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Platinum is a promising candidate for the realization of blocking electrical contacts on cadmium-zinc-telluride (CdZnTe or CZT) radiation detectors. However, the poor mechanical adhesion of this metal often shortens the lifetime of the final device. In this work, a simple and effective procedure to obtain robust platinum contacts by electroless deposition is presented. Microscopical analysis revealed the final thickness and composition of the contact layer and its adhesion to the bulk crystal. The blocking nature of the Pt-CdZnTe junction, essential to obtain low noise devices, was confirmed by current–voltage measurements. The planar Pt-CdZnTe-Pt detectors showed good room temperature spectroscopic performance with energy resolution of 4% (2.4 keV) and 3% (3.7 keV) FWHM at 59.5 and 122.1 keV, respectively. Finally, we showed, for the first time, that platinum contacts allow the estimation of the carrier lifetime and mobility of both holes and electrons by using current transient measurements. This demonstrated the optimal hole extraction capability of such contacts.

In the last two decades, great efforts have been made in the development of 3D cadmium–zinc–telluride (CZT) detectors operating at room temperature for gamma-ray spectroscopic imaging. This work presents the spectroscopic performance of new high-resolution CZT drift strip detectors, recently developed at IMEM-CNR of Parma (Italy) in collaboration with due2lab (Italy). The detectors (19.4 mm × 19.4 mm × 6 mm) are organized into collecting anode strips (pitch of 1.6 mm) and drift strips (pitch of 0.4 mm) which are negatively biased to optimize electron charge collection. The cathode is divided into strips orthogonal to the anode strips with a pitch of 2 mm. Dedicated pulse processing analysis was performed on a wide range of collected and induced charge pulse shapes using custom 32-channel digital readout electronics. Excellent room-temperature energy resolution (1.3% FWHM at 662 keV) was achieved using the detectors without any spectral corrections. Further improvements (0.8% FWHM at 662 keV) were also obtained through a novel correction technique based on the analysis of collected-induced charge pulses from anode and drift strips. These activities are in the framework of two Italian research projects on the development of spectroscopic gamma-ray imagers (10–1000 keV) for astrophysical and medical applications.

We present a study on the Curie transition of austenitic Ni-Mn-In full Heusler compounds when Mn atoms are replaced by Fe or Cu. The substituted compounds are designed to present a relevant magnetocaloric effect at the second order Curie transition of the austenitic phase near room temperature. We show that Fe and Cu modify the magnetic moments and interactions responsible of the localized magnetism in the L21 ordered cubic structure, resulting in a change of the Curie temperature and saturation magnetization of the compound. Neutron diffraction experiments and electron microscopy analysis were used to study the sites occupancy of doping atoms and the presence of secondary phases, thus possibly optimizing the annealing protocols to obtain homogeneous samples even at high Cu/Fe concentrations. On this basis, a series of quinary compounds with a tunable Curie temperature and high values of saturation magnetization (100-110 Am2/kg at 80 K) was successfully synthesized. The obtained results show the feasible fine tuning of the Curie temperature at which the peak of the magnetocaloric effect is realized, highlighting a new promising strategy to design graded regenerators for room temperature magnetocaloric applications.

We report on the C-60, Na, and Li dynamics in NaxLi6xC60 fullerides (x = 0, 1, 5, and 6) in the temperature range 80-550 K by using C-13, Na-23, and Li-7 solid state NMR. The results show that the C-60 reorientation dynamics is hindered at room temperature for the Li-enriched fullerides, but it is active for the Na rich ones with a rate of the order of few kilohertz. Na-23 and Li-7 NMR measurements show the presence of two dominant thermally activated dynamics that can be associated with Li/Na ionic motions within the octahedral sites (intrasite motion) and between the octahedral and tetrahedral sites (intersite motion). The substitution of one Na or one Li ion in the end members Li6C60 and Na6C60, respectively, yields to an increase of the hopping rate of the intersite motion, which is necessary for the ionic diffusion in possible fulleride-based ionic conductors.

