GISAXS Analysis of the In-Depth Morphology of Thick PS-b-PMMA Films

In Situ Grazing-Incidence SAXS Investigation of Thermal-Induced Self-Assembly Process of PS-b-PMMA Films Deposited on Surface-Modified Substrate

Directed self-assembly of block copolymers (BCPs) is widely investigated for its potential application in surface patterning. The self-assembly kinetics of BCP based on modified layers is the key to realizing structural control for obtaining highly ordered lamellar grains. In this study, morphological evolution of PS-b-PMMA films during the thermal-induced self-assembly process was investigated via the in situ grazing-incidence small-angle X-ray scattering (GISAXS) technique. In the first heating stage, reorientation of lamellar grains occurred as the temperature increased above the glass transition temperature. Then, a fast increase in the lamellar repeat period L₀ was observed, which is considered as a phase separation process. Whereas the size of the lamellar grain ξ was observed to have rapidly increased in the stage wherein the temperature was held at 230 °C, the L₀ was almost constant. This result indicates that the formation of ordered structure in PS-b-PMMA films was mainly determined by two periods: phase separation of block molecules followed by growth of grains in the nanodomain. In addition, it was interesting that the better-order nanodomains were obtained with thermal annealing at a faster heating rate. These findings suggest that accomplishing ordered structure control in a large area could be realized via the design of a proper heating profile.

Distributions of Deuterated Polystyrene Chains in Perforated Layers of Blend Films of a Symmetric Polystyrene-block-poly(methyl methacrylate)

We have examined the spatial distributions of polymer chains in blend films of weakly segregated polystyrene-block-poly(methyl methacrylate) [P(S-b-MMA)] and deuterated polystyrene (dPS). By fine-tuning the composition (ϕ_PS+dPS = 63.8 vol %) of the total PS/dPS component and annealing temperature (230 and 270 °C), P(S-b-MMA)/dPS blend films mainly form perforated layers with a parallel orientation (hereafter PLs^//). The distributions of dPS in PLs^// were probed by grazing-incidence small-angle neutron scattering (GISANS) and time-of-flight neutron reflectivity (ToF-NR). GISANS and ToF-NR results offer evidence that dPS chains preferentially locate at the free surface and within the PS layers for blend films that were annealed at 230 °C. Upon annealing at 270 °C, dPS chains distribute within PS layers and perforated PMMA layers. Nevertheless, dPS chains still retain a surface preference for thin films. In contrast, such surface segregation of dPS chains is prohibited for thick films when annealed at 270 °C.

Recent Advances in Sequential Infiltration Synthesis (SIS) of Block Copolymers (BCPs)

In the continuous downscaling of device features, the microelectronics industry is facing the intrinsic limits of conventional lithographic techniques. The development of new synthetic approaches for large-scale nanopatterned materials with enhanced performances is therefore required in the pursuit of the fabrication of next-generation devices. Self-assembled materials as block copolymers (BCPs) provide great control on the definition of nanopatterns, promising to be ideal candidates as templates for the selective incorporation of a variety of inorganic materials when combined with sequential infiltration synthesis (SIS). In this review, we report the latest advances in nanostructured inorganic materials synthesized by infiltration of self-assembled BCPs. We report a comprehensive description of the chemical and physical characterization techniques used for in situ studies of the process mechanism and ex situ measurements of the resulting properties of infiltrated polymers. Finally, emerging optical and electrical properties of such materials are discussed.

Self-assembly of block copolymers under non-isothermal annealing conditions as revealed by grazing-incidence small-angle X-ray scattering

An accurate knowledge of the parameters governing the kinetics of block copolymer self-assembly is crucial to model the time- and temperature-dependent evolution of pattern formation during annealing as well as to predict the most efficient conditions for the formation of defect-free patterns. Here, the self-assembly kinetics of a lamellar PS-b-PMMA block copolymer under both isothermal and non-isothermal annealing conditions are investigated by combining grazing-incidence small-angle X-ray scattering (GISAXS) experiments with a novel modelling methodology that accounts for the annealing history of the block copolymer film before it reaches the isothermal regime. Such a model allows conventional studies in isothermal annealing conditions to be extended to the more realistic case of non-isothermal annealing and prediction of the accuracy in the determination of the relevant parameters, namely the correlation length and the growth exponent, which define the kinetics of the self-assembly.

