Excitations In Sputtering Research Articles

Study of atomic excitation in sputtering in collisions of highly charged Xeq+ ions with Al surface

In this work, the optical spectra emitted from an Al surface induced by 410 keV Xeq+ (10 ≤ q ≤ 23) ions are measured. The intensities of spectral lines of sputtered Al atoms at 308.09, 309.14, 394.52, and 396.27 nm as a function of projectile potential energy are investigated. The result shows that the ratios of Y(308.09)/Y(309.14) and Y(394.52)/Y(396.27) stay constant and are independent of the potential energy. In the collisions, the photon yields of spectral lines increase with increasing potential energy. According to the electron-transfer model, the excitation process of sputtered Al atoms is discussed. It can be concluded that in the collisions of 410 keV Xeq+ (10 ≤ q ≤ 23) ions with the Al surface, nuclear energy loss determines the sputtering yield, and electron energy loss and potential energy deposited on the target surface affect atomic excitation in sputtering.

A molecular dynamics simulation of collisional excitation in sputtering from Al

The molecular dynamics sputtering code SPUT2 was modified to permit investigation of core excitation in Al following bombardment with 5 keV Ar + ions. This code was used to investigate sputtering mechanisms responsible for the ejection of core-excited atoms from solid surfaces. Simulations were carried out with the ion incident along both low- and high-index directions. In contrast to most previous studies, essentially all ejection of core-excited atoms resulted from asymmetric collisions (i.e. collisions between the incident ion and a target atom). When the ion is incident along a low-index direction, core-excited atoms arise almost exclusively from the first layer of the target. When the ion is incident along a high-index direction, core-excited atoms are found to eject from deeper layers as well.

Atomic excitations in sputtering as functions of the projectile energy

We have bombarded Mg, MgO, Al, and Si with Ar ions from 10 to 160 keV and measured yields of sputtered excited neutrals and ions as functions of the projectile energy. The yield curves for different levels within the same charge state and also the same element are essentially proportional. The curves for excited ions are steeper than those for excited neutral atoms. The steepness increases with increasing charge state, and is element dependent. This is presumably related to different velocity distributions for different charge states. The data seem to indicate a difference in excitation mechanism between the jellium-like metals Mg and Al and the semiconductor Si, which can be related to the different bonds (metals and covalent, respectively) of the solids.

Atomic excitations in sputtering studied with the use of composite targets

Atomic excitation phenomena in sputtering have been studied with the following combinations of projectile and target. (i) Be, B, Mg, Al, and Si bombarded with 80 keV Ar+ at UHV as well as with the target chamber backfilled with oxygen. (ii) Mg bombarded with 80 keV O+, F+, Ne+, Na+ Cl+, and Ar+. (iii) MgO, MgF2, MgCl2, MgSO4, and several alkali halides bombarded with 80 keV Ar+ at UHV. Results are discussed. It is concluded that the excited-state formation takes place as electron tunneling at a fairly large separation between the target surface and the particle being sputtered. It is suggested with composite targets containing a metal element that excitation takes place predominantly at locations of the target surface where the work function is low, due to a thin, metallic surface layer, and that production of ground-state, positive secondary ions mainly takes place at target surface regions with high work function. For semiconductors, the changes caused by presence of oxygen are related to the change of the bonds in the solid from being of covalent nature to being fractionally ionic.

Temperature effects in photon emission from sputtered atoms

Abstract The temperature dependence Y∗(T) of ion-bombardment-induced photon emission from sputtered species of a polycrystalline copper target is measured under conditions in which there is a pronounced increase of the sputtering yield Y at elevated temperatures. The dependence Y∗(T) has been found to be qualitatively different for the optical lines of the neutral and ionized sputtered atoms. The dependences Y∗(T) for the CuI lines are similar to the dependence Y(T), whereas the CuII line intensity is practically independent of the target temperature. The dependences of the photon emission for the CuI and CuII lines on ion incidence angle have also been found to be very different. The results obtained are discussed in terms of existing models for atomic excitation in sputtering.

Molecule excitation in sputtering, scattering and electron or photon induced desorption

Simple theoretical considerations are shown to predict significant rotational and vibrational excitation of sputtered, scattered, and energetic desorbed molecules, alignment of the rotation axis, and orientation effects in dissociative and non-dissociative charge exchange cross-sections. Where available, experimental data verifying these predictions is presented. A theory of molecule-surface electronic interactions is outlined, and used to derive, from experimental data, the dependence on ionisation energy of the probability of occupation of a molecular state ( H 2 b 3 Σ u +) following scattering from a metal surface (Ni(111)). It is shown that vibrational excitation may occur as a consequence of non-dissociative charge capture. The possible role of substrate excitation (in the form of electron-hole pair creation) in vibrational quenching of ejected and scattered molecules is suggested.

Study of atomic excitations in sputtering with the use of composite targets

Some Li- and Na-compounds were bombarded with 80keV Ar + ions, and the excitation of sputtered particles was studied with optical spectrometry. Very strong excitation of Li I and Na I was observed, but essentially no excitation of electronegative elements. For levels in Li I and also in Na I with n ⩽ 8, the relative excitation probabilities decrease as power laws versus the effective quantum number of the excited term. However, in some cases, for Na I and with n > 8, the relative level populations fall noticeably above the extrapolation of such power law behaviors. This is discussed and tentatively interpreted in terms of two-step processes, (i) The projectile excites a target electron from the valence band to the conduction band. (ii) Such an excitation is transferred resonantly to the sputtered atom on its way out.

