Carbon-based nanomaterials such as carbon nanotubes and graphene are excellent candidates for superhydrophobic surfaces because of their intrinsically high surface area and nonpolar carbon structure. This paper demonstrates that graphene aerogels with a silane surface modification can provide superhydrophobicity. Graphene aerogels of various concentrations were synthesized and the receding contact angle of a water droplet was measured. It is shown that graphene aerogels are hydrophobic and become superhydrophobic following the application of a fluorinated surfactant. The aerogels produced for this experiment outperform previous carbon nanomaterials in creating superhydrophobic surfaces and offer a more scalable synthetic procedure for production.

Silica nanosphere functionalizationSilica spheres of 700 nm diameter were obtained from Polysciences Inc. as a 10% (by weight) suspension in water. This suspension was filtered on a fine filtration frit, rinsed with tetrahydrofuran and acetone. The powder of spheres was washed with 10 mL of 1:1 methanol/HCl, and rinsed again with acetone. The mostly dried powder was then heated in an oven for 5 minutes at 110 °C and dried under vacuum overnight. To 25 mL toluene in a 50 mL round-bottomed flask, 786 mg of dry silica spheres were suspended and stirred. To this suspension was added 1 mL 3-aminopropyl(diethoxy)methyl silane. The suspension was stirred 72 hours, filtered on a fine frit, rinsed with toluene and dried in vacuo to yield 756 mg dry, amine-functionalized silica spheres. Langmuir-Blodgett depositionA ~1% (by weight) suspension for Langmuir-Blodgett deposition was prepared by suspending 235 mg of functionalized silica spheres in a solution of 4 mL ethanol and 17 mL methylene chloride. We first perform an isotherm measurement where we record the surface pressure of the water as a function of the surface area, which is reduced using the compression barriers of the LB trough. When the area of the trough is large, the surface pressure of the water is around 4 mN/m. The spheres are freely spread on the surface of the water. This is the so-called "gaseous" state. While the LB trough's barriers compress the spheres and reduce the area where the spheres stand on, the surface pressure slowly increases until 5 mN/m. The slope abruptly increases until 10 mN/m. This is the "liquid" state corresponding to a dense and condensed monolayer of hexagonally close packed spheres at the surface of the water. Upon further compression, the slope of the curve decreases and the monolayer collapses into multilayer structures. For our purpose, the optimal point is at the middle of the "liquid" condensed state where the spheres are well close packed and still form a monolayer. This point is reached when the surface pressure is around 7.5 mN/m. In a second step, knowing the optimal surface pressure for the deposition, we perform a dipping experiment. While the spheres are on the surface of the water in the "gaseous" state, we immerse the substrate into the LB trough. We then close the LB's barriers until the surface pressure reaches 7.5 mN/m. From that point, we slowly pull up the substrate at a rate of 1 mm/min while simultaneously keeping the surface pressure constant with a computer controlled feedback system between the electrobalance measuring of the surface pressure and the barrier moving mechanism. Consequently, the floating hexagonally close packed monolayer is adsorbed on the ITO surface. When the structure is totally removed from the water, the part that was initially immersed in the water is coated by a large area of nanoscale dielectric nanospheres on its entire surface. Transfer printing preparationPoly(vinyl alcohol) (avg. MW = 10,000 g/mol, 88% hydrolyzed, Sigma Aldrich) was spin cast from an aqueous solution containing ...

