Paolo Calvani

First neutron and X-ray beam tests on a novel 12-pixel single-crystal diamond mosaic detector are presented and discussed.
Preliminary characterization of single-pixel electronic properties, performed with alpha particles, results in charge carrier mobilities >2000 cm^2/Vs and saturation velocities of the order of 10^7 cm/s. Signal stability over time, measured with a 241Am source (37 kBq activity), is longer than 5 h. Tests under an intense X-ray beam (1 Gy/h dose-rate) show a very good response uniformity (down to about 1% of relative standard deviation from mean value), suggesting a high level of pixel reproducibility at intermediate bias voltages (ranging from
20 to 100 V). Response uniformity reduces at voltages>200 V,
due presumably to radiation-assisted detrapping effects.
Preliminary results of 12-pixel simultaneous acquisitions of
X-ray beam profiles and pulse height spectra under a fast
neutron beam (14 MeV) are also presented.

Black diamond is obtained by a controlled nanoscale periodic texturing of CVD diamond surface, able to drastically modify the interaction with solar radiation from optical transparency up to solar absorptance values even >90%. Surface texturing, performed by the use of an ultra-short pulse laser, is demonstrated to induce an intermediate band within the diamond bandgap supporting an efficient photoelectronic conversion of sub-bandgap photons (<5.5 eV). The intermediate band introduction results in an external quantum efficiency enhanced up to 800 nm wavelengths (and up two orders of magnitude larger than the starting transparent diamond film), without affecting the film transport capabilities. The optical and photoelectronic outstanding results open the path for future application of black diamond as a photon-enhanced thermionic emission cathode for solar concentrating systems, with advantages of excellent electronic properties combined with a potentially very low work function and high thermal stability.

ABSTRACT A cathode structure for photon-enhanced thermionic emission was designed for high temperature energy conversion in solar concentrating systems. Surface-hydrogenated diamond is one of the few semiconductors to show negative electron affinity and a work function as low as 1.7 eV if nitrogen-doped, that is connected to a significant thermionic emission at moderate temperatures (up to 800 °C). But diamond is transparent to solar radiation, consequently advanced techniques for preparing an efficient sunlight absorbing diamond are discussed.

This work proposes the concept of a high-resolution wide-range dynamic neutron monochromator able to operate up to a few eV, thus significantly extending the reliable operating neutron energy range of the state-of-the-art crystal-based devices, and to improve energy resolution in the epithermal range if compared to mechanical choppers. The proposed device is based on a radiation-hard aluminium nitride (AlN)/diamond heterostructure, operating as a super-highfrequency (> 3 GHz) high-speed (> 10000 m/s) acoustic resonator. The resulting surface acoustic wave (SAW) acts as a dynamic grating for the incoming neutrons: as long as neutron speed is lower than (or at least comparable to) SAW speed, diffraction angles are significantly enhanced, thus allowing for neutron beam monochromatization to be effective up to the eV energy range.
SAW amplitude can be electrically tuned to increase first-order reflectivity, leading to an enhanced intensity of the monochromatized beam.

Single crystal Diamond Detectors (SDD) are being increasingly exploited for neutron diagnostics in high power fusion devices, given their significant radiation hardness and high energy resolution capabilities. The geometrical efficiency of SDDs is limited by the size of commercially available crystals, which is often smaller than the dimension of neutron beams along collimated lines of sight in tokamak devices. In this work, we present the design and fabrication of a 14 MeV neutron spectrometer consisting of 12 diamond pixels arranged in a matrix, so to achieve an improved geometrical efficiency. Each pixel is equipped with an independent high voltage supply and read-out electronics optimized to combine high energy resolution and fast signals (<30 ns), which are essential to enable high counting rate (>1 MHz) spectroscopy. The response function of a prototype SDD to 14 MeV neutrons has been measured at the Frascati Neutron Generator by observation of the 8.3 MeV peak from the 12C(n, α)9Be reaction occurring between neutrons and 12C nuclei in the detector. The measured energy resolution (2.5% FWHM) meets the requirements for neutron spectroscopy applications in deuterium-tritium plasmas.

... Autori: Pasciuto, B; Corsaro, A; Sinisi, F;Calvani, P; Rossi, MC; Conte, G; Ciccognani, W; Limiti, E. ... Settore Disciplinare: ING-INF/01. Lingua: eng. Tipologia: Intervento a convegno. Citazione: Pasciuto, B., Corsaro, A., Sinisi, F., Calvani, P., Rossi, MC, Conte, G., et al. (2008). ...

