Sputtering of Ag under C 60 + and Ga + projectile bombardment (original) (raw)
Related papers
Energetic ion bombardment of Ag surfaces by C60+ and Ga+ projectiles
Journal of the American Society for Mass Spectrometry, 2005
The ion bombardment-induced release of particles from a metal surface is investigated using energetic fullerene cluster ions as projectiles. The total sputter yield as well as partial yields of neutral and charged monomers and clusters leaving the surface are measured and compared with corresponding data obtained with atomic projectile ions of similar impact kinetic energy. It is found that all yields are enhanced by about one order of magnitude under bombardment with the C 60 ϩ cluster projectiles compared with Ga ϩ ions. In contrast, the electronic excitation processes determining the secondary ion formation probability are unaffected. The kinetic energy spectra of sputtered particles exhibit characteristic differences which reflect the largely different nature of the sputtering process for both types of projectiles. In particular, it is found that under C 60 ϩ impact (1) the energy spectrum of sputtered atoms peaks at significantly lower kinetic energies than for Ga ϩ bombardment and (2) the velocity spectra of monomers and dimers are virtually identical, a finding which is in pronounced contrast to all published data obtained for atomic projectiles. The experimental findings are in reasonable agreement with recent molecular dynamics simulations.
Formation of sputtered silver clusters under bombardment with SF5+ ions
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2002
The formation of Ag n clusters and Ag þ n cluster ions under bombardment of a silver surface with SF þ 5 and Xe þ projectile ions was investigated experimentally. In order to obtain information about the relative abundance of clusters among the flux of sputtered particles independent of their charge state, mass spectra of both secondary ions and sputtered neutral particles were recorded. The neutral species were post-ionized prior to mass analysis by means of photo-ionization using an intense UV laser at a wavelength of 193 nm. It is found that measured Ag þ n signals increase significantly if SF þ 5 projectiles are used instead of rare gas (Ar þ or Xe þ ) ions of the same kinetic impact energy. The signals of neutral Ag atoms and Ag n clusters, on the other hand, exhibit only a relatively small increase, thus indicating that the enhancement observed for the secondary ions is predominantly caused by an increased ionization probability of sputtered particles under SF þ 5 bombardment rather than by enhanced partial sputtering yields. While the transition from Ar þ to Xe þ projectiles leads to a drastic increase of the relative abundance of larger clusters in the spectrum, practically no such effect can be detected for the transition from Ar þ to SF þ 5 . This finding shows that the use of polyatomic SF 5 projectiles does not lead to a higher efficiency in producing sputtered clusters.
Microscopic Insights into the Sputtering of Ag{111} Induced by C60 and Ga Bombardment
The Journal of Physical Chemistry B, 2004
Molecular dynamics computer simulations have been utilized to compare the differences in the mechanism of sputtering of Ag{111} by kiloelectronvolt Ga and C 60 projectiles. The calculated kinetic energy distributions of Ag monomers and Ag 2 dimers compare favorably with experimental results. The damage caused by the C 60 particle left in the sample is less than the depth of material that the next impinging C 60 particle would remove, thus supporting the preliminary experimental observations that molecular depth profiling is possible with C 60 projectile beams.
Analytical Chemistry, 2003
The mechanism of enhanced desorption initiated by 15-keV C 60 cluster ion bombardment of a Ag single crystal surface is examined using molecular dynamics computer simulations. The size of the model microcrystallite of 165 000 atoms and the sophistication of the interaction potential function yields data that should be directly comparable with experiment. The C 60 model was chosen since this source is now being used in secondary ion mass spectrometry experiments in many laboratories. The results show that a crater is formed on the Ag surface that is ∼10 nm in diameter, a result very similar to that found for Au 3 bombardment of Au. The yield of Ag atoms is ∼16 times larger than for corresponding atomic bombardment with 15-keV Ga atoms, and the yield of Ag 3 is enhanced by a factor of 35. The essential mechanistic reasons for these differences is that the C 60 kinetic energy is deposited closer to the surface, with the deeply penetrating energy propagation occurring via a nondestructive pressure wave. The numbers predicted by the model are testable by experiment, and the approach is extendable to include the study of organic overlayers on metals, a situation of growing importance to the SIMS community.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2010
Sputtering and ion emission rates have been measured from CsI and gold targets under the impact of Au þ n (n = 1-9) clusters at energies between 30 and 350 keV/atom. The two materials have similar behaviors in regard to the variations of the sputtering and anion emission yields with energy and cluster size. The sputtering and anion emission yields increase nonlinearly with the projectile size. The maximum anion yields are found at lower energies than the maximum sputtering yields which themselves occur substantially below the maximum energy losses. The variations with energy of the atomic ion yields differ from those of the cluster ion yields. The experimental results are in agreement with an ion emission from linear collision cascades and spike collisions, the relative contribution of these two processes depending on the size of the cluster projectile and of the emitted ion. In addition they show that the ion emission yield enhancements under cluster impact result from a more effective sputtering mechanism and not from an enhanced ionization of the ejected species.
