Planar Nanoparticles Research Articles

Three-Dimensional Decoupling Co-Catalyst from a Photoabsorbing Semiconductor as a New Strategy To Boost Photoelectrochemical Water Splitting.

A cocatalyst is normally deposited on a photoabsorbing semiconductor (PAS) for photoelectrochemical (PEC) water splitting, but with drawbacks of limited loading, reduced light absorption, and tendency of charge recombination. To tackle these problems, a scheme of three-dimensional (3D) decoupling cocatalysts from the PAS with a pore-spanning crisscross conducting polymer host is proposed in this work. To demonstrate the concept, a facile method was developed for the in situ cogrowth of FeO x nanoparticles and conducting polymer (CP) network in various PAS with different microstructures such as a TiO2 nanorod array, WO3 nanosheet array, and planar TiO2 nanoparticle film, generating the bespoke photoanodes. The as-synthesized photoanodes exhibited a significantly enhanced PEC water splitting performance, which is clearly shown to arise from the improved light utilization, increased catalytic active sites, enhanced charge separation, and decreased electrochemical impedance of the photoelectrode. This 3D decoupling strategy is expected to open a promising direction for designing efficient PEC cells.

Formation of a microheterophase state from planar nanoparticles of graphene at the oil-water interface

It has been found that N aqueous suspension of planar graphite nanoparticles exhibits properties of displacement fluid at the oil–water interface. Experiments with the Hele–Shaw cell showed that the process of oil displacement from the interface is not accompanied by the formation of viscous “fingers” as a result of development of instability at the oil–water interface.

Correlation Between Surface Charge Distribution and Circular Dichroism of Elementary Planar Nanoparticles

A correlation is observed between surface charge distributions and the circular dichroism (CD) signature of nanoparticles excited by circularly polarized waves. These surface charge distributions arise as a result of charge separation and depend on the polarization of the externally excited light. This correlation can be observed by deriving the surface charge distribution profile of excited localized surface plasmon polaritons (SPPs) in elementary metal nanoparticles under the influence of circularly polarized light. Nanoparticles with strong CD signatures are especially desired for sensing of chiral biomolecules as well as to aid in photochemical catalysis. We also found out that CD signatures can even be induced via angular rotation. This is true for elementary non-rotated nanoparticles which do not possess a CD signature. The use of elementary nanoparticles for sensing poses a huge advantage over complex nanostructures due to the ease of fabrication. The observed CD signature can also be validated in accordance with theory and simulation results.

Reversible Surface Engineering via Nitrone-Mediated Radical Coupling.

Efficient and simple polymer conjugation reactions are critical for introducing functionalities on surfaces. For polymer surface grafting, postpolymerization modifications are often required, which can impose a significant synthetic hurdle. Here, we report two strategies that allow for reversible surface engineering via nitrone-mediated radical coupling (NMRC). Macroradicals stemming from the activation of polymers generated by copper-mediated radical polymerization are grafted via radical trapping with a surface-immobilized nitrone or a solution-borne nitrone. Since the product of NMRC coupling features an alkoxyamine linker, the grafting reactions can be reversed or chain insertions can be performed via nitroxide-mediated polymerization (NMP). Poly( n-butyl acrylate) ( Mn = 1570 g·mol-1, D̵ = 1.12) with a bromine terminus was reversibly grafted to planar silicon substrates or silica nanoparticles as successfully evidenced via X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry, and grazing angle attenuated total reflection Fourier-transform infrared spectroscopy (GAATR-FTIR). NMP chain insertions of styrene are evidenced via GAATR-FTIR. On silica nanoparticles, an NMRC grafting density of close to 0.21 chains per nm2 was determined by dynamic light scattering and thermogravimetric analysis. Concomitantly, a simple way to decorate particles with nitroxide radicals with precise control over the radical concentration is introduced. Silica microparticles and zinc oxide, barium titanate, and silicon nanoparticles were successfully functionalized.

Oil Displacement from a Porous Medium with the Aid of a Graphite Suspension

It has been found that N aqueous suspension of planar graphite nanoparticles exhibits properties of displacement fluid at the oil–water interface. Experiments with the Hele–Shaw cell showed that the process of oil displacement from the interface is not accompanied by the formation of viscous “fingers” as a result of development of instability at the oil–water interface.

Plasmonic Screening Effect of Gold Nanoparticles Array on Light Absorption in Poly(3-hexyl)Thiophene Thin Film.

