CN101380693A - A method for preparing micro/nano structures on the surface of metal materials using femtosecond laser - Google Patents

Abstract

A method for preparing a micro/nano structure on the surface of a metal material using a femtosecond laser. The preparation steps are as follows: after the surface of the metal material is mechanically ground and polished, it is cleaned by ultrasonic cleaning with deionized water; In an air environment, use a 10× microscope objective to focus the incident femtosecond laser pulse vertically on the surface of the above material. The radius of the laser beam at the focal point is 5 microns, and adjust the surface of the material to a distance of 10~ from the focal plane of the objective lens along the direction of the reverse beam. At the position of 250 microns, micro/nano structures can be induced on the surface of metal materials. The invention has the advantages of simple process, convenience, practicality and no pollution, and can improve and enhance the thermal radiation efficiency of the material in a wide spectral range.

Description

A method for preparing micro/nano structures on the surface of metal materials using femtosecond laser

(1) Technical field

The invention relates to a method for preparing a micro/nano structure on the surface of a metal material, in particular to a method for preparing a micro/nano structure on the surface of a metal material by using a femtosecond laser.

(2) Background technology

With the increasingly scarce supply of energy today, seeking to develop new energy sources and improve the energy conversion efficiency of materials has attracted widespread attention from all over the world. As an important renewable energy source, thermal photovoltaic cells have attracted more and more attention from researchers at home and abroad due to their unique thermal-to-electrical conversion performance. In this technology, the radiation characteristics of the heat source play a very important role in the whole system. In fact, a high-quality heat radiator will greatly improve the heat-to-electricity conversion efficiency of a thermophotovoltaic system. In addition, a good heat dissipation device is very important for many optoelectronic components and their products. For example, the laser crystal in a solid-state laser usually needs to be placed in a metal cooling jacket with good heat dissipation, so that the gain medium has a A constant lower temperature can ensure the normal operation of the laser. Similarly, the heat dissipation of the chip (CPU) in the computer is also a very important issue, and a relatively inefficient heat dissipation system will seriously reduce the working efficiency of the chip. Therefore, how to develop high-efficiency metal thermal radiation devices in a wide spectral band has become an important topic of scientific research at the present stage.

One of the main means to solve this problem is to enhance or change its optical properties by producing micro/nanostructures on the metal surface. It has been reported that the use of metal surface micro/nanostructures to change its heat radiation documents has: US5079473 discloses the use of electrochemical methods and chemical vapor deposition (CVD) processes to process 200-400 nanometers in diameter and 2 in depth on tungsten wafers. -A series of small holes of 4 microns, and the submicron cavity structure on the surface of the sample has an obvious suppression effect on infrared radiation, which can effectively improve the visible light luminous efficiency of incandescent lamps under the high temperature condition of 1400K. US6433303 discloses using an optical mask and a diffractive optical element to split ultrashort pulse laser or excimer laser into multiple beams, and then focus them on a metal surface. In this way, a hemispherical microcavity array is prepared. In addition, German scientist M.Kreiter et al [Thermally induced emission of light from a metallic diffractiongrating, mediated by surface palsmons, Optics Communication, 1999, 168: 117-122] reported the application of holographic photoresist and ion beam etching The hybrid technology of the present invention realizes the fabrication of diffraction gratings with a period of 485 nm on the gold film. They found in the angular radiation measurement that the sample was heated to 700 ° C: for the radiation light with a wavelength of 710 nanometers, there is an enhanced thermal radiation peak only at a specific angular position, and they attributed this phenomenon to the thermal excitation of the sample surface. The physical mechanism of the mutual coupling of surface plasmons and radiated light waves. Japanese researcher H.Sai et al [Thermophotovoltaic generation with selective radiators based on tungsten surface gratings, Applied Physics Letters, 2004, 85(16): 3399-3401] proposed to use electron beam exposure technology to make a The rectangular microcavity is a two-dimensional grating structure with a period of 1-2 microns. The test results under high temperature conditions show that the radiation spectrum of the sample is accompanied by sharp peaks in the near-infrared band, which has an obvious selective spectral enhancement effect. In addition, French scientist M.Laroche et al [Highly directional radiation generated by a tungsten thermal source, Optics Letters, 2005, 30(19): 2623-2625] used optical exposure technology to etch a period of 3 microns on the smooth surface of metal tungsten , a thin layered grating structure with a depth of about 0.125 microns. Experimental measurements have obtained that the thermal radiation of the metal microstructure has an unusually high directivity in the near-infrared band, which means that the electromagnetic field on the heat source plane has greater spatial coherence.

