We report solar cells based on highly confined nanocrystals of the ternary compound PbSxSe1-x. Crystalline, monodisperse alloyed nanocrystals are obtained using a one-pot, hot injection reaction. Rutherford back scattering and energy filtered transmission electron microscopy suggest that the S and Se anions are uniformly distributed in the alloy nanoparticles. Photovoltaic devices made using ternary nanoparticles are more efficient than either pure PbS or pure PbSe based nanocrystal devices.

CdTe tetrapods have been deposited on a substrate and partially coated with a protective polymer layer, exposing just one arm. The exposed arm was then decorated with Au nanoparticles in a site selective fashion. The modified arms were readily broken off from the remainder ofthe tetrapods and released from the substrate, yielding CdTe nanorods asymmetrically modified with Au nanoparticles. These nanostructures with reduced symmetry may show interesting optoelectronic properties.

Colloidal nanocrystals are nanometer-sized, solution-grown inorganic particles stabilized by a layer of surfactants attached to their surface. The inorganic cores exhibit useful properties controlled by composition as well as size and shape, while the surfactant coating ensures that these structures are easy to fabricate and process. It is this combination of features that makes colloidal nanocrystals attractive and promising building blocks for advanced materials and devices. But their full potential can only be exploited if we achieve exquisite control over their composition, size, shape, crystal structure and surface properties. Here we review what is known about nanocrystal growth and outline strategies for controlling it.

Nanomaterials exhibit unique size-dependent properties, and colloidal, metallic nanocrystals have been utilized in catalytic, biomedical, and optical applications. Observing the dynamics of nanocrystals in their native liquid environment requires the high spatial resolution

of the electron microscope and encapsulation using a thin membrane such as graphene. By understanding and controlling the chemistry during liquid cell electron microscopy reactions, fundamental insights about nanoscale processes can be elucidated to improve colloidal

synthesis of nanocrystals.

Oxidative etching of gold nanocrystals using a combination of preloaded FeCl3 and electron beam-generated radiolysis products was used as a model system for learning about the chemistry of the liquid cell environment. By collecting etching trajectories of multiple

nanocubes and rhombic dodecahedra, with {100} and {110} facets respectively, as they transition through intermediate {hk0} facets, the initial FeCl3 concentration was found to control the chemical potential of the etching process. Using Monte Carlo simulations to help understand the trajectories, the chemical potential was found to change the intermediate facets when etching from cubes but not rhombic dodecahedra due to differences in coordination of inner surface atoms.

The electron beam generates highly reactive radiolysis products during liquid cell imaging, so determining the electron beam's role on the chemistry of the liquid environment is useful for experimental design and reproducibility. Following the volume trajectories of

etching nanocrystals, it was found that the electron beam dose rate controls the etching rate independently of the FeCl3 control of the chemical potential. Further, at low dose rates, the electron beam generates sacrificial reductant hydrogen gas bubbles that prevent premature etching. Ex situ etching experiments using FeCl3 confirmed the dynamics observed in the

liquid cell and provided additional insight into the liquid cell environment. Additional in situ TEM observations of the nanoscale Kirkendall effect of silver nanoparticles and electron stimulated desorption of NaCl nanocubes shows the wide range of processes that can be investigated. Although the chemistry of these liquid cell processes are not as well understood as the gold nanocrystal etching, useful insights about structural transformations were extracted.

Finally, an undergraduate research program for first-year students was designed and implemented using liquid cell TEM data. The structure of the program is presented with feedback from the participants showing quantifiable gains in self-identication as scientist.