Polycrystalline diamond films grown by MWPECVD technique and application in photocathodes

Diamond is an extremely interesting material for photoemission applications, due to the negative electron affinity which can be obtained after suitable surface treatments. In the present work, two sets of polycrystalline diamond films, characterized by dif-ferent thickness and deposition conditions, are ana-lyzed. In particular, the relationship among the grain size, the amount of non-diamond carbon (sp2) located at the grain boundaries and the film sensitivity as a photocathode has been found and carefully investi-gated. The photoemission yield in the UV range has been evaluated for all the samples, before and after hydrogenation process, and after air exposure. The critical 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 percent-age in the gas mixture

Influence of bias voltage on the stability of CsI photocathodes exposed to air

We describe a possible correlation between the bias voltage applied to the substrate during the growth of CsI photocathodes and the variation of quantum efficiency (QE) after one day exposure to humid air. It was found that fresh samples are much less sensitive to humid air when a high negative bias voltage was applied during film growth. A model based on surface film interaction with water molecules is presented for the observed effect. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements have been performed to examine, respectively, the bulk structure and the surface of fresh and exposed CsI samples. Also reported are transmittance measurements for fresh and aged CsI samples in the wavelength range 190-850 nm. (C) 2002 Elsevier Science B.V. All rights reserved

Thermoluminescent response of thin (2 μm) polycrystalline diamond films grown by pulsed and continuous microwave plasmas

Polycrystalline diamond films with a thickness of about 2 μm were deposited by chemical vapour deposition on silicon substrates in continuous and pulsed wave regimes with duty cycle between 25% and 100%. The thermoluminescent behaviour of these films was analysed in the temperature range 323–723 K after β irradiation with doses in the range 7–107 Gy. All the films exhibit a dosimetric peak centred at about 592 K, showing a good linearity in the whole investigated dose range. The thermoluminescence analyses show that the intensity of the dosimetric peak is maximum for the continuous wave film, while it decreases for the pulsed wave samples. The variation of the crystalline quality and the purity of the films with the employed duty cycle, investigated via micro-Raman spectroscopy and room-temperature photoluminescence, indicates that the continuous wave (duty cycle=100%) film has the best quality, corresponding to the highest thermoluminescence efficiency. © 2009 Elsevier B.V. All rights reserve