Freshly Cleaved in Air

Crystals Freshly Cleaved in Air  

• Freshly cleaved crystal surface are normally atomically flat with few steps. This flatness makes it difficult for air-borne gases to be captured onto the surface due to the reactive nature of the exposed surface and the sticking coefficent of the material. As a result, the surface is very clean and will remain clean if sample is properly stored. 
• Cleaving in a UHV vacuum chamber is considered to be the ultimate for obtaining a pristine clean surface.  This is usually true but it depends on the gases that reside inside the analysis chamber which will attack the reactive pristine surface just as though it was cleaved in air.  Subsequent baking of the sample inside the chamber will remove most of the contaminants. 
• For the purpose of XPS, freshly cleaved in air produces surfaces that have less than 1-2 monolayers (5 angstroms) of adventitious carbon and the same amount of adsorbed water, which often forms 1-2 monolayers of hydroxides if the sample can collect water.

Bulk Exposed by Cleaving Crystals

• Silicon wafers, glass sheets, and flat ceramic parts can be cleaved by using a carbide or diamond tip to make a 2-3 mm long scratch at the very edge of the part.  A pair of glass-cutter pliers is then used to pressure the scratch which usually propagates a cleavage line. 
• For some glasses or ceramics, a complete long line must be scribed from edge to edge.  The sample is then placed on a 3 mm tall sheet.  Hand pressure is then used to force the cleavage. As a last resort, a hammer is used to strike the sample.