We report pinning of the emission spectrum in ultrasmall CdSe nanocrystals with a diameter of 1.7... more We report pinning of the emission spectrum in ultrasmall CdSe nanocrystals with a diameter of 1.7 nm and smaller. It was observed that the first emission feature ceased to blueshift once the band edge absorption reached 420 nm, though the band edge absorption continued to blueshift with decreasing nanocrystal diameter.
Cadmium selenide nanocrystals were observed to have a size-dependent melting point which was depr... more Cadmium selenide nanocrystals were observed to have a size-dependent melting point which was depressed relative to the bulk melting temperature. The observed size-dependent melting point ranged from 500-1478 K, while a model based on the surface area to volume ratio predicted that is should range between 774-1250 K. The nanocrystals were heated in situ in the electron microscope, and the melting point was almost immediately followed by the vaporization of the CdSe nanocrystals, allowing for straightforward determination of the melting temperature. The differences between the observed melting point of CdSe nanocrystals and the values predicted by the surface area to volume ratio model indicates that additional factors are involved in the melting point depression of nanocrystals.
Single Molecule Spectroscopy and Imaging III, 2010
We discuss the capabilities for sub-diffraction, single-nanoparticle position determination in a ... more We discuss the capabilities for sub-diffraction, single-nanoparticle position determination in a confocal one-or twophoton microscope with four-focus pulse-interleaved excitation and time-gated single-photon counting. As the technique is scalable to multiple detectors for ...
Ph.D. dissertation describing my work on single molecule spectroscopy and characterization of whi... more Ph.D. dissertation describing my work on single molecule spectroscopy and characterization of white-light CdSe nanocrystals, as well as the synthesis and characterization of magic-sized CdSe nanocrystals.
In situ electron microscopy is a tool which offers great promise for
studying the mechanisms resp... more In situ electron microscopy is a tool which offers great promise for studying the mechanisms responsible for nanoparticle growth. In aqueous solution, the reduction of Pb2+ by the electron beam results in the formation of lead nanoparticles. Here, we directly examined the fundamental processes that influence the growth of lead nanoparticles in solution using in situ transmission electron microscopy. Lead nanoparticle growth was directly monitored at the molecular level and followed the sequence of nucleation, Ostwald ripening, and aggregative growth. The aggregative growth phase resulted in macrostructures having micron-sized dimensions. Importantly, when combined with quantitative measurements, our direct imaging results suggested that the growth properties observed for lead nanoparticles were unique in comparison to other metallic entities.
Single Molecule Spectroscopy and Imaging III, 2010
We discuss the capabilities for sub-diffraction, single-nanoparticle position determination in a ... more We discuss the capabilities for sub-diffraction, single-nanoparticle position determination in a confocal one-or twophoton microscope with four-focus pulse-interleaved excitation and time-gated single-photon counting. As the technique is scalable to multiple detectors for ...
We investigated the origins of the popular Diet Coke and Mentos classroom demonstration. We test... more We investigated the origins of the popular Diet Coke and Mentos classroom demonstration. We tested the effects that regular and diet soda have on generated the geyser as well as the role that the flavored coating and temperature play in the geyser process. During the exploration of the parameter space, we observed that a geyser process for the soda consisted of two distinct steps.
We report pinning of the emission spectrum in ultrasmall CdSe nanocrystals with a diameter of 1.7... more We report pinning of the emission spectrum in ultrasmall CdSe nanocrystals with a diameter of 1.7 nm and smaller. It was observed that the first emission feature ceased to blueshift once the band edge absorption reached 420 nm, though the band edge absorption continued to blueshift with decreasing nanocrystal diameter.
Cadmium selenide nanocrystals were observed to have a size-dependent melting point which was depr... more Cadmium selenide nanocrystals were observed to have a size-dependent melting point which was depressed relative to the bulk melting temperature. The observed size-dependent melting point ranged from 500-1478 K, while a model based on the surface area to volume ratio predicted that is should range between 774-1250 K. The nanocrystals were heated in situ in the electron microscope, and the melting point was almost immediately followed by the vaporization of the CdSe nanocrystals, allowing for straightforward determination of the melting temperature. The differences between the observed melting point of CdSe nanocrystals and the values predicted by the surface area to volume ratio model indicates that additional factors are involved in the melting point depression of nanocrystals.
