Printable Nanoscopic Metamaterial Absorbers and Images with Diffraction-Limited Resolution

The fabrication of functional metamaterials with extreme feature resolution finds a host of applications such as the broad area of surface/light interaction. Non-planar features of such structures can significantly enhance their performance and tunability, but their facile generation remains a challenge. Here, we show that carefully designed out-of-plane nanopillars made of metal-dielectric composites integrated in a metal-dielectric-nanocomposite configuration, can absorb broadband light very effectively. We further demonstrate that electrohydrodynamic printing in a rapid nanodripping mode, is able to generate precise out-of-plane forests of such composite nanopillars with deposition resolutions at the diffraction limit on flat and non-flat substrates. The nanocomposite nature of the printed material allows the fine-tuning of the overall visible light absorption from complete absorption to complete reflection by simply tuning the pillar height. Almost perfect absorption (~95%) over the entire visible spectrum is achieved by a nanopillar forest covering only 6% of the printed area. Adjusting the height of individual pillar groups by design, we demonstrate on-demand control of the gray scale of a micrograph with a spatial resolution of 400 nm. These results constitute a significant step forward in ultra-high resolution facile fabrication of out-of-plane nanostructures, important to a broad palette of light design applications. nanostructures, important to a broad palette of light design applications

Three-dimensional concentration of light in deeply sub-wavelength, laterally tapered gap-plasmon nanocavities

Gap-plasmons (GP) in metal-insulator-metal (MIM) structures have shown exceptional performance in guiding and concentrating light within deep subwavelength layers. Reported designs to date exploit tapered thicknesses of the insulating layer in order to confine and focus the GP mode. Here, we propose a mechanism for the three dimensional concentration of light in planar MIM structures which exploits exclusively the lateral tapering of the front metallic layer while keeping a constant thickness of the insulating layer. We demonstrate that an array of tapered planar GP nanocavities can efficiently concentrate light in all three dimensions. A semi-analytical, one-dimensional model provides understanding of the underlying physics and approximately predicts the behavior of the structure. Three-dimensional simulations are then used to precisely calculate the optical behavior. Cavities with effective volumes as small as 10^(−5) λ^3 are achieved in an ultrathin MIM configuration. Our design is inherently capable of efficiently coupling with free-space radiation. In addition, being composed of two electrically continuous layers separated by an ultrathin dielectric spacer, it could find interesting applications in the area of active metamaterials or plasmonic photocatalysis where both electrical access and light concentration are required

Spontaneous emission enhancement of a single molecule by a double-sphere nanoantenna across an interface

We report on two orders of magnitude reduction in the fluorescence lifetime when a single molecule placed in a thin film is surrounded by two gold nanospheres across the film interface. By attaching one of the gold particles to the end of a glass fiber tip, we could control the modification of the molecular fluorescence at will. We find a good agreement between our experimental data and the outcome of numerical calculations

A planar dielectric antenna for directional single-photon emission and near-unity collection efficiency

Single emitters have been considered as sources of single photons in various contexts such as cryptography, quantum computation, spectroscopy, and metrology. The success of these applications will crucially rely on the efficient directional emission of photons into well-defined modes. To accomplish a high efficiency, researchers have investigated microcavities at cryogenic temperatures, photonic nanowires, and near-field coupling to metallic nano-antennas. However, despite an impressive progress, the existing realizations substantially fall short of unity collection efficiency. Here we report on a theoretical and experimental study of a dielectric planar antenna, which uses a layered structure for tailoring the angular emission of a single oriented molecule. We demonstrate a collection efficiency of 96% using a microscope objective at room temperature and obtain record detection rates of about 50 MHz. Our scheme is wavelength-insensitive and can be readily extended to other solid-state emitters such as color centers and semiconductor quantum dots

Job Satisfaction and its Contributing Factors in Female Faculty Members of Shahid Beheshti University of Medical Sciences

