Au Triangles Research Articles

Photoenhanced Electrocatalytic Hydrogen Evolution Accelerated Dominantly by the Hot Electrons from Intraband Transition rather than Interband Transition.

Plasmonic materials enabling sunlight as an energy input to catalyze the hydrogen evolution reaction (HER) have become the research focus of artificial photosynthesis. Upon visible photoexcitation, there are both intraband transition and interband transition hot carriers generated, and which of them dominates the catalytic reaction remains elusive. Here, the contributions of hot electrons from intraband and interband transitions to the photoelectrocatalytic HER on plasmonic Au triangle nanoprisms (AuTNPs) have been studied. Compared with the dark reaction, the exchange current density increases by 9-fold and 3-fold under intraband and interband excitation, respectively, which is attributed to the higher energy level of intraband transition hot electrons. By calculation of the reaction activation energy with and without illumination, the contributions of the hot electrons from the two photoexcitation modes to the photoenhanced electroreduction reaction (PEER) are quantitatively analyzed, proposing the general standard to measure the effect of different hot electrons in different reactions.

Tunable Mid-Infrared Optical Properties of Monolayer Black Phosphorus Through Au Nanotriangle Arrays via Electric Field Reflection and Surface Plasmon Polaritons

A metamaterial system composed of monolayer black phosphorus and Au triangle arrays is designed. Absorptivity, transmittivity, and reflectivity are investigated in mid-infrared regime. A low transmissivity and high absorptivity can be obtained via surface plasmon polaritons at the black phosphorus and Au triangle array interface. By changing the geometrical parameters, such as angle magnitude and slit width of Au triangle, we can modulate the transmissivity, reflectivity and absorptivity properties. Different from other previous work, it is found the zigzag direction has a better photoresponse than that armchair by changing the slit width. The electric field of the external radiation field is reflected at the Au triangle edges. Thus, electric field component perpendicular to the polarization direction generates, which can also lead to surface plasmon polaritons and is not researched in others’ work. With increase in the angle of Au triangle, transmittivity (or absorptivity) for armchair direction has a blue shift and for zigzag direction has a red shift. The transmittivity decrease ( or absorptivity increase ) for special wavelength caused by the surface plasmon polaritons may be applied to design filter devices.

Synthesis of Au–Ag triangular nanocomposite with promising SERS activity

Synthesis of triangular Au nanoparticles using photochemically reduced phosphomolybdic acid (PMA)-lysine complex was attempted successfully. PMA-lysine complex remained bound on the surface of Au nanotriangles. After removing the free PMA-lysine which was not bound on Au triangles, the bound PMA-lysine complex could be irradiated for the second time exploiting the photo-switchable reducing capability of PMA. When exposed to Ag+ ions, it resulted in the formation of Ag on Au nanotriangles. Ag nanoparticles thus formed, were stacked site selectively over triangular-shaped Au nanoparticles due to localization of PMA-lysine complex over Au nanotriangles only. The bimetallic triangle-shaped nanocomposite was characterized thoroughly with UV–Vis–NIR spectra, TEM, EDAX, STEM-HAADF, XPS and FTIR spectra. Most importantly, this bimetallic nanocomposite showed promising SERS activity when compared to monometallic Au triangle or the molecular L-lysine.

A visible-near infrared wavelength-tunable metamaterial absorber based on the structure of Au triangle arrays embedded in VO2 thin film

Abstract We propose a metamaterial electromagnetic wave absorber which is aimed to achieve the wide tunability of resonance absorption peak in visible and near-infrared (NIR) regime. The metamaterial absorber consists of Au triangle nanoparticle arrays, vanadium dioxide (VO2) film dielectric layer and the gold reflective layer, and the Au triangle arrays are embedded in the VO2 film. We explore the change of resonance wavelengths affected by the thickness of the VO2 dielectric layer. When the thickness of VO2 film is 90 nm, the absorption peak achieves a large tunability of 56.2% while the VO2 undergoes a structural transition from metallic phase (m-VO2) to insulator phase (i-VO2). The large wavelength tunability can be explained by a hybrid electric resonance and magnetic resonance mode from the electromagnetic field distributions at the resonance wavelengths. The absorbers with tunable resonance wavelengths would be beneficial to the sensor and detector applications in terms of heat or light signal.

Shape Sensitivity on Toxicity of Gold Nanoplates in Breast Cancer Cells.

