Showing papers by "Kostya S. Novoselov published in 2017"
TL;DR: This study demonstrates the validity of multiscale control in molybdenum disulfide via overall consideration of the mass transport, and the accessibility, quantity and capability of active sites towards electrocatalytic hydrogen evolution, which may also be extended to other energy-related processes.
Abstract: Hydrogen production through water splitting has been considered as a green, pure and high-efficient technique. As an important half-reaction involved, hydrogen evolution reaction is a complex electrochemical process involving liquid-solid-gas three-phase interface behaviour. Therefore, new concepts and strategies of material design are needed to smooth each pivotal step. Here we report a multiscale structural and electronic control of molybdenum disulfide foam to synergistically promote the hydrogen evolution process. The optimized three-dimensional molybdenum disulfide foam with uniform mesopores, vertically aligned two-dimensional layers and cobalt atoms doping demonstrated a high hydrogen evolution activity and stability. In addition, density functional theory calculations indicate that molybdenum disulfide with moderate cobalt doping content possesses the optimal activity. This study demonstrates the validity of multiscale control in molybdenum disulfide via overall consideration of the mass transport, and the accessibility, quantity and capability of active sites towards electrocatalytic hydrogen evolution, which may also be extended to other energy-related processes. The hydrogen evolution reaction is a complicated process involving liquid-solid-gas three-phase interface behaviour. Here, the authors report the multiscale structural and electronic control of molybdenum disulfide foam and demonstrate its high activity and stability for hydrogen evolution.
456 citations
TL;DR: In this paper, an organic nanoparticle-based surface pre-treatment was applied to textiles to enable all inkjet-printed graphene e-textiles for the first time.
Abstract: Inkjet printing of graphene inks is considered to be very promising for wearable e-textile applications as benefits of both inkjet printing and extra-ordinary electronic, optical and mechanical properties of graphene can be exploited. However, the common problem associated with inkjet printing of conductive inks on textiles is the difficulty to print a continuous conductive path on a rough and porous textile surface. Here we report inkjet printing of an organic nanoparticle based surface pre-treatment onto textiles to enable all inkjet-printed graphene e-textiles for the first time. The functionalized organic nanoparticles present a hydrophobic breathable coating on textiles. Subsequent inkjet printing of a continuous conductive electrical path onto the pre-treated coating reduced the sheet resistance of graphene-based printed e-textiles by three orders of magnitude from 1.09 × 106 Ω sq−1 to 2.14 × 103 Ω sq−1 compared with untreated textiles. We present several examples of how this finding opens up opportunities for real world applications of printed, low cost and environmentally friendly graphene wearable e-textiles.
190 citations
24 Jul 2017
TL;DR: In this article, a solid-state flexible supercapacitor device printed on textiles using graphene oxide ink and a screen-printing technique was reported. But the performance of the printed electrodes exhibited excellent mechanical stability due to the strong interaction between the ink and textile substrate.
Abstract: © 2017 IOP Publishing Ltd Printed graphene supercapacitors have the potential to empower tomorrow’s wearable electronics. We report a solid-state flexible supercapacitor device printed on textiles using graphene oxide ink and a screen-printing technique. After printing, graphene oxide was reduced in situ via a rapid electrochemical method avoiding the use of any reducing reagents that may damage the textile substrates. The printed electrodes exhibited excellent mechanical stability due to the strong interaction between the ink and textile substrate. The unique hierarchical porous structure of the electrodes facilitated ionic diffusion and maximised the surface area available for the electrolyte/ active material interface. The obtained device showed outstanding cyclic stability over 10 000 cycles and maintained excellent mechanical flexibility, which is necessary for wearable applications. The simple printing technique is readily scalable and avoids the problems associated with fabricating supercapacitor devices made of conductive yarn, as previously reported in the literature.
135 citations
TL;DR: It is shown that a signature of the pseudomagnetic field is a local sublattice symmetry breaking observable as a redistribution of the local density of states in graphene, which can be interpreted as a polarization of graphene's pseudospin due to a strain induced pseudom magnetic field.
