Field Ionization Microscopy

Figure 7.8 Set-up for field emission and field ionization microscopy. Both techniques produce an image of the concave end of a single crystal tip on the fluorescent screen, as explained in the text. The tip exposes many facets of different crystallographic orientations.

Long-range periodicity of surface nets is readily obtained from LEED patterns, and unit repeating meshes having dimensions over one hundred angstroms on a side are sometimes measured. This is impossible with field ionization microscopy. Only in rare cases has a periodic overlayer ever been observed by FIM on an individual plane, and structures with repeat distances larger than a few atomic diameters can never be recognized. 

Fast Fourier Transform Flow Injection Analysis Field Ion Atom Probe Flame-Ionization Detector Field Ion Microscopy... 

Atom probe microscopy is a variation of field ion microscopy in which either the field ionized atoms or evaporated atoms from the tip are detected with a mass spectrometer placed behind an aperture in the imaging screen. This allows one to identify the desorbing ions. If the tip is mounted on a manipulator, one can zoom in on a desired surface plane. The technique has, for example, been used to study the composition of alloy surfaces we refer to Tsong [32,33] for reviews. 

Fig. 1.33. Image mechanism of field-ion microscopy. A sharp tip, usually made of refractory metal, is placed in a chamber filled with He at about 10 torr. With an electric field of a few V/A, each of those atoms in the more protruding positions will have a He atom adsorbed on it. The He atom may be ionized to form a He ion, then be accelerated by the electric field to form an image of this surface atom. (Reproduced from Tsong, 1990, with permission.)...

A practical application coming out of field ion emission is the liquid metal ion source. Ion sources of a wide variety of chemical elements, most of them low melting point metals, can be produced by using either liquid metals131,132 or liquid alloys.133 The idea of extracting charged droplets out of liquid by application of an electrostatic field is perhaps older than field ion microscopy. But the development of liquid metal ion sources from liquid capillaries, from slit shaped emitter modules and from wetted field emission tips, etc., as well as the understanding of the mechanisms of ion formation in terms of field evaporation and field ionization theories,... 

The resolution of photoion laser microscopy is limited by two fundamental factors [7] the Heisenberg principle of uncertainty and the presence of the nonzero tangential component of the velocity of the ejected photoion (photoelectron). The same factors restrict the spatial resolution of the field-ion microscopy. It must be emphasized again that the key difference lies in the fact that for photoion microscopy there is no need for a strong (ionizing) electric field that distorts and desorbs the molecules. And also, the femtosecond laser radiation allows the photoion to be photoselectively extracted from certain parts of a molecule. 

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