Field emission scanning electron microscope

About Scanning Electron Microscopy

In general, Scanning Electron Microscopy offers the possibility to examine samples at very high magnifications, which can not be achieved with light microscopes. For this purpose, samples are scanned line by line in a vacuum with a finely bundled electron beam (= "scanned"). Interactions with matter produce several signals which are converted into so-called gray value information and displayed on a screen.

By screening we get the following signals:

1. SekundäreElectrons (SE)
These come from the uppermost nanometers of the surface and reproduce the topography of the observed sample. They provide information about the structure of the surface.

2. Backscattered electrons (back scattered electrons = BSE)
These electrons are "backscattered" by the sample. The intensity of this backscatter allows conclusions to be drawn about the distribution of the materials / elements contained in the sample. So you give information about the composition of the surface.

3. X-rays (energy dispersive x-ray spectroscopy = EDX)
These are used for material analysis and provide information on the elemental composition of the surface.

About the Field Emission Scanning Electron Microscope (FE-REM)

Up to 500.000 magnification and maximum resolution up to 1 nm resolution limit

The FE-SEM offers the possibility to perform examinations with an 500.000 magnification of the sample. Thus, the smallest structures and nanoparticles can be considered. The microscope provides ultra-high resolution images with a resolution limit up to 1 nm (= nanometer, 1 nm = 0,000001 mm). This means that two pixels with a distance of 1 nm can still be distinguished.

3D images

In addition to the two-dimensional image, the pictorial representation in three-dimensional format is possible. The samples to be evaluated can be examined in real time in 3D format. This opens up new perspectives on the structure of the surfaces considered.

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Field emission scanning electron microscope (FE-REM)
Field emission scanning electron microscope (FE-REM)

Schottky field emitter

The emitter sends the electrons in a beam towards the sample to be examined. The special feature of the Schottky field emitter is the more precise definition of the beam already at the emission. The electron beam can be better focused, especially at low acceleration voltages. (Acceleration voltage: The electric field needed to move / "accelerate" the electrons.) Low acceleration voltages are needed to study sensitive samples.

In-beam SE and BSE detectors

The detectors are used to "capture" and display the signals produced during scanning. These are "in-beam detectors" because they are installed inside the microscope - in the column. Conventional detectors are connected externally to the microscope system. On the way the signals have to travel to the detector, they are often disturbed and provide lower results. With the built-in detectors within the microscope, a higher signal yield is possible, which high-resolution images are possible. On SE shots, the contrast is seen in the topography; BSE images show the material contrast. With the FE-REM both images can be simultaneously displayed, z. B. with different color representation, so that the superposition of various information is possible.

RGB detectors
RGB detectors

EDX elemental analysis

EDX = energy dispersive x-ray spectroscopy = energy dispersive X-ray spectroscopy
Information about the layer composition is obtained by means of the EDX element analysis. The type and the respective amount of the chemical elements of a surface can be determined. It can also be displayed how the elements are distributed on the surface. This analysis is made possible by the release of X-rays. The electron beam of the microscope hits the sample, knocking out electrons from the deeper atomic shells of matter. To fill the gap on the deeper atomic shell, electrons from higher layers move behind. By "jumping down" to a deeper shell, X-rays are released. These rays are unique and characteristic for each element, which makes the definition possible. The EDX elemental analysis is helpful in the elucidation of layer compositions and for the monitoring of layer optimizations.

EDX analysis
EDX analysis

Beam Deceleration Technology

BDT, or BDM: BI was Deceleration Mode
Beam Deceleration Technology translates as "electron beam deceleration technology". An electrostatic counter field is applied around the sample to be examined, which ensures that
1. the electron beam is slowed down just before it hits the sample and
2. the impact energy with which the electron beam impinges is lowered.
Since the Beam Deceleration Technology ensures that these processes take place shortly before impinging on the sample, the electron beam can be emitted with a high voltage. The higher precision of the beam is retained longer because the acceleration voltage is lowered only shortly before impacting the sample. Another advantage is that less charging effects than "side effects" occur because the impact energy is lowered. In addition, sensitive samples are not necessarily destroyed. In addition, non-conductive samples (eg plastic surfaces) can be investigated without extensive preparation.