Original Article in 2014

A group of 2D topological insulators BiX/SbX (X=H, F, Cl and Br) monolayers with extraordinarily large bulk gaps from 0.32 to a record value of 1.08 eV were predicated. These giant-gaps result from the strong spin-orbit interaction related to p_x and p_y orbitals of Bi/Sb atoms around the two valleys K and K′. The honeycomb structures of BiX monolayers remain stable even at a temperature of 600 K. The electric field-biased BiX/SbX monolayers become quantum valley Hall insulators, showing valley-selective circular dichroism. These features make the BiX/SbX monolayers an ideal platform to realize many exotic phenomena and fabricate new quantum devices.

Architectured ZnO nanostructures were grown by van der Waals (vdW) heteroepitaxy on hexagonal BN (hBN) layers with artificially patterned atomic ledges. Electron microscopic and theoretical computational analyses presented non-covalent epitaxial features of domain-aligned incommensurate ZnO/hBN heterostructure. The vdW epitaxial ZnO/hBN heterostructures exhibited excellent electrical insulation of hBN, and were applied to fabricate the ultraviolet photodetector devices, as an example of functional optoelectronic device applications.

We presented the novel concept of a hybrid-seawater fuel cell, comprising a closed-negative electrode, a NASICON solid electrolyte, and an open-seawater positive electrode. Hard carbon and a Sn-C nanocomposite were successfully applied as alternative anode materials for this hybrid-seawater fuel cell, presenting a highly stable cycling performance and reversible capacities exceeding 110 mAh g⁻¹ and 300 mAh g⁻¹ for hard carbon and Sn-C, respectively. Particularly, in the case of the Sn-C anode, the performance was substantially enhanced by the almost infinite supply of sodium ions using the open system seawater-based positive electrode. Thus, in addition to the simplicity of the overall concept, the utilization of redox processes in seawater represents a new and very promising approach for cost efficient and environmental friendly large-scale energy storage devices.

Undercoordinated indium (In*) is found to be an intrinsic defect that acts as a strong electron trap in amorphous InGaZnO₄. Conduction electrons couple with the under-coordinated In* via Coulomb attraction, which is the driving force for the formation of an In*–M (M=In, Ga, or Zn) bond. The new structure is stable in the electron-trapped (2–) charge state, and we designate it as an intrinsic (In*–M)²⁻ center in amorphous InGaZnO₄. The (In*–M)²⁻ centers are preferentially formed in heavily n-doped samples, resulting in a doping limit. They are also formed by electrical/optical stresses, which generate excited electrons, resulting in a metastable change in their electrical properties.

Highly porous star-shaped polyhedral oligomeric silsesquioxane (POSS) hybrid films were synthesized using POSS as the starting core followed by polycaprolactone (PCL) extension and polyurethane (PU) cross-linking. The unique three-dimensional nanotopography of these films is conducive for cell growth. The combination of favorable factors such as high porosity, reactive surface topography, excellent biocompatibility and biphasic degradation makes the star-shaped POSS-PCL-PU film a great candidate as a tissue engineering scaffold biomaterial.

This work reports a simple and robust approach to integrate MnO_x nanoparticles onto flexible graphite paper using an ultrathin CNT/RGO supporting layer. Supercapacitor electrodes employing the MnO_x/CNT/RGO nanohybrids without any conductive additives or binders yielded a high specific capacitance. The cycling stability of the nanohybrid electrodes was further improved through functionalizing the CNT/RGO supporting layer with atmospheric-pressure plasmas, demonstrating the synergistic use of nanohybrids and plasma-related effects for enhanced device performance.

Unlike crystalline electrodes wherein ion insertion is crucially dependent on the presence of energetically equivalent sites, nanostructured amorphous iron(III) phosphate hosts prepared by room temperature strategies and possessing porous properties facilitate the insertion of alkali ions with different sizes and also higher charge carriers including divalent cations (Mg²⁺−0.72Å, Zn²⁺-0.74 Å) or trivalent cations (Al³⁺−0.53 Å). This versatile cathode stores electrical energy by a reversible amorphous to crystalline reconstitutive reaction that occurs during electrochemical reaction with monovalent sodium, potassium and lithium. The study presents opportunities to develop amorphous electrodes with similar phase behavior for energy storage applications.

Multifunctional phase-change hybrid materials containing paraffin waxes (PWs) within a microporous conjugated polymer (CP) film were developed for new sensor and actuator applications. The hybrid films were prepared simply by depositing various PWs onto CP films to show critical changes in FL intensity and color during the phase change of PWs. This fascinating FL response behavior to external heat facilitated various applications such as reversible writing/erasing, fingerprinting and thermometer sensors. An appropriate layer-supported hybrid film showed extremely fast and highly reproducible thermomechanical actuation.

