Research topics are focused on quantum effects observable in superconducting and nano-devices. The aim is to exploit new devices and techniques for various aspects of measurement science, spanning from traditional electrical metrology to environmental monitoring, biological measurements and food metrology.
The development of silicon nanosensors and the fundamental study of electronic transport in mesostructures has lead to the evidence of a conductivity gap at room temperature in mesoporous silicon, ascribable to collective Coulomb blockade behavior, when measured in a particular guarded electrode configuration. Such behavior can be explained in the framework of the theory of transport in nanocrystal arrays. Moreover, NO2 molecules are able to reduce the gap, so that highly sensitive threshold sensors can be obtained. The realization of the Electrical Current Standard has been pursued by means of the Single Electron Transistor (SET) and Electronic Pump Devices. First SET demonstrators are being entirely realized at INRIM.
Differential conductance of a mesoporous Si sample. A gap is clearly visible. When the guard is removed, the gap disappears, due to the structural anisotropy of the material.
NO2 molecules narrow the conductivity gap (the arrow indicates the increase of NO2 gas pressure).
The development of optimised junctions for AC and DC Josephson voltage standards, both programmable arrays and Josephson Arbitrary Waveform Synthetizer, has been addressed to the study of the critical parameters of overdamped Nb based Josephson junctions at temperatures above liquid helium.
Experimental and calculated dependence of the critical current on temperature for different types of Josephson junctions.
The best electrode configuration has been evaluated by comparing these junctions with other hysteretic and non-hysteretic structures. In view of using these devices in a compact cryocooler setup RF, induced quantized voltage steps stable for more than ten minutes have been measured on single junctions with nV accuracy up to 6.5 K.
Quantized voltage step measured with nanovoltmeter at a temperature of 6.5 K for a Nb/Al-AlOx/Nb single JJ.
Within the Special Facilities program of the EU, a circuit containing arrays of 1600 Nb/Al-AlOx/Nb junctions coupled to the microwave signal through a microstrip fin.line antenna has been designed and a mask set has been realized in a joint cooperation with the PTB Quantum Metrology group.
Layout of the series array circuit for programmable voltage standard.
MgB2 meanders lines with nanometric lateral resolution have been fabricated by electron beam lithography (EBL)-based technique in view of their applications to fast superconducting single photon detectors. The critical current density of the nanostructures was of 8×106 A/cm2 at 9.5 K close to the depairing critical current of MgB2. The role of disorder on MgB2 film has been investigated by microwave coplanar resonators technique in collaboration with Politecnico di Torino. The results seem to suggest that grain boundaries are responsible for the extrinsic contribution to the nonlinear behaviour of the device.Transition-Edge Sensors (TES) based on Ti/Au films have been fabricated by e-beam evaporation in UHV. Preliminary tests show their ability as single photon detectors in the optical band.
Protein microarrays have been realized on a Porous Silicon (PS) chip by means of electron beam irradiation for simultaneous sensing of different analytes. The biomolecule binding occurs by incubating the activated PS substrate with the desired protein solution. The amount of bound proteins can be easily controlled by tuning the electronic dose, the e-beam energy and the incubation time. Repeating in a serial manner the process, a protein-based multiarray biochip can be obtained.
Fluorescence microscopy image of a porous silicon biochip. Squares array of a Glucose Binding Protein (GBP) microspots.
Fluorescence microscopy image of a porous silicon biochip. Different proteins [GBP and Glutamine Binding Protein (GlnBP)] immobilized on the same chip.
The strong light emission originating from small (˜nm) semiconductor nanocrystals has pushed a strong research worldwide on the possible application of such luminescent markers in biological tissues. There are several advantages with respect to conventional dyes, including stability, wide excitation band, narrow emission band, the dependence of the emission wavelength only on QD size, without any change in chemistry and so on. Thanks to the financial support from the Regione Piemonte, the group has started a research program on all-Si QDs.
Fluorescence image of Quantum Dot all-silicon.
Further efforts were made to improve and optimize the analytical method developed for selectively monitoring ethyl alcohol in wines based on the use of a Porous Silicon (PS) microcavity as optical alcoholmeter. The PS alcoholmeter was then tested by analysing several wine samples. The linear response of the microcavity (shift of the cavity mode) to the alcoholic strength of wines allows us to determine the amount of ethanol in wine with high accuracy and reliability. Moreover, the calculated values differ less than 0.5% from those obtained with the EC method (Regulation no. 128/2004) in accordance with the limits imposed by European laws.
Alcoholmeter design [(a) compact and (b) exploded view].
Dynamic shift of the PS microcavity as a function of the temperature for two reference solutions kept at 38ºC.
Linear behaviour of the PS alcoholmeter as a function of alcoholic strength.