JP2000019572A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium capable of recording information to a high density without impression of electric fields from outside by sufficiently increasing the ratio (D/μ) of a diffusion coefft. D to mobility μwithout excessively making the mobility (μ) small. SOLUTION: This optical recording medium contains a charge generating material, charge transfer material and non-linear optical material and records the information by irradiation with electromagnetic waves. This charge transfer material contains a compd. expressed by the formula. In the formula, R1, R2, R3 and R4 are methyl groups, isopropyl groups, t-butyl groups, aryl groups and heterocyclic groups. Otherwise, at least one of R1 and R2 may form a ring together with part of an adjacent nitrogen atom and benzene ring.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an optical recording medium.

[0002]

2. Description of the Related Art A photorefractive medium is known as one of optical recording media for performing recording at a much higher density than a conventional magneto-optical recording or photothermal phase change type medium (such as an optical disk). This photorefractive medium is a medium that can record large-capacity data such as a high-density image, and changes the refractive index of the recording layer by the following mechanism. That is, by irradiating an electromagnetic wave, the electric charges existing therein are spatially separated, and the electric field generated by the electric charges changes the refractive index of the recording material. Therefore, if the electric field generated inside the medium is increased, it is possible to obtain a larger change in the refractive index due to the electro-optic effect. Since such a photorefractive medium can directly record an interference pattern of an electromagnetic wave as a refractive index grating, it is also expected to be applied to a holographic memory, an optical operation element, and the like.

In recent years, photorefractive media using an organic polymer compound have been actively developed due to ease of production (for example, Japanese Patent Publication No. 6-55901).
However, when using these media, it was necessary to provide electrodes and apply an electric field from the outside (for example, JP-A-6-175167). This is due to the following circumstances.

When a photorefractive medium is irradiated with an interference pattern of electromagnetic waves, non-equilibrium carriers corresponding to the intensity of the electromagnetic waves are generated in the photorefractive medium. The external electric field E _ex is set so as to be parallel to the electromagnetic wave irradiation surface.
Is applied to the photorefractive medium, the electric field E generated is represented by the following equation (1). _{E = E 0 [(1 +} iE ex / E d) / {1 + iE ex / (E d + E q)}] (I 1 + I 0) (1) E 0 = iE d / (1 + E d / E q) (2) E _d = (2πD) / (μΛ) (3) E _q = (eNΛ) / (2πε) (4) I ₀ is the spatial average of the irradiation light intensity, and I ₁ is the maximum value and the minimum value of the irradiation light intensity. And the difference. Λ is the distance (spatial wavelength) between the closest local maximum values. ε is the dielectric constant of the photorefractive medium, N is the space charge concentration, D is the diffusion coefficient, and μ is the mobility. e is an elementary charge amount, i is an imaginary unit, and represents a phase (for example, Pochi Y
eh, Introduction to Photo
refractive Nonlinear Opti
cs, John Wiley & Sons, March 1993
chapter).

Physically, E _d represents the electric field due to charge diffusion, and E _q represents the spatial electric field due to ionized impurities and immobile charges. Usually, between the diffusion coefficient D and the mobility μ, Einstein's relational expression D
/ Μ = kT / e (k is Boltzmann's constant, T is absolute temperature)
Is considered to hold, so that E _d is a constant that does not depend on the substance. Therefore, to obtain a large electric field E,
Large enough to E _q compared to E _d, and it is necessary to increase the E _ex. In order to increase the E _q is compared with the E _d, in the above formula (4), it is necessary to increase the Λ and N. However, when Λ is increased, the density of interference fringes decreases, so that the recording density of a recording element decreases. On the other hand, when the concentration N of the space charge is increased, there is a disadvantage that the mobility is reduced due to scattering by the charge.

[0006] The time required to form an electric field when an external electric field is applied is determined by the drift speed of the electric charge, so that a decrease in the mobility means a decrease in the writing speed. Therefore, a decrease in mobility must be avoided as much as possible.

When an electric field E _ex is applied from the outside,
Movable charges (carriers) move in the direction of the electric field,
E substantially coincides with the direction of the external electric field. Since the refractive index modulation by the Pockels effect is performed in the direction of the electric field, in order to read out the change in the refractive index by using an electromagnetic wave, the direction of the electric field must be made closer to the direction perpendicular to the incident direction of the electromagnetic wave.
For this reason, it is necessary to devise the shape of the electrode to which an electric field is applied, and it has not been possible to manufacture the electrode at low cost. Further, the use has been limited, for example, it cannot be used for an ordinary optical disk.

[0008]

According to the present invention, the ratio (D / μ) of the diffusion coefficient D to the mobility μ is sufficiently increased without excessively reducing the mobility (μ), and the electric field is externally applied. An object of the present invention is to provide an optical recording medium capable of recording information at high density without applying a voltage.

[0009]

According to the present invention, there is provided an optical recording medium containing a charge generating material, a charge transporting material, and a non-linear optical material for recording information by irradiating electromagnetic waves. The charge transport material provides an optical recording medium comprising a compound represented by the following general formula (1).

