We have measured the lifetime τ of the lowest triplet state T1 in free C60 by a pump−probe experiment using
lasers with nanosecond pulse durations. At low pump fluence the population of T1 decays with a distinct,
narrow distribution of lifetimes. τ depends on the pump wavelength (λ = 532, 355, or 266 nm) as well as the
temperature of the source from which C60 is vaporized (420 ≤ T ≤ 510 °C); it ranges from 2 μs to 0.3 μs.
At high pump fluence an additional lifetime as short as 40 ns is observed. A consistent correlation of all
observed lifetimes with the experimental parameters is found if τ is assigned to an ensemble of C60 (T1) that
has absorbed either one or two pump photons with the excess energy being randomized over all vibrational
modes. Thus, τ = 2 μs corresponds to a vibrational energy E
vib = E
total − E
triplet = 4.6 eV (one-photon
absorption at λ = 532 nm, T = 420 °C) while τ = 40 ns corresponds to E
vib = 9.6 eV (two-photon absorption
at 355 nm, 480 °C). This result strongly suggests that delayed electrons that are emitted from highly excited
C60 (E
vib ≫ 10 eV) on the time scale of ≈10 ns to 1 ms are not affected by long-lived electronically excited
states. The frequently questioned description of delayed electron emission from photoexcited C60 as thermionic
emission is, therefore, warranted.
Mn doping in Cu seed has been used to improve EM performance at the 32nm technology node. This paper will show that on an optimized process with CuMn there were different degrees of EM enhancement for geometric variations including line width and electron flow direction. In addition, kinetics experiments on several geometries resulted in activation energies in the range of 0.95-1.33eV. Finally, the Blech threshold (jL)c=338mA/um was derived from the experimental data on various line lengths and current densities.
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