Chemical methods developed over the past two decades enable preparation of colloidal nanocrystals with uniform size and shape. These Brownian objects readily order into superlattices. Recently, the range of accessible inorganic cores and tunable surface chemistries dramatically increased, expanding the set of nanocrystal arrangements experimentally attainable. In this review, we discuss efforts to create next-generation materials via bottom-up organization of nanocrystals with preprogrammed functionality and self-assembly instructions. This process is often driven by both interparticle interactions and the influence of the assembly environment. The introduction provides the reader with a practical overview of nanocrystal synthesis, self-assembly, and superlattice characterization. We then summarize the theory of nanocrystal interactions and examine fundamental principles governing nanocrystal self-assembly from hard and soft particle perspectives borrowed from the comparatively established fields of micro...

Self-Assembly of Colloidal Nanocrystals: From Intricate Structures to Functional Materials

Vascular stenosis triggers adaptive cellular responses that induce adverse remodeling, which can progress to partial or complete vessel occlusion. Despite its severity, cellular interactions and biophysical cues that regulate pathological progression are poorly understood. We report the design and fabrication of a three-dimensional in vitro system to model vascular stenosis so that specific cellular interactions and responses to hemodynamic stimuli can be investigated. Tubular cellularized constructs (cytotubes) were produced using a collagen casting system to generate a stenotic arterial model. Fabrication methods were developed to create cytotubes containing co-cultured vascular cells, where cell viability, distribution, morphology, and contraction were examined (Figure). Fibroblasts, bone marrow primary cells, smooth muscle cells (SMCs), and endothelial cells (ECs) remained viable during culture and developed locationand time-dependent morphologies. We found cytotube contraction to depend on cellular composition, where SMC-EC co-cultures adopted intermediate contractile phenotypes between SMCand EC-only cytotubes. Our fabrication approach and resulting artery model can serve as an in vitro 3D culture system to investigate vascular pathogenesis.

Microscopy and Microanalysis

Technological development of hydrogen production by solid oxide electrolyzer cell (SOEC)

Fundamental mechanisms limiting solid oxide fuel cell durability

High-temperature solid oxide electrolysis cells (SOECs) are advanced electrochemical energy storage and conversion devices with high conversion/energy efficiencies. They offer attractive high-temperature co-electrolysis routes that reduce extra CO2 emissions, enable large-scale energy storage/conversion and facilitate the integration of renewable energies into the electric grid. Exciting new research has focused on CO2 electrochemical activation/conversion through a co-electrolysis process based on the assumption that difficult CO double bonds can be activated effectively through this electrochemical method. Based on existing investigations, this paper puts forth a comprehensive overview of recent and past developments in co-electrolysis with SOECs for CO2 conversion and utilization. Here, we discuss in detail the approaches of CO2 conversion, the developmental history, the basic principles, the economic feasibility of CO2/H2O co-electrolysis, and the diverse range of fuel electrodes as well as oxygen electrode materials. SOEC performance measurements, characterization and simulations are classified and presented in this paper. SOEC cell and stack designs, fabrications and scale-ups are also summarized and described. In particular, insights into CO2 electrochemical conversions, solid oxide cell material behaviors and degradation mechanisms are highlighted to obtain a better understanding of the high temperature electrolysis process in SOECs. Proposed research directions are also outlined to provide guidelines for future research.

A review of high temperature co-electrolysis of H2O and CO2 to produce sustainable fuels using solid oxide electrolysis cells (SOECs): advanced materials and technology

It is commonly accepted that the combination of the anisotropic shape and nanoscale dimensions of the mineral constituents of natural biological composites underlies their superior mechanical properties when compared to those of their rather weak mineral and organic constituents. Here, we show that the self-assembly of nearly spherical iron oxide nanoparticles in supercrystals linked together by a thermally induced crosslinking reaction of oleic acid molecules leads to a nanocomposite with exceptional bending modulus of 114 GPa, hardness of up to 4 GPa and strength of up to 630 MPa. By using a nanomechanical model, we determined that these exceptional mechanical properties are dominated by the covalent backbone of the linked organic molecules. Because oleic acid has been broadly used as nanoparticle ligand, our crosslinking approach should be applicable to a large variety of nanoparticle systems.

Organically linked iron oxide nanoparticle supercrystals with exceptional isotropic mechanical properties

Off-axis electron holography in a transmission electron microscope is used to examine the charge on threading edge dislocations in $n\ensuremath{-}\mathrm{GaN}$ (0001). It is shown that the crystal inner potential is reduced within 10 nm of the dislocation consistent with a negatively charged core. The results can be explained by a simple unscreened potential due to a core charge of about $4\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0ex}{0ex}}\mathrm{electrons}\phantom{\rule{0ex}{0ex}}\mathrm{cm}{}^{\ensuremath{-}1}$. The origin of this charge is discussed. The application of the method to other types of dislocation is also considered.

Electron holography studies of the charge on dislocations in GaN.

Microstructure degradation of an anode/electrolyte interface in SOFC studied by transmission electron microscopy

The measurement of charge on dislocations in GaN by electron holography is described. Recent results are presented showing that edge dislocations in n-doped GaN are highly negatively charged, whereas those in p-doped GaN are positively charged. It is shown that the results are consistent with a model which assumes Fermi level pinning at dislocation states about 2.5 V below the conduction band edge. The application of electron holography to screw dislocations, and the dependence of the observations on the dislocation core structure, are also discussed.

Chengge Jiao

Papers

Organically linked iron oxide nanoparticle supercrystals with exceptional isotropic mechanical properties

Electron holography studies of the charge on dislocations in GaN.

Microstructure degradation of an anode/electrolyte interface in SOFC studied by transmission electron microscopy

Electron Holography Studies of the Charge on Dislocations in GaN

Three-dimensional electron backscattered diffraction analysis of deformation in MgO micropillars