[0010]

Embedded image (In the above general formula (1), R ¹ , R ² , R ³ and R
⁴ is a methyl group, an isopropyl group, a t-butyl group, an aryl group, and a heterocyclic group. Alternatively, at least one of R ¹ and R ² may form a ring together with the adjacent nitrogen atom and part of the benzene ring. The present invention also relates to an optical recording medium that contains a charge-donating molecule and a charge-accepting molecule and records information by irradiation with an electromagnetic wave, wherein the charge-donating molecule has the following general formula (1)
An optical recording medium comprising a compound represented by the formula:

[0011]

Embedded image (In the above general formula (1), R ¹ , R ² , R ³ and R
⁴ is a methyl group, an isopropyl group, a t-butyl group, an aryl group, and a heterocyclic group. Alternatively, at least one of R ¹ and R ² may form a ring together with the adjacent nitrogen atom and part of the benzene ring. Hereinafter, the present invention will be described in detail.

The optical recording medium of the present invention spatially separates charges of different signs by irradiating an electromagnetic wave, and records a light irradiation pattern by a change in optical characteristics due to an internal electric field generated due to the charges. An optical memory comprising a specific compound as a charge transporting material or a charge donating molecule. The form of the aforementioned compound is not limited. The optical characteristics are the energy, wavelength, phase, and the like between the light incident on the substance and the output light, such as the light absorption coefficient or the emission efficiency of fluorescence and phosphorescence or the refractive index of light, and the reflectance and diffraction efficiency of light. , Strength, or physical properties that cause a change in direction.

The present inventors have analyzed the transient photocurrent and found that
Obtained a method that enables simultaneous measurement of mobility and diffusion coefficient (Hirao, Nishizawa, Sugiuchi, Physical Review)
wLetters. Vol. 75, no. 9, pp17
87-1790 (1995)). This method is performed as follows. That is, first, a film-shaped sample is sandwiched between two electrodes, and a specific pulse light is irradiated from one electrode side. Here, the specific pulse light is a pulse light that generates an optical carrier that is absorbed only near the interface, and is, for example, a pulse of about 1 nanosecond. The diffusion coefficient D and the mobility μ can be obtained by combining the experimental value of the transient current flowing at that time with the equation obtained analytically.

Using this method, the diffusion coefficient D and the mobility μ are measured for a system in which various charge transporting materials are dispersed in a polymer, and the ratio of the diffusion coefficient to the mobility (D / μ) is measured. I asked. As a result, the specific charge transport material is extremely large (D /
μ). Then, (D / mu) is the greater, the electric field E _d becomes larger due to the diffusion of the foregoing equation (1), as a result, found that an electric field applied from the outside is not necessary.

Usually, the Einstein relation D / μ
= KT / e (k is Boltzmann's constant, T is absolute temperature), so D / μ is a constant independent of the material. However, in the present invention, the charge transport molecules are used in an amorphous state instead of the most stable crystalline state, and the overlap of the wave functions between the charge transport molecules is sufficiently small. Therefore, there is almost no transfer of energy between the two molecules, and in such a state, the charge cannot always be transferred to a stable molecule. Therefore, in the present invention, a “thermal equilibrium state” which is a condition for satisfying the Einstein relational expression does not occur. (For example, R. Richert, L. Poutme
ier, and H .; Bassler, Phys. Re
v. Lett. 63, 547 (1989)). As a result, D / μ depends on the material.

The possibility that D / μ does not match Einstein's relation has only been suggested using simulation (PM Borsenberge).
r, E. H. Magin, M .; van der Auw
eraer, and F. C. de Schryve
r, Phys. Status Solidi (a), 1
40, 9 (1993)). The present inventors have actually measured and confirmed it.

In the optical recording medium of the present invention, a pair of a positive charge and a negative charge is generated by light irradiation in a random electric field caused by a dipole moment of a matrix or constituent molecules. Charge (carrier) of one of these signs
Since a molecule capable of transporting only electrons is interposed, diffusion is caused by a random electric field, and a positive charge and a negative charge are spatially separated. The electronic structure of the substance is modulated by the diffusion electric field generated at this time, thereby modulating the optical characteristics of the substance such as the absorption coefficient, the luminescence coefficient and the refractive index. Or,
The life of an excited state by application of light, heat, or the like is significantly prolonged by an electric field. The optical recording medium of the present invention is an optical recording medium for reading such changes in characteristics.

First, the optical recording medium of the first invention will be described.

The optical recording medium according to the first invention contains a charge generating material, a charge transporting material, and a material having nonlinear optical characteristics.
It contains a specific compound as a charge transport material.

