Advanced Materials Characterization Chapter 2 Sample Handling

Advanced Materials Characterization Chapter 2 - by Igor Bello

In material analyses, samples are handled with a special care and often analyzed under high vacuum (HV) and ultrahigh vacuum (UHV). Vacuum is needed in the most of surface analyses because: (1) High quality electron and ion beams used for probing surfaces and interfaces, can only be produced at HV, UHV, and extreme high vacuum (XHV) conditions. At such conditions, scattering of beam particles is minimized and beams can be focused to very small spot sizes. (2) Response signals induced by the ion beams are transmitted via analyzers and measured by detectors with minimum scattering. (3) Sorption processes can be tolerated at operation of electron guns. At high vacuum conditions, the mean free path (MFP) of particles is much longer than the physical distance D between the initial and final points that particles travel in an analysis system. However, the boundary condition (D=MFP) does not impose much stringency on the working vacuum of this quality, because at pressure of 10–4 Pa that is in the HV region, MFP is substantially longer than linear dimensions of commercially built vacuum systems. The HV quality may be adequate in some analytical techniques such as scanning and transmission electron microscopy (SEM and TEM) operating with thermionic electron guns, and mass spectrometry. (3) The higher demand for vacuum quality comes from processes related to sorption. Only under UHV and XHV, it is possible to prepare clean surfaces and maintain them for a time longer than the duration of the analysis.