Gold nanomaterials (Au NMs) have been explored for a wide range of applications in catalysis and medicine. Here we report the shape sensitive toxicity of gold nanoplates (Au nanoplates) in breast cancer cell line, MCF7. Au nanoplates induced a dose- and shape-dependent toxicity to cancer cells. Oxidative stress induced by Au nanoplates is believed to be the trigger for the DNA, which resulted in cell apoptosis. In summary, the results from our study demonstrate that morphology appears to play a significant role in mediating the cellular responses and Au triangles nanoplates showed the highest toxicity to the cells. Such findings may be able to shine more light on the shape-dependent interaction between Au NMs and living organisms.

Superresolution fluorescence mapping of single-nanoparticle catalysts reveals spatiotemporal variations in surface reactivity

For the practical application of nanocatalysts, it is desirable to understand the spatiotemporal fluctuations of nanocatalytic activity at the single-nanoparticle level. Here we use time-lapsed superresolution mapping of single-molecule catalysis events on individual nanoparticles to observe time-varying changes in the spatial distribution of catalysis events on Sb-doped TiO2 nanorods and Au triangle nanoplates. Compared with the active sites on well-defined surface facets, the defects of the nanoparticle catalysts possess higher intrinsic reactivity but lower stability. Corners and ends are more reactive but also less stable than flat surfaces. Averaged over time, the most stable sites dominate the total apparent activity of single nanocatalysts. However, the active sites with higher intrinsic activity but lower stability show activity at earlier time points before deactivating. Unexpectedly, some active sites are found to recover their activity ("self-healing") after deactivation, which is probably due to desorption of the adsorbate. Our superresolution measurement of different types of active catalytic sites, over both space and time, leads to a more comprehensive understanding of reactivity patterns and may enable the design of new and more productive heterogeneous catalysts.

Hybridized plasmon resonant modes in molecular metallodielectric quad-triangles nanoantenna

In this study, we examined the plasmon response for both metallic and metallodielectric nanoantennas composed of four gold (Au) triangles in a quadrumer orientation. Tailoring an artificial metallic quad-triangles nanoantenna, it is shown that the structure is able to support pronounced plasmon and Fano resonances in the visible spectrum. Using plasmon transmutation effect, we showed that the plasmonic response of the proposed cluster can be enhanced with the placement of carbon nanoparticles in the offset gaps between the proximal triangles. It is verified that this structural modification gives rise to formation of new collective magnetic antibonding (dark) plasmon modes. Excitation of these subradiant dark modes leads to formation of narrower and deeper Fano resonances in the spectral response of the metallodielectric nanoantenna. To investigate the practical applications of the metallodielectric structure, we immersed the nano-assembly in various liquids with different refractive indices to define its sensitivity to the environmental perturbation as a plasmonic biological sensor.

Tunable Fabrication and Optical Properties of Metal Nano Hole Arrays.

Large area polystyrene sphere (PS) arrays with different diameters were prepared by an interface self-assembly method. The inter-particle spacing of PSs was reduced by O2-plasma treatment. When O2-plasma treatment time was long enough, the space of PS arrays could be relatively large. After deposition of Au film and removing the PS masks, we obtained the Au holes arrays instead of Au triangle arrays as normal. The period and the diameter of the hole arrays can be adjusted by the PS with different size and by the O2-plasma treatment time. Then their optical property can be tuned effectively due to the surface plasmon resonance on these structures.

Selective Excitation of Plasmon Resonances of Single Au Triangles by Polarization-Dependent Light Excitation

The plasmonic properties of single Au triangular nanoprisms are investigated using photoemission electron microscopy with particular emphasis on polarization dependence. Two localized surface plasmon resonances (LSPRs) are studied, namely, the in-plane dipolar and quadrupolar plasmon excitations. Experimental maps of the near-field spatial distribution upon polarization and wavelength of the exciting field are interpreted in the framework of a group theory description and finite difference time domain simulations. This work demonstrates the selective excitations, by lifting of degeneracy, of the different LSPR eigenmodes at the single object level and opens ways for the active control of the angular radiation patterns of optical nanoantennas. This approach is general and applies to any nano-object, whatever its initial shape symmetry.

Iridium–Ruthenium–gold cluster complexes: Structures, and skeletal Rearrangements

Three new IrRuAu trimetallic cluster complexes: IrRu3(CO)13AuPPh3, 1, HIrRu3(CO)12(AuPPh3)2, 2 and IrRu3(CO)12(AuPPh3)3, 3 were obtained in low yields from the reaction of HIrRu3(CO)13 with [(AuPPh3)3O][BF4]. Compounds 1 and 3 were subsequently obtained in much better yields (82%) and (84%) from the reactions of [AuPPh3][NO3] and [(AuPPh3)3O][BF4] with [PPN][IrRu3(CO)13], respectively. The molecular structures of all three compounds were established by single crystal x-ray diffraction methods. Compounds 1 and 2 contain an Au(PPh3) group that bridges one triangular face of a tetrahedral IrRu3 cluster. Compound 2 contains a second Au(PPh3) capping group that bridges an Ir–Ru–Au triangle. Compound 3 consists of a pentagonal bipyramidal Au3IrRu3 cluster that has three gold atoms and two of the ruthenium atoms in the equatorial plane. There is a bond between the apical Ir and Ru atoms. Compounds 2 and 3 exhibit dynamical activity in the metal skeleton that leads to a rapid averaging of the inequivalent Au(PPh3) groups on the NMR timescale at room temperature.

