JP2000321714A - Near field optical recording medium and near field optical recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical recording medium capable of higher density recording and having sufficiently high durability in practical use as the optical recording medium and to provide an optical recording method using the optical recording medium. SOLUTION: The near field optical recording medium enables recording, reproduction and erasure using evanescent light having a smaller beam spot diameter than the wavelength of a light source. A recording layer of the optical recording medium comprises an amorphous layer, based on a photochromic material having >=55 deg.C glass transition temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a near-field optical recording medium and a near-field optical recording method capable of recording, reproducing and erasing using evanescent light having a beam spot diameter smaller than the wavelength of a light source. .

[0002]

2. Description of the Related Art Various attempts have been made to improve the recording density of an optical memory, such as a super-resolution technique, pit edge recording, and a V-groove method. However, since all of them use the heat mode recording method, the increase in recording density has reached its limit. In recent years, photon mode recording that uses optical energy as it is for optical recording is expected to break the limits of the heat mode recording method. In photon mode recording, wavelength multiplexing and polarization multiplexing can be performed, so that a plurality of recordings can be performed in the same pit, and higher density can be achieved.

[0003] However, in the case of wavelength multiplexing, it is difficult to obtain a large number of photochromic materials having different absorption wavelengths, and it is expected that the recording density is improved at most about 5 times. In the case of polarization multiplexing, the recording density can be improved only about twice. Further, in the case of photochemical hole burning, multiplexing of 100 times or more is possible, but there is a disadvantage that a low temperature of 77K or less is required.

In order to overcome these problems, the recording method has been changed to ST.
M using electric field effect and electromagnetic wave irradiation
-98849) or magneto-optical recording using evanescent light (E. Betzig et al., Appl. Phys. Lett.,
61, 142 (1992)).

[0005] However, these methods have a disadvantage that an electrode for applying an electric field or a magnet for magneto-optical recording is required, and the apparatus becomes complicated.

To solve such a problem, Japanese Patent Application Laid-Open No. Hei 6-267071 discloses an evanescent light having a size smaller than a wavelength as a recording / reproducing / erasing light source.
For example, a rewritable optical recording method using a polymer dispersion medium of a photochromic material having thermal irreversibility such as a diarylethene derivative represented by the following structural formula as an optical recording medium is described.

[0007]

Embedded image

According to the method described in JP-A-6-267071, high-density recording can be performed without using electrodes or magnets.

That is, without using electrodes or magnets,
In order to perform optical recording by evanescent light, the recording medium itself reversibly changes color between the two states only by its light source without any other physical or chemical perturbation, and both states are thermally stable. It is necessary to be. JP-A-6-267
No. 071 discloses such a medium as an optical recording medium,
By using evanescent light of a size smaller than the wavelength as a recording / reproducing / erasing light source, it is possible to use 1/10 to 1/1 of the current recording pit size without using electrodes or magnets.
A recording pit having a size of 00 can be formed, and the recording density is improved to 100 to 10,000 times the current level.

Japanese Patent Application Laid-Open No. Hei 9-241254 describes a diheteroarylethene compound having an adamantyl group represented by the following structural formula and an optical recording medium using the same. It is described that since a film obtained by dissolving this compound in a solvent and coating and drying is amorphous, a recording layer of an optical recording medium can be formed without using a binder resin.

[0011]

Embedded image

[0012]

In order to increase the recording density of the recording layer of the optical recording medium, first, it is important that the amount of state change such as absorbance and refractive index caused by light irradiation is large. It is also an extremely important requirement to increase the density of photochromic material molecules in the recording layer. Furthermore,
By increasing the flatness of the recording layer surface, it can be expected that scattering of irradiation light is reduced and the recording density can be improved.

In particular, when information is recorded / reproduced using evanescent light, the distance from the evanescent light source to the recording layer of the medium needs to be very close to 1/4 or less of the wavelength of the light source. From this point, it is desired that the surface smoothness of the recording medium is high.

However, Japanese Patent Application Laid-Open No. Hei 6-26707 describes
In Japanese Patent Laid-Open No. 1-2003, no consideration is given to such improvement in recording density. In other words, since a binder is used to ensure transparency (amorphousness) in a thin film, and the photochromic material is diluted about 20 times,
ε was low and there was a problem in practicality.

