Holographic Storage Based On Photoinduced Charge Transfer At The Interface Of ZnO Nanowires

Holographic storage technology has become an important way of information storage because of its high density,low energy consumption,high redundancy and anti-interference.The development of optical sensitive media with excellent performance is the premise of building an advanced optical information storage system.Photochromic materials show many excellent optical properties under laser irradiation,among which inorganic semiconductor composite system has attracted extensive attention due to its advantages of non-toxic,simple preparation and low cost.Wurtzite ZnO is a typical wide-band-gap semiconductor material with high electron mobility,high exciton binding energy and diverse nanostructures,which can be prepared into a variety of low dimensional structures such as nanowires,nanotubes,nanosheets and so on.Due to the excellent physical and chemical properties,one-dimensional ZnO nanowires have been widely used in many fields,such as photoelectrochemistry,photocatalysis,surface enhanced Raman spectroscopy,etc.In particular,its bending resistance is expected to broaden the application in flexible devices.However,in the field of holographic storage,the research based on ZnO nanowires is rarely reported.In order to fill the research gap in this field and clarify the microscopic mechanism of holographic storage in ZnO nanowire based composite system,the following work has been carried out in this paper:（1）ZnO nanowires were prepared by two-step hydrothermal method.ZnO nanowires with three different lengths were obtained by controlling the hydrothermal time.The surface morphology and nanowire length of the three samples were analyzed by scanning electron microscopy,and the surface density and diameter distribution of nanowires with different lengths were compared.In order to investigate the defects and optical properties of the samples,we carried out the electron paramagnetic resonance,absorption spectrum and photoluminescence spectrum tests.The results show that there are oxygen defects in ZnO nanowires prepared by hydrothermal method,and they have optical absorption ability in visible region.（2）To resolve the issues of the low efficiency of electron transfer from metal to semiconductor and the difficulty of holographic storage in Ag/ZnO nanowires composite system,the immersion method is proposed to prepare Ag⁺/ZnO nanocomposite films with high transparency.Based on the“electron reverse transfer”process,the electrons of ZnO conduction band are transferred to Ag⁺ions through the nanowire interface under the irradiation of blue-violet laser.The reduction reaction takes place,which realizes the transition of silver from Ag⁺to Ag⁰.The spatial confinement effect of one-dimensional nanowires further promotes the formation of Ag nanorods.Holographic optical storage is realized by the spatial arrangement of Ag⁺ions/Ag nanorods.In addition,it is found that the surface uniformity and light scattering characteristics of the nanowire arrays strongly depend on the hydrothermal growth time.The Ag/ZnO nanowire arrays grown by hydrothermal growth for 1 hour show the highest holographic diffraction efficiency and can realize the hologram reconstruction under red light detection.This work opens up a new way for the application of ZnO in short wavelength optical storage.（3）WO₃ nanoparticles/ZnO nanowires composite films were prepared by drop-coating method to solve the problem of poor stability of holographic storage caused by the reverse photochromism of WO₃.High resolution transmission electron microscopy confirmed the formation of point/line heterojunction interface in the composite system.Under the stimulation of blue-violet light,the photogenerated holes formed in the WO₃ valence band are transferred to the ZnO valence band through the point/line interface,which effectively inhibits the recombination of electron-hole pairs,significantly increases the light absorption amplitude,and improves the photochromic performance.The spatially dispersed charge transfer channel extends the relaxation time of WO₃ to 26000 s,which is beneficial to the stable readout of holographic storage.Under low power holographic writing（2 m W）,the diffraction efficiency of the composite system can still reach 1.1%.At the same time,persistent holographic fringes consisting of alternate arrangement of WO₃/Hx WO₃ in ZnO nanowire arrays were observed by confocal laser scanning microscope.Due to the introduction of ZnO nanowires,the photochromic response ability of the composite system in the full visible region is increased.Using red（671 nm）,green（532 nm）and blue（473 nm）lasers as probe sources,the three primary color hologram reconstruction is realized.This work provides an important basis for the development of the nano-devices with integration of high-density optical storage and full-color laser display.