Optical Memory Applications Research Articles

Synthesis, Properties and Application in Optical Memory of a New Photochromic Diarylethene Based on a Chlorine Atom

A new unsymmetrical photochromic diarylethene 1-(2,4-dimethyl-3-isoxazol)-2-[2-methyl-5-(2-chlorophenyl) -3-thienyl] perfluorocyclopentene (1a) has been synthesized. Its photochromic properties in solution and PMMA film were investigated. Diarylethene 1a changed the color from colorless to red upon irradiation with 297 nm UV light, in which absorption maxima were observed at 515 nm in hexane and at 526 nm in PMMA film, The results demonstrated that it can be potentially used as polarization holographic optical recording medium.

Synthesis, Properties and Application in Optical Memory of a New Photochromic Diarylethene Based on a Chlorine Atom

A new unsymmetrical photochromic diarylethene 1-(2,4-dimethyl-3-isoxazol)-2-[2-methyl-5-(2-chlorophenyl) -3-thienyl] perfluorocyclopentene (1a) has been synthesized. Its photochromic properties in solution and PMMA film were investigated. Diarylethene 1a changed the color from colorless to red upon irradiation with 297 nm UV light, in which absorption maxima were observed at 515 nm in hexane and at 526 nm in PMMA film, The results demonstrated that it can be potentially used as polarization holographic optical recording medium.

Synthesis, Properties and Application in Optical Memory of a Photochromic Diarylethene Bearing Pyridine Unit

A new photochromic diarylethene compound, 1-(2-methyl-3-benzothiophene)-2- [2-methyl-5-(2-pyridine)-3-thienyl] perfluorocyclopentene (1a) was synthesized. its photochromic and fluorescent properties have been investigated in detail. It showed good photochromism both in solution and PMMA amorphous film upon photoirradiation. Its fluorescence properties in the solution also were reaearched.

Photoswitchable Biocompatible Polymer Dots Doped with Diarylethene

Molecular photoswitches can be employed for the study of protein trafficking in living cells and applications in optical memories. Especially, to switch fluorescence, fluorescence quenching mechanism via energy or electron transfer is one of the most fundamental pathways to realize the system of photoswitching. In order to achieve fluorescence photoswitching, photochromic compounds such as diarylethene have been used to toggle fluorescence on and off. For example, photochromic diaryethene induces absorption changes upon light irradiations via cyclization reaction, which would trigger the fluorescence toggling. On the other hand, polymer dots (P-dots) is one of the promising fluorescent probes for the biological applications. We assumed that doping diarylethene into P-dots would realize fabrication of photoswhitchable P-dots via energy transfer mechanism between fluorescent polymer and diarylethene. In this study, we synthesized photoswitchable P-dots doped with diarylethene to toggle the fluorescence back and forth via energy transfer mechanism. We also tried to apply synthesized photoswitchable P-dots toward biological imaging. First, we examined the photoswitching properties with absorption and fluorescence measurements. Fluorescence of P-dots was dramatically quenched upon photoirradiation with UV light and recovered after visible light irradiation. Those photoswitching processes were reversible and could go through at least 5 cycles. We are now applying photoswitchable P-dots synthesized as mentioned above to biological imaging. Details will be discussed at the meeting.

Synthesis, Photochromic Properties and Application in Optical Memory of a Diarylethene Based on Pyrrole Ring

A new unsymmetrical photochromic diarylethene compound, 1-[(2-methyl-5-(4-dioxolane-phenyl)-3-thienyl)]-2-(5-cyano-1,5-dimethyl-4-pyrryl)perfluorocyclopentene (1o), was synthesized and its photochemical, fluorescence properties were investigated in detail both in solution and PMMA amorphous film. The results showed that the compound exhibited remarkable photochromism, changing from colorless to violet after irradiation with 297 nm UV light. Finally, using this diarylethene as recording medium, polarization optical recording was carried out successfully.

Synthesis, Properties and Application in Optical Memory of a Novel Photochromic Diarylethene Bearing an Anthracene Ring

In the present study, we designed a novel unsymmetrical isomeric diarylethene derivative bearing both thiophene and anthracene moieties. Its photochromic properties and fluorescence were investigated in detail. In hexane solution, the open-ring isomer of the diarylethene 1 exhibited relatively strong fluorescence. The photochromic reaction kinetics indicated that the cyclization process of 1o belongs to the zeroth order reaction and the cycloreversion process belongs to the first order reaction. This new photochromic system also exhibited remarkable optical storage character.

