My research activity mainly focuses on the design, fabrication and characterization of diamond detectors for ionizing radiations (X-rays, gamma-rays) and nuclear particles (alpha and beta particles, neutrons), together with the development and test of the front-end and read-out electronics. Other research activities include the development of solar energy conversion modules based on photon-enhanced thermionic emission (PETE). Phone: +390690672237 Address: CNR-ISM, Area della Ricerca Roma 1 - Via Salaria km 29,300 - Monterotondo Stazione (RM), Rome, Italy
One of the goals of modern dynamic radiotherapy treatments is to deliver high-dose values in the ... more One of the goals of modern dynamic radiotherapy treatments is to deliver high-dose values in the shortest irradiation time possible. In such a context, fast X-ray detectors and reliable front-end readout electronics for beam diagnostics are crucial to meet the necessary quality assurance requirements of care plans. This work describes a diamond-based detection system able to acquire and process the dose delivered by every single pulse sourced by a linear accelerator (LINAC) generating 6-MV X-ray beams. The proposed system is able to measure the intensity of X-ray pulses in a limited integration period around each pulse, thus reducing the inaccuracy induced by unnecessarily long acquisition times. Detector sensitivity under 6-MV X-photons in the 0.1–10 Gy dose range was measured to be 302.2 nC/Gy at a bias voltage of 10 V. Pulse-by-pulse measurements returned a charge-per-pulse value of 84.68 pC, in excellent agreement with the value estimated (but not directly measured) with a comme...
Gated integrating measurement method represents a widely used approach when fast, repetitive anal... more Gated integrating measurement method represents a widely used approach when fast, repetitive analogue signals are concerned. In this work a compact synchronized gated-integrator prototype has been realized and preliminary characterized. Front-end electronics is based on the mature high-precision switched-integrator transimpedance-amplifier IVC102 whose output is connected to a precision LT1911 inverting amplifier, whereas analogue-to-digital conversion, as well as timing control circuitry, are performed by a high-efficiency LPC845 microcontroller. Synchronizing signal detection with the external trigger generated in coincidence with a source, the proposed circuitry amplifies and integrates the signal only when the pulse is generated, displaying excellent performances in terms of linearity, sensitivity and signal-to-noise ratio. Hence, the proposed solution represents an affordable alternative to continuous-time regime measurement-techniques, usually adopted in radiation dosimetry wh...
The circuit realizes a simple, low-cost lockin amplifier employing an Analog Devices AD630 balanc... more The circuit realizes a simple, low-cost lockin amplifier employing an Analog Devices AD630 balanced modulator-demodulator IC.
Optically triggered UV sensitive receivers were fabricated on polycrystalline diamond as surface ... more Optically triggered UV sensitive receivers were fabricated on polycrystalline diamond as surface channel MESFETs. Opaque gates with asymmetric structure were designed in order to improve charge photogeneration mainly within the gate-drain region. Photogenerated holes contributed to the channel charge by assistance of the local electric field, in such a way improving the current signal at the drain contact. The sensitivity to UV light is demonstrated by using 3 ns wide laser pulses at 193 nm, well over the diamond bandgap. The receiver transient response to such laser pulses shows that the photogeneration process is only limited by the pulse rise time and charge collection at the drain contact completed in a time scale of a few nanoseconds. Such opaque gate three-terminal devices are suitable for application in emerging photonic technologies, for power-management system optical receivers, where copper wires and EM shielding can be replaced by lightweight optical fibers.
