Optical Storage Materials Research Articles

1,2-Bis[5-(1,3-dioxolan-2-yl)-2-ethyl-3-thienyl]-3,3,4,4,5,5-hexafluorocyclopent-1-ene, a photochromic dithienylethene

The title compound, C23H22F6O4S2, a photochromic dithienylethene, is a promising material for optical storage and other optoelectrical devices. The molecule adopts a photoactive antiparallel conformation in the crystalline state. The distance between the two reactive C atoms which are involved in potential ring closure is 3.829 (4) A. The dihedral angles between the central cyclopentene ring and the adjacent thiophene rings are 55.38 (7) and 54.81 (9) degrees. The colourless crystals turn magenta when exposed to UV radiation and the process is reversible.

3,3,4,4,5,5-Hexafluoro-1,2-bis{3-methyl-5-[3-(trifluoromethyl)phenyl]-2-thienyl}cyclopent-1-ene

The title compound, C29H16F12S2, a photochromic dithienyl­ethene, is a potential material for optical storage. It adopts a photo-active antiparallel conformation in the single crystalline phase. The distance between the two reactive C atoms is 3.624 (8) A. The mol­ecule has crystallographic twofold rotation symmetry. The dihedral angles between the cyclo­pentene ring and the attached thio­phene and benzene rings are 47.2 (2) and 17.9 (2)°, respectively.

Identification of Ag37Sn33Te30 Phase-Change Filmsfor Optical Data Storage

The Ag37Sn33Te30 film has been investigated todetermine its suitability as phase change optical recording alloy basedon static tester and atomic force microscopy measurements. Switchingproperties and the recording bit topography of the film are studied.With a writing pulse of power 2.5 mW, width 10 μs, and an erasure pulseof power 0.25 mW, width 10 μs, optical contrast of 31.8% is obtained.Re-crystallization experiments identify the Ag37Sn33Te30film as a suitable phase change material for optical data storage with acomplete erasure time of 1.1 μs at low erasure power.

Multidye Nanostructured Material for Optical Data Storage and Security Labeling

We report the design, synthesis, and application of a multidye polymer nanocomposite with respect to high-density 3D optical data storage and security labeling. Core−shell latex particles containing visible and near-IR dyes in the core-forming polymer and the shell-forming polymer were used as the functional building blocks to produce a multicolored multiphase polymeric material with a minimized energy transfer between the dyes. The core−shell particles were prepared by copolymerizing dye-labeled monomers with the hosting polymer. Data recording was achieved using confocal fluorescent microscopy by selective photobleaching of the dyes periodically distributed in the nanocomposite film.

A Multidye Nanostructured Material for Optical Data Storage and Security Data Encryption

A new class of materials for optical data storage and security data encryption is reported. Multidye colloid particles comprising different dyes in different phases are employed as the building blocks to produce a multicolored multiphase polymeric material. The incorporation of dyes in different phases minimizes energy transfer, provides selective dye photobleaching, and allows storage of different data on a single spot (see Figure and also cover).

Polarization holographic image storage with indolylfulgimide

Co-polarized and cross-polarized holographic gratings were respectively recorded on the indolylfulgimide/PMMA film and their diffracted images were obtained. The experiment indicates that the indolylfulgimide possesses the characteristic of photo-induced anisotropy, therefore it can be used for cross-polarized holographic recording. In polarization holography, the polarization of diffraction beam is dependent on the polarizations of reference beam and object beam. The noise of the diffraction image mainly comes from the diffusion of the readout beam on the sample. Cross-polarized holography can obtain higher signal-to-noise ratio of reconstructed image than that of co-polarized holography. Holographic gratings recorded on the film can be kept for at least five months in darkness at room temperature without decrease of diffraction efficiency. The results show that indolylfulgimide is an erase-rewritable optical storage material that can be used in polarization holography.

UV-laser-light-produced defects and reversible blue–white photoluminescence change in silica

The photoluminescence (PL) color of silica glass changes from weak blue to intense white under irradiation with 325nm laser light at room temperature in vacuum. Irradiation at room temperature with the same laser light under oxygen gas atmosphere erases the white PL state. Through many successive experiments, it is found that the spectral change is a reversible phenomenon. Such intense white PL state is stored for a long time at room temperature in air under room light after removal of the laser light, in spite of any changes of atmosphere. The observed phenomenon may relate to the photo-induced defect formation at the silica glass surface. Such observed reversible phenomenon may well yield materials for erasable optical information storage, oxygen sensors and white-light emitting devices.

Reversible photoinduced spectral transition in Eu2O3–γAl2O3 composites at room temperature

The photoluminescence (PL) intensity of Eu2O3–γAl2O3 composite has been found to decrease at room temperature with 325nm laser light irradiation in vacuum, without any accompanying white luminescence. Then, under the same laser light irradiation in oxygen gas atmosphere, the PL intensity recovers. Through many successive experiments, it is found that the spectral change is nearly reversible. In spite of the changing atmosphere (for example, oxygen gas and air exposures), each PL state is stored for a long time at room temperature after the removal of the laser light under room light. This phenomenon is interpreted as results of photoinduced valence-number change of europium ions, the oxygen vacancy formation and some excitation energy transfer. Such a reversible phenomenon may well yield materials for erasable optical storage and oxygen sensor.