In this work, the spectroscopic performances of new cadmium–zinc–telluride (CZT) pixel detectors recently developed at IMEM-CNR of Parma (Italy) are presented. Sub-millimetre arrays with pixel pitch less than 500 µm, based on boron oxide encapsulated vertical Bridgman grown CZT crystals, were fabricated. Excellent room-temperature performance characterizes the detectors even at high-bias-voltage operation (9000 V cm−1), with energy resolutions (FWHM) of 4% (0.9 keV), 1.7% (1 keV) and 1.3% (1.6 keV) at 22.1, 59.5 and 122.1 keV, respectively. Charge-sharing investigations were performed with both uncollimated and collimated synchrotron X-ray beams with particular attention to the mitigation of the charge losses at the inter-pixel gap region. High-rate measurements demonstrated the absence of high-flux radiation-induced polarization phenomena up to 2 × 106 photons mm−2 s−1. These activities are in the framework of an international collaboration on the development of energy-resolved photon-counting systems for high-flux energy-resolved X-ray imaging.

Cadmium–zinc–telluride (CZT) pixel detectors represent a consolidated choice for the development of room-temperature spectroscopic X-ray imagers, finding important applications in medical imaging, often as detection modules of a variety of new SPECT and CT systems. Detectors with 3–5 mm thicknesses are able to efficiently detect X-rays up to 140 keV giving reasonable room-temperature energy resolution. In this work, the room-temperature performance of 3 mm-thick CZT pixel detectors, recently developed at IMEM/CNR of Parma (Italy), is presented. Sub-millimetre detector arrays with pixel pitch less than 500 µm were fabricated. The detectors are characterized by good room-temperature performance even at high bias voltage operation (6000 V cm−1), with energy resolutions (FWHM) of 3% (1.8 keV) and 1.6% (2 keV) at 59.5 keV and 122.1 keV, respectively. Charge-sharing investigations were performed with both uncollimated and collimated synchrotron X-ray beams with particular attention to recovering the charge losses at the inter-pixel gap region. High rate measurements demonstrated the absence of high-flux radiation-induced polarization phenomena up to 25 × 106 photons mm−2 s−1.

We report on the development and of a complete X/γ rays detection system (10-1000 keV) based on CZT spectrometers with spatial resolution in three dimensions (3D) and a digital electronics acquisition chain. The prototype is made by packing four linear modules, each composed of one 3D CZT sensors. Each sensors is realized using a single spectroscopic graded CZT crystal of about 20×20×5 mm3. An electrode structure consisting of 12 collecting anodes with a pitch of 1.6 mm and 3 drift strips between each pair of anodes for 48 strips (0.15 mm wide) on the anodic side was adopted. The cathode is made of 10 strips with a pitch of 2 mm and orthogonal to anode side strips. Since the reading of the drift strips will carried out by putting in parallel all the strips that occupy the same place with respect to a collecting anode, the channels number for each sensors is only 25. The detector readout front-is based on custom designed low noise charge sensitive pre-amplifiers (CSP) implemented in hybrid 16 channels board. The CZT module and its CSP front-end provide the signals to a multichannel Digital Pulse Processing FPGA based system able to digitize and process continuously the signals. The digital system implement an innovative firmware that allow performing fine time-tagging, online pulse shape and height analysis with good energy resolution.

A system of Fe-filled multiwall carbon nanotubes (MWCNT) was grown by aerosol chemical vapor deposition with three different concentrations of ferrocene as precursor catalyst. The obtained samples were thoroughly analyzed from the point of view of their morphological, microstructural and magnetic properties. It was found that ferrocene concentration did not change the MWCNTs morphology. However, it increases the number of MWCNTs containing Fe and the Fe amount in each MWCNT. The Fe is located either in form of nanorods within the inner channel of the MWCNTs or as nanoparticles of various sizes, sometimes aggregated in clusters. The magnetic results indicate the presence of different phases, identified as α-Fe, Fe3C and Fe3O4, mostly in form of single-domain particles. A simple model of single domain non-interacting particles allows explaining the observed temperature behavior of coercivity and remanence over a wide temperature range, up to 950 K. The different ferrocene concentrations affect only the saturation magnetization but not the coercivity of the samples. As a further result, MWCNT/epoxy nanocomposites, with possible application as electromagnetic shields, were prepared by the “two factor mechanical method”. The nanocomposites exhibit the same magnetic properties of the Fe-filled MWCNTs, in terms of both coercivity and hysteresis loop shape.

