Substrate Dependent Water Splitting with Ultrathin α‑Fe_2O_3 Electrodes

Thin films of hematite (α-Fe_2O_3) were deposited by atomic layer deposition (ALD), and the effects of metal oxide underlayers on the photocatalytic water oxidation performance were investigated. It was found that a Ga_2O_3 underlayer dramatically enhances the water oxidation performance of the thinnest hematite films. The performance enhancement is attributed to the increased crystallinity of the ultrathin films induced by the oxide underlayers. The degree of crystallinity was examined by Raman line shape analysis of the characteristic hematite phonon modes. It was found that multiple metal oxide underlayers, including Nb_2O_5, ITO, and WO_3, increase the film crystallinity compared to hematite deposited on bare FTO. The increased crystallite size was also clearly evident from the high resolution SEM images. The degree of crystallinity was found to correlate with absorbance and the photocatalytic water oxidation performance. These findings shed light on the origin of the dead layer at the interface of the FTO substrate and ultrathin hematite films and elucidate strategies at overcoming it

Magnetic Field Alignment of Randomly Oriented, High Aspect Ratio Silicon Microwires into Vertically Oriented Arrays

External magnetic fields have been used to vertically align ensembles of silicon microwires coated with ferromagnetic nickel films. X-ray diffraction and image analysis techniques were used to quantify the degree of vertical orientation of the microwires. The degree of vertical alignment and the minimum field strength required for alignment were evaluated as a function of the wire length, coating thickness, magnetic history, and substrate surface properties. Nearly 100% of 100 μm long, 2 μm diameter, Si microwires that had been coated with 300 nm of Ni could be vertically aligned by a 300 G magnetic field. For wires ranging from 40 to 60 μm in length, as the length of the wire increased, a higher degree of alignment was observed at lower field strengths, consistent with an increase in the available magnetic torque. Microwires that had been exposed to a magnetic sweep up to 300 G remained magnetized and, therefore, aligned more readily during subsequent magnetic field alignment sweeps. Alignment of the Ni-coated Si microwires occurred at lower field strengths on hydrophilic Si substrates than on hydrophobic Si substrates. The magnetic field alignment approach provides a pathway for the directed assembly of solution-grown semiconductor wires into vertical arrays, with potential applications in solar cells as well as in other electronic devices that utilize nano- and microscale components as active elements

Amorphous TiO_2 coatings stabilize Si, GaAs, and GaP photoanodes for efficient water oxidation

Although semiconductors such as silicon (Si), gallium arsenide (GaAs), and gallium phosphide (GaP) have band gaps that make them efficient photoanodes for solar fuel production, these materials are unstable in aqueous media. We show that TiO_2 coatings (4 to 143 nanometers thick) grown by atomic layer deposition prevent corrosion, have electronic defects that promote hole conduction, and are sufficiently transparent to reach the light-limited performance of protected semiconductors. In conjunction with a thin layer or islands of Ni oxide electrocatalysts, Si photoanodes exhibited continuous oxidation of 1.0 molar aqueous KOH to O_2 for more than 100 hours at photocurrent densities of >30 milliamperes per square centimeter and ~100% Faradaic efficiency. TiO_2-coated GaAs and GaP photoelectrodes exhibited photovoltages of 0.81 and 0.59 V and light-limiting photocurrent densities of 14.3 and 3.4 milliamperes per square centimeter, respectively, for water oxidation

Substrate Dependent Water Splitting with Ultrathin α‑Fe₂O₃ Electrodes

Thin films of hematite (α-Fe₂O₃) were deposited by atomic layer deposition (ALD), and the effects of metal oxide underlayers on the photocatalytic water oxidation performance were investigated. It was found that a Ga₂O₃ underlayer dramatically enhances the water oxidation performance of the thinnest hematite films. The performance enhancement is attributed to the increased crystallinity of the ultrathin films induced by the oxide underlayers. The degree of crystallinity was examined by Raman line shape analysis of the characteristic hematite phonon modes. It was found that multiple metal oxide underlayers, including Nb₂O₅, ITO, and WO₃, increase the film crystallinity compared to hematite deposited on bare FTO. The increased crystallite size was also clearly evident from the high resolution SEM images. The degree of crystallinity was found to correlate with absorbance and the photocatalytic water oxidation performance. These findings shed light on the origin of the dead layer at the interface of the FTO substrate and ultrathin hematite films and elucidate strategies at overcoming it

Magnetic Field Alignment of Randomly Oriented, High Aspect Ratio Silicon Microwires into Vertically Oriented Arrays

