JP2006039225A - Recording medium, recording method and reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a recording method by which high density recording suitable for a digital hologram can be performed, laser light at any wavelength from a near UV region to a visible region can be used, and instant recording with excellent long-term stability can be performed, to provide a reproducing method for reproducing information recorded by the above recording method, and to provide a recording medium for directly using the above recording method or the reproducing method. <P>SOLUTION: A recording medium 17 having a metal thin film 2 in which metal nanoparticles comprising a platinum element are present in a proximity state or a contact with one another on a substrate 1 is irradiated with laser light divided into two beams of information light 40 having information and reference light 30 to interfere with each other. Interference fringes composed of a portion where the metal thin film 2 is aggregated and granulated by the irradiation energy and a portion having no aggregation granulation are formed in the recording medium 17. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a recording method for recording information by irradiating a metal thin film on a substrate with light, a reproducing method for reproducing information recorded by the recording method, and a recording method used directly for carrying out the recording method or reproducing method. It relates to the medium.

  As recording media for music data, moving image data, or application programs for personal computers, optical discs such as CDs and DVDs are widely used. An optical disk reads and reproduces information by irradiating laser light onto a concave and convex pit pattern formed in advance on a substrate, with the point where the amount of reflected light is changed as “1” or “0”. For this reason, in order to improve the recording density, a pit pattern miniaturization technique is required.

  In order to increase the recording density of an optical disk, a metal thin film (island-like metal thin film) in which metal particles having a diameter of 100 nanometers or less are discretely distributed in a two-dimensional manner is used as one optical recording layer, and spectroscopy of gold, silver, copper, etc. An optical disc has been proposed in which a plurality of island-shaped metal thin films having different characteristics are laminated with a transparent resin layer interposed therebetween. This is because the irradiation of high energy density laser light in the vicinity of the resonance wavelength of each metal thin film causes the shape of metal particles or the local melting or deformation of the surrounding transparent resin medium to change the reflectivity of the laser irradiation part. By doing so, a mark is recorded (see Patent Document 1).

  On the other hand, in order to increase the recording density, one using a holographic recording / reproducing technique has been proposed. This is because conventional CDs or DVDs record 1-bit information per recording mark, whereas in holographic recording / reproduction, a data chunk called page data per recording mark is recorded. The amount of information that can be recorded is dramatically increased.

In holographic recording and reproduction, as a recording layer material for recording information, a photorefractive material whose refractive index changes by absorption of light or a photopolymer obtained by adding a sensitizer to a monomer has been attracting attention. Yes. For example, in holographic recording / reproduction using a photopolymer as a recording layer, a strong laser beam during recording is separated into two light beams of information light having information to be recorded and reference light, and the recording layer is irradiated to the recording layer. After changing the structure of the recording layer by exposure to form interference fringes, information is recorded by performing post-processing such as development processing and fixing processing.
JP 2002-11957 A

  However, in the example of Patent Document 1, since laser light having a high energy density in the vicinity of the resonance wavelength of the metal thin film is irradiated, it is specified by the resonance wavelength corresponding to the material of the metal thin film during recording or reproduction. It was necessary to use laser light having a wavelength. Further, since the recording mark recorded in the vicinity of the portion irradiated with the laser beam has only 1-bit information, it has been desired to further increase the recording density.

  In the case of the conventional holographic recording / reproducing, the material of the recording layer is sensitive to light because it has photosensitivity, is unstable to light irradiation, and is exposed to light for a long time. Therefore, it has been required to improve long-term stability as a recording medium. Further, when recording information, post-processing such as development and fixing is necessary after the recording layer is exposed by irradiating a laser beam, and it has been desired to record information by a simple method. Furthermore, when the recording layer is exposed by irradiating the laser beam, if vibration occurs in the recording medium on which the recording layer is formed or the optical system that guides the laser beam to the recording layer, information may not be recorded correctly. There was a need for a mechanism to absorb vibrations.

  The present invention has been made in view of such circumstances, and irradiates light to a metal thin film in a state where metal nanoparticles are in close contact with or in contact with each other, and the metal thin film is agglomerated by the energy of the irradiated light. By providing a recording layer that forms a pattern composed of a portion that has been converted into a non-aggregated portion and a portion that is not agglomerated and granulated, post-processing such as development or fixing is not required, and information can be recorded at high density It is an object to provide a medium and a recording method using the recording medium.

  Another object of the present invention is to coherent light interfere with a metal thin film in a state where the metal nanoparticles are in close contact with or in contact with each other, and the metal thin film is agglomerated and granulated by the energy of the coherent light. And a recording medium capable of forming interference fringes suitable for digital holograms by providing a recording layer for forming interference fringes composed of non-aggregated parts, and a recording method using the recording medium There is to do.

  Another object of the present invention is to provide a laser by providing a metal thin film containing one metal selected from the group consisting of platinum, palladium, platinum and palladium alloys, platinum and nickel alloys, palladium and nickel alloys. It is an object of the present invention to provide a recording medium that has a large change in reflectance and transmittance in the near-ultraviolet to visible region before and after light irradiation, can obtain high spatial resolution, and is excellent in long-term stability.

  Another object of the present invention is to provide a metal thin film in which the particle size and average film thickness of the metal nanoparticles are in the range of 3 to 20 nanometers, so that the reflectance before and after the laser light irradiation. Another object of the present invention is to provide a recording medium that can ensure a change in transmittance and prevent a reduction in resolution of interference fringes.

  Another object of the present invention is to provide a recording medium capable of multiplex recording information by providing a plurality of recording layers stacked on a substrate.

