Helically deployed Au nanoparticles using block copolymer templates as chiral plasmonic monoliths

Using solution micelles formed by a block copolymer template, a variety of highly ordered catalytically active transition metal nanoparticles, ranging from single metallic nanoparticles of Fe, Co, Ni and Au to bimetallic nanoparticles such as Ni/Fe with uniform size and periodicity, have been created. These nanoparticles are excellent catalyst systems for the synthesis of carbon nanotubes and silicon nanowires. High quality, small diameter carbon nanotubes and silicon nanowires with narrow size distribution have been successfully produced. Since this block copolymer is fully compatible with conventional top-down photolithography, spatially selective growth of carbon nanotubes and silicon nanowires on a surface or carbon nanotubes suspended across trenches have been achieved using standard semiconductor processing techniques. The ability of the block copolymer template to generate catalyst with adjustable size and composition on a variety of surfaces not only enhance the manufacturability of these 1D nanobuilding blocks but also facilitates studying the growth mechanism.

Nanopattern generation is required for building various structural entities in every production process that involves nanostructures. Advancing nanopatterning technologies play an important role in developing and broadening the current nanopatterning technologies to meet up with the ever-demanding requirements in the realm of smaller feature sizes, smoother line-edge roughness (LER) and facile pattern transfer in pursuit of faster computer processors, better electrocatalysts and more compact and intelligent sensors, etc. Conventionally, patterning needs are heavily relied on photolithography, a technique that dominate chip-making industry for more than 50 years. However conventional photolithography is bounded by inherent resolution limits and difficult to be applied on non-flat, flexible, or stretchable substrates. Advancement in patterning techniques are urgently needed to enhance the capability for sub-10 nm patterning onto versatile substrates. The patterning techniques adopted in this work is a bottom-up self-assembly driven scheme based on the phase segregation of block copolymers (BCPs). Cleverly designed BCPs system can generate self-assembled pattern to give a sub-10 nm pitch, demonstrating the tremendous potential of novel BCP chemistries in generating sub-10 nm features. Recent excellent works on BCPs with sub-10 nm natural periods are timely reviewed, and key principles in designing next generation BCP candidates for extreme scale lithography are proposed in the outlook. Thin film BCPs templates were leveraged to generate patterns on various substrates including silicon, gold, glassy carbon, reduced graphene oxide, Nafion ® membrane, and perfluorinated anion exchange membrane. The profound meaning of these demonstration is twofold, firstly showcased the robustness and wide portability of the tested BCP patterning scheme, secondly demonstration of introducing the BCP templates onto smart substrates that have special functionality and wide implications. Further ionization and metallization of BCPs templates exemplify the feasibility of fabricating nanostructured electrolytes and metal nanowires with controlled periodic features sizes. Ordered nanostructures with designed ionic loadings, metal densities on functional substrates open up tremendous possibility to be incorporated into sensor, nanoseparators and nanoreactors with novel properties that yet to be uncovered.

The use of precrystallized nanoparticles as nanobuilding blocks (NBBs) is a promising way to obtain mesoporous materials with crystalline walls. In this study, the size effects of both hydroxide NBBs and nonionic block copolymer (BCP) templates on the formation of ordered mesostructures are investigated. The diameter of layered nickel hydroxide NBBs was controlled at the sub-2 nm scale by an epoxide-mediated alkalinization process. Commercially available nonionic BCPs (gyration radii in the range of 11.9-43.9 Å) were used. Mesoperiodic structures were formed by the evaporation-induced self-assembly process. A proper size combination of hydroxide NBBs, smaller than 12.5 Å, and BCPs, larger than 19.9 Å, is shown to be necessary to form ordered mesostructures.

