NOVELTY - A microreactor (10) comprises a base defining at least one channel (3) having a bottom (18), an inlet and an outlet; a substrate (2) which, when associated with the base, forms a reaction chamber with the channel where an average distance from a surface of the substrate facing the channel to the bottom is 0.1-5 mm; and a heating element operatively associated with and capable of transferring heat to the substrate.    USE - As microreactor useful in applications such as producing semiconductors materials and nanomaterials for the optoelectronics, laser, photovoltaic, biosensor, and chemical sensor industries; also in anti-reflective layers, transparent conducting oxide films, absorber layers and buffer layers, nanostructured solar cells, gas sensors, and photocatalysis; as informative research tool for in situ monitoring with electrochemical and optical probes; for analyzing the kinetics of a deposition process and for producing combinatorial arrays that can be used to rapidly screen materials.    ADVANTAGE - The microreactor produces high deposition yields, minimizes waste generated by the deposition process, and can be used to fabricate deposition products having custom designed morphology and properties since it permits relatively precise temperature control in the reactor. The microreactor is also ideal research tool for investigating the reaction kinetics of semiconductor and nanomaterial deposition. The microreactor is capable of fabricating customized deposition materials, particularly well suited for generating components of photovoltaic cells such as anti-reflective layers.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for method for using a microreactor involving introducing a chemical to the microreactor; controlling an environmental condition of the microreactor; depositing the chemical on the substrate, forming a deposition product; and removing the substrate and the deposition product, where during the depositing step, a ratio of a deposition surface on the substrate to a volume of the microreactor is 0.1-10 mm-1.    DESCRIPTION OF DRAWING(S) - The figure shows a cross-sectional view of microreactor.    Substrate (2)    Channel (3)    Microreactor (10)    Cap (11)    Sensors (12)    Sise walls (17)    Bottom (18)    Seal (21)    Substrate receiving area (22)