Jay Gaillard

Clemson University, Clemson, SC, United States

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Publications (23)49.08 Total impact

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    ABSTRACT: We report on the self-assembly of carbon nanotubes (CNTs) in nonpolar dielectric liquids under the influence of DC-generated electric fields. This process gives rise to electrostatic and hydrodynamic interactions of the CNTs in insulating nonpolar solvents. While some studies of the self-assembly of carbon nanotubes in response to a DC-field have been carried out in conductive solvents, the analysis of the self-assembly process is complicated by the current flow temporally affecting the particle charge and an assembly timescale of tenths to hundredths of seconds. In contrast, experiments in insulating liquids allow for the investigation of self-assembly processes where: the particle charge is not expected to change as a function of time and at a timescale of seconds this allows for an investigation of the transient states of the assembly process. In the presence of an electric-field, CNTs present in the solution experience an electrophoretic force due to their surface charges. When a DC field is applied across the electrodes, CNT bundles move according to their electrophoretic mobility. We find that the threshold voltage, above which the insulator-to-conductor transition occurs, varies sensitively as a function of zeta potential and hydrodynamic particle size. In addition, a percolation power law supports the observed threshold voltage as a function of CNT concentration and zeta potential.
    02/2012;
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    ABSTRACT: We find that the electrical and thermal connectivity in multiwalled carbon nanotube buckypaper can be tuned using a spark plasma sintering (SPS) technique. Elevated SPS temperatures promote the formation of inter-tube connections and consequently impact the electrical resistivity, thermoelectric power and thermal conductivity of the buckypaper. In particular, the electrical resistivity as a function of SPS temperature exhibits a percolation-type behavior while the low temperature lattice thermal conductivity shows a crossover behavior in the sample dimensionality. The results are discussed in terms of the quasi-one-dimensional metallic nature of multiwalled carbon nanotubes, the packing density and the electron-phonon coupling.
    Journal of Physics Condensed Matter 08/2010; 22(33):334215. · 2.22 Impact Factor
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    Sensors and Actuators A: Physical. 12/2008; 148(2):472.
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    ABSTRACT: Response characteristics of a microcantilever, such as resonant frequency, amplitude, phase and quality factor, can be used for absolute pressure measurements in the range of 10−4 to 103 Torr. To this end, it would be very convenient to have the resonance of the microcantilever actuated and detected electrostatically. Herein, we report the nonlinear dynamics of microcantilevers under varying pressure and different gases using the harmonic detection of resonance (HDR) technique [J. Gaillard, M.J. Skove, R. Ciocan, A.M. Rao, Electrical detection of oscillations in 340 microcantilevers and nanocantilevers, Rev. Sci. Instrum. 77 (2006) 073907]. The HDR technique exploits nonlinearities in the cantilever-counter electrode system to allow electrostatic actuation and detection of the responses of the microcantilever to the pressure and gas composition. In particular, the 2nd and 3rd harmonics of the measured charge on the cantilever are investigated. The microcantilever demonstrates a quality factor of ∼10,000 at 10−3 Torr, and a usable response in the range from 10−3 to 103 Torr. The use of different harmonics can enable us to adjust the range of pressures over which the sensor has an efficacious response, enhancing its sensitivity to a particular environment. The experimental results are in reasonable agreement with theoretical calculations, despite the nonlinearities involved.
    Sensors and Actuators A: Physical. 09/2008; 147(1):203–209.
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    ABSTRACT: Carbon nanotubes ( ∼ 200 nm diameter) are grown by chemical vapor deposition using catalytic iron particles. Mössbauer spectroscopy enables differentiation among relatively large Fe3C, α-Fe, and nanosized superparamagnetic fcc γ-Fe particles. The antiferromagnetic configuration of γ-Fe nanoparticles yields a significant fraction of uncompensated spins, producing a weak ferromagnetism that allows estimation of size (2–3 nm) via magnetization in zero field versus variable field cooling. This property of γ-Fe nanoparticles has not been previously employed. We propose that the surfaces of 200 nm iron carbide particles are covered with nanosized γ-Fe and graphitized carbon that participate in the catalytic growth of nanotubes.
    Applied Physics Letters 07/2008; 93(1):013103-013103-3. · 3.79 Impact Factor
