Physisorption of an electron in deep surface potentials off a dielectric surface

Abstract

We study phonon-mediated adsorption and desorption of an electron at dielectric surfaces with deep polarization-induced surface potentials where multiphonon transitions are responsible for electron energy relaxation. Focusing on multiphonon processes due to the nonlinearity of the coupling between the external electron and the acoustic bulk phonon triggering the transitions between surface states, we calculate electron desorption times for graphite, MgO, CaO, Al 2 O 3 , and SiO 2 and electron sticking coefficients for Al 2 O 3 , CaO, and SiO 2 . To reveal the kinetic stages of electron physisorption, we moreover study the time evolution of the image-state occupancy and the energy-resolved desorption flux. Depending on the potential depth and the surface temperature, we identify two generic scenarios: (i) adsorption via trapping in shallow image states followed by relaxation to the lowest image state and desorption from that state via a cascade through the second strongly bound image state in not too deep potentials, and (ii) adsorption via trapping in shallow image states but followed by a relaxation bottleneck retarding the transition to the lowest image state and desorption from that state via a one-step process to the continuum in deep potentials.

Wall Charge and Potential from a Microscopic Point of View

“…In order to investigate the dependence of the trapping scenario on material parameters, for instance, the Debye frequency and the dielectric function, and to show trends we applied the model however also to dielectric materials with positive electron affinity [25][26][27]. The basis in which the Hamiltonian is written down, the elementary excitations causing energy relaxation, and the couplingV s depend on the surface.…”

“…We applied the approach just outlined to various uncharged dielectric surfaces assuming electron physisorption to occur in the image potential, which is, as pointed out, rigorously true only for dielectrics with negative electron affinity [25][26][27]. Electron energy relaxation at these surfaces is driven by acoustic phonons whose Debye energy is very often not only too small to connect the lowest bound state to the unbound states but also too small to connect the two lowest bound states.…”

“…The physisorption kinetics of electrons at dielectric surfaces involves therefore multiphonon transitions [25][26][27]. For the plasma context most important is that s e 1 and τ −1 e = 0 [25][26][27], implying that an initially uncharged dielectric surface with a negative electron affinity is not a perfect absorber for electrons. Multiphonon processes contribute very little to it.…”

Development of Barrier Discharges: Operation Modes and Structure Formation

“…The modeling activities -under progress -consider the dominant processes in the discharge volume as well as the interactions of relevant plasma species with dielectric surfaces [20][21][22][23]. The modeling activities -under progress -consider the dominant processes in the discharge volume as well as the interactions of relevant plasma species with dielectric surfaces [20][21][22][23].…”

Electrical conductivity of the thermal dusty plasma under the conditions of a hybrid plasma environment simulation facility

“…For a comprehensive discussion of these plasma types, see the review [23] and references therein. Recent studies based on the treatment of quantum states of the surplus electrons near the surface of charged particles make it possible to calculate such quantities as the electron sticking coefficient and desorption time, to account for the infrared extinction of dielectric particles etc [24][25][26][27].The characteristics of such complex plasmas have implications for applications as disparate as understanding volcanic eruptions, the explosiveness of dust clouds and powders, communications, wildfires, rocket propulsion, and fusion energy. Lightning associated with volcanic plumes is a direct result of the electrification of the particulate matter within the plume.…”