C. Aramo

Innovative carbon nanotube-silicon large area photodetector

We report on a new photodetector fabricated using carbon nanostructures grown on a silicon substrate. This device exhibits low noise, a good conversion efficiency of photons into electrical current and a good signal linearity in a wide range of radiation wavelengths ranging from ultraviolet to infrared at room temperature. The maximum quantum efficiency of 37% at 880 nm has been measured without signal amplification. Such innovative devices can be easily produced on large scales by Chemical Vapour Deposition (CVD) through a relatively inexpensive chemical process, which allows large sensitive areas from a few mm2 up to hundreds of cm2 to be covered.

Observation of a photoinduced, resonant tunneling effect in a carbon nanotube–silicon heterojunction

Summary A significant resonant tunneling effect has been observed under the 2.4 V junction threshold in a large area, carbon nanotube–silicon (CNT–Si) heterojunction obtained by growing a continuous layer of multiwall carbon nanotubes on an n-doped silicon substrate. The multiwall carbon nanostructures were grown by a chemical vapor deposition (CVD) technique on a 60 nm thick, silicon nitride layer, deposited on an n-type Si substrate. The heterojunction characteristics were intensively studied on different substrates, resulting in high photoresponsivity with a large reverse photocurrent plateau. In this paper, we report on the photoresponsivity characteristics of the device, the heterojunction threshold and the tunnel-like effect observed as a function of applied voltage and excitation wavelength. The experiments are performed in the near-ultraviolet to near-infrared wavelength range. The high conversion efficiency of light radiation into photoelectrons observed with the presented layout allows the device to be used as a large area photodetector with very low, intrinsic dark current and noise.

Graphene–polymer coating for the realization of strain sensors

In this work we present a novel route to produce a graphene-based film on a polymer substrate. A transparent graphite colloidal suspension was applied to a slat of poly(methyl methacrylate) (PMMA). The good adhesion to the PMMA surface, combined with the shear stress, allows a uniform and continuous spreading of the graphite nanocrystals, resulting in a very uniform graphene multilayer coating on the substrate surface. The fabrication process is simple and yields thin coatings characterized by high optical transparency and large electrical piezoresitivity. Such properties envisage potential applications of this polymer-supported coating for use in strain sensing. The electrical and mechanical properties of these PMMA/graphene coatings were characterized by bending tests. The electrical transport was investigated as a function of the applied stress. The structural and strain properties of the polymer composite material were studied under stress by infrared thermography and micro-Raman spectroscopy.

Development of a 16-channel matrix of photodetection sensors for medical imaging and astrophysical applications

Recen% developed near W-photosensors are currently adopted in those applications where high sensitivity and good imaging capabilities are required, especially in fields such as astroparticle physics and medical imaging. An example of such applications is the camera of the Schwarzschild Couder Medium Size Telescope prototype (pSCT) which is in construction within the Cherenkov Telescope Array experiment. The camera consists of 177 photo-detection modules grouped into sectors of 25 modules, each based on matrixes of 64 6mm × 6mm pixels of SiUcon PhotomultipUers (SiPMs). Sensors produced by the Fondazione Bruno Kessler (FBK) in Italy are currently under investigation. Here we present a complete characterization of these highly sensitive near UV sensors, the assembly procedure and metrology results on several focal plane elements.

Development and characterization of Near-UV sensitive Silicon Photomultipliers for the Schwarzschild-Couder Telescope prototype for the Cherenkov Telescope Array

Silicon Photomultipliers (SiPM) are standard sensors widely employed for applications in which high sensitivities and fast responses in the detection of low fluxes of visible and UV photons are required. The Italian Institute of Nuclear Physics (INFN), in collaboration with Fondazione Bruno Kessler (FBK), is involved in a R&D project for SiPM sensors sensitive to near UV wavelengths. The performances of the latest technology of NUV-High-Density SiPM have confirmed that the quality of the current production technology opens the possibility to employ these devices for many applications. In this contribution, we review the performances of the latest technology of NUV-High-Density SiPM and the prospects for their use in one of the designs of the camera focal planes of Schwarschild-Couder Telescope prototype, including the development of packaging procedures of single sensors into high-density multi-SiPM modules and the development of a custom front-end ASIC for a high rate waveform sampling of the SiPM signals.

The ARCADE Raman Lidar and atmospheric simulations for the Cherenkov Telescope Array

The CTA is the next generation of ground based very high energy gamma ray Imaging Atmospheric Cherenkov Telescopes. Since observations with this technique are affected by atmospheric conditions, an accurate knowledge of the atmospheric properties is fundamental to improve the precision and duty cycle of the CTA. Measurements of absorption and scattering properties of the atmosphere due to aerosols and molecules can be used in the event reconstruction or in MODTRAN, an analytical code designed to model the propagation of electromagnetic radiation. MODTRAN output is used as an input for the air shower simulation and Cherenkov light production, giving the optical depth profiles that together with the refractive index allow the proper simulation of the gamma ray induced signals and a correct measurement of the primary energy from the detected signals. The ARCADE Raman Lidar will be used for the on site characterization of the aerosol attenuation profiles of the UV light. The collected data will be used in preparation for the full operation of the array, providing nightly information about the aerosol properties such as the vertical aerosol optical depth and the water vapour mixing ratio with an altitude resolution better than 100 m from about 400 m to 10 km above ground level. These measurements will help to define the needs for Monte Carlo simulations of the shower development and of the detector response. This instrument will also be used for the intercalibration of the future Raman Lidars that are expected to operate at the CTA sites. This contribution includes a description of the ARCADE Lidar and the characterization of the performance of the system. The system is expected to be shipped to the northern site of the CTA (La Palma) before the end of 2017, to acquire data locally for 1 year before being moved to the southern site (Chile).

Towards the development of a SiPM-based module for the camera of the Schwarzschild-Couder Telescope prototype of the Cherenkov Telescope Array

The Italian Institute of Nuclear Physics is currently involved in the development of a prototype for a camera based on Silicon Photomultipliers (SiPMs) for the Cherenkov Telescope Array (CTA), a new generation of telescopes for ground{based gamma{ray astronomy. In recent years, SiPMs have proven to be highly suitable devices for applications where high sensitivity to low{intensity light and fast responses are required. Among their many advantages are their low operational voltage when compared with classical photomultiplier tubes, mechanical robustness, and increased photo{detection efficiency (PDE). Moreover, due to the possibility of operating them during bright moonlight, SiPMs can therefore considerably increase telescope duty cycle. Here we present a full characterization of a particular type of SiPM produced in Italy by the Fondazione Bruno Kessler, which is suitable for Cherenkov light detection in the Near-Ultraviolet (NUV). This device is a High{Density (HD) NUV SiPM, based on a micro cell of 40 μm × 40 μm and with an area of 6×6 mm2, providing low levels of dark noise and high PDE peaking in the NUV band. NUV-HD SiPMs will be arranged in a matrix of 8×8 single units to become part of the focal plane of the Schwarzschild-Couder Telescope prototype for CTA. An update on recent tests of the front-end electronics based on signal sampling with the TARGET-7 chip will be given as well.