Bioinspired micrograting arrays mimicking the reverse color diffraction elements evolved by the butterfly Pierella luna

Recently, diffraction elements that reverse the color sequence normally observed in planar diffraction gratings have been found in the wing scales of the butterfly Pierella luna. Here, we describe the creation of an artificial photonic material mimicking this reverse color-order diffraction effect. The bioinspired system consists of ordered arrays of vertically oriented microdiffraction gratings. We present a detailed analysis and modeling of the coupling of diffraction resulting from individual structural components and demonstrate its strong dependence on the orientation of the individual miniature gratings. This photonic material could provide a basis for novel developments in biosensing, anticounterfeiting, and efficient light management in photovoltaic systems and light-emitting diodes.United States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative (Award FA9550-09-1-0669-DOD35CAP)Alexander von Humboldt-Stiftung (Feodor Lynen Postdoctoral Research Fellowship

Fabrication and characterization of high quality factor silicon nitride nanobeam cavities

Si3N4 is an excellent material for applications of nanophotonics at visible wavelengths due to its wide bandgap and moderately large refractive index (n $\approx$ 2.0). We present the fabrication and characterization of Si3N4 photonic crystal nanobeam cavities for coupling to diamond nanocrystals and Nitrogen-Vacancy centers in a cavity QED system. Confocal micro-photoluminescence analysis of the nanobeam cavities demonstrates quality factors up to Q ~ 55,000, which is limited by the resolution of our spectrometer. We also demonstrate coarse tuning of cavity resonances across the 600-700nm range by lithographically scaling the size of fabricated devices. This is an order of magnitude improvement over previous SiNx cavities at this important wavelength range

Liquid-based gating mechanism with tunable multiphase selectivity and antifouling behaviour

Living organisms make extensive use of micro- and nanometre-sized pores as gatekeepers for controlling the movement of fluids, vapours and solids between complex environments. The ability of such pores to coordinate multiphase transport, in a highly selective and subtly triggered fashion and without clogging, has inspired interest in synthetic gated pores for applications ranging from fluid processing to 3D printing and lab-on-chip systems. But although specific gating and transport behaviours have been realized by precisely tailoring pore surface chemistries and pore geometries a single system capable of controlling complex, selective multiphase transport has remained a distant prospect, and fouling is nearly inevitable. Here we introduce a gating mechanism that uses a capillary-stabilized liquid as a reversible, reconfigurable gate that fills and seals pores in the closed state, and creates a non-fouling, liquid-lined pore in the open state. Theoretical modelling and experiments demonstrate that for each transport substance, the gating threshold—the pressure needed to open the pores—can be rationally tuned over a wide pressure range. This enables us to realize in one system differential response profiles for a variety of liquids and gases, even letting liquids flow through the pore while preventing gas from escaping. These capabilities allow us to dynamically modulate gas–liquid sorting in a microfluidic flow and to separate a three-phase air–water–oil mixture, with the liquid lining ensuring sustained antifouling behaviour. Because the liquid gating strategy enables efficient long-term operation and can be applied to a variety of pore structures and membrane materials, and to micro- as well as macroscale fluid systems, we expect it to prove useful in a wide range of applications.Engineering and Applied Science

Factors Impacting Social Commerce Use Intention

The research paper objective is to study and examine the factors influencing on social commerce use intention amongst students all over Pakistan. For this purpose, explanatory research is conducted to find out the problem which has not been studied in this context before. This is not a conclusive aid to the problems faced by social commerce businesses in Pakistan but it can help us understand the problem better. Our research is based on developed theory and explains the positive and significant relationship between the dependent variable which is intention towards usage of social commerce and independent variables which re social norms, perceived behavioral control, perceived value and attitude. The research is quantitative as it is more convenient to collect this type of data and convert it into numerical form for statistical calculation and conclusions. The data was collected through a survey on Google forms distributed to the students of Iqra University, Karachi. A total of 500 responses were found usable. In this research, correlation design is utilized to discover the connection between independent variable such as SN, PBC, PV, A and dependent variable SCUI. The theory used in this research is Social identity theory to find out how the variables effect on social commerce use intentions. By this research we came to know how does the variables attitude, perceived behavioral control, perceived value, social norms has an effect on the social commerce use intentions. There were many limitations to this investigation. To begin with of all, the time given for investigate was brief as such a detail inquire about cannot be drained a brief period of time. Furthermore, the respondents were restricted to the Karachi as it were and we may not cover the individuals of diverse cities of Pakistan

