Physical characteristics : HOPG, graphite monochromators, doubly bent graphite monochromators


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Graphite monochromators | Doubly-bent monochromators | HAPG optics | STM substrates | Thermal management

Physical characteristics

The Optigraph technology allows to manufacture HOPG of any fancy shape

Graphite structure

Highly Oriented Pyrolytic Graphite (HOPG) and Thermoconductive Pyrolytic Graphite (TCPG) are forms of high purity Pyrolytic Graphite annealed under pressure at temperatures about 3000ºC. Its main physical characteristics (at 20ºC) are summarized in the following Table.

interlayer distance (002)	3.354-3.358 Å
density	2.24-2.25 g/cm³
thermal conductivity parallel (002) thermal conductivity perpendicular (002)	1700+/-100 W/(m·K) 8+/-1 W/(m·K)
thermal expansion parallel (002) thermal expansion perpendicular (002)	-1x10^-6 K^-1 20x10^-6 K^-1
electrical conductivity parallel (002) electrical conductivity perpendicular (002)	2.1+/-0.1x10⁶ [(W·m)^-1] 5x10² [(W·m)^-1]
purity	> 99.99 %

HOPG crystals are used as monochromators and focusing optics for x-ray beams. Some typical parameters of the HOPG optics are shown in the following Table.

Energy range	2-120 keV
Reflection coefficient	15-50%
Integral reflectivity	up to 0.01 rad
Rocking curve width	0.3º-0.4º
Solid angle of capture	up to 0.1 sr
Focal spot size	100-500 µm

HOPG-based monochromators and focusing optics can be also used for neutron beams.