As the charge generating material, any material that absorbs writing light and generates charges can be used. Such materials include, for example, selenium and selenium alloys,
Inorganic photoconductors such as CdS, CdSe, AsSe, ZnO, α-Si, etc .; phthalocyanine dyes / pigments such as metal phthalocyanine, metal-free phthalocyanine, and derivatives thereof; naphthalocyanine dyes / pigments; azo such as monoazo, disazo and trisazo Dyes / pigments, perylene dyes, indigo dyes, quinacridone dyes, polycyclic quinone dyes and pigments such as anthraquinone and anthantrone, cyanine dyes and pigments such as TTF-TCNQ Examples include a charge transfer complex comprising an acceptor and an electron donor, an azulenium salt, fullerene represented by C ₆₀ and C ₇₀ , and derivatives thereof.

These charge generating materials may be used alone or in combination of two or more compounds.

Since the charge generating material needs to absorb writing light and generate charges, when a charge generating material having an extremely high optical density with respect to the writing light is used, the charge inside the element is reduced. The writing light may not reach the generated material. In order to avoid such inconvenience, it is preferable that the optical density of the element is in the range of 10 ^-6 to 10.

Also, when the addition concentration of the charge generating material is too high, the writing light does not reach the inside, so that it is difficult to write the inside. On the other hand, when the addition concentration is excessively low, the generated charge density is low, and a desired internal electric field cannot be obtained. Therefore, it is preferable to adjust the addition concentration of the charge generating material so that the optical density of the device is in the range of 10 ^-6 to 10.

Specifically, it is desired that the amount of the charge generating material added is about 0.001 to 15% by weight based on the entire recording medium. When the content is less than 0.001% by weight, the charge per unit volume generated by light irradiation is small,
If the internal charge exceeds 15% by weight, the probability of association between the charge generating materials increases, and the conductivity of the medium may increase, so that a high internal electric field may not be generated.

The charge transporting material transports holes or electrons, and has a function of transporting charges by hopping conduction, for example. The charge transporting material contained in the optical recording medium of the first invention needs to contain a compound represented by the following general formula (1).

[0026]

Embedded image (In the above general formula (1), R ¹ , R ² , R ³ and R
⁴ is a methyl group, an isopropyl group, a t-butyl group, an aryl group, and a heterocyclic group. Alternatively, at least one of R ¹ and R ² may form a ring together with the adjacent nitrogen atom and part of the benzene ring. In the general formula (1), examples of the aryl group that can be introduced as R ^{1 to} R ⁴ include phenyl C ₆ H
₅ -, tolyl CH ₃ C ₆ H ₄ -, xylyl (CH _{3) 2}
C ₆ H ₃ —, naphthyl C ₁₀ H ₇ — (CH ₃ ) ₃ C ₆ H ₄
-And the like. These may be introduced with the following substituents.

[0027]

Embedded image In consideration of compatibility with the matrix, a phenyl group is particularly preferable as the aryl group.

Examples of the heterocyclic group include the following.

[0029]

Embedded image When at least one of R ¹ and R ² forms a ring together with an adjacent nitrogen atom and part of a benzene ring, the number of atoms constituting the ring is preferably 4 to 6, preferably 5 or 6. Most preferably, it forms a member ring. Specific examples of such compounds include the following.

[0030]

Embedded image The compounds described above can be used as a charge transporting material in the optical recording medium of the first invention using only one kind or a plurality of kinds.

In the optical recording medium of the first invention, it is necessary that the compound represented by the general formula (1) is contained in the charge transporting material in an amount of at least 50% by weight. When the content is less than 50% by weight, it is difficult to form a high internal electric field without applying a voltage to obtain a high refractive index modulation.

If this condition is satisfied, another compound may be contained as the second charge transporting material. In the case where the second charge transporting material functions as a trapping material, the ionization potential of the second charge transporting material is preferably not significantly different from the ionization potential of the first charge transporting material. It is desired that the difference in ionization potential is 0.5 eV or less.

The second charge transporting material may be a molecule alone or a polymer, or may be a copolymer with another polymer. For example, the following are listed.
That is, indole, carbazole, oxazole,
Nitrogen-containing cyclic compounds such as isoxazole, thiazole, imidazole, pyrazole, oxadiazole, pyrazoline, thithiazole, and triazole, or derivatives thereof, or compounds having these in the main chain or side chain, hydrazone compounds, triphenylamines Quinone compounds such as triphenylmethanes, butadienes, stilbenes, anthraquinone diphenoquinone or derivatives thereof, or compounds having these in the main chain or side chain, fullerenes such as C ₆₀ and C ₇₀ and derivatives thereof. . Further, π-conjugated polymers and oligomers such as polyacetylene, polypyrrole, polythiophene, and polyaniline; or σ-conjugated polymers and oligomers such as polysilane and polygermane; and polycyclic aromatic compounds such as anthracene, pyrene, phenanthrene, and coronene And the like.

The charge transport material may be added in an amount of 5 to 5 in the optical recording medium.
It is desired to be about 90% by weight. If the content is less than 5% by weight, it is difficult to obtain a sufficient function, while 90%
If the content is more than 10% by weight, the space charge may not be easily held, and may not function as an optical recording medium.

