Enhancing hologram memory via deposition of plasmonic nanocubes on orderly mesoporous titania

Hologram is regarded as a key platform for large-volume data storage and information encryption. Diversity of plasmonic nanostructures makes it being a kind of vibrant hologram memory media. However, recording of amplitude, phase and polarization of light is restricted by difficulty to obtain anisotropic morphology of metal particles. Photocatalysis approach allows wide size distribution of Ag plasmonic nanoparticles after a long growth time on titania but suffers from the disadvantage that the shape of plasmonic nanostructures is mostly isotropic, which weakens optical vector sensitivity and information stability. Herein, Ag nanocubes exhibiting high polarization response ability are deposited on orderly mesoporous titania via UV photocatalysis. Recording efficiency of hologram by orthogonally linearly polarized lights is enhanced and the memorized information can be resistant to UV-erasure, both benefiting from the distal resonance of Ag nanocubes. This work delivers a guideline for long-term data storage and high-efficiency display devices.

Photoelectrochemical Behavior of Silver Nanoparticles inside Mesoporous Titania: Plasmon-Induced Charge Separation Effect

The self-assembly block copolymer method was used to synthesize mesoporous titania films and silver nanoparticles (NPs) were grown inside the films. Such silver NPs-titania films are known for their multicolor photochromic properties due to a photo-oxidation reaction of silver in the presence of titania under light excitation which is attributed to a plasmon induced charge separation. Here, the photoelectrochemical properties of these composite films have been investigated at different light wavelengths and chemical environment in order to characterize the light-induced redox reactivity modifications. Cyclic voltammetry study shows that the Ag⁺ electro-reduction peak potential varies depending on the light irradiation, which determines the state of the silver nanoparticles complexed or not by titania.

Characterization techniques for nanoparticles: comparison and complementarity upon studying nanoparticle properties

Nanostructures have attracted huge interest as a rapidly growing class of materials for many applications. Several techniques have been used to characterize the size, crystal structure, elemental composition and a variety of other physical properties of nanoparticles. In several cases, there are physical properties that can be evaluated by more than one technique. Different strengths and limitations of each technique complicate the choice of the most suitable method, while often a combinatorial characterization approach is needed. In addition, given that the significance of nanoparticles in basic research and applications is constantly increasing, it is necessary that researchers from separate fields overcome the challenges in the reproducible and reliable characterization of nanomaterials, after their synthesis and further process (e.g. annealing) stages. The principal objective of this review is to summarize the present knowledge on the use, advances, advantages and weaknesses of a large number of experimental techniques that are available for the characterization of nanoparticles. Different characterization techniques are classified according to the concept/group of the technique used, the information they can provide, or the materials that they are destined for. We describe the main characteristics of the techniques and their operation principles and we give various examples of their use, presenting them in a comparative mode, when possible, in relation to the property studied in each case.

Selective photo-oxidation induced bi-periodic plasmonic structures for high-density data storage

Stable and controllable optical memory is necessary for the development of current information technology. In this context, Ag/TiO₂ films have received much attention for their photosensitivity in wavelength and polarization, which can be applied to high-density optical storage. Here, we carried out dual-wavelength holographic recording using 403.4 nm and 532 nm lasers, and obtained mixed microfringes based on selective photodissolution of Ag nanoparticles of various sizes in TiO₂ nanoporous films. Two recording methods of simultaneous and sequential multiplexing were investigated. It was found that using simultaneous irradiation it is easier to obtain equivalent efficiency in both spectral hole burning and multiplexed grating diffraction, compared with the sequential one. The results can be explained by the Time-accumulation effect during Ag⁺ ion diffusion and migration in holographic recordings. Based on such properties, multiplexed-holographic fringes with uniform contrast were reserved by simultaneous recording in Ag/TiO₂ films. This work provides a new strategy for fabrication of photonic devices with complex microstructures.

Blu-ray-sensitive localized surface plasmon resonance for high-density optical memory

Tunable spectrum-response is desired for efficient photo-energy transformation. Blu-ray (~405 nm) and polarization sensitive Ag/TiO₂ nanocomposite films are thus fascinating in application of fast-response and high-density optical memory device. The Ag/TiO₂ film has the ability of replicating hologram based on optical coherence by laser-stimulated dissolution of Ag nanoparticles (NPs). The rate and efficiency of the dissolution are supposed to be enhanced by introducing uniform and small-sized Ag NPs in TiO₂ nanoporous films. However, no effective methods have been proposed to resolve this issue by now. Here, we develop a simple method of thermal-reduction to obtain high-density, space-dispersed and extremely small-sized Ag NPs in TiO₂ nanoporous films pretreated with tannic acid. The film shows both high and narrow absorbance band centered at ~405 nm. Diffraction efficiency of the blu-ray holographic storage in the Ag/TiO₂ film is improved by one order of magnitude compared to the traditional UV-reduced sample. Based on such properties, polarization-multiplexing holograms are able to be written at 405 nm and readout with little crosstalk. This work provides effective solutions for sensitizing localized surface plasmon resonance at near-UV region, extending the growth range of Ag NPs in the volume of TiO₂, and resultantly, realizing high-density optical memory.