Nanotube film-enhanced 3-D photoanode for application in microsystems technology

Surface area plays an important factor in the energy conversion performance of solar cells. It has also emerged as a critical factor in the evolution of high-performance micro-electro-mechanical systems (MEMS) and multifunctional microstructures most of which will benefit from integrated on-chip solar power. Presented here is the hierarchical fabrication and characterization of TiO2 nanotubes on non-planar 3-dimensional microstructures for enhanced performance of the photoanode in dye-sensitized solar cells (DSSCs). The objective is to increase photoanode performance within a 1 cm2 lateral footprint area by increasing the vertical surface area through the formation of TiO2 nanotubes on 3-D microstructures. In the interest of the seamless integration of DSSCs into MEMS applications, bulk micromachining using wet-etching was employed to fabricate 3-D microstructures in silicon. Anodization was used to form titania nanotubes within sputtered titanium thin films. Film quality, adhesion, and the formation of the nanotubes are discussed. Nanotubes with approximate outer diameter dimensions of 180 nm, inner diameter of 75 nm, and heights of 340 nm on 15 um-sq x 15 um-deep micro-wells were fabricated resulting in more than 5 times the increase in surface area over planar surfaces. Grazing incidence diffraction measurements were used to negate the substrate contribution while providing a detailed in-depth profile analysis to validate the preferred polycrystalline rutile and anatase orientation on the 3D surface-texture photoanode. The increase in surface area resulted in an equal increase in dye adsorption capacity and a 78% reduction in spectral reflectance. The optical enhancement of this hierarchically-structured nanotube film-enhanced (NFE) 3D photoanode correlated well to a high current density increase 10 times that of its flat counterpart. Fabrication of a DSSC utilizing the NFE 3D photoanode was also performed and tested for its photocurrent performance under solar simulation. Results suggest that although the surface-textured anode increases the performance of the photoanode, efficiency of the overall cell significantly depends on the architecture. A conceptual implementation of the NFE 3-D photoanode into microsystems is also discussed along with conclusions and suggestions for future work

Carbonated 3D-Printable Polymer Composite for Thermo-Mechanically Stable Applications

In this report, we investigate the infusion of carbon dioxide into a 3D-printable photosensitive polymer. The result is a carbonated polymer composite material. In use, polymer composite materials expect to succeed where ordinary polymers and metals fail. This is due to the tailorability of composite materials for specific applications. Usually, micro/nano-particulates are embedded as fillers within a polymer matrix, enhancing the overall material properties. Here, carbon dioxide (CO2) microbubbles serve as the filler within a nylon-like polymer matrix. Additive manufacturing by stereolithography (SLA) of the carbonated polymer composite proved possible using the digital light projection (DLP) 3D printing technique. Post-heat treatment using thermogravimetric analysis of the samples at elevated temperatures resulted in a 33% mass reduction, indicative of nearly complete solvent removal and curing. An initial increase in polymer carbonation duration showed a 16% increase in porosity, more stable thermal profiles, and a 40% decrease in specific heat capacity. Thermo-mechanical compressive tests on an optimal carbonated sample revealed a 70% increase in compressive strength over its neat counterpart and a peak modulus at 50 °C of 60 MPa. Such 3D-printable carbonated polymer composites may find use in applications requiring high strength-to-weight ratio thermally stable polymers and applications requiring a versatile and convenient storage medium for on-demand CO2 deposition or supercritical fluid phase transformation

Macrocycle-derived functional xanthenes and progress towards concurrent detection of glucose and fructose

The detection of saccharides in biological media is of great current importance for the monitoring of disease states. We have previously reported that solutions of boronic acid-functionalized macrocycles form acyclic oligomeric materials in situ. The oligomers contain fluorescent xanthene moieties. Current efforts are aimed at modulating the spectroscopic responses of these materials for the analysis of specific sugars. We describe conditions whereby the xanthene boronic acids exhibit high colorimetric fructose selectivity. In contrast, at physiological levels selective glucose monitoring can be achieved via fluorescence. Additionally, we describe a method which exhibits promise for detecting both glucose and fructose at dual wavelengths in the UV-Vis region. Mechanistic rationale for each of these findings is presented

Visual Detection of Cysteine and Homocysteine

The determination of cysteine and homocysteine levels is of great current interest for the monitoring of desease states. A new colorimetric method for the simultaneous detection of L-cysteine and L-homocysteine has been developed. A fluorescein derivative reacts with the above amino acids, producing their respective thiazolidines resulting in color changes. Interference from other amino acids and proteins is minimal. Copyright © 2004 American Chemical Society