Tuning the reactivity of nanostructured indium tin oxide electrodes toward chemisorption.

This contribution highlights correlation between the surface concentration of a chemisorbed organophosphorous probe (flavin mononucleotide) and the relative hydroxyl surface coverage of nanostructured ITO electrodes, which can be tuned during post-deposition reductive annealing. The resulting modified electrodes are very stable in aqueous solution, highly hydrophilic and fully-accessible to the bulk solution.

Spectroelectrochemistry of Fe(III)- and Co(III)-mimochrome VI artificial enzymes immobilized on mesoporous ITO electrodes.

UV-visible absorption spectroelectrochemistry elucidated the different redox behaviours of Fe(III)- and Co(III)-mimochrome VI artificial enzymes, adsorbed on mesoporous conductive films of ITO. The reduction of the ferric complex was rapid and reversible, while the cobaltic complex exhibited irreversible processes probably related to multiple coordination states.

Conductivity control of as-grown branched indium tin oxide nanowire networks.

Branched indium tin oxide (ITO) nanowire networks are promising candidates for transparent conductive oxide applications, such as optoelectronic electrodes, due to their high porosity. However, these branched networks also present new challenges in assessing conductivity. Conventional four-point probe techniques cannot separate the effect of porosity on the long-range conductivity from the intrinsic material conductivity. Here we compare the average nanoscale conductivity within the film measured by terahertz time-domain spectroscopy (THz-TDS) to the film conductivity measured by four-point probe in a branched ITO nanowire network. Both techniques report conductivity increases with deposition flux rate from 0.5 to 3.0 nm s(-1), achieving a maximum of ~ 10 (Ω cm)(-1). Modeling the THz-TDS conductivity data using the Drude-Smith model allows us to distinguish between conductivity increases resulting from morphological changes and those resulting from the intrinsic properties of the ITO. In particular, the intrinsic material conductivity within the nanowires can be extracted, and is found to reach a maximum of ~ 3000 (Ω cm)(-1), comparable to bulk ITO. To determine the mechanism responsible for increasing conductivity with flux rate, we characterize dopant concentration and morphological changes (i.e., to branching behavior, nanowire diameter and nucleation layers). We propose that changes in the electron density, primarily due to changes in O-vacancy concentration at different flux rates, are responsible for the observed conductivity increase. This understanding will assist balancing structural and conductivity requirements in applications of transparent conductive oxide networks.

Ultrathin-layer chromatography nanostructures modified by atomic layer deposition.

Stationary phase morphology and surface chemistry dictate the properties of ultrathin-layer chromatography (UTLC) media and interactions with analytes in sample mixtures. In this paper, we combined two powerful thin film deposition techniques to create composite chromatography nanomaterials. Glancing angle deposition (GLAD) produces high surface area columnar microstructures with aligned macropores well-suited for UTLC. Atomic layer deposition (ALD) enables precise fabrication of conformal, nanometer-scale coatings that can tune surfaces of these UTLC films. We coated ∼5µm thick GLAD SiO2 UTLC media with <10nm thick ALD metal oxides (Al2O3, ZrO2, and ZnO) to decouple surface chemistry from the underlying GLAD scaffold microstructure. The effects of ALD coatings on GLAD UTLC media were investigated using transmission electron microscopy (TEM), gas adsorption porosimetry, and lipophilic dye separations. The results collectively show that the most significant changes occur over the first few nanometers of ALD coating. They further demonstrate independent control of film microstructure and surface characteristics. ALD coatings can enhance complex GLAD microstructures to engineer new composite nanomaterials potentially useful in analytical chromatography.

Polarity-adjustable reversed phase ultrathin-layer chromatography.

Reversed phase thin layer chromatography (TLC) or high performance thin layer chromatography (HPTLC) plates modified with C18, C8 or C2 to provide the silica-gel stationary phase with different polarities are available on the market, however, reversed phase plates with tunable polarity have not been reported. Given the limited variety of reversed phase plates, mobile phase composition optimization is necessary to obtain better separation of analytes with similar characteristics, which is often a time consuming step. We present polarity-adjustable reversed phase ultrathin-layer chromatography (UTLC) plates, which simplifies the mobile phase screening process and greatly expands the selection of reversed phase plates. The plates were fabricated on glass substrates with SiO(2) nanopillars deposited using the glancing angle deposition (GLAD) technique. SiO(2) nanopillars were functionalized with octadecyltrichlorosilane to generate a super hydrophobic stationary phase. Unlike commercial silica-gel based stationary phases, the isolated nanopillar architecture presented here exposes a high surface area to post-fabrication surface treatments. In our work, an O(2) plasma treatment at different powers, pressures and exposure times was used to shorten the silane carbon chain and introduce COOH groups to the surface, producing plates with finely tunable polarities. Separation of a model dye mixture of Sudan blue and Sudan IV confirmed the tuning of surface polarities by measurement of retention behavior changes. The dye elution order reversed as a result of the change in surface polarity. When the same plasma treatment process was tested on commercial reversed phase plates, separation behavior did not change because the disordered and tortuous silica gel restricts the accessible surface area. Plasma treatment of GLAD structures with highly accessible surfaces improved control over interfacial properties, producing better reverse phase separations.