According to Japanese Patent Application Laid-Open No. 9-241254, a diheteroarylethene compound having an adamantyl group described in the publication is dissolved in a solvent, coated and dried, and the film obtained is amorphous. It is said that a recording layer of an optical recording medium can be formed without using a resin, but the compound having an adamantyl group described herein has a low glass transition point of 40 ° C. In a recording layer of an optical recording medium formed using such a compound, under high temperature and high humidity, the phase of a pit portion after recording changes, so that a signal becomes unclear and information may not be accurately read. is there.

The present invention solves the above-mentioned conventional problems, and provides an optical recording medium and an optical recording method capable of performing higher-density recording and having sufficient durability for practical use as an optical recording medium. The purpose is to do.

[0017]

A near-field optical recording medium according to the present invention is a near-field optical recording medium capable of recording / reproducing / erasing using evanescent light having a beam spot diameter smaller than the wavelength of a light source. The medium is characterized in that the recording layer of the optical recording medium is an amorphous layer mainly composed of a photochromic material having a glass transition point of 55 ° C. or higher.

In the near-field optical recording method of the present invention, the near-field optical recording medium of the present invention is used, and the entire surface of the recording layer of the near-field optical recording medium is irradiated with ultraviolet rays in advance to be included in the recording layer. After the photochromic material is closed, a signal is recorded by opening the photochromic material with evanescent light having a beam spot diameter smaller than the wavelength of the light source.

The near-field optical recording medium of the present invention is capable of recording / reproducing / erasing using evanescent light, has a recording layer mainly composed of an amorphous photochromic material, and has a glass transition point of 55 ° C. or higher. And a relatively high point.

If the photochromic material is amorphous, no irregularities due to the crystal of the photochromic material molecules are generated on the surface of the recording layer, the surface is excellent in flatness, and scattering of irradiation light is prevented. In addition, the anisotropy due to the crystal is eliminated. As a result, optical recording with a small spot diameter becomes possible.

When the glass transition point of the photochromic material is 55 ° C. or higher, it is considered that signal deterioration of the recorded optical recording medium in an environment conceivable in normal use can be avoided. The glass transition point is more preferably 60 ° C. or higher.

The recording layer in the near-field optical recording medium of the present invention is mainly composed of a photochromic material, which is about 80% by weight or more, preferably 90% by weight or more of the recording layer. It means that it is formed from a material. More preferably, the recording layer is formed substantially only of the photochromic material. That is, as components other than the photochromic material in the recording layer, various additives and dyes, a binder described later, and the like can be cited. From the viewpoint of increasing the density of the photochromic material and improving ε, as much as possible other than the photochromic material It is preferable not to include the component of

[0023]

Embodiments of the present invention will be described below in detail.

First, the photochromic material used in the present invention will be described.

As a preferred photochromic material for the near-field optical recording medium of the present invention, a diheteroarylethene-based compound can be mentioned. Among them, those having a pyrrole ring, a thiophene ring, a furan ring or a selenophene ring in the heteroaryl moiety are more preferred.

Particularly, as the diheteroarylethene compound according to the present invention, a compound represented by the following general formula (I) is preferable.

[0027]

Embedded image

The following chain alkyl, alkoxy and alkylthio groups exemplified as substituents in the present specification may be straight-chain or branched.

In the above structures (a) and (b), R ¹ is specifically an optionally substituted chain having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group or a butyl group. Or cyclic alkyl group having 1 carbon atom such as methoxy group, ethoxy group, propoxy group and butoxy group
And 4 alkoxy groups which may be substituted. As the “substituent” in “may be substituted”, a halogen atom such as a fluorine atom and a chlorine atom, an alkoxy group having 1 to 6 carbon atoms, and the like can be mentioned. Preferably, R ¹ is a chain alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to 3 carbon atoms.

