The fabrication strategy takes advantage of ion beam induced damage to convert diamond into graphite, which is characterized by a higher reactivity to oxidative etching with respect to the chemically inert pristine structure. This phase transition occurs in sub-superficial layers thanks to the peculiar damage profile of MeV ions, which mostly damage the target material at their end of range. The structures were obtained by irradiating commercial CVD diamond samples with a micrometric collimated C+ ion beam at three different energies (4 MeV, 3.5 MeV and 3 MeV) at a total fluence of 2 × 1016 cm−2. The chosen multiple-energy implantation strategy allows to obtain a thick box-like highly damaged region ranging from 1.6 μm to 2.1 μm below the sample surface. High-temperature annealing was performed to both promote the graphitization of the ion-induced amorphous layer and to recover the pristine crystalline structure in the cap layer. Finally, the graphite was removed by ozone etching, obtaining monolithic microfluidic structures. These prototypal microfluidic devices were tested injecting aqueous solutions and the evidence of the passage of fluids through the channels was confirmed by confocal fluorescent microscopy.

Ni 80 Fe 20 antidot arrays having different lattice geometrical properties and irregularities were prepared via electron beam lithography and self-assembling of polystyrene nanospheres. All the samples were experimentally characterised by magnetic force microscopy and room-temperature magneto-resistance measurements in different configurations. The analysis, supported by micromagnetic simulations, has been focused on the effect of lattice geometry on the magneto-resistance behaviour of these systems. The detailed investigation through micromagnetic simulations of the magnetic domain configuration as a function of the applied field allows a complete understanding of the qualitative and quantitative difference of anisotropic magneto-resistance properties that have been measured in samples with different lattice geometries and in different measurement configurations.

Cylinder forming PS-b-PMMA block copolymer (BCP) thin films were deposited on pre-patterned surfaces with densely packed and nanometer wide trenches defined by conventional top down approaches and arranged to form a periodic grating. The films were subsequently annealed at 250 °C for times ranging from 30 s to 900 s in a rapid thermal processing device and their morphology evolution within the topographically defined structures was systematically investigated. Irrespective of the surface neutralization, an irreversible orientational flipping of the BCP microdomains inside the trenches was observed and attributed to de-swelling of the polymeric film as a consequence of a progressive desorption of the solvent retained inside the film. Systematic investigation of the annealing process indicates that the flipping is strongly dependent on the geometric parameters of the trenches and on the relative position of the analysed trench with respect to the periodic topographic structure. © 2014 The Royal Society of Chemistry.

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

We propose the concept of a quantized single-electron source based on the interplay between Coulomb blockade and magnetic flux-controllable superconducting proximity effect. We show that flux dependence of the induced energy gap in the density of states of a nanosized metallic wire can be exploited as an efficient tunable energy barrier which enables charge pumping configurations with enhanced functionalities. This control parameter strongly affects the charging landscape of a normal metal island with non-negligible Coulombic energy. Under a suitable evolution of a time-dependent magnetic flux the structure behaves likewise a turnstile for single electrons in a fully electrostatic regime., Comment: 6 pages, 4 colour figures

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

Silicon offers a compelling platform for developing hybrid architectures that exploit novel functionalities. Heteroepitaxial growth of Ge on Si is a prominent approach to tailor material properties to achieve this goal. However, designing Ge-based heterostructures, which fulfill ever-demanding photonic and electronic applications, demands crucial control over the unavoidable non-radiative recombinations occurring at free surfaces and growth defects like dislocations. Yet the mitigation over such parasitic optical activity remains an open issue. Here we tackle this problem and demonstrate a more than 2 orders of magnitude photoluminescence (PL) enhancement achieved via confinement of threading dislocations and carefully controlled surface passivation of micron-scale Ge on Si crystals. By spectrally resolving interband and dislocation-related PL, we underpin the role played by dislocations in limiting the radiative emission, and we identify effective solutions based upon bandgap engineering to further boosting light emission efficiency. Noticeably, by combining steady state and time-resolved PL we disentangle non-radiative channels due to free surfaces and dislocations, eventually shining light on their relative impact at various temperature regimes. These findings have the potential of being beneficial for numerous applications of Ge-based heterostructures, in particular for moving forward their exploitation within the fast-growing field of Si-photonics.

