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 influence of electron transport on the signal generation process in electron beam techniques is reviewed. A survey of the fundamental physical quantities for the electron–solid interaction is presented and sources for these quantities in the literature as well as semi-empirical formulae are given. The theoretical approaches used to describe multiple scattering in solids are outlined. These include the partial intensity approach and the continuous slowing down approximation to describe multiple energy losses and the transport approximation to tackle multiple deflections. A detailed description of the Monte Carlo technique is presented because this constitutes an effective means to study transport processes. The different theoretical approaches are illustrated in a survey of applications. These include: quantitative description of the surface sensitivity in Auger and photoelectron spectroscopy; line shape analysis of electron spectra; extracting information on the compositional depth profile from the combined energy/angular distribution in an electron spectrum; quasi-elastic electron reflection; inelastic electron backscattering; depth distribution of production of x-rays caused by electron bombardment; and the surface sensitivity in total electron yield electron spectroscopy. These applications demonstrate that the outlined approaches have a broad field of application, not only for electrons with energies ranging from thermal to the relativistic energy range, but also for other microbeam analysis techniques. Copyright © 2001 John Wiley & Sons, Ltd.

Electron transport in solids for quantitative surface analysis

The evolution of silicon cryoetching is reported in this topical review, from its very first introduction by a Japanese team to today's advanced technologies. The main advances in terms of the performance and comprehension of the mechanisms are chronologically presented. After presenting the principle of silicon cryoetching, the main defects encountered in cryoetching (such as undercut, bowing and crystal orientation dependent etching) are presented and discussed. Mechanisms involved in SiOxFy passivation layer growth in standard cryoetching are investigated through several in situ characterization experiments. The STiGer process and alternative cryoetching processes for high-aspect-ratio structures are also proposed to enhance the process robustness. The over-passivation regime, which can provide self-organized columnar microstructures, is presented and discussed. Finally, advanced technologies, such as the cryoetching of sub-20 nm features and porous OSG low-k cryoetching, are described.

https://iopscience.iop.org/article/10.1088/0022-3727/47/12/123001/pdf

Plasma cryogenic etching of silicon: from the early days to today's advanced technologies

This article discusses the current status of the rapidly evolving area of field emitter arrays. The development of field emitter arrays is reviewed in the context of major applications of the devices, such as flat panel displays and cathodes for microwave power amplifiers. State-of-the art technologies for fabrication of field emitter arrays as well as recently reported results on electrical performance of the devices are reviewed. Remaining challenges in the major applications in conjunction with some of the potential pathways to device improvement are discussed.

Recent progress in field emitter array development for high performance applications

ZnO nano-mushrooms for photocatalytic degradation of methyl orange

The secondary electron (SE) yield, delta, was measured from 24 different elements at low primary beam energy (250-5,000 eV). Surface contamination affects the intensity of delta but not its variation with primary electron energy. The experiments suggest that the mean free path of SEs varies across the d bands of transition metals in agreement with theory. Monte Carlo simulations suggest that surface plasmons may need to be included for improved agreement with experiment.

The secondary electron emission yield for 24 solid elements excited by primary electrons in the range 250–5000 ev: a theory/experiment comparison

There is an urgent need for fast, non-destructive and quantitative two-dimensional dopant profiling of modern and future ultra large-scale semiconductor devices. The low voltage scanning electron microscope (LVSEM) has emerged to satisfy this need, in part, whereby it is possible to detect different secondary electron yield values (brightness in the SEM signal) from the p-type to the n-type doped regions as well as different brightness levels from the same dopant type. The mechanism that gives rise to such a secondary electron (SE) contrast effect is not fully understood, however. A review of the different models that have been proposed to explain this SE contrast is given. We report on new experiments that support the proposal that this contrast is due to the establishment of metal-to-semiconductor surface contacts. Further experiments showing the effect of instrument parameters including the electron dose, the scan speeds and the electron beam energy on the SE contrast are also reported. Preliminary results on the dependence of the SE contrast on the existence of a surface structure featuring metal-oxide semiconductor (MOS) are also reported. Copyright © 2005 John Wiley & Sons, Ltd.

Why is it possible to detect doped regions of semiconductors in low voltage SEM: a review and update

Imaging of As- and B-doped silicon regions has been performed in a scanning electron microscope operated in the cathode lens mode, with incident electron energies (EP) as low as 15 eV. The doped regions of n+ (As, 2.5×1020 cm−3) and p+ (B, 8×1019 cm−3) on n-type silicon (∼1015 cm−3) show distinct contrast with electron energies of about 3 keV. The brightest region is n+ followed by p+, then the n-type substrate. The highest contrast for the p+ and n+ type regions is reached at about EP=300 and 15 eV, respectively. The contrast mechanisms are explained in terms of metal-semiconductor contact assuming an adventitious carbon film at the surface.

Very-low-energy electron microscopy of doped semiconductors

Imaging of the boron doping in silicon using low energy SEM

Although doped regions in semiconductors have been shown to give a different secondary electron yield in low-voltage scanning electron microscopy, the basic interpretation of this contrast has been difficult. It is accepted that this contrast stem from electronic phenomenon rather than atomic number differences between differently doped regions. However, the question is whether variations in the patch fields above the sample surface, balancing variations in the inner potentials, or surface coatings and/or surface states are the mechanisms responsible for the observed contrast. The present study reports on comparative experiments of these two models and demonstrates that the image contrast can be controlled by the presence of thin-surface metallic coatings. These results are the first evidence of the adlayer contacts, i.e., the subsurface electric fields instead of the patch fields above the surface, being responsible for the secondary electron contrast of doped semiconductors imaged in low voltage scanning electron microscopes under standard vacuum conditions, and they pave the way for the routine use of this method in semiconductor research and industry.

Mohamed M. El-Gomati

Papers

The secondary electron emission yield for 24 solid elements excited by primary electrons in the range 250–5000 ev: a theory/experiment comparison

Why is it possible to detect doped regions of semiconductors in low voltage SEM: a review and update

Very-low-energy electron microscopy of doped semiconductors

Imaging of the boron doping in silicon using low energy SEM

Why is it that differently doped regions in semiconductors are visible in low voltage SEM