Mart-Mari Duvenhage

Correlating the magnetism and gas sensing properties of Mn-doped ZnO films enhanced by UV irradiation

In this study, we report on the correlation between the magnetism and gas sensing properties of Mn-doped ZnO films grown via aerosol spray pyrolysis. The evolution of the structure, morphology, optical properties, and chemical state of ZnO with the Mn concentration was also investigated. ZnO doped with Mn (0.1 at%) demonstrated room-temperature ferromagnetism (RTFM) due to the uncompensated surface spins primarily originating from structural defects and oxygen vacancies (VO) on the surface, which act as active sites for the adsorption of oxygen species. The undoped ZnO structure revealed both FM and paramagnetism (PM) at the near surface of the film. Increased Mn doping destroyed the RTFM ordering due to improved PM features induced by Mn clusters on the ZnO surface and reduced amount of VO on the surface. However, ZnO films doped with Mn (0.1 at%) exhibited an improved sensing response to oxidizing gases compared to their counterparts, showing that films with RTFM with no PM contribution exhibit improved sensing properties. These analyses revealed that the nature of the film surface plays a substantial role in both their magnetic and sensing behaviors.

Ultra-broadband luminescent from a Bi doped CaO matrix

CaO:Bi phosphor powders were successfully synthesized by the sol–gel combustion method. Post heat treatment led to the enrichment of the Ca2+ site with multiple Bi centers. These centers were responsible for the change in the ultra-broadband cathodoluminescence (CL) emission as a function of different electron beam currents/beam voltages. The CaO phase formation and the presence of the enrichment of Bi was confirmed by using the X-ray diffraction and X-ray photoelectron spectroscopy techniques. The thermoluminescence afterglow spectra for the samples annealed at 800 °C and 1200 °C were strongly modified for the CaO and the presence of the multiple Bi centers. Of particular interest was that the ultra-broadband CL may have potential applications in inorganic single-emitting components that produce various colours under different beam currents/beam voltages or in a variety of optical devices if it can be better controlled.

Compositional, ultrastructural and nanotechnological characterization of the SMA strain of Saccharomyces pastorianus: Towards a more complete fermentation yeast cell analysis

Nano scanning Auger microscopy (NanoSAM) and time-of-flight secondary ion mass spectrometry (TOF-SIMS) have been used in materials science research for some time, but NanoSAM, in particular, has only recently been applied to biological specimens. Here, the first concurrent utilization of NanoSAM, TOF-SIMS and microscopic techniques for the examination of a standard beverage fermentation strain of Saccharomyces pastorianus uncovered the presence of intracellular networks of CO2 in fermenting cells. Respiring cells produced few bubbles and instead had large internal vacuolar structures. Transmission electron microscopy analysis also showed osmiophilic layers at the cell exterior of fermenting cells that became more prevalent with fermentation duration, while osmiophilic layers were largely absent in respiring cells. TOF-SIMS analysis showed a compositional difference at the exterior and interior of SMA cells and between fermenting and respiring cells. Fermenting cells also appeared to have different 3-OH oxylipin profiles compared to respiring cells based upon examination with immunofluorescence microscopy. The results of this work and further study using these materials science techniques will substantially enhance our understanding of the chemical, ultrastructural and metabolic changes that occur in fermentation yeasts.

The fluoretic difference in homoleptic mononuclear and dinuclear indium species

Quinolinol derivatives have been since envisaged as promising fluorophores based on their peculiarities since the birth of Alq3 entities as the prototype complex which was discovered by Tang and Van Slyke back in 1987.[1] As a result, that has prompted growth along the science of these M(Ox)3 entities with other triels down the boron group such as gallium (Ga) and indium (In) as potential electroluminescence layer in the edifice of OLED’s devices. There have been structural discrepancies for over two decades posed by the perturbed geometrical conformation of these complexes resorting to isomerism (meridional vs. facial) which potentially significantly impacts on the luminescence properties thereof. It was mainly the aforementioned effect that shaded the trials of varying many substitutions (EDG and EWG’s) on the backbone (to increase the efficiency of this complexes) and potentially set astray the postulated light outcome (unpredictable wavelength shifts).[2] What has been very true and crucial is the ability of this quinolinol framework to give light and form very rigid inorganic complexes with various metal centers and that is directly related to their chelato-aromatic properties, stability and tuneable luminescence properties.