Susan B. Sinnott

A second-generation reactive empirical bond order (REBO) potential energy expression for hydrocarbons

A second-generation potential energy function for solid carbon and hydrocarbon molecules that is based on an empirical bond order formalism is presented. This potential allows for covalent bond breaking and forming with associated changes in atomic hybridization within a classical potential, producing a powerful method for modelling complex chemistry in large many-atom systems. This revised potential contains improved analytic functions and an extended database relative to an earlier version (Brenner D W 1990 Phys. Rev. B 42 9458). These lead to a significantly better description of bond energies, lengths, and force constants for hydrocarbon molecules, as well as elastic properties, interstitial defect energies, and surface energies for diamond.

Model of carbon nanotube growth through chemical vapor deposition

Abstract This Letter outlines a model to account for the catalyzed growth of nanotubes by chemical vapor deposition. It proposes that their formation and growth is an extension of other known processes in which graphitic structures form over metal surfaces at moderate temperatures through the decomposition of organic precursors. Importantly, the model also states that the form of carbon produced depends on the physical dimensions of the catalyzed reactions. Experimental data are presented that correlate nanotube diameters to the size of the catalyst particles. Nanotube stability as a function of nanotube type, length and diameter are also investigated through theoretical calculations.

Carbon Nanotubes: Synthesis, Properties, and Applications

The goal of this article is to provide an updated and in-depth review of some of the most exciting and important developments in the processing and properties of carbon nanotubes. Nanotubes can be formed in various structures using several different processing methods. The synthesis methods used to produce specific kinds of nanotubes are discussed and a comparison is made between the methods used by researchers and industrial producers. This is followed by an overview and discussion of what makes carbon nanotubes interesting to so many: their mechanical, chemical, electrical, thermal, and optical properties. The article ends with a discussion of the future outlook for the study of carbon nanotubes.

Effect of chemical functionalization on the mechanical properties of carbon nanotubes

Abstract Carbon nanotubes (CNTs) have been proposed as ideal fibers for the manufacture of the next generation of composite materials. To ultimately increase the interaction of the CNTs with polymer matrices, researchers have attached chemical functional groups to the nanotube walls. The effects of covalent chemical attachments on the mechanical properties of single-walled CNTs are examined with classical molecular dynamics simulations. The maximum compressive (buckling) force for various functionalized and non-functionalized CNTs is calculated. It is found that covalent chemical attachments decrease the maximum buckling force by about 15% regardless of tubule helical structure or radius.

Mechanical properties of nanotubule fibers and composites determined from theoretical calculations and simulations

Theoretical Youngs moduli have been estimated for carbon fibers composed of single-walled fullerene nanotubules aligned in the direction of the tubule axis. In the limit of infinitely long tubules, the fibers can have a Youngs modulus comparable to that of diamond. Exploiting this property of nanotubule fibers, we investigate a new carbon composite composed of layered nanotubule fibers and diamond. Such a composite is found to be a high-modulus, low-density material that is quite stable to shear and other distortions.

Molecular dynamics simulations of the filling and decorating of carbon nanotubules

Carbon nanotubes (CNTs) have been proposed as excellent materials for the construction of new, precisely tailored ultrafiltration membranes and as promising fibres for the construction of new, stronger composite materials. In this paper classical molecular dynamics simulations are used to investigate the potential use of CNTs in these applications. Functional groups have been covalently attached to the walls of CNTs to provide more extensive interactions between these new fibres and a polymer matrix. We examine the effects of these attachments on the mechanical properties of the tubules. The diffusive molecular flow of methane, ethane and ethylene through single tubules at room temperature are also studied. The simulations predict normal-mode molecular diffusion for methane. However, diffusion that is intermediate between normal-mode and single-file diffusion is predicted for ethane and ethylene. These diffusion results are found to be similar to results predicted for molecular diffusion in zeolites.

The growth and modification of materials via ion-surface processing

A wide variety of gas phase ions with kinetic energies from 1–10 7 eV increasingly are being used for the growth and modification of state-of-the-art material interfaces. Ions can be used to deposit thin films; expose fresh interfaces by sputtering; grow mixed interface layers from ions, ambient neutrals, and/or surface atoms; modify the phases of interfaces; dope trace elements into interface regions; impart specific chemical functionalities to a surface; toughen materials; and create micron- and nanometer-scale interface structures. Several examples are developed which demonstrate the variety of technologically important interface modification that is possible with gas phase ions. These examples have been selected to demonstrate how the choice of the ion and its kinetic energy controls modification and deposition for several different materials. Examples are drawn from experiments, computer simulations, fundamental research, and active technological applications. Finally, a list of research areas is provided for which ion–surface modification promises considerable scientific and technological advances in the new millennium. 2001 Elsevier Science B.V. All rights reserved.

Density functional study of the bonding in small silicon clusters

We report the ground electronic state, equilibrium geometry, vibrational frequencies, and binding energy for various isomers of Sin(n = 2–8) obtained with the linear combination of atomic orbitals‐density functional method. We used both a local density approximation approach and one with gradient corrections. Our local density approximation results concerning the relative stability of electronic states and isomers are in agreement with Hartree–Fock and Mo/ller–Plesset (MP2) calculations [K. Raghavachari and C. M. Rohlfing, J. Chem. Phys. 89, 2219 (1988)]. The binding energies calculated with the gradient corrected functional are in good agreement with experiment (Si2 and Si3) and with the best theoretical estimates. Our analysis of the bonding reveals two limiting modes of bonding and classes of silicon clusters. One class of clusters is characterized by relatively large s atomic populations and a large number of weak bonds, while the other class of clusters is characterized by relatively small s atomic p...

Ion separation using a Y-junction carbon nanotube

Using molecular dynamics simulations, we show that a Y-junction carbon nanotube can be used to separate K+ and Cl− ions from a KCl solution. The Y-junction nanotube is formed by connecting two smaller carbon nanotube branches of sizes (5, 5) and (6, 6) to a larger (8, 8) carbon nanotube. While uncharged (5, 5) and (6, 6) carbon nanotubes show close to zero occupancy of K+ and Cl− ions, we show that a negatively charged (5, 5) carbon nanotube and a positively charged (6, 6) carbon nanotube can be selective to K+ and Cl− ions, respectively. By performing molecular dynamics simulations on the entire system comprising the Y-junction carbon nanotube, the KCl solution chamber, the push plate and the receiving chamber, we show that as the electrolyte moves through the (8, 8) carbon nanotube the K+ and the Cl− ions can be selectively transported through the (5, 5) and the (6, 6) carbon nanotube, respectively. The formation of ion pairs can affect the separation efficiency and we discuss the conditions under which perfect separation can be obtained.

A reactive empirical bond order (REBO) potential for hydrocarbon–oxygen interactions

The expansion of the second-generation reactive empirical bond order (REBO) potential for hydrocarbons, as parametrized by Brenner and co-workers, to include oxygen is presented. This involves the explicit inclusion of C–O, H–O, and O–O interactions to the existing C–C, C–H, and H–H interactions in the REBO potential. The details of the expansion, including all parameters, are given. The new, expanded potential is then applied to the study of the structure and chemical stability of several molecules and polymer chains, and to modelling chemical reactions among a series of molecules, within classical molecular dynamics simulations.