Large-depth-of-field four-dimensional surface topography thermodetector and temperature measurement method

Abstract

The invention provides a large-depth-of-field four-dimensional surface topography thermodetector and a temperature measurement method. The thermodetector comprises an imaging module, a temperature measurement module and a control analysis module; the imaging module comprises a line light source, an imaging lens group, an area-array camera and a one-dimensional displacement table; the temperature measuring module comprises a shaping lens group, a dichroscope, a microlens group and a spectrograph which are sequentially arranged along the same optical axis; the control analysis module is a computer; the imaging module and the temperature measuring module respectively acquire distance height and temperature height information on a single line of a to-be-measured object with the surface coated with a heat-sensitive material film, data are fused to obtain four-dimensional information of morphology and temperature on the single line, and finally four-dimensional information of the surface of the whole object is acquired through push-broom of the one-dimensional displacement table. The four-dimensional surface topography thermodetector has the characteristics of low cost, large measurement range, high recovery surface resolution and high temperature sensitivity. The method can be used in the application fields of integrated circuits, metal coating, fine part pouring and the like.

Description

Technical Field

[0001] The present invention belongs to the field of surface topography and temperature measurement, and particularly relates to a four-dimensional surface topography temperature measuring instrument with a large depth of field and a temperature measuring method. Background Art

[0002] A fine metal mask (FMM) is an essential material in the display production process. To form a three-pixel RGB light-emitting layer, an organic film layer of small molecule OLED needs to be evaporated and precisely deposited onto the corresponding pixels. Since OLED materials are very sensitive to water vapor, it is impossible to achieve film layer patterning through traditional lithography technology. Therefore, in most of the evaporation equipment in the current OLED mass production line, FMM is used to achieve the separate deposition of the RGB pixel light-emitting layer.

[0003] In the evaporation chamber, a thin layer of FMM is closely attached to the glass substrate through the magnetic adsorption of the FMM by a magnet array. The glass substrate is then pressed against a cooling plate to control the temperature of the glass and the FMM, ensuring that the temperatures of the glass substrate and the FMM are at a relatively low level in the high-temperature environment during the evaporation process, thereby avoiding the thermal deformation of the FMM and the glass substrate. Temperature monitoring during the evaporation process is particularly important. The mainstream temperature monitoring technology is a small infrared thermometer. However, the infrared thermal imaging sensor is restricted by environmental factors and the detection space structure, etc. Its surface recovery accuracy of the mask plate is relatively low, and it needs to be used in combination with other detectors. Moreover, the temperature measurement reading is greatly affected by bright or polished metal surfaces. For the temperature monitoring of the FMM with a complex surface, the temperature measurement results of the small infrared thermometer fluctuate greatly. Summary of the Invention

[0004] To solve the deficiencies of the small infrared temperature measurement technology in aspects such as the surface recovery accuracy and the large influence on the temperature measurement reading on the complex metal mask plate surface, the purpose of the present invention is to provide a four-dimensional surface topography temperature measuring instrument with a large depth of field and a temperature measuring method. The four-dimensional surface topography temperature measuring instrument has the characteristics of low cost, large measurement range, high surface resolution recovery, and high temperature sensitivity.

[0005] The technical solution adopted by the present invention is as follows: A four-dimensional surface topography temperature measuring instrument with a large depth of field, comprising an imaging module, a temperature measuring module, and a control and analysis module; The imaging module includes a line light source, a first microscopic objective lens, a first double-glued achromatic lens, a first CMOS area array camera, and a one-dimensional displacement stage; the temperature measurement module includes an imaging lens, a dichroic mirror, a second microscopic objective lens, a second double-glued achromatic lens, and a spectrometer, which are arranged in sequence along the same optical axis; the control and analysis module is a computer; the plane of the line light source, the equivalent lens plane of the imaging lens group, and the plane of the area array camera intersect at a line; when the line laser scans the surface of the sample to be measured, a laser line is formed, and the temperature-sensitive spectral information is emitted by the thermosensitive material coated on the surface of the sample to be measured. The temperature measurement module converts the spectral information into the temperature information of each point on the laser line by using the calibrated parameters. The imaging module restores the surface topography information according to the corresponding image plane positions of each point on the laser line, fuses the data with the same height information, and obtains the four-dimensional information of the topography and temperature on a single line. Finally, the temperature topography information of the entire object surface is obtained by the translation scanning of the one-dimensional displacement stage.

