Secondary Electron Beam Research Articles

A calculation approach for current density distribution evolution of secondary electrons using differential algebra method

In this study, the concept of the current density distribution (CDD) evolution of secondary electron (SE) beam is presented, and a novel approach using the differential algebra (DA) method is proposed to calculate the CDD evolution of the SE beam. Firstly, the emitted SE beam is divided into some beamlets in polar and azimuth angle directions. For each beamlet only one reference trajectory is traced using DA method. As a result, the transfer properties for this beamlet are obtained. Using the transfer properties, the current density function at arbitrary plane for the beamlet can be derived, in which the initial angle distribution, energy distribution and emission source size are considered. And then, the current density function is integrated, resulting in the CDD of this beamlet at arbitrary plane. Finally, the CDD evolution of the whole SE beam is obtained by superposing the CDDs of all beamlets. As an example, a SE detection system for a scanning electron microscope (SEM) is calculated using the proposed approach and therefore the SE CDD evolution is obtained and analyzed. Furthermore, experiments for observing the SE image of detector are performed, and the calculated SE CDD and the corresponding simulation images well explained the experimental results, validating the proposed calculation method. The proposed approach can be potentially applied for optimizing the SE detection system and therefore improving the collection efficiency of SE.

Using secondary electron electron beam induced current for characterization of nanoparticle morphologies

Using secondary electron electron beam induced current for characterization of nanoparticle morphologies

LOW INTENSITY BEAMS OF ELECTRONS AND POSITRONS IN THE ENERGY RANGE UP TO 100 MeV AT IHEPNP FACILITY

The article considers possible characteristics of low-intensity secondary positron and electron beams, which can be obtained using an electron accelerator with energy of ~100 MeV and average current of some μA. Preliminary simulation shows that using a tungsten converter of 2X0 thick and collimation of secondary particles beam, such accelerator allows one to get electron and positron secondary beams with energy of ~ 5…70 MeV, intensity of ~10-6-8 from the primary electron beam intensity, and energy spread of about some percent. Such low-intensity beams can be used for researches in the field of interaction of radiation with amorphous ubstances and crystals, testing detectors and scintillation materials.

Parasitic p–n junctions formed at V-pit defects in p-GaN

The luminescent and recombination properties of V-pit defects in p-GaN(Mg) grown by metalorganic chemical vapor deposition (MOCVD) were studied by scanning electron microscopy (SEM) in the secondary electron, cathodoluminescence (CL), and electron beam induced current (EBIC) modes, combined with CL spectra measurements and EBIC collection efficiency measurements. Similar studies were performed on low-dislocation-density freestanding n-GaN crystals. For MOCVD p-GaN films, the SEM investigations were supplemented by capacitance–voltage, current–voltage, deep level transient spectroscopy analysis with Ni Schottky diode, and Ohmic contacts. These experiments show that V-pits in p-GaN increase the leakage current of Schottky diodes, as in n-GaN films and crystals. EBIC imaging and EBIC collection efficiency results suggest that in the region of V-pits, a parasitic p–n junction is formed. We also observe that, in V-pits, the CL spectra the contribution of the 3.2 eV defect band is strongly enhanced compared to the 3 eV blue CL band that dominates the spectra.

Estimation of Radiation Doses Delivered by Terrestrial Gamma Ray Flashes Within Leader‐Based Production Models

AbstractWith a typical production altitude of ∼12 km, Terrestrial Gamma ray Flash (TGF) sources are close to commercial flight altitudes, and these events could potentially be an unforeseen exposure to ionizing radiation for aircraft passengers and crews. Dwyer et al. (2010) estimated the dose that a TGF could produce, and showed that TGFs in principle could be an additional non‐negligible factor to the exposure for aircraft passengers. The regulations for aircrew protection against radiation, only consider the radiation of galactic and solar origin (Bottollier‐Depois et al., 2012; ICRP, 2007). Other possible sources of exposure, such as TGFs, are not yet considered, mainly because of the lack of reliable data on possible dose levels and on the probability for an airplane to be in the vicinity of such an event. In order to improve the evaluation of the TGF exposure level and associated risks, and as there is still a divergence of opinion about the exact source mechanisms, we present calculations of doses produced by high‐energy electrons in TGF sources, within two different lightning leader‐based production models: (1) a pure lightning leader model and (2) considering further avalanches in a homogeneous electric field region. We find that although the doses from photon and secondary electron beams are weak, the dose potentially received by passengers inside the TGF electron source regions may be very high (>20 mSv). The results reported in the present paper call for a need to perform a thorough risk assessment including the probability for an aircraft to be in a TGF source region.

