Ag nanowire with the receiving and transmitting Ag bow tie antenna pairs at its incident and emission ends was patterned on the SiO(2) substrate to realize an enhanced surface plasmon emission with a factor of 45 compared to the single Ag nanowire without antenna pairs. The receiving and transmitting bow tie antenna pairs enhanced the plasmon coupling and emission efficiencies of the Ag nanowire. And the maximum plasmon emission sensitively depended on the length of Ag nanowire, the arm length of bow tie antennas, and the incident angle of optical excitation. This enhanced plasmon emission was confirmed by finite-difference time-domain simulations and explored with analytical calculations using the impedance matching theory at optical frequency.

Ordered configurations of hydrogen adatoms on graphene have long been proposed, calculated and searched for. Here we report direct observation of several ordered configurations of H adatoms on graphene by scanning tunneling microscopy. On the top side of the graphene plane, H atoms in the configurations appear to stick to carbon atoms in the same sublattice. A gap larger than 0.6 eV in the local density of states of the configurations was revealed by scanning tunneling spectroscopy measurements. These findings can be well explained by density functional theory calculations based on double sided H configurations. In addition, factors that may influence H ordering are discussed.

With the rapid increase in Android device popularity, the capabilities that the diverse user base demands from Android have significantly exceeded its original design. As a result, people have to seek ways to obtain the permissions not directly offered to ordinary users. A typical way to do that is using the Android Debug Bridge (ADB), a developer tool that has been granted permissions to use critical system resources. Apps adopting this solution have combined tens of millions of downloads on Google Play. However, we found that such ADB-level capabilities are not well guarded by Android. A prominent example we investigated is the apps that perform programmatic screenshots, a much-needed capability Android fails to support. We found that all such apps in the market inadvertently expose this ADB capability to any party with the INTERNET permission on the same device. With this exposure, a malicious app can be built to stealthily and intelligently collect sensitive user data through screenshots. To understand the threat, we built Screenmilker, an app that can detect the right moment to monitor the screen and pick up a user's password when she is typing in real time. We show that this can be done efficiently by leveraging the unique design of smartphone user interfaces and its public resources. Such an understanding also informs Android developers how to protect this screenshot capability, should they consider providing an interface to let third-party developers use it in the future, and more generally the security risks of the ADB workaround, a standard technique gaining popularity in app development. Based on the understanding, we present a mitigation mechanism that controls the exposure of the ADB capabilities only to authorized apps. Permission to freely reproduce all or part of this paper for noncommercial purposes is granted provided that copies bear this notice and the full citation on the first page. Reproduction for commercial purposes is strictly prohibited without the prior written consent of the Internet Society, the first-named author (for reproduction of an entire paper only), and the author's employer if the paper was prepared within the scope of employment.

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Highly corrugated, stepped surfaces present regular 1D arrays of binding sites, creating a complex, heterogeneous environment to water. Rather than decorating the hydrophilic step sites to form 1D chains, water on stepped Cu(511) forms an extended 2D network that binds strongly to the steps but bridges across the intervening hydrophobic Cu(100) terraces. The hydrogen-bonded network contains pentamer, hexamer, and octomer water rings that leave a third of the stable Cu step sites unoccupied in order to bind water H down close to the step dipole and complete three hydrogen bonds per molecule.

SUMMARYProperties of prey sensory systems are important factors shaping the design of signals generated by organisms exploiting them. In this study we assessed how prey sensory preference affected the exploiter signal design by investigating the evolutionary relationship and relative attractiveness of linear and cruciate form web decorations built by Argiope spiders. Because insects have an innate preference for bilaterally symmetrical patterns, we hypothesized that cruciate form decorations were evolved from linear form due to their higher visual attractiveness to insects. We first reconstructed a molecular phylogeny of the Asian members of the genus Argiope using mitochondrial markers to infer the evolutionary relationship of two decoration forms. Results of ancestral character state reconstruction showed that the linear form was ancestral and the cruciate form derived. To evaluate the luring effectiveness of two decoration forms, we performed field experiments in which the number and orientation of decoration bands were manipulated. Decoration bands arranged in a cruciate form were significantly more attractive to insects than those arranged in a linear form, no matter whether they were composed of silks or dummies. Moreover, dummy decoration bands arranged in a cruciate form attracted significantly more insects than those arranged in a vertical/horizontal form. Such results suggest that pollinator insects' innate preference for certain bilateral or radial symmetrical patterns might be one of the driving forces shaping the arrangement pattern of spider web decorations.

Planar plasmonic focusing of surface plasmon polaritons (SPPs) by an in-plane nanostructure consisting of Ag-column arrays and an in-plane Fresnel zone plate (FZP) with a Cu grating underneath for energy compensation was demonstrated. The CdS-based hybrid plasmonic waveguide generated in the Ag-column arrays was characterized with a scanning near-field optical microscope. By using the FZP focusing structure, the SPP modes were separated from the CdS photoluminescence background and focused at the FZP focus area, and in this way, were used as the source for the SPP waveguide. Finite-difference time-domain simulations correspond with the experimental observations, suggesting that this is indeed an effective approach to control SPP coupling within the dielectric nanoribbon waveguide.

Local or global ordering of chiral molecules at a surface is a key step in both chiral separation and heterogeneous enantioselective catalysis. Using density functional theory and scanning probe microscopy results, we find that the accepted structural model for the well known bitartrate on Cu(110) chiral system cannot account for the chiral segregation observed. Instead, we show that this strongly bound, chiral adsorbate changes its adsorption footprint in response to the local environment. The flexible adsorption geometry allows bitartrate to form stable homochiral trimer chains in which the central molecule restructures from a rectangular to an oblique footprint, breaking its internal hydrogen bonds in order to form strong intermolecular hydrogen bonds to neighbouring adsorbates. Racemic structures containing mixed enantiomers do not form strong hydrogen bonds, providing the thermodynamic driving force for the chiral separation that is observed experimentally. This result shows the importance of considering the dynamical response of molecular adsorption footprints at the surface in directing chiral assembly and segregation. The ability of strongly-chemisorbed enantiomers to change footprint depending on the local adsorption environment indicates that supramolecular assemblies at surfaces may exhibit more complex dynamical behaviour than hitherto suspected, which, ultimately, could be tailored to lead to environment and stimuli-responsive chiral surfaces.