Volume 13

  • No. 12 December 2018

    Fast meets small in compensated ferrimagnets

    Topologic spin textures such as skyrmions or domain walls are robust against perturbation and can be manipulated all-electrically. To make them useful for information storage and processing, there is a need for fast, room-temperature manipulation and small footprints. Caretta et al. drove domain walls with a speed of 1.3’km’s–1 and created skyrmions down to 10-nm diameter at room temperature in a compensated ferrimagnet. The cover art depicts skyrmions (white swirls with a red or blue centre) within three domains of the ferrimagnet (red and blue, respectively), which are separated by domain walls (white). The orientation of each arrow indicates a spin and its colour the local net magnetization.

    See Beach et al.

  • No. 11 November 2018

    Probing intersubbands in 2D materials

    The device operation of quantum-well infrared photodetectors and quantum-cascade lasers rely on intersubband transitions — that is, transitions that occur between quantized states in quantum wells that are typically fabricated from different III–V semiconductor alloys. The combination of materials in these structures is limited by strict lattice-matching conditions, which may deteriorate the device performance. Owing to their design versatility, van der Waals quantum wells naturally formed in 2D materials heterostructures are not impaired by these restrictions. However, until now, intersubband transitions in van der Waals quantum wells have not been observed experimentally. Now, Schmidt et al. employ near-field local probing to spectrally resolve intersubband transitions in layered transition metal dichalcogenides (TMDs) providing the opportunity to study these phenomena in van der Waals quantum wells for future applications. The cover is the artist’s depiction of an optically excited van der Waals layered structure formed by terraced TMDs.

    See Koppens et al.

  • No. 10 October 2018

    Pushing engine efficiency to the limit

    A heat engine extracts work as heat flows from the hot to the cold reservoir. In macroscopic systems this is achieved by avoiding direct contact between them; rather, the engine is cyclically connected to and disconnected from the reservoirs. This mode of operation, however, is rather impractical to be implemented at the nanoscale and nanoengines with no moving parts have been theorized. Linke and co-workers have now experimentally demonstrated a nanoscale heat engine in which only electrons at a specific energy flow between the reservoirs generating an electric current. The image on the cover is an artist’s impression of the nanoengine with the hot and cold reservoirs coloured in red and blue respectively.

    See Li et al.

  • No. 9 September 2018

    Direct observation of thermal atomization

    Metal atoms tend to sinter at high temperature, leading to a decrease in the reactivity of atomically dispersed catalysts. Y. Li and co-workers report an unexpected phenomenon. After encapsulating palladium, platinum and gold nanoparticles in ZIF-8, they observed the progressive atomic dispersion of these noble metal atoms as single sites in the nitrogen-doped carbon derived from ZIF-8 pyrolysis. The cover is an artist's depiction of the thermal atomization process that requires the interaction of noble metal atoms with the defects of N-doped carbon. The thermally stable single atoms exhibit promising performance towards the semi-hydrogenation of acetylene.

    See Li et al.

  • No. 8 August 2018

    Phase separation of single-stranded DNA

    DNA is widely explored as a programmable element to fabricate nanostructures, while it faces challenges when forming assemblies at larger length scale without the aid of polymers or nanomaterials. Now, A. Walther and co-workers found single-stranded DNA with purine-rich poly-A and poly-G sequences can itself undergo a defined lower critical solution temperature-type phase transition at elevated temperature like other polymers, and exploited this to realize all-DNA superstructures. The cover art depicts DNA protocells containing liquid DNA encapsulated in a DNA hydrogel shell, which are formed via a quick one-step heating cycle exploiting this newly discovered concept, as well as their higher-level organization into cellular hydrogel.

    See Walther et al.

  • No. 7 July 2018

    Stress-free strong carbon bundles

    Carbon nanotubes (CNTs) are renowned for their exceptional mechanical properties, and especially for being one of the strongest materials known to date. When assembled in bundles, however, their tensile strength drops significantly below that of single CNTs due to misalignment, defects and impurities. Now, Bai and co-workers have obtained centimetre-long CNT bundles fabricated via a synchronous tightening and relaxing strategy aimed to release the non-uniform initial strains of individual CNTs. The mechanical properties of this CNT-based material show a significant macroscale enhancement with respect to other reported strong fibres as evidenced by a record high tensile strength of 80 GPa. The artist’s impression on the cover image shows such an aligned and defect-free ultralong bundle consisting of many individual CNTs.