  Another object of the present invention is to irradiate a metal thin film with a single pulse laser beam having an energy density of 0.5 millijoule / square millimeter or more and a pulse width of 5 nanoseconds or less. An object of the present invention is to provide a recording method in which a quasi-continuous metal thin film is agglomerated and granulated within a unit time to eliminate a mechanism for absorbing vibration.

  Another object of the present invention is to provide a reproduction method capable of reproducing recorded information based on the reflectance of irradiated light.

  Another object of the present invention is to reproduce information by irradiating light having the same wavelength as the coherent light at the time of recording. An object of the present invention is to provide a reproducing method capable of reproducing with light of a wavelength.

  A recording medium according to a first aspect of the present invention is a recording medium for recording information on a recording layer formed on a substrate, wherein the recording layer is a metal thin film in which metal nanoparticles are in close proximity or in contact with each other. And

  The recording medium according to a second invention is the recording medium according to the first invention, wherein the metal thin film is one metal selected from the group consisting of platinum, palladium, an alloy of platinum and palladium, an alloy of platinum and nickel, an alloy of palladium and nickel. It is characterized by including.

  The recording medium according to a third invention is characterized in that, in the second invention, the average film thickness of the metal thin film and the particle size of the metal nanoparticles are in the range of 3 nanometers to 20 nanometers.

  A recording medium according to a fourth aspect of the present invention is the recording medium according to any one of the first to third aspects, wherein a plurality of the recording layers are laminated on a substrate.

  According to a fifth aspect of the present invention, there is provided a recording method for recording information by irradiating light to a recording medium, wherein a metal thin film is formed on a substrate in a state in which the metal nanoparticles are in proximity or in contact with each other. Information is recorded by using a recording medium to form the metal nanoparticles by agglomeration and granulation by irradiation energy and forming a pattern composed of the agglomerated and non-agglomerated parts.

  The recording method according to a sixth aspect of the present invention is the recording method according to the fifth aspect, wherein the metal thin film is irradiated with and interferes with the coherent light separated into the two light beams of the information light having information and the reference light to coagulate and granulate It is characterized in that an interference fringe composed of unexposed portions is formed.

  In a recording method according to a seventh aspect, in the sixth aspect, the coherent light applied to the metal thin film has an energy density of 0.5 millijoule / square millimeter or more and a pulse width of 5 nanoseconds or less. It is a single pulse laser beam.

  According to an eighth aspect of the present invention, there is provided a reproducing method for reproducing information by irradiating light onto a recording medium on which information is recorded by a recording method for recording information by irradiating light, wherein the recording method comprises: The recording method according to the fifth aspect of the invention is characterized in that information is reproduced based on a difference in reflectance of irradiated light.

  According to a ninth aspect of the present invention, there is provided a reproducing method for reproducing information by irradiating light onto a recording medium on which information is recorded by a recording method for recording information by interfering with coherent light, wherein the recording method comprises: The recording method according to the sixth or seventh invention is characterized in that information is reproduced by irradiating light having the same wavelength as the coherent light.

  In the first invention and the fifth invention, the metal thin film is irradiated with a laser beam through a mask on which an information pattern has been recorded in advance by electron beam drawing. In the part of the metal thin film irradiated with laser light, the metal nanoparticles that absorbed the energy of the irradiated light generate heat and melt, and a plurality of metal nanoparticles merge and form spherical droplets due to surface tension. The metal nanoparticles are agglomerated and granulated. The energy of the light to irradiate should just be more than energy required for a metal nanoparticle to fuse | melt, and the irradiation time of light may be the time until a metal nanoparticle melt | dissolves. On the other hand, in the metal thin film that is not irradiated with the laser beam by the mask, the structural change of the metal thin film does not occur and the particles are not aggregated. Thereby, the pattern comprised from the part which the metal nanoparticle aggregated and granulated and the part which is not aggregated granulated is formed.

  The light absorption of the metal nanoparticles is caused by collective excitation (surface plasmon) of free electrons confined in a small space of the metal nanoparticles. In a metal thin film in which metal nanoparticles are in close contact or in contact with each other, light is absorbed in the visible region due to the interaction between adjacent surface plasmons, and has a reflectance and transmittance of several tens of percent. On the other hand, in a metal thin film in which metal nanoparticles are agglomerated and granulated, a plurality of metal nanoparticles before light irradiation are merged, and the agglomerated and granulated metal nanoparticles are mutually independent at an average interval of about 10 nanometers. Therefore, there is no interaction between surface plasmons, optical properties (optical density, reflectance, transmittance, etc.) change, light absorption decreases, reflectance decreases, and transmittance increases. . Thereby, information is recorded by utilizing the fact that the optical properties of the recording layer differ before and after the light irradiation.

  In the sixth aspect of the invention, the two light beams obtained by separating the coherent light emitted from the same light source into the information light and the reference light are caused to interfere with each other in the metal thin film, thereby canceling the light intensity and the light intensity enhancing portion. Interference fringes composed of matching portions are formed. In the part where the intensity of light is intensified, the metal nanoparticles that absorbed the energy of the irradiated light generate heat and melt, and a plurality of metal nanoparticles merge and form spherical droplets due to surface tension. The particles are agglomerated and granulated. The energy of the light to irradiate should just be more than energy required for a metal nanoparticle to fuse | melt, and the irradiation time of light may be the time until a metal nanoparticle melt | dissolves. On the other hand, in the portion where the light intensity cancels out, the structural change of the metal thin film does not occur and the particles are not aggregated. Thereby, the interference fringe comprised from the part which the metal nanoparticle aggregated and granulated and the part which is not aggregated granulated is formed.