R ² is an optionally substituted alkyl group having 1 to 20 carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group, an octyl group, a decyl group; a methoxy group, an ethoxy group, a propoxy group; A group having 1 to 20 carbon atoms such as a group, a butoxy group, an octyloxy group, and a decyloxy group;
An optionally substituted alkoxy group; an optionally substituted alkylthio group having 1 to 20 carbon atoms, such as a methylthio group, an ethylthio group, a propylthio group, a butylthio group, an octylthio group, and a decylthio group; A 2-thiophenyl group, a 2-furanyl group, a phenyl group,
Examples thereof include an optionally substituted aromatic ring group (including a heterocyclic group) having 4 to 20 carbon atoms, such as a naphthyl group. Examples of the “substituent” in “optionally substituted” for a group other than the aromatic ring group include a halogen atom such as a fluorine atom and a chlorine atom, and an alkoxy group having 1 to 6 carbon atoms. Substituents for “optionally substituted” on the aromatic ring will be described later in the section of the partial structure (a ′). Preferably, R ² is an optionally substituted aromatic ring group (including a heterocyclic group).

R ³ is a hydrogen atom; an optionally substituted cyclic or chain having 1 to 10 carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group, a t-amyl group and a t-hexyl group. Alkyl group; having 1 carbon atom such as methoxy, ethoxy, butoxy, t-hexyloxy, etc.
And 10 to 10 optionally substituted alkoxy groups. As the “substituent” in “may be substituted”, a halogen atom such as a fluorine atom and a chlorine atom, an alkoxy group having 1 to 6 carbon atoms, and the like can be mentioned. Preferably, R ³ is a chain alkyl group having 1 to 3 carbon atoms or an alkoxy group having 1 to 3 carbon atoms.

R ⁴ is a hydrogen atom; a t-butyl group;
C 4-8 having a tertiary or quaternary carbon atom, such as a t-amyl group, a t-hexyl group, a cyclohexyl group, etc.
A chain or cyclic alkyl group; a fluorine atom and / or a phenyl group such as a trifluoromethyl group, a tetrafluoroethyl group, a perfluoroethyl group, a perfluoropropyl group, and a di (trifluoromethyl) phenylmethyl group An alkyl group having 1 to 10 carbon atoms; an alkenyl group having 4 to 8 carbon atoms such as a vinyl group, a methylvinyl group and a methylethylvinyl group; a trifluoromethyldiphenylvinyl group and a diphenylvinyl group An alkenyl group having 2 to 15 carbon atoms substituted with a fluorine atom and / or a phenyl group; a t-butoxy group, a t-
An alkoxy group having a tertiary or quaternary carbon atom and having 4 to 8 carbon atoms, such as an amyloxy group and a t-hexyloxy group; a trifluoromethoxy group, a tetrafluoroethoxy group, a perfluoroethoxy group, a perfluoro group A C1-C15 alkoxy group substituted by a fluorine atom and / or a phenyl group such as a propyl group or a di (trifluoromethyl) phenylmethoxy group; a t-butylthio group, a t-amylthio group, a t-hexylthio group An alkylthio group having a tertiary or quaternary carbon atom and having 4 to 8 carbon atoms; a trifluoromethylthio group, a tetrafluoroethylthio group, a pentafluoroethylthio group, a perfluoropropylthio group, a di ( Trifluoromethyl)
A C1-C10 alkylthio group substituted with a fluorine atom and / or a phenyl group such as a phenylmethylthio group; an optionally substituted aromatic ring such as a phenyl group, a naphthyl group, a thiophene group and an indole group; Groups (including heterocyclic groups); such as phenoxy groups and naphthoxy groups,
Optionally substituted aryloxy group; optionally substituted heteroaryloxy group such as thiophenoxy group and indoleoxy group; optionally substituted arylthio group such as phenylthio group and naphthylthio group; thiophenthio A heteroarylthio group which may be substituted, such as a group or an indolethio group; Note that an aromatic ring group (including a heterocyclic group), that is,
(Hetero) aryl group, (hetero) aryloxy group,
The “substituent” in “optionally substituted” for the (hetero) arylthio group is a halogen atom such as a fluorine atom or a chlorine atom, or an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms. And the like.

The partial structure (a) is preferably the following structure (a ′).