Stimulus-sensitive composite hydrogels with both pH and temperature responsiveness were prepared to simulate the mucus on fish skin and were found to have superior performance to that of the mimicked substance. The coefficients of friction (COFs) of the gels were found to be easily tunable, from a low to moderate, and then a high level. Importantly, the COF can be reversibly switched for many times by the sequential regulation of external pH and temperature.

By electroplating the unidirectionally <111>-oriented nanotwinned and fine-grained Cu on a Si wafer surface and followed by annealing at 400–500 °C up to an hour, we grow a number of extremely large <100>-oriented single crystals of Cu of sizes from 200 to 400 μm, as illustrated by the left figure. By patterning the nanotwinned Cu film (middle figure), we grow an array of <100>-oriented single crystals of Cu of sizes from 25 to 100 μm on Si after the annealing, as shown in the right figure.

By applying single-molecule imaging technique in free solution, we visually observed polymer chains break apart when they collide with each other just because of their Brownian motion. The oxidation scission reaction is catalyzed by the leverage effect, analogous to breaking a stiff wooden stick over the knee. Our surprising results suggest that new catalysts could be designed with the idea of stiff molecules working as ‘knives’ and ‘leverages’ breaking chemical bonds. We believe that our work opens up the possibility of monitoring chemical processes in solution at the single-molecule level.

A highly stretchable CuNW electrode was fabricated on PDMS substrate by the vacuum filtration method. The fundamental stretchability of CuNW films was demonstrated with a newly structured PDMS matrix. Our novel helix-structured CuNW/PDMS electrode showed excellent stretchability at an extremely high strain of 700%, showing a resistance variation of 3.9.

Graphene-supported polymer brushes were developed as a new type of functional quasi-2D polymers that are transparent, lightweight, freestanding, flexible, transferable and patternable. These 2D objects are demonstrated to be functional sheets for the responsive control of surface wettability and DNA biosensors.

We constructed a novel and universal biosensing platform based on polymerase-nicking enzyme synergetic isothermal quadratic DNA machine (ESQM). It tactfully integrates two signal amplification modules including strand displacement amplification (SDA) and nicking enzyme signal amplification (NESA) into a one-step biosensing system via a bifunctional DNA probe with stem-loop structure. ESQM can be activated to afford a high amplified signal in the presence of target. The ultrasensitive detection of Pb²⁺ (30 fM) even in real water sample was achieved within 40 min, and the practicability of ESQM in DNA methyltransferase activity analysis demonstrated the universality of this biosensing platform.

Highly efficient liquid transfer is realized using an open radial glass fibers array bio-inspired by the dandelion pappus. The highly adhesive property and the elastic nature of the fiber, together with the large open angle between the fibers, endow the open radial fibers array the ability to encapsulate huge amount of water.

Mesoporous low-temperature LiCoO₂ nanowire arrays can be directly prepared by a two-step hydrothermal method and they can be easily converted into chain-like high-temperature LiCoO₂ nanowire arrays through further calcination. The layered LiCoO₂ nanowire arrays exhibit both high gravimetric capacity and areal capacity, while maintaining good cycling stability and rate capability, make them promising for application in microbatteries.

Efficient thermal spin injection can be achieved by using CoFeAl alloy in which the sign of the Seebeck coefficients for up and down spins are opposite each other.

Combining a stimulus-responsive material and the Marangoni effect, a smart microactuator consisting of UV-responsive photoresist and surfactant was fabricated. The locomotion of a device loaded with the microactuator was initiated upon irradiation with 365-nm UV light, stopped when the light was turned off, and restarted when the light was turned back on. This work is the first example using the chemical Marangoni effect to produce photoresponsive motion on a water surface.

A novel and cost-effective activation process has been developed to macroscopically produce three-dimensional (3D) porous Ni@NiO core-shell electrode by activated Ni foam (ANF) in HCl aqueous solution. The ANF electrode yielded a remarkable areal capacitance of 2.0 F cm⁻² at a high current density of 8 mA cm⁻² and exhibited ultrahigh long-term cycling stability without any decay of capacitance after 100 000 cycles.

Irradiated vertically aligned supported 2.5 dimensional nanowires (NWs) show strong optical absorption due to the leaky mode resonance (LMR), and optical standing waves (SWs) created by waveguiding effects. Silver nanoparticles (AgNPs) have their plasmonic electric (E) field strengths modulated under the effect of the LMR and SW as a function of the optical indices (n, k) of the NWs. At (n=3.88, k=0), a theoretical maxima of the E-field was obtained, which matches closely with the Si (3.84, 0.02) system. The optimized hybrid system, AgNPs on silicon NW, demonstrates pico-femto molar detection of marine toxins by surface plasmon-aided SERS.