Single Molecule Spectroscopy and Imaging III, 2010
We discuss the capabilities for sub-diffraction, single-nanoparticle position determination in a ... more We discuss the capabilities for sub-diffraction, single-nanoparticle position determination in a confocal one-or twophoton microscope with four-focus pulse-interleaved excitation and time-gated single-photon counting. As the technique is scalable to multiple detectors for ...
Ph.D. dissertation describing my work on single molecule spectroscopy and characterization of whi... more Ph.D. dissertation describing my work on single molecule spectroscopy and characterization of white-light CdSe nanocrystals, as well as the synthesis and characterization of magic-sized CdSe nanocrystals.
In situ electron microscopy is a tool which offers great promise for
studying the mechanisms resp... more In situ electron microscopy is a tool which offers great promise for studying the mechanisms responsible for nanoparticle growth. In aqueous solution, the reduction of Pb2+ by the electron beam results in the formation of lead nanoparticles. Here, we directly examined the fundamental processes that influence the growth of lead nanoparticles in solution using in situ transmission electron microscopy. Lead nanoparticle growth was directly monitored at the molecular level and followed the sequence of nucleation, Ostwald ripening, and aggregative growth. The aggregative growth phase resulted in macrostructures having micron-sized dimensions. Importantly, when combined with quantitative measurements, our direct imaging results suggested that the growth properties observed for lead nanoparticles were unique in comparison to other metallic entities.
Single Molecule Spectroscopy and Imaging III, 2010
We discuss the capabilities for sub-diffraction, single-nanoparticle position determination in a ... more We discuss the capabilities for sub-diffraction, single-nanoparticle position determination in a confocal one-or twophoton microscope with four-focus pulse-interleaved excitation and time-gated single-photon counting. As the technique is scalable to multiple detectors for ...
We investigated the origins of the popular Diet Coke and Mentos classroom demonstration. We test... more We investigated the origins of the popular Diet Coke and Mentos classroom demonstration. We tested the effects that regular and diet soda have on generated the geyser as well as the role that the flavored coating and temperature play in the geyser process. During the exploration of the parameter space, we observed that a geyser process for the soda consisted of two distinct steps.
Controlling the morphology of semiconductor nanocrystals has typically relied on controlling the ... more Controlling the morphology of semiconductor nanocrystals has typically relied on controlling the concentration and type of surface ligands utilized during synthesis. We demonstrate the temperature is also a significant factor in determining the final morphology of CdSe nanocrystals. Morphology was characterized by imaging the nanocrystals utilizing scanning transmission electron microscopy. In this work we quantify how the morphology changes as the reaction temperature is modulated. When the reaction temperature is above 280°C a dot morphology is predominant. However, when the reaction temperature is lowered, the nanocrystals exhibit a branched morphology, with a bi-pod structure being the most abundant.
We report a simple method for modulating the morphology of CdSe nanocrystals. By lowering the tem... more We report a simple method for modulating the morphology of CdSe nanocrystals. By lowering the temperature of the cadmium oleate to 250 C prior to injecting the selenium precursor, nanocrystals exhibiting bi-pod morphology can be synthesized. Unlike the traditional dot morphology, the electron-hole pairof the bi-pod is not confined in all three dimensions.
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Papers by Albert Dukes
studying the mechanisms responsible for nanoparticle growth. In
aqueous solution, the reduction of Pb2+ by the electron beam results
in the formation of lead nanoparticles. Here, we directly examined the
fundamental processes that influence the growth of lead nanoparticles
in solution using in situ transmission electron microscopy.
Lead nanoparticle growth was directly monitored at the molecular
level and followed the sequence of nucleation, Ostwald ripening, and
aggregative growth. The aggregative growth phase resulted in
macrostructures having micron-sized dimensions. Importantly, when
combined with quantitative measurements, our direct imaging results
suggested that the growth properties observed for lead nanoparticles
were unique in comparison to other metallic entities.
studying the mechanisms responsible for nanoparticle growth. In
aqueous solution, the reduction of Pb2+ by the electron beam results
in the formation of lead nanoparticles. Here, we directly examined the
fundamental processes that influence the growth of lead nanoparticles
in solution using in situ transmission electron microscopy.
Lead nanoparticle growth was directly monitored at the molecular
level and followed the sequence of nucleation, Ostwald ripening, and
aggregative growth. The aggregative growth phase resulted in
macrostructures having micron-sized dimensions. Importantly, when
combined with quantitative measurements, our direct imaging results
suggested that the growth properties observed for lead nanoparticles
were unique in comparison to other metallic entities.