      Human resources can play a crucial role in enhancing output in different social establishments, including universities and educational systems, if they are satisfied with their job condition. Nowadays nearly half the resources belong to female employees in different organizations such as universities and educational settings. The attitude of this number of employees, including female faculty members of universities, is of special significance if the quality of work is to be enhanced in universities or other educational establishments. Bearing in mind this significance, the current study investigated job satisfaction among female faculty members at Shahid Beheshti University of Medical Sciences (SBMU) in 2008, Tehran. The assumption was that the satisfaction level of faculty member from their job could significantly enhance the quality of education and clinical care at different colleges and teaching hospitals of the university. According to the results, university authorities and managers are expected to adopt due measures to improve faculty members' satisfaction scores if they are to enhance the quality of works to meet their educational ends. As a descriptive research, the study investigated job satisfaction among female faculty members at SBMU in 2008. Altogether a total of 116 subjects, selected randomly, were asked to complete the questionnaires. The Minnesota questionnaire and the Personal and Managerial questionnaire were used to measure the satisfaction level of the participant from their career. The researchers referred to different colleges and hospitals of SBMU to ask the participants to fill out the questionnaires. Then, following the data collection procedure and questionnaire analysis, the data were subjected to numerous statistical tests such as t-test, One- way ANOVA and Multiple comparisons tests. Job satisfaction among female faculty members at SBMU was low to some extent. The main factors accounting for a rather low satisfaction score was limited welfare facilities, low salaries and unpaid arrears, improper work environment and limited promotion opportunities.  Greater attention to these variables seemed to be essential if faculty members, attitude toward their job were to be enhanced.

Detergency and its implications for oil emulsion sieving and separation

Separating petroleum hydrocarbons from water is an important problem to address in order to mitigate the disastrous effects of hydrocarbons on aquatic ecosystems. A rational approach to address the problem of marine oil water separation is to disperse the oil with the aid of surfactants in order to minimize the formation of large slicks at the water surface and to maximize the oil-water interfacial area. Here we investigate the fundamental wetting and transport behavior of such surfactant-stabilized droplets and the flow conditions necessary to perform sieving and separation of these stabilized emulsions. We show that, for water soluble surfactants, such droplets are completely repelled by a range of materials (intrinsically underwater superoleophobic) due to the detergency effect; therefore, there is no need for surface micro/nanotexturing or chemical treatment to repel the oil and prevent fouling of the filter. We then simulate and experimentally investigate the effect of emulsion flow rate on the transport and impact behavior of such droplets on rigid meshes to identify the minimum pore opening (w) necessary to filter a droplet with a given diameter (d) in order to minimize the pressure drop across the mesh and therefore maximize the filtering efficiency, which is strongly dependent on w. We define a range of flow conditions and droplet sizes where minimum droplet deformation is to be expected and therefore find that the condition of is sufficient for efficient separation. With this new understanding, we demonstrate the use of a commercially available filter--without any additional surface engineering or functionalization--to separate oil droplets from a surfactant stabilized emulsion with a flux of 11,000 L m$^{-2}$ hr$^{-1}$ bar$^{-1}$. We believe these findings can inform the design of future oil separation materials

Facile multifunctional plasmonic sunlight harvesting with tapered triangle nanopatterning of thin films

Plasmonic absorbers have recently become important for a broad spectrum of sunlight-harvesting applications exploiting either heat generation, such as in thermal photovoltaics and solar thermoelectrics, or hot-electron generation, such as in photochemical and solid state devices. So far, despite impressive progress, combining the needed high performance with fabrication simplicity and scalability remains a serious challenge. Here, we report on a novel solar absorber concept, where we demonstrate and exploit simultaneously a host of absorption phenomena in tapered triangle arrays integrated in a metal–insulator–metal configuration to achieve ultrabroadband (88% average absorption in the range of 380–980 nm), wide-angle and polarization-insensitive absorption. Furthermore, this absorber is subwavelength in thickness (260 nm) and its fabrication is based on a facile, low-cost and potentially scalable method. In addition, the geometry of our design makes it compatible for both heat and hot electron generation

Rapid-Response Low Infrared Emission Broadband Ultrathin Plasmonic Light Absorber

Plasmonic nanostructures can significantly advance broadband visible-light absorption, with absorber thicknesses in the sub-wavelength regime, much thinner than conventional broadband coatings. Such absorbers have inherently very small heat capacity, hence a very rapid response time, and high light power-to-temperature sensitivity. Additionally, their surface emissivity can be spectrally tuned to suppress infrared thermal radiation. These capabilities make plasmonic absorbers promising candidates for fast light-to-heat applications, such as radiation sensors. Here we investigate the light-to-heat conversion properties of a metal-insulator-metal broadband plasmonic absorber, fabricated as a free-standing membrane. Using a fast IR camera, we show that the transient response of the absorber has a characteristic time below 13 ms, nearly one order of magnitude lower than a similar membrane coated with a commercial black spray. Concurrently, despite the small thickness, due to the large absorption capability, the achieved absorbed light power-to-temperature sensitivity is maintained at the level of a standard black spray. Finally, we show that while black spray has emissivity similar to a black body, the plasmonic absorber features a very low infra-red emissivity of almost 0.16, demonstrating its capability as selective coating for applications with operating temperatures up to 400°C, above which the nano-structure starts to deform