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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. [ABSTRACT FROM AUTHOR]

Nanodiamond (ND) layers on silicon substrate are deposited by the pulsed spray technique starting from nanoparticles of about 250 nm dispersed in 1,2-dichloroethane solvent. The aim of this letter is to investigate the quantum efficiency (QE) of photocathodes based on ND particles in the vacuum ultraviolet spectral range. Various ND layers are examined employing as-received and hydrogenated nanoparticles. As expected, the hydrogen plasma treatment improves strongly the photoemission of the layer giving a QE of 22% at 146 nm. Indeed, this efficiency value is achieved only if the particles are treated in H2 microwave plasma before the growth of the sprayed layer rather than to hydrogenate the already formed one. These QE values are higher than those of photocathodes based on plasma chemical vapor deposition diamond films, but with the advantage of being much stable, too. The highest QE values are explained to be due to the intrinsic chemical and structural features of utilized ND particles. [ABSTRACT FROM AUTHOR]

Nanocrystalline diamond (NCD) films with and without a diamond buffer layer (BL) have been grown on p-type silicon substrates by microwave plasma enhanced chemical vapor deposition technique at different values of deposition temperature (652–884 °C). The photo- and thermionic electron emission properties of NCD films have been investigated, illustrated and explained by analyzing the surface morphology and the grain shape determined by atomic force microscopy, the chemical-structural properties by Raman spectroscopy and nanocrystallites size by X-ray diffraction. The NCD films with BL grown at the highest deposition temperature have shown the highest photo- and thermionic emission currents. [ABSTRACT FROM AUTHOR]

Abstract: Diamond is an extremely interesting material for photoemission applications, due to the negative electron affinity of its surface, which can be obtained after suitable treatments. In the present work two sets of polycrystalline diamond films, characterized by different thicknesses and deposition conditions, are analyzed. In particular, in the examined films the relationship among the grain size, the amount of non-diamond carbon (sp2) located at the grain boundaries and their efficiency as photocathodes has been found and carefully investigated. The photoemission yield in the UV range is evaluated for all the samples, before and after hydrogenation, and after air exposure. The crucial parameter for the photocathode performances has been found not to be the film thickness, but the properties of polycrystalline diamond films, tunable with the plasma modulation and the methane percentage in the gas mixture. [Copyright &y& Elsevier]

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 photoemission measurements performed by a KrF nanosecond excimer laser (λ = 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. [ABSTRACT FROM AUTHOR]

Abstract: The results of the external Quantum Efficiency (QE) measurements, in the range 150–210nm, of Poly-, Nano- and Single-Crystalline Diamond (PCD, NCD and SCD) film photocathodes (PCs) are reported and discussed. The diamond films, grown by Microwave Plasma Assisted Chemical Vapour Deposition (MPACVD) technique, have been analyzed with the aim to define which characteristics enhance their QE. It has been found that NCD film PCs, generally showing a lower QE with respect to PCD ones, enhance their photoemission if a graphitic component is present in the film. Surface hydrogenation effects on the photoemissivity of PCs have been investigated. Comparative studies between the QE of an untreated and a hydrogenated-treated diamond film PC show that the hydrogenated sample exhibits Negative Electron Affinity (NEA) properties. An ageing test of 24h air exposure shows a stability of the hydrogenated diamond PC higher than that of the CsI one. Moreover, the PC conditioning by means of plasma allows to recover almost completely the loss of PC QE due to ageing effect caused by the air exposure of a previously hydrogenated sample. The sensitivity of PCs depends strongly on the topography of diamond films. [Copyright &y& Elsevier]