  In the second invention, the metal thin film is made of a platinum group element of platinum or palladium. In metal thin films where platinum group metal nanoparticles are in close proximity or in contact with each other, the interaction between surface plasmons produces a substantially flat light absorption characteristic in the entire region from the near ultraviolet to the visible region. The optical properties are about 30% transmittance and about 30% reflectance. On the other hand, in the portion where the metal nanoparticles are aggregated and granulated by light irradiation, the surface plasmon absorption when the metal nanoparticles of the platinum group element are present alone is in the ultraviolet region, so that the light absorption is in the visible region. Does not occur. For this reason, in the visible region, the optical properties are such that the transmittance is about 90% or more and the reflectance is about 10% or less. Also in the ultraviolet region, it shows a transmittance of about 60% and a reflectance of about 10%.

  The platinum group element has a thermal conductivity as small as about 1/5 compared to gold, silver, or copper. Thereby, when light is irradiated on the metal thin film of a platinum group element, the conduction or diffusion of heat due to the irradiated energy is suppressed, and the range in which the metal nanoparticles are coalesced and aggregated is suppressed. In addition, platinum group elements are superior in long-term chemical stability and thermal stability compared to gold, silver, or copper. Further, by making the metal thin film an alloy of platinum and palladium, or an alloy of platinum or palladium and nickel, the metal nanoparticle contains an element harder than platinum, and the mechanical strength of the metal thin film, Increase adhesion strength.

  In the third invention, the particle diameter of the metal nanoparticles and the average film thickness of the metal thin film are in the range of 3 nanometers to 20 nanometers. When the particle size and average film thickness are smaller than 3 nanometers, the film thickness is too thin to absorb light enough to record information based on the difference in transmittance or reflectance before and after light irradiation. It does not show enough optical change. When the particle size and the average film thickness exceed 20 nanometers, the degree of adhesion between the metal nanoparticles increases, so when the metal thin film is irradiated with light, before the metal nanoparticles melt and agglomerate and granulate Then, heat due to the energy of the irradiated light is conducted or diffused through the metal thin film, the formation of spherical droplets of the metal nanoparticles is suppressed, and interference fringes cannot be obtained. By making the particle size of the metal nanoparticles and the average film thickness of the metal thin film within the range of 3 nanometers to 20 nanometers, an optical change sufficient to record information before and after the light irradiation is generated. At the same time, interference fringes are formed.

  In the fourth invention, a plurality of recording layers are provided on the substrate. As a result, separate information is multiplexed and recorded for each recording layer.

  In the seventh invention, the metal thin film is irradiated with a single pulse laser beam having an energy density of 0.5 millijoule / square millimeter or more and a pulse width of 5 nanoseconds or less. When laser light having an energy density of less than 0.5 millijoule / square millimeter is irradiated, the metal nanoparticles do not generate heat sufficiently and do not melt, so that the metal nanoparticles are not aggregated and granulated. By irradiating the metal thin film with a single pulse laser beam having a pulse width of 5 nanoseconds or less, the metal nanoparticles are melted into spherical droplets and then agglomerated and granulated during nanosecond units.

  In the eighth invention, recording is performed by irradiating the metal thin film with light to agglomerate and granulate the metal nanoparticles and form a pattern composed of the agglomerated and non-agglomerated parts. The information is reproduced using the difference in reflectance of the irradiated light.

  In the ninth invention, the recorded information is reproduced by irradiating light having the same wavelength as the wavelength of the coherent light irradiated when recording information. Interference fringes are formed in the recording layer by causing two light beams (information light and reference light) to interfere with each other during recording. Information is reproduced by irradiating the interference fringes with light having the same wavelength as the light at the time of recording, whereby the interference fringes serve as a diffraction grating, and the original information recorded in the interference fringes is reproduced.

  In the first invention, the fifth invention, and the sixth invention, it has a simple configuration in which a metal thin film is formed on a substrate in a state in which the metal nanoparticles are close to or in contact with each other, and is easy to manufacture. A recording medium can be provided. Also, before and after the light irradiation, the metal nanoparticles are aggregated and granulated to change the optical properties and record information, so no post-processing such as development or fixing is required, and high-density information is recorded. Can do. Furthermore, when interference fringes are formed in the recording layer by causing the two light beams to interfere with each other, it is possible to record high-density information suitable for a multiplex digital hologram.

  In the second invention, light of an arbitrary wavelength can be used over a wide range from the near ultraviolet to the visible region. In addition, since the light transmittance and the reflectance are greatly different before and after the light irradiation, either transmitted light or reflected light can be used when reproducing recorded information. In addition, by suppressing the range of aggregation and granulation of metal nanoparticles, the width of the interference fringes can be reduced, and good spatial resolution can be obtained. Furthermore, it has excellent long-term mechanical, chemical, and thermal stability.

  In the third aspect of the invention, since the optical property changes greatly before and after the light irradiation and the resolution of the interference fringes is high, an interference fringe having a high definition of the interference fringes and suitable for a multiplex digital hologram can be obtained.

  In the fourth aspect of the invention, information can be multiplexed and recorded for each recording layer, and the recording density can be improved.

  In the seventh invention, information can be recorded in a short time of nanosecond units, and is not affected by vibration of the recording medium or the optical system during exposure.

  In the eighth invention, the recorded information can be reproduced using the reflectance of the irradiated light.

  In the ninth invention, if the wavelength of the reproduction light is the same as the wavelength of the light at the time of recording, the reproduction of information is transmitted or reflected light having an arbitrary wavelength in a wide range from the near ultraviolet to the visible region. Can be used.

