Here we demonstrate Au nanoparticle self-similar chain structure organized by triangle DNA origami with well-controlled orientation and <10 nm spacing. We show for the first time that a large DNA complex (origami) and multiple AuNP conjugates can be well-assembled and purified with reliable yields. The assembled structure could be used to generate high local-field enhancement. The same method can be used to precisely localize multiple components on a DNA template for potential applications in nanophotonic, nanomagnetic, and nanoelectronic devices.
O rganic-based photovoltaic cells (OPVs) are of great interest owing to their potential for low-cost solar energy conversion. 1 An important breakthrough for OPVs was the use of a heterojunction (HJ) structure, in which the difference of the energy levels of two materials (donor and acceptor) can lead to efficient dissociation of photogenerated excitons at the HJ interfaces. 1 Since then, tremendous efforts have been taken to optimize the carrier donor/acceptor (DA) interface morphology to improve the photogenerated exciton dissociation and consequently the overall power conversion efficiency. 2 One successful approach is to use a bulk heterojunction (BHJ) structure that can create dissociation centers everywhere within the active layer. 2 Typically, the formation of a BHJ structure can be achieved via self-assembly of nanostructured soft materials by spontaneous phase separation in a number of solution processed polymer/ fullerene systems, yet efficiency in these structures might be significantly reduced through unpredicted shunt paths and isolated islands of materials. 3 Nanoimprint lithography (NIL) offers a potential solution for producing well-defined interpenetrating networks at the DA interface and is compatible with roll-to-roll manufacturing for lowcost and high-throughput nanopatterning. 4,5 To efficiently harvest photogenerated excitons, densely packed nanoimprinted OPV structures with halfpitch smaller than 2 times that of the exciton diffusion length are needed (typically sub-20 nm regime). 6 Recent efforts in this field have been mainly focusing on polymeric PV materials. However, OPVs with small-molecular weight materials could also benefit from similar morphologies. In addition, small-molecular weight OPV materials provide additional advantages over polymers, such as higher chemical/thermal stability and higher material purity. 7 Previous work has shown relatively poor stability of imprinted nanostructures in smallmolecular compounds. 8Ϫ10 Problems arise due to pronounced surface diffusion and self-faceting and are exacerbated when features head toward the sub-20 nm regime. 11,12 These instabilities must be understood and overcome to achieve efficient nanostructured OPVs.Boron subphthalocyanines (SubPcs) are a class of photoactive small-molecularweight materials with unique physical properties. 13 A typical SubPc has a nonplanar pyramid-shaped structure, in which the boron atom is surrounded by three coupled
Two-dimensional monolayer transition metal dichalcogenide semiconductors are ideal building blocks for atomically thin, flexible optoelectronic and catalytic devices. Although challenging for two-dimensional systems, sub-diffraction optical microscopy provides a nanoscale material understanding that is vital for optimizing their optoelectronic properties. Here we use the ‘Campanile' nano-optical probe to spectroscopically image exciton recombination within monolayer MoS2 with sub-wavelength resolution (60 nm), at the length scale relevant to many critical optoelectronic processes. Synthetic monolayer MoS2 is found to be composed of two distinct optoelectronic regions: an interior, locally ordered but mesoscopically heterogeneous two-dimensional quantum well and an unexpected ∼300-nm wide, energetically disordered edge region. Further, grain boundaries are imaged with sufficient resolution to quantify local exciton-quenching phenomena, and complimentary nano-Auger microscopy reveals that the optically defective grain boundary and edge regions are sulfur deficient. The nanoscale structure–property relationships established here are critical for the interpretation of edge- and boundary-related phenomena and the development of next-generation two-dimensional optoelectronic devices.
guide is schematically presented in Fig. S1a. As the name "MIM" implies, a structural symmetry exists with respect to the mirror plane that cuts through the center of the SiO 2 layer and is parallel to the x-y plane. As a result, supported SPP modes in the guide can be classified into two major types, each with its own distinctive eigenstates [1][2][3][4][5]. One is symmetric (S), and the other is antisymmetric (AS). In a symmetric mode, the electric-field distribution is symmetric around the mirror plane, while in an anti-symmetric mode, the distribution is anti-symmetric, as shown in Fig. S2. Figure S1b shows the existing AS-and S-modes supported by the proposed MIM gap plasmon waveguide structure with thickness h between 50 and 300 nm. The width of the waveguide w is related to h through the equation w = (500 nm/200 nm) × h, and the frequency of interest is 360 THz. In this figure, the fundamental AS mode (or AS1) does not exhibit any cut-off for h between 50 and 300 nm, and theoretically, AS1 can still be supported in the waveguide even if h of the SiO 2 layer becomes infinitesimally small [1]. We are most interested in the fundamental AS1 mode because it achieves the best confinement of energy, which can be clearly observed in Fig. S2. A more detailed description of this mode is provided in Section 2. The other two antisymmetric modes supported in this geometry are the AS2 and AS3 modes. Those modes are oscillatory along the y-direction and originate from the finite width of SiO 2 (Fig. S2). They are cut off when h becomes smaller than 85 nm and 185 nm, respectively (Fig. S1b). The symmetric modes, S1 and S2, are shown in the region of low effective refractive index. The cross-sectional field profiles of S1 and S2 modes show resemblance to monopole and dipole distributions, respectively, as seen in Fig. S2. The S1 mode does not have cut-off, and the S2 mode has cut off when h becomes smaller than 88 nm.
