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Anisotropic multi-step etching for large-area fabrication of surface microstructures on stainless steel to control thermal radiation

View Article: PubMed Central - PubMed

ABSTRACT

Controlling the thermal radiation spectra of materials is one of the promising ways to advance energy system efficiency. It is well known that the thermal radiation spectrum can be controlled through the introduction of periodic surface microstructures. Herein, a method for the large-area fabrication of periodic microstructures based on multi-step wet etching is described. The method consists of three main steps, i.e., resist mask fabrication via photolithography, electrochemical wet etching, and side wall protection. Using this method, high-aspect micro-holes (0.82 aspect ratio) arrayed with hexagonal symmetry were fabricated on a stainless steel substrate. The conventional wet etching process method typically provides an aspect ratio of 0.3. The optical absorption peak attributed to the fabricated micro-hole array appeared at 0.8 μm, and the peak absorbance exceeded 0.8 for the micro-holes with a 0.82 aspect ratio. While argon plasma etching in a vacuum chamber was used in the present study for the formation of the protective layer, atmospheric plasma etching should be possible and will expand the applicability of this new method for the large-area fabrication of high-aspect materials.

No MeSH data available.


Absorptance spectra of micro-holes with depth 490 nm compared with simulation result using RCWA. The simulated model shows 0.82 aspect ratio and has tapered walls. The blue line with square dots shows the simulation results without an oxide layer, and the red line with square dots represents a model with a 0.3 μm oxide layer.
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Figure 6: Absorptance spectra of micro-holes with depth 490 nm compared with simulation result using RCWA. The simulated model shows 0.82 aspect ratio and has tapered walls. The blue line with square dots shows the simulation results without an oxide layer, and the red line with square dots represents a model with a 0.3 μm oxide layer.

Mentions: The hemispherical reflectance spectra of the fabricated samples were measured using a spectrophotometer (Lambda 900; Perkin Elmer) for the visible light range and a Fourier transform infrared spectrophotometer (FT-IR: Spectrum-GX; Perkin Elmer) for the infrared range. Integrating spheres with 15 mm diameter were used for both measurements. The absorptance of the samples calculated from the measured reflectance is shown in figure 5. The optical absorption peak attributed to electromagnetic waves confined by the micro-holes appeared at around 0.8 μm, and the peak shifted to longer wavelengths with increasing depth. The small sharp peak at 0.85 μm did not shift with changing micro-hole depth. Therefore, the small peak seems to be related to the surface coupling mode such as surface plasmon–polariton propagation. The peak attributed to the confined mode broadened and its intensity increased steadily with increasing micro-hole depth. The peak absorptance exceeded 0.8 for the sample with a micro-hole depth of 490 nm and aspect ratio of 0.82, although the simulation indicated the peak absorptance should reach 1.0. As shown in figure 4, oxide material appears to be on the walls and wall tops, judging by the contrast difference in the SEM image. A simulation result taking this factor into consideration is shown in figure 6 as a red line. Changes in reduction in the optical absorption peak and decrease in the absorptance slope at the cut-off wavelength were consistent with the measured result. Therefore, spectral selectivity improved with the removal of the surface oxide material.


Anisotropic multi-step etching for large-area fabrication of surface microstructures on stainless steel to control thermal radiation
Absorptance spectra of micro-holes with depth 490 nm compared with simulation result using RCWA. The simulated model shows 0.82 aspect ratio and has tapered walls. The blue line with square dots shows the simulation results without an oxide layer, and the red line with square dots represents a model with a 0.3 μm oxide layer.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036480&req=5

Figure 6: Absorptance spectra of micro-holes with depth 490 nm compared with simulation result using RCWA. The simulated model shows 0.82 aspect ratio and has tapered walls. The blue line with square dots shows the simulation results without an oxide layer, and the red line with square dots represents a model with a 0.3 μm oxide layer.
Mentions: The hemispherical reflectance spectra of the fabricated samples were measured using a spectrophotometer (Lambda 900; Perkin Elmer) for the visible light range and a Fourier transform infrared spectrophotometer (FT-IR: Spectrum-GX; Perkin Elmer) for the infrared range. Integrating spheres with 15 mm diameter were used for both measurements. The absorptance of the samples calculated from the measured reflectance is shown in figure 5. The optical absorption peak attributed to electromagnetic waves confined by the micro-holes appeared at around 0.8 μm, and the peak shifted to longer wavelengths with increasing depth. The small sharp peak at 0.85 μm did not shift with changing micro-hole depth. Therefore, the small peak seems to be related to the surface coupling mode such as surface plasmon–polariton propagation. The peak attributed to the confined mode broadened and its intensity increased steadily with increasing micro-hole depth. The peak absorptance exceeded 0.8 for the sample with a micro-hole depth of 490 nm and aspect ratio of 0.82, although the simulation indicated the peak absorptance should reach 1.0. As shown in figure 4, oxide material appears to be on the walls and wall tops, judging by the contrast difference in the SEM image. A simulation result taking this factor into consideration is shown in figure 6 as a red line. Changes in reduction in the optical absorption peak and decrease in the absorptance slope at the cut-off wavelength were consistent with the measured result. Therefore, spectral selectivity improved with the removal of the surface oxide material.

View Article: PubMed Central - PubMed

ABSTRACT

Controlling the thermal radiation spectra of materials is one of the promising ways to advance energy system efficiency. It is well known that the thermal radiation spectrum can be controlled through the introduction of periodic surface microstructures. Herein, a method for the large-area fabrication of periodic microstructures based on multi-step wet etching is described. The method consists of three main steps, i.e., resist mask fabrication via photolithography, electrochemical wet etching, and side wall protection. Using this method, high-aspect micro-holes (0.82 aspect ratio) arrayed with hexagonal symmetry were fabricated on a stainless steel substrate. The conventional wet etching process method typically provides an aspect ratio of 0.3. The optical absorption peak attributed to the fabricated micro-hole array appeared at 0.8 μm, and the peak absorbance exceeded 0.8 for the micro-holes with a 0.82 aspect ratio. While argon plasma etching in a vacuum chamber was used in the present study for the formation of the protective layer, atmospheric plasma etching should be possible and will expand the applicability of this new method for the large-area fabrication of high-aspect materials.

No MeSH data available.