Growing Embossed Nanostructures of Polymer Brushes on Wet-Etched Silicon Templated via Block Copolymers

Abstract

Block copolymer nanolithography has attracted enormous interest in chip technologies, such as integrated silicon chips and biochips, due to its large-scale and mass production of uniform patterns. We further modified this technology to grow embossed nanodots, nanorods, and nanofingerprints of polymer brushes on silicon from their corresponding wet-etched nanostructures covered with pendent SiHx (X = 1-3) species. Atomic force microscopy (AFM) was used to image the topomorphologies, and multiple transmission-reflection infrared spectroscopy (MTR-IR) was used to monitor the surface molecular films in each step for the sequential stepwise reactions. In addition, two layers of polymethacrylic acid (PMAA) brush nanodots were observed, which were attributed to the circumferential convergence growth and the diffusion-limited growth of the polymer brushes. The pH response of PMAA nanodots in the same region was investigated by AFM from pH 3.0 to 9.0.

Figure 1. Schematic procedure for the fabrication of embossed polymer brush nanodots and their corresponding AFM images.

The schematic cartoons and their corresponding AFM images are shown as follows: (a and A), diblock copolymer template of PS-b-P4VP; (b and B), etched nanopits; (c and C), initiator monolayer covalently bound to nanopits; (d and D), PMAA brush nanodots. The three steps are as follows: (1) wet etching, (2) initiator grafting, and (3) SI-ATRP. The physical meanings of the schematic labels are illustrated at the bottom.

Figure 2. “Defects” of the PMAA nanodot array:

(a) PMAA nanodot array with some empty nanopits, and (b) two layers of PMAA nanodots.

Figure 3. MTR-IR spectra.

α-bromoisobutyrate-ended initiator monolayer (Initiator), sodium polymethacrylate (Na-PMAA), PMAA (HOOC-PMAA), and polymethacrylic anhydride (Anhydride-PMAA).

Figure 4. AFM images of pH stimulus of PMAA nanodots.

Two corresponding AFM images of PMAA dots at pH 3.0 (a) and 9.0 (b) were scanned in the same region, illustrating the PMAA dot swelling and topomorphological evolution. The swelling volume factor estimated from unlabeled dots is 2.0, whereas that for the Arabic number labeled pairs of 1′/1 and 2′/2 is 5.0, for 3′/3 and 4′/4 is 10, and for 5′/5 is infinite. For the interpretation, please see the text.

Figure 5. Rod-like arrays from a high molecular weight of PS-b-P4VP (330,000-125,000 g/mol):

(a) P4VP rods surrounded by PS corona, (b) wet-etched nanoslits after relieving PS-b-P4VP, and (c) PMAA brush rods grown via SI-ATRP.

Figure 6. Schematic procedure for the fabrication of embossed nanofingerprints of PMAA and corresponding AFM images.

Their corresponding cartoons and AFM images are shown as: (a and A), micellar diblock copolymer nanodot array of PS-b-P2VP; (b and B), solvent-annealed PS-b-P2VP fingerprints in a THF/H₂O = 10:1 solution for 36 h; (c and C), platinichloride-deposited fingerprints after immersion in a 0.9% HCl and 70 mmol/L Na₂PtCl₄ solution for 3 h; (d and D), platinum dotted fingerprints after O₂ plasma for 60 s at 30 W to remove PS-b-P2VP; (e and E), SiHx pendant fingerprints after etching in a HF/H₂O₂/EtOH (v/v/v = 1:1:3) solution for 3–6 min; (f and F) the initiator fingerprints; (g and G), PMAA brush fingerprints. The six steps are as follows: (1) solvent annealing, (2) platinichloride incubation, (3) O₂ plasma etching, (4) wet etching, (5) initiator grafting, and (6) SI-ATRP. The physical meanings of the schematic labels different from Fig. 1 are illustrated at the bottom.