Unique porous anodic aluminum oxide (PAAO) films with a completely flat barrier layer and an extremely porous loofah-like structure were fabricated by anodizing aluminum in an alkaline sodium metaborate solution. High-purity aluminum plates were anodized in a 0.3 M sodium metaborate solution at various applied voltages in the range of 0.1–200 V. A typical PAAO film with a spherical cap barrier layer was formed at voltages lower than 50 V, whereas a PAAO film with a flat barrier layer was formed at voltages higher than 100 V; this film formation was not based on the Keller-Hunter-Robinson model with the spherical barrier layer. The growth interface of the flat barrier layer exhibited an ultra-flat morphology with a minimum roughness value of 0.4 nm, which is much smaller than that of an electropolished aluminum surface. Such barrier layer morphology is expected to be formed by field-assisted dissolution without oxide flow. Although the current density slightly decreased with the applied voltage, a relatively higher current density of 6.8 Am⁻² was still measured at the lowest voltage of 0.1 V. The alumina walls and the bottom barrier layer gradually thinned as the applied voltage decreased, and a loofah-like PAAO film with an ultra-high porosity of 0.93 was successfully fabricated at 0.1 V. The anodic oxide consisted of amorphous, anion-free aluminum oxide.

通过在碱性偏硼酸钠溶液中对铝进行阳极氧化，制造出具有完全平坦阻挡层和极其多孔的丝瓜络状结构的独特多孔阳极氧化铝 (PAAO) 薄膜。高纯度铝板在 0.3 M 偏硼酸钠溶液中在 0.1-200 V 范围内的各种施加电压下进行阳极氧化。在低于 50 V 的电压下形成具有球帽阻挡层的典型 PAAO 膜，而 PAAO 膜在高于 100 V 的电压下形成平坦的阻挡层；这种成膜不是基于具有球形阻挡层的 Keller-Hunter-Robinson 模型。平坦阻挡层的生长界面呈现出超平坦形态，最小粗糙度值为 0.4 nm，远小于电解抛光铝表面的粗糙度。预计这种阻挡层形态是通过场辅助溶解形成的，而没有氧化物流动。虽然电流密度随外加电压略有下降，但相对较高的电流密度 6.8 Am^-2仍在最低电压 0.1 V 下测量。随着施加电压的降低，氧化铝壁和底部阻挡层逐渐变薄，在 0.1 V 下成功制备了具有 0.93 超高孔隙率的丝瓜络状 PAAO 薄膜. 阳极氧化物由无定形、无阴离子的氧化铝组成。