Enhanced photocatalytic efficiency in zirconia buffered n-NiO/p-NiO single crystalline heterostructures by nanosecond laser treatment

Abstract

Epitaxial La 0.7 Sr 0.3 Mn O 3 thin films with two in-plane orientations on silicon substrates with yttria-stabilized zirconia and Y Ba 2 Cu 3 O 7 − δ as buffer layers J. Appl. Phys. 97, 073905 (2005); 10.1063/1.1876577Large low-field magnetoresistance observed in twinned La 2 ∕ 3 Ca 1 ∕ 3 MnO 3 thin films epitaxially grown on yttria-stabilized zirconia-buffered silicon on insulator substratesWe report the formation of NiO based single crystalline p-n junctions with enhanced photocatalytic activity induced by pulsed laser irradiation. The NiO epilayers were grown on Si(001) substrates buffered with cubic yttria-stabilized zirconia (c-YSZ) by using pulsed laser deposition. The NiO/ c-YSZ/Si heterostructures were subsequently laser treated by 5 pulses of KrF excimer laser (pulse duration ¼ 25 Â 10 À9 s) at lower energies. Microstructural studies, conducted by X-ray diffraction (h-2h and u techniques) and high resolution transmission electron microscope, showed a cube-oncube epitaxial relationship at the c-YSZ/Si interface; the epitaxial relationship across the NiO/c-YSZ interface was established as NiOh111 ijjc-YSZh001i and in-plane NiOh110ijjc-YSZh100i. Electron microscopy studies showed that the interface between the laser annealed and the pristine region as well as the NiO/c-YSZ interface was atomically sharp and crystallographically continuous. The formation of point defects, namely oxygen vacancies and NiO, due to the coupling of the laser photons with the NiO epilayers was confirmed by XPS. The p-type electrical characteristics of the pristine NiO epilayers turned to an n-type behavior and the electrical conductivity was increased by one order of magnitude after laser treatment. Photocatalytic activity of the pristine (p-NiO/c-YSZ/Si) and the laser-annealed (n-NiO/p-NiO/c-YSZ/Si) heterostructures were assessed by measuring the decomposition rate of 4-chlorophenol under UV light. The photocatalytic reaction rate constants were determined to be 0.0059 and 0.0092 min À1 for the as-deposited and the laser-treated samples, respectively. The enhanced photocatalytic efficiency was attributed to the suppressed charge carrier recombination in the NiO based p-n junctions and higher electrical conductivity. Besides, the oxygen vacancies ease the adsorption of 4-chlorophenol, hydroxyl, and water molecules to the surface. Thus, n-NiO/p-NiO single crystalline catalysts can be introduced as a potent candidate to remediate the environmental pollution. V C 2013 AIP Publishing LLC. [http://dx.

Multifunctional heterostructures integrated on Si (100)

“…MgO and TiN were found to be non-magnetic. The fact that the XRD and XPS data did not reveal any indication of secondary impurities, before or after laser annealing, coupled with the observation of no FE features after laser irradiation, leads us to believe that oxygen vacancies 34,35,[66][67][68]78,79 (cause leakage currents, adversely affecting ferroelectricity) are responsible for the observed FM features. This finding is similar to many other reports.…”

“…Doping of (Mn 76 and Nb 77 ) STO crystal and thin films has been shown to be one means of inducing ferromagnetism. In addition, recent studies here at North Carolina State University [66][67][68] suggest that laser irradiation/annealing processes offer an alternative approach for introducing magnetism. Similarly, the irradiation-or defect-induced ferromagnetism has been widely reported in a variety of solids.…”

“…[65][66][67][68][69][70][71] It was suggested that the combination of magnetic defects arising from various defects such as vacancies, interstitials, deformation and partial destruction of the lattice structure may explain the onset of magnetic order. This represents an alternative approach to introducing magnetic moments into the multifunctional heterostructures considered in this study.…”

Enhanced Photocatalytic Activity in p-NiO Grafted n-TiO2 Porous Coatings

“…Due to the enhanced charge separation, the positive holes which are prerequisite for photocatalytic decomposition of 4CP (reactions (3) and (7)) can diffuse toward the surface to participate in the chemical reactions without recombination with electrons [12] .…”

“…Recently, fabrication of p-n junctions has been proposed as an effective approach to suppress the recombination of charge carriers which in turns increases the yield of photocatalytic reactions [11][12][13][14][15][16][17] . Titania is an n-type oxide semiconductor and this electrical behavior originates from its native point defects, i.e.…”