Carriers generated from the above-described charge generating material are injected into the charge transporting material, and then move between the charge transporting materials to form an electric field. Therefore, it is desirable that the ionization potential and the electron affinity of the used charge transporting material have the following relationship with other molecules. That is, when the carrier is a hole, it is preferable that the ionization potential I _P (CGM) of the charge generation material and the ionization potential I _P (CTM) of the charge transport material satisfy the following relationship.

I _P (CTM) <I _P (CGM) At this time, since it is required that electrons do not move from the charge generating material, the electron affinity of the charge generating material Ｃ (CGM)
And the electron affinity と (CTM) of the charge transport material preferably satisfy the following relationship.

Χ (CTM) <χ (CGM) On the other hand, when the carrier is an electron, the ionization potential and the electron affinity of the charge generating material and the charge transporting material are desired to have the following relationship.

I _P (CGM) <I _P (CTM) χ (CGM) <χ (CTM) Furthermore, it is desirable that there is no interaction with other molecules such as a nonlinear optical material or a host matrix.

Examples of the nonlinear optical material contained in the first optical recording medium include the following.

1) The absorption coefficient or the reflectance changes due to the Franz-Keldysh effect, for example, Si, Ge,
_{Si x Ge (1-x)} IV group semiconductor and the eutectic, and mixtures thereof, such as; III-V group semiconductor materials such as GaAs; ZnSe
II-VI semiconductor materials such as chalcopyrite-based semiconductor materials; 2) those whose absorption coefficient, reflectance or luminous efficiency changes due to exciton effect, for example, phthalocyanine and its derivatives, fullerenes and the like. Its derivatives, pyrrolopyrrole and its derivatives, anthracene and its derivatives, azulene and its derivatives, molecular crystals and organic semiconductor materials such as azo compounds, polyacetylene and its derivatives, polydiacetylene and its derivatives, polysilane and its derivatives, polyparaphenylene And its derivatives, polyparaphenylenevinylene and its derivatives, polythiophene and its derivatives, polyparathienylenevinylene and its derivatives, polypyrrole and its derivatives, and polyaniline and its derivatives. Low-dimensional materials typified by molecules and σ-conjugated polymers 3) Materials whose refractive index changes due to the Pockels effect or Kerr effect, for example, second-order nonlinear optical materials such as BaSrO and DAN 4) Changes in optical characteristics in the excited state 4-1) Those which are excited by light and can stabilize the dipole moment of the excited state by an electric field, for example, photochromic materials such as spiropyran and derivatives thereof, fulgides and derivatives thereof 4-2) Thermochromic materials such as those that can be excited by heat and stabilize the dipole moment in the excited state by an electric field These materials can be used alone or in combination and mixed in a medium in a molecular state or a particle state. It is desirable. Note that the nonlinear optical material may also serve as the charge generation material and the charge transport material as described above.

In any case, the nonlinear optical material is preferably contained in the optical recording medium of the first invention in an amount of about 0.1% by weight to 90% by weight. If the amount is less than 0.1% by weight, it is difficult to obtain a sufficient refractive index modulation due to an electro-optic effect caused by an internal electric field. On the other hand, when the content exceeds 90% by weight, when the nonlinear optical material does not have the charge transport function, the charge is not transported, and the internal electric field may not be formed.

The optical recording medium of the first invention can be produced, for example, by mixing a charge generating material, a charge transporting material and a nonlinear optical material to obtain a solution and evaporating the solvent. Examples of the solvent that can be used here include trichloroethane, toluene and the like. Alternatively, the optical recording medium of the first invention may be manufactured without using a solvent, for example, by mixing fine particles in a state where a molecular mixture is heated and rapidly cooling the mixture. When the components such as the charge generation material are not polymers, an inorganic or organic substance may be added as a matrix to the first optical recording medium.

As the inorganic matrix, SiO ₂
Amorphous structure represented by
It may be a porous matrix. For example, SiO ₂ , Zr
O ₂ , TiO ₂ , Al ₂ O ₃ , Na ₂ O, K ₂ O, Li
₂ O, MgO, ZnO, CaO, PbO, BaO, B ₂
O ₃ , P ₂ O ₅ , SrO, La ₂ O _{3 and the} like. Further, fine particles of a compound semiconductor or metal containing a chalcogen element as a component may be contained. further,
To develop the Pockels effect, use LiNbO ₃ or K
A material exhibiting an electro-optical effect, such as a dielectric such as DP, may be contained.

A typical example of the organic matrix is a polymer having an amorphous structure.
For example, polyethylene resin, nylon resin, polyester resin, polystyrene resin, polycarbonate resin, acrylic resin, phenoxy resin, polyarylate resin, butyral resin, styrene-butadiene copolymer resin, polyvinyl acetal resin, diallyl phthalate resin, silicone resin, polysulfone Resin, vinyl acetate resin, polyphenylene oxide resin, alkyd resin, styrene
Maleic anhydride copolymer resin, phenol resin, vinyl chloride-vinyl acetate copolymer resin, polyester carbonate, polyvinyl chloride, polyvinyl acetal, paraffin wax, and the like. Further, a material having a function as a charge transporting material such as polysilane can also be used.

The above-mentioned polymers can be used alone or in combination of two or more.