Photocatalytic self-cleaning coatings with a high surface area are important for a wide range of applications, including optical coatings, solar panels, mirrors, etc. Here, we designed a highly porous TiO2 coating with photoinduced self-cleaning characteristics and very high hydrophilicity. This was achieved using the swelling-assisted sequential infiltration synthesis (SIS) of a block copolymer (BCP) template, which was followed by polymer removal via oxidative thermal annealing. The quartz crystal microbalance (QCM) was employed to optimize the infiltration process by estimating the mass of material infiltrated into the polymer template as a function of the number of SIS cycles. This adopted swelling-assisted SIS approach resulted in a smooth uniform TiO2 film with an interconnected network of pores. The synthesized film exhibited good crystallinity in the anatase phase. The resulting nanoporous TiO2 coatings were tested for their functional characteristics. Exposure to UV irradiation for 1 h induced an improvement in the hydrophilicity of coatings with wetting angle reducing to unmeasurable values upon contact with water droplets. Furthermore, their self-cleaning characteristics were tested by measuring the photocatalytic degradation of methylene blue (MB). The synthesized porous TiO2 nanostructures displayed promising photocatalytic activity, demonstrating the degradation of approximately 92% of MB after 180 min under ultraviolet (UV) light irradiation. Thus, the level of performance was comparable to the photoactivity of commercial anatase TiO2 nanoparticles of the same quantity. Our results highlight a new robust approach for designing hydrophilic self-cleaning coatings with controlled porosity and composition.

Metal nanoparticles (NPs) can exhibit unique electronic, magnetic, optical, and catalytic properties. Highly ordered, dense arrays of non-close-packed, surface-supported metal NPs are thus of potential use in a wide range of applications. Implementing such arrays over large surfaces can, however, be both technologically challenging and prohibitively expensive using conventional top-down nanofabrication techniques. Moreover, many existing patterning methods are too harsh for sensitive substrate surfaces and their applications. To address this, we here investigate a fabrication protocol involving a water-based lift-off scheme in which the template pattern generation is rapidly and inexpensively achieved through block copolymer (BCP) self-assembly. A three-layer lift-off stack consisting of, from top to bottom, a poly(styrene-block-2-vinyl pyridine) template, a SiO x intermediate hardmask, and a water-soluble poly(vinyl alcohol) sacrificial layer is employed in this endeavor. Solvent-induced surface reconstruction (SISR) is used to generate an initial surface topography in the BCP template which is subsequently transferred to the layers beneath in a sequence of reactive ion etching steps. Through judicious selection of stack materials and dry etch chemistries, a layered, high-aspect-ratio, nanoporous mask is thus implemented. After metal deposition, the mask and excess material are simply removed in a lift-off step by dissolving the bottommost sacrificial layer in water. The incorporation of an intermediate hardmask and a water-soluble sacrificial layer obviates the need for harmful and/or corrosive lift-off solvents and decouples the BCP self-assembly process from the influence of substrate properties. We demonstrate the generation of well-ordered arrays of Au NPs capable of supporting sharp, localized surface plasmon resonances. We also investigate improvements to large-scale uniformity, as this is found sensitive to the SISR termination step in the original protocol. Extensions of the technique to other BCP morphologies and materials deposited ought to be straightforward.

Arrays of oriented polyaniline (PANI) nanostructures of different shape and size were fabricated on transparent ITO substrates using block copolymer nanotemplate as scaffold material. Polyaniline in these nanostructures was synthesized by electropolymerization. The electrochemical deposition requires only a single step where the size and shape of the nanostructures vary with time and can be tailored easily. Both AFM and SEM studies were carried out in order to study the morphology of different polyaniline nanostructures fabricated using block copolymer nanotemplates. SEM investigations confirm that the morphology of fabricated polyaniline nanostructures is different from the polyaniline simply grown on blank ITO using the same experimental conditions. The optical, electrical and electrochemical properties of these polyaniline nanostructures have been studied. These polyaniline nanostructures show different optical and electrochemical properties as compared to randomly grown polyaniline thin film on blank ITO. Polyaniline nanostructures fabricated using block copolymer templates have an additional absorption peak near 510 nm which is due to different chain conformations of polyaniline growing inside the block copolymer template. The polyaniline deposited using the block copolymer nanotemplate has additional redox peaks as compared to polyaniline deposited on bare ITO. The presence of an extra redox couple (around 0.515/0.487 V) clearly indicates that polyaniline nanostructures have some quinone type defect which is absent in the polyaniline deposited on bare ITO. We have studied the electric properties of these polyaniline nanostructures using conducting AFM. The discrete bright spots in the current image indicating the areas where current flows, correspond to the individual polyaniline nanostructures. In contrast, the current image of the polyaniline film prepared on blank ITO, indicates that polyaniline covers the entire surface.