Study of atomic excitations in sputtering with the use of N, O, F, Ne, Na, Cl and Ar projectiles

Solid magnesium has been bombarded with 80 keV ions of N, O, F, Ne, Na, Cl, and Ar, and excitation of sputtered magnesium atoms and ions has been studied. Relative level excitation probabilities depend strongly on the projectile, the dependences for Mg I levels being different from those for Mg II levels. With all projectiles, the resonance level in Mg II was more strongly excited than the resonance level in Mg I. Very little radiation was observed from the projectiles except for sodium.

Study of atomic excitations in sputtering with targets partially covered with oxygen

We bombarded pure elemental targets of beryllium, boron, magnesium, aluminium, silicon, titanium and gold with 80 keV Ar + ions and studied the excitation of sputtered atoms or ions under ultrahigh vacuum conditions as well as with oxygen present at the target surface. The measurements on magnesium, aluminium, silicon and titanium were made at projectile incidence angles from 0° to 85°. Excitation probabilities for gold were found to be very little influenced by oxygen, but for beryllium, boron, magnesium, aluminium, silicon and titanium the excitation probabilities were in many, but not all, cases found to depend strongly on the oxygen pressure as well as on the beam current density. This indicates that the excitation mechanism is markedly dependent on the initial electronic conditions in the solid.

Study of atomic excitation in sputtering as a function of the projectile incidence angle

Solid targets of beryllium, boron and magnesium have been bombarded with 80 keV Ar + ions. Intensities of photons emitted from sputtered particles have been measured as functions of the angle of incidence of the projectile. Generally, the excitation intensities increase with increasing angle of incidence, but a few levels show much stronger angular variations than the majority of levels do. The results are discussed. It is concluded that whereas the common increase in excitation is caused by the general increase in the number of swift, sputtered atoms, a few levels are in addition selectively excited through molecular-orbital electron-promotion processes taking place in binary collisions.

Study of atomic excitations in sputtering with the use of Cu, Ag, and Au targets

Solid targets of Cu, Ag, and Au have been bombarded with 80 keV Ar + ions, and photons emitted from sputtered atoms have been measured. From the photon intensities, relative level populations have been deduced. The results are discussed in terms of the initial and the final conditions, i.e., the electronic structures of the solids as well as of the free atoms.

Study of atomic excitations in sputtering with the use of Mg, Al, Ca, and Cd targets

Solid targets of Mg, Al, Ca, and Cd have been bombarded with 80-keV ${\mathrm{Ar}}^{+}$ ions. Photon emission from sputtered particles has been measured and converted to relative level populations. The experimental results are discussed in terms of a set of basic considerations outlined for atomic excitations in sputtering processes.

Study of atomic excitation in sputtering as a function of the projectile incidence angle

Solid targets of elemental beryllium, boron, magnesium, and gold have been bombarded with 80-keV ${\mathrm{Ar}}^{+}$ ions. Intensities of photons emitted from sputtered particles have been measured as functions of the angle of incidence of the projectile. Generally, the excitation intensities increase with increasing angle of incidence, but a few levels show much stronger angular variations than the majority of levels do. The results are discussed. It is concluded that whereas the common increase in excitation is caused by the general increase in the number of swift, sputtered atoms, a few levels are in addition selectively excited through molecular-orbital electron-promotion processes taking place in binary collisions.

A semi-classical description of excitation in sputtering and in electron-atom collisions

The application of a simplistic, semi-classical approach for describing excitation in sputtering and in electron-atom collisions is discussed. It is shown that the approach is able to describe relative populations when Si I, Si II and Si III are formed in sputtering as well as relative populations when Rb I, Rb II and Rb III are formed in electron-atom impact. The approach also compares favorably with the Born-approximation calculations of Vainshtein et al. for Rb I, provided it is again used to describe populations in a relative (rather than absolute) sense.

Study of atomic excitations in sputtering with the use of Be, B, and C targets

Solid targets of Be, B, and C have been bombarded with 80-keV ${\mathrm{Ar}}^{+}$ ions, and photon emission from sputtered particles has been studied. For beryllium, several strong BeI and BeII emission lines have been observed, and the photon intensities have been converted to relative level population data. Essentially no radiation could be detected with a boron target, and only weak molecular emission was observed for carbon. The results are discussed. They are in accordance with the ideas behind a newly proposed electron-pickup model for atomic excitation in sputtering, but seem not to support a statistical (or binary-collision) model.

Atomic excitations in sputtering studied with group two element targets

Solid targets of Be, Mg, Zn, and Cd have been bombarded with 50 keV Ar + ions. The relative excitation of lowest-lying excited levels in sputtered neutrals and singly-charged ions have been measured using optical spectrometry. It is found that singly charged ions are excited much more efficiently than neutral atoms. This is discussed, and it is concluded that atomic excitation in sputtering results from electron pick-up to excited states in initially ionized atoms rather than from inelastic atom-atom or electron-atom collisions.

Atomic excitations in sputtering studied with group two element targets

Solid targets of Be, Mg, Zn, and Cd have been bombarded with 50 keV Ar + ions. The relative excitation of the lowest-lying excited levels in sputtered neutrals and singly-charged ions have been measured using optical spectrometry. It is found that singly-charged ions are excited much more efficiently than neutral atoms. This is discussed, and it is concluded that atomic excitation in sputtering results from electron pick-up to excited states in initially ionized atoms rather than from inelastic atom-atom or electron-atom collisions.

Atomic excitations in sputtering studied with group two element targets

Atomic excitations in sputtering studied with group two element targets

Energy dependence of excitation in sputtering

Energy dependence of excitation in sputtering