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Mesoporous thin film architectures are an important class of materials that exhibit unique properties, which include high surface area, versatile surface functionalization, and bicontinuous percolation paths through a broad library of pore arrangements on the 10 nm length scale. Although porosimetry of bulk materials via sorption techniques is common practice, the characterization of thin mesoporous films with small sample volumes remains a challenge. A range of techniques are geared toward providing information over pore morphology, pore size distribution, surface area and overall porosity, but none of them offers a holistic evaluation and results are at times inconsistent. In this work, we present a tutorial overview for the reliable structural characterization of mesoporous films. Three model samples with variable pore size and porosity prepared by block copolymer (BCP) coassembly serve for a rational comparison. Various techniques are assessed side-by-side, including scanning electron microscopy (SEM), atomic force microscopy (AFM), grazing incidence small-angle X-ray scattering (GISAXS), and ellipsometric porosimetry (EP). We critically discuss advantages and limitations of each technique and provide guidelines for reliable implementation.

Block copolymers offer the fabrication of mesoporous thin films with distinct nanoscale structural features. In this contribution, we present the use of acetic acid (CH3COOH) as a low‐molecular‐weight guest molecule to tune the supramolecular assembly of poly[styrene‐block‐(4‐vinylpyridine)] (PS‐b‐P4VP), offering a versatile and straightforward method to obtain tailored nanostructured films with controlled topography and pore size. Spin‐coating toluene solutions of PS‐b‐P4VP, with a variable amount of CH3COOH, leads to micellar thin films, where the micelles contain the carboxylic acid as a guest molecule. The size can be conveniently modified in these films (from 48 to 75 nm) by varying the amount of organic acid in the starting solutions. Subsequent surface reconstruction of micellar films using ethanol leads to ring‐shaped copolymer nanoporous films with modulated diameter. Controlling the micelle reconstruction process, cylindrical porous films are also obtained. Interestingly, changing the type of aliphatic carboxylic acid leads to a modification of the observed film morphology from micelles to out‐of‐plane P4VP cylinders (or lamellae) in a PS matrix., This work was supported by Spanish MINECO (grants FIS2013‐45469 and FIS2016‐76058 (AEI/FEDER, EU)).

[Image: see text] The processing of mesoporous inorganic coatings typically requires a high-temperature calcination step to remove organic precursors that are essential during the material assembly. Lowering the fabrication energy costs and cutting back on the necessary resources would provide a greater scope for the deployment in applications such as architectural glass, optical components, photovoltaic cells, and energy storage, as well as further compatibilize substrates with low temperature stability. Organic removal methods based on UV–ozone treatment are increasing in popularity, but concerns remain regarding large-scale ozone generation and usage of mercury-containing UV lamps. To this end, we present a method that relies on non-ozone-generating UV radiation at 254 nm (UV(254)) and incorporation of small amounts of photocatalytic material in the formulation, here demonstrated with TiO(2) nanocrystals. At concentrations as low as 5 wt % relative to the main inorganic aluminosilicate material, the TiO(2) nanocrystals catalyze a “cold combustion” of the organic components under UV(254) irradiation to reveal a porous inorganic network. Using block copolymer-based co-assembly in conjunction with photocatalytic template removal, we produce well-defined mesoporous inorganic thin films with controlled porosity and refractive index values, where the required processing time is governed by the amount of TiO(2) loading. This approach provides an inexpensive, flexible, and environmentally friendly alternative to traditional organic removal techniques, such as UV–ozone degradation and thermal calcination.

International audience; Optical metamaterials are artificially engineered architectures that exhibit desired optical properties not found in nature. Bespoke design requires the ability to define shape, size, orientation and composition of material structures on the nanometre length scale. Bottom-up self-assembly methods, such as block copolymer (BCP) templating, offer unique pathways to tailored features, at spatial resolution not routinely achieved by conventional top-down techniques. In this review, we provide the general readership with basic concepts of the underlying fabrication processes and examine optical phenomena arising from BCP-derived metamaterials and nanoresonators, with both dielectric and plasmonic characteristics.

