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A characterization of optical and electronic properties is presented for p‐type (Mg‐doped) and n‐type (Si‐doped) iron oxides used in the photoelectrolysis of water. Photocurrent vs. wavelength spectra for these electrodes indicate that α‐Fe2O3 is the active optical component for both p‐type and n‐type materials. Band‐edge locations for p‐type and n‐type iron oxides in sodium hydroxide aqueous solution are determined from differential capacitance measurements. The thermodynamic feasibility of the catalytic photodissociation of water without external potential is demonstrated for a short‐circuited p/n diode assembly on an energy level diagram of the electrode/electrolyte interfaces. The open‐circuit voltage false(VOCfalse) and short‐circuit current false(ISCfalse) generated by the p/n assembly as a function of the intensity of laser irradiation indicate that these doped iron oxides are low mobility, high carrier density semiconductors. Photo‐oxidation of water at the n‐type anode is verified through oxygen detection. Gas evolution is monitored from an operating diode assembly using mass spectrometry and isotopically labeled water false(H218Ofalse) . Photocurrents from these p/n assemblies show excellent long‐term stability in aqueous solution and Auger analysis of the semiconductor surfaces indicates no evidence of electrode dissolution.

We report here plasma-induced formation of Ag nanostructures for surface-enhanced Raman scattering (SERS) applications. An array of uniform Ag patterned structures of 150 nm diameter was first fabricated on a silicon substrate with imprint lithography; then the substrate was further treated with an oxygen plasma to fracture the patterned structures into clusters of smaller, interconnected, closely packed Ag nanoparticles (20-60 nm) and redeposited Ag nanodots ( approximately 10 nm) between the clusters. The substrate thus formed had a uniform ultrahigh SERS enhancement factor (1010) over the entire substrate for 4-mercaptophenol molecules. By comparison, Au patterned structures fabricated with the same method did not undergo such a morphological change after the plasma treatment and showed no enhancement of Raman scattering.

We propose an efficient hyperentanglement source emitting photon pairs entangled in both energy and polarization. The compact electrically driven room-temperature source, based on intersubband two-photon emission from semiconductor quantum wells (QWs) exhibits pair generation rates several orders of magnitude higher than alternative conventional schemes. A theoretical formalism is derived for the calculation of photon pair generation spectra and rates. The results are presented for superlattice structures similar to quantum cascade lasers of GaAs/AlGaAs QWs emitting in the mid-IR and far-IR and for InN/AlN QW structures suitable for telecommunication wavelengths.