Showing papers in "Nature Nanotechnology in 2016"
TL;DR: A mesoporous carbon foam co-doped with nitrogen and phosphorus that has a large surface area and good electrocatalytic properties for both ORR and OER and is tested as an air electrode for primary and rechargeable Zn-air batteries.
Abstract: A co-doped carbon material, methods of making such materials, and electrochemical cells and devices comprising such materials are provided. The co-doped carbon material comprises a mesoporous carbon material doped with nitrogen and phoshporous (NPMC). The present NPMC exhibit catalytic activity for both oxygen reduction reaction and oxygen evolution reaction and may be useful as an electrode in an electrochemical cell and particularly as part of a battery. The present NPMC materials may be used as electrodes in primary zinc-air batteries and in rechargeable zinc-air batteries and many other energy systems.
2,425 citations
TL;DR: A solution-processed lead halide perovskite solar cell that has p-type NiO(x) and n-type ZnO nanoparticles as hole and electron transport layers, respectively, and shows improved stability against water and oxygen degradation when compared with devices with organic charge transport layers is reported.
Abstract: Lead halide perovskite solar cells have recently attracted tremendous attention because of their excellent photovoltaic efficiencies. However, the poor stability of both the perovskite material and the charge transport layers has so far prevented the fabrication of devices that can withstand sustained operation under normal conditions. Here, we report a solution-processed lead halide perovskite solar cell that has p-type NiOx and n-type ZnO nanoparticles as hole and electron transport layers, respectively, and shows improved stability against water and oxygen degradation when compared with devices with organic charge transport layers. Our cells have a p–i–n structure (glass/indium tin oxide/NiOx/perovskite/ZnO/Al), in which the ZnO layer isolates the perovskite and Al layers, thus preventing degradation. After 60 days storage in air at room temperature, our all-metal-oxide devices retain about 90% of their original efficiency, unlike control devices made with organic transport layers, which undergo a complete degradation after just 5 days. The initial power conversion efficiency of our devices is 14.6 ± 1.5%, with an uncertified maximum value of 16.1%. Using metal oxides for both the hole- and electron-transport layers in perovskite solar cells significantly improves their stability compared with devices containing organic transport layers.
1,834 citations
TL;DR: A perovskite mixed material comprising a series of differently quantum-size-tuned grains that funnels photoexcitations to the lowest-bandgap light-emitter in the mixture functions as charge carrier concentrators, ensuring that radiative recombination successfully outcompetes trapping and hence non-radiatives recombination.
Abstract: Organometal halide perovskites exhibit large bulk crystal domain sizes, rare traps, excellent mobilities and carriers that are free at room temperature-properties that support their excellent performance in charge-separating devices. In devices that rely on the forward injection of electrons and holes, such as light-emitting diodes (LEDs), excellent mobilities contribute to the efficient capture of non-equilibrium charge carriers by rare non-radiative centres. Moreover, the lack of bound excitons weakens the competition of desired radiative (over undesired non-radiative) recombination. Here we report a perovskite mixed material comprising a series of differently quantum-size-tuned grains that funnels photoexcitations to the lowest-bandgap light-emitter in the mixture. The materials function as charge carrier concentrators, ensuring that radiative recombination successfully outcompetes trapping and hence non-radiative recombination. We use the new material to build devices that exhibit an external quantum efficiency (EQE) of 8.8% and a radiance of 80 W sr-1 m-2. These represent the brightest and most efficient solution-processed near-infrared LEDs to date.
1,756 citations
TL;DR: Recent advances in the use of graphene and other 2D materials in catalytic applications are reviewed, focusing in particular on the catalytic activity of heterogeneous systems such as van der Waals heterostructures (stacks of several 2D crystals).
Abstract: Graphene and other 2D atomic crystals are of considerable interest in catalysis because of their unique structural and electronic properties. Over the past decade, the materials have been used in a variety of reactions, including the oxygen reduction reaction, water splitting and CO2 activation, and have been shown to exhibit a range of catalytic mechanisms. Here, we review recent advances in the use of graphene and other 2D materials in catalytic applications, focusing in particular on the catalytic activity of heterogeneous systems such as van der Waals heterostructures (stacks of several 2D crystals). We discuss the advantages of these materials for catalysis and the different routes available to tune their electronic states and active sites. We also explore the future opportunities of these catalytic materials and the challenges they face in terms of both fundamental understanding and the development of industrial applications.
