Defect Chemistry and Ion Intercalation During the Growth and Solid-State Transformation of Metal Halide Nanocrystals

Abstract of the Dissertation Defect Chemistry and Ion Intercalation During the Growth and Solid-State Transformation of Metal Halide Nanocrystals Semiconductor metal halides as light-sensitive materials have applications in multiple areas, such as photographic film, antibacterial agents and photocatalysts. One focus of this dissertation is to achieve novel morphologies of ternary silver bromoiodide (AgBr1-xIx, 0 For the silver halide system, we demonstrate that the anion composition of AgBr1-xIx nanocrystals determines their shape through the introduction of twin defects as the nanocrystals are made more iodide-rich. AgBr1-xIx nanocrystals grow as single-phase, solid solutions with the rock salt crystal structure for anions compositions ranging from 0 ≤ x \u3c 0.38. With increasing iodide content the morphology of the nanocrystals evolves from cubic to truncated cubic to hexagonal prismatic. Structural characterization indicates the cubic nanocrystals are bound by {100} facets whereas the hexagonal platelet nanocrystals possess {111} facets as their top and bottom surface. Calculations based on first-principles density functional theory show that iodide substitution in AgBr stabilizes {111} surfaces and that twin defects parallel to these surfaces possess a low formation energy. Our experimental observations and calculations are consistent with a growth model in which the presence of multiple twin defects parallel to a {111} surface enhances lateral growth of the side facets and changes the nanocrystal shape. To study the reaction kinetics of solid-state conversion in the lead halide system, we use the change in fluorescence brightness to image the transformation of individual lead bromide (PbBr2) nanocrystals to methylammonium lead bromide (CH3NH3PbBr3) via intercalation of CH3NH3Br. Analyzing this reaction one nanocrystal at a time reveals information that is masked when the fluorescence intensity is averaged over many particles. Sharp rises in the intensity of single nanocrystals indicate they transform much faster than the time it takes for the ensemble average to transform. Furthermore, the intensity rises for individual nanocrystals are insensitive to the CH3NH3Br concentration. To explain these observations, we propose a phase transformation model in which the reconstructive transitions necessary to convert a PbBr2 nanocrystal into CH3NH3PbBr3 initially create a high energy barrier for ion intercalation. A critical point in the transformation occurs when the crystal adopts the perovskite phase, at which point the activation energy for further ion intercalation becomes progressively smaller. Monte Carlo simulations that incorporate this change in activation barrier into the likelihood of reaction events reproduce key experimental observations for the intensity trajectories of individual particles. The insights gained from this study may be used to further control the crystallization of CH3NH3PbBr3 and other solution-processed semiconductors. In this dissertation, we focus on two different systems, silver halide and lead halide perovskite. Even though the systems are different, we find that solid-state immiscibility between different halide compounds plays an important role in both reactions we are studying. In AgBr1-xIx, the structural immiscibility between rock salt AgBr and wurtzite AgI causes the formation of twin boundaries, which change the nanocrystal morphology. For the lead halide system, the sharp transition in fluorescence intensity observed in single nanocrystals is also due to structural immiscibility, which causes the sudden phase transition from PbBr2 to the perovskite phase. This structural immiscibility between different halide compounds plays a critical role for both metal halide systems

Synthesis of inorganic dyes based on plasmonic silver nanoparticles for the visible and infrared regions of the spectrum

The effect of various technological factors during the multistage synthesis of plasmonic silver particles in aqueous solutions on nanoparticle size, morphology, and color is studied. The synthesized suspensions are found to contain tabular silver nanoparticles of hexagonal and triangular shape. The foundations of the technology for synthesizing stable silver colloids with a high silver concentration for the visible and nearinfrared regions of the spectrum are developed

Electronic properties study of sensitizing centers in chemical sensitization

Reduction sensitization, sulfur sensitization and sulfur-plus-gold sensitization are th

