JP5305928B2 - How to create a periodic structure - Google Patents

Description

  The present invention relates to a method for creating a periodic structure that develops color using optical reflection and diffraction.

  In recent years, studies have been made to generate various functions such as optical functions and wettability control by forming a fine structure on a solid surface. Among them, by forming a periodic fine structure on the surface of a workpiece made of solid, the surface of the workpiece can be colored with a specific color by utilizing reflection of light and interference of diffracted light. There is a coloring structure technology that can. As an application example of the present technology, there is a case where a fine structure is formed on the surface of the exterior part to develop a color for decoration of the exterior part.

  The present technology is realized by processing a surface of a workpiece with a structure such as a V-groove, for example, at a periodic interval of about a wavelength. Examples of the fine shape processing method include machining, electron beam drawing, and laser processing. Machining has the feature that the machining shape has a high degree of freedom, but there is a limit to the miniaturization of the machining shape, and the machining time is enormous because each shape is processed sequentially with a single tool. There is a problem of becoming. In addition, although electron beam drawing processing can process a fine shape of the order of μm or less, there is a problem that the processing range is limited because the processing speed is low.

On the other hand, it is known that a fine periodic structure can be formed by irradiating the surface of a workpiece with a linearly polarized laser beam at a fluence (energy density) near the processing threshold (see Non-Patent Documents 1 and 2). In this method, a periodic structure of the wavelength order of the laser can be formed in a self-organized manner on a workpiece made of a material such as a metal, a semiconductor, or a polymer. The range in which the periodic structure is formed is limited to the irradiation range, but as shown in FIG. 6, the laser irradiation unit 1 of the femtosecond laser is scanned with the workpiece 2 placed on the processing stage. It is known that the periodic structure 5 can be formed over a wide range on the surface of the workpiece 2 by scanning while overlapping the boundary portion 3 (see Patent Document 1). This processing method (periodic structure creation method) is capable of processing by scanning a workpiece 2 with a laser expanded to a certain irradiation range, so that processing of a large area is possible and processing speed is another method. There is an advantage that it is large compared to. In FIG. 6, in order to facilitate understanding of such a formation state, a peak (or valley) portion of the periodic structure 5 is indicated by a solid line.
AE Siegman, PM Fauchet: Stimulated Wood's anomalies on laser-illuminated surfaces, IEEE J. Quantum Electron., QE-20, 8 (1986) P.1384 Minamishimasa, Toyoda Koichi: Dependence of Ripple Formation Angle of Incidence on Metals and Semiconductors by Laser-Induced Surface Electromagnetic Waves, Laser Research, 28, 12 (2000) P.824. International Publication WO 2004/035255

  However, when the periodic structure is formed over a wide range while overlapping the laser irradiation parts using the conventional method for creating a periodic structure, the base point of the periodic structure formed in each laser scanning is different, and therefore, as shown in FIG. Thus, the problem that the periodic structure 5 becomes discontinuous at the laser scanning boundary 3 has occurred. In the discontinuous portion of the periodic structure 5 (laser scanning boundary portion 3), since the diffraction wavelength is different from the surroundings, the color development changes compared to the continuous portion of laser scanning (portion other than the laser scanning boundary portion 3). As a result, the laser scanning boundary 3 becomes conspicuous, and there is a problem as a decoration application for exterior parts and the like.

  Further, when the periodic structure 5 is created using a femtosecond laser, the period of the periodic structure 5 to be formed is determined by the laser wavelength and the incident angle. Therefore, when the laser wavelength and the incident angle are constant, the period of the periodic structure 5 to be formed is the same in the processing surface of the same workpiece 2. Therefore, when the periodic structure 5 created by the conventional processing method is used for structural color development, there is a problem that the color condition cannot be changed because the color to be colored is single.

  The present invention solves the above-described conventional problems, and a method for creating a periodic structure in which a laser scanning boundary is not noticeable even if a periodic structure is created over a wide range by scanning a laser irradiation portion on the surface of a workpiece. Another object of the present invention is to provide a method for producing a periodic structure capable of producing a light intermediate color.