We report chemical modification of self-assembled block copolymer thin films by ultraviolet light that enhances the block-selective affinity of organometallic precursors otherwise lacking preference for either copolymer block. Sequential precursor loading and reaction facilitate formation of zinc oxide, titanium dioxide, and aluminum oxide nanostructures within the polystyrene domains of both lamellar- and cylindrical-phase modified polystyrene-block-poly(methyl methacrylate) thin film templates. Near-edge X-ray absorption fine structure measurements and Fourier transform infrared spectroscopy show that photo-oxidation by ultraviolet light creates Lewis basic groups within polystyrene, resulting in an increased Lewis base-acid interaction with the organometallic precursors. The approach provides a method for generating both aluminum oxide patterns and their corresponding inverses using the same block copolymer template.

ABSTRACTThe overall goal of this research is to explore techniques for the development of novel binary magnetic oxide nanoclusters uniformly distributed within a polymer matrix. These CoFe2O4 nanoclusters were synthesized at room temperature, and are confined within the self-assembled nanoscale structure exhibited by block copolymers templates. The diblock copolymers were synthesized by ring opening metathesis polymerization of norbornene and norbornene trimethylsilane and the binary magnetic oxide was introduced through a nanoreaction scheme using wet chemical methods. Transmission electron micrographs of microtomed thin sections of these nanocomposites show that the metal oxide nanoclusters are ellipsoidal in shape and are uniformly distributed within the polymer matrix. A SQUID magnetometer was used to study the magnetic properties of the polymeric nanocomposites at applied fields up to 5 Tesla and at a temperature range between 300 °K and 5 °K. Mössbauer spectroscopy was used to study the structure of the nanoconfined metal oxide, and confirmed the synthesis of CoFe2O4 nanoclusters exhibiting an inverse spinel structure. This study provided a better understanding of the nucleation, growth and distribution of metal oxide nanoclusters within block copolymers and indicated ways to control the magnetic properties of polymeric based nanocomposite materials. The development of such binary metal oxide - block copolymer nanocomposites is targeting the functionalization of such nanostructures into magnetic device technologies.

Mesoporous basic Mg-Al mixed metal oxides (MMOs) with a high surface area and large pore size have been prepared through the assembly of monodispersed layered double hydroxide nanoparticles (LDHNPs) with block copolymer templates. The particle sizes of the LDHNPs were mainly controlled by varying the concentration of tris(hydroxymethyl)aminomethane (THAM), which was used as a surface stabilizing agent. LDHNPs and micelles of a block copolymer (Pluronic F127) were assembled to form a composite. The composites were calcined to transform them into mesoporous MMOs and to remove the templates. The Brunauer-Emmett-Teller surface areas, mesopore sizes, and pore volumes increased as a result of using the templates. Moreover, the pore sizes of the mesoporous MMOs could be controlled by using LDHNPs of different sizes. The mesoporous MMOs prepared from the LDHNPs showed much higher catalytic activity than a conventional MMO catalyst for the Knövenagel condensation of ethyl cyanoacetate with benzaldehyde. The mesoporous MMO catalyst prepared using the smallest LDHNPs, about 12 nm in size, showed the highest activity. Therefore, the use of monodispersed LDHNPs and templates is effective for preparing highly active mesoporous solid base catalysts.

Five commercial poly(ethylene oxide)/poly(butylene oxide) (PEO/PBO) triblock copolymer surfactants were utilized as structure-directing agents to synthesize mesoporous silica under acidic conditions. The structures of these materials were characterized by using powder X-ray diffraction (XRD), nitrogen adsorption analysis, and transmission electron micrographs (TEM). The relationship between the pore sizes of silica mesostructures and hydrophobic block weight as well as block architecture of their block copolymer templates was discussed. From the comparison of the critical micelle concentration (CMC) values of these PEO−PBO copolymers and the resultant silica mesostructures, it is proposed that the CMC of block copolymers correlates to the final silica mesostructures and can be used as an important criterion for the rational design of ordered mesoporous materials especially when they are synthesized as precipitates from solutions. Such conclusions are useful to fabricate ordered and large pore mesoporous materials.

