Metal Oxide/Polymer Hybrid Nanoparticles with Versatile Functionality Prepared by Controlled Surface Crystallization

Metal oxide/polymer hybrids are prepared from polystyrene nanoparticles functionalized at the surface with phosphonate and phosphate groups. The polymer particles are synthesized with specifically designed surface‐active monomers (surfmers) and used as nucleation surfaces for the controlled in situ crystallization of cerium, iron, and zinc oxide nanocrystals. The formation of the metal oxide is driven by the addition of a base to suspensions of the polymer particles containing the corresponding precursor. The crystal formation at the particle surface is studied for the different hybrid systems by X‐ray diffraction and transmission electron microscopy (TEM). The potential catalytic activity of CeO₂/polymer hybrid particles is proven with the example of the photodegradation of rhodamine B. For the case of magnetic iron oxide‐functionalized latex, a superparamagnetic behavior is found above a blocking temperature of 225 K. ZnO/polymer hybrids present a strong yellow visible photoluminescence. The approach is shown to be versatile not only in terms of the variety in the metal oxides deposited on the surface, but also because the crystallization can take place in both aqueous and alcoholic media.     

Hybrid Solar Cells from Regioregular Polythiophene and ZnO Nanoparticles

Blends of nanocrystalline zinc oxide nanoparticles (nc‐ZnO) and regioregular poly(3‐hexylthiophene) (P3HT) processed from solution have been used to construct hybrid polymer–metal oxide bulk‐heterojunction solar cells. Thermal annealing of the spin‐cast films significantly improves the solar‐energy conversion efficiency of these hybrid solar cells to ～ 0.9 %. Photoluminescence and photoinduced absorption spectroscopy demonstrate that charge‐carrier generation is not quantitative, because a fraction of P3HT appears not to be in contact with or in close proximity to ZnO. The coarse morphology of the films, also identified by tapping‐mode atomic force microscopy, likely limits the device performance.     

Chemical Bonding Assembly of Multifunctional Oxide Nanocomposites

The synthesis, functionalization and assembly of metal oxide nanoparticles BaTiO₃ and CoFe₂O₄ is presented. The ferroelectric (BaTiO₃) and ferromagnetic (CoFe₂O₄) oxide nanoparticle surfaces are directly functionalized via the anchoring of phosphonic acid and aminosilane molecules that engender the nanoparticles with terminal carboxylic acid and amine functional groups, respectively. These promote the electrostatic self‐assembly of the particles in non‐polar solvents and permit the synthesis of more chemically robust assemblies linked by the covalent amide bond via the addition of the chemical coupling agent N‐N′‐dicyclohexylcarbodiimide. This functionalization and assembly procedure is applied to two systems: the first comprised of 50 nm BaTiO₃ and 10 nm CoFe₂O₄ particles and the second of 200 nm BaTiO₃ and 12.5 nm CoFe₂O₄ particles. The latter composites possess magnetoelectric properties when processed into dense ceramics and, as a direct result of the assembly performed in solution, have a high degree of homogeneity between the ferroelectric and ferromagnetic phases. The developed functionalization and assembly procedure is considered to be adaptable to the preparation of other hybrid oxide nanomaterials with different property combinations.     

Soft Lithography of Ceramic Patterns

Polymer‐based precursor solutions are patterned using a soft‐lithographic patterning technique to yield sub‐micrometer‐sized ceramic patterns. By using a polymer–metal‐nitrate solution as a lithographic resist, we demonstrate a micromolding procedure using a simple rubber stamp that yields a patterned precursor layer. A subsequent high‐temperature annealing step degrades the polymer giving rise to a patterned metal oxide film. This procedure is demonstrated for three different ceramic materials: Al₂O₃, ZnO, and PbTiO₃. Al₂O₃ initially forms an amorphous phase that is subsequently converted into a polycrystalline material upon electron irradiation. The formed ZnO and PbTiO₃ are polycrystalline. PbTiO₃ exhibits epitaxial alignment when cast onto a SrTiO₃(001) surface that matches its lattice periodicity. This epitaxial alignment is maintained when the PbTiO₃ phase is patterned by micromolding, giving rise to epitaxially grown PbTiO₃ patterns with feature sizes down to 300 nm.     

