Amount Of Secondary Electrons Research Articles

Secondary-electron emission from multi-layer graphene: time-dependent first-principles study

The amount of secondary electrons (SEs) emitted from multi-layer graphene under electron impact was calculated using time-dependent density functional theory, and the dependence on the incident energy and number of layers was determined. The amount of SEs converges to a certain value with an increase in the number of layers, which is successfully interpreted as attenuation of the incident wave packet by scattering at each graphene layer. The present study enables direct evaluation of the amount of SEs emitted from bulk graphite and provides useful insight into the SE emission from surfaces covered with layered materials.

Application of channel electron multipliers in an electron detector for low‐voltage scanning electron microscopy

An electron detector containing channel electron multipliers was built and tested in the range of low-voltage scanning electron microscopy as a detector of topographic contrast. The detector can detect backscattered electrons or the sum of backscattered electrons and secondary electrons, with different amount of secondary electrons. As a backscattered electron detector it collects backscattered electrons emitted in a specific range of take-off angles and in a large range of azimuth angles enabling to obtain large solid collection angle and high collection efficiency. Two arrangements with different channel electron multipliers were studied theoretically with the use of the Monte Carlo method and one of them was built and tested experimentally. To shorten breaks in operation, a vacuum box preventing channel electron multipliers from an exposure to air during specimen exchanges was built and placed in the microscope chamber. The box is opened during microscope observations and is moved to the side of the scanning electron microscope chamber and closed during air admission and evacuation cycles enabling storing channel electron multipliers under vacuum for the whole time. Experimental tests of the detector included assessment of the type of detected electrons (secondary or backscattered), checking the tilt contrast, imaging the spatial collection efficiency, measuring the noise coefficient and recording images of different specimens.

Measurement of Strain and Stress Distribution of Composite Materials by Electron Moiré Method

A method for measuring the stress and strain distribution in the composite materials and residual stress at the interface in the fiber reinforced composite has been developed. The strains are measured using an electron Moiré method and then the stresses are calculated from these strains. A very fine model grid with frequencies up to 10,000lines/mm can be fabricated using the optical and electron lithography techniques on the surface of the specimen and an electron beam scan which spaces are almost same as that of model grid the can be used for master-grid. The difference of the amount of secondary electrons per a primary electron makes Moiré fringes that consists bright and dark parts. Micro-creep deformation and residual strain and stress near the fibers of composite materials were measured by this method.

Analysis of ion noise with beam-wave interaction in klystron by two dimensional particle simulation method

Ion noise in output signal of klystrons was obtained by particle-in-cell method. The interactions between beam electron, ion, secondary electron and electromagnetic field are illustrated. The mechanism of ion noise is analyzed. It shows that phase fluctuation in output signal is caused by the change of the beam current DC velocity which is affected by the change of the amount of ions. The ion interacts with beam electron and has no equilibration state. The amount of secondary electrons is small and it has little effect on ion noise, but its behaviors reflect the process of ion noise. The amplitude fluctuation of output signal is caused by the change of beam velocity and beam radius. It is also affected by the ion behaviors.

Collection Efficiency Calculation in the Weak Electric Field Limit of Scanning Electron Microscopes (SEM) and Its Application to SEM Image Generation

Collection efficiencies of secondary electrons in SEM are analyzed theoretically in the weak electric field limit. Collection efficiency is determined by the amount of secondary electrons which can reach the electron detectors. The effects of the screening of local topographies around the incident points are analyzed in order to calculate this collection efficiency. We constructed a weak electric field limit model based on simple assumptions including (1) straight motion of emitted electrons near the sample surface, (2) complete absorption of once-blocked electrons, (3) full detection of emitted electrons departed from the near neighbor of the sample surface. In some special cases, collection efficiencies are calculated analytically. We generated a few SEM images combining them with a model of the secondary electron yield.