Ion trajectory simulation

Ion trajectory simulations allow for the visualization of the ion motions while travelling through a quadrupole mass analyzer (Fig. 4.36). Furthermore, the optimum number of oscillations to achieve a certain level of performance can be determined. It turns out that best performance is obtained when ions of about 10 eV kinetic energy undergo a hundred oscillations. [110]... 

Besides the chamber diameter, the width of the apertures is an important structural parameter. It affects the density (pressure) of the sample gas and the overall gas flow into the system. Ion trajectory simulations identified an optimum ion yield for entrance and exit orifices of 40 pm and a chamber diameter of 320 pm [19], as experimentally validated in the real systems. 

Figure 7 shows the structures of the ion optics with the ionization chamber on the left and the entrance of the mass-analyzer on the right, which are described in the next section. The arrangement and shape of these structures were also computed via ion trajectory simulations. A result is shown in Fig. 8. At an extraction voltage (IE) of -25 V and separator input voltage (WFP) of 0 V an ion focus voltage (IFO) of 67 V generates the highest ion yield for the separator.

Fig. 20.8. Discrimination factor as a function of the initial kinetic energy of a fragment ion obtained by ion trajectory simulations. For the present simulations the ion source and the electrostatic lenses were treated fully three-dimensionally (see Fig. 20.1) and the maximum deviation from the real ion source was less than 5%. The dashed line represents the discrimination factors that were derived by Poll et al. [13] approximating the lenses infinitely long in the z-direction. The dash-dotted line are the discrimination factors that were derived in [34]. The potential array was more than a factor 10 smaller (less RAM of the computer) and thus the differences between simulation and reality were in the order of 15%...

To our knowledge, this is the first study of the relaxations of an oxide surface by GIXS, and the first experimental determination of the relaxation and termination of the a-Al203(0001) surface. Another determination has been performed very recently by combining time-of-flight scattering and recoiling spectrometry with LEED and classical ion trajectory simulations [59], with essentially the same results. 

Fig. 1.21. Schematic layout of the ion mobility instrument employed in metal cluster ion studies. The setup consists of different cluster sources housed in a source chamber, a time-of-flight mass spectrometer, a helium filled drift cell, and a quadru-pole mass filter for final ion detection (from right to left). Also displayed is an ion trajectory simulation of cluster ions of a mass of 500 amu drawn through the helium filled (7 mbar) drift cell at 300 K. The simulations show that under these conditions roughly 1% of the ions hnally escape through the 0.5 mm diameter exit hole [137]...

The resolution of a SIMION model is limited by manory constraints. The accuracy of ion trajectory simulations is highly dependent on the spatial resolution of the PA naturally, higher resolution models provide better approximations of smooth electrode surfaces and hence a better description of the electric field. Unfortunately, high-resolution models are memory-intensive each point in the PA requires 8-10 bytes of dynamic memory. SIMION v. 8.0 has an upper limit of 2x 10 points, which corresponds to ca 1.8 GB of RAM. Thus, the maximum cubic PA allowed is approximately 580x 580x 580 points. However, in order to run efficiently simulations of dynamic... 

Classical Ion Trajectory Simulations. Classical ion trajectory simulations were carried out by means of the three-dimensional scattering and recoiling imaging code (SARIC) developed in this laboratory. SARIC is based on the binary collision approximation, uses the ZBL universal potential to describe the interactions between atoms, and includes both out-of-plane and multiple scattering. Details of the simulation have been published elsewhere 11). 

Ion trajectory simulations were carried out for the 5-scans of Figure 4. Good agreement of the the simulated and experimental data could only be obtained by combining two domains which were rotated by 60° from each other. The results are shown in Figure 5. Combining the two domains results in symmetrical 5-scans which are a good reproduction of the experimental scans. 

Aqueous processing, precursors for ferroelectric thin films, 95-104 Autocompensated surface structure of GaN film on sapphire experimental description, 26-27 experimental procedure classical ion trajectory simulations, 28 GaN sample, 27 first-layer species... 

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