The thermal transmission process induced by single-shot femtosecond laser pulses in Sb70Te30 phase change thin films with or without a Ag thermal-conductive layer was studied numerically with a two-temperature model. The distribution of electron and lattice temperatures was calculated by a one-dimensional finite difference method. The different temperature evolution characteristics on different time scales (from several picoseconds, to tens of picoseconds and to several nanoseconds) are discussed based on the electron-phonon coupling theory. The influence of a special point in the lattice temperature evolution curves on the crystallization time of phase change thin films is analyzed. The results will be helpful to the deeper understanding of the ultrafast phase transition mechanism of phase change memory materials.
Laser thermal lithography has been proposed for a few years, which has the advantages of breaking through the optical diffraction limit, operation in far-field and in air, and low production cost. In this paper, a new hydrazone metal complex is used as the laser thermal lithography material due to its feature of the one-step fabrication of micro/nano structure without mask and wet-etching process. Based on the laser thermal lithography method, super resolution nano-information pits are directly written on the surface of hydrazone metal complex thin films. Pits with a minimum feature size of about 79 nm are successfully obtained, which is only about 1/7 of the writing spot size. Moreover, the reactive ion etching method can be applied to transfer the pits onto a silica substrate. These results suggest the potential applications of the new material in high density optical data storage and semiconductor industries.
Preparation of recording materials with high two-photon absorption activities is one of the important issues to superhigh- density two-photon absorption (TPA) three-dimensional (3D) optical data storage. In this paper, three new carbazole derivatives containing nitrogen heterocyclic ring with symmetric and asymmetric structures are prepared using ethylene as the π bridge between the carbazole unit and nitrogen heterocyclic ring, namely, 9-butyl-3-(2-(1,8- naphthyridin)vinyl)-carbazole (material 1), 9-butyl-3,6-bis(2-(1,8-naphthyl)vinyl)-carbazole (material 2) and 9-butyl-3,6- bis(2-(quinolin)vinyl)-carbazole (material 3). Their one photon properties including linear absorption spectra, fluorescence emission spectra, and fluorescence quantum yields are studied. The fluorescence excited by 120 fs pulse at 800 nm Ti: sapphire laser operating at 1 kHz repetition rate with different incident powers of 9-butyl-3-(2-(quinolin) vinyl)-carbazole (material 3) was investigated, and two-photon absorption cross-sections has been obtained. It is shown that material 3 containing quinoline rings as electron acceptor with symmetric structure exhibit high two-photon absorption activity. The result implies that material 3 (9-butyl-3-(2-(quinolin) vinyl)-carbazole) is a good candidate as a promising recording material for super-high-density two-photon absorption (TPA) three-dimensional (3D) optical data storage. The influence of chemical structure of the materials on the optical properties is discussed.
Phase change lithography has pretty potential applications for high density optical data storage mastering and micro/nano structure patterning because it is not restricted by optical diffraction limitation and at relatively low cost. GeSbTe, as an initially investigated material for phase change lithography, its mechanism of selective etching in inorganic or organic alkaline aqueous solutions, such as NaOH and tetramethylammonium hydroxide (TMAH), is still unknown. In this paper, XPS measurement is used to study the selective wet etching mechanism of GeSbTe phase change thin films with TMAH solution, and the results show that oxidization played an important role in the etching process. Ge, Sb and Te are oxidized into GeO2, Sb2O5 and TeO2, respectively, and then as the corresponding salts dissolved into the etchant solution. Ge-X (X is Ge, Sb or Te) bonds are first broken in the etching, then Sb-X bonds, and finally Te-Te bonds. To confirm the effect of oxidization in the etching, H2O2 as an oxidant is added into the TMAH solution, and the etching rates are increased greatly for both amorphous and crystalline states. The selective etching mechanism of Ge2Sb2Te5 phase change films is discussed by the difference of bonds breakage between the amorphous and crystalline states.
