Do SEII Electrons Really Degrade SEM Image Quality?

Generally, in scanning electron microscopy (SEM) imaging, it is desirable that a high‐resolution image be composed mainly of those secondary electrons (SEs) generated by the primary electron beam, denoted SE_I. However, in conventional SEM imaging, other, often unwanted, signal components consisting of backscattered electrons (BSEs), and their associated SEs, denoted SE_II, are present; these signal components contribute a random background signal that degrades contrast, and therefore signal‐to‐noise ratio and resolution. Ideally, the highest resolution SEM image would consist only of the SE_I component. In SEMs that use conventional pinhole lenses and their associated Everhart–Thornley detectors, the image is composed of several components, including SE_I, SE_II, and some BSE, depending on the geometry of the detector. Modern snorkel lens systems eliminate the BSEs, but not the SE_IIs. We present a microfabricated diaphragm for minimizing the unwanted SE_II signal components. We present evidence of improved imaging using a microlithographically generated pattern of Au, about 500 nm thick, that blocks most of the undesired signal components, leaving an image composed mostly of SE_Is. We refer to this structure as a “spatial backscatter diaphragm.” SCANNING 35:1‐6, 2013. © 2012 Wiley Periodicals, Inc.     

Resolution in low voltage scanning electron microscopy

As the energy of an electron beam is reduced, the range falls and the secondary electron yield rises. A low voltage scanning electron microscope can therefore, in principle, examine without damage or charging samples such as insulators, dielectrics or beam sensitive materials. This paper investigates the way in which the choice of beam energy affects the spatial resolution of a secondary electron image. It is shown that for samples which are thin compared to the electron range, the edge resolution and contrast in the image improve with increasing beam energy. In samples that are thicker than the electron range, the resolution can be optimized at either high or low energies, but low energy operation will produce images of higher contrast. At an energy of 2 keV or less beam interaction limited resolutions of the order of 3 nm should be possible.     

A simple method for SEM examination of sectioned diatom frustules

We describe an innovative yet straightforward method to obtain high quality thin sections of diatom exoskeletons for observation by scanning electron microscopy (SEM). The use of this new technique allows for clear observations of some ultrastructural valve features, including the raphe, which are generally difficult to observe and describe accurately using transmission electron microscopy analysis of thin sections or SEM of randomly fractured diatom valves. In addition, because this method involves the complete removal of the organic content of the diatom cells, resulting in clean and mostly undisturbed skeletal thin cross-sections, even the intact valvar structures of weak girdle bands can be studied.     

An improved model for gaseous amplification in the environmental SEM

We present a new model for the gas amplification effect used in many environmental scanning electron microscopes, wherein molecular complexity is shown to be the critical factor. Monte Carlo simulations, based on experimental electron scattering cross-sections, are used to deduce a predictive model for the amplification process that is superior to the Townsend gas capacitor model. These predictions are compared with experimentally obtained amplification curves. Significantly, it is shown that the ionization efficiency of the electrons changes dramatically over the gap distance, and a constant value cannot be assumed. Atomic and molecular excitations affect the amplification process in two ways: first, they serve to lower the average kinetic energy of the imaging electrons, thereby keeping a greater fraction near the ionization threshold energy. Second, molecular normal modes determine the effectiveness of positive gas ions in producing additional secondaries upon surface impact. Practical implications such as signal gain and fraction of useful signal as a function of operating conditions are discussed in the light of the new model. Finally, we speculate on potential new contrast mechanisms brought about by the presence of an imaging gas.     

Orientation averaging of electron backscattered diffraction data

The use of data averaging to improve the angular precision of electron backscattered diffraction (EBSD) maps is discussed. It is shown that orientations may be conveniently and rapidly averaged using the four Euler-symmetric parameters which are coefficients of a quaternion representation. The processing of EBSD data requires the use of an edge preserving filter and a modified Kuwahara filter has been successfully implemented and tested. Three passes of such a filter have been shown to reduce orientation noise by a factor of ∼10. Application of the method to deformed and recovered aluminium alloys has shown that such data processing enables small subgrain misorientation (< 0.5°) to be detected reliably.     

A novel method for acquiring large-scale automated scanning electron microscope data

Recent software and hardware advances in the field of electron backscatter diffraction have led to an increase in the rate of data acquisition. Combining automated stage movements with conventional beam control have allowed researchers to collect data from significantly larger areas of samples than was previously possible. This paper describes a LabVIEW? and AutoIT^© code which allows for increased flexibility compared to commercially available software. The source code for this software has been made available in the online version of this paper.     

Properties and structures of Co-based metallic glasses

A fundamental study on Co-based metallic glasses has been conducted. The study focused on understanding the changes of the properties and structures of an Fe-B-Si glass as a function of Co, Co-Ni, Co-Mn, and Co-Ni-Mo additions. The separate addition of Co, Co-Ni, Co-Mn, and Co-Ni-Mo elements was successful in such a way that four new metallic glasses were produced. The compositions of the new glasses are Fe₆₆Co₁₈B₁₅Si₁, Co₆₆Fe₄B₁₄Si₁₅, Co₇₆Fe₂Mn₄B₁₂Si₆, and Co₆₉Fe₄Mo₂B₁₂Si₁₂. Consequently, an evaluation of the physical and magnetic properties was determined. Furthermore, the internal and surface structures of the glasses have been characterized by a transmission electron microscope (TEM), and a scanning tunneling microscope (STM), respectively. A comparison between the internal and surface structures of the glasses was carried out on both amorphous and crystalline forms. As a result, a correlation between the properties and structures of the glasses is established.