The ability to control and manipulate the polarization state of light is of crucial importance in many modern optical applications ranging from quantum technologies to biomedical sciences. Here we design, fabricate, and experimentally demonstrate an ultrathin quarter-wave plate (QWP) with a gap-surface plasmon metasurface, allowing for broadband and efficient conversion between circular and linear polarizations with ~85% average reflectance across a 200-nm-wide bandwidth in the near-infrared range (750-950 nm). Based on the QWP design, we further derive a general method to generate vector vortex beams (VVBs) that possess spatially-varied distributions of the polarization vector and carry specified orbital angular momentums (OAMs) by using space-variant QWP unit cells. The fabricated metasurface exhibits highly-efficient VVB generation over a wavelength range from 750 to 950 nm, with the average efficiencies of ~72% and ~68% for the right circularlypolarized (RCP) and left circularly-polarized (LCP) incident light, respectively. The developed approach allows one to realize compact, cost-effective and high-performance polarization converters, paving the way for ultimate miniaturization of optical devices with arbitrary control of light fields.

We observe strongly dissimilar scattering from two types of edges in hexagonal quasimonocrystalline gold flakes with thicknesses around 1 micron. We identify as the origin the interference between a direct, quasi-specular scattering and an indirect scattering process involving an intermediate surface-plasmon state. The dissimilarity between the two types of edges is a direct consequence of the three-fold symmetry around the [111]-axis and the intrinsic chirality of a face-centered cubic lattice. We propose that this effect can be used to estimate flake thickness, crystal morphology, and surface contamination.

The widespread use of transparent conductive films in modern display and solar technologies calls for engineering solutions with tunable light transmission and electrical characteristics. Currently, considerable effort is put into the optimization of indium tin oxide, carbon nanotube-based, metal grid, and nano-wire thin-films. The indium and carbon films do not match the chemical stability nor the electrical performance of the noble metals, and many metal films are not uniform in material distribution leading to significant surface roughness and randomized transmission haze. We demonstrate solution-processed masks for physical vapor-deposited metal electrodes consisting of hexagonally ordered aperture arrays with scalable aperture-size and spacing in an otherwise homogeneous noble metal thin-film that may exhibit better electrical performance than carbon nanotube-based thin-films for equivalent optical transparency. The fabricated electrodes are characterized optically and electrically by measuring transmittance and sheet resistance. The presented methods yield large-scale reproducible results. Experimentally realized thin-films with very low sheet resistance, R sh = 2.01 ± 0.14 Ω/sq, and transmittance, T = 25.7 ± 0.08 %, show good agreement with finite-element method simulations and an analytical model of sheet resistance in thin-films with ordered apertures support the experimental results and also serve to aid the design of highly transparent conductive films. A maximum Haacke number for these 33 nm thin-films, φ H = 10.7 × 10 −3 Ω −1 corresponding to T 80 % and R sh 10 Ω/sq, is extrapolated from the theoretical results. Increased transparency may be realizable using thinner metal films trading off conductivity. Nevertheless, the findings of this article indicate that colloidal lithographic patterned transparent conductive films can serve as vital components in technologies with a demand for transparent electrodes with low sheet resistance.

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We report on the structure and morphology of 5,5'-bis(naphth-2-yl)-2,2'-bithiophene (NaT2) films in bottom-contact organic field-effect transistors (OFETs) with octadecyltrichlorosilane (OTS) coated SiO gate dielectric, characterized by atomic force microscopy (AFM), grazing-incidence X-ray diffraction (GIXRD), and electrical transport measurements. Three types of devices were investigated with the NaT2 thin-film deposited either on (1) pristine SiO (corresponding to higher surface energy, 47 mJ/m) or on OTS deposited on SiO under (2) anhydrous or (3) humid conditions (corresponding to lower surface energies, 20-25 mJ/m). NaT2 films grown on pristine SiO form nearly featureless three-dimensional islands. NaT2 films grown on OTS/SiO deposited under anhydrous conditions form staggered pyramid islands where the interlayer spacing corresponds to the size of the NaT2 unit cell. At the same time, the grain size measured by AFM increases from hundreds of nanometers to micrometers and the crystal size measured by GIXRD from 30 nm to more than 100 nm. NaT2 on OTS/SiO deposited under humid conditions also promotes staggered pyramids but with smaller crystals 30-80 nm. The NaT2 unit cell parameters in OFETs differ 1-2% from those in bulk. Carrier mobilities tend to be higher for NaT2 layers on SiO (2-3 × 10 cm/(V s)) compared to NaT2 on OTS (2 × 10-1 × 10 cm/(V s)). An applied voltage does not influence the unit cell parameters when probed by GIXRD in operando.

Falcarindiol (FaDOH) is a cytotoxic and anti-inflammatory polyacetylenic oxylipin found in food plants of the carrot family (Apiaceae). FaDOH has been shown to activate PPARγ and to increase the expression of the cholesterol transporter ABCA1 in cells, both of which play an important role in lipid metabolism. Thus, a common mechanism of action of the anticancer and antidiabetic properties of FaDOH may be due to a possible effect on lipid metabolism. In this study, the effect of sub-toxic concentration (5 μM) of FaDOH inside human mesenchymal stem cells (hMSCs) was studied using white light microscopy and Raman imaging. Our results show that FaDOH increases lipid content in the hMSCs cells as well as the number of lipid droplets (LDs) and that this can be explained by increased expression of PPARγ2 as shown in human colon adenocarcinoma cells. Activation of PPARγ can lead to increased expression of ABCA1. We demonstrate that ABCA1 is upregulated in colorectal neoplastic rat tissue, which indicates a possible role of this transporter in the redistribution of lipids and increased formation of LDs in cancer cells that may lead to endoplasmic reticulum stress and cancer cell death.

M. (2018). Structural basis for a naphthyl end-capped oligothiophene with embedded metallic nanoparticles for organic field-effect transistors. Applied Physics Letters, 113(25), [251903]. https://doi.

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