Abstract: One of the intriguing characteristics of honeycomb lattices is the appearance of a pseudomagnetic field as a result of mechanical deformation. In the case of graphene, the Landau quantization resulting from this pseudomagnetic field has been measured using scanning tunneling microscopy. Here we show that a signature of the pseudomagnetic field is a local sublattice symmetry breaking observable as a redistribution of the local density of states. This can be interpreted as a polarization of graphene’s pseudospin due to a strain induced pseudomagnetic field, in analogy to the alignment of a real spin in a magnetic field. We reveal this sublattice symmetry breaking by tunably straining graphene using the tip of a scanning tunneling microscope. The tip locally lifts the graphene membrane from a SiO2 support, as visible by an increased slope of the I(z) curves. The amount of lifting is consistent with molecular dynamics calculations, which reveal a deformed graphene area under the tip in the shape of a Gaussian...
121 citations
TL;DR: It is shown that graphene superlattices support a different type of quantum oscillation that does not rely on Landau quantization, and this work hints at unexplored physics in Hofstadter butterfly systems at high temperatures.
Abstract: Cyclotron motion of charge carriers in metals and semiconductors leads to Landau quantization and magneto-oscillatory behavior in their properties. Cryogenic temperatures are usually required to observe these oscillations. We show that graphene superlattices support a different type of quantum oscillation that does not rely on Landau quantization. The oscillations are extremely robust and persist well above room temperature in magnetic fields of only a few tesla. We attribute this phenomenon to repetitive changes in the electronic structure of superlattices such that charge carriers experience effectively no magnetic field at simple fractions of the flux quantum per superlattice unit cell. Our work hints at unexplored physics in Hofstadter butterfly systems at high temperatures.
121 citations
TL;DR: Mechanical exfoliation is utilized to produce a two-dimensional form of a mineral franckeite and it is shown that the phase segregation of chemical species into discrete layers at the sub-nanometre scale facilitates franckeites' layered structure and basal cleavage down to a single unit cell thickness.
Abstract: Weak interlayer interactions in van der Waals crystals facilitate their mechanical exfoliation to monolayer and few-layer two-dimensional materials, which often exhibit striking physical phenomena absent in their bulk form. Here we utilize mechanical exfoliation to produce a two-dimensional form of a mineral franckeite and show that the phase segregation of chemical species into discrete layers at the sub-nanometre scale facilitates franckeite's layered structure and basal cleavage down to a single unit cell thickness. This behaviour is likely to be common in a wider family of complex minerals and could be exploited for a single-step synthesis of van der Waals heterostructures, as an alternative to artificial stacking of individual two-dimensional crystals. We demonstrate p-type electrical conductivity and remarkable electrochemical properties of the exfoliated crystals, showing promise for a range of applications, and use the density functional theory calculations of franckeite's electronic band structure to rationalize the experimental results.
92 citations
TL;DR: Material and crystal thickness sensitivity of the presented imaging technique makes it a powerful tool for characterization of van der Waals heterostructures assembled by a wide variety of methods, using combinations of materials obtained through mechanical or chemical exfoliation and crystal growth.
Abstract: Vertically stacked atomic layers from different layered crystals can be held together by van der Waals forces, which can be used for building novel heterostructures, offering a platform for developing a new generation of atomically thin, transparent, and flexible devices. The performance of these devices is critically dependent on the layer thickness and the interlayer electronic coupling, influencing the hybridization of the electronic states as well as charge and energy transfer between the layers. The electronic coupling is affected by the relative orientation of the layers as well as by the cleanliness of their interfaces. Here, we demonstrate an efficient method for monitoring interlayer coupling in heterostructures made from transition metal dichalcogenides using photoluminescence imaging in a bright-field optical microscope. The color and brightness in such images are used here to identify mono- and few-layer crystals and to track changes in the interlayer coupling and the emergence of interlayer e...
82 citations
TL;DR: The measurement of interlayer separations provide the first evidence for impurity species being trapped at buried interfaces with hBN interfaces that are flat at the nanometer length scale and adopting glovebox transfer significantly improves the quality of interfaces for WSe2 compared to processing in air.
