Nano-organization of amylose-b-polystyrene block copolymer films doped with bipyridine

Interface Manipulations Using Cross-Linked Underlayers and Surface-Active Diblock Copolymers to Extend Morphological Diversity in High-χ Diblock Copolymer Thin Films

Top and bottom interfaces of high-χ cylinder-forming polystyrene-block-maltoheptaose (PS-b-MH) diblock copolymer (BCP) thin films are manipulated using cross-linked copolymer underlayers and a fluorinated phase-preferential surface-active polymer (SAP) additive to direct the self-assembly (both morphology and orientation) of BCP microdomains into sub-10 nm patterns. A series of four photo-cross-linkable statistical copolymers with various contents of styrene, a 4-vinylbenzyl azide cross-linker, and a carbohydrate-based acrylamide are processed into 15 nm-thick cross-linked passivation layers on silicon substrates. A partially fluorinated analogue of the PS-b-MH phase-preferential SAP additive is designed to tune the surface energy of the top interface. The self-assembly of PS-b-MH thin films on top of different cross-linked underlayers and including 0-20 wt % of SAP additive is investigated by atomic force microscopy and synchrotron grazing incidence small-angle X-ray scattering analysis. The precise manipulation of the interfaces of ca. 30 nm thick PS-b-MH films not only allows the control of the in-plane/out-of-plane orientation of hexagonally packed (HEX) cylinders but also promotes epitaxial order-order transitions from HEX cylinders to either face-centered orthorhombic or body-centered cubic spheres without modifying the volume fraction of both blocks. This general approach paves the way for the controlled self-assembly of other high-χ BCP systems.

Ordered Microdomain Structures in Saccharide-Polystyrene-Saccharide Hybrid Conjugates

Hybrid conjugates consist of synthetic polymers and naturally occurring saccharides, and are capable of microphase separation at small molecular weights to form ordered domain structures. In this study, we synthesize ABA triblock-like conjugates with polystyrene as the synthetic mid-segment and either trisaccharide maltotriose (MT) or disaccharide maltose (Mal) as the end unit. Hybrid conjugates of varying compositions are prepared by a combination of atom transfer radical polymerization and a click reaction, and their morphologies are examined by small-angle X-ray scattering and transmission electron microscopy. The MT-containing conjugates are found to form well-ordered domain structures with a sub-10 nm periodicity, and morphology transition from cylinders to spheres to disordered spheres is observed with decreasing saccharide weight fraction. The Mal-containing conjugates also show microphase separation. However, the observed domain morphologies lack regular packing due to the close proximity of polymer glass transition temperature and order-disorder transition temperature. The saccharide-containing conjugates are also found to undergo an irreversible morphology change at high temperatures, attributed to saccharide dehydration-induced pentablock-like structure formation.

Self-assembly of copper-free maltoheptaose-block-polystyrene nanostructured thin films in real and reciprocal space

The promising carbohydrate-based block copolymer maltoheptaose-block-polystyrene (MH-b-PS) has been used for high-performance memory transistors and next generation nanolithography. In order to realize the potential of MH-b-PS especially in microelectronic applications, we firstly improved its synthetic method for obtaining large amount of copper-free MH-b-PS. The main improvement relies on the removal of the residual copper catalyst by using a chelating resin. Then, the microphase separation of copper-free MH-b-PS in both thin film and bulk states under different solvent vapor annealing conditions were investigated comprehensively and compared with our previous report by using both real-space and reciprocal-space techniques. A phase transition of MH-b-PS from hexagonal close-packed horizontal cylinders to face-centered cubic were observed when increasing the amount of tetrahydrofuran in the mixture annealing solvent of tetrahydrofuran and H₂O. More details about self-assembled MH-b-PS nanostructures were analyzed by comparing grazing incidence small angle X-ray scattering patterns with corresponding atomic force microscopy phase images.

Computational Design of High-χ Block Oligomers for Accessing 1 nm Domains

Molecular dynamics simulations are used to design a series of high-χ block oligomers (HCBOs) that can self-assemble into a variety of mesophases with domain sizes as small as 1 nm. The exploration of these oligomers with various chain lengths, volume fractions, and chain architectures at multiple temperatures reveals the presence of ordered lamellae, perforated lamellae, and hexagonally packed cylinders. The achieved periods are as small as 3.0 and 2.1 nm for lamellae and cylinders, respectively, which correspond to polar domains of approximately 1 nm. Interestingly, the detailed phase behavior of these oligomers is distinct from that of either solvent-free surfactants or block polymers. The simulations reveal that the behavior of these HCBOs is a product of an interplay between both "surfactant factors" (headgroup interactions, chain flexibility, and interfacial curvature) and "block polymer factors" (χ, chain length N, and volume fraction f). This insight promotes the understanding of molecular features pivotal for mesophase formation at the sub-5 nm length scale, which facilitates the design of HCBOs tailored toward particular desired morphologies.

