Three-dimensional line edge roughness in pre- and post-dry etch line and space patterns of block copolymer lithography.

In this work, we employ large-scale coarse-grained molecular dynamics (CGMD) simulations to study the three-dimensional line edge roughness associated with line and space patterns of chemo-epitaxially directed symmetric block copolymers (BCPs) on a flat substrate. The di-block copolymer chain length and interaction parameters are validated with the experimental BCP period, L0 and corresponding molecular weight. Defect-free lamellae are formed, after which the system is quenched below the glass transition temperature before selectively dry-etching off one of the BCP phases. The effect of varying etch-selectivity on post-etch resist domain morphology was studied. The roughness of the polymer domain was evaluated over three process stages: annealing, pre-etching, and post-etching. Power spectral density plots were then generated to elucidate the contributions of low and high frequency roughness for the three process stages. The roughness results obtained from simulations are shown to be in close agreement with the roughness result obtained from analyzing experimental SEM images. Parameters like the Hurtz roughness exponent and correlation length inherent to the process and the BCP were also revealed from the experimental study.

Designing an ordered template of cylindrical arrays based on a simple flat plate confinement of block copolymers: a coarse-grained molecular dynamics study.

In this paper we study the morphology formed by asymmetric di-block copolymers (di-BCPs) under various confinements using a large-scale coarse-grained molecular dynamics (CGMD) framework. We start with a simple flat plate confinement with the bottom and the top substrate attractive to the minor phase. Studies at a lower confinement length of 17σ have shown that there exists a critical chain length above which a transition from a three-domain morphology to a two-domain morphology is observed. Increasing the confinement length to 42σ, where the chains experience considerably lower confinement effects, also revealed the existence of a critical chain length - a transition from a multi-domain morphology (>3) to a three-domain morphology. The results obtained from the flat plate study with two confinement dimensions were used to design a topography of silica pillars with and without a bottom substrate to form ordered cylindrical BCP arrays. The least and highest radial separation lengths between adjacent pillars are kept at 17σ and 42σ, respectively. A direct correlation was observed in the number of continuous micro-domains of the maximum and minimum confinement dimensions with the 17σ and 42σ flat plate trials. With the optimum chain length employed, the surfaces with affinity to the minor phase can direct the BCP self-assembly to form ordered arrays of minor phase cylinders. The current study thus elucidates a useful tool to predict the morphology formed in an intricate nano-lithographic template by using simple length scale arguments derived from a flat plate confinement study.

Surface-initiated polymerization from carbon nanotubes: strategies and perspectives.

Carbon nanotubes (CNTs) represent one of the most promising materials in nanoscience today, with their unique electronic, chemical and mechanical properties. Strong van der Waals interactions and poor solubility greatly affect their potential for applications in various fields. In the past decade, great efforts have been undertaken to modify CNTs into organophilic material via covalent and non-covalent grafting strategies. This review focuses on advances in various strategies used for the surface initiated polymerization and provides perspectives on grafting polymers covalently from CNTs.

Polypeptide grafted hyaluronan: A self-assembling comb-branched polymer constructed from biological components.

Rheological evidence is provided demonstrating that covalent grafting of monodisperse isotactic poly(L-leucine) branches onto linear hyaluronan (HA) polysaccharide chains yields comb-branched HA chains that self-assemble into long-lived physical networks in aqueous solutions driven by hydrophobic interactions between poly(L-leucine) chains. This is in stark contrast to native (unmodified) HA solutions which exhibit no tendency to form long-lived physical networks.

Polypeptide grafted hyaluronan: synthesis and characterization.

Poly(l-leucine) grafted hyaluronan (HA-g-PLeu) has been synthesized via a Michael addition reaction between primary amine terminated poly(l-leucine) and acrylate-functionalized HA (TBAHA-acrylate). The precursor hyaluronan was first functionalized with acrylate groups by reaction with acryloyl chloride in the presence of triethylamine in N,N-dimethylformamide. (1)H NMR analysis of the resulting product indicated that an increase in the concentration of acryloylchoride with respect to hydroxyl groups on HA has only a moderate effect on functionalization efficiency, f. A precise control of stoichiometry was not achieved, which could be attributed to partial solubility of intermolecular aggregates and the hygroscopic nature of HA. Michael addition at high [PLeu-NH(2)]/[acrylate](TBAHA) ratios gave a molar grafting ratio of only 0.20 with respect to the repeat unit of HA, indicating grafting limitation due to insolubility of the grafted HA-g-PLeu. Soluble HA-g-PLeu graft copolymers were obtained for low grafting ratios (<0.039) with <8.6% by mass of PLeu and were characterized thoroughly using light scattering, (1)H NMR, FT-IR, and AFM techniques. Light scattering experiments showed a strong hydrophobic interaction between PLeu chains, resulting in aggregates with segregated nongrafted HA segments. This yields local networks of aggregates, as demonstrated by atomic force microscopy. Circular dichroism spectroscopy showed a ß-sheet conformation for aggregates of poly(l-leucine).

Highly efficient recyclable hydrated-clay supported catalytic system for atom transfer radical polymerization.

Atom transfer radical polymerization of methacrylates has been performed using hydrated natural clay as a support for a CuBr(2)-ligand complex and the supported clay catalyst has been recycled for 21 batch polymerizations without losing its activity.

Grafting reactions of living macroanions with multi-walled carbon nanotubes.

Grafting reactions of living polystyryllithium (PSLi) with acid chloride containing multi-walled carbon nanotubes (MWNTs-COCI) were performed under vacuum in benzene at room temperature. Covalent grafting of polystyrene (PS) was characterized using spectroscopic, microscopic, and thermogravimetric analyses. Grafting at different ratios of macroanion to acylchloride of the carbon nanotubes showed that the grafting efficiency was not dependent on the concentration of the macroanions. The mole percent of PS present in the MWNTs-g-PS samples was inversely proportional to the precursor molecular weight of PSLi. Direct reactions of PSLi, polybutadienyllithium and n-butyllithium with pristine MWNTs without any functional groups were also performed in the presence and in the absence of tetrahydrofuran in benzene. The grafting reactions of living macroanions either with MWNTs-COCl or with pristine MWNTs indicated a partial grafting of polymer on the carbon nanotubes in benzene at room temperature.

Carbon nanotubes with covalently linked porphyrin antennae: photoinduced electron transfer.

Single- and multiwalled carbon nanotubes have been covalently functionalized with free-base porphyrin. The quantity of porphyrin linked to the surface was determined from thermogravimetric and UV-vis analysis. A reversible protonation equilibrium between the attached porphyrin and the residual acid groups of the carbon nanotubes has been identified. Steady-state fluorescence emission spectrum of the solutions of porphyrin-linked carbon nanotubes shows that the porphyrins act as energy absorbing and electron transferring antennae, and the carbon nanotubes act as efficient electron acceptors. The porphyrin-linked carbon nanotubes show 95-100% emission quenching, indicating a fast photoinduced electron transfer.