Accelerated ions

Finally, the metallisation layer usually requires patterning, which can be done by reactive ion etching (RIE) or back-sputtering. The two processes are similar. In both techniques accelerated ions hit the substrate and forcibly detach atoms or molecules from the surface. RIE uses reactive gases such as chlorine, Cl or trichlorofluoromethane [75-69-4] CCl E. Inert gases such as argon or neon are used in back-sputtering. 

In single focusing instruments the beam of accelerated ions enters a magnetic field of constant intensity H, and experiences a force perpendicular to the field. Undef the influence of this force the ions assume a radial path in accordance with the relation... 

FIGURE B.5 A mass spectrometer is used to measure the masses of atoms. As the strength of the magnetic field is changed, the path of the accelerated ions moves from A to C. When the path is at B, the ion detector sends a signal to the recorder. The mass of the ion is proportional to the strength of the magnetic field needed to move the beam into position. 

Like diamond, DLC can be obtained by CVD by plasma action in a hydrocarbon atmosphere. Its deposition process differs from that of diamond in as much as the activation is not so much chemical (i.e., the use of hydrogen atoms) but physical. This physical activation is usually obtained by colliding accelerated ions produced by a high-frequency discharge. 

Magnetic sector mass spectrometers accelerate ions to more than 100 times the kinetic energy of ions analysed in quadrupole and ion trap mass spectrometers. The higher accelerating voltage contributes to the fact that ion source contamination is less likely to result in degraded sensitivity. This is particularly important for analysis that requires stable quantitative accuracy. 

Mass spectrometry Ionization Accelerated ions Ionsensitive multiplier tubes, dynodes Spectrum Digitalized data... 

Removal of all possible contaminants is not the only reason for sample preparation, since each clean and purified material has then to be converted into the chemical form suitable for the accelerator ion source. In most cases (as explained in the previous section), samples are put into the caesium sputtering source as graphite, solid elemental carbon, and for this reason samples are first burnt and then chemically reduced to graphite. 

Practicable isotopic enrichment has the following prerequisites adequately short time for the enrichment process, acceptable asymptotic enrichment factor, and adequate accuracy for the estimation of the enrichment factor. (When total activity, rather than specific activity, is limiting, one must also pay attention to losses during enrichment.) For the argon and carbon enrichments referred to above, enrichment factors of about 100 and 500 were obtained within a week and a few hours, respectively and enrichment factors were deduced from direct observations of adjacent, stable isotopes. The 14C enrichment process provided extra dividends for AMS measurement the sample was implanted in an ideal form for the accelerator ion source, and it was spatially localized (depth) which gave added signal-to-noise enhancement. 

Fig. 8.6 The principle underlying electromagnetic separation of isotopes. Electrostatically accelerated ions enter at the left. A magnetic field perpendicular to the plane of the paper causes the circular orbits shown in the sketch (See text for further detail)...

The ions of the selected polarity will be accelerated down the drift region, left to right in Figure 10.1, while ions of the opposite polarity are repelled and pushed left. An important feature is the reverse flow air, a moderate velocity stream that resists the movement of the accelerating ions and sweeps the nonionized molecules and the ions of the opposite polarity into the exhaust stream. 

There are several designs of accelerators for industrial use. They are mainly used to accelerate electrons, although they can be adapted to accelerate ions... 

Time of flight analyzers use an electric field to accelerate ions to the same kinetic energy and then measure the time it takes for the ions to reach the detector. The velocity of the ions, and thus the time of flight to the detector, depends only on the mass-to-charge ratio... 

---