The localized surface plasmon (LSP) photophysical phenomenon occurring in metal nanostructures is often presented as a way to effectively couple light into sub-wavelength-scale photovoltaic devices, which would otherwise suffer from a weak light absorption. The simultaneous complementary effect of localized optical field depletion receives far less attention. We studied a system consisting of a planar gold nanoparticles array (AuNP) deposited at the surface of a semiconducting polymer thin film (P3HT). By comparing the UV-vis spectra of P3HT with and without the AuNP array, we have estimated that the AuNPs screen the optical absorption in the interfacial layer of about 3.8 nm effective thickness due the near-field depletion effect. It suggests that the AuNP array may be used to practically "hide" a thin semiconductor layer, e.g., in order to tune the perceived color of the photovoltaic cell embedded in architecture, or in wearable devices.

Вытеснение нефти из пористой среды с использованием графитовой суспензии

AbstractIt has been found that N aqueous suspension of planar graphite nanoparticles exhibits properties of displacement fluid at the oil–water interface. Experiments with the Hele–Shaw cell showed that the process of oil displacement from the interface is not accompanied by the formation of viscous “fingers” as a result of development of instability at the oil–water interface.

Characteristics of copper sulfide nanoparticles obtained in the copper sulfate–sodium thiosulfate system

Stable hydrosols of copper sulfide nanoparticles are synthesized by heating aqueous solutions with different ratios of sodium thiosulfate and copper sulfate in the presence of polyvinylpyrrolidone and studied by a number of physicochemical methods in situ (optical spectroscopy, dynamic light scattering) and ex situ (transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy). The main product is CuS covellite nanoparticles with some impurities of other phases (Cu2S, Cu1,8S, Cu7S4). With an increase in the initial molar ratio S2O 2−3 / Cu from 0.2 to 5 the nanoparticle size increases from 1-5 nm to 30-50 nm and then decreases to 4 nm at a ratio of 10. A substantial increase in the intensity of plasmon absorption within 800-1500 nm is observed during the formation of planar nanoparticles with a lateral size of about 30 nm at S2O 2−3:Cu = 5. A band gap obtained from both direct and indirect optical absorption spectra of sulfides (2.6 eV and 1.7 eV respectively) remains constant for all particles.

Effect of Ga seeding layer on formation of epitaxial Y-shaped GaN nanoparticles on silicon

Silicon and aluminium nitrides, commonly used as buffer layers for GaN growth on Si are wide gap insulators, preventing barrier free charge-carrier transport across the heterojunction and limiting the functionality of GaN-on-silicon technology. In this work we explore possibility of direct growth of GaN on Si nano-heterostructures by PA-MBE with use of Ga-nanodroplets as seeds. It is demonstrated that use of seeding layer can result in formation of Y-shaped planar GaN nanoparticles (GaN tripods) along with commonly observed GaN nanowires. Growth mechanism, morphology and structural characterization of GaN/Si nano-heterostructures is discussed.

Optical Chirality from Dark‐Field Illumination of Planar Plasmonic Nanostructures

AbstractDark‐field illumination is shown to make planar chiral nanoparticle arrangements exhibit circular dichroism in extinction, analogous to true chiral scatterers. Single oligomers, consisting rotationally symmetric arrangements of gold nanorods, are experimentally observed to exhibit circular dichrosim at their maximum scattering with strong agreement to numerical simulation. A dipole model is developed to show that this effect is caused by a difference in the projection of a nanorod onto the handed orientation of electric fields created by a circularly polarized dark‐field normally incident on a glass‐air interface. Owing to this geometric origin, the wavelength of the peak chiral response is experimentally shown to shift depending on the separation between nanoparticles. All presented oligomers have physical dimensions less than the operating wavelength, and the applicable extension to closely packed planar arrays of oligomers is demonstrated to amplify the magnitude of circular dichroism. This realization of strong chirality in these oligomers demonstrates a new path to engineer optical chirality from planar devices using dark‐field illumination.

Supra-Nanoparticle Functional Assemblies through Programmable Stacking.

