Materials For Optical Data Storage Research Articles

Recent Advances in Functional Materials for Optical Data Storage.

In the current data age, the fundamental research related to optical applications has been rapidly developed. Countless new-born materials equipped with distinct optical properties have been widely explored, exhibiting tremendous values in practical applications. The optical data storage technique is one of the most significant topics of the optical applications, which is considered as the prominent solution for conquering the challenge of the explosive increase in mass data, to achieve the long-life, low-energy, and super high-capacity data storage. On this basis, our review outlines the representative reports for mainly introducing the functional systems based on the newly established materials applied in the optical storage field. According to the material categories, the representative functional systems are divided into rare-earth doped nanoparticles, graphene, and diarylethene. In terms of the difference of structural features and delicate properties among the three materials, the application in optical storage is comprehensively illustrated in the review. Meanwhile, the potential opportunities and critical challenges of optical storage are also discussed in detail.

Employing defect luminescence of LiGaO2 to realize dynamic readout and multiplexing of optical information

Optical data storage (ODS) materials have attracted much attention due to their unparalleled advantages, including outstanding low cost, high speed, and high storage density. The dynamic readout of high-resolution optical information in a single medium has always been a hotspot in the design of ODS materials. This work successfully developed a multi-mode dynamic luminescent material LiGaO2. By adjusting the defect states in different synthetic atmospheres, LiGaO2 materials with different luminescence properties were obtained, it appears green glow in air and nitrogen atmospheres and orange-red glow in reductive atmospheres. LiGaO2 material synthesized in a reduction atmosphere (R–LiGaO2) not only has the characteristics of rapid filling, but also has more abundant trap distribution, so it has a good optical information storage capacity, which is very suitable for the field of ODS. Through the analysis and characterization of R–LiGaO2 material in thermally-stimulated luminescence (TSL) and photostimulated luminescence (PSL), it is found that the dynamic optical information readout based on intensity-color-wavelength multiplexing in undoped single ODS materials is realized through the synergistic effect of trap centers and luminescence centers. This work provides a new strategy for the design and application of ODS materials.

Order-disorder structural transition in Pr3+-doped Ba3Ga2O6 for rewritable and write-once-read-many optical data storage

The emerging challenges of the big data era, both in storage density and security, require the development of the next-generation optical data storage materials. Here, we report for the first time a photo-stimulated luminescence (PSL) material, Ba3Ga2O6: Pr3+, for rewritable optical storage and write-once-read-many data preservation. Ba3Ga2O6: Pr3+, with an isolated deep trap depth in the range 1.26–1.53eV, has been used for data encoding/decoding under the excitation of 254 nm UV light and by the simulation of an 808 nm NIR laser. Meanwhile, the phosphor allows for high-security write-once-read-many optical memory by taking advantage of the irreversible change of the photoluminescence (PL) color from blue to green (a binary blue ‘0’ and green ‘1’ code) irradiated by 365 nm UV light. The comprehensive investigations indicate that the irreversible PL switching is as a result of the order-disorder structural transition by thermal treatment. The new persistent luminescence material not only exhibits promising applications in sustainable rewritable data storage, but also paves the way for write-once-read-many optical information storage with a high level of security.

Rhenium doped Sb2Te phase change material with ultrahigh thermal stability and high speed

Sb2Te material is an important base material for phase change memory or optical data storage, but the poor amorphous stability of Sb2Te severely limits its application. In this work, we proposed a superhard and infusible Rhenium (Re) doped Sb2Te (RST) phase change material to improve the properties of Sb2Te. The data retention of RST was remarkably increased to 152 °C@10 years, which is much higher than those of traditional Ge2Sb2Te5 (87 °C@10 years) and Sb2Te (56 °C@10 years). The operation speed of the RST based device is as fast as 10 ns and the resistance ratio is more than 102 times. The density change of RST (4.2%) is smaller than those of Ge2Sb2Te5 (6.5%) and Sb2Te (5.7%). Furthermore, the operation voltage and power consumption of RST based device are much lower than those of Ge2Sb2Te5 and Sb2Te based devices. The results indicate that the RST is a promising material for high performance phase change memory or optical data storage applications.