Optomechanical and photothermal interactions in suspended photonic crystal membranes

We present here an optomechanical system fabricated with novel stress management techniques that allow us to suspend an ultrathin defect-free silicon photonic-crystal membrane above a Silicon-on-Insulator (SOI) substrate with a gap that is tunable to below 200 nm. Our devices are able to generate strong attractive and repulsive optical forces over a large surface area with simple in- and out- coupling and feature the strongest repulsive optomechanical coupling in any geometry to date (g[subscript OM]/2π ≈ −65 GHz/nm). The interplay between the optomechanical and photo-thermal-mechanical dynamics is explored, and the latter is used to achieve cooling and amplification of the mechanical mode, demonstrating that our platform is well-suited for potential applications in low-power mass, force, and refractive-index sensing as well as optomechanical accelerometry.United States. Defense Advanced Research Projects Agency. (Contract N66001-09-1-2070-DOD)National Science Foundation (U.S.) (CAREER Grant

Optical bistability with a repulsive optical force in coupled silicon photonic crystal membranes

We demonstrate actuation of a silicon photonic crystal membrane with a repulsive optical gradient force. The extent of the static actuation is extracted by examining the optical bistability as a combination of the optomechanical, thermo-optic, and photo-thermo-mechanical effects using coupled-mode theory. Device behavior is dominated by a repulsive optical force which results in displacements of ≈ 1 nm/mW. By employing an extended guided resonance which effectively eliminates multi-photon thermal and electronic nonlinearities, our silicon-based device provides a simple, non-intrusive solution to extending the actuation range of micro-electromechanical devices.United States. Defense Advanced Research Projects Agency. (Contract N66001-09-1-2070-DOD

Fabrication of Diamond Nanowires for Quantum Information Processing Applications

We present a design and a top-down fabrication method for realizing diamond nanowires in both bulk single crystal and polycrystalline diamond. Numerical modeling was used to study coupling between a Nitrogen Vacancy (NV) color center and optical modes of a nanowire, and to find an optimal range of nanowire diameters that allows for large collection efficiency of emitted photons. Inductively coupled plasma (ICP) reactive ion etching (RIE) with oxygen is used to fabricate the nanowires. Drop-casted nanoparticles (including $\mathrm{Au}$, $\mathrm{SiO_{2}}$ and $\mathrm{Al_2O_3}$) as well as electron beam lithography defined spin-on glass and evaporated $\mathrm{Au}$ have been used as an etch mask. We found $\mathrm{Al_2O_3}$ nanoparticles to be the most etch resistant. At the same time FOx e-beam resist (spin-on glass) proved to be a suitable etch mask for fabrication of ordered arrays of diamond nanowires. We were able to obtain nanowires with near vertical sidewalls in both polycrystalline and single crystal diamond. The heights and diameters of the polycrystalline nanowires presented in this paper are \unit[\approx1]{\mu m} and \unit[120-340]{nm}, respectively, having a \unit[200]{nm/min} etch rate. In the case of single crystal diamond (types Ib and IIa) nanowires the height and diameter for different diamonds and masks shown in this paper were \unit[1-2.4]{\mu m} and \unit[120-490]{nm} with etch rates between \unit[190-240]{nm/min}.Comment: 11 pages, 26 figures, submitted to Diamond and related Materials; http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TWV-4Y7MM1M-1&_user=10&_coverDate=01%2F25%2F2010&_rdoc=1&_fmt=high&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=6dc58b30f4773a710c667306fc541cc