This thesis concerns the discovery of superconductivity in the intercalated graphite compounds C6Yb and C6Ca. A novel technique for synthesis of these intercalates has been developed, and is presented in detail. These two materials are shown to superconduct at 6.5K and 11.5K respectively. The superconductivity is demonstrated by measurements of the magnetisation and resistivity. Initial measurements of the superconducting transition of these materials as a function of pressure shows an increase in the transition with increasing pressure.

Superconductivity in the intercalated graphite compounds C6Yb and C6Ca

We report an ab initio density functional theory study of the interaction of four nucleobases, cytosine, thymine, adenine, and guanine, with a novel graphene nanopore device for detecting the base sequence of a single-stranded nucleic acid (ssDNA or RNA). The nucleobases were inserted into a pore in a graphene nanoribbon, and the electrical current and conductance spectra were calculated as functions of voltage applied across the nanoribbon. The conductance spectra and charge densities were analyzed in the presence of each nucleobase in the graphene nanopore. The results indicate that due to significant differences in the conductance spectra the proposed device has adequate sensitivity to discriminate between different nucleotides. Moreover, we show that the nucleotide conductance spectrum is affected little by its orientation inside the graphene nanopore. The proposed technique may be extremely useful for real applications in developing ultrafast, low-cost DNA sequencing methods.

http://absimage.aps.org/image/MAR10/MWS_MAR10-2009-001318.pdf

Detection of Nucleic Acids with Graphene Nanopores: Ab Initio Characterization of a Novel Sequencing Device

Graphene, a single two-dimensional sheet of carbon atoms with an arrangement mimicking the honeycomb hexagonal architecture, has captured immense interest of the scientific community since its isolation in 2004. Besides its extraordinarily high electrical conductivity and surface area, graphene shows a long spin lifetime and limited hyperfine interactions, which favors its potential exploitation in spintronic and biomedical applications, provided it can be made magnetic. However, pristine graphene is diamagnetic in nature due to solely sp2 hybridization. Thus, various attempts have been proposed to imprint magnetic features into graphene. The present review focuses on a systematic classification and physicochemical description of approaches leading to equip graphene with magnetic properties. These include introduction of point and line defects into graphene lattices, spatial confinement and edge engineering, doping of graphene lattice with foreign atoms, and sp3 functionalization. Each magnetism-imprinting strategy is discussed in detail including identification of roles of various internal and external parameters in the induced magnetic regimes, with assessment of their robustness. Moreover, emergence of magnetism in graphene analogues and related 2D materials such as transition metal dichalcogenides, metal halides, metal dinitrides, MXenes, hexagonal boron nitride, and other organic compounds is also reviewed. Since the magnetic features of graphene can be readily masked by the presence of magnetic residues from synthesis itself or sample handling, the issue of magnetic impurities and correct data interpretations is also addressed. Finally, current problems and challenges in magnetism of graphene and related 2D materials and future potential applications are also highlighted.

Emerging chemical strategies for imprinting magnetism in graphene and related 2D materials for spintronic and biomedical applications

Liquid crystals are an integral part of a mature display technology, also establishing themselves in other applications, such as spatial light modulators, telecommunication technology, photonics, or sensors, just to name a few of the non-display applications. In recent years, there has been an increasing trend to add various nanomaterials to liquid crystals, which is motivated by several aspects of materials development. (i) addition of nanomaterials can change and thus tune the properties of the liquid crystal; (ii) novel functionalities can be added to the liquid crystal; and (iii) the self-organization of the liquid crystalline state can be exploited to template ordered structures or to transfer order onto dispersed nanomaterials. Much of the research effort has been concentrated on thermotropic systems, which change order as a function of temperature. Here we review the other side of the medal, the formation and properties of ordered, anisotropic fluid phases, liquid crystals, by addition of shape-anisotropic nanomaterials to isotropic liquids. Several classes of materials will be discussed, inorganic and mineral liquid crystals, viruses, nanotubes and nanorods, as well as graphene oxide.

https://www.mdpi.com/2079-4991/7/10/305/pdf

Lyotropic Liquid Crystal Phases from Anisotropic Nanomaterials

Graphene shows excellent mechanical, electrical, and optical properties. Its unique structure and attributes have made it and its derivatives (e.g., graphene oxide (GO) and reduced graphene oxide (rGO)) promising candidates in molecular separation. Excellent molecular separation performance, including permeability and selectivity, has been demonstrated by GO membranes recently. In this review, the mechanisms, i.e., in-plane pores (defects), interlayer spacing, and functional group assisted molecular separation, of selective molecular transport through GO membranes are summarized. In addition, preparation and interlayer spacing tuning strategies of GO membranes are provided. This timely review aims to present the latest advancements in both the theoretical and experimental demonstration of GO membranes for molecular separation. Moreover, current challenges and emerging perspectives of GO membranes for separation are also discussed.