In the optical recording medium of the first invention, when the recording light is irradiated, the charge generating material absorbs the recording light to generate carriers. The carriers thus generated are transported by the charge transport material to generate a spatial electric field inside the medium, and recording is performed. The charge transport material contained in the optical recording medium has a carrier diffusion coefficient (D) when no electric field is applied, which is much larger than the drift mobility (μ). Therefore, (D / μ) can be remarkably increased while securing a certain degree of mobility μ.
A high internal electric field is formed in the optical recording medium of the first invention.

Next, the optical recording medium of the second invention will be described in detail.

The optical recording medium of the second invention contains a charge-donating molecule and a charge-accepting molecule, and contains a specific compound as a charge-donating molecule.

The charge-donating molecule has a property of transporting holes. In the recording medium of the second invention, the general formula (1) described in the first invention is used.
It is necessary to contain the compound represented by

As in the case of the first invention, the compound represented by the general formula (1) may be compounded as a charge-donating molecule in the optical recording medium of the second invention by using only one kind or a plurality of kinds. can do.

In the optical recording medium of the second invention, the compound represented by the general formula (1) needs to be contained at least 50% by weight or more in the charge donating molecule. When the content is less than 50% by weight, it is difficult to form an internal electric field of a desired size only by light irradiation without applying an electric field from the outside.

If this condition is satisfied, another compound may be contained as the second charge-donating molecule. It is preferable that the difference between the ionization potential of the second charge-donating molecule and the ionization potential of the first charge-donating molecule is 0.5 eV or less.

As the second charge-donating molecule, for example,
A trapping material for trapping charges by using a material having a smaller ionization potential than the first charge-donating molecule is given.

It is desired that the amount of the charge-donating molecule added is about 30 to 95% by weight in the optical recording medium of the second invention. When the content is less than 30% by weight, it is difficult to obtain a sufficient function. On the other hand, if it exceeds 95% by weight, the film forming property of the medium may be extremely deteriorated.

The charge-accepting molecule, which is another component of the optical recording medium of the second invention, is a molecule having a property of easily receiving electrons, and specifically, 1,3,5-trinitrobenzene, picrin Acids, nitro compounds such as 9-nitroanthracene and 3,6-dinitrocarbazole, cyanides such as 9-cyanoanthracene, acid anhydrides such as phthalic anhydride, tetrabromo-p-xylene;
Halogen compounds such as triphenylchloromethane, chloranyl, quinones such as acenaphthenequinone, benzyl,
Examples include aromatic ketones such as benzoyl and 2,4,5,7-tetranitrofluorenone.

In the optical recording medium according to the second aspect, the above-described charge-accepting molecules are different from the charge-donating molecules by
It is preferable to be blended at a ratio of about 0.001 to 10% by weight. When the amount is less than 0.001% by weight, the amount of charge generation is small because the concentration of the charge transfer complex is extremely low.
Writing becomes difficult. On the other hand, if it exceeds 10% by weight,
The concentration of the charge transfer complex becomes too high, the optical density of the medium increases, and the recording / reading light does not reach the inside of the medium,
Recording / reproduction may not be possible.

The optical recording medium of the second invention can be produced by dissolving a charge-donating molecule and a charge-accepting molecule in a predetermined solvent to obtain a solution, and then evaporating the solvent. Alternatively, the optical recording medium of the second invention may be manufactured without using a solvent, for example, by mixing fine particles in a state where a molecular mixture is heated and rapidly cooling the mixture.

As in the case of the first optical recording medium,
When none of the components such as the charge-donating molecule is a polymer, a polymer as a matrix may be blended. Examples of the polymer that can be used here include those described above.

In the optical recording medium of the second invention, a charge transfer complex is formed by the interaction between the charge-donating molecule for transporting holes and the charge-accepting molecule for transporting electrons.
This charge transfer complex has a charge generation ability. By appropriately combining the charge-donating molecule and the charge-accepting molecule, the optical density of the medium and the carrier generation efficiency can be arbitrarily designed. The generated carriers are mainly transported by the charge-donating molecules, and a spatial electric field is generated inside the medium without applying an electric field from the outside. Refractive index modulation occurs due to the electro-optic effect of the molecules that make up the medium, which makes it possible to read. Since the charge transfer complex formed in the medium has a large contribution to the electro-optic effect, the optical recording medium of the second invention exhibits high refractive index modulation.

The optical recording medium of the present invention as described above can record / reproduce information using any recording device and reproducing device.

One example of the use of the optical recording medium of the present invention is a holographic memory. In this case, information is recorded by forming interference fringes by two light beams. (Coherent) light can be used. In order to obtain interference fringes, it is preferable to use the light of the same light source after splitting it. However, the two light sources having the same output wavelength are fed back to each other (output light is input to the other light source), and so on. Can also be used.