Molecular dynamics study of the dewetting of copper on graphite and graphene: Implications for nanoscale self-assembly

Thin-film dewetting can be exploited to self-assemble and organize nanoparticles. Crucial to this effort is the understanding of the nanoscale liquid phase dynamics, and molecular dynamics simulations (MD) provide a powerful tool in this respect. In this paper we demonstrate that MD simulations utilizing a Lennard-Jones (LJ) interface potential can be effectively used to study various wetting regimes of nanoscale Cu disks on graphite. It was found that both the dewetting velocity and the equilibrium contact angle increase with a decrease in the Cu-C potential, and that the retraction velocities obtained are characteristic of dewetting phenomena governed by inertial and capillary forces. This phenomena leads to a change in morphology, from disks to nanodroplets, which, in turn, when using the most accurate LJ potential, jump off the graphitic substrate with a velocity on the order of 140 m/s. This ejection velocity is consistent with the previous experimental observation that nanoscale Au triangles deposited on graphite or glass jump when exposed to a pulsed laser above the melting threshold. Interestingly, the Cu ejection velocity decreases when the liquid Cu disks are deposited on a suspended graphene membrane. Finally, a Rayleigh-Plateau-like instability, which leads to the breakup of a pseudo-one-dimensional liquid Cu nanowire in nanodroplets, is revealed when the MD simulations are performed using different LJ interface potentials.

Halide ion controlled shape dependent gold nanoparticle synthesis with tryptophan as reducing agent: Enhanced fluorescent properties and white light emission

We report the synthesis of Au nanoparticles in presence of two surfactants cetyltrimethyl ammonium chloride (CTAC) and cetyltrimethyl ammonium bromide (CTAB) by reducing Au 3+ ions with tryptophan. Interestingly, triangular shaped particles were seen to form in presence of CTAB, while spherical nanoparticles resulted with CTAC. The highlight of this result is the white light emission from the Au triangles obtained when CTAB is used. These results are supported by lifetime measurements and fluorescence.

Transferring metallic nano-island on hydrogen passivated silicon surface for nano-electronics

In a planar configuration, precise positioning of ultra-flat metallic nano-islands on semiconductor surface opens a way to construct nanostructures for atomic scale interconnects. Regular triangular Au nano-islands have been grown on atomically flat MoS2 substrates and manipulated by STM to form nanometer gap metal-pads connector for single molecule electronics study. The direct assembly of regular shaped metal nano-islands on H-Si(100) is not achievable. Here we present how to transfer Au triangle nano-islands from MoS2 onto H-Si(100) in a clean manner. In this experiment, clean MoS2 substrates are patterned as array of MoS2 pillars with height of 8 μm. The Au triangle nano-islands are grown on top of the pillars. Successful printing transfer of these Au nano-islands from the MoS2 pillars to the H-Si(100) is demonstrated.

High Sensitivity of Plasmonic Microstructures near the Transition from Short-Range to Propagating Surface Plasmon

The optical properties of Au triangles with 700 and 950 nm and 1.8 μm edge length and of microhole arrays with a 3 μm periodicity show a strong absorption peak highly sensitive to refractive index with excitation in the Kretschmann configuration of surface plasmon resonance (SPR). This absorption peak is due to a SPR phenomenon only present with microstructures of micrometer length, as demonstrated with SPR active materials, Au and Ag; but absent in SPR inactive materials, TiOxNy and Ag triangles covered with a thin film of silver oxide. The Au triangle arrays were exhibiting: 1) two transmission minima at λ = 525 and 800 nm with low refractive index sensitivity and 2) a transmission maximum near λ = 600 nm exhibiting a high sensitivity to bulk refractive index for the triangles with an edge length of 950 nm (1993 nm/RI) and 1.8 μm (1038 nm/RI). This is a significant improvement of the sensitivity compared to nanoparticles and is near the sensitivity of SPR on a smooth film. The transmission minima at λ = 800 nm was also present in microhole arrays in a Au film, but of reduced intensity as the size of the hole decreases. Moreover, the microhole arrays with smaller holes also presented a strong transmission minimum around λ = 600 nm, with a similar wavelength, bandwidth and sensitivity as SPR on a smooth gold film. Lastly, the response measured for the formation of a monolayer on the triangle arrays results in a large shift of the SPR response of 13 ± 3 nm, which correlates to a short penetration depth of 24 nm. Triangle arrays investigated in the present configuration could significantly improve SPR biosensing by increasing the measured response from a binding event and could decrease the temperature drift due to a lower bulk refractive index sensitivity.