1,683 citations
TL;DR: This Review presents a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index met amaterials and anisotropic metammaterials, and discusses current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics.
Abstract: The ideal material for nanophotonic applications will have a large refractive index at optical frequencies, respond to both the electric and magnetic fields of light, support large optical chirality and anisotropy, confine and guide light at the nanoscale, and be able to modify the phase and amplitude of incoming radiation in a fraction of a wavelength. Artificial electromagnetic media, or metamaterials, based on metallic or polar dielectric nanostructures can provide many of these properties by coupling light to free electrons (plasmons) or phonons (phonon polaritons), respectively, but at the inevitable cost of significant energy dissipation and reduced device efficiency. Recently, however, there has been a shift in the approach to nanophotonics. Low-loss electromagnetic responses covering all four quadrants of possible permittivities and permeabilities have been achieved using completely transparent and high-refractive-index dielectric building blocks. Moreover, an emerging class of all-dielectric metamaterials consisting of anisotropic crystals has been shown to support large refractive index contrast between orthogonal polarizations of light. These advances have revived the exciting prospect of integrating exotic electromagnetic effects in practical photonic devices, to achieve, for example, ultrathin and efficient optical elements, and realize the long-standing goal of subdiffraction confinement and guiding of light without metals. In this Review, we present a broad outline of the whole range of electromagnetic effects observed using all-dielectric metamaterials: high-refractive-index nanoresonators, metasurfaces, zero-index metamaterials and anisotropic metamaterials. Finally, we discuss current challenges and future goals for the field at the intersection with quantum, thermal and silicon photonics, as well as biomimetic metasurfaces.
1,634 citations
TL;DR: A composite lithium metal anode is reported that exhibits low dimension variation (∼20%) during cycling and good mechanical flexibility and a full-cell battery with a LiCoO2 cathode shows good rate capability and flat voltage profiles.
Abstract: Metallic lithium is a promising anode candidate for future high-energy-density lithium batteries. It is a light-weight material, and has the highest theoretical capacity (3,860 mAh g–1) and the lowest electrochemical potential of all candidates. There are, however, at least three major hurdles before lithium metal anodes can become a viable technology: uneven and dendritic lithium deposition, unstable solid electrolyte interphase and almost infinite relative dimension change during cycling. Previous research has tackled the first two issues, but the last is still mostly unsolved. Here we report a composite lithium metal anode that exhibits low dimension variation (∼20%) during cycling and good mechanical flexibility. The anode is composed of 7 wt% ‘lithiophilic’ layered reduced graphene oxide with nanoscale gaps that can host metallic lithium. The anode retains up to ∼3,390 mAh g–1 of capacity, exhibits low overpotential (∼80 mV at 3 mA cm–2) and a flat voltage profile in a carbonate electrolyte. A full-cell battery with a LiCoO2 cathode shows good rate capability and flat voltage profiles. Volumetric changes during cycling in lithium metal anodes can be largely suppressed by using a lithophilic carbonaceous host.
1,459 citations
TL;DR: G graphene doped with gold and combined with a gold mesh has improved electrochemical activity over bare graphene, sufficient to form a wearable patch for sweat-based diabetes monitoring and feedback therapy and can be thermally actuated to deliver Metformin and reduce blood glucose levels in diabetic mice.
Abstract: Owing to its high carrier mobility, conductivity, flexibility and optical transparency, graphene is a versatile material in micro- and macroelectronics. However, the low density of electrochemically active defects in graphene synthesized by chemical vapour deposition limits its application in biosensing. Here, we show that graphene doped with gold and combined with a gold mesh has improved electrochemical activity over bare graphene, sufficient to form a wearable patch for sweat-based diabetes monitoring and feedback therapy. The stretchable device features a serpentine bilayer of gold mesh and gold-doped graphene that forms an efficient electrochemical interface for the stable transfer of electrical signals. The patch consists of a heater, temperature, humidity, glucose and pH sensors and polymeric microneedles that can be thermally activated to deliver drugs transcutaneously. We show that the patch can be thermally actuated to deliver Metformin and reduce blood glucose levels in diabetic mice.