International audience; Assembling ultra-high molecular weight (UHMW) block copolymers (BCPs) in rapid timescales is perceived as a grand challenge in polymer science due to slow kinetics. Through surface engineering and identifying a non-volatile solvent (propylene glycol methyl ether acetate, PGMEA) we showcase the impressive ability of a series of lamellar poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) BCPs to self-assemble directly after spin-coating. In particular, we show the formation of large period (≈ 111 nm) lamellar structures from a neat UHMW PS-b-P2VP BCP. The significant influence of solvent-polymer solubility parameters are explored to enhance polymer chain mobility. After optimization using solvent vapor annealing, increased feature order of ultra large period PS-b-P2VP BCP patterns in 1 hr is achieved. The methods described in this article center on industry compatible patterning schemes, solvents and deposition techniques. Isolated metallic and dielectric features are also demonstrated exemplifying the promise that large BCP periods offer for functional applications. Thus, our straightforward UHMW BCP strategy potentially paves a viable and practical path forward for large-scale integration in various sectors, e.g. photonic band gaps, polarizers, and membranes that demand ultra large period sizes.

International audience; In the field of functional nanomaterials, core-satellite nanocluster have recently elicited great interest due to their unique optoelectronic properties. However, core-satellite synthetic routes to date are hampered by delicate and multistep reaction conditions and no practical method has been reported for the ordering of these structures onto a surface monolayer. Herein we show a reproducible and simplified thin film process to fabricate bimetallic raspberry nanoclusters using block copolymer (BCP) lithography. Inorganic raspberry nanoclusters fabricated consisted of a ~ 36 nm alumina core decorated with ~15 nm Au satellites after infusing multilayer BCP nanopatterns. A series of cylindrical BCPs with different molecular weights allowed us to dial in specific nanodot periodicities (from 30 to 80 nm). Highly ordered BCP nanopatterns were then selectively infiltrated with alumina and Au species to develop multi-level bimetallic raspberry features. Microscopy and x-ray reflectivity analysis were used at each fabrication step to gain further mechanistic insights and understand the infiltration process. Furthermore, grazing-incidence small-angle X-ray scattering studies of infiltrated films confirmed the excellent order and vertical orientation over wafer scale areas of Al2O3/Au raspberry nanoclusters. We believe our work demonstrates a robust strategy towards designing hybrid nanoclusters since BCP blocks can be infiltrated with various low cost salt-based precursors. The highly controlled nanocluster strategy disclosed here could have wide ranging uses, in particular for metasurface and optical based sensor applications.

International audience; Materials with a high and tunable refractive index are attractive for nanophotonic applications. In this contribution, we propose a straightforward fabrication technique of high-refractive index surfaces based on self-assembled nanostructured block copolymer thin films. The selective and customizable metal incorporation within out-of-plane polymer lamellae produces azimuthally isotropic metallic nanostructures of defined geometries, which were analysed using microscopy and small-angle X-ray scattering techniques. Variable-angle spectroscopic ellipsometry was used to relate the geometrical parameters of the metallic features and the resulting refractive index of the patterned surfaces. In particular, nanostructured gold patterns with a high degree of homogeneity and a gold content as low as 16 vol% reach a refractive index value of more than 3 in the visible domain. Our study thus demonstrates a new route for the preparation of high refractive index surfaces with a low metal content for optical applications.

This work was supported by Spanish MINECO (FIS2013-45469 and FIS2016-76058 (AEI/FEDER,EU)).