Hybrid Solar Cells Using a Zinc Oxide Precursor and a Conjugated Polymer

We describe a new method towards bulk‐heterojunction hybrid polymer solar cells based on composite films of zinc oxide (ZnO) and a conjugated polymer poly[2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylene vinylene] (MDMO‐PPV). Spin‐coating diethylzinc as a ZnO precursor and MDMO‐PPV from a common solvent at 40 % humidity and annealing at 110 °C provides films in which crystalline ZnO is found to be intimately mixed with MDMO‐PPV. Photoluminescence and photoinduced spectroscopy demonstrate that photoexcitation of these hybrid composite films results in a fast and long‐lived charge transfer from the polymer as a donor to ZnO as ato be obtained n acceptor. Using the ZnO‐precursor method, hybrid polymer solar cells have been made with an estimated air‐mass of 1.5 (AM 1.5) energy conversion efficiency of 1.1 %. This new method represents a fivefold improved performance compared to similar hybrid polymer solar cells based on amorphous TiO₂.     

Hybrid Titanium Oxide/Polymer Amphiphilic Nanomaterials with Controlled Size for Drug Encapsulation and Delivery

This work describes for the first time the synthesis of hybrid drug‐loaded TiO₂/polymer amphiphilic nanoparticles of finely controlled size utilizing a simple and reproducible sol–gel process that comprises the formation of a titanium(IV)/acetone oxo‐organo complex followed by its blending with an amphiphilic poly(ethylene oxide)‐b‐poly(propylene oxide) block copolymer in acetone and its aqueous‐phase nanoprecipitation. The size of the hybrid nanoparticles is governed by the complex aging, e.g., hybrid nanoparticles display diameter between 228 and 53 nm for aging of 1 and 36 days, respectively (dynamic light scattering). In addition, they show excellent physical stability in water owing to the coating of the surface with poly(ethylene oxide) blocks of the copolymer. Conversely, polymer‐free TiO₂ particles are large and precipitate fast. Incorporation of a model hydrophobic drug, nitazoxanide, to the precursor solution results in hybrid nanoparticles containing 12.9% w/w cargo that is released following a bimodal profile. High‐resolution transmission electron microscopy (Titan Cubed Themis G2 300) analysis reveals the porous amorphous nanostructure of these novel hybrids and colocalization of drug and copolymer in the nanoparticle bulk. Finally, upon ultrasonication, our hybrid nanoparticles produce reactive oxygen species in vitro which paves the way for their use in sonodynamic and drug release therapies.     

One‐Step Synthesis of Highly Ordered Mesoporous Silica Monoliths with Metal Oxide Nanocrystals in their Channels

A simple, one‐step synthetic route to prepare ordered mesoporous silica monoliths with controllable quantities of metal oxide nanocrystals in their channels is presented. The method is based on the assisted assembly effect for mesostructure‐directing of the metal complexes formed by the interaction of metal ions with the –O– groups of copolymers. Highly ordered hexagonal silica monoliths, loaded with various metal oxide nanocrystals, including those of Cr₂O₃, MnO, Fe₂O₃, Co₃O₄, NiO, CuO, ZnO, CdO, SnO₂, and In₂O₃, can be obtained by this one‐step pathway. In the NiO/SiO₂ nanocomposite, nickel oxide nanorods with face‐centered cubic lattices are formed at low doping ratios, and they can be transformed into nanowires by increasing the quantities of the precursors. In the Fe₂O₃/SiO₂ nanocomposites, a one‐dimensional assembly of iron oxide nanoparticles is observed. In the In₂O₃/SiO₂ nanocomposites, single crystal nanowires with high aspect ratios are obtained. For the other metal oxide nanocomposites, including Cr₂O₃, MnO, Co₃O₄, CuO, ZnO, CdO, and SnO, only crystalline nanorods are obtained. N₂ sorption results of the metal oxide/SiO₂ mesostructured nanocomposites reveal that nanocrystals inside the pores do not severely decrease the pore volume or the Brunauer–Emmett–Teller (BET) surface area of the mesoporous silica host. The bandgaps of SnO₂ and In₂O₃ nanocrystals, calculated from UV‐vis spectra, are much larger than the corresponding bulk materials, implying the quantum confinement effect in the small particles. Co₃O₄/SiO₂ mesostructured nanocomposites catalyze the complete combustion of CH₄. These studies provide a new and simple method for templating synthesis of metal oxide nanostructures.     

