Source: http://www.google.com/patents/US7351460?ie=ISO-8859-1
Timestamp: 2015-05-06 19:33:38
Document Index: 462341713

Matched Legal Cases: ['art 362', 'art 364', 'art 364', 'art 355', 'art 366', 'art 372']

Patent US7351460 - Information recording medium, information recording device, and information ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsAn information recording medium includes an insulating member, first and second electrodes formed in one plane of the insulating member, and a conductive layer having an electrochromic material providing continuity with the first and second electrodes. A gap between the first and second electrodes is...http://www.google.com/patents/US7351460?utm_source=gb-gplus-sharePatent US7351460 - Information recording medium, information recording device, and information recording methodAdvanced Patent SearchPublication numberUS7351460 B2Publication typeGrantApplication numberUS 10/928,284Publication dateApr 1, 2008Filing dateAug 30, 2004Priority dateJul 21, 2004Fee statusPaidAlso published asUS20060018231Publication number10928284, 928284, US 7351460 B2, US 7351460B2, US-B2-7351460, US7351460 B2, US7351460B2InventorsKyoko Kojima, Motoyasu TeraoOriginal AssigneeHitachi, Ltd.Export CitationBiBTeX, EndNote, RefManPatent Citations (23), Non-Patent Citations (2), Referenced by (4), Classifications (27), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetInformation recording medium, information recording device, and information recording method
US 7351460 B2Abstract
An information recording medium includes an insulating member, first and second electrodes formed in one plane of the insulating member, and a conductive layer having an electrochromic material providing continuity with the first and second electrodes. A gap between the first and second electrodes is insulated.
said first and second electrodes are one of ITO (indium tin oxide), IZO (indium zinc oxide), and tin oxide SnO2.
17. An information recording method of the information recording device for recording information on an information recording medium and for reading information from the information recording medium which comprises an insulating member, first and second electrodes formed in one plane of the insulating member, and a conductive layer including an electrochromic material providing continuity with said first and second electrodes, the method comprising the steps of:
U.S. patent application Ser. Nos. 10/817,863 and 10/763,274 are co-pending applications of the present application. The disclosures of these co-pending applications are incorporated herein by cross-reference.
[Patent document 1] JP-A No. 122032/1983 [Patent document 2] JP-A No. 30878/2004 [Patent document 3] JP-A No. 82360/2002 [Patent document 4] JP-A No. 185288/1999 [Patent document 5] JP-A No. 346378/2003 [Non-patent document 1] Proceedings SPIE vol. 5069, p 300 [Non-patent document 2] http://www.sanyovac.co.jp/Englishweb/products/EITOonglass.html [Non-patent document 3] J. C. Street et. al. Physical Review B, Vol. 28, No. 4, p. 2140-2145 SUMMARY OF THE INVENTION
(1) In the method described in non-patent document 1 (Proceedings SPIE vol. 5069, p. 300), if the number of layers is increased, the quantity of light reaching the deeper layers would be decreased because a transparent electrode, which is sandwiching an electrochromic recording layer and to which a voltage is applied to color the recording layer, exhibits some absorption. For the transparent electrode layer, light transmittance close to 100% is required for making the light efficiency as high as possible, and electrical resistivity not more than 50 Ω/sq is required for coloring the recording layer quickly and uniformly. However, it is known that a transparent electrode actually has an absorption in the visible range and that high light transmittance and electric resistivity do not coexist. It will be explained as follows using the principal of the manifestation of electroconductivity in the transparent electrode material. The conductivity of a compound such as ITO used for the transparent electrode is given by the defining equation for electrical conductivity (expression 1). Here, electron conduction is considered.
Here, n is the carrier density, ε∞ is the optical dielectric constant, and m∞ is the optical effective mass. With increasing n, ω becomes greater and light from near infrared to the visible region becomes absorbed.
(2) Moreover, in the investigation of the electrochromic element lamination process tested by the inventors, it was discovered that an increase in driving voltage of the electrochromic element and worsening of the coloring cycle characteristics happened because of the degradation introduced to the electrolyte layer and electrochromic layer caused by the damage when the transparent electrode layer such as ITO was directly formed by the RF magnetron sputtering technique on an electrolyte layer consisting of a solid polymer electrolyte and an electrochromic layer including a conductive polymer electrochromic material. On the other hand, according to the lamination method of the present invention, degradation introduced in the elements caused by damage while sputtering can be avoided because it is not necessary to form ITO electrodes directly on the electrochromic layer and the electrolyte layer. It will be described concretely as follows.
