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A recent algorithm developed by Tripathi et al. [J. Appl. Phys. 128, 025017 (2020); Erratum, J. Appl. Phys. 131, 169901 (2022)] is modified to study the effects of thermal contact resistance on the field emission (FE) properties of a carbon nanotube (CNT). The model takes into account the temperature dependence of the CNT electrical and thermal conductivities. The boundary condition proposed by Huang et al. [Phys. Rev. Lett. 93, 7 (2004)] is used to include the effects of thermal contact resistance at a CNT/chuck interface located at x = 0 , i.e., T c = T (x = 0) = λ π r 2 κ (T c) (∂ T / ∂ x) x = 0 + T 0 , where r is the CNT radius, κ (T c) is the heat conduction coefficient at x = 0 , and λ is the thermal resistivity of the CNT/chuck interface. The chuck is assumed to be a perfect heat sink at temperature T 0. For a given set of CNT parameters and values of the applied external electric field, it is shown that current constriction at the CNT/chuck contact point leads to self-heating effects which increase with the value of the thermal contact resistance, leading to an increase in the temperature profile along the CNT (including the temperature at its tip) and the FE current above their values obtained assuming the CNT/chuck interface is at the heat sink temperature T 0. The fractional change of the emission current versus applied external electric field is calculated for increasing values of the parameter λ. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) fiber-based emitters have shown great potential to deliver stable, high current beams for various potential applications. Because of joule heating, CNT field emitters are heated to high temperatures during field emission. It is important to improve the thermal management of emitters to increase their reliability and prevent premature failure. This paper compares the field emission characteristics and the temperature distribution of a new configuration of a looped CNT fiber emitter with a traditional single vertical CNT fiber emitter. It is found that the maximum temperature of the looped fiber emitter (~300 °C) is significantly reduced compared to that of the vertical fiber (~600 °C) at the same emission current of 3 mA. The experimentally measured temperature distribution is compared with a recent theory on joule heating of a one-dimensional conductor. This study provides new insights into the design of high performance field emitters. [ABSTRACT FROM AUTHOR]

Field emission (FE) measurements are reported from carbon nanotube (CNT) fibers and laser-patterned free standing films fabricated by direct online condensation from a floating catalyst chemical vapor deposition reactor. Fiber and film cathodes showed stable emission in the 1–2 mA current (I) range at maximum cathode temperatures less than 1000 °C; film cathodes show localized heating at the triangular tips and higher maximum temperatures than the fibers. Fowler–Nordheim (FN) analysis indicated a change in the morphology of the emitters with increasing external electrical field (Eext). Fiber cathode I–Eext data are interpreted as FN emission from the fiber tip which is eventually limited by space-charge effects. At higher Eext, FN emission from the fiber sidewall occurs. The single fiber cathode stopped emitting abruptly when field induced self-heating effects became significant. For CNT films, self-heating effects can destroy a portion of the film, but FE can still occur from other areas. [ABSTRACT FROM AUTHOR]

A multiwalled carbon nanotube (MWCNT)-based electrochemical biosensor is developed for monitoring microcystin-LR (MC-LR), a toxic cyanobacterial toxin, in sources of drinking water supplies. The biosensor electrodes are fabricated using vertically well-aligned, dense, millimeter-long MWCNT arrays with a narrow size distribution, grown on patterned Si substrates by water-assisted chemical vapor deposition. High temperature thermal treatment (2500 °C) in an Ar atmosphere is used to enhance the crystallinity of the pristine materials, followed by electrochemical functionalization in alkaline solution to produce oxygen-containing functional groups on the MWCNT surface, thus providing the anchoring sites for linking molecules that allow the immobilization of MC-LR onto the MWCNT array electrodes. Addition of the monoclonal antibodies specific to MC-LR in the incubation solutions offers the required sensor specificity for toxin detection. The performance of the MWCNT array biosensor is evaluated using micro-Raman spectroscopy, including polarized Raman measurements, X-ray photoelectron spectroscopy, cyclic voltammetry, optical microscopy, and Faradaic electrochemical impedance spectroscopy. A linear dependence of the electron-transfer resistance on the MC-LR concentration is observed in the range of 0.05 to 20 μg L−1, which enables cyanotoxin monitoring well below the World Health Organization (WHO) provisional concentration limit of 1 μg L−1 for MC-LR in drinking water. [ABSTRACT FROM AUTHOR]

The promise of carbon nanotube (CNT)-based technology has driven colossal research efforts for the past three decades. Integration of CNTs onto functional devices often involves the use of time-consuming and laborious patterning techniques to obtain spatially selective growth. In this manuscript, we present a single-step route for CNT forest growth in patterned areas using a novel catalyst support activation process which does not require the use of masks, resists or stencils. The process uses an electron-beam (e-beam) in the presence of water vapor to activate a catalyst support at select locations, on which CNT forests can grow selectively when exposed to the CNT catalyst and precursor. The process, therefore referred to as e-beam chemistry, modifies the support stoichiometry and surface roughness using a radiolysis-driven mechanism to yield catalytically active patterns on an otherwise inactive catalyst support. Because of its simplicity and effectiveness, the presented technique holds great promise in producing high fidelity, chemically-selective patterns. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) have been grown using Fe, Co, Ni, and Co/Fe spin-on-catalyst (SOC) systems, involving the metal salt dispersed with a spin-on-glass precursor. During initial growth runs (CH4/H2/900 °C), the CNT yield followed the order Co-SOC > Fe-SOC ⪢ Ni-SOC. The Fe catalysts produced the longest nanotubes at the expense of a larger average CNT diameter and broader diameter distribution than the Co-SOC system. A series of Co/Fe-SOCs were prepared where as the atomic percentage of Co is increased nucleation of CNT increases but the CNT length decreases. The linear relationship between the diameter and length of CNTs grown from the Co/Fe-SOC suggests that slow growth is beneficial with respect to control over CNT diameter. After initial CNT growth, the original samples were subjected to additional growth runs. Four individual reactions were observed in the Fe-SOC and binary Co/Fe-SOC: regrowth (amplification), double growth (a second CNT growing from a previously active catalyst), CNT etching, and nucleation from initially inactive catalysts (new growth). CNT etching was observed for the mixed catalyst systems (Co/Fe-SOC) but not for either Fe-SOC or Co-SOC. During the regrowth experiments, CNTs were observed that were not present after the initial growth run (and were not as a result of amplification or double growth). Thus, catalysts, which were initially inactive toward nucleation of CNTs in the original growth run, are capable of becoming activated when placed back into the furnace and submitted to regrowth under identical conditions. [ABSTRACT FROM AUTHOR]