Rohit Kothari

Mesoporous silica/nanoparticle composites prepared by 3-D replication of highly filled block copolymer templates

The incorporation of iron platinum (FePt) nanoparticles (NPs) within the walls of mesoporous silica was achieved at high NP loadings using highly filled amphiphilic poly(ethylene oxide-b-propylene oxide-b-ethylene oxide) (Pluronic®) copolymer templates prepared by exploiting selective hydrogen bonding between the pre-synthesized nanoparticles and the hydrophilic portion of the block copolymer. The mesoporous silica/NP composites were then synthesized by means of phase selective condensation of tetraethylorthosilicate (TEOS) within the NP loaded block copolymer templates dilated with supercritical carbon dioxide (scCO2) followed by calcination. The resulting mesoporous silica composites were prepared at nanoparticle loadings as high as 25 wt% relative to the template (15 wt% relative to mesoporous silica) and were characterized by electron microscopy, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The method described in this report is general and may be applied to a variety of NPs for encapsulation within the pore walls of mesoporous silica.

Direct imprint patterning of 2-D and 3-D nanoparticle/polymer hybrid and crystalline metal oxide structures for printed optical, electronic, and energy devices

Nanoimprint lithography (NIL) offers high precision patterning of structures as small as 50 nm using wafer-based or roll-to-roll process platforms, however current resist systems offer little functionality. We developed hybrid UV-NIL resists containing up to 90 wt. % nanoparticles with excellent optical transparency for direct patterning of device structures including a readily scalable print, lift, and stack approach for producing large-area, 3D photonic crystal (PC) structures and optical gratings. We have also extended the NIL approach to directly print dimensionally stable metal oxide nanostructures using inks containing high concentrations of crystalline nanoparticles.

Wavelength-Selective Three-Dimensional Thermal Emitters via Imprint Lithography and Conformal Metallization

Metallic photonic crystals (MPCs) exhibit wavelength-selective thermal emission enhancements and are promising thermal optical devices for various applications. Here, we report a scalable fabrication strategy for MPCs suitable for high-temperature applications. Well-defined double-layer titanium dioxide (TiO2) woodpile structures are fabricated using a layer-by-layer soft-imprint method with TiO2 nanoparticle ink dispersions, and the structures are subsequently coated with high purity, conformal gold films via reactive deposition from supercritical carbon dioxide. The resulting gold-coated woodpile structures are effective MPCs and exhibit emissivity enhancements at a selective wavelength. Gold coatings deposited using a cold-wall reactor are found to be smoother and result in a greater thermal emission enhancement compared to those deposited using a hot-wall reactor.