Secondary Ion Energy Spectra Research Articles

A new technique to study the stages of oxidation of metals using oxidation induced changes in the shape of secondary ion energy spectra

A new technique to study the oxidation process in metals based on the yield variation with oxygen dose of secondary ions whose ejection mechanisms are identified with distinctly different dynamical sputtering processes is presented. When applied to a polycrystalline copper sample the method identifies four possible oxidation stages, from adsorption into the surface layer for doses up to about 10 4L, followed by a rapid reconstruction to a Cu 2O structure at 10 4L, followed by a slow growth of bulk oxide up to 10 4L and a further physisorption of oxygen or transition to a surface CuO structure at higher doses. The technique provides a significant increase in the versatility and usefulness of SIMS equipment incorporating appropriate energy analysis facilities.

A computerized system for determining secondary ion energy spectra

A computer program and computer-directed high-voltage sample potential controller which allow a rapid determination of the energy spectrum of an ion species in a secondary ion mass spectrometer are presented. An electrostatic sector energy analyzer on the mass spectrometer provides high energy resolution. The spectra are obtained by stepping the sample accelerating potential by small voltage steps and determining the detector pulse count rate at each energy. The computer program controls the sample potential, collects the data, makes corrections for ion optical and geometric effects, calculates several important parameters of the energy distribution, and outputs the corrected and uncorrected results to line printer and a plotter. The system is fast, accurate, and very easy to operate. It should be necessary only to change the ion optical correction procedure in order to use the system with other mass spectrometers.

Discrimination effects in SIMS. Part III. Ion optical and energy discrimination

Discrimination effects caused by the convolution of the diverse shapes of the secondary ion energy spectra with the fixed ion optical and energy-bandpass characteristics of the CAMECA IMS-300 ion microanalyzer are discussed. Substantial differences in the transmission efficiency of the ion optics between atomic ions, and very large differences between atomic and polyatomic ions have been found. The influence of discrimination effects on the appearance of a SIMS spectrum is illustrated, and the potential influence of the effects on quantitative analysis is discussed.

A study of the energy spectra of secondary ions from metal matrices

The energy spectra of secondary ions sputtered from 28 metal matrices by O 2 + ions have been studied. The spectra resemble those obtained from the sputtering of pure elements under similar conditions, with the presence of oxygen gas yielding a better correlation than sputtering in residual vacuum. The ionization processes are apparently the same as those which occur in pure samples, but the most probable en'ergies of the distributions are different owing to the difference in surface binding energies or efficiency of momentum transfer. The statistical model of cluster ion formation does not properly describe the details of the spectra. As a direct result of the similarity of the energy spectra of ions from various matrices to the spectra of those ions from pure elements, the bandpass efficiencies of the instrumentation for the various ions are very similar. Therefore, in quantitative analysis, the transmission of the ion optics can be assumed to be the same as when pure samples are bombarded, making the correction of energy discrimination effects feasible. The best analytical condition is obtained with a high partial pressure of oxygen.

The effects of oxygen and nitrogen adsorption on secondary ion energy spectra

The detailed variation of the energy spectra of ions sputtered from pure materials as the partial pressure of reactive gas changes was studied. The results show that the contribution of secondary ions from reacted versus clean surfaces varies smoothly as the gas pressure (and thus coverage) is increased for most surfaces. Sudden changes in the energy spectra are observed for Ni, Co, and W in the presence of oxygen, apparently corresponding to incorporation of oxygen into the surface lattice. The energy spectra are therefore very sensitive to changes in the surface, and should be very useful in oxidation or adsorption studies. The analytical consequences of changes in the energy spectra are discussed. As the spectra change, the transmission coefficients (bandpass efficiencies) for the ions alter, thereby affecting the apparent signal intensities. The optimum analytical condition is deduced from the data.

Secondary ion energy per unit mass spectra from polycrystalline copper

An improved version of the time-of-flight spectrometer “ASSIMOF” is described, capable of obtaining secondary ion energy spectra in the energy range 10 eV to 10 keV, with an energy resolution (for copper) varying between 1.4 and 17%. Application of the instrument to a study of the ion emission due to 600-μA cm −2, 47-keV Ar + bombardment of 5N polycrystalline copper at a scattering angle of 84° and oxygen partial pressures between 3 × 10 −8 and 1 × 10 −5 torr demonstrates the existence of a number of mechanisms for the creation of an ionized state on particles ejected owing to collisions describable by the random cascade theory of sputtering. In addition, it is shown that at this geometry the probability of ionization convoluted with the probability of ejection, for particles with energies equal to or exceeding the direct target recoil energy, is higher for non-random than for random collision events. Evidence is presented to suggest that experiments designed to investigate the physical mechanisms associated with the ionization phenomena should be restricted to primary ion doses not exceeding 10 14 ions cm −2.

