Advanced Materials

The stability and association of polymer–fullerene films upon thermal annealing depends strongly on exposure to light, even at ambient conditions, as reported by João T. Cabral and co-workers on page 985. As a result, the coupling of self-assembly in polymer nanocomposites and photo-transformation provides an extremely promising route for patterning the stability (wetting/dewetting), morphology and characteristic dimensions in thin film composites.

High-quality graphene polycrystalline films are directly synthesized on dielectric silicon nitride substrates by using two-stage metal-catalyst-free chemical vapor deposition. Thus large-scale electronic devices are easily fabricated on these films without complicated transfer processes and their associated problems. The method is compatible with current Si processing techniques. Further details can be found in the article by Yunqi Liu and co-workers on page 992.

The back cover illustrates scanning electron micrographs of copper(II) hydroxide (elongated crystals) and HKUST-1 (octahedral crystals). Javier Pérez-Ramírez and Gerardo Majano demonstrate on page 1052 a sustainable and scalable route to quantitatively converting an insoluble layered hydroxide into the pure metal-organic framework (MOF) with the highest reported productivities. This simple and low-cost synthesis is expected to bring an expanded use of this MOF in laboratory investigations and in industrial scenarios.

Flexoelectricity describes the phenomenon in which electrical polarization is induced by a strain gradient. Due to size-dependent scaling of the strain gradient, the flexoelectric effect is particularly important in nanoscale systems. It has also been observed in biological systems, making flexoelectricity an exciting field of study as nano-bio hybrid systems gain prominence.

Interconnected mesoporous NiCo₂O₄ nanosheets can be directly grown on various conductive substrates including Ni foam, stainless steel, Ti foil, and flexible graphite paper through a simple solution method. The NiCo₂O₄ nanosheets-Ni foam structure exhibits superior pseudocapacitive performance with a high capacitance of 1743 F g⁻¹ under a constant current density of 7.08 A g⁻¹ and a capacitance loss of only 6.7% after 3000 cycles. More details can be found in the article by Xiong Wen (David) Lou and Genqiang Zhang on page 976.

Mesoporous NiCo₂O₄ nanosheets can be directly grown on various conductive substrates, such as Ni foam, Ti foil, stainless-steel foil and flexible graphite paper, through a general template-free solution method combined with a simple post annealing treatment. As a highly integrated binder- and conductive-agent-free electrode for supercapacitors, the mesoporous NiCo₂O₄ nanosheets supported on Ni foam deliver ultrahigh capacitance and excellent high-rate cycling stability.

An abnormal behavior of increasing magnetic anisotropy with temperature in magnetic thin films fabricated by a gradient-composition sputtering technique is observed and consistently confirmed by two independent measurements of static magnetic hysteresis loops and dynamic magnetic permeability spectra. This peculiar behavior is suggested to be due to the physical origin of stress-induced magnetic anisotropy.

The stability and association of polymer–fullerene films upon thermal annealing depends strongly on exposure to light, even at ambient conditions. As a result, dewetting of nanocomposite films can be prevented and the characteristic lengthscales of phase separated morphologies finely tuned. Coupling photopatterning with either self-organization process provides a powerful route for the directed assembly of fullerene-based nanocomposites into functional “circuits”.

By using two-stage, metal-catalyst-free chemical vapor deposition (CVD), it is demonstrated that high-quality polycrystalline graphene films can directly grow on silicon nitride substrates. The carrier mobility can reach about 1500 cm² V⁻¹ s⁻¹, which is about three times the value of those grown on SiO₂/Si substrates, and also is better than some examples of metal-catalyzed graphene, reflecting the good quality of the graphene lattice.

A simple, yet versatile strategy to prepare size-controlled and monodisperse carbon sub-micrometer spheres is developed based on the biomolecule dopamine. Unlike traditional carbon materials, the resulting carbon sub-micrometer spheres contain much less sp³ carbon with high-level electroactive nitrogen. Moreover, metal–carbon hybrid sub-micrometer spheres can be easily obtained, and show highly promising catalytic properties in the oxygen-reduction reaction.

Contrary to theoretical estimates based on the conventional binary collision model, experimental results indicate that the number of defects in the lower layer of the bi-layer graphene sample is smaller than in the upper layer. This observation is explained by in situ self-annealing of the defects.

A unique procedure is developed to capture carbon nanotubes into closed virus-like protein cages with a controllable shell. The cross-linked shell varies in thickness within ≈10⁰–10² nm, and can be entirely removed by enzyme degradation. The cytotoxicity is entirely suppressed, but can be promoted again by enzymes and near-infrared light. These hybrids can be decorated with functional inorganic nanoparticles or processed into nanocomposites.

