#TeddersRecommends

A cavity optomechanical magneto­meter operating in the 100 pT range is reported. The device operates at earth field, achieves tens of megahertz bandwidth with 60 μm spatial resolution and microwatt optical-power requirements. These unique capabilities may have a broad range of applications including cryogen-free and microfluidic magnetic resonance imaging (MRI), and investigation of spin-physics in condensed matter systems.

A facile and passive multiply flexible thin-film sensor is demonstrated based on thermoelectric effects in graphene. The sensor is highly conductive, free-standing, flexible, and elastic. It senses heat and cold, and measures heated/cooled areas; it also discerns human touch from other pressures, locates human touch, and measures pressure levels. All of these sensing abilities are demonstrated without any internal/external power supply.

Inspired by the fog-harvesting behavior of the cactus, a novel fog collector is fabricated on a large scale by K. Liu and co-workers through integrating hydrophobic cone arrays with a hydrophilic matrix. This can spontaneously and continuously collect, transport, and preserve fog water. This facile approach offers new ideas for solving the water crisis, for example, the fog collector can supply water for saplings living in arid and foggy regions.

Ultrathin monolayer graphene as a welldefined sub-nanospacer between Ag NPs and Ag film is demonstrated by C. H. Choy and co-workers. Their results show that the system offers a tremendous near-field enhancement with one of the highest enhancement ratios reported to date in the graphene–metal plasmonic combination system. There is an additional chemical enhancement from the interaction between graphene sub-nanospacer and detection molecules.

Chemical vapor deposition (CVD) of polymer films represent the marriage of two of the most important technological innovations of the modern age. CVD as a mature technology for growing inorganic thin films is already a workhorse technology of the microfabrication industry and easily scalable from bench to plant. The low cost, mechanical flexibility, and varied functionality offered by polymer thin films make them attractive for both macro and micro scale applications. This review article focuses on two energy and resource efficient CVD polymerization methods, initiated Chemical Vapor Deposition (iCVD) and oxidative Chemical Vapor Deposition (oCVD). These solvent-free, substrate independent techniques engineer multi-scale, multi-functional and conformal polymer thin film surfaces and interfaces for applications that can address the main sustainability challenges faced by the world today.

CVD polymerization for engineering macro and micro scale interfaces for a sustainable world is reviewed.

Transformation from a film into a sphere, rapid merging of separate objects, controlled self-rotation, and planar locomotion are the very unusual phenomena observed in liquid metals under application of an electric field to a liquid metal immersed in or sprayed with water. A mechanism for these effects is suggested and potential applications – for example the recovery of liquid metal previously injected into the body for therapeutic purposes – are outlined.

Due to its amphiphilic property, graphene oxide (GO) can achieve a variety of nanostructures with different morphologies (for example membranes, hydrogel, crumpled particles, hollow spheres, sack-cargo particles, Pickering emulsions, and so on) by self-assembly. The self-assembly is mostly derived from the self-concentration of GO sheets at various interfaces, including liquid-air, liquid-liquid and liquid-solid interfaces. This paper gives a comprehensive review of these assembly phenomena of GO at the three types of interfaces, the derived interfacial self-assembly techniques, and the as-obtained assembled materials and their properties. The interfacial self-assembly of GO, enabled by its fantastic features including the amphiphilicity, the negatively charged nature, abundant oxygen-containing groups and two-dimensional flexibility, is highlighted as an easy and well-controlled strategy for the design and preparation of functionalized carbon materials, and the use of self-assembly for uniform hybridization is addressed for preparing hybrid carbon materials with various functions. A number of new exciting and potential applications are also presented for the assembled GO-based materials. This contribution concludes with some personal perspectives on future challenges before interfacial self-assembly may become a major strategy for the application-targeted design and preparation of functionalized carbon materials.

With its amphiphilic nature, graphene oxide as a 2D soft molecule is characterized by many self-concentration phenomena at interfaces, and these interesting interfacial properties, together with developed self-assembly techniques, indicate a simple and effective strategy for producing a variety of novel carbon nanostructures and final bulk materials with designed functions.

The power conversion efficiency of solar cells based on copper (I) oxide (Cu₂O) is enhanced by atomic layer deposition of a thin gallium oxide (Ga₂O₃) layer. By improving band-alignment and passivating interface defects, the device exhibits an open-circuit voltage of 1.20 V and an efficiency of 3.97%, showing potential of over 7% efficiency.