The authors report here on the optical response and extraction of the morphological properties of three sizes of self-assembled nearly hexagonal arrays of gold (Au) nanoparticles (NPs), deposited on the native oxide on c-Si. The arrays were prepared by templating gold NP growth with self-assembled cylindrically organized block copolymer thin films, with consecutive removal of the polymer matrix by plasma etching. The particle sizes were controlled by using block copolymers of different molecular weights when assembling the templates. The resulting gold nanostructures were characterized by scanning probe microscopy. Spectroscopic ellipsometry was used to record the optical response of the samples, and the modeling of the spectra and the extraction of morphological parameters were performed using a modification of the Bedeaux–Vlieger formalism implemented in GranFilm. The modeling issues upon the introduction of a thin intermediate (oxide) layer between the particle and the substrate are discussed in detail, and a solution to the model procedure is proposed. The particles were modeled as truncated oblate Au spheroids in a hexagonal lattice on the native oxide on c-Si. The model fit converged to a solution indicating that the particles present a low wetting of the native oxide substrate, with parameters describing the particles and lattice in good correspondence with AFM. The extended GranFilm model simulations are also supported by finite element modeling. The authors report here on the optical response and extraction of the morphological properties of three sizes of self-assembled nearly hexagonal arrays of gold (Au) nanoparticles (NPs), deposited on the native oxide on c-Si. The arrays were prepared by templating gold NP growth with self-assembled cylindrically organized block copolymer thin films, with consecutive removal of the polymer matrix by plasma etching. The particle sizes were controlled by using block copolymers of different molecular weights when assembling the templates. The resulting gold nanostructures were characterized by scanning probe microscopy. Spectroscopic ellipsometry was used to record the optical response of the samples, and the modeling of the spectra and the extraction of morphological parameters were performed using a modification of the Bedeaux–Vlieger formalism implemented in GranFilm. The modeling issues upon the introductio...

The functionality and applications of mesoporous inorganic films are closely linked to their mesopore dimensions. For material architectures derived from block copolymer (BCP) micelle co-assembly, the pore size is typically manipulated by changing the molecular weight corresponding to the pore-forming block. However, bespoke BCP synthesis is often a costly and time-consuming process. An alternative method for pore size tuning involves the use of swelling agents, such as homopolymers (HPs), which selectively interact with the core-forming block to increase the micelle size in solution. In this work, poly(isobutylene)-block-poly(ethylene oxide) (PIB-b-PEO) micelles were swollen with poly(isobutylene) HP in solution and co-assembled with aluminosilicate sol with the aim of increasing the resulting pore dimensions. An analytical approach implementing spectroscopic ellipsometry (SE) and ellipsometric porosimetry (EP) alongside the more commonly used atomic force microscopy (AFM) and small angle x-ray scattering in transmission (SAXS) and grazing-incidence (GISAXS) modes enabled to study the material evolution from solution processing through to the manifestation of the mesoporous inorganic film after BCP removal. In-depth SE/EP analysis evidenced an increase of over 40% in mesopore diameter with HP swelling and a consistent scaling of the overall void volume and number of pores. Importantly, our analytical tool-box enabled us to study the effect of swelling on the connecting necks between adjacent pores, with observed increases as high as ≈35%, knowledge of which is crucial to sensing, electrochemical and other mass transfer-dependent applications.

International audience; Nanotemplates derived from the self-assembly of AB-type block copolymers provide an elegant route to achieve well-defined metallic dot arrays, even if the variety of pattern symmetries is restricted due to the limited number of structures offered by microphase separated diblock copolymers. A strategy that relies on the use of complex network structures accessible through the self-assembly of linear ABC-type terpolymers is presented for the formation of metallic nanodots arrays with “outside-the-box” symmetries. Patterned templates formed by the cubic Q214 and orthorhombic O70 network structures are used as excellent platforms to build well-ordered gold nanodot arrays with unique p3m1 and p2 symmetries, respectively. A simple yet efficient blending strategy is used to tune the critical dimensions of the p3m1 pattern while laterally ordered gold nanodot arrays are also demonstrated through a directed self-assembly approach. Such highly ordered gold nanodots with tunable particle dimensions and array periods, enabling the control of their plasmonic responses, are attractive probes for biological imaging.