Nosipho Moloto

Efficient luminescent down-shifting detectors based on colloidal quantum dots for dual-band detection applications.

A colloidal quantum dot (QD) luminescent down-shifting (LDS) layer is used to sensitize an InGaAs short wavelength infrared photodetector to the near UV spectral band. An average improvement in the external quantum efficiency (EQE) from 1.8% to 21% across the near UV is realized using an LDS layer consisting of PbS/CdS core/shell QDs embedded in PMMA. A simple model is used to fit the experimental EQE data. A UV sensitive InGaAs imaging array is demonstrated and the effect of the LDS layer on the optical resolution is calculated. The bandwidth of the LDS detector under UV illumination is characterized and shown to be determined by the photoluminescence lifetime of the QDs.

Optical and morphological properties of ZnO- and TiO2-derived nanostructures synthesized via a microwave-assisted hydrothermal method

A microwave-assisted hydrothermal method was used to synthesize ZnO and TiO2 nanostructures. The experimental results show that the method resulted in crystalline monodispersed ZnO nanorods that have pointed tips with hexagonal crystal phase. TiO2 nanotubes were also formed with minimum bundles. The mechanism for the formation of the tubes was validated by HRTEM results. The optical properties of both ZnO and TiO2 nanostructures showed characteristics of strong quantum confinement regime. The photoluminescence spectrum of TiO2 nanotubes shows good improvement from previously reported data.

Complexity of Stakeholder Interaction in Applied Research

Applied research in complex integrated settings should be recognized as an endeavor that requires transdisciplinary and multisectoral stakeholder interactions. The problems faced in society are quite complex, requiring participation and knowledge from diverse aspects of society, including different disciplines (academia), communities, civil society, and government. Successful applied research relies on nurturing these key stakeholder relationships and interactions. This paper explores the key challenges of stakeholder interaction in applied research in three disciplines in the South African context, based on literature and the experience of authors in their disciplines. The three disciplines include information and communication technology for development, town and regional planning, and natural resource management. We attempt to also compare and contrast these challenges across the disciplines, to identify any commonalities and differences. After considering the mutual challenges and adaptive solutions to address these challenges in the different disciplines, we identify that all three areas in relation to stakeholder interaction appear to exhibit characteristics of complex systems, hence motivating to view applied research as a complex system. In this sense, complexity theory may provide a common language between the different disciplines examining transdisciplinary stakeholder interaction in applied research from a shared perspective.

Structural modification and band-gap crossover in indium selenide nanosheets

Herein, we report on the synthesis of InSe nanosheets. We further report on the interdependency of concentration and time on the evolution of the nanosheets as well as the role of the capping agents on the crystal phase and morphology of the resultant particles. Our results show that hexagonal-like InSe nanosheets were synthesized at different optimum times depending on the amount of indium precursor. Regardless of the amount of indium precursor used, the product remained unchanged, i.e. InSe. This was attributed to the nature of the oleylamine capping agent. Oleylamine is known to be a reducing agent and in this case resulted in the reduction of In3+ to In2− and elemental selenium to Se2−, thus always resulting in the formation of rhombohedral InSe nanosheets. A non-reducing 1-dodecanthiol co-surfactant was thus used. Dodecanthiol was thought to stabilize the In3+ ions by coordinating and forming a complex, thus preserving the 3+ oxidation state of indium, resulting in the formation of the final product of In2Se3 nanocrystals. The morphology of In2Se3 changed depending on the amount of oleylamine used. The optical properties of the InSe were further evidence that nanosheets had been synthesized due to the band gap crossover.

UV-assisted synthesis of indium nitride nano and microstructures

Indium nitride (InN) has been made the first time by a combined thermal/UV photo-assisted process. Indium oxide (In2O3) was reacted with ammonia using two different procedures in which either the ammonia was photolysed or both In2O3 and ammonia were photolysed. A wide range of InN structures were made by these procedures that were determined by the reaction conditions (time, temperature). The reaction of In2O3 with photolysed NH3 gave InN rod-like structures that were made of stacked cones (6 h/750 °C) or discs (6 h/800 °C) and that contained some In2O3 residue. In contrast, photolysis of both In2O3 and NH3 gave InN nanowires and pure InN nanotubes filled with In metal (>90%). The transformation of the 3D In2O3 particles to the tubular 1D InN was monitored as a function of time (1–4 h) and temperature (700–800 °C); the product formed was very sensitive to temperature. The band gap of the In filled InN nanotubes was found to be 1.89 eV.

Improved efficiency of organic solar cells using Au NPs incorporated into PEDOT:PSS buffer layer

The University of theWitwatersrand, Material Physics Research Institute, School of Physics & Chemistry; and MMU facilities at Wits, NRF and Material Energy Research Group (MERG).

