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Irradiation of lithium fluoride with protons causes the formation of electronic defects, known as colour centres, in the crystal lattice. Two stable defects among them, the F2 and F3+ aggregate ones, under blue light simultaneous excitation show broad photoluminescence in the red and green visible spectral ranges, respectively, their peculiar characteristics being well known for applications in optically-pumped tuneable lasers, broad-band miniaturized light-emitting photonic devices and passive radiation imaging detectors. Recently, exploitation of their radiophotoluminescence has been successfully proposed for proton-beam advanced diagnostics and dosimetry, even at low dose values typical of radiotherapy. In the present study, lithium fluoride crystals were irradiated with 2.3 MeV protons in the dose range from ∼104 to ∼107 Gy and their dynamic range, that is the capability of detecting the widest possible range of radiophotoluminescence intensity emitted by the colour centres, was found to be 114 dB at the F2 peak emission wavelength of 675 nm under continuous-wave laser excitation at 445 nm. Moreover, after including in the analysis a set of lithium fluoride crystals irradiated with 26.1 MeV protons in the dose range from 0.5 to 48 Gy at a much lower dose-rate, it was found that the radiophotoluminescence intensity of the F2 colour centres shows a linear dependence with dose from 0.5 to ∼2 × 105 Gy.

Solid-state radiation detectors based on the visible photoluminescence of radiation-induced F2 and F3+ color centers in lithium fluoride crystals have been used for advanced diagnostics of 18 and 27 MeV proton beams, produced by the TOP-IMPLART linear accelerator, which is under development for protontherapy applications at ENEA C.R. Frascati, Italy. Visible fluorescence microscopy was successfully used to read the latent proton beam images stored in the lithium fluoride crystals, thanks to high emission efficiency of the F2 and F3+ color centers obtained by simultaneous optical excitation in the blue spectral range. High intrinsic spatial resolution and wide dynamic range of these novel LiF detectors allow obtaining two-dimensional images of both the beam transverse intensity distribution and of the Bragg curve. By using a simple defect formation model that takes into account the energy released in the material and the saturation of defect concentration, not only the two-dimensional dose map was obtained from the beam transverse intensity distribution image, but also the full Bragg curve was reconstructed, allowing the thorough characterization of proton beams produced by the accelerator.

Terahertz image sensors have large potential in time-domain spectroscopy, radio astronomy, security control, communications, and biomedical imaging. We present a new structure for THz imaging, obtained by the combination of a CMOS photodetector, and a rectennas composed by a tapered μ-helix monopole and a rectifying device. The antenna consists in a truncated conical helix extruded from a planar spiral and in a nanometric metallic whisker connected to one of its edges. We introduce the new structure together with an accurate study of the effect of electric field enhancement and of parasitic elements which affect the overall sensitivity of the device.

Static leakage currents represent a major issue in nano-scale CMOS. In digital VLSI circuits, the most relevant contributions to the overall leakage current are subthreshold conduction, gate current and band-to-band-tunneling (BTBT) current, which flows from drain/source to bulk through the reverse biased diffusion junctions. While the latter has been recognized as an important effect in digital nano-CMOS, yet no compact model of it has ever been included in the industry-standard device model BSIM4. In this work, we show that the lack of a BTBT current model leads to discrepancies between SPICE and device-level simulations and that adding a BTBT current source into BSIM4 DC model can correct this. The new current source follows a widely accepted physical model of the BTBT phenomenon with a rectangular junction approximation. Test case results show a good agreement between the new circuit-level simulations and the device-level extracted currents.