Silicon-containing block copolymers for lithographic applications

Sequential Self-Assembly of Polystyrene-block-Polydimethylsiloxane for 3D Nanopatterning via Solvent Annealing

This study aims to develop a strategy for the fabrication of multilayer nanopatterns through sequential self-assembly of lamella-forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS) block copolymer (BCP) from solvent annealing. By simply tuning the solvent selectivity, a variety of self-assembled BCP thin-film morphologies, including hexagonal perforated lamellae (HPL), parallel cylinders, and spheres, can be obtained from single-composition PS-b-PDMS. By taking advantage of reactive ion etching (RIE), topographic SiO2 monoliths with well-ordered arrays of hexagonally packed holes, parallel lines, and hexagonally packed dots can be formed. Subsequently, hole-on-dot and line-on-hole hierarchical textures can be created through a layer-by-layer process with RIE treatment as evidenced experimentally and confirmed theoretically. The results demonstrated the feasibility of creating three-dimensional (3D) nanopatterning from the sequential self-assembly of single-composition PS-b-PDMS via solvent annealing, providing an appealing process for nano-MEMS manufacturing based on BCP lithography.

Synthesis and Structural Insight into poly(dimethylsiloxane)-b-poly(2-vinylpyridine) Copolymers

In this study, the use of anionic polymerization for the synthesis of living poly(dimethylsiloxane) or PDMS-Li+, as well as poly(2-vinylpyridine) or P2VP-Li+ homopolymers, and the subsequent use of chlorosilane chemistry in order for the two blocks to be covalently joined leading to PDMS-b-P2VP copolymers is proposed. High vacuum manipulations enabled the synthesis of well-defined materials with different molecular weights (Μ¯n, from 9.8 to 36.0 kg/mol) and volume fraction ratios (φ, from 0.15 to 0.67). The Μ¯n values, dispersity indices, and composition were determined through membrane/vapor pressure osmometry (MO/VPO), size exclusion chromatography (SEC), and proton nuclear magnetic resonance spectroscopy (1H NMR), respectively, while the thermal transitions were determined via differential scanning calorimetry (DSC). The morphological characterization results suggested that for common composition ratios, lamellar, cylindrical, and spherical phases with domain periodicities ranging from approximately 15 to 39 nm are formed. A post-polymerization chemical modification reaction to quaternize the nitrogen atom in some of the P2VP monomeric units in the copolymer with the highest P2VP content, and the additional characterizations through 1H NMR, infrared spectroscopy, DSC, and contact angle are reported. The synthesis, characterization, and quaternization of the copolymer structure are important findings toward the preparation of functional materials with enhanced properties suitable for various nanotechnology applications.

Nanocarbon Black and Molybdenum Disulfide Hybrid Filler System for the Enhancement of Fracture Toughness and Electromechanical Sensing Properties in the Silicone Rubber-Based Energy Harvester

Recently, hybrid fillers have been found to be more advantageous in energy-harvesting composites. This study investigated the mechanical and electromechanical performances of silicone rubber-based composites made from hybrid fillers containing conductive nanocarbon black (NCB) and molybdenum disulfide (MoS₂). A hybrid filler system containing only 3 phr (per hundred grams of rubber) MoS₂ and 17 phr NCB provided higher fracture strain, better tensile strength, and excellent toughness values compared to the 20 phr NCB-only-filled and 5 phr MoS₂-only-filled rubber composites. The chemical cross-link densities suggest that NCB promoted the formation of cross-links, whereas MoS₂ slightly reduced the cross-link density. The higher mechanical properties in the hybrid filler systems suggest that the filler particles were more uniformly distributed, which was confirmed by the scanning electron microscope study. Uniformly distributed filler particles with moderate cross-link density in hybrid filler systems greatly improved the fracture strain and fracture toughness. For example, the hybrid filler with a 17:3 ratio of NCB to MoS₂ showed a 184% increment in fracture toughness, and a 93% increment in fracture strain, compared to the 20 phr NCB-only-filled composite. Regarding electromechanical sensing with 2 kPa of applied cyclic pressure, the hybrid filler (17:3 CB to MoS₂) performed significantly better (~100%) than the 20 phr NCB-only compound. This may have been due to the excellent distribution of conducting NCB networks and piezoelectric MoS₂ that caused symmetric charging-discharging in the toughened hybrid composite. Thus, hybrid composites with excellent fatigue resistance can find dynamic applications, such as in blood pressure measurement.

