International and National Journals
G. Ghigo, D. Botta, R. Gerbaldo, L. Gozzelino, F. Laviano, B. Minetti, D. Andreone, E. Monticone, E. Mezzetti
MgB2 thin films for radiation detectors operating at microwave frequencies
CP824, Advances in Cryogenic Engineering: Trans. of the International Cryogenic Materials Conference (ICMC), Vol. 52B, p. 463, edited by U. Balachandran, AIP 2006.
The aim of this work is to investigate the potential of superconducting magnesium diboride (MgB2) thin films, prepared by the in-situ method, as broadband radiation detectors based on the microwave measurement of the complex impedance. The characterization of the films at microwave frequencies has been obtained by a coplanar resonator technique. The data analysis results in the determination of penetration depth, surface impedance and energy gap. In view of their microwave properties, particularly of the gap structure, the possible use of such MgB2 films as photon detectors is discussed in detail.
S. Borini, L. Boarino, G. Amato
Coulomb blockade tuned by NO2 molecules in nanostructured silicon
Advanced Materials, Vol. 18, no. 18, pp. 2422-2425, 2006.
S. Borini, L. Boarino, G. Amato
Anisotropic resistivity of (100)-oriented mesoporous silicon
Applied Physics Letters, Vol. 89, p. 132111, 2006; Virtual Journal of Nanoscale Science and Technology, October 2006.
The resistivity of (100)-oriented mesoporous silicon has been studied using two different electrode configurations. The authors observed that the electronic transport along the longitudinal direction (parallel to the sample surface) is strongly inhibited at room temperature but not along the perpendicular direction. They show that such electrical anisotropy can be removed by heating the material, reporting an increase of six orders of magnitude of the longitudinal conductivity when the temperature rises from 20 to 100 ºC. These experimental findings are interpreted on the basis of the material morphology and nanostructuration, which determine the availability of percolative pathways for free charge carriers.
S. D'Auria, M. de Champdoré, V. Aurilia, A. Parracino, M. Staiano, A. Vitale, M. Rossi, I. Rea, L. Rotiroti, A. M. Rossi, S. Borini, I. Rendina, L. De Stefano
Nanostructured silicon-based biosensors for the selective identification of analytes of social interest
Journal of Physics-Condensed Matter, Vol. 18, no. 33, pp. S2019-S2028, 2006.
Small analytes such as glucose, L-glutamine (Gln), and ammonium nitrate are detected by means of optical biosensors based on a very common nanostructured material, porous silicon (PSi). Specific recognition elements, such as protein receptors and enzymes, were immobilized on hydrogenated PSi wafers and used as probes in optical sensing systems. The binding events were optically transduced as wavelength shifts of the porous silicon reflectivity spectrum or were monitored via changes of the fluorescence emission. The biosensors described in this article suggest a general approach for the development of new sensing systems for a wide range of analytes of high social interest.
C. Portesi, S. Borini, G. Amato, E. Monticone
Fabrication of superconducting MgB2 nanostructures by an electron beam lithography-based technique
Journal of Applied Physics, Vol. 99, no. 6, art. no. 066115, 2006.
In this work, we present the results obtained in fabrication and characterization of magnesium diboride nanowires realized by an electron beam lithography EBL-based method. For fabricating MgB2 thin films, an all in situ technique has been used, based on the coevaporation of B and Mg by means of an e-gun and a resistive heater, respectively. Since the high temperatures required for the fabrication of good quality MgB2 thin films do not allow the nanostructuring approach based on the lift-off technique, we structured the samples combining EBL, optical lithography, and Ar milling. In this way, reproducible nanowires 1 µm long have been obtained. To illustrate the impact of the MgB2 film processing on its superconducting properties, we measured the temperature dependence of the resistance on a nanowire and compared it to the original magnesium diboride film. The electrical properties of the films are not degraded as a consequence of the nanostructuring process, so that superconducting nanodevices may be obtained by this method.
L. De Stefano, K. Malecki, A. M. Rossi, L. Rotiroti, F. G. Della Corte, L. Moretti, I. Rendina
Integrated silicon-glass opto-chemical sensors for lab-on-chip applications
Sensors and Actuators B-Chemical, Vol. 114, no. 2, pp. 625-630, 2006.
The compatibility of porous silicon and anodic bonding technologies for the realization of sensing micro-components in lab-on-chip applications is demonstrated. In particular, we have developed and tested an innovative anodic bonding process: voltage, time and temperature have been properly matched in order not to affect the properties of the transducing material, which can be strongly modified by thermal treatments through oxidation. Two devices for chemical and biological sensing have been designed, fabricated and tested. The results obtained are very promising, especially regarding further integration of porous silicon and glass with optical and microelectromechanical instruments.