Ambient Layer‐by‐Layer ZnO Assembly for Highly Efficient Polymer Bulk Heterojunction Solar Cells

The use of metal oxide interlayers in polymer solar cells has great potential because metal oxides are abundant, thermally stable, and can be used in flexible devices. Here, a layer‐by‐layer (LbL) protocol is reported as a facile, room‐temperature, solution‐processed method to prepare electron transport layers from commercial ZnO nanoparticles and polyacrylic acid (PAA) with a controlled and tunable porous structure, which provides large interfacial contacts with the active layer. Applying the LbL approach to bulk heterojunction polymer solar cells with an optimized ZnO layer thickness of ≈25 nm yields solar cell power‐conversion efficiencies (PCEs) of ≈6%, exceeding the efficiency of amorphous ZnO interlayers formed by conventional sputtering methods. Interestingly, annealing the ZnO/PAA interlayers in nitrogen and air environments in the range of 60–300 °C reduces the device PCEs by almost 20% to 50%, indicating the importance of conformational changes inherent to the PAA polymer in the LbL‐deposited films to solar cell performance. This protocol suggests a new fabrication method for solution‐processed polymer solar cell devices that does not require postprocessing thermal annealing treatments and that is applicable to flexible devices printed on plastic substrates.     

Fabrication of CdSe‐Nanofibers with Potential for Biomedical Applications

The design and synthesis of nanostructured functional hybrid biomaterials are essential for the next generation of advanced diagnostics and the treatment of disease. A simple route to fabricate semiconductor nanofibers by self‐assembled, elastin‐like polymer (ELP)‐templated semiconductor nanoparticles is reported. Core–shell nanostructures of CdSe nanoparticles with a shell of ELPs are used as building blocks to fabricate functional one‐dimensional (1D) nanostructures. The CdSe particles are generated in situ within the ELP matrix at room temperature. The ELP controls the size and the size‐distribution of the CdSe nanoparticles in an aqueous medium and simultaneously directs the self‐assembly of core–shell building blocks into fibril architectures. It was found that the self‐assembly of core–shell building blocks into nanofibers is strongly dependent on the pH value of the medium. Results of cytotoxicity and antiproliferation of the CdSe‐ELP nanofibers demonstrate that the CdSe‐ELP does not exhibit any toxicity towards B14 cells. Moreover, these are found to be markedly capable of crossing the cell membrane of B14. In contrast, unmodified CdSe nanoparticles with ELPs cause a strong toxic response and reduction in the cell proliferation. This concept is valid for the fabrication of a variety of metallic and semiconductor 1D‐architectures. Therefore, it is believed that these could be used not only for biomedical purposes but for application in a wide range of advanced miniaturized devices.     

Spray‐Coating Magnetic Thin Hybrid Films of PS‐b‐PNIPAM and Magnetite Nanoparticles

Spray coating is employed to fabricate magnetic thin films composed of the diblock copolymer polystyrene‐block‐poly(N‐isopropylacrylamide) and Fe₃O₄ magnetic nanoparticles (MNPs) functionalized with hydrophobic coatings. The kinetics of structure formation of the hybrid films is followed in situ with grazing incidence small angle X‐ray scattering during the spray deposition. To gain a better understanding of the influence of MNPs on the overall structure formation, the pure polymer film is also deposited as a reference via an identical spray protocol. At the initial spraying stage, the hybrid film (containing 2 wt% of MNPs) exhibits a faster formation process of a complete film as compared to the reference. The existence of MNPs depresses the dewetting behavior of polymer films on the substrate at macroscale and simultaneously alters the polymer microphase separation structure orientation from parallel to vertical. As spraying proceeds, MNPs aggregate into agglomerates with increasing sizes. After the spray deposition is finished, both samples gradually reach an equilibrium state and magnetic films with stable structures are achieved in the end. Superconducting quantum interference device investigation reveals the superparamagnetic property of the sprayed hybrid film. Consequently, potential application of sprayed films in fields such as magnetic sensors or data storage appears highly promising.     