[0034]

Embedded image

In the above structure (a ′), R ⁵ and R
^{As 6} each independently includes all the groups described above as R ⁴ . Further, in R ⁵ and R ⁶ , the bonding position of a group that is not a hydrogen atom is preferably para to the thiophene ring. When neither R ⁵ nor R ⁶ is a hydrogen atom, it is preferable that one of them is bonded to the thiophene ring at the para position.

As the diheteroarylethene compound in the present invention, particularly preferably, X in the general formula (I)
And Y both have a partial structure (b), X has a partial structure (a ′) and Y has a partial structure (b) (provided that R ⁴ , R ⁵ and R ⁶ in the same molecule are all X and Y both have a partial structure (a ′) (however, R ⁵ and R ⁶ in the same molecule cannot all be hydrogen atoms) Is.

In the near-field optical recording medium of the present invention,
The diheteroarylethene compound used for the layer is
Am transition point of 55 ° C or higher, preferably 60 ° C or higher
In order to be fuzzy and amorphous,
In the general formula (I), R represented by the partial structure (a ′)
⁵Or R⁶Or the partial structure (b) has
R ⁴, At least one of which is a relatively bulky group
Is preferred.

However, even if this group is a bulky group, it may be unsuitable for the present invention. For example, if the molecular weight is too large, the density of photochromic material molecules in the recording layer will be low, and Since the transition point tends to decrease, it is not preferable as an optical recording medium.

As a result of considering these, R⁴, R⁵, And
And R⁶Is selected from a hydrogen atom and the groups exemplified below.
It is particularly preferred that it is removed. However, one compound has
R ⁴, R⁵, And R⁶Are all hydrogen atoms
Absent.

[0040]

Embedded image

[0041]

Embedded image

Specific examples of the diheteroarylethene compound in the present invention include the following compounds (A) to (M).

[0043]

Embedded image

[0044]

Embedded image

[0045]

Embedded image

[0046]

Embedded image

[0047]

Embedded image

In the present invention, an amorphous recording layer containing the photochromic material is formed on a substrate by using such a photochromic material such as a diheteroarylethene compound.

In order for the photochromic material in the recording layer to be amorphous, the recording layer needs to be transparent. That is, if there is a crystallized portion, an opaque portion exists in the recording layer. This can be confirmed more accurately by the X-ray diffraction diagram of the recording layer. For example, when the X-ray diffraction pattern of the recording layer powder separated from the optical recording medium is measured, since the amorphous photochromic material has a state in which long-range order has disappeared and only short-range order remains, scattering of incident X-rays has occurred. You can see the halo figure by.

The method for forming the recording layer in the near-field optical recording medium of the present invention is not particularly limited, but generally it can be formed by a coating method, a vapor deposition method or the like.

In the case of a coating method, a photochromic material such as the above-mentioned diheteroarylethene-based compound is used by adding carbon tetrachloride, benzene, cyclohexane, methyl ethyl ketone,
Dispersed or dissolved in a solvent such as tetrachloroethane,
A film can be formed by applying the composition on a substrate by a coating means such as bar coating, roll coating, and spin coating.

At this time, it is desirable to form the film without using a binder substantially. If a binder is used, the amount of the binder used is preferably 5% by weight or less based on the photochromic material. That is, as described above, the feature of using the diheteroarylethene-based compound, which is a preferred compound of the present invention, is that the recording layer can be formed substantially without using a binder, whereby the dichromate as a photochromic material molecule can be formed. An optical recording medium having a high density of the heteroarylethene compound and capable of recording at a high density can be obtained.

In the near-field optical recording medium of the present invention, the optical density (OD value) of the recording layer is usually 0.4 or more, preferably 0.6 or more for a film thickness of 100 nm.

The substrate used for the near-field optical recording medium of the present invention may be either transparent or opaque to the light used. Examples of the material of the substrate include supports of general recording materials such as glass, plastic, paper, plate-like or foil-like metal, and among these, plastic is suitable from various points. As plastic, acrylic resin,
Methacrylic resin, vinyl acetate resin, vinyl chloride resin,
Examples include nitrocellulose, polyethylene resin, polypropylene resin, polycarbonate resin, polyimide resin, and polysulfone resin.