A concrete configuration of the present invention will be described as follows. As described above, the information recording medium of the present invention has a basic unit of an electrochromic element illustrated in the cross-sectional structure in FIG. 1, in which the basic unit consists of the conductive layer 7 including an electrochromic material formed connecting to both the first electrode 2 and the second electrode 3 deposited on the insulating substrate 1. That is, the information recording medium of the present invention consists of the insulating member, the first and second electrodes formed on one plane of the aforementioned insulating member, and the conductive layer including an electrochromic material providing continuity with aforementioned first and second electrodes, wherein the aforementioned gap between the first and second electrodes is insulated. Moreover, the conductive layer 7 consists of two layers, the electrochromic layer and the electrolyte layer, along the direction of the layer parallel to the arrangement of the first electrode 2 and the second electrode 3. Two different types of structure are possible for the two-layer configuration. Concretely, the electrochromic layer 14 is formed so as to connect with both the first electrode 12 and the second electrode 13 in the first structure as shown in the cross-sectional structure of FIG. 2.
Moreover, the electrolyte layer 104 is formed on the electrochromic layer 14 so as not to connect with the insulating substrate 11, the first electrode 12, and the second electrode 13. Wiring between the first electrode 12 and the second electrode 13 is from the power supply 15, thus a voltage can be supplied. The structure illustrated in FIG. 3 is also possible in which the two-layer structure of the conductive layer 57 is laminated in the opposite order. Here, the structures illustrated in FIGS. 2 and 3 are called the first structure and the second structure, respectively. In the element having the second structure shown in FIG. 3, the electrolyte layer 104 is formed so as to connect with both the first electrode 12 and the second electrode 13 deposited on the insulating substrate 11. Moreover, the electrochromic layer 14 is formed on the electrolyte layer 104 so as not to connect with the first electrode 12 and the second electrode 13. Wiring between the first electrode 12 and the second electrode 13 is from the power supply 15, thus a voltage can be supplied.
FIG. 4 illustrates a structure viewing the element shown in the cross-sectional structure FIG. 2 from above the electrolyte layer 104. The first electrode 12 and the second electrode 13 are formed on the insulating substrate 11, and the electrochromic layer and the electrolyte layer 107 are laminated on top of them. Here, the electrochromic layer exists under the electrolyte layer 104. The gap between the first electrode 12 and the second electrode 13 is wired from the power supply 15. Here, except for polycarbonate which is generally used for optical disks, a polymeric material such as polyolefin, polyethylene, polypropylene, polyethylene terephthalate (PET) and acrylate resin or inorganic materials such as glass, quartz, and sapphire is used for the insulating substrate.
The above-described operation occurs except for polythiophene, polyaniline, polypyrrole, and polyphenylenevinylene, which are nondegenerate conductive polymers in which the ground state does not degenerate. Non-patent document 3 (J. C. Street et. al., Physical Review B, Vol. 28, No. 4, p. 2140-2145) described that the electrochromism of nondegenerate conductive polymers is explained by polarons and bipolarons as follows. FIG. 6 shows the change of the molecular structure of polythiophene by doping. When an acceptor is doped in the neutral state 23 of polythiophene, 1 electron oxidation 24 first occurs, becoming 1 electron oxidation state 25. Here, halogens such as Br2, I2, and Cl2, Lewis acids such as BF3, PF5, AsF5, SbF5, SO3, BF4 −, PF6 −, AsF6 −, SbF6, proton acids such as HNO3, HCl, H2SO4, HClO4, HF, and CF3SO3H, transition metal halogenides such as FeCl3, MoCl3, and WCl5, and organic materials such as tetracyanoethylene (TCNE), 7,7,8,8-tetracyanoquinodimethane (TCNQ) are listed as the acceptors used for doping. 1 electron oxidation state 25 becomes a positive charged polaron state 27 through the relaxation process 26. According to the fifth edition of the Physics and Chemistry Dictionary (1998, Iwanami Shoten Publishers), a polaron is a state in which conduction electrons in a crystal move accompanied by deformation of the surrounding crystal lattice.