We have correlated the surface conductivity of hydrogen-terminated diamond to the electronic stru... more We have correlated the surface conductivity of hydrogen-terminated diamond to the electronic structure in the Fermi region. Significant density of electronic states (DOS) in proximity of the Fermi edge has been measured by photoelectron spectroscopy (PES) on surfaces exposed to air, corresponding to a p-type electric conductive regime, while upon annealing a depletion of the DOS has been achieved, resembling the diamond insulating state. The surface and subsurface electronic structure has been determined, exploiting the different probing depths of PES applied in a photon energy range between 7 and 31 eV. Ab initio density functional calculations including surface charge depletion and band-bending effects favorably compare with electronic states measured by angular-resolved photoelectron spectroscopy. Such states are organized in the energy-momentum space in a twofold structure: one, bulk-derived, band disperses in the-X direction with an average hole effective mass of (0.43 ± 0.02)m 0 , where m 0 is the bare electron mass; a second flatter band, with an effective mass of (2.2 ± 0.9)m 0 , proves that a hole gas confined in the topmost layers is responsible for the conductivity of the (2 × 1) hydrogen-terminated diamond (100) surface.
A prototype Single crystal Diamond Detector (SDD) was installed at the Joint European Torus (JET)... more A prototype Single crystal Diamond Detector (SDD) was installed at the Joint European Torus (JET) in 2013 along an oblique line of sight and demonstrated the possibility to carry out neutron spectroscopy measurements with good energy resolution and detector stability in discharges heated by neutral beam injection and radio-frequency waves. Starting from these positive results, within the Vertical Neutron Spectrometer project of the Joint European Torus, we have developed a pixelated instrument consisting of a matrix of 12 independent SDDs, called the Diamond Vertical Neutron Spectrometer (DVNS), which boosts the detection efficiency of a single SDD by an order of magnitude. In this paper we describe the main features of the DVNS, including the detector design, energy resolution, and data acquisition system for on-line processing. Preliminary spectroscopy measurements of 2.5 MeV neutrons from the present deuterium plasma at JET are finally presented.
Black diamond, namely a surface textured diamond film able to absorb efficiently the sunlight, is... more Black diamond, namely a surface textured diamond film able to absorb efficiently the sunlight, is developed by the use of ultrashort pulse laser treatments. With the aim of fabricating a 2D periodic surface structure, a double-step texturing process is implemented and compared to the single-step one, able to induce the formation of 1D periodic structures. Although the obtained sub-microstructure does not show a regular 2D periodicity, a solar absorptance of about 98% is achieved as well as a quantum efficiency enhanced of one order of magnitude with respect to the 1D periodic surface texturing.
Graphite conductive vertical microchannels, fabricated by femtosecond laser treatment, are propos... more Graphite conductive vertical microchannels, fabricated by femtosecond laser treatment, are proposed as distributed electrodes in defect-engineered (" black ") single-crystal diamond cathodes for innovative solar cells. Energy conversion is based on photon-enhanced thermionic emission, where the reduction of the cathode series resistance is crucial to preserve conversion efficiency. Process yield higher than 80% and resistivity as low as 0.75 ± 0.15 U cm were achieved by the optimization of laser parameters and the use of a multi-pass writing technique. A 100 Â 100 array of graphite electrodes was integrated in a diamond-based cathode prototype, reducing the series resistance of more than 10 orders of magnitude with respect to bulk diamond.
The need for large active volume detectors for ionizing radiations and particles, with both large... more The need for large active volume detectors for ionizing radiations and particles, with both large area and thickness, is becoming more and more compelling in a wide range of applications, spanning from X-ray dosimetry to neutron spectroscopy. Recently, 8.0 Â 8.0 mm 2 wide and 1.2 mm thick single-crystal diamond plates have been put on the market, representing a first step to the fabrication of large area monolithic diamond detectors with optimized charge transport properties, obtainable up to now only with smaller samples. The more-than-double thickness, if compared to standard plates (typically 500 mm thick), demonstrated to be effective in improving the detector response to highly penetrating ionizing radiations, such as grays. Here we report on the first measurements performed on large active volume single-crystal diamond plates, both in the dark and under irradiation with optical wavelengths (190–1100 nm), X-rays, and radioactive g-emitting sources (57 Co and 22 Na).
Black diamond is obtained by a controlled nanoscale periodic texturing of CVD diamond surface, ab... more 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.
