Self-assembled Templates Research Articles

Self-assembly of single-walled carbon nanotubes arrays with different line width

Single-walled carbon nanotubes (SWNTs) are one of the most promising nanoelectronic materials, However, there are still some application challenges, including purification, regular arrangement, interconnection, and so on. There is evidence that the array assembly can improve the performance of SWNTs. In this work, we develop a line-width controllable large-scale assembly of SWNTs based on aqueous solution, using electron beam (E-beam) lithography to construct self-assembled templates. The results show that SWNTs arrays of different line-width are obtained, which is possible to design the structure of SWNTs assembly to meet different functions.

1-nm-Wide Hydrated Dipole Arrays Regulate AuNW Assembly on Striped Monolayers in Nonpolar Solvent

Summary We show that striped phases of horizontally oriented phospholipids presenting 1-nm-wide orientable dipole arrays can order and straighten flexible 2-nm-diameter gold nanowires (AuNWs) with lengths (up to 1 μm) that greatly exceed the template pitch (∼7.5 nm). AuNW ordering can extend over areas > 100 μm2. Whereas wires bundle in solution, with contact between ligand shells, wires adsorbing to the template separate to much larger center-to-center distances (e.g., 12–30 nm) near multiples of the template pitch, consistent with repulsive interactions between wires emerging during interactions with dipole arrays in the template. AuNW assembly was carried out in cyclohexane, a nonpolar solvent. Interestingly, we found that wire ordering was contingent on the extent of phospholipid headgroup hydration and the presence of excess oleylamine, which assembled into hemicylindrical micelles around the hydrated headgroups. Together, these components generated a protected polar environment that enabled the phospholipid headgroups to function collectively to regulate AuNW assembly.

Facile synthesis of 3D ordered macro-mesoporous Ce1-xZrxO2 catalysts with enhanced catalytic activity for soot oxidation

Abstract A series of three-dimensionally ordered macroporous-mesoporous (3DOM-m) ceria-zirconia oxide (Ce1-xZrxO2) catalysts were synthesized successfully by combined methods of the evaporation-induced interfacial self-assembly and colloidal crystal templates (EISA−CCT). The hierarchical porous nanostructure of 3DOM-m Ce1-xZrxO2 catalysts possess the highly ordered macroporous framework with the average pore size of 250 nm; and the plenty of ordered mesopores (5 nm) are dispersed on the inner walls of spherical macropores. 3DOM-m Ce1-xZrxO2 catalysts with abundant oxygen vacancies have the excellent storage oxygen capacity, which is benefit for improving the catalytic activity for soot oxidation. Ordered macroporous framework enhances the contact efficiency between solid soot particles and catalysts, while the ordered mesoporous nanostructure improves the specific surface area dramatically for promoting the contact efficiency of gaseous reactants (O2 and NO) and active sites. The enrichment of Ce component as active sites was observed on the inner wall of ordered mesopores formed by the Kirkendall effect during thermal treatment, which can improve the adsorption-activation ability for gaseous reactants. 3DOM-m Ce1-xZrxO2 catalysts with hierarchical porous nanostructure exhibit high catalytic activity and stability for soot oxidation. The facile fabrication strategy of 3DOM-m catalysts can be extended to other oxides. And insight into the catalytic activity dependence on the both elemental composition and porous nanostructure is not only meaningful for development of advanced catalysts for soot oxidation, but also supports the development of 3DOM-m catalysts for practical applications.

Porous N-doped carbon nanostructure integrated with mesh current collector for Li-ion based energy storage

A self-assembled mesoporous silica sphere templating process was developed to create hierarchical continuous porous coral reef like N-doped carbon nanostructures on stainless steel meshes as bifunctional electrodes for ultrahigh performance lithium ion based energy storage devices. The coral reef like carbon nanostructure achieved a high specific surface area of 1229 m2 g−1 and a large specific pore volume of 2.21 cm3 g−1, without application of chemical activations. The electrode, when serving as an anode for lithium ion batteries (LIB) or lithium ion capacitors (LIC), delivered an ultrahigh specific capacity of 2058 mAh g−1 at 0.2 A g−1. If used as a cathode for LICs, it generated a high specific capacity of 125 mAh g−1 at 0.1 A g−1. The LICs assembled from using the electrode as both the cathode and anode, exhibited a high energy density of 145 Wh kg−1 at a power density of 1.4 kW kg−1 and maintained an energy density of 58 Wh kg−1 under an ultrahigh power density of 27.3 kW kg−1, among the top tie of the state-of-the-art LICs. The cycling stability of the LIC was outstanding with a 85% capacity retention after 5000 cycle operations at 5 A g−1. The hierarchical continuous porous coral reef like N-doped carbonaceous nanostructure provides micropores as micro-reservoirs of Li ions for local and fast Li ion intercalation/de-intercalation, edge N-doping for additional redox pseudo-capacitances, and large pore volumes to accommodate the volume expansion/shrinkage at the charge/discharge cycles and to offer fast mass transfer path for electrolyte ions, altogether leading to the successful applications as bifunctional electrodes for Li ion based energy storage devices.