CdZnTe is nowadays a reference semiconductor for detection of X and γ-radiation. The electrical properties of CdZnTe-based (CZT) detectors are strongly affected by the surface and subsurface defects, which can cause an excessive surface leakage current (SLC). This issue strongly degrades the sensor performance and becomes critical for multi-stripes detectors, where the stripes are kept at different voltage potentials in order to shape the electric field inside the semiconductor material.In this work, we propose a passivation method based on the deposition of a thin Al 2 O 3 film on the non-metallized CZT surface. To demonstrate the effectiveness of the method, we fabricated several 19.4x19.4x5 mm3 CZT multi-stripes detectors with 48 parallel Au stripes on the anode face (12 collecting anodes and 36 drift stripes) and subsequently deposited a Al 2 O 3 polycrystalline thin film on the CZT surface between the stripes. Al 2 O 3 deposition was achieved by sputtering technique. Electrical characterization of surface leakage current before and after Al 2 O 3 is presented.Al 2 O 3 coating treatment allowed us to obtain exceptionally low surface leakage current values, 10 to 100 times lower than those measured after our best wet passivation method for CZT surface chemical oxidation. Since Al 2 O 3 passivation significantly reduces surface leakage current and thus improves the signal-to-noise ratio, our finding is very promising for a substantial advancement of multi-stripe detectors performance.

We herein report on the synthesis of mixed alkali cluster intercalated fullerides NaxLiy−xC60 (y = 12; x = 1–6) by a two-steps mechanochemical reaction of fullerene with sodium and lithium. These compounds crystallize in the cubic lattice of C60 displaying a contracted lattice parameter with respect to the Na6C60 parent structure. The analysis of the hydrogen sorption behaviour shows a slight decrease in the dehydrogenation enthalpy for y = 12 with respect to the sodium free member. Raman spectroscopy highlighted a partial electron transfer from alkali metals to C60, suggesting the presence of charged sodium/lithium clusters. Finally, we applied muon spectroscopy to understand the different hydrogenation mechanisms in NaxLi6−xC60 and NaxLi12−xC60 and explain their different performance.

Li6C60 has been chosen as the most representative system to study the hydrogenation mechanism in alkali-cluster intercalated fullerides. We present here a muon spin relaxation (mu SR) experiment that hints the chance to achieve a higher storage capacity on fullerene with respect to the values suggested in literature. Moreover, a linear relationship between the muonium adduct radical hyperfine frequency and the level of C-60 hydrogenation was found and it can be exploited to probe the C-60 hydrogenation level, giving more credit to this technique in the field of hydrogen storage materials. (C) 2017 Elsevier Ltd. All rights reserved.

Detectors based on compound semiconductor materials like CdTe and CdZnTe are more susceptible to defect-related spectral distortions than elemental semiconductors like Si or Ge. During the design process of new detectors based on these materials it is crucial to consider the effect of these distortions on the detector performance. Due to the diverse range of application areas in which these detectors may be used, the detector geometry must be selected to match the desired application of the device. For those requiring the detection of photons across a broad energy range (1 – 1000 keV), the detector design must account for a variety of different interaction processes. The simulation framework presented in this paper includes all the physical processes involved in the formation of the detector signal, from the radiation absorption mechanisms to the influence of the electrode geometry. A simulation system based on first principle calculations is used which consists of a Monte Carlo simulator, a Finite Elements Method (FEM) calculator and numerical computation software. The framework simulates the radiation–semiconductor interaction, the charge carrier transport and the role of the electric field and weighting field in signal induction on the electrodes. This tool allows to simulate the entire experimental arrangement including the use of attenuators, collimators and scattering surfaces. The ability to accurately simulate the detector response to radiation and its surroundings provides a powerful tool for the realization of a new generation of detector systems. In order to validate the simulation framework, CdZnTe-based detectors with several contact geometries have been modelled and the output of the simulations have been compared to experimental data. A comparison between the simulated and measured responses demonstrate the power of this technique.