ANALYZING THE EFFECT OF MICRO RUBBER, MICRO SIO2, AND NANO SIO2 IN MICROCRACKS IN SELF-CONSOLIDATING CONCRETE (SEM OBSERVATION)


 
 
 The present study is an attempt to analyze the effect of micro rubber waste in self- consolidating concrete (SCC) and to compare the concrete containing SCC with conventional additives such as micro SiO2 and nano SiO2. The use of rubber waste can be substantially important from the environmental point of view. Hence, concrete specimens containing 1, 3 and 5% micro rubber waste were made. Moreover, specimens containing 1, 3 and 5% nano SiO2 and 4, 8 and 12% micro SiO2 were prepared to compare their behaviour and microstructure with each other and with the witness specimens. The effect of the other parameters such as the specimen age and the w/c ratio on the microstructure of concrete containing rubber waste was also studied. Thereafter, the specimens were imaged using a scanning electron microscope (SEM) to observe and compare the microcracks in the concrete and secondary electron beam (SE) was used to obtain their images. The results of the microstructural consideration of different specimens showed that 1% of micro rubber waste can improve the behaviour of self-consolidating concrete, but the concrete microstructure strength and quality decline with an increase in its amount.
 
 

Auroral‐Enhanced Plasma Lines by Suprathermal Electrons Observed by EISCAT

AbstractPlasma lines (PLs) observed by the European Incoherent Scatter Scientific Association (EISCAT) incoherent scatter radar (ISR) data set during the recent solar maximum 2014 are investigated. To statistically analyze the PLs in the EISCAT data set, we develop an algorithm for the automatic extraction of naturally enhanced PLs from the ISR spectra. Two typical types of auroral‐enhanced PLs at high latitude, namely, secondary electron and electron beam, are analyzed based on this PL extraction algorithm. Our results show that PL enhancements originating from secondary electrons and electron beams present evident magnetic local time dependence. Moreover, the statistical study indicates that the PL enhancements are correlated with the geomagnetic and solar activities. These results can provide insights into solar wind‐magnetosphere‐ionosphere coupling mechanisms.

Energy transfer and defect formation processes in nano silicon under the influence of epithermal neutrons

The neutrons scattering and capture cross-section processes has been calculated for natural 28 Si , 29 Si , 30 Si isotopes which are main part of nanosilicon samples when irradiated for 20 hours by epithermal neutron flux. The values of energies has been determined which given to nanosilicon nuclei as a result of scattering processes in the energy intervals of investigated neutrons. The cross-sections of radiation capture process and the amount of 31 Si radioactive isotope which can be formed by by 30 Si isotope in the energy interval of epithermal neutrons, the parameters of energy supply and ionization processes has been determined by interaction between energy carried of β - particles which disseminated in evironment and silicon atoms as a result of their β - decay. The formed defects has been determined in electron structure of nanosilicon under the influence of primary and secondary electron beams. Characterized interaction processes between nanosilicon and gamma rays irradiated from radioactive isotopes in impurities up to 1% in nanosilicon which formed under the influence of neutron flux. As a result of SEM investigation, interaction between surface defects inherent to nanoscale systems and O 2 , H 2 O active components that arranged environment and increasing number of surface oxidation atoms determined under the influence of radiation from radioactive isotopes which are product of radiation capture processes when impact by neutron flux. The progression of agglomeration processes of nanosilicon particles under the influence of secondary radiation processes that caused by neutron flux has also been proved experimentally by SEM investigations. The characteristic of identification and generation processes of paramagnetic defects, that formed as a result of secondary radiation processes investigated by electron paramagnetic resonance spectroscopy method.

Measurements of beam current density and space potential in a highly focused ion beam of extremely low energy

Using an electrostatic double probe, profiles of the ion beam current density, electron density, and electron temperature were measured in the background plasma that appears by injecting a hydrogen ion beam into low-pressure hydrogen gas in a propagation chamber. The hydrogen ion beam is extracted using concave-shaped electrodes at extremely low energies (Eib = 60–120 eV). Focusing of the beam occurs when Eib exceeds a certain threshold. One probe electrode P3 is far from the beam source and is set in the shadow of another electrode in the beam trajectory. The ion saturation current in P3 is then estimated without considering the beam contribution. The measured electron densities are much larger than those of the ion beam density, the electron temperatures are very low (<1 eV), and the ion beam current densities exhibit fairly good agreement with those measured by Faraday cups. The profiles of the space potential are also estimated by measuring the potential of P3 with respect to ground with a voltage divider having an extremely high resistance. The space potentials obtained are quite low at <10 eV with focusing and ∼23 eV without focusing. The data with and without focusing are compared and conditions for focusing are examined. Focusing achieved through additional electron beam injection in the ground electrode is also examined. The results obtained indicate that a large electron source is required to balance the ion charges. Secondary electron emissions and/or small electron beam injection are effective sources.