  In order to achieve the above object, a method for producing a periodic structure according to claim 1 of the present invention is configured to scan a laser irradiation portion for irradiating a laser while superimposing the laser irradiation portion on the surface of a workpiece at a laser scanning boundary portion. A periodic structure creation method for creating a periodic structure by processing the surface of the workpiece, wherein the crystal grain size of the laser scanning boundary portion is larger than the crystal grain size of the portion other than the laser scanning boundary portion. First, a femtosecond laser is scanned at a fluence near the processing threshold so that the laser scanning boundary portion becomes a boundary of a laser scanning path with respect to the workpiece that has been miniaturized and the laser scanning boundary portion has been miniaturized. After the first laser processing, a second laser that scans the workpiece with a fluence near the processing threshold so as to overlap the workpiece at the laser scanning boundary portion. The period and the height of the periodic structure formed at the laser scanning boundary portion are distributed in a state in which the period and the height of the periodic structure formed other than the laser scanning boundary portion are smaller. It is characterized by forming a structure. In other words, the crystal grain size at the laser scanning boundary of the workpiece is locally refined in advance, and processing is performed while scanning the femtosecond laser at a fluence near the processing threshold so that this laser scanning boundary becomes the boundary. It is characterized by.

  Here, when a workpiece is irradiated with a linearly polarized femtosecond laser, a periodic structure is formed in a self-organized manner at wavelength intervals due to interference between incident light of p-polarized components and surface scattered light. At this time, when a grain boundary exists on the surface of the workpiece, the interval between the incident light and the scattered light changes due to the surface step at the grain boundary part. And the height becomes discontinuous.

  Therefore, according to the present method, by forming a large number of crystal grain boundaries by refining the crystal grain size at the laser scanning boundary part, many discontinuous parts of the period and height of the periodic structure formed at the time of laser irradiation are formed. be able to. Since grain boundaries exist in all orientations, as a result, the period and height of the periodic structure at the laser scanning boundary are in a small range compared to the periodic structure formed outside the grain boundary on a macro scale. Therefore, the boundary of the laser scanning boundary portion does not form a clear periodic structure boundary. In this way, since there is no clear boundary in the periodic structure, it becomes a surface state in which the boundary line cannot be visually recognized, and it is possible to solve the appearance quality problem that has occurred conventionally. it can.

The method for creating a periodic structure according to claim 2 of the present invention is characterized in that the crystal grain size at the laser scanning boundary portion is made finer by irradiating the laser scanning boundary portion with a laser in advance. According to this method, the crystal grain size can be refined by locally heating the surface of the laser scanning boundary portion of the workpiece to the recrystallization temperature by laser irradiation to recrystallize the irradiated portion. . Note that a CO ₂ laser, a YAG laser, or the like may be appropriately selected according to the absorption rate with respect to the wavelength of the workpiece. Further, the irradiation spot diameter may be selected as appropriate according to the region in which the crystal grain size is made fine and the laser output.

The exterior component according to claim 3 of the present invention is an exterior component created by the periodic structure creation method according to claim 1 or 2, and has a period and a depth distributed with a predetermined value as a center value. By having such a periodic structure, it is characterized in that light having a wavelength within a certain range is diffracted around a predetermined wavelength. In this way, by distributing the period and height of the periodic structure formed on the surface of the exterior part so as to be small within a certain range, the color to be developed is not a specific color defined in the central range, but a light color. An intermediate color can be developed.

Further, as described in claim 4 of the present invention, when the surface of the electronic device is constituted by an exterior part that develops color, a painting process is not required, and the manufacturing cost and the environmental load can be reduced.

