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Living systems employ cilia to control and to sense the flow of fluids for many purposes, such as pumping, locomotion, feeding, and tissue morphogenesis. Beyond their use in biology, functional arrays of artificial cilia have been envisaged as a potential biomimetic strategy for inducing fluid flow and mixing in lab-on-a-chip devices. Here we report on fluid transport produced by magnetically actuated arrays of biomimetic cilia whose size approaches that of their biological counterparts, a scale at which advection and diffusion compete to determine mass transport. Our biomimetic cilia recreate the beat shape of embryonic nodal cilia, simultaneously generating two sharply segregated regimes of fluid flow: Above the cilia tips their motion causes directed, long-range fluid transport, whereas below the tips we show that the cilia beat generates an enhanced diffusivity capable of producing increased mixing rates. These two distinct types of flow occur simultaneously and are separated in space by less than 5 μm, approximately 20% of the biomimetic cilium length. While this suggests that our system may have applications as a versatile microfluidics device, we also focus on the biological implications of our findings. Our statistical analysis of particle transport identifying an enhanced diffusion regime provides novel evidence for the existence of mixing in ciliated systems, and we demonstrate that the directed transport regime is Poiseuille–Couette flow, the first analytical model consistent with biological measurements of fluid flow in the embryonic node.

Electrical devices based on suspended multi-wall carbon nanotubes were constructed and studied. The chiral structure of each shell in a particular nanotube was determined using nanobeam electron diffraction in a transmission electron microscope. The transport properties of the carbon nanotube were also measured. The nanotube device length was short enough that the transport was nearly ballistic, and multiple subbands contributed to the conductance. Thermal excitation of carriers significantly affected nanotube resistance at room temperature.

Nanoscale electronics seeks to decrease the critical dimension of devices in order to improve performance while reducing power consumption. Single-walled carbon nanotubes fit well with this strategy because, in addition to their molecular size, they demonstrate a number of unique electronic, mechanical and electromechanical properties. In particular, theory1,2,3,4,5,6,7,8 predicts that strain can have a large effect on the band structure of a nanotube, which, in turn, has an influence on its electron transport properties. This has been demonstrated in experiments where axial strain was applied by a scanning probe9,10,11,12. Theory also predicts that torsional strain can influence transport properties, which was observed recently in multiwalled nanotubes13. Here we present the first experimental evidence of an electromechanical effect from torsional strain in single-walled nanotubes, and also the first measurements of piezoresistive response in a self-contained nanotube-based nanoelectromechanical structure.

We present a procedure for producing high-aspect-ratio cantilevered micro- and nanorod arrays of a PDMS-ferrofluid composite material. The rods have been produced with diameters ranging from 200 nm to 1 mum and aspect ratios as high as 125. We demonstrate actuation of these superparamagnetic rod arrays with an externally applied magnetic field from a permanent magnet and compare this actuation with a theoretical energy-minimization model. The structures produced by these methods may be useful in microfluidics, photonic, and sensing applications.

We present a design methodology for a nanoscale self-assembling fabrication process that uses the specificity of DNA hybridization to guide the formation of electrical circuitry. Custom design software allows us to specify the function of a structure in a way similar to that used by VLSI circuit designers. In an analogous manner to generating masks for a photolithographic process, our software generates an assembly procedure including DNA sequence allocation. We have found that the number of unique DNA sequences needed to assemble a structure scales with its surface area. Using a simple face-serial assembly order we can specify an unambiguous assembly sequence for a structure of any size with only 15 unique DNA sequences.

Molecular motors, as autonomous transporting and sensing systems, may play an important role in nanoscale technologies such as analytical and electromechanical systems. It is important to establish control of the patterning of deposition and to control the molecular motor-induced transport. Application of electrical signals to control motor motility is necessary for their integration with silicon electronics. We have applied dielectrophoretic (DEP) forces with quadrupole electrodes to pattern actin on a substrate. In addition, DEP torque(s) directed the motion of actin on myosin substrates along electric field lines. These are our first steps toward building an on-chip, integrated, biomotor analytical system.

We present here the use of amino-terminated DNA strands in functionalizing the open ends and defect sites of oxidatively prepared single-walled carbon nanotubes, an important first step in realizing a DNA-guided self-assembly process for carbon nanotubes.

