We report the degradation of low temperature photoluminescence (PL) from Si/SiGe three-dimensional cluster morphology nanostructures under continuous photoexcitation. The PL intensity initially decreases slowly for about 15 minutes, and then decreases rapidly, until only ∼ 10% of the original PL intensity remains. A complete recovery of the PL requires restoring the sample temperature to ∼ 300K. We propose that a slow accumulation of charge in SiGe clusters enhances the rate of Auger recombination and results in the observed PL degradation.

We demonstrate that the anisotropic optical response of metal (cobalt) slanted columnar thin films (STF) at THz frequencies strongly depends on the dielectric properties of the dielectric ambient surrounding the slanted columnar thin films. An effective medium dielectric function approach is used to describe the combined optical response of metal slanted columnar thin film and dielectric ambient. Our observations indicate that metal (cobalt) slanted columnar thin films can be used as sensors which will enable detection and characterization of minute amounts of dielectrics at THz frequencies, such as for flow-based detection of liquid chemical constituents.

Aging effects of as-deposited and passivated slanted columnar thin films from cobalt determined by generalized ellipsometry within the visible spectral region are reported. Slanted columnar thin films have been grown by glancing angle electron beam deposition and sub-sequently coated with Al2O3 by an atomic layer deposition process. An anisotropic Bruggeman effective medium approximation developed for highly ordered three dimensional metal nanostructures is employed to analyze spectroscopic Mueller matrix ellipsometry data. Our model approach allows for determination of biaxial optical and structural properties as well as fractions of multiple film constituents. While the optical properties of the uncoated film change over time, the alumina passivation layer prevents oxidation in air and therefore aging effects; however, it affects the intrinsic bulk-like Co optical properties.

To develop alternative and low cost photovoltaic technologies we have synthesized CuInS2 nanocrystals with tunable optical properties and characterization was carried out thoroughly with TEM, SEM, EDAX and XRD. Furthermore large self-organized arrays of TiO2 nanotubes were fabricated on Ti foil followed by simple electrochemical anodization technique and characterized their structure by SEM and then for the first time coupled both the nanocrystals and nanotubes to form a p-n junction type photovoltaic device. The current-voltage (I-V) characteristics of photovoltaic cells were measured to test the proof of concept. Some preliminary experiments showed that device generates some current upon illumination. However, in our case we fabricated a device without sandwiching any buffer or barrier layers in between nanocrystals and nanotube arrays. We have been optimizing our solar cells efficiency by improving quality of nanotubes and nanocrystals. Some of the interesting finding are presented and discussed.

We report the novel use of semiconductor photocatalysis for the deposition of metal onto insulating surfaces and the in-process formation of nano-structured porosity within this metal. In the process of Photocatalytically Initiated Electroless Deposition (PIED) we have developed a controllable, spatially selective and versatile metallisation technique with several advantages over traditional, non-photocatalytic techniques such as enhanced controllability and purity of the deposit as well as reduced operational costs and environmental impact. With the addition of a self-assembled, hexagonally close-packed microparticle template to the substrate prior to metal deposition, PIED can be used to fabricate thin metal films with highly ordered porosity on the nano-scale. Nanoporous metallisation in this way is able to produce substrates with potentially wide applications such as membrane and separation technology, energy storage and sensors – especially surface enhanced resonance Raman spectroscopy (SERRS).

Its intrinsic nontoxicity makes the direct band gap InP/ZnS core/shell be one of the most promising semiconductor nanocrystals for optoelectric applications, with the advantage of tuning the optical absorption range in the desired solar spectrum region. Highly luminescent and monodisperse InP/ZnS nanocrystals were synthesized in a non-coordinating solvent under a thorough degassing process. By varying synthesis scheme, different size InP/ZnS nanocrystals were grown. For the purpose of ensuring air stability, ZnS shell was grown. This ZnS shell improves the chemical stability in terms of oxidation prevention. Measurements of absorption and emission were performed on different InP/ZnS nanocrystals with different sizes. As expected, the measurements show a red-shift as the size of the InP/ZnS nanocrystals increased.