External magnetic fields have been used to vertically align ensembles of silicon microwires coated with ferromagnetic nickel films. X-ray diffraction and image analysis techniques were used to quantify the degree of vertical orientation of the microwires. The degree of vertical alignment and the minimum field strength required for alignment were evaluated as a function of the wire length, coating thickness, magnetic history, and substrate surface properties. Nearly 100% of 100 μm long, 2 μm diameter, Si microwires that had been coated with 300 nm of Ni could be vertically aligned by a 300 G magnetic field. For wires ranging from 40 to 60 μm in length, as the length of the wire increased, a higher degree of alignment was observed at lower field strengths, consistent with an increase in the available magnetic torque. Microwires that had been exposed to a magnetic sweep up to 300 G remained magnetized and, therefore, aligned more readily during subsequent magnetic field alignment sweeps. Alignment of the Ni-coated Si microwires occurred at lower field strengths on hydrophilic Si substrates than on hydrophobic Si substrates. The magnetic field alignment approach provides a pathway for the directed assembly of solution-grown semiconductor wires into vertical arrays, with potential applications in solar cells as well as in other electronic devices that utilize nano- and microscale components as active elements

Phototropic growth control of nanoscale pattern formation in photoelectrodeposited Se-Te films

Photoresponsive materials that adapt their growth rates dynamically to the local incident electromagnetic field would provide a remarkable route to the synthesis of complex three-dimensional mesoscale structures via feedback between illumination and the morphol. that develops in response to the optical excitation. We report the spontaneous development of ordered, complex nanoscale lamellar patterns in electrodeposited seleniumtellurium (Se-Te) alloy films that are grown under uniform illumination on unpatterned substrates in an isotropic electrolyte soln. These inorg. nanostructures exhibited phototropic growth in which lamellar stripes grew towards the incident light source, adopted an orientation parallel to the light polarization direction, and showed an increased growth rate with increasing light intensity. The illumination wavelength controlled the lamellar period, which varied from 130 nm for UV light to 412 nm for near-IR light. The height modulation of the lamellar morphol. was detd. by the ratio of the photocurrent-mediated growth rate to the growth rate mediated by the dark current at a given applied potential. Highly anisotropic features, exhibiting av. lamellar heights of 938 nm and widths of 164 nm, were formed under incident light intensities of 18.6 mW/cm2 at a potential of -0.40 V referenced to a std. calomel electrode. Furthermore, the patterns responded dynamically to changes during growth in the polarization, wavelength, and angle of the incident light, enabling the templatefree and pattern-free synthesis of woodpile, spiral, or branched structures. Full-wave electromagnetic simulations were used to model the light-matter interactions in Se-Te films. In combination with Monte Carlo growth simulations, this approach produced a model for the morphol. evolution of the lamellar structures under phototropic growth conditions. The simulations and expts. are consistent with a phototropic growth mechanism in which the optical near-field intensity profile selects and reinforces the dominant morphol. mode in the developing nanoscale patterns

Detection of Anti-IgG Using Cantilever-type Resonant Microstructures Vibrating in In-plane Flexural Modes

This work presents a cantilever-based mass-sensitive microsensor platform for the detection of biomolecules in the liquid phase. The resonant microstructures feature integrated thermal excitation and piezoresistive detection elements to excite and sense the structure\u27s fundamental in-plane flexural mode. A gold film on the cantilevers allows for the local immobilization of biomolecules using gold-thiol chemistry. Using the in-plane flexural mode, quality factors of the order of 30-50 are obtained in water at resonance frequencies around 500 kHz. The reduced liquid damping enables closed-loop operation of the resonators with frequency stabilities in the ppm-range. Using a microfabricated flow cell, anti-IgG is detected in PBS with limits of detection on the order of 50 ng/ml

Structure of HIV TAR in complex with a Lab-Evolved RRM provides insight into duplex RNA recognition and synthesis of a constrained peptide that impairs transcription

Natural and lab-evolved proteins often recognize their RNA partners with exquisite affinity. Structural analysis of such complexes can offer valuable insight into sequence-selective recognition that can be exploited to alter biological function. Here, we describe the structure of a lab-evolved RNA recognition motif (RRM) bound to the HIV-1 trans-activation response (TAR) RNA element at 1.80 Å-resolution. The complex reveals a trio of arginines in an evolved β2-β3 loop penetrating deeply into the major groove to read conserved guanines while simultaneously forming cation-π and salt-bridge contacts. The observation that the evolved RRM engages TAR within a double-stranded stem is atypical compared to most RRMs. Mutagenesis, thermodynamic analysis and molecular dynamics validate the atypical binding mode and quantify molecular contributions that support the exceptionally tight binding of the TAR-protein complex (K[subscript D,App] of 2.5 ± 0.1 nM). These findings led to the hypothesis that the β2-β3 loop can function as a standalone TAR-recognition module. Indeed, short constrained peptides comprising the β2-β3 loop still bind TAR (K[subscript D,App] of 1.8 ± 0.5 μM) and significantly weaken TAR-dependent transcription. Our results provide a detailed understanding of TAR molecular recognition and reveal that a lab-evolved protein can be reduced to a minimal RNA-binding peptide