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Open Access Publications from the University of California

Scholarly Works (17 results)

  • Article
LBL Publications (2011)
Direct imaging of nanoparticle solutions by liquid phase transmission electron microscopy has enabled unique in-situ studies of nanoparticle motion and growth. In the present work, we report on real-time formation of two-dimensional nanoparticle arrays in the very low diffusive limit, where nanoparticles are mainly driven by capillary forces and solvent fluctuations. We find that superlattice formation appears to be segregated into multiple regimes. Initially, the solvent front drags the nanoparticles, condensing them into an amorphous agglomerate. Subsequently, the nanoparticle crystallization into an array is driven by local fluctuations. Following the crystallization event, superlattice growth can also occur via the addition of individual nanoparticles drawn from outlying regions by different solvent fronts. The dragging mechanism is consistent with simulations based on a coarse-grained lattice gas model at the same limit.
    Cover page: Direct observation of two-step crystallization in nanoparticle superlattice formation
    • Article
    • Peer Reviewed
    Lawrence Berkeley National Laboratory (2010)
      Cover page: Hetero-Epitaxial Anion Exchange Yields Single-Crystalline Hollow Nanoparticles
      • Thesis
      • Peer Reviewed
      UC Berkeley Electronic Theses and Dissertations (2012)

      Colloidal semiconductor and metal nanocyrstals receive attention from studying their physical properties to application in biology, electronics, optics, and catalyst. In addition, colloidal nanocrystals as artificial building blocks construct assemblies in solution phase and on substrate to exploit coupled properties of individual nanocrystals. A facile control of physical properties by tuning size, shape, and composition of nanocrystals can be achieved in solution phase synthetic protocols and now we have a library of literatures about them.

      However, most of nanocrystal synthesis and their use are developed empirically, perhaps in a lack of fundamental understanding. Growth kinetics during synthesis, motion and behavior of nanocrystals in liquid and at interfaces include many questions which await mechanistic studies.

      This dissertation explores direct observation of nanocrystals in liquid by using liquid cell transmission electron microscopy. Growth of nanocrystals from molecular precursor in solvent requires observation in atomistic resolution of a single particle level. Chapter 1 describes single particle growth trajectories of metal nanocrystals investigated by using graphene liquid cell in transmission electron microscopy. This cell is employed to achieve high-resolution imaging of colloidal platinum nanocrystal growth. The ability to directly image and resolve critical steps at atomistic resolution provides new insights into colloidal nanocrystal growth.

      Control of nanocrystal interaction and drying condition of solvent determines the final morphology of nanocrystal self-assembly. Chapter 2 presents direct imaging of nanocrystal motions in solution and real-time formation of two-dimensional nanocrystal superlattices by using liquid phase transmission electron microscopy. Nucleation and growth processes are introduced accompanying with detailed mechanistic steps and single particle trajectories. The important role of solvent fluctuation for self-assembly of nanocrystals is explored in experiment and coarse-grained lattice gas modeling.

      Concluding remarks are presented in Chapter 3.