Time resolved chromatograms in ultra-thin layer chromatography.

Ultrathin-layer chromatography (UTLC) is a recently developed analytical method intended for compact, rapid separations of nanolitre analyte volumes. Optimizing this method's performance requires new measurement techniques compatible with the millimetre length scales and rapid separation dynamics observed in UTLC. We have designed, implemented and characterized a measurement system which records UTLC separations in full color with 32 µm spatial resolution and 33 ms temporal resolution. Our code analyzes multiple tracks per plate, filters analyte spots by color, and automatically generates time-resolved figures of merit. The instrument presented here captures a wealth of information from a UTLC separation, and should provide insight into UTLC physics and improved analytical performance.

Indium tin oxide nanowhisker morphology control by vapour-liquid-solid glancing angle deposition.

A new growth technique for indium tin oxide nanowhiskers with increased control over feature size and spacing is reported. The technique is based on a unique combination of self-catalysed vapour-liquid-solid (VLS) growth and glancing angle deposition (GLAD). This VLS-GLAD technique provides enhanced control over nanowhisker morphology as the effect of typical VLS growth parameters (e.g. flux rate, temperature) is amplified at large deposition angles characteristic of GLAD. Spatial modulation of the collimated growth flux controls trunk width, number and orientation of branches, and overall nanowhisker density. Here we report the influence of growth conditions (including deposition angle, flux rate, nominal pitch and substrate temperature) on nanowhisker morphology, with specific focus on the effect of large deposition angles. Sheet resistance and transmission of the films were measured to characterize their performance as transparent conductive oxides. Hybrid nanostructured films grown in this study include high surface area nanowhiskers protruding from a conductive film, ideal for transparent conductive electrode applications.

Morphological modification of nanostructured ultrathin-layer chromatography stationary phases.

Ultrathin-layer chromatography (UTLC) provides the high sensitivities and rapid separations over short distances desirable in many analytical applications. The dependence of these performance benefits on UTLC layer microstructure motivates continued stationary phase engineering efforts. A new method of modifying the elution behaviours of nanostructured thin film UTLC stationary phases is investigated in this report. Macroporous normal phase silica thin films ∼5 µm thick were fabricated using glancing angle deposition (GLAD). Reactive ion etching (RIE) and a subsequent annealing treatment modified stationary phase morphology to tune migration velocity, analyte retention, and overall separation performance. Combining this technique with a RIE shadow mask enabled fabrication of adjacent concentration and separation zones with markedly different elution properties. Although produced using an entirely new approach, GLAD UTLC concentration zone media behaved in a manner consistent with traditional thin-layer chromatography (TLC) and high-performance TLC (HPTLC) concentration zone plates. In particular, these new media focused large volume, low concentration dye mixture spots into narrow bands to achieve high-quality separations. The described approach to modifying the morphology and resultant elution behaviours of nanostructured stationary phases expands the capabilities of the GLAD UTLC technique.

Analyte migration in anisotropic nanostructured ultrathin-layer chromatography media.

We investigate the performance of highly anisotropic nanostructured thin film ultrathin-layer chromatography (UTLC) media with porosity and architecture engineered using the glancing-angle deposition (GLAD) process. Our anisotropic structures resemble nanoblades, producing channel-like features that partially decouple analyte migration from development direction, offering new separation behaviours. Here we study GLAD-UTLC plate performance in terms of migration distance, plate number, retention factor and a figure of merit specific to GLAD-UTLC, track deviation angle. Migration distances increase with porosity by a factor of two for all feature orientations (up to a maximum of 22 mm) over the range of porosities considered in this study. Plate numbers approaching 1100 are observed for GLAD-UTLC plates when the nanoblade features are aligned with the development direction. We present a theoretical model describing mobile phase flow in anisotropic GLAD-UTLC media, and find good agreement with experimental results. Our plates provide channel features that reduce transverse spot broadening while providing the wide pores required for rapid migration and high separation performance. These improvements may enable a greater number of parallel separations on miniaturized GLAD-UTLC plate formats. Their small sizes should also make them compatible with the Office Chromatography concept in which office peripherals (inkjet printers and flatbed scanners) replace conventional TLC instruments. Equipped with a better understanding of the unique GLAD-UTLC elution behaviours, we expect to further improve performance in the future.

Engineered anisotropic microstructures for ultrathin-layer chromatography.