1,301 citations
TL;DR: The results suggest that ferumoxytol could be applied 'off label' to protect the liver from metastatic seeds and potentiate macrophage-modulating cancer immunotherapies.
Abstract: Until now, the Food and Drug Administration (FDA)-approved iron supplement ferumoxytol and other iron oxide nanoparticles have been used for treating iron deficiency, as contrast agents for magnetic resonance imaging and as drug carriers. Here, we show an intrinsic therapeutic effect of ferumoxytol on the growth of early mammary cancers, and lung cancer metastases in liver and lungs. In vitro, adenocarcinoma cells co-incubated with ferumoxytol and macrophages showed increased caspase-3 activity. Macrophages exposed to ferumoxytol displayed increased mRNA associated with pro-inflammatory Th1-type responses. In vivo, ferumoxytol significantly inhibited growth of subcutaneous adenocarcinomas in mice. In addition, intravenous ferumoxytol treatment before intravenous tumour cell challenge prevented development of liver metastasis. Fluorescence-activated cell sorting (FACS) and histopathology studies showed that the observed tumour growth inhibition was accompanied by increased presence of pro-inflammatory M1 macrophages in the tumour tissues. Our results suggest that ferumoxytol could be applied 'off label' to protect the liver from metastatic seeds and potentiate macrophage-modulating cancer immunotherapies.
1,089 citations
TL;DR: This work designed cobalt-based multilayered thin thin metals in which the cobalt layer is sandwiched between two heavy metals and so provides additive interfacial Dzyaloshinskii-Moriya interactions (DMIs), which reach a value close to 2 mJ m(-2) in the case of the Ir|Co|Pt asymmetric multilayers.
Abstract: Facing the ever-growing demand for data storage will most probably require a new paradigm. Nanoscale magnetic skyrmions are anticipated to solve this issue as they are arguably the smallest spin textures in magnetic thin films in nature. We designed cobalt-based multilayered thin films in which the cobalt layer is sandwiched between two heavy metals and so provides additive interfacial Dzyaloshinskii-Moriya interactions (DMIs), which reach a value close to 2 mJ m(-2) in the case of the Ir|Co|Pt asymmetric multilayers. Using a magnetization-sensitive scanning X-ray transmission microscopy technique, we imaged small magnetic domains at very low fields in these multilayers. The study of their behaviour in a perpendicular magnetic field allows us to conclude that they are actually magnetic skyrmions stabilized by the large DMI. This discovery of stable sub-100 nm individual skyrmions at room temperature in a technologically relevant material opens the way for device applications in the near future.
1,023 citations
TL;DR: The results show that in addition to reducing protein adsorption, PEG, and now PEEPs, can affect the composition of the protein corona that forms around nanocarriers, and the presence of distinct proteins is necessary to prevent non-specific cellular uptake.
Abstract: The current gold standard to reduce non-specific cellular uptake of drug delivery vehicles is by covalent attachment of poly(ethylene glycol) (PEG). It is thought that PEG can reduce protein adsorption and thereby confer a stealth effect. Here, we show that polystyrene nanocarriers that have been modified with PEG or poly(ethyl ethylene phosphate) (PEEP) and exposed to plasma proteins exhibit a low cellular uptake, whereas those not exposed to plasma proteins show high non-specific uptake. Mass spectrometric analysis revealed that exposed nanocarriers formed a protein corona that contains an abundance of clusterin proteins (also known as apolipoprotein J). When the polymer-modified nanocarriers were incubated with clusterin, non-specific cellular uptake could be reduced. Our results show that in addition to reducing protein adsorption, PEG, and now PEEPs, can affect the composition of the protein corona that forms around nanocarriers, and the presence of distinct proteins is necessary to prevent non-specific cellular uptake.
901 citations
TL;DR: This work reports on the observation of stable skyrmions in sputtered ultrathin Pt/Co/MgO nanostructures at room temperature and zero external magnetic field, substantiated by micromagnetic simulations and numerical models.