Synthesis, Optoelectronic Property and Application in Optical Memory of a Novel Type Diarylethene Based on a Six Unit

A unsymmetrical diarylethene derivative bearing both indole and phenyl moieties was synthesized. At the same time, its photochromic properties and fluorescence switch were investigated in detail. The results showed that this compound exhibited reversible photochromism, undergoing reversible cyclization and cycloreversion reactions upon alternating irradiation with UV and visible light in solution, and its absorption maxima were observed at 625 nm in hexane, upon irradiation with 297 nm UV light. The fluorescence intensity of diarylethene decreased dramatically along with the photochromism from open-ring isomer to closed-ring isomer upon irradiation with 297 nm UV light in PMMA. In hexane solution, the open-ring isomer of the diarylethene 1 exhibited relatively strong fluorescence at 439 nm when excited at 385 nm.This new photochromic system also exhibited remarkable optical storage character.

Synthesis, Properties and Application in Optical Memory of a Photochromic Diarylethene Based on Benzene Ring

A new photochromic diarylethene compound, 1-(2-methyl-5-(2,4-difluorophenyl)-3-thienyl)-2-(2-cyanophenyl)perfluorocyclopentene (1a), was synthesized and its photochromism and photo-induced anisotropy was investigated. The results showed that this compound exhibited reversible photochromism, changing from colorless to purple after irradiation with UV light both in solution and in PMMA amorphous film. In hexane, the open-ring isomer of the diarylethene 1a exhibited relatively strong fluorescence at 459 nm when excited at 316 nm. The fluorescence intensity decreased along with the photochromism upon irradiation with 297 nm light and its closed-ring isomer showed weak fluorescence.

Synthesis，Properties and Application in Optical Memory of a Novel Photochromic Diarylethene Bearing a Six-Membered Aryl Unit

A new unsymmetrical photochromic diarylethene 1-(2-ethyl-3-benzothienyl)-2-[2-octyl-5-formyl-3-thienyl]perfluorocyclopentene (1a) has been synthesized. Its photochromic properties in solution and PMMA film were investigated. Diarylethene 1a changed the color from colorless to blue upon irradiation with 297 nm UV light, in which absorption maxima were observed at 581 nm in hexane and at 582 nm in PMMA film, The results demonstrated that it can be potentially used as polarization holographic optical recording medium.

Synthesis, Properties and Application in Optical Memory of a Photochromic Diarylethene Bearing Chlorine Atoms

A new unsymmetrical photochromic diarylethene compound, 1-(2,4-dimethyl-5-thiazolyl)-2-[5-(2-chlorobenzene)-2-methyl-3-thienyl]perfluorocyclopentene(1a), was synthesized and its photochromism and photo-induced anisotropy was investigated. Diarylethene 1a changed the color from colorless to Orange-red upon irradiation with 297 nm UV light, in which absorption maxima were observed at 479 nm in hexane and at 485 nm in PMMA amorphous film, respectively. It also showed good photochromism and functioned as an effective fluorescent photoswitch in solution. In hexane, the open-ring isomer of the diarylethene 1a exhibited relatively strong fluorescence at 428 nm when excited at 315 nm. This new photochromic system also exhibited remarkable optical storage character.

Synthesis, Properties and Application in Optical Memory of a New Type Diarylethene with Benzene Ring

A new type photochromic diarylethene, 1-(2-ethylbenzo[b]thiophen-3-yl)-2- (2-methylphenyl)perfluorocyclopentene (1o), was synthesized, and its photochromic and fluorescent properties were investigated. This compound exhibited reversible photochromism and notable fluorescence photoswitches both in solution and in PMMA films. In addition, the fluorescence spectra of diarylethene 1o evidently depended on the concentration in hexane. Using diarylethene 1c/PMMA film as recording medium, optical recording was carried out successfully.

