Graphene oxide suspended in ethanol undergoes reduction as it accepts electrons from UV-irradiated TiO(2) suspensions. The reduction is accompanied by changes in the absorption of the graphene oxide, as the color of the suspension shifts from brown to black. The direct interaction between TiO(2) particles and graphene sheets hinders the collapse of exfoliated sheets of graphene. Solid films cast on a borosilicate glass gap separated by gold-sputtered terminations show an order of magnitude decrease in lateral resistance following reduction with the TiO(2) photocatalyst. The photocatalytic methodology not only provides an on-demand UV-assisted reduction technique but also opens up new ways to obtain photoactive graphene-semiconductor composites.

Graphene oxide sheets suspended in ethanol interact with excited ZnO nanoparticles and undergo photocatalytic reduction. The luminescence quenching of the green emission of ZnO serves as a probe to monitor the electron transfer from excited ZnO to graphene oxide. Anchoring of ZnO nanoparticles on 2-D carbon nanostructures provides a new way to design semiconductor-carbon nanocomposites for catalytic applications.

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The first superlattice avalanche photodiode (APD) is reported. The high field region of this p-i-n structure consists of 50 alternating Al0.45Ga0.55As (550 Å) and GaAs (450 Å) layers. A large ionization rate ratio has been measured in the field range (2.1–2.7)×105 V/cm, with α/β≃10 at a gain of 10 giving a McIntyre noise factor Fn = 3. The ionization rate ratio enhancement with respect to bulk GaAs and AlGaAs is attributed to the large difference in the band edge discontinuities for electrons and holes at the heterojunction interfaces. The superlattice APD is a new device concept which can be used to develop low noise APD’s in a variety of III-V materials including long wavelength 1.3–1.6-μm semiconductors.

The organic/electrode interfaces in organic solar cells are systematically studied for their light, heat, and electrical stability in an inert atmosphere. Various extraction layers are examined for their effect on device stability, including poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) and MoO 3 for hole extraction layers, as well as LiF, Cs 2 CO 3 , and lithium acetylacetonate (Liacac) for electron extraction layers. The organic/ metal interface is shown to be inherently photo-unstable, resulting in significant losses in device effi ciency with irradiation. X-ray photoelectron spectroscopy measurements of the organic/aluminum interface suggest that the photo-induced changes are chemical in nature. In general, interfacial layers are shown to substantially reduce photo-degradation of the active layer/ electrode interface. In spite of their photo-stability, several interfacial layers present at the active layer/cathode interface suffer from thermal degradation effects due to temperature increases under exposure to light. Electrical aging effects are proven to be negligible in comparison to other major modes of degradation.