Here, in the polaron state, �crystal� is replaced with �neutral state in a polythiophene molecule� and �deformation of crystal lattice� is thought to be �appearance of a partial quinoid structure of a polythiophene molecule due to 1 electron oxidation�. If an acceptor is additionally doped to the polythiophene in the polaron state 12, oxidation proceeds further, resulting in a positive bipolaron state 28. On the other hand, a negatively charged polaron and bipolaron are generated by donor doping according to the reduction reaction 29. Here, alkaline metals such as Li, Na, K, and Cs, and quaternary ammonium ions such as tetraethylammonium and tetrabutylammonium are listed as donors used for doping. Because both polarons and bipolarons are transported on the polymer chains, they contribute to current. Polymer electrolytes, so called polymer dopants, can also be used in addition to the above-mentioned dopants. For instance, polystyrene sulfonate, polyvinyl sulfonate, and sulfonated polybutadiene are examples. When polyaniline, polythiophene, and polypyrrole are polymerized with the presence of these polymer electrolytes, the conductive polymers formed are obtained as ion complexes with the polymer electrolyte used. Using polymer dopants effective to improve the processability, for instance, insoluble conductive polymers can be made soluble.
The relationship between polaron, bipolaron, and electrochromism will be described in FIG. 7, in which the electron state of the nondegenerate conductive polymer is illustrated according to the band structures. Here, the change in electron state with acceptor doping is shown. In the non-doped neutral state band structure 32, the electron energy 36, the so-called forbidden band width 35, exists as the energy difference between the lowest energy of the conduction band 34 and the highest energy of the valence band 33, and light which has the energy corresponding to the forbidden band width 35 is absorbed as the allowed transition 37. If the wavelength of the absorbed light is in the wavelength region of visible light, it looks colored. Here the forbidden band width 35 of the nondegenerate conductive polymers is generally from 0.1 eV to 3 eV which is the same as an inorganic semiconductor. The two polaron levels, bipolaron level p+ 39 and bipolaron level p− 40, are created between the valence band 33 and the conduction band 34 in the band structure 38 in the positive polaron state formed as a result of acceptor doping. Because the allowed transition 41 in the polaron state is different from the allowed transition 37 in the neutral state, the absorption characteristics of light are changed, and the change in the visible light region is observed as a change in color. Moreover, in the band structure 42 in the bipolaron state where doping is taking place, two new bipolaron levels, bipolaron level BP+ 43 and bipolaron level BP− 44, are formed, and the light absorption characteristics are changed even more because the allowed transition 45 in the bipolaron state is changed. In the case of donor doping in a nondegenerate conductive polymer, the change of allowed transition behavior caused by the change of the band structure with the formation of polaron levels and bipolaron levels is similarly observed as electrochromism.
Because the electrochromic characteristics accompanying doping in nondegenerate conductive polymers are used for the electrochromic element, especially here, the nondegenerate conductive polymer is called a �conductive polymer electrochromic material�. Compounds selected from tungsten oxide, iridium oxide, nickel oxide, titanium oxide, and vanadium pentoxide, etc. are used for the transition metal oxide electrochromic material. The electrochromism of tungsten oxide will be explained as an example. Tungsten oxide itself is colorless or buff yellow, but it changes reversibly into deep blue by reducing a part. The electrochromism of tungsten oxide is described in (expression 3).
WO3+xM++xe−⇄MxWO3 (expression 3)
Here, x is an arbitrary number from 0 to 1, M+ is a proton or a cation such as a lithium ion, and e− is an electron, respectively. The reduction reaction shown in (expression 3) takes place electrochemicaly. The right side of (expression 3) means the state in which tungsten oxide is partially reduced, and pentavalent and hexavalent tungsten atoms are coexisting �mixed valence state�, thereby chromophores appear because of �intervalence transition adsorption� which is the transition between tungsten atoms with different valences. In general, the electrochromism of transition metal oxides is closely related to a phenomenon of the mixed valence.
