Optical interference structures exist in nature, e.g., in feathers of birds and wings of insects, and exhibit vivid colors, which originate from the mechanism of optical interference and thus can vary notably with the viewing-angle and the refractive index of the dielectric medium surrounding the optical interference structures. [1][2][3] Because of the attractive applications of optical interference structures in color display, decoration, anti-counterfeiting and liquid sensors, considerable attention has been paid to the construction of man-made systems with interference colors, such as multilayer structures, [4] silicon dimple arrays, [5] and anodic aluminum oxide (AAO) thin films embedded with metal. [6,7] Recently, it has been reported that AAO thin films embedded with carbon nanotubes (CNTs) (denoted as CNTs@AAO composite thin films) display brilliant colors, which stem from the interference between the reflected light from the AAO top planar surface and the emergent light reflected on the AAO-Al interface.[8] As colors of the CNTs@AAO composite thin films are mainly determined by the interference band with the maximum reflectance (B max ) in the visible region, and B max shifts by changing the AAO film thickness, color tuning of the CNTs@AAO composite thin films can be attained by varying the AAO film thickness in the anodization. However, B max is very sensitive to the thickness of the AAO film, and the pore growth rate of the AAO in the anodization is very fast, so it would be difficult for this approach to tune the color of the CNTs@AAO composite thin film in a well-controlled manner. In addition, the as-prepared CNTs@AAO composite thin films are hydrophobic and thus prohibit water infusion.[9] If the CNTs@AAO composite thin films can be changed into hydrophilic, the composite thin films might be used as water sensors. Here, by applying wetchemical etching to porous AAO thin films to thin the AAO films and widen the AAO pores isotropically before CNTs growth, controllable precise color tuning of the CNTs@AAO composite thin films has been achieved. Moreover, via further plasma cleaning, the CNTs@AAO composite thin films with large AAO pore diameter can change their colors remarkably after water infusion. Additionally, via applying wet-chemical etching to different areas of one piece of AAO film for rationally different durations, patterned CNTs@AAO composite thin film with each area showing a unique color has been obtained. The details of the fabrication of the AAO, the etching of the AAO, and the growth of the CNTs are given in the Experimental section. Figure 1a and b are SEM images of the CNTs released from the CNTs@AAO composite thin films. Figure 1a shows free-standing CNTs aggregating into clumps and formed inside the pores of the AAO films without being etched. Figure 1b Figure 1d is the TEM image of the CNTs from Figure 1b. The outer diameter and wall thickness of the CNTs are estimated to be 90 and 6 nm, respectively. Therefore, etching AAO films before CNTs growth can cause remarkable increase ...

A large variety of interconnected nanowire/nanotube (NW/NT) and nanotube/nanowire/nanotube (NT/NW/NT, see picture) hybrid architectures with branched topology have been prepared using a combinatorial process of electrodepositing nanowires in the branched channels of anodic aluminum oxide templates, selectively etching part of the deposited nanowires, and growing nanotubes in the remaining empty channels on the ends of the nanowires.