Kostya S. Novoselov

Bio: Kostya S. Novoselov is an academic researcher from National University of Singapore. The author has contributed to research in topics: Graphene & Bilayer graphene. The author has an hindex of 115, co-authored 392 publications receiving 207392 citations. Previous affiliations of Kostya S. Novoselov include University of Manchester & Russian Academy of Sciences.

Electrically pumped single-defect light emitters in WSe$_2$

Abstract: Recent developments in fabrication of van der Waals heterostructures enable new type of devices assembled by stacking atomically thin layers of two-dimensional materials. Using this approach, we fabricate light-emitting devices based on a monolayer WSe$_2$, and also comprising boron nitride tunnelling barriers and graphene electrodes, and observe sharp luminescence spectra from individual defects in WSe$_2$ under both optical and electrical excitation. This paves the way towards the realization of electrically-pumped quantum emitters in atomically thin semiconductors. In addition we demonstrate tuning by more than 1 meV of the emission energy of the defect luminescence by applying a vertical electric field. This provides an estimate of the permanent electric dipole created by the corresponding electron-hole pair. The light-emitting devices investigated in our work can be assembled on a variety of substrates enabling a route to integration of electrically pumped single quantum emitters with existing technologies in nano-photonics and optoelectronics.

Discovery of 2D van der Waals layered MoSi2N4 family.

Abstract: spectroscopy (XPS) measurements gave direct evidence that there existed strong interactions between single-site Sn and Zn promoters in this Zn1-Sn1/CuO catalyst, leading to a significant increase of the electron density on the Cu atoms in CuO. Density functional theory (DFT) calculations show that on the Sn-doped CuO(110) surface, the formation energy of Cu vacancy is 0.78 eV lower than that on the clean CuO(110), indicating that it is easier to form Cu vacancies in the Sn-doped surface.The calculation results also support that Zn prefers to fill in the nearbyCu vacancies caused by Sndoping to form Sn-Zn pairs. Compared with conventional catalysts with promoters in the form of nanoparticles, this novel catalyst exhibits much higher activity, selectivity and stability in the synthesis of dimethyldichlorosilane via the industrially important Rochow reaction. The enhanced catalytic performance is attributed to the generated cooperative electronic interaction of single-site Sn and Zn with the CuO support, which further promotes the adsorption of reactant molecules. The authors demonstrated the obvious advantages of the single-site promoters, not only helping to elucidate their real promotion mechanism in the catalytic reaction, but also opening up a new path to optimize catalyst performance. On one hand, the single-site promoters can maximize the catalytic interfaces between the promoter and the catalyst; on the other hand, the specific coordination between the single-site promoters and the catalyst can generate unique electronic properties, thereby promoting the catalytic reaction. As two or more types of promoters are often used in one industrial catalyst, thisworkwill stimulate research in singlesite promoters in catalyst design and thus provide better understanding of the synergistic effect among various promoters. In a certain distance range, the multiple single-site promoters will have strong electronic interactions with the catalyst, which can optimize the electronic structure of the catalyst and thus change its surface adsorption properties. Therefore, it is believed that optimizing the distance between metal atoms is the key to achieving synergy of multiple singlesite promoters. Moreover, as the catalyst support is the bridge of electronic interaction, the synergy is expected to be further optimized by adjusting the local microstructure of the catalyst support. Conflict of interest statement.None declared.

Surface Hydrogenation and Optics of a Graphene Sheet Transferred onto a Plasmonic Nanoarray

Abstract: We report properties of a plasmonic nanoarray coupled to a single layered graphene sheet transferred on the top of the nanoarray. We observe significant (up to 1000 times) enhancements of resonant Raman scattering from a graphene layer generated by near fields of a plasmonic nanoarray. This enhancement is quantitatively explained by the electromagnetic mechanism. We experimentally demonstrate a significant spectral shift of diffractive coupled plasmon resonances induced by the graphene presence and show that the collective plasmon resonances can be used to study surface chemistry of graphene. Our results emphasize prospective capabilities of graphene-functionalized plasmonics.

