Investigation of surface reactions by the static method of secondary ion mass spectrometry: II. The oxidation of chromium in the monolayer range

By means of the static method of secondary ion mass spectrometry the oxidation of a polycrystalline chromium surface cleaned by ion bombardment was investigated at room temperature in the oxygen dose range up to 1600 L. Two different oxide phases are formed on the surface, one covering the other. The secondary ion yield for the Cr⁺ ions from an oxidized surface amounts to 1.1.     

Investigation of surface reactions by the static method of secondary ion mass spectrometry: III. The oxidation of vanadium,niobium and tantalum in the monolayer range

By means of the static method of secondary ion mass spectrometry the oxidation of a polycrystalline vanadium, niobium, and tantalum surface, cleaned by ion bombardment was investigated in the oxygen dose range up to 1000 L at room temperature. Two different oxide phases with different sputtering rates were found, one covering the other.     

Investigation of surface reactions by the static method of secondary ion mass spectrometry: IV. The oxidation of magnesium,strontium, and barium in the monolayer range

The oxidation of a polycrystalline magnesium, strontium, and barium surface, cleaned by ion bombardment, was investigated at room temperature in the oxygen dose range up to 12000 L by the static method of secondary ion mass spectrometry. Two different oxide phases with different sputtering rates were found, one covering the other.     

The use of secondary ion mass spectrometry in surface analysis

Secondary ion mass spectrometry (SIMS) is based on the bombardment of solids by ions and subsequent mass analysis of the sputtered ions or of the post-ionized neutrals. Various models have been proposed for the emission of secondary ions from the target. These models can roughly be grouped into two categories: (a) lonization takes place outside the target; the sputtered particles are assumed to leave the target in an excited or super-excited state; ionization can then result from such processes as Auger de-excitation or resonance ionization. (b) Ions are generated inside the target by collision cascades initiated by a primary impinging ion. Experimental data of the element- and matrix-dependent ion yield and estimates of the minimum detectable concentrations are shown as well as the rate of consumption of the target. Methods for efficient use of the sputtered material will be discussed. Examples of the wide range of applications of SIMS for determination of the chemical composition and structure of the surface layer and for imaging of the distribution of elements in the surface are given. The SIMS results are compared with those of Auger and Ion Scattering Spectrometry. The essentially non-destructive method of static SIMS is shown to be a powerful tool for the investigation of the outermost atomic layers of a solid.     

Molecular ion yield enhancement induced by gold deposition in static secondary ion mass spectrometry

Static ToF-SIMS was used to evaluate the effect of gold condensation as a sample treatment prior to analysis. The experiments were carried out with a model molecular layer (Triacontane M = 422.4 Da), upon atomic (In⁺) and polyatomic (Bi₃⁺) projectile bombardment. The results indicate that the effect of molecular ion yield improvement using gold metallization exists only under atomic projectile impact. While the quasi-molecular ion (M+Au)⁺ signal can become two orders of magnitude larger than that of the deprotonated molecular ion from the pristine sample under In⁺ bombardment, it barely reaches the initial intensity of (M−H)⁺ when Bi₃⁺ projectiles are used. The differences observed for mono- and polyatomic primary ion bombardment might be explained by differences in near-surface energy deposition, which influences the sputtering and ionization processes.     

Oxygen distribution in nickel silicide films analyzed by time-of-flight secondary ion mass spectrometry

The oxygen distribution in Ni₂Si and NiSi films formed during a two-step silicidation process was analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS). TOF-SIMS mass spectra revealed that both silicon and nickel reacted with oxygen at the Ni₂Si surface. In addition, silicon nitride was formed at the surface by the reaction of silicon with nitrogen in the TiN capping layer during the first silicidation annealing. The amount of nitrogen at the NiSi surface varied with silicidation annealing temperature and with the formation conditions of the TiN capping layer. We also showed that a small amount of oxygen was penetrated into the NiSi film and strongly affected the level of junction leakage current in n⁺–p junctions in n-channel MOSFETs. The oxygen concentration in the NiSi film decreased with an increase in the amount of nitrogen at the NiSi surface.     

The use of secondary ion mass spectrometry for studies of oxygen adsorption and oxidation

Thin oxide layers on silicon and tantalum as well as oxygen saturated silicon surfaces have been investigated by means of SIMS. Sputter depth profiling was achieved using a raster scanned 2 keV argon ion beam. The results clearly indicate that oxygen adsorption does not lead to on oxide-like structure. Moreover it is found that air-grown room temperature oxides on silicon are depleted of oxygen as compared to the composition of thick silicon dioxides. The results are discussed with reference to recently reported SIMS studies on oxygen covered surfaces.     

