Umklapp processes ( or U-processes ) change the momentum of the particle after scattering and are therefore limiting the conduction in semiconductor crystals.
2.
In low-dimensional systems, it is difficult to conserve both energy and momentum for Umklapp processes, and so it may be possible that Umklapp scattering is suppressed in nanotubes relative to 2-D or 3-D forms of carbon.
3.
"' Umklapp scattering "'( also "'U-process "'or "'Umklapp process "') is the transformation, like a reflection or a translation, of a wave vector to another Brillouin zone as a result of a scattering process, for example an reflecting an electronic state or creating a phonon with a momentum " k "-vector outside the first Brillouin zone.
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