Abstract: Magnetic skyrmions are chiral spin structures with a whirling configuration. Their topological properties, nanometre size and the fact that they can be moved by small current densities have opened a new paradigm for the manipulation of magnetization at the nanoscale. Chiral skyrmion structures have so far been experimentally demonstrated only in bulk materials and in epitaxial ultrathin films, and under an external magnetic field or at low temperature. Here, we report on the observation of stable skyrmions in sputtered ultrathin Pt/Co/MgO nanostructures at room temperature and zero external magnetic field. We use high lateral resolution X-ray magnetic circular dichroism microscopy to image their chiral Neel internal structure, which we explain as due to the large strength of the Dzyaloshinskii–Moriya interaction as revealed by spin wave spectroscopy measurements. Our results are substantiated by micromagnetic simulations and numerical models, which allow the identification of the physical mechanisms governing the size and stability of the skyrmions.
TL;DR: This work shows that chalcogenide-based phase-change materials can be used to create an artificial neuron in which the membrane potential is represented by the phase configuration of the nanoscale phase- change device and shows that the temporal integration of postsynaptic potentials can be achieved on a nanosecond timescale.
Abstract: A nanoscale phase-change device can be used to create an artificial neuron that exhibits integrate-and-fire functionality with stochastic dynamics.
TL;DR: In this paper, the authors demonstrate room-temperature, polarized and ultrabright single-photon emission from a color center in two-dimensional hexagonal boron nitride.
Abstract: Artificial atomic systems in solids are widely considered the leading physical system for a variety of quantum technologies, including quantum communications, computing and metrology. To date, however, room-temperature quantum emitters have only been observed in wide-bandgap semiconductors such as diamond and silicon carbide, nanocrystal quantum dots, and most recently in carbon nanotubes. Single-photon emission from two-dimensional materials has been reported, but only at cryogenic temperatures. Here, we demonstrate room-temperature, polarized and ultrabright single-photon emission from a colour centre in two-dimensional hexagonal boron nitride. Density functional theory calculations indicate that vacancy-related defects are a probable source of the emission. Our results demonstrate the unprecedented potential of van der Waals crystals for large-scale nanophotonics and quantum information processing.
TL;DR: The results suggest that harnessing swarms of microorganisms exhibiting magneto-aerotactic behaviour can significantly improve the therapeutic index of various nanocarriers in tumour hypoxic regions.
Abstract: Magnetotactic bacteria that respond to oxygen gradients can be used to carry drug payloads deep into the hypoxic regions of tumours, offering a way to improve the therapeutic index of various nanocarriers.
TL;DR: This work shows real-time (response time of ∼20 ms), large-area, normal pressure monitoring under different, complex bending conditions, and test the suitability of the sensor for soft robotics and medical applications.
Abstract: Measuring small normal pressures is essential to accurately evaluate external stimuli in curvilinear and dynamic surfaces such as natural tissues. Usually, sensitive and spatially accurate pressure sensors are achieved through conformal contact with the surface; however, this also makes them sensitive to mechanical deformation (bending). Indeed, when a soft object is pressed by another soft object, the normal pressure cannot be measured independently from the mechanical stress. Here, we show a pressure sensor that measures only the normal pressure, even under extreme bending conditions. To reduce the bending sensitivity, we use composite nanofibres of carbon nanotubes and graphene. Our simulations show that these fibres change their relative alignment to accommodate bending deformation, thus reducing the strain in individual fibres. Pressure sensitivity is maintained down to a bending radius of 80 μm. To test the suitability of our sensor for soft robotics and medical applications, we fabricated an integrated sensor matrix that is only 2 μm thick. We show real-time (response time of ∼20 ms), large-area, normal pressure monitoring under different, complex bending conditions. A composite fibrous material made of carbon nanotubes and graphene responds to small pressure but not to bending deformation.
TL;DR: It is shown that few-layered vertically aligned MoS2 (FLV-MoS2) films can be used to harvest the whole spectrum of visible light (∼50% of solar energy) and achieve highly efficient water disinfection.