As the demand for ultrahigh density information storage continues to grow, recording mark size of several tens nanometer which is smaller than the optical diffraction limit is required in optical memory. Functional film super-resolution technique is one of practical approaches to overcome the optical diffraction limit. Optical constants are important parameters to optical films as super-resolution masks. In this paper, the influence of film thickness on optical constants of antimony-based bismuth-doped super-resolution mask layer is investigated. The structure of the samples with different thickness was studied by X-ray diffraction. The transmission spectrum was measured by spectrophotometry. The optical constants of the films in the range of 300-800 nm were measured by spectroscopic ellipsometry. The results show that the structure of the film transforms from amorphous state to crystal state when the thickness increases from 7 nm to 300 nm. In the range of 300-800 nm, the refractive index and extinction coefficient increase with increasing wavelength. The transmission decreases rapidly when the thickness increases from 7 nm to 30 nm. The influences of film thickness on optical constants are more significant in the thickness range of 7-50 nm than that in the thickness above 50 nm.
Anthracene derivative is one of the important two photon absorption materials. In this work, novel symmetric-type D- π-D anthracene derivative, 2, 6 - di- substituted anthracene chromophore with 4-methylstyrene has been synthesized via Heck reaction. The two-photon absorption (TPA) fluorescence emission property and TPA absorption coefficient are investigated by Sapphire femtosecond laser pulses at the wavelength of 800nm, repetition rate of 1 KHz and pulse width of 120fs, in an attempt to obtain the TPA cross-sections of this compound (σfilm=695.8×10–50cm4s/photon). Finally, Three-dimensional (3D) optical data storage experiments are carried out and realized by two-photon absorption with 800nm-fs laser in the compound films.
KEYWORDS: Silver, Nanoparticles, Near field, Near field optics, Diffraction, Finite-difference time-domain method, Surface plasmons, Super resolution, Optical resolution, Optical storage
Super-resolution near-field structure (super-RENS) is a functional structure which can overcome the optical diffraction limit and play an important role in nano scale optical data storage. The resolution enhancement of the scatter-type super- RENS optical disk is related to the localized surface plasmon of silver particles dissociated from the AgOx layer and its near-field interaction with the recording pits in the phase change layer. Recently, a new method for optically synthesizing silver nanoparticles in a phase change matrix has been proposed by our group [Mater. Chem. Phys. 135, 467-473(2012)], which provides a potential approach to forming a more simple plasmonic recording structure than the traditional AgOx-type structure. In this paper, field distribution of silver-nanoparticles-embedded Ge2Sb2Te5 phase change recording pits is numerically analyzed by the finite-difference time-domain (FDTD) method. The optical contrast enhancement capability is confirmed for the optimized recording structures when the pit size is smaller than the optical diffraction limit.
A nickel(II)-azo dye was synthesized in order to obtain a suitable optical recording medium for write-once blu-ray recording with low-to-high signal polarity. Smooth thin film of the nickel(II)-azo dye was prepared by spin-coating method. Absorption, reflectance spectra and optical constants (complex refractive indices N=n+ik) of the thin film were investigated in the wavelength region of 300-700 nm. To demonstrate the physical basis of low-to-high polarity, the relationships between the absorption, reflectivity and optical constants for the nickel(II)-azo dye in spin-coated films were discussed. It is found that the thin film has a strong absorption band in the wavelength region of 370-500 nm and a strong absorbance at 405 nm. The reflectance spectra show that a low reflectivity of the unrecorded thin film at 405 nm can be obtained. The thin film of the nickel(II)-azo dye gives a relatively low n value of 1.36 and a relatively high k value of 0.51 at 405 nm. In addition, in order to examine its possible use as a blu-ray recording medium, the spin-coated film of the nickel(II)-azo dye was studied by a static optical recording testing system. The results demonstrate that high reflectivity contrast (85%) with low-to-high polarity can be obtained at an optimum laser writing power and pulse width using the nickel(II)-azo dye thin film as the recording layer. Moreover, the recording marks on the film are clear, circular, regular, and their size is as small as 200 nm or even less. These results indicate that the nickel(II)-azo dye is promising for applications in high-performance write-once blu-ray recording systems at 405 nm.
KEYWORDS: Bismuth, Super resolution, Antimony, Near field, Data storage, Optical storage, Gallium nitride, Current controlled current source, Sputter deposition, Silver indium antimony tellurium
Super-resolution near-field structures (super-RENS) with antimony bismuth mask layer (Sb1-xBix, X =0, 0.1, 0.2 and 0.9) were fabricated by magnetron sputtering. AgInSbTe and ZnS-SiO2 were used as recording layer and dielectric layer respectively. Static recording tests with and without super-RENS were carried out using static recording tester whose laser wavelength is 406.7 and numerical aperture is 0.8. The recorded marks were observed by atomic force microscopy (AFM). The influences of Bi proportion in the films on the super-resolution recording properties were investigated.