In summary, these existing research reports use the micro/nano structure of the metal surface to control the directionality, coherence and spectral selectivity of its thermal radiation, and the thermal radiation enhancement phenomenon observed in experiments They are all concentrated in a narrow spectral range, and the enhanced thermal radiation effect in a wide spectral range has not been reported yet. In addition, in the above-mentioned studies, the fabrication process of micro/nanostructures on the metal surface mainly relies on the planar process of traditional lithography. procedures, and the types of materials and processing patterns have great limitations.

(3) Contents of the invention

The object of the present invention is to address the above-mentioned problems, to provide a method for preparing micro/nano structures on the surface of metal materials using femtosecond lasers, which is simple in process, convenient and practical, non-polluting, and can improve and enhance the thermal radiation efficiency of materials in a wide spectral range. method.

Technical scheme of the present invention:

A method for preparing a micro/nano structure on the surface of a metal material using a femtosecond laser, characterized in that the preparation steps are as follows:

1) After the surface of the metal material is mechanically ground and polished, it is ultrasonically cleaned with deionized water, and then fixed on a three-dimensional precision mobile platform in an air environment, and the spatial position of the above metal material is realized by computer control. movement on

2) Take the femtosecond laser beam as the main optical path, use the helium-neon laser beam as the auxiliary optical path, adjust the helium-neon laser beam and the femtosecond laser beam to propagate in the same direction, and make the two overlap each other on the optical path, and then pass through the focusing mirror together Reaching the surface of the metal material vertically;

3) Turn off or block the femtosecond laser beam so that only the helium-neon laser beam irradiates a certain position on the surface of the above material at this time, and then place a beam splitter at an angle of 45 degrees on the optical path away from the focusing mirror along the reverse beam direction , so that the laser beam reflected from the surface of the metal material and returned through the focusing mirror is spatially separated from the original incident beam, and is collected and imaged in real time by a photodetector;

4) Move the above-mentioned metal material in a two-dimensional plane perpendicular to the incident laser beam, and adjust the horizontal inclination of the processing platform by observing the change of the spot size in the imaging system, so that the entire surface of the above-mentioned metal material and the incident laser beam interact with each other vertical;

5) adjusting the position of the above-mentioned metal material along the direction parallel to the incident light beam, so that the spot size observed from the imaging system is the smallest;

6) Turn off or block the helium-neon laser beam, so that the femtosecond laser beam directly irradiates the surface of the above-mentioned metal material, and by controlling the three-dimensional processing platform to make the above-mentioned material move forward or backward parallel to the direction of the incident laser beam, each time a device is moved After a certain step length, only 1-3 femtosecond laser pulses ablate the above metal materials;

7) Use a microscope to observe the size of the ablation area of the surface of the above-mentioned metal material after each movement of the femtosecond laser, and find the spatial position of the metal material surface corresponding to the minimum ablation area, which is the femtosecond laser beam after focusing Focus position behind the mirror, and move the surface of the metal material to this position by controlling the three-dimensional processing platform;

8) moving the above-mentioned metal material on the focal plane of the focusing mirror for a set distance along the direction of the reverse beam, and making the surface of the above-mentioned metal material and the incident laser beam maintain perpendicular to each other during the entire movement process;

9) Keeping the direction of the incident femtosecond laser beam unchanged, control the processing table so that the above-mentioned metal material performs two-dimensional mobile scanning in a plane perpendicular to the beam direction, and by changing the incident laser energy, prepare different laser beams on the surface of the above-mentioned metal material. Types of micro/nanostructures.

The metal material is titanium-nickel alloy.

The parameters of the femtosecond laser are: a pulse repetition frequency of 1 kilohertz, a pulse width of 50 femtoseconds, a pulse center wavelength of 800 nanometers, and a beam polarization direction of linear polarization.

The focusing lens is a 10× microscope objective lens.

The range in which the metal material moves forward or backward parallel to the beam direction is 500 microns, and the moving step is 5-10 microns.

The set distance that the metal material deviates from the focal plane of the focusing mirror along the reverse beam direction is 10-250 microns.

