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S.-Z. Qiao, X.-W. Du, and co-workers report on page 740 the preparation of nanoflake arrays (NFAs) with appropriate size and their unprecedented light absorption properties. Intriguingly, after a thin-layer of an organic absorber is loaded on NFAs, extraordinarily high absorption efficiency (95%) is realized. As a result, the hybrid solar cell consisting of NFAs and the organic absorber yields a photo-current that is ten times higher than that of the counterpart device with common planar structure.

Lead sulfide quantum dots represent an emerging photovoltaic absorber material. While their associated optical qualities are true for the colloidal solution phase, they change upon processing into thin-films. A detailed view to the optical key-parameters during solid-film development is presented and the limits and outlooks for this versatile and promising absorber are discussed.

Zero-dimensional ZnS/CdS nanocomposites (NCs) are designed based on the controlled growth of ZnS nanoparticles by X. S. Fang and team on page 445. The as-obtained NCs are functionally versatile and offer great optoelectronic properties. For example, the photo-degradation rate of ZnS/CdS NCs towards organic dyes under UV light is three times as much as that of pure ZnS nano-particles, due to the effective charge separation and increased specific surface area.

Although many two-dimensional (2D) hybrid nanostructures are being prepared, the engineering of epitaxial 2D semiconductor hetero-nanostructures in the liquid phase still remains a challenge. The preparation of 2D semiconductor hetero-nanostructures by epitaxial growth of metal sulfide nanocrystals, including CuS, ZnS and Ni₃S₂, is achieved on ultrathin TiS₂ nanosheets by a simple electrochemical approach by using the TiS₂ crystal and metal foils. Ultrathin CuS nanoplates that are 50–120 nm in size and have a triangular/hexagonal shape are epitaxially grown on TiS₂ nanosheets with perfect epitaxial alignment. ZnS and Ni₃S₂ nanoplates can be also epitaxially grown on TiS₂ nanosheets. As a proof-of-concept application, the obtained 2D CuS–TiS₂ composite is used as the anode in a lithium ion battery, which exhibits a high capacity and excellent cycling stability.

Epitaxial growth of metal sulfide nanoplates, including CuS, ZnS, and Ni₃S₂, on ultrathin TiS₂ nanosheets is achieved by a simple electrochemical approach. Ultrathin triangular/hexagonal CuS nanoplates (50–120 nm) are grown on TiS₂ nanosheets with perfect epitaxial alignment. The 2D CuS–TiS₂ composite is used as anode in a lithium-ion battery, which exhibits high capacity and excellent cycling stability.

The typical two-dimensional (2D) semiconductors MoS₂, MoSe₂, WS₂, WSe₂ and black phosphorus have garnered tremendous interest for their unique electronic, optical, and chemical properties. However, all 2D semiconductors reported thus far feature band gaps that are smaller than 2.0 eV, which has greatly restricted their applications, especially in optoelectronic devices with photoresponse in the blue and UV range. Novel 2D mono-elemental semiconductors, namely monolayered arsenene and antimonene, with wide band gaps and high stability were now developed based on first-principles calculations. Interestingly, although As and Sb are typically semimetals in the bulk, they are transformed into indirect semiconductors with band gaps of 2.49 and 2.28 eV when thinned to one atomic layer. Significantly, under small biaxial strain, these materials were transformed from indirect into direct band-gap semiconductors. Such dramatic changes in the electronic structure could pave the way for transistors with high on/off ratios, optoelectronic devices working under blue or UV light, and mechanical sensors based on new 2D crystals.

Unlike black phosphorus, both arsenic and antimony are typical semimetals in their natural, layered bulk state. However, monolayered arsenene and antimonene are indirect wide-band-gap semiconductors, and under strain, they become direct band-gap semiconductors. Owing to these band-gap transitions, these materials could find applications in nano- and optoelectronic devices.

In this work, a new, universal method is described that uses the photopatterning of liquid crystals, which is accurately translated into a controlled, intricately wrinkled metal surface. Remarkably, the patterns have an oscillation in amplitude of the wrinkles. This rapid method allows generation of intricate multidomain patterns and continuous circular structures, including azimuthal, radial, and even higher complexity arrangements as examples. These wrinkled gold surfaces are also strikingly visual, which is interesting for applications ranging from diffractive elements to fine jewelry.

Unique wrinkling patterns with oscillating amplitudes in any arbitrarily complex fashion are generated by controlling the alignment director of a liquid crystal network using photoalignment layers in combination with photomasks. The wrinkled gold surfaces are strikingly visual which is interesting for applications ranging from diffractive elements to fine jewelry. Image adapted with permission. Copyright 1973, Pink Floyd Music Ltd.