Abstract: Vertically stacked van der Waals heterostructures are a lucrative platform for exploring the rich electronic and optoelectronic phenomena in two-dimensional materials. Their performance will be strongly affected by impurities and defects at the interfaces. Here we present the first systematic study of interfaces in van der Waals heterostructure using cross-sectional scanning transmission electron microscope (STEM) imaging. By measuring interlayer separations and comparing these to density functional theory (DFT) calculations we find that pristine interfaces exist between hBN and MoS2 or WS2 for stacks prepared by mechanical exfoliation in air. However, for two technologically important transition metal dichalcogenide (TMDC) systems, MoSe2 and WSe2, our measurement of interlayer separations provide the first evidence for impurity species being trapped at buried interfaces with hBN interfaces that are flat at the nanometer length scale. While decreasing the thickness of encapsulated WSe2 from bulk to monola...
71 citations
TL;DR: A threshold voltage for electroluminescence significantly lower than the corresponding single particle band gap of monolayer WSe2 is observed, interpreted by considering the Coulomb interaction and a tunneling process involving excitons, well beyond the picture of independent charge carriers.
Abstract: We report on experimental investigations of an electrically driven WSe2 based light-emitting van der Waals heterostructure. We observe a threshold voltage for electroluminescence significantly lower than the corresponding single particle band gap of monolayer WSe2. This observation can be interpreted by considering the Coulomb interaction and a tunneling process involving excitons, well beyond the picture of independent charge carriers. An applied magnetic field reveals pronounced magneto-oscillations in the electroluminescence of the free exciton emission intensity with a 1/B periodicity. This effect is ascribed to a modulation of the tunneling probability resulting from the Landau quantization in the graphene electrodes. A sharp feature in the differential conductance indicates that the Fermi level is pinned and allows for an estimation of the acceptor binding energy.
47 citations
TL;DR: In this paper, hexagonal boron nitride (hBN) is used to protect hot graphene filaments even at temperatures well above 2000 K. The results demonstrate that hBN/graphene heterostructures can be used to conveniently explore the technologically important high-temperature regime and to pave the way for future optoelectronic applications of graphene-based systems.
Abstract: The excellent electronic and mechanical properties of graphene allow it to sustain very large currents, enabling its incandescence through Joule heating in suspended devices. Although interesting scientifically and promising technologically, this process is unattainable in ambient environment, because graphene quickly oxidises at high temperatures. Here, we take the performance of graphene-based incandescent devices to the next level by encapsulating graphene with hexagonal boron nitride (hBN). Remarkably, we found that the hBN encapsulation provides an excellent protection for hot graphene filaments even at temperatures well above 2000 K. Unrivalled oxidation resistance of hBN combined with atomically clean graphene/hBN interface allows for a stable light emission from our devices in atmosphere for many hours of continuous operation. Furthermore, when confined in a simple photonic cavity, the thermal emission spectrum is modified by a cavity mode, shifting the emission to the visible range spectrum. We believe our results demonstrate that hBN/graphene heterostructures can be used to conveniently explore the technologically important high-temperature regime and to pave the way for future optoelectronic applications of graphene-based systems.
41 citations
08 Nov 2017
TL;DR: In this article, hexagonal boron nitride (hBN) is used to protect hot graphene filaments even at temperatures well above 2000 K. The results demonstrate that hBN/graphene heterostructures can be used to conveniently explore the technologically important high-temperature regime and to pave the way for future optoelectronic applications of graphene-based systems.
Abstract: The excellent electronic and mechanical properties of graphene allow it to sustain very large currents, enabling its incandescence through Joule heating in suspended devices. Although interesting scientifically and promising technologically, this process is unattainable in ambient environment, because graphene quickly oxidises at high temperatures. Here, we take the performance of graphene-based incandescent devices to the next level by encapsulating graphene with hexagonal boron nitride (hBN). Remarkably, we found that the hBN encapsulation provides an excellent protection for hot graphene filaments even at temperatures well above 2000 K. Unrivalled oxidation resistance of hBN combined with atomically clean graphene/hBN interface allows for a stable light emission from our devices in atmosphere for many hours of continuous operation. Furthermore, when confined in a simple photonic cavity, the thermal emission spectrum is modified by a cavity mode, shifting the emission to the visible range spectrum. We believe our results demonstrate that hBN/graphene heterostructures can be used to conveniently explore the technologically important high-temperature regime and to pave the way for future optoelectronic applications of graphene-based systems.
01 Feb 2017
TL;DR: In this paper, annealing effects on the self rotation of a graphene flake on a graphene substrate were investigated using both ab initio calculations and molecular dynamics simulations, and it was found that small flakes (of about 4 nm) are more sensitive to temperature and initial misorientation angles than larger ones (beyond 10 nm).
