Photoemission response of spray deposited diamond layers at low temperature

Highly efficient MWPECVD diamond based photocathodes have been demonstrated to be more stable than conventional materials such as CsI in UV detection. Poly- and nano-crystalline diamond films are still investigated and tested. Many research groups have found that photoemission properties are function of grain size, surface morphology and presence of defects (sp2 carbon bonding, carbon-hydrogen bond) within the grain boundaries [1]. One of the issues of diamond application in photocathodes, if compared with the CsI, is the very high temperature used during its growth, thus restricting the application fields. In this work, we present a study of photocathodes based on diamond layer deposited at low temperature by spray technique [1]. Diamond powders, with different grain sizes, were dispersed in the non-polar 1,2-dichloroethane (DCE) solvent by sonication for 30 minutes and successively sprayed on the substrates. The sprayed diamond films have been characterized by Raman spectroscopy, Atomic Force Microscopy and Photoemission measurements. Quantum efficiency (QE) measurements of the photocathodes have been assessed at normal incidence in reflective mode in the UV spectral range (150-210 nm) by means of a 30 W deuterium lamp (Mc Pherson TM) under vacuum. The photocathode was mounted in a multi-wire proportional chamber, not operating in electron multiplication mode. The absolute QE was evaluated by means of a NIST calibrated standard photodiode. The results have shown a QE dependence on the grain sizes and properties of the starting diamond powders. Moreover, the photoemissive properties of the low temperature (100 °C) sprayed diamonds are comparable with MWPECVD ones, these last produced at high temperature (>= 700 °C).