Photography equipment and techniques. A survey of NASA developments

The Apollo program has been the most complex exploration ever attempted by man, requiring extensive research, development, and engineering in most of the sciences before the leap through space could begin. Photography has been used at each step of the way to document the efforts and activities, isolate mistakes, reveal new phenomena, and to record much that cannot be seen by the human eye. At the same time, the capabilities of photography were extended because of the need of meeting space requirements. The results of this work have been applied to community planning and ecology, for example, as well as to space and engineering. Special uses of standard equipment, modifications and new designs, as well as film combinations that indicate actual or potential ecological problems are described

Electron Microscopy Studies of Insoluble Inorganic Materials Grown in Gels

The fascinating morphologies of metal oxides, oxyhydroxides, carbonates, silicates, and metals grown in gels have been observed in the present study. Morphologies resulting from some metal compounds grown in mobile solutions have been also studied for the purpose of comparison. Silica, carrageenan and mixed gel were widely used as particle growth media. Several alkali sources have been used as the precipitating agent. The colloidal particles from metal ions (Ag1+, Al3+, Ba2+, Ca2+, Cd2+, Co2+, Cu2+, Fe3+, Mg2+, Mn2+, Ni2+, Pb2+, Pd2+, Pt2+, Sr2+ and Zn2+) grown in gels were observed and their morphologies and diffraction patterns studied by transmission (and in some cases, scanning) electron microscopy. Hydrolysis of urea and hexamine solutions were used for homogeneous precipitation of metal salt solutions in silica gel at higher temperature (8.5-9

Cryo-analytical STEM of frozen, aqueous dispersions of nanoparticles

In situ characterisation of nanoparticle dispersion and surface coatings is required to further our understanding of the behaviour of nanoparticles in aqueous suspension. Using cryogenic transmission electron microscopy (cryo-TEM) it is possible to analyse a nanoparticle suspension in the frozen, hydrated state; however, this analysis is often limited to imaging alone. This work demonstrates the first use of analytical scanning TEM (STEM) in the examination of nanoparticles captured in a layer of vitreous ice. Imaging and analysis of frozen hydrated suspensions by both STEM energy dispersive X-ray (EDX) spectroscopy and electron energy loss spectroscopy (EELS) under cryogenic conditions demonstrates the identification and separation of CeO₂ , Fe₂ O₃ , ZnO and Ag nanoparticles in suspension. Damage caused by the electron beam was shown to occur at far higher electron fluences in STEM (<2000 e − /Å 2 ) compared to CTEM (<100 e − /Å 2 ) due to diffusion limited damage by the radiolysis products generated in vitreous ice. Further application of cryo-analytical STEM was undertaken on barium titanate biomarker nanoparticles dispersed in cell culture media to show the formation of a Ca and P rich coating around the nanoparticles when suspended in the media. This previously unreported coating changes the surface chemistry of the biomarkers when exposed to cells. Thus we show that the technique has the potential to advance our understanding of the fundamental behaviour of nanoparticles in complex aqueous suspensions

The effects of Co-60 gamma radiation on the thermal decomposition of carbonate compounds

Call number: LD2668 .T4 1969 L3Master of Scienc

Mineralogy of Noble Metals and “Invisible” Speciations of These Elements in Natural Systems, Volume II

This Special Issue book includes one review and eleven research articles. This review presents the results of studies on the noble metal forms in pyrite, arsenopyrite, chalcopyrite, sphalerite, and greenockite and summarizes the distribution and speciations of noble metals in base metal sulfides of Au and Au-bearing deposits of the Urals (Russia). Nine research articles are devoted to studying gold mineralization at different types of gold deposits and the characterization of the conditions of its formation. The typomorphism of placer gold and its distribution mechanisms in the east of the Siberian Platform were studied, and the diagnostic method and morphogenetic criteria for identifying the genesis of placers and different sources in the platform areas were proposed in other research articles. One research article presents an experimental study of Pt solubility in a CO-CO2-rich fluid. These studies contribute to a better understanding of the behavior of Au, Ag, and other noble metals; their forms in ore-forming systems; and the genesis of ore deposits. I sincerely appreciate the efforts and contributions of the Authors and Reviewers and would also like to express gratitude to the Editor-in-Chief, other Editors, and Assistant Editors of Minerals for their help