Since the exciting discovery that binding of 4-ethynylaniline on the inert Cu2O cubes makes the functionalized cubes highly photocatalytically active toward methyl orange (MO) degradation, binding of 2-ethynyl-6-methoxynaphthalene (2E-6MN) molecules...

The inert Cu2O cubes exhibit a superior photocatalytic activity after functionalized with 4-nitrophenylacetylene (4-NA). The 4-NA-modifed Cu2O octahedra and rhombic dodecahedra also show significant activity enhancement. Infrared and X-ray photoelectron...

Previously, Cu2O cubes have been shown to remain photocatalytically inert toward methyl orange degradation even after surface decoration with ZnO, ZnS, CdS, and Ag3PO4 nanostructures. Surprisingly, when Ag2S nanoparticles are lightly deposited on Cu2O cubes as seen through scanning electron microscopy (SEM) images, the heterostructures become highly photocatalytically active. X-ray diffraction (XRD) patterns show mainly Cu2O diffraction peaks due to lightly deposited Ag2S, but Ag2S peaks can emerge with increased Ag2S deposition. X-ray photoelectron spectroscopy (XPS) analysis also supports Ag2S formation on Cu2O crystals. The Ag2S-deposited Cu2O octahedra and rhombic dodecahedra show the expected activity enhancement. Electron paramagnetic resonance (EPR) measurements, as well as electron, hole, and radical scavenger tests, all confirmed the emergence of photocatalytic activity from the Ag2S–Cu2O cubes. Photoluminescence lifetimes are shortened after Ag2S deposition. Electrochemical impedance measurements revealed a large decrease in charge transfer resistance for Cu2O cubes after the Ag2S deposition. Unexpectedly, the separately synthesized Ag2S particles are also photocatalytically inactive. No specific lattice planes of Ag2S are formed directly over the {100} face of Cu2O. Diffuse reflectance and ultraviolet photoelectron spectral data were used to construct band diagrams of different Cu2O crystals and Ag2S nanoparticles. A Z-scheme charge transfer mechanism may be involved at the heterojunction interface to promote charge carrier separation. However, to explain the sudden appearance of photocatalytic activity from the Ag2S-deposited Cu2O cubes, a large change in the {100} surface band bending after Ag2S deposition should be used. This work illustrates that an unusual photocatalytic outcome is possible to semiconductor heterojunctions, where two photocatalytically inert components can become highly active when joined together.

An analytical technique based on resonance-enhanced laser-induced plasma spectroscopy was demonstrated. Pellets of potassium iodate containing trace amounts of sodium were ablated by a 532-nm laser pulse in air. After 30 ns, the plasma plume was intercepted by a 404.4-nm laser pulse to resonantly photoionize the potassium atoms in the vapor plume. The 589-nm emissions of the sodium were found to be significantly enhanced. The enhancement was shown to depend critically on the profile of the 532-nm beam as well as the spatial overlap of the two laser pulses. Using this double-pulse scheme, the mass detection limit for sodium was estimated to be about 200 pg, which was five times better than that obtained by using the 532-nm laser pulse alone.

We have investigated in a systematic way the interface properties of Fe 2 O 3 grown on different buffer layers using an electron beam deposition technique. For films deposited directly onto Si(001) substrate and on Al buffer layer, we observed the presence of metallic Fe at the Si(001) and Al interfaces, respectively. We also detected the presence of SiO 2 and Al 2 O 3 by x-ray photoelectron spectroscopy. For Fe 2 O 3 films deposited on Cu buffer layer, however, no other phases were observed at the interface. We explain our results using the enthalpy of formation. The enthalpy of formation of SiO 2 and Al 2 O 3 is much lower than that of Fe 2 O 3 , thus inhibiting the crystalline growth of Fe 2 O 3 at the interface. The enthalpy of formation of CuO is, however, greater than that of Fe 2 O 3 , and thus promoting the growth of Fe 2 O 3 to be crystalline. These results were corroborated by our transmission electron microscopy studies.