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Highly Annealed Pyrolytic Graphite (HAPG)

Highly Annealed Pyrolytic Graphite (HAPG) is a mosaic crystal and a further improvement of the well-known Highly Oriented Pyrolytic Graphite (HOPG) mosaic crystals, by means of a much narrower mosaicity.

Mosaic crystals, in contrast to ideal crystals, consist of many small ideal crystals, called crystallites. One important parameter of these crystals is the so called mosaicity which gives the distribution function of the crystallites’ surface normals in comparison to the crystal surface normal. The full width at half maximum of the mosaicity is the so called mosaic spread and is normally used to describe these types of crystals.

HAPG mosaic crystals show the highest integrated reflectivity among all known crystals, which is at least one order of magnitude higher than for example for Silicon 111 reflection. This increased integrated reflectivity is due to the so called mosaic focussing, which leads to a fulfilment of the Johannson geometry even for flat crystals in the dispersion plane.

HAPG crystals have usually thicknesses in the range of a few tens of microns up to 100 micrometers. The achievable mosaic spread lies between  <0.1° and 0.4°. With optimized optics we spectral resolving powers E/ΔE of 2000 and even higher are feasible in the first order of reflection while getting the mentioned high integrated reflectivity.

Point of contact: Christopher Schlesiger, Wolfgang Malzer

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