1,067 research outputs found
Local Semiconducting Transition in Armchair Carbon Nanotubes: The Effect of Periodic Bi-site Perturbation on Electronic and Transport Properties of Carbon Nanotubes
In carbon nanotubes, the most abundant defects, caused for example by
irradiation or chemisorption treatments, are small perturbing clusters, i.e.
bi-site defects, extending over both A and B sites. The relative positions of
these perturbing clusters play a crucial role in determining the electronic
properties of carbon nanotubes. Using bandstructure and electronic transport
calculations, we find out that in the case of armchair metallic nanotubes a
band gap opens up when the clusters fulfill a certain periodicity condition.
This phenomenon might be used in future nanoelectronic devices in which certain
regions of single metallic nanotubes could be turned to semiconducting ones.
Although in this work we study specifically the effect of hydrogen adatom
clusters, the phenomenon is general for different types of defects. Moreover,
we study the influence of the length and randomness of the defected region on
the electron transport through it.Comment: 5 Pages, 5 Figure
Differential Bloch Oscillating Transistor Pair
We examine a Bloch Oscillating Transistor pair as a differential stage for
cryogenic low-noise measurements. Using two oppositely biased, nearly symmetric
Bloch Oscillating Transistors, we measured the sum and difference signals in
the current gain and transconductance modes while changing the common mode
signal, either voltage or current. From the common mode rejection ratio we find
values dB even under non-optimal conditions. We also characterize the
noise properties and obtain excellent noise performance for measurements having
source impedances in the M range.Comment: 8 pages, 3 figure
Wigner molecules in polygonal quantum dots: A density functional study
We investigate the properties of many-electron systems in two-dimensional
polygonal (triangle, square, pentagon, hexagon) potential wells by using the
density functional theory. The development of the ground state electronic
structure as a function of the dot size is of particular interest. First we
show that in the case of two electrons, the Wigner molecule formation agrees
with the previous exact diagonalization studies. Then we present in detail how
the spin symmetry breaks in polygonal geometries as the spin density functional
theory is applied. In several cases with more than two electrons, we find a
transition to the crystallized state, yielding coincidence with the number of
density maxima and the electron number. We show that this transition density,
which agrees reasonably well with previous estimations, is rather insensitive
to both the shape of the dot and the electron number.Comment: 8 pages, 11 figure
Electonic transport properties of nitrate-doped carbon nanotube networks
The conductivity of carbon nanotube (CNT) networks can be improved markedly
by doping with nitric acid. In the present work, CNTs and junctions of CNTs
functionalized with NO molecules are investigated to understand the
microscopic mechanism of nitric acid doping. According to our density
functional theory band structure calculations, there is charge transfer from
the CNT to adsorbed molecules indicating p-type doping. The average doping
efficiency of the NO molecules is higher if the NO molecules form
complexes with water molecules. In addition to electron transport along
individual CNTs, we have also studied electron transport between different
types (metallic, semiconducting) of CNTs. Reflecting the differences in the
electronic structures of semiconducting and metallic CNTs, we have found that
besides turning semiconducting CNTs metallic, doping further increases electron
transport most efficiently along semiconducting CNTs as well as through a
junction between them.Comment: 13 pages, 12 figure
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