Ultrathin AAO template is one of the most popular type of AAO templates. Ultrathin AAO templates have self-organized honeycomb-like nanopores, and they are usually from several ten nanometers to several hundred nanometers in thickness. Ultrathin AAO templates have been widely used for fabrication of large-scale ordered arrays of surface nanostructures such as nanodots and nanoholes on the surface of substrates. Pores of ultrathin AAO template are uniform in diameter and highly ordered in a short-range. In addition, the material (Al) is transparent in the near-infrared and visible spectrum, and is electrically insulated. Compared to other technology for making ordered nanostructures, ultrathin AAO template has special advantages such as large pattern area (>1 cm2), high throughput, ultrahigh density (1010–1012 cm2) of the surface nanostructures, and low equipment costs.
Fig. 1. Up: Schmatic of our ultrathin AAO template product; bottom: a photo of large area PMMA/ultrathin AAO template film.
Fig. 2. The product of ultrathin AAO template.
Fig. 3. Schmatic of our ultrathin AAO template product in the package.
Because of the all thickness (less than one micron), handling of ultrathin AAO template is a great challenge. In addition, it is very fragile and inconvenient to use. Here, a layer of Polymethyl methacrylate (PMMA) is coated on the surface of ultrathin AAO template (fig. 1, up) to assist the transfer process. With the assistance of PMMA layer, ultrathin AAO template up to 80cm2 can be easily manipulated (fig. 1, bottom). This technique allows users to carry, cut, or transfer ultrathin AAO template to any substrate easily. A all piece of PMMA/ultrathin AAO template film with typical package is shown in Fig. 2. Typically, PMMA side is at the bottom of the package without further instruction (fig. 3).
Fig. 4. The schematic of transferring ultrathin AAO template in three steps. Step 1, clean the substrate and treat into slightly hydrophilic; step 2, place the AAO membrane on the substrate with AAO side facing to the substrate and wet with deionized water; step 3, remove PMMA in acetone bath.
Generally, ultrathin AAO template is used by transferring on the other substrates. Fig. 4 illustrate the process of transferring in three steps. Step 1: clean and hydrophilic treatment. Hydrophilic treatment allows the membrane to be contact with the substrate more tightly. A low power oxygen plaa or ozone plaa could work. Step 2: Wet the membrane. Step 3: removing of PMMA in acetone bath.
Note: don’t touch the surface of ultrathin AAO template after transfer.
Fig. 5. Top view (left) and section view (right) of ultrathin AAO template on Si wafer.
Fig. 6. ultrathin AAO template on silicon (left), glass (middle) and fused silica (right).
With our transferring technique, AAO template can be transferred onto various substrates, such as silicon, sapphire, fused silica, glass, stainless steel, SiC、ZnO、GaN、ITO、FTO、PDMS、PET, etc. Taking ultrathin AAO template as mask, we can easily make metal or semiconductor nanostructures, including nanoparticle and nanowire arrays. In addition, AAO can be used as masking for etching the substrates.
You can image the structure with either SEM or AFM. Due to the all thickness, sputtering gold or carbon before SEM test is not necessary, given the substrate is conductive. Ultrathin AAO template can be removed by 5% phosphate acid at 30℃ slowly, or by 5wt.% NaOH at room temperature quickly. Alternatively, the membrane can be removed by Kapton tape.
