Self-organized porous anodic alumina (PAA) formed by electrochemical anodization have become a fundamental tool to develop various functional nanomaterials. However, it is still a great challenge to break the interpore distance (Dint) limit (500 nm) by using current anodization technologies of mild anodization (MA) and hard anodization (HA). Here, we reported a new anodization mode named “Janus anodization” (JA) to controllably fabricate self-ordered PAA with large Dint at high voltage of 350–400 V. JA naturally occurs as anodizing Al foils in citric acid solution, which possessing both the characteristics of MA and HA. The process can be divided into two stages: I, slow pore nucleation stage similar to MA; II, unequilibrium self-organization process similar to HA. The as-prepared films had the highest modulus (7.0 GPa) and hardness (127.2 GPa) values compared with the alumina obtained by MA and HA. The optical studies showed that the black films have low reflectance (<10 %) in the wavelength range of 250–1500 nm and photoluminescence property. Dint can be tuned between 645–884 nm by controlling citric acid concentration or anodization voltage. JA is a potential technology to efficiently and controllably fabricate microstructured or hybrid micro- and nanostructured materials with novel properties.

We have demonstrated that self-ordered porous alumina with large period can be obtained by stable anodization in citric acid at high voltage (400 V). Pore nucleation, which determines the final morphology of the alumina, is a very slow process. By comparing the alumina films obtained in different citric acid concentrations and temperatures, we found the amount of free citric acid anions is critical to pore nucleation. Surface chemistry and the detail structural composition of the porous alumina were investigated by XPS and TEM, respectively. The results show that uniform black alumina surface (forming ordered nanopores) cannot be obtained in low or high citric acid concentrations; the carbon element content of the black is obviously higher than that of gray surface (pores cannot well develop); citric acid is incorporated into the porous alumina cell, where the thickness ratio of compact skeleton and acid incorporated part is 1:3. Accordingly, the pore nucleation has two stages: I, fast forming flat barrier-type alumina film, alumina form and deposit at metal-oxide and oxide-electrolyte interface, respectively. II, Al-citric complex in electrolyte slowly transform to citric acid incorporated alumina and unevenly deposit on barrier-type alumina, which results in electric field concentration between protuberances and pore development.

Transparent coatings with antireflection, antifogging, antifrosting, antifouling, and moisture self‐cleaning properties can dramatically improve the efficiency and convenience of optical elements and thus are highly desirable for practical applications. Here, it is demonstrated that a bionic nanocone surface (BNS) fabricated by a facile, low‐cost process consisting of template‐assisted prepolymer curing followed by surface modification can possess the multiple functions listed above. The polymer coating firmly adheres to a glass substrate due to bonding agents. After SiO2 nanoparticle deposition and low‐surface‐energy fluorosilane modification, the coating shows low microdroplet adhesion. As a result, the as‐prepared BNS exhibits a high transmittance when exposed to fog and good clarity even when the temperature decreases to −20 °C in a humid environment. Dipping the BNS into exemplified graphite powder has almost no influence on the transparency, and the BNS can realize self‐cleaning of moisture when the surface is covered with a thick layer of man‐made contaminants.

The designed superhydrophobic−superhydrophilic hybrid surface (SSHS) with highly ordered tip-capped nanopore arrays can be used as an intelligent and fast platform to realize different analyte solutions with different concentrations to be detected at the same time by surfaceenhanced Raman spectroscopy. This surface is fabricated in a large area by a facile and low-cost method of programmed multistep anodization of aluminum and pore widening process followed by selective chemical modification. The highly ordered tip-capped nanopore arrays can induce the highly sensitive and reproducible Raman signal, whose enhanced factor for rhodamine 6G (R6G) at 1358 cm −1 is 4.46 × 10 6 . The superhydrophobic− superhydrophilic hybrid property can realize the homogeneous distribution of the concentrated analyte in a droplet at the fixed place, which can avoid the diffusion-limit problem and further enhance the Raman signal. Surface-enhanced Raman spectroscopy of dried droplets with different concentrations of R6G or thiram is tested on SSHS, which show good reproducibility. The detection limits of R6G and thiram on SSHS are 10 −10 and 10 −7 M in 50 μL droplets, respectively. Due to the industrial compatibility of the fabrication technique, this smart surface has the potential to evolve into a general platform to develop various advanced chemical and biological sensors.

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