Abstract: An injector head for atomic layer deposition on a substrate, comprising a plurality of bars coupled to a connection unit. The bars have side walls with a spacer profile, respectively stacked against side walls of a neighbouring bar to form a plurality of stacked bars. The bars comprise slots extending over a length of the bar in communication with a respective slot in the connection unit. A flow path is defined through the bar with a relatively low friction factor to form a respective precursor drain; reactant drain or barrier gas drain. The spacer profiles define slits extending between adjacent bars in communication with a respective slot in the connection unit. A further flow path is formed along the bar with a relatively high friction factor, to form a respective precursor gas supply; reactant gas supply or flow barrier.