Measuring Local Optical Properties: Near-Field Polarimetry of Photonic Block Copolymer Morphology

Ultrahigh molecular weight polystyrene-$b$-polyisoprene block copolymers (BCs), noted for their photonic behavior, were imaged using transmission near-field scanning optical microscopy (NSOM) and NSOM polarimetry. Our improved scheme for polarization modulation (PM) polarimetry, which accounts for optical anisotropies of the NSOM aperture probe, enables mapping of the local diattenuation and birefringence (with separately aligned diattenuating and fast axes) in these specimens with subdiffraction limited resolution. PM-NSOM micrographs illuminate the mesoscopic optical nature of these BC specimens by resolving individual microphase domains and defect structures.

Figure 1

NSOM images of PS-$b$-PI BC. Transmission (top), topography (middle). The plot (bottom) shows topography (solid) and transmission (dashed) along the white line ($2.1\mu \mathrm{m}$) in the topography image, smoothed over a three-pixel bin. Labels $a$ and $b$ show edge dislocations and lamellar separations, respectively.

Figure 2

PM-NSOM images of PS-$b$-PI BC. Color scale ranges given as [minimum, maximum]. (a) Diattenuation [0%, 5%]; (b) transmission (normalized intensity) [0.6, 1.0]; (c) diattenuation angle [$0^{°}$, ${180}^{°}$]; topography [0 nm, 25 nm]. The bottom plot shows transmission (dotted) and diattenuation (solid) along white line ($1.5\mu \mathrm{m}$) in (a), smoothed over a three-pixel bin.

Figure 3

PM-NSOM images of PS-$b$-PI symmetric tilt boundary. (a) Topography [0 nm, 25 nm]; (b) transmission [0.8, 1.0]; (c) diattenuation [0%, 9%]; (d) retardance [$0^{°}$, $7°$]; (e) relative angle of diattenuating axis [$0^{°}$, $180°$]; (f) relative angle of fast axis [$0^{°},180°$]. White scale bar in (a) is $1\mu \mathrm{m}$.