Embodiment 1
FIG. 1 is an explanatory view showing an observation example of the metal thin film 2 of the recording medium 17 (see FIG. 3) according to the present invention, and FIG. 2 is an explanatory view showing the structure of the recording medium 17 according to the present invention. In the figure, reference numeral 1 denotes a substrate. The substrate 1 is optically smooth and light-transmitting such as mica or glass, and a platinum element metal thin film 2 deposited by sputtering is formed on the substrate 1. The metal thin film 2 has a particle size of 5 nanometers to 10 nanometers, and the state or contact where the spheroid metal nanoparticles 2a are close to each other at a distance of several nanometers or less (including point contact or surface contact) It is a thin film in a state (quasi-continuous). The average film thickness of the metal thin film 2 is 7 nanometers to 8 nanometers. Nanoparticles generally have a particle size of 100 nanometers or less.

  The quasi-continuous metal thin film 2 can be formed using a DC sputtering method. The substrate 1 and a source containing a platinum element thin film material are placed in a vacuum vessel filled with argon gas, the argon gas pressure is about 0.15 Torr, the temperature of the substrate 1 is about 150 ° C., and the deposition rate of the thin film The metal thin film 2 is prepared under the condition of about 2 nanometers / minute.

  FIG. 1 shows an example of observation of the metal thin film 2 by an atomic force microscope, and FIG. 2 shows an example of an enlarged model of the metal thin film 2 of FIG.

  FIG. 3 is a schematic diagram of an apparatus for carrying out the recording method according to the present invention. In the figure, 10 is a laser. The laser 10 is a small pulse YAG laser that outputs linearly polarized laser light having a pulse width of 5 nanoseconds and a wavelength of 532 nanometers. Laser light has coherency. On the optical axis of the laser 10, a beam diameter conversion lens 11 for enlarging or reducing the beam size of the output parallel beam to a required value, a half mirror for separating incident laser light into transmitted light and reflected light 12 and a prism 14 for changing the path of the laser beam are arranged in this order. The prism 14 converges the incident laser light to a required range (for example, a range of the order of 100 μm in diameter) on the recording medium 17 described later.

  Further, a mirror 13 is arranged with an appropriate separation distance facing the half mirror 12. The center of the mirror 13 is the central axis of the half mirror 12 and is on the optical axis perpendicular to the optical axis of the laser 10, and the reflection surface of the mirror 13 is arranged in parallel with the reflection surface of the half mirror 12. On the axis parallel to the optical axis of the laser 10 passing through the center of the mirror 13, an objective lens 15 for converging parallel light on the recording medium 17, a page composer 16 in which information to be recorded is arranged in a grid as page data, A recording medium 17 having a metal thin film 2 as a recording layer formed on the substrate 1 is arranged in this order.

  The page composer 16 is a spatial light modulator, and two polarizers are stacked with a magnetic film interposed therebetween. Depending on the magnetization direction of the magnetic film, the plane of polarization rotates positively or negatively, and by controlling the polarization direction of the incident laser light, the output of the laser light is switched corresponding to the pixels arranged in a lattice pattern.

The optical path length L1 of the laser light from the half mirror 12 to the recording medium 17 via the prism 14, and the optical path length L2 from the half mirror 12 to the recording medium 17 via the mirror 13, the objective lens 15, and the page composer 16. The optical path length difference L is shorter than the coherence length of the laser beam. As a result, the two light beams separated by the half mirror 12 are caused to interfere on the metal thin film 2 of the recording medium 17 to form interference fringes at each point where the optical path length difference L changes periodically.

  The laser beam output from the laser 10 passes through the beam diameter conversion lens 11 to have a required beam diameter and is incident on the half mirror 12. The half mirror 12 separates the incident laser light into transmitted light and reflected light, and transmits the transmitted light to the prism 14. The prism 14 is incident on the recording medium 17 at an incident angle θ using the laser light transmitted through the half mirror 12 as reference light 30.

  On the other hand, the half mirror 12 makes the reflected laser light enter the mirror 13. The mirror 13 makes the incident laser light enter the objective lens 15. The objective lens 15 makes the incident laser light enter the page composer 16 and converge on the recording medium 17. The page composer 16 makes the laser light incident from the objective lens 15 enter the recording medium 17 as information light 40 based on the page data arranged in a two-dimensional lattice at an incident angle of zero. The information light 40 has information in which the output of the laser light is switched for each pixel corresponding to the page data of the page composer 16.

  The reference light 30 and the information light 40 irradiated on the metal thin film 2 of the recording medium 17 interfere with each other and form a rectangular interference fringe composed of a portion where the intensity of the laser light is intensified and a portion where the intensity is canceled out by a predetermined distance d. Formed. The distance d between the interference fringes is determined by the wavelength λ of the laser light and the incident angle θ of the reference light. Based on the principle of holography, the wavefront of the information light 40 is recorded as it is on the interference fringes, and information is recorded on the metal thin film 2.

  In the portion where the laser beam interferes and strengthens the intensity, the metal thin film 2 locally changes in structure due to the energy of the laser beam. FIG. 4 is an explanatory view showing an example of observation of the metal thin film of the recording medium after laser light irradiation, and FIG. 5 is an explanatory view showing the structure of the recording medium after laser light irradiation. The irradiated laser light is a pulse laser having a wavelength of 532 nanometers and 5 nanoseconds, and the energy density is in the range of 0.6 millijoule / square millimeter to 2.0 millijoule / square millimeter. FIG. 4 shows an example of observation of the metal thin film 3 after irradiation with a laser beam by an atomic force microscope, and FIG. 5 shows an example in which the metal thin film 3 of FIG. 4 is enlarged and modeled.