Shape Control of Mn3O4 Nanoparticles on Nitrogen‐Doped Graphene for Enhanced Oxygen Reduction Activity

Three kinds of Mn₃O₄ nanoparticles with different shapes (spheres, cubes, and ellipsoids) are selectively grown on nitrogen‐doped graphene sheets through a two‐step liquid‐phase procedure. These non‐precious hybrid materials display an excellent ORR activity and good durability. The mesoporous microstructure, nitrogen doping, and strong bonding between metal species and doped graphene are found to facilitate the ORR catalytic process. Among these three kinds of Mn₃O₄ particles, the ellipsoidal particles on nitrogen‐doped graphene exhibit the highest ORR activity with a more positive onset‐potential of –0.13 V (close to that of Pt/C, –0.09 V) and a higher kinetic limiting current density (J_K) of 11.69 mA cm^–2 at –0.60 V. It is found that the ORR performance of hybrid materials can be correlated to the shape of Mn₃O₄ nanocrystals, and specifically to the exposed crystalline facets associated with a given shape. The shape dependence of Mn₃O₄ nanoparticles integrated with nitrogen‐doped graphene on the ORR performance, reported here for the first time, may advance the development of fuel cells and metal‐air batteries.     

Vertically Well‐Aligned ZnO Nanowires on c‐Al2O3 and GaN Substrates by Au Catalyst

In this letter, we report that vertically well‐aligned ZnO nanowires were grown on GaN epilayers and c‐plane sapphire via a vapor‐liquid‐solid process by introducing a 3 nm Au thin film as a catalyst. In our experiments, epitaxially grown ZnO nanowires on Au‐coated GaN were vertically well‐aligned, while nanowires normally tilted from the surface when grown on Au‐coated c‐Al₂O₃ substrates. However, pre‐growth annealing of the Au thin layer on c‐Al₂O₃ resulted in the growth of well‐aligned nanowires in a normal surface direction. High‐resolution transmission electron microscopy measurements showed that the grown nanowires have a hexagonal c‐axis orientation with a single‐crystalline structure.     

Ultrafast Assembly of PS‐PDMS Block Copolymers on 300 mm Wafers by Blending with Plasticizers

Next‐generation lithography techniques based on the self‐assembly of block copolymers (BCPs) are promising methods for high‐resolution pattering. BCPs with a high incompatibility (high‐χ), such as polystyrene‐polydimethylsiloxane (PS‐PDMS), show encouraging results in terms of resolution. In the strong segregation regime, the high diffusive energy barrier of PS‐PDMS excessively reduces the self‐assembly kinetics; this is why solvent–vapor annealing is typically adopted to shorten the self‐assembly time. Plasticizers are generally used to reduce the glass transition temperature (T_g) of polymers. In this study, commercial plasticizers such as dioctylsebacate and diisooctyl adipate are blended with PS‐PDMS polymers, and their influence on the self‐assembly process is investigated. The intrinsic PS selectivity of the plasticizers brings the BCP to form PS‐PDMS micelles, which results in highly ordered self‐assembled body‐centered cubic spherical PS‐PDMS after spin‐coating without any annealing. The negligible vapor pressure of plasticizers and the decrease of T_g allow the high mobility of PS‐PDMS micelles in thin films. A transition into a stable horizontal cylindrical morphology is then possible by ultrafast thermal annealing (30 s). The complete process, from the BCP deposition to the final pattern transfer into Si, is presented on 300 mm standard wafers, which makes this method promising for microelectronic industrial integration.     

Structural and Electrical Properties of Atomic Layer Deposited Al‐Doped ZnO Films

Structural and electrical properties of Al‐doped ZnO (AZO) films deposited by atomic layer deposition (ALD) are investigated to study the extrinsic doping mechanism of a transparent conducting oxide. ALD‐AZO films exhibit a unique layer‐by‐layer structure consisting of a ZnO matrix and Al₂O₃ dopant layers, as determined by transmission electron microscopy analysis. In these layered AZO films, a single Al₂O₃ dopant layer deposited during one ALD cycle could provide ≈4.5 × 10¹³ cm^?2 free electrons to the ZnO. The effective field model for doping is suggested to explain the decrease in the carrier concentration of ALD‐AZO films when the interval between the Al₂O₃ layers is reduced to less than ≈2.6 nm (>3.4 at% Al). By correlating the electrical and structural properties, an extrinsic doping mechanism of ALD‐AZO films is proposed in which the incorporated Al atoms take oxygen from the ZnO matrix and form doubly charged donors, such as oxygen vacancies or zinc interstitials.     

