Nonvolatile Plasmonic Holographic Memory Of Ag/TiO₂ Nanocomposite Films

The stability of data storage is essential for optical information processing.Recently,Ti O₂ nanoporous films loaded with small-sized Ag nanoparticles,serving as an important class of photochromic materials,attracted much attention for their possible applications in data storage,localized surface plasmon resonance?LSPR?sensors,polarization transformation and nanoscale optical manipulation.These applications benefit from the effective optical response of the Ag nanoparticles?NPs?interfaced with TiO2,where the particle size and shape are well sensitive to the wavelength and polarization of the excitation light,respectively.However,no effective method is found to inhibit the UV erasure of the recorded hologram,so as to improve the storage stability and life for the application of the plasmonic nanocomposite film in nonvolatile-memory devices.A systematic exploration to improve the nonvolatile property of Ag/TiO2 film is carried out in this thesis.The micro-mechanism of anti-erasure performance is also proposed.Meanwhile,we discussed the holographic storage efficiency and stability for the nanocomposite system.In this work,we adopt two methods to improve the anti-erasure performance of the recorded information for Ag/TiO2 films.The first one is that nonvolatile memory is obtained via adjusting recording mode,prolonging exposure time and modulating sample nanostructures.After analyzing such results as the oscillation process of holographic kinetic,the photochromism property,the dynamics for alternating recording-erasing,the scalar-vector property of grating under polarizing microscope and the anti-erasure performance for different irradiation times,a model based on photo-driven ion migration is proposed.The model is used to explain the micro-mechanism for improving the UV resistance of Ag/TiO2 nanocomposite film.For the second method,ultrasmall-sized dispersed charge-centers are introduced into the metal/semiconductor nanocomposite system in order to control the motive behaviour of electrons at interface.After investigating the size distribution of silver nanoparticles?NPs?in the nanocomposite system,the temporal response of photocurrent as well as the modulation of reversible photochromism,the advantage of anionic tungstophosphate(H₃PW₁₂O₄₀,denoted as PW₁₂)-modified Ag/TiO₂ nanocomposite system in improving the efficiency of holographic storage is verified.It is also found that the resident diffraction efficiency can be accumulated with increasing the recording-erasure cycle times,which provides the basis for achieving anti-erasure holographic storage.Diffraction efficiency and holographic images can be both enhanced in the Ag/PW12/TiO2 even under the direct illumination of UV light,while the Ag/TiO₂ film shows almost no optical response.The introduction of PW₁₂2 provides new electron transferring channel.Based on such a mechanism,the experimental phenomenon can be well explained.The PW12-modified-Ag/TiO2 hetero-junction presents nonvolatile performance in high density optical storage,which can be regarded as environmentally-stable holographic storage system.