Localized and Propagating Surface Plasmons in Gold Particles of Near-Micron Size

In this letter, we demonstrate that Au triangles between approximately 200 nm and 1.5 μm are transitioning from a predominantly localized surface plasmon resonance (LSPR) character to a regime where both LSPR and a short-range SPR mode are concomitantly present. The Au triangles are active in LSPR between approximately λ = 700 nm for the smaller triangles and λ = 2.5 μm for the largest Au triangles. Triangles with a base length of 200 and 300 nm do not exhibit an active short-range SPR mode, while triangles with 500 and 700 nm and 1.5 μm base lengths show a strong absorption peak in SPR at approximately λ = 800 nm, attributed to the short-range SPR mode. A low sensitivity of <50 nm/RIU is observed with this short-range SPR mode in triangles of near-micron size. Also, Au nanohole arrays exhibit features in both the submicron size, with gold “island” between neighboring nanoholes, and on the order of tens of microns, with gold “strips” along rows of nanoholes. The excitation of nanohole arrays in total internal reflection (TIR) results in the presence of both a short-range SPR mode similar to that of gold triangles and a propagating SPR mode similar to that of a thin Au film of macroscopic surface. For Au nanohole arrays of 820 nm periodicity, TIR experiments result in two overlapping absorption peaks at λ = 650 and 800 nm, corresponding respectively to propagating SPR in thin films (typically around λ = 615 nm) and the short-range SPR mode in Au triangles.

Coherent acoustic oscillations of nanoscale Au triangles and pyramids: influence of size and substrate

We investigate the impulsively excited acoustic dynamics of nanoscale Au triangles of different sizes and thicknesses on silicon and glass substrates. We employ high-speed asynchronous optical sampling in order to study the damping of the acoustic vibrations with high sensitivity in the time domain. From the observed damping dynamics we deduce the reflection coefficient of acoustic energy from the gold–substrate interface. The observed damping times of coherent acoustic vibrations are found to be significantly longer than expected from the acoustic impedance mismatch for an ideal gold–substrate interface, hence pointing towards a reduced coupling strength. The strength of the coupling can be determined quantitatively. For Au triangles with large lateral size-to-thickness ratio, i.e. a small aspect ratio, the acoustic dynamics is dominated by a thickness oscillation similar to that of a closed film. For triangles with large aspect ratio the coherent acoustic excitation consists of a superposition of different three-dimensional modes which exhibit different damping times.

Structures of Nucleobases Trapped within Au Triangles and Its Effects on Hydrogen Bonding in Base Pairs of DNA

Nucleobases (adenine (A), thymine (T), cytosine (C), and guanine (G)) trapped within two metal clusters such as Au(3) undergo expansion. Our investigation reveals that this primarily arises due to the concomitant increase in all the bond lengths in molecules. Such expansion of the molecules can be qualitatively understood on the basis of classical harmonic potentials in the bonds and loss of aromaticity in the rings. Specifically, the highly electronegative O and N elements in the base pairs anchor to Au atoms and form X-Au bonds, which leads to charge redistribution within the molecules. As a very important consequence of this, the nature of the hydrogen bonds (in Au(3)-A...T-Au(3) and in Au(3)-G...C-Au(3)) change substantially within these electrodes in comparison to gas-phase structures. These hydrogen bonds have a single-well potential energy profile (of the type N...H...O and N...H...N) instead of double-well potentials (like N-H...O or N-H...N/ N...H-N types). A detailed energy calculation along the proton movement pathway supports our conclusions.

Gap-Dependent Optical Coupling of Single “Bowtie” Nanoantennas Resonant in the Visible

Metallic “bowtie” nanoantennas consisting of two opposing tip-to-tip Au triangles have been fabricated with triangle lengths of 75 nm and gaps ranging from 16 to 488 nm. For light polarized along the line between the two triangles, the plasmon scattering resonance first blue-shifts with increasing gap, and then red-shifts as the particles become more and more uncoupled, while perpendicularly polarized excitation shows little dependence upon gap size. This behavior may be approximately understood in a coupled-dipole approximation as changes in the phase between static dipole−dipole interactions and dipole radiative interaction effects.