  As described above, according to the method for creating a periodic structure of the present invention, even if the periodic structure is created over a wide range by scanning the laser irradiation part by controlling the crystal grain size on the surface of the work material, the scanning boundary It is possible to form a periodic structure over a wide range with no conspicuous portion and no problem in appearance quality. In addition, it is possible to form a periodic structure that can develop a light intermediate color.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment 1)
In the method for creating a periodic structure according to Embodiment 1 of the present invention, the surface of the workpiece is scanned by causing a laser irradiation unit that irradiates a laser to scan the surface of the workpiece while overlapping the laser scanning boundary. A method for creating a periodic structure in which a periodic structure is formed by processing a wide area of the laser, wherein the crystal grain size at the laser scanning boundary is made finer in advance than the crystal grain size at locations other than the laser scanning boundary. First, the femtosecond laser is scanned at a fluence near the processing threshold so that a part of the laser scanning boundary portion becomes a boundary portion of the laser scanning path with respect to the workpiece whose scanning boundary portion has been miniaturized. Laser processing is performed, and after this first laser processing, a femtosecond laser is applied near the processing threshold so as to overlap the workpiece including the unprocessed portion of the laser scanning boundary portion at the laser scanning boundary portion. The period and height of the periodic structure formed at the laser scanning boundary portion is higher than the period and height of the periodic structure formed at other than the laser scanning boundary portion. A periodic structure distributed in a reduced state is formed. In other words, the crystal grain size at the laser scanning boundary in the workpiece is locally refined and processed while scanning the femtosecond laser at a fluence near the processing threshold so that this laser scanning boundary becomes the boundary. It is characterized by.

FIG. 1 shows a main part of a workpiece in which a periodic structure is formed by the method for creating a periodic structure according to Embodiment 1 of the present invention.
As shown in FIG. 1, when the surface of the workpiece 2 is scanned with a linearly polarized femtosecond laser irradiation unit 1 formed into an elliptical shape, a p-polarized component of incident light and a p-polarized component of surface scattered light are obtained. Interference occurs, and the periodic structure 5 having the laser wavelength interval is formed. In the embodiment of the present invention, before performing laser irradiation, the crystal grain size of a laser scanning boundary portion 3 to be described later is made finer in advance than the crystal grain size of portions other than the laser scanning boundary portion. When the material of the workpiece 2 is single crystal or amorphous, or when the size of the crystal grains is sufficiently large with respect to the wavelength, the periodic structure 5A to be formed is formed with a periodic interval and height. When there is a crystal grain refinement region 4 in which crystal grains are refined on the surface of the workpiece 2, the interval at which the interference between the incident light and the scattered light changes due to a step in the crystal grain boundary. The starting point at which the periodic structure 5B is formed is different. For this reason, a large number of periodic structures 5B having different starting points are formed in the crystal grain refinement region 4, and in the crystal grain refinement region 4, the period and height of the periodic structure 5B are predetermined values ( It is distributed in a certain range centered on a predetermined value that is equal to or less than the period and height of the periodic structure 5A at a portion that is not the crystal grain refinement region 4. When the laser irradiation unit 1 is scanned over the surface of the workpiece 2 while being overlapped by a predetermined scanning path, a crystal grain is formed around the laser scanning boundary 3 when the workpiece 2 is processed over a wide range. By forming the miniaturized region 4, it is possible to form the periodic structure 5 having no clear periodic structure shift at the laser scanning boundary portion 3. Considering the application of the periodic structure 5 to a use in which the appearance of coloring and decoration is important, the shift of the periodic structure at the laser scanning boundary 3 of the scanning path is a visual problem. As described above, by distributing the period and height of the periodic structure 5B around the laser scanning boundary 3 within a certain range, the boundary cannot be visually recognized, so that the appearance problem can be solved.

  In FIG. 1, the crest (or valley) of the periodic structure 5 (5A, 5B) is indicated by a solid line, and the crystal grain boundary is indicated by a dotted line for easy understanding. As shown in FIG. 1, the area of the crystal grain refinement region 4, that is, the area corresponding to each crystal grain on the surface of the workpiece 2 in and around the laser scanning boundary 3 is the crystal grain refinement region 4. The area is smaller than the area corresponding to each crystal grain in the other region, and the periodic structure 5 is formed for each region corresponding to each crystal grain.