Phase transition kinetics of Sb2Te3 phase change thin films was investigated in this paper. Sb2Te3 thin films, with
thickness of ~100nm, were deposited on K9 glass substrates by DC magnetron sputtering with an alloy target. The
crystallization kinetics of Sb2Te3 thin films under isothermal and non-isothermal annealing was analyzed by a
home-made in situ temperature-dependent reflectivity tester. From the heating rate dependences of phase transition
temperatures, the activation energy was derived. The obtained values of the Avrami indexes indicate that a two
dimension growth crystallization mechanism is responsible for the amorphous-crystalline transformation of Sb2Te3
phase change thin films. Although phase transition of Sb2Te3 thin film is confirmed to be continuous in a larger
temperature range, but short laser pulse can easily trigger its crystallization process and form clear and confined
crystalline marks.
Sheet resistance of laser-irradiated Ge2Sb2Te5 films prepared by magnetron sputtering was measured by the four-point
probe method. With increasing laser power the sheet resistance underwent an abrupt change of four orders of magnitude
(107→103 Ω/sq) at about 580mW , x-ray diffraction studies of the three samples before, at and after the abrupt point
revealed the phase change process of the Ge2Sb2Te5 thin films from amorphous to crystal states. Optical constants of the
three samples were measured by ellipsometry. Based on the experimental results, the relationship between the electrical /
optical properties and the structure of the Ge2Sb2Te5 thin films is discussed and it is shown that optical-electrical hybrid
data storage may be realized using optical writing and electrical reading.
Three kinds of novel metal(II)-azo complexes based on indandione were synthesized in order to obtain a suitable optical
recording medium for blu-ray disc-recordable (BD-R). Smooth thin films of these metal(II)-azo complexes were
prepared by spin-coating method. Absorption spectra, thermal decomposition and blu-ray static recording properties of
the thin films were investigated. These metal(II)-azo complexes, with absorption peaks at 435 - 444nm wavelength
region, have high thermal stability with sharp thermal decomposition thresholds. The results of the blue-ray (405nm)
static optical recording test of these metal(II)-azo complexes indicated that high reflectivity contrast (>50%) can be
obtained at appropriate laser power and pulse width, and the size of the recording mark on the Co(II) complex film is as
small as 200nm at writing laser power of 2mW and pulse width of 300ns. These results imply that metal(II)-azo
complexes based on indandione are promising candidates as recording media of BD-R.
Optical limiting [OL] property of naphthalocyanine zinc [ZnNc] in DMSO solution was first studied with 30 Ps laser
pulses at the wavelength of 532 nm. For comparison, OL measurement of C60 was performed under the same
experimental conditions. The results indicate that the optical limiting ability of ZnNc is similar to that of C60. To
investigate the mechanism of OL effect, Z-scan measurements were carried out with 30 ps laser pulses at the wavelength
of 532 nm, the repetition of 2 Hz. The ZnNc solution sample displays strong reverse saturable absorption effect. The OL
effect of ZnNc results from nonlinear absorption, and it can be considered as one of the most promising OL materials.
Three kinds of novel metallized azo dyes based on 4-methylthiazole, 5-methyl-3-isoxazole and 5-methyl-1,3,4-thiadiazole were synthesized in order to obtain a suitable optical recording medium for digital versatile disc-recordable(DVD-R). The absorption spectra, optical constants and thermal decomposition as well as red-light (650nm) static recording properties of three nickel-azo dye films were investigated. Particularly, the nickel-azo dye film based on 5-methyl-1,3,4-thiadiazole, peaking at 554nm and 602nm, with higher refractive index (n=2.41) and lower extinction coefficient (k=0.042) at the wavelength 650nm and a sharp threshold of thermal decomposition at 335°C was obtained. The results of the red-light(650nm) static optical recording test of this dye film indicated that higher reflectivity contrast of 35% can be obtained at a laser writing power of 7.5mW and pulse width of 200ns. These results imply the nickel-azo dye based on 5-methyl-1,3,4-thiadiazole is a promising candidate as a recording medium of DVD-R.