Fluorochromic polymer films containing ultrasmall silver nanoclusters

Fluorochromic materials that change their emission properties in response to their environment are of interest for the development of sensors, optical data storage and light-emitting materials. A thermally fluorochromic elastic polymer film that exhibits remarkable fluorochromism (from red to yellow) and enhancement of fluorescence intensity after thermal treatment (>120 °C) is designed by the incorporation of silver nanoclusters. The thermal treatment also leads to a significant increase of quantum yield and fluorescence lifetime. It is found that the thermo-induced etching on larger silver nanoclusters generates smaller silver nanoclusters. This simple and efficient size-tuning process in solid state is responsible for the thermo-fluorochromism and enhancement of fluorescence emission from silver nanoclusters. Such a thermo-fluorochromic polymer material is finally demonstrated to be useful for thermo-printing. This material illustrates a new way to make smart optical materials, particularly for potential applications in optical data storage and soft OLED display.

Modified Density Functional Dispersion Correction for Inorganic Layered MFX Compounds (M = Ca, Sr, Ba, Pb and X = Cl, Br, I).

MFX (M = Ca, Ba, Sr, Pb and X = Cl, Br, I) compounds have received considerable attention due to their technological application as X-ray detectors, pressure sensors, and optical data storage materials, when doped with rare-earth ions. MFX compounds belong to the class of layered materials with a tetragonal Matlockite crystal structure, characterized by weakly stacked double-halide layers along the crystallographic c-axis. These layers predominantly determine phase transitions, elastic, and mechanical properties. However, the correct description of the lattice parameter c is a challenge for most standard DFT functionals, which tend to overestimate the lattice parameter c. Because of the weak interactions between the halide layers, dispersion-corrected functionals seem to be a better choice. We investigated 11 different inorganic layered MFX compounds for which experimental data are available, with standard and dispersion-corrected functionals to assess their performance in reproducing the lattice parameter c, structural, and vibrational properties of the MFX compounds. Our results revealed that these functionals do not describe the weak interactions between the halide layers in a balanced way. Therefore, we modified Grimme's popular DFT-D2 dispersion correction scheme in two different ways by (i) replacing the dispersion coefficients and van der Waals radii with those of noble gas atoms or (ii) increasing the van der Waals radii of the MFX atoms up to 40%. Comparison with the available experimental data revealed that the latter approach applied to the PBE (Perdew-Burke-Ernzerhof)-D2 functional with 30% increased van der Waals radii, which we coined PBE-D2* (Srvdw 1.30) is best suited to fine-tune the description of the weak interlayer interactions in MFX compounds, thus significantly improving the description of their structural, vibrational, and mechanical properties. Work is in progress applying this new, computationally inexpensive scheme to other inorganic layered compounds and periodic systems with weakly stacked layers.

Photochromic effect of transparent lead-free ferroelectric KSr2Nb5O15 ceramics

Transparent KSr2Nb5O15 (KSN) lead-free ferroelectric ceramics have been synthesized via modified pressureless sintering method. A significant photochromic effect was observed for the transparent KSN ceramics prepared without rare-earth dopant modification. The piezoelectric properties depend on the grain orientations were investigated. The optical transmittance of the KSN ceramics is greater than 40% in the wavelength range of 530–800 nm. After NUV irradiation, the absorbance was enhanced by more than 40% in a broad visible range (more than 79%). The absorbance returned to the initial value after a thermal bleaching process. The results of the cycling tests and response experiments showed the stability and saturation of the photochromic effect. In addition, the possible photochromic mechanism of the KSN ceramics is discussed and the photochromic centers are identified. This transparent KSN ceramics exhibits an obvious photochromic effect and is a potential candidate materials for optical data storage and information recording applications.

Physical properties of third generation multicomponent Ge10-xSe60Te30Inx (x = 0, 2, 4, 6) chalcogenide glasses

Abstract Selenium-based chalcogenide glasses are best suitable materials for optical data storage due to their amorphous-to-crystalline phase transformation. Average coordination number and number of constraints for Ge10-xSe60Te30Inx (x = 0, 2, 4, 6) system have been discussed with two topological effects, floppy and rigid transition. Mean bond energy and glass transition temperature have been investigated using chemical bond approach to understand structural features of glasses. Heat of atomization, mean bond energy and glass transition temperature have been studied theoretically.