  When the metal thin film 2 is irradiated with laser light, the metal nanoparticles 2a, 2a,... Absorb the energy of the laser light and generate heat to melt. Since platinum element has a thermal conductivity as small as about 1/5 compared to metals such as gold, silver, and copper, thermal conduction or thermal diffusion due to irradiated light energy is suppressed. For this reason, the melted metal nanoparticles 2a are combined with at least one or two other metal nanoparticles 2a that are close to or in contact with each other, and are formed into spherical droplets by surface tension to be combined into metal nanoparticles 3a. When the laser beam is no longer irradiated, the combined metal nanoparticles 3a are rapidly cooled and solidified in an independent granular state. Thereby, the structure of the metal nanoparticles 2a, 2a,... Of the quasi-continuous metal thin film 2 is changed to the metal nanoparticles 3a agglomerated and granulated by laser light irradiation. The thin film 3 is formed.

  FIG. 6 is an explanatory view showing an interference fringe model by laser light irradiation, and FIG. 7 is an explanatory view showing a change in absorption spectrum by laser light irradiation. By irradiating the metal thin film 2 with laser light, rectangular interference fringes of equal intervals constituted by the metal thin film 2 and the metal thin film 3 are formed as shown in FIG.

  The light absorption of metal nanoparticles is caused by collective excitation of free electrons confined in a small space of metal nanoparticles called surface plasmons, and the wavelength region where the absorption occurs is a complex dielectric constant of the metal given as a function of wavelength. Depends on.

  In the quasi-continuous metal thin film 2 of the metal nanoparticles 2a made of platinum element, a substantially flat light absorption characteristic is generated in the entire region from the near ultraviolet to the visible region due to the interaction between adjacent surface plasmons. The optical properties are such that the density is about 0.45, the transmittance is about 30%, and the reflectance is about 30%.

  On the other hand, in the metal thin film 3 in which the metal nanoparticles 2a are agglomerated and granulated, a plurality of metal nanoparticles 2a before irradiation with light are combined, and the agglomerated and granulated metal nanoparticles 3a are at an average interval of about 10 nanometers. Exist independently of each other. Since the surface plasmon absorption in the case where the metal nanoparticles 3a of the platinum group element exist alone is in the ultraviolet region, light absorption does not occur in the visible region. Therefore, in the visible region, the optical density is about 0.05 or less, the transmittance is about 90% or more, and the reflectance is about 10% or less. Even in the ultraviolet region, the optical density is about 0.2, the transmittance is about 60%, and the reflectance is about 10%. As shown in FIG. 7, the optical properties (optical density) of the metal thin film 2 and the metal thin film 3 change greatly before and after the laser beam irradiation.

  FIG. 8 is an explanatory diagram showing the relationship between the degree of spatial modulation of the energy density of laser light caused by interference and the line width of interference fringes. When the energy density level of the laser beam increases as a whole and the width (L1) of the section exceeding the threshold value P (0.5 millijoule / square millimeter) increases, the metal thin film 3 containing the aggregated and granulated metal nanoparticles 3a. The range of becomes larger. Thereby, the line width of the metal thin film 3 of interference fringes increases. Further, when the energy density of the laser light exceeds the threshold P, when the energy further increases, the absorbed excess energy is conducted or diffused to the adjacent section exposed at a level not exceeding the threshold P. The agglomeration and granulation proceeds in both sections, and the normal interference fringes shown in FIG. 8 in which the region composed of the metal thin films 2 and 3 is clearly separated cannot be obtained.

  On the other hand, when the energy density of the laser beam is kept low as a whole and the width of the section exceeding the threshold P (L2 <L1) is reduced, the range of the metal thin film 3 containing the aggregated and granulated metal nanoparticles 3a is reduced. Thereby, the line width of the metal thin film 3 of interference fringes decreases. Under such exposure conditions, interference fringes are not broken (or the boundary between the metal thin films 2 and 3 is not blurred) due to conduction or diffusion of excess energy between adjacent sections having different exposure amounts.

  By making the energy density of the laser beam to be irradiated as close as possible to the threshold value P, the line width of the metal thin film 3 of the interference fringes can be reduced, and the line width of the metal thin film 2 can be increased. The area of the thin film 2 increases. As a result, multiple recording described later can be easily performed. Accordingly, the energy density is more preferably in the range of 0.9 millijoule / square millimeter to 1.7 millijoule / square millimeter. It is preferable that the energy density of the reference light 30 is set to a value slightly smaller than the threshold value P, and the energy density of the information light 40 is set to about ¼ of the reference light 30.

  FIG. 9 is an explanatory diagram showing the concept of angle multiplex recording. As shown in the figure, the information beam 40 is incident from the normal direction of the recording medium 17 and the reference beam 30 is incident at a predetermined incident angle to perform the first exposure, and then the reference beam 30 is transmitted to the information beam. The second exposure is performed by entering from the direction rotated by 90 degrees around 40, and the direction of the incident plane determined by the information light 40 and the reference light 30 is further rotated by 45 degrees and 90 degrees three times, and A fourth exposure is performed. When the energy density of the laser beam is large, the line width of the metal thin film 3 is large, so that the range of the metal thin film 2 remaining after four exposures is almost eliminated. On the other hand, when the energy density is reduced, the line width of the metal thin film 3 is small, so that the area of the remaining metal thin film 2 is large even after four exposures. Thus, multiple recording can be easily performed by making the energy density of the irradiated laser light larger than the threshold value P and close to the threshold value P.

