Multiscale simulation of carbon nanotube devices

MRS Proceedings, 2003

A comprehensive understanding of nanotube materials requires the ability to link different carbon nanotube models, which were developed to work at different length scales. Here we describe the mapping of a molecular dynamics (MD) model for single-wall carbon nanotubes onto a wormlike chain. This mapping employs a mode analysis of the bending fluctuations of the nanotube, similar to those used in experiments [1]. The essence of this mapping is to find an appropriate bending stiffness for the wormlike cha in in order to represent the nanotube on a coarsened scale. We find that this mapping will only work well, if the wavelength probing the nanotube stiffness is sufficiently large. For single-wall (9,9) armchair nanotubes vibration modes with node distances of 3 nm underestimate the long wavelength limit of the bending constant by about 50%. This mismatch tends to increase for tubes with larger radii.

Reports on Progress in Physics, 2006

Carbon nanotubes (CNTs) are amongst the most explored one-dimensional nanostructures and have attracted tremendous interest from fundamental science and technological perspectives. Albeit topologically simple, they exhibit a rich variety of intriguing electronic properties, such as metallic and semiconducting behaviour. Furthermore, these structures are atomically precise, meaning that each carbon atom is still three-fold coordinated without any dangling bonds. CNTs have been used in many laboratories to build prototype nanodevices. These devices include metallic wires, field-effect transistors, electromechanical sensors and displays. They potentially form the basis of future all-carbon electronics. This review deals with the building blocks of understanding the device physics of CNT-based nanodevices. There are many features that make CNTs different from traditional materials, including chirality-dependent electronic properties, the one-dimensional nature of electrostatic screening and the presence of several direct bandgaps. Understanding these novel properties and their impact on devices is crucial in the development and evolution of CNT applications.

Solid-State Device …, 2005

A three-dimensional simulation approach for the investigation of Carbon NanoTube Field Effect Transistors (CNTFETs) is presented, based on the self-consistent solution of the 3D Poisson-Schrödinger equation with open boundary conditions, within the Non-Equilibrium Green's Function formalism. This approach enables accurate simulations of transport through ballistic CNTFETs for generic device structures, eliminating the use of ideal geometries, such as coaxial devices, often used in order to simplify the electrostatics of the device.

Proceedings - Seventh International Conference on High Performance Computing and Grid in Asia Pacific Region, HPCAsia 2004, 2004

Nano carbon materials as nanotubes (CNTs) and fullerenes in nanotechnology have a lot of potential for industrial applications. On the efforts of developing applications, it has been recognized that computational simulations are powerful and efficient tools to find and create new materials from nano scale. Aiming at realistic simulations for nonmaterial, we have developed a large-scale computation technique utilizing tight binding molecular dynamic method, ab initio density functional theory (DFT), GSW rearrangement and time-dependent DFT method. We have studies various physical properties of nano-carbon and applications e.g., (1) Nano-structural deformation by ion irradiation, (2) Atomic and Electronic Structures of Contact between Carbon Nanotube and Titanium, (3) Generation of new atomic structure using GSW rearrangement, (4) Composite material formed from twisted CNTs, (5) Hole-doped diamond superconductor. In addition to nano carbon as nanotube, diamond and graphite of traditional carbon material came into limelight. Along these works, we have realized that the Earth Simulator is a very powerful tool for large-scale material simulations.

