Superenhancers: Novel opportunities for nanowire optoelectronics

Cataloged from PDF version of article.Nanowires play a crucial role in the development of new generation optoelectronic devices ranging from photovoltaics to photodetectors, as these designs capitalize on the low material usage, utilize leaky-mode optical resonances and possess high conversion efficiencies associated with nanowire geometry. However, their current schemes lack sufficient absorption capacity demanded for their practical applicability, and more efficient materials cannot find widespread usage in these designs due to their rarity and cost. Here we suggest a novel and versatile nanoconcentrator scheme utilizing unique optical features of non-resonant Mie (NRM) scattering regime associated with low-index structures. The scattering regime is highly compatible with resonant Mie absorption effect taking place in nanowire absorbers. This technique in its optimized forms can provide up to 1500% total absorption enhancement, 400-fold material save and is suitable for large-area applications with significant area preservation compared to thin-film of same materials. Proposed superenhancer concept with its exceptional features such as broadband absorption enhancement, polarization immunity and material-independent manner paves the way for development of efficient nanowire photosensors or solar thermophotovoltaic devices and presents novel design opportunities for self-powered nanosystems

Biomimicry of multifunctional nanostructures in the neck feathers of mallard (Anas platyrhynchos L.) drakes

Cataloged from PDF version of article.Biological systems serve as fundamental sources of inspiration for the development of artificially colored devices, and their investigation provides a great number of photonic design opportunities. While several successful biomimetic designs have been detailed in the literature, conventional fabrication techniques nonetheless remain inferior to their natural counterparts in complexity, ease of production and material economy. Here, we investigate the iridescent neck feathers of Anas platyrhynchos drakes, show that they feature an unusual arrangement of two-dimensional (2D) photonic crystals and further exhibit a superhydrophobic surface, and mimic this multifunctional structure using a nanostructure composite fabricated by a recently developed top-down iterative size reduction method, which avoids the above-mentioned fabrication challenges, provides macroscale control and enhances hydrophobicity through the surface structure. Our 2D solid core photonic crystal fibres strongly resemble drake neck plumage in structure and fully polymeric material composition, and can be produced in wide array of colors by minor alterations during the size reduction process

Non-resonant Mie scattering: Emergent optical properties of core-shell polymer nanowires

Cataloged from PDF version of article.We provide the in-depth characterization of light-polymer nanowire interactions in the context of an effective Mie scattering regime associated with low refractive index materials. Properties of this regime sharply contrast with these of resonant Mie scattering, and involve the formation of strictly forward-scattered and coupling-free optical fields in the vicinity of core-shell polymer nanowires. Scattering from these optical fields is shown to be non-resonant in nature and independent from incident polarization. In order to demonstrate the potential utility of this scattering regime in one-dimensional (1D) polymeric nanostructures, we fabricate polycarbonate (PC) -polyvinylidene difluoride (PVDF) core-shell nanowires using a novel iterative thermal drawing process that yields uniform and indefinitely long core-shell nanostructures. These nanowires are successfully engineered for novel nanophotonics applications, including size-dependent structural coloration, efficient light capture on thin-film solar cells, optical nano-sensors with ultrahigh sensitivity and a mask-free photolithography method suitable for the straightforward production of 1D nanopatterns

Tailoring self-organized nanostructured morphologies in kilometer-long polymer fiber

Cataloged from PDF version of article.While nanowires and nanospheres have been utilized in the design of a diverse array of nanoscale devices, recent schemes frequently require nanoscale architectures of higher complexity. However, conventional techniques are largely unsatisfactory for the production of more intricate nanoscale shapes and patterns, and even successful fabrication methods are incompatible with large-scale production efforts. Novel top-down, iterative size reduction (ISR)-mediated approaches have recently been shown to be promising for the production of high-throughput cylindrical and spherical nanostructures, though more complex architectures have yet to be created using this process. Here we report the presence of a hitherto-undescribed transitory region between nanowire and nanosphere transformation, where a diverse array of complex quasi one-dimensional nanostructures is produced by Rayleigh-Plateau instability-mediated deformation during the progress of a combined ISR/thermal instability technique. Temperature-based tailoring of architecturally diverse, indefinitely long, globally parallel, complex nanostructure arrays with high uniformity and low size variation facilitates the development of in-fiber or free-standing nanodevices with significant advantages over on-chip devices

Room temperature large-area nanoimprinting for broadband biomimetic antireflection surfaces