S. Maggi, N. De Leo, V. Lacquaniti, A. Agostino, R. Gonnelli, P. Verhoeve
Nb/Al STJ detectors with sub-nA subgap current
Physica C, Vol. 435, pp. 103-106, 2006.
Superconducting tunnel junctions (STJ) are promising high-resolution radiation detectors because of their larger energy resolution with respect to conventional Si-based detectors. We have developed a fabrication process for Nb/Al-AlOx/Nb STJ devices which produces junctions with subgap currents below 50 pA at 300 mK, a factor of 10-6less than the subgap current at 4.2 K. We report the details of the fabrication process and preliminary results on x-ray measurements at 300 mK with a 5 mC 55 Fe source.
S. Maggi, A. Agostino, C. Cagliero, R. Gonnelli, V. Lacquaniti, P. Verhoeve
Development of low subgap current Nb/Al STJ detectors
Journal of Physics: Conference Series (7th European Conference on Applied Superconductivity), Vol. 43, pp. 1330-1333, 2006.
We have developed a fabrication process for Nb-based STJ detectors which allows to fabricate junctions with subgap currents close to 20 pA at 300 mK, more than six orders of magnitude less than the subgap current at 4.2 K. The junctions are diamond-shaped devices, with areas between 20×20 and 100×100 µm2 We report the details of the fabrication process, together with an analysis of the grain structure of the films by AFM and XRD. We show the measured I- V curves at 300 mK and the temperature dependence of the subgap current between 300 and 1100 mK. We also report preliminary results on x-ray measurements at 300 mK with a 5 mC 55 Fe source.
C. Portesi, D. Mijatovic, D. Veldhuis, A. Brinkman, E. Monticone, R.S. Gonnelli
MgB2 magnetometer with a directly coupled pick-up loop
Superconductor Science and Technology, Vol. 19, pp. S303-S306, 2006.
In this work, we show the results obtained in the fabrication and characterization of an MgB2 magnetometer with a directly coupled pick-up loop. We used an all in situ technique for fabricating magnesium diboride films, which consists of the co-evaporation of B and Mg by means of an e-gun and a resistive heater respectively. Consequently, we realized the superconducting device, which incorporates two nanobridges as weak links in a superconducting loop. The nanobridges were realized by focused ion beam milling; they were 240 nm wide and had a critical current density of 107 A cm-2. The magnetometer was characterized at different temperatures and also measurements of the noise levels have been performed. The device shows Josephson quantum interference up to 20 K and the calculated effective area at low temperatures was 0.24 mm2. The transport properties of the magnetometer allow determining fundamental materials properties of the MgB2 thin films, such as the penetration depth.
V. Lacquaniti, D. Andreone, S. Maggi, R. Rocci, A. Sosso, R. Steni
Temperature behavior of SNS-like Nb/Al-AlOx/Nb Josephson junctions
Physica C: Superconductivity and its applications, Vol. 435, no. 1-2, pp. 99-102, 2006.
Overdamped Nb/Al-AlOx/Nb Josephson junctions are an intermediate state between the SIS and SNS Josephson junctions. Stable and reproducible non-hysteretic current-voltage characteristics have been obtained with a proper choice of the fabrication parameters, featuring critical current densities Jc up to 25 kA/cm2 and characteristic voltages up to 450 µV. While these values make the junctions interesting for RSFQ electronic circuits, their response to an RF signal at 70 GHz has demonstrated their suitability for both programmable and ac voltage standard. In these work we analyse the temperature behavior of these junctions up to T/Tc = 1, Tc being the niobium critical temperature, which gives relevant information on the junction structure and, especially, on the oxide insulator/metallic film barrier, which is the key for the reproducible transition from an hysteretic to a non-hysteretic behavior. The results are also compared with other data of hysteretic and overdamped junctions.
E. Monticone, C. Portesi, M. Rajteri, A. Rossi
Electrical and optical properties of MgB2 grown by co-evaporation method
Journal of Physics and Chemistry of Solids, Vol. 67, no. 1-3, pp. 305-307, 2006.
In this work we report details on fabrication and characterization of MgB2 films grown on silicon nitride by co-evaporation of B and Mg and post annealing in-situ. The optimised films show critical temperatures between 32 and 36 K with a residual resistivity ratio around 1.1-1.3. The critical current densities at 4.2 K, evaluated by transport method is close to 5×106 A/cm2. Optical and morphological characterizations show that films have smooth surfaces with a reflectance typical of MgB2 with clean surface.
