HOPG

Highly Ordered Pyrolytic Graphite

Graphite belongs to lamellar materials and consists of identical staked planes. Carbon atoms within a single plane interact much stronger than with those from adjacent planes. That explains lamellar behavior of graphite. Each atom within a single plane has three nearest neighbours. Network of carbon atoms connected by shortest bonds looks like honeycomb. This two-dimensional and single-atom thick plane is called "graphene".
 
Positional relationship between two identical graphene planes A and B. Graphite structure can be described as an alternite succession of these planes ...ABABAB...

"Usual" graphite, especially natural one, exhibits quite imperfect structure due to plenty of defects and inclusions. A number of technologies are developed for preparation of perfect graphite samples to take advantage of its unique structure. Of these, pyrolysis of organic compounds is the most common and effective.

To characterize perfection of HOPG samples, one uses term "mosaic spread" which originates from X-ray crystallography. Similar to mica, HOPG specimens are layered polycrystals resembling a mosaic of microscopic monocrystal grains that are slightly disoriented with respect to each other. The disorientation of the graphene sheets is responsible for the broadening of the (002) diffraction peak.

The mosaic spread is characterized by measuring (in degrees) a full width at half maximum (FWHM) of the rocking curve (Cu-Ka radiation peak).

There are several grades of HOPG:
 
Grade Mosaic Spread Lateral grain size (typical)
 Density, g/cm3
 Thermal Conductivity, Watt/mK Chip size, mm
Value Accuracy along (0001) axis in surface plane
ZYA* 0.8° ±0.2° 10 µm 2,266 8±2 1800±200 10 x 10
ZYB 1.2° ±0.2° 1 µm
ZYC 3.5° ±1.5° 30-40 nm
*Not for calibration of X-ray equipment.
Application

HOPG terminated with graphene layer can serve as an ideal atomically flat surface to be used as a substrate or standard for SPM investigations. This is also an easily "cleavable" material with a smooth surface, which is vital for SPM measurements that require a uniform, flat, and clean substrates.
Typical STM image of HOPG surface.
Corresponding fragment of graphene structure is superimposed.

ORDERING

 
ZYA Grade.
1-mm thick. 1 pc. View price
2-mm thick. 1 pc. View price
 
ZYB grade.
1 mm thick. 3 pcs. View price
2 mm thick. 3 pcs. View price
1.75 mm thick. 3 pcs. View price
 
ZYH Grade.
1 mm thick. 5 pcs. View price
2 mm thick. 5 pcs. View price
1.75 mm thick. 5 pcs. View price
 
 

 

 

 

 
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