Assembly Of Nanocubes Research Articles

Designer Metasurfaces via Nanocube Assembly at the Air-Water Interface.

The advent of metasurfaces has revolutionized the design of optical instruments, and recent advancements in fabrication techniques are further accelerating their practical applications. However, conventional top-down fabrication of intricate nanostructures proves to be expensive and time-consuming, posing challenges for large-scale production. Here, we propose a cost-effective bottom-up approach to create nanostructure arrays with arbitrarily complex meta-atoms displaying single nanoparticle lateral resolution over submillimeter areas, minimizing the need for advanced and high-cost nanofabrication equipment. By utilizing air/water interface assembly, we transfer nanoparticles onto templated polydimethylsiloxane (PDMS) irrespective of nanopattern density, shape, or size. We demonstrate the robust assembly of nanocubes into meta-atoms with diverse configurations generally unachievable by conventional methods, including U, L, cross, S, T, gammadion, split-ring resonators, and Pancharatnam-Berry metasurfaces with designer optical functionalities. We also show nanocube epitaxy at near ambient temperature to transform the meta-atoms into complex continuous nanostructures that can be swiftly transferred from PDMS to various substrates via contact printing. Our approach potentially offers a large-scale manufacturing alternative to top-down fabrication for metal nanostructuring, unlocking possibilities in the realm of nanophotonics.

Template-confined assembly of Ag nanocubes: An approach to fabricate SERS substrate with good performance

Surface-enhanced Raman scattering (SERS) is an important analytical technique. Its detection sensitivity and reproducibility depend on the density and distribution of SERS hotspots. Self-assembly is an efficient method to produce of SERS substrates due to its easy accessibility. However, the assembled defects can hardly be avoided on large area, which could lower the density and uniformity of the hotspots, leading to poor SERS performance. Herein, we report a method to reduce the defects by taking a patterned substrate as template to confine the assembly of Ag nanocubes. The template was prepared based on the combination of photo lithography and self-assembly. Confined by the template, the Ag nanocubes were assembled closely in each dots of the pattern. The limit of detection (LOD) is down to 3.42 × 10−17 M and the enhanced factor (EF) is up to 3.44 × 1010 on the prepared substrate for detecting rhodamine 6G (R6G). In addition, the relative standard deviation (RSD) of the different substrates is 8.75 %. The assembled Ag nanocubes exhibits high sensitivity and reproducibility as SERS substrate, which are contributed by the formation of high-density and uniform hotspots. The prepared substrate can be used for detecting trace amounts of melamine in milk with LOD of 2.06 × 10−7 M and RSD of 6.91 %, so the substrate is applicable for analyzing various analytes.

Enhanced Magnetic Anisotropy for Reprogrammable High‐Force‐Density Microactuators

AbstractThe precise control of magnetic properties at the microscale has transformative potential in healthcare and human‐robot interaction. This research focuses on understanding the magnetic interactions in nanostructure assemblies responsible for microactuation. By combining experimental measurements and micromagnetic simulations, the interactions in both nanocube and nanochain assemblies are elucidated. Hysteresis measurements and first‐order reversal curves (FORC) reveal that the spatial arrangement of these assemblies governs their collective magnetism. A critical concentration threshold is observed where a transition from ferromagnetic‐like to antiferromagnetic‐like coupling occurs. Leveraging the high uniaxial anisotropy of 1D nanochains, the remanent magnetization of assembled chain structures is maximized for efficient magneto‐mechanical energy transduction. By utilizing an optimized magnetic nanostructure concentration, a flexible film is fabricated, and its significantly enhanced mechanical deformation response to a small magnetic field, surpassing conventional particle‐based samples by a factor of five, is demonstrated. Demonstrating excellent transduction efficiency, visible deformations such as bending and S‐shaped twisting modes are achieved with an applied field of less than 400 Oe. Furthermore, the reprogrammability of the actuator, achieving a U‐shaped bending mode by altering its magnetization profile, is showcased. This research provides valuable insights for designing reconfigurable and effective microactuators and devices at significantly smaller scales than previously possible.