The strong dependence of separation behavior on ultrathin-layer chromatography (UTLC) stationary phase microstructure motivates continued UTLC plate design optimization efforts. We fabricated 4.6-5.3 mum thick normal phase silica UTLC stationary phases with several types of in-plane macropore anisotropies using the glancing angle deposition (GLAD) approach to engineering nanostructured thin films. The separation behaviors of two new media, isotropic vertical posts and anisotropic bladelike films, were compared to that of anisotropic chevron media. Channel-like structures within the anisotropic media introduced preferential mobile phase flow directions that could be exploited to give separation tracks diagonal to the development direction. Extraction of chromatograms from these angled tracks required the development of a new analytical approach that involved a commercial flatbed film scanner and custom numerical image analysis software. GLAD stationary phase performance was quantified using the Dimethyl Yellow dye separated from a lipophilic dye mixture over migration distances less than approximately 10 mm. The limits of detection were 10 +/- 4 ng for the vertical posts and 11 +/- 3 ng for the bladelike media. We obtained theoretical plate heights that varied with film microstructure between 12 and 28 mum. Unoptimized separation performance was comparable to that of other planar chromatography media. Macropore anisotropies engineered by GLAD may expand the capabilities of future UTLC stationary phases.

Interferometric sensing platform with dielectric nanostructured thin films.

A new interferometer-based optical sensing platform with nanostructured thin films of ZrO2 or TiO2 as sensing environment has been developed. With the application of an IC compatible Si(3)N(4) waveguide technology, Mach-Zehnder interferometer devices have been fabricated. The application of the glancing angle deposition technique allowed fabrication of nanostructured thin films as the optical sensing environment. Sensing ability of fabricated devices has been demonstrated through the refractive index measurement of a known gas. The transmission spectra and time response measurements have demonstrated a maximum phase shift of Delta phi=pi/10 and a |Delta P(out)|=0.65 dBm. Devices with TiO2 film on the sensing region performed much better than devices with ZrO2, with sensitivity twice as high.

Optimization of periodic column growth in glancing angle deposition for photonic crystal fabrication.

We investigate the growth of periodically aligned silicon microstructures for the fabrication of square spiral photonic crystals using the glancing angle deposition phi-sweep process. We report the optimization of the phi-sweep offset angle for fabrication of microstructures with more precise geometry. The effects of varying the sweep offset angle of the phi-sweep process are studied for films deposited onto a square lattice array of growth seeds. To represent one growth segment of the phi-sweep process, we fabricate 15 nm silicon thin films using several azimuthal substrate offsets from 0° to 45° at a vapor incidence angle of 85°. We also deposit silicon square spirals on square lattice arrays with the phi-sweep method, using various sweep offset angles from γ = 0° to 45°. We find that using an offset angle of γ = 26.5° optimizes the shadowing geometry, which minimizes anisotropic broadening, producing greater quality photonic crystal structures. From normal incidence reflection spectroscopy, a maximum full width at half-maximum of 273 ± 3 nm and a relative peak width (Δλ/λ) of 16.1 ± 0.1% were found for a sweep offset angle of γ = 26.5°.

Evaporated nanostructured Y2O3:Eu thin films.

Europium-doped yttrium oxide (Y2O3:Eu) is a well-known luminescent material that in recent years has been studied in thin-film form. However, to date there has not been a great effort put into altering the nanostructure of these films. A thin-film deposition technique called glancing angle deposition allows for a high degree of control over the nanostructure of the thin film, resulting in thin films with nanostructure geometries ranging from chevron and post to helix. Glancing-angle deposition was used to make europium-doped yttrium oxide thin films with slanted-post nanostructures. Portions of the films were annealed in air at 850 degrees C for 10 hours following deposition. Scanning electron microscopy was used to characterize the nanostructures of the films, while UV laser excitation was used to characterize the photoluminescence properties of the films. The annealed samples exhibited increased photoluminescent responses compared to unannealed samples; however, the porous nanoscale geometry of the films was unaffected. In order to optimize the photoluminescence properties of the films, both the partial pressure of oxygen during film deposition and the level of europium doping in the source material used were varied. Films fabricated from the source material with a greater amount of europium doping had larger photoluminescent responses, while the optimal partial pressure of oxygen during electron-beam evaporation was found to be less than 1.0 x 10(-4) torr.

Direct formation of grating structures on silicon using KrF laser radiation.

Surface grating structures with a periodicity of 1.46 microm and depth of modulation of 20 nm have been produced on single crystal silicon by irradiation with two coherent interfering beams of 248-nm laser light at energy densities of 1.4-1.8 J cm(-2). The resulting structures are consistent with the expected melting and resolidification of the surface layer of the sample.

The effect of D-xylose, beta-D-xylosides and beta-D-galactosides on chondroitin sulphate biosynthesis in embryonic chicken cartilage.

The incorporation of [3H]acetate into chondroitin sulphate was used as a measure of the rate of synthesis of this polysaccharide in whole tibias and femurs of embryonic chicken cartilage in vitro. The incorporation is inhibited by puromycin and by cycloheximide, but the inhibition is relieved by the addition of D-xylose, beta-D-xylosides and beta-D-galactosides to the incubation medium. Beta-D-Xylosides can stimulate the incorporation to 300% of that of controls incubated in the absence of cycloheximide or puromycin, D-Xylose, beta-D-xylosides and beta-D-galactosides appear to act as artificial initiators of chondroitin sulphate synthesis and enable polysaccharide-chain synthesis to be studied as an event separate from the synthesis of intact proteoglycan.