A novel metallized azo dye has been synthesized and its thin film on K9 glass has been prepared. The absorption spectra, thermal character and static optical recording properties with Bi mask layer super-resolution near-field structure (Super-RENS) of the dye were investigated. The results show that the dye film has a broad absorbance band in the region of 450-650nm and the maximum absorbance wavelength is located at 603nm, which is red shifted 17nm comparing with that of its chloroform solution, a steep absorbance falling edge in 603-650 is observed. It is found that the new metallized azo dye occupies excellent thermal stability, initiatory decomposition temperature is at 270°C and the mass loss is about 48% in a narrow temperature region (15°C). Static optical recording tests with and without Super-RENS were carried out using a 650nm semiconductor diode laser with recording power of 7mW and laser pulse duration of 200ns. The AFM images show that the diameter of recording mark on the dye film with Bi mask layer is reduced about 42% comparing with that of recording mark on the dye film without super-resolution near-field structure. It is indicate that Bi can well performed as a mask layer of dye recording layer and the metallized azo dye can be a promising candidate for recording medium with super-resolution near-field structure.
High-density Optical storage technology which uses a 405 nm laser and an objective lens of high numerical aperture (NA)of 0.85 is developing rapidly due to its high capacity over 23 GB on a single layer of a 120mm-diameter optical disc and great commercial demands. New storage media have been the bottleneck in high density optical storage. Organic material can be an attractive optical storage medium with various advantages, such as good sensitivity, easy fabrication, reasonable cost and structural flexibility, etc, compared with inorganic storage material. Efforts have been made to seek for new organic storage materials with high performance matching the 405 nm short wavelength laser. In this paper, recent progresses in developing organic materials as recording media for high density blue laser optical storage are presented. The recording mechanism of recordable dye layer and basic requirements for the dye materials are analyzed and discussed.
Thin film of a novel charge-transfer complex CuTCNQ derivative was prepared by spin-coating. Experimental results of this film for red-light rewritable optical storage are as follows: writing power13mW, writing pulse duration 200ns; erasing power 3mW, erasing pulse duration1000ns; reflectivity contrast C is greater than or equal to 27%; numbers of write-erase cycle N is greater than or equal to 1000.
Metal-azo complex is a new class of optical strorage medium and nonlinear optical material. The complex refractive indices N(N=n-ik), dielectric constants ε(ε=ε1-iε2), and absorption coefficients α of four kinds of novel azo dyes based on 4-methylthiazole, 5-methyl-3-isoxazole spin-coated thin films are determined from an scanning ellipsometer in the wavelength 400-700nm region. The molecular structural relationships on optical constants of metallized azo dyes were investigated. Metal chelation strongly (about one times) enhances the optical constants at the peaks and results in large bathochromic shift (ca.60-70nm) of absorption band. Bathochromic shift of Ni-azo complex is about 10nm larger than that of Zn-azo complex due to different spatial configurations formed in the metal-azo complexes. Meanwhile, the diazonium components of azo dye also affect the optical constants and maximum absorption.
Three kinds of novel rare earth metal β-diketone bipy complexes have been synthesized. Smooth films of the complexes on K9 glass substrates and single-crystal silicon substrates were prepared by spin-coating method. The absorption spectra of these new materials were measured in solution and in film. The optical constants (complex refractive index N=n+ik ) of the films on single-crystal silicon substrates at 405nm were determined with scanning ellipsometer. The thermo-gravimetric analysis (TGA) of the materials was also carried out. It is found that the absorption spectra of these films have comparatively broad band in the wavelength region 300-400nm, the peek is at ~345nm and the absorption edge is steep in the wavelength region 350-400nm, which indicates that the absorption of the films is well matched with the wavelength of GaN semiconductor laser diode (405nm). The refractive index (n) of the films is above 1.9 and the extinction coefficient (k) of is 0.1-0.3 at 405nm. The reflection peeks are located near 405nm. And also the new materials possess excellent thermal stability (their decomposition temperatures are higher than 300°C). The results imply that these novel materials are promising candidates for the recording media of blue discs.