Direct Visualization of the Self-Alignment Process for Nanostructured Block Copolymer Thin Films by Transmission Electron Microscopy

Herein, this work aims to directly visualize the morphological evolution of the controlled self-assembly of star-block polystyrene-block-polydimethylsiloxane (PS-b-PDMS) thin films via in situ transmission electron microscopy (TEM) observations. With an environmental chip, possessing a built-in metal wire-based microheater fabricated by the microelectromechanical system (MEMS) technique, in situ TEM observations can be conducted under low-dose conditions to investigate the development of film-spanning perpendicular cylinders in the block copolymer (BCP) thin films via a self-alignment process. Owing to the free-standing condition, a symmetric condition of the BCP thin films can be formed for thermal annealing under vacuum with neutral air surface, whereas an asymmetric condition can be formed by an air plasma treatment on one side of the thin film that creates an end-capped neutral layer. A systematic comparison of the time-resolved self-alignment process in the symmetric and asymmetric conditions can be carried out, giving comprehensive insights for the self-alignment process via the nucleation and growth mechanism.

Electrostatic crosslinking-enabled highly asymmetric lamellar nanostructures of polyzwitterionic block copolymers for lithography

For the bulk self-assembly of traditional diblock copolymers (di-BCPs), lamellar structures only occur when two constituents have similar volume fractions (f) and two alternating layers tend to have similar thicknesses. Highly asymmetric lamellar (A-LAM) structures, in which the thickness of one layer is several times higher than the other, are hardly formed in di-BCPs, while they have potential applications in nanolithography. In this work, A-LAM structures with different dimensions were constructed using a type of simple linear di-BCP, polystyrene-b-poly(4-vinylpyridine)propane-1-sulfonate (PS-b-PVPS) with the polyzwitterionic block PVPS in minority. The origin of the A-LAM structure was ascribed to the electrostatic crosslinking and confirmed by doping PS-b-PVPS block copolymers (BCPs) with N-butyl pyridinium methane sulfonate (BPMS). The morphology of compositionally asymmetric PS-b-PVPS BCPs changed from A-LAM to cylindrical structures upon salt-doping, i.e. the phase behavior of common BCPs was recovered. In addition, the morphologies of PS-b-PVPS BCPs with similar molecular weights but varied compositions were also studied, and only two kinds of structures (lamellar or ill-defined spherical structure) were observed when the volume fraction of PVPS (f_PVPS) was less than 0.5, and the composition range for the formation of the lamellar structure was found to be f_PVPS ≥ 0.188.

Thermal and Bulk Properties of Triblock Terpolymers and Modified Derivatives towards Novel Polymer Brushes

We report the synthesis of three (3) linear triblock terpolymers, two (2) of the ABC type and one (1) of the BAC type, where A, B and C correspond to three chemically incompatible blocks such as polystyrene (PS), poly(butadiene) of exclusively (~100% vinyl-type) -1,2 microstructure (PB_1,2) and poly(dimethylsiloxane) (PDMS) respectively. Living anionic polymerization enabled the synthesis of narrowly dispersed terpolymers with low average molecular weights and different composition ratios, as verified by multiple molecular characterization techniques. To evaluate their self-assembly behavior, transmission electron microscopy and small-angle X-ray scattering experiments were conducted, indicating the effect of asymmetric compositions and interactions as well as inversed segment sequence on the adopted morphologies. Furthermore, post-polymerization chemical modification reactions such as hydroboration and oxidation were carried out on the extremely low molecular weight PB_1,2 in all three terpolymer samples. To justify the successful incorporation of -OH groups in the polydiene segments and the preparation of polymeric brushes, various molecular, thermal, and surface analysis measurements were carried out. The synthesis and chemical modification reactions on such triblock terpolymers are performed for the first time to the best of our knowledge and constitute a promising route to design polymers for nanotechnology applications.

Syndiotactic Poly(4-methyl-1-pentene)-Based Stereoregular Diblock Copolymers: Synthesis and Self-Assembly Studies

Syndiotactic poly(4-methyl-1-pentene) (sP4M1P)-based stereoregular diblock copolymers, namely sP4M1P-b-polystyrene and sP4M1P-b-polymethylmethacrylate, were prepared from an α-bromoester-capped sP4M1P macroinitiator, which was chain extended with styrene and methyl methacrylate, respectively, via the atom transfer radical polymerization reaction. The α-bromoester-capped sP4M1P was generated by the esterification of hydroxyl-capped sP4M1P with α-bromoisobutyryl bromide. The hydroxyl-capped sP4M1P was synthesized by inducing a selective chain transfer reaction to aluminum during the syndiospecific polymerization of 4-methyl-1-pentene in the presence of a syndiospecific metallocene catalyst. As stereoregular diblock copolymers are difficult to prepare using existing methods, the current study offers an effective process for the preparation of sP4M1P-based stereoregular diblock copolymers. These copolymers were found to have well-defined architectures and they can undergo molecular self-assembly into ordered nanostructures, as evidenced by small-angle X-ray scattering analyses.