We report the discovery of a new and unexpected kind of metal in two dimensions (2D), which exists in the presence of scattering by local magnetic moments. The experiment was carried out on a 2D electron system in silicon, where the local magnetic moments have been induced by disorder and their number was varied using substrate bias ( V sub ). In the new metal, the conductivity decreases as σ ( n s , T )= σ ( n s , T =0)+ A ( n s ) T 2 ( n s – carrier density) to a non-zero value as temperature T →0. In three dimensions, this T 2 dependence is well known, and results from Kondo scattering by local magnetic moments. In 2D, however, the existence of a metal with d σ /d T >0 is very surprising. As the number of local moments is reduced, the range of temperatures [ T T m ( V sub )] where they dominate transport becomes smaller. For T > T m , we observe the usual 2D metallic behavior with d σ /d T

Metallic properties in two-dimensional electron systems appear in different trends to asymptotes of non-zero conductivity σ at zero temperature T. The spin interaction plays a crucial role in the metallic behavior, and interactions with localized moments lead to a Kondo effect, but they do not destroy the metal. Different scaling forms with one or two parameters are used to describe the dependence of σ in different ranges of T and carrier concentration ns. The two-parameter scaling form describes both the “Kondo metal” and the more conventional metal at all temperatures.

In many cases in experimental science, the instrument interface becomes a limiting factor in the efficacy of carrying out unusual experiments or prevents the complete understanding of the acquired data. We have developed an advanced interface for scanning probe microscopy (SPM) that allows intuitive rendering of data sets and natural instrument control, all in real time. The interface, called the nanoManipulator, combines a high-performance graphics engine for real-time data rendering with a haptic interface that places the human operator directly into the feedback loop that controls surface manipulations. Using a hand-held stylus, the operator moves the stylus laterally, directing the movement of the SPM tip across the sample. The haptic interface enables the user to “feel” the surface by forcing the stylus to move up and down in response to the surface topography. In this way the user understands the immediate location of the tip on the sample and can quickly and precisely maneuver nanometer-scale objects. We have applied this interface to studies of the mechanical properties of nanotubes and to substrate-nanotube interactions. The mechanical properties of carbon nanotubes have been demonstrated to be extraordinary. They have an elastic modulus rivaling that of the stiffest material known, diamond, while maintaining a remarkable resistance to fracture. We have used atomic-force microscopy (AFM) to manipulate the nanotubes through a series of configuration that reveal buckling behavior and high-strain resilience. Nanotubes also serve as test objects for nanometer-scale contact mechanics. We have found that nanotubes will roll under certain conditions. This has been determined through changes in the images and through the acquisition of lateral force during manipulation. The lateral force data show periodic stick-slip behavior with a periodicity matching the perimeter of the nanotube.

The consequences of quantum behavior of charge carriers in devices, while entertaining, is detrimental to the device performance. Chaos leads to unmanageable and unpredictable response in different devices to the same drive and bias inputs.

We review some experimental and theoretical results on the metal-to-insulator transition (MIT) observed at zero magnetic field (B=0) in several two-dimensional electron systems (2DES). Scaling of the conductance and magnetic field dependence of the conductance provide convincing evidence that the MIT is driven by Coulomb interactions among the carriers and is dramatically sensitive to spin polarization of the carriers., Comment: 8 pages, LaTeX, figure label changed

We present our results on the manipulation of individual viruses using an advanced interface for atomic force microscopes (AFMs). We show that the viruses can be dissected, rotated, and translated with great facility. We interpret the behavior of tobacco mosaic virus with a mechanical model that makes explicit the competition between sample-substrate lateral friction and the flexural rigidity of the manipulated object. The manipulation behavior of tobacco mosaic virus on graphite is shown to be consistent with values of lateral friction observed on similar interfaces and the flexural rigidity expected for macromolecular assemblies. The ability to manipulate individual samples broadens the scope of possible studies by providing a means for positioning samples at specific binding sites or predefined measuring devices. The mechanical model provides a framework for interpreting quantitative measurements of virus binding and mechanical properties and for understanding the constraints on the successful, nondestructive AFM manipulation of delicate samples.

