ABSTRACT
We have grown vertically aligned single-walled carbon nanotube forests with an area density of 1.5 × 10(13) cm(-2), the highest yet achieved, by reducing the average diameter of the nanotubes. We use a nanolaminate Fe-Al(2)O(3) catalyst design consisting of three layers of Al(2)O(3), Fe, and Al(2)O(3), in which the lower Al(2)O(3) layer is densified by an oxygen plasma treatment to increase its diffusion barrier properties, to allow a thinner catalyst layer to be used. This high nanotube density is desirable for using carbon nanotubes as interconnects in integrated circuits.
ABSTRACT
We present a general catalyst design to synthesize ultrahigh density, aligned forests of carbon nanotubes by cyclic deposition and annealing of catalyst thin films. This leads to nanotube forests with an area density of at least 10(13) cm(-2), over 1 order of magnitude higher than existing values, and close to the limit of a fully dense forest. The technique consists of cycles of ultrathin metal film deposition, annealing, and immobilization. These ultradense forests are needed to use carbon nanotubes as vias and interconnects in integrated circuits and thermal interface materials. Further density increase to 10(14) cm(-2) by reducing nanotube diameter is possible, and it is also applicable to nanowires.
ABSTRACT
We analyze the high-energy Raman modes, G+ and G-, in a pair of one metallic and one semiconducting nanotubes. By combining Rayleigh scattering with Raman resonance profiles of the radial breathing mode and the high-energy modes, we show that the observed G- and G+ peaks can originate from longitudinal optical phonons of different tubes. The G- peak is the longitudinal mode of the metallic tube; it is broadened and downshifted due to strong electron-phonon coupling in the metallic nanotube. The G+ peak is due to the longitudinal mode in the semiconducting tube. This result resolves an ongoing debate in the literature.
