M. Stamenova and S. Sanvito
This article reviews recent advances towards the development of a truly atomistic time-dependent theory for spin-dynamics. The focus is on the s-d tight-binding model [where conduction electrons (s) are exchange-coupled to a number of classical spins (d)], including electrostatic corrections at the Hartree level, as the underlying electronic structure theory. In particular, the article considers one-dimensional (1D) magnetic atomic wires and their electronic structure, described by means of the s-d model. The discussion begins with an overview of the model spin Hamiltonian, followed by molecular-dynamics simulations of spin-wave dispersion in a s-d monoatomic chain and spin impurities in a non-magnetic chain. The current-induced motion in a magnetic domain wall (DW) is also explored, along with how an electric current can affect the magnetization landscape of a magnetic nano-object. The article concludes with an assessment of spin-motive force, and especially whether a driven magnetization dynamics can generate an electrical signal.
A. Burke, D. Carroll, Frank Torti, and S.V. Torti
This article examines the potential of bifunctional nanomaterials for the imaging and treatment of cancer. Several nanomaterials possess properties desirable for a cancer therapy and have been the subject of research as anticancer agents. Those that have received the most attention include encapsulated iron oxides, single- and multiwalled carbon nanotubes, gold nanorods and gold nanoshells. This article first considers thermal ablative therapy incancer, focusing on the mechanisms of thermotoxicity and thermoresistance before discussing a number of nanomaterials with applications for cancer treatment. In particular, it evaluates the use of nanomaterials in thermal therapy. It also looks at gold nanoshells and nanorods, taking into account their physical properties, and concludes with an assessment of iron-oxide nanoparticles and future directions for nanomaterials as multifunctional agents for cancer therapy.
P. Zrazhevskiy and X. Gao
This article discusses the use of bioconjugated quantum dots (QDs) for tumor molecular imaging and profiling. The need for personalized diagnostics and therapy is becoming apparent in all areas of medicine, and especially urgent and sought after in treating cancer. Mechanisms of cancerogenesis and cancer response to therapy remain poorly understood, thus precluding accurate cancer diagnosis, prognosis, and effective treatment. Accurate molecular profiling of individual tumors is one key to effective treatment. This article first considers the photophysical properties of QDs before reviewing the most common methods for engineering QD-based probes for biomedical applications, including water solubilization and bioconjugation approaches. It also describes a number of techniques for molecular imagingand profiling of tumors, ranging from QD-based multicolor flow cytometry and applications of QDs in high-resolution correlated fluorescence/electron microscopy, QD bioprobes for molecular profiling of tumor-tissue sections and microarrays, and QD-oligonucleotide bioconjugates for in-situ hybridization.
Carbon-nanotube field emission electron and X-ray technology for medical research and clinical applications
Sigen Wang, Otto Zhou, and Sha Chang
This article describes carbon-nanotube based X-ray technologies for medical research and clinical applications, including an X-ray source, microfocus X-ray tube, microcomputed tomography scanner, stationary digital breast tomosynthesis, microradiotherapy system, and single-cell irradiation system. It first examines electron field emission from carbon nanotubes before discussing carbon-nanotube field emission electron and X-ray technologies in greater detail. It highlights the enormous promise of these systems in commercial and research application for the future in diagnostic medical imaging; in-vivo imaging of small-animal modelsfor pre-clinical cancer studies; security screening; industrial inspection; cancer radiotherapy of small-animal models for pre-clinical cancer studies; and basic cancer research using single-cell irradiation.
K.S. Thygesen and A. Rubio
This article focuses on correlated electron transport in molecular junctions. More specifically, it considers how electronic correlation effects can be included in transport calculations using many-body perturbation theory within the Keldysh non-equilibrium Green’s function formalism. The article uses the GW self-energy method (G denotes the Green’s function and W is the screened interaction) which has been successfully applied to describe quasi-particle excitations in periodic solids. It begins by formulating the quantum-transport problem and introducing the non-equilibrium Green’s function formalism. It then derives an expression for the current within the NEGF formalism that holds for interactions in the central region. It also combines the GW scheme with a Wannier function basis set to study electron transport through two prototypical junctions: a benzene molecule coupled to featureless leads and a hydrogen molecule between two semi-infinite platinum chains. The results are analyzed using a generic two-level model of a molecular junction.
