Showing papers by "Rodney S. Ruoff published in 2003"

Mechanics of a Carbon Nanocoil

Abstract: An individual carbon nanocoil was clamped between two AFM cantilevers and loaded in tension to a maximum relative elongation of ∼42%. The deformation of the nanocoil agrees well with an analytical ...

Direct Observation of Polymer Sheathing in Carbon Nanotube-Polycarbonate Composites

Abstract: A series of observations of polymer sheathing in multiwalled carbon nanotube (MWCNT)−polycarbonate composites are presented. This sheathing was observed in images of the composite fracture surface and is consistent with diameter distributions of the as-received and embedded MWCNTs. A novel nanomanipulation experiment, where the sheathing balls up when contacted by an AFM tip, confirms this phenomenon. This sheathing layer is direct evidence of substantial MWCNT−polymer interaction and will influence the mechanical properties of MWCNT-polymer composites.

Resonance vibration of amorphous SiO2 nanowires driven by mechanical or electrical field excitation

Abstract: In this work, we have used the mechanical resonance method to determine the bending modulus of amorphous SiO2 nanowires and to study an electron charge trapping effect that occurs in these nanowires. For uniform amorphous nanowires having diameter ∼100 nm and length over 10 μm, the fit modulus values cluster near 47 GPa; this value is lower than the commonly accepted value of ∼72 GPa for fused silicon oxide (glass) fibers. For some SiO2 nanowires, we observed up to three closely spaced resonances that are a result of the nanowire anisotropy. We have compared the resonance vibration of nanowires driven by mechanical and also ac electrical field loading. All of the measurements were done inside the chamber of a scanning electron microscope where the nanowires were under bombardment of a flux of ∼3 keV energy electrons. By watching the interaction between the ac electrical field and exposed nanowire when driven at resonance frequency, we have observed significant charge trapping in the nanowires. The combina...

Dynamical-mechanical and thermal analysis of carbon nanotube-methyl-ethyl methacrylate nanocomposites

Abstract: Composites were prepared by using carbon nanotubes (CNTs) and methyl-ethyl methacrylate copolymer, modified with nonionic surfactant to improve the carbon nanotube dispersion and workability. The thermal results show that the polymer glass transition temperature increases up to 10°C and that only 1wt% CNT content improves the mechanical response by more than 200%, substantially above other reports where large quantities of CNTs were used.

An improved method to strip aluminum from porous anodic alumina films

Abstract: Aluminas having porous structure and fabricated by anodization of aluminum have been studied for more than 40 years.1 In the past decade there has been a particular focus on the fabrication of porous anodic alumina (PAA) films with an ordered array of holes.2-7 The pore diameter distribution in such films is a function of the film preparation and is typically close to monodisperse. PAA films with pore diameter ranging from 4 to 250 nm, density as high as 1015 pores/m2, and film thickness varying from 0.1 to 300 μm have been realized.4-7 The applications of PAA films that have been explored include template growth of nanotubes and nanowires;8-12 creation of nanoholes, nanodots, and nanopillars;13-16 and fabrication of micro-electromechanical systems (MEMS) devices.17,18 A two-step anodization is used to fabricate the PAA film.2,3 During the fabrication of through-hole PAA film (Figure 1), use of a protective coating is required.3 This coating protects the pore morphology so that it will not be altered during removal of the underlying aluminum substrate and the subsequent process of opening of the nanopores. The protective coating also makes the fragile PAA film more flexible so that it is easier to handle. The requirements for an ideal protective coating are (1) it remains intact during the process of removing the aluminum substrate and during the pore-opening process, (2) there is no residue left on the PAA film following its removal, (3) it is easy to handle, and (4) it is inexpensive. To our knowledge, little information has been provided on selection of a suitable protective coating.3-5 Masuda et al. reported using a protective layer made of a mixture of nitrocellulose and polyester resin in ethyl acetate, butyl acetate, and heptane.3 The preparation of this protective coating was nontrivial. Li et al. mentioned using a protective layer during fabrication. However, no detailed information was given.4,5 In this paper, we report the use of nail polish as the protective layer during the fabrication of PAA films. The ingredients of nail polish are similar to those of the protective layer Masuda used.5 We find nail polish fulfills the suggested requirements mentioned above: it remains intact during processing to complete the nanopore film, the film is residue-free following its removal, it is easy to handle, and it is inexpensive. The as-fabricated PAA film has a mean pore diameter of∼60 nm, an interpore distance of∼100 nm, and a film thickness of∼100 μm. The evolution of surface morphology (both top and bottom surfaces) of the PAA film was characterized by both atomic force microscopy (AFM) and scanning electron microscopy (SEM).

