  Using a recently-developed time-of-flight measurement technique with 1 ps
time resolution and electron-energy spectroscopy, we developed a method to
measure the longitudinal-optical-phonon emission rate of hot electrons
travelling along a depleted edge of a quantum Hall bar. A comparison of the
experimental results to a single-particle model implies that the main
scattering mechanism involves a two-step process via intra-Landau-level
transition. We show this scattering can be suppressed by controlling the edge
potential profile, and a scattering length > 1 mm can be achieved, allowing the
use of this system for scalable single-electron device applications.