When recording information, information is added to one of the two lights, and interference fringes generated between the two lights are recorded on a medium. For this reason, an optical path difference is generated between the two lights, so that interference fringes do not occur if the light has a short coherent length. For this reason, a laser or etalon having a coherence longer than the optical path difference is preferable as the light source. Usually, considering the application to computer terminals, video editing, database memory, etc., the optical path difference inside the device is considered to be about 1 cm or more, so gas lasers and semiconductor lasers, especially feedback, reduce the coherence length. An elongated semiconductor laser is preferably used as a light source.

Although writing may be performed by applying an electric field from the outside, the optical recording medium of the present invention is particularly effective when writing is performed without applying an electric field.

Further, the apparatus for recording information on an optical recording medium according to the present invention has the following features:
It is preferable to have a function that can also move a light source or a medium by also having a drive motor in the x, y, and z directions, or a function that can also change mirrors, such as a micromirror, and change the optical path.

The optical recording medium of the present invention can be used as a holographic memory or a bit memory.

A device to which the optical recording medium of the present invention can be applied will be described with reference to the drawings. FIG. 1 shows an outline of an example of an apparatus that can be used.

The illustrated device is a kind of holographic memory device, and simultaneously irradiates a medium with a signal light (or object light) 18 and a reference light 19 to record or read out interference fringes generated at that time. Device. As a method of producing the signal light 18, a method of passing light through a spatial modulator made of liquid crystal or the like is generally used. In the illustrated device, a micromirror is used as the spatial light modulator.

As shown in FIG. 1, the light emitted from the laser light source 13 is first
Divided into two. One of the divided lights is applied to the spatial light modulator 15 which is a micromirror array, and information of a digital signal is put on the light. That is, the signal light 18 is created by adding information depending on whether the light is guided to the optical path of the signal light or not depending on the inclination of the mirror. At this time, the beam diameter of the light applied to the micromirror array may be expanded by a beam expander or the like depending on the size of the micromirror array.

On the other hand, the other light split by the beam splitter 14 becomes the reference light 19.

The signal light 18 is transmitted to the micro mirror array 21
The recording is performed by simultaneously irradiating light from two directions to a desired position on the medium 25 after being reflected by the mirror 22.

For reading the recording, the reference beam 19 is reflected by the micromirror array in the same manner as during recording, and the medium 2 is read.
5 by irradiation. Regenerated light 20
Is a micromirror array or lens 2 located on the opposite side of the micromirror array used for recording via the medium.
3. The information is guided to the photodetector 24 using the mirror 16 and the information is detected as an electric signal.

FIG. 2 schematically shows another example of an apparatus to which the optical recording medium of the present invention can be applied.

The illustrated device is also a kind of holographic memory, and includes a signal light (or object light) 18 and a reference light 1.
And 9 are simultaneously irradiated on the medium, and the interference fringes generated at that time are recorded. As a method of producing the signal light 18, a method of passing light through a spatial modulator made of liquid crystal or the like is generally used. In the illustrated device, a micromirror is used as the spatial light modulator. The optical recording apparatus shown in FIG. 2 differs from that shown in FIG. 1 in that a micromirror array is not used for determining the optical path of the reference light.

As shown in FIG. 2, light emitted from the laser light source 13 is first
Divided into two lights. Light is applied to a spatial light modulator, which is a micromirror array, and information of a digital signal is carried on the light. That is, information is added depending on whether or not light is guided to the optical path of the signal light by the inclination of the mirror,
A signal light 18 is created. At this time, the micromirror array also has a function of guiding the signal light to a desired position on the medium 25. Further, as in the case of the optical recording apparatus shown in FIG. 1, the beam irradiated on the micromirror array may have a beam diameter expanded by a beam expander or the like depending on the size of the micromirror array.

On the other hand, the other light split by the beam splitter 14 becomes reference light.

Recording is performed by arranging the mirror 16 at a desired position on the recording medium 25 to guide the reference light 19 and irradiating the medium simultaneously with the signal light 18.

The recording is read out by irradiating the medium with the reference beam 19 in the same manner as during recording. The reproduced light 20 is guided to a photodetector using a mirror or a lens 23 located on the opposite side of the mirror used for recording via a medium, and detects information as an electric signal.

The information recorded on the optical recording medium of the present invention is:
Erasing can be performed in two ways as described below. The first method is to redistribute the trapped charge by uniformly irradiating the medium with light or applying heat,
The second method is to make the charge distribution uniform, and the second method is to recombine the trapped charges with charges of the opposite polarity.

The first method for making the charge distribution uniform is a method suitable for erasing information recorded in a wide area of the medium, while the second method for erasing the charge is local. It is suitable for erasing a record written in the. In this case, it is necessary to provide a mechanism for generating a charge having the opposite polarity to the medium. For example, when the generated charge is a carrier, it is necessary to include an electron generating material and a transport material thereof.

The optical recording medium of the present invention contains a specific compound as a charge transporting material or a charge donating molecule. Since this compound has a very large (D / μ), the electric field due to diffusion is large. As a result, an optical recording medium having a large recording capacity was obtained without requiring an electrode for applying an external electric field.