Abstract: Few-layered, vertically aligned MoS2 films can efficiently harvest visible light for photocatalytic water disinfection, allowing >99.999% bacteria to be rapidly inactivated.
TL;DR: Different approaches to using graphene nanodevices for DNA sequencing, which involve DNA passing through graphene nanopores, nanogaps, and nanoribbons, and the physisorption of DNA on graphene nanostructures are reviewed.
Abstract: Fast, cheap, and reliable DNA sequencing could be one of the most disruptive innovations of this decade, as it will pave the way for personalized medicine. In pursuit of such technology, a variety of nanotechnology-based approaches have been explored and established, including sequencing with nanopores. Owing to its unique structure and properties, graphene provides interesting opportunities for the development of a new sequencing technology. In recent years, a wide range of creative ideas for graphene sequencers have been theoretically proposed and the first experimental demonstrations have begun to appear. Here, we review the different approaches to using graphene nanodevices for DNA sequencing, which involve DNA passing through graphene nanopores, nanogaps, and nanoribbons, and the physisorption of DNA on graphene nanostructures. We discuss the advantages and problems of each of these key techniques, and provide a perspective on the use of graphene in future DNA sequencing technology.
TL;DR: An overview of nanostructured materials that are either already commercialized or close to commercialization for hybrid electric vehicle applications, as well as those under development with the potential to meet the requirements for long-range electric vehicles are offered.
Abstract: This Review discusses how nanostructured materials are used to enhance the performances and safety requirements of Li batteries for hybrid and long-range electric vehicles. A significant amount of battery research and development is underway, both in academia and industry, to meet the demand for electric vehicle applications. When it comes to designing and fabricating electrode materials, nanotechnology-based approaches have demonstrated numerous benefits for improved energy and power density, cyclability and safety. In this Review, we offer an overview of nanostructured materials that are either already commercialized or close to commercialization for hybrid electric vehicle applications, as well as those under development with the potential to meet the requirements for long-range electric vehicles.
TL;DR: Some of the general principles of enzymatic reactions confined on surfaces, at interfaces, and inside small volumes are discussed and some of the necessary future steps to improve fundamental understanding of these systems are critically evaluated.
Abstract: Within each biological cell, surface- and volume-confined enzymes control a highly complex network of chemical reactions. These reactions are efficient, timely, and spatially defined. Efforts to transfer such appealing features to in vitro systems have led to several successful examples of chemical reactions catalysed by isolated and immobilized enzymes. In most cases, these enzymes are either bound or adsorbed to an insoluble support, physically trapped in a macromolecular network, or encapsulated within compartments. Advanced applications of enzymatic cascade reactions with immobilized enzymes include enzymatic fuel cells and enzymatic nanoreactors, both for in vitro and possible in vivo applications. In this Review, we discuss some of the general principles of enzymatic reactions confined on surfaces, at interfaces, and inside small volumes. We also highlight the similarities and differences between the in vivo and in vitro cases and attempt to critically evaluate some of the necessary future steps to improve our fundamental understanding of these systems.
TL;DR: This study demonstrates that graphene/WSe2/graphene heterostructures ally the high photodetection efficiency of transition-metal dichalcogenides with a picosecond photoresponse comparable to that of graphene, thereby optimizing both speed and efficiency in a singlePhotodetector.
Abstract: Photodetectors based on graphene/WSe2/graphene heterostructures combine an ultrafast photoresponse with high quantum efficiency. Two-dimensional crystals such as graphene and transition-metal dichalcogenides1 demonstrate a range of unique and complementary optoelectronic properties2,3. Assembling different two-dimensional materials in vertical heterostructures4 enables the combination of these properties in one device, thus creating multifunctional optoelectronic systems with superior performance. Here, we demonstrate that graphene/WSe2/graphene heterostructures ally the high photodetection efficiency of transition-metal dichalcogenides5,6 with a picosecond photoresponse comparable to that of graphene7,8,9, thereby optimizing both speed and efficiency in a single photodetector. We follow the extraction of photoexcited carriers in these devices using time-resolved photocurrent measurements and demonstrate a photoresponse time as short as 5.5 ps, which we tune by applying a bias and by varying the transition-metal dichalcogenide layer thickness. Our study provides direct insight into the physical processes governing the detection speed and quantum efficiency of these van der Waals heterostuctures, such as out-of-plane carrier drift and recombination. The observation and understanding of ultrafast and efficient photodetection demonstrate the potential of hybrid transition-metal dichalcogenide-based heterostructures as a platform for future optoelectronic devices.