A General Synthesis of Crumpled Metal Oxide Nanosheets as Superior Chemiresistive Sensing Layers

Metal oxide nanosheets having high mesoporosity, grain size distribution of 5–10 nm, and ultrathin thickness have attracted much attention due to their intriguing properties such as high surface‐to‐volume ratio and superior chemical activities. However, 2D nanostructures tend to restack, inducing a decrease in accessible surface area and a number of pores. To solve this problem, herein, a unique synthetic method of crumpled metal oxide nanosheets using spray pyrolysis of metal ion–coated graphene oxide, followed by heat treatment, is reported. This method is applicable not only to single‐component metal oxides but also to heterogeneous multicomponent metal oxides in which composition can be controlled. Crumpled SnO₂, ZnO, and Co₃O₄ as well as SnO₂/ZnO and SnO₂/Co₃O₄ nanosheets with heterogeneous interfaces are successfully synthesized and used as superior gas sensing layers. Because of the abundant reaction sites, well‐developed porosity for high gas accessibility, the formation of heterojunctions, the crumpled SnO₂/ZnO and SnO₂/Co₃O₄ nanosheets exhibit outstanding sensing performance (R_air/R_gas = 20.25 toward 5 ppm formaldehyde, and R_air/R_gas = 14.13 toward 5 ppm acetone, respectively). This study can contribute to the realization of a family of heterogeneous crumpled metal oxide nanosheets that can be applied to various research fields.     

Conjugated Polyelectrolyte Hybridized ZnO Nanoparticles as a Cathode Interfacial Layer for Efficient Polymer Light‐Emitting Diodes

Alkoxy side‐chain tethered polyfluorene conjugated polyelectrolyte (CPE), poly[(9,9‐bis((8‐(3‐methyl‐1‐imidazolium)octyl)‐2,7‐fluorene)‐alt‐(9,9‐bis(2‐(2‐methoxyethoxy)ethyl)‐fluorene)] dibromide (F8imFO₄), is utilized to obtain CPE‐hybridized ZnO nanoparticles (NPs) (CPE:ZnO hybrid NPs). The surface defects of ZnO NPs are passivated through coordination interactions with the oxygen atoms of alkoxy side‐chains and the bromide anions of ionic pendent groups from F8imFO₄ to the oxygen vacancies of ZnO NPs, and thereby the fluorescence quenching at the interface of yellow‐emitting poly(p‐phenylene vinylene)/CPE:ZnO hybrid NPs is significantly reduced at the CPE concentration of 4.5 wt%. Yellow‐emitting polymer light‐emitting diodes (PLEDs) with CPE(4.5 wt%):ZnO hybrid NPs as a cathode interfacial layer show the highest device efficiencies of 11.7 cd A^?1 at 5.2 V and 8.6 lm W^?1 at 3.8 V compared to the ZnO NP only (4.8 cd A^?1 at 7 V and 2.2 lm W^?1 at 6.6 V) or CPE only (7.3 cd A^?1 at 5.2 V and 4.9 lm W^?1 at 4.2 V) devices. The results suggest here that the CPE:ZnO hybrid NPs has a great potential to improve the device performance of organic electronics.     

A Top Coat with Solvent Annealing Enables Perpendicular Orientation of Sub‐10 nm Microdomains in Si‐Containing Block Copolymer Thin Films

Achieving sub‐10 nm high‐aspect‐ratio patterns from diblock copolymer self‐assembly requires both a high interaction parameter (χ, which is determined by the incompatibility between the two blocks) and a perpendicular orientation of microdomains. However, these two conditions are extremely difficult to achieve simultaneously because the blocks in a high‐χ copolymer typically have very different surface energies, favoring in‐plane microdomain orientations. A fully perpendicular orientation of a high‐χ block copolymer, poly(styrene‐block‐dimethylsiloxane) (PS‐b‐PDMS) is realized here using partially hydrolyzed polyvinyl alcohol (PVA) top coats with a solvent annealing process, despite the large surface energy differences between PS and PDMS. The PVA top coat on the block copolymer films under a solvent vapor atmosphere significantly reduces the interfacial energy difference between two blocks at the top surface and provides sufficient solvent concentration gradient in the through‐thickness direction and appropriate solvent evaporation rates within the film to promote a perpendicular microdomain orientation. The effects of interfacial energy differences and the swellability of PVA top coats controlled by the degree of hydrolysis on the orientation of micro­domains are examined. The thickness of the BCP film and top coats also affects the orientation of the BCP film.     

