587 research outputs found
Production of L-Leucine Nanoparticles under Various Conditions Using an Aerosol Flow Reactor Method
We have studied the formation of L-leucine nanoparticles under various conditions using an aerosol flow reactor method. Temperatures and L-leucine concentrations for the experiments were selected to vary the saturation conditions for L-leucine in the reactor. In the two extreme cases, L-leucine is either in (i) the condensed phase (110 ∘C) or completely in (ii) the vapour phase (200 ∘C) for all concentrations; (iii) at the intermediate temperature (150 ∘C), the extent of evaporation of L-leucine depends notably on the concentration, and thus partial evaporation and production of residual particles are expected. The size distribution of particles and the particle morphology varied according to formation mechanism with the geometric mean diameter of the particles between 30 nm and 210 nm. Hollow, spherical particles were obtained with the droplet-to-particle method without vaporisation of L-leucine; whereas leafy-looking particles were produced by homogeneous nucleation of supersaturated L-leucine vapour and subsequent growth by heterogeneous vapour deposition.Peer reviewe
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
High-Yield of Memory Elements from Carbon Nanotube Field-Effect Transistors with Atomic Layer Deposited Gate Dielectric
Carbon nanotube field-effect transistors (CNT FETs) have been proposed as
possible building blocks for future nano-electronics. But a challenge with CNT
FETs is that they appear to randomly display varying amounts of hysteresis in
their transfer characteristics. The hysteresis is often attributed to charge
trapping in the dielectric layer between the nanotube and the gate. This study
includes 94 CNT FET samples, providing an unprecedented basis for statistics on
the hysteresis seen in five different CNT-gate configurations. We find that the
memory effect can be controlled by carefully designing the gate dielectric in
nm-thin layers. By using atomic layer depositions (ALD) of HfO and
TiO in a triple-layer configuration, we achieve the first CNT FETs with
consistent and narrowly distributed memory effects in their transfer
characteristics.Comment: 6 pages, 3 figures; added one reference, text reformatted with
smaller addition
CVD Synthesis of Hierarchical 3D MWCNT/Carbon-Fiber Nanostructures
Multiwalled carbon nanotubes (MWCNTs) were synthesized by CVD on industrially manufactured highly crystalline vapor-grown carbon fibers (VGCFs). Two catalyst metals (Ni and Fe) and carbon precursor gases (C2H2 and CO) were studied. The catalysts were deposited on the fibers by sputtering and experiments carried out in two different reactors. Samples were characterized by electron microscopy (SEM and TEM). Iron was completely inactive as catalyst with both C2H2 and CO for reasons discussed in the paper. The combination of Ni and C2H2 was very active for secondary CNT synthesis, without any pretreatment of the fibers. The optimal temperature for CNT synthesis was 750 ∘C, with total gas flow of 650 cm exp 3 min exp -1  of C2H2, H2, and Ar in 1.0:6.7:30 ratio.Peer reviewe
Catalyst-free growth of In(As)P nanowires on silicon
The catalyst-free metal organic vapor phase epitaxialgrowth of In(As)P nanowires on silicon substrates is investigated using in situ deposited In droplets as seeds for nanowiregrowth. The thin substrate native oxide is found to play a crucial role in the nanowire formation. The structure of the nanowires is characterized by photoluminescence and electron microscopy measurements. The crystal structure of the InPnanowires is wurtzite with its c axis perpendicular to the nanowire axis. Adding arsenic precursor to the gas phase during growth results in a bimodal photoluminescence spectrum exhibiting peak at the InAsP and InP band gap energies.Peer reviewe
Enhanced luminescence from catalyst-free grown InP nanowires
The surface effects in the optical properties of catalyst-free grownInPnanowires are investigated. Both as-grown nanowires and nanowires treated with hydrofluoric acid are studied using low- and room-temperature continuous-wave and time-resolved photoluminescence measurements and transmission electron microscopy. It is shown that the room-temperature photoluminescence intensity is increased by two orders of magnitude after the surface treatment, and that there is also a significant increase in the double-exponential photoluminescence decay time.Peer reviewe
Robust Bessel-function-based method for determination of the (n, m) indices of single-walled carbon nanotubes by electron diffraction
We report a calibration-free method for the determination of chiral indices (n,m) of single-walled carbon nanotubes from their electron diffraction patterns based on Bessel function analysis of the diffracted layer lines. An approach has been developed for confident identification of the orders of the Bessel functions from the intensity modulations of the diffraction layer lines, to which (n,m) are correlated. In particular, we critically evaluate the effect of nanotube inclination on the validity of the method and show that the layer lines governed by high-order Bessel functions tolerate higher tilt angles than those of low-order Bessel functions and thus are favored for (n,m) evaluation. The method is of particular significance in that it considerably enhances the precision of chiral indexing and makes possible the analysis of high-order Bessel functions, especially when EDPs are of relatively low pixel resolution. The technique can be extended to structural analysis of double-walled carbon nanotubes.Peer reviewe
Determination of helicities in unidirectional assemblies of graphitic or graphiticlike tubular structures
Here we propose a universal method for the determination of all helicities present in unidirectional assemblies of hexagon-based graphitic or graphiticlike tubular structures, e.g., multiwalled or bundled carbon nanotubes(CNTs) or boron-nitride nanotubes and their structural analogs. A critical dimension characteristic of a fundamental structural property, i.e., the atomic bond length, is discerned from electron diffraction patterns by which all helicities present in the assemblies are identified. Using this method, we determine the helicity population in a single-walled CNT sample produced by laser ablation technique.Peer reviewe
Controlling supercurrents using single-walled carbon nanotube weak links
We have investigated proximity-induced supercurrents in single-walled carbon nanotubes. Phase diffusion is found to be present in the maximum measured supercurrent of 4.8 nA, which results in a minimum of 100Ω zero bias resistance in superconducting state. We also observe that the supercurrent is very sensitive to the measurement bandwidth and large phase fluctuations can even destroy the supercurrents. Our results shed light on the methods of how to improve the performance of high frequency superconducting single-walled nanotube devices.Peer reviewe
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