Low-temperature grown vertically aligned carbon nanotube array for an optimal infrared bolometer.

Vertically aligned carbon nanotube (VACNT) arrays have been explored as an absorber of thermal-type photodetectors. A long and dense VACNT array absorbs a wide spectral range of incident light with high absorption rate, but has a high thermal mass that results in a low response speed. To achieve a small thermal mass, a shorter and less dense VACNT array is needed.

Synthesis and interface characterization of CNTs on graphene.

Carbon nanotubes (CNTs) and graphene are potential candidates for future interconnect materials. CNTs are promising on-chip via interconnect materials due to their readily formed vertical structures, their current-carrying capacity, which is much larger than existing on-chip interconnect materials such as copper and tungsten, and their demonstrated ability to grow in patterned vias with sub-50 nm widths; meanwhile, graphene is suitable for horizontal interconnects. However, they both present the challenge of having high-resistance contacts with other conductors.

Effect of improved contact on reliability of sub-60 nm carbon nanotube vias.

Advances in semiconductor technology due to the aggressive downward scaling of on-chip feature sizes have led to rapid rises in the resistivity and current density of interconnect conductors. As a result, current interconnect materials, Cu and W, are subject to performance and reliability constraints approaching or exceeding their physical limits. Therefore, alternative materials are being actively considered as potential replacements to meet such constraints.

Electron-beam and ion-beam-induced deposited tungsten contacts for carbon nanofiber interconnects.

Ion-beam-induced deposition (IBID) and electron-beam-induced deposition (EBID) with tungsten (W) are evaluated for engineering electrical contacts with carbon nanofibers (CNFs). While a different tungsten-containing precursor gas is utilized for each technique, the resulting tungsten deposits result in significant contact resistance reduction. The performance of CNF devices with W contacts is examined and conduction across these contacts is analyzed.

Carbon nanofiber interconnect RF characteristics improvement with deposited tungsten contacts.

Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are potential materials for high-performance electronic devices and circuits due to their light weight and excellent electrical properties such as high current capacity and tolerance to electromigration. In addition, at high frequencies, these materials exhibit transport behavior which holds special promise for applications as on-chip interconnects. Contact resistance at CNF-metal interface is a major factor in limiting the electrical performance of CNF interconnects at all frequencies.

Modeling of a carbon nanotube ultracapacitor.

The modeling of carbon nanotube ultracapacitor (CNU) performance based on the simulation of electrolyte ion motion between the cathode and the anode is described. Using a molecular dynamics (MD) approach, the equilibrium positions of the electrode charges interacting through the Coulomb potential are determined, which in turn yield the equipotential surface and electric field associated with the capacitor. With an applied ac voltage, the current is computed based on the nanotube and electrolyte particle distribution and interaction, resulting in the frequency-dependent impedance Z(ω).

Temperature dependence of carbon nanofiber resistance.

Transport properties under current stress are examined for a carbon nanofiber (CNF) on an insulating substrate between tungsten-deposited gold electrodes. The temperature dependence of CNF resistance is determined based on our previously reported heat transport model. The measured devices exhibit a thermal activation behavior, suggesting transport in a disordered medium.

The effect of catalysts and underlayer metals on the properties of PECVD-grown carbon nanostructures.

The growth behaviors and contact resistances of vertically aligned carbon nanotubes (CNTs) and carbon nanofibers (CNFs) grown on different underlayer metals are investigated. The average diameter, diameter distribution, density, growth rate and contact resistance exhibit strong correlation with the choice of catalyst/underlayer combination. These observations are analyzed in terms of interactions between the catalyst and the underlayer metal.

High efficient electrical stimulation of hippocampal slices with vertically aligned carbon nanofiber microbrush array.

Long-term neuroprostheses for functional electrical stimulation must efficiently stimulate tissue without electrolyzing water and raising the extracellular pH to toxic levels. Comparison of the stimulation efficiency of tungsten wire electrodes (W wires), platinum microelectrode arrays (PtMEA), as-grown vertically aligned carbon nanofiber microbrush arrays (VACNF MBAs), and polypyrrole coated (PPy-coated) VACNF MBAs in eliciting field potentials in the hippocampus slice indicates that, at low stimulating voltages that preclude the electrolysis of water, only the PPy-coated VACNF MBA is able to stimulate the CA3 to CA1 pathway. Unlike the W wires, PtMEA, as-grown VACNF MBA, and the PPy-coated VACNF MBA elicit only excitatory postsynaptic potentials (EPSPs).

Growth of carbon nanofibers on nanoscale catalyst strips fabricated with a focused ion beam.

We studied the growth mode of vertically aligned carbon nanofibers (CNFs) on Ni catalyst strips fabricated using a focused ion beam (FIB). We found that the CNF growth on Ni catalysts was strongly affected by the geometry of the microfabricated Ni catalyst strips. Selective growth of vertically aligned CNFs requires ion milling from the outside edge of the sample so that the milled materials are effectively evacuated.