Multifunctional Materials: A Case Study of the Effects of Metal Doping on ZnO Tetrapods with Bismuth and Tin Oxides

Hybrid metal oxide nano‐ and microstructures exhibit novel properties, which make them promising candidates for a wide range of applications, including gas sensing. In this work, the characteristics of the hybrid ZnO‐Bi₂O₃ and ZnO‐Zn₂SnO₄ tetrapod (T) networks are investigated in detail. The gas sensing studies reveal improved performance of the hybrid networks compared to pure ZnO‐T networks. For the ZnO‐T‐Bi₂O₃ networks, an enhancement in H₂ gas response is obtained, although the observed p‐type sensing behavior is attributed to the formed junctions between the arms of ZnO‐T covered with Bi₂O₃ and the modulation of the regions where holes accumulate under exposure to H₂ gas. In ZnO‐T‐Zn₂SnO₄ networks, a change in selectivity to CO gas with high response is noted. The devices based on individual ZnO‐T‐Bi₂O₃ and ZnO‐T‐Zn₂SnO₄ structures showed an enhanced H₂ gas response, which is explained on the basis of interactions (electronic sensitization) between the ZnO‐T arm and Bi₂O₃ shell layer and single Schottky contact structure, respectively. Density functional theory‐based calculations provide mechanistic insights into the interaction of H₂ and CO gas molecules with Bi‐ and Sn‐doped ZnO(0001) surfaces, revealing changes in the Fermi energies, as well as charge transfer between the molecules and surface species, which facilitate gas sensing.     

One‐Step Hierarchical Assembly of Spheres‐in‐Lamellae Nanostructures from Solvent‐Annealed Thin Films of Binary Diblock Copolymer Micelles

Hierarchical assemblies of dissimilar block copolymers (BCPs) can reveal interesting perspectives on material properties and device performance by providing multiple functionalities. Up to now, hierarchical assemblies of BCPs have been mostly prepared by stepwise assembling methods, in which the first type of BCP nanodomains is used as predefined patterns to guide the second‐level assembly of another BCP. On the other hand, single‐step blending methods suffer from a dilemma in the creation of hierarchical patterns because blending dissimilar BCPs typically induces either macrophase separation of component BCPs or chain‐level hybridization into a single morphology. The present study is designed to overcome this apparent dilemma in polymer blends by exploiting a solvent annealing method. In particular, hierarchically assembled spheres‐in‐lamellae structures from a solvent‐annealed blended film of binary polystyrene‐block‐poly(2‐vinylpyrdine) and polystyrene‐block‐poly(4‐vinyl pyridine) micelles are prepared. The focus of the current study is to understand the different effects of solvent vapor on the component BCPs and the molecular mechanism for the one‐step assembling process. By addressing this issue, the parallelism in the phase behavior of BCP micelles and inorganic nanoparticles is highlighted, the underlying physical processes of which could be suggested as a one‐step assembly principle for hierarchical superstructures beyond the previously reported multistep methods.     

Hierarchical Self‐Organization of Nanomaterials into Two‐Dimensional Arrays Using Functional Polymer Scaffold

Fabrication of two and three‐dimensional nanostructures requires the development of new methodologies for the assembly of molecular/macromolecular objects on substrates in predetermined arrangements. Templated self‐assembly approach is a powerful strategy for the creation of materials from assembly of molecular components or nanoparticles. The present study describes the development of a facile, template directed self‐assembly of (metal/organic) nanomaterials into periodic micro‐ and nanostructures. The positioning and the organization of nanomaterials into spatially well‐defined arrays were achieved using an amphiphilic conjugated polymer‐aided, self‐organization process. Arrays of honeycomb patterns formed from conjugated C₁₂PPPOH film with homogenous distribution of metal/organic nanomaterials. Our approach offers a straightforward and inexpensive method of preparation for hybrid thin films without environmentally controlled chambers or sophisticated instruments as compared to multistep micro‐fabrication techniques.