Field ionisation microscopy

In field ionisation microscopy (FIM), helium at low pressure is introduced into the above system and the polarity of the applied potential difference is reversed. Helium atoms in the vicinity of the now positively charged metal tip are stripped of an electron and the resulting helium ions are accelerated radially to the negatively charged fluorescent screen. 

The stmctures of HA and FA are not yet determined. A combination of many techniques is required to determine the structure of HSs. Schulten et al. have employed p)>Tolysis-gas chromatography with electron impact and field ionisation mass spectrometry (Py-GC/MS), in-source pyrolysis-field ionisation mass spectrometry (Py-FIMS), CP/MS NMR, oxidative and reductive degradation, colloid chemical methods, and electron microscopy to develop a carbon network structure for soil HS (Schulten (1994), Schulten and Schnitzer (1993)). The elemental composition of FLA was C3()8H32s09oN5 fot MW of 5540 Da. This indicates of the complexity of such compounds and the extensive techniques required. If carbohydrates or proteinaceous materials are bonded covalently with HA, %C content decreases and %0 content increases. 

The work that has to be done to remove an electron from a metal into vacuum with zero kinetic energy at zero K is termed the work function, and this is the same as the ionisation potential, but is larger than that of the free atom because of the space charge or surface dipole that exists at the surface, due to the asymmetry of electron density. Work function is greatest at planes having a high concentration of atoms (i.e. generally low-index planes), and decreases with step density at stepped surfaces. Variation of work function with crystal plane underlies the technique of Field-Emission Microscopy (FEM). 

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