Although the conventional recording element has a large recording capacity, it requires electrodes, which limits its use as an element. However, as described above, the present invention does not require electrodes, so Applications can be significantly expanded and inexpensive to manufacture. Further, in the conventional material, since the refractive index is changed, it is necessary to increase the optical path difference by increasing the film thickness. However, in the present invention, the film thickness can be reduced. Therefore, it is easy to produce a uniform film,
This has made it possible to stabilize the characteristics of the device and to manufacture it at low cost.

In this way, an internal electric field can be formed without applying an external electric field, and an optical recording medium having high diffraction efficiency and capable of recording information at a high density has been realized.

[0083]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples of the present invention, but the present invention is not limited to these examples.

Example 1 A compound represented by the following chemical formula and a bisphenol A-type polycarbonate were mixed at a weight ratio of 2: 1 as a charge transporting material, and this was dissolved in trichloroethane to prepare a solution.

[0085]

Embedded image The obtained solution was applied to a substrate provided with a translucent aluminum electrode on quartz, and dried to form a film having a thickness of 10.2 μm. Gold was deposited on the upper surface of this film to obtain a sample for measuring mobility and diffusion coefficient.

The mobility and the diffusion coefficient of the obtained sample were determined by using Hirao, Nishizawa, Sugiuchi and Physical Review Le.
ters. Vol. 75, No. 9, pp1
787-1790 (1995). That is, a positive potential is applied to the aluminum side of the sample, and a smaller resistance (1 KΩ in the case of the present sample) is applied to the gold side than the sample, and the voltage is set to 0V. 0.9 ns from aluminum side
Irradiate a pulse of nitrogen laser and record the transient current flowing at this time. Since the penetration length of the light of the wavelength of the nitrogen laser into this film is about 1/50 of the film thickness, the carrier may be regarded as being generated in a sheet form at the aluminum electrode interface by this light. The diffusion coefficient D and the mobility μ are obtained by fitting the transient current using the Monte Carlo method according to the following equation.

[0087]

(Equation 1) In the equation, e and d are constants, each of which is an elementary charge amount and a film thickness, and J and t are variables, respectively, a current density and a time,
ν, D, and n ₀ are fitting parameters, which are a velocity (= μE, E is an electric field), a diffusion coefficient, and the number of carriers, respectively.

As a result, the logarithm of D and μ was proportional to the 乗 power of the electric field. Therefore, the logarithm of D is 1
/ 2 plotted from the extrapolated value to electric field 0 to D
_{E = 0} was determined, and similarly, the logarithm of μ was plotted against the 乗 power of the electric field, and μ _{E = 0} was calculated from the extrapolated value to the zero electric field. Finally, when D / μ at no electric field was obtained,
4.0. From this evaluation result, it was considered that the optical recording medium using the above-described charge transporting material can form a high internal electric field without applying an external electric field.

Next, in order to evaluate the performance as an optical recording medium, the diffraction efficiency of a diffraction grating due to a change in optical characteristics caused by an electric field formed in a film formed by light irradiation was measured.

FIG. 3 schematically shows an apparatus used for measuring diffraction efficiency.
Shown in

As shown in the figure, the beam of the helium-neon laser is divided into two beams, an object beam 33 and a reference beam 35.
By irradiating so as to intersect on the sample 31 formed on the transparent support layer 32, interference fringes due to laser light were formed on the sample. Due to the interference fringes thus generated, an internal electric field is generated to modulate optical characteristics, and a diffraction grating is formed on the medium. When used as an optical recording medium, the sample is irradiated with reflected light from an object for recording object light or light transmitted through a transmission type image display element (pager) 38 composed of a liquid crystal display element or the like. The reference light is applied so as to intersect and cover the irradiation surface. Writing was performed by leaving the apparatus as it was for 1 minute.

Thereafter, reproduction was performed by cutting off the object light 33 and irradiating only the reference light 35 as in writing. If writing has been performed, since the diffraction grating is formed in the medium as described above, the reference light 35 is diffracted by the medium, and the components of the reference light 35, the reflection direction component 36 of the object light, and the transmission direction component 34 And divided into

Therefore, the direction 34 in which the object light is transmitted
If an optical power beam for measuring the intensity of the reproducing beam and a photodetector 37 such as a CCD for taking in the reproduced image are installed in advance, the object light which should not be irradiated by the photodetector, That is, a reproduced image is observed and functions as an optical memory.

Here, the ratio (I _obj. / I _ref. ) Of the intensity (I _obj. ) Of the object light reproduced to the reference light and the intensity (I _ref. ) Of the irradiated reference light is obtained as the diffraction efficiency _. Was.

The sample was made of the above-described charge transport material, bisphenol A-type polycarbonate as a matrix, and fine particles of titanyl phthalocyanine as a charge generating material.
2- (N, N-dimethylamino) -5-nitroacetanilide (DAN), a molecule exhibiting nonlinear optical properties, is dissolved in methylene chloride at a weight ratio of 40: 20: 8: 32 to form a solution. Prepared. This methylene chloride solution was cast on a quartz substrate and dried to form a film having a thickness of 150 μm. When the diffraction efficiency of the obtained film was measured,
15.5%.

