3 research outputs found
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Real time imaging of two-dimensional iron oxide spherulite nanostructure formation
The formation of complex hierarchical nanostructures has attracted a lot of attention from both the fundamental science and potential applications point of view. Spherulite structures with radial fibrillar branches have been found in various solids; however, their growth mechanisms remain poorly understood. Here, we report real time imaging of the formation of two-dimensional (2D) iron oxide spherulite nanostructures in a liquid cell using transmission electron microscopy (TEM). By tracking the growth trajectories, we show the characteristics of the reaction front and growth kinetics. Our observations reveal that the tip of a growing branch splits as the width exceeds certain sizes (5.5–8.5 nm). The radius of a spherulite nanostructure increases linearly with time at the early stage, transitioning to nonlinear growth at the later stage. Furthermore, a thin layer of solid is accumulated at the tip and nanoparticles from secondary nucleation also appear at the growing front which later develop into fibrillar branches. The spherulite nanostructure is polycrystalline with the co-existence of ferrihydrite and Fe3O4 through-out the growth. A growth model is further established, which provides rational explanations on the linear growth at the early stage and the nonlinearity at the later stage of growth. [Figure not available: see fulltext.]
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Translatable Research Group-Based Undergraduate Research Program for Lower-Division Students
Participating in undergraduate research yields positive outcomes for undergraduate students, and universities are seeking ways to engage more students in undergraduate research earlier in their academic careers. Typically, undergraduate students perform research either as part of an apprenticeship where a student receives individual mentorship in a research lab setting from an experienced researcher in the field of interest or in a course-based undergraduate research experience where students work in a classroom or teaching laboratory to investigate open-ended research questions. In this work, we implement a model of undergraduate research that combines aspects of those two methods to provide benefits to undergraduate students and research groups. A cohort of 20 first-year undergraduate students at the University of California-Berkeley were recruited to work on a project investigating data previously collected by the Alivisatos research group. Over a semester, these students learned about nanomaterials and the research process, pursued curiosity-driven research in teams, and presented their results at a formal poster session. Students from this program showed quantifiable gains in their self-identification as researchers and scientists. This program was developed to be a model for other research groups, departments, and universities to combine the benefits of traditional apprenticeship research and course-based undergraduate research to provide a research experience for large numbers of undergraduate students early in their college education
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Nucleation, growth, and superlattice formation of nanocrystals observed in liquid cell transmission electron microscopy
This article reviews the advancements and prospects of liquid cell transmission electron microscopy (TEM) imaging and analysis methods in understanding the nucleation, growth, etching, and assembly dynamics of nanocrystals. The bonding of atoms into nanoscale crystallites produces materials with nonadditive properties unique to their size and geometry. The recent application of in situ liquid cell TEM to nanocrystal development has initiated a paradigm shift, (1) from trial-And-error synthesis to a mechanistic understanding of the synthetic reactions responsible for the emergence of crystallites from a disordered soup of reactive species (e.g., ions, atoms, molecules) and shape-defined growth or etching; and (2)A from post-processing characterization of the nanocrystals' superlattice assemblies to inA situ imaging and mapping of the fundamental interactions and energy landscape governing their collective phase behaviors. Imaging nanocrystal formation and assembly processes on the single-particle level in solution immediately impacts many existing fields, including materials science, nanochemistry, colloidal science, biology, environmental science, electrochemistry, mineralization, soft condensed-matter physics, and device fabrication