Synthesis and characterization of the photoswitchable poly(methyl methacrylate- random-methacrylate spirooxazine)

Abstract The photoswitchable poly(methyl methacrylate-random-methacrylate spirooxazine) was synthesized via atom transfer radical polymerization with the feed mole ratio of MMA/MSp comonomer of about 5.5/1. Well-defined poly(methyl methacrylate- random-methacrylate spirooxazine) have been obtained with the average molecular weight (Mn) of 6500 g/mol and polydispersity of 1.21. The structure and properties of the resulting copolymers were characterized by proton nuclear magnetic resonance (1H NMR), gel permeation chromatography, Fourier Transform infrared, UV-visible spectroscopy, and differential scanning calorimetry. Moreover, the copolymer exhibited the erasable and rewritable photoimaging on the solid state film which could to be as potential candidate for optical data storage materials.

Synthesis of a Novel Fluorescent Cyanide Chemosensor Based on Photoswitching Poly(pyrene-1-ylmethyl-methacrylate-random-methyl methacrylate-random-methacrylate spirooxazine)

The photoswitching poly(pyrene-1-ylmethyl-methacrylate-random-methyl methacrylate-random-methacrylate spirooxazine) was synthesized via atom transfer radical polymerization and characterized by proton nuclear magnetic resonance (1H NMR), gel permeation chromatography (GPC), Fourier transform infrared (FTIR) spectroscopy, UV-visible spectroscopy, and differential scanning calorimetry (DSC). The obtained copolymer exhibited the capability of erasable and rewritable photoimaging, making it a potential candidate for optical data storage materials. Moreover, the copolymer also showed the sensing ability for cyanide anions effect in aqueous solutions.

Structural and optical properties of In doped Se–Te phase-change thin films: A material for optical data storage

Se75−xTe25Inx (x=0, 3, 6, & 9) bulk glasses were obtained by melt quench technique. Thin films of thickness 400nm were prepared by thermal evaporation technique at a base pressure of 10−6Torr onto well cleaned glass substrate. a-Se75−xTe25Inx thin films were annealed at different temperatures for 2h. As prepared and annealed films were characterized by X-ray diffraction and UV–Vis spectroscopy. The X-ray diffraction results show that the as-prepared films are of amorphous nature while it shows some poly-crystalline structure in amorphous phases after annealing. The optical absorption spectra of these films were measured in the wavelength range 400–1100nm in order to derive the extinction and absorption coefficient of these films. It was found that the mechanism of optical absorption follows the rule of allowed non-direct transition. The optical band gap of as prepared and annealed films as a function of photon energy has been studied. The optical band gap is found to decrease with increase in annealing temperature in the present glassy system. It happens due to crystallization of amorphous films. The decrease in optical band gap due to annealing is an interesting behavior for a material to be used in optical storage. The optical band gap has been observed to decrease with the increase of In content in Se–Te glassy system.

High refractive index coumarin-based photorefractive polysiloxanes

In the past decades the development of photorefractive devices evolved rapidly as can be seen by the increasing number of publications and numerous applications. There is still need of innovative materials which are suitable for a broad range of applications through tailored properties. We present photorefractive linear and crosslinked polysiloxanes with refractive indices of up to n=1.603 which may be tuned in their refractive index in a range of up to Δn=0.04 photochemically. The polysiloxanes, more commonly named silicones, have side chains containing coumarin which are attached to the polymer backbone via different spacers ranging in length from 3 to 9 methyl groups. The coumarins undergo wavelength-dependent photodimerization and photocleavage in the polymer which cause the desired refractive index changes. The polysiloxanes have low glass transition temperatures ranging from −2°C to 35°C and show a high thermal stability (T5%>410°C). These properties make these materials promising candidates for the manufacture of photo tunable polymers, e.g. for the use as optical data storage materials, alignment of liquid crystals, and photorefractive intraocular lenses.