During the two-dimensional moving scanning process, the distance between adjacent laser scribe lines is 10-50 microns, and the moving scanning speed is 0.2-2 mm/s.

The incident laser energy is adjusted within the range of 50-300 microjoules, and there are three types of micro/nano structures induced on the surface of metal materials, including coral-like microcavity structures and nanoparticle-covered grating-like subwavelength structures And a honeycomb-like micro grating-nano hole composite structure.

The advantages of the present invention are: 1) Since the duration of the femtosecond laser pulse is extremely short, about 50 femtoseconds, even a small laser pulse energy can have a very high peak power. The peak power of a single laser pulse in the present invention can reach up to 4×10 ¹⁰ watts. On the one hand, it will cause many nonlinear physical effects in the process of femtosecond laser action, so that the metal surface can self-organize to form micro/nano On the other hand, the ultra-fast pulse duration will fundamentally weaken and eliminate the heat conduction effect of the material during the laser action, so that the spatial range of laser processing can be controlled at the submicron or nanometer level. Compared with the traditional planar exposure technology, the femtosecond laser technology described in the present invention is more convenient, faster and does not require other auxiliary conditions. The surface of the sample can self-organize to form micro/nano structures in various forms, and there is no pollution in the entire processing and manufacturing process. production and many other advantages. 2) The influence of surface micro/nanostructures on the thermal radiation of metal materials reported in literature and patents is mainly concentrated in a relatively narrow spectral bandwidth (about 400 nanometers), and the thermal radiation enhancement effect has obvious spectral selection. sex. The heat radiation efficiency of the material with the surface micro/nano structure described in the present invention can be significantly improved and enhanced in the wide spectral range of 7-16 microns. For example: for the metal or alloy surface of coral-like microcavity structure, its enhanced heat radiation efficiency can maintain 90% in the wide spectral range of 7-16 microns, such a high material heat radiation efficiency is expected to be used in thermo-photovoltaic systems , Broadband high-efficiency light sources and heat dissipation devices have important and extensive applications.

(4) Description of drawings

Figure 1 is a scanning photo of the coral-like microcavity structure on the surface of the titanium alloy material prepared in Example 1 of the present invention.

Fig. 2 is a scanning photo of a grating-like sub-wavelength structure covered by nanoparticles on the surface of the titanium alloy material prepared in Example 2 of the present invention.

FIG. 3 is a scanning photo of a honeycomb-like micro-grating-nanopore composite structure on the surface of the titanium alloy material prepared in Example 3 of the present invention.

Fig. 4 is an X-ray photoelectric energy spectrum diagram of titanium element in the micro/nano structure region on the surface of the sample material prepared in Examples 1, 2, and 3 of the present invention.

Fig. 5 is an X-ray photoelectric energy spectrum diagram of nickel element in the micro/nano structure region on the surface of the sample material prepared in Examples 1, 2, and 3 of the present invention.

Fig. 6 is a spectral diagram of material enhanced thermal radiation efficiency corresponding to Example 1 of the present invention.

FIG. 7 is a spectral diagram of material-enhanced thermal radiation efficiency corresponding to Example 2 of the present invention.

Fig. 8 is a spectral diagram of material-enhanced thermal radiation efficiency corresponding to Example 3 of the present invention.

Fig. 9 is a spectral diagram of thermal radiation efficiency corresponding to a planar titanium alloy material without femtosecond laser treatment.

(5) Specific implementation methods

Example 1:

1) The titanium-nickel alloy material of 10×10×2mm ³ was polished step by step with 400-800 water sandpaper, cleaned ultrasonically with deionized water, and then fixed on a three-dimensional precision mobile platform in the air environment , and realize the movement of the above-mentioned materials in the spatial position through computer control;

2) The femtosecond laser beam is used as the main optical path, and the helium-neon laser beam is used as the auxiliary optical path. After the focusing mirror reaches the surface of the metal material vertically, the femtosecond laser parameters are: pulse repetition frequency 1 kHz, pulse width 50 femtoseconds, pulse center wavelength 800 nanometers, beam polarization direction is linear polarization;

3) Turn off the femtosecond laser beam so that only the helium-neon laser beam is irradiated at a certain position on the surface of the above-mentioned material, and then place a beam splitter at an angle of 45 degrees on the optical path away from the focusing mirror along the direction of the reverse beam, so that The laser beam reflected from the surface of the metal material and returned through the focusing mirror is spatially separated from the original incident beam, and is collected and imaged in real time by a photodetector (CCD);