[0006] The positional relationship among the plane of the line light source, the equivalent lens plane of the imaging lens group, and the plane of the area array camera satisfies the following relationship: ; where a is the angle between the equivalent lens plane and the object plane, f is the equivalent lens focal length, L is the distance from the center of the equivalent lens to the three-plane intersection line, and b is the angle between the image plane and the equivalent lens plane.

[0007] The line light source is formed by the divergence of a point laser light source through a Powell prism.

[0008] The spectrometer includes a first concave mirror, a second concave mirror, a slit, a grating, and a second CMOS area array camera; The slit is located at the focal plane of the first concave mirror; the grating is arranged on the parallel optical path reflected by the first concave mirror. The grating disperses the light of each wavelength and then parallelly injects it into the second concave mirror; the second CMOS area array camera is located at the focal plane of the second concave mirror and receives the light of different wavelengths.

[0009] The thermosensitive material is temperature-sensitive micro-nano particles, including thermosensitive fluorescent powder and upconversion material, which are mixed with hydroxypropyl cellulose and can be coated on the surface of the object to form a nano-scale transparent film.

[0010] The dichroic mirror is a low-pass dichroic mirror and is placed at 45° to the temperature measurement optical path.

[0011] A four-dimensional surface topography temperature measurement method with a large depth of field using the temperature measurement instrument described above, Step 1: Determine the angle b between the image plane and the equivalent lens plane according to the angle a between the equivalent lens plane and the object plane, the equivalent lens focal length f, and the distance L from the center of the equivalent lens to the three-plane intersection line, so as to fix the positions of the components of the imaging system: ; Step 2: Centrifugally mix the thermosensitive material particles with hydroxypropyl cellulose, coat them on the surface of the object to be measured to form a nanoscale transparent film, and place the sample to be measured on the one-dimensional displacement stage of the imaging module; Step 3: The line light source 1 irradiates the surface of the sample to be measured, and the control and analysis module controls the movement of the displacement stage to push and scan the sample to be measured and record the surface topography and temperature information on the laser line in real time; Step 4: After the scanning is completed, the control and analysis module fuses the surface topography and temperature data with the same height information to obtain the four-dimensional information of the topography and temperature on a single line. At the same time, all single-line data are stitched together to obtain the four-dimensional information of the temperature topography of the entire surface of the sample to be measured.

[0012] The four-dimensional surface topography temperature measurement method with large depth of field is applied to the evaporation process of OLED devices. Sodium yttrium tetrafluoride doped with erbium NaYF4:Er + and ytterbium tungstate doped with neodymium Yb2W3O 12 :Nd + and hydroxypropyl cellulose are centrifugally and uniformly coated on a fine metal mask template at a mass ratio of 1:3. The fine metal mask template is placed in a glass evaporation chamber for evaporation operation; after the 980nm line laser is reflected by the dichroic mirror and focused by the imaging lens, it scans the fine metal mask template in real time, and the two peaks of the excited fluorescence signal are received by the first microscope objective lens, the second microscope objective lens and the first doublet achromatic lens respectively; the angle b between the first CMOS area camera in the imaging module and the equivalent lens plane is 40°, and the angle a between the equivalent lens plane and the 980nm laser light sheet is 34°; the temperature measurement module is imaged on the second CMOS area camera through the slit, the first concave mirror, the second concave mirror and the reflection grating; the whole set of temperature measuring instruments is fixed on the one-dimensional displacement stage by an optical flat plate, and the displacement is controlled by the analysis and control module to realize the rapid push and scan of the fine metal mask template in the evaporation chamber.

[0013] The four-dimensional surface topography temperature measurement method with large depth of field is applied to the fields of vacuum organic evaporation, integrated circuits, metal coating, fine part casting and solar cells.

