A nanosynthesis apparatus includes an outer tube and an inner tube with surfaces that oppose each other across a gap as part of a reaction chamber. A deposition fluid flows along the reaction chamber to grow nanostructures such as graphene or carbon nanotubes on a substrate in the reaction chamber. The reaction chamber may have an annular cross-section, and the growth substrate may wrap around the inner tube in a helical manner. This configuration can allow a flexible film substrate to travel through the reaction chamber along a path that is significantly longer than the length of the reaction chamber while maintaining a uniform gap between the substrate and the reaction chamber wall, which can facilitate a uniform temperature distribution and fluid composition across the width of the substrate.