Cataloged from PDF version of article.Ordered arrays of subwavelength hydrogen silsesquioxane (HSQ) nanorods on glass substrates are fabricated using room temperature nanoimprint lithography and anodized aluminum oxide membranes. Moth-eye type nanorod arrays exhibited superior omnidirectional antireflection characteristics in visible wavelengths. The ellipsometric measurements revealed that average specular reflection is remaining below 1% up to 55 degrees incidence angles. Transmission measurements at normal incidence resulted in significant increase in transmitted light intensity with respect to plain glass. Simulations showed that up to 99% transmission could be obtained from double sided tapered HSQ nanorod arrays on HSQ thin film and glass substrates. Achieving large-area, broadband and omnidirectional antireflective surfaces on glass pave the way for applications including photovoltaics. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3657766

Structural Coloring in Large Scale Core-Shell Nanowires

Cataloged from PDF version of article.We demonstrated two complementary size-dependent structural coloring mechanisms, interference and scattering, in indefinitely long core-shell nanowire arrays. The unusual nanostructures are comprised of an amorphous semiconducting core and a polymer shell layer with disparate refractive indices but with similar thermomechanical properties. Core-shell nanowires are mass produced from a macroscopic semiconductor rod by using a new top-to-bottom fabrication approach based on thermal size reduction. Nanostructures with diameters from 30 to 200 nm result in coloration that spans the whole visible spectrum via resonant Mie scattering. Nanoshell coloration based on thin film interference is proposed as a structural coloration mechanism which becomes dominant for nanowires having 700-1200 nm diameter. Controlled color generation in any part of visible and infrared spectral regions can be achieved by the simple scaling down procedure. Spectral color generation in mass-produced uniform core-shell nanowire arrays paves the way for applications such as spectral authentication at nanoscale, light-scattering ingredients in paints and cosmetics, large-area devices, and infrared shielding

Nanosprings harvest light more efficiently

Nanotechnology presents versatile architectural designs for the purpose of utilization as a building block of 1D optoelectronic nanodevices because current nanowire-based schemes require more effective solutions for low absorption capacity of nanoscale volumes. We report on the potential of nanospring absorbers as an alternative light-harvesting platform with significant advantages over conventional nanowires. Absorption capacity of nanospring geometry is found to be superior to cylindrical nanowire shape. Unlike nanowires, they are able to trap a larger amount of light thanks to characteristic periodic behavior that boosts light collection for the points matched with Mie resonances. Moreover, nanospring shape supplies compactness to a resulting device with area preservation as high as twofold. By considering that a nanospring array with optimal periods yields higher absorption than individual arrangements and core-shell designs, which further promote light collection due to unique antireflection features of shell layer, these nanostructures will pave the way for the development of highly efficient self-powered nanosystems. © 2015 Optical Society of America

Iterative size reduction technique for optical nanostructures

One-dimensional optical nanostructures are mass produced from a macroscopic semiconductor rod by using a new top-to-bottom fabrication approach. These nanostructures, which can be easily scaled up to 2D and 3D, exhibit sizedependent double coloration mechanisms. © OSA 2012

Soft biomimetic tapered babostructures for large-area antireflective surfaces and SERS sensing

Cataloged from PDF version of article.We report a facile fabrication method for the fabrication of functional large area nanostructured polymer films using a drop casting technique. Reusable and tapered silicon molds were utilized in the production of functional polymers providing rapid fabrication of the paraboloid nanostructures at the desired structural heights without the requirement of any complex production conditions, such as high temperature or pressure. The fabricated polymer films demonstrate promising qualities in terms of antireflective, hydrophobic and surface enhanced Raman spectroscopy (SERS) features. We achieved up to 92% transmission from the single-side nanostructured polymer films by implementing optimized nanostructure parameters which were determined using a finite difference time domain (FDTD) method prior to production. Large-area nanostructured films were observed to enhance the Raman signal with an enhancement factor of 4.9 x 10(6) compared to bare film, making them potentially suitable as freestanding SERS substrates. The utilized fabrication method with its demonstrated performances and reliable material properties, paves the way for further possibilities in biological, optical, and electronic applications

Superhydrophobic and Omnidirectional Antifreflective Surfaces from Nanostructured Ormosil Colloids

Cataloged from PDF version of article.A large-area superhydrophobic and omnidirectional antireflective nanostructured organically modified silica coating has been designed and prepared. The coating mimics the self-cleaning property of superhydrophobic lotus leaves and omnidirectional broad band antireflectivity of moth compound eyes, simultaneously. Water contact and sliding angles of the coating are around 160 and 10, respectively. Coating improves the transmittance of the glass substrate around 4%, when coated on a single side of a glass, in visible and near-infrared region at normal incidence angles. At oblique incidence angles (up to 60) improvement in transmission reaches to around 8%. In addition, coatings are mechanically stable against impact of water droplets from considerable heights. We believe that our inexpensive and durable multifunctional coatings are suitable for stepping out of the laboratory to practical outdoor applications