Influence of Interpenetrating Chains on Rigid Domain Dimensions in Siloxane-Based Block-Copolymers

¹H spin-diffusion solid-state NMR was utilized to elucidate the domain size in multiblock-copolymers (BCPs) poly-(block poly(dimethylsiloxane)-block ladder-like poly(phenylsiloxane)) and poly-(block poly((3,3′,3″-trifluoropropyl-methyl)siloxane)-block ladder-like poly(phenylsiloxane). It was found that these BCPs form worm-like morphology with rigid cylinders dispersed in amorphous matrix. By using the combination of solid-state NMR techniques such as ¹³C CP/MAS, ¹³C direct-polarization MAS and 2D ¹H EXSY, it was shown that the main factor which governs the diameter value of these rigid domains is the presence of interpenetrating segments of soft blocks. The presence of such interpenetrating chains leads to an increase of rigid domain diameter.

Vacuum-Driven Orientation of Nanostructured Diblock Copolymer Thin Films

This work aims to demonstrate a facile method for the controlled orientation of nanostructures of block copolymer (BCP) thin films. A simple diblock copolymer system, polystyrene-block-polydimethylsiloxane (PS-b-PDMS), is chosen to demonstrate vacuum-driven orientation for solving the notorious low-surface-energy problem of silicon-based BCP nanopatterning. By taking advantage of the pressure dependence of the surface tension of polymeric materials, a neutral air surface for the PS-b-PDMS thin film can be formed under a high vacuum degree (∼10^-4 Pa), allowing the formation of the film-spanning perpendicular cylinders and lamellae upon thermal annealing. In contrast to perpendicular lamellae, a long-range lateral order for forming perpendicular cylinders can be efficiently achieved through the self-alignment mechanism for induced ordering from the top and bottom of the free-standing thin film.

Well-Ordered Nanonetwork Metamaterials from Block Copolymer Templated Syntheses

ConspectusThrough the morphological evolution to give highly optimized complex architectures at different length scales, fine-tuned textures for specific functions in living organisms can be achieved in nature such as a bone core with very complicated porous architecture to attain a significant structural efficiency attributed to delicately structured ligaments and density gradients. As inspired by nature, materials with periodic network structures (i.e., well-defined porous textures) in the nanoscale are appealing and promising for innovative properties. Biomimicking from nature, organic and/or inorganic nanonetworks can be synthetically fabricated, giving broadness and effectiveness when tuning the desired properties. Metamaterials are materials whose effective properties do not result from the bulk behavior of the constituent materials but rather mainly from their deliberate structuring. The performances of fabricating metamaterials will depend on the control of size, shape, order, and orientation of the forming textures. One of the appealing textures for the deliberate structuring is network architecture. Network materials possess self-supporting frameworks, open-cell character, high porosity, and large specific surface area, giving specific functions and complexity for diverse applications. As demonstrated by recent studies, exceptional mechanical performances such as negative thermal expansion, negative Poisson's ratio, and twisting under uniaxial forces can be achieved by the effect of the deliberate structuring with nanonetwork textures. In contrast to a top-down approach, a bottom-up approach is cost-effective, and also it can overcome the size limitation to reach nanoscale fabrication. It can be foreseen that network metamaterials with a feature size of tens of nanometers (referred as nanonetwork metamaterials) may provide new comprehension of the structure and property relationships for various materials. The self-assembly of block copolymers (BCPs) is one of the most used methods to build up well-ordered nanostructured phases from a bottom-up approach with precise control of size, shape, and orientation in the thin films for realistic applications. In this account, we summarize recent advancements in the fabrication of nanohybrids and nanoporous materials with well-ordered nanonetwork textures even with controlled helicity by combining block copolymer self-assembly and templated syntheses for mechanical and optical applications with superior properties beyond nature as metamaterials as well as chiral metamaterials with new properties for chiroptic applications such as chiral plasmonics, beam splitter, and negative refraction. The description of the fundamental facets of a nonconventional structure-property relationship with the characters of metamaterials and the state-of-the-art methodologies to fabricate nanonetworks using block copolymer self-assembly will stimulate research activities for the development of nanonetwork metamaterials with exceptional individual and multifunctional properties for futuristic devices.

