HOPG

TipsNano supply with Highly Oriented Pyrolytic Graphite (HOPG). It’s a type of pure, highly laminar graphite used as an atomic-scale calibration standard for atomic force microscopy and scanning tunnelling microscopy.

HOPG crystals are widely used as substrates in STM (Scanning Tunneling Microscopy). The most distinguishing features of HOPG which enable this application are a very smooth surface and electro conductivity.

HOPG has a layered structure which makes sample preparation very simple. By pressing a double-stick tape to a HOPG piece and peeling it off, one gets a fresh conductive surface which is very smooth. This surface can be examined in STM or serve as a substrate for other materials under investigation.

HOPG itself is an interesting object for STM investigations. One can measure the surface roughness, microscopic surface features, arrangement of the carbon atoms on the HOPG surface, etc. Besides, HOPG images at the atomic level can be used for calibrating STM for high-resolution imaging.

For use in STM the main HOPG parameters are the size of crystallites and the number of interlayer defects, which, in turn, defines the number of layers splitting of the sample. The mosaic distribution of crystallites doesn’t matter, so there is no sense to make measurement of FWHM that entails additional costs for selection and certification of the samples.

For monochromator application the mosaic spread is of primary importance, so each crystal must be certified by FWHM measured on a diffractometer.

Difference in the HOPG types:

For STM – HOPG samples are obtained at the certain annealing regime which provides the exact meaning of mosaic spread.

Graphite monochromators – it is the STM HOPG samples with individually measured FWHM on a diffractometer and divided in two groups depending on the mosaicity. 

3 HOPG types (ZYA, ZYB, ZYH) which differ by meaning of mosaic spread are available.
Double-sided HOPG can be used from both sides and its properties are not changed in depth.
For one-sided piece the not working side is mat, glare less and can’t be cleaved. The number of working side cleavages of one-sided piece is limited in comparison with double sided substrate. The properties for one-sided piece are changed in depth.