Self-Assembly in ultrahigh molecular weight sphere-forming diblock copolymer thin films under strong confinement

Ultrahigh molecular weight (UHMW) diblock copolymers (DBCs) have emerged as a promising template for fabricating large-sized nanostructures. Therefore, it is of high significance to systematically study the influence of film thickness and solvent vapor annealing (SVA) on the structure evolution of UHMW DBC thin films. In this work, spin coating of an asymmetric linear UHMW polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) DBC is used to fabricate thin films, which are spherically structured with an inter-domain distance larger than 150 nm. To enhance the polymer chain mobility and facilitate approaching equilibrium nanostructures, SVA is utilized as a post-treatment of the spin coated films. With increasing film thickness, a local hexagonal packing of PMMA half-spheres on the surface can be obtained, and the order is improved at larger thickness, as determined by grazing incidence small angle X-ray scattering (GISAXS). Additionally, the films with locally hexagonal packed half-spherical morphology show a poor order-order-poor order transition upon SVA, indicating the realization of ordered structure using suitable SVA parameters.

In Situ Monitoring Mesoscopic Deformation of Nanostructured Porous Titania Films Caused by Water Ingression

Nanostructured porous titania films are used in many energy-related applications. In this work, the temporal evolution of the mesoscopic deformation of mesoporous titania films synthesized via block copolymer-assisted sol-gel chemistry is investigated with in situ grazing incidence small-angle neutron scattering (GISANS) during exposure to D₂O vapor. Two types of mesoporous titania films are compared, which have a different degree of structural stability, depending on the applied annealing temperature (400 °C vs 600 °C) in a nitrogen atmosphere. Water ingression causes a gradual structure deformation in terms of decreasing center-to-center distances and broadening of the size distribution of the titania nanostructures. Based on the evolution of the mesopore size obtained from in situ GISANS measurements, the results show that structures synthesized at lower temperature undergo a stronger deformation because of the lower elastic modulus originating from larger pores, despite having a higher degree of order.

Self-Organization of Triblock Copolymer Melt Chains Physisorbed on Non-neutral Surfaces

We here report the self-organization process of poly(styrene-b-ethylene/butadiene-b-styrene) (SEBS) triblock copolymer chains physically adsorbed on a non-neutral surface. Spin-cast SEBS thin films were prepared on silicon (Si) substrates and then annealed at a high temperature far above the bulk glass transition temperatures of the two constituent blocks. To reveal the buried interfacial structure, we utilized solvent rinsing processes and a suite of surface-sensitive techniques including ellipsometry, X-ray reflectivity, atomic force microscopy, and grazing incidence small angle X-ray scattering. We revealed that the SEBS chains form two different chain structures on the substrate simultaneously: (i) "flattened chains" with the average height of 2.5 nm but without forming microdomain structures; (ii) "loosely adsorbed chains" with the average height of 11.0 nm and the formation of perpendicularly oriented cylindrical microdomains to the substrate surface. In addition, the kinetics to form the perpendicular-oriented cylinder was sluggish (∼200 h) and proceeded via multistep processes toward the equilibrium state. We also found that the lateral microdomain structures were distorted, and the characteristic lengths of the microdomains were slightly different from the bulk even after reaching "quasiequilibrium" state within the observed time window. Furthermore, we highlight the vital role of the adsorbed chains in the self-assembling process of the entire SEBS thin film: a long-range perturbation associated with the adsorbed chains propagates into the film interior, overwhelming the free surface effect associated with surface segregation of the lower surface tension of polystyrene blocks.

Flexible sample cell for real-time GISAXS, GIWAXS and XRR: design and construction

Since the properties of functional materials are highly dependent on their specific structure, and since the structural changes, for example during crystallization, induced by coating and annealing processes are significant, the study of structure and its formation is of interest for fundamental and applied science. However, structure analysis is often limited to ex situ determination of final states due to the lack of specialized sample cells that enable real-time investigations. The lack of such cells is mainly due to their fairly complex design and geometrical restrictions defined by the beamline setups. To overcome this obstacle, an advanced sample cell has been designed and constructed; it combines automated doctor blading, solvent vapor annealing and sample hydration with real-time grazing-incidence wide- and small-angle scattering (GIWAXS/GISAXS) and X-ray reflectivity (XRR). The sample cell has limited spatial requirements and is therefore widely usable at beamlines and laboratory-scale instruments. The cell is fully automatized and remains portable, including the necessary electronics. In addition, the cell can be used by interested scientists in cooperation with the Institute for Crystallography and Structural Physics and is expandable with regard to optical secondary probes. Exemplary research studies are presented, in the form of coating of P3HT:PC₆₁PM thin films, solvent vapor annealing of DRCN5T:PC₇₁BM thin films, and hydration of supported phospholipid multilayers, to demonstrate the capabilities of the in situ cell.

Well-ordered self-assembled nanostructures of block copolymer films via synergistic integration of chemoepitaxy and zone annealing

The integrated chemical template/zone annealing method has the capability to rapidly fabricate well-aligned and well-oriented nanostructures over a macroscopic area.