Synthesis of Benzimidazo[2,1-a]isoquinoline and Indolo[2,1-a]isoquinoline Derivatives via Copper-Catalyzed Silylation/Methylation of 2-Arylindoles and 2-Arylbenzimidazoles

A one-pot method for the synthesis of silylsubstituted/methylsubstituted indolo[2,1-a]isoquinolin-6(5H)-ones and benzimidazo[2,1-a]isoquinoline-6(5H)-ones via copper(II)-initiated silylation/methylation of 2-arylindoles and 2-arylbenzimidazoles was developed. In this procedure, the C-Si bond and C-C bond were constructed by radical addition and cyclization. A series of 2-arylindole and 2-arylbenzimidazole derivatives were facilely transformed to indolo[2,1-a]isoquinolines and benzimidazo[2,1-a]isoquinolines in 39-83% yields.

Fabrication of Ultrafine, Highly Ordered Nanostructures Using Carbohydrate-Inorganic Hybrid Block Copolymers

Block copolymers (BCPs) have garnered considerable interest due to their ability to form microphase-separated structures suitable for nanofabrication. For these applications, it is critical to achieve both sufficient etch selectivity and a small domain size. To meet both requirements concurrently, we propose the use of oligosaccharide and oligodimethylsiloxane as hydrophilic and etch-resistant hydrophobic inorganic blocks, respectively, to build up a novel BCP system, i.e., carbohydrate-inorganic hybrid BCP. The carbohydrate-inorganic hybrid BCPs were synthesized via a click reaction between oligodimethylsiloxane with an azido group at each chain end and propargyl-functionalized maltooligosaccharide (consisting of one, two, and three glucose units). In the bulk state, small-angle X-ray scattering revealed that these BCPs microphase separated into gyroid, asymmetric lamellar, and symmetric lamellar structures with domain-spacing ranging from 5.0 to 5.9 nm depending on the volume fraction. Additionally, we investigated microphase-separated structures in the thin film state and discovered that the BCP with the most asymmetric composition formed an ultrafine and highly oriented gyroid structure as well as in the bulk state. After reactive ion etching, the gyroid thin film was transformed into a nanoporous-structured gyroid SiO₂ material, demonstrating the material’s promising potential as nanotemplates.

Selective sequential infiltration synthesis of ZnO in the liquid crystalline phase of silicon-containing rod-coil block copolymers

The combination of block copolymer (BCP) thin film self-assembly and selective infiltration synthesis of inorganic materials into one BCP block provides access to various organic-inorganic hybrids. Here, we apply sequential infiltration synthesis, a vapor-phase hybridization technique, to selectively introduce ZnO into the organic microdomains of silicon-containing rod-coil diblock copolymers and a triblock terpolymer, polydimethylsiloxane (PDMS)-b-poly{2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene} (PDMS-b-PMPCS) and PDMS-b-polystyrene-b-PMPCS (PDMS-b-PS-b-PMPCS), in which the PMPCS rod block is a liquid crystalline polymer. The in-plane cylindrical PDMS-b-PMPCS and core-shell cylindrical and hexagonally perforated lamellar PDMS-b-PS-b-PMPCS films were infiltrated with ZnO with high selectivity to the PMPCS. The etching contrast between PDMS, PS and the ZnO-infused PMPCS enables the fabrication of ZnO/SiO_x binary composites by plasma etching and reveals the core-shell morphology of the triblock terpolymer.

Blending Linear and Cyclic Block Copolymers to Manipulate Nanolithographic Feature Dimensions

Block copolymers (BCPs) consist of two or more covalently bound chemically distinct homopolymer blocks. These macromolecules have emerging applications in photonics, membrane separations, and nanolithography stemming from their self-assembly into regular nanoscale structures. Theory suggests that cyclic BCPs should form features up to 40% smaller than their linear analogs while also exhibiting superior thin-film stability and assembly dynamics. However, the complex syntheses required to produce cyclic polymers mean that a need for pure cyclic BCPs would present a challenge to large-scale manufacturing. Here, we employ dissipative particle dynamics simulations to probe the self-assembly behavior of cyclic/linear BCP blends, focusing on nanofeature size and interfacial width as these qualities are critical to nanopatterning applications. We find that for mixtures of symmetric cyclic and linear polymers with equivalent lengths, up to 10% synthetic impurity has a minimal impact on cyclic BCP feature dimensions and interfacial roughness. On the other hand, blending with cyclic BCPs provides a route to "fine-tune" linear BCP feature sizes. We analyze simulated blend domain spacings within the context of strong segregation theory and find significant deviations between simulation and theory that arise from molecular-level packing motifs not included in theory. These insights into blend self-assembly will assist experimentalists in rationally designing BCP materials for advanced nanolithography applications.

Si containing block copolymers quickly assemble into sub-6 nm domains

The directed self-assembly (DSA) of block copolymers (BCPs) is a potential patterning technology for sub-7 nm lithography.

para-Fluoro/thiol click chemistry-driven pentafluorostyrene-based block copolymer self-assembly: to mimic or not to mimic the solubility parameter?