The thickness of the recording layer formed on such a substrate is preferably 0.05 to 1 μm, particularly preferably 0.1 to 0.6 μm.

When a binder is used for forming the recording layer, the binder may be polyester resin, polystyrene resin, polyvinyl butyral resin, polyvinylidene chloride, polyvinyl chloride, polymethyl methacrylate, polyvinyl acetate, or cellulose acetate. ,Epoxy resin,
A phenol resin or the like can be used.

When a recording layer is formed on a substrate, a reflective layer, an undercoat layer, a protective layer, and the like can be provided as necessary.

The recording layer formed in this way is an amorphous layer of a photochromic material, and therefore has a very smooth surface. In particular, in the present invention, the recording layer is used for a near-field optical recording medium. The surface of the recording layer has a flatness (Ra) of 3 nm or less, preferably 1 nm.
It is preferable to have the following excellent smoothness.

In order to perform near-field optical recording using the optical recording medium of the present invention, since the distance from the evanescent light source to the surface of the recording medium is about several hundreds of nanometers, the surface of the recording medium must be uneven. The difference is preferably 100 nm or less.

In the near-field optical recording method for a near-field optical recording medium of the present invention, the near-field optical recording medium of the present invention is used, and the entire surface of the recording layer of the optical recording medium is irradiated with ultraviolet rays in advance. After the photochromic material contained in the recording layer is closed, a signal is recorded by opening the photochromic material with evanescent light having a beam spot diameter smaller than the wavelength of the light source.

Hereinafter, the near-field optical recording method of the present invention will be described more specifically with reference to the drawings.

FIG. 1 is a schematic diagram showing an example of a recording / reproducing / erasing apparatus suitable for the present invention.

A light source having a size smaller than the wavelength is a capillary for a microelectrode (having a pore size smaller than the wavelength, for example, 0.5 μm or less, preferably 0.2 μm or less, more preferably 0.2 μm or less. 0.1 μm or less) 10, He-Ne laser light 1, Ar laser light 2, or semiconductor laser light is introduced by glass fiber 4 via half mirror 3, or an EL element is built in microelectrode capillary 10. Can be obtained.

For recording, reproduction and erasing, the principle of a near-field optical scanning microscope (photon STM) is adopted. That is, for recording, the light source is mounted in the electrostrictive element 5, and the position control circuit 7 first approaches the recording medium 9 from the Z-axis direction (normally 0.1 μm).
Then, scanning is performed in the X- and Y-axis directions, and the light source is turned ON / OFF in accordance with the input information and recorded. This recording induces a change in the absorbance of the medium 9.

Reproduction is performed as follows. A light source similar to the above is used. However, light having a different wavelength from that for recording may be introduced into the same capillary 10 for use. By modulating the intensity of the reproducing light source or modulating the position in the Z-axis direction, reflected light from the recording surface (in this case, a reflective film is provided below the recording surface) or transmitted light is transmitted to the front or rear surface of the recording surface. It is detected by the photoelectric conversion element 6 placed. Alternatively, detection may be directly performed without performing such modulation. Since the reflected light or transmitted light from the portion where the absorbance has changed by recording has changed, the difference between the recorded pits and the pits that have not been recorded, that is, the recorded information is based on the difference in reflected light or transmitted light intensity. Can be read. Reference numeral 8 denotes a read signal processing circuit for reading.

Erasing is performed using ultraviolet light.

As described above, by using the photochromic material as the recording material and using the evanescent light having the beam spot diameter smaller than the wavelength of the light source as the recording / reproducing / erasing light source, the size of the beam spot diameter becomes zero. .1 .mu.m, 100 times the density of the current optical recording, and 0.01 .mu.m, 1 times the density of the current optical recording.
Recording at a density of 0000 times becomes possible. Moreover, in the present invention, since the recording layer is an amorphous layer of a photochromic material, high density recording can be performed on a recording layer having a high density of photochromic material molecules and excellent surface smoothness.

[0068]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to Production Examples, Examples, and Comparative Examples. However, the present invention is not limited to the following Examples unless it exceeds the gist thereof. .

