This dissertation describes advances toward creating programmable building blocks and assembling them into new, tailored materials. I describe extended materials formed of bonded sets of cobalt selenide clusters. Rationally designed chemical transformations that form these sets give us precise control over the extent and dimensionality of the material. The cobalt selenide clusters fundamental to this study are members of a larger class of clusters with the M6E8 core (M = metal, E = chalcogen). Chapter 1 introduces this family of clusters and reviews examples of previously made materials. Chapter 2 unveils a family of site-differentiated clusters, Co6Se8(CO)x(PEt3)6-x, their substitution reactions, and assembly into bridged dimers and trimers. Electrochemical methods were used to investigate electronic coupling between the cores, by comparing the electrochemical behavior of the dimer and trimer relative to their monomeric counterparts. We further performed magnetic susceptibility measurements of the monomers and assemblies. Chapter 3 introduces electrocrystallization as a method to synthesize extended, crystalline, solid state compounds from superatomic building blocks. By electrocrystallizing redox-active [Co6Se8] clusters with labile ligands in the presence of an ionic template, we created a crystalline polymeric material that exhibits weaving at the nanoscale. Chapter 4 presents a metal coordination approach to [Co6Se8] materials via reactive groups on the capping ligands. The redox-activity and multinuclearity of the superatom components creates a new level of complexity and synthetic sophistication to previously reported frameworks. In collaboration with Prof. Christopher Bejger (University of North Carolina at Charlotte), I installed carboxylate groups on the surface of the cluster. With this building block in hand and a simple metal salt, Zn(NO3)2, we discovered two sets of distinct solvothermal reaction conditions that yielded two different solids. Both are homogenous, crystalline, porous solids whose dimensionality is tuned by subtle changes in reaction conditions. I further showed that the dimensionality could be further reduced by chemical exfoliation to yield free-floating sheets of zinc-coordinated clusters in which the porosity and redox-activity of the bulk solid is preserved. Finally, Chapter 5 outlines a novel chemical transformation that dimerizes [Co6Se8] units to form a material with an expanded core, [Co12Se16], that exhibits electronic and optical properties distinct from the parent monomer. To accomplish this dimerization, I installed a reactive carbene on the [Co6Se8] core to create a latent fusion site. We show by cyclic voltammetry, infrared spectroscopy, single crystal X-ray diffraction, and density functional theory calculations that the resulting fused [Co12Se16] material exhibits strong electronic coupling and electron delocalization. These chapters present novel synthetic approaches toward creating [Co6Se8] materials with tuned dimensionality, size, and extensive charge delocalization.