Energy spectra of secondary ions and secondary ion emission (SIE) mechanisms

Analysis, presented in this work, shows that a considerable amount of experimental data on energy spectra and yield of sputtered neutral atoms, ejected from transition metals under bombardment by ions of energies of 102–103 eV, is in satisfactory agreement with a description of the sputtering process within the framework of the simple model in which atomic collisions are considered as the collisions of absolutely elastic hard spheres. A new method, based on this conclusion, allowing to obtain information about a relative role of different mechanisms of the secondary ion emission (SIE) which are distinguished by its sensitivity to the kinetic energy changes of the bombarding ions, has been proposed. The investigation of energy spectra of sputtered ions, ejected from Ta, Nb, V and Mo under bombardment by Hg+ ions of energies from 250 up to 2000 eV has been performed with the purpose of elucidating (by the proposed method) the mechanism of secondary ion emission. The experiments have been carried out under ultra-high vacuum conditions with control of the necessary purity of the surface under investigation. The SIE mechanism during Ta, Nb and Mo sputtering is shown to be determined by the electron exchange between a sputtered atom and a metal, and independent of the primary ion energy. In the case of vanadium a mechanism sensitive to the kinetic energy of the primary ions is added to the mentioned one. The experimentally obtained energy dependence of the ionization degree of sputtered atoms is compared with those predicted by different theories.

Secondary ion energy spectra of polycrystalline transition metals and aluminium

Secondary ion energy spectra from polycrystalline Al, Sc, Ti, V, Cr, Fe, Ni, Cu, Hf, W and Au are presented, exhibiting a complex structure in the region 0–55 eV which is shown to be dependent on surface contamination levels. The design limitations present in existing ion energy and mass analysers, which have prevented the observation of these effects in the past, are defined and methods for their correction are suggested. The changing shape of the ion energy spectrum as a function of the local matrix and surface environment of the departing particle is shown to represent a fundamental difficulty for conventional quantitative SIMS analysis.

A comparison of experimental secondary ion energy spectra of polycrystalline metals with theory

Abstract The ability of relevant current theories of secondary ion emission to explain experimental ion energy spectra obtained from polycrystalline Al, Sc, Ti, V, Cr, Fe, Ni, Cu, Hf, W and Au is analysed. It is shown that our present understanding or interpretation of the physics of the emission of secondary ions seems incapable of accounting for the observed changes in the energy spectra as a function of surface contamination or oxidation.

The energy spectra of secondary ions emitted during ion bombardment

Abstract Secondary ion energy spectra have been measured for singly charged ions emitted from targets irradiated with 43 keV A+ ions. Targets studied include the 3d transition metals (Sc, Ti, V, Cr, Fe, Ni) Cu and Zn, Zr, Al and Si and the compounds SiO2, Al2O3, NaCl, KCl. Energy spectra were measured in the energy range 1–600 eV. In several cases a peak in the energy spectrum in the region around 200 eV has been found. This is in addition to the usual low energy peaks in the region of 5–10 eV. In many cases the low energy peak was observed to decay steadily with irradiation time or to increase with oxygen pressure. In the case of the cleanest Zn spectrum, only the high energy peak can be detected. The data are discussed in relation to current models of secondary ion emission. We conclude that, in general, elemental metal targets which are clean are characterised by the high energy peak in the secondary ion energy spectrum. The slower ions emitted have been neutralised by electron exchange processes. The ...

Current density effects in secondary ion emission studies

The influence of the primary ion current density on the secondary ion emission from clean surfaces has been investigated. The experiments were carried out in a quadrupole equipped mass spectrometer using 10–12 keV argon primary ions. A focussing device in the vicinity of the target allowed the current densities to be varied between some 10 μA/cm 2 and 10 mA/cm 2 at beam currents between 1 and 5 μA. Energy spectra of secondary ions could be obtained by use of a suitable energy analyser preceding the quadrupole mass filter. Due to focussing the secondary ion intensities increased markedly for a variety of metal targets. The effects were most pronounced for noble metals, in particular for gold where the yield increased by up to a factor of 20. The enhancement is attributed to ionization taking place in vacuum at large distances from the target surface. Several ionization processes are considered which may account quantitatively for the magnitude of the effects observed.

957. Angular dependence of energy spectra of secondary ions scattered by the surface of single crystals: U A Arifov and A A Aliev,Zh Eksper Teor Fiz, 54 (2), Feb 1968, 354– 361 ( in Russian)

957. Angular dependence of energy spectra of secondary ions scattered by the surface of single crystals: U A Arifov and A A Aliev,Zh Eksper Teor Fiz, 54 (2), Feb 1968, 354– 361 ( in Russian)