Critical Roles of Impurities and Imperfections in Various Phases of Materials.

In many materials, impurities and imperfections play a critical role on the physical and chemical properties. In the present review, some examples of such materials are discussed. A bulk nanobubble (an ultrafine bubble) is stabilized against dissolution by hydrophobic impurities attached to the bubble surface. An acoustic cavitation threshold in various liquids decreases significantly by the presence of impurities such as solid particles, etc. The strength of brittle ceramics is determined by the size and number of pre-existing microcracks (imperfections) in the specimen. The size effect of a BaTiO3 nanocrystal is influenced by the amount and species of adsorbates (impurities) on its surface as adsorbate-induced charge-screening changes the free energy. The dielectric constant of an assembly of BaTiO3 nanocubes is influenced by a small tilt angle (imperfection) between two attached nanocubes, which induces strain inside a nanocube, and is also influenced by the spatial strain-relaxation due to defects and dislocations (imperfections), resulting in flexoelectric polarization.

Highly Controlled Zigzag Perovskite Nanocrystals Enabled by Dipole‐Induced Self‐Assembly of Nanocubes for Low‐Threshold Amplified Spontaneous Emission and Lasing

AbstractSelf‐assembly of nanocrystals into controlled structures while uncompromising their properties is one of the key steps in optoelectronic device fabrication. Herein, zigzag CsPbBr3 perovskite nanocrystals are demonstrated with a precise number of components with nanocube morphology, these can be successfully obtained through a dipole‐induced self‐assembly process. The addition of a trace amount of deionized water facilitates the transfer from CsPbBr3 nanocubes to intermediates of CsPb2Br5 and Cs3In2Br9, which then fastly release reaction monomers leading to further homogenous nucleation of CsPbBr3 nanocubes, followed by the formation of zigzag CsPbBr3 nanocrystals through a dipole‐induced self‐assembly process. Dipole moment along <110> axis is found to be the driving force for the assembly of nanocubes into zigzag nanocrystals. The zigzag CsPbBr3 nanocrystals exhibit desirable optical properties comparable to their nanocube counterparts and offer advantages for amplified spontaneous emission and lasing applications with low pump thresholds of 3.1 and 6.02 µJ cm−2, respectively. This study not only develops a strategy for producing highly controlled zigzag perovskite nanocrystals and provides insights on the dipole‐induced self‐assembly mechanisms, but also opens an avenue for their application in lasing.

Catalytic hairpin assembly-mediated Cu2O nanocubes as the competitive dual-quenching tags for photoelectrochemical bioassay of miR-141

MicroRNAs (miR) as newly identified biomarkers are closely associated with various cancers, and sensitive monitoring of abnormal miR is great importance in cancer diagnosis. In this work, a novel photoelectrochemical biosensor was developed to sensitively detect miR-141 by the competitive dual-quenching of catalytic hairpin assembly (CHA)-dependent Cu2O nanocubes (NCs) toward β-CD-functionalized CdS nanorods (β-CD@CdS NRs). The biosensing platform was constructed by the stepwise assembly of β-CD@CdS NRs and adamantane-labeled hairpin DNA probe 1 on ITO electrode. In the presence of miR-141, CHA recycling was triggered to immobilize the capture DNA-labeled Cu2O NCs with the aid of hairpin DNA probe 2. The assembly of Cu2O NCs could largely reduce the photocurrent response of CdS NRs based on the competitive consumption of light energy and electron donor. The designed biosensor showed a wide linear range (1.0 pM–100 nM) and a detection limit of 0.47 pM, as well as excellent selectivity and satisfactory stability. Based on the above outcomes, the proposed biosensing device was also applied to miR-141 analysis in human serum with the recoveries ranging from 95.9 % to 104.7 %, achieving a great prospect in clinical application.

