Universitäre Service-Einrichtung für Transmissionselektronenmikroskopie
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Imaging techniques

The visualization of the smallest particles, layers and lattice defects is very important in Nano-Technology. USTEM is very well equipped for this type of work with its state-of-the-art equipment which includes the following instruments:

 

DualBeam FIB-SEM for 3D analysis

Scanning Electron Microscopy (SEM):

2 scanning electron microscopes (SEM), with tungsten and/or field emission sources. Possible magnifications from 10 to 100,000 times. Material science or biological problems can be worked on. The illustration shows the vacuum conditions used for secondary electron detectors (SE) and backscattering electron detectors (BSE).

The scanning electron microscopes with USTEM are equipped with the following attachments:

  • Energy dispersive X-Ray (EDX) for chemical analysis
  • Orientation Imaging Microscopy (OIM) for structural analysis
  • Focused Ion Beam (FIB) for 3D analysis using EDX, OIM, SE and/or BSE imaging.
  • Field emission source (FEGSEM) for highest local dissolution
  • Cryo holder and transfer mechanism for the investigation of biological materials in high vacuum conditions
  • Heating table for investigations under extreme temperature conditions to 1000°C
  • Environmental SEM mode for investigations of damp samples
  • Low vacuum SEM mode for investigations of non-conductive samples
  • 3D topographic models of surfaces with MeX software

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TEM image of a grain boundary with a precipitation free zone in an aluminum alloy

Transmission Electron Microscopy (TEM):

3 transmission electron microscopes with magnifications of 25 to 1.080.000 times are available. Recording images is made by CCD cameras or photographic films. It is possible to use in the scanning transmission mode the intensity of diffracted and/or undiffracted electrons for imaging. Samples must have a maximum diameter of 3 mm and in the region of interest a thickness of 20-100 Nm.

The TEMs of USTEM permits the following experiments:

 

 

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ZnSe on GaAs showing dislocations

High Resolution Electron Microscopy (HRTEM):

For atomic imaging of structures within the nanometer range. Magnifications from 230.000 to 1.080.000 are used. Structural analysis and imaging of the smallest structures (quantum dots and wells) are possible.

Measuring of such structures is accurate to 0.1 nm. Burgers vectors can be imaged directly. Explanation to the illustration: Shockley partial dislocations imit here a stacking fault between C and D. Burgers vector around the transfers and the locking error of the partial dislocations in projection [110] are shown.

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STEM image showing three quantum-wells, appearing as bright lines due to the presence of heavy elements.

Scanning Transmission Electron Microscopy (STEM):

Magnification range: 10.000 - 20.000.000

The big advantage of scanning transmission electron microscopy (STEM) is the fact that by means of a High Annular Dark Field (HAADF) detector images with up to 0.2 nm resolution can produced with Z-contrast. In this imaging mode heavier elements (and their compounds) appear brighter than light elements. A rapid identification is easily achieved. In addition, the electron beam with a diameter of less than 1 nm can be placed on the sample in order to make EDX or EELS measurements from smallest sample volumes. Also EDX and EELS line profiles can be laid over the structure in order to examine local changes of the chemical composition.

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Confocal and conventional optical microscopy

Classical, conventional optical microscopy is used for investigations at low magnifications.  Confocal microscopy (laser scanning microscopy) allows 3D reconstructions of optical cross sections.

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