(Invited) Covalent Functionalization of Graphene and MoS2: Chemical Versus Electrochemical Routes

Atomically thin sheets of materials, the so-called two-dimensional (2D) materials arrived on the scene in early 2000s with the successful isolation of graphene as freestanding monolayer films. Graphene, a single atom thick sheet of sp2-hybridized carbon bonded in a honeycomb lattice, has exceptional electronic, optical, mechanical and thermal properties that outperform those of most of the existing materials. The research on graphene further fuelled emergence of related 2D materials such as black phosphorous, silicene, germanene and transition metal dichalcogenides (TMDs) such as MoS2. Due to their exotic properties, these materials offer virtually endless opportunities for fundamental research as well as cutting edge applications. Most of these 2D materials however exist as single layers only when supported by another solid surface or when stabilized by physisorbed or chemisorbed organic molecules. Given their layered nature, most 2D materials are extremely difficult to disperse in typical solvents. Chemisorption of organic molecules onto their basal plane allows dispersion of these materials in (organic) solvents thereby improving their solution processability. Such dispersions can be used in composite materials and as functional inks. Moreover, covalent functionalization allows modification of the intrinsic electrical, electronic and optical properties of these 2D materials. In this talk, I will discuss covalent modification graphene, graphite and MoS2 using diazonium chemistry. Two different routes for reductive decomposition of diazonium salts namely, chemical and electrochemical, will be discussed in detail. Special focus is on sub-nanometer characterization of modified materials using scanning tunneling and atomic force microscopy (STM and AFM). Initial results towards patterned covalent functionalization using physisorbed self-assembled templates will also be presented besides the discussion on the use of such surfaces as seed layers for atomic layer deposition (ALD).

Relationship between Nd content and magnetic properties of Nd2Fe14B/Nd nanocomposites chemically synthesized using self-assembled block copolymer templates

To synthesize nanocomposite magnets with controlled high magnetic performance, Nd2Fe14B/Nd nanocomposites were chemically synthesized using self-assembled block copolymer templates. The Nd, Fe, and B ratios in the raw materials used to synthesize the nanocomposites were adjusted to control the nanocomposites’ magnetic properties. Nd2Fe14B/Nd nanocomposites with large coercivity were obtained from a Nd-rich mixture of raw materials. In the nanocomposites, Nd2Fe14B was surrounded by a nonmagnetic Nd phase that weakened the magnetic coupling of Nd2Fe14B grains and prevented magnetic field inversion. With increasing Nd content, the coercivity increased and the magnetization decreased. The simple process described herein, which involved chemical synthesis using self-assembled block copolymer templates, enabled the synthesis of nanocomposite magnets with controlled high magnetic performance through adjustment of the ratios of the raw materials.

Foam as a self-assembling amorphous photonic band gap material

We show that slightly polydisperse disordered 2D foams can be used as a self-assembled template for isotropic photonic band gap (PBG) materials for transverse electric (TE) polarization. Calculations based on in-house experimental and simulated foam structures demonstrate that, at sufficient refractive index contrast, a dry foam organization with threefold nodes and long slender Plateau borders is especially advantageous to open a large PBG. A transition from dry to wet foam structure rapidly closes the PBG mainly by formation of bigger fourfold nodes, filling the PBG with defect modes. By tuning the foam area fraction, we find an optimal quantity of dielectric material, which maximizes the PBG in experimental systems. The obtained results have a potential to be extended to 3D foams to produce a next generation of self-assembled disordered PBG materials, enabling fabrication of cheap and scalable photonic devices.

