This PDF file contains the front matter associated with SPIE Proceedings Volume 7399, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

We investigated the effects of hydrogen pretreatment on nickel catalyst of different thicknesses and deposition methods on a silicon substrate and how it will affect the growth of carbon nanotubes using microwave plasma enhanced chemical vapor deposition (MPECVD). Nickel catalyst of 10, 50, 100, 200, 350 and 500 Å thickness was treated with hydrogen flowing at 135 standard cubic centimeter per minute (sccm), substrate temperature of 400 °C, microwave power of 400 W, and pressure of 20 torr. The treated catalyst granule size and density was determined optically through scanning electron microscope (SEM) images and atomic force microscope (AFM) measurements. We found that sputtered catalyst needs a longer pretreatment than evaporated catalyst. As expected, the pretreatment time must be increased as the catalyst thickness increases to get granule sizes and densities favorable for carbon nanotube (CNT) growth. CNT growth took place with a hydrogen flow of 120 sccm, methane flow of 15 sccm, substrate temperature of 650 °C, microwave power of 1000 W and a pressure of 20 torr. We determined the catalyst can be over treated causing catalyst conglomeration that result in poor CNT growth.

We have developed a simple and unique metal-free chemical vapor deposition technique in mild condition for the synthesis of carbon nanotubes on carbon black and graphite surfaces. The existence of topologically heterogeneous surfaces is a key factor for inducing the growth of the CNTs. Surface functional groups also play an important role in manipulating the reaction path of the carbon deposition reaction. A surface structure-related model was proposed to describe the growth procedure of CNTs on carbon surfaces. We anticipate that this method will be useful for controlling the growth of metal-free CNTs at desired sites on various carbon surfaces.

We demonstrate doping-free and adaptive inverter to verify that the single ambipolar SWCNT transistors can be utilized both p- and n-type. Furthermore, we fabricate an adaptive logic circuit that can reveal multifunctions such as NOR and NAND gate using four ambipolar transistors. This new approach is innovative in several aspects, for instance, in improving integration density, simplicity without intentional doping, and its multifunctionality and ensures multidisciplinary interests in materials, physics, mechanics, and electronics areas.

The effect of using EBL with devices incorporating CNT has also been investigated. The effect on metallic and semiconducting CNT exposure in the channel of the transistor devices was examined and a physical mechanism for the variations discussed. We show that the subsequent generation of trap states along the CNT channel varies the conduction mechanism of the nanotube and has a significant effect on device performance. Metallic and semiconducting CNT react very differently, with an apparent increased localization effect in the metallic tubes responsible for dramatic decreases in conductance.

Our study deals with the utilization of carbon nanotubes networks based transistors with different metal electrodes for highly selective gas sensing. Indeed, carbon nanotubes networks can be used as semi conducting materials to achieve good performances transistors. These devices are extremely sensitive to the change of the Schottky barrier heights between Single Wall Carbon Nanotubes (SWCNTs) and drain/source metal electrodes: the gas adsorption creates an interfacial dipole that modifies the metal work function and so the bending and the height of the Schottky barrier at the contacts. Moreover each gas interacts specifically with each metal identifying a sort of electronic fingerprinting. Using airbrush technique for deposition, we have been able to achieve uniform random networks of carbon nanotubes suitable for large area applications and mass production such as fabrication of CNT based gas sensors. These networks enable us to achieve transistors with on/off ratio of more than 5 orders of magnitude. To reach these characteristics, the density of the CNT network has been adjusted in order to reach the percolation threshold only for semi-conducting nanotubes. These optimized devices have allowed us to tune the sensitivity (improving it) of our sensors for highly selective detection of DiMethyl-Methyl-Phosphonate (DMMP, a sarin stimulant), and even volatile drug precursors using Pd, Au and Mo electrodes.

Nanodispersion of single-walled carbon nanotubes (SWCNTs) has been systematically investigated with the use of sodium dodecyl sulfate (SDS) and poly(vinylpyrrolidone) (PVP) surfactant in de-ionized water. A high concentration of nanodispersed SWCNTs up to 0.08 mg/mL was achieved with introduction of an additional dispersant of PVP by optimizing surfactant concentration, sonication time, and centrifugation speed, which was crucial to obtaining a high concentration of SWCNTs in the supernatant solution. We also demonstrate that diameters of the nanodispersed nanotubes can be sorted out by controlling the centrifugation speed and furthermore the saturated SWCNT concentration was nearly constant, independent of the initial concentration at high centrifugation speed. Two dispersion states were identified depending on the centrifugation speed: an intermediate dispersion of nanodispersion mixed with macrodispersion (I) and nanodispersion (II). This was verified by Raman spectroscopy, scanning probe microscopy, optical absorption spectroscopy, and photoluminescence measurements. The obtained SWCNT solution was stable up to about ten days. Some aggregated SWCNT solution after a long period of time was fully recovered to initial state of dispersion after re-sonication for a few minutes. Our systematic study on high concentration nanodispersion of SWCNTs with selective diameters provides an opportunity to extend the application areas of high quality SWCNTs in large quantity.

