Proton Reduction Using a Hydrogenase-Modified Nanoporous Black Silicon Photoelectrode.

Metalloenzymes featuring earth-abundant metal-based cores exhibit rates for catalytic processes such as hydrogen evolution comparable to those of noble metals. Realizing these superb catalytic properties in artificial systems is challenging owing to the difficulty of effectively interfacing metalloenzymes with an electrode surface in a manner that supports efficient charge-transfer. Here, we demonstrate that a nanoporous "black" silicon (b-Si) photocathode provides a unique interface for binding an adsorbed [FeFe]-hydrogenase enzyme ([FeFe]-H2ase).

Oxidatively stable nanoporous silicon photocathodes with enhanced onset voltage for photoelectrochemical proton reduction.

Stable and high-performance nanoporous "black silicon" photoelectrodes with electrolessly deposited Pt nanoparticle (NP) catalysts are made with two metal-assisted etching steps. Doubly etched samples exhibit an ∼300 mV positive shift in photocurrent onset for photoelectrochemical proton reduction compared to oxide-free planar Si with identical catalysts. We find that the photocurrent onset voltage of black Si photocathodes prepared from single-crystal planar Si wafers by an Ag-assisted etching process increases in oxidative environments (e.

Angle-resolved XPS analysis and characterization of monolayer and multilayer silane films for DNA coupling to silica.

We measure silane density and Sulfo-EMCS cross-linker coupling efficiency on aminosilane films by high-resolution X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements. We then characterize DNA immobilization and hybridization on these films by (32)P-radiometry. We find that the silane film structure controls the efficiency of the subsequent steps toward DNA hybridization.

An 18.2%-efficient black-silicon solar cell achieved through control of carrier recombination in nanostructures.

Silicon nanowire and nanopore arrays promise to reduce manufacturing costs and increase the power conversion efficiency of photovoltaic devices. So far, however, photovoltaic cells based on nanostructured silicon exhibit lower power conversion efficiencies than conventional cells due to the enhanced photocarrier recombination associated with the nanostructures. Here, we identify and separately measure surface recombination and Auger recombination in wafer-based nanostructured silicon solar cells.

Diffractive light trapping in crystal-silicon films: experiment and electromagnetic modeling.

Diffractive light trapping in 1.5 μm thick crystal silicon films is studied experimentally through hemispherical reflection measurements and theoretically through rigorous coupled-wave analysis modeling. The gratings were fabricated by nanoimprinting of dielectric precursor films.

High-resolution X-ray photoelectron spectroscopy of mixed silane monolayers for DNA attachment.

The amine density of 3-aminopropyldimethylethoxysilane (APDMES) films on silica is controlled to determine its effect on DNA probe density and subsequent DNA hybridization. The amine density is tailored by controlling the surface reaction time of (1) APDMES, or (2) n-propyldimethylchlorosilane (PDMCS, which is not amine terminated) and then reacting it with APDMES to form a mixed monolayer. High-resolution X-ray photoelectron spectroscopy (XPS) is used to quantify silane surface coverage of both pure and mixed monolayers on silica; the XPS data demonstrate control of amine density in both pure APDMES and PDMCS/APDMES mixed monolayers.

Understanding the clean interface between covalent Si and ionic Al2O3.

The atomic and electronic structures of the (001)-Si/(001)-gamma-Al(2)O(3) heterointerface are investigated by first principles total energy calculations combined with a newly developed "modified basin-hopping" method. It is found that all interface Si atoms are fourfold coordinated due to the formation of Si-O and unexpected covalent Si-Al bonds in the new abrupt interface model. And the interface has perfect electronic properties in that the unpassivated interface has a large LDA band gap and no gap levels.

Bistability-mediated carrier recombination at light-induced boron-oxygen complexes in silicon.

A first-principles study of the BO2 complex in B-doped Czochralski Si reveals a defect-bistability-mediated carrier recombination mechanism, which contrasts with the standard fixed-level Shockley-Read-Hall model of recombination. An O2 dimer distant from B causes only weak carrier recombination, which nevertheless drives O2 diffusion under light to form the BO2 complex. Although BO2 and O2 produce nearly identical defect levels in the band gap, the recombination at BO2 is substantially faster than at O2 because the charge state of the latter inhibits the hole capture step of recombination.

Electric-field assisted immobilization and hybridization of DNA oligomers on thin-film microchips.

Single, square voltage pulses in the microsecond timescale result in selective 5'-end covalent bonding (immobilization) of thiolated single-stranded (ss) DNA probes to a modified silicon dioxide flat surface and in specific hybridization of ssDNA targets to the immobilized probe. Immobilization and hybridization rates using microsecond voltage pulses at or below 1 V are at least 10(8) times faster than in the passive control reactions performed without electric field (E), and can be achieved with at least three differently functionalized thin-film surfaces on plastic or glass substrates. The systematic study of the effect of DNA probe and target concentrations, of DNA probe and target length, and the application of asymmetric pulses on E-assisted DNA immobilization and hybridization showed that: (1) the rapidly rising edge of the pulse is most critical to the E-assisted processes, but the duration of the pulse is also important; (2) E-assisted immobilization and hybridization can be performed with micrometre-sized pixels, proving the potential for use on microelectronic length scales, and the applied voltage can be scaled down together with the electrode spacing to as low as 25 mV; and (3) longer DNA chains reduce the yield in the E-assisted immobilization and hybridization because the density of physisorbed single-stranded DNA is reduced.

Immobilization and hybridization by single sub-millisecond electric field pulses, for pixel-addressed DNA microarrays.

Single square voltage pulses applied to buried electrodes result in dramatic rate increases for (1) selective covalent bonding (immobilization) of single-stranded DNA (ssDNA) probes to a functionalized thin film SiO(2) surface on a plastic substrate and (2) hybridization of ssDNA to the immobilized probe. DNA immobilization and hybridization times are 100 ns and 10 micros, respectively, about 10(9) times faster than the corresponding passive reactions without electric field. Surface coverage is comparable.

Hydrogen above saturation at silicon vacancies: H-pair reservoirs and metastability sites.

We propose that hydrogen-passivated multivacancies which appear to be fully saturated with H can actually capture additional H in electrically inactive sites. In silicon, first-principles total energy calculations show that splitting an (m>or=2) multivacancy into a mono- and an (m-1) vacancy provides a low-strain pairing site for H, 0.4 eV per H lower than any known bulk pairing site.

Nonradiative electron-hole recombination by a low-barrier pathway in hydrogenated silicon semiconductors.

A microscopic pathway for nonradiative electron-hole recombination by large structural reconfiguration in hydrogenated Si is found with first-principles calculations. Trapped-biexciton formation leads to a low-barrier reconfiguration of the H atom, accompanied by crossing of doubly occupied electron and hole levels in the band gap. This crossing represents the nonradiative recombination of the carriers, without multiphonon emission.