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This paper reports on the electron scattering, charge transport and charge trapping of a polymer subjected to intermediate-energy electron beam in a self-consist charging model. Numerical simulation of a charging balance is performed using incident intermediate-energy electron current and leakage current, and the space charging characteristics are examined. The mechanisms involve various microscopic parameters that are related to the space potential and the characteristics of the polymer as well as to the effects of the space charge, electron charge, hole charge and trapped charge itself. The dynamic transporting and trapping properties of a polymer are investigated, and the space potential is evaluated using various parameters of irradiation. Trapping of electrons is determined using Poole-Frenkel trapping-detrapping mechanisms. Various types of space charging behavior are observed by controlling irradiation conditions. Furthermore, the peak location of space charge is simulated and validated by Sessler's experimental data in microscopic perspective. [ABSTRACT FROM AUTHOR]

In this study, based on a comprehensive numerical simulation of self-consistent charging, we investigate the formation, evolution and influencing factors of space charge distributions for a grounded insulating thin film of SiO2 negatively charged by a keV non-penetrating focused electron beam. The simulated space charge presents first positive distributions and then negative ones along both the radial and depth directions because of the difference between electron and hole transports. The variations in distribution occur within a range of the minimum potential acting as a potential barrier for carrier transport. The negative space charge is distributed more widely and deeply, though its peak value in density is usually lower than that of the positive one. Electrons trapped outside the minimum potential range dominate the strength of negative charging. With the increase in potential barrier and the occurrence of leakage current, the space charge eventually reaches equilibrium and exhibits an approximately one-dimensional axial distribution outside the minimum potential range. Distribution features of the space charge density in the equilibrium state correlate with the film and beam parameters via transients of the leakage current. These results and analyses provide new insights into the negative charging effects involved in various electron-beam-based surface microscopic methods, analyses and fabrication techniques. [ABSTRACT FROM PUBLISHER]

Image blurring of MeV transmission electrons for gold nanoparticles on the top surface of micrometer-thick specimens has been investigated using the Monte Carlo simulation. Both the simulated line density profile and therefore image blurring were in good agreement with the experimental ones in the ultrahigh voltage electron microscope. Quantitative effects of specimen thickness and electron energy on image blurring were presented, in which the specimen thickness had a greater influence. Image blurring was demonstrated to be caused mainly by multiple elastic scattering, but it could be reduced to several nanometers for a 5 µm thick epoxy-resin specimen at the electron energy of 2 MeV. [ABSTRACT FROM PUBLISHER]

Abstract: We have investigated the linear attenuation range of electron transmission through film specimens and its dependence on the electron energy, the acceptance half-angle of a detector or an objective aperture, and specimen properties, in the scanning transmission electron microscope (STEM) and the conventional transmission electron microscope (TEM). Electron transmission in the bright-field mode was calculated by the Monte Carlo simulation of electron scattering, and its range of the linear attenuation in film thickness was then determined by a linear least squares fit. The corresponding linear thickness range was shown to increase with the electron energy and the acceptance half-angle, although it decreased with the increase in the atomic number of specimen materials. Under the condition of a 300kV STEM or a 3MV ultra-high voltage electron microscope (ultra-HVEM), the linear attenuation range could extend to several microns for light specimen materials, and this was validated by experimental data in the ultra-HVEM. The presented results can be helpful for accurately measuring the specimen thickness or mass from electron transmission, and estimating the deviation of electron transmission from linearity when tilting a specimen in electron tomography. [ABSTRACT FROM AUTHOR]

Abstract: Image quality of MeV transmission electrons is an important factor for both observation and electron tomography of microns-thick specimens with the high voltage electron microscope (HVEM) and the ultra-HVEM. In this work, we have investigated image quality of a tilted thick specimen by experiment and analysis. In a 3MV ultra-HVEM, we obtained transmission electron images in amplitude contrast of 100nm gold particles on the top surface of a tilted 5μm thick amorphous epoxy-resin film. From line profiles of the images, we then measured and evaluated image blurring, contrast, and the signal-to-noise ratio (SNR) under different effective thicknesses of the tilted specimen and accelerating voltages of electrons. The variation of imaging blurring was consistent with the analysis based on multiple elastic scattering. When the effective thickness almost tripled, image blurring increased from ∼3 to ∼20nm at the accelerating voltage of 3MV. For the increase of accelerating voltage from 1 to 3MV in the condition of the 14.6μm effective thickness, due to the reduction of multiple scattering effects, image blurring decreased from ∼54 to ∼20nm, and image contrast and SNR were both obviously enhanced by a factor of ∼3 to preferable values. The specimen thickness was shown to influence image quality more than the accelerating voltage. Moreover, improvement on image quality of thick specimens due to increasing the accelerating voltage would become less when it was further increased from 2 to 3MV in this work. [Copyright &y& Elsevier]

Abstract: We report on the surface potential characteristics in the equilibrium state of the grounded insulating thin films of several 100nm thickness negatively charged by a low-energy (<5keV) focused electron beam, which have been simulated with a newly developed two-dimensional self-consistent model incorporating electron scattering, charge transport and charge trapping. The obtained space charge is positive and negative within and outside the region, respectively, where the electron and hole densities are greater than the trap density. Thus, the surface potential is relatively high around the center, then it decreases to a maximum negative value and finally tends to zero along the radial direction. The position of the maximum value is far beyond the range of e-beam irradiation as a consequence of electron scattering and charge transport. Moreover, a positive electric field can be generated near the surface in both radial and axial directions. The surface potential at center exhibits a maximum negative value in the condition of the ∼2keV energy non-penetrating e-beam in this work, which is supported by some existing experimental data in scanning electron microscopy. Furthermore, the surface potential decreases with the increase in beam current, trap density and film thickness, but with the decrease in electron mobility. [Copyright &y& Elsevier]

Abstract: Multiple scattering has an important influence on the analysis of microns-thick specimens with MeV electrons. In this paper, we report on effects of multiple scattering of MeV electrons on electron transmission and imaging of tilted and thick amorphous film specimens by experiment and theoretical analysis. Electron transmission for microns-thick epoxy-resin and SiO2 specimens calculated by the multiple elastic-scattering theory is in good agreement with measurements in the ultrahigh voltage electron microscope (ultra-HVEM) at Osaka University. Electron transmission and electron energy are then presented in an approximate power law. The bright-field ultra-HVEM images of gold particles on the top or bottom surfaces of 5 and 15μm thick specimens further illustrate the effect of multiple scattering on image quality. The observed top‐bottom effect for the very thick specimens appears to be mainly caused by multiple elastic scattering. With increase in the accelerating voltage from 1 to 2MV, image blurring, contrast, the signal-to-noise ratio, and the top‐bottom effect are improved because of reduction in the influence of multiple scattering. However, the effect of specimen thickness on image blurring is shown to be stronger than that of accelerating voltage. At the 2MV accelerating voltage, the 100nm gold particle can be imaged with less blurring of ∼4nm when located at the bottom surface of a 15μm thick epoxy-resin specimen. [Copyright &y& Elsevier]