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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.


Contour map of simulated absorptance as a function of micro-hole aspect ratio. The inset shows the model parameters for micro-holes arrayed in hexagonal symmetry. The micro-holes width w and pitch Λ are set to 0.60 and 0.82 μm, respectively.
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Figure 2: Contour map of simulated absorptance as a function of micro-hole aspect ratio. The inset shows the model parameters for micro-holes arrayed in hexagonal symmetry. The micro-holes width w and pitch Λ are set to 0.60 and 0.82 μm, respectively.

Mentions: Enhancement of optical absorption as a function of aspect ratio, which is the ratio of aperture diameter and depth of the micro-holes, was evaluated by numerical simulation based on the rigorous coupled-wave analysis (RCWA) method [21]. The simulation was performed for 2D periodic micro-holes arrayed on a stainless steel substrate, as shown in the inset of figure 2. In the simulation, since it is difficult to measure optical constants for stainless steel, optical constants for iron from literature [22] were used. Simulation results using various aspect ratios for the micro-holes are represented in figure 2. Enhancement of optical absorption at short wavelengths, attributed to the confined effect of micro-holes, is found to be weak when the aspect ratio is lower than 0.3. Optical absorption peak almost reaches 1.0 when the aspect ratio is over 0.8. Therefore, we focused on 0.8 aspect ratios to control the thermal radiation spectrum. A similar result has been seen for a spectrally selective emitter using tungsten 2D microcavities [9].


Anisotropic multi-step etching for large-area fabrication of surface microstructures on stainless steel to control thermal radiation
Contour map of simulated absorptance as a function of micro-hole aspect ratio. The inset shows the model parameters for micro-holes arrayed in hexagonal symmetry. The micro-holes width w and pitch Λ are set to 0.60 and 0.82 μm, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: Contour map of simulated absorptance as a function of micro-hole aspect ratio. The inset shows the model parameters for micro-holes arrayed in hexagonal symmetry. The micro-holes width w and pitch Λ are set to 0.60 and 0.82 μm, respectively.
Mentions: Enhancement of optical absorption as a function of aspect ratio, which is the ratio of aperture diameter and depth of the micro-holes, was evaluated by numerical simulation based on the rigorous coupled-wave analysis (RCWA) method [21]. The simulation was performed for 2D periodic micro-holes arrayed on a stainless steel substrate, as shown in the inset of figure 2. In the simulation, since it is difficult to measure optical constants for stainless steel, optical constants for iron from literature [22] were used. Simulation results using various aspect ratios for the micro-holes are represented in figure 2. Enhancement of optical absorption at short wavelengths, attributed to the confined effect of micro-holes, is found to be weak when the aspect ratio is lower than 0.3. Optical absorption peak almost reaches 1.0 when the aspect ratio is over 0.8. Therefore, we focused on 0.8 aspect ratios to control the thermal radiation spectrum. A similar result has been seen for a spectrally selective emitter using tungsten 2D microcavities [9].

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.