Carbohydrate-based block copolymer systems: directed self-assembly for nanolithography applications

Self-assembly of block copolymers (BCPs) provides an attractive nanolithography approach, which looks especially promising for fabrication of regular structures with characteristic sizes below 10 nm. Nevertheless, directed self-assembly (DSA) and pattern transfer for BCPs with such small features remain to be a challenge. Here we demonstrate DSA of the maltoheptaose-block-polystyrene (MH_1,2k-b-PS_4,5k) BCP system using graphoepitaxy. BCP thin films were self-organized by solvent vapor annealing in tetrahydrofuran (THF) and water into sub-10 nm scale cylinders of the maltoheptaose (MH) block oriented horizontally or perpendicularly to the surface in a polystyrene (PS) matrix. The guiding patterns for graphoepitaxy were made by the electron beam lithography (EBL) and lift-off process with the distance gradually varying between 0 and 200 nm. Atomic force microscopy (AFM) investigation of MH_1,2k-b-PS_4,5k BCP DSA patterns revealed good ordering of vertical and horizontal cylindrical MH arrays for DSA lines with 150-200 nm separation. Reactive ion etching (RIE) of MH_1,2k and PS_4,5k thin films in O₂ and CF₄ plasma showed up to 14 times higher etch rate of MH compared to PS. These results indicate that MH_1,2k-b-PS_4,5k is a promising BCP for nanolithographic applications below 10 nm.

Carbohydrate-Based Block Copolymer Thin Films: Ultrafast Nano-Organization with 7 nm Resolution Using Microwave Energy

Block copolymers (BCP) can self-assemble into nanoscale patterns with a wide variety of applications in the semiconductor industry. The self-assembly of BCPs is commonly accomplished by solvent vapor or thermal annealing, but generally these methods require long time (few hours) to obtain nanostructured thin films. In this contribution, a new and ultrafast method (using microwaves) is proposed-high temperature solvent vapor annealing (HTSVA), combining solvent vapor annealing with thermal annealing, to achieve fast and controllable self-assembly of amphiphilic BCP thin films. A promising carbohydrate-based BCP capable of forming cylindrical patterns with some of the smallest feature sizes is used for demonstrating how to obtain a highly ordered vertical cylindrical pattern with sub-10 nm feature sizes in few seconds by HTSVA. HTSVA provides not only a simple way to achieve BCP fast self-assembly in practical applications but also a tool to study the self-assembly behavior of BCPs under extreme conditions.

Self-assembly of maltoheptaose-b-PMMA block copolymer systems: 10nm Resolution in thin film and bulk states

This paper describes the self-assembly of oligosaccharide-based hybrid block copolymers (BCPs) consisting of maltoheptaose (MH) and poly(methyl methacrylate) (PMMA) into 10nm scale lamellar and cylindrical phases depending on the volume fractions of MH (ϕ_MH) and the annealing process. Time resolved SAXS study of the BCP bulk samples during thermal annealing indicated that the BCPs phase separate into 10nm scale periodical structures. The solvent vapor annealing induced self-organizations of the BCP into different phases depending on ϕ_MH and the weight fraction of THF/H₂O. BCPs with relatively higher Ø_MH, MH-b-PMMA_3k (ϕ_MH=0.27) and MH-b-PMMA_5k (ϕ_MH=0.16) self-organized into lamellar phases while the BCP sample with relatively lower ϕ_MH, MH-b-PMMA_9k (ϕ_MH=0.10), self-organized into cylindrical phase by using THF/H₂O=1/4 (w/w). On the other hand, the solvent vapor annealing with larger fraction of THF, i.e. THF/H₂O=2/3 (w/w), induced cylindrical phases for MH-b-PMMA_3k and MH-b-PMMA_5k.

Synthesis, morphology, and electrical memory application of oligosaccharide-based block copolymers with π-conjugated pyrene moieties and their supramolecules

Transistor memory applications of maltoheptaose-block-poly(1-pyrenylmethyl methacrylate), and their supramolecules with (4-pyridyl)-acceptor-(4-pyridyl).

High χ-Low N Block Polymers: How Far Can We Go?

Block polymers incorporating highly incompatible segments are termed "high χ" polymers, where χ is the Flory-Huggins interaction parameter. These materials have attracted a great deal of interest because low molar mass versions allow for the formation of microphase-separated domains with very small (<10 nm) feature sizes useful for nanopatterning at these extreme dimensions. Given that well-established photolithographic techniques now face difficult challenges of implementation at scales of 10 nm and below, the drive to further develop high χ block polymers is motivated by trends in the microelectronics industry. This Viewpoint highlights our perspective on this niche of block polymer self-assembly. We first briefly review the relevant recent literature, exploring the various block polymer compositions that have been specifically designed for small feature size patterning. We then overview the now standard method for the benchmarking χ values between different pairs of polymers and the consequences of low N and high χ on the thermodynamic aspects of microphase separation. Finally, we comment on restrictions going forward and offer our perspective on the future of this exciting area of block polymer self-assembly.