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    Advanced Materials 12/2007; 20(1):179 - 182. · 14.83 Impact Factor
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    ABSTRACT: We have studied the nonlinear dynamics of micro- and nano-cantilevers under varying ambient conditions using the Harmonic Detection of Resonance technique (HDR)^1. In our studies, a cantilever is either microstructure shaped like a diving board, or a cantilevered MWNT. In this work, we report the dependence of the amplitude and Q of a silicon microcantilever (300 mum long, 35 mum wide, 2 mum thick) on ambient pressure. An environment of air at a pressure of 10-3 Torr gives a high quality factor of ˜7000. The response of higher harmonics of the ac voltage that drives the cantilever is also observed with varying chamber pressure. An investigation of the influence of ac and dc voltages on sensitivity shows very good agreement with a model calculation. The shift in the resonant frequency of cantilevers under different environments such as helium, air and argon at different pressures will be discussed. References: 1. J. Gaillard, M. J. Skove, R. Ciocan, and A. M. Rao, Rev. Sci. Instrum. 77, 073907 (2006). Contact Info: arao@clemson.edu
    03/2007;
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    ABSTRACT: In nonlinear dynamics, mechanical motion can be made up of a complicated mixture of vibrations. In resonating structures, nonlinearities are ubiquitous and more often than not are undesirable. On the other hand, nonlinear dynamics and chaos in electrostatic microelectro-mechanical systems (MEMS) has been shown to be useful for various applications, including secure communications, MEMS filters, and scanning force microscopy. Exploiting these dynamics opens the door for nanoelectro-mechanical systems (NEMS) by providing signals with higher quality factors and better signal-to-background ratios. In cantilever-based MEMS, the nonlinear dynamics usually stem from harmonically forced excitation in which only the second superharmonic has been theorized or detected. Here we measure the nonlinearly modulated charge on a silicon microcantilever up to the seventh superharmonic of the fundamental resonant mode via electrostatic actuation/detection. In agreement with experiment, simulated results reveal that the time dependence of the modulated charge due to the cantilever's motion carries a set of harmonics for each superharmonic of order φ0/n. We propose that using a system of harmonics and modes of the cantilever increases applications for cantilevered and doubly-clamped microbeams, and that exploiting the nonlinearities in the modulated charge provides a valuable tool for the study of the dynamics in electrostatic transduction.
    03/2007;
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    ABSTRACT: Precise determination of the resonant frequency, phase, and quality factor in micromechanical and nanomechanical oscillators would permit, among other things, (i) the detection of trace amounts of adsorbed molecules through a shift in the resonant frequency, and (ii) pressure variations in the environment which affect the mechanical damping of the oscillator. The major difficulty in making these measurements in many cases is the ancillary equipment such as lasers or high magnetic fields that must be used. Being able to make precise measurements with a fully electrical actuation and detection method would greatly extend the usefulness of these oscillators. Detecting the oscillation through changes in the capacitance between the oscillator and a counter electrode is difficult because the static capacitance between them as well as the parasitic capacitance of the rest of the circuitry overwhelm the detection. We have found that the charge on a microcantilever or nanocantilever when driven by a nearby counter electrode contains higher harmonics of the driving signal with appreciable amplitude. This allows detection at frequencies well removed from the driving frequency, which increases the signal to background ratio by approximately three orders of magnitude. With this method, we show clear electrical detection of mechanical oscillations in ambient conditions for two systems: Si-based microcantilevers and multiwalled carbon nanotube based nanocantilevers.
    Review of Scientific Instruments 07/2006; 77(7):073907-073907-5. · 1.60 Impact Factor
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    ABSTRACT: Y-junction based carbon nanotube (CNT) transistors exhibit interesting switching behaviors, and have the structural advantage that the electrical gate for current modulation can be formed by any of the three constituent branches. In this letter, we report on the gating characteristics of metallic Y-CNT morphologies. By measuring the output conductance and transconductance we conclude that the efficiency and gain depend on the branch diameter and is electric field controlled. Based on these principles, we propose a design for a Y-junction based CNT switching device, with tunable electrical properties.