Would Diamond Nanorods Be Stronger than Fullerene Nanotubes

Abstract: On the basis of literature ab initio data, we show that diamond nanorods would have a brittle fracture force and a zero strain stiffness that exceeds carbon nanotubes for radii greater than about 1-3 nm, depending on the orientation of the diamond nanorod. The energetic stability of diamond nanorods is predicted by molecular modeling to be comparable to single-walled carbon nanotubes. It is concluded that diamond nanorods represent an important and viable target structure for synthesis. With its exceedingly high bulk modulus and hardness, diamond has historically been considered the strongest material. Recently, however, it has been claimed based on both theory and experiment that carbon nanotubes are both stiffer and stronger along their axis than diamond. A problem with this claim is that it is difficult to make a fair comparison between these two representatives from the macro- and nanoscales unless some additional assumptions about their structure are made, for example an effective “thickness” of a sheet of carbon atoms comprising a nanotube. In this paper the mechanical properties of single-walled nanotubes (SWNTs) and multiwalled nanotubes (MWNTs) are compared to the predicted properties of an equivalent nanoscopic-scale diamond structure, namely a diamond nanorod (DNR). Our general analysis suggests that while a SWNT will have a higher strength-to-weight ratio, above a critical radius between about 1 and 3 nm (depending on the DNR structure) the force needed for brittle fracture of a DNR exceeds that of a SWNT. This higher fracture force, which at the nanoscopic scale is a less ambiguous property than fracture stress, results from the larger load-bearing crosssectional area of DNRs compared to SWNTs at the same diameter. Similarly, the calculations show that the zero strain stiffness of DNRs will exceed that of SWNTs for radii greater than about 1 nm. Experimental loading of SWNTs in ropes has yielded estimates for the tensile Young’s modulus that range from 320 GPa to 1.47 TPa, 1 and breaking strengths that range from 13 to 52 GPa (a strain of up to almost 6%), 1 values that

Bone-Shaped Nanomaterials for Nanocomposite Applications

Abstract: A novel template synthesis of bone-shaped (dumbbell-shaped, dogbone-shaped) nanomaterials is demonstrated. Porous anodic alumina (PAA) templates with uniform nanochannels were fabricated using a four-step anodization process and used to form bone-shaped carbon nanostructures with stem and end diameters and lengths of 40 nm, 70 nm, and 5 Im, respectively. These nanomaterials, which we refer to as bone-shaped T-CNTs (templated carbon nanotubes), have potential application in nanocomposites, where improved strength and toughness through mechanical interlocking is anticipated.

Atomic Force Microscopy Study of Clay Nanoplatelets and Their Impurities

Abstract: The results of an in-depth study of 1 nm thick individual clay sheets by atomic force microscopy (AFM) are presented. Several techniques have been employed, including lateral force microscopy (LFM) and force modulation microscopy (FMM). The individual clay sheets, also referred to as clay nanoplatelets in the literature, were found to be extremely compliant and strongly adhered to a variety of substrates. In all cases, these nanoplatelets were accompanied by mobile impurities that could not be separated from the nanoplatelets. A detailed examination of these impurities using AFM suggests that they are comprised of low molecular weight silicates as well as the intercalating salt used to process the clay. An understanding of the nature and chemistry of these impurities will be necessary as models of these clays are developed for various applications, such as reinforcement in composite materials or elements for molecular electronics. Further, these clay nanoplatelets and their impurities present a novel two-...

Effect of interlayer potential on mechanical deformation of multiwalled carbon nanotubes.

Abstract: A study on the modeling and simulation of interlayer interaction in the multiwalled carbon nanotube (MWCNT) system is presented. We use an interlayer Morse potential previously developed from a local density approximation (LDA) treatment of a bilayer of graphite. We have fit this Morse potential to experimental high-pressure compressibility data for graphite and to a more extensive LDA equation of state (EOS) for graphite, and excellent agreement is observed. We employ this potential to treat the interlayer mechanics of MWCNTs, where the MWCNT is so highly deformed that interlayer separation well below approximately 0.34 nm, such as down to approximately 0.26 nm, is occurring. This, to our knowledge, is the first treatment that attempts to account for deformations that have the layers approaching each other at very high local (interlayer) stress levels. Since evaluating the interlayer potential for a large MWCNT system is computationally intensive, a continuum simulation approach is proposed that saves on computational time and thus on cost. Comparisons with experimental results of buckled and highly kinked MWCNTs are presented.

Boric acid nanotubes, nanotips, nanorods, microtubes, and microtips

Abstract: Thin films containing boron, carbon, and oxygen were synthesized by plasma-enhanced chemical vapor deposition (PE-CVD). When the thin films were exposed to humid atmosphere, nano- or micro-scale boric acid structures were observed to grow spontaneously. Depending on the relative humidity, temperature, and exposure time to the humid atmosphere, these boric acid structures were either nanotubes, nanotips, nanorods, microtubes, or microtips. X-ray photoelectron spectroscopy (XPS) studies on the thin film surface suggested that the thin films contained B2O3, BCO2, and C−C clusters. The relative amounts of boron, carbon, and oxygen in the thin films were about 41.3, 14, and 43.9% respectively. Secondary ion mass spectrometry (SIMS) results indicated that the elemental distribution of boron, carbon, and oxygen in the thin films was rather homogeneous. X-ray diffraction (XRD) was used to study the time evolution of these boric acid structures at 23 °C and 45 ± 3% relative humidity. Scanning electron microscopy (...