Dielectric properties of Ge2Sb2Te5 phase-change films

The static (εs) and high-frequency (ε∞) dielectric constants of amorphous and NaCl-type crystalline Ge2Sb2Te5 were measured and the relaxation effects in films were studied using impedance spectroscopy. On the basis of a simple method that allows obtaining the dielectric constant in the low resistivity planar structure, static and high frequency dielectric constants and their temperature dependencies were calculated in both phases. A surprising value of εs ≈ 750 in crystalline films was obtained, but the effective dielectric constant, εeff, estimated from the Maxwell-Wagner effective medium model, is significantly lower (εeff ≈ 34.9). Such a high value of εs obtained by electrical impedance measurements has been explained by Maxwell-Wagner relaxation, the separation of charges at the interface between grains and grain boundaries. Additionally, three relaxation processes (alpha, beta, and Ohmic relaxation) were observed in the amorphous phase and four relaxations (dipolar relaxation of grains, Ohmic relaxation of grains, dipolar relaxation of grain boundaries, and Maxwell-Wagner relaxation) were observed in the crystalline phase. From these results, a new rule for the selection of materials for optical phase-change data storage is proposed: polycrystalline films must have a high volume fraction of grain boundaries. This requirement increases the effective dielectric constant and the reflectance contrast between amorphous and crystalline phases.

Synthesis and properties of Mo and W ions co-doped porous nano-structured VO2 films by sol–gel process

Porous nano-structured vanadium dioxide (VO2) films doped with Mo and W ions had been synthesized by sol gel process by employing a sol containing ammonium molybdate and ammonium tungstate with the addition of cetyltrimethyl ammonium bromide (CTAB). The effects of molybdenum and tungsten co-doping and CTAB addition on the structure, morphologies, crystalline and optical properties of VO2 films were investigated systematically in this study. The composition and microstructure were detected by X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy. The Mo and W ions co-doped porous nano-structured VO2 films showed excellent infrared transmittance (nearly 70 %), large transmittance difference (55 %) before and after the phase transition, low transition temperature (35 °C), wide hysteresis width (22 °C) and fast phase transition. The results suggest that such Mo and W ions co-doped porous nano-structured VO2 film is an ideal fundamental material for optical data storage.

Optically active methacrylic copolymers with side-chain azoaromatic and 9-phenylcarbazole moieties

The synthesis and structural characterization of optically active copolymers such as poly[( S)-(+)- MCPP- co-( S)- MAP- N] and poly[( S)-(+)- MCPP- co-( S)- MAP- C] has been performed in order to obtain a multifunctional photonic material for chiroptical switches and for optical storage applications. The observed chiroptical properties suggest the presence of ordered chiral conformations at least for the chain segments of the macromolecules. Spectroscopic, thermal and chiroptical characterization of these copolymers demonstrate the occurrence of significant electronic interactions between the carbazole chromophores and the azobenzene moieties. The photoinduction of birefringence of copolymer films has been investigated in order to evaluate their behavior as a material for optical data storage. Surface-relief gratings (SRG) have also been inscribed on the material. The results are interpreted in terms of copolymer composition, cooperative behavior and conformational stiffness of the chromophoric co-units.

Extraordinary Large Refractive Index Change of Poly(phenylene vinylene) Derivatives induced by Photo- or Quantum Beam Irradiation

Poly(phenylene vinylene) structure is one of the chromophore with large two photon absorption (TPA) cross section, which is expected as the materials for high density optical data storage with the TPA induced reaction. Photo-irradiation to a poly(phenylene vinylene) derivative changes the refractive index of the polymer by the magnitude as high as 0.7. The mechanism involves photo-induced electron transfer from the TPA dye to matrix for the reaction of a distyrylarene derivative. The refractive index of the polymer also can be changed by the electron beam irradiation.

Nonparaxial singular beams inside the focal region of a high numerical-aperture lens