  Next, a specific processing example of the method for creating the periodic structure 5 will be described in detail. FIG. 2 is a diagram schematically showing a periodic structure creating apparatus for creating a periodic structure. The periodic structure creation device supports a femtosecond laser generator 6 (wavelength 800 nm, repetition frequency 1 kHz, energy 284 mW, pulse width 200 fs) 6, a plurality of folding mirrors 7, a condenser lens 8, and a workpiece 2. An XY stage 9 as a processing stage is provided. The femtosecond laser generator 6 is configured to irradiate the laser beam onto the workpiece 2 placed on the XY stage 9 through the folding mirror 7 and the condenser lens 8.

  Here, the material of the workpiece 2 is SUS304 having an average particle diameter of 40 μm and a region of about 1 mm in width on the overlapping part (laser scanning boundary part 3) of the laser scanning path subjected to heat treatment to an average particle diameter of 5 μm. Was used. Note that the workpiece 2 in the present embodiment may be a workpiece that has been subjected to a refinement process in advance at a location corresponding to the laser scanning boundary portion 3 on the XY stage 9. You may use what was refined | miniaturized by rapid heating by irradiating the laser which adjusted irradiation energy. In addition, it is important that the crystal grain size is not reduced rapidly at the laser scanning boundary 3 but gradually reduced around the laser scanning boundary 3.

  As a more specific example, a laser focused at an elliptical shape with a width of 4 mm by the condenser lens 8 is used to scan the workpiece 2 so that the lasers overlap with each other. / sec, the scanning path line pitch was 3.8mm. As a result of measuring the shape of the created periodic structure 5 in a 4 μm square region, a uniform periodic structure 5A having a period of 580 nm and a height of 220 nm was obtained in the region outside the overlapping portion (corresponding to the laser scanning boundary portion 3). On the other hand, the periodic structure 5B distributed in a period of 495 to 580 nm and a height of 130 to 217 nm was formed in the overlapping portion. Further, in the processing range formed by this processing method, the boundary line of the overlapped portion could not be confirmed in appearance.

(Embodiment 2)
In the method for creating a periodic structure according to the second embodiment of the present invention, the periodic structure is formed by processing the surface of the workpiece by scanning the surface of the workpiece with a laser irradiation unit that irradiates a laser. A method for creating a periodic structure, wherein a coarse crystal grain region having a large average value of crystal grain size within a laser irradiation region and a fine crystal grain region having a small mean value of crystal grain size are formed on a surface of a workpiece. And processing the surface of the workpiece provided with these coarse crystal grain regions and fine crystal grain regions while scanning the femtosecond laser with a fluence near the processing threshold, thereby obtaining the fine crystal grain regions. A periodic structure distributed in a state where the period and the height of the periodic structure formed in the above are smaller than the period and the height of the periodic structure formed in the coarse crystal grain region is formed.

  FIG. 3 shows a main part of a workpiece in which a periodic structure is formed by the method for creating a periodic structure according to Embodiment 2 of the present invention. 3, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals, and the description thereof is omitted.