Cluster formation at metal surfaces under bombardment with SFm+ (m=1,…,5) and Ar+ projectiles
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms - NUCL INSTRUM METH PHYS RES B, 2004
We investigate the formation of ionic and neutral clusters emitted from a polycrystalline indium surface under bom- bardment with SFþ m (m =1 , ... , 5) and Ar + projectile ions at 10 keV impact energy. Mass spectra of secondary ions and sputtered neutral particles are recorded under otherwise identical conditions. The neutral species are post-ionized prior to mass analysis by means of single photon-ionization using an intense UV laser at a wavelength of 193 nm. It is found that the measured secondary ion signals increase much more than those of the corresponding neutral particles if SFþ m projectiles are used instead of Ar+ ions, indicating that the ionization probability under bombardment with SFþm is enhanced by a chemical matrix effect induced by fluorine incorporation into the surface. Interestingly, the largest values of the ionization probability are observed for SFþ 3 projectiles. The total sputtering yield is found to be larger for SF þ m compared to Ar+ projectiles and to ...
Energy distributions of atomic and molecular ions sputtered by C60+ projectiles
Applied Surface Science, 2006
In the process of investigating the interaction of fullerene projectiles with adsorbed organic layers, we measured the kinetic energy distributions (KEDs) of fragment and parent ions sputtered from an overlayer of polystyrene (PS) oligomers cast on silver under 15 keV C 60 + bombardment. These measurements have been conducted using our TRIFT TM spectrometer, recently equipped with the C 60 + source developed by Ionoptika, Ltd. For atomic ions, the intensity corresponding to the high energy tail decreases in the following order: C + (E À0.4 ) > H + (E À1.5 ) > Ag + (E À3.5 ). In particular, the distribution of Ag + is not broader than those of Ag 2 + and Ag 3 + clusters, in sharp contrast with 15 keV Ga + bombardment. On the other hand, molecular ions (fragments and parent-like species) exhibit a significantly wider distribution using C 60 + instead of Ga + as primary ions. For instance, the KED of Ag-cationized PS oligomers resembles that of Ag + and Ag n + clusters. A specific feature of fullerene projectiles is that they induce the direct desorption of positively charged oligomers, without the need of a cationizing metal atom. The energy spectrum of these PS + ions is significantly narrower then that of Ag-cationized oligomers. For characteristic fragments of PS, such as C 7 H 7 + and C 15 H 13 + and polycyclic fragments, such as C 9 H 7 + and C 14 H 10 + , the high energy decay is steep (E À4 À E À8 ). In addition, reorganized ions generally show more pronounced high energy tails than characteristic ions, similar to the case of monoatomic ion bombardment. This observation is consistent with the higher excitation energy needed for their formation. Finally, the fraction of hydrocarbon ions formed in the gas phase via unimolecular dissociation of larger species is slightly larger with gallium than with fullerene projectiles. #
Sputtered neutral silver clusters up to Ag18
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms
Neutral silver clusters Ag n with n < 18 sputtered from a polycrystalhne silver surface under bombardment with 5 keV Ar + ions were detected by means of energy resolved brae-of-flight mass spectrometry. Post~onIzat~on of the ejected neutral particles was performed by an exclmer laser operated with ArF (hv = 6 4 eV) The kinetic energy of the detected particles was determined from their fl~ght time interval between the sputter pulse and the ~onlzlng laser pulse By saturating the lomzahon of the sputtered neutrals, relative cluster sputtering yields Y(Agn) were determined as a function of the cluster s~ze For n _< 6, the value of Y(Ag~) is found to drop by approximately one order of magmtude If n IS increased by one atom, whereas for cluster s~zes larger than SLX atoms the decrease becomes significantly less pronounced and an odd-even intensity alternation s~mdar to that observed for sputtered 1on clusters becomes visible The kinetic energy &stnbut~ons of sdver atoms, dlmers, tnmers, tetramers and pentamers determined from the time-of-flight method all look very slmdar and, m particular, show essentmlly the same high-energy dependence for sputtered atoms and molecules In comparison, corresponding data taken by electron impact ionization with subsequent electrostatic energy analys~s exhibit a slgmficantly different asymptotic behav~our, the high energy slope of the energy spectra becoming steeper as the cluster size increases. From a detaded analys~s of the measured s~gnals, it ~s concluded that due to the concurrence of single-and mulhphoton absorphon processes the laser postlomzat~on results may be corrupted by photo-fragmentation.