NOVELTY - The apparatus comprises micromixers (52) that are fluidly coupled to a first fluid source and a second fluid source and are arranged for receiving and mixing first and second fluids comprising reactants to initiate formation of a deposition material, a temperature controlled reaction time channel for receiving and controlling reaction time of the reactants, a substrate support for positioning a substrate (62) for receiving the deposition material, a substrate heater having a temperature control unit operatively associated with the substrate, and a microchannel applicator.    USE - The apparatus is useful for chemical deposition of thin films on the substrate, where the thin film is an epitaxial nanostructured thin film, a nanocrystalline thin film, an epitaxial thin film, a superlattice thin film, a composition gradient thin film and a composite thin film and is useful in electronic devices including flexible transistors, solar cells, LEDs, detectors, sensors and switches.    ADVANTAGE - The apparatus ensures reliable and reproducible chemical deposition of smooth and uniform thin films on the substrate with high growth rate and without high temperature annealing processes, and minimizes unwanted particle formation and deposition.    DETAILED DESCRIPTION - The apparatus comprises micromixers (52) that are fluidly coupled to a first fluid source and a second fluid source and are arranged for receiving and mixing first and second fluids comprising reactants to initiate formation of a deposition material, a temperature controlled reaction time channel for receiving and controlling reaction time of the reactants, a substrate support for positioning a substrate (62) for receiving the deposition material, a substrate heater having a temperature control unit operatively associated with the substrate, a microchannel applicator for receiving deposition material and applying the deposition material to a heated substrate, a pump for pumping the first and/or second fluids to the micromixer, and a continuous susceptor. The micromixer is an interdigital micromixer, a nozzle micromixer or a microjet mixer. The apparatus comprises a continuous production apparatus and chip-based apparatus. A third fluid source is operably coupled to the micromixer. The first and second fluids are introduced to the micromixer as counter-flowing fluid streams. The temperature controlled reaction time channel is immersed in a water bath to provide temperature control. A length of the channel, temperature of reactants in the channel, material flow rate through the channel and material residence time in the channel are selected to control homogeneous chemistry of the deposition material for application to the substrate. The continuous susceptor is a continuous roll-to-roll susceptor or a rotating disk substrate susceptor.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of an impinging flow bath deposition reactor with an interdigital micromixer.    Micromixer (52)    First reactant stream (54)    Second reactant stream (56)    Third reactant stream (58)    Channel (60)    Substrate. (62)