On the high performance of a core-shell structured CaO-CuO/MgO@Al2O3 material in calcium looping integrated with chemical looping combustion (CaL-CLC)

Calcium looping (CaL) is extensively used in post-combustion capture of CO2 and sorption-enhanced steam methane reforming because of its advantages of low cost and theoretically high CO2-capture capacity. Despite this, unstable reactivity of sorbent (CaO) and significant heat requirement for CaCO3 calcination were always encountered in CaL. To address the aforementioned issues, a core-shell structured CaO-CuO/MgO@Al2O3 sorbent (CCMA for short) was synthesized via the self-assembly template synthesis (SATS) method, and systematically investigated in terms of carbonation, calcination-reduction and oxidation cycles. In comparison to wet-mixing CaO-CuO material (CC), MgO-supported CaO-CuO (CCM) and Al2O3-supported CaO-CuO (CCA), the CCMA performed the highest CO2 uptake capacity, which was quite stable at around 0.08 [g CO2∙(g material)−1] in the 30 cyclic tests. In calcination-reduction stage, CaO in CCMA can be fully recovered by the decomposition of CaCO3, meanwhile the corresponding heat requirement can be compensated by the exothermic reaction between CuO and CH4, i.e., thermal neutrality can be achieved by using CCMA. The Cu in reduced CCMA can be subsequently oxidized back to CuO in the oxidation stage with a conversion of 97–98%, which is much higher than CC, CCM and CCA. After cycles, no serious sintering was observed for the CCMA and the measured crushing strength (1.4 N) was sufficient for fluidization, which, in combination with its high reactivity, makes this material very promising for CaL-CLC process.

Very High Refractive Index Transition Metal Dichalcogenide Photonic Conformal Coatings by Conversion of ALD Metal Oxides

Materials for nanophotonic devices ideally combine ease of deposition, very high refractive index, and facile pattern formation through lithographic templating and/or etching. In this work, we present a scalable method for producing high refractive index WS2 layers by chemical conversion of WO3 synthesized via atomic layer deposition (ALD). These conformal nanocrystalline thin films demonstrate a surprisingly high index of refraction (n > 3.9), and structural fidelity compatible with lithographically defined features down to ~10 nm. Although this process yields highly polycrystalline films, the optical constants are in agreement with those reported for single crystal bulk WS2. Subsequently, we demonstrate three photonic structures - first, a two-dimensional hole array made possible by patterning and etching an ALD WO3 thin film before conversion, second, an analogue of the 2D hole array first patterned into fused silica before conformal coating and conversion, and third, a three-dimensional inverse opal photonic crystal made by conformal coating of a self-assembled polystyrene bead template. These results can be trivially extended to other transition metal dichalcogenides, thus opening new opportunities for photonic devices based on high refractive index materials.

Boron-Carbon-Nitride Sheet as a Novel Surface for Biological Applications: Insights from Density Functional Theory.

Understanding the interaction between nanoscale materials and nucleobases is essential for their use in nanobiotechnology and nanomedicine. Our ab initio calculations indicate that the interaction of nucleobases [adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U)] with boron–carbon–nitride (BCN) is mainly governed by van der Waals interactions. The adsorption energies, ranging from −0.560 to −0.879 eV, decrease in the order of G > A > T > C > U, which can be attributed to π–π interactions and different side groups of the nucleobases. We found that anions (N and O atoms) of nucleobases prefer to stay on top of cation (B) of the substrate. The results also showed that BCN exhibits superior binding strength than graphene and boron–nitride-based materials. We also found that upon adsorption, the fundamental properties of BCN and nucleobases remains unaltered, which suggests that BCN is a promising template for self-assembly of nucleobases.

Silver Nanoparticle-Based Arrays into Mesoporous Thin Films Structures for Photoelectronic Circuits

Background: Silver nanosystems have attracted considerable attention for numerous applications in optoelectronics. The localized surface plasmon of silver nanoparticles embedded into mesoporous titania gives rise to an enhancement of local optical field in the vicinity of Ag nanoparticles which act as efficient light-trapping components, resulting in a visible wavelength-dependent photocurrent. Objective: In this paper, we synthetized patterned nanocomposites formed by titania mesoporous thin films loaded with alkanethiol functionalized Ag nanoparticles and we demonstrated that these stable and accessible nanostructures possess a photocurrent response. Method: Mesoporous thin films are created by combining sol-gel synthesis and template selfassembly. Based on a photolithography technique, silver nanoparticles were selectively photodeposited and then stabilized with octanethiols. Current vs. voltage curves with and without light were compared, where selective light wavelength measurements were achieved by using visible bandpass filters. The optofluidic behavior was evaluated by placing a drop of solutions on the mesoporous film. Results: We demonstrate photocurrent in these mesoporous thin film structures decorated with chemistabilized Ag nanoparticle-based conductive arrays, with significantly enhanced photocurrent peak at the plasmon resonant wavelength around 540 nm. Our findings offer a possibility to perform improved fluid detection with silver-mesoporous titania electronic devices. Conclusion: We showed that an optofluidic sensitive nanocomposite circuit consisting of alkanethiol- functionalized metal nanoparticles embedded in a mesoporous oxide thin film matrix can be produced.