Key optical technologies, including lithography, data storage, optical tweezers, microscopy, and ultrafast laser materials processing, rely on strongly fo- cused light beams. Such beams are often used to exploit a vectorial nature of light and so detailed knowledge of the field structure inside a tight focus becomes in- creasingly important. So far, theoretical studies of intra-focal optical field compo- nents have been mainly concentrated on spatially homogeneous states of light po- larisation. In this work we present a new development in the calculations of local polarisation structure of tightly focused singular beams, including radially and azi- muthally polarised hollow beams. A rapidly increasing number of various practical applications in the last few years have attracted significant interest to studies related to three-dimensional structure of the field inside a focus of high numerical-aperture optical systems (1-5). Experimental intrafocal mapping of the squared electric field components is usually indirectly achieved with near field probes (6), point scatterers (7), fluorescent molecules and beads (8, 9), and the knife edge method (10). Recently, a new ap- proach has been developed (2) for visualising nanoscale structure of the electric field inside the focal volume of tightly focused singular beams, which is based on permanent imprinting of the field in transparent media. From the theoretical point of view, the first comprehensive studies of tightly focused linearly and circularly polarised Laguerre-Gaussian beams have been performed in Refs. (11-13). In Refs. (1, 14), the authors have attempted to analyse the focal spot of both radially and azimuthally polar- ised beams. The problem has been qualitatively solved in Ref. (14) for the case of non-apodised cylindrical vector beams, hence providing basic understanding of the focal structure of real beams. The general method allowing one to solve such problems is based on Debye vector integrals. A complexity of the problem for some types of vector beams, e.g., radially or azimuthally polarised beams, is related to finding an integrand  which would satisfy the conditions for the paraxial waves ( 2 1 ( 4 ) 0 z i          ) and simultaneously describe the vector field components. In the

Structurally defective cerium doped lutetium–yttrium oxyorthosilicates for optically stimulated luminescence imaging devices

The paper reports experimental data concerning the feasibility of structurally defective cerium doped Lu1.8Y0.2SiO5 oxyorthosilicates (Ce:LYSO) as optical stimulated luminescence (OSL) devices with emission at the Ce3+ recombination sites. The total OSL signal was evaluated as a function of continuous irradiation at 514.5 nm and compared to the curve obtained with a commercial C:Al2O3 sample. By assuming a single type of trap and a single recombination centre model for the OSL mechanism, the photoionization cross-section was estimated to be 1.7 × 10−17 cm2. The stimulation spectrum of the OSL signal evidences a single maximum at about 470 nm and a smooth decrease down to 650 nm. The recombination mechanism as well as the nature of the trapping site was studied by means of thermo-stimulated luminescence (TSL) measurements and analysed according to the generalized order kinetics model. The results confirm a single type of trap and a thermally activated tunnelling mechanism between the electrons trapped in the oxygen vacancies and holes localized at the Ce3+ centres. The analysis is further confirmed by TSL measurements after illumination with monochromatic lights in the range of the OSL stimulation spectrum. Finally, due to the high localization of trapping sites and recombination centres, we propose cerium doped oxyorthosilicates as efficient OSL imaging devices and UV based optical data storage materials: direct applications of defective Ce:LYSO as OSL imaging devices are shown.

Two-Photon Lithography in the Future of Cell-Based Therapeutics and Regenerative Medicine: A Review of Techniques for Hydrogel Patterning and Controlled Release

In recent decades, there has been considerable interest in using photochemistry to produce biomaterials, owing to their ability to be used in the presence of biological material. Two-photon-induced photoreactions have been used to produce materials for optical data storage and microfabrication and, recently, researchers have exploited two-photon-induced chemical processes to create biomaterials. Researchers have used two-photon-induced lithography to fabricate hydrogels with well-defined chemical and physical properties in 3D through network polymerization, functionalization, uncaging and degradation, as described in this article. Fabrication and modification of chemical and physical architecture of biomaterials in 3D with submicron resolution will allow the elucidation of more complex relationships in cell behavior and tissue development and introduce pathways to engineering complex tissues.

Theoretical Study of Photochromic Compounds. 1. Bond Length Alternation and Absorption Spectra for the Open and Closed Forms of 29 Diarylethene Derivatives

We apply several exchange-correlation functionals in combination with time-dependent density functional theory to predict the maximum wavelengths in the absorption spectra for 29 diarylethene derivatives in both open and closed isomeric forms. Solvent effects and accurate molecular geometries are found to be important to obtain good agreement with experimental absorption wavelengths. In order to evaluate the quality of geometry optimization, we compare predicted bond length alternation parameters with experimental ones. We find the TD-M05/6-31G*/PCM//M05-2x/6-31G*/PCM theory level to give the best predictions for the structural and spectral parameters of the diarylethene derivatives. Applications of the photochromic diarylethene compounds as materials for optical switching and data storage based on their photocyclization properties are also discussed.