4) Move the above-mentioned metal material in a two-dimensional plane perpendicular to the incident laser beam, and adjust the horizontal inclination of the processing platform by observing the change of the spot size in the imaging system, so that the entire surface of the above-mentioned metal material and the incident laser beam interact with each other vertical;

5) adjusting the position of the above-mentioned metal material along the direction parallel to the incident light beam, so that the spot size observed from the imaging system is the smallest;

6) Turn off the helium-neon laser beam, make the femtosecond laser beam directly irradiate the surface of the above-mentioned metal material, and control the three-dimensional processing platform to make the above-mentioned material move forward 500 microns along the direction parallel to the incident laser beam, after every 5-10 microns , only 1-3 femtosecond laser pulses ablate the above metal materials;

7) Use a microscope to observe the size of the ablation area of the surface of the above-mentioned metal material after each movement of the femtosecond laser, and find the spatial position of the metal material surface corresponding to the minimum ablation area, which is the femtosecond laser beam after focusing Focus position behind the mirror, and move the surface of the metal material to this position by controlling the three-dimensional processing platform;

8) Moving the above-mentioned metal material on the focal plane of the focusing mirror for 10-250 microns along the direction of the reverse beam, and making the surface of the above-mentioned metal material and the incident laser beam can be kept perpendicular to each other during the entire movement process;

9) Keep the direction of the incident femtosecond laser beam unchanged, control the processing table so that the above-mentioned metal material performs two-dimensional mobile scanning in the plane perpendicular to the beam direction, set the single pulse energy to 300 microjoules, and the adjacent laser scribe line The distance between them is 10-50 microns, and the moving scanning speed is 0.2-2 mm/s, and the micro/nano structure of the coral-like microcavity structure can be induced on the surface of the titanium-nickel alloy material.

The above-mentioned titanium alloy material with a microcavity structure surface can be observed through a scanning electron microscope to form a peculiar microstructure in the laser irradiation area of the sample surface, as shown in Figure 1. It is formed by a dense arrangement of many cylindrical cavities of different sizes. The opening directions of these cavities tend to be randomly distributed. The diameter of the cavities varies between 2-35 microns, and the depth is about several microns. There are many irregularly shaped small protrusions distributed on the edge of the microcavity; further microscopic observation shows that these protrusions are actually composed of many solid particles with a size of nanometer scale. The rough inner walls of these microcavity structures and their The peripheral bumps greatly increase the surface area of the metal sample, making it resemble a porous structure absorber, which is a "coral-like microcavity structure".

The above-mentioned titanium alloy material with microcavity structure surface was analyzed by X-ray photoelectric energy spectrometer for the chemical composition of this surface microcavity structure, and the test results are shown in Figure 4(b) and Figure 5(b) . Apparently, its main constituents are the corresponding metal oxides: titanium dioxide and nickel oxide. Figure 4(a) and Figure 5(a) are the X-ray photoelectric spectrometer test results of metal materials that have not been treated by femtosecond laser.

The above-mentioned titanium alloy material with a microcavity structure surface is placed in an infrared Fourier spectrometer and heated, and then the thermal radiation spectrum is measured in a direction perpendicular to the metal surface. The thermal radiation efficiency of a material can be obtained by comparing the actual measured radiation spectral lines with the standard black body thermal radiation spectral lines at the same temperature. Figure 7 shows the thermal emissivity curves measured under two different temperatures (T=373K and T=333K, represented by solid line and dashed line respectively); The thermal radiation performance test of the alloy material is carried out, and the measurement results are shown in Fig. 9 . Through comparative analysis, we found that the titanium-nickel alloy material on the surface of the microcavity structure not only has a thermal radiation rate as high as 90% in the spectral range of 7-16 microns, which is comparable to that of the planar metal material without femtosecond laser treatment. The ratio is about 4 times higher, and this enhanced thermal radiation efficiency hardly changes with the wavelength, that is, the titanium-nickel alloy material on the surface of the microcavity structure has a high spectral range in the near-infrared band. Thermal Radiation Efficiency.

