Diamond films exhibit interesting properties, such as a wide bandgap (5.5 eV) and very low electron affinity which favours the electron photoemission. Diamond based cold photocathode is well known and demonstrated, due also to its chemical stability and mechanical robustness. In this work, a comparative study on photoemission of nanocrystalline diamond (NCD) film and nanodiamond (ND) layers obtained by microwave plasma enhanced chemical vapour deposition and pulsed spray technique, respectively, is presented and discussed evidencing advantages and drawbacks. The first technique permits to obtain thin NCD films at high deposition temperature (650-900 C) with excellent homogeneity and adhesion; whereas the second one allows to deposit thin ND layer at a temperature of 120 C with poor adhesion and low uniformity. Both NCD film and ND layers have been characterized by Raman spectroscopy, atomic force microscopy (AFM) and photoemission measurements.