[0014] The beneficial effects of this invention patent are as follows: The present invention uses the method of light sheet push brooming to restore the surface topography of an object, which greatly improves the restoration speed compared with the traditional point-by-point scanning restoration. The line light source plane, the equivalent lens plane of the imaging lens group, and the area array camera plane in the system satisfy specific geometric relationships with a line and can greatly improve the surface topography restoration accuracy within a large depth of field, monitor the thermal deformation of the fine metal mask in real time, improve the evaporation accuracy of the organic layer, and make the subsequent temperature matching more accurate. Within a measurement range of 4 mm, the surface topography restoration accuracy can reach 2 μm, and the relative temperature sensitivity can be up to 15.3% / K The present invention utilizes the high sensitivity and low error of thermosensitive material particles to temperature and combines with high surface topography restoration accuracy to achieve the precise restoration of four-dimensional information of the temperature topography of the surface of a micro complex surface object. This system can be applied to the restoration of the surface topography and temperature of a complex metal mask during the evaporation process of the OLED organic layer.

[0015] The optical path structure of the present invention is relatively simple, with low requirements for optical path components. The method of line laser push brooming only requires a one-dimensional displacement stage, and the synthetic route of the upconversion nanomaterial is simple. On the premise of ensuring the stability of the system, the cost is significantly reduced. Description of the Drawings

[0016] Figure 1 It is a schematic structural diagram of the present invention (the one-dimensional displacement stage is not shown).

[0017] Figure 2 It is the fluorescence spectrum diagram of common thermosensitive fluorescent powder and upconversion material.

[0018] Figure 3 It is the schematic diagram of the functional relationship of the spatial positions of the components of the imaging module.

[0019] Figure 4 It is the system structure diagram in Example 1, and the push brooming is realized by using a one-dimensional displacement stage.

[0020] Figure 5 It is the relationship diagram between the camera pixel points and the object distance of the imaging module in Example 1.

[0021] Figure 6 It is the distance resolution diagram of the imaging module in Example 1.

[0022] Figure 7 It is the relationship diagram between the fluorescence intensity and temperature and the relative temperature sensitivity diagram of the temperature measurement module in Example 1.

[0023] Among them, there are a line light source 1, a dichroic mirror 2, an imaging lens 3, a sample to be measured 4, an imaging module 5, a first microscope objective 6, a second microscope objective 10, a first doublet achromatic lens 7, a second doublet achromatic lens 11, a first CMOS area camera 8, a second CMOS area camera 17, a temperature measurement module 9, a slit 12, a plane mirror 13, a first concave mirror 14, a reflection grating 15, a second concave mirror 16, an analysis and control module 18, a one-dimensional displacement stage 19, and a fine metal mask 20. Specific embodiments

[0024] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0025] As Figure 1 、 Figure 4 shown, a four-dimensional surface topography thermometer with a large depth of field includes an imaging module 5, a temperature measurement module 9, and an analysis and control module 18.

[0026] The imaging module 5 includes a line light source 1, a first microscope objective 6, a first doublet achromatic lens 7, a first CMOS area camera 8, and a one-dimensional displacement stage 19; the temperature measurement module includes an imaging lens 3, a dichroic mirror 2, a second microscope objective 10, a second doublet achromatic lens 11, and a spectrometer, which are arranged in sequence along the same optical axis; the control and analysis module 18 is a computer; the line light source plane, the equivalent lens plane of the imaging lens group, and the area camera plane intersect at a line; when the line laser scans the surface of the sample to be measured, a laser line is formed, and the thermosensitive material coated on the surface of the sample to be measured emits temperature-sensitive spectral information. The temperature measurement module converts the spectral information into temperature information of each point on the laser line using the calibrated parameters. The imaging module 5 restores the surface topography information according to the corresponding image plane positions of each point on the laser line, fuses the data with the same height information, and obtains the four-dimensional information of the topography and temperature on a single line. Finally, the temperature topography information of the entire object surface is obtained through the translational scanning of the one-dimensional displacement stage 19.

[0027] The positions among the line light source plane, the equivalent lens plane of the imaging lens group, and the area camera plane satisfy the following relationship: ; where a is the angle between the equivalent lens plane and the object plane, f is the equivalent lens focal length, L is the distance from the center of the equivalent lens to the three-plane intersection line, and b is the angle between the image plane and the equivalent lens plane.

[0028] The line light source 1 is formed by diverging a point laser light source through a Powell prism.

[0029] The described spectrometer includes a first concave mirror 14, a second concave mirror 16, a slit 12, a grating 15, and a second CMOS area camera 17; the slit is located at the focal plane of the first concave mirror 14; the grating is arranged on the parallel optical path reflected by the first concave mirror 14, and the grating 15 disperses light of each wavelength and then parallelly injects it into the second concave mirror 16; the second CMOS area camera 17 is located at the focal plane of the second concave mirror 16 to receive light of different wavelengths.

