We are developing gaseous photon detectors for Cherenkov imaging applications in the experiments at the future Electron Ion Collider. CsI, converting photons in the far ultraviolet range, is, so far, the only photoconverter compatible with the operation of gaseous detectors. It is very delicate to handle due to its hygroscopic nature: the absorbed water vapour decomposes the CsI molecule. In addition, its quantum efficiency degrades under ion bombardment. These are the key reasons to quest for novel, less delicate materials for photocathodes adequate for gaseous photon detectors. Layers of hydrogenated nanodiamond particles have recently been proposed as an alternative material and have shown promising characteristics. The performance of nanodiamond photocathodes coupled to thick GEM-based detectors is the objects of our ongoing R&D. The first phase of these studies includes the characterization of thick GEM coated with nanodiamond layers and the robustness of its photoconverting properties with respect to the bombardment by ions from the multiplication process in the gaseous detector. The approach is described in detail as well as all the results obtained so far within these exploratory studies.

In this work, the geometric and electromagnetic characteristics of electron beams generated by three photocathodes (PCs), two based on nanodiamond (ND) layers and one based on Cu (generally used as reference) were investigated. Specifically, the active layers of the ND-based PCs consisted of untreated and hydrogenated (H-ND) nanoparticles (250 nm in size) deposited by pulsed spray technique on p-doped silicon substrates as uniform coating. Photoemission measurements carried out by a KrF nanosecond excimer laser (lambda = 248 nm) in a vacuum chamber at 10(-6) mbar and the emittance evaluation, performed by the pepper pot method, are reported and discussed. For the last, radio-chromic films (HD-810 Gafchromic) were used as sensible screen for electrons. The study of the emittance was performed by varying the laser spot onto the PC surface and the accelerating voltage (5, 10 and 15 kV). From emittance values, the normalized brightness was also estimated for all the cathodes. The obtained results showed quantum efficiency values of the ND-based photocathodes higher than that of the reference Cu one, but, at the same time, higher emittances and therefore worse performancers as the result of the enlarged beam divergence. Despite this, H-ND resulted to be the best PC between those investigated for the highest normalized beam brightness, thanks to its high electron current and low normalized emittance.

In this work we study the emittance of electron beams generated by three photocathodes (PCs), one based on Cu sample and two on different nanodiamond (ND) layers. The active layers of the ND-based PCs consisted of untreated and hydrogenated ND particles, 250 nm in size, sprayed on alluminum substrates. We show photo-emission measurements performed by a KrF nanosecond excimer laser (lambda = 248 nm) in a vacuum chamber at 10(-6) mbar and the study of emittance. This last was carried out by the pepper pot method using radiochromic films, HD-810 Gafchromic, as sensible detectors for electrons. The study of the emittance was performed by varying the laser spot onto the PC surface and the accelerating voltage (5, 10 and 15 kV). The obtained results showed quantum efficiencies of the ND-based photocathodes higher than that of the reference Cu one, which instead exhibited the lowest value of normalized emittance, 0.2 mm mrad.

The design of a Ring Imaging CHerenkov (RICH) detector for the identification of high momentum particles at the future Electron Ion Collider (EIC) is extremely challenging by using current technology. Compact collider setups impose to construct RICH with short radiator length, hence limiting the number of generated photons. The number of detected photons can be increased by selecting the far UV region. As standard fused-silica windows is opaque below 165 nm, a windowless RICH can be a possible approach. CsI is widely used photocathode (PC) for photon detection in the far UV range. Due to its hygroscopic nature it is very delicate to handle. In addition, its Quantum Effciency (QE) degrades in high intensity ion fluxes. These are the key reasons to quest for novel PC with sensitivity in the far UV region. Recent development of layers of hydrogenated nanodiamond powders as an alternative PC material and their performance, when coupled to the THick Gaseous Electron Multipliers (THGEM)-based detectors, are the objects of an ongoing R&D. We report here some preliminary results on the initial phase of these studies.

Identification of high momentum hadrons at the future EIC is crucial, gaseous RICH detectors are therefore viable option. Compact collider setups impose to construct RICHes with small radiator length, hence significantly limiting the number of detected photons. More photons can be detected in the far UV region, using a windowless RICH approach. QE of CsI degrades under strong irradiation and air contamination. Nanodiamond based photocathodes (PCs) are being developed as an alternative to CsI. Recent development of layers of hydrogenated nanodiamond powders as an alternative photosensitive material and their performance, when coupled to the THick Gaseous Electron Multipliers (THGEM)-based detectors, are the objects of an ongoing R&D. We report about the initial phase of our studies.