Non-destructive chemical functionalization of graphene for applications in electronic devices (e.g., sensors or transducers) is achieved via assembly of carbon nanomembrane (CNM)/single-layer graphene (SLG) van der Waals heterostructures. The CNMs are 1 nm-thick, dielectric molecular sheets terminated with functional amino groups. The structure and performance of heterostructured field-effect transistors (FETs) are characterized by photoelectron/Raman spectroscopy and by electric transport measurements in vacuum, ambient conditions and water.

A quantum-dot (QD) p-i-n heterojunction solar cell with an increased depletion region is demonstrated by depleting the QD layer from both the front and back junctions. Due to a combination of improved charged extraction and increased light absorption, a 120% increase in the short-circuit current is achieved compared with that of conventional ZnO/QD devices.

A new benchmark for DSSC performances is set using a novel dye and fabricating a very efficient resonant light-scattering device with a high photocurrent and good stability.

A novel method for performing in situ characterization of the electrical properties of pristine, ultrafine nanopowders is reported. A modified dilatometer, with a spring-loaded push rod and electrodes, allows for the simultaneous monitoring of the packed nanopowder's lateral displacement as well as its complex impedance spectroscopy as a function of temperature within a controlled environment. Anatase TiO₂ quantum dots of 2 nm diameter, on average, are examined and found to simultaneously shrink and become more resistive upon initial heating. The resistance changes by approximately 3 orders of magnitude upon heating, associated with the desorption of adsorbed water, demonstrating the need for sample preconditioning. Subsequent electrical resistivity measurements, as a function of oxygen partial pressure, over approximately 40 orders of magnitude, at temperatures between 300 °C and 400 °C, exhibit nearly 9 orders of magnitude change in conductivity. The data are consistent with a Frenkel-based defect disorder model characterized by an enthalpy of reduction of 5.5 ± 0.5 eV.

Anatase TiO₂ quantum dots exhibit a Frenkel defect disorder when characterized as loose powder in a modified dilatometer setup, which allows electrical impedance spectroscopy measurements. In addition, lateral expansion indicates necessity of preconditioning to attain equilibrium electronic parameters by eliminating protonic conduction on the surface of the quantum dots.

In this study, T. Chen and co-workers present a cancer-targeted MSN drug-delivery system carrying ruthenium complexes (RuPOP@MSNs), that allows the direct fluorescence monitoring of the cellular uptake and localization of theranostic agents in cancer cells. On page 2754 the nanoparticles exhibit unprecedented enhanced cytotoxicity toward cancer cells overexpressing integrin receptors through the induction of apoptosis. Moreover, the strong autofluorescence of Ru complex extends the power of theranostics to a subcellular level.

L. Dai, D. Cao, and co-workers develop on page 3315 a new strategy to obtain N-doped holey graphitic carbon materials using covalent organic polymer precursors with controlled locations for the N-atoms. These N-doped holey graphene analogues are promising candidates for efficient energy conversion and storage, particularly as efficient metal-free electrocatalysts for oxygen reduction reaction in fuel cells.

A layered stacking growth route for the hierarchical assembly of graphene on a liquid copper catalyst by chemical vapor deposition is described by G. Yu and co-workers on page 3218. These hierarchical graphene architectures, displaying a snow-like morphology, reveal the non-equilibrium growth processes of multi-layer graphene and present electrical anisotropy. This work potentially offers impetus for the application of graphenebased electronics.

K. Cho and co-workers develop on page 3213 a water-free transfer method for placing chemical vapor depositiongrown graphene onto arbitrary substrates. Transferring graphene without water enables water-sensitive substrates to be used in graphene electronics. Using this method, high-performance flexible air-stable graphene transistors are fabricated. A polymeric bilayer (poly(methyl methacrylate)/polybutadiene) is used as supporting layer during the transfer process, which provides not only robust support but also effective passivation that protects graphene from undesirable charged impurities.

A hybrid comprising a three-dimensional N-doped graphene aerogel and iron nitride is fabricated via a facile two step synthesis strategy, namely hydrothermal assembly and annealing. This hybrid, created by Y. Hou and co-workers, exhibits outstanding catalytic activity for the oxygen reduction reaction in fuel cells and superior stability and selectivity compared to commercial Pt/C. The covalent interaction between the two components contribute greatly to the synergistic catalytic performance. This low-cost and high-performance catalyst is a promising replacement for commercial Pt/C.

On page 2947, N. R. Sottos and co-workers report the preparation of robust microcapsules that contain high concentration carbon black suspensions. Prior to encapsulation, carbon black particles are surface functionalized with octadecyl chains to create stable particle suspensions, which is critical for the release of carbon black. When ruptured, these microcapsules exhibit significant particle release, enabling full conductivity restoration of damaged battery electrodes.