Fabrication of Complex Three-Dimensional Nanostructures from Self-Assembling Block Copolymer Materials on Two-Dimensional Chemically Patterned Templates with Mismatched Symmetry

A study is presented of the self-assembly of a lamella-forming blend of a diblock copolymer and its respective homopolymers on periodically patterned substrates consisting of square arrays of spots, that preferentially attract one component, as a function of pattern dimensions and film thickness. The blend morphology follows the pattern at the substrate and forms a single quadratically perforated lamella (QPL). At intermediate film thicknesses necks connect this QPL to the film surface, resulting in a bicontinuous morphology. The necks do not register with the underlying square lattice but exhibit a substantial amount of hexagonal short-range order. For thicker films we observe bicontinuous morphologies consisting of parallel lamellae with disordered perforations. These results demonstrate a promising strategy for the fabrication of complex interfacial nanostructures from two-dimensional chemically patterned templates.

Figure 1

Morphology of a copolymer/homopolymer blend film of thickness $D_0=0.63L_0$ and lateral dimensions of $9.77L_0$ on a patterned substrate with $\lambda =1.21L_0$ and $R=0.30L_0$. Top left: SCMF simulation showing only the top view of the PS-rich domains (white/yellow online) and the interface between PS and PMMA (dark gray/blue online). Regions on top of the spots are PMMA-rich (transparent) and one looks through to the substrate (black). The position between two PMMA-attracting spots of the substrate is denoted as “bridge,” while the position at the center of a plaquette of four spots is denoted “interstitial.” The Voronoi tessellation of the necks is indicated by thin white lines. The lower left inset presents the time-averaged morphology in the MC simulations using the same color scheme as for the SCMF simulations. The MC simulation cell is replicated once in each direction. Top right: SEM image of the composition at the film surface. The PS domains are shown in light gray while PMMA-rich surface areas correspond to dark gray regions. Note that the PS domains appear artificially larger in the SEM images so a more accurate view of the domain sizes is provided by an AFM phase image shown as an inset at the lower right corner. Bottom left: 3D view of the morphology in the MC simulations. The QPL and PS-rich necks are indicated. Bottom right: Probability distribution of the coordination (number of edges) of Voronoi cells (cf. top left panel). The “errorbars” of experimental data (shown in gray) characterize the variance of results obtained by analyzing different SEM images of size $9.77L_0$. SCMF simulation results are shown as open bars.

Figure 2

Morphologies observed for $\lambda =1.21L_0$, $R=0.41L_0$ (top) and $\lambda =1.64L_0$, $R=0.51L_0$ (bottom). The lateral dimensions are $9.77L_0$ and $13.2L_0$, respectively. The left panels show SCMF and MC (insets) simulation results. The corresponding SEM and AFM images are shown on the main and inset plates of the panels on the right.

Figure 3

“Swiss cheese” morphology formed in the SCMF simulations on the same pattern as in Fig. 1 but for twice the film thickness, $D_0=1.27L_0$. In the lower left corner the upper half of the film is removed revealing a morphology similar to Fig. 1.