Structural Color Of Cu @ PAA Composite Films And Influence Of Oxygen Vacancy On The Properties Of The Ordered Porous Metal Oxide Thin Film

Structural colors have long attracted the attention of biologists due to their many useful characters including iridescence, high reflectivity and polarization. In recent years, a large amount of experimental work has been undertaken to clarify the relationship between the brilliant colors and the microstructures involved. Therefore, considerable attention has been paid to the construction of man- made systems with interference colors. Some people found that the PAA thin film with structural color. This method for creating colored thin films can have a wide variety of applications such as for decoration, display, and multifunctional anti-counterfeiting. In this article, a series of PAA/Al films were prepared in phosphoric acid electrolyte using once anodic oxidation method. Then, porous anodic alumina embedded C u nanocomposite films with structural color was synthesized by an ac electrodeposition method. It was found that the films all displayed highly saturated colors. The microstruc tures and the optical characteristics of the films have been discussed. Beside, due to the highly ordered nano-hole array, PAA film prepared by the two-step anodic oxidation is widely applied. As we all know, the porous anodic alumina films have high surface-area-to-volume ratio, which forms a large quantity of oxygen vacancies in the inner surface and may play a critical role in physical property, such as ferromagnetism, resistance switching behavior. Thus, porous Cu2 O and TiO₂ films are deposited on porous anodic alumina（PAA） substrates by direct current reactive magnetron sputtering, and we discuss the physical properties. The results are as follows:（1） A series of PAA/Al films were prepared in phosphoric acid electrolyte using once anodic oxidation method at room temperature. Then, porous anodic alumina embedded C u with iridescent colors were fabricated in copper sulfate electrolyte. The films display highly saturated colors after being synthesized by an ac electrodeposition method. Tunable color in the films is obtained by adjusting anodization time, and can be adjusted across the entire visible range. The reflectance spectra of the films show a red-shift with the increasing anodization times. In addition, theoretical results of the effective refractive index and maximum reflected wavelength λmax of PAA/Al films according to the Bragg–Snell formula are consistent with the experimental results. Finally, multicolor patterns are obtained by an organics-assisted process.（2） Cu₂O films were fabricated on a PAA substrate at 573 K by DC-reactive magnetron sputtering. Without magnetic bias field, the magnetization of the C u2O/PAA composite films can be controlled by an applied dc elecrtic field in a reversible and reproducible way and shows an analogous on-off behavior. The PL spectra prove that there are a large number of oxygen vacancies in as-prepared Cu₂O/PAA films. Futher analysis indicates that the formation/rupture of conduting filaments composed by oxygen vacancies would be responsible for the changes of magnetization, as well as the resistivity caused by the electric field. The magnetization of the Cu₂O/PAA films can be manipulated by applying the small electric field.（3） TiO₂ films were fabricated on a PAA substrate at 573 K by DC-reactive magnetron sputtering. The PL spectra prove that there are a large number of oxygen vacancies in as-prepared TiO₂/PAA films. The bipolar RS properties were observed in the Ag/TiO₂/PAA/Al devices, which are induced upon the formation/disruption of the filament paths, as co nfirmed by the oxygen vacancies dependent resistances relationships at different resistance states. We found that the resistance would be significantly switched under low voltages. A significant ferromagnetism, accompanied by stable bipolar resistive switc hing behavior, was observed in as-prepared nanoporous composite films. The magnetization of the films into the high resistance state is about three times larger than that in the as-prepared state. The endurance test of 10 cycles for Ag/TP/Al devices provides evidence of more stable performance.