Sample Introduction and Handling for Surface Analysis

Sample holders range from those that accommodate samples of 1-2 cm diameter and about 1 cm in thickness to custom-designed sample chambers that can hold much bigger samples and those that are of irregular size and shape. Chambers designed for 95 mm diameter computer hard disks are 

Even under vacuum, gas molecules will reabsorb onto a clean sample surface. Hercules and Hercules describe that at pressures between 10 and 10 ° torr, a surface can be covered by a mono-layer of adsorbed gas molecules in from 1 to 10 h, while at 10 torr, the same process occurs in a few seconds. This rapid recontamination of a cleaned surface makes clear the need for UHV conditions for accurate surface analysis. 

Some surface analysis instruments are equipped with apparatus to fracture or cleave a material within the UHV chamber to expose a fresh surface for analysis. Metal samples are routinely fractured in UHV to expose grain boundaries. This permits XPS or AES detection of bulk impurities that have segregated to grain boundaries, for example. Grain boundary chemistry is of great interest to metallurgists for many reasons. As noted, even under UHV conditions, a limited time is available for contamination-free analysis of freshly exposed surfaces. 

---