A study of in-the-column detector micrograph contrast in low-voltage scanning electron microscopy

Scanning electron microscopy (SEM) is a widely used technique in science and engineering, traditionally performed at electron beam acceleration voltages (BAVs) above 5 kV. However, progress in field emission guns and SEM technology have made low-voltage SEM imaging more available. Low-voltage SEM offers significant advantages, such as high-resolution imaging and the imaging of non-coated insulating specimens without charging artifacts. Nevertheless, there is limited research on electron-specimen interactions and the influence of SEM operational parameters on the obtained micrograph at the low-voltage range. This study focuses on low-voltage SEM imaging, below 2 kV, using a high-resolution in-the-lens detector. We investigated the effects of BAV and working distance (WD) on micrograph contrast and resolution. Carbon nanotubes and boron nitride nanotubes, two very important advanced materials, were used as model specimens of conductive and non-conductive materials, respectively, and silicon wafers and glass slides were used as model conductive and non-conductive substrates. We found that optimal imaging conditions differ with specimen properties; optimal results were typically obtained at low BAV (0.8-1.2 kV) and short WD (below 3 mm). Additionally, we show that substrate conductivity affects micrograph quality. Counterintuitively, insulating substrates provide better results in some cases. These findings emphasize the importance of optimizing SEM imaging parameters, and choosing the substrate according to sample properties for optimal imaging at low-voltage conditions.