646 Double Tilt

Detailed analysis of crystalline TEM specimens requires the application of electron diffraction in addition to EDX. In these cases, the 646 Double Tilt Analytical Holder has the capability of up to +/-60° main tilt and up to +/-30° secondary tilt as well as excellent low background performance. The ToggleTilt™ drive mechanism used for the second tilt is simple, reliable, and eliminates the need for complicated tilt drive endstops. For TEMs with small objective lens polepiece gaps, holders are available with thinner cross-sections to provide higher tilt capability. Special double tilt holders are also available having electrical terminals close to the tilt cradle in order to perform electrical experiments on the specimen while it is in the TEM.

Analytical TEM

To obtain good EDX spectra and accurate compositional analyses from specimens in a TEM, a well-designed specimen holder is essential. The Gatan range of Analytical TEM Holders meets the requirements for good EDX analysis without compromising TEM image resolution.

Low Background Design

The beryllium specimen cup and clamping ring of the single and double tilt analytical holders minimize the non-specimen x-ray signal, particularly that from the specimen holder. Beryllium is chosen for its low fluorescent yield and for the low detection efficiency of its characteristic radiation. Also, because the characteristic x-rays from beryllium have such a low energy, they are not able to cause other materials around the specimen to fluoresce. Furthermore, beryllium, unlike carbon or graphite, possesses good mechanical properties, is UHV compatible, and is easy to clean. Other parts of the specimen holder tip that cannot be made from beryllium are mostly made from high-strength aluminum alloys in a further attempt to minimize the x-ray signal from the holder and the surrounding microscope. This intelligent choice of materials makes the Gatan analytical holders particularly suitable for high spatial resolution EDX by STEM or small-probe TEM.

Reduced Shadowing

Having minimized the unwanted signal from the specimen holder, the specimen signal is further optimized by removing those parts of the specimen cup that are along the line of sight of the EDX detector. In the final design, low-angle detectors require minimal tilting of the holder to stop shadowing, while high-angle detectors require no tilting.

Integral Faraday Cup

Accurate quantitative analysis requires a knowledge of the electron current incident on the specimen. Gatan analytical holders have a miniature Faraday cup in the holder tip, close to the specimen cup. An electrical socket is provided at the end of the holder to connect the Faraday cup to a picoammeter. An alignment tool, which fits between the holder and the TEM stage, allows the holder to be positioned quickly and easily to place the Faraday cup exactly in the path of the electron beam.