This article examines many novel effects related to the magnetic, electric, elastic and transport properties of Josephson nanocontacts and nanogranular superconductors using a realistic model of two-dimensional Josephson junction arrays. The arrays were created by a 2D network of twin-boundary dislocations with strain fields acting as an insulating barrier between hole-rich domains in underdoped crystals. The article first describes a model of nanoscopic Josephson junction arrays before discussing some interesting phenomena, including chemomagnetism and magnetoelectricity, electric analog of the ‘fishtail‘ anomaly and field-tuned weakening of the chemically induced Coulomb blockade, a giant enhancement of the non-linear thermal conductivity in 2D arrays, and thermal expansion of a singleJosephson contact.
Philip G. Collins
This article examines the physical consequences of defects and disorder in carbon nanotubes (CNTs). It begins with a pedagogical categorization of the types of defects and disorder found in CNTs, including lattice vacancies and bond rotations, and goes on to discuss considers two primary sources of disorder: the environment surrounding a CNT and the substrate supporting it. It then considers various experimental methods for locating defects in CNTs, including atomic-resolution scanning tunnelling microscopy, transmission electron microscopy, electrochemical and chemoselective labelling, optical spectroscopy, and electrical conductance. The article concludes with a review of the long-range consequences of defects and disorder on the physical properties of CNTs such as chemical reactivity, electrical transport, and mechanical effects.
Nian Lin and Sebastian Stepanow
This article describes the use of supramolecular chemistry to design low-dimensional nanostructures at surfaces. In particular, it discusses the design strategies of two types of low-dimensional supramolecular nanostructures: structures stabilized by hydrogen bonds and structures stabilized by metal-ligand co-ordination interactions. After providing an overview of hydrogen-bond systems such as 0D discrete clusters, 1D chains, and 2D open networks and close-packed arrays, the article considers metal-co-ordination systems. It also presents experimental results showing that both hydrogen bonds and metal co-ordination offer protocols to achieve unique nanostructured systems on 2D surfaces or interfaces. Noting that the conventional 3D supramolecular self-assembly has generated a vast number of nanostructures revealing high complexity and functionality, the article suggests that 2D approaches can be applied to substrates with different symmetries as well as physical and chemical properties.
Sven Stafström and Mikael Unge
This article examines disorder-induced electron localization in molecular-based materials, using DNA and pentacene molecular crystals as examples. In DNA, the disorder is intrinsic and strong, resulting in very short localization lengths. The pentacene crystal, on the other hand, is intrinsically homogeneous and the disorder is extrinsic and weak, which makes a metal–insulator transition (MIT) possible. After providing an overview of carbon-based materials for electronic applications, the article explains the methodology for calculating the localization properties of a DNA double strand and a pentacene molecular crystal, namely Hamiltonian, transfer matrix, and finite-size scaling. It also discusses the results, which show a substantial increase in the localization length of the electronic state with correlated disorder as compared to the case of uncorrelated disorder.
Joshua D. Carter, Chenxiang Lin, Yan Liu, Hao Yan, and Thomas H. LaBean
This article examines the DNA-based self-assembly of nanostructures. It first reviews the development of DNA self-assembly and DNA-directed assembly, focusing on the main strategies and building blocks available in the modern molecular construction toolbox, including the design, construction, and analysis of nanostructures composed entirely of synthetic DNA, as well as origami nanostructures formed from a mixture of synthetic and biological DNA. In particular, it considers the stepwise covalent synthesis of DNA nanomaterials, unmediated assembly of DNA nanomaterials, hierarchical assembly, nucleated assembly, and algorithmic assembly. It then discusses DNA-directed assembly of heteromaterials such as proteins and peptides, gold nanoparticles, and multicomponent nanostructures. It also describes the use of complementary DNA cohesion as 'smart glue' for bringing together covalently linked functional groups, biomolecules, and nanomaterials. Finally, it evaluates the potential future of DNA-based self-assembly for nanoscale manufacturing for applications in medicine, electronics, photonics, and materials science.
