Showing papers by "Rodney S. Ruoff published in 2004"
TL;DR: In this paper, the role of vacancy defects in the fracture of carbon nanotubes under axial tension was investigated using density functional theory and semi-empirical methods, and molecular mechanics (MM) calculations with a Tersoff-Brenner potential.
370 citations
TL;DR: In this article, a new energy-based theory, quantized fracture mechanics (QFM), is presented that modifies continuum-based fracture mechanics; stress-and strain-based QFM analogs are also proposed.
Abstract: A new energy-based theory, quantized fracture mechanics (QFM), is presented that modifies continuum-based fracture mechanics; stress- and strain-based QFM analogs are also proposed. The differentials in Griffith's criterion are substituted with finite differences; the implications are remarkable. Fracture of tiny systems with a given geometry and type of loading occurs at ‘quantized’ stresses that are well predicted by QFM: strengths predicted by QFM are compared with experimental results on carbon nanotubes, β-SiC nanorods, α-Si3N4 whiskers, and polysilicon thin films; and also with molecular mechanics/dynamics simulation of fracture of carbon nanotubes and graphene with cracks and holes, and statistical mechanics-based simulations on fracture of two-dimensional spring networks. QFM is self-consistent, agreeing to first-order with linear elastic fracture mechanics (LEFM), and to second-order with non-linear fracture mechanics (NLFM). For vanishing crack length QFM predicts a finite ideal strength in agre...
296 citations
TL;DR: In this paper, the growth of boron nanoribbons was observed by pyrolysis of diborane at 630−750 °C and ∼200 mTorr in a quartz tube furnace.
Abstract: Catalyst-free growth of boron nanoribbons was observed by pyrolysis of diborane at 630−750 °C and ∼200 mTorr in a quartz tube furnace. Nanodiffraction analysis indicates the nanoribbons are single crystal α-tetragonal boron. TEM images show the nanoribbon is covered by a 1−2 nm thick amorphous layer. Elemental analysis by EELS, EDX, and XPS shows the nanoribbons consist of boron with small amounts of oxygen and carbon. Infrared and Raman spectra are also reported.
196 citations
TL;DR: Repeated trials demonstrated accurate, discrete, and aligned deposition at room temperature with 90% yield over an electrode array having 100 gaps.
Abstract: This paper presents a large-scale assembly method to deposit discrete multiwalled carbon nanotubes (MWCNTs) across gaps present in an electrode array. A parametric study showed that MWCNTs dispersed in a liquid could be deposited to individually span gaps by combining an alternating current (ac) and a direct current (dc) electric field in a given ratio; it was shown that the ac field (5 MHz) serves to selectively attract and the dc field to guide individual deposition. Repeated trials demonstrated accurate, discrete, and aligned deposition at room temperature with 90% yield over an electrode array having 100 gaps.
156 citations
TL;DR: In this article, double-walled carbon nanotubes (DWCNTs) were used as rotational bearings and the interlayer energy surface of the bearings was shown to be nearly flat.
Abstract: Atomistic simulations of double-walled carbon nanotubes (DWCNTs) as rotational bearings were performed. Molecular mechanics (MM) calculations show that the interlayer energy surface of the bearings is nearly flat. Thermal effects on the bearings were studied with molecular dynamics (MD) simulations at finite temperature. These simulations show that the interlayer corrugation against rotation, and hence the interlayer friction coefficient, is extremely small, suggesting the possible application of DWCNTs as wearless bearings. Extreme operational conditions of the bearings for which the bearings disintegrate are also reported.
132 citations
TL;DR: In this article, a single-crystal calcium hexaboride (CaB6) nanowires were generated by pyrolysis of diborane (B2H6) over calcium oxide (CaO) powders at 860−900 °C and ∼155 mTorr in a quartz tube furnace.
Abstract: Catalyst-assisted growth of single-crystal calcium hexaboride (CaB6) nanowires was achieved by pyrolysis of diborane (B2H6) over calcium oxide (CaO) powders at 860−900 °C and ∼155 mTorr in a quartz tube furnace. TEM electron diffraction and Raman spectroscopy indicate that the nanowires are single-crystal CaB6 and have a preferred [001] growth direction. Analysis of TEM/EDX/EELS data proves the nanowires consist of CaB6 cores and thin (1−2 nm) amorphous oxide shell material. The CaB6 nanowires have diameters of ∼15−40 nm, and lengths of ∼1−10 μm.
