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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.


Related in: MedlinePlus

MNHS with micropillars using asher-mediated process. (a, b) top-view images; (c, d) tilted-view images. The width of a square micropillar and the inter-pillar distance (gap distance between pillars) are both 200 μm.
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Figure 4: MNHS with micropillars using asher-mediated process. (a, b) top-view images; (c, d) tilted-view images. The width of a square micropillar and the inter-pillar distance (gap distance between pillars) are both 200 μm.

Mentions: Because the silver ions attach themselves to the surface of the silicon, and a thin C4F8 polymer layer is deposited on the sidewalls of micropatterns during the silicon dry etching process for passivation [21], we can manipulate the nanowire-formation characteristics at the boundaries of the micropillars. Specifically, the polymer layer deposited on the sidewalls of the micropatterns during DRIE may also act as a mask for the SiNWs etching. Following DRIE, PR stripping is accomplished using acetone or the microwave plasma asher process. Liquid acetone can only remove the PR layer, while the asher process (which uses oxygen plasma) can remove both the PR and the sidewall polymer. Figure 3 shows the thin sidewalls that were formed by conglomeration of nanowires and undamaged silicon surrounding the boundaries of micropillars. Using the asher process after the micropattern fabrication, it is possible to retain a more porous structure without thin sidewall silicon barrier. In Figure 4, one can clearly see that sharp, thin walls are not formed at the boundaries of the micropillars, whereas they are wholly formed from Figure 3. Using an EDS for MNHS fabricated by the acetone process, we confirmed that small quantities of C and F remained on the sidewalls of the micropillars. On a sidewall of MNHS fabricated by acetone-treated process, C and F were detected by 10.83 and 0.42 wt%, respectively. On the other hand, there were not any elemental compositions of polymeric passivation layer on the sidewalls of MNHS by asher-treated process. This explains the existence of the polymeric C4F8 passivation layer that covers the sidewalls and acts as a protective layer against the etching solution.


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)

MNHS with micropillars using asher-mediated process. (a, b) top-view images; (c, d) tilted-view images. The width of a square micropillar and the inter-pillar distance (gap distance between pillars) are both 200 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 4: MNHS with micropillars using asher-mediated process. (a, b) top-view images; (c, d) tilted-view images. The width of a square micropillar and the inter-pillar distance (gap distance between pillars) are both 200 μm.
Mentions: Because the silver ions attach themselves to the surface of the silicon, and a thin C4F8 polymer layer is deposited on the sidewalls of micropatterns during the silicon dry etching process for passivation [21], we can manipulate the nanowire-formation characteristics at the boundaries of the micropillars. Specifically, the polymer layer deposited on the sidewalls of the micropatterns during DRIE may also act as a mask for the SiNWs etching. Following DRIE, PR stripping is accomplished using acetone or the microwave plasma asher process. Liquid acetone can only remove the PR layer, while the asher process (which uses oxygen plasma) can remove both the PR and the sidewall polymer. Figure 3 shows the thin sidewalls that were formed by conglomeration of nanowires and undamaged silicon surrounding the boundaries of micropillars. Using the asher process after the micropattern fabrication, it is possible to retain a more porous structure without thin sidewall silicon barrier. In Figure 4, one can clearly see that sharp, thin walls are not formed at the boundaries of the micropillars, whereas they are wholly formed from Figure 3. Using an EDS for MNHS fabricated by the acetone process, we confirmed that small quantities of C and F remained on the sidewalls of the micropillars. On a sidewall of MNHS fabricated by acetone-treated process, C and F were detected by 10.83 and 0.42 wt%, respectively. On the other hand, there were not any elemental compositions of polymeric passivation layer on the sidewalls of MNHS by asher-treated process. This explains the existence of the polymeric C4F8 passivation layer that covers the sidewalls and acts as a protective layer against the etching solution.

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