Synthesis of Amphiphilic Naturally-Derived Oligosaccharide-block-Wax Oligomers and Their Self-Assembly

Self-assembly characteristics of amphiphilic macromolecules into micelles, nanoparticles and vesicles has been of fundamental interest for many applications including designed nanoscale therapeutic delivery systems and enzymatic reactors. In this work, a class of amphiphilic block oligomers was synthesized from naturally occurring oligosaccharides and aliphatic alcohol precursors, which are all currently prominent in the pharmaceutical, food, and supplement industries. These block oligomer materials were synthesized by functionalization of the precursor materials followed by subsequent coupling by azide-alkyne cycloaddition and their bulk self-assembly was investigated after solvent vapor annealing. Self-assembly of the amphiphilic materials into liposomes in aqueous solution was also investigated after preparing solutions using a nanoprecipitation method. Encapsulation of hydrophobic components was demonstrated and verified using dynamic light scattering, transmission electron microscopy, and fluorescence spectroscopy experiments.

Surface mediated L-phenylalanyl-L-phenylalanine assembly into large dendritic structures

We report a new class of dipeptide dendritic structures fabricated on the surface of mica via spin casting and the conditions required to achieve them. Both their structure and formation mechanism have been investigated in detail using Atomic Force Microscopy (AFM) at the nanometre scale. Formation of nanotubular structures and their further interaction is shown to be a key step in dendritic structure growth. A possible candidate for the primary building block in the nanotubular structure has been identified. The dendritic structures were found to be stable in ambient conditions for several months, however, they transform into needle-like crystals upon exposure to 100% (relative humidity) humid air.

Control of 10 nm scale cylinder orientation in self-organized sugar-based block copolymer thin films

The present paper describes the orientational control of 10 nm scale cylinders in sugar-based block copolymer thin films by simply varying the composition of the annealing co-solvent. The affinity of the block copolymer to the solvent vapor could be systematically adjusted in this way.

10 nm Scale Cylinder-Cubic Phase Transition Induced by Caramelization in Sugar-Based Block Copolymers

To date, the feature size of microphase separation in block copolymers has been downsizing to 10 nm scale. However, morphological control for such a small feature is still a challenging task. The present Letter discusses a phase transition in a natural/synthetic "hybrid" block copolymer system based on an oligosaccharide and poly(ε-caprolactone) via thermal annealing. Time-resolved small-angle X-ray scattering investigation as a function of temperature indicated the phase transition from hexagonally close-packed cylinder to body-centered cubic at 10 nm scale. Atomic force microscope images of the block copolymer thin films annealed at different temperatures clearly confirmed the existence of these morphologies. The driving force of this phase transition (from cylinder to cubic) is the change of volume fraction of the block copolymer due to thermal caramelization.

Oligosaccharide/silicon-containing block copolymers with 5 nm features for lithographic applications

Block copolymers demonstrate potential for use in next-generation lithography due to their ability to self-assemble into well-ordered periodic arrays on the 3-100 nm length scale. The successful lithographic application of block copolymers relies on three critical conditions being met: high Flory-Huggins interaction parameters (χ), which enable formation of <10 nm features, etch selectivity between blocks for facile pattern transfer, and thin film self-assembly control. The present paper describes the synthesis and self-assembly of block copolymers composed of naturally derived oligosaccharides coupled to a silicon-containing polystyrene derivative synthesized by activators regenerated by electron transfer atom transfer radical polymerization. The block copolymers have a large χ and a low degree of polymerization (N) enabling formation of 5 nm feature diameters, incorporate silicon in one block for oxygen reactive ion etch contrast, and exhibit bulk and thin film self-assembly of hexagonally packed cylinders facilitated by a combination of spin coating and solvent annealing techniques. As observed by small angle X-ray scattering and atomic force microscopy, these materials exhibit some of the smallest block copolymer features in the bulk and in thin films reported to date.

Sweet block copolymer nanoparticles: preparation and self-assembly of fully oligosaccharide-based amphiphile

The preparation of biocompatible nanocarriers that have potential applications in the cosmetic and health industries is highly desired. The self-assembly of amphiphilic block copolymers displaying biosourced polysaccharides at the surface is one of the most promising approaches. In the continuity of our works related to the preparation of "hybrid" amphiphilic oligosaccharide-based block copolymers, we present here the design of a new generation of self-assembled nanoparticles composed entirely of oligosaccharide-based amphiphilic block co-oligomers (BCO). These systems are defined by a covalent linkage of the two saccharidic blocks through their reducing end units, resulting in a sweet "head-to-head" connection. As an example, we have prepared and studied a BCO in which the hydrophilic part is composed of a free maltoheptaosyl derivative clicked to a hydrophobic part composed of a peracetylated maltoheptaosyl derivative. This amphiphilic BCO self-assembles to form spherical micelles in water with an average diameter of 30 nm. The efficient enzymatic hydrolysis of the maltoheptaose that constitutes the shell of the micelles was followed by light scattering and colorimetric methods.