10 research outputs found

    Design for Approaching Cicada-Wing Reflectance in Low- and High-Index Biomimetic Nanostructures

    No full text
    Natural nanostructures in low refractive index Cicada wings demonstrate ≤1% reflectance over the visible spectrum. We provide design parameters for Cicada-wing-inspired nanotip arrays as efficient light harvesters over a 300–1000 nm spectrum and up to 60° angle of incidence in both low-index, such as silica and indium tin oxide, and high-index, such as silicon and germanium, photovoltaic materials. Biomimicry of the Cicada wing design, demonstrating gradient index, onto these material surfaces, either by real electron cyclotron resonance microwave plasma processing or by modeling, was carried out to achieve a target reflectance of ∼1%. Design parameters of spacing/wavelength and length/spacing fitted into a finite difference time domain model could simulate the experimental reflectance values observed in real silicon and germanium or in model silica and indium tin oxide nanotip arrays. A theoretical mapping of the length/spacing and spacing/wavelength space over varied refractive index materials predicts that lengths of ∼1.5 μm and spacings of ∼200 nm in high-index and lengths of ∼200–600 nm and spacings of ∼100–400 nm in low-index materials would exhibit ≤1% target reflectance and ∼99% optical absorption over the entire UV–vis region and angle of incidence up to 60°

    Coherent Brightfield Microscopy Provides the Spatiotemporal Resolution To Study Early Stage Viral Infection in Live Cells

    No full text
    Viral infection starts with a virus particle landing on a cell surface followed by penetration of the plasma membrane. Due to the difficulty of measuring the rapid motion of small-sized virus particles on the membrane, little is known about how a virus particle reaches an endocytic site after landing at a random location. Here, we use coherent brightfield (COBRI) microscopy to investigate early stage viral infection with ultrahigh spatiotemporal resolution. By detecting intrinsic scattered light <i>via</i> imaging-based interferometry, COBRI microscopy allows us to track the motion of a single vaccinia virus particle with nanometer spatial precision (<3 nm) in 3D and microsecond temporal resolution (up to 100,000 frames per second). We explore the possibility of differentiating the virus signal from cell background based on their distinct spatial and temporal behaviors <i>via</i> digital image processing. Through image postprocessing, relatively stationary background scattering of cellular structures is effectively removed, generating a background-free image of the diffusive virus particle for precise localization. Using our method, we unveil single virus particles exploring cell plasma membranes after attachment. We found that immediately after attaching to the membrane (within a second), the virus particle is locally confined within hundreds of nanometers where the virus particle diffuses laterally with a very high diffusion coefficient (∼1 μm<sup>2</sup>/s) at microsecond time scales. Ultrahigh-speed scattering-based optical imaging may provide opportunities for resolving rapid virus–receptor interactions with nanometer clarity

    Coherent Brightfield Microscopy Provides the Spatiotemporal Resolution To Study Early Stage Viral Infection in Live Cells

    No full text
    Viral infection starts with a virus particle landing on a cell surface followed by penetration of the plasma membrane. Due to the difficulty of measuring the rapid motion of small-sized virus particles on the membrane, little is known about how a virus particle reaches an endocytic site after landing at a random location. Here, we use coherent brightfield (COBRI) microscopy to investigate early stage viral infection with ultrahigh spatiotemporal resolution. By detecting intrinsic scattered light <i>via</i> imaging-based interferometry, COBRI microscopy allows us to track the motion of a single vaccinia virus particle with nanometer spatial precision (<3 nm) in 3D and microsecond temporal resolution (up to 100,000 frames per second). We explore the possibility of differentiating the virus signal from cell background based on their distinct spatial and temporal behaviors <i>via</i> digital image processing. Through image postprocessing, relatively stationary background scattering of cellular structures is effectively removed, generating a background-free image of the diffusive virus particle for precise localization. Using our method, we unveil single virus particles exploring cell plasma membranes after attachment. We found that immediately after attaching to the membrane (within a second), the virus particle is locally confined within hundreds of nanometers where the virus particle diffuses laterally with a very high diffusion coefficient (∼1 μm<sup>2</sup>/s) at microsecond time scales. Ultrahigh-speed scattering-based optical imaging may provide opportunities for resolving rapid virus–receptor interactions with nanometer clarity

    Packing Principles for Donor–Acceptor Oligomers from Analysis of Single Crystals

    No full text
    D–A conjugated molecules are complicated in both their molecular and their packing structures. In this perspective, we summarize more than 40 crystal lattices of conjugated oligomers to identify the morphological influence of each building block on the D–A molecules. These lattice structures reveal not only the packing preferences of the conjugated oligomers but also the conformational disorder in the lattices. The presence of this disorder in slowly grown crystals implies that attaining total long-range conformational order is challenging for D–A oligomers, which are structurally complicated and readily distorted and which have building blocks of incommensurate packing dimensions. In optoelectronic applications, a decreased duration of processing can prevent ordering and trap the thin films of D–A oligomers from becoming crystalline phases. Although D–A oligomers conform to packing principles in the formation of a single crystal, their phase behaviors in the formation of active thin films are much more difficult to comprehend. Continuous advances in methods of characterization are still strongly required for the steps of attaining a true structure–property relation of D–A oligomers in active films for optoelectronic applications

    Theoretical Study of Plasmon-Enhanced Surface Catalytic Coupling Reactions of Aromatic Amines and Nitro Compounds