Tunable Orientation and Assembly of Polymer-Grafted Nanocubes at Fluid–Fluid Interfaces

Self-assembly of faceted nanoparticles is a promising route for fabricating nanomaterials; however, achieving low-dimensional assemblies of particles with tunable orientations is challenging. Here, we demonstrate that trapping surface-functionalized faceted nanoparticles at fluid-fluid interfaces is a viable approach for controlling particle orientation and facilitating their assembly into unique one- and two-dimensional superstructures. Using molecular dynamics simulations of polymer-grafted nanocubes in a polymer bilayer along with a particle-orientation classification method we developed, we show that the nanocubes can be induced into face-up, edge-up, or vertex-up orientations by tuning the graft density and differences in their miscibility with the two polymer layers. The orientational preference of the nanocubes is found to be governed by an interplay between the interfacial area occluded by the particle, the difference in interactions of the grafts with the two layers, and the stretching and intercalation of grafts at the interface. The resulting orientationally constrained nanocubes are then shown to assemble into a variety of unusual architectures, such as rectilinear strings, close-packed sheets, bilayer ribbons, and perforated sheets, which are difficult to obtain using other assembly methods. Our work thus demonstrates a versatile strategy for assembling freestanding arrays of faceted nanoparticles with possible applications in plasmonics, optics, catalysis, and membranes, where precise control over particle orientation and position is required.

Confined Growth of DNA-Assembled Superlattice Films.

We study the assembly of DNA-functionalized nanocubes under lateral confinement in microscale square trenches on a DNA-functionalized substrate. Microfocus small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) are used to characterize the superlattices (SLs). The results indicate that nanocubes form simple-cubic SLs with square-prism morphology and a (100) out-of-plane orientation to maximize DNA bonding. In-plane, SLs align with the template, exposing their {100} side facets, and the degree of alignment depends on trench size. Interestingly, the distribution of in-plane orientations determined from SAXS and SEM do not agree, indicating that the internal and external structures of the SLs differ. To understand this discrepancy, X-ray ptychography is employed to image the internal structures of the SLs, revealing that SLs which appear to be single-crystalline in SEM may have subsurface grain boundaries, depending on trench size. SEM reveals that the SLs grow via nucleation and growth of randomly oriented domains, which then coalesce; this mechanism explains the observed dependence of alignment and defect structure on size. Interestingly, crystallization occurs via an unusual growth mode, whereby continuous SL layers grow on top of several misoriented islands. Overall, this work elucidates the effect of lateral confinement on the crystallization of DNA-functionalized nanoparticles and shows how X-ray ptychography can be used to gain insight into nanoparticle crystallization.

Coexistence of Flexo- and Ferro-Electric Effects in an Ordered Assembly of BaTiO3 Nanocubes.

It has been reported that the flexoelectric effect could be dominant in the nanoscale. The discrepancy between theory and experiments on the frequency dependence of the dielectric constant of an ordered assembly of BaTiO3 nanocubes is nearly resolved by assuming the coexistence of flexo- and ferro-electric effects. Although flexoelectric polarizations perpendicular to the applied alternating electric field contribute to the dielectric constant, those parallel to the electric field do not contribute because the magnitude of the flexoelectric polarization does not change due to the mismatch of strain at the interface of the nanocubes. On the other hand, some dielectric response is possible for the ferroelectric component of the polarization parallel to the electric field.

Assembly mechanism of surface-functionalized nanocubes.

Faceted nanoparticles can be used as building blocks to assemble nanomaterials with exceptional optical and catalytic properties. Recent studies have shown that surface functionalization of such nanoparticles with organic molecules, polymer chains, or DNA can be used to control the separation distance and orientation of particles within their assemblies. In this study, we computationally investigate the mechanism of assembly of nanocubes grafted with short-chain molecules. Our approach involves computing the interaction free energy landscape of a pair of such nanocubes via Monte Carlo simulations and using the Dijkstra algorithm to determine the minimum free energy pathway connecting key states in the landscape. We find that the assembly pathway of nanocubes is very rugged involving multiple energy barriers and metastable states. Analysis of nanocube configurations along the pathway reveals that the assembly mechanism is dominated by sliding motion of nanocubes relative to each other punctuated by their local dissociation at grafting points involving lineal separation and rolling motions. The height of energy barriers between metastable states depends on factors such as the interaction strength and surface roughness of the nanocubes and the steric repulsion from the grafts. These results imply that the observed assembly configuration of nanocubes depends not only on their globally stable minimum free energy state but also on the assembly pathway leading to this state. The free energy landscapes and assembly pathways presented in this study along with the proposed guidelines for engineering such pathways should be useful to researchers aiming to achieve uniform nanostructures from self-assembly of faceted nanoparticles.