This investigation reports the controlled transition from disordered/nano-segregated poly(styrene-b-pentafluorostyrene) (PS-b-PPFS)-based block copolymers after a subsequent para-fluoro/thiol click reaction with different functional thiol agents.

Dry-Etching Processes for High-Aspect-Ratio Features with Sub-10 nm Resolution High-χ Block Copolymers

Directed self-assembly of block copolymers (BCP) is a very attractive technique for the realization of functional nanostructures at high resolution. In this work, we developed full dry-etching strategies for BCP nanolithography using an 18 nm pitch lamellar silicon-containing block copolymer. Both an oxidizing Ar/O₂ plasma and a nonoxidizing H₂/N₂ plasma are used to remove the topcoat material of our BCP stack and reveal the perpendicular lamellae. Under Ar/O₂ plasma, an interfacial layer stops the etch process at the topcoat/BCP interface, which provides an etch-stop but also requires an additional CF₄-based breakthrough plasma for further etching. This interfacial layer is not present in H₂/N₂. Increasing the H₂/N₂ ratio leads to more profound modifications of the silicon-containing lamellae, for which a chemistry in He/N₂/O₂ rather than Ar/O₂ plasma produces a smoother and more regular lithographic mask. Finally, these features are successfully transferred into silicon, silicon-on-insulator, and silicon nitride substrates. This work highlights the performance of a silicon-containing block copolymer at 18 nm pitch to pattern relevant hard-mask materials for various applications, including microelectronics.

Linear/Ladder-Like Polysiloxane Block Copolymers with Methyl-, Trifluoropropyl- and Phenyl- Siloxane Units for Surface Modification

Multiblock copolymers containing linear polydimethylsiloxane or polymethyltrifluoropropylsiloxane and ladder-like polyphenylsiloxane were synthesized in a one-step pathway. The functional homopolymer blocks and final multiblock copolymers were characterized using solution and solid-state multinuclear ¹H, ¹³C, ¹⁹F, and ²⁹Si NMR spectroscopy. It was shown that the ladder-like block contains silanol units, which influence the adhesion properties of multiblock copolymers and morphology of their casted films. The adhesion to metals and mechanical properties of multiblock copolymers were tested. The SEM study of casted films of multiblock copolymers shows the variety of formed morphologies, including long-strip-like or globular.

Supramolecular Chirality Transfer toward Chiral Aggregation: Asymmetric Hierarchical Self-Assembly

Self-assembly, as a typical bottom-up strategy for the fabrication of functional materials, has been applied to fabricate chiral materials with subtle chiral nanostructures. The chiral nanostructures exhibit great potential in asymmetric catalysis, chiral sensing, chiral electronics, photonics, and even the realization of several biological functions. According to existing studies, the supramolecular chirality transfer process combined with hierarchical self-assembly plays a vital role in the fabrication of multiscale chiral structures. This progress report focuses on the hierarchical self-assembly of chiral or achiral molecules that aggregate with asymmetric spatial structures such as twisted bands, helices, and superhelices in different environments. Herein, recent studies on the chirality transfer induced self-assembly based on a variety of supramolecular interactions are summarized. In addition, the influence of different environments and the states of systems including solutions, condensed states, gel systems, interfaces on the asymmetric hierarchical self-assembly, and the expression of chirality are explored. Moreover, both the driving forces that facilitate chiral bias and the supramolecular interactions that play an important role in the expression, transfer, and amplification of the chiral sense are correspondingly discussed.

Bending Behavior and Directed Self-Assembly of Rod-Coil Block Copolymers

The formation of zigzags, chevrons, Y-junctions, and line segments is demonstrated in thin films formed from cylindrical morphology silicon-containing conformationally asymmetric rod-coil diblock copolymers and triblock terpolymers under solvent annealing. Directed self-assembly of the block copolymers within trenches yields well-ordered cylindrical microdomains oriented either parallel or transverse to the sidewalls depending on the chemical functionalization of the sidewalls, and the location and structure of concentric bends in the cylinders is determined by the shape of the trenches. The innate etching contrast, the spontaneous sharp bends and junctions, and the range of demonstrated periodicity and line/space ratios make these conformationally asymmetric rod-coil polymers attractive for nanoscale pattern generation.

Synthesis, characterization and self-assembly of linear and miktoarm star copolymers of exclusively immiscible polydienes

Model linear PB_1,4-b-PI_3,4 and the corresponding miktoarm star copolymers PB_1,4(PI_3,4)_n=2,3 were synthesized by anionic polymerization/selective chlorosilane chemistry, molecularly characterized and the morphological/thermal properties were reported.