Production Example 1

[0070]

Embedded image

The above compound (i) 1.4 g (2.99 mm
ol), 15 ml of nitrobenzene was added, the mixture was cooled with ice water, and 0.3 ml (3 mmol) of Cl ₂ CHOCH ₃ was added. Here, 403 mg (3 mmol) of AlCl ₃
Was added by grinding, extracted with chloroform, and subjected to column separation with a solvent of hexane-chloroform (1: 1) to obtain the above compound (ii). The reaction yield was 70%.

Next, 27.4 g of bromodiphenylmethane
(100 mmol) and triphenylphosphine 28.8
g (110 mmol) was dissolved in 250 ml of benzene and heated under reflux for 16 hours. After cooling, the deposited precipitate was filtered to obtain a white solid (iii). The reaction yield was 30%.

1.06 g of the obtained compound (iii)
(2.09 mmol) in THF (tetrahydrofuran)
, And 1.3 ml (2.09 mmol) of n-butyllithium was added dropwise at 0 ° C under an argon gas atmosphere. After stirring for 20 minutes, 1 g of compound (ii) (2.0 g)
2 mmol) and stirred at room temperature for 24 hours.

Extraction was performed with diethyl ether, and separation and purification were performed using a chloroform solvent column.

Example 1 A hexane solution (10%) of the following compound (Exemplified Compound (D) having a glass transition point of 75 ° C.) obtained in Production Example 1
0 mg / 10 ml) was dropped on a glass substrate, and a thin film was formed by spin coating.

[0076]

Embedded image

The spin coating conditions were as follows: rotation speed 1000 rpm
For 5 minutes and then at a rotation speed of 3000 rpm for 10 seconds to form a 350 nm thick amorphous recording layer. The OD value per 100 nm of the film thickness of this recording layer was 0.7.

The average surface roughness (Ra) of the formed amorphous film was measured by AFM (scanning tunneling microscope) and found to be 1 nm or less. The obtained recording layer was entirely transparent without any opaque portions.

Next, recording, reproduction, and erasing were performed using the optical recording medium thus prepared.

Optical recording was performed as follows. First, the entire surface of the recording layer was irradiated with ultraviolet light (366 nm) to be colored blue. Next, a near-field microscope (NSOM (near
field scanning optical mi
(crossscope): TM manufactured by Topometrix, Inc.
X2100 Aurora) and irradiated with 632.8 nm light from a He-Ne laser beam for 1 minute. Thereafter, the entire surface was scanned with the laser light intensity reduced to 1/20. As a result, it was confirmed that a spot having a diameter of about 80 nm was recorded. These writing spots were erased by irradiation with ultraviolet light (366 nm).

The temperature of the optical recording medium is 80
After conducting a storage stability test under high humidity and high temperature of 200 ° C. and a humidity of 85% for 200 hours, recording, reproduction and erasing were performed in the same manner as above, and a signal spot was normally detected and erased similarly. It was possible.

Example 2 In accordance with Production Example 1, bis (2,4
-Dimethyl-5- (4-t-butyl) phenylthiophen-3-yl) perfluorocyclopentene (the above exemplified compound (A); glass transition point was 70 ° C).

[0083]

Embedded image

When this compound (A) was used to form a film on a glass substrate in the same manner as in Example 1, a 350 nm thick amorphous recording layer was formed. The OD value per 100 nm of the film thickness of this recording layer was 0.65.

When the average surface roughness (Ra) of the formed amorphous film was measured by AFM (scanning tunneling microscope), it was 1 nm or less. The obtained recording layer was entirely transparent without any opaque portions.

Next, recording, reproduction and erasing were performed in the same manner as in Example 1 using this optical recording medium. As a result, FIG.
As shown in (a), it was confirmed that a spot having a diameter of about 80 nm was recorded.

Next, the same write operation was performed once again at another place, and read was performed. As a result, FIG.
As shown in (b), the second minute spot (about 80 nm)
Diameter) writing was achieved.

These writing spots are made of ultraviolet light (3
66 nm).

After the storage stability test under high humidity and high temperature conducted in the same manner as in Example 1, the signal recording spot was normally detected and the erasure was possible.