A thesis submitted in fulfilment of the requirements for the degree of Doctor of Philosophy in the School of Chemistry Faculty of Science, University of Witwatersrand, 2017 / Advancements in nanotechnology and nanosystems promise to extend limits of sustainable development and environment remediation in an attempt to address some of the world most challenging problems. Specifically, nanotechnology has played an important role in the design, synthesis, and characterization of various new and novel functional nanomaterials possessing extremely unique properties. For example, low dimensional nanostructures such as semiconductor nanocrystals with well controlled sizes, shapes, porosities, crystalline phases, and structures have been prepared via various synthetic methods. In addition these semiconductor nanocrystals have attracted research attention because of their fundamental role in the comprehension of the quantum size effect and great potential applications to save resources and improve the environment. Tremendous studies have established that morphological, optical, catalytic and electronic properties of semiconductor nanocrystals can be manipulated during synthesis by simply varying the growth parameters. Herein we establish the effect of different synthetic methods and several growth parameters on the properties of the as-synthesized semiconducting metal selenides nanocrystals (NixSey and InxSey) including structural, optical, electronic and catalytic properties. For example, reducing coordinating solvent oleylamine was seen to favour a particular morphologies and stoichiometries despite the duration of synthesis. In the case of InxSey nanocrystals, oleylamine favoured indium monoselenide (InSe) nanosheet formation while addition of 1-DDT as a co-surfactant to oleylamine produces In2Se3 nanowires. For NixSey nanocrystals, TOP as a co-surfactant to different ligands favoured the formation Ni3Se2 with different shapes including dots, plates, rods and wires in different solvents. Other parameters studied included the reaction time and temperature. Besides the properties, we probe the potential applications of these materials in dye sensitized solar cells as counter electrodes as well in chemical sensor as the sensing material. NixSey nanocrystals were employed as CE in DSSCs in an attempt to replace the noble expensive platinum conventionally used as CE in most DSSCs. It was established that different stoichiometry played a significant role in the catalytic reduction of I3-. Thus, different photovoltaic performance parameters were obtained with NiSe2 giving a higher PCE of 1.5 % followed Ni3Se4 then Ni3Se2. These values were however very low compared to the ones reported in literature, something that was attributed to low electron mobility, enhanced recombination and reduced catalytic performance as a result of poor device assembly and the organic ligand layer encapsulating the nanocrystal. In another scenerio, indium monoselenide nanocrystals were employed in chemiresistive sensors to detect the presence of a number of VOCs including formaldehyde, methanol, chloroform and acetone in the ambient. Indeed despite the well-known electrical, optical and structural properties previously reported in literature, metal selenides such as CdSe, PbSe and ZnSe among others present lack of investigation for gas sensing. The experimental results showed that different morphologies of InSe nanostructures interacted differently to the analyte gas suggesting difference in the electronic properties of different morphologies. The InSe nanoparticle based sensors gave a good response to HCHO and MeOH fumes and were more selective to HCHO fumes than chloroform and acetone. While those fabricated using the InSe nanosheets though responding well to HCHO recovered half way when exposed back in air and resulted in relatively high noise to signal ratio when exposed to MeOH. The operating temperature range for the InSe sensor devices were determined to be near room temperature. The sensors response was observed to decrease with increasing temperature from 30 °C to 90 °C. Evident from the results, the surface capping molecule (oleylamine) employed to stabilize the nanostructures during synthesis was responsible for the poor sensing abilities of the nanostructures. / XL2018

In this experiment, selenides are used as the precursor and CIGS thin films are synthesized through selenization. At the first stage, the precursor with the layers of In-Se/Ga-Se/Cu-Se failed to produce CIGS thin films when the temperature is going up 10¢J per minute to the target temperature during selenization and the change of the composition of the precursor, the temperature duration and the temperature of selenization is tried. Later, the reaction is successfully done when the layers are changed into In-Ga-Se/Cu-Se with the temperature going up 10¢J per minute to 550¢J, lasting for 5 minutes. With various Ga containments, I analyize the optical and electronic properties. In order to see the composition of CIGS thin films in different propotion of Cu/In+Ga and Ga/In+Ga, I use EPMA and the properties of XRD peak shift with the containment of Ga to estimate the proportion of the containment of Ga. I found the conclusions by EPMA and XRD are very similar. At 150¢J, the precursors Cu-Se, In-Se and Ga-Se are fabricated and XPS, Raman, XRD or else are used to speculate the bonding of them. In addition, using XRD and Raman to analyze In-Ga-Se/Cu-Se selenides, I found, between 150¢J and 300¢J, Cu2-xSe bonding is the main; at 350¢J, InSe bonding intensifies obviously; at 400¢J, CIGS is formed.

This experiment was growing CZTSe (Cu2ZnSnSe4) single phase thin film by using rapid thermal selenization process on Se/Cu/Sn/Zn/SLG thin film. It can complete the reaction to avoid Cu2SnSe3 appearing during the RTP. To discuss the effect of nitrogen and selenium flow rates on the thin film quality and adhesion, and to confirm the composition of the CZTSe single phase thin film. And I also annealed and changed the Se/Cu/Zn/Sn/SLG stacked layer to improve the thin film uniformity. Finally, it was stacked on the Mo/SLG and annealed by varying raising rate of temperature in order to enhance the adhesion. The results indicated that the various flow of nitrogen could cause different conditions. The element selenium easily escaped due to lower nitrogen flow could not provide enough outer pressure; larger nitrogen flow carried the extra high vapor pressure gas go through the surface of substrate and lead to the worse adhesion with the substrate. Unfortunately, using the analysis of X-ray diffraction and Raman spectrum couldn¡¦t determine the single phase of CZTSe. However, it has been confirmed by optical bandgap. In this experiment, the compositions of CZTSe single phase are found to be Cu-poor and Zn-poor, the optical bandgap (Eg) is 0.88~1.04 eV, and the resistivity (£l) is 1~10-2 £[-cm. By the rapid thermal selenization process, because of the rapid gradient of temperature, it brought out the diffused non-uniformly among the precursors. Therefore, the uniformity of thin films would not be perfect. As the result, re-annealing and change are the efficient methods to improve the uniformity of the thin film. The problems are un-wetting effect exists in the stacked liquid phase Se/Cu/Zn/Sn and the sodium glass substrates. The morphologies of the thin films are island connection. Finally, increasing the temperature in 15 oC per second and annealing the thin film for one minute at 250 oC with the stacked layer of Se/Cu/Sn/Zn/Mo/SLG are successful to promote the adhesion between the CZTSe and Mo.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 156-166).

