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Micro-nano hybrid structures with manipulated wettability using a two-step silicon etching on a large area.

Kim BS, Shin S, Shin SJ, Kim KM, Cho HH - Nanoscale Res Lett (2011)

Bottom Line: The fabrication process is readily capable of producing MNHS covering a wafer-scale area.By controlling the removal of polymeric passivation layers deposited during silicon dry etching (Bosch process), we can control the geometries for the hierarchical structure with or without the thin hydrophobic barriers that affect surface wettability.MNHS without sidewalls exhibit superhydrophilic behavior with a contact angle under 10°, whereas those with sidewalls preserved by the passivation layer display more hydrophobic characteristics with a contact angle near 60°.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical Engineering, Yonsei University, 262, Seongsanno, Seodaemun-gu, Seoul 120-749, Korea. hhcho@yonsei.ac.kr.

ABSTRACT
Nanoscale surface manipulation technique to control the surface roughness and the wettability is a challenging field for performance enhancement in boiling heat transfer. In this study, micro-nano hybrid structures (MNHS) with hierarchical geometries that lead to maximizing of surface area, roughness, and wettability are developed for the boiling applications. MNHS structures consist of micropillars or microcavities along with nanowires having the length to diameter ratio of about 100:1. MNHS is fabricated by a two-step silicon etching process, which are dry etching for micropattern and electroless silicon wet etching for nanowire synthesis. The fabrication process is readily capable of producing MNHS covering a wafer-scale area. By controlling the removal of polymeric passivation layers deposited during silicon dry etching (Bosch process), we can control the geometries for the hierarchical structure with or without the thin hydrophobic barriers that affect surface wettability. MNHS without sidewalls exhibit superhydrophilic behavior with a contact angle under 10°, whereas those with sidewalls preserved by the passivation layer display more hydrophobic characteristics with a contact angle near 60°.

No MeSH data available.


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Schematics of the fabrication processes for MNHS: (a) MNHS with micropillar and nanowires using acetone-based PR stripping and asher-mediated process; (b) MNHS with microcavities and nanowires using acetone-based PR stripping and asher-mediated process.
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Figure 2: Schematics of the fabrication processes for MNHS: (a) MNHS with micropillar and nanowires using acetone-based PR stripping and asher-mediated process; (b) MNHS with microcavities and nanowires using acetone-based PR stripping and asher-mediated process.

Mentions: To fabricate the MNHS with micropillars or microcavities, we used a two-step silicon etching process, consisting of dry etching (DRIE) and wet etching (electroless etching). The processes for MNHS with micropillars/microcavities with SiNWs are outlined schematically in Figure 2a,b, respectively. First, the silicon was dry etched to fabricate the microstructures. In the general silicon DRIE process (Bosch process) that is widely used as a dry etching method for fabricating deep silicon trenches, a polymeric C4F8 passivation layer is precoated to prevent over-etching of the sidewalls of the silicon patterns. This can be left in place or removed from MNHS by choosing the appropriate PR stripping method. MNHS with thin sidewall structures are fabricated by removing the PR layer with acetone, which leaves the polymeric passivation layer intact. On the other hand, to fabricate MNHS with no thin sidewall structures, the PR and polymeric passivation layer deposited on the sidewalls are removed by the asher process.


Micro-nano hybrid structures with manipulated wettability using a two-step silicon etching on a large area.

Kim BS, Shin S, Shin SJ, Kim KM, Cho HH - Nanoscale Res Lett (2011)

Schematics of the fabrication processes for MNHS: (a) MNHS with micropillar and nanowires using acetone-based PR stripping and asher-mediated process; (b) MNHS with microcavities and nanowires using acetone-based PR stripping and asher-mediated process.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211421&req=5

Figure 2: Schematics of the fabrication processes for MNHS: (a) MNHS with micropillar and nanowires using acetone-based PR stripping and asher-mediated process; (b) MNHS with microcavities and nanowires using acetone-based PR stripping and asher-mediated process.
Mentions: To fabricate the MNHS with micropillars or microcavities, we used a two-step silicon etching process, consisting of dry etching (DRIE) and wet etching (electroless etching). The processes for MNHS with micropillars/microcavities with SiNWs are outlined schematically in Figure 2a,b, respectively. First, the silicon was dry etched to fabricate the microstructures. In the general silicon DRIE process (Bosch process) that is widely used as a dry etching method for fabricating deep silicon trenches, a polymeric C4F8 passivation layer is precoated to prevent over-etching of the sidewalls of the silicon patterns. This can be left in place or removed from MNHS by choosing the appropriate PR stripping method. MNHS with thin sidewall structures are fabricated by removing the PR layer with acetone, which leaves the polymeric passivation layer intact. On the other hand, to fabricate MNHS with no thin sidewall structures, the PR and polymeric passivation layer deposited on the sidewalls are removed by the asher process.

Bottom Line: The fabrication process is readily capable of producing MNHS covering a wafer-scale area.By controlling the removal of polymeric passivation layers deposited during silicon dry etching (Bosch process), we can control the geometries for the hierarchical structure with or without the thin hydrophobic barriers that affect surface wettability.MNHS without sidewalls exhibit superhydrophilic behavior with a contact angle under 10°, whereas those with sidewalls preserved by the passivation layer display more hydrophobic characteristics with a contact angle near 60°.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Mechanical Engineering, Yonsei University, 262, Seongsanno, Seodaemun-gu, Seoul 120-749, Korea. hhcho@yonsei.ac.kr.

ABSTRACT
Nanoscale surface manipulation technique to control the surface roughness and the wettability is a challenging field for performance enhancement in boiling heat transfer. In this study, micro-nano hybrid structures (MNHS) with hierarchical geometries that lead to maximizing of surface area, roughness, and wettability are developed for the boiling applications. MNHS structures consist of micropillars or microcavities along with nanowires having the length to diameter ratio of about 100:1. MNHS is fabricated by a two-step silicon etching process, which are dry etching for micropattern and electroless silicon wet etching for nanowire synthesis. The fabrication process is readily capable of producing MNHS covering a wafer-scale area. By controlling the removal of polymeric passivation layers deposited during silicon dry etching (Bosch process), we can control the geometries for the hierarchical structure with or without the thin hydrophobic barriers that affect surface wettability. MNHS without sidewalls exhibit superhydrophilic behavior with a contact angle under 10°, whereas those with sidewalls preserved by the passivation layer display more hydrophobic characteristics with a contact angle near 60°.

No MeSH data available.


Related in: MedlinePlus