    No full text
    Taking advantage of the unique capacity of surface plasmon resonance, plasmon-enhanced heterogeneous catalysis has recently come into focus as a promising technique for high performance light-energy conversion. This work performs a theoretical study on the reaction mechanism for conversions of p-aminothiophenol (PATP) and p-nitrothiophenol (PNTP) to aromatic azo species, <i>p</i>,<i>p</i>′-dimercaptoazobenzene (DMAB). In the absence of O<sub>2</sub> or H<sub>2</sub>, the plasmon-driven photocatalysis mechanism (hot electron–hole reactions) is the major reaction channel. In the presence of O<sub>2</sub> or H<sub>2</sub>, the plasmon-assisted surface catalysis mechanism (activated oxygen/hydrogen reactions) is the major reaction channel. The present results show that the coupling reactions of PATP and PNTP strongly depend on the solution pH, the irradiation wavelength, the irradiation power, and the nature of metal substrates as well as the surrounding atmosphere. The present study has drawn a fundamental physical picture for understanding plasmon-enhanced heterogeneous catalysis

    Stepwise Structural Evolution of a DTS‑F<sub>2</sub>BT Oligomer and Influence of Structural Disorder on Organic Field Effect Transistors and Organic Photovoltaic Performance

    No full text
    An A–D–A oligomer, DTS­(F<sub>2</sub>BT)<sub>2</sub>, was synthesized; its structural evolution was studied with DSC, POM, 2D-WAXD, and in-situ GI-XRD. The structural evolution of DTS­(F<sub>2</sub>BT)<sub>2</sub> is stepwise and kinetically slow. Both rapid drying and the presence of PC<sub>71</sub>BM trapped DTS­(F<sub>2</sub>BT)<sub>2</sub> in a less ordered nematic (N) phase. PDMS-assisted crystallization enabled a pristine DTS­(F<sub>2</sub>BT)<sub>2</sub> thin film to attain a more ordered equilibrium phase, and enhanced the OFET mobility of DTS­(F<sub>2</sub>BT)<sub>2</sub>. In OPV devices, DIO additive drove the DTS­(F<sub>2</sub>BT)<sub>2</sub> domains in the DTS­(F<sub>2</sub>BT)<sub>2</sub>:PC<sub>71</sub>BM blended film from the N phase toward the equilibrium phase, and resulted in enhanced OPV performances. These results reveal the slow ordering process of the A–D–A oligomer, and the importance of monitoring the degree of structural evolution of the active thin films in organic optoelectronics

    Influences of Out-Of-Plane Lattice Alignment on the OFET Performance of TIPS-PEN Crystal Arrays

    No full text
    In organic field-effect transistors (OFETs), the quality of charge-transport pathway, controlled by crystal structures of organic semiconductors (OSCs), strongly affects the performance of the device. To achieve higher charge mobility, solution-processed single-crystal (SPSC) techniques have been used to decrease crystal defects by aligning the crystals of OSCs in the in-plane direction. Nonetheless, through SPSC techniques, whether the crystalline lattices are well-aligned in the out-of-plane direction and how the out-of-plane lattice misorientaion affects OFET performances remain unclear. Here, a characterization protocol based on polarized optical microscope, X-ray diffraction, and electron diffraction is established to identify the lattice structure, the in-plane and out-of-plane lattice alignment in the crystal array of 6,13-bis­(triisopropylsilylethynyl)­pentacene (TIPS-PEN). Regardless of the solvents used in the PDMS-assisted crystallization, the characterization protocol confirms that all the crystal arrays share the same lattice structure (form I phase), and have similar in-plane lattice alignment. However, TIPS-PEN molecules have sufficient time to unify their out-of-plane orientation and prevent the formation of low angle grain boundary (LAGB) during crystal growth if high boiling temperature solvents are used. The improved out-of-plane lattice alignment increases the hole mobility and decreases the performance fluctuations of devices. The results confirm that the out-of-plane lattice alignment significantly impacts the performance of the devices and the reproducibility of the solution-processed TIPS-PEN OFETs

    Understanding the Interplay between Molecule Orientation and Graphene Using Polarized Raman Spectroscopy

    No full text
    We present a systematic study in investigating the orientation characteristics of pentacene molecules grown on graphene substrates using polarized Raman spectroscopy. The substrate-induced orientation alignment of pentacene can be well distinguished through the polarized Raman spectra. Interestingly, we found that the nature of polycrystalline graphene not only provides efficient route to control molecular orientation, but also acts as an excellent template allowing conjugated molecules to stack accordingly. The relative orientation of the well-aligned pentacene molecules and the nearby graphene domains exhibits several preferred angles due to atomic interactions. This unique feature is further examined and verified by single domain graphene. Furthermore, polarized Raman spectroscopy contains abundant information allowing us to analyze the ordering level of pentacene films with various thicknesses, which provides insightful perspectives of manipulating molecular orientations with graphene and spatial organization between conjugated systems, in a more quantitative manner

    High <i>K</i> Nanophase Zinc Oxide on Biomimetic Silicon Nanotip Array as Supercapacitors

    No full text
    A 3D trenched-structure metal–insulator–metal (MIM) nanocapacitor array with an ultrahigh equivalent planar capacitance (EPC) of ∼300 μF cm<sup>–2</sup> is demonstrated. Zinc oxide (ZnO) and aluminum oxide (Al<sub>2</sub>O<sub>3</sub>) bilayer dielectric is deposited on 1 μm high biomimetic silicon nanotip (SiNT) substrate using the atomic layer deposition method. The large EPC is achieved by utilizing the large surface area of the densely packed SiNT (∼5 × 10<sup>10</sup> cm<sup>–2</sup>) coated conformally with an ultrahigh dielectric constant of ZnO. The EPC value is 30 times higher than those previously reported in metal–insulator–metal or metal–insulator–semiconductor nanocapacitors using similar porosity dimensions of the support materials
    corecore