One of the goals of modern dynamic radiotherapy treatments is to deliver high-dose values in the ... more One of the goals of modern dynamic radiotherapy treatments is to deliver high-dose values in the shortest irradiation time possible. In such a context, fast X-ray detectors and reliable front-end readout electronics for beam diagnostics are crucial to meet the necessary quality assurance requirements of care plans. This work describes a diamond-based detection system able to acquire and process the dose delivered by every single pulse sourced by a linear accelerator (LINAC) generating 6-MV X-ray beams. The proposed system is able to measure the intensity of X-ray pulses in a limited integration period around each pulse, thus reducing the inaccuracy induced by unnecessarily long acquisition times. Detector sensitivity under 6-MV X-photons in the 0.1–10 Gy dose range was measured to be 302.2 nC/Gy at a bias voltage of 10 V. Pulse-by-pulse measurements returned a charge-per-pulse value of 84.68 pC, in excellent agreement with the value estimated (but not directly measured) with a comme...
Gated integrating measurement method represents a widely used approach when fast, repetitive anal... more Gated integrating measurement method represents a widely used approach when fast, repetitive analogue signals are concerned. In this work a compact synchronized gated-integrator prototype has been realized and preliminary characterized. Front-end electronics is based on the mature high-precision switched-integrator transimpedance-amplifier IVC102 whose output is connected to a precision LT1911 inverting amplifier, whereas analogue-to-digital conversion, as well as timing control circuitry, are performed by a high-efficiency LPC845 microcontroller. Synchronizing signal detection with the external trigger generated in coincidence with a source, the proposed circuitry amplifies and integrates the signal only when the pulse is generated, displaying excellent performances in terms of linearity, sensitivity and signal-to-noise ratio. Hence, the proposed solution represents an affordable alternative to continuous-time regime measurement-techniques, usually adopted in radiation dosimetry wh...
The circuit realizes a simple, low-cost lockin amplifier employing an Analog Devices AD630 balanc... more The circuit realizes a simple, low-cost lockin amplifier employing an Analog Devices AD630 balanced modulator-demodulator IC.
Optically triggered UV sensitive receivers were fabricated on polycrystalline diamond as surface ... more Optically triggered UV sensitive receivers were fabricated on polycrystalline diamond as surface channel MESFETs. Opaque gates with asymmetric structure were designed in order to improve charge photogeneration mainly within the gate-drain region. Photogenerated holes contributed to the channel charge by assistance of the local electric field, in such a way improving the current signal at the drain contact. The sensitivity to UV light is demonstrated by using 3 ns wide laser pulses at 193 nm, well over the diamond bandgap. The receiver transient response to such laser pulses shows that the photogeneration process is only limited by the pulse rise time and charge collection at the drain contact completed in a time scale of a few nanoseconds. Such opaque gate three-terminal devices are suitable for application in emerging photonic technologies, for power-management system optical receivers, where copper wires and EM shielding can be replaced by lightweight optical fibers.
We have correlated the surface conductivity of hydrogen-terminated diamond to the electronic stru... more We have correlated the surface conductivity of hydrogen-terminated diamond to the electronic structure in the Fermi region. Significant density of electronic states (DOS) in proximity of the Fermi edge has been measured by photoelectron spectroscopy (PES) on surfaces exposed to air, corresponding to a p-type electric conductive regime, while upon annealing a depletion of the DOS has been achieved, resembling the diamond insulating state. The surface and subsurface electronic structure has been determined, exploiting the different probing depths of PES applied in a photon energy range between 7 and 31 eV. Ab initio density functional calculations including surface charge depletion and band-bending effects favorably compare with electronic states measured by angular-resolved photoelectron spectroscopy. Such states are organized in the energy-momentum space in a twofold structure: one, bulk-derived, band disperses in the-X direction with an average hole effective mass of (0.43 ± 0.02)m 0 , where m 0 is the bare electron mass; a second flatter band, with an effective mass of (2.2 ± 0.9)m 0 , proves that a hole gas confined in the topmost layers is responsible for the conductivity of the (2 × 1) hydrogen-terminated diamond (100) surface.