[0030] The described thermosensitive material is temperature-sensitive micro-nano particles, including thermosensitive fluorescent powder and upconversion material, and after being mixed with hydroxypropyl cellulose, it can be coated on the surface of an object to form a nano-scale transparent film.

[0031] As Figure 1 shown, the red optical path is the excitation signal, and the blue optical path is the fluorescence signal. The line light source 1 used in the present invention is emitted by a specific wavelength point laser light source corresponding to the excitation peak of the thermosensitive material nanoparticles, and after passing through the Powell prism, the point laser diverges in a fan shape to form a line laser light surface. The dichroic mirror 2 used in the present invention is a low-pass dichroic mirror, placed at 45° to the temperature measurement optical path, which can effectively reflect the excitation light and transmit the thermosensitive fluorescence signal of the material. After the light surface contacts the dichroic mirror 2, it is reflected into the imaging lens 3 and then irradiates on the surface of the object to be measured 4. Since the surface of the object to be measured 4 is coated with a transparent film of thermosensitive material particles, the excitation of the transparent film generates a temperature-related fluorescence signal. The imaging module 5 passes through the first microscopic objective lens 6 and the first double-convex achromatic lens 7 to image the fluorescence signal with surface topography information on the first CMOS area camera 8.

[0032] Figure 2 are the spectral information of common thermosensitive fluorescent powder and upconversion material, and the peak value of its fluorescence peak changes significantly with the increase of temperature. Among them, (a) is the spectral temperature change diagram of the thermosensitive fluorescent powder Mg4FGeO6:Mn; (b) is the spectral temperature change diagram of the upconversion material NaYF4 particles doped with Er.

[0033] Since the line light source plane, the equivalent lens plane of the microscopic lens group, and the area camera plane are in a specific geometric relationship with respect to a straight line and their positions satisfy specific geometric relationships, based on as Figure 3 shown imaging model, the relationship between the detection distance and the system parameters can be deduced as follows: ; In the formula, z is the distance from the point on the object to be measured 4 to the center of the equivalent lens; L is the distance from the center of the equivalent lens to the three-plane intersection line; b is the angle between the image plane and the equivalent lens plane; a is the angle between the equivalent lens plane and the object plane; P IIt is the pixel position of the image point on the image sensor. From this, the distance information of each point on the laser line on the surface of the object 4 to be measured can be obtained. Then, according to the magnification coefficient M1 of the calibrated microscopic system, the distance height information of each point on the laser line can be obtained.

[0034] Meanwhile, as Figure 1 shown, the temperature measurement module 9 collects the fluorescence signal through the imaging lens 3 and the dichroic mirror 2, and images it at the slit 12 by using the second microscopic objective lens 10 and the second doublet achromatic lens 11 of the microscopic lens system. After the fluorescence signal passes through the slit, it enters the first concave mirror 14 through the plane mirror 13. Since the slit 12 is located at the focal plane of the first concave mirror 14, its reflected light is parallel light. The dispersion angles of the fluorescence signals with different wavelengths are different. Through the reflection grating 15, the fluorescence signals of each wavelength are separated. The second CMOS area array camera 17 is located at the focal plane of the second concave mirror 16, and the second concave mirror 16 converges the fluorescence signals of each wavelength at different points on the area array camera in the direction perpendicular to the slit 12. From this, the fluorescence intensity information of different wavelengths of each point on the laser line on the surface of the object 4 to be measured can be obtained. Then, according to the relationship between the fluorescence intensity ratio of the calibrated thermosensitive material and the temperature and the magnification coefficient M2 of the microscopic system, the temperature and height information of each point on the laser line can be obtained.