Photodeposition of silver at the interface of a heterojunction based on a solid electrolyte: The case of CdSe-As2S3:Agx (x=0.9–2.4) heterojunctions

The phenomenon of photodeposition of silver has been detected in CdSe-As2S3:Agx (x=0.9–2.4) heterojunctions. The mass transfer of silver ions to the interface is caused by an electric field arising due to separation of electron-hole pairs in the space-charge regions of the heterojunction upon photovoltage generation. The migration of ions is also stimulated by their entrainment by the electron flow. Recombination of electrons with ions at the interface causes photodeposition of clusters of a chemical element responsible for ionic conduction in the solid electrolyte. A new method is suggested for preparing materials for optical data storage. The method is based on the phenomenon of photostimulated transport of ions and photodeposition of a metal at the interfaces of heterojunctions based on solid electrolytes.

Syntheses and properties of polyurethanes containing side‐chain azobenzene groups

AbstractPolymers containing azobenzene groups have the characteristic reaction of photo‐induced cis–trans isomerism. The study of new materials for optical information storage has prompted making use of these photo‐isomerizations. In this study, we report the syntheses and properties of four different polyurethanes (DR‐PUns) containing azobenzene groups in the side‐chains. The structurally similar polyurethanes (DR‐PUns) were synthesized by the polycondensation reaction of Disperse Red 19 (DR 19) and four different diisocyanates in dimethylformamide. By introducing of DR 19 into the polymer, we obtained polymers containing a photochromic group in the side‐chain. The weight‐average molecular weights of the DR‐PUns were in the range 5500–12 900. The Tgs of the DR‐PUns range from 119.5 °C to 157.0 °C, depending on the structure of the diisocyanate. Optical properties and solubilities of the polyurethanes were compared. The diffraction efficiencies of films were measured as a function of the reaction time. Typically, the diffraction efficiencies of the DR‐PU1 film prepared from toluene 2,4‐diisocyanate were observed up to a level of 0.25%. For the DR‐PU1 film, the effect of the intensity of the induced laser beam on the diffraction efficiency is also discussed.© 2003 Society of Chemical Industry

Massive enhancement of persistent spectral hole-burning in the R-lines of NaMgAl(oxalate) 3 · 9H 2O:Cr(III) by partial deuteration

Partial deuteration of NaMgAl(oxalate) 3 · 9H 2O:Cr(III) (0.5%) increases the quantum efficiency for persistent spectral hole-burning in the R 1-line by three orders of magnitude. A 50% deuterated crystal shows an impressive initial hole-burning efficiency of ≈0.1% and sharp anti-holes are observed in the range of ±15 GHz. A decrease of the quantum efficiency upon deuteration has often been reported in the literature and this has been rationalized on the basis of the lower tunnelling probability of the deuteron in the double well potential of hydrogen bonds. In contrast, the present findings of a sensational increase can be rationalized by a hole-burning mechanism based on 180° flip motions of the lattice water molecules around their pseudo C 2 axes. Considering the spin-flip nature of the electronic excitation this is an extraordinary finding. The deuteration effect may be used to design high-efficiency hole-burning materials for optical storage at liquid nitrogen temperatures.

Chalcogenide glasses as prospective materials for optical memories and optical data storage

This paper first reviews recent progress in the understanding of the nanometer-scale mechanism of reversible photostructural changes in chalcogenide glasses, and its relevance to various photo-induced phenomena. Then the principles of phase-change optical recording are described. Finally, a novel technique for overcoming the diffraction limit in optical recording is considered, namely the super-resolution near-field structure. This technique, used in combination with multicomponent Te-based chalcogenides as a recording medium, is believed to be a prototype for future optical-storage devices.

Chemical characterization of optical data storage materials by EPMA

Chemical characterization of optical data storage materials by EPMA

Thin film alloy mixtures for high speed phase change optical storage: A study on (Ge1Sb2Te4)1−x(Sn1Bi2Te4)x

An approach is proposed to develop recording materials for high speed phase change optical data storage. It utilizes a thin film alloy mixture between a stoichiometric GeSbTe alloy and an additive ternary telluride alloy. Selection rules for an additive alloy are suggested. For a test, (Ge1Sb2Te4)1−x(Sn1Bi2Te4)x thin films are deposited by co-sputtering and their structural and thermal properties are studied. Ge1Sb2Te4 and Sn1Bi2Te4 are found to form a completely soluble pseudo-binary system, whose crystalline lattice parameters obey Vegard’s rule over the entire range of x (0<x<1). Furthermore, the alloy mixtures display an increasing tendency for crystallization with Sn1Bi2Te4 content. Dynamic tests of disk samples are made to show the effectiveness of the approach for high speed erasure.

