Electro-optical evidence for the chelate effect at semiconductor surfaces.

Monoamines and diamines dissolved in cyclohexane solution reversibly enhance the band-edge photoluminescence (PL) intensity of immersed n-type cadmium sulfide (n-CdS) and n-type cadmium selenide (n-CdSe) substrates through adsorption. The magnitude of the PL increase is used to estimate amine-induced contractions in the semiconductor's depletion width, and the dependence of the PL intensity on amine concentration provides an estimate of the adduct formation constant. Two diamines, ethylenediamine and o-phenylenediamine, exhibit unusually low reductions in depletion width and substantially larger adduct equilibrium constants relative to the other amines studied, consistent with chelation to surface Cd(2+) ions. These studies demonstrate that PL can be used as a contactiess, in situ technique for characterizing the steric and electronic landscape of semiconductor surfaces and for correlating molecular and surface chemistry.

Comparison of the strength and holding power of 4 pin designs for use with half pin (type I) external skeletal fixation.

The strength and holding power of four pin designs for use with half pin (type I) external skeletal fixation were evaluated. Pins that were tested were fully threaded, nonthreaded, two cortices partially threaded, and one cortex partially threaded. The study involved three parts: (1) resistance of the pins to axial extraction immediately after insertion; (2) resistance of the pins to axial extraction 8 weeks after being inserted into the tibiae of live dogs; and (3) resistance of the pins to bending load. Pins with threads engaging two cortices were more resistant to axial extraction than nonthreaded pins in both the acute (p less than 0.0001) and chronic (p less than 0.0001) studies. Nonthreaded pins were more resistant to bending than fully threaded and two cortices partially threaded pins (p less than 0.0005). One cortex partially threaded pins possessed similar bending strength to nonthreaded pins (p = 0.21) and had 5.3 times more resistance to axial extraction in the acute study (p less than 0.0001) and 6.9 times more in the chronic study (p less than 0.0001). Though one cortex partially threaded pins were not as resistant to axial extraction as pins with threads engaging two cortices (p less than 0.0001), they were more resistant to bending loads (p less than 0.0005). Loss of holding power and pin failure are two of the most serious problems associated with fracture stabilization using external skeletal fixation. The results of this study suggest that one cortex partially threaded pins are better at maintaining holding power and resisting bending and breaking than nonthreaded pins.(ABSTRACT TRUNCATED AT 250 WORDS)

Mediation of retinal photoisomerization by adduct formation with tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)-europium(II).

Several retinal isomers are shown to form adducts in isooctane solution with a lanthanide beta-diketonate complex, tris(6,6,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium(III) [Eu(fod)3]. The adducts are characterized by an absorption band whose lambda max at approximately 420 nm is red-shifted by approximately 60 nm from the lowest-energy absorption band in the free retinal isomers. Irradiation into this adduct band leads to photoisomerization. For example, photolysis of a 1 mM all-trans-retinal/3 mM Eu(fod)3 isooctane solution at 514.5 nm leads, with reasonable quantum efficiency (phi greater than or equal to 0.05), to isomeric mixtures that are considerably different from these produced with UV excitation in the absence of Eu(fod)3. Particularly noteworthy for a photolysis conducted in a nonpolar solvent is the presence of an appreciable quantity of 11-cis-retinal in the adduct photolysate.

n-Type Si-based photoelectrochemical cell: New liquid junction photocell using a nonaqueous ferricenium/ferrocene electrolyte.

n-Type Si has been shown to serve as a stable photoanode in a cell for the conversion of light to electricity. The other components of the cell are a Pt cathode and an electrolyte consisting of an ethanol solution of [n-Bu(4)N]ClO(4) with a redox couple of ferricenium/ferrocene. Data from a two-compartment cell show that ferrocene is oxidized to ferricenium with 100 +/- 2% current efficiency at the Si photoanode. Furthermore, prolonged irradiation of the Si in a one-compartment cell yields constant photocurrent and output characteristics. The maximum open-circuit photopotential is approximately 700 mV, and the short-circuit quantum yield for electron flow at low light intensity exceeds 0.5. Conversion of monochromatic 632.8-nm light to electricity with approximately 2% power efficiency at an output voltage of approximately 200 mV has been sustained. These results represent a stable n-type Si-based photoelectrochemical cell.

Photoassisted electrolysis of water by irradiation of a titanium dioxide electrode.

Ultraviolet irradiation (351, 364 nm) of the n-type semiconductor TiO(2) as the single crystal electrode of an aqueous electrochemical cell evolves O(2) at the TiO(2) electrode and H(2) at the Pt electrode. The gases are typically evolved in a two: one (H(2):O(2)) volume ratio. The photoassisted reaction seems to require applied voltages, but values as low as 0.25 V do allow the photoassisted electrolysis to proceed. Prolonged irradiation in either acid or base evolves the gaseous products in amounts which clearly demonstrate that the reaction is catalytic with respect to the TiO(2). The wavelength response of the TiO(2) and the correlation of product yield and current are reported. The results support the claim that TiO(2) is a true photoassistance agent for the electrolysis of water. Minimum optical storage efficiencies of the order of 1% can be achieved by the production of H(2).