[0035] After that, the analysis and control module 18 matches the data information collected by the first CMOS area array camera 8 and the second CMOS area array camera 17, fuses the object point information with the same height information, and finally obtains the temperature, distance height information of each point on the laser line. Embodiment

[0036] Using the topography and temperature measuring instrument to perform real-time topography restoration and temperature monitoring on the surface of the fine metal mask (FMM, Fine Metal Mask) in the evaporation chamber, and using a cooling plate to control the temperature of the glass and FMM, ensuring that the temperatures of the glass substrate and FMM are at a relatively low level in the high-temperature environment during the evaporation process, thereby avoiding the thermal deformation of the FMM and the glass substrate and improving the accuracy of organic layer evaporation. It can be widely used in vacuum organic evaporation fields such as small and medium-sized RGB color separation, AMOLED displays, and large-sized WOLED displays. It can also be applied in fields such as integrated circuits, metal coating, fine part casting, and solar cells.

[0037] Figure 4 For the application of the present invention in the evaporation process of OLED devices, sodium yttrium fluoride doped with erbium (NaYF4:Er + ), and ytterbium tungstate doped with neodymium (Yb2W3O 12 :Nd +)(After centrifuging and uniformly mixing with hydroxypropyl cellulose in a mass ratio of 1:3, it is coated on a fine metal mask plate. The fine metal mask plate is placed in a glass evaporation chamber for evaporation operation. In the present invention, the 980 nm line laser 1 is reflected by a dichroic mirror 2 (900 nm low-pass) and focused by an imaging lens 3 (focal length 25 mm), and then performs real-time scanning on the fine metal mask plate 20 in the evaporation chamber. The excited fluorescence signals (the two peaks are 540 nm and 799 nm, corresponding to the dotted line and the solid line) are received by the microscopic objectives 6, 10 (4X, NA = 0.1) and the first doublet achromatic lens 7, 11 (focal length 50 mm) respectively. The angle b between the first CMOS area camera 8 (1936*1216, pixel size 5.84 um *5.84um) in the imaging module 5 and the equivalent lens plane is 40°, and the angle a between the equivalent lens plane and the 980 nm laser light sheet is 34°. The temperature measurement module 9 passes through a slit 12 (width 30 um), the first concave mirror 14, the second concave mirror 16 (focal length 200 mm), and a reflection grating 15 (300 lines / mm) and then images on the second CMOS area camera 17 (4656*3520, pixel size 3.8 um *3.8um). The whole set of temperature measuring instrument is fixed on a one-dimensional displacement stage 19 by an optical flat plate, and its displacement is controlled by an analysis control module 18 to achieve rapid push-scanning of the fine metal mask plate 20 in the evaporation chamber.) Figure 5 When it is Example 1, the relationship diagram between the camera pixel points and the object distance of the imaging module 5. Figure 6 When it is Example 1, the distance resolution diagram of the imaging module. Figure 7 When it is Example 1, the relationship diagram between the fluorescence intensity and temperature and the temperature relative sensitivity diagram of the temperature measurement module. It can be seen that the surface topography recovery accuracy of the instrument can reach the micron level, and the highest temperature relative sensitivity can reach 15.3% / K, meeting the requirements of temperature monitoring of the FMM with complex surfaces.)

[0038] (The implementation schemes in the above description can be further combined or replaced, and the implementation schemes only describe the preferred embodiments of the present invention for patents, and do not limit the concept and scope of the present invention for patents. Without departing from the design idea of the present invention for patents, various changes and improvements made by those skilled in the art to the technical solutions of the present invention for patents all belong to the protection scope of the present invention.)

Claims

1. A four-dimensional surface topography thermometer with a large depth of field, characterized in that: It includes an imaging module, a temperature measurement module, and a control and analysis module; The imaging module includes a line light source, a first microscopic objective lens, a first double-glued achromatic lens, a first CMOS area array camera, and a one-dimensional displacement stage; the temperature measurement module includes an imaging lens, a dichroic mirror, a second microscopic objective lens, a second double-glued achromatic lens, and a spectrometer, which are arranged in sequence along the same optical axis; the control and analysis module is a computer; the planes of the line light source, the equivalent lens plane of the imaging lens group, and the plane of the area array camera intersect at a line; when the line laser scans the surface of the sample to be measured, a laser line is formed, and the temperature-sensitive spectral information is emitted by the thermosensitive material coated on the surface of the sample to be measured. The temperature measurement module converts the spectral information into the temperature information of each point on the laser line by using the calibrated parameters. The imaging module restores the surface topography information according to the corresponding image plane positions of each point on the laser line, fuses the data with the same height information, and obtains the four-dimensional information of the topography and temperature on a single line. Finally, the temperature topography information of the entire object surface is obtained by the translation scanning of the one-dimensional displacement stage.

