Injector head for atomic layer deposition on a substrate, comprising: - a deposition space provided with a precursor supply and a precursor drain; said supply and drain arranged for providing a precursor gas flow from the precursor supply via the deposition space to the precursor drain; the deposition space in use being bounded by the injector head and the substrate surface; - a flow barrier arranged for injecting a barrier gas flow between the injector head and the substrate surface; and - a further deposition space provided with a reactant supply, the further deposition space in use being bounded from precursor gas by the flow barrier, and arranged for providing at least one of a reactant gas, a plasma, laser-generated radiation, and ultraviolet radiation for reacting the precursor after deposition of the precursor gas on at least part of the substrate surface; - a connection unit connectable to a respective plurality of gas supply sources and drain collectors thus providing access for respective gases via said connection unit, to a respective precursor deposition space, reactant deposition space and flow barrier; wherein - a plurality of bars is coupled to the connection unit, the bars having side walls with a spacer profile, respectively stacked against side walls of a neighbouring bar to form a plurality of stacked bars; the bars comprising slots extending over a length of the bar in communication with a respective slot in the connection unit, thus defining a flow path through the bar with a relatively low friction factor, to form a respective precursor drain; reactant drain or barrier gas drain; - said spacer profiles defining slits extending between adjacent bars in communication with a respective slot in the connection unit, thus defining a further flow path along the bar with a relatively high friction factor, to form a respective precursor gas supply; reactant gas supply or flow barrier. - a deposition space provided with a precursor supply and a precursor drain; said supply and drain arranged for providing a precursor gas flow from the precursor supply via the deposition space to the precursor drain; the deposition space in use being bounded by the injector head and the substrate surface; - a flow barrier arranged for injecting a barrier gas flow between the injector head and the substrate surface; and - a further deposition space provided with a reactant supply, the further deposition space in use being bounded from precursor gas by the flow barrier, and arranged for providing at least one of a reactant gas, a plasma, laser-generated radiation, and ultraviolet radiation for reacting the precursor after deposition of the precursor gas on at least part of the substrate surface; - a connection unit connectable to a respective plurality of gas supply sources and drain collectors thus providing access for respective gases via said connection unit, to a respective precursor deposition space, reactant deposition space and flow barrier; wherein - a plurality of bars is coupled to the connection unit, the bars having side walls with a spacer profile, respectively stacked against side walls of a neighbouring bar to form a plurality of stacked bars; the bars comprising slots extending over a length of the bar in communication with a respective slot in the connection unit, thus defining a flow path through the bar with a relatively low friction factor, to form a respective precursor drain; reactant drain or barrier gas drain; - said spacer profiles defining slits extending between adjacent bars in communication with a respective slot in the connection unit, thus defining a further flow path along the bar with a relatively high friction factor, to form a respective precursor gas supply; reactant gas supply or flow barrier.