This Resource Letter provides a guide to the literature on quantum interference in macroscopic systems. The main topics included are weak localization, interference‐induced fluctuations, Aharonov–Bohm effect, ballistic transport, and numerical methods. Our compilation of references is intended to help the nonspecialist who wishes to study the main topics covered. [The letter E after an item indicates elementary level or material of general interest to persons becoming informed in the field. The letter I, for intermediate level, indicates material of somewhat more specialized nature; and the letter A indicates rather specialized or advanced material.]

A brief review of quantum interference in small conductors is followed by a discussion of quantum interference in ballistic conductors. The ballistic conductors are characterized by conservation of the momentum vector and this leads to a simple model for the details of the conductance of the system. In contrast, for diffusive conductors one can only predict the statistical behavior of the interference contributions to the conductance. The response of the ballistic interferometers is governed by semiclassical physics of the electron momentum states (i.e. the modes) in the quantum conductor. Under circumstances of reduced backscattering of the modes, the interference pattern appears to imitate that from a simple optical interferometer. New results from ballistic interferometers are reviewed briefly.

We present a quartz tuning-fork-based atomic force microscopy (AFM) setup that is capable of mapping the surface contact resistance while scanning topography. The tuning-fork setup allows us to use etched Pt/Ir tips, which have higher durability and better conductivity than probes used in earlier AFM conductance measurements. The performance of the method is demonstrated with contact resistance measurements of gold lines on silicon dioxide and carbon nanotubes on graphite.

We present a fast, high yield, low cost method for the production of scanning probes with aligned carbon nanotubes protruding from the ends. The procedure is described and images of undercut films are used to demonstrate the improved probe quality for topography measurements. A magnetophoretic model of the attachment and alignment processes is discussed.

In GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As coupled four-ring and two-ring samples, large Aharonov-Bohm (AB) oscillations have been observed for magnetic fields 0B4.5 T. The oscillation spectrum changes systematically corresponding to the subband (Landau level) population inside the one-dimensional channels. Multiple tunneling between the edge states encircling the lithographically defined islands causes well-resolved high harmonics ne/h of the fundamental Aharonov-Bohm oscillation frequency with n\ensuremath{\le}8. Such high harmonics indicate participation from several islands and require very long phase coherence lengths ${\mathit{l}}_{\mathrm{\ensuremath{\varphi}}}$. The frequencies ${\mathit{f}}_{\mathit{n}}$=ne/h of all harmonics decrease with increasing B in accord with a simple model. These findings are evidence for ballistic transport in these large complex devices. The B dependence of the quantum interference amplitudes ${\mathit{G}}_{\mathit{n}}$(B) for AB oscillations of frequency ne/h is qualitatively different from the previously published results: They increase by about an order of magnitude with increasing B before decaying at very high field. The increase in ${\mathit{G}}_{\mathit{n}}$(B) is exploited to infer ${\mathit{l}}_{\mathrm{\ensuremath{\varphi}}}$ and indicates that ${\mathit{l}}_{\mathrm{\ensuremath{\varphi}}}$(B) increases with B at a rate \ensuremath{\ge}1.3 \ensuremath{\mu}m/T.

In a GaAs/AlGaAs 4-coupled-ring sample, large Aharonov-Bohm (AB) oscillations were studied up to harmonic order n = 8 for magnetic fields 0 < B < 4.5T. The frequencies of all harmonics of the AB oscillations decrease as predicted by a simple model. The results also suggest an increase of the quantum mechanical phase coherence length (lφ) with increased B.

We have studied the response of the tunnel current and the feedback circuit during surface modification by an STM tip. Our studies show that several classes of events occur when “writing” by applying voltage pulses. We have studied W and Au tips on Au surfaces and PtRh tips on Pt surfaces. Strong correlation is found between the tunnel current response and the kind of surface change that occurs. One dramatic discovery is the formation of a wire between the tip and surface, which is characterized by an electrical shorting of the tip to the surface until the feedback circuit of the tip retracts enough to break the wire. Using a sophisticated graphics display system and allowing pulse placement by pointing at the desired location, we are able to distinguish easily between changes in surface morphology and changes in tip shape and length.