Tailored Synthesis of Iron Oxide Nanocrystals for Formation of Cuboid Mesocrystals.

In this work, we systematically studied the shape- and size-controlled monodisperse synthesis of iron oxide nanocrystals (IONCs) for their use as building blocks in the formation of mesocrystals. For this aim, on understanding the influence of the oleic acid concentration, iron-oleate concentration, and heating rate on the synthesis of robust and reproducible IONCs with desired sizes and shapes, we synthesized highly monodisperse ∼11 nm sized nanocubes and nanospheres. Magnetic measurements of both cubic and spherical IONCs revealed the presence of mixed paramagnetic and superparamagnetic phases in these nanocrystals. Moreover, we observed that the magnetic moments of the nanocubes are more substantial compared to their spherical counterparts. We then demonstrated a simple magnetic-field-assisted assembly of nanocubes into three-dimensional (3D) cuboid mesocrystals while nanospheres did not form any mesocrystals. These findings indicate that small cubic nanocrystals hold great promise as potential building blocks of 3D magnetic hierarchical structures with their superior magnetic properties and mesocrystal assembly capability, which may have high relevance in various fields ranging from high-density data storage to biomedical applications.

Effect of heat treatment on internal stress in barium titanate nanocube assemblies and their dielectric property

Heat treatment is a key process to determine the dielectric properties of nanocrystalline barium titanate (BaTiO3) ceramics, which are a prospective candidate to realize further miniaturization of dielectric components in electric devices. Here, we use Raman spectroscopy and scanning microwave impedance microscopy to investigate the dependence of the internal stress and the relative permittivity of BaTiO3 nanocube three-dimensional assemblies on heat treatment temperature. We show that heat treatment in the temperature range from 700 °C to 1000 °C causes internal compressive stress in the nanocube assemblies without grain growth. The internal compressive stress is caused by formation of tight attachments between neighboring BaTiO3 nanocubes and of Ti-rich phases in the nanocube assemblies in the lower and higher temperature ranges, respectively. We also show that the relative permittivity of the nanocube assemblies at 3 GHz shows a positive correlation with the internal compressive stress. The result indicates that the internal compressive stress enhances the relative permittivity of BaTiO3 nanocubes.

Dynamic dielectric-response model of flexoelectric polarization from kHz to MHz range in an ordered assembly of BaTiO3 nanocubes

Due to the strain gradient near each surface of a BaTiO3 nanocube in their ordered assembly, electric polarization appears due to flexoelectric effect. The magnitude of the flexoelectric polarization could be one order of magnitude larger than that of ferroelectric spontaneous polarization of BaTiO3. Thus, dielectric response of an assembly could be dominated by that of the flexoelectric polarization if there is no ferroelectric domain-wall motion. Numerical simulations of the dielectric response of a BaTiO3 nanocube in an ordered assembly are performed from kHz to MHz range based on a dynamic model of flexoelectric polarization assuming anharmonic potential. The calculated temperature dependence of the dielectric constant is consistent with the experimental data of high dielectric constant with nearly-flat temperature dependence. It is suggested that high dielectric constant with nearly-flat temperature dependence is not originated in ferroelectric nature of BaTiO3 nanocubes but originated in flexoelectric polarization in nanocubes which is also seen in non-ferroelectric materials.

Two-Stage Assembly of Mesocrystal Fibers with Tunable Diameters in Weak Magnetic Fields.