LiCoO2/Li7La3Zr2O12 nanocomposite cathodes synthesized via self-assembled block copolymer templates and used in all-solid-state lithium batteries

Nanocomposite cathodes comprising an active cathode material (LiCoO2) and a solid lithium electrolyte (Li7La3Zr2O12) were synthesized by using a self-assembled polystyrene‑b‑poly(4‑vinylpyridine) block copolymer template containing precursors of the active cathode material and solid electrolyte. Calcination at 1023 K was used to remove the block copolymer template and crystallize the active cathode material and solid electrolyte. The molecular weight of the block copolymer template was controlled to optimize the structure of the nanocomposite cathode and maximize capacity. When the nanocomposite cathode that was obtained by using the block copolymer template with the highest molecular weight was used in an all-solid-state lithium battery, the obtained discharge capacity per electrode (98.2 mAh/g) was substantially higher than literature values for other cathodes used in all-solid-state lithium batteries. We conclude that increasing the molecular weight of the block copolymer template allowed for greater dispersion of the precursors and binding of the well-dispersed nanoparticles of active cathode material and solid lithium electrolyte, which promoted the formation of fine conducting paths and an electrochemically effective interface between the active cathode material and solid lithium electrolyte.

Realizing the Control of Electronic Energy Level Structure and Gas-Sensing Selectivity over Heteroatom-Doped In2O3 Spheres with an Inverse Opal Microstructure.

Understanding the effect of substitutional doping on gas-sensing performances is essential for designing high-activity sensing nanomaterials. Herein, formaldehyde sensors based on gallium-doped In2O3 inverse opal (IO-(Ga xIn1- x)2O3) microspheres were purposefully prepared by a simple ultrasonic spray pyrolysis method combined with self-assembled sulfonated polystyrene sphere templates. The well-aligned inverse opal structure, with three different-sized pores, plays the dual role of accelerating the diffusion of gas molecules and providing more active sites. The Ga substitutional doping can alter the electronic energy level structure of (Ga xIn1- x)2O3, leading to the elevation of the Fermi level and the modulation of the band gap close to a suitable value (3.90 eV), hence, effectively optimizing the oxidative catalytic activity for preferential CH2O oxidation and increasing the amount of adsorbed oxygen. More importantly, the gas selectivity could be controlled by varying the energy level of adsorbed oxygen. Accordingly, the IO-(Ga0.2In0.8)2O3 microsphere sensor showed a high response toward formaldehyde with fast response and recovery speeds, and ultralow detection limit (50 ppb). Our findings finally offer implications for designing Fermi level-tailorable semiconductor nanomaterials for the control of selectivity and monitoring indoor air pollutants.

Controlling self-assembly and buckling in nano fluid droplets through vapour mediated interaction of adjacent droplets

HypothesisSessile droplets of contrasting volatilities can communicate via long range (∼O (1) mm) vapour-mediated interactions which allow the remote control of the flow driven self-assembly of nanoparticles in the drop of lower volatility. This allows morphological control of the buckling instability observed in evaporating nanofluid droplets. ExperimentsA nanofluid droplet is dispensed adjacent to an ethanol droplet. Asymmetrical adsorption induced Marangoni flow (∼O (1) mm/s) internally segregates the particle population. Particle aggregation occurs preferentially on one side of the droplet leaving the other side to develop a relatively weaker shell which buckles under the effect of evaporation driven capillary pressure. FindingsThe inter-droplet distance is varied to demonstrate the effect on the precipitate shape (flatter to dome shaped) and the location of the buckling (top to side). In addition to being a simple template for hierarchical self-assembly, the presented exposition also promises to enhance mixing rates (∼1000 times) in droplet-based bioassays with minimal contamination.