  FIG. 10 is an explanatory view showing an example of a square lattice hologram by double recording. The information light 40 is incident from the normal direction of the recording medium 17 and the reference light 30 is incident at a predetermined incident angle to perform the first exposure, and then the reference light 30 is rotated 90 degrees around the information light 40. Interference fringes forming a square lattice are formed by performing the second exposure by making the light incident from the rotated direction.

  FIG. 11 is a schematic diagram of an apparatus for carrying out the reproducing method according to the present invention. In the figure, reference numeral 17 denotes a recording medium. Information is recorded in the recording medium 17 in advance by causing the reference light 30 and the information light 40 to interfere with each other. Position at which the objective lens 18 for irradiating the recording medium 17 with reproduction light 50 (transmitted light) conjugate to the reference light 30 and having the same wavelength as the reference light 30 converges the reproduction light 50 on the recording medium 17 It is arranged in. A reproduction lens 19 having an optical axis that coincides with an axis passing through the center of the recording medium 17 is disposed in the vicinity of the recording medium 17, and two-dimensionally arranged photodiodes 20 having the center positioned on the optical axis. Is arranged so as to have an appropriate separation distance from the reproducing lens 19. The energy density of the laser beam during reproduction is made smaller than that during recording. Thereby, the structural change of the metal thin film 2 does not occur due to the reproduction light.

  When linearly polarized laser light (pulse laser or CW laser) enters the objective lens 18, the objective lens 18 enters the recording medium 17 using the incident laser light as reproduction light 50. When the reproduction light 50 is incident on the recording medium 17, equidistant rectangular interference fringes composed of the metal thin film 2 and the metal thin film 3 recorded on the recording layer of the recording medium 17 serve as a diffraction grating. A diffracted wave including information recorded from the recording medium 17 having 1 is incident on the reproducing lens 19. The reproduction lens 19 converges the incident diffracted wave on the photodiode 20 and outputs the recorded information as an electrical signal, thereby reproducing the recorded information. By using the conjugate light of the reference light 30 as the reproduction light 50, it is possible to irradiate the recording medium 17 with the reproduction light 50 and the reference light 30 at the same time, and it is possible to reproduce the recorded information at the same time while recording. Become. Note that the recording medium 17 may be irradiated with the reproduction light 50 from the same direction as the reference light 30 without using the light conjugate with the reference light 30 as the reproduction light 50.

  FIG. 12 is an explanatory view showing an example of a recording medium according to the present invention. As shown in the figure, a recording layer made of a metal thin film 2 is formed on a substrate 1 with a transparent resin layer 4 having an appropriate length interposed therebetween. The upper recording layer is the first layer and the lower recording layer is the second layer in the direction in which the laser light is incident. The objective lens 15 is arranged at a position where the information light 40 is converged on the metal thin film 2 with the optical axis aligned with the normal direction on the surface of the metal thin film 2. Note that the reference light 30 is the same as described above, and thus the description thereof is omitted below.

  First, the information contained in the information light 40 is recorded while focusing on the first layer. The irradiated information light 40 reaches the second layer, but its intensity is weakened by reflection and absorption of the first layer, and the information is not recorded on the second layer because it is not focused on the second layer. I will not.

  Next, when the objective lens 15 is focused on the second layer and irradiated with the information light 40, the information contained in the information light 40 is recorded on the second layer. In this case, since the focus of the information light 40 is shifted in the first layer, information is not recorded in the first layer. The information light 40 is set so that the intensity of the laser light is greater than or equal to the threshold value P in the second layer, although the light intensity is reduced by passing through the first layer. As described above, by changing the depth of focus of the information light 40, information can be recorded in multiple layers and the recording density can be improved.

  FIG. 13 is an explanatory diagram showing an example of a recording medium according to the present invention. As shown in the figure, a recording layer made of a metal thin film 2 is formed on a substrate 1 with a transparent resin layer 4 having a thickness of about several nanometers interposed therebetween. The upper recording layer is the first layer and the lower recording layer is the second layer in the direction in which the laser light is incident. The objective lens 15 is arranged at a position where the information light 40 is converged on the metal thin film 2 with the optical axis aligned with the normal direction on the surface of the metal thin film 2. Note that the reference light 30 is the same as described above, and thus the description thereof is omitted below.

  First, when linearly polarized information light 40 is irradiated onto the first layer (first exposure), strip-shaped interference fringes composed of the metal thin film 2 and the metal thin film 3 are formed at equal intervals on the first layer. . The transmittance of the first-layer metal thin film 3 is increased to 90% or more by the first exposure. In the second layer, since the intensity of the laser beam is not more than the threshold value P, no interference fringes are formed.

  Next, when the reference light 30 is rotated 90 degrees around the information light 40 and irradiated to the first layer (second exposure), the first layer is rotated 90 degrees composed of the metal thin film 2 and the metal thin film 3. A band-shaped interference fringe is formed, and a lattice-like interference fringe is formed together with the interference fringe formed by the first exposure. The information light 40 is transmitted through the metal thin film 3 whose transmittance has increased to 90% or more in the first exposure, so that the second layer has a square-shaped metal thin film 3 where lattice-like interference fringes overlap. An interference fringe is formed. Thereby, the same information as the information recorded in the first layer by one exposure can be recorded in the second layer, and the area of the metal thin film 2 remaining without being exposed in the second layer is the first layer. Since it is larger than the case of one layer, it is possible to perform multiple recording. As a result, the number of times of multiple recording can be increased and the recording density can be improved as compared with the case where only one layer is used.

