<i>Foundations of Vacuum Science and Technology</i>

Lafferty, J. M.; Rubin, Lawrence G.

doi:10.1063/1.882616

Cited by 101 publications

(79 citation statements)

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“…The linear behavior in both cases under low input power implies ohmic contact, while the nonlinear behavior at higher power densities can be analyzed with an analytical model similar to that of a thermal conductivity gauge or Pirani gauge. 15,16 To characterize the temperature resistance responses, the resistances of this single MWCNT have been measured over the range of 200 to 400 K, and the extracted temperature coefficient of resistance (TCR) has shown linear behavior as -0.137% K -1 (See Figure 5 in Supporting Information). On the basis of this information, a 1 V bias voltage applied to the MWCNT in an argon environment is estimated to increase the average MWCNT temperatures by 40 and 140 K over the ambient temperature under the pressures of 10 5 Pa and 6.5 × 10 3 Pa, respectively.…”

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confidence: 99%

“…In the molecular regime, gas density is low, and the molecules are assumed to experience essentially no collisions among themselves as they travel along the path between the MWCNT and the surrounding walls. Gas molecules arriving at the hot wire will have a Maxwellian energy distribution corresponding to T 0 (ambient temperature), as explained in the classic thermal conductivity gauge theories, 15,16 and these molecules dwell on the surface for a short time and depart with an energy distribution corresponding to T CNT . The heat transfer via gas between a MWCNT and an imaginary coaxial cylindrical wall can be approximate as 18 where p is the pressure, γ the ratio of specific heats of the gas, R the universal gas constant, and M the molecular mass of the gas.…”

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An Electrothermal Carbon Nanotube Gas Sensor

et al. 2007

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We show both gas pressure and species sensing capabilities based on the electrothermal effect of a multiwalled carbon nanotube (MWCNT). Upon exposure to gaseous environments, the resistance of a heated MWCNT is found to change following the conductive heat-transfer variances of gas molecules. To realize this mechanism, a suspended MWCNT is constructed by synthesis and assembly in localized chemical vapor deposition that is accomplished within seconds via real-time electrical feedback control. Vacuum pressure sensitivity and gas species differentiability are observed and analyzed. Such MWCNT electrothermal sensors are compact, fast and reversible in responses, and fully integratable with microelectronics.Carbon nanotube (CNT) gas sensors based on fundamentally different mechanisms have been demonstrated, 1 including electrical conductance or capacitance changes 2-4 or using the sharp tips of the CNT as gas ionization sensors. 5 Limiting factors for sorption-based CNT sensors include low adsorption energies, diffusion kinetics, response speed, selectivity, and reversibility. We report on the electrothermal effect of a single multiwalled carbon nanotube (MWCNT) suspended between two silicon microbridges. When a Joule-heated MWCNT is exposed to different pressures, the electrical resistance change follows the conductive heat-transfer variances of gas molecules. The MWCNT is grown on silicon using the local synthesis method and is accomplished within tens of seconds via real-time electrical feedback control. Our findings suggest that the MWCNT electrothermal mechanism has applications to both gas sensing and species differentiation, with advantages of compactness, fast and reversible responses, low power consumption, and being fully integratable with microelectronics.The electrothermal gas sensing mechanism is schematically illustrated in Figure 1a. A single MWCNT is suspended between two silicon microstructures and heated by electrical current in the system. Energy conservation calls for total heat generation equal to the summation of heat conduction to the two microstructures (W C ), heat transfer via gases (W G , shown in the figure as W gas1 and W gas2 representing the case of two types of gases of different thermal conductivity values), and heat radiation (W R ). Both gas pressure and species can affect the heat-transfer process and result in MWCNT temperature changes and therefore resistance changes.To realize this architecture, we use a complementary metal oxide semiconductor (CMOS)-compatible, in situ controlled synthesis, assembly, and integration process previously reported in the literature. 6-9 Synthesis and assembly of carbon nanotubes has been heavily investigated with various device demonstrations using high-temperature synthesis processes 10,11 and labor-intensive assembly steps, 12,13 but assembly and heterogeneous integration of CNTs with microelectronics such as standard CMOS circuitry are still problematic. Many issues still need to be resolved, such as the synthesis and accurate placement...

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An Electrothermal Carbon Nanotube Gas Sensor

et al. 2007

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“…Rarefied gas dynamics is relevant to a large number of different applications such as vacuum technology and space dynamics, all characterized by a low pressure environment [11,12]. Nowadays, it is also becoming more and more relevant to the design and study of microfluidic devices intended for several applications.…”

Section: Introductionmentioning

confidence: 99%

“…One disadvantage in decreasing the aspect ratio is that the heat transfer also decreases. The portion of mass flow rate that goes through a channel is defined by the "transmission coefficient", α, which is also known as conductance [11] or dimensionless mass flow rate [20,25]. It is the actual mass flow rate to the mass flow rate in free molecular limit ratio, which is expressed in the form of α =ṁ/ṁ f m , meaning that for an infinitely thin channel, the transmission coefficient is equal to 1.…”

Section: Introductionmentioning

confidence: 99%

“…It is the actual mass flow rate to the mass flow rate in free molecular limit ratio, which is expressed in the form of α =ṁ/ṁ f m , meaning that for an infinitely thin channel, the transmission coefficient is equal to 1. For a cylindrical channel with an aspect ratio of 5, a typical value of the transmission coefficient is 0.19 [11,20].…”

Section: Introductionmentioning

confidence: 99%

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Analysis of Nonisothermal Rarefied Gas Flow in Diverging Microchannels for Low-Pressure Microresistojets

Guerrieri

Cervone

Gill

2016

Journal of Heat Transfer

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Heat transfer and fluid flow through different microchannel geometries in the transitional regime (rarefied flow) are analysed by means of Direct Simulation Monte Carlo simulations. Four types of three-dimensional microchannels, intended to be used as expansion slots in micro-resistojet concepts, are investigated using Nitrogen as working fluid. The main purpose is to understand the impact of the channel geometry on the exit velocity and the transmission coefficient, parameters which are well known to affect directly the thruster performance. Although this analysis can be applied in principle to several possible microfluidics scenarios, particular focus is given to its application in the field of space propulsion for micro-, nano-and pico-satellites, for which the requirements ask for low thrust levels from some µN to a few mN and moderate specific impulse, as well as a low power consumption in the order of a few W. Analysis shows that the thrust produced by one single microchannel can be increased by about 480% with a careful selection of the channel geometry, decreasing at the same time the specific impulse by just 5%, with a power consumption decrease of more than 66.7%.

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