The growth and structural properties of GaN/AlN core-shell nanowire heterostructures have been studied using a combination of resonant x-ray diffraction, Raman spectroscopy and high resolution transmission electron microscopy experiments. For a GaN core of 20 nm diameter on average surrounded by a homogeneous AlN shell, the built-in strain in GaN is found to agree with theoretical calculations performed using a valence force field model. It is then concluded that for an AlN thickness up to at least 12 nm both core and shell are in elastic equilibrium. However, in the case of an inhomogeneous growth of the AlN shell caused by the presence of steps on the sides of the GaN core, plastic relaxation is found to occur. Consistent with the presence of dislocations at the GaN/AlN interface, it is proposed that this plastic relaxation, especially efficient for AlN shell thickness above 3 nm, is promoted by the shear strain induced by the AlN inhomogeneity.

Coherent diffraction imaging (CDI) on Bragg reflections is a promising technique for the study of three-dimensional (3D) composition and strain fields in nanostructures, which can be recovered directly from the coherent diffraction data recorded on single objects. In this article we report results obtained for single homogeneous and heterogeneous nanowires with a diameter smaller than 100 nm, for which we used CDI to retrieve information about deformation and faults existing in these wires. The article also discusses the influence of stacking faults, which can create artefacts during the reconstruction of the nanowire shape and deformation.

The molecular-beam epitaxy growth of AlN/GaN nanowire superlattices has been studied by using a combination of in situ x-ray diffraction experiments, high-resolution electron-microscopy analysis and theoretical calculations performed in a valence force field approach. It is found that the nanowire superlattices are in elastic equilibrium, in contrast with the two-dimensional case but in line with the predicted increase in the critical thickness in the nanowire geometry.

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The strain state of 1 and 2.5 nm thick GaN insertions in GaN/AlN nanocolumn heterostructures has been studied by means of a combination of high resolution transmission electron microscopy, Raman spectroscopy and theoretical modeling. It is found that 2.5 nm thick GaN insertions are partially relaxed, which has been attributed to the presence of dislocations in the external AlN capping layer, in close relationship with the morphology of GaN insertions and with the AlN capping mechanism. The observed plastic relaxation in AlN is consistent with the small critical thickness expected for GaN/AlN radial heterostructures.

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For organic solar cells (OSC) such as dye-sensitized cell (DSSC) to compete with silicon-based cells in terms of stability, there is a need to further improve components which causes degradation. To answer the stability issue with liquid electrolyte, solid state dye-sensitized solar cell (SS-DSSC) was introduced. SS-DSSC promises performance consistency due to less power degradation compared to standard DSSC that uses liquid-based electrolyte. Pentacene (PEN), a semiconductor usually used on field-effect transistors is a material that has a higher hole and electron mobility when compared to amorphous silicon and also has a band gap suitable for solar energy conversion. In this study, PEN used as hole transporting layer in SS-DSSC was fabricated through spin coating and heating using a precursor and through vapour transport using powder. The PEN samples were then doped with bromine through different methods - immersion and vaporization. Characterization of the PEN samples through X-ray Diffraction, Energy Dispersive X-ray Fluorescence, and Atomic Force Microscopy reveal orthorhombic, thin film, and crystalline bulk phases present on different fabricated PEN samples as well as confirmed successful doping. Furthermore, the light harvesting parameters are analysed through SolarTM Light LS1000 Solar Simulator (AM 1.5, 100 mW/cm2) which confirm correlation between the increased efficiency, PEN layer growing methods, and bromine doping methods.

Titanium dioxide (TiO2) has been long used as a photoanode for dye-sensitized solar cells (DSSC) for its high photoreductive capability. One approach towards increasing the performance of TiO2 is to load silver nanoparticles (Ag NP) unto the substrate. In this study, hydrothermal treatment of as-received TiO2 anatase was utilized to fabricate nanostructures that could increase the overall efficiency of DSSC. This hydrothermally-treated TiO2 was loaded with Ag NP via the photodegration of silver nitrate (AgNO3). Characterization of Ag-loaded TiO2 (Ag-TiO2), done using Raman Spectroscopy and Field Emission Scanning Electron Microscopy (FESEM), reveal the anatase characteristic of the samples after hydrothermal treatment, as well as the crystalline structure transformation from tetragonal to monoclinic. Furthermore, upon application of the produced TiO2 samples in DSSC, photovoltaic characteristics were obtained. There was an increase in the current density of all of the Ag-TiO2 samples as compared to the untreated TiO2 sample. The DSSC produced using 0.20 Ag-TiO2 ratio exhibited the highest conversion efficiency, resulting to more than 3000% increase in conversion efficiency from the untreated TiO2 sample.