We report on the precise placement of a single carbon nanotube (CNT) onto a microlectromechanial system (MEMS) structure. Using a hybrid atomic force microscope/scanning electron microscope (AFM/SEM) system, an individual multiwalled CNT was retrieved from a cartridge by the AFM tip, translated to a MEMS device, and then placed across a gap between an actuating and a stationary structure. Progress toward a resistance versus stress/strain measurement on a CNT will be discussed, including SEM images of a MEMS structure we have designed specifically for such a measurement. © 2002 American Institute of Physics.

We report measurements of the shear modulus of each shell and the friction between the two shells of double-shell carbon nanotubes in single nanotube-based nanoelectromechanical devices operated in a transmission electron microscope. In situ nanobeam electron diffraction is applied to obtain the chiral indices of each shell of the nanotube and it allows us to establish a quantitative correlation between the atomic structure and properties of the nanotube under investigation.

Metal-Cd 0.42 Te 0.58 -metal nanowires were electrodeposited into the pores of anodized aluminum oxide (AAO) membranes, and the polarization sensitive photoconductance was analyzed for individual nanostructures. Non-linear I– V curves were observed, and the short-circuit current density, open-circuit voltage, and fill factor were determined. These nanowires exhibited a power conversion efficiency of 0.56%, which is higher than some comparable nanomaterials of greater complexity.

The authors review conductance effects in small samples at low temperatures where quantum confinement and quantum interference are significant perturbations on the classical Drude conductance. In disordered materials, the elastic scattering of the carriers from impurities leads to random conductance fluctuations or resistance fluctuations. The fluctuations arise because of interference among the scattered waves, and they are random and sample specific because the impurity potential is. The fluctuations appear in response to changes in many extrinsic parameters such as the carrier density, the applied measuring current, external electric fields and external fields. The interface fluctuations have consequences for much larger samples, particularly in flicker noise, even though quantum coherence is obtained only over regions much smaller than the sample size, in completely phase coherent conductors a number of purely quantum effects are observed, including non-local response and Aharonov-Bohm effects. Other 'applications' of the quantum fluctuations include studies of reciprocity (which is related to time-reversal symmetry) and of the effects of the measurement probes on a quantum system. Interestingly, these are two areas where disagreements remain with theoretical calculations. The size and correlation scale of the fluctuations, however, are mainly in agreement with theoretical calculations of the same quantities, although one or two other small disagreements of detail remain. In very clean semiconductor heterostructures, the mean free path length between scattering events is large enough to allow for studies of ballistic transport that reveal a variety of conductance anomalies that result from device shape (as opposed to fortuitous placement of impurities as in the metals). These ballistic effects are reviewed briefly and connection is made to the effects of disorder in ballistic systems, and experiments on disordered metal samples are reviewed in detail.

Tunnel junctions often have conductances that are linear in voltage over wide voltage ranges. Although this linear conductance background has received much attention recently in connection with the high-${\mathit{T}}_{\mathit{c}}$ superconductors, it is found in many systems. Previous work has shown that the discontinuity in slope of the linear conductance background at zero bias is thermally smeared by \ensuremath{\sim}5kT, consistent with inelastic tunneling from a broad, flat continuum of states. In this paper we concentrate on a particular system, junctions with ${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$ in the barrier region, in which the size of the effect can be adjusted by changing the barrier composition. Careful analysis of the Pb strong-coupling phonon structure in Al-${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$-Pb junctions is consistent with the inelastic-tunneling hypothesis, and inconsistent with a voltage-dependent matrix-element explanation for this effect. Suppression of the Al gap signature, as well as Zeeman splitting of the conductance background near zero bias, indicates that strong spin interactions occur in the barrier region in these junctions. We present Monte Carlo simulations of multiple-scattering strong inelastic tunneling to explain the very wide voltage range over which the linear background occurs. We argue that the same basic mechanism is probably responsible for the linear background in junctions involving high-${\mathit{T}}_{\mathit{c}}$ junctions as for the junctions studied in detail here.