TL;DR: A new structure with the third geometry, that is, with the easy axis collinear with the current (along the x axis), is presented and the switching operation driven by the spin-orbit torque due to Ta with a negative spin Hall angle is demonstrated.
Abstract: Spin-orbit torque, a torque brought about by in-plane current via the spin-orbit interactions in heavy-metal/ferromagnet nanostructures, provides a new pathway to switch the magnetization direction. Although there are many recent studies, they all build on one of two structures that have the easy axis of a nanomagnet lying orthogonal to the current, that is, along the z or y axes. Here, we present a new structure with the third geometry, that is, with the easy axis collinear with the current (along the x axis). We fabricate a three-terminal device with a Ta/CoFeB/MgO-based stack and demonstrate the switching operation driven by the spin-orbit torque due to Ta with a negative spin Hall angle. Comparisons with different geometries highlight the previously unknown mechanisms of spin-orbit torque switching. Our work offers a new avenue for exploring the physics of spin-orbit torque switching and its application to spintronics devices.
TL;DR: For the Ta/Ta2O5 system, a rutile-type TaO2 film is believed to mediate switching, and it is shown that devices can be switched from a valence change mode to an electrochemical metallization mode by introducing an intermediate layer of amorphous carbon.
Abstract: A detailed understanding of the resistive switching mechanisms that operate in redox-based resistive random-access memories (ReRAM) is key to controlling these memristive devices and formulating appropriate design rules. Based on distinct fundamental switching mechanisms, two types of ReRAM have emerged: electrochemical metallization memories, in which the mobile species is thought to be metal cations, and valence change memories, in which the mobile species is thought to be oxygen anions (or positively charged oxygen vacancies). Here we show, using scanning tunnelling microscopy and supported by potentiodynamic current-voltage measurements, that in three typical valence change memory materials (TaO(x), HfO(x) and TiO(x)) the host metal cations are mobile in films of 2 nm thickness. The cations can form metallic filaments and participate in the resistive switching process, illustrating that there is a bridge between the electrochemical metallization mechanism and the valence change mechanism. Reset/Set operations are, we suggest, driven by oxidation (passivation) and reduction reactions. For the Ta/Ta2O5 system, a rutile-type TaO2 film is believed to mediate switching, and we show that devices can be switched from a valence change mode to an electrochemical metallization mode by introducing an intermediate layer of amorphous carbon.
TL;DR: In this article, a hybrid membrane made from protein amyloid fibrils and activated porous carbon is used to remove heavy metal ions and radioactive waste from water, and the performance of the membrane is enabled by the ability of the amyloids to selectively absorb heavy metal pollutants from solutions.
Abstract: Industrial development, energy production and mining have led to dramatically increased levels of environmental pollutants such as heavy metal ions, metal cyanides and nuclear waste. Current technologies for purifying contaminated waters are typically expensive and ion specific, and there is therefore a significant need for new approaches. Here, we report inexpensive hybrid membranes made from protein amyloid fibrils and activated porous carbon that can be used to remove heavy metal ions and radioactive waste from water. During filtration, the concentration of heavy metal ions drops by three to five orders of magnitude per passage and the process can be repeated numerous times. Notably, their efficiency remains unaltered when filtering several ions simultaneously. The performance of the membrane is enabled by the ability of the amyloids to selectively absorb heavy metal pollutants from solutions. We also show that our membranes can be used to recycle valuable heavy metal contaminants by thermally reducing ions trapped in saturated membranes, leading to the creation of elemental metal nanoparticles and films.
TL;DR: The antiferromagnetic IrMn layer supplies an in-plane exchange bias field, which enables all-electrical deterministic switching of perpendicular magnetization without any assistance from an external magnetic field, and together with sizeable spin-orbit torques, these features make antiferromeagnets a promising candidate for future spintronic devices.