We investigated the temperature dependence of the Stokes shift of PbS quantum dots (diameter 4.7 nm) deposited from solution on glass using a specially designed apparatus. By measuring the thermal alteration of the optical absorbance and photoluminescence in the range of 5 K – 300 K, we demonstrate that the Stokes shift shrinks from 135 meV at 5 K to 62 meV at 300 K. Extrapolation of the data presented predict an elimination temperature of the Stokes shift of about 460 K, corresponding to the thermal energy of the sum of prominent PbS phonon energies.

CdSe/CdS colloidal nanocrystals are light-emitting nanoparticles with remarkable optical properties such as suppressed fluorescence blinking and enhanced emission from multiexciton states. These properties have been attributed to the suppression of non-radiative Auger recombination. In this work we employ ultrafast spectroscopy techniques to identify optical signatures of neutral and charged excitonic and multiexcitonic states.

BiI3 is a semiconductor layered compound of growing interest for direct and digital imaging. This structure determines that bismuth tri-iodide crystals can grow with platelet habit. Thereby, we consider of great importance to study if such structure can determine nanoparticles of this material as well, that means, if such layers can be rolled in order to form nanotubes and/or nanorods. In light of this, the present work reports the synthesis of bismuth tri-iodide nanoparticles by the suspension method.

Bi(NO3)3.5H2O, I2 and KI were used as source materials, and 1-octadecene was used as suspension agent. The intermediate and final synthesized compounds were characterized by Xray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM).

Results clearly show that BiI3 nanoparticles can be synthesized by the suspension method, which means that the layer structure of these compounds can determine the growth of nanostructures. Nanoparticles of different sizes and morphologies were obtained, depending on the synthesis conditions. There has been not possible to control such conditions in order to obtain uniform size and morphology distributions. The use of these nanostructures may be an interesting way of improving nucleation and further growth of bismuth tri-iodide films.

Synthesis of wurtzite-type ZnS nanoparticles by an electric discharge submerged in molten sulfur is reported. By the pulsed plasma between two zinc electrodes of 5 mm diameter in molten sulfur, we have synthesized high-temperature phase (wurtzite-type) ZnS nanocrystals with an average size of about 20 nm. Refined lattice parameters of the synthesized wurtzite-type ZnS nanoparticles were found to be larger than those of the reported ZnS (JCPDS 36-1450). UV-Visible absorption spectroscopy analysis showed that the absorption peak of the as-prepared ZnS sample (319 nm) displays a blue-shift comparing to the bulk ZnS (335 nm). Photoluminescence spectra of the samples revealed peaks at 340, 397, 423, 455 and 471 nm, which were related to excitonic emission and stoichiometric defects. Synthesis of ZnMgS (solid solution of ZnS and MgS) was achieved by using ZnMg alloys as both cathode and anode electrodes. Also, rocksalt structure MgS was synthesized by using magnesium rods as both cathode and anode electrodes.

Exchanging the original organic ligands of colloidal CdSe quantum dots (QDs) with metal chalcogenide SnS4 ligands resulted in absorption peak redshifts and complete photoluminescence quenching in QD solids. The ITO/QDs/Al structure with SnS4-capped QDs showed much higher electrical conductivity and reduced space-charge limited current. These results are indicative of carrier delocalization as well as enhanced inter-QD electronic coupling caused by the inorganic ligands. The SnS4-capped QDs were able to retain strong excitonic absorption. The photocurrent spectral response of the all-inorganic QD film resembled its absorption spectra, and was three orders of magnitude stronger than that of QDs with organic ligands. It was found that mild annealing at ∼ 200 oC transformed the SnS4-capped QD film into to a more conductive assembly, degrading its absorption and photocurrent generation. These findings suggest that colloidal QDs with metal chalcogenide ligands are better suited for solar energy conversion and photodetection than use in light-emitting devices as luminophores.