(Color online) Schematic of the process flow for fabricating Ni nanopillar arrays on n-GaAs substrates: (a) neutral brush-layer formation by spin coating; (b) PS-b-PMMA diblock copolymer self-assembly on the brush layer; (c) selective removal of PMMA cylinders by UV exposure and acetic-acid development; (d) removal of the brush layer within each hole of the PS template using O2 plasma RIE to expose the highly doped GaAs surface for Ni electrodeposition; (e) Ni nanopillars formation within each hole of the PS template by electrodeposition; and (f) removal of PS template using O2 plasma, leaving behind Ni nanopillar arrays on n-GaAs substrates.
Plane-view SEM images of (a) large-area PS template on a n-GaAs substrate after selective removal of PMMA cylinders; (b) the PS template at higher magnification, with holes hexagonally arranged, of ∼18 nm diameter and a center-to-center spacing of ∼34 nm; (c) large-area fabricated Ni nanopillar arrays on a n-GaAs substrate; and (d) the fabricated Ni nanopillar arrays at higher magnification. Scale bars are (a) 200 nm, (b) 20 nm, (c) 300 nm, and (d) 100 nm wide.
(a) Tilted SEM image of PS template after Ni electrodeposition. (b) Tilted SEM image of Ni nanopillar arrays after PS removal via O2 plasma. Scale bars are (a) 100 nm and (b) 200 nm wide.
(Color online) Hole-diameter distribution of the PS template after (a) PMMA cylinder removal; (b) 8 s of 150-W, O2-plasma RIE to remove the brush layer within each hole; and (c) the Ni nanopillar diameter distribution after removing the PS template. The red curves in (a)–(c) are computed Gaussian fitting curves for which the calculated mean diameters are 18, 24, and 24 nm, respectively. (d) and (e) Plane-view SEM images of the PS template after only 6 s of 150-W, O2-plasma RIE for brush removal before and after Ni electrodeposition. The mean diameter of the holes in the PS template [inset in (d)] is ∼21 nm. Scale bars are 40 nm wide.
Plane-view SEM image of PS templates prepared on a 5-nm-thick Ni, conductive seed layer evaporated on GaAs substrates (a) after Ni electrodeposition at a plating-current density of 25 μA/cm2; (b)–(d) after an in situ electrochemical etch step and Ni electrodeposition at a plating-current density of 25, 100, and 125 μA/cm2, respectively. Scale bars are (a) 50 nm, (b) 50 nm, (c) 100 nm, and (d) 100 nm wide.
Plane-view SEM image of a PS template on a GaAs substrate after e-beam evaporation of 3 nm of Ni and liftoff. Inset: tilted SEM image of thePS template after brush-layer removal within each hole (scale bar corresponds to 100 nm). Scale bars are 200 nm wide.
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