Recently, there have been extensive research efforts on developing high performance organolead halide based perovskite solar cells. While most studies focused on optimizing the deposition processes of the perovskite films, the selection of the precursors has been rather limited to the lead halide/methylammonium (or formamidium) halide combination. In this work, we developed a new precursor, HPbI₃, to replace lead halide. The new precursor enables formation of highly uniform formamidium lead iodide (FAPbI₃) films through a one-step spin-coating process. Furthermore, the FAPbI₃ perovskite films exhibit a highly crystalline phase with strong (110) preferred orientation and excellent thermal stability. The planar heterojunction solar cells based on these perovskite films exhibit an average efficiency of 15.4% and champion efficiency of 17.5% under AM 1.5 G illumination. By comparing the morphology and formation process of the perovskite films fabricated from the formamidium iodide (FAI)/HPbI₃, FAI/PbI₂, and FAI/PbI₂ with HI additive precursor combinations, it is shown that the superior property of the HPbI₃ based perovskite films may originate from 1) a slow crystallization process involving exchange of H⁺ and FA⁺ ions in the PbI₆ octahedral framework and 2) elimination of water in the precursor solution state.

HPbI₃is introduced as a novel precursor to solve the non-uniformity problem of formamidium lead iodide (FAPbI₃) perovskite films from one-step solution-­processed method. Interestingly, the FAPbI₃ films exhibit high crystallinity with (110) plane orientation and the corresponding devices yield an average photo­voltaic efficiency of 15.4% under 1 sun illumination. Present results demonstrate that precursor engineering is an effective approach to produce perovskites with attractive properties.

An unexpected polymorph of the highly energetic phase CuN₃ has been synthesized and crystallizes in the orthorhombic space group Cmcm with a=3.3635(7), b=10.669(2), c=5.5547(11) Å and V=199.34(7) ų. The layered structure resembles graphite with an interlayer distance of 2.777(1) Å (= c). Within a single layer, considering N₃⁻ as one structural unit, there are 10-membered almost hexagonal rings with a heterographene-like motif. Copper and nitrogen atoms are covalently bonded with CuN bonds lengths of 1.91 and 2.00 Å, and the N₃⁻ group is linear but with NN 1.14 and 1.20 Å. Electronic-structure calculations and experimental thermochemistry show that the new polymorph termed β-CuN₃ is more stable than the established α-CuN₃ phase. Also, β-CuN₃ is dynamically, and thus thermochemically, metastable according to the calculated phonon density of states. In addition, β-CuN₃ exhibits negative thermal expansion within the graphene-like layer.

Are there others azide from me? A new CuN₃ polymorph with a heterographene-like motif was synthesized and characterized. Experimental and theoretical investigations give insight to its thermochemistry and its electronic and vibrational properties. Not only is β-CuN₃ identified as the ground-state structure, the compound exhibits negative thermal expansion in the ab plane, similar to, but more pronounced, than in graphite.

Manipulation of the self-assembly of magnetic colloidal particles by an externally applied magnetic field paves a way toward developing novel stimuli responsive photonic structures. Using microradian X-ray scattering technique we have investigated the different crystal structures exhibited by self-assembly of core–shell magnetite/silica nanoparticles. An external magnetic field was employed to tune the colloidal crystallization. We find that the equilibrium structure in absence of the field is random hexagonal close-packed (RHCP) one. External field drives the self-assembly toward a body-centered tetragonal (BCT) structure. Our findings are in good agreement with simulation results on the assembly of these particles.

An external magnetic field stimulates core–shell magnetite/silica nanoparticles to self-assemble to a body-centered tetragonal crystalline structure. In the absence of magnetic field, the self-organization is governed by the hard-sphere repulsion between the particles and a combination of electrostatic repulsion and van der Waals attraction, leading to the formation of a random hexagonal close-packed structure.

Controllable synthesis of large domain, high-quality monolayer MoS₂ is the basic premise both for exploring some fundamental physical issues, and for engineering its applications in nanoelectronics, optoelectronics, etc. Herein, by introducing H₂ as carrier gas, the successful synthesis of large domain monolayer MoS₂ triangular flakes on Au foils, with the edge length approaching to 80 mm is reported. The growth process is proposed to be mediated by two competitive effects with H₂ acting as both a reduction promoter for efficient sulfurization of MoO₃ and an etching reagent of resulting MoS₂ flakes. By using low-energy electron microscopy/diffraction, the crystal orientations and domain boundaries of MoS₂ flakes directly on Au foils for the first time are further identified. These on-site and transfer-free characterizations should shed light on the initial growth and the aggregation of MoS₂ on arbitrary substrates, further guiding the growth toward large domain flakes or monolayer films.