  As described above, a metal whose optical density, transmittance, and reflectance change greatly over a wide range from the near ultraviolet to the visible region by irradiating the laser beam to the quasi-continuous metal thin film 2 made of platinum element to cause interference. A rectangular interference fringe composed of the thin film 2 and the metal thin film 3 can be formed. That is, a high-definition pattern (at least 2000 lines per 1 mm) in which two types of phases having different optical properties and structures such as transmittance and reflectance and structures are regularly arranged at intervals of about 1 micron or less is arbitrarily selected on the substrate. It can be easily formed at the position. For example, when a laser beam of 532 nanometers is used, the spatial frequency is about 2000 lines / mm, the line width of the metal thin film 2 is about 0.2 microns, and the line width of the metal thin film 3 is about 0.3. It becomes micron.

  In addition, since the recording method and the recording medium of the present invention are based on on / off recording characteristics in which the optical properties change greatly with the threshold value P as a boundary, the linearity of the interference fringes is high, the diffraction efficiency is increased, and the digital hologram is formed. It is suitable.

  In addition, it has a very simple configuration using a quasi-continuous metal thin film made of platinum metal nanoparticles as the only functional material, and can be easily manufactured by a film forming apparatus. For information recording, lasers of any wavelength in the wide range from the near ultraviolet to the visible range can be used, and no post-processing such as development or fixing is necessary with only exposure, and a single pulse laser of nanosecond or less is used. Instant recording is possible and it is not affected by vibration.

  In addition, the recording medium of the present invention only changes the structure of the metal nanoparticles by laser light irradiation, no metal is discarded, and 100% of the metal used when the used recording medium is recovered is recovered. It is also excellent in terms of environment.

  In addition, while using an extremely thin metal thin film of about 10 nanometers, a high-definition two-dimensional regular lattice whose transmittance and reflectance change by several tens of percent between two phases before and after laser irradiation is formed. Forming a thin film of a material that reversibly responds to light (for example, reversible photochromism that changes its color by absorption of light and returns to its original state when heated) on the recorded recording medium. By using the information recorded in the above as tracking information, it can be applied to a rewritable optical memory. Further, by forming a magnetic metal thin film on the recording medium, it can be applied to magnetic recording and reproduction.

  As described above, the present invention has not only a large industrial ripple effect for the application and development of holography as a next-generation optical memory technology, but also a specific application example of nanotechnology based on metal nanoparticles. It can be said that the industrial utility value is extremely high.

  In the above-mentioned embodiment, the particle diameter of the metal nanoparticles 2a is in the range of 5 nanometers to 10 nanometers, and the average film thickness of the metal thin film 2 is 7 nanometers to 8 nanometers. It is not limited. As described above, in order to increase the resolution and improve the recording density, the smaller the particle size of the metal nanoparticles, the better. However, when the particle size of the metal nanoparticles is reduced, the average film thickness is also reduced in proportion thereto, and a change in optical density necessary for information recording cannot be obtained. That is, when the particle size and the average film thickness are smaller than 3 nanometers, the film thickness is too thin to absorb light sufficiently and the optical density is reduced to about 0.2. It does not show enough optical change to record information based on the difference in reflectance or reflectance. On the other hand, when the particle size of the metal nanoparticles is increased, the average film thickness is also increased, and the optical density is increased, but the degree of adhesion between the metal nanoparticles is increased. Heat due to the energy of the metal easily conducts or diffuses through the metal thin film, and the energy threshold required for agglomeration and granulation is greatly increased. Furthermore, when trying to give a large energy exceeding this threshold value, agglomeration granulation is caused by heat diffused from the surroundings even in a portion exposed at a level below the energy threshold value (a portion where the light intensity is weakened by interference). Clear interference fringes cannot be obtained. From the above, the particle size of the metal nanoparticles may be in the range of 3 to 20 nanometers, and the average film thickness may be in the range of 3 to 20 nanometers. In order to further enhance the above effect, the particle size of the metal nanoparticles is in the range of 5 nanometers to 10 nanometers, and the average film thickness is preferably in the range of 5 nanometers to 10 nanometers. preferable. As a result, the optical density is in the range of 0.3 to 0.6, and an optical change sufficient to record information based on the difference in transmittance or reflectance before and after light irradiation can be shown. .

  In the above-described embodiment, the energy density of the laser beam is in the range of 0.6 millijoule / square millimeter to 2.0 millijoule / square millimeter. However, the energy density is not limited to this. The average film thickness of the metal thin film 2 can be changed. For example, when the average film thickness is 3 nanometers, the range is from 1.4 millijoules / square millimeter to 8.0 millijoules / square millimeter, and when the average film thickness is 5 nanometers, 1.1 millijoules. / Square millimeter to 2.2 millijoules / square millimeter, and for an average film thickness of 10 nanometers, a range of 1.0 millijoule / square millimeter to 1.2 millijoules / square millimeter may be used. preferable.

  In the above-described embodiment, the metal nanoparticles 2a are made of platinum element. However, the present invention is not limited to this, and is not limited to this, but a platinum group element such as palladium, an alloy of platinum and palladium, or platinum and nickel. Or an alloy of palladium and nickel. By alloying, the mechanical strength of the metal thin film or the adhesion strength to the substrate is increased.

  In the above-described embodiment, the transmitted light conjugate with the reference light is used at the time of reproduction. However, the present invention is not limited to this. In other words, not only the transmittance changes by several tens of percent due to the structural change of the metal thin film before and after the light irradiation, but also the reflectance changes by several tens of percent, so it is possible to reproduce information using reflected light. is there.