Due to their outstanding mechanical properties, diamond and diamond-like materials find significant technological applications ranging from well-established industrial fields (cutting tools, coatings, etc.) to more advanced mechanical devices as micro- and nano-electromechanical systems. The use of energetic ions is a powerful and versatile tool to fabricate three-dimensional micro-mechanical structures. In this context, it is of paramount importance to have an accurate knowledge of the effects of ion-induced structural damage on the mechanical properties of this material, firstly to predict potential undesired side-effects of the ion implantation process, and possibly to tailor the desired mechanical properties of the fabricated devices. We present an Atomic Force Microscopy (AFM) characterization of free-standing cantilevers in single-crystal diamond obtained by a FIB-assisted lift-off technique, which allows a determination of the Young's modulus of the diamond crystal after the MeV ion irradiation process concurrent to the fabrication of the microstructures, and subsequent thermal annealing. The AFM measurements were performed with the beam-bending technique and show that the thermal annealing process allows for an effective recovery of the mechanical properties of the pristine crystal., 15 pages, 5 figures

We describe the first use of a novel photoresist-free X-ray nanopatterning technique to fabricate an electronic device. We have produced a proof-of-concept device consisting of a few Josephson junctions by irradiating microcrystals of the Bi2Sr2CaCu2O8+δ (Bi-2212) superconducting oxide with a 17.6 keV synchrotron nanobeam. Fully functional devices have been obtained by locally turning the material into a nonsuperconducting state by means of hard X-ray exposure. Nano-XRD patterns reveal that the crystallinity is substantially preserved in the irradiated areas that there is no evidence of macroscopic crystal disruption. Indications are that O ions have been removed from the crystals, which could make this technique interesting also for other oxide materials. Direct-write X-ray nanopatterning represents a promising fabrication method exploiting material/material rather than vacuum/material interfaces, with the potential for nanometric resolution, improved mechanical stability, enhanced depth of patterning, and absence of chemical contamination with respect to traditional lithographic techniques.

Germanium has been under the spotlight of researchers for several decades and it has been studied both from the theoretical and experi- mental point of view. Its characteristic conduction band, with four minima at the edges of the Brillouin zone, is a playground for material scientists. Here we present the magnetic resonance of conduction electrons in bulk Ge crystal and in Ge quantum wells (QWs). The carriers were generated in the bulk by illumi- nation, while they were introduced in the QWs by modulation doping. In the bulk, we observed ESR lines with axial symmetry and principal g values gp=1.920 and gt=0.839, as expected for electrons in conduction band-like states. In the QWs there is a dependency on the thickness of the well, in agreement with the model proposed by Baron et al. [1]. Relaxation times have been estimated by the saturation curves and linewidth, providing exceptionally long values with respect to the bulk. The ability of tailoring the g factor in a semiconductor is appealing because it opens new pathways, allowing spintronic functionalities on a silicon-compatible technolo- gy. References. 1. F. Baron et al., Phys. Rev. B 2003, 68, 195306

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

The ability of tailoring the Landé g-factor in semiconductors is appealing because it is related to the possibility of tuning the spin-orbit interaction in the solid state and ultimately to control the spin-dependent properties via external fields in spintronic devices. Quantum confinement has been shown to be an effective mean to tailor the electron g-factor in III-V heterostructures. Nevertheless, to date no experimental proof was shown in Ge which is a CMOS compatible material, although such an effect was predicted in Ge quantum wells (QWs) by Baron et al., Phys. Rev. B 68,195306 (2003). Here we report the first Electron Spin Resonance (ESR) measurements of conduction electrons in Ge/SiGe QWs on Si. ESR lines in the 0.8 to 1.93 g-factor range are observed, showing that the g-factor of confined electrons in the L valley is highly anisotropic, similarly to the bulk. Our data prove that confinement increases the g-factor in QWs with respect to bulk Ge, in full agreement with the theoretical predictions. The lineshape study highlighted that the spin relaxation is governed by Elliot-Yafet type processes, typical for centrosymmetric materials. Longitudinal spin relaxation times were measured from the power dependence of the lines, providing exceptionally long values with respect to bulk Ge. These findings open new pathways for manipulating spin properties in Ge-based nanostructures, encouraging the development of spintronic functionalities on the mainstream Si platform