312 research outputs found
Field emission from Luttinger liquids and single-wall carbon nanotubes
We develop a theory for the field emission effect in Luttinger liquids and
single-wall carbon nanotubes at the level of the energy resolved current
distribution. We generalise Fowler-Nordheim relations. Just below the Fermi
edge, we find a power-law vanishing current distribution with the density of
states exponent. The current distribution above the Fermi edge owes its
existence to a peculiar interplay of interactions and correlated tunnelling. It
displays a non-trivial power-law divergence just above the Fermi energy.Comment: 4 pages, 2 figures (eps files
Determination of the Intershell Conductance in Multiwalled Carbon Nanotubes
We report on the intershell electron transport in multiwalled carbon
nanotubes (MWNT). To do this, local and nonlocal four-point measurements are
used to study the current path through the different shells of a MWNT. For
short electrode separations 1 m the current mainly flows
through the two outer shells, described by a resistive transmission line with
an intershell conductance per length of ~(10 k\Omega)^{-1}/m. The
intershell transport is tunnel-type and the transmission is consistent with the
estimate based on the overlap between -orbitals of neighboring shells.Comment: 5 pages, 4 figure
Geometrical Dependence of High-Bias Current in Multiwalled Carbon Nanotubes
We have studied the high-bias transport properties of the different shells
that constitute a multiwalled carbon nanotube. The current is shown to be
reduced as the shell diameter is decreased or the length is increased. We
assign this geometrical dependence to the competition between electron-phonon
scattering process and Zener tunneling.Comment: 4 pages, 4 figure
Magnetization of carbon-coated ferromagnetic nanoclusters determined by electron holography
The magnetic properties of carbon-coated Co and Ni nanoparticles aligned in chains were determined using transmission electron holography. The measurements of the phase change of the electron wave due to the magnetization of the sample were performed. The ratio of remnant magnetization to bulk saturation magnetization Mr/Ms of Co decreased from 53% to 16% and of Ni decreased from 70% to 30% as the particle diameter increased from 25 to 90 nm. It was evident that the inhomogenous magnetic configurations could diminish the stray field of the particles. After being exposed to a 2-Tesla external magnetic field, the Mr/Ms of Co increased by 45% from the original values with the same dependency on the particle size. The Mr/Ms of Ni particles, on the other hand, increased only 10%. The increased magnetization could be attributed to the merging of small domains into larger ones after the exposure to the external magnetic field. The validity of the interpretation of the holograms was established by simulatio
Field emission properties of nano-composite carbon nitride films
A modified cathodic arc technique has been used to deposit carbon nitride
thin films directly on n+ Si substrates. Transmission Electron Microscopy
showed that clusters of fullerene-like nanoparticles are embedded in the
deposited material. Field emission in vacuum from as-grown films starts at an
electric field strength of 3.8 V/micron. When the films were etched in an
HF:NH4F solution for ten minutes, the threshold field decreased to 2.6
V/micron. The role of the carbon nanoparticles in the field emission process
and the influence of the chemical etching treatment are discussed.Comment: 22 pages, 8 figures, submitted to J. Vac. Sc. Techn.
Hydrogen passivation of boron acceptors in as-grown boron-doped CVD diamond epilayers
A homoepitaxial boron-doped diamond single layer is investigated by means of Fourier transformed infrared spectroscopy (FTIR) and cathodoluminescence (CL). Both techniques are shown to be complementary. ÎĽ-FTIR mapping allows to determine the location of active boron while CL allows discernability between passivation
and compensation. Hydrogen incorporation during chemical vapour deposition (CVD) growth is revealed to passivate boron acceptors. The obtained results highlight that plasma etching can induce a dissociation of B–H centres.4 page
Multi-particle effects in non-equilibrium electron tunnelling and field emission
We investigate energy resolved electric current from various correlated host
materials under out-of-equilibrium conditions. We find that, due to a combined
effect of electron-electron interactions, non-equilibrium and multi-particle
tunnelling, the energy resolved current is finite even above the Fermi edge of
the host material. In most cases, the current density possesses a singularity
at the Fermi level revealing novel manifestations of correlation effects in
electron tunnelling. By means of the Keldysh non-equilibrium technique, the
current density is calculated for one-dimensional interacting electron systems
and for two-dimensional systems, both in the pure limit and in the presence of
disorder. We then specialise to the field emission and provide a comprehensive
theoretical study of this effect in carbon nanotubes.Comment: 22 pages, 8 figures (eps files
The Physicist's Guide to the Orchestra
An experimental study of strings, woodwinds (organ pipe, flute, clarinet,
saxophone and recorder), and the voice was undertaken to illustrate the basic
principles of sound production in music instruments. The setup used is simple
and consists of common laboratory equipment. Although the canonical examples
(standing wave on a string, in an open and closed pipe) are easily reproduced,
they fail to explain the majority of the measurements. The reasons for these
deviations are outlined and discussed.Comment: 11 pages, 10 figures (jpg files). Submitted to European Journal of
Physic
Carbon Nanotubes Generated from Polyphenyl Acetylene
The carbonization of polyphenyl acetylene in alumina matrix yields uniform, cylindrical, monodisperse carbon nanotubes with outer diameter almost equal to pore diameter of the alumina membrane used. The electrochemical characteristics reveal that the charge transfer at the composite electrode based on carbon
nanotube might be higher compared to that of planar graphite, glassy carbon and composite electrode based
on commercially available Vulcan XC72R carbon. Pt-Ru nanoparticles are highly dispersed inside the tube
with an average particle size of 1.7 nm as revealed by HR-TEM images
- …