Local modification and characterization of the electronic structure of carbon nanotubes (original) (raw)
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In 1959, a physicist Richard Feynman visualized this theoretical capability in which one can manipulate and control individual atoms and molecules. Over a period of ten year Professor Norio Taniguchi discovered the term “Nanotechnology” with the development of the scanning tunneling microscope which helps to see each atoms. He stated that “nanotechnology mainly consists of the processing steps of the sorting out, combining, and distortion of materials by one atom or one molecule [1]. According to National Science Foundation, nanotechnology has competency to understand, utilize and control matter at the level of individual atoms and molecules [2]. Nanotechnology is the study to manage the matter on an atom and molecular scale. Generally, nanotechnology deals with structures sized between 1-100 nm and at least one dimension (1D). It also include re -construct or developing materials within that size. The material developed by this technology is lighter, powerful, faster, smaller and m...
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The present paper discusses some aspects of the research landscape related with nanotechnology, starting from Kroto’s announcement of the discovery of fullerene and Iijima’s seminal work on carbon nanotubes. In particular, we analyse the issue of competition within the nanotechnology research field, as regards both physical properties and performance of CNTs and the commitments of national states in boosting this research field. We also discuss the inherent interdisciplinary character of nanotechnological research and we offer some reflections on the looseness of disciplinary boundaries.
The discovery of fullerene in 1985, and the discovery of nanotubes in 1991 formed from combinations of other elements have attracted tremendous interest worldwide. It led to intensified research into the science of nanostructures. Low dimension systems are those in which at least one of the three dimensions exist between those characteristic of atoms/molecules and those of the bulk material, generally in the range from 1 nm to 100 nm. For e.g. quantum dots, nanowires, nanotubes etc. In these systems, surface area to volume ratio i.e. aspect ratio is high. So, the surface states come into account and become dominant. In addition to this, the dimensional constraint on the system gives rise to quantum size effects, which can significantly change the energy spectrum of electrons and their behavior. Due to which some properties of such systems become different from those of their bulk counterparts and have extraordinary electronic, optical, thermal, mechanical and chemical properties, which may result in their use in wide range of nanotechnology.
Electronic structure at carbon nanotube tips
Applied Physics A: Materials Science & Processing, 1999
We discuss a number of recent observations on carbon nanotubes tips. Evidence from scanning tunneling microscopy (STM) and spectroscopy (STS) experiments [1] indicates that the topology of the carbon bond network at the tip, and in particular the relative location of pentagons in the curved regions of the caps, is ultimately responsible for the space-resolved electronic properties of the tubes. The theoretical analysis of the local density of (electronic) states (LDOS) is shown to be a powerful tool to rationalize the experimental data. Images of carbon nanotube tips acquired in field emission microscopy (FEM) experiments [2] can be related to the STM/STS observations.
Spectroscopic properties and STM images of carbon nanotubes
Applied Physics A: Materials Science & Processing, 1999
We present a theoretical study of the role of the local environment in the electronic properties of carbon nanotubes: isolated single-and multi-wall nanotubes, nanotube-ropes, tubes supported on gold and cutted to finite length. Interaction with the substrate or with other tubes does not alter the scanning-tunneling-microscopy (STM) patterns observed for isolated tubes. A finite length nanotube shows standing-wave patterns that can be completely characterized by a set of four different threedimensional shapes. These patterns are understood in terms of a simple π-electron tight-binding (TB) model. STM-topographic images of topological defects ani (pentagon/heptagon pair) and tube-caps have also been studied. In both cases the obtained image depends on the sign of the applied voltage and it can be described in terms of the previous catalog of STM-images (interference between electronic waves scattered by the defect). We also have computed the electronic density of states for isolated tubes with different chiralities and radii confirming a correlation between the peak-structure in the DOS and the nanotube diameter, however the metallic plateau in the DOS also depends on the nanotube chirality. Furthermore, the conduction and valence band structures are not fully symmetrical to one another. This anisotropy shows up in the DOS and indicates the limitations of the π-TB model to describe spectroscopic data. In contrast to STM images, the interaction with the substrate does modify the energy levels of the nanotube. We observe opening of small pseudogaps around the Fermi level and broadening of the sharp van Hove singularities of the isolated single-walled-nanotubes that can be used to extract useful information about the tube structure and bonding. The combination of STM and spectroscopic studies opens a new technique to address the electronic and structural properties of carbon and composite nanotubes. PACS: 71.20.Tx, 81.05.Tp, 71.15.Fv Carbon is an extraordinary element that appears in a wide variety of network-like structures with new potential technological applications . Among these new forms, carbon nanotubes [5] are the most promising class of new carbon-based materials for either electronic and optic nanodevices as well as composite reinforcement materials. The quasi-one dimensional structure and crystallinity of the sample is responsible for the unique electronic and mechanical properties of carbon nanotubes. The special geometry makes the nanotubes excellent candidates for use as nanoscopic quantum wires.
New direction in nanotube science
Materials Today, 2004
demonstrated that it can form various allotropes, including graphite, diamond, and fullerene-like structures 1-3 . In particular, graphite is a semimetal and, when a single sheet of the carbon honeycomb is rolled, it is possible to generate seamless carbon cylinders (termed nanotubes), which can be either metallic or semiconducting, depending on their diameter and chirality 1-3 (see Textbox 1).
The effect of structural distortions on the electronic structure of carbon nanotubes
Chemical Physics Letters, 1998
We calculated the effects of structural distortions on the electronic structure of carbon nanotubes. The main effect of nanotube bending is an increased mixing of s and p states. This mixing leads to an enhanced density-of-states in the valence band near the Fermi energy. While in a straight tube the states accessible for electrical conduction are essentially Ž .
Effects of Finite Length on the Electronic Structure of Carbon Nanotubes
The Journal of Physical Chemistry B, 1999
The electronic structure of finite-length armchair carbon nanotubes has been studied using several ab-initio and semi-empirical quantum computational techniques. The additional confinement of the electrons along the tube axis leads to the opening of a band-gap in short armchair tubes. The value of the band-gap decreases with increasing tube length, however, the decrease is not monotonic but shows a well defined oscillation in short tubes. This oscillation can be explained in terms of periodic changes in the bonding characteristics of the HOMO and LUMO orbitals of the tubes. Finite size graphene sheets are also found to have a finite band-gap, but no clear oscillation is observed. As the length of the tube increases the density of states (DOS) spectrum evolves from that characteristic of a zero-dimensional (0-D) system to that characteristic of a delocalized one-dimensional (1-D)