E. Vittone

A determination of the Avogadro constant

We have determined Avogadros constantNA using a direct method. The result ofNA=6.0221363×1023 mol−1 differs from the most recent CODATA value of 6.0221367×1023 mol−1 by only 0.07 ppm, the relative uncertainties being 1.1. ppm and 0.6 ppm, respectively. The value was derived from the determination of the lattice parameter, the density and the molar mass of a silicon single crystal. It will be possible in the future to further reduce the uncertainties of measurement by the procedure described here.

Review of the development of diamond radiation sensors

Abstract Diamond radiation sensors produced by chemical vapour deposition are studied for the application as tracking detectors in high luminosity experiments. Sensors with a charge collection distance up to 250 μm have been manufactured. Their radiation hardness has been studied with pions, proton and neutrons up to fluences of 1.9×10 15 π cm −2 , 5×10 15 p cm −2 and 1.35×10 15 n cm −2 , respectively. Diamond micro-strip detectors with 50 μm pitch have been exposed in a high-energy test beam in order to investigate their charge collection properties. The measured spatial resolution using a centre-of-gravity position finding algorithm corresponds to the digital resolution for this strip pitch. First results from a strip tracker with a 2×4 cm 2 surface area are reported as well as the performance of a diamond tracker read out by radiation-hard electronics with 25 ns shaping time. Diamond pixel sensors have been prepared to match the geometries of the recently available read-out chip prototypes for ATLAS and CMS. Beam test results are shown from a diamond detector bump-bonded to an ATLAS prototype read-out. They demonstrate a 98% bump-bonding efficiency and a digital resolution in both dimensions.

Fabrication and electrical characterization of three-dimensional graphitic microchannels in single crystal diamond

We report on the systematic characterization of conductive micro-channels fabricated in single-crystal diamond with direct ion microbeam writing. Focused high-energy ( MeV) helium ions are employed to selectively convert diamond with micrometric spatial accuracy to a stable graphitic phase upon thermal annealing, due to the induced structural damage occurring at the end-of-range. A variable-thickness mask allows the accurate modulation of the depth at which the microchannels are formed, from several µm deep up to the very surface of the sample. By means of cross-sectional transmission electron microscopy (TEM), we demonstrate that the technique allows the direct writing of amorphous (and graphitic, upon suitable thermal annealing) microstructures extending within the insulating diamond matrix in the three spatial directions, and in particular, that buried channels embedded in a highly insulating matrix emerge and electrically connect to the sample surface at specific locations. Moreover, by means of electrical characterization at both

A new determination of N/sub A/

The Avogadro constant was determined by measurements of the (220) lattice spacing, density, and molar mass of silicon crystals. The measured value is N/sub A/=(6.0221379/spl plusmn/0.0000025)/spl times/10/sup 23/ mol/sup -1/. >

Theory of ion beam induced charge collection in detectors based on the extended Shockley–Ramo theorem

Abstract An analysis of the charge collection process induced by focused MeV ion beams in semiconductor devices is presented. It is based on the extended Shockley–Ramo theorem that provides a rigorous mathematical tool for the calculation of the induced charge and current under the assumption of a quasi-steady-state operation of the semiconductor device. A complete description of the theory and underlying assumption is given as well as a simple application of the method aimed to evaluate the main transport properties of fully depleted semiconductors from the analysis of frontal and lateral ion beam induced charge collection (IBICC) measurements.

CVD diamond tips as X-ray detectors

Abstract Diamond is a very attractive material for use as a radiation detector due to its inertness, radiation hardness and tissue equivalence. The development of diamond radiation detectors was limited by the availability of good and reproducible natural samples. The advent of chemical vapour deposition techniques has allowed these drawbacks to be overcome and applications of CVD diamond in X-ray and nuclear dosimetry to be explored by several researchers. In this paper, we report the fabrication and characterisation of miniaturised (0.1 mm3) X-ray detectors made from polycrystalline diamond films ( 10 20 μm thick) deposited by hot filament vapour deposition technique on metallic (tungsten) 300-μm-diameter tips. The detector response to X-ray flux produced by an X-ray generator with peak energies ranging from 50 to 250 keV and by electron linear accelerator used in radiotherapy with a peak energy of 6 MeV has been investigated. The linearity and the sensitivity of the detector as a function of dose rate at different photon energies has been evaluated, and the collection length has been estimated by analysing the behaviour of the photocurrent as a function of the applied bias voltage.

Systematic study of defect-related quenching of NV luminescence in diamond with time-correlated single-photon counting spectroscopy

We report on the systematic characterization of photoluminescence (PL) lifetimes in NV- and NV0 centers in 2 MeV H+ implanted type Ib diamond samples by means of a time correlated single photon counting (TCSPC) microscopy technique. A dipole-dipole resonant energy transfer model was applied to interpret the experimental results, allowing a quantitative correlation of the concentration of both native (single substitutional nitrogen atoms) and ion-induced (isolated vacancies) PL-quenching defects with the measured PL lifetimes. The TCSPC measurements were carried out in both frontal (i.e. laser beam probing the main sample surface along the same normal direction of the previously implanted ions) and lateral (i.e. laser beam probing the lateral sample surface orthogonally with respect to the same ion implantation direction) geometries. In particular, the latter geometry allowed a direct probing of the centers lifetime along the strongly nonuniform damage profiles of MeV ions in the crystal. The extrapolation of empirical quasi-exponential decay parameters allowed the systematic estimation of the mean quantum efficiency of the centers as a function of intrinsic and ion-induced defect concentration, which is of direct relevance for the current studies on the use of diamond color centers for photonic applications.

Tracking with CVD diamond radiation sensors at high luminosity colliders

Recent progress on developing diamond-based sensors for vertex detection at high luminosity hadron colliders is described. Measurements of the performance of diamond sensors after irradiation to fluences of up to 5/spl times/10/sup 15/ hadrons/cm/sup 2/ are shown. These indicate that diamond sensors will operate at distances as close as 5 cm from the interaction point at the Large Hadron Collider (LHC) for many years at full luminosity without significant degradation in performance. Measurements of the quality of the signals from diamond sensors as well as spatial uniformity are presented. Test beam results on measurements of diamond-based microstrip and pixels devices are described.

Defect enhanced funneling of diffusion current in silicon

We report a current transport mechanism observed during electrochemical anodization of ion irradiated p-type silicon, in which a hole diffusion current is highly funneled along the gradient of modified doping profile towards the maximum ion induced defect density, dominating the total current flowing and hence the anodization behaviour. This study is characterized within the context of electrochemical anodization but relevant to other fields where any residual defect density may result in similar effects, which may adversely affect performance, such as in wafer gettering or satellite-based microelectronics. Increased photoluminescence intensity from localized buried regions of porous silicon is also shown.

The (220) lattice spacing of silicon

Further details are given of an experiment based on combined X-ray and optical interferometry to measure the (220) lattice spacing of silicon. A resolution of 5/spl times/10/sup -9/ d/sub 220/ was achieved and the silicon d/sub 220/ was determined to 3/spl times/10/sup -8/ d/sub 220/ accuracy. The measured value is d/sub 220/=(192015.551/spl plusmn/0.005) fm. After correction for the impurity-induced lattice strain, d/sub 220/=(192015.569/spl plusmn/0.006) fm was obtained. >