Example 2:

Except that the single pulse energy of the incident femtosecond laser is adjusted to 50 microjoules, other technical steps and process conditions are the same as those in Example 1. In this case, it was observed that the surface self-organization of the titanium alloy material after femtosecond laser irradiation produced a periodic stripe-like microstructure, and its atomic force micrograph is shown in Figure 2. The direction of the stripes of this microstructure is perpendicular to the polarization direction of the incident laser light and the scanning direction of the sample, the average interval of the stripes is 630 nanometers, the height of the stripes is about 150 nanometers, and the width is about 290 nanometers. More importantly, a large number of irregularly shaped solid particles are covered on this subwavelength grating-like microstripes, and their geometric size distribution is between tens and two hundred nanometers, which can be obtained in titanium-nickel alloys. A grating-like subwavelength structure covered by nanoparticles is induced on the surface of the material.

Through the test and analysis of X-ray photoelectric spectrometer, the chemical composition of the surface of this sub-wavelength grating microstructure has also been confirmed to be the corresponding metal oxide: titanium dioxide and nickel oxide, and the measurement results are shown in Figure 4 ( d) and Figure 5(d).

We measured the thermal radiation spectrum of the titanium-nickel alloy material on the surface of this grating-like micro/nano structure, and the measurement results are shown in Figure 7. When the sample temperature T=373K, as shown by the solid line, its thermal radiation efficiency in the 7-16 micron band range gradually decreases from 90% to 60% with the increase of wavelength; when T=333K, as shown by the dotted line, As the wavelength increases, its thermal radiation efficiency gradually decreases from 60% to 50%. Nevertheless, the thermal radiation efficiency of this micro/nano-structured metal surface is about 2-4 times higher than that of the planar metal sample without femtosecond laser treatment; in addition, Figure 7 also shows that this enhanced thermal radiation efficiency even In the case of two very similar temperatures, they are also clearly separated, which indicates that the material with a grating-like micro/nano-structured surface enhances the thermal radiation efficiency and has a strong sensitivity to temperature changes.

Example 3:

Except that the energy of the incident femtosecond laser pulse is adjusted to 150 microjoules, other technical steps and process conditions are the same as in Example 1. In this case, it was observed that the surface self-organization of the titanium-nickel alloy material after femtosecond laser irradiation produced a honeycomb-like composite structure composed of subwavelength gratings and nanopores, and its scanning electron micrograph is shown in Figure 3 shows. Similar to the case in Example 2, the stripe direction in this composite structure is perpendicular to the laser polarization direction and the sample scanning direction, but the stripe interval varies between 400–600 nm, and the length of each group of stripes is shortened to about 1 μm . In addition, compared with the case of the microcavity in Example 1, the size of the cavities in this composite structure is significantly smaller, with a diameter of about 500 nanometers, and their distribution density in space becomes relatively sparse, that is, A honeycomb-like micro-grating-nanohole composite structure is induced on the surface of a titanium-nickel alloy material.

By using X-ray photoelectric spectrometer to test, the chemical composition of the honeycomb-like micro/nano structure surface has also been confirmed to be the corresponding metal oxides: titanium dioxide and nickel oxide. The measurement results are shown in Figure 4(c) And shown in Figure 5(c).

We measured the thermal radiation spectrum of this titanium-nickel alloy material with a honeycomb-like micro/nano structure on the surface, and the measurement results are shown in Figure 8. When the sample temperature T=373K, as shown by the solid line, its thermal radiation efficiency in the range of 7-16 micron wave band gradually decreases from 90% to 50% with the increase of wavelength; when T=333K, as shown by the dotted line, As the wavelength increases, its thermal radiation efficiency gradually decreases from 80% to 50%. Nevertheless, the thermal radiation efficiency of such micro/nanostructured metal surfaces is about 3-4 times higher than that of untreated planar metal samples. The downward trend of the thermal radiation efficiency curve shown in Fig. 8 in the NIR measurement range shows that it still has a certain dependence on the radiation wavelength. In addition, the thermal radiation efficiency of this composite micro/nano-structured surface is no longer sensitive to temperature changes in the long-wave part of the spectral measurement range, which is similar to the thermal radiation of the planar metal sample without femtosecond laser treatment shown in Figure 9. have similarities.