Controlling the morphology and crystallographic coherence of assemblies of magnetic nanoparticles is a promising route to functional materials. Time-resolved small-angle X-ray scattering (SAXS) was combined with microscopy and scaling analysis to probe and analyze evaporation-induced assembly in levitating drops and thin films of superparamagnetic iron oxide nanocubes in weak magnetic fields. We show that assembly of micrometer-sized mesocrystals with a cubic shape preceded the formation of fibers with a high degree of crystallographic coherence and tunable diameters. The second-stage assembly of aligned cuboidal mesocrystals into fibers was driven by the magnetic field, but the first-stage assembly of the oleate-capped nanocubes was unaffected by weak magnetic fields. The transition from 3D growth of the primary mesocrystals to the second stage 1D assembly of the elongated fibers was related to the size and field dependence of isotropic van der Waals and directional dipolar interactions between the interacting mesocrystals.

Quantifying Electrocatalytic Reduction of CO2 on Twin Boundaries

Summary A protocol relying on the use of silver nanostructures with well-defined dimensions and morphologies (e.g., nanocubes and nanowires) has been developed to differentiate and quantitatively determine the atom-specific activities of different surface atoms toward catalyzing electrochemical CO2 reduction reaction (CO2RR). The atom-specific activity of the twin-boundary edges (TBEs) is comparable to (or slightly higher than) that of the single-crystal edges (SCEs) formed from the crossing of two {100} surfaces, and it is on the order of ∼16 attoampere/atom (aA/atom) toward electrochemical CO2RR. This value is more than two orders higher than the atom-specific activity of the {100} surface atoms, i.e., ∼0.1 aA/atom. The high catalytic activity of the TBEs, which represent a class of commonly existing surface defects in stable metal nanostructures with face-centered cubic lattices, is consistent with the DFT calculations, in which the bridge-type binding configuration of COOH∗ at the TBEs stabilizes this intermediate to promote overall CO2RR.

Machine Learning to Reveal Nanoparticle Dynamics from Liquid-Phase TEM Videos.

Liquid-phase transmission electron microscopy (TEM) has been recently applied to materials chemistry to gain fundamental understanding of various reaction and phase transition dynamics at nanometer resolution. However, quantitative extraction of physical and chemical parameters from the liquid-phase TEM videos remains bottlenecked by the lack of automated analysis methods compatible with the videos’ high noisiness and spatial heterogeneity. Here, we integrate, for the first time, liquid-phase TEM imaging with our customized analysis framework based on a machine learning model called U-Net neural network. This combination is made possible by our workflow to generate simulated TEM images as the training data with well-defined ground truth. We apply this framework to three typical systems of colloidal nanoparticles, concerning their diffusion and interaction, reaction kinetics, and assembly dynamics, all resolved in real-time and real-space by liquid-phase TEM. A diversity of properties for differently shaped anisotropic nanoparticles are mapped, including the anisotropic interaction landscape of nanoprisms, curvature-dependent and staged etching profiles of nanorods, and an unexpected kinetic law of first-order chaining assembly of concave nanocubes. These systems representing properties at the nanoscale are otherwise experimentally inaccessible. Compared to the prevalent image segmentation methods, U-Net shows a superior capability to predict the position and shape boundary of nanoparticles from highly noisy and fluctuating background—a challenge common and sometimes inevitable in liquid-phase TEM videos. We expect our framework to push the potency of liquid-phase TEM to its full quantitative level and to shed insights, in high-throughput and statistically significant fashion, on the nanoscale dynamics of synthetic and biological nanomaterials.

Programmable ROS-Mediated Cancer Therapy via Magneto-Inductions.

Reactive oxygen species (ROS), a group of oxygen derived radicals and derivatives, can induce cancer cell death via elevated oxidative stress. A spatiotemporal approach with safe and deep‐tissue penetration capabilities to elevate the intracellular ROS level is highly desirable for precise cancer treatment. Here, a mechanical‐thermal induction therapy (MTIT) strategy is developed for a programmable increase of ROS levels in cancer cells via assembly of magnetic nanocubes integrated with alternating magnetic fields. The magneto‐based mechanical and thermal stimuli can disrupt the lysosomes, which sequentially induce the dysfunction of mitochondria. Importantly, intracellular ROS concentrations are responsive to the magneto‐triggers and play a key role for synergistic cancer treatment. In vivo experiments reveal the effectiveness of MTIT for efficient eradication of glioma and breast cancer. By remote control of the force and heat using magnetic nanocubes, MTIT is a promising physical approach to trigger the biochemical responses for precise cancer treatment.