Abstract: The self rotation of a graphene flake over graphite is controlled by the size, initial misalignment and temperature. Using both ab initio calculations and molecular dynamics simulations, we investigate annealing effects on the self rotation of a graphene flake on a graphene substrate. The energy barriers for rotation and drift of a graphene flake over graphene is found to be smaller than 25 meV/atom which is comparable to thermal energy. We found that small flakes (of about ~4 nm) are more sensitive to temperature and initial misorientation angles than larger one (beyond 10 nm). The initial stacking configuration of the flake is found to be important for its dynamics and time evolution of misalignment. Large flakes, which are initially in the AA- or AB-stacking state with small misorientation angle, rotate and end up in the AB-stacking configuration. However small flakes can they stay in an incommensurate state specially when the initial misorientation angle is larger than . Our results are in agreement with recent experiments.
06 Sep 2017
TL;DR: It is shown that van der Waals stacking of graphene onto hexagonal boron nitride offers a natural platform for valley control and the tunable inversion of spin and valley states should enable coherent superposition of these degrees of freedom as a first step towards graphene-based qubits.
Abstract: Coherent manipulation of binary degrees of freedom is at the heart of modern quantum technologies. Graphene offers two binary degrees: the electron spin and the valley. Efficient spin control has been demonstrated in many solid state systems, while exploitation of the valley has only recently been started, yet without control on the single electron level. Here, we show that van-der Waals stacking of graphene onto hexagonal boron nitride offers a natural platform for valley control. We use a graphene quantum dot induced by the tip of a scanning tunneling microscope and demonstrate valley splitting that is tunable from -5 to +10 meV (including valley inversion) by sub-10-nm displacements of the quantum dot position. This boosts the range of controlled valley splitting by about one order of magnitude. The tunable inversion of spin and valley states should enable coherent superposition of these degrees of freedom as a first step towards graphene-based qubits.
TL;DR: In this article, an atomically thick tunable quantum tunnelling device was used as a building block for quantum plasmonics, which consists of two layers of graphene separated by 1 nm (three monolayers) of h-BN, and a bias voltage between the layers generated an electron gas coupled to a hole gas.
Abstract: The ultimate limit of control of light at the nanoscale is the atomic scale. By stacking multiple layers of graphene on hexagonal boron nitride (h-BN), heterostructures with unique nanophotonic properties can be constructed, where the distance between plasmonic materials can be controlled with atom-scale precision. Here we show how an atomically thick tunable quantum tunnelling device can be used as a building block for quantum plasmonics. The device consists of two layers of graphene separated by 1 nm (three monolayers) of h-BN, and a bias voltage between the layers generates an electron gas coupled to a hole gas. We show that, even though its total charge is zero, this system is capable of supporting propagating graphene plasmons.
TL;DR: In this article, the authors demonstrate the possibility to couple the MoS2 mono-and bi-layers emission when integrated on top of a 1D photonic crystal to a BSW.
Abstract: Due to their extraordinary quality factor and extreme sensitivity to surface perturbations, Bloch surface waves (BSW) have been widely investigated for sensing applications so far. Over the last few years, on-chip control of optical signals through BSW has experienced a rapidly-expanding interest in the scientific community, attesting to BSW’s position at the forefront towards on-chip optical operations. The backbone of on-chip optical devices requires the choice of integrated optical sources with peculiar optic/optoelectronic properties, the efficient in-plane propagation of the optical signal and the possibility to dynamic manipulate the signal through optical or electrical driving. In this paper, we discuss our approach in addressing these requirements. Regarding the optical source integration, we demonstrate the possibility to couple the MoS2 mono- and bi-layers emission—when integrated on top of a 1D photonic crystal—to a BSW. Afterward, we review our results on BSW-based polariton systems (BSWP). We show that the BSWPs combine long-range propagation with energy tuning of their dispersion through polariton–polariton interactions, paving the way for logic operations.
16 Oct 2017
TL;DR: In this article, different two-dimensional (2D) atomic layers are stacked in order to create unique multilayered van der Waals heterostructures with desired properties.