Abstract: Spin-orbit torques arising from the spin-orbit coupling of non-magnetic heavy metals allow electrical switching of perpendicular magnetization. However, the switching is not purely electrical in laterally homogeneous structures. An extra in-plane magnetic field is indeed required to achieve deterministic switching, and this is detrimental for device applications. On the other hand, if antiferromagnets can generate spin-orbit torques, they may enable all-electrical deterministic switching because the desired magnetic field may be replaced by their exchange bias. Here we report sizeable spin-orbit torques in IrMn/CoFeB/MgO structures. The antiferromagnetic IrMn layer also supplies an in-plane exchange bias field, which enables all-electrical deterministic switching of perpendicular magnetization without any assistance from an external magnetic field. Together with sizeable spin-orbit torques, these features make antiferromagnets a promising candidate for future spintronic devices. We also show that the signs of the spin-orbit torques in various IrMn-based structures cannot be explained by existing theories and thus significant theoretical progress is required.
TL;DR: It is shown that ultrasmall (< 10 nm in diameter) poly(ethylene glycol) (PEG)-coated silica nanoparticles, functionalized with melanoma-targeting peptides, can induce a form of programmed cell death known as ferroptosis in starved cancer cells and cancer-bearing mice.
Abstract: The design of cancer-targeting particles with precisely tuned physicochemical properties may enhance the delivery of therapeutics and access to pharmacological targets. However, a molecular-level understanding of the interactions driving the fate of nanomedicine in biological systems remains elusive. Here, we show that ultrasmall (<10 nm in diameter) poly(ethylene glycol)-coated silica nanoparticles, functionalized with melanoma-targeting peptides, can induce a form of programmed cell death known as ferroptosis in starved cancer cells and cancer-bearing mice. Tumour xenografts in mice intravenously injected with nanoparticles using a high-dose multiple injection scheme exhibit reduced growth or regression, in a manner that is reversed by the pharmacological inhibitor of ferroptosis, liproxstatin-1. These data demonstrate that ferroptosis can be targeted by ultrasmall silica nanoparticles and may have therapeutic potential. Starved cancer cells and xenograft tumours in mice treated with ultrasmall silica nanoparticles undergo ferroptosis — a form of programmed cell death.
TL;DR: This work demonstrates robust zero-field SOT switching of a perpendicular CoFe free layer where the symmetry is broken by magnetic coupling to a second in-plane exchange-biased CoFe layer via a nonmagnetic Ru or Pt spacer.
Abstract: A new approach to magnetic switching by spin–orbit torque uses interlayer exchange coupling to overcome the need for an external magnetic field. Manipulation of the magnetization of a perpendicular ferromagnetic free layer by spin–orbit torque (SOT)1,2,3,4 is an attractive alternative to spin-transfer torque (STT) in oscillators and switches such as magnetic random-access memory (MRAM) where a high current is passed across an ultrathin tunnel barrier5. A small symmetry-breaking bias field is usually needed for deterministic SOT switching but it is impractical to generate the field externally for spintronic applications. Here, we demonstrate robust zero-field SOT switching of a perpendicular CoFe free layer where the symmetry is broken by magnetic coupling to a second in-plane exchange-biased CoFe layer via a nonmagnetic Ru or Pt spacer6. The preferred magnetic state of the free layer is determined by the current polarity and the sign of the interlayer exchange coupling (IEC). Our strategy offers a potentially scalable solution to realize bias-field-free switching that can lead to a generation of SOT devices, combining a high storage density and endurance with a low power consumption.
TL;DR: It is shown that at low Péclet (Pe) numbers, at which diffusion and deterministic displacement compete, nano-DLD arrays separate particles between 20 to 110 nm based on size with sharp resolution, which opens up the potential for on-chip sorting and quantification of these important biocolloids.
