Study Of Characterized Microstructure Array Of Ground Surface And Its Functional Properties

The micro-structured surface can generate additional properties, a micro-grinding is developed to machine the micro-structure array on hard and brittle material surfaces such as monocrystalline silicon, optical glass, silicon carbide ceramics and so on. Compared with the chemical material removal, such as laser, lithography and chemical etching techniques, the form and profile accuracies of the micro-structured surface fabricated by physical removal of micro-grinding are rather higher. Therefore, the micro-grinding process of the materials single crystal silicon, optical glass and silicon carbide has been studied, the relationships of the remove mechanism of materials, abrasive grain size of grinding wheel and process conditions with the surface roughness, profile accuracy and abrasion ratio of grinding wheel have been systematically revealed. Then, the micro-grinding was applied to precisely machining the gradient micro-structure array on Si surface and micro-optics lens array on glass. To explore dynamics characteristic of the droplet self-movement and the micro-optics characteristics of photovoltaic cell, the microstructure scale effect models of wettability and photovoltaic properties were build.(1) The influence of material itself, such as monocrystalline silicon, optical glass and silicon carbide, on surface roughness is little, but on form accuracy is great. The machining accuracy of #3000 grinding wheel was at least 20% higher than #600 grinding wheel. When the V-tip angle of grinding wheel cutting edge was no more than 60°, the roughness of the microstructured surface was higher, but the abrasion ratio of grinding wheel was relatively less and it reaches to the minimum value when the feed speed vf was 200 mm/min. It shows that the #600 diamond grinding wheel can be used for precisely rapid forming process and the #3000 diamond grinding wheel can be used for the subsequent mirror grinding.(2) On the basis of white light interference, the multi-step space measurement of micro geometric pattern surface was constructed, and the precise reconstruction model of microstructured surface was established. The micro-alignment method based on ICP algorithm was presented to improve the surface reconstruction accuracy. It shows that the characterized micro-profile error was reduced by more than 30% and the micro-form accuracy was improved by as much as 40%. The slash model may be used to rapidly and precisely register measured micro-structured surface rather than the traditional grid model.(3) The microstructure scale effect models of anisotropic wetting and droplet self-movement were established based on the gradient micro-grinding of silicon micro-structured surface. The sliding angle on the gradient micro-V-grooved surface was decreased from the original 65 degrees to 5 degrees and the gradient micro-V-grooved surface may easily produce a droplet self-movement trend to micro-grooves with large micro-groove gradient and large micro-Vgroove ratio. In addition, the wetting anisotropy and droplet anisotropy both reach to the largest and disappear when the micro-V-groove ratio is equal to 0.70 and 2.58, respectively. The droplet impact experiment shows that the threshold Weber number is 29.9 for the wetting transfer from a composite state to a noncomposite state.(4) The volume ratio is proposed through the 3D characterization of micro-structured surface in contrast to traditional roughness factor, fractal dimension and aspect ratio through 2D characterization in order to characterize the wettability of irregularly micro-structured surfaces. The classical Wenzel and Cassie models are unable to characterize the wetting mode of the irregularly micro-structured surface, thus, the irregular wetting model was introduced by considering the volume ratio as characterized parameter. The contact angles increases with decreasing volume ratio, their correlation agrees well with the proposed irregular wetting model.(5) Based on the precision grinding of microlens surface on glass, the microgroove lens with two internal total reflections is proposed on the glass substrate of thin-film amorphous silicon solar cell. The 800-μm-depth microgroove lens is able to absorb and scatter the inclined light to solar cell, although the conversion efficiency was improved by 38%, the electricity generation were increased by 51%, 118% and 185% in cloudy and overcast days, respectively. Besides, the greatest electricity generation capacity of the microgroove lens was on cloudy day rather than on sunny day.(6) The diffraction microlens array on α-Si solar cell surface that allows the infrared authormalization and visible light trapping was proposed by micro-grinding fabrication. The micro-optical characteristic was studied by using Monte-Carlo simulation and optical effects of diffraction microlens were theoretically analyzed by using rigorous coupled wave theory. It shows that the average reflectance of visible light was decreased from the original 8.93% to 6.95%, meanwhile, the average reflectance of infrared light was increased from the original 16.73% to 22.86%. It enhances the electricity generation by 206.3%, 108.6% and 125% in outdoor sunny, cloudy and overcast days, respectively. And the electricity capacity of diffraction microlens cell generated on sunny day was averagely 20% higher than the one of conventional microlens cell.