258 research outputs found
Shot Noise with Interaction Effects in Single Walled Carbon Nanotubes
We have measured shot noise in single walled carbon nanotubes (SWNT) with
good contacts at 4.2 K at low frequencies ( MHz). We find a strong
modulation of shot noise over the Fabry-Perot pattern; in terms of differential
Fano factor the variation ranges over 0.4 - 1.2. The shot noise variation, in
combination with differential conductance, is analyzed using two
(spin-degenerate) modes with different, energy-dependent transmission
coefficients. No power law dependence of shot noise, as expected for Luttinger
liquids, was found in our measurements.Comment: 5 pages, 4 figure
Influence of nanotube length and density on the plasmonic terahertz response of single-walled carbon nanotubes
We measure the conductivity spectra of thin films comprising bundled
single-walled carbon nanotubes (CNTs) of different average lengths in the
frequency range 0.3-1000 THz and temperature interval 10-530 K. The observed
temperature-induced changes in the terahertz conductivity spectra are shown to
depend strongly on the average CNT length, with a conductivity around 1 THz
that increases/decreases as the temperature increases for short/long tubes.
This behaviour originates from the temperature dependence of the electron
scattering rate, which we obtain from Drude fits of the measured conductivity
in the range 0.3-2 THz for 10 m length CNTs. This increasing scattering
rate with temperature results in a subsequent broadening of the observed THz
conductivity peak at higher temperatures and a shift to lower frequencies for
increasing CNT length. Finally, we show that the change in conductivity with
temperature depends not only on tube length, but also varies with tube density.
We record the effective conductivities of composite films comprising mixtures
of WS nanotubes and CNTs vs CNT density for frequencies in the range 0.3-1
THz, finding that the conductivity increases/decreases for low/high density
films as the temperature increases. This effect arises due to the density
dependence of the effective length of conducting pathways in the composite
films, which again leads to a shift and temperature dependent broadening of the
THz conductivity peak.Comment: Submitted to Journal of Physics D. Main manuscript: 9 pages, 8
figures. Supplementary material: 5 pages, 6 figure
The dynamics of the cellular composition of urine sediment in conditions of an artificial bladder
The evaluation of the urine cytological profile in the dynamics of adaptation of the orthotopic bladder to the functional properties of the urinary reservoir and determination of the connection between the cellular composition of the urine with the functional role of the formed from the intestinal fragment neocyst in experimental conditions and in humans. The material in experimental study were the results of a cytological study of the urine sediment obtained from 21 female pigs (mini-pigs). The portion of urine had received in experimental animals one month after orthotopic ileocystoplasty, 6 months and 1 year later and prepared as smear from the resulting precipitate. The level of lymphocytes, neutrophils, erythrocytes, as well as the superficial, intermediate and basal
epitheliocytes evaluated during study. An analysis of the cell composition of centrifugal smears from the neocyst were performed in 21 patients with bladder cancer undergoing cystectomy and the formation of an orthotopic bladder, at various periods after surgery, from 3 months to 5 years. The preparation of a centrifugal sediment and the subsequent production of smears carried out as well as experimental animals
Inverted loss engineering in functional material covered waveguides
Optical waveguides, covered with thin films, which transmittance can be
controlled by external action, are widely used in various applications from
optical modulators to saturable absorbers. It is natural to suggest that the
waveguide losses will be proportional to the covering material absorption. We
demonstrate that under certain conditions this simple assumption fails.
Instead, we observe the reduction of the film material absorption can lead to
an increase in the waveguide propagation losses. For this, we use a side
polished fiber covered with a single-walled carbon nanotube thin film whose
absorption is attenuated either due to saturable absorption or electrochemical
gating. For the films thicker than 50 nm, we observe saturable absorption to
turn into light induced absorption with nonmonotonic dependence on the incident
power. With a numerical simulation and analytical approach, we identify that
this nontrivial behavior comes from mode reshaping and predict required
parameters for its observation.Comment: 7 pages, 3 figure
Heat-mode excitation in a proximity superconductor
Mesoscopic superconductivity deals with various quasiparticle excitation
modes, only one of them -- the charge-mode -- being directly accessible for
conductance measurements due to the imbalance in populations of quasi-electron
and quasi-hole excitation branches. Other modes carrying heat or even spin,
valley etc. currents populate the branches equally and are charge-neutral that
makes them much harder to control. This noticeable gap in the experimental
studies of mesoscopic non-equilibrium superconductivity can be filled by going
beyond the conventional DC transport measurements and exploiting spontaneous
current fluctuations. Here, we perform the first experiment of this kind and
investigate the transport of heat in an open hybrid device based on a
superconductor proximitized InAs nanowire. Using shot noise measurements we
observe a novel effect of sub-gap Andreev heat guiding along the
superconducting interface and fully characterize it in terms of the thermal
conductance on the order of , tunable by a back gate
voltage. Understanding of the heat-mode also uncovers its implicit signatures
in the non-local charge transport. Our experiments open a direct pathway to
probe generic neutral excitations in superconducting hybrids.Comment: revised, 20 pages with supplementa
Gas phase synthesis of non-bundled, small diameter single-walled carbon nanotubes with near-armchair chiralities
We present a floating catalyst synthesis route for individual, i.e., non-bundled, small diameter single-walled carbon nanotubes (SWCNTs) with a narrow chiral angle distribution peaking at high chiralities near the armchair species. An ex situ spark discharge generator was used to form iron particles with geometric number mean diameters of 3–4 nm and fed into a laminar flow chemical vapour deposition reactor for the continuous synthesis of long and high-quality SWCNTs from ambient pressure carbon monoxide. The intensity ratio of G/D peaks in Raman spectra up to 48 and mean tube lengths up to 4 μm were observed. The chiral distributions, as directly determined by electron diffraction in the transmission electron microscope, clustered around the (n,m) indices (7,6), (8,6), (8,7), and (9,6), with up to 70% of tubes having chiral angles over 20°. The mean diameter of SWCNTs was reduced from 1.10 to 1.04 nm by decreasing the growth temperature from 880 to 750 °C, which simultaneously increased the fraction of semiconducting tubes from 67% to 80%. Limiting the nanotube gas phase number concentration to ∼10 exp 5 cm exp −3 prevented nanotube bundle formation that is due to collisions induced by Brownian diffusion. Up to 80% of 500 as-deposited tubes observed by atomic force and transmission electron microscopy were individual. Transparent conducting films deposited from these SWCNTs exhibited record low sheet resistances of 63 Ω/□ at 90% transparency for 550 nm light.Peer reviewe
Infrared properties of randomly oriented silver nanowires
We experimentally investigated the infrared properties of a set of randomly oriented silver nanowires films deposited onto glass substrate. Infrared emission of the obtained films was characterized in the long infrared range, i.e., 8–12 μm, by observing their temperature evolution under heating regime with a focal plane array infrared camera as well as a thermocouple. The obtained experimental results showed that the infrared emission from a mesh composed of silver nanowires might be tailored by opportunely assessing preparation condition, such as the metal filling factor. From the theoretical point of view, the real and imaginary part of the electrical permittivity components were retrieved from the calculations of effective permittivities of in-plane randomly oriented metallic wires, thus giving the refractive index and extinction coefficients for the four different silver nanowires meshes. Due to the correspondence between emissivity and absorbance, the experimental results are interpreted with the reconstructed corresponding absorbance spectra, thus suggesting that these coatings are suitable for infrared signature reduction applications.Peer reviewe
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