Synthetic diamond films have attracted great attention for their extreme properties and potential engineering applications as protective and wear-resistant coating for cutting tools. Nanocrystalline diamond (NCD) coatings were synthesized from CH/H/Ar (1/10/89%) microwave plasma at four deposition temperatures (T) ranging from 653 to 884 °C. The hardness (H) and Young's modulus (E) of NCD coatings measured at three different loads (10, 25 and 47 mN) depended on the nanoindentation load-level. The NCD coating produced at the lowest T showed values of H = 121 ± 25 GPa and E = 1036 ± 163 GPa at the highest load. This result was attributed to the formation of elongated nanocrystallites at low deposition temperature. Further, the NCD coating obtained at lower deposition temperature exhibited an anomalous indentation size effect (ISE), i.e. a reverse ISE (RISE), which was ascribed to the heterogeneity of grain sizes along the [220] and [111] directions. Finally, a positive and negative (inverse) Hall-Petch behavior was observed for grain sizes along the [111] and [220] directions, respectively.

In this work we investigate on the characteristics of electron beams generated by three photocathodes (PC), one based on Cu sample and two on different nanodiamond (ND) layers. Specifically, the active layers of the ND-based PCs consisted of untreated and hydrogenated ND particles, 250 nm in size, sprayed on p-doped silicon substrates. We show photoemission measurements, carried out by a KrF nanosecond excimer laser (l=248 nm; photon energy 5 eV) in a vacuum chamber at 10-6 mbar. We also make a study of the n-photon emission processes for all the PCs. The obtained results showed QE values of the ND-based photocathodes higher than that of the reference Cu one. In particular, the hydrogenated ND-based PC showed the highest QE thanks to the negative electron affinity of its surface.

The investigation of two different photocathodes (PCs) based on nanodiamond (ND) layers, irradiated by a KrF nanosecond excimer laser (wavelength, lambda=248 nm; photon energy, EPh=5 eV) is reported. The ND layers were deposited by means of a pulsed spray technique. Specifically, the active layer of each PC consisted of untreated (as-received) and hydrogenated ND particles, 250 nm in size, sprayed on a p-doped silicon substrate. The ND-based photocathodes were tested in a vacuum chamber at 10-6 mbar and compared to a Cu-based one, used as reference. All the photocathodes were irradiated at normal incidence. The quantum efficiency (QE) of the photocathodes was assessed. QE values of the ND-based photocathodes were higher than that of the reference one. In particular, the hydrogenated ND-based PC exhibited the highest QE due to the negative electron affinity that results from the surface terminated by hydrogen. Additionally, the photocathode surface/local temperature and the multiphoton process contribution to the electron emission were studied.

In this work we report the investigation of two different photocathodes (PCs) based on nanodiamonds (NDs) irradiated by a nanosecond excimer laser (KrF) operating at 248 nm (5eV). The ND layers of cathodes were deposited by means of pulsed spray technique. Specifically, the active ND layer of each PC consists of untreated or hydrogenated particles, 250 nm in size, sprayed on p-doped silicon substrate. The ND-based photocathodes were tested in a vacuum chamber at 10-5 Pa and compared to a conventional Cu one. They were irradiated at normal incidence, and the anode-cathode distance was set at 3 mm. The maximum applied accelerating voltage was 7 kV, while the laser energy ranged from 10-3 to 10-2 J/cm2, limited by the electrical breakdown of the photodiode gap and by the plasma formation. The quantum efficiency of the photocathodes was assessed in the saturation regime. We also calculated the target temperature and the contribution of multiphoton processes to the photoemission mechanism. The obtained results showed QE values for the ND-based photocathodes higher than that of a conventional Cu. In particular, the hydrogenated ND-based PC exhibited, the highest QE value due to the negative electron affinity of its surface terminated by hydrogen.

Two different photocathodes (PCs) based on nanodiamonds (NDs) have been realized at the MWPECVD Laboratory of CNR-NANOTEC of Bari. Each PC consisted of layers of untreated or hydrogenated ND particles of 250 nm deposited on p-doped silicon substrate by means of pulsed spray technique. The quantum efficiency (QE) of the cathodes has been assessed at the UV wavelength of a KrF laser i.e. 248 nm. The laser energy used for the irradiation ranged from 10-3 to 10-2 J/cm2. The ND photocathodes exhibited QE values higher than those shown by conventional Cu ones

This work deals with photochatodes (PCs) based on as-received and treated nanodiamond (ND) particles, 250 nm in size. The aim of this study is the hydro-, hydro-/nitro- and nitro-genation of NDs performed in microwave plasmas adding different N2 percentages (0, 50 and 100 %) to pure H2 gas. Untreated and treated NDs are dispersed in solvents such as 1,2-dichloroethane and deionized water, and then deposited, as continuous layers, on p-Si and kapton substrates by the pulsed spray technique. The produced layers are characterized by Raman, photoluminescence spectroscopies and photoemission measurements. The quantum efficiency (QE), a merit figure for photocathodes, is assessed in the UV spectral range from 146 to 210 nm.