The quest for the by-design assembly of material and devices from nanoscale inorganic components is well recognized. Conventional self-assembly is often limited in its ability to control material morphology and structure simultaneously. Here, we report a general method of assembling nanoparticles in a linear "pillar" morphology with regulated internal configurations. Our approach is inspired by supramolecular systems, where intermolecular stacking guides the assembly process to form diverse linear morphologies. Programmable stacking interactions were realized through incorporation of DNA coded recognition between the designed planar nanoparticle clusters. This resulted in the formation of multilayered pillar architectures with a well-defined internal nanoparticle organization. By controlling the number, position, size, and composition of the nanoparticles in each layer, a broad range of nanoparticle pillars were assembled and characterized in detail. In addition, we demonstrated the utility of this stacking assembly strategy for investigating plasmonic and electrical transport properties.

Spatial evolution of the near-field distribution on planar gold nanoparticles with the excitation wavelength across dipole and quadrupole modes

We investigate the superposition properties of the dipole and quadrupole plasmon modes in the near field both experimentally, by using photoemission electron microscopy (PEEM), and theoretically. In particular, the asymmetric near-field distributions on gold (Au) nanodisks and nanoblocks under oblique incidence with different polarizations are investigated in detail. The results of PEEM measurements show that the evolutions of the asymmetric near-field distributions are different between the excitation with s-polarized and p-polarized light. The experimental results can be reproduced very well by numerical simulations and interpreted as the superposition of the dipole and quadrupole modes with the help of analytic calculations. Moreover, we hypothesize that the electrons collected by PEEM are mainly from the plasmonic hot spots located at the plane in the interface between the Au particles and the substrate in the PEEM experiments.

Tuning the electrical property of a single layer graphene nanoribbon by adsorption of planar molecular nanoparticles

In this study, a simple and fast approach of band gap formation in a single layer graphene nanoribbon (sGNR) is demonstrated by using hexaazatriphenylenehexacarbonitrile (HAT-CN6) as an adsorbate molecule. sGNRs were successfully synthesized through the unzipping of double-walled carbon nanotubes followed by casting HAT-CN6 in acetone solution to alter the electronic properties of the sGNRs. Then, the electrical property of a sGNR was measured using a field effect transistor structure and also by point-contact current imaging atomic force microscopy. The results demonstrate the formation of electron trapping sites with the nanoparticles and the neck structure of the sGNR near the adsorbed region of the molecule. Therefore, the charge carriers on the sGNR can only pass through the neck region, which works similarly to a narrow sGNR. Such a narrow sGNR has a lateral confinement of charge carriers around the neck region; hence, the device becomes semiconducting. The fabricated semiconducting sGNR could be widely used in electronic devices.

Theory of patch-antenna metamaterial perfect absorbers

A metasurface that absorbs waves from all directions of incidence can be achieved if the surface impedance is made to vary as a function of incidence angle in a specific manner. Here we show that a periodic array of planar nanoparticles coupled to a metal film can act as an absorbing metasurface with an angle-dependent impedance. Through a semi-analytical calculation based on coupled-mode theory, we find the perfect absorbing condition is equivalent to balancing the Ohmic and radiative losses of the nanoparticles at normal incidence. Absorption over a wide range of incidence angles can then be obtained by tailoring the scattered far-field pattern of the individual planar nanoparticles such that their radiative losses remain constant. The theory provides a means of understanding the behavior of perfect absorbing structures that have been observed experimentally or numerically, reconciling previously published theories and enabling the optimization of absorbing surfaces.

Circular dichroism induced by Fano resonances in planar chiral oligomers

AbstractWe present a general theory of circular dichroism in planar chiral nanostructures with rotational symmetry. It is demonstrated, analytically, that the handedness of the incident field's polarization can control whether a nanostructure induces either absorption or scattering losses, even when the total optical loss (extinction) is polarization‐independent. We show that this effect is a consequence of modal interference so that strong circular dichroism in absorption and scattering can be engineered by combining Fano resonances with planar chiral nanoparticle clusters.image

Simulation of Absorption Spectra of Metal Nanoparticles Embedded in Organic Media

Metal nanoparticles, silver and gold, of different sizes and shapes are actively being researched in a variety of different fields such as solar cells. The unique plasmonic properties of these particles, especially in the visible and NIR-region ranging from 400-1200 nm, are the basis for most of these applications. The absorption spectra are calculated using the discrete dipole approximation (DDA) in the wavelength region of 300 to 1200 nm. The modeled samples for calculating are planar array nanoparticles, basically two particles and more than two particles. The influences of the nanoparticle size, interparticle distance and polarization direction of excited light on the absorption spectra are investigated. Moreover, the optical absorption can be tuned by adjusting sizes and shape of nanoparticles to obtain the enhanced absorption. The influence of the surrounding medium is also presented.

