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.

The rise of graphene

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.

Fast parallel algorithms for short-range molecular dynamics

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

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.

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The electronic properties of graphene

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.

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Two-dimensional gas of massless Dirac fermions in graphene

Personal protective clothing is critical to shield users from highly infectious diseases including COVID-19. Such clothing is predominantly single-use, made of plastic-based synthetic fibres such as polypropylene and polyester, low cost and able to provide protection against pathogens. However, the environmental impacts of synthetic fibre-based clothing are significant and well-documented. Despite growing environmental concerns with single-use plastic-based protective clothing, the recent COVID-19 pandemic has seen a significant increase in their use, that could result in a further surge of oceanic plastic pollution, adding to mass of plastic waste that already threatens marine life. In this review, we briefly discuss the nature of the raw materials involved in the production of such clothing, as well as manufacturing techniques and the PPE supply chain. We identify the environmental impacts at critical points in the protective clothing value chain from production to consumption, focusing on water use, chemical pollution, CO2 emissions and waste. On the basis of these environmental impacts, we outline the need for fundamental changes in the business model, including increased usage of reusable protective clothing, addressing supply chain bottlenecks, establishing better waste management, and the use of sustainable materials and processes without associated environmental problems.

Environmental Impacts of Personal Protective Clothing Used to Combat COVID-19

Comprehensive Characterization of Gas Diffusion Through Graphene Oxide Membranes

Patterning antidots ("voids") into well-defined antidot lattices creates an intriguing class of artificial structures for the periodic modulation of 2D electron systems, leading to anomalous transport properties and exotic quantum phenomena as well as enabling the precise bandgap engineering of 2D materials to address technological bottleneck issues. However, realizing such atomic-scale quantum antidots (QADs) is infeasible by current nanolithographic techniques. Here, we report an atomically-precise bottom-up fabrication of a series of atomic-scale QADs with elegantly engineered quantum states through a controllable assembly of a chalcogenide single vacancy (SV) in 2D PtTe2, a type-II Dirac semimetal. Te SVs as atomic-scale"antidots"undergo thermal migration and assembly into highly-ordered SV lattices spaced by a single Te atom, reaching the ultimate downscaling limit of antidot lattices. Increasing the number of SVs in QADs strengthens the cumulative repulsive potential and consequently enhances collective interference of multiple-pocket scattered quasiparticles inside QADs, creating multi-level quantum hole states with tunable gap from telecom to far-infrared regime. Moreover, precisely engineered quantum hole states of QADs are symmetry-protected and thus survive upon atom-by-atom oxygen substitutional doping. Therefore, SV-assembled QADs exhibit unprecedented robustness and property tunability, which not only holds the key to their future applications but also embody a wide variety of material technologies.

Atomically-precise Vacancy-assembled Quantum Antidots

Gold is a unique element, characterized not only by limited, though still reasonable, availability (useful for monetary applications) but also for its rather unique properties useful formany industries [1]: chemical inertness, high electrical conductivity, plasticity, etc. As gold reserves in Earth’s crust diminish with traditional mining, ‘urban mining’ that recycles gold from gold-containing wastes (such as electronic waste, e-waste) has emerged as an important supply method for gold sustainability [2]. One critical step in such a recycling process is the use of an adsorbent to extract gold from e-waste leachate that contains complex metal elements. Therefore, the gold adsorbent shouldhave ahigh extraction capacity, selectivity and, importantly, economic viability. Although many porous materials have been developed for gold extraction from e-waste [3–6], materials that show high gold extraction capacity with precise gold selectivity to ppmor even lower concentrations are highly required. 2D materials, especially graphene, have one of the highest specific surface area, essential for a high adsorption capacity. Early research on gold-doped graphene showed that graphene could chemically reduce aqueous gold ions to metallic gold driven by a redox reaction between graphene and gold ions [7,8]. Together, these two properties suggest that graphene could be a good candidate for gold extraction. However, possibly because of an intrinsic hydrophobicity, which offers graphene a poor dispersibility in aqueous gold solution and sacrifices its large surface area, the demonstration of graphene for gold extraction was lacking. Recently, the research group led by Yang Su from Tsinghua Shenzhen International Graduate School, Hui-Ming Cheng from the Shenzhen Institute of Advanced Technology of the Chinese Academy of Sciences and Andre K. Geim from the University of Manchester discovered that reduced graphene oxide (rGO), a chemical derivative of graphene, extracts gold from e-waste with ultra-high capacity and very good selectivity [9]. The technology can be scaled up for industrial applications. After rGO is directly mixed with gold solution for a few minutes, the metallic gold is extracted and deposited on rGO. Notably, >95% of gold ions are reduced to metallic gold by rGO, which avoids the elution and precipitation necessary in post-adsorption processing. The rGO shows a gold extraction capacity of ∼1000 mg/g to 1 ppm gold solution, which is significantly higher than stateof-the-art gold adsorbents [3–6]. Even if the gold concentration is as low as 20 ppt, the rGO can achieve effective gold extraction. More interestingly, the rGO exclusively extracts gold without contamination of other 14 coexisting metallic elements generally seen in e-waste, manifesting excellent extraction selectivity. The heterogeneous structure of rGO plays a critical role in the reported ultra-high extraction capacity and precise selectivity (Fig. 1).The pristine graphene areas of rGO adsorb and reduce gold ions, similarly to gold ion doped graphene. The residual oxidized regions of rGO provide a good dispersibility so that graphene areas are readily available for gold extraction. This research further shows that the gold ions are adsorbed and reduced at the pristine graphene areas, while other coexisting metal elements are adsorbed at the oxidized regions via coordination, ion exchange, etc. Exploiting such site-specific adsorption by pristine graphene areas and oxidized regions, the coexisting metal

Graphene for gold extraction

The topological structure associated with the branchpoint singularity around an exceptional point (EP) provides new tools for controlling the propagation of electromagnetic waves and their interaction with matter. To date, observation of EPs in light-matter interactions has remained elusive and has hampered further progress in applications of EP physics. Here, we demonstrate the emergence of EPs in the electrically controlled interaction of light with a collection of organic molecules in the terahertz regime at room temperature. We show, using time-domain terahertz spectroscopy, that the intensity and phase of terahertz pulses can be controlled by a gate voltage which drives the device across the EP. This fully electrically-tuneable system allows reconstructing the Riemann surface associated with the complex energy landscape and provides a topological control of light by tuning the loss-imbalance and frequency detuning of interacting modes. We anticipate that our work could pave the way for new means of dynamic control on the intensity and phase of terahertz field, developing topological optoelectronics, and studying the manifestations of EP physics in the quantum correlations of the light emitted by a collection of emitters coupled to resonators.

Kostya S. Novoselov

Papers

Environmental Impacts of Personal Protective Clothing Used to Combat COVID-19

Comprehensive Characterization of Gas Diffusion Through Graphene Oxide Membranes

Atomically-precise Vacancy-assembled Quantum Antidots

Graphene for gold extraction

Non-Hermitian engineering of terahertz light using exceptional points in electrically tuneable collective light-matter interactions