Wenjing Xu

Magnetic Assembly and Field‐Tuning of Ellipsoidal‐Nanoparticle‐Based Colloidal Photonic Crystals

Anisotropic nanostructures provide an additional degree of freedom for tailoring the collective properties of their ensembles. Using Fe@SiO2 nanoellipsoids as anisotropic building blocks, herein we demonstrate a new class of magnetically responsive photonic structures whose photonic properties can be dynamically tuned by controlling the direction of the magnetic fields they are exposed to. These novel photonic structures diffract at a minimum wavelength when the field direction is perpendicular to the incident angle, and a maximum wavelength when the field is switched to parallel direction; and the diffraction intensity reaches maximum values when the fields are either parallel or perpendicular to the incident light, and decreases when the field direction is moved off-angle.

Controllable Fabrication of Au Nanocups by Confined-Space Thermal Dewetting for OCT Imaging

Here, this study reports a novel confined-space thermal dewetting strategy for the fabrication of Au nanocups with tunable diameter, height, and size of cup opening. The nanocup morphology is defined by the cup-shaped void space created by a yolk-shell silica template that spontaneously takes an eccentric configuration during annealing. Thermal dewetting of Au, which is sandwiched between the yolk and shell, leads to the desired nanocup morphology. With strong scattering in near infrared, the Au nanocups exhibit superior efficiency as contrast agents for spectral-domain optical coherence tomography imaging. This confined-space thermal dewetting strategy is scalable and general, and can be potentially extended to the synthesis of novel anisotropic nanostructures of various compositions that are difficult to produce by conventional wet chemical or physical methods, thus opening up opportunities for many new applications.

Chemical Transformation of Colloidal Nanostructures with Morphological Preservation by Surface-Protection with Capping Ligands

When nanocrystals are made to undergo chemical transformations, there are often accompanying large mechanical deformations and changes to overall particle morphology. These effects can constrain development of multistep synthetic methods through loss of well-defined particle morphology and functionality. Here, we demonstrate a surface protection strategy for solution phase chemical conversion of colloidal nanostructures that allows for preservation of overall particle morphology despite large volume changes. Specifically, via stabilization with strong coordinating capping ligands, we demonstrate the effectiveness of this method by transforming β-FeOOH nanorods into magnetic Fe3O4 nanorods, which are known to be difficult to produce directly. The surface-protected conversion strategy is believed to represent a general self-templating method for nanocrystal synthesis, as confirmed by applying it to the chemical conversion of nanostructures of other morphologies (spheres, rods, cubes, and plates) and compositions (hydroxides, oxides, and metal organic frameworks).

Photomechanically Induced Magnetic Field Response by Controlling Molecular Orientation in 9‐Methylanthracene Microcrystals

A surfactant-assisted seeded-growth method is used to form single-crystal platelets composed of 9-methylanthracene with two different internal molecular orientations. The more stable form exhibits a photoinduced twisting, as observed previously for 9-methylanthracene microribbons grown by the floating drop method. However, the newly discovered elongated hexagonal platelets undergo a photoinduced rolling-up and unrolling. The ability of the rolled-up cylindrical shape to trap superparamagnetic nanoparticles enables it to be carried along in a magnetic field gradient. The new photoinduced shape change, made possible by a novel surfactant-assisted crystal growth method, opens up the possibility of using light to modulate the crystal translational motion.

Surface Engineering of Nanostructured Energy Materials

All nanostructures share a common feature of large surface-to-volume ratio, which makes surface engineering a vital tool for exploring their new and important applications in many different areas. Particularly, inorganic nanostructures represent a class of intriguing catalysts that can find wide uses in energy conversion, energy storage, and environmental remediation. Here, a number of surface engineering strategies, including morphology control, defect incorporation, and interface manipulation for tailoring the shape, facet, defect, interfacial property, and composition of nanostructures, aiming at controlling the chemical and physical properties such as energy bandgap and surface energy toward great enhancement in catalytic performance, are discussed.