2. The four-dimensional surface topography thermometer with a large depth of field according to claim 1, characterized in that: The positions among the plane of the line light source, the equivalent lens plane of the imaging lens group, and the plane of the area array camera satisfy the following relationship: ； where a is the angle between the equivalent lens plane and the object plane, f is the equivalent lens focal length, L is the distance from the center of the equivalent lens to the three-plane intersection line, and b is the angle between the image plane and the equivalent lens plane.

3. The four-dimensional surface topography thermometer with a large depth of field according to claim 1, characterized in that: The line light source is formed by diverging a point laser light source through a Powell prism.

4. The four-dimensional surface topography thermometer with a large depth of field according to claim 1, characterized in that The spectrometer includes a first concave mirror, a second concave mirror, a slit, a grating, and a second CMOS area array camera; The slit is located at the focal plane of the first concave mirror; the grating is arranged on the parallel optical path reflected by the first concave mirror. The grating disperses the light of each wavelength and then parallelly injects it into the second concave mirror; the second CMOS area array camera is located at the focal plane of the second concave mirror and receives the light of different wavelengths.

5. The four-dimensional surface topography thermometer with a large depth of field according to claim 1, characterized in that The thermosensitive material is temperature-sensitive micro-nano particles, including thermosensitive fluorescent powder and upconversion material, which are mixed with hydroxypropyl cellulose and can be coated on the object surface to form a nano-scale transparent film.

6. The four-dimensional surface topography thermometer with a large depth of field according to claim 1, characterized in that The dichroic mirror is a low-pass dichroic mirror and is placed at 45° to the temperature measurement optical path.

7. A large-depth four-dimensional surface topography temperature measurement method using the temperature measurement instrument according to claim 1, characterized in that: Step 1: Determine the angle b between the image plane and the equivalent lens plane according to the angle a between the equivalent lens plane and the object plane, the equivalent lens focal length f, and the distance L from the center of the equivalent lens to the three-plane intersection line, so as to fix the positions of the components of the imaging system: ； Step 2: Centrifugally mix the thermosensitive material particles with hydroxypropyl cellulose, coat them on the surface of the object to be measured to form a nano-scale transparent film, and place the sample to be measured on the one-dimensional displacement stage of the imaging module; Step 3: The line light source 1 irradiates on the surface of the sample to be measured, and the control and analysis module controls the movement of the displacement stage to push-scan the sample to be measured and record the surface topography and temperature information on the laser line in real time; Step 4: After the scanning is completed, the control and analysis module fuses the surface topography and temperature data with the same height information to obtain the four-dimensional information of the topography and temperature on a single line. At the same time, all single-line data are stitched together to obtain the four-dimensional information of the temperature topography of the entire surface of the sample to be measured.

8. The four-dimensional surface topography temperature measurement method with large depth of field according to claim 7, characterized in that: Applied to the evaporation process of OLED devices, sodium yttrium fluoride doped with erbium NaYF4:Er + and ytterbium tungstate doped with neodymium Yb2W3O 12 :Nd + are centrifuged and uniformly mixed with hydroxypropyl cellulose at a mass ratio of 1:3 and then coated on a fine metal mask plate. The fine metal mask plate is placed in a glass evaporation chamber for evaporation operation. After the 980nm line laser is reflected by the dichroic mirror and focused by the imaging lens, it scans the fine metal mask plate in real time. The two peaks of the fluorescence signal obtained are received by the first microscope objective lens, the second microscope objective lens and the first doublet achromatic lens respectively. The included angle b between the first CMOS area camera in the imaging module and the equivalent lens plane is 40°, and the included angle a between the equivalent lens plane and the 980nm laser light sheet is 34°. The temperature measurement module is imaged on the second CMOS area camera after passing through the slit, the first concave mirror, the second concave mirror and the reflection grating. The whole set of temperature measuring instrument is fixed on a one-dimensional displacement table by an optical flat, and the displacement is controlled by the analysis control module to realize the rapid push-scan of the fine metal mask plate in the evaporation chamber.

9. The four-dimensional surface topography temperature measurement method with large depth of field according to claim 7, characterized in that: Applied to the fields of vacuum organic vapor deposition, integrated circuits, metal coating, precision part casting, and solar cells.

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