Journal of Molecular Modeling, 2006

Monte Carlo simulations of the single-and double-walled carbon nanotubes (CNT) intercalated with different metals have been carried out. The interrelation between the length of a CNT, the number and type of metal atoms has also been established. This research is aimed at studying intercalated systems based on CNTs and d-metals such as Fe and Co. Factors influencing the stability of these composites have been determined theoretically by the Monte Carlo method with the Tersoff potential. The modeling of CNTs intercalated with metals by the Monte Carlo method has proved that there is a correlation between the length of a CNT and the number of endo-atoms of specific type. Thus, in the case of a metallic CNT (9,0) with length 17 bands (3.60 nm), in contrast to Co atoms, Fe atoms are extruded out of the CNT if the number of atoms in the CNT is not less than eight. Thus, this paper shows that a CNT of a certain size can be intercalated with no more than eight Fe atoms. The systems investigated are stabilized by coordination of 3d-atoms close to the CNT wall with a radius-vector of (0.18-0.20) nm. Another characteristic feature is that, within the temperature range of (400-700) K, small systems exhibit ground-state stabilization which is not characteristic of the higher ones. The behavior of Fe and Co endo-atoms between the walls of a double-walled carbon nanotube (DW CNT) is explained by a dominating van der Waals interaction between the Co atoms themselves, which is not true for the Fe atoms.

The extraordinary mechanical properties and unique electrical properties of carbon nanotubes (CNTs) have stimulated extensive research activities across the world since their discovery by Sumio Iijima of the NEC Corporation in the early 1990s. Although early research focused on growth and characterization, these interesting properties have led to an increase in the number of investigations focused on application development in the past 5 years. The breadth of applications for carbon nanotubes is indeed wide ranging: nanoelectronics, quantum wire interconnects, field emission devices, composites, chemical sensors, biosensors, detectors, etc. There are no CNT-based products currently on the market with mass market appeal, but some are in the making. In one sense, that is not surprising because time-to-market from discovery typically takes a decade or so. Given that typical time scale, most current endeavors are not even halfway down that path. The community is beginning to move beyond the wonderful properties that interested them in CNTs and are beginning to tackle real issues associated with converting a material into a device, a device into a system, and so on. At this point in the development phase of CNT-based applications, this book attempts to capture a snap shot of where we are now and what the future holds. Chapter 1 describes the structure and properties of carbon nanotubes — though well known and described in previous textbooks — both as an introduction and for the sake of completeness in a book like this one. In understanding the properties, the modeling efforts have been trailblazing and have uncovered many interesting properties, which were later verified by hard characterization experiments. For this reason, modeling and simulation are introduced early in Chapter 2. Chapter 3 is devoted to the two early techniques that produced single-walled nanotubes, namely, arc synthesis and laser ablation. Chemical vapor deposition (CVD) and related techniques (Chapter 4) emerged later as a viable alternative for patterned growth, though CVD was widely used in early fiber development efforts in the 1970s and 1980s. These chapters on growth are followed by a chapter devoted to a variety of imaging techniques and characterization (Chapter 5). Important techniques such as Raman spectroscopy are covered in this chapter. The focus on applications starts with the use of single-walled and multiwalled carbon nanotubes in scanning probe microscopy in Chapter 6. In addition to imaging metallic, semiconducting, dielectric, and biological surfaces, these probes also find applications in semiconductor metrology such as profilometry and scanning probe lithography. Chapter 7 summarizes efforts to date on making CNT-based diodes and transistors and attempts to explain the behavior of these devices based on well-known semiconductor device physics theories explained in undergraduate and graduate textbooks. It is commonly forecast that silicon CMOS device scaling based on Moore’s law may very well end in 10 or 15 years. The industry has been solving the technical problems in CMOS scaling impressively even as we embark on molecular electronics, as has been the case with the semiconductor industry in the past 3 decades. Therefore, for those pursuing alternatives such as CNT electronics and molecular electronics, the silicon electronics is a moving target and the message is clear: replacing silicon-conducting channel simply with a CNT-conducting channel in a CMOS may not be of much value — alternative architectures;different state variable (such as spin)-based systems; and coupling functions such as computing, memory, and sensing are what can set the challengers apart from the incumbent. Unfortunately, at the writing of this book, there is very little effort in any of these directions, and it is hoped that such alternatives emerge, succeed, and flourish. Field emission by carbon nanotubes is very attractive for applications such as flat panel displays, x-ray tubes, etc. The potential for commercial markets in television and computer monitors, cell phones, and other such displays is so enormous that this application has attracted not only much academic research but also substantial industrial investment. Chapter 8 discusses principles of field emission, processes to fabricate the emitters, and applications. One application in particular, making an x-ray tube, is covered in great detail from principles and fabrication to testing and characterization. With every atom residing on the surface in a single-walled carbon nanotube, a very small change in the ambient conditions can change the properties (for example, conductivity) of the nanotube. This change can be exploited in developing chemical sensors. The nanotubes are amenable to functionalization by attaching chemical groups, DNA, or proteins either on the end or sidewall. This also allows developing novel sensors using nanotubes. Chapter 9 discusses principles and development of chemical and physical sensors. Likewise, Chapter 10 describes biosensor development. The mechanical, thermal, and physical properties of carbon nanotubes have resulted in numerous studies on conducting polymer films, composites, and other structural applications. Chapter 11 captures these developments. Finally, all other applications that elude the above prime categories are summarized in Chapter 12. This is an edited volume, and various authors who practice the craft of carbon nanotubes day to day have contributed to this volume. I have made an effort to make this edited volume into a cohesive text. I hope that the readers — students and other researchers getting into this field, industry, and even the established experts — find this a valuable addition to the literature in carbon nanotubes. I would like to thank Nora Konopka of the CRC Press for her support throughout this work. Finally, this book would not have been possible without the help and skills of my assistant Amara de Keczer. I would like to thank her also for the cover design of the book.

