A photo cathode for use in a vacuum tube including a cathode layer, having an entrance face capable of absorbing photons impinging on the cathode layer, and an exit face for releasing electrons upon impinging of the photons, and an electron exit layer, in facing relationship with the exit face of the cathode layer for improving the releasing of the electrons, and a carbon containing layer, positioned between the exit face of the cathode layer and the electron exit layer, for bonding the electron exit layer to the cathode layer.