BSE Detectors

Backscattered electrons (BSEs) are high-energy electrons generated as a result of elastic interactions between the primary electron beam and the sample. The range energy of BSEs is from 50 eV up to the energy of the electron beam. BSEs are emitted from a broad region within the interaction volume (the region in the sample where all the beam-sample interactions take place) with a range of penetration that can be as deep as a few microns for high-energy beams to hundreds or even a few tens of nanometres for low beam energies
 

The backscatter coefficient η (the ratio between BSEs generated and the number of incident beam electrons in the sample) strongly depends on the mean atomic number of the specimen (areas with a larger mean atomic number will appear brighter than those with lower mean atomic number). For this reason, the BSE signal provides material contrast in imaging.

BSE detectors

TESCAN offers variety of premium backscattered (BSE) detectors in two main categories:
BSE Detectors
BSE Detector

Scintillation crystal-based BSE detectors

TESCAN systems are equipped with first-class crystal-based scintillators. These types of detectors achieve high sensitivity and high resolution in atomic number (0.1 Z) for enhanced imaging quality. Their large detection area allows the acquisition of quality images at high scanning speeds.
The main advantages of the scintillation crystal-based detectors are:
  • High imaging rate up to 20 ns / pixel
  • Temperature stability (no signal drift)
  • Low noise, super-clear image
  • Inert to IR light of the chamber scope
  • Suitable for low vacuum observations
TESCAN has designed different scintillators detectors which – depending on the system – form part of either standard or optional configurations.
 

BSE detector (fixed) is an annular scintillation crystal-based BSE detector placed in the optical axis of the SEM column directly under the objective lens allowing high-quality imaging at low and high vacuum. It provides both topographical and compositional contrast from wide-angle BSEs, suitable for imaging low-contrast specimens such as biological samples. It achieves a resolution in atomic number of 0.1 Z.

Retractable BSE detector. With the same features and capabilities as the fixed version, the advantage of this detector is that it can be retracted whenever not in used. This feature allows freely adjusting the working distance to optimal values for SE imaging. Retractability can be either manual or motorised.


Mid-Angle BSE detector located inside the column allows low-noise volume compositional mapping. It collects medium-angle BSEs providing compositional contrast as well as topographical information of the sample. Suited for imaging at short working distances.  The Mid-Angle BSE detector is a unique integral part of the universal detection system in Triglav™, the newly designed TESCAN ultra-high resolution electron column. In the beam deceleration mode (BDM), this detector collects BSEs. This detector is capable of operating over the entire range of beam energies: 200 eV to 30 keV.


In-Beam BSE detector. Annular scintillator-based BSE detector located inside the column for detecting axial BSEs thus providing pure compositional contrast, suited for imaging at short working distances. The In-Beam BSE detector can be simultaneously used with the fixed/retractable detector (collecting mostly wide-angle BSEs) and their signals can be added for enhanced material as well as topographical contrast.  In systems equipped with BDT, this detector collects SEs in the beam deceleration mode (BDM) achieving ultimate resolution (the resolution achieved depends on the particular system).


Low energy BSE (LE-BSE) detector. This detector is specially designed to increase detection sensitivity at low energies and capable of operating over the entire range of beam energies: 200 eV to 30 keV. The in-beam version (In-Beam LE-BSE detector) can operate in the range of 500 eV to 30 keV. The LE-BSE detectors are well-suited for FIB-SEM tomography applications.


Retractable BSE dual-scintillation detector equipped with two scintillation monocrystals; one for collecting wide-angle BSEs, and the other (lateral) for low-angle BSEs.  The two scintillators work independently and their signals can be combined to obtain images with enhanced compositional or topographical contrast. The lateral crystal can be manually covered by a shutter so that the detector behaves as a standard BSE detector.


Al-coated BSE detector. This detector makes simultaneous acquisition of cathodoluminescence (CL) and BSE signals possible. When both CL and BSE detectors are used, photons emitted from the scintillation crystal of the BSE detector are collected by the CL detector thus interfering with the true CL signal from the sample. In order to avoid this cross-talking between detectors, the crystal of the BSE detector is covered with an aluminium layer preventing in this way that photons emitted from the scintillator can reach the CL detector. This detector is particularly relevant to applications in mineralogy where simultaneous acquisition of CL and BSE images is important.


BSE / CL detector. This type of detector can be used as both cathodoluminescence (CL) detector, for the characterisation of samples by using the information that visible light provides, and, as a BSE detector for material contrast. Switching between the two operational working modes requires exchanging (manually) the light guide.


Water-cooled BSE detector. This retractable motorised annular scintillation detector is specially designed for applications in which the sample needs to be heated to such high temperatures that would damage the standard BSE detector. The detector can operate at temperatures up to 900°C thanks to a water circulation cooling system.

4-Quadrant semiconductor (solid-state) BSE detectors

Retractable 4Q BSE detector. This is an annular 4-quadrant solid-state detector that acquires four independent BSE signals emitted from different directions. The SEM electronics adjusts the signal from all four quadrants separately and /or mixes, adds or subtract into a resulting image. Thus, advanced imaging features such as compositional and topographical mode or four independent images optimised for 3D reconstruction of the sample surface are possible. 3-dimensional imaging is possible thanks to the software that combines the four signals from different directions in one image.
  • Separated signal from all four quadrants
  • Mixed signal into a resulting image
  • Compositional and topographical mode
  • 3D reconstruction of the sample surface
  • Retractable design (motorised option)