The properties of a carbon nanotube (CNT), in particular a single-wall carbon nanotube (SWNT), are highly sensitive to the atomic structure of the nanotube described by its chirality (chiral indices). We have grown isolated SWNTs on a silicon substrate using chemical vapor deposition (CVD) and patterned sub-micron probes using electron beam lithography. The SWNT was exposed by etching the underlying substrate for transmission electron microscope (TEM) imaging and diffraction studies. For each individual SWNT, its electrical resistance was measured by the four-probe method at room temperature and the chiral indices of the same SWNT were determined by nano-beam electron diffraction. The contact resistances were reduced by annealing to typically 3-5 kΩ. We have measured the I-V curve and determined the chiral indices of each nanotube individually from four SWNTs selected randomly – two are metallic and two are semiconducting. We will present the electrical resistances in correlation with the carbon nanotube diameter as well as the band gap calculated from the determined chiral indices for the semiconducting carbon nanotubes. These experimental results are also discussed in connection with theoretical estimations.

We have fabricated a quantum dot with four leads attached via variable-width constrictions. At high magnetic fields and low temperatures, the h/2${\mathit{e}}^{2}$ and h/4${\mathit{e}}^{2}$ quantized Hall pleateaux observed for wide constrictions are replaced by a series of minima that go to zero or below as the constrictions are squeezed. These resonances are explained well by a recent model proposed by Kirczenow (following paper) to describe this structure, in which each lead transmits only one edge state. The minima can be explained by interference between edge states near the constrictions.

We present observations of resonance behavior in a torsional nanoelectromechanical device built with an individual single-walled carbon nanotube. The effect of applied torsional strain on the transport properties of the nanotube provides an electrical signal transducer and hence a means of measuring oscillation amplitude, resonance frequency, and quality factor. The mechanical resonance is confirmed by imaging and the electromechanical signal is compared to quasi-static measurements.

In narrow high-mobility conductors the predominant source of scattering is reflection of carriers off the confining potential. We demonstrate that by changing the geometry of the intersection of the Hall probes with the conductor, the Hall resistance can be quenched, negative or enhanced. More complex junction geometries can lead to one of these phenomena for one field polarity and to another for the other field polarity. At liquid helium temperatures these results can be explained by following trajectories. In the milli-Kelvin range fluctuations are superimposed. At high fields strong resonant depressions of the Hall resistance are found which may be associated with bound states in the region of the cross.

We have fabricated gated, asymmetric rings which, in principle, enable interference between electron waves to be varied with a gate voltage. Although close to the minimum dimensions currently achievable, the results are far from clear-cut, and imply that there are many problems to be overcome before useful devices based on quantum interference can be demonstrated, even supposing that the geometries proposed will actually work. We describe the methods used to analyse our data to show any consistent interference effects caused by the gate voltage variation. Narrower, higher-mobility devices are required in order to produce more easily-resolved gate voltage-controlled interference effects.

is preferred over sliding, and it is expected to have an equally important role in the microscopic domain. Although progress has been made in our understanding of the dynamics of sliding at the atomic level 4 ,w e have no comparable insight into rolling owing to a lack of experimental data on microscopic length scales. Here we produce controlled rolling of carbon nanotubes on graphite surfaces using an atomic force microscope. We measure the accompanying energy loss and compare this with sliding. Moreover, by repro- ducibly rolling a nanotube to expose different faces to the substrate and to an external probe, we are able to study the object over its complete surface. The microscopic aspects of tribology have been explored by means of the surface force apparatus (SFA) 5 and atomic force microscopy (AFM) 6 , which have identified the intrinsic dependence of sliding friction on contact area 7,8 and crystallographic orientation 9,10 . Further, AFM has been used to perform friction mapping of surfaces with atomic resolution 4 and has identified stick-slip motion in the sliding of nanometre-scale objects 11 . Using AFM manipulation 12,13 of multiwall carbon nanotubes (CNTs), we have observed sliding and rolling. CNTs, with a range of available sizes down to the molecular scale, serve as interesting model systems for tribological studies. In addition, nanotubes are expected to play a part in future nanometre-scale electrical-mechanical devices, and rolling fullerenes have been proposed as ideal lubricants 14-16 . Our evidence for sliding and rolling comprises sequences of topogra- phical images of manipulated nanotubes and lateral force data acquired during the manipulation to measure energy loss. Samples were prepared by solvent evaporation on mica and graphite substrates from an ethanol solution of raw carbon soot produced by the carbon arc technique 17 . The multiwall CNTs were imaged and manipulated under ambient conditions. The nanomanipulator AFM system 18,19 , designed for manipulation, comprises an advanced visual interface, teleoperation capabilities for manual control of the AFM tip and haptic (touch) presentation of the AFM data (Topometrix Discoverer). Normal force, lateral force and AFM tip trajectory are recorded simultaneously for strict correlation. The AFM tip is used to apply lateral forces at locations along the tube to produce translations and rotations. These tubes are free of pinning material and move without deformation. The lateral force values have been calibrated from measured cantilever and tip geometry, literature values for the cantilever (Si) elastic moduli and the detector response from the z-translation of the cantilever. We estimate the absolute error in this calibration to be about 30%, with the largest contribution in the uncertainty coming