Organometallic photochromic complexes, which are more stable than those traditional pure organic photochromic compounds, have a wide variety of potential applications in high-density optical storage. In this paper, Ag-TCNQ and Cu-TCNQ thin films were prepared by physical vapor deposition method. The proportion dependence of the spectral and optical properties of Ag-TCNQ thin films were studied and discussed. Multilayer film configuration was designed and prepared for optical memory study and its short-wavelength (514.5 nm) photochromic characteristics were reported. A recommendation of application of Metal TCNQ complexes for high-density and super high density optical storage was proposed as well.
Metallized azo dyes are paid much attention as recording media of digital versatile disc-recordable (DVD-R) due to their excellent optical and thermal properties within short wavelength (630 to approximately 650 nm). In this paper, a novel metallized azo dye has been synthesized. Smooth films on optical glass and single-crystal silicon were prepared by spin-coating method. The UV-Vis absorption spectra of the dye were measured in solution and in film. The optical constants (complex refractive index N=n+\ik) of the film on single-crystal silicon have been determined using scanning ellipsometer. The variation of the complex refractive index N with wavelength λ was obtained. Thermo-gravimetric analysis (TGA) of the dye showed clear threshold of thermal decomposition. Static optical recording tests were carried out to evaluate the performance of the optical recording medium. The results show that the dye is a promising candidate as a recording medium of DVD-R.
In this paper, spin-coated thin films of phthalocyanine dye were prepared. Absorption spectrum of the thin film shows a comparatively broad absorption at the wavelength region 630 - 770 nm and there is a steep absorption edge at the wavelength 750 nm, which is crucial to high reflectivity. Optical parameters of the thin film was measured by a spectroscopic ellipsometer. Extinction coefficient found to be very little at the wavelength 780 - 810 nm. 5-in CD-R discs made of this dye exhibit good performance after recorded in Yamaha 20 speed recorder. Jitters of land or pit are less than 35 ns and the 3T-11T's signals show very good quality. This dye is promising recording media for CD-R for much higher speed recording in the future.
Optical and morphological properties induced by laser irradiation in oxotitanium phthalocyanine (TiOPc) film were investigated at 650 nm wavelength with semiconductor laser. The reversible changes of spectra in the region of 610 - 730 nm wavelength were observed. The varieties of refractive index and extinction coefficient of the film before and after laser irradiation were detected. The morphological structure was investigated with transmission electron microscope (TEM) as well. The results suggest that the changes of the film optical properties are induced by photo-thermal processes, and this characteristic is significant to phthalocyanine film as promising candidate for DVD-rewritable recording medium (DVD-RW).
Nickel phthalocyanine thin film was prepared by vacuum deposition, the absorption and transmission spectra, the thermal stability of the film were reported. And the static optical recording properties of the thin film were investigated with a self-developed short-wavelength optical tester with high NA objective lens. The results show that this film occupied suitable absorption and transmission properties for short-wavelength (514.5 nm) optical recording, excellent thermal stability and outstanding thermal decomposition characteristics. And high reflectivity contrast was obtained at low writing power and short writing pulse width using the Ar+ laser (514.5 nm) irradiation. The results indicate that metal phthalocyanine is not only qualified for traditional near infrared optical recording medium of CD-R, but also a promising candidate for the recording medium of green-light DVD-R.
In this paper, the optical properties induced by laser irradiation in managanese phthalocyanine [Mn(OH)Pc] thin film were investigated with the Ar+ laser (514.5 nm) irradiation. The reversible changes of spectra in the region of 630 - 750 nm were observed. The refractive index and extinction coefficient before and after laser irradiation were determined. The results imply that the changes of the film optical properties are induced by photo-thermal processes, and this characteristic is significant to phthalocyanine film as promising candidate for DVD-rewritable recording medium (DVD-RW).
The optical limiting properties of eight-bromo-2, 3- Naphthalocyanine Zinc(II) were studied by using of double frequency ns/ps Nd:YAG laser system at 532 nm with pulse width of 21 ps. The optical limiting properties of a novel Naphthalocyanine are better than those of Fullerene toluene solution. By using the singlet excited absorption theory, optical limiting properties were analyzed, the theoretical fitting results of excited state absorption agree well with the experimental result of optical limiting. The singlet excited state absorption agree well with the experimental results of optical limiting. The singlet excited state absorption is the predominant mechanisms causing the optical limiting properties.
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