Prantik Mazumder

Durable, superhydrophobic, antireflection, and low haze glass surfaces using scalable metal dewetting nanostructuring

AbstractIn this paper we report a multifunctional nanostructured surface on glass that, for the first time, combines a wide range of optical, wetting and durability properties, including low omnidirectional reflectivity, low haze, high transmission, superhydrophobicity, oleophobicity, and high mechanical resistance. Nanostructures have been fabricated on a glass surface by reactive ion etching through a nanomask, which is formed by dewetting ultrathin metal films (< 10 nm thickness) subjected to rapid thermal annealing (RTA). The nanostructures strongly reduce the initial surface reflectivity (∼4%), to less than 0.4% in the 390–800 nm wavelength range while keeping the haze at low values (< 0.9%). The corresponding water contact angle (θc) is ∼24.5°, while that on a flat surface is ∼43.5°. The hydrophilic wetting nanostructure can be changed into a superhydrophobic and oleophobic surface by applying a fluorosilane coating, which achieves contact angles for water and oil of ∼156.3° and ∼116.2°, respectively. The multicomponent composition of the substrate (Corning® glass) enables ion exchange through the surface, so that the nanopillars’ mechanical robustness increases, as is demonstrated by the negligible changes in surface morphology and optical performance after 5,000-run wipe test. The geometry of the nanoparticles forming the nanomask depends on the metal material, initial metal thickness and RTA parameters. In particular we show that by simply changing the initial thickness of continuous Cu films we can tailor the metal nanoparticles’ surface density and size. The developed surface nanostructuring does not require expensive lithography, thus it can be controlled and implemented on an industrial scale, which is crucial for applications.

Self-referencing a single waveguide grating sensor in a micron-sized deep flow chamber for label-free biomolecular binding assays

In order to allow the design of increasingly sensitive label-free biosensors, compensation of environmental fluctuations is emerging as the dominant hurdle. The system and technique presented here utilize a unique combination of microfluidics, optical instrumentation, and image processing to provide a reference signal for each label-free biomolecular binding assay. Moreover, this reference signal is generated from the same sensor used to detect the biomolecular binding events. In this manner, the reference signal and the binding signal share nearly all common-mode noise sources (temperature, pressure, vibration, etc.) and their subtraction leaves the purest binding signal possible. Computational fluid dynamic simulations have been used to validate the flow behavior and thermal characteristics of the fluids inside the sensing region. This system has been demonstrated in simple bulk refractive index tests, as well as small molecule (biotin/streptavidin) binding experiments. The ability to perform not only simple binding but also control experiments has been discussed, indicating the wide applicability of the technique.

On the origin of excess loss in highly GeO/sub 2/-doped single-mode MCVD fibers

Index profile grading and elimination of the central dip have yielded the lowest loss ever reported for modified chemical vapor deposition-made highly GeO/sub 2/-doped single-mode fibers (1.33 dB/km at 1550 nm for /spl Delta/=2.9%). Investigation of the angular distribution of scattering has shown that much of the optical loss in such fibers is due to anomalous scattering. This scattering arises in the region of the central dip in the refractive index profile and at the core-cladding interface.

Analysis of excess scattering in optical fibers

We have systematically analyzed the excess scattering in a relatively large index optical fiber operating in the single mode regime. A mathematical model based on the theory of scattering of plane waves from a randomly perturbed core-clad interface is presented that predicts excess scattering confined within a small angle in the forward direction. An experimental system is developed that can measure the angular distribution of the scattering over ∼0°–180°. Excellent agreement between computed and measured scattering distribution is observed over multiple wavelengths and wide angular range. The spectral and angular distribution of the excess scattering and its response to the perturbation parameters are analyzed.

Mathematical analysis of the reaction–diffusion of water in glass tubes

The diffusion and reaction of water with glass tubes are mathematically analyzed. A general mathematical model is developed that takes into account the absorption of molecular water from the vapour phase on to the glass tube surface, its subsequent diffusion, and both the forward and backward reactions of formation of the silanol groups. The general solutions are obtained numerically while analytical solutions are obtained for special cases of small time or fast reaction. An approximate integral solution is obtained for the latter and it is shown that the equilibrium model with fast reaction can be cast into a simple yet accurate algebraic form which is easy to implement. The models are applied to few cases of practical importance to optical fiber processing.