Quantification routines for adsorption studies in static secondary ion mass spectrometry and the effect of ionisation probability

It is shown that the usual method of quantification of surface composition in static secondary ion mass spectrometry (SSIMS), which is purely comparative in nature, is unsuitable for adsorption studies by SSIMS. This is because of the effect of the ionisation efficiency and ion stability of a particular ion produced from a molecule adsorbed on the surface of a substrate. The established routine results in a non-linear relationship between calculated relative surface coverage and the ion selected to characterise the adsorbate. The application of a new normalisation routine to time-of-flight secondary ion mass spectrometry (ToF-SIMS) data has been used to account for this discrepancy, and also takes into account the effect of a possible contribution from the clean substrate to the ion selected to characterise the adsorbate molecule. This routine is suggested only for use with organic secondary ions, where the ionisation potential of such ions is of a comparable magnitude, and should prove particularly useful in the application of surface analysis techniques to adsorption studies.     

Analysis of solids by secondary ion and sputtered neutral mass spectrometry

A mass spectrometer is described, which allows the analysis of sputtered neutral and charged particles as well as of residual gas composition. This combined SIMS, SNMS, and RGA instrument consists of a scanning primary ion beam column, an electron impact ionizer, an electrostatic energy filter and an rf quadrupole mass analyzer.Various examples of surface and bulk analysis are presented which demonstrate the beneficial complementary features of these techniques. These are, in particular: a substantial reduction of the matrix effect and fewer complications with samples of low electrical conductivity in SNMS, and the possibility of measuring the depth distribution of gases included in small cavities in the solid in the SNMS/RGA mode. SIMS, on the other hand, allows in many cases higher detection sensitivities.EURATOM Association     

Uranium passivation by C implantation: A photoemission and secondary ion mass spectrometry study

Implantation of 33 keV C⁺ ions into polycrystalline U²³⁸ with a dose of 4.3 × 10¹⁷ cm⁻² produces a physically and chemically modified surface layer that prevents further air oxidation and corrosion. X-ray photoelectron spectroscopy and secondary ion mass spectrometry were used to investigate the surface chemistry and electronic structure of this C⁺ ion implanted polycrystalline uranium and a non-implanted region of the sample, both regions exposed to air for more than a year. In addition, scanning electron microscopy was used to examine and compare the surface morphology of the two regions. The U 4f, O 1s and C 1s core-level and valence band spectra clearly indicate carbide formation in the modified surface layer. The time-of-flight secondary ion mass spectrometry depth profiling results reveal an oxy-carbide surface layer over an approximately 200 nm thick UC layer with little or no residual oxidation at the carbide layer/U metal transitional interface.     

On the abundance of molecular ions in secondary ion mass spectrometry

Changes in molecular secondary ion intensities brought about by working in an environment of oxygen can be rationalised in simple statistical terms.     

Application of molecular (static) secondary ion mass spectroscopy to detection of organic molecules in amorphous titanium carbide

Molecular, or static, secondary ion mass Spectroscopy (SIMS) is applied to the detection of organic molecules in amorphous titanium carbide films. The presence of such organic clusters is thought to stabilize the amorphous phase to higher temperatures (>1000°C) and greater thicknesses. The high corrosion resistance properties of the TiC deposits are also attributed to the inclusion of such molecular entities. The processes whereby these molecular entities in the films are transformed into secondary ions during SIMS analysis are also investigated. It is shown that the dominant ionization mechanisms in this case are electron and momentum transfer.     

On the bond breaking model of polyatomic ion emission in secondary ion mass spectrometry

The cluster size distribution (number of clusters versus number of atoms in the cluster) resulting from a simple nearest neighbor Bond Breaking Model (BBM) of Secondary Ion Mass Spectroscopy (SIMS) is studied for one- and two-dimensional and Bethe lattices. In one dimension, the distribution is monotonic. In two dimensions, however, irregularities can occur as a function of the probability β of breaking any given bond. These irregularities differentiate between square, honeycomb, and triangular lattices and are most pronounced if the overall probability of breaking any bond in the lattice is small.     

Diffusion of iron in lithium niobate: a secondary ion mass spectrometry study

Iron-doped X-cut lithium niobate crystals were prepared by means of thermal diffusion from thin film varying in a systematic way the process parameters such as temperature and diffusion duration. Secondary Ion Mass Spectrometry was exploited to characterize the iron in-depth profiles. The evolution of the composition of the Fe thin film in the range between 600°C and 800°C was studied, and the diffusion coefficient at different temperatures in the range between 900°C and 1050°C and the activation energy of the diffusion process were estimated.     

Investigations of near region of surface of soda-lime-silica glass and lithium-silica glass with secondary ion mass spectrometry

Investigations on the layers near the surface of different glasses by means of secondary ion mass spectrometry are described. Both enrichment- and depletion zones can be demonstrated. The results are discussed on the basis of the model on corrosion behaviour by Hench.     