The novel thermal conductance mechanism, theoretically predicted and experimentally measured in nanotube field-effect transistors (FET), is discussed with respect to the power dissipation problem of modern carbon-based electronics. Such an effect is due to the near-field coupling of the charge carriers in the transistor channel with the local electric field of the surface electromagnetic modes. The coupling leads to a quantum electrodynamic (QED) energy exchange between the hot electrons in FET channel and the optical polar phonon bath being in thermal equilibrium with the substrate. For an example of a NT on silica, this QED coupling mechanism is shown to exceed significantly the interface Kapitza conductance, that is, the classical phonon heat transport. The QED thermal conductance is proposed to play dominant role in the energy dissipation in nanoelectronics with a hetero-interface between the device channel and the polar substrate.

In this paper, we propose a new design configuration for a carbon nanotube (CNT) array based pulsed field emission device to stabilize the field emission current. In the new design, we consider a pointed height distribution of the carbon nanotube array under a diode configuration with two side gates maintained at a negative potential to obtain a highly intense beam of electrons localized at the center of the array. The randomly oriented CNTs are assumed to be grown on a metallic substrate in the form of a thin film. A model of field emission from an array of CNTs under diode configuration was proposed and validated by experiments. Despite high output, the current in such a thin film device often decays drastically. The present paper is focused on understanding this problem. The random orientation of the CNTs and the electromechanical interaction are modeled to explain the self-assembly. The degraded state of the CNTs and the electromechanical force are employed to update the orientation of the CNTs. Pulsed field emission current at the device scale is finally obtained by using the Fowler-Nordheim equation by considering a dynamic electric field across the cathode and the anode and integration of current densities over the computational cell surfaces on the anode side. Furthermore we compare the subsequent performance of the pointed array with the conventionally used random and uniform arrays and show that the proposed design outperforms the conventional designs by several orders of magnitude. Based on the developed model, numerical simulations aimed at understanding the effects of various geometric parameters and their statistical features on the device current history are reported.

Since it was isolated in 2004, graphene, the first known 2D crystal, is the object of a growing interest, due to the range of its possible applications as well as its intrinsic properties. From large scale electronics and photovoltaics to spintronics and fundamental quantum phenomena, graphene films have attracted a large community of researchers. But bringing graphene to industrial applications will require a reliable, low cost and easily scalable synthesis process. In this paper we present a new growth process based on plasma enhanced chemical vapor deposition. Furthermore, we show that, when the substrate is an oxidized silicon wafer covered by a nickel thin film, graphene is formed not only on top of the nickel film, but also at the interface with the supporting SiO₂ layer. The films grown using this method were characterized using classical methods (Raman spectroscopy, AFM, SEM) and their conductivity is found to be close to those reported by others.

The need to have a complete control of the length of the carbon nanotubes is one of the most limiting factor in using nanotubes based devices. In fact their treatments often lead to have different length distribution involving therefore different properties. In this work we aim at controlling the length of the nanotubes adjusting the oxidation temperature. Temperature dependence of SWNTs oxidation was analyzed by Raman spectroscopy. AFM images shows the height of micropatterned self-assembled monolayers of carboxylated SWNTs. SWNTs forest with different height could be fabricated controlling oxidation temperature in the range of 303K-313K.

Highly crystalline few-graphene layers were synthesized on poly-nickel, Ni(111) and Ni-deposited substrates by optimizing the mixing ratio of C₂H₂/H₂ and C₂H₄/H₂ and growth time. The hydrogen effect was investigated to minimize defects and maintain uniformity of the synthesized few-layer graphenes. Using the optimized ratio of hydrogen and acetylene mixture, few graphene layers with large sizes of up to 4 inches in diameter were also synthesized on Ni evaporated Si substrate with different thicknesses and were transferred successfully onto PET film. We also found that the wrinkles, different from inherent ripples, were formed in the graphene layer independent of the location of the grain boundary of poly-Ni substrate and growth conditions. This was attributed to the formation of a step terrace followed by the terrace bunching to result in higher wrinkles due to the thermal mismatch existing between Ni substrate and graphene layers during thermal quenching. A sheet resistance of 233 Ω/sq was obtained at a transmittance of 65%.

This paper investigates the radiation characteristics of a Vee dipole antenna operating in the near infra-red and optical frequency regimes. Antenna properties, such as far-field radiation patterns, coupling coefficient, measured by the scattering parameter S11, and directivity are provided. The resonance and directivity behavior of the optical Vee dipole, which is based on Multi-Wall Carbon Nano Tube (MWCNT), are investigated by varying the dipole length in order to exploit the effective operating frequency in the near infra-red range (~120 to 400 THz) and the visible light range (~400- 750 THz). Moreover, a parametric study aimed at optimizing the antenna directivity is performed by varying the angle between the two arms of the dipole using CST Microwave Studio simulation software which is based on the Finite Integration Technique (FIT). The proposed antenna achieved a directivity 3.767 dB higher than the traditional dipole in the visible regime while maintaining the same directivity in the near infrared regime.