Synthesis of SnO2/CuO/SnO2 Multi-layered Structure for Photoabsorption: Compositional and Some Interfacial Structural Studies

Many metal oxide heterostructures have been synthesized as mixed oxides or layered structures for photocatalytic, photodegradation of pollutants and light-harvesting applications. However, in the layered structures the effects of interfacial properties and composition have largely not been explored. Hence, the effects of interfacial mixing and diffusion of sandwiched thin CuO layer on optical absorption of as-deposited and heat-treated multi-layered structured SnO2/CuO/SnO2 films were studied. The RBS analysis of the as-deposited films showed the presence of a minute amount of Cu in the surface and bottom SnO2 layers of the structure. We attributed this to inhomogeneous layer thickness evidenced by very low Sn/Cu atoms ratio of the CuO layer. However, the thermal treatment of the layered structure led to pronounced interlayer mixing and consequent formation of SnO2-CuO solid solutions throughout the layered structure. The layer integrity of the inserted CuO of the as-deposited films was very high and the as-deposited structure was far more optically absorbing. However, the annealed structure showed lesser optical absorption because of the onset of interfacial mixing and improved crystallization. This reflected in the optical bandgap variations of the as-deposited and annealed multilayered structures. The significance of this result is that the multi-layered films possess band narrowing – evidence of increased photon absorption - making it a better candidate than pure SnO2 oxide for photocatalysis, photodegradation and photodetection applications. It also pointed to the fact that attention must be paid to effects of heat treatments or annealing when inserting an absorbing layer into a photocatalyst or a material meant for photodegradation or any light-harvesting material.

Pseudo-Planar Organic Heterojunctions by Sequential Printing of Quasi-Miscible Inks

This work deals with the interfacial mixing mechanism of picoliter (pL)-scale droplets produced by sequential inkjet printing of organic-based inks onto ITO/PET surfaces at a moderately high Weber number (~101). Differently from solution dispensing processes at a high Bond number such as spin coating, the deposition by inkjet printing is strictly controlled by droplet velocity, ink viscosity, and surface tension. In particular, this study considers the interfacial mixing of droplets containing the most investigated donor/acceptor couple for organic solar cells, i.e., poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl-C61-butyric acid methyl ester (PCBM), showing how low-viscosity and low-surface energy inks can be leveraged for the fabrication of an interface suitable for a pseudo-planar heterojunction (pseudo-PHJ) organic solar cell (OSC) that is a convenient alternative to a bulk heterojunction (BHJ) OSC. The resulting thin-film morphology and molecular organization at the P3HT/PCBM interface are investigated, highlighting the roles of dissolution-driven molecular recirculation. This report represents a first step toward the sequential inkjet printing fabrication of pseudo-PHJ OSCs at low consumption of solvents/chemicals.

The Effect of Bottom – Generated Tidal Mixing on Tidally Pulsed River Plumes

The mixing of river plumes into the coastal ocean influences the fate of river-borne tracers over the inner-shelf, though the relative importance of mixing mechanisms under different environmental conditions is not fully understood. In particular, the contribution to plume mixing from bottom generated shear stresses, referred to as tidal mixing, is rarely considered important relative to frontal and stratified shear (interfacial) mixing in surface advected plumes. The effect of different mixing mechanisms is investigated numerically on an idealized, tidally pulsed river plume with varying river discharge and tidal amplitudes. Frontal, interfacial, and tidal mixing are quantified via a mixing energy budget to compare the relative importance of each to the overall buoyancy flux over one tide. Results indicate that tidal mixing can dominate the energy budget when the tidal mixing power exceeds that of the input buoyancy flux. This occurs when the non-dimensional number, RiE (the estuarine Richardson number divided by the mouth Rossby number), is generally less than 1. Tidal mixing accounts for between 60% and 90% of the net mixing when RiE < 1, with the largest contributions during large tides and low discharge. Interfacial mixing varies from 10% to 90% of total mixing and dominates the budget for high discharge events with relatively weaker tides (RiE > 1). Frontal mixing is always less than 10% of total mixing and never dominates the budget. This work is the first to show tidal mixing as an important mixing mechanism in surface advected river plumes.