Escape Rate Of Electrons Research Articles

Observation of charge storage and intersubband relaxation in resonant tunneling via a high sensitivity capacitive technique

In suitably designed resonant tunneling double barriers the capacitance-voltage curve exhibits well-defined features corresponding to the charging and discharging of the quantum well. From the bias dependence of the electron density in the well we find that in our thick parabolic wells, electrons tunneling into the excited states relax to the lowest subband and sequentially tunnel out. Our experiments allow us to obtain the charge density accumulated in the well and the tunneling escape rate of electrons out of the well.

Heavy ion beam‐ionosphere interactions: Charging and neutralizing the payload

The argon release controlled studies (ARCS 1‐3) rocket flights carried ion generators to altitudes of 400‐500 km in the nighttime auroral ionosphere. Three distinct electrical charging and neutralization processes were seen on the payloads during gun operation: steady or dc vehicle charging, brief charging at gun turn‐on, and extended oscillatory sequences. Many of the unexpected consequences of gun firings are attributed to these payload charging and neutralization processes. Electrical charging is regulated by the rate at which low‐energy electrons escape from the generator, which in turn is dependent on magnetic field geometry. Each ion generator produced a dipolar magnetic field which merged with the Earth's field near the rocket. The resulting local magnetic field guided electrons back to the rocket for certain gun orientations, thereby inhibiting neutralization. Transient charging was attributed to the formation of an electron cloud around at least some vehicles, while dc charging altered the rocket's surroundings until the electron escape rate balanced the ion beam flux. We concluded that during oscillatory events the entire environment of a payload could alternate between hot electron and cold electron configurations at very high rates, possibly exceeding 10 kHz. These changes in the plasma environment did not produce substantial electric field perturbations at the dc or ac high impedance electric field sensors, so were not seen in data from typical wave detectors. However, changes in plasma density and temperature produced dramatic effects on low impedance electric current sensors such as Langmuir probes. These observations illustrate the importance of carrying both low and high impedance detectors on vehicles involved in active experiments. A number of possible future experiments are suggested to test and extend our understanding of the proposed charging and neutralization mechanisms.

Evaporation and quantum tunneling of electrons from a helium surface.

We have measured the escape rate of electrons from two-dimensional surface states of bulk helium. These measurements were made through a range of densities, external field, and temperature where thermal activation dominates (T\ensuremath{\ge}0.6 K) into the range where quantum tunneling dominates (T\ensuremath{\le}0.6 K). Both processes are sensitive to electron-electron correlation effects. The thermal activation rates depend only on the barrier height for which a relatively simple approximation of the correlation is adequate. However, observed tunneling rates are many orders of magnitude greater than would be predicted by this same approximation.

Escape rates of electrons from the surface of liquid helium

Electrons on the surface of liquid helium are confined to the plane of the surface by the image potential in the liquid. The confining field can be further increased by an external electric fild normal to the surface. If these potentials are sufficiently weak, electrons can escape from the surface. As an electron moves off of the surface the potential barrier includes additional contributions from the electrostatic field of the electrons remaining on the surface and their correlations. These contributions depend on the electron density. Electrons escape by thermal activation over the barrier at high temperatures and /or small external field. At low temperatures and/or high applied the electrons escape by quantum tunneling. We have measured the escape rate of electrons from the surface of liquid helium as a function of temperature and the electrostatic field normal to the surface. The results show the transition from thermal activation to tunneling and the increase in correlation energy with increasing density.

Tunneling escape rate of electrons from quantum well in double-barrier heterostructures.

A tunneling escape rate 1/${\mathrm{\ensuremath{\tau}}}_{\mathrm{T}}$ of electrons from a single quantum well through thin barriers was successfully determined by measurement and analysis of the lifetime ${\mathrm{\ensuremath{\tau}}}_{\mathrm{e}}$ of electrons generated in 6.2-nm GaAs single quantum wells by a picosecond laser pulse. The measured ${\mathrm{\ensuremath{\tau}}}_{\mathrm{e}}$ was found to decrease systematically as the AlAs barrier thickness ${\mathrm{L}}_{\mathrm{B}}$ was reduced. The ${\mathrm{\ensuremath{\tau}}}_{\mathrm{e}}$ for ${\mathrm{L}}_{\mathrm{B}}$4 nm was found to agree very well with the lifetime ${\mathrm{\ensuremath{\tau}}}_{\mathrm{T}}$ predicted from the energy width of the resonance transmission. Irrelevance of coherence versus incoherence in the tunneling escape process is also pointed out.

Modulation of Jovian electron intensity in interplanetary space by corotating interaction regions

Large-scale intensity variations of Jovian electrons in the energy range from 3 to 6 MeV persisting for several days were observed with instrumentation on the Pioneer 10 and Pioneer 11 spacecraft out to several AU from Jupiter along the pre- and post-planetary encounter trajectories. The corotating interaction regions (CIRs), found by Smith and Wolfe (1976) on these missions to be approximately 25-day recurring regions of enhanced magnetic fields bounded by jumps in solar-wind velocity and frequently shocks, are shown to be impenetrable 'barriers' for the Jovian electrons propagating in the interplanetary medium. Thus, the principal electron-intensity variations are due to the modulating effects of CIRs and are not due to either variations in escape rate of electrons from the magnetosphere or interplanetary electron acceleration. The implications for electron observations at the orbit of earth are discussed.