Fundamental Transport Mechanisms and Advancements of Graphene Oxide Membranes for Molecular Separation

This spotlight discusses intriguing properties and diverse applications of graphene (Gr) and Gr analogs. Gr has brought us two-dimensional (2D) chemistry with its exotic 2D features of density of states. Yet, some of the 2D or 2D-like features can be seen on surfaces and at interfaces of bulk materials. The substrate on Gr and functionalization of Gr (including metal decoration, intercalation, doping, and hybridization) modify the unique 2D features of Gr. Despite abundant literature on physical properties and well-known applications of Gr, spotlight works based on the conceptual understanding of the 2D physical and chemical nature of Gr toward vast-ranging applications are hardly found. Here we focus on applications of Gr, based on conceptual understanding of 2D phenomena toward 2D chemistry. Thus, 2D features, defects, edges, and substrate effects of Gr are discussed first. Then, to pattern Gr electronic circuits, insight into differentiating conducting and nonconducting regions is introduced. By utiliz...

Graphene and Graphene Analogs toward Optical, Electronic, Spintronic, Green-Chemical, Energy-Material, Sensing, and Medical Applications

Perfect spin filtering is an important issue in spintronics. Although such spin filtering showing giant magnetoresistance was suggested using graphene nanoribbons (GNRs) on both ends of which strong magnetic fields were applied, electric field controlled spin filtering is more interesting due to much easier precise control with much less energy consumption. Here we study the magnetic/nonmagnetic behaviors of zigzag GNRs (zGNRs) under a transverse electric field and by edge functionalization. Employing density functional theory (DFT), we show that the threshold electric field to attain either a half-metallic or nonmagnetic feature is drastically reduced by introducing proper functional groups to the edges of the zGNR. From the current–voltage characteristics of the edge-modified zGNR under an in-plane transverse electric field, we find a remarkable perfect spin filtering feature, which can be utilized for a molecular spintronic device. Alteration of magnetic properties by tuning the transverse electric fie...

Lower Electric Field-Driven Magnetic Phase Transition and Perfect Spin Filtering in Graphene Nanoribbons by Edge Functionalization

Designing and fabricating nanosize spintronic devices is a crucial task to develop information technology of the future. However, most of the introduced spin filters suffer from several limitations including difficulty in manipulating the spin current, incapability in utilizing a wide range of dopants to provide magnetism, or obstacles in their experimental realization. Here, by employing first principles calculations, we introduce a structurally simple and functionally efficient spin filter device composed of a zigzag graphene nanoribbon (ZGNR) with an embedded nitrogenated divacancy. We show that the proposed system, possessing a robust ferromagnetic (FM) ordering, exhibits perfect half metallic behavior in the absence of frequently used transition metals (TMs). Our calculations also show that the suggested system is compatible with a wide range of adatoms including basic metals, metalloids, and TMs. It means that besides d electron magnetism originating from TMs, p electrons of incorporated elements of the main group can also cause half metallicity in the electronic structure of the introduced system. Our system exploiting the robustness of doping-induced FM ordering would be beneficial for promising multifunctional spin filter devices.

/pdf/a-high-performance-n-doped-graphene-nanoribbon-based-ghc60equ5y.pdf

M. Reza Rezapour

Papers

Graphene and Graphene Analogs toward Optical, Electronic, Spintronic, Green-Chemical, Energy-Material, Sensing, and Medical Applications

Lower Electric Field-Driven Magnetic Phase Transition and Perfect Spin Filtering in Graphene Nanoribbons by Edge Functionalization

A high performance N-doped graphene nanoribbon based spintronic device applicable with a wide range of adatoms

An effective approach to realize graphene based p-n junctions via adsorption of donor and acceptor molecules