Colloidal synthesis of pure CuInTe2 crystallites based on the HSAB theory

The colloidal method has extensively been used to synthesize ternary and quaternary copper sulfides and selenides. The formation pathway and the crystallization mechanism of these nanostructures have also been investigated. Although tellurides form part of the chalcogenides, little has been reported on them particularly the crystallization mechanism of these nanostructures. Herein, we report on the colloidal synthesis of CuInTe2. Typically reaction temperatures play a vital role in the formation of colloidal nanostructures. At temperatures below 250 °C, no formation of CuInTe2 was seen. At 250 °C formation of CuInTe2 could be observed with formation of binary impurities. A change in the sequence in which precursors were added at 250 °C yielded pure CuInTe2. Therefore starting with InCl3 and elemental Te dissolved in OLA and TOP, respectively, then adding CuCl dissolved in OLA yielded a pure CuInTe2 phase with agglomerated cubic structures. The pure CuInTe2 crystallites had an optical band gap of 1.22 eV in comparison to 0.93 eV of the impure CuInTe2 phase.

The Effect of Structural Properties of Cu2Se/Polyvinylcarbazole Nanocomposites on the Performance of Hybrid Solar Cells

It has been said that substitution of fullerenes with semiconductor nanocrystals in bulk heterojunction solar cells can potentially increase the power conversion efficiencies PCE of these devices far beyond the 10% mark. However new semiconductor nanocrystals other than the potentially toxic CdSe and PbS are necessary. Herein we report on the synthesis of Cu2Se nanocrystals and their incorporation into polyvinylcarbazole PVK to form polymer nanocomposites for use as active layers in hybrid solar cells. Nearly monodispersed 4 nm Cu2Se nanocrystals were synthesized using the conventional colloidal synthesis. Varying weight % of these nanocrystals was added to PVK to form polymer nanocomposites. The 10% polymer nanocomposite showed retention of the properties of the pure polymer whilst the 50% resulted in a complete breakdown of the polymeric structure as evident from the FTIR, TGA, and SEM. The lack of transport channels in the 50% polymer nanocomposite solar cell resulted in a device with no photoresponse whilst the 10% polymer nanocomposite resulted in a device with an open circuit voltage of 0.50 V, a short circuit current of 7.34 mA/cm2, and a fill factor of 22.28% resulting in a PCE of 1.02%.

Synthesis and characterization of Cu3N nanoparticles using pyrrole-2-carbaldpropyliminato Cu(II) complex and Cu(NO3)2 as single-source precursors: the search for an ideal precursor

Herein, we report the synthesis and characterization of Cu3N nanocrystals using two single-source precursors, bis(pyrrole-2-carbalpropyliminato) Cu(II) (PPC) and Cu(NO3)2·3H2O. The optical and structural properties were investigated and the suitability of the two precursors was studied in terms of producing good quality Cu3N nanocrystals without the detection of Cu or oxidation to CuO. Both precursors resulted in crystalline Cu3N with an anti-ReO3 cubic structure with no presence of copper impurities, however, peaks due to excess capping agent were detected by XRD and confirmed with XPS. The PPC complex resulted in spherical nanocrystals whilst the copper nitrate resulted in nanocubes. The band gaps were in the visible region with the copper nitrate nanocrystals slightly red shifted from the PPC derived particles due to larger crystal sizes. The emission spectra were blue-shifted from the absorption band edges hence indicating an up-conversion process.

Effect of diphenylphosphinic acid on cesium lead iodide perovskite stability

Cesium lead iodide nanocrystals (NCs) are one of the best perovskites to date. The quality of CsPbI3 tends to degrade with time and many researchers have embarked on studies for the improvement of CsPbI3 stability. Herein, CsPbI3 nanoparticles were synthesized via a colloidal approach by varying the capping agent and the coordinating solvent. The effect of a phosphinic ligand on the synthesis of CsPbI3 was assessed with the aim of getting new properties and/or improving its existing properties. The stability of the synthesized CsPbI3 perovskites was evaluated through photoluminescence emission over time. A nearly cubic phase of CsPbI3 was obtained through synthesis with diphenylphosphinic acid (DPPA) in benzyl ether (BE). Smaller nanocubes with an average size of 14 nm were prepared using DPPA in BE. The emission intensity lasted beyond 6 days with only 40% emission lost compared to that of materials prepared using a mixture of solvents and the conventional method. In order to illustrate possible applications, the NCs were used in a simple solar cell device with the configuration substrate-FTO-TiO2-CsPbI3/NiO-Au. A power conversion efficiency and a fill factor of 2.0% and 38%, respectively, were obtained from a 2,2′,7,7′-tetrakis-(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-MeOTAD)-free solar device which was made of the more stable synthesized CsPbI3.