One of the main tasks in the investigation of 2-dimensional transition metal dichalcogenides is the determination of valley lifetimes. In this work, we combine time-resolved Kerr rotation with electrical transport measurements to explore the gate-dependent valley lifetimes of free conduction band electrons of monolayer WSe2. When tuning the Fermi energy into the conduction band we observe a strong decrease of the respective valley lifetimes which is consistent with both spin-orbit and electron-phonon scattering. We explain the formation of a valley polarization by the scattering of optically excited valley polarized bright trions into dark states by intervalley scattering. Furthermore, we show that the conventional time-resolved Kerr rotation measurement scheme has to be modified to account for photo-induced gate screening effects. Disregarding this adaptation can lead to erroneous conclusions drawn from gate-dependent optical measurements and can completely mask the true gatedependent valley dynamics.
Carbon Nanotubes are intensively studied as a new functional material for nanoelectronics and nano electromechanical
systems, including nanosensor devices. Single-walled carbon nanotubes (SWNTs) show unique mechanical
and electromechanical properties and they change electronic properties by interacting with the environment
(this can be e.g. used for chemical and biochemical sensing). Therefore nanotubes are very promising candidates
for active elements in future nanoscaled transducers. Concepts for carbon nanotube sensors for mechanical and
chemical detection schemes are presented. We focus on single-walled carbon nanotubes as natural macro molecular
functional structures with an option for low scale integration in micro and nano electromechanical systems
(MEMS and NEMS).
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