67 citations
TL;DR: In this article, a microelectromechanical system (MEMS) stress-strain device for testing the mechanical properties of nanomaterials is presented, with a working range from tens of nanometers up to 10 micrometers.
Abstract: The design, fabrication, and characterization of a microelectromechanical systems (MEMS) stress–strain device for testing the mechanical properties of nanomaterials is presented. Thermal actuation, with integrated motion amplification structures, was used to both minimize the operating temperature of the device as well as realize fine motion control over large displacements. The device has a working range from tens of nanometers up to 10 micrometers. Displacements as small as 30 nm per 10 mA input dc current increments were obtained for the first time with thermal actuators micromachined by deep reactive ion etching (DRIE). The height difference (offset) between the moving and fixed platforms was less than 40 nm over the entire working range of the device for the input power range studied. A 0.27 μN force is predicted for an actuator displacement of 30 nm based on mechanical models of the device; the calculated force increases linearly up to 88 μN for the maximum 9.7 μm displacement. The operating charact...
48 citations
TL;DR: In this article, the authors measured the mechanical resonance of microscale quartz fibers to qualify the method of obtaining the Young's modulus of nanowires from their resonance frequency and geometry, and established a model to discuss the boundary condition effect on the resonance frequency.
Abstract: We have measured the mechanical resonance of microscale quartz fibers to qualify the method of obtaining the Young’s modulus of nanowires from their resonance frequency and geometry. An equation for a circular beam with a linearly varying cross-section is derived and used to calculate the resonance frequency shift. We have established a model to discuss the boundary condition effect on the resonance frequency. The Young’s modulus of the quartz fibers has been determined by measuring the resonance frequency, and the geometry, and by applying the model that treats the influence of the type of clamp. The mean value from measurements of the fundamental resonance on 14 different microfibers is 70±6 GPa. This mean value is close to 72 GPa, the Young’s modulus of bulk fused quartz. Four resonance modes were observed in high vacuum and air. The mechanical resonance in high vacuum is linear at the fundamental vibration mode, and nonlinear for higher modes.
44 citations
TL;DR: In this article, the presence or movement of impurities or defects in the carbon nan- otube can radically change its low-temperature transport characteristics, such that the low temperature conductance can either decrease monotonically with decreasing temperature, or show a sud- den increase at very low temperatures, sometimes in the same sample at different times.
Abstract: We report here on electrical measurements on individual multi-walled carbon nanotubes that show that the presence or movement of impurities or defects in the carbon nan- otube can radically change its low-temperature transport characteristics. The low-temperature conductance can either decrease monotonically with decreasing temperature, or show a sud- den increase at very low temperatures, sometimes in the same sample at different times. This unusual behavior of the temperature dependence of the conductance is correlated with large variations in the differential conductance as a function of the dc voltage across the wire. The effect is well described as arising from quantum interference of conduction channels correspond- ing to direct transmission through the nanotube and resonant transmission through a discrete electron state, the so-called Fano resonance.
18 citations
TL;DR: A series of scanning electron microscope images was acquired at different view angles, thus providing a set of image pairs that were used to generate three‐dimensional representations using a matlab program and an error analysis as a function of the view angle between the two images is presented and discussed.
Abstract: Nanostructures, such as nanowires, nanotubes and nanocoils, can be described in many cases as quasi one-dimensional curved objects projecting in three-dimensional space. A parallax method to construct the correct three-dimensional geometry of such one-dimensional nanostructures is presented. A series of scanning electron microscope images was acquired at different view angles, thus providing a set of image pairs that were used to generate three-dimensional representations using a matlab program. An error analysis as a function of the view angle between the two images is presented and discussed. As an example application, the importance of knowing the true three-dimensional shape of boron nanowires is demonstrated; without the nanowire's correct length and diameter, mechanical resonance data cannot provide an accurate estimate of Young's modulus.
15 citations
01 Jan 2004
TL;DR: In this paper, a hybrid nano-electromechanical system for study of the mechanics of nanostructures is presented, which has a testing platform based on a deep reactive ion-etched high aspect ratio MEMS device.