Resist-Free Directed Self-Assembly Chemo-Epitaxy Approach for Line/Space Patterning

This work reports a novel, simple, and resist-free chemo-epitaxy process permitting the directed self-assembly (DSA) of lamella polystyrene-block-polymethylmethacrylate (PS-b-PMMA) block copolymers (BCPs) on a 300 mm wafer. 193i lithography is used to manufacture topographical guiding silicon oxide line/space patterns. The critical dimension (CD) of the silicon oxide line obtained can be easily trimmed by means of wet or dry etching: it allows a good control of the CD that permits finely tuning the guideline and the background dimensions. The chemical pattern that permits the DSA of the BCP is formed by a polystyrene (PS) guide and brush layers obtained with the grafting of the neutral layer polystyrene-random-polymethylmethacrylate (PS-r-PMMA). Moreover, data regarding the line edge roughness (LER) and line width roughness (LWR) are discussed with reference to the literature and to the stringent requirements of semiconductor technology.

Effect of chain architectures on the domain spacing of block copolymers with equivalent segregation degrees

It is crucial to lower the domain spacing in the application of directed self-assembly (DSA) of block copolymers. Architectural design of block copolymers provides a possible route. However, the change of the segregation degree is always coupled with that of domain spacing. Therefore, we rescale the segregation degrees of different multiblock copolymers with reference to that of the AB diblock using self-consistent field theory (SCFT), including the [AB]n linear multiblock, AnBn multi-arm star and Ad,nBd,n dendron-like, such that the density profiles of the lamellar morphology are consistent. Then we compare the lamellar periods of these different copolymers under the condition of equivalent segregation degrees. We find that the star and dendron-like architectures can significantly lower the domain spacing relative to that of the AB diblock, especially when the arm number or the generation number is large. On one hand, our work presents a simple criterion for quantifying the reduction of domain spacing of a specific multiblock architecture relative to that of the AB diblock. On the other hand, our conclusion provides a useful guide for the application of directed self-assembly.

Highly asymmetric lamellar nanostructures from nanoparticle-linear hybrid block copolymers

The highly asymmetric lamellar (A-LAM) nanostructure is one of the most important template geometries for block copolymer (BCP) lithography. However, A-LAM is unattainable from conventional BCPs, and there is no general molecular design strategy for A-LAM-forming BCP. Herein, a nanoparticle-linear hybrid BCP system is reported, which is designed based on the intramolecular crosslinking technique, as a remarkably effective platform to obtain the A-LAM morphology. The hybrid BCPs consisting of polystyrene single-chain nanoparticles and linear polylactide segments show a remarkable capability to form the A-LAM morphology in bulk, where a maximum width ratio of 4.1 between the two domains is obtained. This unusual phase behavior is attributed to the bulky and rigid characteristics of the nanoparticle block. Furthermore, the thin films of these hybrid BCPs show perpendicularly oriented A-LAM morphology on a chemically modified Si substrate, allowing promising application in the fabrication of asymmetric line-and-space nanopatterns.

Vertical Lamellae Formed by Two-Step Annealing of a Rod-Coil Liquid Crystalline Block Copolymer Thin Film

Silicon-containing block copolymer thin films with high interaction parameter and etch contrast are ideal candidates to generate robust nanotemplates for advanced nanofabrication, but they typically form in-plane oriented microdomains as a result of the dissimilar surface energies of the blocks. Here, we describe a two-step annealing method to produce vertically aligned lamellar structures in thin film of a silicon-containing rod-coil thermotropic liquid crystalline block copolymer. The rod-coil block copolymer with the volume fraction of the Si-containing block of 0.22 presents an asymmetrical lamellar structure in which the rod block forms a hexatic columnar nematic liquid crystalline phase. A solvent vapor annealing step first produces well-ordered in-plane cylinders of the Si-containing block, then a subsequent thermal annealing promotes the phase transition from in-plane cylinders to vertical lamellae. The pathways of the order-order transition were examined by microscopy and in situ using grazing incidence small-angle X-ray scattering and wide-angle X-ray scattering.

Curved block copolymer nanodiscs: structure transformations in cylindrical nanopores using the nonsolvent-assisted template wetting method

In this work, we study the structure transformations of cylinder-forming polystyrene-block-polydimethylsiloxane (PS31k-b-PDMS14.5k) confined in cylindrical nanopores. PS-b-PDMS nanotubes, nanospheres, and curved nanodiscs are ingeniously prepared by a facile template wetting strategy using anodic aluminum oxide (AAO) templates. Quantitative analyses of the structure transformations from nanospheres to curved nanodiscs are also conducted, showing that the lengths of the curved nanodiscs can be controlled by adjusting the annealing temperature and time. Furthermore, the PDMS domains of the nanostructures can be selectively etched using HF solutions, generating porous PS nanostructures. This work not only offers versatile routes to prepare block copolymer nanostructures with controlled shapes but also provides a deeper understanding of the structure transformation of block copolymers in confined geometries.