Method for the production of high efficiency photocathodes for ultraviolet based on nanodiamonds, comprising providing a support capable of conducting electrons, and producing a photosensitive layer of nanodiamonds on the support. Production of the photosensitive layer includes providing nanodiamond particles in the form of powder, hydrogenating the nanoparticles in a H2 plasma, preparing a dispersion of the hydrogenated particles in a solvent and spraying the dispersion onto the support and waiting for the solvent to evaporate from the support, the spray and waiting cycle being repeated several times in order to obtain a continuous photosensitive layer.

Chemical, structural, morphological and micro-/macro-electrical properties of undoped and nitrogen-(N-)doped diamond films are determined by X-ray photoelectron spectroscopy, Raman and photoluminescence spectroscopies, field emission scanning electron microscopy, atomic force microscopy, scanning capacitance microscopy (SCM) and two points technique for I-V characteristics, respectively. The characterization results are very useful to examine and understand the relationship among these properties. The effect of the nitrogen incorporation in diamond films is investigated through the evolution of the chemical, structural, morphological and topographical features and of the electrical behavior. The distribution of the electrical current is first assessed at millimeter scale on the surface of diamond films and then at micrometer scale on small regions in order to establish the sites where the carriers preferentially move. Specifically, the SCM images indicate a non-uniform distribution of carriers on the morphological structures mainly located along the grain boundaries. A good agreement is found by comparing the electrical currents at the micro- and macro-scale. This work aims to highlight phenomena such as photo- and thermionic emission from N-doped diamond useful for microelectronic engineering. (C) 2017 Elsevier B.V. All rights reserved.

In this paper, we present an investigation on two types of nanodiamond (ND) powders with average size of particles around 250 nm and having different sp(2) (graphite phase) and sp(3) (diamond phase) carbon contents. The ND surface modification is carried out by physical methods i.e. treatments in H-2 microwave plasma. The quantum efficiency (QE) of photocathodes and the stability of aqueous dispersions are assessed by photoemission and zeta potential (ZP) measurements, respectively. The resultant hydrogenated surface affects in the solid state the QE of ND-based photocathodes and in solution the particle ZP. The effect of the hydrogen treatment is beneficial inducing an enhancement of photocathode QE and a corresponding increase of the ZP. A schematized energy diagram is proposed to illustrate and explain the strong correlation between QE and ZP parameters.

Photocathodes working in reflection-mode are made of rich-diamond (R-D) and rich-graphite (R-G) nanodiamond (ND) layers, deposited on different conductive substrates by means of the pulsed spray technique at low deposition temperatures (120 and 150 C-omicron) and starting from two types of ND particles. The two powders with an average grain size of 250 nm have variable sp(2) (graphite phase) and spa (diamond phase) hybridized carbon contents, as assessed by Raman spectroscopy and transmission electron microscopy. The ND particles are employed as-received or treated in H2 microwave plasmas. The principal aim of the paper is the comparative study of R-D and R-G photocathodes in the vacuum ultraviolet spectral range from 140 to 210 nm, where they exhibit a high quantum efficiency and a good stability over time upon exposure to air. Specifically, the quantum efficiency values at 140 nm of photocathodes based on hydrogenated R-D and R-G layers are 26.8 and 47%, respectively, proving that the more defective ND particles are, the more efficiently they emit. Moreover, these QE values are higher than those derived by photocathodes based on microwave plasma enhanced chemical vapor deposition diamond films (14% at 140 nm) and the highest recorded in the state of international art. (C) 2017 Elsevier B.V. All rights reserved.

Obiettivo di questa attività é stato l'utilizzo di film di diamante nanocristallino e di diamante drogati con azoto prodotti con il reattore MWPECVD (MicroWave Plasma Enhanced Chemical Vapor Deposition) presso i laboratori del CNR-NANOTEC in fotocatodi e in catodi neutralizzatori.

Generally materials, having a low/negative electron affinity (NEA) and/or a low work function which facilitate the electron escape from their surfaces, exhibit good photo- and thermo-emission properties. From this point of view, natural and synthetic diamond is an interesting material because possesses a low EA that becomes negative when the surface is treated in H2 plasma. Moreover, as-grown diamond films produced by microwave plasma enhanced chemical vapour deposition and starting from CH4:H2 (1:99%) gas mixture exhibit hydrogenated surfaces, suitable for photocathodes, neutralizer cathode, energy converters and so on. Very recently the authors of this contribution have patented a new methodology (easy, inexpensive and working at temperature of 120°C) to fabricate layers of nanodiamond (ND) particles. In the present work, the photoemission behaviour of ND layers produced by this new methodology i.e. the pulsed spray technique is presented. Commercial (Diamonds & Tools srl) ND particles, 250 nm in size, were utilized. Layers of untreated and treated (in pure H2 or N2 plasmas) NDs were produced. The photoemission quantum efficiency (QE), a merit figure for photocathode applications, was assessed in the UV range (140-210 nm), showing a QE enhancement for both hydrogenated and nitrogenated ND particles.