The monolayer molybdenum disulfide growth process is proposed to be mediated by two competitive effects with hydrogen acting as both a reduction promoter for efficient sulfurization of MoO₃ and an etching reagent of resulting molybdenum disulfide flakes. By using low-energy electron microscopy/diffraction, the crystal orientations and domain boundaries of molybdenum disulfide flakes are identified directly on Au foils for the first time.

Tin is a promising anode candidate for next-generation lithium-ion batteries with a high energy density, but suffers from the huge volume change (ca. 260 %) upon lithiation. To address this issue, here we report a new hierarchical tin/carbon composite in which some of the nanosized Sn particles are anchored on the tips of carbon nanotubes (CNTs) that are rooted on the exterior surfaces of micro-sized hollow carbon cubes while other Sn nanoparticles are encapsulated in hollow carbon cubes. Such a hierarchical structure possesses a robust framework with rich voids, which allows Sn to alleviate its mechanical strain without forming cracks and pulverization upon lithiation/de-lithiation. As a result, the Sn/C composite exhibits an excellent cyclic performance, namely, retaining a capacity of 537 mAh g⁻¹ for around 1000 cycles without obvious decay at a high current density of 3000 mA g⁻¹.

High capacity anodes: A tin/carbon hierarchical structure was designed, in which some of the nanosized Sn particles are anchored on the tips of carbon nanotubes that are rooted on the surfaces of microsized hollow carbon cubes while other Sn nanoparticles are encapsulated in the hollow carbon cubes. Such a unique structure allows the Sn particles to accommodate the volume change upon lithiation.

The spatial location of the predominant source of performance-limiting recombination in today's best colloidal quantum dot (CQD) cells is identified, pinpointing the TiO₂:CQD junction; then, a highly n-doped PCBM layer is introduced at the CQD:TiO₂ heterointerface. An n-doped PCBM layer is essential to maintain the depletion region and allow for efficient current extraction, thereby producing a record 8.9% in overall power conversion efficiency.

For building high-energy density asymmetric supercapacitors, developing anode materials with large specific capacitance remains a great challenge. Although Fe₂O₃ has been considered as a promising anode material for asymmetric supercapacitors, the specific capacitance of the Fe₂O₃-based anodes is still low and cannot match that of cathodes in the full cells. In this work, a composite material with well dispersed Fe₂O₃ quantum dots (QDs, ≈2 nm) decorated on functionalized graphene-sheets (FGS) is prepared by a facile and scalable method. The Fe₂O₃ QDs/FGS composites exhibit a large specific capacitance up to 347 F g⁻¹ in 1 m Na₂SO₄ between –1 and 0 V versus Ag/AgCl. An asymmetric supercapacitor operating at 2 V is fabricated using Fe₂O₃/FGS as anode and MnO₂/FGS as cathode in 1 m Na₂SO₄ aqueous electrolyte. The Fe₂O₃/FGS//MnO₂/FGS asymmetric supercapacitor shows a high energy density of 50.7 Wh kg⁻¹ at a power density of 100 W kg⁻¹ as well as excellent cycling stability and power capability. The facile synthesis method and superior supercapacitive performance of the Fe₂O₃ QDs/FGS composites make them promising as anode materials for high-performance asymmetric supercapacitors.

Hematite quantum-dot/functionalized graphene-sheet composites are prepared and the composite electrode can reach a maximum specific capacitance of 347 F g⁻¹, which is much larger than the reported values for the Fe₂O₃-based electrodes in neutral aqueous electrolyte. A high-performance 2 V asymmetrical supercapacitor is fabricated using Fe₂O₃/FGS as anode and MnO₂/FGS as cathode in 1 m Na₂SO₄ electrolyte.

This review outlines the up-to-date research progress on controllable interfacial friction on both solid/solid and solid/liquid surfaces. Environment-sensitive materials at a frictional interface react to certain external stimuli and provoke changes in surface chemistry, interfacial charge, and/or topography, which then cause a change in the coefficient of friction. The external stimuli might be solvent, electrolyte, pH, temperature, light, electric potential, and magnetic field etc. In a similar way, controllable fluid–solid friction (i.e., boundary slippage versus non-slippage) can also be achieved by reversibly generating a gas lubricating layer at the interface or by changing the fluid–solid adhesion via physicochemical methods. The author comments are presented and outlooks proposed.

The interfacial friction is regulated using external stimuli. The application of external stimuli on surfaces changes the microtopography, chemical composition, molecular conformation and adsorption, interfacial charge, etc. and consequently the interfacial friction. Friction control over several important stimuli, including solvent, electrolyte, pH, thermal, electric potential and magnetic field, is reviewed in detail.