Veena Verma

Elastic moduli of a boron nitride nanotube

The elastic properties of boron nitride nanotubes have been calculated using the Tersoff–Brenner potential which is a bond order potential used successfully previously for carbon nanotubes. In the present calculation, the same form of potential is used with adjusted parameters for hexagonal boron nitride. The Youngs modulus and shear modulus for single-walled armchair and zigzag tubes of different radii have been calculated. The effects of tube diameter are investigated. The computational results show the variation of Youngs modulus and shear modulus of boron nitride nanotubes with nanotube diameter. The results have been compared with available data, experimental as well as calculated.

Elastic Moduli of Carbon Nanotubes Using Second Generation Improved Brenner Potential

Soon after the discovery of carbon nanotubes, it was realized that the theoretically predicted mechanical properties of these interesting structures could make them ideal for a wealth of technological applications. A number of computer simulation methods applied to their modeling, has led over the past decade to an improved but by no means complete understanding of the mechanics of carbon nanotubes. Tersoff potential has been widely used but it has since been modified many times. The latest is the second-generation reactive empirical bond order potential by Brenner and co workers, which is being used in this work for manipulating these tiny structures. We outline the computational approaches that have been taken. The elastic moduli of armchair, zigzag and chiral nanotubes have been computed. We generate the coordinates of carbon nanotubes of different chirality’s and size. Each and every structure thus generated is allowed to relax till we obtain minima of energy. We then apply the requisite compressions, elongations and twists to the structures and compute the elastic moduli. Young’s modulus is found to be dependent on tube radius for thinner tubes and attains a constant value of the order 1TPa. Our results of Poisson’s ratio and shear modulus are also encouraging and compare well with other theoretical and experimental work.

Elastic moduli of carbon nanohorns

Carbon nanotube is a special case of carbon nanohorns or carbon nanocones with zero apex angle. Research into carbon nanohorns started almost at the same time as the discovery of nanotubes in 1991. Most researchers focused on the investigation of nanotubes, and the exploration of nanohorns attracted little attention. To model the carbon nanohorns, we make use of a more reliable second-generation reactive empirical bond-order potential by Brenner and coworkers. We investigate the elastic moduli and conclude that these nanohorns are equally strong and require in-depth investigation. The values of Youngs and Shear moduli decrease with apex angle.

Investigation of optical properties of pristine and functionalized single-walled carbon nanotubes

Single-walled carbon nanotubes have been synthesized by chemical vapor deposition technique followed by hydroxyl addent functionalization. Crystallographic, topographic and morphological analyses of pristine and functionalized single walled carbon nanotubes (SWCNTs) have been studied via powder X-ray diffraction, field emission scanning electron microscope, high resolution transmission electron microscope and atomic force microscope respectively. UV–Vis absorption, Raman spectroscopy, thermogravemetric analysis, X-ray photo electron spectroscopy and Fourier transform infra-red spectroscopic studies have been carried out for confirmation of functionalization. Optical, quantitative and qualitative analysis of the pristine and functionalized SWCNTs have been completed via energy resolved and time resolved photoluminescence and energy dispersive X-ray spectroscopic studies respectively. Spectroscopic studies confirm the formation of good quality pristine and functionalized SWCNTs with hydroxyl addent. Recorded electron micrographs reveal the formation of fragmented functionalized SWCNTs with high aspect ratio whereas recorded diffraction patterns show the good crystallinity of synthesized nanostructures. Structural analyses of pristine and functionalized SWCNTs have been studied using Brunauer–Emmett–Teller surface area analysis, Barrett–Joyner–Halenda pore size and volume analysis technique. Improved CVD method used in present studies is an eco-friendly method, which gives good yield of high quality SWCNTs.

Microwave-assisted synthesis and characterization of silver nanowires by polyol process

Silver nanowires have been synthesized by the polyol process with ethylene glycol as a reducing agent and polyvinylpyrrolidone as a stabilizer, using microwave technique. Crystallographic, topographic, and morphological characterizations of the synthesized nanostructures have been studied via powder X-ray diffraction and electron microscopy (Field Emission Scanning Electron Microscope) and Transmission Electron Microscope, respectively. Fourier Transform-Infrared Spectroscopy, UV–Vis absorption spectroscopy, Raman spectroscopy, Thermogravometric analysis, and X-ray photoelectron spectroscopy have been carried out for the detailed quantitative and qualitative analyses. Optical characterizations of the synthesized silver nanowires have been concluded via energy-resolved and time-resolved photoluminescence and energy dispersive X-ray spectroscopic studies, respectively. Spectroscopic studies confirm the formation of good-quality silver nanowires. The X-ray photoelectron spectroscopy investigation and Raman spectra further show that the PVP molecules are adsorbed on the surface of Ag nanowires through Ag: O coordination. A possible growth mechanism of the Ag nanowires has been proposed. It is implied that the PVP molecules are used as both a protecting agent and a structure-directing agent for the growth of Ag nanowires. These studies confirm the formation of high-quality silver nanowires. Topographic and morphological studies confirm that average grain size of silver nanowires is in the nanometer range.