Vu Thien Binh
This article reviews recent advances in field emission cathodes and their applications, focusing on a number of possibilities emerging from the field of nanotechnology. It begins with an overview of the driving forces for the evolution of cold cathodes, laying emphasis on their fundamental characteristics and industrial applications as well as the bottlenecks of metallic field emitters. It then considers single-atom emitters, followed by different examples where the advent of nanotechnology has contributed towards improving new cold cathodes. It also discusses the Fresnel projection microscope and the microgun, a route to the microcolumn approach which is associated with the nanotip; a host of material issues for field emitters, taking into account carbon nanocompounds; carbon-nanotube field emitters; and carbon-nanopearl field emitters. The article concludes with an evaluation of the applications and uses of carbon nanocompounds, carbon nanotubes and carbon nanopearls as cold cathodes.
M.-V. Fernandez-Serra and X. Blase
This article describes a number of theoretical works and methods dedicated to the analysis of the atomic and electronic structure, doping properties and transport characteristics of silicon nanowires (SiNWs). The goal is to show how quantum confinement and dimensionality effects can intrinsically change the behavior of SiNWs as compared to their bulk and thin film counterparts. The article begins with a review of work done on surface reconstructions and electronic structure of SiNWs as a function of system doping and passivation. It then considers the problem of doping in SiNWs as well as the methodology typically used to analyze the problems of transport. It also discusses the electronic transport properties of SiNWs as a function of dopant type, along with their chemical functionalization. Finally, it demonstrates how surface dangling-bond defects trap the impurities in SiNWs and neutralize them.
The electronic structure of epitaxial graphene—A view from angle-resolved photoemission spectroscopy
S.Y. Zhou and A. Lanzara
This article analyzes the electronic structure of epitaxial graphene using angle-resolved photoemission spectroscopy (ARPES). It first describes how the carbon atoms in graphene are arranged before discussing the growth and characterization of graphene samples. It then considers the electronic structure of epitaxial graphene, along with the gap opening in single-layer epitaxial graphene. It also examines possible mechanisms for the gap opening in graphene, including quantum confinement, mixing of the states between the Brillouin zone corner K points induced by scattering, and hybridization of the valence and conduction bands caused by symmetry breaking in carbon sublattices. Clear deviations from the conical dispersions are observed near the Diracpoint energy, which can be interpreted as a gap opening attributed to graphene–substrate interaction. Graphene–substrate interaction is thus a promising route for engineering the bandgap in graphene.
K. Thomas, N. Monteiro-Riviere, D. Warheit, and N. Savage
This article discusses the risks associated with nanomaterials. The use of nanomaterials in consumer products and industrial applications is becoming more prevalent owing to their range of benefits. Nanomaterials have found uses in energy production, home appliances, water treatment, novel therapeutic delivery techniques and dietary supplements, consumer electronics, and sports equipment. While considerable attention has been given to the likely commercial advantages associated with nanomaterials, less emphasis has been placed on the development of a systematic approach for characterizing the human health and environmental risks from exposure to nanomaterials. This article first considers the use of nanomaterials in consumer products and the characterization of nanomaterials before describing a systematic evaluation of the hazards associated with nanomaterials. It also examines pulmonary exposure assessment and dermal exposure assessment, along with risk assessment for exposure to nanomaterials. Finally, it outlines research priorities for the development of more refined estimates of nanomaterial risk.
D.V. Melnikov, J. Kim, L.-X. Zhang, and J.-P. Leburton
This article examines the spin and charge properties of double and triple quantum dots (QDs) populated containing just a few electrons, with particular emphasis on laterally coupled QDs. It first describes the theoretical approach, known as exact diagonalization method, utilized on the example of the two-electron system in coupled QDs that are modelled as two parabolas. The many-body problem is solved via the exact diagonalization method as well as variational Heitler–London and Monte Carlo methods. The article proceeds by considering the general characteristics of the two-electron double-QD structure and limitations of the approximate methods commonly used for its theoretical description. It also discusses the stability diagram for two circular dots and investigates how its features are affected by the QD elliptical deformations. Finally, it assesses the behavior of the two-electron system in the realistic double-dot confinement potentials.