    Applied Physics Letters 06/2006; · 3.79 Impact Factor
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    ABSTRACT: Resonance vibration of micro and nano sized cantilevers can be used to measure elastic constants and mass, detect absorbed material, and form part of mechanically resonant filters in electronic devices. We have measured the harmonic content of cantilevers driven by electrostatic forces containing two harmonically related terms, as well as nonlinear terms and parametric terms. The results are compared to numerical simulations of the forces between the cantilever and the counter electrode and the resulting motion of the cantilever.
    03/2006;
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    ABSTRACT: Recently, we have shown evidence for a dramatic electrical switching behavior in a Y-junction carbon-nanotube morphology [1]. The mutual interaction of the electron currents in the three branches of the Y-junction is shown to be the basis for a potentially new logic device. The Y-junction nanotubes that were prepared using our thermal CVD process [2] typically show the presence of a catalyst particle at the junction. The observed modulation of the current from an on- to an off state could be mediated by defects and the topology of the junction, or due to the presence of catalyst particle at the junction. We will compare the switching characteristics observed in a Y- junction nanotube that does not contain the catalyst particle to those reported in Ref. 1 with a view to elucidating the switching mechanism in branched nanotubes. (1) P. Bandaru et al., Nature Materials, vol. 4(9), 663-666, (2005) (2) N. Gothard, et al., Nanoletters 4, 213-217 (2004)
    03/2006;
  • R Ciocan, J Gaillard, M J Skove, A M Rao
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    ABSTRACT: We report a new method of measuring the amplitude and phase of oscillations of individual multiwall carbon nanotubes (MWNTs). As in many other experiments, we excite the oscillations electrostatically, but we show that we can detect the amplitude and phase of the resulting oscillation electrically. As an example, we present measurements of the fundamental and first two overtones of the diving board resonance of a MWNT at 0.339, 2.42, and 5.31 MHz in ambient conditions. The corresponding quality factors were 67, 36, and 25.
    Nano Letters 01/2006; 5(12):2389-93. · 13.03 Impact Factor
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    ABSTRACT: Electrical Detection of Oscillations in Micro- and Nano- Cantilevers We described a fully electrical actuation and detection method for measuring mechanical oscillations in ambient conditions for two systems: Si-based micro- and multi-walled carbon nanotube (MWNT) based nano-cantilevers. In our studies, a cantilever is either a silicon microstructure shaped like a diving board, or a cantilevered MWNT. The cantilever is placed parallel to and within 1-10 mum from a counter electrode and is forced into resonance by applying an ac voltage (Vac) with a dc offset (Vdc) on the counter electrode under ambient conditions. We measure the magnitude and phase of the electrical signal due to the charge induced on the cantilever. The signal showing the resonance frequency of the cantilever is best measured at harmonics of Vac. A model describing the response of our electrical actuation and detection of resonance oscillations will be presented.
    01/2006;
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    ABSTRACT: Bulk Bi<sub>2</sub>Te<sub>3</sub> is one of the best known thermoelectric materials with a ZT ∼1 at room temperature. Theoretical studies have suggested that low-dimensional materials may exhibit ZT values that exceed 1. In this study, we used the pulsed laser deposition method to prepare Bi<sub>2</sub>Te<sub>3</sub> nanostructures by ablating a rotating Bi<sub>2</sub>Te<sub>3</sub> target in an inert atmosphere. Silicon or quartz substrates are pretreated with poly-1-lysine to form an adhesion layer for 10, 20, and 30 nm colloidal Au particles which serve as catalyst seed particles for the growth of the nanostructures. Alternatively, we have also prepared Bi<sub>2</sub>Te<sub>3</sub> nanostructures by subliming Bi<sub>2</sub>Te<sub>3</sub> powder in the presence of gold coated substrates. Results from electron microscopy and vibrational spectroscopic studies are presented.
    Thermoelectrics, 2005. ICT 2005. 24th International Conference on; 07/2005
  • Jay Gaillard, Malcolm Skove, Apparao M. Rao
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    ABSTRACT: The bending modulus (Young’s modulus) of several chemical vapor deposition-grown multiwalled nanotubes (MWNTs) have been measured using a vibrating reed technique. Three different precursors were used to produce MWNTs with differing densities of defects in the tube walls. Individual MWNTs were electrostatically driven in air over a dark-field light microscope and the bending modulus of the nanotubes was determined from the frequency of the first vibrational resonance. A correlation between the defect density and the bending modulus was found which implies that the bending modulus is relatively more sensitive to wall defects than the nanotube diameter.