Elastic moduli of boron nitride, aluminium nitride and gallium nitride nanotubes using second generation reactive empirical bond order potential

Purpose – The purpose of this paper is to study elastic properties of III-V nitride nanotubes (NNTs) using second generation (REBO) potential. Design/methodology/approach – In the present research paper elastic properties of BN, AlN and GaN nanotubes have been investigated, using the second generation REBO potential by Brenner and co-workers, which is a bond order potential earlier used for carbon nanostructures successfully. In the present calculation, the same form of potential is used with adjusted parameters for h-BN, h-AlN and h-GaN. In all these cases the authors have considered graphite like network and strongly polar nature of these atoms so electrostatic forces are expected to play an important role in determining elastic properties of these nanotubes. The authors generate the coordinates of nanotubes of different chirality’s and size. Each and every structure thus generated is allowed to relax till the authors obtain minima of energy. The authors then apply the requisite compressions, elongation...

Some Mechanical Properties of Carbon NanotubesHeterojunctions

Some Mechanical Properties of Carbon Nanotubes Heterojunctions In the present research work, the structure of linear heterojunctions between two CNTs of different chirality’s, but similar radii, joined together through an interface that require more than one pentagon-heptagon defects have been studied. The elastic properties of carbon nanotube heterojunctions are investigated using secondgeneration improved reactive empirical bond order potential by Brenner and co-workers. In this study, the coordinates of carbon nanotube heterojunctions are generated. Each and every structure thus generated is allowed to relax till a minimum of energy is obtained. The requisite compressions, elongations and twists to the structures are applied and thus computed elastic moduli. Young’s Modulus increases with radius for small radii and attains a constant value of the order 1TPa. Poisson’s ratio and shear modulus have also been computed.

Structure and Elastic Modulii Of Silicon Nanotubes

Based on the assumption that sp3 hybridization is more stable in bulk silicon, this study is a step forward in understanding the structures and mechanical properties of silicon nanotubes (SiNT). Using the well tested form of Tersoff potential we have calculated cohesive energy and other parameters for SiNT of various diameters and chiralities. Using this potential, the results obtained for bulk silicon are satisfactory, so we expect that the same potential would work well with SiNT as well. We calculated Young’ modulus and shear modulus for SiNT. Young’s modulus lies in the range of 100- 200 GPa which is about 10-20 times lower than CNT and shear modulus lies between 200-300 GPa. This work shall motivate further theoretical and experimental work in the field of nanostructures.

Structure and Strength of Carbon Nanohorns

Research into Carbon Nano Horns or Cones (CNCs) started almost at the same time as the discovery of CNTs in 1991. The official report of the discovery of isolated Nano Cones was made in 1993, when Ge and Sattler from the University of Hawaii reported their observations of Carbon Cones mixed together with tubules on a flat graphite surface. The products were generated by quenching hot carbon vapor on th e substrate. Ge and Sattler also predicted that five apex angles, 19.2°, 38.9°, 60°, 86.6°, and 123.6°, could be used to distinguish CNCs. However, only the angle of 19.2° was found in the opening angles of their samples. The observed cones were up to 24 nm in length and 8 nm in base diameter. At that time, most of researchers focused on the investigation of CNTs, and the exploration of horns attracted little attention. Present paper converse about the structure and elastic moduli of these less explored nanostructures. The second‐generation reactive bond order potential by Brenner and coworkers has been use...

Stability of Thin Gold Nano Wires

Various gold nanowires with very small cross-sections (few atoms) have been studied using the Gupta potential. Gold nanowire icosa structure is found to be most stable among structures studied. The values of cohesive energy, Young’s modulus and shear modulus have been computed and all the values (except poisson ratio) are more than that of bulk gold. Another striking observation about gold nanostructures is that the Young’s modulus increases with tube radius whereas shear modulus decreases.