Dephasing times in a nondegenerate two-dimensional electron gas

Studies of weak localization by scattering from vapor atoms for electrons o n a liquid helium surface are reported. There are three contributions to th e dephasing time. Dephasing by the motion of vapor atoms perpendicular to t he surface is studied by varying the holding field to change the characteri stic width of the electron layer at the surface. A change in vapor density alters the quasielastic scattering length and the contribution to dephasing due to the motion of atoms both perpendicular and parallel to the surface. Dephasing due to the electron-electron interaction is dependent on the ele ctron density.