245 research outputs found
Current carrying capacity of carbon nanotubes
The current carrying capacity of ballistic electrons in carbon nanotubes that
are coupled to ideal contacts is analyzed. At small applied voltages, where
electrons are injected only into crossing subbands, the differential
conductance is . At applied voltages larger than
( is the energy level spacing of first non crossing subbands),
electrons are injected into non crossing subbands. The contribution of these
electrons to current is determined by the competing processes of Bragg
reflection and Zener type inter subband tunneling. In small diameter nanotubes,
Bragg reflection dominates, and the maximum differential conductance is
comparable to . Inter subband Zener tunneling can be non negligible as
the nanotube diameter increases because is inversely
proportional to the diameter. As a result, with increasing nanotube diameter,
the differential conductance becomes larger than , though not
comparable to the large number of subbands into which electrons are injected
from the contacts. These results may be relevant to recent experiments in large
diameter multi-wall nanotubes that observed conductances larger than .Comment: 12 pages, 4 figure
Charging effects in the ac conductance of a double barrier resonant tunneling structure
There have been many studies of the linear response ac conductance of a
double barrier resonant tunneling structure (DBRTS). While these studies are
important, they fail to self-consistently include the effect of time dependent
charge density in the well. In this paper, we calculate the ac conductance by
including the effect of time dependent charge density in the well in a
self-consistent manner. The charge density in the well contributes to both the
flow of displacement currents and the time dependent potential in the well. We
find that including these effects can make a significant difference to the ac
conductance and the total ac current is not equal to the average of
non-selfconsitently calculated conduction currents in the two contacts, an
often made assumption. This is illustrated by comparing the results obtained
with and without the effect of the time dependent charge density included
properly
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