Abstract: Lateral displacement pillar arrays can now be used to separate nanoscale colloids including exosomes, offering new opportunities for on-chip sorting and quantification of biocolloids by size. Deterministic lateral displacement (DLD) pillar arrays are an efficient technology to sort, separate and enrich micrometre-scale particles, which include parasites1, bacteria2, blood cells3 and circulating tumour cells in blood4. However, this technology has not been translated to the true nanoscale, where it could function on biocolloids, such as exosomes. Exosomes, a key target of ‘liquid biopsies’, are secreted by cells and contain nucleic acid and protein information about their originating tissue5. One challenge in the study of exosome biology is to sort exosomes by size and surface markers6,7. We use manufacturable silicon processes to produce nanoscale DLD (nano-DLD) arrays of uniform gap sizes ranging from 25 to 235 nm. We show that at low Peclet (Pe) numbers, at which diffusion and deterministic displacement compete, nano-DLD arrays separate particles between 20 to 110 nm based on size with sharp resolution. Further, we demonstrate the size-based displacement of exosomes, and so open up the potential for on-chip sorting and quantification of these important biocolloids.
TL;DR: The observation of the integer quantum Hall effect in a high-quality black phosphorus 2DES is reported, and important information on the energetics of the spin-split Landau levels in black phosphorus is gained.
Abstract: The development of new, high-quality functional materials has been at the forefront of condensed-matter research. The recent advent of two-dimensional black phosphorus has greatly enriched the materials base of two-dimensional electron systems (2DESs). Here, we report the observation of the integer quantum Hall effect in a high-quality black phosphorus 2DES. The high quality is achieved by embedding the black phosphorus 2DES in a van der Waals heterostructure close to a graphite back gate; the graphite gate screens the impurity potential in the 2DES and brings the carrier Hall mobility up to 6,000 cm(2) V(-1) s(-1). The exceptional mobility enabled us to observe the quantum Hall effect and to gain important information on the energetics of the spin-split Landau levels in black phosphorus. Our results set the stage for further study on quantum transport and device application in the ultrahigh mobility regime.
TL;DR: An artificial microswimmer that can sense and orient to the illumination direction of an external light source and a school of microswimmers that mimics the collective phototactic behaviour of green algae in solution is shown.
Abstract: Phototaxis is commonly observed in motile photosynthetic microorganisms. For example, green algae are capable of swimming towards a light source (positive phototaxis) to receive more energy for photosynthesis, or away from a light source (negative phototaxis) to avoid radiation damage or to hide from predators. Recently, with the aim of applying nanoscale machinery to biomedical applications, various inorganic nanomotors based on different propulsion mechanisms have been demonstrated. The only method to control the direction of motion of these self-propelled micro/nanomotors is to incorporate a ferromagnetic material into their structure and use an external magnetic field for steering. Here, we show an artificial microswimmer that can sense and orient to the illumination direction of an external light source. Our microswimmer is a Janus nanotree containing a nanostructured photocathode and photoanode at opposite ends that release cations and anions, respectively, propelling the microswimmer by self-electrophoresis. Using chemical modifications, we can control the zeta potential of the photoanode and program the microswimmer to exhibit either positive or negative phototaxis. Finally, we show that a school of microswimmers mimics the collective phototactic behaviour of green algae in solution.
TL;DR: 'softening' of the core-shell confinement potential strongly suppresses non-radiative Auger processes in charged nanocrystals, with successful non-blinking implementations demonstrated in CdSe-CdS core-thick-shell nanocry crystals and their modifications.
Abstract: Semiconductor nanocrystals offer an enormous diversity of potential device applications, based on their size-tunable photoluminescence, high optical stability and 'bottom-up' chemical approaches to self-assembly. However, the promise of such applications can be seriously limited by photoluminescence intermittency in nanocrystal emission, that is, 'blinking', arising from the escape of either one or both of the photoexcited carriers to the nanocrystal surface. In the first scenario, the remaining nanocrystal charge quenches photoluminescence via non-radiative Auger recombination, whereas for the other, the exciton is thought to be intercepted before thermalization and does not contribute to the photoluminescence. This Review summarizes the current understanding of the mechanisms responsible for nanocrystal blinking kinetics as well as core-shell engineering efforts to control such phenomena. In particular, 'softening' of the core-shell confinement potential strongly suppresses non-radiative Auger processes in charged nanocrystals, with successful non-blinking implementations demonstrated in CdSe-CdS core-thick-shell nanocrystals and their modifications.