3D printing of sacrificial templates into hierarchical porous materials

Hierarchical porous materials are widespread in nature and find an increasing number of applications as catalytic supports, biological scaffolds and lightweight structures. Recent advances in additive manufacturing and 3D printing technologies have enabled the digital fabrication of porous materials in the form of lattices, cellular structures and foams across multiple length scales. However, current approaches do not allow for the fast manufacturing of bulk porous materials featuring pore sizes that span broadly from macroscopic dimensions down to the nanoscale. Here, ink formulations are designed and investigated to enable 3D printing of hierarchical materials displaying porosity at the nano-, micro- and macroscales. Pores are generated upon removal of nanodroplets and microscale templates present in the initial ink. Using particles to stabilize the droplet templates is key to obtain Pickering nanoemulsions that can be 3D printed through direct ink writing. The combination of such self-assembled templates with the spatial control offered by the printing process allows for the digital manufacturing of hierarchical materials exhibiting thus far inaccessible multiscale porosity and complex geometries.

Mesoporous carbon film via spin coating soft templating method for supercapacitor electrode

Mesoporous carbon (MPC) films were prepared by using spin coating self-assembly soft templating method onto titanium (Ti) foils as substrates. Carbon precursor of resorcinol (R), formaldehyde (F) and a surfactant of triblock copolymer Pluoronic F127 (F127) which may act as a structure directing agent (SDA) for the pore structure geometry tuning were used in the preparation of the mesoporous carbon films. The samples were then carbonised to obtain the final product of MPC films. The mesostructure was characterised by thermogravimetry (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) patterns, field emission scanning electron microscopy (FESEM) and electrochemical analyses. The MPC film showed excellent electrochemical property for supercapacitor application by achieving specific capacitance value of 15.23 mF cm-2 at the scan rate of 5 mV s−1 in 1.0 M potassium chloride (KCl) neutral aqueous electrolyte which was approximately 88 times higher than as prepared samples. F127/RF carbon film also displayed outstanding cycle stability with 98% capacitance retention after 1000 cycles. This has proven that the synthesised MPC film-coated titanium foil may be a promising candidate for high performance electric double layer capacitors (EDLC).

Electrochemical synthesis of core-shell Co-Ni nanorod arrays with facilely regulated magnetic properties

Ordered Co-Ni core-shell magnetic nanorod arrays were fabricated by a two-step electrodeposition into a self-assembled anodic alumina oxide template. The characterizations of the morphology and elemental distribution indicated the successful fabrication of ∼260 nm Co core nanorods surrounded by ∼20 nm concentric Ni shell. The magnetization measurement revealed that the synthesized Co-Ni core-shell nanorod arrays exhibited lower coercivity and higher remanence ratio than plain Co nanorod arrays, offering a possibility to regulate suitable coercivity at the nanoscale. It was also demonstrated combing tube and rod to form core-shell structure offered the perspective for engineering the magnetic properties without changing geometric parameters or with minimally altered crystalline structure.

Research Progresses in the Preparation of Co-based Catalyst Derived from Co-MOFs and Application in the Catalytic Oxidation Reaction

Co-based metal organic frameworks (Co-MOFs) are porous crystalline materials formed by the coupling of metallic cobalt ions and organic ligands. Co3O4 based catalysts derived from Co-MOFs have attracted great attention in the field of catalysis. In this paper, some familiar Co-MOFs materials and the latest progress are introduced, such as ZIF-67, Co-MOF-71 and Co-MOF-74. The preparation techniques of these Co-MOFs are described in detail, including co-precipitation, sol–gel method, dipping method, hydrothermal method, solid phase grinding method, self-assembled template method and so on. The research progress of its application in the field of catalytic oxidation reaction is also highlighted. Based on the report of published literatures, we analyzed the design ideas of Co-MOFs materials and put forward the prospect for the future development.

Mesoporous PtCu Alloy Nanoparticles with Tunable Compositions and Particles Sizes Using Diblock Copolymer Micelle Templates.

A simple, scalable route for the generation of mesoporous Rh particles by chemical reduction on self-assembled block-copolymer micelle templates was reported recently (Nat. Commun. 2017, 8, 15581). Here, this concept is extended to generate mesoporous PtCu alloy nanoparticles through the same approach. The PtCu alloy particles possess high-surface-area nanoporous architectures and good chemical stability for applications in catalysis. Both the composition and diameter of the bimetallic PtCu nanoparticles can be controlled by adjusting the amount of precursor in the reaction, which affects the electrochemical properties of the material. The combination of the mesoporous structure with the synergistic bimetallic electronic effects of PtCu gives rise to enhanced activity for the catalytic oxidation of methanol compared with commercial Pt black.

Fabrication of One- and Two-Dimensional Gold Nanoparticle Arrays on Computationally Designed Self-Assembled Peptide Templates

Templating methods, combined with colloidal chemistry synthesis, provide a strategy to fabricate inorganic nanomaterials with controllable architectures. Computationally designed peptide assemblies...