Immiscible blend of cholesteric copolymers as a new type of material with photoregulated optical properties

A blend containing two immiscible cholesteric comb-shaped polyacrylates was prepared. Upon light irradiation, one of the components is able to change the pitch of the cholesteric helix due to the isomerization of chiral photochromic side groups. The phase behavior and optical properties of the above blend were studied. Planarly oriented films based on the above blend show the two well-pronounced peaks of selective light reflection: one peak is seen in the visible spectral region whereas the other peak is observed in the near-IR region. Under the action of light, the long-wavelength peak is shifted to higher wavelengths whereas the second peak remains almost unchanged. The specific features of the kinetics of the photooptical processes taking place in this system were studied. The above immiscible blend is shown to be a new unique material for optical data recording and storage.

Photoinduced effects in amorphous semiconductor Ge(S, Se)2 chalcogenide films

The blue shift of optical transmittance edges were observed in amorphous semiconductor Ge(S, Se)2 chalcogenide films with light illumination. The shift in well-annealed films could be recovered by annealing the films near the glass-transition temperature again. The photocrystallization was also observed in amorphous Ge(S,Se)2 films with light illumination by the transmitting electron microscope measurement. The photoinduced phenomina of the amorphous Ge(S,Se)2 films could be applied to designing some new kinds of optical storage materials.

Reversible dye-doped holographic photopolymer materials for reconfigurable optical data storage

New self-developing reversible dye-doped holographic photopolymer materials were recently developed in our laboratory, which are sensitive to light from the green to near infrared wavelengths (500–850 nm) [1]. Previously, we have used liquid crystals in similar polymer matrices to increase the refractive index modulation [2]. In this work, we show that a new functionality of optical reconfiguration may be introduced if a reversible photosensitive dye is doped in the material. The compound we have used in this experiment is a multifunctional acrylic-based photopolymerizable material. Reversible dye and organic compound are added to serve as solvent and refractive index increasing agents. In addition, this dye may partially replace the liquid crystal’s role. Holographic recording characteristics of these materials were investigated. We have demonstrated that, the diffraction efficiency of recorded holograms and material sensitivity are high. We believe that these materials are very promising for applications in permanent, but reconfigurable diffractive optical elements.

Mechanical stresses upon crystallization in phase change materials

Crystallization processes in different Te alloys, employed in phase change materials for optical data storage, have been investigated by in situ mechanical stress measurements. Upon crystallization a considerable stress buildup is observed, which scales with the volume change upon crystallization. Nevertheless the observed stress change only corresponds to approximately 9% of the stress estimated for a purely elastic transformation. Further evidence of stress relief phenomena comes from the temperature dependence of the stress in the crystalline and amorphous states. Ultrathin dielectric layers have a profound influence on the crystallization process as evidenced by simultaneous optical reflectance and mechanical stress measurements. This observation can be explained by heterogeneous nucleation of crystallites at the interface between the dielectric layer and the phase change film.

Polymeric nanostructured material for high-density three-dimensional optical memory storage

The unique properties of a polymer photonic crystal are examined with respect to applications as a medium for high-density three-dimensional optical data storage media. The nanocomposite material was produced from core-shell latex particles, in which the latex cores contained dye-labeled polymer. Nonfluorescent latex shells were attached to the core particles. Upon annealing, the close-packed core-shell particles formed a nanostructured material with the fluorescent particles periodically embedded into the optically inert matrix in a hexagonal close-packed structure. A two-photon laser scanning microscope was used to write bits of information into the material by photobleaching the optically sensitive particles and, under much lower fluence, read out the resulting image. Relative to conventional homogeneous storage media, the nanostructured periodic material is shown to increase the effective optical storage density by at least a factor of 2 by spatially localizing the optically active region and imposing an optically inactive barrier to cross-talk between bits. This polymer photonic crystal has the potential to dramatically improve performance further through the improved capabilities to optimize the photochemical processes and more fully exploiting the periodic nature of the information domains in the image processing.

New Chiral-Photochromic Dopant with Variable Helical Twisting Power and its use in Photosensitive Cholesteric Materials

A new photosensitive chiral dopant based on cinnamic acid and isosorbide was synthesised. UV light action leads to E-Z photoisomerization of the dopant about C=C double bond of cinnamoyl fragment. Mixtures of the dopant with nematic and cholestric polymers were studied. It was shown, that planarly-oriented films of mixtures possess a selective light reflection in ultraviolet, visible and infrared regions of spectrum depending on the dopant concentration. The helical twisting power of the chiral dopant was calculated. UV light action on mixture films leads to a shift of selective light reflection peak to the long wavelength region of spectrum, which is explained by photoisomerization and decrease of the helical twisting power of the dopant. Kinetics of the process of photoinduced untwisting of the cholesteric helix was studied. Advantages of the use of the synthesised dopant and of mixtures based on it were demonstrated in comparison to earlier studied chiral-photochromic materials for optical data recording and storage.