Soft Plasmonic Assemblies Exhibiting Unnaturally High Refractive Index.

The increases in refractive indices (n) of materials are crucial for transformative optical technologies. With the progress of monolithic lithography, large advances have been achieved with several semiconductors, including silicon, germanium, and gallium arsenide, which generally provide higher n of ∼4.0 compared to those of other elements. Nevertheless, above this upper limit of naturally available n, the range of light-matter interactions could be unprecedentedly expanded, which in turn enriches the possible applications. Here, we present a soft self-assembly of polyhedral Au colloids as a promising method to achieve unnaturally high n values. The interfacial assembly of Au nanocubes provides n of 6.4 at the resonant wavelength (near-infrared) and 4.5 in the off-resonant regimes (mid-infrared), which have not been previously reached. The soft self-assembly of polyhedral Au colloids can be a versatile and highly effective route for the fabrication of optical metamaterials with unnaturally high n values.

Magnetic Assembly of Nanocubes for Orientation-Dependent Photonic Responses.

Close packing is the most favorable manner in colloidal self-assembly, producing superstructures with a limited variety of spatial configurations. This challenge can be overcome by incorporating anisotropic interactions into the assembly process. Using magnetite nanocubes as the building blocks, we show that they can be magnetically assembled into one-dimensional nanochains in an edge-to-edge rather than close-packed face-to-face manner. The cubic shape of the building blocks plays a key role: it decouples the easy magnetization from any of the three geometric axes favoring close packing. Therefore, under magnetic fields, the induced competition between the long-range Zeeman coupling and the short-range dipole-dipole coupling determines the assembly of nanocubes along the [110] directions. The photonic properties of the edge-to-edge configuration are dependent on both chain orientation and viewing angle. Unlike nanosphere assemblies where the strongest diffraction occurs parallel to the chain (or field) direction, the nanocubes allow one to define their long-range periodicity in the plane of a thin film while diffracting light out of the plane, making it particularly useful for applications that desire the achievement of structural colors of sufficient intensity in a film with a minimum thickness. For example, their unique photonic property can be taken advantage of to design "magic" patterns whose rotation is perceived to be opposite to the actual rotational direction of the film. It is difficult to reproduce such unusual optical effects by other means; thereby, many new ways for designing novel security devices are provided. This work reveals the enormous potential of the magnetic assembly strategy, when combined with the use of well-defined nonspherical building blocks, for controlling the spatial configurations of colloidal assemblies and exploiting their novel physical properties for intriguing applications.

Magnetic field-assisted assembly of iron oxide mesocrystals: a matter of nanoparticle shape and magnetic anisotropy.

This letter describes the formation and detailed characterization of iron oxide mesocrystals produced by the directed assembly of superparamagnetic iron oxide-truncated nanocubes using the slow evaporation of the solvent within an externally applied homogeneous magnetic field. Anisotropic mesocrystals with an elongation along the direction of the magnetic field can be produced. The structure of the directed mesocrystals is compared to self-assembled mesocrystalline films, which are formed without the influence of a magnetic field. The remarkable structural difference of mesocrystals produced within the external magnetic field from those self-assembled without field indicates that the specific nanoparticle ordering within the superstructure is driven by competing of two types of anisotropic interactions caused by particle shape (i.e., faceting) and orientation of the magnetic moment (i.e., easy axes: <111>magnetite). Hence, these findings provide a fundamental understanding of formation mechanisms and structuring of mesocrystals built up from superparamagnetic nanoparticles and how a magnetic field can be used to design anisotropic mesocrystals with different structures.