Conducting scanning probe microscopy provides a powerful tool for measuring electric transport through small surface features. In this chapter, carbon nanotubes and carbon nanotube networks are analyzed with a scanning probe microscopy method that employs solid metal tips to provide improved electrical contact to the nanotubes. The study reveals paths of electrical transport through carbon nanotubes and provides a means to differentiate between semiconducting and metallic nanotubes. Finally, high-resolution images provide insight into the conductance decay around nanotube junctions.

We report the selective functionalization of uniform and heterostructured nanowires with self-assembled monolayers (SAMs) of (3-mercaptopropyl)trimethoxysilane (MPTMS). The wires were grown electrochemically in anodic aluminum oxide (AAO) templates. Selective deposition and removal of SAMs during nanowire growth permits the decoration of specific regions of the surface along the length of the nanowires. This technique presents a facile method for the tailored functionalization of nanowires, but does not rely on the intrinsic chemical properties of the nanowires as previous methods have.

We report on the characterization of nanometer-scale torsional devices based on individual single-walled carbon nanotubes as the spring elements. The axial shear moduli of the nanotubes are obtained through modeling of device reaction to various amounts of applied electrostatic force and are compared to theoretical values.

The curling of a graphitic sheet to form carbon nanotubes produces a class of materials that seem to have extraordinary electrical and mechanical properties. In particular, the high elastic modulus of the graphite sheets means that the nanotubes might be stiffer and stronger than any other known material, with beneficial consequences for their application in composite bulk materials and as individual elements of nanometre-scale devices and sensors. The mechanical properties are predicted to be sensitive to details of their structure and to the presence of defects, which means that measurements on individual nanotubes are essential to establish these properties. Here we show that multiwalled carbon nanotubes can be bent repeatedly through large angles using the tip of an atomic force microscope, without undergoing catastrophic failure. We observe a range of responses to this high-strain deformation, which together suggest that nanotubes are remarkably flexible and resilient.

Radio frequency (rf) antennae, coated with glass, were inductively coupled to an Ar plasma inside the processing chamber. Coupling efficiency η and electron density Ne were measured for moderate pressures (0.1–200 T) and rf power (10–2000 W). Decreasing the dielectric thickness between the antenna and the Ar led to an increase in η and a decrease in Ne. Instabilities and hysteresis were observed for the internal antennae.

We have measured the decay of local conductance in single-wall carbon nanotubes directly using conductance imaging atomic force microscopy. The decay lengths were in the range from $190\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ to well over $3\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$. There are strong indications that these decay lengths are the result of depletion lengths around metallic/semiconducting carbon nanotube junctions, and that they are related to defects in the tubes.

This chapter presents these microscope systems, along with brief descriptions of the science experiments driving the development of each system. Beginning with a discussion of the philosophy that has driven the Nanoscale Science Research Group (NSRG) and the methods used, the chapter describes the lessons learned during system development, including both useful directions and blind alleys. The first lesson is to begin software development at least as soon as hardware development. The second lesson is to partner with experts in required technologies. The NSRG attempts to use the best available computer technology to develop effective systems for use by the physical science team, which then become cost-effective and can be deployed on widely available hardware as technology marches on. The chapter also describes techniques to enable telemicroscopy in the context of remote experiments and outreach.