Synthesis, Properties and Application in Optical Memory of a New Photochromic Diarylethene

A new photochromic diarylethene compound, 1-[2-methyl-3-benzothiophene]-2- [5-(3-chlorobenzene)-2-methyl-3-thienyl]perfluorocyclopentene(1a), was synthesized and its photochromism and photo-induced anisotropy was investigated. It showed good photochromism and functioned as an effective fluorescent photoswitch in solution. In hexane, the open-ring isomer of the diarylethene 1a exhibited relatively strong fluorescence at 417 nm when excited at 315 nm. In PMMA film, diarylethene 1a also showed good photochromism.

Synthesis and Photochromism of Tungstophosphate-Functionalized Ordered Mesoporous Hybrid Silica

New tungstophosphate-functionalized ordered mesoporous silica was synthesized based on monovacant PW11 and block copolymer template. Upon characterizations of the as-obtained PW11/MHS samples by FT-IR, XRD, ICP-AES and N2 adsorption-desorption measurements, it was revealed that Keggin units were retained perfectly in hexagonally symmetrical mesopore channels and bound covalently onto the pore walls of mesoporous silica. The material exhibits stable and reversible photochromic property upon UV irradiation even though no a special organic component was supplied as electron donor. This may provide a new approach to construct photochromic materials of potential applications in high-density optical memories and other optical devices.

Molecular Switches Based on Spironaphthoxazine

Spironaphthoxazines (SPO) are well-known photochromic compounds of interest from the viewpoint of fundamental elucidation of photochemical switches and potential applications in optical memories. This paper reports on the conductivity switches, viscosity switches, fluorescence switches and gel switches of SPO. In addition, bistable photoswitching in poly (N-isopropylacrylamide) with SPO hydrogel for optical data storage is described.

Physical properties of silver oxide thin films by pulsed laser deposition: effect of oxygen pressure during growth

Silver oxide thin films have potential applications in ultra-high density optical non-volatile memories and in fluorescence imaging. In this paper, the physical properties of silver oxide thin films prepared at room temperature by the pulsed laser deposition (PLD) technique with varying oxygen pressure during growth are reported. The oxygen pressure in the growth chamber is varied between 9 and 50 Pa. The x-ray diffraction (XRD) analysis showed that all the films were polycrystalline. With increasing oxygen pressure in the growth chamber, it is observed that (i) the hexagonal Ag2O transforms to monoclinic AgO, (ii) the grain size in the film increases from 59 to 200 nm, (iii) the surface roughness of the film increases from 9 to 42 nm, (iv) the resistivity of the films increases from 1 to 4 × 104 Ω m, (v) the surface work function of the films increases from 5.47 to 5.61 eV and (vi) the optical band gap of AgO thin films decreases from 1.01 to 0.93 eV. Raman spectroscopy on AgO thin films shows low wave number peaks corresponding to the stretching vibration of Ag–O bonds. This study shows that single phase AgO thin films, a requirement for plasmonic devices, can be prepared at room temperature by the PLD technique with an oxygen pressure of 20 Pa.

Fast simulation of phase-change processes in chalcogenide alloys using a Gillespie-type cellular automata approach

A stochastic cellular automata simulator capable of spatiotemporal modeling of the crystallization and amorphization behavior of phase-change materials during the complex annealing cycles used in optical and electrical memory applications is presented. This is based on consideration of bulk and surface energies to generate rates of growth and decay of crystallites built up from “monomers” that may themselves be quite complex molecules. The approach uses a stochastic Gillespie-type time-stepping algorithm to deal with events that may occur on a very wide range of time scales. The simulations are performed at molecular length scale and using an approximation of local free energy changes that depend only on immediate neighbors. The approach is potentially capable of spanning the length scales between ab initio atomistic modeling methods, such as density functional theory, and bulk-scale methods, such the Johnshon–Mehl–Avrami–Kolmogorov formalism. As an example the model is used to predict the crystallization behavior in the chalcogenide Ge2Sb2Te5 alloy commonly used in phase-change memory devices. The simulations include annealing cycles with nontrivial spatial and temporal variations in temperature, with good agreement to experimental incubation times at low temperatures while modeling nontrivial crystal size distributions and melting dynamics at higher temperatures.

