High power pulsed magnetron sputtering (HPPMS) is an emerging technology that has gained substantial interest among academics and industrials alike. HPPMS, also known as HIPIMS (high power impulse ...

High power pulsed magnetron sputtering: A review on scientific and engineering state of the art

We review the data and models describing the production of the electrons, termed secondary electrons, that initiate the secondary and subsequent feedback avalanches required for the growth of current during breakdown and for the maintenance of low-current, cold-cathode discharges in argon First we correlate measurements of the production of secondary electrons at metallic cathodes, ie the yields of electrons induced by Ar+ ions, fast Ar atoms, metastable atoms and vuv photons The yields of electrons per ion, fast atom and photon vary greatly with particle energy and surface condition Then models of electron, ion, fast atom, excited atom and photon transport and kinetics are fitted to electrical-breakdown and low-current, discharge-maintenance data to determine the contributions of various cathode-directed species to the secondary electron production Our model explains measured breakdown and low-current discharge voltages for Ar over a very wide range of electric field to gas density ratios E/n, ie 15 Td to 100 kTd We review corrections for nonequilibrium electron motion near the cathode that apply to our local-field model of these discharges Analytic expressions for the cross sections and reaction coefficients used by this and related models are summarized

https://iopscience.iop.org/article/10.1088/0963-0252/8/3/201/pdf

Cold-cathode discharges and breakdown in argon: surface and gas phase production of secondary electrons

The high power impulse magnetron sputtering (HiPIMS) discharge is a recent addition to plasma based sputtering technology. In HiPIMS, high power is applied to the magnetron target in unipolar pulse ...

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High power impulse magnetron sputtering discharge

The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE FWHM/E≈15 %. The dominant ion species (H+, He+, and O+) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance.

https://link.springer.com/content/pdf/10.1007%2Fs11214-013-9968-7.pdf

Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer for the Radiation Belt Storm Probes Mission

The buildup of static charge on satellite surfaces is an important issue in the utilization of satellite systems. The analysis of this phenomenon has required important advances in basic charging theory and the development of complex codes to evaluate the plasma sheaths that surround satellites. The results of these theories and calculations have wide application in space physics in the design of systems and in the interpretation of low-energy plasma measurements. In this review, those aspects of charge buildup on satellite surfaces relevant to the space physics community are summarized. The types of charging processes, models of charge buildup, satellite sheath theories, and charging observations are described with emphasis on basic concepts.

The charging of spacecraft surfaces

Ion-induced electron emission from clean metals

We have measured the electron emission yields of clean Li, Al, Cr, Cu, Ag, and Au surfaces under bombardment with ${\mathrm{H}}^{+}$, ${\mathrm{H}}_{2}^{+}$, ${\mathrm{D}}^{+}$, ${\mathrm{D}}_{2}^{+}$, and ${\mathrm{He}}^{+}$ ions in the energy range 2-50 keV. The clean surfaces were produced by in-situ evaporation of high-purity metals under ultrahigh-vacuum conditions. It is found that the ${Z}_{2}$ dependence of the yields for hydrogen and helium projectiles are very similar, that the yields for ${\mathrm{H}}^{+}$ and ${\mathrm{D}}^{+}$ show the same energy dependence as that of the electronic stopping powers, that molecular ions give lower yields per atom than atomic ions, and that isotope effects are negligible in our energy range. It is proposed that kinetic-electron emission under low-energy-light-ion bombardment results mainly from the escape of excited electrons produced by direct binary collisions between the projectile and the valence electrons of the target.

Electron emission from clean metal surfaces induced by low-energy light ions

We have observed Al L/sub 2,3/ Auger electrons from clean aluminum surfaces bombarded by mass-analyzed beams of noble-gas ions at 45/sup 0/ incidence, and in the energy range 600 eV--15 keV. The electron energy spectra show a wide structure similar, though not identical, to those observed under electron impact, and sharp lines. These lines are identified as resulting from the Auger decay of 2p-excited Al and Al/sup +/. The decay occurs in vacuum from sputtered particles, as suggested by the asymmetric Doppler broadening of the Auger lines. The Auger yields can be scaled when plotted against the maximum energy transfer in a projectile-Al collision, indicating that the excitation occurs mainly in symmetric collisions between target atoms. Exceptions are the cases of impact with He/sup +/ and low-energy Ne/sup +/ ions where projectile-Al collisions are responsible for the excitation, possibly by two-electron transitions.

Ion-induced Auger-electron emission from aluminum

We have studied the dependence of electron yields ..gamma.. from clean Cu and Au surfaces on the incidence angle theta of 5--50-keV He/sup +/, Ar/sup +/, and Xe/sup +/ projectiles, in the angular range 0--80 /sup 0/, and under ultrahigh-vacuum conditions. We have found that, at small angles, ..gamma..proportionalsec/sup f/theta, with f generally different from unity. For Xe/sup +/ on Cu, ..gamma..(theta) presents an energy-dependence maximum, similar to that obtained for sputtering. The results are explained in terms of the anisotropy of the electron cascade in the solid, the depth distribution of the inelastic energy deposited by the projectile and by rapidly recoiling target atoms in the near-surface region of the solid.

Dependence of ion-electron emission from clean metals on the incidence angle of the projectile

Reports measurements of electron emission yields of clean molybdenum surfaces under bombardment with H+, H2+, D+, D2+, He+, N+, N2+, O+, O2+, Ne+, Ar+, Kr+ and Xe+ in the wide energy range 0.7-60.2 keV. The clean surfaces were produced by inert gas sputtering under ultrahigh vacuum. The results were compared with those predicted by a core-level excitation model. The disagreement found when using correct values for the energy levels of Mo is traced to wrong assumptions in the model. A substantially improved agreement with experiment is obtained using a model in which electron emission results from the excitation of valence electrons from the target by the projectiles and fast recoiling target atoms.

http://iopscience.iop.org/article/10.1088/0022-3727/14/9/018/pdf

E. V. Alonso

Papers

Ion-induced electron emission from clean metals

Electron emission from clean metal surfaces induced by low-energy light ions

Ion-induced Auger-electron emission from aluminum

Dependence of ion-electron emission from clean metals on the incidence angle of the projectile

Electron emission from molybdenum under ion bombardment