Example 2 A charge-donating molecule represented by the following chemical formula was evaluated in the same manner as in Example 1 described above, and D / μ in the absence of an electric field was determined to be 29.

[0097]

Embedded image This charge-donating molecule, chloranil as a charge-accepting molecule, and bisphenol A-type polycarbonate as a matrix were mixed at a weight ratio of 30: 1: 70, and dissolved in methylene chloride to prepare a solution. . The resulting solution was cast on a quartz substrate, dried and dried to a thickness of 150 μm.
m was formed as a sample.

When the same measurement as in Example 1 was performed,
The diffraction efficiency was 12.1%.

Example 3 A charge-donating molecule represented by the following chemical formula was evaluated in the same manner as in Example 1, and D / μ in an electric field-free state was 30.

[0100]

Embedded image This charge-donating molecule, p-nitroanthracene as a charge-accepting molecule, and bisphenol A-type polycarbonate as a matrix were mixed in a weight ratio of 60: 1: 40.
And dissolved in methylene chloride to prepare a solution. The obtained solution was cast on a quartz substrate and dried to form a film having a thickness of 100 μm, which was used as a sample.

When the same measurement as in Example 1 was performed,
The diffraction efficiency was 13.0%.

(Comparative Example 1) A charge transporting material represented by the following chemical formula was evaluated in the same manner as in Example 1, and the charge transporting material under no electric field was evaluated.
/ Μ was 2.0.

[0103]

Embedded image This charge transporting material, bisphenol A-type polycarbonate as a matrix, titanyl phthalocyanine fine particles as a charge generating material, and 2- (N, N-dimethylamino) -5-nitroacetanilide ( DNA) with a weight ratio of 40:20:
The mixture was mixed at a ratio of 8:32 and dissolved in methylene chloride to prepare a solution. Cast the resulting solution on a quartz substrate,
After drying, a film having a thickness of 150 μm was formed to obtain a sample.

When the same measurement as in Example 1 was performed,
The diffraction efficiency was 0.015%. (Comparative Example 2) A charge-donating molecule represented by the following chemical formula was evaluated in the same manner as in Example 1, and D / μ in the absence of an electric field was 2.0.

[0105]

Embedded image This charge-donating molecule, chloranil as a charge-accepting molecule, and bisphenol A-type polycarbonate as a matrix were mixed at a weight ratio of 30: 1: 70, and dissolved in methylene chloride to prepare a solution. . The resulting solution was cast on a quartz substrate, dried and dried to a thickness of 150 μm.
m was formed as a sample.

When the same measurement as in Example 1 was performed,
No diffraction was observed.

[0107]

As described above, according to the present invention, the ratio (D / μ) between the diffusion coefficient D and the mobility μ can be sufficiently increased without excessively reducing the mobility (μ), and An optical recording medium capable of recording information at a high density without applying an electric field is provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of a recording apparatus to which an optical recording medium of the present invention can be applied.

FIG. 2 is a schematic diagram showing another example of a recording apparatus to which the optical recording medium of the present invention can be applied.

FIG. 3 is a schematic diagram of an apparatus used for measuring diffraction efficiency.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 13 ... Laser light source 14 ... Beam splitter 15 ... Spatial light modulator 16 ... Mirror 18 ... Signal light (writing) 19 ... Reference light 20 ... Signal light (reading) 21 ... Micromirror array device 22 ... Micromirror 23 ... Lens 24 ... Photodetector 25 Optical recording medium 31 Sample 32 Transparent support layer 33 Object light 34 Transmission component of object light 35 Reference light 36 Opposite-direction component of reference light 37 Photodetector 38 Transmission image Display element

Continuing from the front page (72) Inventor Takayuki Tsukamoto 1-term, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa F-term in Toshiba R & D Center (reference) 2K002 AB10 BA02 CA02 HA03 HA27 5D029 JA04 JC09 VA08

Claims (2)

[Claims] 1. An optical recording medium containing a charge generating material, a charge transporting material, and a nonlinear optical material for recording information by irradiating an electromagnetic wave, wherein the charge transporting material is represented by the following general formula (1). An optical recording medium comprising a compound according to the present invention. Embedded image (In the above general formula (1), R ¹ , R ² , R ³ and R
⁴ is a methyl group, an isopropyl group, a t-butyl group, an aryl group, and a heterocyclic group. Alternatively, at least one of R ¹ and R ² may form a ring together with the adjacent nitrogen atom and part of the benzene ring. ) 2. An optical recording medium containing a charge-donating molecule and a charge-accepting molecule and recording information by irradiating an electromagnetic wave, wherein the charge-donating molecule is represented by the following general formula (1). An optical recording medium comprising a compound. Embedded image (In the above general formula (1), R ¹ , R ² , R ³ and R
⁴ is a methyl group, an isopropyl group, a t-butyl group, an aryl group, and a heterocyclic group. Alternatively, at least one of R ¹ and R ² may form a ring together with the adjacent nitrogen atom and part of the benzene ring. )