        Cover page: Direct Observation of Colloidal Nanocrystals by Using Liquid Cell Transmission Electron Microscopy
        • Article
        • Peer Reviewed
        UC Berkeley Previously Published Works (2015)
        We present two examples of the use of liquid cells to study colloidal inorganic nanocrystals using in situ transmission electron microscopy. The first uses a liquid cell to quantify the interaction potential between pairs of colloidal nanocrystals, and the second demonstrates direct imaging of nanocrystal growth and structure in the liquid cell.
          Cover page: Spiers Memorial Lecture New tools for observing the growth and assembly of colloidal inorganic nanocrystals
          • Article
          LBL Publications (2013)
            Cover page: Revealing Bismuth Oxide Hollow Nanoparticle Formation by the Kirkendall Effect
            • Article
            • Peer Reviewed
            LBL Publications (2018)
            Heterostructures constructed of graphene and colloidal nanocrystals provide a unique way to exploit the coupled physical properties of the two functional building blocks. Studying the interface structure between the two constituent materials is important to understand the formation mechanism and the resulting physical and chemical properties. Along with ab initio calculations, we elucidate that the bending rigidity and the strong van der Waals interaction of graphene to the metal surface guide the formation of a tight and conformal interface. Using theoretical foundations, we construct colloidal nanocrystal-graphene heterostructures with controlled interfacial structures and directly investigate the cross-sectional structures of them at high resolution by using aberration-corrected transmission electron microscopy. The experimental method and observations we present here will link the empirical methods for the formation of nanocrystal-graphene heterostructures to the mechanistic understanding of their properties.
              Cover page: Rational design and observation of the tight interface between graphene and ligand protected nanocrystals
              • Article
              • Peer Reviewed
              LBL Publications (2015)
              Recent development of liquid phase transmission electron microscopy (TEM) enables the study of specimens in wet ambient conditions within a liquid cell; however, direct structural observation of biological samples in their native solution using TEM is challenging since low-mass biomaterials embedded in a thick liquid layer of the host cell demonstrate low contrast. Furthermore, the integrity of delicate wet samples is easily compromised during typical sample preparation and TEM imaging. To overcome these limitations, we introduce a graphene liquid cell (GLC) using multilayer graphene sheets to reliably encapsulate and preserve biological samples in a liquid for TEM observation. We achieve nanometer scale spatial resolution with high contrast using low-dose TEM at room temperature, and we use the GLC to directly observe the structure of influenza viruses in their native buffer solution at room temperature. The GLC is further extended to investigate whole cells in wet conditions using TEM. We also demonstrate the potential of the GLC for correlative studies by TEM and fluorescence light microscopy imaging.
                Cover page: Direct Observation of Wet Biological Samples by Graphene Liquid Cell Transmission Electron Microscopy
                • Article
                • Peer Reviewed
                UC Berkeley Previously Published Works (2013)
                Liquid-phase transmission electron microscopy (TEM) can probe and visualize dynamic events with structural or functional details at the nanoscale in a liquid medium. Earlier efforts have focused on the growth and transformation kinetics of hard material systems, relying on their stability under electron beam. Our recently developed graphene liquid cell technique pushed the spatial resolution of such imaging to the atomic scale but still focused on growth trajectories of metallic nanocrystals. Here, we adopt this technique to imaging three-dimensional (3D) dynamics of soft materials instead, double strand (dsDNA) connecting Au nanocrystals as one example, at nanometer resolution. We demonstrate first that a graphene liquid cell can seal an aqueous sample solution of a lower vapor pressure than previously investigated well against the high vacuum in TEM. Then, from quantitative analysis of real time nanocrystal trajectories, we show that the status and configuration of dsDNA dictate the motions of linked nanocrystals throughout the imaging time of minutes. This sustained connecting ability of dsDNA enables this unprecedented continuous imaging of its dynamics via TEM. Furthermore, the inert graphene surface minimizes sample-substrate interaction and allows the whole nanostructure to rotate freely in the liquid environment; we thus develop and implement the reconstruction of 3D configuration and motions of the nanostructure from the series of 2D projected TEM images captured while it rotates. In addition to further proving the nanoconjugate structural stability, this reconstruction demonstrates 3D dynamic imaging by TEM beyond its conventional use in seeing a flattened and dry sample. Altogether, we foresee the new and exciting use of graphene liquid cell TEM in imaging 3D biomolecular transformations or interaction dynamics at nanometer resolution.
                  Cover page: 3D Motion of DNA-Au Nanoconjugates in Graphene Liquid Cell Electron Microscopy
                  • Article
                  • Peer Reviewed
                  UC Berkeley Previously Published Works (2022)
                    Cover page: Response to Comment on "Reversible disorder-order transitions in atomic crystal nucleation"Creative Commons 'BY' version 4.0 license
                    • Article
                    • Peer Reviewed
                    LBL Publications (2024)
                    In situ structures of Platinum (Pt) nanoparticles (NPs) can be determined with graphene liquid cell transmission electron microscopy. Atomic-scale three-dimensional structural information about their physiochemical properties in solution is critical for understanding their chemical function. We here analyze eight atomic-resolution maps of small (<3 nm) colloidal Pt NPs. Their structures are composed of an ordered crystalline core surrounded by surface atoms with comparatively high mobility. 3D reconstructions calculated from cumulative doses of 8500 and 17,000 electrons/pixel, respectively, are characterized in terms of loss of atomic densities and atomic displacements. Less than 5% of the total number of atoms are lost due to dissolution or knock-on damage in five of the structures analyzed, whereas 10-16% are lost in the remaining three. Less than 5% of the atomic positions are displaced due to the increased electron irradiation in all structures. The surface dynamics will play a critical role in the diverse catalytic function of Pt NPs and must be considered in efforts to model Pt NP function computationally.
                      Cover page: Small, solubilized platinum nanocrystals consist of an ordered core surrounded by mobile surface atoms
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