Kinetic sputtering

Kinetic sputtering describes the removal of surface-bound atoms, ions, or molecules, which occurs purely through the momentum transfer (elastic collisions). This form includes knock-on sputtering and recoil sputtering. 

As electronic excitation is not considered within kinetic sputtering, the collisions can be likened to an atomic-scale billiard ball game that is initiated on primary ion impact. The valence electron shells of the atoms/ions involved would thus represent the billiard ball s surfaces. The linear cascade model, which describes the most prevalent form of ion-induced sputtering, at least that from atomic ions and ions comprising small molecules (common examples used in SIMS include 0 , 02 , Cs, Ar" ", Xe" ", and Ga ), assumes a specific form of kinetic sputtering in which a full isotropic collision cascade is produced close to the surface. This is one form of knock-on sputtering. 

Lastly, sputtering can occur through potential processes alone. This has only been observed on specific nonmetallic substrates under inert gas ion impact with the sputter yield increasing with the primary ion charge. This charge dependence is not observed or predicted during kinetic sputtering. 

Potential sputtering thus serves to explain why sputtering can be noted, albeit at extremely low yields, below the kinetic sputtering threshold (the kinetic sputtering threshold is between 15 and 40 eV depending on the system) that scales with the primary ion charge (Malherbe 1994). 

Kinetic sputtering is initially considered because this is conceptually the simplest form of sputtering and the best understood of the sputtering processes. This is also the most common form of sputtering in SIMS as used in elemental analysis. Discussion of the other sputtering processes will follow. 

Kinetic sputtering Removal of atoms/molecules through kinematic processes... 

At aU but the lowest bombarding energies, the flux of atoms that are sputtered from the surface leaves the surface with a cosine distribution (Fig. 6). The sputtered atoms have kinetic energies higher than those of thermally vaporized atoms, as well as a high energy tail in the energy distribution that can be several tens of eV. 

The quantitative effect of the mass, energy, and angle of impact on the sputter yield for impacting deuterium ions is shown in Figs. 12a and b. As the kinetic energy... 

The incident ions cause recoil in the surface atoms. In studies of ionic liquids, only direct recoil - that is, motion in the forward direction - was measured. Watson and co-workers [56, 57] used time-of-flight analysis with a pulsed ion beam to measure the kinetic energies of the scattered and sputtered ions and therefore determine the masses of the recoiled surface atoms. By relating the measured intensities of the... 

GP 4] [R 11] For methanol conversion over sputtered silver catalyst, reaction rates and an activation energy (Figure 3.36) of 14.3 kcal moh were reported (8.5 vol.-% methanol balance oxygen 10 ms slightly > 1 atm) [72]. Since the latter is much lower than literature values (about 22.5-27 kcal moh ), different kinetics may occur or limitations of the reactor model may become evident. 

GP16][R14] First-order kinetics of the reaction rates were found for sputtered andimpregnatedPtcataly sts (< 1 mlmin 100-150°C 100-600ms) [76]. 

The kinetic ion energy flux, (efimax, which is typically 20 W m - [163, 301], will raise the substrate temperature by only a few degrees. Therefore, the influence of ions will be limited to the vicinity of impact. Furthermore, typical ion energies are below the sputtering threshold of silicon [134]. 

The impact of an ion beam on the electrode surface can result in the transfer of the kinetic energy of the ions to the surface atoms and their release into the vacuum as a wide range of species—atoms, molecules, ions, atomic aggregates (clusters), and molecular fragments. This is the effect of ion sputtering. The SIMS secondary ion mass spectrometry) method deals with the mass spectrometry of sputtered ions. The SIMS method has high analytical sensitivity and, in contrast to other methods of surface analysis, permits a study of isotopes. In materials science, the SIMS method is the third most often used method of surface analysis (after AES and XPS) it has so far been used only rarely in electrochemistry. 

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