We report an extended Hall‐effect study of ion‐bombarded poly(benzimididazobenzophenanthroline ladder), which resembles a disordered metal. We have investigated the dependence of carrier concentration and mobility on ion energy and sample temperature during bombardment and on measurement temperature. The dramatic increases in mobility and conductivity with bombardment energy and temperature indicate increased cross‐link density. Concomitant slight decreases in carrier concentration may result from fewer defects in the cross‐linked network. The mobility decreases slightly with measurement temperature while the conductivity is dominated by the gradually increasing carrier density.

High power microwave tubes are used for both civilian and military applications. Due to the power requirement, tremendous amounts of electrons (up to 100A/cm2) are extracted from the cathodes and bombard on the anodes with very high kinetic energy. Overheating, out-gassing, and formation of secondary electrons of the anode cause serious problems. Preliminary results at the AFRL suggest that carbon coating can reduce SE. We investigated the effect of carbon nanotube (CNT) coating on the anode surface. Initial experiments show that CNT is more efficient in absorbing SE compared to the reference metal at low energy. Further experiments are required to study and understand the effect at high energy.

We report on the characterization of nanometer-scale resonators. Each device incorporates one multiwalled carbon nanotube (MWNT) as a torsional spring. The devices are actuated electrostatically, and their deflections, both low frequency and on resonance, are detected optically. These are some of the smallest electromechanical devices ever created and are a demonstration of practical integrated MWNT-based oscillators. The results also show surprising intershell mechanical coupling behavior in the MWNTs.

An in vitro model was used to investigate the effect of mechanical stimuli on adaptation to load and calcium signaling in aligned medial collateral ligament cells (MCL). This model used a patterned silicone membrane to align the cells parallel with the direction of the microgrooves. Alignment created an architecture that simulated a degree of cell orientation in native ligament tissue. It was hypothesized that aligned ligament cells would be more efficient at calcium wave propagation than cells that were randomly oriented. It was further hypothesized that calcium wave propagation would be greater among cells that were both aligned and subjected to mechanical stretch compared to cells that were aligned but not stretched. Rat MCL cells were loaded with Fura-2AM, a calcium-binding dye, and mechanically indented using a micropipette tip. A ratio-imaging fluorescence technique was used to quantitate the calcium (Ca2+) response. It was concluded that stretching ligament cells prior to stimulation increased their sensitivity to load and their ability to propagate a calcium wave. However, the ability of aligned cells to propagate this wave was not significantly different when compared to nonaligned cells. Treatment of cultures with inhibitors such as apyrase and suramin significantly reduced the number of cells recruited in the calcium response. Hence, it was concluded that ATP released from mechanically stimulated cells was a principal mediator responsible for the rise in intracellular calcium in ligament cells. Further, purinoceptor activation may amplify the signal to alert and recruit more cells in a response to mechanical stimulation.

We present local conductance measurements of carbon nanotube networks with nanometer scale resolution and show that there are discrete drops in conductance that correspond to junctions of metallic nanotubes and semiconducting nanotubes. The anomalies of these networks compared to thin films are shown, and a new method of discerning between semiconducting and metallic single-wall carbon nanotubes is demonstrated.

Two planar coil designs for a high pressure rf plasma source are investigated using spectroscopic techniques and circuit analysis. In an Ar plasma a truncated version of the commonly used ‘‘spiral’’ coil is found to produce improvements in peak electron density of 20% over the full version. A coil with figure‐8 geometry is found to move plasma inhomogeneities off of center and produce electron densities comparable to the spiral coils. Both of these characteristics are advantageous in industrial applications. Coil design characteristics for favorable power coupling are also determined, including the necessity of closed hydrodynamic plasma loops and the drawback of closely situated antiparallel coil currents.

We report on the fabrication of nanometer-scale mechanical devices incorporating multiwalled carbon nanotubes (MWNTs) as the torsional spring elements. We have employed electron beam lithography to pattern device elements directly onto individual MWNTs on a silicon dioxide substrate. The structures were suspended by etching the substrate and subsequent critical-point drying of the sample. We also briefly present characterization of the torsional properties of an individual MWNT. The techniques described are applicable to other nanometer-scale rod-like objects. © 2003 American Institute of Physics.