Detection of secondary and backscattered electrons for 3D imaging with multi-detector method in VP/ESEM

A calculation approach for current density distribution evolution of secondary electrons using differential algebra method

In this study, the concept of the current density distribution (CDD) evolution of secondary electron (SE) beam is presented, and a novel approach using the differential algebra (DA) method is proposed to calculate the CDD evolution of the SE beam. Firstly, the emitted SE beam is divided into some beamlets in polar and azimuth angle directions. For each beamlet only one reference trajectory is traced using DA method. As a result, the transfer properties for this beamlet are obtained. Using the transfer properties, the current density function at arbitrary plane for the beamlet can be derived, in which the initial angle distribution, energy distribution and emission source size are considered. And then, the current density function is integrated, resulting in the CDD of this beamlet at arbitrary plane. Finally, the CDD evolution of the whole SE beam is obtained by superposing the CDDs of all beamlets. As an example, a SE detection system for a scanning electron microscope (SEM) is calculated using the proposed approach and therefore the SE CDD evolution is obtained and analyzed. Furthermore, experiments for observing the SE image of detector are performed, and the calculated SE CDD and the corresponding simulation images well explained the experimental results, validating the proposed calculation method. The proposed approach can be potentially applied for optimizing the SE detection system and therefore improving the collection efficiency of SE.

Vertical distance from shading in the SEM

Vertical data collected by Scanning Electron Microscopy (SEM) are important for sample characterization, 3D reconstruction, and flex manipulation. Traditional methods are limited by the extent to which the probe obstructs the view of the sample along the vertical axis. Herein, we propose a novel SEM microprobe for measuring the vertical distance between the probe and substrate. To form a semi-transparent hole that is set as the objective regions in processing of the SEM images, an epoxy film was embedded in the through-hole at the tip of the microforce probe with 3D printing. The film can be modified with a focused ion beam (FIB) system. The motion of the modified probe along the vertical axis is controlled by a nanopositioner and the process is recorded by taking a real-time SEM video. The change in gray contrast caused by the semi-transparent epoxy is corrected during the SEM image processing of the video. By comparing the gray contrast with the nanopositioner motion data, we find that the change in gray contrast can provide feedback for adjusting the displacement between the probe and the substrate, and the resolution can be up to 100 nm. We propose a novel and simple method for measuring vertical distances in the SEM, which is useful for in-situ measurements and nanomanipulations.

Direct Observation of the Surface Topography at High Temperature with SEM

High-temperature scanning electron microscopy allows the direct study of the temperature behavior of materials. Using a newly developed heating stage, tilted images series were recorded at high temperature and 3D images of the sample surface were reconstructed. By combining 3D images recorded at different temperatures, the variations of material roughness can be accurately described and associated with local changes in the topography of the sample surface.

Specific features of the miniature ionisation BSE multi-detector unit for 3D imaging in environmental conditions

The author has been striving to develop SEM equipment that could extend the capabilities of standard instruments to allow advanced environmental techniques, including 3D imaging. Now its improved version is presented in a form of the miniature ionisation multi-detector unit that can be accommodated inside a bore of the objective lens and does not limit the minimal Working Distance (WD). The miniature detector unit seems well suited to VP/ESEM of any type to be used instead a standard Pressure Limiting Aperture and even to the classic SEM when combined with the vacuum-detector head and an intermediate vacuum system. An acceptable pressure of the environmental gas (preferably water vapour of ca 10 hPa) and the capability of 3D imaging make this solution particularly suitable in applications for highly hydrated samples of smooth surfaces. The unit can also deliver an abundance of signals which may be a source of better contrasts and additional information when digitally processed. Its present investigations are focused on the surface shape fidelity obtainable with the system working in gaseous environment of air or water and tested on metal and glass wires or hydrated organic samples. The detector unit may be reckoned an underpass electron energy filter which facilitates imaging details under sample surface, the feature demanded strongly in biomedical applications.