Abstract: We present a hybrid nano-electromechanical system for study of the mechanics of nanostructures. The system has a testing platform based on a deep reactive ion-etched high aspect ratio MEMS device. A new approach has been developed with top-down manufacturing of the micro-device and bottom-up post-fabrication assembly of samples (nanostructures) to be tested. A process that minimizes chemical or physical damage of the sample is used to integrate suspended nanowires/nanotubes into the system. The system provides nanoscale resolution of displacement and force. The device is used in an SEM and is being tested for in situ experiments on various nanowires or nanotubes.Copyright © 2004 by ASME
05 Jan 2004
TL;DR: In this article, a simple and inexpensive device to allow the rapid insertion and withdrawal of samples from a tube furnace is described, which allows the study of the short time kinetics of chemical vapor deposition processes and may allow for the growth of structures that could not be achieved using the conventional sample insertion and extraction procedure.
Abstract: In this article, a simple and inexpensive device to allow the rapid insertion and withdrawal of samples from a tube furnace is described. The device operates in an atmosphere that is separate from ambient. This device shortens sample insertion and extraction times, which allows the study of the short time kinetics of chemical vapor deposition processes, and may allow for the growth of structures that could not be achieved using the conventional sample insertion and extraction procedure. The use of magnets to provide actuation through the walls of a quartz tube furnace is entirely general to any procedure using a tube furnace.
TL;DR: In this article, a parallax method to reconstruct the correct 3D geometry of 1D nanostructures is presented, where a series of images were acquired at different view angles, and from those image pairs, 3D representations were constructed using a MATLAB program.
Abstract: Nanostructures, such as nanowires, nanotubes, and nanocoils, can be described in many cases as quasi one-dimensional (1D) curved objects projecting in three-dimensional (3D) space. A parallax method to reconstruct the correct three-dimensional geometry of such 1D nanostructures is presented. A series of images were acquired at different view angles, and from those image pairs, 3D representations were constructed using a MATLAB program. Error analysis as a function of view-angle between the two images is discussed. As an example application, we demonstrate the importance of knowing the true 3D shape of Boron nanowires. Without precise knowledge of the nanowire's dimensions, diameter and length, mechanical resonance data cannot be properly fit to obtain an accurate estimate of the Young's modulus.
01 Jan 2004
TL;DR: In this article, the composite electric-field-guided assembly (CEGA) method was used for assembly of carbon nanotubes (CNTs) with an accuracy approaching tens of nanometers.
Abstract: Recently there has been significant progress in assembling an array of individual carbon nanotubes (CNTs) on microfabricated electrodes using the Composite Electric-field Guided Assembly (CEGA) method. This technology allows for integrating individual nano components with micro/nano systems, and should find application in areas such as sensors and NEMS devices. For realizing this as a viable technology, it is crucial to understand the electric-field-driven flow around the nanostructures being deposited. We previously discovered that the flow patterns that are present can lead to deposition of a periodic array CNTs. Here, we present recent experimental observations and the results of modeling/simulation on the electric-field-driven flow around CNTs. The results suggest that this method of assembling nanostructures be used for integration with an accuracy approaching tens of nanometers.Copyright © 2004 by ASME
01 Jan 2004
TL;DR: In this paper, a new energy-based theory, Quantized Fracture Mechanics (QFM), is presented that modifies continuum-based fracture mechanics, and the differentials in Griffith's criterion are substituted with finite differences; the implications are remarkable.
Abstract: A new energy-based theory, Quantized Fracture Mechanics (QFM), is presented that modifies continuum-based fracture mechanics. The differentials in Griffith’s criterion are substituted with finite differences; the implications are remarkable. Fracture of tiny systems with a given geometry and type of loading occurs at quantized stresses that are well predicted by QFM. QFM is self-consistent, agreeing to first-order with linear elastic fracture mechanics (LEFM), and to second-order with non-linear fracture mechanics (NLFM): the equation of the R-curve is consequently derived. For vanishing crack length QFM predicts a finite ideal strength in agreement with Orowan’s prediction. The different fracture Modes (opening I, sliding II and tearing III), and the stability of the fracture propagations, are treated in a simple way. In contrast to LEFM, QFM has no restrictions on treating defect size and shape. As an example, strengths predicted by QFM are compared with experimental and numerical results on carbon nanotubes containing defects of different size and shape.