    Applied Physics Letters 06/2005; 86(23):233109-233109-3. · 3.79 Impact Factor
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    ABSTRACT: Accurate determination of the resonant frequency, phase and quality factor in micro and nano-mechanical oscillators permits the detection of: (i) trace amounts of specific adsorbed molecules which affect the resonant frequency; (ii) pressure variations which affect the mechanical damping of the oscillator; or (iii) the temperature dependence of the elastic properties of the oscillator through a shift in the resonant frequency. To date, electrical detection of oscillations in cantilevered multiwalled carbon nanotubes (MWNTs) has eluded researchers in the field. Electrical detection allows a simple means for measuring the resonance frequency, phase and quality factor of cantilevers built into integrated circuits, or cantilevers whose response can be monitored as a function of any external parameter such as temperature or pressure. To this end, we described a fully electrical (actuation and detection) method termed harmonic detection of resonance (HDR) to measure mechanical oscillations in ambient conditions for two systems: Si-based micro- and MWNT based nano-cantilevers. Furthermore, we demonstrate that the resonant frequency in micro- and nano-cantilevers can be tuned without appreciable change in the quality factor which suggests that HDR is an ideal platform in device design and applications.
    MRS Proceedings. 12/2004; 888.
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    ABSTRACT: We demonstrate a bulk process for the synthesis of Y-junction carbon nanotubes using Ti-doped Fe catalysts. It is shown that the nanotube branching can be induced or stopped at will by tuning the Ti composition in the catalyst particle that seeds the growth of nanotubes. Detailed electron microscopic studies suggest that the mechanism for the observed Y-junction formation is mediated via catalyst particle attachment on the walls of a growing MWNT, from which the branching nanotubes nucleate and grow. By controlling the Ti concentration in the precursor, cascading Y-junction series as well as quadruple junctions have been successfully synthesized, offering the possibility for interesting device applications. The simplicity and controllability of such an in-situ Y-junction fabrication technique make it an excellent source of ready-made networks for potential nanoscale devices.
    Nano Letters - NANO LETT. 01/2004; 4(2).
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    ABSTRACT: Photoinduced phenomena are of general interest for new materials. Recently, photoinduced molecular desorption of oxygen has been reported in carbon nanotubes. Here we present, using thermopower measurements, that carbon nanotubes when exposed simultaneously to UV light and oxygen exhibit photoinduced oxidation of the nanotubes. At least two plausible mechanisms for the experimentally observed photoinduced oxidation are proposed: (i) a lower energy barrier for the adsorption of photo-generated singlet oxygen, or (ii) due to the presence of defects in carbon nanotubes that may facilitate the formation of locally electron-deficient and electron-rich regions on the nanotubes which facilitate the adsorption of oxygen molecules on the nanotubes.
    Journal of Physics Condensed Matter 08/2003; 15(35):5915. · 2.22 Impact Factor
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    ABSTRACT: We present the design and development of highly sensitive and fast-responsive microwave resonant sensors for monitoring the presence of ammonia gas. The sensor consists of a circular disk electromagnetic resonant circuit coated with either single- or multiwalled carbon nanotubes that are highly sensitive to adsorbed gas molecules. Upon exposure to ammonia, the electrical resonant frequency of the sensor exhibits a dramatic downshift of 4.375 MHz. The recovery and response times of these sensors are nominally 10 min. This technology is suitable for designing remote sensor systems to monitor gases inside sealed opaque packages and environmental conditions that do not allow physical wire connections. © 2002 American Institute of Physics.
    Applied Physics Letters 06/2002; 80(24):4632-4634. · 3.79 Impact Factor

Publication Stats

329 Citations
49.08 Total Impact Points

Institutions

  • 2002–2010
    • Clemson University
      • • Department of Physics and Astronomy
      • • Department of Electrical and Computer Engineering
      Clemson, SC, United States
  • 2007
    • Carnegie Mellon University
      • Department of Materials Science and Engineering
      Pittsburgh, PA, United States