Implementation of multistrip crystals to protect the septum magnets and to generate gamma radiation

Recently studies are started on the application of volume reflection of particles in crystals for the steering beams (for extraction and collimation of a circulating beam in accelerators). Volume reflection is more efficient than channeling, but requires amplification of the deflection angle by applying multicrystals. The report discusses two new applications of multicrystals made like multistrip structures: (i) the property of effective deflection of particle beam was used to protect the septum magnets of the U-70 in the process of extraction of the proton beam with energy of 50 GeV; (ii) the possibility of generation of gamma radiation was studied in the secondary electron beam with energy of 7 GeV. In both cases, promising preliminary data were obtained.

Emission of Photons at the Interaction of a High-Energy Electron Beam with a Sequence of Bent Single Crystals

A radiation source based on the emission of electrons and positrons moving in a short bent crystal has been recently discovered. The emission of particles is due to oscillations of their trajectories near the point of reflections, where trajectories approach a tangent to bent atomic planes. In the experiment performed with the secondary electron beam of the U70 accelerator, it has been shown that the emission intensity can be increased by using a sequence of oriented bent crystals. Passing through six 2.5-mm-long silicon crystals, 7-GeV electrons lose on average 2.0 GeV on emission. This value is several times larger than that in an amorphous medium. Thus, an intense source of radiation has been demonstrated with prospects of application at accelerators.

Selection and design of the secondary electron channel of the time-of-flight mass spectrometer

Computer simulation is carried out for selecting a compact electron-optical system of the channel for detecting secondary electrons formed during the interaction of xenon atoms or ions with energy of 1-30 keV with Xe atoms. The solid angle of passage of secondary electron beams in a wide range of their initial energies is calculated. The energy spectrum of secondary electrons with various energies is determined by constructing their deceleration curve.

Penentuan Ketebaan Lapisan Polistiren dan Zinc Phthalocyanine (ZnPc) dengan Modifikasi Persamaan Sauerbrey dan Scanning Electron Microscope (SEM)

The thickness measurement of PS thin films on QCM surface and ZnPc layer on QCM/PS using Sauerbrey equation and Scanning Electron Microscope (SEM) has been investigated. Calculation result using a modified Sauerbrey equation show the thickness of PS layer and ZnPc one are 0,45 μm and 0,0676 μm respectively. Additionally the thickness measurement by using SEM shows the thickness of PS layer is 5,33 μm and the thickness of ZnPc layer is 10,44 μm. The differences thickness between Sauerbrey equation and SEM topograph is due to layers porosity. The topography of thin films produced by the secondary electron beam scanning allows to get a magnification of SEM image so that it can be measured directly. While the thickness calculation using the Sauerbrey equation is based on the change in the resonance frequency of QCM.

Structural defects responsible for excessive leakage current in Schottky diodes prepared on undoped n-GaN films grown by hydride vapor phase epitaxy

Schottky diodes fabricated on undoped n-GaN films grown by hydride vapor phase epitaxy showed more than two orders of magnitude higher reverse current if the films contained open core defects. The open core defects were revealed by scanning electron microscope observation in secondary electrons, microcathodoluminescence (MCL), and electron beam induced current (EBIC) modes. Plan-view EBIC imaging showed that such films contained a relatively high density of large (∼10 μm in diameter) dark defects that were absent in good films with low leakage current. In plan-view scanning electron microscope images, pits with the density similar to the density of dark defects were observed. Cross-sectional MCL observation showed that the pits terminated the vertical micropipes starting near the interface with the substrate. Some of the micropipes closed approximately halfway through the grown thickness. The regions of micropipes, either closed or not, showed a higher intensity of bandedge and defect MCL bands. Possible reasons for the formation of such structures are discussed.

On-Line Measurement of Ion Density in Atmospheric Nitrogen Discharge Filaments via Radiation Signals from Plasma Oscillation

Diagnosis of the particle number density of plasma plays an important role in the understanding of plasma sources and processing. Regular radiation signals from plasma oscillation in filaments of atmospheric nitrogen discharge, which were excited by the injection of secondary electron beams during the propagation of the streamer, are employed to determine the ion density of plasma and its evolution in the filaments. Results show that the density of N+4 in a filament of atmospheric nitrogen discharge is of the order of 1013 cm−3. It is also found that the recombination processes play a dominant role in plasma decay, and that the ion density decreases non-monotonically with time during streamer propagation.