Co/Pd multilayered films with perpendicular magnetic anisotropy were patterned using block copolymer templating. Two methods of achieving phase separation of the block copolymer were compared. A matrix study of etch time and etch angle was carried out for each phase separation method, and their effects on the magnetic properties were studied. It was found that ion milling at 45° and 3.5 minutes for the heptane annealing method yielded the highest coercivity, 3.2 kOe, a 246% increase over that of an unpatterned film.

Abstract3D interconnected nitrogen‐doped carbon nanoscale networks (N‐CNNs) with designable pore geometries are prepared by vapor‐phase polymerization approach and subsequent carbonization using self‐assembled block copolymer (BCP) polystyrene‐block‐poly(4‐vinylpyridine) (PS‐b‐P4VP) with bicontinuous structures as templates. PS‐b‐P4VP monolithic membranes composed of interconnected micellar fibers or spheres with PS@P4VP core–shell structure are obtained by swelling lamellar supramolecular membranes of PS‐b‐P4VP and 3‐n‐pentadecylphenol (PDP) via hydrogen bonding. Importantly, the morphologies of self‐assembled BCP can be tuned by just adjusting swelling time for the same PS‐b‐P4VP(PDP). The vapor‐phase polymerization strategy is adopted for the first time to complex iodine to P4VP shell layers and subsequently initiates the polymerization of pyrrole to form polypyrrole on the outside of PS@P4VP core–shell structures. After carbonization, the BCP templates are removed and N‐CNNs with different pore geometries are obtained. The interconnected network structures and the introduction of nitrogen in carbon nanoscale networks make them particularly promising in many applications such as oxygen reduction reaction (ORR). The N‐CNN templated from micellar fibers (N‐CNN‐F), as a metal‐free ORR catalyst, displays comparable performance with Pt/C in alkaline media. The study provides not only a new synthesis method, but also important insight into designing 3D networks with open‐celled pores for ORR and other applications.

Block copolymer (BCP) templated inorganic material nanopatterning, often termed as BCP lithography, has received significant attention in recent years because of its self-assembly property offering direct synthesis of nanostructures with different morphologies. In this paper, we report an approach combining BCP template and pulsed laser deposition (PLD) to synthesize TiO2 nanodots of sub-50 nm dimension. Our results show that the BCP templated TiO2 nanodots maintained the exact form of the top of polystyrene cylindrical template in the growth process as seen from the top view of scanning electron microscopy images. X-ray photoelectron spectroscopy confirms the presence of Ti and O, and X-ray diffraction results show existence of both anatase and rutile TiO2 crystalline phase in the nanodot films. The photoluminescence spectrum for the fabricated TiO2 is dominated by a broad peak extending from visible to near-infrared (NIR) that appears because of overlap of the characteristic peaks for TiO2 anatase (visible) and rutile phase (NIR). The formation of crystalline TiO2 nanodots can be explained by crystallization by particle attachment phenomena around the BCP cylindrical domains during annealing. Fabrication of nanostructured titania or any other materials in combination with PLD and BCP as template has not been explored so far with the exception of lead titanate (PbTiO3) nanostructures; hence, our demonstrated approach could be extended to fabricate other inorganic nanostructures integrated with BCP lithography for optoelectronics, sensing, and catalysis applications.

Highly aligned, large pore ordered mesoporous carbon films by solvent vapor annealing with soft shear

Preparation of high-performance and durable electrocatalysts for anion exchange membrane water electrolysis is a crucial step toward the broad implementation of this technology. Here, we present an easily tunable, one-step hydrothermal method for the preparation of Ni-based (NiX, X = Co, Fe) layered double hydroxide nanoparticles (LDHNPs) for the oxygen evolution reaction (OER), using tris(hydroxymethyl)aminomethane (Tris-NH2) for particle growth control. The LDHNPs are used as building blocks of mesoporous mixed metal oxides (MMOs) with a block copolymer template (Pluronic F127), followed by thermal treatment at 250 °C. NiX MMOs have a significantly larger surface area compared to the analogous LDHNPs. NiX LDHNPs and MMOs exhibit excellent performance and long-term cycling stability, making them promising OER catalysts. Moreover, this versatile method can be easily tailored and scaled up for the preparation of platinum group metal-free electrocatalysts for other reactions of interest, which highlights the relevance of this work to the field of electrocatalysis.