Tailored Nanopatterning by Controlled Continuous Nanoinscribing with Tunable Shape, Depth, and Dimension

We present that the tailored nanopatterning with tunable shape, depth, and dimension for diverse application-specific designs can be realized by utilizing controlled dynamic nanoinscribing (DNI), which can generate bur-free plastic deformation on various flexible substrates via continuous mechanical inscription of a small sliced edge of a nanopatterned mold in a compact and vacuum-free system. Systematic controlling of prime DNI processing parameters including inscribing force, temperature, and substrate feed rate can determine the nanopattern depths and their specific profiles from rounded to angular shapes as a summation of the force-driven plastic deformation and heat-driven thermal deformation. More complex nanopatterns with gradient depths and/or multidimensional profiles can also be readily created by modulating the horizontal mold edge alignment and/or combining sequential DNI strokes, which otherwise demand laborious and costly procedures. Many practical user-specific applications may benefit from this study by tailor-making the desired nanopattern structures within desired areas, including precision machine and optics components, transparent electronics and photonics, flexible sensors, and reattachable and wearable devices. We demonstrate one vivid example in which the light diffusion direction of a light-emitting diode can be tuned by application of specifically designed DNI nanopatterns.

Hybrid patterns from directed self-assembly of diblock copolymers by chemical patterns

The surface affinity is a critical factor for controlling the formation of monolayer nanostructures in block copolymer thin films. In general, strong surface affinity tends to induce the formation of domains with low spontaneous curvature. Abiding by this principle, we propose a facile chemoepitaxial scheme for producing large-scale ordered hybrid patterns by the directed self-assembly of diblock copolymers. The guiding chemical pattern is designed as periodic stripes with alternately changing surface affinities. As a consequence, two different geometries of domains are formed on the stripes with different affinities. The self-assembly process of block copolymers guided by the stripe patterns is investigated using cell dynamics simulations based on time-dependent Ginzburg-Landau theory, and the kinetic stability diagram is estimated. Hybrid patterns are successfully achieved with both cylinder-forming and sphere-forming diblock copolymers. In the cylinder-forming system, the major hybrid pattern exhibiting a considerable stability window is composed of parallel cylinders and perforated lamellae, while it is composed of monolayer spheres and parallel cylinders in the other system. Encouragingly, the chemoepitaxial method is valid till the period of the guiding pattern is a large multiple of the domain spacing. The chemoepitaxial scheme demonstrated in this work serves as a nice supplement to the graphoepitaxial one proposed in our previous work.

Core-Shell and Zigzag Nanostructures from a Thin Film Silicon-Containing Conformationally Asymmetric Triblock Terpolymer

The self-assembly of multiblock copolymers generates diverse hierarchical nanostructures and greatly extends the range of microdomain geometries beyond those produced by diblock copolymers. We report the synthesis of a conformationally asymmetric ABC triblock terpolymer in which the end blocks are a mesogen-jacketed liquid crystalline polymer and poly(dimethylsiloxane), respectively, and its self-assembly under mixed solvent vapor annealing forms a range of sphere, cylinder, and perforated lamellar core-shell morphologies, as well as stacked multilevel structures. Sub-7 nm diameter SiO_x nanopatterns were generated by selective plasma etching of the small volume fraction Si-containing core block giving a line/space ratio of ∼1:4. Moreover, the conformational asymmetry of this terpolymer leads to zigzag cylinders on a flat substrate and stable cylinder alignment transverse to template sidewalls within lithographically patterned trenches.

Synthesis of a Fluoromethacrylate Hydroxystyrene Block Copolymer Capable of Rapidly Forming Sub-5 nm Domains at Low Temperatures

A series of poly(pentadecafluorooctyl methacrylate)-block-polyhydroxystyrene (PPDFMA-b-PHS) block copolymers (BCPs) were synthesized via reversible addition-fragmentation chain-transfer polymerization and subsequent deprotection. Because of the high incompatibility between hydroxyl groups and fluoro groups, the interaction parameter (χ) of these BCPs, determined by temperature-resolved small-angle X-ray scattering (SAXS), was extremely high. The χ value of PPDFMA-b-PHS was 0.48 at 150 °C, 16× larger than the χ of polystyrene-block-poly(methyl methacrylate). The microphase behavior of PPDFMA-b-PHS with various volume fractions of PHS block was determined by SAXS, yielding ordered lamellar morphologies with different sizes of domain spacing (d), and further confirmed by transmission electron microscopy. The minimum d obtained was 9.8 nm annealed at a mild temperature for a short time (80 °C for 1 min) by SAXS analysis, indicating the width of each lamellar domains was <5 nm.

