Solar energy represents one of the most abundant and yet least harvested sources of renewable energy. In recent years, tremendous progress has been made in developing photovoltaics that can be potentially mass deployed. Of particular interest to cost-effective solar cells is to use novel device structures and materials processing for enabling acceptable efficiencies. In this regard, here, we report the direct growth of highly regular, single-crystalline nanopillar arrays of optically active semiconductors on aluminium substrates that are then configured as solar-cell modules. As an example, we demonstrate a photovoltaic structure that incorporates three-dimensional, single-crystalline n-CdS nanopillars, embedded in polycrystalline thin films of p-CdTe, to enable high absorption of light and efficient collection of the carriers. Through experiments and modelling, we demonstrate the potency of this approach for enabling highly versatile solar modules on both rigid and flexible substrates with enhanced carrier collection efficiency arising from the geometric configuration of the nanopillars.
Plasmonic color filtering has provided a range of new techniques for "printing" images at resolutions beyond the diffraction-limit, significantly improving upon what can be achieved using traditional, dye-based filtering methods. Here, a new approach to high-density data encoding is demonstrated using full color, dual-state plasmonic nanopixels, doubling the amount of information that can be stored in a unit-area. This technique is used to encode two data sets into a single set of pixels for the first time, generating vivid, near-full sRGB (standard Red Green Blue color space)color images and codes with polarization-switchable information states. Using a standard optical microscope, the smallest "unit" that can be read relates to 2 × 2 nanopixels (370 nm × 370 nm). As a result, dual-state nanopixels may prove significant for long-term, high-resolution optical image encoding, and counterfeit-prevention measures. over their microscale, dye-based counterparts. Chief among these are their subwavelength dimensions (leading to ultradense, ultrathin pixel arrays), and their long-term environmental stability (they do not degrade or fade over time due to radiation exposure). As a result, plasmonic filters have been positioned as new technological solutions for subwavelength color printing, [1,4,[7][8][9]12] anticounterfeiting measures, [19,20] and RGB splitting for image sensors; [2,17,21,22] thus representing one of the most promising, technologically relevant areas of current plasmonic research activity. Here, we explore a new application of polarizationcontrolled plasmonic filters: dual output, full-color optical image encoding. Recent developments in the engineering and manipulation of materials on the nanoscale have given rise to a number of new techniques with the potential for physically encoding data and images into optically readable volumes and surfaces. [23,24] Using semiconductor quantum dots, [25][26][27] graphene, [28] and various super-resolution lithography techniques, [29][30][31][32][33][34] researchers are demonstrating novel 2D and 3D techniques that may enable the next generation of optical storage and encoding technologies. Plasmonic particles and filters have also seen applications in these research areas, with the aforementioned image encoding examples having been joined by demonstrations of their use in optical data storage. [23,24,[35][36][37] Here, we show a new utilization of image encoding using polarization multiplexed plasmonic filters, where, unlike previous studies that employed color or position switching in fixed images, [14,38] we show that two arbitrary, full-color images can be encoded into a single array of pixels. Our individual pixels are comprised of asymmetric cross-shaped nanoapertures in a thin film of aluminum. Each aperture is engineered to exhibit two independent plasmonic resonances which can be tuned across the sRGB (standard Red Green Blue) color-space (a single pixel can be encoded with any two arbitrary colors). We go on to show that by using the smallest visible unit ...
The reflection and refraction of light at a dielectric interface gives rise to forces due to changes in the photon momentum. At the microscopic level, these forces are sufficient to trap and rotate microscopic objects. Such forces may have a profound impact in the emergent area of microfluidics, where there is the desire to process minimal amounts of analyte. This places stringent criteria on the ability to pump, move and mix small volumes of fluid, which will require the use of micro-components and their controlled actuation. We demonstrate the modelling, fabrication and rotation of microgears based on the principle of form birefringence. Using a geometric anisotropy (a one-dimensional photonic crystal etched into the microgear), we can fabricate microgears of known birefringence, which may be readily rotated by manipulating the input polarization in a standard optical trap. This methodology offers a new and powerful mechanism for generating a wide range of microfabricated machines, such as micropumps, that may be driven by purely optical control.
We introduce NanoPen, a novel technique for low optical power intensity, flexible, real-time reconfigurable, and large-scale light-actuated patterning of single or multiple nanoparticles such as metallic spherical nanocrystals, and one-dimensional nanostructures such as carbon nanotubes. NanoPen is capable of dynamically patterning nanoparticles over thousands of μm 2 areas with light intensities <10 W/cm 2 (using a commercial projector) within seconds. Various arbitrary nanoparticle patterns and arrays (including a 10×10 array covering a 0.025 mm 2 area) are demonstrated using this capability. One application of NanoPen is presented through the creation of surface-enhanced Raman spectroscopy (SERS) hot-spots by patterning gold nanoparticles of 90 nm diameters with enhancement factors exceeding 10 7 and pico-molar concentration sensitivities.The ability to pattern nanostructures has important applications in medical diagnosis 1,2 , sensing 3 , nano-and optoelectronic device fabrication 4,5 , nanostructure synthesis 6 , and photovoltaics 7 . Several techniques such as dip-pen nanolithography [8][9][10][11][12][13] , nanofabrication 14 , contact printing [15][16][17][18] , self-assembly 19,20 , and Langmuir-Blodgett 21 have been used to pattern nanostructures. However, these techniques lack the capability to create real-time reconfigurable patterns without the use of complicated instrumentation or processing steps. Various optical patterning techniques [22][23][24][25][26] have tried to overcome this challenge. Optical patterning of nanoparticles has been achieved previously by actuating an indium-tin oxide (ITO) layer as a photoconductive material and generating local current densities to concentrate the nanoparticles. However, these methods suffer from a slow patterning process 22 (several minutes to hours) or they require very high optical intensities 23 (∼10 5 W/cm 2 ) to pattern the nanostructures. These limitations prevent the widespread application of such techniques. Alternatively, optical tweezers have been used to manipulate and permanently assemble nanostructures onto the substrate 24,25 . Moreover, optical tweezers have been combined with local heating of nanoparticles to create convective flows for collection and patterning of particles 26 . However, optical tweezers are also limited to using very high optical intensities 32,33 and electrothermal (ET) 34 flow. In this paper, we report the novel use of OET optofluidic platform for "directly writing" patterns of nanoparticles. We call this novel technique NanoPen. NanoPen uses various electrokinetic forces (DEP, LACE, and ET) to collect and permanently immobilize nanoparticles on the OET surface. NanoPen can be operated to collect and immobilize single and multiple nanoparticles such as spherical metallic nanocrystals and one-dimensional nanostructures such as multi-wall carbon nanotubes. We would like to note that the name NanoPen refers to a method for patterning nanoparticles (a Nanoparticle Pen) and does not mean nanoscale positioning accu...
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