Comparative Example 1 A perfluorocyclopentene-based photochromic compound having a glass transition point of 40 ° C. represented by the following structural formula was used in place of the compound (D) in Example 1.
When a film was formed on a glass substrate in the same manner as in the above, an amorphous layer made of the compound was obtained.
The OD value per 00 nm was as low as 0.035.
Was 1/20.

[0091]

Embedded image

Next, Example 1 was performed using this optical recording medium.
Similarly to the above, when optical recording was performed on the obtained layer,
The sensitivity was low, and it was confirmed that a spot having a diameter of about 80 nm was recorded. However, after performing a storage stability test under high temperature and high humidity as in Example 1, the recorded spot was observed. The shape was deformed and could not be detected normally.

[0093]

As described in detail above, according to the present invention, by using an amorphous photochromic material having a glass transition point of 55 ° C. or higher for a recording layer, recording is performed using evanescent light having a size smaller than the wavelength. It is possible to provide a near-field optical recording medium that can be reproduced / erased and has little deterioration of a signal after recording.

Moreover, the near-field optical recording medium and the near-field optical recording method, which are amorphous, have a high density of photochromic material molecules, have excellent surface smoothness, and are capable of extremely high-density recording. You. Further, it is presumed that the glass transition point of the photochromic material is 55 ° C. or higher, so that signal deterioration of the recorded optical recording medium in an environment conceivable in normal use is avoided and the photochromic material is stably maintained. You.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of a recording / reproducing / erasing apparatus suitable for the present invention.

FIG. 2 is an NSOM optical image of a recording spot in Example 1.

[Explanation of symbols]

 Reference Signs List 1 He-Ne laser 2 Ar laser 3 Half mirror 4 Glass fiber 5 Electrostrictive element (for X, Y, Z axis control) 6 Photoelectric conversion element (detector) 7 Position control circuit 8 Readout signal processing circuit 9 Recording medium 10 Micro Capillary for electrode

Claims (12)

[Claims] 1. A near-field optical recording medium capable of recording / reproducing / erasing using evanescent light having a beam spot diameter smaller than the wavelength of a light source, wherein a recording layer of the optical recording medium has a glass transition. A near-field optical recording medium comprising an amorphous layer mainly composed of a photochromic material having a temperature of 55 ° C. or higher. 2. The near-field optical recording medium according to claim 1, wherein the photochromic material is a diheteroarylethene-based compound having a glass transition point of 55 ° C. or higher. 3. The near-field optical recording medium according to claim 2, wherein the diheteroarylethene compound has a pyrrole ring, a thiophene ring, a furan ring, or a selenophene ring in a heteroaryl portion. 4. The near-field optical recording medium according to claim 2, wherein the diheteroarylethene-based compound is a compound represented by the following general formula (I). Embedded image 5. The near-field optical recording medium according to claim 4, wherein at least one of X and Y in the general formula (I) has the following structure (a ′). Embedded image 6. The near-field optical recording medium according to claim 4, wherein both X and Y in the general formula (I) have the structure (b). 7. The method according to claim 5, wherein X in the general formula (I) is the structure (a ′) and Y is the structure (b) (provided that R ⁴ , R ⁵ and R ⁶ is not a hydrogen atom). 8. The method according to claim 5, wherein both X and Y in the general formula (I) have the structure (a ′) (provided that:
R ⁵ and R ⁶ in the same molecule are not all hydrogen atoms). 9. The near-field optical recording medium according to claim 1, wherein the glass transition point of the photochromic material is 60 ° C. or higher. 10. The recording layer according to claim 1, wherein the recording layer is a layer containing the amorphous diheteroarylethene-based compound and formed substantially without a binder. Characteristic near-field optical recording medium. 11. The near-field according to claim 1, wherein the optical density (OD value) of the recording layer is 0.4 or more when the film thickness is 100 nm. Optical recording medium. 12. The near-field optical recording medium according to claim 1, wherein the entire surface of the recording layer of the near-field optical recording medium is irradiated with ultraviolet rays in advance and is included in the recording layer. A near-field optical recording method, comprising: forming a ring of a photochromic material; and recording a signal by opening the photochromic material with evanescent light having a beam spot diameter smaller than the wavelength of a light source.