Kun Huang

Well-Defined Organic Nanotubes from Multicomponent Bottlebrush Copolymers

Bottlebrush copolymers are comblike macromolecules with densely grafted polymeric branches that adopt a cylindrical shape in solutions. We demonstrate a new method for the preparation of organic nanotubes by single molecule templating of core-shell bottlebrush copolymers. Multicomponent bottlebrush copolymers with well-defined structural parameters are synthesized by a combination of different living polymerization methods. Tubular structures can be prepared by cross-linking the shell layer and selectively etching out the core. The shape and size of original bottlebrush macromolecules are preserved during these transformations, which leads to the formation of well-defined organic nanotubes. The length and diameter of nanotubes are dictated by the length of the backbones and branches of the polymeric precursors, respectively. Water-soluble nanotubes with a hydrophobic interior can be prepared from bottlebrush copolymers with triblock copolymer branches. Herein, we outline molecular design strategies to fabricate nanotubes with controlled lengths, open pores, and different solubility characteristics.

Charge and Size Selective Molecular Transport by Amphiphilic Organic Nanotubes

Amphiphilic constructs with accessible, nanometer-size cavities can enable selective encapsulation, separation, and purification of nanomaterials and biomacromolecules on a similar length scale. We have developed a new method for the fabrication of amphiphilic organic nanotubes from multicomponent bottlebrush copolymers with triblock terpolymer side chains. The obtained nanotubes were demonstrated to be very effective and highly selective carriers for positively charged molecules and nanometer-size macromolecules by means of liquid-liquid extractions. Unprecedented discrimination between dendrimers with about 2 nm size differential was achieved.

Studies on Nanostructures of Conducting Polymers via Self-assembly Method

We report nanostructures (nanotubes, nanofibers, hollow spheres) of conducting polymers and their functionalized composite nanostructures synthesized by a self-assembly method. Effects of the synthesis conditions on the morphology and physical properties of the resulting nanostructures were studied. The micelles formed by the self-assembly of dopant molecule and/or their monomer salt into a micro/nanostructrural intermediate as supermolecular template is proposed to interpret the formation of those nanostructures.

De Novo Synthesis and Cellular Uptake of Organic Nanocapsules with Tunable Surface Chemistry

Water-soluble organic nanocapsules were prepared from bottlebrush copolymers with triblock terpolymer side chains composed of a degradable inner block (polylactide), a cross-linkable middle block (poly(4-butenylstyrene)), and a functional outer block (poly(styrene-co-maleic anhydride)). Bottlebrush copolymers are macromolecules with a long linear backbone and shorter polymeric side chains densely grafted onto the backbone. Hollow cylindrical nanoparticles were prepared by peripheral cross-linking of the bottlebrush copolymers and subsequent selective removal of the core. Reactive anhydride groups of the outer functional layer allowed for the preparation of nanocapsules with tunable surface characteristics. Cellular uptake of negatively charged organic nanocapsules showed strong surface chemistry dependence. The presence of hydrophobic groups on the nanocapsule surface was necessary for their nonspecific association with the cell membrane and subsequent internalization by endocytosis. The length of surface grafted oligoethylene glycol chains also had a dramatic influence on the intracellular accumulation of nanocapsules. Macropinocytosis was shown to be the predominant pathway for the cellular uptake of organic nanocapsules.

Electrical conductivity of a single Au/polyaniline microfiber

We report the measurements of conductivity, I-V curve, and magnetoresistance of a single Au/polyaniline microfiber with a core-shell structure, on which a pair of platinum microleads was attached by focused ion beam. The Au/polyaniline microfiber shows a much higher conductivity (∼110S∕cm at 300K) and a much weaker temperature dependence of resistance [R(4K)∕R(300K)=5.1] as compared with those of a single polyaniline microtube [σRT=30–40S∕cm and R(4K)∕R(300K)=16.2]. The power-law dependence of R(T)∝T−β, with β=0.38, indicates that the measured Au/polyaniline microfiber is lying in the critical regime of the metal-insulator transition. In addition, the microfiber shows a H2 dependent positive magnetoresistance at 2, 4, and 6K.

One-step synthesis of 3D dendritic gold/polypyrrole nanocomposites via a self-assembly method

Nove ls pherical three-dimensional (3D) dendritic gold–polypyrrole nanocomposites were successfully prepared in the presence of an amphiphilic p-toluene sulfonic acid (TSA) as dopant and surfactant via a self-assembly process which is based on the oxidation of pyrrole (Py) and the reduction of the chloroaurate ions, yielding PPy and Au(0) simultaneously. It was found that the probability of obtaining dendritic Au@PPy/TSA nanostructures depended on the concentration of TSA and the rate of addition of the oxidant (HAuCl4) .I tw as also proposed that the supramolecular micelles formed b yP y and TSA play the role of a ‘soft template’ to produce the dendritic Au@PPy/TSA nanocomposites.

Interface structure and lattice mismatch of epitaxial CoSi2 on Si(111)

We have used the x‐ray standing‐wave technique and bulk x‐ray diffraction to investigate the structural properties of thin CoSi2 layers grown epitaxially on Si(111). The perpendicular lattice mismatch with respect to the Si substrate was found to be −0.0152±0.0003 and −0.016±0.001 for 6‐nm‐thick and 16‐nm‐thick layers, respectively. The distance between Si(111) and the first Co layer was measured to be (0.288±0.005) nm and is thus stretched by (0.014±0.005) nm compared with a value determined by Si‐like bulk bond length. The Co atoms are attached to the Si(111) dangling bonds in agreement with the model of fivefold coordinated metal atoms at the interface.

Temporal and spectral control of single-photon frequency upconversion for pulsed radiation

We demonstrate efficient single-photon detection at 1.04u2002μm with quite low background counts by using the frequency upconversion detection technique with pulsed single-photon source and strong pump field prepared from two synchronized fiber lasers. Temporal and spectral control of the pump and signal lasers enabled an upconversion efficiency of 81.1%. As the system was pumped at a wavelength longer than that of the signal, the corresponding background counts were reduced down to 1.5×103u2002s−1 due to efficient suppression of parametric fluorescence in the periodic poled lithium niobate crystal.

Optical Synthesis of Large-Amplitude Squeezed Coherent-State Superpositions with Minimal Resources.

We propose and experimentally realize a novel versatile protocol that allows the quantum state engineering of heralded optical coherent-state superpositions. This scheme relies on a two-mode squeezed state, linear mixing, and a n-photon detection. It is optimally using expensive non-Gaussian resources to build up only the key non-Gaussian part of the targeted state. In the experimental case of a two-photon detection based on high-efficiency superconducting nanowire single-photon detectors, the freely propagating state exhibits a 67% fidelity with a squeezed even coherent-state superposition with a size |α|(2)=3. The demonstrated procedure and the achieved rate will facilitate the use of such superpositions in subsequent protocols, including fundamental tests and optical hybrid quantum information implementations.

Synchrotron x‐ray standing‐wave study of arsenic on Si(100)

The position of As atoms on the silicon(100) surface has been determined using the x‐ray standing‐wave technique and synchrotron radiation. Since the experiments were performed in air, the As‐covered (100) surface was capped with amorphous silicon. The results of the measurements are in agreement with the symmetric As dimer model for the (100) surface. The distance of the As dimers normal to the ideal (100) surface was found to be 1.26±0.01 A which agrees with the value obtained from total energy minimization calculations. With no protective coating the As position was higher.