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The nanoporous Ti[O.sub.2] network sensitized by ZnS nanospheres is produced and described as an idealized scheme to facilitate interfacial charge transfer effects. The findings suggest that when a large band gap material is restricted in a confined geometry of lower energy band gap then the surface states are mainly responsible in the charge transport phenomena.

In this work, we show that anatase nanoporous titanium dioxide (TiO2) structures can be sensitized by adequate PbS molecular adsorption. This was substantiated through x-ray diffraction, electron microscopy, atomic force microscopy, and nitrogen adsorption/desorption studies. The atomic force micrograph of the PbS/TiO2 system is characterized by a smooth surface topography as compared to the untreated TiO2 network. Further, N2 adsorption/desorption studies have revealed that the pores having a size greater than the Bohr exciton size (∼3.1 nm) of TiO2 can be efficiently filled by PbS molecules, whereas the smaller pores remain unfilled. The pore filling aspects, along with the kinetics of molecular adsorption in the coupled heterogeneous nanostructured system, would help to reveal the underlying mechanism of interfacial charge leakage phenomena in miniaturized nanoelectronic and nanophotonic junctions/components. [ABSTRACT FROM AUTHOR]

Inexpensive fabrication of europium (Eu3+)-doped zinc oxide (ZnO) nanoparticles, nanorods, and urchin systems obtained by rapid thermal annealing is being reported. The polyvinyl alcohol films containing a reactant mixture [Zn(CH3COO)2, Eu(CH3COO)3, and NaOH] were casted on Al-foils followed by thermal annealing at 80, 300, and 650 °C. Gradual change-over from spherically symmetric nanoparticles to nanorods along with urchin like structures are obtained under different annealing environment. The nanorods and urchins are expected to have grown as a result of spontaneous decomposition of Zn(OH)2 followed by unidirectional growth. The nanorods are dislodged from the regular urchin structures at a high annealing temperature of 650 °C because of the loss of the crystalline substrate support. The as-received ZnO products possessed hexagonal wurtzite structure for all the annealing cases-as evident from the x-ray diffraction patterns. The photoluminescence study on the samples has revealed dominant defect related emissions compared to the near band edge emission. The band edge emission (∼382 nm) is recovered in the urchin systems whereas Eu3+ related transitions observed at ∼591 nm (5D0→7F1) and ∼613 nm (5D0→7F2) remained intact with structural modification. [ABSTRACT FROM AUTHOR]

We report on the production of nanoporous TiO2 network sensitized by ZnS nanospheres as an idealized scheme to facilitate interfacial charge transfer effects. The nanoporous TiO2 system was fabricated on the 0.1 μm thick Al substrate from titanium isopropoxide [Ti(i-OC3H7)] and 1-butanol (C4H9OH) as requisite precursor. The Zn++ ions are internally adsorbed to provide heterogeneous coupled TiO2–ZnS nanosystem. The I-V response shows transistor characteristics which suggests sharp rise in current with forward biasing voltage before attaining saturation. It is expected that with the increase in signal frequency more number of trap carriers being able to follow signal assist higher carrier transfer rate across the interface in the coupled system and hence saturation current (IS) increases. However, in all the cases saturation occurs around finite biasing voltage, i.e., 3.6 V. This ensures that the surface states (which normally lie within the forbidden gap and below the conduction bands for electrons) mainly participate in carrier transfer mechanism within the device. A phenomenon in understanding highly controlled interfacial carrier transport process would find potential in nanoelectronics, e.g., single electron transistor and other single electron devices. [ABSTRACT FROM AUTHOR]

We report here synthesis and optical absorption study of energetic ion-irradiated hydroxyl-free ZnO semiconductor quantum dots. Quantum dot samples were synthesized by a quenching technique and 100-MeV chlorine ion was selected for the irradiation experiment with doses 1 × 10[sup 11], 5 × 10[sup 11], 5 × 10[sup 12], and 10[sup 13] ions/cm². With an increase in fluence, the optical absorption spectra of irradiated quantum dots reveal redshift of the energy-gap parameter with respect to unirradiated (virgin) quantum dots. The narrowing of the energy gap of nanoparticles indicate particle growth under ion irradiation which is confirmed from transmission electron microscope images. The possible reason for such variations was encountered using an effective-mass approximation model which fits well for small effective mass and high-dielectric constant (∈[sub 0]). [ABSTRACT FROM AUTHOR]