X-ray transition radiation of electrons with energy of 300 to 900 MeV in periodic multifoil radiators

Results of experiments conducted at the Tomsk synchrotron to study resonant X-ray transition radiation generated by relativistic electrons in periodic multifoil radiators are reviewed. Both the internal synchrotron beam and the external secondary electron beam from the pair magnetic γ-spectrometer with energies ranging from 300 to 900 MeV were used in the experiments. The radiators consisted of many thin amorphous foils of various materials. The generation of X-ray radiation in a compound radiator consisting of a multifoil radiator and a crystal is also studied. In this case, the resonant X-ray transition radiation generated in the multifoil radiator is diffracted in the crystal and emitted at Bragg angles, together with the parametric X-ray radiation generated in the crystal. Spectral and angular properties of the resonant X-ray transition radiation and diffracted resonant X-ray transition radiation are investigated. The ratio between the contributions from the diffracted resonant X-ray transition radiation and other types of radiation to the total coherent X-ray radiation flux generated by electrons in periodic structures and crystals is estimated.

Carrier dynamics and doping profiles in GaAs nanosheets

We have recently demonstrated that GaAs nanosheets can be grown by metal-organic chemical vapor deposition (MOCVD). Here, we investigate these nanosheets by secondary electron scanning electron microscopy (SE-SEM) and electron beam induced current (EBIC) imaging. An abrupt boundary is observed between an initial growth region and an overgrowth region in the nanosheets. The SE-SEM contrast between these two regions is attributed to the inversion of doping at the boundary. EBIC mapping reveals a p-n junction formed along the boundary between these two regions. Rectifying I–V behavior is observed across the boundary further indicating the formation of a p-n junction. The electron concentration (ND) of the initial growth region is around 1 × 1018 cm−3, as determined by both Hall effect measurements and low temperature photoluminescence (PL) spectroscopy. Based on the EBIC data, the minority carrier diffusion length of the nanosheets is 177 nm, which is substantially longer than the corresponding length in unpassivated GaAs nanowires measured previously.

Comparison between Secondary Electron Microscopy Dopant Contrast Image (SEMDCI) and Electron Beam Induced Current (EBIC) for Laser Doping of Crystalline Silicon

Laser doping of crystalline silicon has been the subject of intense research over the past decade, due to its potential to enable the fabrication of high efficiency and low-cost crystalline silicon solar cells. Information regarding the doping profile created by the process is critical for process optimisation, however is generally difficult to obtain. In this paper, a relatively new technique for characterising laser doping cross-sections — Secondary Electron Microscopy Dopant Contrast Image (SEMDCI) — is compared with the widely used Electron Beam Induced Current (EBIC) method. A good agreement between the two techniques regarding the p-n junction profile is demonstrated. The differences between the methods are attributed to the difference of the sensitivity. The comparison demonstrates the reliability and usefulness of the SEMDCI as a characterisation method for laser doping, which shows both the p-n junction outline and dopant distribution within the doped regions. The differences between the methods and the challenges associated with the application of the SEMDCI method are also discussed.

Muon Elastic Scattering with MUSE at PSI

The proton radius puzzle is the disagreement between the much more precise radius determined from muonic hydrogen spectroscopy and the numerous atomic hydrogen and electron scattering determinations. The puzzle has several possible resolutions, including physics beyond the Standard Model, missing conventional physics, and errors or underestimated uncertainties in the extraction of the radius from the data. New experiments are needed to confirm and / or resolve the puzzle. The MU on S cattering E xperiment (MUSE) recently approved at PSI has been designed to help resolve the puzzle by measuring the radius in a way not yet done. Similar to electron scattering, the radius will be extracted from the observed change of the charge form factor with momentum transfer. The experiment uses the π M1 beamline to provide a mixed secondary muon and electron (and pion) beam of either positive or negative charge. The comparison of muon and electron scattering measured simultaneously determines the consistency of the form factors in the two cases with high precision. Comparison of yields from both charge signs will at the same time disentangle the effect of two-photon exchange. The proton charge radius can be extracted from each set of scattering data. The physics case and status of MUSE will be discussed.

Comparison endpoint study of process plasma and secondary electron beam exciter optical emission spectroscopy

Traditionally process plasmas are often studied and monitored by optical emission spectroscopy. Here, the authors compare experimental measurements from a secondary electron beam excitation and direct process plasma excitation to discuss and illustrate its distinctiveness in the study of process plasmas. They present results that show excitations of etch process effluents in a SF6 discharge and endpoint detection capabilities in dark plasma process conditions. In SF6 discharges, a band around 300 nm, not visible in process emission, is observed and it can serve as a good indicator of etch product emission during polysilicon etches. Based on prior work reported in literature the authors believe this band is due to SiF4 gas phase species.