HOPG Substrates – Highly Ordered Pyrolytic Graphite

HOPG – Highly Ordered Pyrolytic Graphite is a very pure and highly ordered form of synthetic graphite. It is characterised by by the mosaic spread angle. HOPG is a laminar material and consists of layered polycrystals resembling a mosaic of monocrystals grains which are slightly disorientated with respect to each other. The size of the individual crystals varies from 1-10um. A lower mosaic spread angle represents a better alignment of the graphite crystals. The best HOPG samples have a mosaic spread value of less than 1 degree. The freshly cleaved HOPG substrates provides atomically flat areas which are used as a specimen substrate and for magnification calibration in scanning probe microscopy techniques (AFM, SPM, STM). Similar to mica, fresh surfaces can be made by cleaving the samples.