Drastic chemical interface plasmon damping is induced by the ultrathin (∼2 nm) titanium (Ti) adhesion layer; alternatively, molecular adhesion is implemented for lithographic fabrication of plasmonic nanostructures without significant distortion of the plasmonic characteristics. As determined from the homogeneous linewidth of the resonance scattering spectrum of individual gold nanorods, an ultrathin Ti layer reduces the plasmon dephasing time significantly, and it reduces the plasmon scattering amplitude drastically. The increased damping rate and decreased plasmon amplitude are due to the dissipative dielectric function of Ti and the chemical interface plasmon damping where the conduction electrons are transferred across the metal-metal interface. In addition, a pronounced red shift due to the Ti adhesion layer, more than predicted using electromagnetic simulation, suggests the prevalence of interfacial reactions. By extending the experiment to conductively coupled ring-rod nanostructures, it is shown that a sharp Fano-like resonance feature is smeared out due to the Ti layer. Alternatively, vapor deposition of (3-mercaptopropyl)trimethoxysilane on gently cleaned and activated lithographic patterns functionalizes the glass surface sufficiently to link the gold nanostructures to the surface by sulfur-gold chemical bonds without observable plasmon damping effects.
Optical antennas have generated much interest in recent years due to their ability to focus optical energy beyond the diffraction limit, benefiting a broad range of applications such as sensitive photodetection, magnetic storage, and surface-enhanced Raman spectroscopy. To achieve the maximum field enhancement for an optical antenna, parameters such as the antenna dimensions, loading conditions, and coupling efficiency have been previously studied. Here, we present a framework, based on coupled-mode theory, to achieve maximum field enhancement in optical antennas through optimization of optical antennas’ radiation characteristics. We demonstrate that the optimum condition is achieved when the radiation quality factor (Q rad) of optical antennas is matched to their absorption quality factor (Q abs). We achieve this condition experimentally by fabricating the optical antennas on a dielectric (SiO2) coated ground plane (metal substrate) and controlling the antenna radiation through optimizing the dielectric thickness. The dielectric thickness at which the matching condition occurs is approximately half of the quarter-wavelength thickness, typically used to achieve constructive interference, and leads to ∼20% higher field enhancement relative to a quarter-wavelength thick dielectric layer.
A new characterization approach is employed in this study that enables the measurement of the surface area of each reactive mineral located within the connected pore network of a sandstone from a carbon sequestration pilot site in Cranfield, Mississippi. The mineral distribution is measured in 2D by chemical mapping using Energy Dispersive X-ray Spectroscopy-Scanning Electron Microscopy (SEM-EDX) coupled with an image segmentation technique. The pore structure is mapped at high resolution using a pixel contrast thresholding technique applied to 2D Backscattered Electron Microscopy (BSE-SEM) images. After merging the mineral distribution and porosity maps, the accessibilities of each mineral present in the rock sample are quantified. These quantifications require characterizing in advance the connected pore network in the merged maps, which is done considering the permeability of chlorite measured at the nano-scale in three dimensions by Focus Ion BeamScanning Electron Microscopy (FIB-SEM). The accessible surface area of each reactive mineral is finally determined by multiplying the fraction of each reactive mineral next to the connected pore network, measured in 2D, with the surface area of the connected pore network in the rock, which is measured in 3D from X-ray based micro tomography (μ-CT) images and subsequently refined with a correction factor that accounts for the missing pore connectivity. This is necessary since μ-CT voxel resolution (880 nm) is lower than the pixel resolution achieved with BSE-SEM (330 nm). The accessible surface areas of the reactive minerals present in the sandstone rock can be used to accurately scale the rate constants for quantitative prediction and ultimately control of CO 2 injection in the subsurface at the Cranfield pilot site.
Using first-principles theory and experiments, chemical contributions to surface-enhanced Raman spectroscopy for a well-studied organic molecule, benzene thiol, chemisorbed on planar Au(111) surfaces are explained and quantified. Density functional theory calculations of the static Raman tensor demonstrate a strong mode-dependent modification of benzene thiol Raman spectra by Au substrates. Raman active modes with the largest enhancements result from stronger contributions from Au to their electron-vibron coupling, as quantified through a deformation potential. A straightforward and general analysis is introduced to extract chemical enhancement from experiments for specific vibrational modes; measured values are in excellent agreement with our calculations.
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