Toward the pursuit of high-performance Ni 2+ /Co 2+ /Fe 3+relevant oxygen evolution reaction (OER) electrocatalysts, the modulation of local electronic structure of the active metal sites provides the fundamental motif, which could be achieved either through direct modifications of local chemical environment or interfacial interaction with a second metal substrate which possesses high electronegativity (typically noble metal Au). Herein, we report that the local electronic structure of Ni− Fe layered double hydroxide (LDH) could be favorably modulated through strong interfacial interactions with FeOOH nanoparticles (NPs). The biphasic and multiscale composites FeOOH/LDH demonstrated an increasingly pronounced synergy effect for OER catalysis when the average size of FeOOH NPs decreases from 18.0 to 2.0 nm. Particularly, the composite with average size of FeOOH NPs of 2.0 nm exhibited an overpotential of 174 mV at 10 mA cm −2 and a tafel slope of 27 mV dec −1 in 1.0 M KOH, outmatching all the noble and non-noble OER catalysts reported so far; it also operates smoothly in various stability tests. A mechanistic study based on XANES and EXAFS analysis, d.c. voltammetry and large amplitude Fourier Transformed a.c. voltammetry proved the presence of high-oxidation-state Fe (3+δ)+ sites with relatively short Fe (3+δ)+ −O bond from the highly unsaturated ultrafine FeOOH NPs which could reform the local electronic structure and favorably manipulate the electronic oxidation and thus electrocatalytic behaviors of the Ni 2+ species in the Ni−Fe LDH, hence leading to the easy formation, excellent OER activity, and extraordinary structural and catalytic stability. Our work puts an emphasis on the role of the solid−solid interfacial chemistry between a Ni−Fe LDH and a non-noble-metal component in engineering the local electronic structure of the active metal sites, which successfully pushed forward the catalytic activity of the well-studied Ni−Fe LDH far beyond its current limit in OER catalysis and opened up an avenue for rational design of OER electrocatalysts.

Systematic manipulation of nanocrystal shapes is prerequisite for revealing their shape-dependent physical and chemical properties. Here we successfully prepared a complex shape of Pt micro/nanocrystals: convex hexoctahedron (HOH) enclosed with 48 {15 5 3} high-index facets by electrochemical square-wave-potential (SWP) method. This shape is the last crystal single form that had not been achieved previously for face-centered-cubic (fcc) metals. We further realized the shape evolution of Pt nanocrystals with high-index facets from tetrahexahedron (THH) to the HOH, and finally to trapezohedron (TPH) by increasing either the upper (EU) or lower potential (EL). The shape evolution, accompanied by the decrease of low-coordinated kink atoms, can be correlated with the competitive interactions between preferentially oxidative dissolution of kink atoms at high EU and the redeposition of Pt atoms at the EL.

Reported here is femtosecond laser mediated bandgap tailoring of graphene oxides (GOs) for direct fabrication of graphene-based microdevices. When femtosecond laser pulses were used to reduce and pattern GO, oxygen contents in the reduced region could be modulated by varying the laser power. In this way, the bandgap of reduced GO was precisely modulated from 2.4 to 0.9 eV by tuning the femtosecond laser power from 0 to 23 mW. Through the first-principle study, the essence of GO bandgap tailoring is proved to be femtosecond laser reduction induced oxygen-content modulation. As representative illustrations, bottom-gate graphene FETs were fabricated in situ by using femtosecond laser reduced GO as the channel material, and an optimized room temperature on–off ratio of 56 is obtained. The controlled reduction of GO by femtosecond laser contributes great potential for bandgap tailoring and microdevices patterning of graphene toward future electronics.

In recent years, metal nanowiring for circuitry and electronic interconnection has attracted much attention due to the growing requirements of highly integrated microcircuits, and is of benefit to the miniaturization of device features. [1] Generally, ultraviolet photolithography, which was considered a typical processing route for metal wiring, has already greatly contributed to integrated circuits. [2] However, the lithographic route shows strong demands on the surface flatness of each layer in the multilevel chip architectures. To meet the processing nature of lithography, a global planarization of interlayer metals by chemical-mechanical polishing is therefore needed to reduce the interval between the metal layer and the photomask, and to guarantee exposure resolution when wires reach the sub-300 nm scale. Two-photon absorption (TPA) has also been tried for the fabrication of metal microstructures by using suitable salt solutions as the metal source and photosensitive molecules as the photoinitiator. [3][4][5] However, these studies aimed at refined planar periodic gratings or dot arrays [6] for plasmonic wave coupling or three-dimensional (3D) mold making, which more or less ignore the conductivity of these precise metal structures. For example, by using surfactants as particle-growth inhibitor, delicate 3D structures with a smooth surface were achieved, [7] whereas the conductivity of these metal microstructures was significantly debased due to the residual organic components.To the best of our knowledge, both the photolithography and TPA micro/nanoprocessing conducted so far have focused on fabrication on flat substrates. [8][9][10] These methods cannot meet the increasing demands of circuitry and electronic connections on nonplanar substrates in microelectromechanical systems (MEMS), [1] lab on a chip (LoC), [11] and other intelligent microsystems. Taking LoC as an example, if an appropriate microheater could be embedded on the immediate base inside a microfluidic channel instead of sitting several hundreds of micrometers apart on the rear of the substrate, as is usually done with Peltier thermoelectric elements, [12] integrated resistive heaters, [13][14][15][16][17] and Joule heating of ionic liquids, [18] then local temperature regulation of fluids with higher precision, quicker response, and smarter switching at the exact point of care may be realized due to the effectively reduced thermal inertia. Such a capability is particularly desired for temperature regulation of miniaturized LoC systems that involve repeated thermal cycling, such as DNA amplification by the polymerase chain reaction (PCR), which comprises three sequential steps of denaturation (95 8C), annealing (55 8C), and extension (72 8C). [12] Nevertheless, convenient introduction of a local heating circuit inside a ready channel is almost inaccessible for lithography and other currently available micro/nanofabrication methods. Therefore, there is an urgent need for flexible micro/nanoprocessing technologies for metal nanowiring on nonplan...