Electronic Properties of Graphene Encapsulated with Different Two-Dimensional Atomic Crystals

Abstract: Hexagonal boron nitride is the only substrate that has so far allowed graphene devices exhibiting micron-scale ballistic transport. Can other atomically flat crystals be used as substrates for making quality graphene heterostructures? Here we report on our search for alternative substrates. The devices fabricated by encapsulating graphene with molybdenum or tungsten disulphides and hBN are found to exhibit consistently high carrier mobilities of about 60,000 cm$^{2}$V$^{-1}$s$^{-1}$. In contrast, encapsulation with atomically flat layered oxides such as mica, bismuth strontium calcium copper oxide and vanadium pentoxide results in exceptionally low quality of graphene devices with mobilities of ~ 1,000 cm$^{2}$ V$^{-1}$s$^{-1}$. We attribute the difference mainly to self-cleansing that takes place at interfaces between graphene, hBN and transition metal dichalcogenides. Surface contamination assembles into large pockets allowing the rest of the interface to become atomically clean. The cleansing process does not occur for graphene on atomically flat oxide substrates.

Failure Processes in Embedded Monolayer Graphene under Axial

Abstract: Exfoliated monolayer graphene flakes were embedded in a polymer matrix and loaded under axial compression. By monitoring the shifts of the 2D Raman phonons of rectangular flakes of various sizes under load, the critical strain to failure was determined. Prior to loading care was taken for the examined area of the flake to be free of residual stresses. The critical strain values for first failure were found to be independent of flake size at a mean value of –0.60% corresponding to a yield stress up to -6 GPa. By combining Euler mechanics with a Winkler approach, we show that unlike buckling in air, the presence of the polymer constraint results in graphene buckling at a fixed value of strain with an estimated wrinkle wavelength of the order of 1–2 nm. These results were compared with DFT computations performed on analogue coronene/ PMMA oligomers and a reasonable agreement was obtained.

The rise of graphene

Abstract: Graphene is a rapidly rising star on the horizon of materials science and condensed-matter physics. This strictly two-dimensional material exhibits exceptionally high crystal and electronic quality, and, despite its short history, has already revealed a cornucopia of new physics and potential applications, which are briefly discussed here. Whereas one can be certain of the realness of applications only when commercial products appear, graphene no longer requires any further proof of its importance in terms of fundamental physics. Owing to its unusual electronic spectrum, graphene has led to the emergence of a new paradigm of 'relativistic' condensed-matter physics, where quantum relativistic phenomena, some of which are unobservable in high-energy physics, can now be mimicked and tested in table-top experiments. More generally, graphene represents a conceptually new class of materials that are only one atom thick, and, on this basis, offers new inroads into low-dimensional physics that has never ceased to surprise and continues to provide a fertile ground for applications.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

The electronic properties of graphene

Abstract: This article reviews the basic theoretical aspects of graphene, a one-atom-thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. The Dirac electrons behave in unusual ways in tunneling, confinement, and the integer quantum Hall effect. The electronic properties of graphene stacks are discussed and vary with stacking order and number of layers. Edge (surface) states in graphene depend on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. Different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.

Two-dimensional gas of massless Dirac fermions in graphene

Abstract: Quantum electrodynamics (resulting from the merger of quantum mechanics and relativity theory) has provided a clear understanding of phenomena ranging from particle physics to cosmology and from astrophysics to quantum chemistry. The ideas underlying quantum electrodynamics also influence the theory of condensed matter, but quantum relativistic effects are usually minute in the known experimental systems that can be described accurately by the non-relativistic Schrodinger equation. Here we report an experimental study of a condensed-matter system (graphene, a single atomic layer of carbon) in which electron transport is essentially governed by Dirac's (relativistic) equation. The charge carriers in graphene mimic relativistic particles with zero rest mass and have an effective 'speed of light' c* approximately 10(6) m s(-1). Our study reveals a variety of unusual phenomena that are characteristic of two-dimensional Dirac fermions. In particular we have observed the following: first, graphene's conductivity never falls below a minimum value corresponding to the quantum unit of conductance, even when concentrations of charge carriers tend to zero; second, the integer quantum Hall effect in graphene is anomalous in that it occurs at half-integer filling factors; and third, the cyclotron mass m(c) of massless carriers in graphene is described by E = m(c)c*2. This two-dimensional system is not only interesting in itself but also allows access to the subtle and rich physics of quantum electrodynamics in a bench-top experiment.