On page 1017, Martin Möller, Xiaomin Zhu, and co-workers report a facile and universal approach for the preparation of silica particles of various mesostructures based on the self-assembly of amphiphilic precursor polymers in water and subsequent condensation. Depending on the hydrophilization degree of hyperbranched polyethoxysiloxane, various silica morphologies including mesoporous particles, hollow nanospheres and ultrasmall particles with high application potential can be fabricated.

A facile and universal approach is reported for the preparation of silica particles of various mesostructures based on the self-assembly of amphiphilic precursor polymers in water and subsequent condensation. Depending on the hydrophilization degree of hyperbranched polyethoxysiloxane, various silica morphologies including mesoporous particles, hollow nanospheres and ultrasmall particles with high application potential are fabricated.

Conventional SERS probes suffer from limited brightness and poor reproducibility and stability making them unsuitable for routine in vivo applications. A novel class of layered SERS probes is demonstrated in which individual nanostructures host electromagnetic hotspots, thus increasing brightness by more than two orders magnitide compared to conventional individual nanostructures.

Intergrowth of two partially miscible phases of BiFeO₃ and BiMnO₃ gives a new class of room-temperature multiferroic phase, Bi₃Fe₂Mn₂O_10+δ, which has a unique supercell (SC) structure. The SC heterostructures exhibit simultaneously room-temperature ferrimagnetism and remanent polarization. These results open up a new avenue for exploring room-temperature single-phase multiferroic thin films by controlling the phase mixing of two perovskite BiRO₃ (R = Cr, Mn, Fe, Co, Ni) materials.

Interface modification in transport properties of single elemental polycrystalline Bi via spark plasma sintering results in ‘double-decoupling’ (simultaneous decoupling of thermopower, electrical, and thermal conductivity) of otherwise coupled entities. In spark plasma sintering, the DC pulse current helps in controlling the nature and extent of surfaces of ball-milled Bi and hence results in six-fold improvement in the dimensionless figure of merit (ZT) relative to as-purchased samples.

Low lying excited states of the fullerene anion promote a faster charge separation in organic solar cells containing fullerene derivatives as electron acceptors. Alternative electron acceptors, not based on fullerenes but that share the same property, can be easily designed. On the other hand, it is unlikely for a generic electron acceptor to replicate this fullerene characteristic by chance.

This work employs novel SnO₂ gel-like precursors in conjunction with sol–gel deposited ZrO₂ gate dielectrics to realize high-performance transparent transistors. Representative devices show excellent performance and transparency, and deliver mobility of 103 cm² V⁻¹ s⁻¹ in saturation at operation voltages as low as 2 V, a sub-threshold swing of only 0.3 V/decade, and I_on/I_off of 10⁴∼10⁵.

A new approach is proposed for the synthesis of molecularly imprinted polymers (MIPs) (synthetic antibodies) as soluble nanogels with sizes close to the size of real antibodies. To imprint a molecular memory in particles consisting of only a few polymer chains, an initiator carrying multiple iniferter moieties is used. This allows for the simultaneous initiation of several polymer chains, and yields molecularly imprinted nanogels (17 nm, molecular weight (MW) = 97 kDa) with good affinity and selectivity for the target.

Copper(II) hydroxide is converted directly to HKUST-1 (Cu₃(btc)₂) after only 5 min at room-temperature in aqueous ethanolic solution without the need of additional solvents. Scale up to the kilogram scale does not influence porous properties yielding pure-phase product with a remarkable total surface area exceeding 1700 m² g⁻¹ featuring aggregates of nanometer-sized crystals (<600 nm) and extremely high space-time yields.

Highly stretchable, integrated, single-walled carbon nanotube (SWCNT) film supercapacitors are prepared by combining directly grown SWCNT films with continuous reticulate architecture with polydimethylsiloxane with enhanced prestrain. The performance of the prepared stretchable supercapacitors remains nearly unchanged even during the stretching process under 120% strain.

Thin films of magnetically doped topological insulators Cr_0.22(Bi_xSb_1-x)_1.78Te₃ are found to possess carrier-independent long-range ferromagnetic order with perpendicular magnetic anisotropy. The anomalous Hall resistance is greatly enhanced, up to one quarter of quantum Hall resistance, by depletion of the carriers. The results demonstrate this material as a promising system to realize the quantized anomalous Hall effect.

Order of dipole moment layers at donor and acceptor interfaces in bilayer organic solar cells is manipulated reversibly by applying bias voltages. The energy level shifts at the interfaces induce reversible changes in the open circuit voltage and the diode properties. This finding could lead to a better understanding of the structure–property relationship at the materials interfaces in organic optoelectronic devices.