Ultrathin metals and nano-structuring for photonic applications

Ultrathin materials and nano-structuring are becoming essential for the functionalization of optical surfaces. In the talk we will show how ultrathin metals can be exploited to create competitive transparent electrodes. At the same time they can be used to create nanostructured surfaces through mass scalable dewetting and etching techniques. After presenting the techniques, we will focus on the applications made possible by these materials and technologies, including self-cleaning or easy-to-clean display screens, efficient indium-free light emitting diodes and solar cells, antireflective structures for the laser industry and super-wetting surfaces for biology.

First Solar Cell Results on Novel Direct-Cast Silicon Wafers

Today’s costs of silicon wafer material of a photovoltaic module are around 30-40% of its total production costs including feedstock, ingot casting and wafering. Therefore, there is a substantial interest in the development of a kerf-loss free and thus cost-saving silicon wafer production. One method amongst various technologies for direct wafer production is the Direct-Cast Silicon (DCS) process. In this wafer casting process, molten silicon is directly crystallized on a re-usable substrate. The exploration of the solar cell efficiency potential and the characterization of DCS wafer material are of immanent relevance for future development of the DCS technology. A high efficiency solar cell process, developed for defect-rich multicrystalline silicon material at the University of Konstanz, was applied on DCS wafers. IV measurements, Light Beam Induced Current (LBIC) and electroluminescence (EL) were performed. The goal was to gain insight into the material quality and material properties, and to provide feedback for wafer production. Thereby, with 16.0%, the highest solar cell efficiency for this material could be obtained so far.

Superhydrophobic sputtered Al 2 O 3 coating films with high transparency

Summary form only given. Antireflection, self-cleaning coatings are widely used in various applications such as display panels, solar cells and optical lenses [1]. Many surfaces in nature are highly hydrophobic, making the deposition of a water drop almost impossible. Examples include the wings of butterflies and the leaves of plants. The best known illustration of a self-cleaning surface is indubitably that of the leaves of the lotus plant (Nelumbo nucifera) [2]. The key feature of the lotus leaf is a microscopically rough surface consisting of randomly distributed arrays of micropapillae with length-scale ranging from 5 to 200 microns. In order to obtain this biomimetic surface, several approaches have been proposed mostly based on sol-gel method [3,4].We have prepared superhydrophobic and highly oleophobic Al2O3 coating on fused silica substrates by the sputtering method. Deposition conditions, thickness and density of the film play critical roles in establishing the omniphobic behaviour of the substrates. By choosing the right process parameters, it is possible to form a nanoflower like structure (Fig. 1 left) of 20nm to 50nm with enough porosity to affect the surface free energy. The size of the microstructure is too small to scatter visible light leaving the material to have high transparency, 96% (Fig. 1 right), while maintaining low haze <; 2%. With the addition of a fluoropolymer coating, the water repellency became superhydrophobic with a contact angle greater than 165°. The oleophobicity of the coatings was greater than typical fluoropolymer coatings on flat surface with a contact angle equal to 130°.The capability of having high transparency, low haze and a high degree of water and oil repellency creates a great potential for an anti-reflection coating on glass. More details about the preparation method, surface structure, optical transparency, mechanical tests and contact angle for water and hexadecane of superhydrophobic Al2O3 thin film microstructures on fused SiO2 substrates, will be presented at the Conference.

CLEO ® /Europe — IQEC 2013 durable, superhydrophobic, antireflection and low haze glass surfaces using scalable metal dewetting nanostructuring

Nanostructures have been fabricated on a glass surface by reactive ion etching through a metallic nano-mask, refer to Figure 1. The metallic nano-mask is formed by dewetting ultrathin metal films (<;10nm thickness) subjected to rapid thermal annealing (RTA) [1].

Nanostructuring of Glass Surfaces Starting from Ultrathin Metals

Monolithic surface nanostructures can be formed in glass from metal dewetted nanoparticles. This results in antireflection, low scattering, superhydrophobic and mechanically resistant surfaces. The technique is industrially scalable and usable on optical fibre surfaces.