Abstract: Stacking different two-dimensional (2D) atomic layers is a feasible approach to create unique multilayered van der Waals heterostructures with desired properties. 2D materials, graphene, hexagonal boron nitride (h-BN), molybdenum disulphate (MoS2) and graphene based van der Waals heterostructures, such as h-BN/graphene and MoS2/graphene have been investigated by means of Scanning Transmission Electron Microscopy (STEM).
TL;DR: In this paper, the authors predict superlubricity of the graphene flake for motion along and between particular defect lines, which can be used to control the thermally induced motion of the flake.
Abstract: The force between a sharp scanning probe tip and a surface can drive a graphene flake over crystalline substrates. The recent design of particular patterns of structural defects on a graphene surface allows us to propose an alternative approach for controlling the motion of a graphene flake over a graphene substrate. The thermally induced motion of a graphene flake is controlled by engineering topological defects in the substrate. Such defect regions lead to an inhomogeneous energy landscape and are energetically unfavorable for the motion of the flake, and will invert and scatter graphene flakes when they are moving toward the defect line. Engineering the distribution of these energy barriers results in a controllable trajectory for the thermal motion of the flake without using any external force. We predict superlubricity of the graphene flake for motion along and between particular defect lines. This Rapid Communication provides insights into the frictional forces of interfaces and opens a route to the engineering of the stochastic motion of a graphene flake over any crystalline substrate.
Patent•
19 Jun 2017
TL;DR: In this article, a textile-based sensor which incorporates graphene into the fibre is described. But this sensor is used for a variety of sensing applications such as wearable technology, such as sensing and sensing applications.
Abstract: The present invention relates to a textile-based sensor which incorporates graphene into the fibre The graphene is incorporated by a dyeing process in which a liquid composition containing the graphene is contacted with the fibre The present invention thus also relates to a process for the preparation of a graphene-based yarn and the use of the resulting yarn in a variety of sensing applications The graphene-based yarns of the invention may be derived from naturally occurring materials such as cotton or may be based on synthetic materials such as polyester, nylon, viscose, etc, or may be a blend of natural and synthetic materials The present invention also relates to a screen-printed textile or a porous material, such as paper, printed on its surface with a 2D material such as graphene This printed textile (fabric) has the 2D material incorporated by a screen-printing process in which a liquid or paste composition containing the 2D material is contacted with the textile or paper substrate The present invention thus also relates to a process for the preparation of a graphene-or other 2D material-printed substrate and the use of the resulting printed substrate in a variety of applications such as wearable technology The textiles of the invention may be derived from naturally occurring materials such as cotton or may be based on synthetic materials such as polyester, nylon, viscose, etc, or may be a blend of natural and synthetic materials
Posted Content•
30 Aug 2017
TL;DR: In this paper, van-der-Waals stacking of 2D materials offers a natural platform for valley control due to the relatively strong and spatially varying atomic interaction between adjacent layers.
Abstract: Coherent manipulation of binary degrees of freedom is at the heart of modern quantum technologies. Graphene, the first atomically thin 2D material, offers two binary degrees: the electron spin and the valley degree of freedom. Efficient spin control has been demonstrated in many solid state systems, while exploitation of the valley has only recently been started without control for single electrons. Here, we show that van-der Waals stacking of 2D materials offers a natural platform for valley control due to the relatively strong and spatially varying atomic interaction between adjacent layers. We use an edge-free quantum dot, induced by the tip of a scanning tunneling microscope into graphene on hBN. We demonstrate a valley splitting, which is tunable from -5 meV to +10 meV (including valley inversion) by sub-10-nm displacements of the quantum dot position. This boosts controlled valley splitting of single electrons by more than an order of magnitude, which will probably enable robust spin qubits and valley qubits in graphene.
TL;DR: In this article, cross sectional imaging using atomic resolution transmission electron microscopy (TEM) was used to characterize the nature of buried interfaces in these engineered van der Waals crystals and showed that the performance of such materials is strongly dependent on the quality of the crystals and the interfaces between different crystals.
Abstract: The emerging area of two dimensional (2D) materials has attracted a great deal of scientific attention in recent years. Like graphene, these materials can be exfoliated to single atom thickness and can then be mechanically layered together to create new van der Waals crystals with bespoke properties. However the performance of such materials is strongly dependent on the quality of the crystals and the interfaces between different crystals. Cross sectional imaging using atomic resolution transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) is the only technique able to characterize the nature of buried interfaces in these engineered van der Waals crystals [1].