2013

Elastic properties of single walled carbon nanotubes (SWCNTs) have been determined using molecular dynamics (MD) simulation. Mechanical properties of three types of SWCNTs viz., armchair, zigzag and chiral nanotubes have been evaluated. From computational results, it can be concluded that the Young"s moduli of SWCNTs decrease with increase in radius of SWCNT and increase with increase in CNT volume fractions (V f ) and aspect ratios (l/d).

… Journal of Electronic Engineering Research, ISSN

As the scaling of Si MOSFET approaches towards its limiting value, new alternatives are coming up to overcome these limitations. In this paper first we have reviewed carbon nanotube field effect transistor (CNTFET) and types of CNTFET. We have then studied the effect of channel length and chirality on the drain current for planer CNTFET. The I d~Vd curves for planer CNTFETs having different channel lengths and diameters are plotted. For the same, I d~Vd curves for different applied gate voltages are also plotted. We have then discussed the effect of diameter on the characteristic curves for a cylindrical CNTFET. Finally a brief comparison between the performance of Si-MOSFET and CNTFET is given.

Journal of Experimental and Theoretical Physics Letters, 2002

A microscopic model is developed for calculating electrostatic properties of nanotube devices. It is shown that the quantum-mechanical approach yields the same results as the statistical calculation in the limit of a thin tube suspended over a conducting gate at a distance exceeding the nanotube radius. A closed analytic expression is obtained for the atomistic capacitance of a straight nanotube and for a nanotube with a modest curvature. This method allows the fast and exact calculation of device parameters for the nanotube electromechanical systems and nanotube electronic devices. © 2002 MAIK "Nauka/Interperiodica".

A multiscale computational framework is presented for developing a coupled selfconsistent system of equations involving molecular mechanics at the small scale and quasicontinuum mechanics at the very large scale. The finite element method developed on the multiscale variational framework furnishes a two level statement of the problem. It provides the multiple-scale analysis capability by concurrently feeding the information at the molecular scale, formulated in terms of the nano-scale material moduli, into the quasicontinuum equations. Interatomic interactions are incorporated into the model through a set of analytical equations with internal variables that are a function of the local state of deformation [1]. Multi-body potentials of the Tersoff-Brenner type are employed to model point defects that affect atomic structure locally, and therefore generate localized displacements with localized force fields. The nano-scale material moduli are integrated into a modified form of the Geometrically Exact Shell Model [2] to model nanotubes. Representative numerical examples are shown to validate the model and demonstrate its range of applicability.