NOVELTY - Depositing gradient films on a substrate surface by atomic layer deposition (ALD), involves (a) exposing the substrate to a vapor of a first precursor that is reactive with the surface of the substrate thus forming a layer of first precursor molecules on the surface of the substrate; removing non-reacted first precursor; exposing the substrate to a vapor of a second precursor that is reactive with the first precursor, thus forming a film of reacted first and second precursors on the surface of the substrate; removing non-reacted second precursor.    USE - For depositing gradient films on a substrate surface (claimed), used in photocatalysis applications, photonics, catalysis, solar cells and electronics industries, for example in the form of photonic crystals, nanocatalysts and nanofilms.    ADVANTAGE - The method produces smoothly varying gradient films or nanofilms in nanoporous materials. The gradient photonic crystals (GPCs) are non-periodic photonic crystals which possess superior or improved photonic properties as compared to the periodic or regular photonic crystals. The wider photonic band gaps and slow group velocities at the band edges of gradient photonic crystals (GPCs) provide the basis for enhancing solar cell efficiency. The gradient inverse opal structures has the ability to reduce the group velocity of light in a broader wavelength range because of the smoothly shifted photonic bandgap characteristics; and reducing the group velocity to the fraction of light speed in vacuum in a wider frequency regime facilitates a largely increased yield of photochemical processes due to enhanced light-matter interactions.    DETAILED DESCRIPTION - Depositing gradient films on a substrate surface by atomic layer deposition (ALD), involves (a) exposing the substrate to a vapor of a first precursor that is reactive with the surface of the substrate thus forming a layer of first precursor molecules on the surface of the substrate; removing non-reacted first precursor; exposing the substrate to a vapor of a second precursor that is reactive with the first precursor, thus forming a film of reacted first and second precursors on the surface of the substrate; removing non-reacted second precursor; and repeating steps (a)-(d) in cycles, where (i) in a first number of cycles of the cycles, the exposure dosage of the first precursor and the exposure dosage of the second precursor is equal to or above a respective saturation exposure dosage of the respective precursor, and in subsequent cycles, the exposure dosage of the first precursor or the exposure dosage of the second precursor is reduced to below the respective saturation exposure dosage of the respective precursor; or in a first number of cycles of the cycles, the exposure dosage of the first precursor and the exposure dosage of the second precursor is below the respective saturation exposure dosage of the respective precursor, and in subsequent cycles, the exposure dosage of the first precursor or the exposure dosage of the second precursor is increased to be equal to or above the respective saturation exposure dosage of the respective precursor. INDEPENDENT CLAIMS are included for the following:    (1) substrate comprising at least one void extending at least partially through the substrate, and films of a material, where the films disposed on an internal surface of the void, where the films have a total thickness that decreases along a length of the void; and    (2) an inverse photonic crystal comprising substantially spherical voids arranged in a lattice arrangement, and films of a material, where the films disposed in at least one interstitial space bounded by the spherical voids, where the films have a total thickness that decreases along a length of the interstitial space.