Direct patterning of oxides: From nanoimprint lithography to self-assembly of block copolymers

Ph.DDOCTOR OF PHILOSOPH

Robust Superamphiphobic Film from Electrospun TiO₂ Nanostructures

Rice-shaped TiO₂ nanostructures are fabricated by electrospinning for creating a robust superamphiphobic coating on glass substrates. The as-fabricated TiO₂ nanostructures (sintered at 500 °C) are superhydrophilic in nature which upon silanization turn into superamphiphobic surface with surface contact angle (SCA) values achieved using water (surface tension, γ = 72.1 mN/m) and hexadecane (surface tension, γ = 27.5 mN/m) being 166° and 138.5°, respectively. The contact angle hysteresis for the droplet of water and hexadecane are measured to be 2 and 12°, respectively. Thus, we have successfully fabricated superior self-cleaning coatings that possess exceptional superamphiphobic property by employing a simple, cost-effective, and scalable technique called electrospinning. Furthermore, the coating showed good mechanical and thermal stability with strong adherence to glass surface, thus revealing the potential for real applications

Thermo-solvent annealing of polystyrene-polydimethylsiloxane block copolymer thin films

10.1021/acsmacrolett.5b00108ACS Macro Letters45500-50

Large Area Plasmonic Color Palettes with Expanded Gamut Using Colloidal Self-Assembly

Optical resonances in metallic nanostructures are promising in enabling high-resolution plasmonic color prints, color filters, and in rendering colors for plastic consumer products. However, nanostructure patterning approaches have relied on charged-particle beam lithography, with limited throughput. For the purpose of visually evaluating colors spanning a large parameter space, it is important to develop a rapid and cost-effective approach to patterning large areas. The speed at which the parameter space is explored experimentally needs to be comparable to the time it takes to run full electromagnetic simulations. Here, we used a bottom-up approach to cost-effectively create periodic nanostructures on centimeter-scale samples. Upon further processing, this approach produced more complex geometries, such as rings and domes, compared to the standard structures consisting of metal disks. By adjusting various geometric parameters, vivid colors with an expanded gamut were obtained

Fabrication of highly uniform and porous MgF2 anti-reflective coatings by polymer-based sol-gel processing on large-area glass substrates

10.1088/0957-4484/24/50/505201Nanotechnology2450-NNOT

UV-solvent annealing for morphology and orientation control in self-assembled PS-PDMS thin films

The response of polystyrene-block-poly(dimethylsiloxane) (PS-b-PDMS) thin films to UV exposure during solvent vapor annealing is described, in order to improve their applicability in nanolithography and nanofabrication. Two BCPs were examined, one with the PS block as majority (f[subscript PS] = 68%, M[subscript n] = 53 kg mol⁻¹), the other with PDMS block as majority (f[subscript PDMS] = 67%, M[subscript n] = 44 kg mol⁻¹). A 5 min UV irradiation was applied during solvent vapor annealing which led to both partial crosslinking of the polymer and a small increase in the temperature of the annealing chamber. This approach was effective for improving the correlation length of the self-assembled microdomain arrays and in limiting subsequent flow of the PDMS in the PDMS-majority BCP to preserve the post-anneal morphology. Ordering and orientation of microdomains were controlled by directed self-assembly of the BCPs in trench substrates. Highly-ordered perpendicular nanochannel arrays were obtained in the PDMS-majority BCP

Amorphous ruthenium nanoparticles for enhanced electrochemical water splitting

© 2015 IOP Publishing Ltd.This paper demonstrates an optimized fabrication of amorphous Ru nanoparticles through annealing at various temperatures ranging from 150 to 700 °C, which are used as water oxidation catalyst for effective electrochemical water splitting under a low overpotential of less than 300 mV. The amorphous Ru nanoparticles with short-range ordered structure exhibit an optimal and stable electrocatalytic activity after annealing at 250 °C. Interestingly, a small quantity of such Ru nanoparticles in a thin film on fluorine-doped tin oxide glass is also effectively driven by a conventional crystalline silicon solar cell that has excellent capability for harvesting visible light. Remarkably, it achieves an overall solar-to-hydrogen efficiency of 11.3% in acidic electrolyte.Link_to_subscribed_fulltex

Multiscale Ommatidial Arrays with Broadband and Omnidirectional Antireflection and Antifogging Properties by Sacrificial Layer Mediated Nanoimprinting

Moth’s eye inspired multiscale ommatidial arrays offer multifunctional properties of great significance in optoelectronic devices. However, a major challenge remains in fabricating these arrays on large-area substrates using a simple and scalable technique. Here we present the fabrication of these multiscale ommatidial arrays over large areas by a distinct approach called sacrificial layer mediated nanoimprinting, which involves nanoimprinting aided by a sacrificial layer. The fabricated arrays exhibited excellent pattern uniformity over the entire patterned area. Optimum dimensions of the multiscale ommatidial arrays determined by the finite-difference time domain simulations served as the design parameters for replicating the arrays on glass. A broadband suppression of reflectance to a minimum of ∼1.4% and omnidirectional antireflection for highly oblique angles of incidence up to 70° were achieved. In addition, superhydrophobicity and superior antifogging characteristics enabled the retention of optical properties even in wet and humid conditions, suggesting reliable optical performance in practical outdoor conditions. We anticipate that these properties could potentially enhance the performance of optoelectronic devices and minimize the influence of in-service conditions. Additionally, as our technique is solely nanoimprinting-based, it may enable scalable and high-throughput fabrication of multiscale ommatidial arrays