Downsizing feature of microphase-separated structures via intramolecular crosslinking of block copolymers

A novel strategy for downsizing the feature of microphase-separated structures was developed via the intramolecular crosslinking reaction of block copolymers (BCPs) without changing the molecular weight. A series of BCPs consisting of poly[styrene-st-(p-3-butenyl styrene)] and poly(rac-lactide) (SBS-LA) was subjected to Ru-catalyzed olefin metathesis under highly diluted conditions to produce intramolecularly crosslinked BCPs (SBS(cl)-LAs). Small-angle X-ray scattering measurement and transmission electron microscopy observation of the SBS(cl)-LAs revealed feature size reduction in lamellar (LAM) and hexagonally close-packed cylinder (HEX) structures in the bulk state, which was surely due to the restricted chain dimensions of the intramolecularly crosslinked SBS block. Notably, the degree of size reduction was controllable by varying the crosslink density, with a maximum decrease of 22% in the LAM spacing. In addition, we successfully observed the downsizing of the HEX structure in the thin film state using atomic force microscopy, indicating the applicability of the present methodology to next-generation lithography technology.

Self-assembly of a silicon-containing side-chain liquid crystalline block copolymer in bulk and in thin films: kinetic pathway of a cylinder to sphere transition

The self-assembly of a high-χ silicon-containing side-chain liquid crystalline block copolymer (LC BCP) in bulk and in thin films is reported, and the structural transition process from the hexagonally packed cylinder (HEX) to the body-centered cubic structure (BCC) in thin films was examined by both reciprocal and real space experimental methods. The block copolymer, poly(dimethylsiloxane-b-11-(4'-cyanobiphenyl-4-yloxy)undecylmethacrylate) (PDMS-b-P(4CNB11C)MA) with a molecular weight of 19.5 kg mol-1 and a volume fraction of PDMS 27% self-assembled in bulk into a hierarchical nanostructure of sub-20 nm HEX cylinders of PDMS with the P(4CNB11C)MA block exhibiting a smectic LC phase with a 1.61 nm period. The structure remained HEX as the P(4CNB11C)MA block transformed to an isotropic phase at ∼120 °C. In the thin films, the PDMS cylindrical microdomains were oriented in layers parallel to the substrate surface. The LC block formed a smectic LC phase which transformed to an isotropic phase at ∼120 °C, and the microphase-separated nanostructure transformed from HEX to BCC spheres at ∼160 °C. The hierarchical structure as well as the dynamic structural transition of the thin films were characterized using in situ grazing-incidence small-angle X-ray scattering and grazing-incidence wide-angle X-ray scattering. The transient morphologies from the HEX to BCC structure in thin films were captured by scanning electron microscopy and atomic force microscopy, and the transition pathway was described.

Directed Self-Assembly of High χ Poly(styrene-b-(lactic acid-alt-glycolic acid)) Block Copolymers on Chemical Patterns via Thermal Annealing

We demonstrated the synthesis and directed self-assembly (DSA) of poly(styrene-b-(lactic acid-alt-glycolic acid)) (PS-b-PLGA). Lamellae-forming PS-b-PLGAs with a range of molecular weights were synthesized by ring-opening polymerization (ROP) of LGA (d,l-3-methyl-1,4-dioxane-2,5-dione) from hydroxy-terminated polystyrene (PS-OH) with stannous octoate as the catalyst and characterized by ¹H NMR spectroscopy, GPC, DSC, TGA, SAXS, and rheometry. The order-disorder transition temperatures (T_ODT) of four PS-b-PLGA block copolymers were determined by temperature sweep measurements and verified by variable-temperature SAXS, which were used to determine the temperature dependence of χ. The χ value of PS-b-PLGA is twice as large as that of poly(styrene-b-racemic lactide) (PS-b-PDLLA) at 150 °C, while the surface energies (γ) of PS and PLGA are nearly equal. Thin films of PS-b-PLGA were successfully directed to assemble on stripe chemical patterns with a range of pattern periods (L_S) upon thermal annealing. SEM analysis of the assembled films revealed that long-range ordered perpendicularly oriented lamellae were registered on chemical patterns with 2× density multiplication. These results qualify PS-b-PLGA as an attractive candidate for next-generation lithography with sub-10 nm resolution.