Spectral study of the properties of photochromic polysubstituted lactones

The spectral and photothermal properties of thermally irreversible derivatives of dihetarylethenes, lactones, whose open form shows fluorescence, are studied. It is shown that the nature of substituents determines not only the absorptive but also the luminescent properties of these compounds, as well as their photocoloration and fluorescence quantum yields. The obtained dependences of the properties of lactones on their structure are important for targeted synthesis of compounds that can be used in the creation of two-photon reversible recording media with fluorescence reading of optical information suitable for application in 3D optical memory on optical disks.

Photopolymerizable recording media for three-dimensional holographic optical memory

The development of investigations in recent years on photopolymerizable recording holographic media for using as photosensitive layers of holographic optical disks, which satisfy the conditions for the application in archive optical memory is analyzed. It is shown that the main emphasis in the development of photopolymerizable holographic recording media is put on the improvement of their component composition. Formulations that permit joint radical and cationic photopolymerization were designed for thermally stable holographic recording. The holographic characteristics achieved for these media ensure the fabrication of single-layer optical disks 150 mm in diameter with the information capacity of 200 GB instead of 5 GB for modern optical disks. Ways of improving photopolymerizable holographic recording media for the manufacture of optical disks with an information capacity of more than 1 Tb cm−3 are considered.

Understanding Structural Changes in Phase Change Memory Alloys

AbstractIn addition to their wide-spread application in the re-writable optical memory markets, phase-change memory alloys are also poised to take a prominent role in future non-volatile memory applications due to their potential for low-energy usage and indefinite cyclability compared with their silicon-based flash memory counterparts. In contrast with their widespread use, however, the details of the crystalline to amorphous switching process utilized for memory storage remain an active research topic with many details still lacking. Considering the conflicting requirements for high-speed switching, yet long term data storage integrity, a deeper understanding of these materials is essential for insightful application development. We have used x-ray absorption fine structure spectroscopy (XAFS), a technique equally suitable for amorphous and crystalline phases to elaborate details in structural changes in the phase-change process for a variety of phase-change alloys in static measurements. As the kinetics of the switching process are the linchpin for optimizing switching characteristics, we have recently initialted dynamic measurements of light -induced structural changes in Ge-Sb-Te (GST) alloys. These measurements have been carried out synchronously using both femtosecond and nanosecond laser pump pulses in conjunction with 100~ps x-ray pulses generated by an electron storage ring. By synchronously triggering the laser with a variable sub-nanosecond delay, we have been able to use XAFS to probe details of the dynamics of the switching process. Preliminary results learned from this approach applied to GST alloys are presented.

Electrical percolation characteristics of Ge2Sb2Te5 and Sn doped Ge2Sb2Te5 thin films during the amorphous to crystalline phase transition

Percolation effects are studied in phase change materials used for optical and electrical nonvolatile memory applications. Simultaneous measurements of the electrical resistivity and optical reflectivity allow experimental assessment of the percolation behavior associated with the mixed amorphous and crystalline phases in this class of chalcogenide materials. Dynamic analysis of the isothermal amorphous to crystalline phase transition in as-deposited amorphous Ge2Sb2Te5 and Sn doped Ge2Sb2Te5 thin films are performed. A significantly earlier onset and saturation for the change of electrical resistivity in comparison to the optically measured phase transition is observed. This behavior reflects a significant influence of percolation on the electrical properties of this class of materials, leading to a nonlinear relationship between crystallization degree and electrical resistivity. This nonlinearity is associated with the formation of highly conducting crystalline paths in a lower conducting amorphous matrix. The influence of percolation on optical properties is found to be negligible. The experimental results are quantitatively compared to Wiener bounds and Bruggeman percolation models. Substantial differences in the crystallization behavior of Ge2Sb2Te5 and Sn doped Ge2Sb2Te5 are observed: while heterogeneous nucleation induced by an interfacial layer resulting in layer-by-layer growth is observed for Ge2Sb2Te5, homogeneous nucleation and formation of prism shaped crystallites dominate in Sn doped Ge2Sb2Te5. The presented data represent the experimental analysis of percolation for the electrical resistivity in this class of materials, indicating the relevance of this effect for the adequate modeling and systematic optimization of future phase change random access memories and cognitive devices.