Unravelling kinetic and thermodynamic effects on the growth of gold nanoplates by liquid transmission electron microscopy.

The growth of colloidal nanoparticles is simultaneously driven by kinetic and thermodynamic effects that are difficult to distinguish. We have exploited in situ scanning transmission electron microscopy in liquid to study the growth of Au nanoplates by radiolysis and unravel the mechanisms influencing their formation and shape. The electron dose provides a straightforward control of the growth rate that allows quantifying the kinetic effects on the planar nanoparticles formation. Indeed, we demonstrate that the surface-reaction rate per unit area has the same dose-rate dependent behavior than the concentration of reducing agents in the liquid cell. Interestingly, we also determine a critical supply rate of gold monomers for nanoparticle faceting, corresponding to three layers per second, above which the formation of nanoplates is not possible because the growth is then dominated by kinetic effects. At lower electron dose, the growth is driven by thermodynamic and the formation and shape of nanoplates are directly related to the twin-planes formed during the growth.

Supramolecular structure of chitin nanofibrils

The structure of chitin nanofibrils as a promising filler for bioresorbable suture materials and matrixes for cellular technologies and tissue engineering is investigated via the methods of X-ray diffraction and scanning electron microscopy. It is shown that the powder microparticles obtained via lyophilization of an aqueous dispersion of chitin nanofibrils have a band structure with a cross-sectional size of 30 μm and a thickness of 0.1 μm. The bands consist of nanoparticles 25 nm in thickness and 400–500 nm in length. The chitin nanofibrils are composed of two crystallites with cross-sectional sizes of 11–12 nm and b axes perpendicular to the nanofibril axis. The chitin nanofibrils tend to form planar elements with a layered structure on both the microlevel and the nanolevel. The addition of chitin nanofibrils to a chitosan solution leads to a rise in its viscosity. However, the action of shear stresses leads to a substantial decrease in the chitosan-chitin solution viscosity, a phenomenon that is due to the presence of planar anisodiametric nanoparticles of chitin.

Coupled-mode theory for film-coupled plasmonic nanocubes

Planar metallic nanoparticles separated by nanoscale distances from a metal film support unique plasmonic resonances useful for controlling a wide range of photodynamic processes. The fundamental resonance of a film-coupled planar nanoparticle arises from a transmission-line mode localized between nanoparticle and film, whose properties can be roughly approximated by closed form expressions similar to those used in patch antenna theory. The insight provided by the analytical expressions, and the potential of achieving similar closed-form expressions for a range of plasmonic phenomenon such as spasing, fluorescence enhancement, and perfect absorbers, motivates a more detailed study of the film-coupled patch. Here, we present an expanded analytical analysis of the plasmonic patch geometry, applying an eigenmode expansion method to arrive at a more accurate description of the field distribution underneath a film-coupled plasmonic nanocube. The fields corresponding to the inhomogeneous Maxwell's equations are expanded in a set of lossless waveguide eigenmodes. Radiation damping and Ohmic losses are then perturbatively taken into account by considering an equivalent surface impedance. We find that radiative loss couples the lossless eigenmodes, leading to discernible features in the scattering spectra of the nanocubes. The method presented can be further applied to the case of point source excitations, in which accounting for all potential eigenmodes becomes essential.

Rhodium Nanoparticle Anchoring on AlPO4 for Efficient Catalyst Sintering Suppression

Rhodium catalysts exhibited higher dispersion with tridymite-type AlPO4 supports than with Al2O3 during thermal aging at 900 °C under an oxidizing atmosphere. The local structural analysis via X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray absorption fine structure, and infrared spectroscopy suggested that the sintering of AlPO4-supported Rh nanoparticles was significantly suppressed because of anchoring via a Rh–O–P linkage at the interface between the metal and support. Most of the AlPO4 surface was terminated by phosphate P–OH groups, which were converted into a Rh–O–P linkage when Rh oxide (RhOx) was loaded. This interaction enables the thin planar RhOx nanoparticles to establish close and stable contact with the AlPO4 surface. It differs from Rh–O–Al bonding in the oxide-supported catalyst Rh/Al2O3, which causes undesired solid reactions that yield deactivated phases. The Rh–O–P interfacial linkage was preserved under oxidizing and reducing atmospheres, which contrasts with conventional metal oxide supports that only present the anchoring effect under an oxidizing atmosphere. These experimental results agree with a density functional theory optimized coherent interface RhOx/AlPO4 model.