The measurement of the density of occupied states as a function of the applied electric field, performed on single-crystal chemical vapour deposition diamond by x-ray modulated photocurrent technique, is reported. Two regimes of non-linear charge transport were observed: a classical Frenkel-Poole (FP) process at high electric fields (>6800 V/cm), and a radiation-assisted transport mechanism at intermediate electric fields (2000 to 6800 V/cm), consisting of a double-step process in which the direct re-emission into the extended band occurs following multiple photo-induced FP-like hopping transitions.

We report on the fabrication of graphitic columns induced in single-crystal diamond plates using 100 fs laser pulses at 800 nm wavelength. Different values of laser fluence (0.6–1.2 J/cm2) and graphitization speed (1–100 μm/s) were used for the laser treatment. A Raman investigation was performed aimed at evaluating the structural properties of the fabricated columns, showing that a lower laser fluence and a proper choice of graphitization speed may improve the degree of graphite crystallinity, and suppress the residual diamond content.

Surface texturing by fs-laser pulses has been performed in order to enhance optical absorptance of chemical vapour deposited diamond. The induced surface structures have been studied as a function of treatment dose D. Periodic structure with ripples of 170 nm has been observed for a D = 5.0 kJ cm−2, although not well defined texturing and damaged structures have been obtained for both lower and higher doses. Raman investigations point out negligible changes in crystal bulk for all investigated samples, thus suggesting that physical properties of the crystal were not changed by the treatment. Optical absorptance is strongly enhanced by fs-laser texturing and it is an increasing function of the treatment dose. The absorptance of solar spectrum saturates up to values larger than 90%. The obtained outstanding enhancement of photon absorption represents a preliminary and promising step for the exploitation of synthetic diamond in future high-efficient conversion devices for solar concentration based on photon-enhanced thermionic emission effect.Surface texturing by fs-laser pulses has been performed in order to enhance optical absorptance of chemical vapour deposited diamond. The induced surface structures have been studied as a function of treatment dose D. Periodic structure with ripples of 170 nm has been observed for a D = 5.0 kJ cm−2, although not well defined texturing and damaged structures have been obtained for both lower and higher doses. Raman investigations point out negligible changes in crystal bulk for all investigated samples, thus suggesting that physical properties of the crystal were not changed by the treatment. Optical absorptance is strongly enhanced by fs-laser texturing and it is an increasing function of the treatment dose. The absorptance of solar spectrum saturates up to values larger than 90%. The obtained outstanding enhancement of photon absorption represents a preliminary and promising step for the exploitation of synthetic diamond in future high-efficient conversion devices for solar concentration based on photon-enhanced thermionic emission effect.

Sub-micron gate length Metal Semiconductor Field Effect Transistors (MESFETs) have been realized on polycrystalline diamond samples supplied by Element Six Ltd. and by Russian Academy of Science. RF performances are shown for devices realized on polycrystalline diamond samples of different quality, stating the successfully improvement and reliability of realization technology.

On the basis of RF characteristics and measured small-signal parameters, an equivalent circuit model was formulated and characterized for metal-semiconductor field effect transistors based on H-terminated polycrystalline diamond. Starting from on-wafer measurements, a bias-dependent transistor behavior representation was fully determined. Such an equivalent circuit model is the first important step to realize an RF IC based on diamond. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2783–2786, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24734

ABSTRACT — Diamond is one of the suitable semi-conductor for vacuum electronics replacement in high power and high frequency applications. Sub-micron gate-length (200 nm) Metal Semiconductor Field Effect Transistor (MESFETs) have been fabricated on h-terminated polycrystalline ...

Abstract Diamond is in principle the highest performance widegap semiconductor. Its outstanding electronic and thermal properties make it an attractive material for high power radiofrequency (RF) and microwave electron devices. In this paper, the authors present RF power measurements of submicron H-terminated FETs on polycrystalline diamond up to 2 GHz, showing the potential of such substrate for the development of microwave power devices.

Abstract — Metal–Semiconductor Field Effect Transistors (MESFETs) were fabricated on polycrystalline diamond. Devices were realized to be employed in Microwave Integrated Circuits for satellite communications and high frequency power amplification, areas were diamond promise ...

I. INTRODUCTION Thanks to its exceptional properties, diamond in principle match the challenges of high tech applications. It cumulates extreme and unsurpassed electronic and thermal properties, such as large mobility for both electrons and holes, the best thermal ...