Claims (8)

1. method of utilizing femtosecond laser to prepare little/micro-nano structure at metal material surface is characterized in that preparation process is as follows:

1) metal material surface is carried out mechanical grinding and the polishing after, clean with the deionized water ultrasonic cleaning, in air ambient, be fixed in then on the three-dimensional precise mobile platform, and realize above-mentioned metal material moving on the locus by computer control;

2) be main optical path with the femtosecond laser beam, as auxiliary optical path, adjust He-Ne Lasers and femtosecond laser beam co-propagate, and make both can be overlapped on light path, then together through the above-mentioned metal material surface of vertical arrival behind the focus lamp with helium neon laser beam;

3) close or stop femtosecond laser beam, have only feasible this moment helium neon laser beam to shine a certain position on above-mentioned material surface, placing a beam splitter with miter angle along backlight Shu Fangxiang on away from the light path of focus lamp then, make and carry out separating on the space with former incident beam, and adopt photodetector its collection and real time imagery from above-mentioned metal material surface reflection and through the laser beam that focus lamp is returned;

4) above-mentioned metal material is moved in perpendicular to the two dimensional surface of incoming laser beam, by observing the variation of spot size in the imaging system, adjust the horizontal tilt degree of processing platform, make the whole surface of above-mentioned metal material vertical mutually with incoming laser beam;

5) adjust the residing position of above-mentioned metal material on the direction of incident beam along being parallel to, making observed spot size minimum from imaging system;

6) close or stop helium neon laser beam, make femtosecond laser beam shine directly into above-mentioned metal material surface, and above-mentioned material is moved forward or backward along being parallel to the incoming laser beam direction by controlling three-dimensional processing platform, whenever after moving the step-length of a setting, only there be 1-3 femto-second laser pulse that above-mentioned metal material is ablated;

7) with the above-mentioned metal material of the microscopic area size that femtosecond laser causes ablation to its surface after each moving, therefrom seek and obtain the pairing metal material surface of minimum ablated area locus, be femtosecond laser beam through the focal position behind the focus lamp, and above-mentioned metal material surface moved to this position by controlling three-dimensional processing platform;

8) the above-mentioned metal material that will be positioned on the focus lamp focal plane moves the distance of a setting along backlight Shu Fangxiang, and makes that above-mentioned metal material surface can keep vertical mutually with incoming laser beam in whole moving process;

9) keep the femtosecond laser beam direction of incident constant, the control machine table makes above-mentioned metal material carry out two-dimentional motion scan in perpendicular to the plane on the beam direction, and, prepare dissimilar little/micro-nano structures at above-mentioned metal material surface by changing incident laser energy.

2. the method for utilizing femtosecond laser to prepare little/micro-nano structure at metal material surface according to claim 1 is characterized in that: described metal material is titanium-nickel alloy.

3. the method for utilizing femtosecond laser to prepare little/micro-nano structure at metal material surface according to claim 1 is characterized in that: described femtosecond laser parameter is: pulse recurrence frequency 1 KHz, pulse width 50 femtoseconds, pulse center wavelength 800 nanometers, light beam are linearly polarized light.

4. the method for utilizing femtosecond laser to prepare little/micro-nano structure at metal material surface according to claim 1 is characterized in that: described focus lamp is the microcobjective of 10x.

5. the method for utilizing femtosecond laser to prepare little/micro-nano structure at metal material surface according to claim 1 is characterized in that: described metal material is 500 microns along being parallel to beam direction to front or rear mobile scope, and moving step length is the 5-10 micron.

6. the method for utilizing femtosecond laser to prepare little/micro-nano structure at metal material surface according to claim 1 is characterized in that: described metal material is the 10-250 micron along the setpoint distance that backlight Shu Fangxiang departs from the focus lamp focal plane.

7. the method for utilizing femtosecond laser to prepare little/micro-nano structure at metal material surface according to claim 1 is characterized in that: in the described two-dimentional motion scan process between the adjacent laser scoring apart from 10-50 micron, sweep speed 0.2-2 mm/second.

8. the method for utilizing femtosecond laser to prepare little/micro-nano structure at metal material surface according to claim 1, it is characterized in that: described incident laser energy is regulated in little joule of scope of 50-300, induce the little/micro-nano structure of generation to have three types at metal material surface, comprise class raster-like sub-wavelength structure and the cellular low-light grid of class-nano-pore composite construction that the coralloid micro-cavity structure of class, nano particle cover.

Images