RESUMO
HYPOTHESIS: Micro/nanopatterning on a 2D surface is apt for cutting-edge miniaturization technology, which directly or indirectly requires high-end expensive lithographic tools. The evaporative deposition at the receding contact-line of a polymer solution, termed as Dynamic Contact Line Lithography (DCLL), can be a potential inexpensive technique for template-less meso-patterning if the deposition patterns from DCLL can be predicted a priori. EXPERIMENTS: A deposition map (morphological phase diagram) from the myriads of patterns is constructed in terms of contact-line velocity and the polymer concentration. Specifically, two combinations: polystyrene (PS)/cyclohexane and poly (methyl methacrylate) (PMMA)/toluene are used to show the generic nature of the phase diagrams. The surface wettability of Si (water contact angle, CA ~15°) is tuned from CA ~35° to ~98° by patterning with DCLL. FINDINGS: Directed by the phase diagrams, fabrication of a complex rectangular cross-pattern of PS and PMMA micro-threads with a periodicity of ~65 µm and ~50 µm respectively on a Si surface is demonstrated to establish the robustness and potential of the DCLL and predictive phase diagram.
RESUMO
Strategic electron beam (e-beam) irradiation on the surface of an ultrathin (<100 nm) film of polystyrene-poly(methyl methacrylate) (PS-PMMA) random copolymer followed by solvent annealing stimulates a special variety of dewetting, leading to large-area hierarchical nanoscale patterns. For this purpose, initially, a negative (positive) tone of resist PS (PMMA) under weak e-beam exposure is exploited to produce an array of sites composed of cross-linked PS (chain-scissioned PMMA). Subsequently, annealing with the help of a developer solvent engenders dewetted patterns in the exposed zones where PMMA blocks are confined by the blocks of cross-linked PS. The e-beam dosage was systematically varied from 180µC cm-2to 10 000µC cm-2to explore the tone reversal behavior of PMMA on the dewetted patterns. Remarkably, at relatively higher e-beam dosing, both PMMA and PS blocks act as negative tones in the exposed zone. In contrast, the chain scission of PMMA in the periphery of the exposed regions due to scattered secondary electrons caused confined dewetting upon solvent annealing. Such occurrences eventually lead to pattern miniaturization an order of magnitude greater than with conventional thermal or solvent vapor annealed dewetting. Selective removal of PMMA blocks of RCP using a suitable solvent provided an additional 50% reduction in the size of the dewetted features.
RESUMO
Micro phase separation in a thin film of a polymer blend leads to interesting patterns on different substrates. A plethora of studies in this field discussed the effect of the surface energy of the underlying tethered polymer brush or substrate on the final morphology of the polymer blend. The conventional process toward the final morphology is rather slow. Here, aiming fast lithography, we induce the kinetically driven morphological evolution by rapid thermal annealing (RTA) of the polymer blend of polystyrene (PS) and polymethylmethacrylate (PMMA) in bilayer settings at a very high temperature. The underlying film consists of untethered constituent homopolymers or their blend or random-co-polymer (RCP). Apart from the phase inversion of the blend on the PS homopolymer, a rich morphology of the blend on the RCP underlayer is uncovered with systematic investigation of the film using sequential washing with selective solvents. The dissolution characteristics and the thermal stability of the constituent polymers corroborated the observation. Based on the understanding of the morphological evolution, fabrication of a complex shaped micro/nano-pattern with multiple length scales is demonstrated using this blend/RCP system. This study shows a novel methodology for easy fabrication of hierarchical small length scale complex structures.