  In FIG. 3, the femtosecond laser irradiation unit 1 is preliminarily subjected to heat treatment on the work piece 2, whereby a region (coarse crystal grain region) 10 having coarse crystal grains on the surface of the work piece 2 is fine. A region having fine crystal grains (fine crystal grain region: a portion indicated by a P-shape in FIG. 3) 11 is formed, and a femtosecond laser is irradiated so as to irradiate the entire region. Thereby, in the coarse crystal grain region 10, a regular periodic structure 5 </ b> C of about the wavelength is formed, whereas in the fine crystal grain region 11, due to the influence of the step at the crystal grain boundary and the change of the processing threshold value. Many periodic structures 5D having different starting points are formed. Therefore, in the fine crystal grain region 11, macroscopically, the period and height of the periodic structure 5 </ b> D are centered on a predetermined value (predetermined value equal to or less than the period and height of the periodic structure 5 </ b> C of the coarse crystal grain region 10). It will be distributed in a certain range. In the method for creating the periodic structure, the ratio of the size of the coarse crystal grains to the size of the fine crystal grains is sufficiently increased, whereby the region of the regular periodic structure 5C (the region corresponding to the coarse crystal grain region 10). And the region of the irregular periodic structure 5D (region corresponding to the fine crystal grain region 11) become clear enough to be recognized by human eyes, and the region of the regular periodic structure 5C (coarse crystal) The region corresponding to the grain region 10) and the region of the irregular periodic structure 5D (the region corresponding to the fine crystal grain region 11) have different wavelength bands of light diffracted with respect to the incident light. The hue of the region of the periodic structure 5D (the region corresponding to the fine crystal grain region 11) can be changed.

  Note that the workpiece 2 in the present embodiment may be a workpiece corresponding to the fine crystal grain region 11 that has been subjected to a refinement process in advance, or irradiation energy may be applied on the XY stage 9. You may use what was refined | miniaturized by rapid heating by irradiating the adjusted laser.

  A specific processing example of the method for creating the periodic structure 5 will be described below. The configuration of the periodic structure creation device that creates the periodic structure is the same as that of the first embodiment. A femtosecond laser is applied to a workpiece 2 made of SUS304 in which a workpiece material in which a fine crystal grain region 11 having a crystal grain size of 5 μm is formed in a 3 mm square in a coarse crystal grain region 10 having a crystal grain size of 110 μm. The irradiation unit 1 was scanned so as to irradiate the entire coarse crystal grain region 10 including the fine crystal grain region 11. As a result, a periodic structure 5C having a period of about 600 nm and a height of about 200 nm was formed in the coarse crystal grain region 10, and blue diffracted light was emitted in appearance. On the other hand, in the fine crystal grain region 11, a periodic structure 5D having a period of 495 to 600 nm and a height of 100 to 200 nm is formed, and the diffracted light becomes a light blue color. .

(Embodiment 3)
In the method for creating a periodic structure according to the third embodiment of the present invention, the surface of the workpiece is processed by causing a laser irradiation unit that irradiates a laser to scan the surface of the workpiece, thereby forming the periodic structure. A method for creating a periodic structure, which is formed by processing a workpiece having a crystal grain size within a predetermined range while scanning a femtosecond laser with a fluence near a processing threshold. A periodic structure having a period and a height smaller than a period and a height formed for a single crystal material is produced.

  FIG. 4 shows a main part of a workpiece in which a periodic structure is formed by the periodic structure creating method according to Embodiment 3 of the present invention. 3, the same components as those in FIGS. 1 and 2 are denoted by the same reference numerals, and the description thereof is omitted. FIG. 5 is a schematic diagram of a periodic structure formed by the method for creating a periodic structure. The entire surface of the workpiece 2 to be irradiated with laser is subjected to a process of refining crystal grains to provide a region 11 (fine crystal grain region) having fine crystal grains, and then the femtosecond laser 1 is applied to the entire surface. , The periodic structure 5 (single crystal) in which the period p and the height h as shown in FIG. 5 are distributed over a predetermined range around a predetermined value over the entire surface of the workpiece 2. Periodic structures smaller than the period and height formed for the material can be formed.

  The period p and the height h of the periodic structure 5 formed by this processing method have a correlation with the number of crystal grain boundaries in the fine crystal grain region 11, but for example, a workpiece having a crystal grain size of 5 to 10 μm On the other hand, when the femtosecond laser was irradiated under the same conditions as in the first embodiment, a periodic structure having a period of 495 to 600 nm and a height of 100 to 200 nm was formed. In general, when color is generated using reflection and diffraction of a periodic structure, only a single wavelength is diffracted in a periodic structure with a uniform period, so the color to be colored is limited, but as in this embodiment, the period is By distributing the period p and height h of the structure 5 in a certain range (a range smaller than the period and height formed for a single crystal material), the wavelength and intensity of the diffracted light are distributed in a certain range, so that color development Since the color to be lightened, a more preferable periodic structure was obtained as an exterior part.

