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The real-time shape evolution of nanoimprinted polymer patterns is measured as a function of annealing time and temperature using critical dimension small-angle X-ray scattering (CD-SAXS). Periodicity, line width, line height, and sidewall angle are reported with nanometer resolution for parallel line/space patterns in poly(methyl methacrylate) (PMMA) both below and above the bulk glass transition temperature (T(G)). Heating these patterns below T(G) does not produce significant thermal expansion, at least to within the resolution of the measurement. However, above T(G) the fast rate of loss in pattern size at early times transitions to a reduced rate in longer time regimes. The time-dependent rate of polymer flow from the pattern into the underlying layer, termed pattern "melting", is consistent with a model of elastic recovery from stresses induced by the molding process.

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Characterization of sub-100 nm photolithographic patterns with nanometer scale resolution is demonstrated using small angle x-ray scattering. The transmission scattering geometry employed potentially enables high throughput measurements for future technology nodes of the semiconductor industry, organic and inorganic nanoscale devices, and three-dimensional structures. The method is demonstrated through the characterization of a series of polymer photoresist gratings using a synchrotron x-ray source. Quantities, such as periodicity and line width, are extracted using minimal modeling. Additional quantities and the potential of a laboratory-based x-ray system are briefly discussed.

By using free-radical RAFT living polymerization, we successfully grafted linear poly(N-isopropylacrylamide) (PNIPAM) chains onto a spherical PNIPAM/HEA copolymer microgel to form a novel core−shell nanostructure. Both the tethered PNIPAM shell and the copolymer microgel core shrunk as the temperature increased, but in different temperature ranges. In the range ∼28−32 °C, the tethered PNIPAM chains underwent a coil-to-globule transition, while in the range ∼32−35 °C, the shrinking of the copolymer core induced a re-stretching of the collapsed PNIAPM chains on its surface to form a polymer brush in poor solvent. Our results showed that in the re-stretching process, the average hydrodynamic volume per tethered PNIPAM chain remained a constant, confirming a prediction made a long time ago that the collapsed chains in poor solvent were incompressible.

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High-volume fabrication of nanostructures requires nondestructive metrologies capable of measuring not only the pattern size but also the pattern shape profile. Measurement tool requirements will become more stringent as the feature size approaches 50 nm and tolerances of pattern shape will reach a few nanometers. A small angle x-ray scattering (SAXS) based technique has been demonstrated to have the capability of characterizing the average pitch size and pattern width to subnanometer precision. In this study, we report a simple, modeling-free protocol to extract cross-section information such as the average sidewall angle and the pattern height of line grating patterns from the SAXS data. Diffraction peak intensities and reciprocal space positions are measured while the sample is rotated around the axis perpendicular to the grating direction. Linear extrapolations of peak positions in reciprocal space allow a precise determination of both the sidewall angle and the pattern height.

Poly(ethylene oxide) (PEO) chains were grafted onto a spherical thermally sensitive poly(Nisopropylacrylamide) microgel with a low critical solution temperature of ϳ32 ± C. The shrinking of the microgel at higher temperatures led to a dramatic decrease in its surface area, providing a convenient way to increase the grafting density of a polymer brush. As expected, we observed a repulsion-induced stretching of the PEO chains at the initial stage of the shrinking. However, as the grafting density increases, an unexpected collapse of the grafted PEO chains was observed, which can be attributed to a long predicted n-clustering attractive interaction among densely grafted polymer chains. PACS numbers: 64.70.Dv, 83.70.Hq Polymer chains can be grafted onto a surface to form a polymer brush. If the surface is planar, cylindrical, or spherical, the brush will be one, two, or three dimensional [1]. Polymer brushes are so useful that a number of theoretical models have been developed [1-6] and many experimental results have been reported [7][8][9][10][11][12][13]. Generally, the grafted polymer chains in a good solvent are swollen and have an extended conformation so that the brush is made of a single layer of polymer chains with an abrupt concentration drop at the outer end.In 1993, a different scheme was also proposed for some special cases, particularly for water-soluble polymers, in which two monomers repel each other, but n monomers can form a certain form of "cluster" [6]. According to this scheme, there could exist two additional regimes besides the swollen state: in one regime ͑a͒, two dense phases coexist; and in another regime ͑b͒, one dense phase is in equilibrium with a dilute phase. For a given grafting density, varying temperature can, in principle, induce the transitions from the swollen state to the a regime and from the a regime to the b regime. Experimentally, the temperature range for water-soluble polymers is limited in the range 0-100 ± C. On the other hand, at a proper temperature, increasing the grafting density can also induce the transitions. However, it is difficult, if not impossible, to continuously vary the grafting density in practice. To our knowledge, the predicted n-clustering induced collapse of a polymer brush as the grafting density increases has not been observed yet.In this study, on the basis of our previous studies of poly(N-isopropylacrylamide) chains (PNIPAM) [14-17], we prepared narrowly distributed spherical PNIPAM microgels grafted with linear poly(ethylene oxide) (PEO) chains. As a thermally sensitive polymer, PNIPAM is soluble only in water at lower temperatures with a lower critical solution temperature of ϳ32 ± C [18]. In the temperature range 25-35 ± C, the microgel can shrink ϳ3 times in its diameter; i.e., its surface area can decrease ϳ10 times, providing a convenient way to continuously increase the grafting density because the average number of the PEO chains grafted on each microgel is fixed, which is schematically shown in Fig. 1. Our previous results showed that t...