E. Taralli, C. Portesi, C. Ricciardi, E. Tresso, M. Rajteri
Improvement of titanium film absorption with antireflection coatings
Nuclear Instruments and Methods in Physics Research, A, Vol. 559, no. 2, pp. 757-759, 2006.
One of the materials widely used in the fabrication of transition-edge sensor for photon counting is titanium. In the visible-near infrared spectral region the photon absorption occurs directly in the film and the quantum efficiency of the detector is limited by the reflection losses at the film surface, which are around 60%. For many applications like quantum cryptography these losses are too high. One way to reduce the reflection is to apply an antireflection coating on the films. In this work we present different solutions based on the deposition of few layers of amorphous silicon-nitrogen alloys, a material with a tunable refraction index. The design of multilayer is based on an optimisation program which adopts a genetic algorithm to find out the global minimum of the reflectivity among a wide range of thickness possibilities for the different layers. We present solutions that minimize the reflectivity simultaneously at different telecommunication wavelengths or in a continuum band. The simulations are compared with experimental results.
R. S. Gonnelli, D. Daghero, A. Calzolari, G. A. Ummarino, M. Tortello, V. A. Stepanov, N. D. Zhigadlo, K. Rogacki, J. Karpinski, C. Portesi, E. Monticone, D. Mijatovic, D. Veldhuis, A. Brinkman
Recent achievements in MgB2 physics and applications: a large-area SQUID magnetometer and point-contact spectroscopy measurements
Physica C-Superconductivity and its Applications, Vol. 435, nos. 1-2, pp. 59-65, 2006.
In the first part of the present paper we discuss the fabrication and the characterization of an MgB2-based SQUID magnetometer with a directly coupled large-area pick-up loop, made on an MgB2 film deposited by an all in situ technique. The coarse structure of the SQUID was defined by optical lithography and Ar-ion milling, while the two nanobridges acting as weak links in the superconducting loop were made by focused ion beam (FIB) milling. The device was characterized at different temperatures and showed Josephson quantum interference up to 20 K as well as a noise level already compatible with the recording of an adult magnetocardiogram. In the second part, concerning the fundamental physics of MgB2, we present the results of very recent point-contact measurements on Mg1-xMnxB2 single crystals with 34.1>Tc>13.3 K (i.e. 0.37%<x<1.5%). The experimental conductance curves were fitted with the generalized two-band BTK model and their behaviour in magnetic fields was studied to check if both the order parameters (OPs) of the σand πbands were present in the whole doping range. The dependence of the OPs (evaluated through the fit) on the Andreev critical temperature of the junctions is analyzed in the framework of the two- band Eliashberg theory by including the effects of magnetic impurities. The results give an evidence of a dominant effect of the magnetic impurities on the σ-band channel.
C. Gandini, M. Rajteri, C. Portesi, E. Monticone, A. Masoero, P. Mazzetti
Investigation of the resistive transition of MgB2 thin film through current noise
Journal of Physics: Conference Series (7th European Conference on Applied Superconductivity), Vol. 43, pp. 313-316, 2006.
In this paper we present measurements concerning the current noise produced during the resistive transition in a MgB2 polycrystalline thin film. The power spectrum of the current noise, observed when the temperature is slowly changed across its critical value, presents a large electrical noise of the 1/fntype (n˜=3) over a quite wide range of frequencies. This noise may be considered as generated by the abrupt creation of resistive strips across the specimen constituted by grains which have undergone the resistive transition. A computer model that takes into account fluctations of the grain critical currents and of the number of grain per strips, has been developed to simulate the resistive transition and to evaluate the noise power spectrum. When the temperature is incresed and reaches its critical value, resistive strips are formed according to a percolative process, giving rise to resistance steps which are at the origin of the noise. The theoretical results obtained by this model are in good agreement, concerning both the shape and intensity of the noise power spectrum, with the experimental data directly measured on the specimen.
Technical Reports
F. Bellotti, G. Amato, R. Rocci
Evaporatore ad effetto Joule
Rapporto Tecnico INRIM n. 2, gennaio 2006.
Viene qui descritto il funzionamento di un evaporatore ad effetto Joule e di tutti i dispositivi che lo compongono: pompe meccaniche, pompe turbomolecolari, misuratori di pressione.
F. Bellotti, R. Rocci, M. Bertinetti, V. Fornero, M. Rocchia
Progettazione e realizzazione di un apparato per la fabbricazione di strutture ottiche in Silicio Poroso a basse temperature
Rapporto Tecnico INRIM n. 30, settembre 2006.
Vengono qui elencati i vantaggi dell'utilizzo delle basse temperature nella fabbricazione di strutture ottiche in silicio poroso quali riflettori di Bragg e microcavità Fabry-Perot.