Conduction in Carbon Nanotubes Through Metastable Resonant States

Abstract: We report here on electrical measurements on individual multi-walled carbon nanotubes (MWNTs) that show that the presence or movement of impurities or defects in the carbon nanotube can radically change its low temperature transport characteristics. The low temperature conductance can either decrease monotonically with decreasing temperature, or show a sudden 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 corresponding to direct transmission through the nanotube and resonant transmission through a discrete electron state, the so-called Fano resonance.

Nanofluidic Channel Fabrication and Characterization by Micromachining

Abstract: The well-established microfabrication techniques of complementary metallic oxide silicon (CMOS) selective oxidation and wafer-wafer fusion bonding were used to fabricate sub-micrometer silicon fluidic channels as small as 30 nm between extremely thin SiO2 top and bottom layers of 30 nm thicknesses. Trenches a few tens of nanometer deep were patterned in 10-cm diameter Si wafers by selective oxidation and their depth measured by atomic force microscopy (AFM); the AFM measured depths showed that the trench depth could be controlled to nanometer resolution. The resolution of the photolithography employed determined the trench width resolution. Nanochannels were formed with direct wafer-wafer fusion bonding. Channels of 30-nm depth or greater between the bonded wafer pair were nondestructively detected by a simple infrared (IR) image system; channels less than this depth collapsed for the overall channel geometry employed. Thus the nanofluidic structures survived the pressure and high temperature anneal of wafer bonding. Experimental results agree well with a theoretical prediction for which depths nanochannels would collapse.Copyright © 2003 by ASME

Carbon Nanotubes: Objects of Well-defined Geometry for New Studies in Nanotribology

Abstract: Carbon nanotubes, including both multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs), are fascinating low dimensional systems for studies in electronics and mechanics Their applications in nano-electronic or nano-mechanical systems have been suggested For example, ‘on-nanotube’ devices such as diode, bucky shuttle, or multiple terminal logic circuits have been treated by theory for electronic systems1, 2, 3, 4, and the use of nanotubes as nano-pistons, nanosyringes, and rotors for mechanical systems have also been modeled5, 6, 7

Electrical and Mechanical Properties of Boron and Metal-boride Nanowires, and Devices Built from Them

Abstract: Much progress has been made in the last few years on nanoelectronic devices constructed from nanotubes, nanowires, or their crossed junctions, including field-effect transistors, singleelectron transistors, p-n diodes, and Schottky-barrier rectifiers. Such devices may serve as building blocks for future memory devices and logic circuits, and will require both conducting interconnects and semiconducting components. Nanodevice construction using C nanotubes has received considerable attention, although the electrical properties of C nanotubes depend markedly upon diameter and chirality (wall orientation). Here we investigate the synthesis, electrical-transport behavior and mechanical properties of boron nanowires, which we believe should have mechanical strengths, chemical and thermal stabilities, and electrical conductivities that may surpass those of C nanotubes and other related families of 1D nanostructures. In our studies to date, we find that Ni and Ti electrodes make ohmic and Schottky-barrier contacts to the B nanowires, respectively. Gate-dependent measurements establish them to be p-type semiconductors. We have applied the metal-specific contact behavior to fabricate nanowire rectifying devices. We have also measured the bending moduli of boron nanowires in electrically and mechanically induced resonance experiments. Synthetic methods under development include catalyzed CVD and plasma-based techniques. These fundamental studies, which will inform subsequent device construction, are summarized below. A high resistance gap around 0 V was apparent in boron nanowire devices fabricated with Ti electrodes, as is typical for nanowire devices with Schottky barrier contacts on both sides. However, the I ‐ V response of boron-nanowire devices with Ni electrodes (top inset of Fig. 1a) did not show such a gap (Fig 1a). The I ‐ V measurements made on three segments of differing length for the device in Fig 1a (top inset) showed the resistance to be proportional to the length of the nanowire segment (Fig. 1c), which implied that the resistance was dominated by the nanowire itself rather than the contact. These results establish that Ni forms ohmic contact with the B nanowires. The conductivity of the nanowire in this device determined to be 10 -2 (! cm) -1 from the slope of the fitted line in the R vs. L plot (Fig 1c inset). This value is higher than that of pure bulk boron (σ ≈10 -6 (_ cm) -1 for the _-rhombohedral structure). 2 We tentatively attribute the

Field emission from graphite platelet nanofibers (GPNs)

Abstract: In this paper, the fibers were catalytically grown using a chemical vapor deposition method. The graphite nanofiber powder was then ultrasonically dispersed in ethanol. One drop of suspension was put onto a 20-nm thick gold layer deposited on a 1 cm /spl times/ 1 cm silicon substrate and spun to obtain a uniform coating of nanofibers. The fiber density was obtained from SEM images. There was plenty of room between the fibers so that electrostatic screening effects, which occur when field emitter tips or carbon nanotubes are stacked too close together, should not play a significant role in a field emitter testing.