Bill Gong

XPS study of Nb-doped oxygen sensing TiO2 thin films prepared by sol-gel method

Abstract Titanium dioxide (TiO2) thin films have been prepared using the sol-gel method and subsequently doped with niobium oxide (Nb2O5) for use in oxygen sensing applications. The chemical composition of the resultant film sensor surface has been investigated using X-ray photoelectron spectroscopy (XPS). Films are essentially stoichiometric with carbon as the dominant impurity at the surface. The film electrical resistance has been examined for detection of oxygen at concentrations of 1 ppm to 1%. Doping resulted in a 40% increase in the oxygen gas sensitivity of the thin films at an operating temperature, as low as 190°C.

Investigation on ozone-sensitive In2O3 thin films

Abstract Indium oxide (In2O3) thin films have been prepared by sol–gel and RF sputtering techniques. The sol–gel film appeared to be much more sensitive to ozone compared to the RF sputtered film. The morphology of both films was examined by SEM, while their chemical composition was analyzed using X-ray photoelectron spectroscopy (XPS) in order to understand the properties responsible for the high sensitivity of sol–gel films. The examination results showed that the sol–gel films are very porous and uniform in grain size, but the RF films are relatively dense and of coalescent grains. XPS analysis also highlighted that there may be oxygen vacancies on the surface of sol–gel films. The large surface areas of sol–gel films and oxygen deficiency in the film structure are responsible for its higher sensitivity.

Towards the development of a virtual organic solar cell: An experimental and dynamic Monte Carlo study of the role of charge blocking layers and active layer thickness

Monte Carlo (MC) simulations have been used to fully model organic solar cells. The quantum efficiency and short-circuit current of these virtual devices are in excellent agreement with experimental measurements. Simulations show that, contrary to expectation, indium tin oxide/poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)/poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methylester (PCBM)/aluminium devices lack effective charge blocking layers at the electrode interfaces. X-ray photoelectron spectroscopy depth profiling shows that despite a PCBM-rich region near the cathode, interface intermixing at the electrodes combined with incomplete PCBM coverage leads to significant interface recombination. This work highlights the effectiveness of MC simulations as a predictive tool and emphasizes the need to control electrode interface processes.

Comparative degradation and regeneration of polymer solar cells with different cathodes.

A comparative degradation study of solar cells based on a bulk-heterojunction (BHJ) blend of poly(3-hexylethiophene) (P3HT) and phenyl [6,6] C61 butyric acid methyl ester (PCBM) with two different cathodes is reported. Poly(ethylene-dioxythiphene):poly(styrene sulfonate) (PEDOT:PSS) coated ITO electrodes were used as the anode, whereas Ca/Al and Ca/Ag electrodes were used as cathodes. Fully degraded devices were subjected to thermal annealing under inert atmosphere. The performance of degraded solar cells with a Ca/Al cathode exhibited no improvement after treatment. However the solar cells with a Ca/Ag cathode exhibited a considerable recovery in their performance following annealing under a nitrogen atmosphere. Indeed, these solar cells could be subjected to many degradation and regeneration cycles. Current density-voltage (J-V) characteristics and X-ray photoelectron spectroscopy (XPS) studies show that this behavior arises from the complex chemical thermodynamics of the reactions that can occur at the cathode/active layer interface. In particular, the recovery of device performance for solar cells with a Ca/Ag cathode is due to the reversible oxidation of Ag upon thermal annealing.

Subcellular tracking reveals the location of dimethylsulfoniopropionate in microalgae and visualises its uptake by marine bacteria

Phytoplankton-bacteria interactions drive the surface ocean sulfur cycle and local climatic processes through the production and exchange of a key compound: dimethylsulfoniopropionate (DMSP). Despite their large-scale implications, these interactions remain unquantified at the cellular-scale. Here we use secondary-ion mass spectrometry to provide the first visualization of DMSP at sub-cellular levels, tracking the fate of a stable sulfur isotope (34S) from its incorporation by microalgae as inorganic sulfate to its biosynthesis and exudation as DMSP, and finally its uptake and degradation by bacteria. Our results identify for the first time the storage locations of DMSP in microalgae, with high enrichments present in vacuoles, cytoplasm and chloroplasts. In addition, we quantify DMSP incorporation at the single-cell level, with DMSP-degrading bacteria containing seven times more 34S than the control strain. This study provides an unprecedented methodology to label, retain, and image small diffusible molecules, which can be transposable to other symbiotic systems. DOI: http://dx.doi.org/10.7554/eLife.23008.001

The effect of calcium-induced fullerene migration on the performance of thermally stable nanoparticle organic solar cells

The impact of a calcium interface layer in combination with a thermal annealing treatment on the performance of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-buteric acid methylester (PCBM) nanoparticle photovoltaic devices is investigated. Annealing is found to disrupt the microstructure of the nanoparticle active layer leading to a reduction in fill factor. However, X-ray photoelectron spectroscopy measurements show that the calcium interface layer causes PCBM to preferentially migrate to the cathode interface upon annealing, resulting in better charge extraction from the PCBM moiety, an increase in the built-in voltage, open-circuit voltage, and power conversion efficiency. Moreover, the annealing trends could be completely explained by the observed PCBM migration. Unlike P3HT:PCBM bulk heterojunction devices, the P3HT:PCBM nanoparticle devices showed a remarkable thermal stability up to 120 °C. As such, OPVs fabricated from aqueous nanoparticle inks provide an attractive alternative to conventional o...