Moreover, the ionic conductivity of the electrolyte is preferably 10−5 S/cm or more at around 25� C. The matrix material itself has preferably no photoabsorption. Polymethyl methacrylate (PMMA), polyvinyl butyral (PVP), polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polyethylene carbonate (PEC), and polypropylene carbonate (PPC) are used as the polymer material for matrix. These polymers can be used either singly or in the form of plural combinations.
Here, the principles of operation of the electrochromic element with the first structure constituting the information recording medium of the present invention will be described using FIG. 8. An element using an electrochromic compound which is colorless in the steady state and deeply colored by doping lithium ions is used in this description, such as poly (3,4-ethylene dioxythiophene)-polystyrene sulfonate complex and tungsten oxide. The power supply 56 is connected to the gap between the first electrode 52 and the second electrode 53 formed on the insulating substrate 51, and a voltage is applied. The applied voltage is controlled to be from 2 V to 20 V in this case. The electric field 208 generated between the electrodes exists on the insulating substrate 51, inside the electrochromic layer 54, which is provided so as to connect with the first electrode 52 and the second electrode 53, and inside the electrolyte layer 55 deposited on the electrochromic layer. The electric field 208 is also formed inside the electrolyte layer 55 through the electrochromic layer 54, and migration of lithium ions 207 occurs in the region where the potential gradient is generated from the electrolyte layer 55 with a relatively high potential to the electrochromic layer 54 with a lower potential. At the area of the electrochromic layer 54 in which lithium ions 206 are injected, coloring 209 appears. It is possible to delete this coloring 209 reversibly by stopping the applied voltage or by applying a voltage with reverse polarity for a short time.
Next, the principles of operation of the electrochromic element with the second structure constituting the information recording medium of the present invention will be described using FIG. 9. Here, an element using an electrochromic compound which is colorless in the steady state and deeply colored by doping lithium ions is also used in this description, such as poly (3,4-ethylene dioxythiophene)-polystyrene sulfonate complex and tungsten oxide. The power supply 15 is connected to the gap between the first electrode 12 and the second electrode 13 formed on the insulating substrate 11, and a voltage is applied. The applied voltage is controlled to be from 2 V to 20 V in this case. The electric field 228 generated between the electrodes exists on the insulating substrate 11 inside the electrolyte layer 104, which is provided so as to connect with the first electrode 12 and the second electrode 13, and inside the electrochromic layer 14 deposited on the electrolyte layer. The electric field 228 is also formed inside the electrochromic layer 14 through the electrolyte layer 224, and migration of lithium ions 227 occurs in the region where the potential gradient is generated from the electrolyte layer 104 with a relatively high potential to the electrochromic layer 14 with a lower potential. At the area of the electrochromic layer 14 in which lithium ions 226 are injected, coloring 229 appears. It is possible to delete this coloring 229 reversibly by stopping the applied voltage or by applying a voltage with opposite polarity for a short time.
a. the conversion ratio to the polaron state and bipolaron state by doping is reduced because of cutting conjugate groups, converting a single bond to a double bond, and oxidation of the conductive polymer in the information layer which has the electrochromic properties. b. the electric resistivity increases locally because of a hardening reaction caused by crosslinking, polymerization reactions, and crystallization reactions in the electrolyte layer, therefore, reversible doping becomes difficult to accomplish in the information layer. c. the chemical reaction such as heat curing occurs in the information layer and at the interface with the adjacent electrode layer, resulting in the electric resistivity increasing. d. the chemical reaction such as heat curing occurs in the information layer and at the interface with the adjacent electrolyte layer, resulting in the electric resistivity increasing. Recording is possible if at least one of the above-mentioned from a to d occurs. If a plurality of these things happens, higher sensitivity recording is achieved.
The information storage medium of the present invention, in a read/write device having a mechanism, which supplies a current to the information layer, is suitable for use in the form of an optical disk such as a CD-R and DVD-R. FIG. 13 is a configuration illustrating a medium at this time. Light is illustrated as irradiating from the upper side of the figure. The medium consists of the laminated protection substrate 338, protection layer 331, electrolyte layer 333, electrochromic layer 334, electrode layer 335 which is a transparent electrode, ultraviolet curable resin layer 336, laminated protection substrate 337 from the light irradiation side 341, and 339 and 340 correspond to the land part and groove part, respectively.
