Post-ionization imaging

One of the recent advances in mass spectrometry (MS) instrn-mentation is the incorporation of post-ionization separations on the basis of ion mobility (IM) combined with snbseqnent MS analysis (IM-MS). Importantly, IM-MS adds an additional dimension of separations on the basis of analyte strnctnre to facilitate interpretation of MS spectra directly from complex biological samples. Typically separations in the IM dimension are completed in 100 s of microseconds to milliseconds, thus imaging... 

FIGURE 5.8 Schematic diagram of a SIMS-TOF imaging system with post-ionizing laser. (Reprinted with permission from reference 20). 

Fig. 2.12 Average charge state in field evaporation of Mo as a function of the applied field, obtained by Kellogg.68 The field evaporation rate is kept nearly constant by adjusting the temperature of the pulsed-laser heating. Curves are theoretical results A from the image-hump model, B from the same calculation with post field ionization correction. Calculations are based on those of...

The trees seem to be formed by stacking of the crystallites in size ranging Ifom 30 to 50 nm which is apparently much smaller than the particle size in the film deposited without DC bias. The mechanism to make the difference is not clear at present time. We assume that the application of the DC bias increased the concentration of species in the gas phase, i.e. the flux of the arriving atoms or clusters on the substrate, as well as the concentration of the ionized species, which results in more nuclei on the substrate. The increase of the concentration of species in the gas phase can also lead to less time for the adatoms to diffuse on the surface of the substrate or the deposited film, which can result in small particle in the deposited films. The similarity of the microstructures of the films deposited under DC bias and that deposited at high reagent concentration (see Fig. If) can support our assumption. The low density films in the forest-like microstructure can be densified by post thermal treatment. The images in Figure 7 indicate both the... 

Our typical NO-Ar system has 2 atm of Ar backing both valves with one doped with 5% NO. Two laser beams are used to ionize NO, one laser beam is resonant with a transition in the (0,0) band of the A-X system near 226 nm, thereby selecting a particular rotational state which is then ionized near threshold with a 300 nm laser beam. This technique is known as (1 + l )REMPI. Images similar to Fig. 8.2 are taken for each product NO rotational state. By measuring the velocity profile of the molecules scattered in the direction of the laboratory origin, the crossing point of the two beams, we can measure the post collision velocity distributions for the side scattered molecules as a function of rotational state, see Fig. 8.4. 

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