124 research outputs found
Significantly enhanced critical current densities in MgB2 tapes made by a scaleable, nano-carbon addition route
Nanocarbon-doped Fe-sheathed MgB2 tapes with different doping levels were
prepared by the in situ powder-in-tube method. Compared to the undoped tapes,
Jc for all the C-doped samples was enhanced by more than an order of magnitude
in magnetic fields above 9 T. At 4.2 K, the transport Jc for the 5 at% doped
tapes reached 1.85x104 A/cm2 at 10 T and 2.8x103 A/cm2 at 14 T, respectively.
Moreover, the critical temperature for the doped tapes decreased slightly.
Transmission electron microscopy showed a number of intra-granular dislocations
and the dispersed nanoparticles embedded within MgB2 grains induced by the C
doping. The mechanism for the enhancement of flux pinning is also discussed.
These results indicate that powder-in-tube-processed MgB2 tape is very
promising for high-field applications.Comment: 13 pages, 5 figures. to be published soo
Systematic Determination of Absolute Absorption Cross-section of Individual Carbon Nanotubes
Determination of optical absorption cross-section is always among the central
importance of understanding a material. However its realization on individual
nanostructures, such as carbon nanotubes, is experimentally challenging due to
the small extinction signal using conventional transmission measurements. Here
we develop a technique based on polarization manipulation to enhance the
sensitivity of single-nanotube absorption spectroscopy by two-orders of
magnitude. We systematically determine absorption cross-section over broad
spectral range at single-tube level for more than 50 chirality-defined
single-walled nanotubes. Our data reveals chirality-dependent one-dimensional
photo-physics through the behaviours of exciton oscillator strength and
lifetime. We also establish an empirical formula to predict absorption spectrum
of any nanotube, which provides the foundation to determine quantum
efficiencies in important photoluminescence and photovoltaic processes
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