Tomás Vystavel

Improving SEM Imaging Performance Using Beam Deceleration

Beam Deceleration is a relatively simple method to reduce electron beam energy and improve imaging parameters such as resolution and contrast. The scanning electron microscope (SEM) uses a sharply focused electron beam to probe the specimen surface. The energy of the electrons forming such a probe is determined by the electrical potential of the electron source, referred to as accelerating voltage or high voltage (HV). No matter how many times the electrons are accelerated or decelerated inside the column, they leave the column with an energy corresponding to the high voltage. The high voltage is usually controllable within a range of 200 V to 30 kV for most commercially available SEMs, allowing the operator to select the electron beam energy suitable for the application. Imaging with very low electron beam energy has great importance, which is illustrated by SEM instrumentation development over the last few decades [1–2]. Low voltage microscopy is a topic discussed at most microscopy-related conferences these days, but generally, it is approached with an immersion lens and field emission gun (FEG) SEM system because of the better beam current densities. However, beam deceleration is also a means to bring low kV improvement to SEMs with thermionic electron sources.

Optimized Electron Column and Detection Scheme for Advanced Imaging and Analysis of Metals

In recent years, there has been a large growth in the development of detectors for FIB/SEM systems as the number of applications and techniques is growing. In-lens detectors have traditionally been optimized for imaging low take-off-angle back-scattered electrons with higher energies (low loss). This signal typically generates images which are high in materials contrast [1]. Conversely, below-lens detectors have the ability to capture much higher take-off-angle backscattered electrons due to their geometry [2]. Recent advances in detector segmentation with concentric rings have further allowed the separation of take-off angle signal without the need to change the working distance between the final lens and the sample. This higher take off angle delivers a strong channeling contrast in the specimen, while the highest take off angle reveals topographic information.