Minimizing Joule heating remains an important goal in the design of electronic devices. The prevailing model of Joule heating relies on a simple semiclassical picture in which electrons collide with the atoms of a conductor, generating heat locally and only in regions of non-zero current density, and this model has been supported by most experiments. Recently, however, it has been predicted that electric currents in graphene and carbon nanotubes can couple to the vibrational modes of a neighbouring material, heating it remotely. Here, we use in situ electron thermal microscopy to detect the remote Joule heating of a silicon nitride substrate by a single multiwalled carbon nanotube. At least 84% of the electrical power supplied to the nanotube is dissipated directly into the substrate, rather than in the nanotube itself. Although it has different physical origins, this phenomenon is reminiscent of induction heating or microwave dielectric heating. Such an ability to dissipate waste energy remotely could lead to improved thermal management in electronic devices.

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The ability to tune the thermal resistance of carbon nanotube mechanical supports from insulating to conducting could permit the next generation of thermal management devices. Here, we demonstrate fabrication techniques for carbon nanotube supports that realize either weak or strong thermal coupling, selectively. Direct imaging by in-situ electron thermal microscopy shows that the thermal contact resistance of a nanotube weakly-coupled to its support is greater than 250 K·m/W and that this value can be reduced to

We discuss the design, operation, and calibration of two versions of a xenon gas purity monitor (GPM) developed for the EXO double beta decay program. The devices are sensitive to concentrations of oxygen well below 1 ppb at an ambient gas pressure of one atmosphere or more. The theory of operation of the GPM is discussed along with the interactions of oxygen and other impurities with the GPM's tungsten filament. Lab tests and experiences in commissioning the EXO-200 double beta decay experiment are described. These devices can also be used on other noble gases.Comment: 41 pages, 26 figure

We describe the design and operation of a system for xenon liquefaction in which the condenser is separated from the liquid storage vessel. The condenser is cooled by a pulse tube cryocooler, while the vessel is cooled only by the liquid xenon itself. This arrangement facilitates liquid particle detector research by allowing easy access to the upper and lower flanges of the vessel. We find that an external xenon gas pump is useful for increasing the rate at which cooling power is delivered to the vessel, and we present measurements of the power and efficiency of the apparatus.

We study heat dissipation of a multi-wall carbon nanotube (MWCNT) device fabricated from two crossed nanotubes on a SiN x substrate under the influence of a constant (DC) electric bias. By monitoring the temperature of the substrate, we observe negligible Joule heating within the nanotube lattice itself and instead heating occurs in the insulating substrate directly via a remote-scattering heating effect. Using finite element analysis, we estimate a remote heating parameter, β , as the ratio of the power dissipated directly in the substrate to the total power applied. The extracted parameters show two distinct bias ranges; a low bias regime where about 85% of the power is dissipated directly into the substrate and a high bias regime where β decreases, indicating the onset of traditional Joule heating within the nanotube. Analysis shows that this reduction is consistent with enhanced scattering of charge carriers by optical phonons within the nanotube. The results provide insights into heat dissipation mechanisms of Joule heated nanotube devices that are more complex than a simple heat dissipation mechanism dominated by acoustic phonons, which opens new possibilities for engineering nanoelectronics with improved thermal management.

Presently, most space missions rely on large, heavy, and high-power instrumentation such as mass spectrometers for chemical analysis on planetary bodies. The weight of these payloads is prohibitive to mission cost, and ultimately hinders scientific advancement. This hindrance has driven us to develop a multi-functional gas sensor platform based on the additive manufacturing of low-dimensional materials. The discovery of low-dimensional materials such as graphene and carbon nanotubes (CNTs) has instigated a push to apply these materials in device design. The unique electrical and physical properties of these materials coupled to their high surface area to volume ratio make them outstanding candidates as extremely sensitive gas sensing elements for both chemiresistive and field effect transistor (FET) based devices. The detection of gases using low-dimensional materials as sensing elements relies on change in the resistance of the sensing element associated with electron donation or extraction by the gas to be detected. For most low-dimensional materials, this mechanism is not especially selective. This lack of selectivity necessitates the functionalization of said materials with catalytically appropriate functional units to promote device selectivity while maintaining the high sensitivity of the low-dimensional materials. We will present our efforts on the functionalization of chemiresistive and FET gas sensors using CNTs, graphene and transition metal dichalcogenides with both physical vapor deposition and solution phase approaches. This functionalization will ultimately allow for the fabrication of an array of gas sensors with each sensor demonstrating varied selectivity for the gases of interest. Our functional group choice, process optimization and ultimately sensor performance will be demonstrated.

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