Thesis (M.Mat.S.E.)--University of Delaware, 2008. / Principal faculty advisor: Robert W. Birkmire, Dept. of Materials Science & Engineering. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (leaves 123-139).

Since the discovery of graphene, a new era of physics called "Two Dimensional (2D)Materials" has emerged. Group IV and Group III Selenides such as SnSe and InSe arepromising members of the 2D family. Structure of Group IV selenides is unique and highlysensitive to pressure and temperature. To further tweaking their properties by structuralchanges, thorough understanding of how the structure relates to the electronic bands is veryimportant. Based on the results from DFT calculations, I carefully analyzed electronic bandstructures of layered SnSe with various interlayer stacking. The first part of this dissertationdiscussed the possible stacking-dependent indirect-direct transition of bilayer SnSe.By further analysis, these results reveal that the directionality of interlayer interactionsdetermine the critical features of their electronic band structures. Further, it demonstratedthat such changes can be achieved by substitutional chemical doping. Using a multi-scalemodeling approach by combining the result of DFT and Boltzmann Transport Theory, Idiscussed the electron transport properties of co-doped SnSe, a class of thermodynamicallyand dynamically stable structures. The second part discussed on charge transfer across InSe/Gas interface, which showsbi-polar transport properties. This finding is in a good agreement with the recent experimentalobservations. Fundamental understanding of charge transfer in few-layer InSe /gasinterfaces at the atomic level is expected to pave the path for designing gas sensing devices.

No description available.

Studying quasi-one-dimensional (1D) semiconductor nanostructures is an attractive and active research field in nanoscience and nanotechnology. Their controllable growth is the foundation for observing novel properties and fabricating useful nano-devices and is also a challenge. / We believe that our work in perfecting the fabrication of aligned 1D semiconductor nanostructures and control of their morphology, crystal structure and orientation will shed more light on the understanding on 1D physics and advancement in nanotechnology. / We have studied the control of the structure, morphology and alignment of Zn-Cd-Se 1D nanostructures by fine tuning their growth conditions and judiciously choosing substrates in a metalorganic chemical vapor deposition (MOCVD) reactor. We found that the products are zincblende structured nanoneedles at relatively low temperatures and pressures, and wurtzite structured nanowires at high temperatures and pressures. We have fabricated aligned 1D nanostructures of different chemical compositions by exploiting the epitaxial relationship between the lattices of Zn-Cd-Se system and GaAs substrate. From the systematic studies of the orientations of the aligned samples, we demonstrated that they can be controlled by the crystallographic surface of the substrate. We also found that the orientation can be affected by the growth temperature. Three growth models are suggested to explain the aligned growth for zincblende and wurtzite 1D nanostructures and complex shaped three-bladed nanoswords. Observations and angular measurements of the orientations and growth directions by electron microscopy and analyses by pole stereographs offer supporting evidences for the models. Polarized photoluminescence studies of individual CdSe nanowires obtained under controlled growth have been achieved. / Liu, Zhuang = 通過金屬有機物化學氣相沉積法合成晶體結構, 形貌及生長取向性可控的硒鋅鎘族准一維納米結構 / 劉壯. / "July 2007." / Adviser: Sui Kong Hark. / Source: Dissertation Abstracts International, Volume: 69-02, Section: B, page: 1062. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2007. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307. / Liu, Zhuang = Tong guo jin shu you ji wu hua xue qi xiang chen ji fa he cheng jing ti jie gou, xing mao ji sheng chang qu xiang xing ke kong de xi xin ge zu zhun yi wei na mi jie gou / Liu Zhuang.