Empirical evaluation of metal deposition for the analysis of organic compounds with static secondary ion mass spectrometry (S-SIMS)

Metal-assisted (MetA) SIMS using the deposition of a thin Au or Ag layer on non-conducting samples prior to analysis has been advocated as a means to improve the secondary ion (S.I.) yields of organic analytes. This study focuses on the influence of time and temperature on the yield enhancement in MetA-SIMS using thick layers of poly(vinylbutyral-co-vinylalcohol-co-vinylacetate) (PVB) containing dihydroxybenzophenone (DHBPh) or a cationic carbocyanine dye (CBC) and spin-coated layers of the cationic dye on Si. Pristine samples as well as Au- and Ag-coated ones were kept between −8 °C and 80 °C and analysed with S-SIMS at intervals of a few days over a period of 1 month. The yield enhancement was found to depend strongly on the kind of evaporated metal, the storage temperature and time between coating and analysis.     

Ion-molecule reactions in the vinyl methyl ether system studied by ion cyclotron resonance mass spectrometry

The main reactions of the molecular ion of vinyl methyl ether with its parent molecule are the formation of the ions C₄H₈O₂⁺, C₅H₈O⁺ and C₃H₇O₂⁺ with relative rate constants of 0.20, 0.10 and 0.70 respectively. These reactions and those in the presence of acetone-d₆ and hexan-2-one clearly distinguish the ion from other C₃H₆O⁺ isomers, and this is supported by observation of the metastable transitions of the ion. Deuterium labelling studies indicate that H/D scrambling occurs only in the formation of the C₄H₈O₂⁺ ion and possible reaction mechanisms are discussed in the light of this.     

Studies of CdTe surfaces with secondary ion mass spectrometry,rutherford backscattering and ellipsometry

The composition and the stability of chemically etched, mechanically polished and oxidized surfaces of single crystals of cadmium-telluride were studied by secondary ion mass spectroscopy (SIMS), Rutherford backscattering (RBS) and ellipsometry. CdTe surfaces etched using a solution of bromine in methanol were found to be enriched in cadmium but a film, identified to be an oxide of tellurium, was observed to grow on it at room temperature and in air. The thickness of this film increased over long periods of timet linearly versus lnt. Mechanically polished samples and also chemically etched surfaces which were oxidized in a solution of hydrogen peroxide in amoniac were found to be stable.     

Photoelectron spectroscopy of nickel on zinc oxide in the monolayer and submonolayer range

Nickel films of thicknesses between 0.05 and 5 monolayers were deposited by evaporation onto the polar ZnO(0001)Zn and ZnO(000$\text{1}$)O surfaces. The character and thickness of the Ni films were determined by Auger electron spectroscopy. The work function, the bending of the substrate bands and the emission from the Ni 3d states were studied by UV photoelectron spectroscopy. After deposition of about 2 monolayers of Ni the O face showed an upward band bending whereas the Zn face showed hardly any at all. After reaching a film thickness of about one monolayer the emission from the Ni 3d states becomes similar to that from the 3d band of bulk Ni. For a film thickness below 0.2 of a monolayer the emission features at ?4.3 eV and ?6.0 eV were attributed to Ni atoms interacting with oxygen from the substrate and the features at ?2.1 and ?1.3 to Ni atoms and two-dimensional Ni clusters.     

Determination of the spatial distribution of trace elements in stainless steel by imaging microprobe secondary ion mass spectrometry

Imaging microprobe secondary ion mass spectrometry (SIMS) using a liquid metal ion source (LMIS) has been used to determine the spatial distribution of metal ions in stainless steel. This scanning ion microprobe is used to achieve high resolution chemical maps of the surface of a sample. For conductive samples such as stainless steel, the practical spatial resolution approaches 0.2 μm and the sensitivity varies with the ion of interest. We have obtained important information relating to the distribution of surface contaminants, segregation, and corrosion phenomena of the elements in these alloys. In this report we hope to demonstrate the usefulness of this important new technique by describing its capabilities and by reviewing data obtained from two separate studies involving stainless steel.

Significant findings obtained in these mapping experiments were:

• . Stainless steel 316 tubing, which had been found previously to be catalytically active, showed remarkable differences between the used and unused samples. Sodium, potassium, and hydrocarbons were found to exist in agglomerations (islands) in the unused tubing, but were very well distributed in the used tubing.

• . A used stainless steel impeller was found to be inhomogeneous with respect to iron and chromium. The surface was entirely covered by chlorine, which is believed to be responsible for the corrosion. Water and elevated levels of chloride ion were found inside numerous scratches or fissures covering the surface. The unused stainless steel showed no signs of streaks or segregated metal regions, and was free from fissures.