We experimentally demonstrate near-unity, unselective absorption, broadband, angle-insensitive, and polarization-independent absorption, in sparse InP nanowire arrays, embedded in flexible polymer sheets via geometric control of waveguide modes in two wire motifs: (i) arrays of tapered wires and (ii) arrays of nanowires with varying radii. Sparse arrays of these structures exhibit enhanced absorption due to strong coupling into the first order azimuthal waveguide modes of individual nanowires; wire radius thus controls the spectral region of the absorption enhancement. Whereas arrays of cylindrical wires with uniform radius exhibit narrowband absorption, arrays of tapered wires and arrays with multiple wire radii expand this spectral region and achieve broadband absorption enhancement. Herein, we present an economic, top-down lithographic/etch fabrication method that enables fabrication of multiple InP nanowire arrays from a single InP wafer with deliberate control of nanowire radius and taper. Using this method, we create sparse tapered and multiradii InP nanowire arrays and demonstrate optical absorption that is broadband (450−900 nm), angle-insensitive, and near-unity (>90%) in roughly 100 nm planar equivalence of InP. These highly absorbing sparse nanowire arrays represent a promising approach to flexible, high efficiency optoelectronic devices, such as photodetectors, solar cells, and photoelectrochemical devices.

COMMUNICATIONshadow loss, and the sheet resistance and absorption losses associated with planar layers that facilitate lateral carrier transport to the grid fi ngers. [ 22,23 ] For high effi ciency silicon heterojunction (HIT) solar cells, contact design requires a trade-off between grid fi nger resistance and the sheet resistance and transmission losses of the transparent conducting oxide (TCO)/ amorphous silicon structures coating the cell front surface. [ 24 ] In this paper, we describe a new front contact design principle that overcomes both shadowing losses and parasitic absorption without reducing the conductivity. By redirecting the scattered light incident on the front contact to the solar cell active absorber layer surface, micrometer-scale triangular crosssection grid fi ngers can perform as effectively transparent and highly conductive front contacts. Previously, researchers have designed light harvesting strings that serve to obliquely refl ect light, which is then redirected into the cell by total internal refl ection from the encapsulation layers. [ 16 ] By contrast our front contact design does not require total internal refl ection at the encapsulation layer. Furthermore in our design, the contact fi ngers are micrometer sized and can be placed very close together such that a TCO with reduced thickness can be used-and in some cases the TCO layer might possibly be omitted completely. We demonstrate with simulations and experimental results that designs utilizing effectively transparent triangular cross-section grid fi ngers rather than conventional front contacts have the potential to provide 99.86% optical transparency while ensuring effi cient lateral transport corresponding to a sheet resistance of 4.8 Ω sq −1 due to their close spacing of only 40 µm. Thus effectively transparent contacts have potential as replacements for both the front grid and TCO layer used, e.g., in HIT solar cells. While related schemes for contacts were envisioned early in the development of photovoltaics technology, [ 25 ] they have not found application in current photovoltaic technology, which is increasingly dominated by high effi ciency silicon photovoltaics. Moreover, the effectively transparent front contact design is conceptually quite general and applicable to almost any other front-contacted solar cell or optoelectronic device. For example, we obtained similar experimental results when applying our structures to InGaP-based solar cells.Figure 1 a,b shows the steady-state electric fi eld magnitude distribution of a freestanding triangular contact and a fl at contact, respectively, with 550 nm monochromatic plane wave illumination normally incident at the top of the simulation cell. For planar grid fi ngers, part of the incident light is refl ected back toward the incidence direction, as is apparent from the high electric fi eld density above the contact plane. By contrast, the triangular cross-section grid fi nger does not exhibit a similar back refl ection, as indicated by the lack of an increased electric

Rapid advances in image sensor technology have generated a mismatch between the small size of image sensor pixels and the achievable filter spectral resolution. This mismatch has prevented the realization of chip-based image sensors with simultaneously high spatial and spectral resolution. We report here a concept that overcomes this tradeoff, enabling high spectral resolution (transmission FWHM < 31 nm) filters with subwavelength dimensions operating at optical and near infrared wavelengths. An inverse design methodology was used to realize a new type of plasmonic cavity that efficiently couples an in-plane Fabry-Perot resonator to a single plasmonic slit that supports surface plasmon polaritons. This design principle, combined with a new metal imprinting method that yields metallic nanostructures with both top and bottom surfaces that are extremely smooth, enabled demonstration of high spectral resolution transmission filters with smaller area than any previously reported.