As an example, when used for an exterior part of an electronic device such as a television or a personal computer, the exterior part emits a blue intermediate color, and a complicated painting process can be omitted.
As described above, according to the method for creating a periodic structure of the present invention, a periodic structure in which a laser scanning boundary portion does not stand out even when a laser irradiation portion is scanned to create a periodic structure in a wide range and a period in which light is colored with a light color. A structure can be created.

  Furthermore, the periodic structure can be processed on the surface of a metal mold by the method for creating a periodic structure of the present invention. In this way, by resin injection molding using a mold having a periodic structure on the surface, it is possible to produce a resin part (such as an exterior part that decorates the exterior) whose surface is structurally colored. In addition, it is possible to create an electronic device whose surface is composed of this exterior component, which eliminates the need for a coating process for the exterior component and the electronic device, thereby reducing manufacturing costs and environmental impact. Become.

  The method for creating a periodic structure according to the present invention can be applied to processing various types of exterior decorative parts and the like that generate structural colors.

The figure which shows the principal part of the workpiece which formed the periodic structure with the preparation method of the periodic structure which concerns on Embodiment 1 of this invention. The figure which showed the periodic structure creation device which creates the periodic structure typically The figure which shows the principal part of the to-be-processed object which formed the periodic structure with the preparation method of the periodic structure which concerns on Embodiment 2 of this invention. The figure which shows the principal part of the to-be-processed object which formed the periodic structure with the preparation method of the periodic structure which concerns on Embodiment 3 of this invention. Schematic diagram of a periodic structure formed by the method for creating a periodic structure according to Embodiment 3 of the present invention Schematic diagram of the periodic structure formed in the conventional method

1 Laser irradiation part (femtosecond laser irradiation part)
2 Workpiece 3 Laser scanning boundary 4 Crystal grain refinement region 5, 5A to 5D Periodic structure 6 Femtosecond laser generator 7 Mirror 8 Condensing lens 9 XY stage (processing stage)
10 Coarse crystal grain region 11 Fine crystal grain region p Pitch of periodic structure to be formed h Height of periodic structure to be formed

Claims (4)

A periodic structure creation method for creating a periodic structure by processing a surface of the workpiece by scanning a laser irradiation portion for irradiating a laser while overlapping the surface of the workpiece at a laser scanning boundary portion. There,
The crystal grain size at the laser scanning boundary is made finer than the crystal grain size at locations other than the laser scanning boundary,
First laser processing for scanning a femtosecond laser with a fluence near the processing threshold so that the laser scanning boundary portion becomes a boundary of a laser scanning path with respect to the workpiece on which the laser scanning boundary portion is miniaturized. And
After the first laser processing, the laser scanning boundary portion is subjected to second laser processing for scanning the workpiece with a fluence near the processing threshold so as to overlap the workpiece at the laser scanning boundary portion. Forming a periodic structure distributed in a state in which the period and height of the periodic structure formed in the region are smaller than the period and height of the periodic structure formed outside the laser scanning boundary portion How to create a structure.   2. The method for creating a periodic structure according to claim 1, wherein the crystal grain size of the laser scanning boundary portion is made finer by irradiating the laser scanning boundary portion in advance. The exterior part created by the method for creating a periodic structure according to claim 1 or 2 , wherein a periodic structure having a period and a depth distributed with a predetermined value as a center value has a wavelength of a predetermined value. An exterior part configured to diffract light having a wavelength within a certain range as a center. An electronic apparatus comprising a surface made of the exterior component according to claim 3 .

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