Wubin Bai

A universal block copolymer pattern transfer method was demonstrated to produce Co nanostructures consisting of arrays of lines or dots from a polystyrene-block-polydimethylsiloxane (PS-b-PDMS) diblock copolymer. Three processes were used: liftoff, a damascene process, and ion beam etching using a hard mask of tungsten, including a sacrificial poly(methyl methacrylate) layer under the PS-b-PDMS for the etch and liftoff processes. The ion beam etch process produced the most uniform magnetic arrays. A structural and magnetic comparison in terms of uniformity, edge roughness and switching field distribution has been reported.

ABSTRACT A combined thermal and solvent vapor annealing process for block copolymer self-assembly is demonstrated. Films of cylinder-forming poly(styrene-b-dimethylsiloxane) (SD45, 45.5 kg/mol, fPDMS = 31%) were preheated for 2 min above the glass transition temperature of both blocks, followed by immediate introduction into a chamber containing room temperature saturated vapors of toluene and n-heptane. After quenching in air, microdomains had better order than those obtained from thermal or solvent annealing alone. The short time during which the film is both heated and exposed to solvent vapor played an important role in determining the final morphology.

ABSTRACT Transmission electron microscope (TEM) tomography was used to visualize the morphology and 3D connectivity of a lithographically templated, self-assembled bilayer film of cylinder-forming 45.5 kg/mol polystyrene-block-polydimethylsiloxane. The structure, formed after a 5 min solvothermal anneal, was imaged with a resolution of ≈3 nm in 3D, enabling a comparison between measurement and self-consistent mean-field theory (SCFT) calculations. Images of etched and unetched samples showed that etching collapsed the PDMS microdomain structure and reduced the template dimensions. In addition to the general comparison between modeled and measured dimensions, the tomography revealed connections between the orthogonal layers of cylinders at their crossing points. Comparison with the SCFT model, even under solvothermal annealing conditions, shows that it is helpful in understanding the detailed nanoscale structure of features created by directed self-assembly (DSA), which is essential in developing nanomanufacturing processes based on DSA.

A high-pressure chamber was designed to study crumpling beyond the power-law regime. Preceded by a smooth transition, the crumpled ball that characterizes the high-pressure state contains less than 50% air and exhibits separate ordered domains. All data for different sheet thicknesses, sizes, and numbers were found to collapse to a master line when using volume ratio and pressure as the plotting parameters, which suggests the existence of a scaling relation. Based on these findings, we deduced a bundled-layer model that could consistently explain six outstanding properties at both low and high pressures. This successful union of theory and experiment has strong bearings on other soft-matter systems where similar changes in mechanical response are also linked to reorganization of structure.

Perpendicular orientation of lamellar microdomains in a high interaction parameter block copolymer was obtained within high aspect ratio gratings functionalized with a preferential sidewall brush. The experiments used polystyrene-block-polydimethylsiloxane (PS-b-PDMS) with molecular weight 43 kg/mol within trenches made using interference lithography. The perpendicular alignment was obtained for both thermal and solvent annealing, using three different solvent vapors, for a range of film thicknesses and trench widths. A platinum (Pt) layer at the base of the trenches avoided the formation of a wetting layer, giving perpendicular orientation at the substrate surface. The results are interpreted using self-consistent field theory simulation and a Ginzburg-Landau analytic model to map the energies of lamellae of different orientations as a function of the grating aspect ratio and the surface energies of the sidewalls and top and bottom surfaces. The model results agree with the experim...