  In the above embodiment, the laser beam is used. However, the present invention is not limited to this, and an electron beam having a shorter wavelength can be used.

  In the above-described embodiment, the multiplex recording is performed by rotating the reference light 30 around the information light 40. However, the present invention is not limited to this, and the incident angle of the reference light 30 is changed or the wavelength is changed. It is possible to multiplex-record different information in the same place by changing the.

Embodiment 2
In the above-described first embodiment, the laser light is separated into two light beams of the reference light 30 and the information light 40 and interferes in the metal thin film 2. The case where the single light is irradiated on the metal thin film 2 will be described below.

  An optical mask in which an information pattern is written in advance by electron beam drawing or the like is created. The optical mask is placed on the recording medium 17 having the metal thin film 2 in contact with the metal thin film 2. A laser beam having low energy is scanned on the optical mask. In the portion of the optical mask that passes the laser beam, the metal nanoparticles that absorbed the energy of the irradiation light that passed through are heated and melted, and a plurality of metal nanoparticles are combined and formed into spherical droplets by surface tension. The metal nanoparticles are agglomerated and granulated.

  On the other hand, in the portion of the optical mask that does not pass the laser beam, the energy necessary for melting the metal nanoparticles is not supplied, and therefore the metal nanoparticles are not agglomerated. Thus, information is recorded by forming a pattern composed of a portion where the metal nanoparticles are agglomerated and a portion not agglomerated corresponding to the information pattern of the optical mask.

  This allows information to be recorded in a very short time by performing scan exposure only once using a low-energy laser beam, and no post-processing such as development or fixing is required, and information is densely recorded. Can be recorded, and a recording method using the recording medium can be provided.

  The portion where the metal nanoparticles are agglomerated and the portion where the agglomeration is not agglomerated are different in optical properties, and the reflectance changes greatly. Accordingly, the recorded information can be reproduced by irradiating the recording medium on which the information is recorded by the above-described recording method with light and detecting a change in reflectance.

  In the above-described embodiment, the optical mask is used. However, the configuration is not limited to this, and information may be directly recorded on the recording medium by electron beam drawing.

It is explanatory drawing which shows the example of observation of the metal thin film of the recording medium based on this invention. It is explanatory drawing which shows the structure of the recording medium based on this invention. It is a schematic diagram of the apparatus for enforcing the recording method concerning this invention. It is explanatory drawing which shows the example of observation of the metal thin film of the recording medium after laser beam irradiation. It is explanatory drawing which shows the structure of the recording medium after laser beam irradiation. It is explanatory drawing which shows the interference fringe model by laser beam irradiation. It is explanatory drawing which shows the change of the absorption spectrum by laser beam irradiation. It is explanatory drawing which shows the relationship between the degree of the spatial modulation of the energy density of the laser beam produced by interference, and the line width of an interference fringe. It is explanatory drawing which shows the concept of angle multiplexing recording. It is explanatory drawing which shows the example of the square-lattice hologram by double recording. It is a schematic diagram of the apparatus for enforcing the reproduction | regenerating method based on this invention. It is explanatory drawing which shows the example of the recording medium based on this invention. It is explanatory drawing which shows the example of the recording medium based on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2,3 Metal thin film 2a, 3a Metal nanoparticle 4 Transparent resin layer 10 Laser 11 Beam diameter conversion lens 12 Half mirror 13 Mirror 14 Prism 15, 18 Objective lens 16 Page composer 17 Recording medium 19 Reproduction lens 20 Photodiode 30 Reference light 40 Information light 50 Reproduction light

Claims (9)

In a recording medium for recording information on a recording layer formed on a substrate,
The recording layer is a metal thin film in which metal nanoparticles are in close proximity or in contact with each other.   2. The recording according to claim 1, wherein the metal thin film includes one metal selected from the group consisting of platinum, palladium, an alloy of platinum and palladium, an alloy of platinum and nickel, an alloy of palladium and nickel. Medium.   3. The recording medium according to claim 2, wherein an average film thickness of the metal thin film and a particle diameter of the metal nanoparticles are each in a range of 3 nanometers to 20 nanometers.   4. A recording medium according to claim 1, wherein a plurality of the recording layers are laminated on a substrate. In a recording method for recording information by irradiating a recording medium with light,
Using a recording medium on which a metal thin film is formed in a state in which metal nanoparticles are close to or in contact with each other on a substrate,
The metal nanoparticles are agglomerated and granulated by irradiation energy,
A recording method characterized in that information is recorded by forming a pattern composed of an agglomerated part and a non-agglomerated part. Irradiating the metal thin film with coherent light separated into two light fluxes of information light and information light having information to cause interference,
6. The recording method according to claim 5, wherein an interference fringe composed of an agglomerated and non-agglomerated part is formed.   7. The coherent light applied to the metal thin film is a single pulse laser beam having an energy density of 0.5 millijoule / square millimeter or more and a pulse width of 5 nanoseconds or less. The recording method described in 1. In a reproducing method for reproducing information by irradiating light on a recording medium on which information is recorded by a recording method of irradiating light to record information,
6. The recording method according to claim 5, wherein information is reproduced based on a difference in reflectance of irradiated light. In a reproduction method for reproducing information by irradiating light onto a recording medium on which information is recorded by a recording method for recording information by interfering with coherent light,
The recording method is the recording method according to claim 6 or claim 7,
A reproduction method comprising reproducing information by irradiating light having the same wavelength as the coherent light.

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