351 is the center line of the disk; 352 is the hole of the disk; 353 is the electrode connected to the electrode on the disk receiving side when it is placed in the disk receiving part and the electrode used to apply a voltage to color the electrochromic layer; 354, 362, 364, 365, 366, 359 is the insulating part consisting of polycarbonate; 355 is the transparent electrode, 356 is the electrochromic layer colored while recording; 357 is the electrolyte layer; and 358 is the insulating part to separate the transparent electrode. 360, which is the part applying a voltage from the electrode and recording by coloring, really has a land-groove structure, but it is omitted in FIG. 14. FIG. 15 is an enlarged view illustrating a part of the recording part of the disk. FIG. 24 is a view seen from the face 361 of the lower side of the information recording medium shown in FIG. 14. The information recording medium has the same shape as an optical disk 512 such as a DVD etc. and consists of the insulating part 362, electrode 353, insulating part 364, and electrode 303, in order, from the center hole part of the disk 352. The electrode 353 and the electrode 363 are separated by the insulating part 364, and they constitute a mutual pair to color and decolor the recording layer by applying a voltage. In order toward the outer edge are the insulating part 355, electrode 365, insulating part 366, and electrode 355.
First, as shown in FIG. 16, tracking grooves (0.35 μm wide) for in-groove recording (herein, it is land recording as seen from the beam spot) with a track pitch of 0.74 μm and a depth of 23 nm are provided by molding on the surface of a dummy substrate 371 which is 12 cm in diameter and 0.6 mm thick. And, the insulating part 372 made by polycarbonate is formed with a thickness of 50 μm, on which the address is expressed by the wobble of the grooves. The positive type resist pattern 373 with a thickness of 1 μm is obtained through coating, UV exposure (248 nm wavelength) using a mask, and an alkali developer. And then, through the dry-etching process 374, the sputter process 375 for the transparent electrode with the composition of (In2O3)90(SnO2)10, the lift-off resist removing process 376, and the ITO electrode formation process 377, the electrode is formed, which is used for coloring the electrochromic layer for recording. The 100 nm thick electrochromic layer 379 and the 150 nm thick electrolyte layer 380 are provided on the electrode by the electrochromic layer-electrolyte layer fabrication process 378 using a coating technique. Thereafter, a disk is similarly obtained through the fabrication process 381 for the insulating part and electrode.
Even when the line speed was changed from 8 m/s, this range did not change so much. Reading was carried out with 1 mW without applying the voltage. Practical reading could be done within the range from 0.2 mW to 2 mW. Deterioration in the recorded data was observed when it was read for a long time with a power exceeding 2 mW. Moreover, in the above mentioned record waveform generating circuit, the signals with 3 T-14 T are made to alternately correspond to �0� and �1� in the time series. In this case, the electrochromic characteristics are deteriorated at the area to which the high power level pulse is irradiated, and coloring does not occur easily. Moreover, in the above-mentioned record waveform generating circuit 433, there is a multi-pulse waveform table corresponding to the method (adaptive record waveform control), in which the first pulse width and the last pulse width of the multi-pulse waveform are changed corresponding to the length of space part before and after the mark part, when a string of high power pulse lines is formed to create the mark part. Thereby, the multi-pulse record waveform is generated in which the effect of the thermal interference generated between the marks can be eliminated as much as possible.
Optical characteristics in which there is no absorption in the wavelength of the recording laser beam, that is, transparent, is important for the electrode material. A material with the composition of (In2O3)x(SiO2)1-x, where x is within a range from 5% to 99%, can be used for the transparent electrode. Specifically, from the point of view of electric resistivity, materials can be used in which the x value is within the range from 90% to 98%, to which 50 mol % or less of SiO2 is added, and other oxides such as 2 to 5 mol % of Sb2O3, etc. are added to SnO2.