Free-standing grid-like nanostructures assembled into 3D open architectures for photovoltaic devices
X.Y. Kong, Y.C. Wang, X.F. Fan, G.F. Guo, and L.M. Tong
This article describes three-dimensional open architectures with free-standing grid-like nanostructure arrays as photocatalytic electrodes for a new type of dye-sensitized solar cell. It introduces a novel technique for fabricating a series of semiconducting oxides with grid-like nanostructures replicated from the biotemplates. These semiconducting oxides, including n-type titanium dioxide or p-type nickel oxide nanogrids, were sensitized with the dye molecules, then assembled into 3D stacked-grid arrays on a flexible substrate by means of the Langmuir–Blodgett method or the ink-jet printing technique for the photocatalytic electrodes. The article first considers the fabrication of photoelectrodes with 2D grid-like nanostructures by means of the biotemplating approach before discussing the assembly and photophysicsof grid-like nanostructures into 3D open architectures for the photocatalytic electrodes.
R. Graupner and F. Hauke
This article examines the chemical functionalization and structural alteration of single-walled carbon nanotubes (SWCNTs). It describes the covalent functionalization of the SWCNT framework that is the covalent attachment of functional entities onto the CNT scaffold. In particular, it considers the chemical modification and reactivity of SWCNTs in the context of the reactivity of graphite and fullerenes. It also discusses the defect and sidewall functionalization of SWCNTs, along with various techniques used in the characterization ofSWCNTs upon functionalization, namely: thermogravimetric analysis, spectroscopic techniques such as UV-Vis-NIR spectroscopy and Raman spectroscopy, and microscopic techniques like transmission electron microscopy, atomic force microscopy and scanning tunnelling microscopy.
Harmonic detection of resonance methods for micro- and nanocantilevers: Theory and selected applications
J.D. Taylor, B. Elliott, D. Dickel, G. Keskar, J. Gaillard, M.J. Skove, and A.M. Rao
This article examines the harmonic detection of resonance (HDR) methods for micro- and nanocantilevers, with particular emphasis on theory and selected applications. Micro- and nanocantilevers have the potential to revolutionize physical, chemical, and biological sensing. Microcantilevers in particular are easily integrated into standard high-volume silicon manufacturing processes, making them relatively inexpensive and mass-producible. This article begins with an overview of basic transduction mechanisms applicable to micro- and nanocantilever-based systems. It then considers several detection schemes for measuring the static and/or dynamic response of micro- and nanocantilevers. It goes on to discuss electrostatic actuation and capacitive detection, how HDR works, and the differences between the mechanical and electrical responses of an electrostatically actuated microcantilever. Finally, it presents a number of applications for micro- and nanocantilevers, along with detection results for cantilevered multiwall carbon nanotubes.
Satoru Shoji, Remo Proietti Zaccaria, and Satoshi Kawata
This article describes a holographic laser-processing method for independently controlling the lattice symmetry and lattice constant in three-dimensional photonic lattices. With this approach, optical periodicity is created in lower dimensions and three-dimensional periodicity is obtained by a combination of several lower-dimensional periodic structures. The proposed holographic laser-processing method is compared with the standard four-beam technique. Examples of experimental demonstration achieved in photosensitive polymers are given. The article also introduces a multiphoton direct-writing technique for creating defect structures in lattices towards production of defect cavity-functionalized photonic crystal devices. It shows that all Bravais lattices can be produced by choosing proper incident vectors of laser beams. The lattice constant of the structure can be changed without distorting its lattice symmetry and lattice elements.
Katalin Kamarás and Àron Pekker
This article describes the identification and separation of metallic and semiconducting carbon nanotubes according to their electric properties. It first provides an overview of the electronic structure of nanotubes, focusing on how their metallic and semiconducting properties arise. It then considers the most widely used characterization techniques used in determining metallic or semiconducting behavior, including Raman spectroscopy and photoluminescence measurements. It also discusses specific chirality-selective growth techniques, physical postgrowth selection methods, enrichment by chirality-sensitive chemical reactions, and modification of transport properties without change in chirality. The article concludes with a review of some applications of metallic and semiconducting carbon nanotubes as transparent conductive coatings.