    See Zhang et al.

  • No. 6 June 2018

    When light becomes water

    Solar water evaporation has the potential to offer an attractive method of energy harvesting for water desalination and purification. To fare well in real-life applications, this technology requires cost-effective, high-performance and compact solar vapour generators. Zhao, Zhou and co-workers have designed a hierarchically nanostructured gel formulated of hydrophilic polyvinyl alcohol (PVA) and light absorbing polypyrrole (PPy) capable of fast and efficient solar energy conversion into pure water. The water collected in a PVA network can rapidly diffuse via multiple micron channels and internal gaps, allowing the PVA molecular meshes to replenish with water to match high-rate vapour generation. The cover image represents water molecules confined in the molecular mesh of the PVA network.

    See Zhao, F et al.

  • No. 5 May 2018

    Synergy between neighbouring Pt monomers

    Atomically dispersed catalysts are reported to exhibit remarkable activity in various reactions due to the high atom utilization, low-coordination environment of metal atoms and strong metal–support interaction. However, it remains unknown whether there is any interaction between the active metal monomers in the atomically dispersed catalysts. Zeng and co-workers have now demonstrated that the synergetic interaction between neighbouring Pt monomers on MoS2 enhanced the CO2 hydrogenation catalytic activity relative to isolated monomers. The cover is an artist's depiction of CO2 hydrogenation to methanol via synergy between neighbouring Pt monomers. The curved surface represents the MoS2 surface decorated with different types of neighbouring Pt monomer. The yellow sphere (S atom) between neighbouring white spheres (Pt atoms) is shining, as a reflection of a synergetic interaction.

    See Zeng et al.

  • No. 4 April 2018

    In vivo decompression of genetic messages

    DNA can encode man-made genetic programs that perform specific tasks in live cells. The delivery of a DNA program to a cell is akin to sending a message. Lapique and Benenson show that a DNA message can be compressed like a computer file to reduce its size, and can then be decompressed in a cell after being delivered. The cover is an artist's depiction of the decompression process that requires a site-specific recombinase protein and takes place in the nucleus. The fact that the chemical structure of DNA is also an information carrier is illustrated using the wireframe extrapolation.

    See Benenson, Y et al.

  • No. 3 March 2018

    Computational quest for 2D materials

    Two-dimensional materials with a unique set of physical and chemical properties and the tangible potential for various electronic and optoelectronic applications have generated a substantial amount of experimental studies. Yet, all these works are based on only a few dozens of practically exfoliable materials. Using high-throughput calculations, N. Mounet and co-workers have now succeeded in identifying 1,825 potentially exfoliable two-dimensional materials and predicted some of their essential physical properties. The cover is an artist's depiction of diverse two-dimensional materials. The different colours represent different atoms in each flake. Some of the flakes are atomically thin and some consists of a few atomic layers.]

    See Mounet, N et al. and Eriksson, O

  • No. 2 February 2018

    Cooling the junction

    It has been theoretically predicted that certain molecules can have a large Seebeck coefficient and therefore be useful in thermoelectric power conversion applications. Now, Cui et al. have developed a very sensitive calorimeter that allows the direct determination of the heat absorbed or dissipated in a molecular junction with picowatt sensitivity. With this instrument they observe refrigeration (Peltier cooling) in several molecular systems. The image is an artist's depiction of the molecular junction based on an oil painting on masonite by Sara Adlerstein. The blue (cold) and red (hot) regions are bridged by aromatic molecules. The red spheres represent electrons that are carrying heat from the cold to the hot region

    See Cui, L et al.

  • No. 1 January 2018

    How to resist silver

    The resistance of bacteria against antibiotics represents one of the biggest issues of the 21st century. Nanotechnologies applying silver nanoparticles are considered an emerging tool in antimicrobial therapies as their action has not yet been associated with any resistance. A. Panáček, L. Kvítek, R. Zbořil and co-workers have now discovered that gram-negative bacteria repeatedly exposed to silver nanoparticles can develop resistance to their antibiotic activity. The cover is an artist’s rendition of the resistance mechanism based on the production of flagellin — an adhesive protein of bacterial flagellum, which causes nanoparticles’ aggregation and thereby eliminates their antibacterial effect. Importantly, the resistance evolves without any genetic changes and can be overcome by the addition of pomegranate rind extract inhibiting the flagellin production in bacteria.

    See Panáček et al.