A prototype Single crystal Diamond Detector (SDD) was installed at the Joint European Torus (JET)... more A prototype Single crystal Diamond Detector (SDD) was installed at the Joint European Torus (JET) in 2013 along an oblique line of sight and demonstrated the possibility to carry out neutron spectroscopy measurements with good energy resolution and detector stability in discharges heated by neutral beam injection and radio-frequency waves. Starting from these positive results, within the Vertical Neutron Spectrometer project of the Joint European Torus, we have developed a pixelated instrument consisting of a matrix of 12 independent SDDs, called the Diamond Vertical Neutron Spectrometer (DVNS), which boosts the detection efficiency of a single SDD by an order of magnitude. In this paper we describe the main features of the DVNS, including the detector design, energy resolution, and data acquisition system for on-line processing. Preliminary spectroscopy measurements of 2.5 MeV neutrons from the present deuterium plasma at JET are finally presented.
Black diamond, namely a surface textured diamond film able to absorb efficiently the sunlight, is... more Black diamond, namely a surface textured diamond film able to absorb efficiently the sunlight, is developed by the use of ultrashort pulse laser treatments. With the aim of fabricating a 2D periodic surface structure, a double-step texturing process is implemented and compared to the single-step one, able to induce the formation of 1D periodic structures. Although the obtained sub-microstructure does not show a regular 2D periodicity, a solar absorptance of about 98% is achieved as well as a quantum efficiency enhanced of one order of magnitude with respect to the 1D periodic surface texturing.
Graphite conductive vertical microchannels, fabricated by femtosecond laser treatment, are propos... more Graphite conductive vertical microchannels, fabricated by femtosecond laser treatment, are proposed as distributed electrodes in defect-engineered (" black ") single-crystal diamond cathodes for innovative solar cells. Energy conversion is based on photon-enhanced thermionic emission, where the reduction of the cathode series resistance is crucial to preserve conversion efficiency. Process yield higher than 80% and resistivity as low as 0.75 ± 0.15 U cm were achieved by the optimization of laser parameters and the use of a multi-pass writing technique. A 100 Â 100 array of graphite electrodes was integrated in a diamond-based cathode prototype, reducing the series resistance of more than 10 orders of magnitude with respect to bulk diamond.
The need for large active volume detectors for ionizing radiations and particles, with both large... more The need for large active volume detectors for ionizing radiations and particles, with both large area and thickness, is becoming more and more compelling in a wide range of applications, spanning from X-ray dosimetry to neutron spectroscopy. Recently, 8.0 Â 8.0 mm 2 wide and 1.2 mm thick single-crystal diamond plates have been put on the market, representing a first step to the fabrication of large area monolithic diamond detectors with optimized charge transport properties, obtainable up to now only with smaller samples. The more-than-double thickness, if compared to standard plates (typically 500 mm thick), demonstrated to be effective in improving the detector response to highly penetrating ionizing radiations, such as grays. Here we report on the first measurements performed on large active volume single-crystal diamond plates, both in the dark and under irradiation with optical wavelengths (190–1100 nm), X-rays, and radioactive g-emitting sources (57 Co and 22 Na).
Black diamond is obtained by a controlled nanoscale periodic texturing of CVD diamond surface, ab... more 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.
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Papers by Marco Girolami
pixelated instrument consisting of a matrix of 12 independent SDDs, called the Diamond Vertical Neutron Spectrometer (DVNS), which boosts the detection efficiency of a single SDD by an order of magnitude. In this paper we describe the main features of the DVNS, including the detector
design, energy resolution, and data acquisition system for on-line processing. Preliminary spectroscopy measurements of 2.5 MeV neutrons from the present deuterium plasma at JET are finally
presented.
pixelated instrument consisting of a matrix of 12 independent SDDs, called the Diamond Vertical Neutron Spectrometer (DVNS), which boosts the detection efficiency of a single SDD by an order of magnitude. In this paper we describe the main features of the DVNS, including the detector
design, energy resolution, and data acquisition system for on-line processing. Preliminary spectroscopy measurements of 2.5 MeV neutrons from the present deuterium plasma at JET are finally
presented.