In the pursuit of modern microfluidic chips with multifunction integration, micronanofabrication techniques play an increasingly important role. Despite the fact that conventional fabrication approaches such as lithography, imprinting and soft lithography have been widely used for the preparation of microfluidic chips, it is still challenging to achieve complex microfluidic chips with multifunction integration. Therefore, novel micronanofabrication approaches that could be used to achieve this end are highly desired. As a powerful 3D processing tool, femtosecond laser fabrication shows great potential to endow general microfluidic chips with multifunctional units. In this review, we briefly introduce the fundamental principles of femtosecond laser micronanofabrication. With the help of laser techniques, both the preparation and functionalization of advanced microfluidic chips are summarized. Finally, the current challenges and future perspective of this dynamic field are discussed based on our own opinion.

Asymmetric molecular brushes emerge as a unique class of nanostructured polymers, while their versatile synthesis keeps a challenge for chemists. Here we show the synthesis of well-defined asymmetric molecular double-brushes comprising two different side chains linked to the same repeat unit along the backbone by one-pot concurrent atom transfer radical polymerization (ATRP) and Cu-catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The double-brushes are based on a poly(Br-acrylate-alkyne) homopolymer possessing an alkynyl for CuAAC reaction and a 2-bromopropionate initiating group for ATRP in each repeat unit. The versatility of this one-shot approach is demonstrated by CuAAC reaction of alkynyl/poly(ethylene oxide)-N3 and ATRP of various monomers. We also show the quantitative conversion of pentafluorophenyl ester groups to amide groups in side chains, allowing for the further fabrication of diverse building blocks. This work provides a versatile platform for facile synthesis of Janus-type double-brushes with structural and functional control, in a minimum number of reactions.

A novel single-source precursor was synthesized by the reaction of an allyl hydrido polycarbosilane (SMP10) and tetrakis(dimethylamido)hafnium(iv) (TDMAH) for the purpose of preparing dense monolithic SiC/HfC(x)N(1-x)-based ultrahigh temperature ceramic nanocomposites. The materials obtained at different stages of the synthesis process were characterized via Fourier transform infrared (FT-IR) as well as nuclear magnetic resonance (NMR) spectroscopy. The polymer-to-ceramic transformation was investigated by means of MAS NMR and FT-IR spectroscopy as well as thermogravimetric analysis (TGA) coupled with in situ mass spectrometry. Moreover, the microstructural evolution of the synthesized SiHfCN-based ceramics annealed at different temperatures ranging from 1300 °C to 1800 °C was characterized by elemental analysis, X-ray diffraction, Raman spectroscopy and transmission electron microscopy (TEM). Based on its high temperature behavior, the amorphous SiHfCN-based ceramic powder was used to prepare monolithic SiC/HfC(x)N(1-x)-based nanocomposites using the spark plasma sintering (SPS) technique. The results showed that dense monolithic SiC/HfC(x)N(1-x)-based nanocomposites with low open porosity (0.74 vol%) can be prepared successfully from single-source precursors. The average grain size of both HfC0.83N0.17 and SiC phases was found to be less than 100 nm after SPS processing owing to a unique microstructure: HfC0.83N0.17 grains were embedded homogeneously in a β-SiC matrix and encapsulated by in situ formed carbon layers which acted as a diffusion barrier to suppress grain growth. The segregated Hf-carbonitride grains significantly influenced the electrical conductivity of the SPS processed monolithic samples. While Hf-free polymer-derived SiC showed an electrical conductivity of ca. 1.8 S cm(-1), the electrical conductivity of the Hf-containing material was analyzed to be ca. 136.2 S cm(-1).

Silver microflower arrays constructed by upright nanoplates and attached nanoparticles were fabricated inside a microfluidic channel, thus a robust catalytic microreactor for allowing in situ SERS monitoring was proposed. On-chip catalytic reduction shows that the silver microflowers have high catalytic activity and SERS enhancement.