Moreover, fluorine-doped SnO2 has a high electric resistivity as well as high light transmittance, so that it is possible to be used. Or, because IZO (indium zinc oxide) has the advantage that it can be fabricated with less surface roughness, it can be used for the electrode. A high transparency is not always required for the electrode placed at the deeper side as seen from the irradiation side of the laser beam to the information storage medium, so that metals preferable for optical disks can also be used. A metallic layer which has a high radiation coefficient and thermal conductivity is preferable because it is effective in preventing temperature rise at the substrate surface. In the case of Al or an Al alloy, it should be a high thermal conductivity material including 4 atomic % or less of added elements such as Cr, Ti, etc. Next, the layer may be used in which a single element selected from Au, Ag, Cu, Ni, Fe, Co, Cr, Ti, Pd, Pt, W, Ta, Mo, Sb, Bi, Dy, Cd, Mn, Mg, and V, or an alloy including these materials as a main component such as a Au alloy, Ag alloy, Cu alloy, Pd alloy, Pt alloy, Sb�Bi, SUS, Ni�Cr or an alloy of these elements. Thus, electrode and reflection layer consist of metallic elements, semiconductor elements, and alloys and mixtures thereof. Among these, single elements of Cu, Ag, and Au or Cu alloys, Ag alloys, specifically ones with 8 atomic % or less of added elements such as Pd and Cu, etc. and ones having a high thermal conductivity such as Au alloys etc. suppress heat deterioration of the organic materials. Conductive organic materials which have no absorption band in the visible region can also be used, such as polythiophene derivatives, polypyrrole derivatives, and polyacetylene, etc. which have narrow band gap structure.
A polycarbonate substrate having grooves for tracking directly on the surface is used in this embodiment. A substrate having grooves for tracking means a substrate which has grooves deeper than λ/15n (where n is the refractive index of the substrate material) when the read/write wavelength is λ. The grooves may be formed continuously per revolution or divided midway. It is understood that the balance of tracking and noise is good when the groove depth is about λ/12n. Moreover, the groove width may be different depending on the location. A substrate which has the format to be able to read/write on both the groove part and land part or to read/write on either of these may be used. In the case of a type recording only on the groove, it is preferable that the track pitch is about 0.7 times the wavelength/NA of aperture lens, and the groove width about � of it.
After forming the first electrode 532, the second electrode 534, and the wiring on the glass substrate 531, the electrolyte layer 544 (200 nm in thickness) and the electrochromic layer 543 (100 nm in thickness) are formed in order by rotation coating and a subsequent heating process. A 300 nm thick polyvinyl alcohol layer was deposited on it as the insulating protection layer 546. The first electrode 532 is used as a reference electrode for coloring/decoloring, and the recording information is written on the second electrode 534 which has a relatively larger surface area.
The electrochromic unit cell shown in FIG. 25 is arranged two-dimensionally in the same layer as shown in FIG. 26. FIG. 26 is a structure illustrating an optical memory, in which four layers of an electrochromic element having two arrays with six cells per array are laminated. In FIG. 26, electricity is supplied from the power supply to the array with six cells in a horizontal direction by wiring 552 and wiring 553 for the first electrode group. Electricity is supplied from the power supply to the second electrode group by wiring 555 and wiring 556. The aluminum reflection layer (50 nm in thickness) and the bottom protection layer (500 nm in thickness) 561 are formed at the bottom of the four layers.
FIG. 28B is the cross-sectional view of the electrochromic unit cell at the center crossing line. After forming the first electrode 602, the second electrode 604, the third electrode 605, the fourth electrode 606, the fifth electrode 607 and the wiring on the glass substrate 601, the electrolyte layer 617 (200 nm in thickness) and the electrochromic layer 618 (100 nm in thickness) are formed in order by rotation coating and a subsequent heating process. A 300 nm thick polyvinyl alcohol layer was deposited on it as the insulating protection layer 619. The first electrode 602 is used as a reference electrode for coloring/decoloring, and the recording information is written on the second electrode 604, the third electrode 605, the fourth electrode 606, and the fifth electrode 607, which has a relatively larger surface area.
The electrochromic unit cell shown in FIG. 28 is fabricated so that the four electrodes, from the second to the fifth, have equal potential. In FIG. 29A, when a voltage is applied to the first electrode 602 to make the potential from the second to the fifth electrode 6 V, parts of the electrochromic layer on the second electrode 624, the third electrode 625, the fourth electrode 626, and the fifth electrode 627 were colored, as shown in FIG. 29A. It is also shown in the cross-sectional view of FIG. 29B. The colored part was turned clear by stopping the applied voltage or by applying a voltage not more than 6 V with an opposite polarity. This coloring/decoloring could be repeated one million times when a voltage �6 V was applied respectively for one second.
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