Secondary Ion Mass Spectrometry Experiments Research Articles

Sputtering of Molecules From ZnS, CdS, and FeS2

It has been the general consensus in the sputtering community that molecules are sputtered from a clean metal surface in much smaller quantities than atoms. Some of the existing models further suggest that the sputter yield of molecules should be even lower from a compound than from a pure metal when the constituents of the molecule do not reside on neighboring sites in the solid.In our experiments, neutral species sputtered from single crystals of ZnS, CdS, and FeS2by a 3 keV Ar+beam have been observed by laser photo-ionization followed by time-of-flight mass spectrometry. While the atomic metal (Fe, Zn, Cd) and S2were the predominant species observed, substantial amounts of S, FeS, Zn2, ZnS, Cd2, and CdS were also detected. The experimental results demonstrate that molecules represent a larger fraction of the sputtered yield than was previously believed from secondary ion mass spectrometry experiments. In addition, our data suggest that the sputtered molecules are not necessarily formed from adjacent atoms in the solid. The applicability of various sputtering models will be discussed in the light of these results.

Nickel deposition on TiO 2(100): Characterization by AES and SIMS

The first stages in the growth of a nickel deposit on to the (100) face of TiO 2 was investigated using mainly Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS). Auger intensities of both adsorbate (Ni) and substrate (Ti, O) were followed versus deposition time. A layer-by-layer growth of three nickel layers is obtained followed by a nucleation stage. The attenuation coefficients for adsorbate and substrate Auger peaks through a monolayer of adsorbate are calculated. In dynamic SIMS experiments secondary ionic intensities of the deposit and of the substrate were measured during sputtering. By using the sequential layer sputtering (SLS) model for the sputtering process, the morphology of the deposit obtained by AES is confirmed.

Mass and energy dependence of depth resolution in secondary-ion mass spectrometry experiments with iodine, oxygen, and cesium beams on AlGaAs/GaAs multilayer structures

The use of an I+2 and I+ primary ion beam in secondary-ion mass spectrometry measurements was studied to investigate its depth profiling properties. A comparison with the results of a Cs+, O+2, and O+ primary beam was made. Experiments were performed with low impact energy (down to 1.7 keV) and glancing angle of incidence on molecular beam epitaxy AlGaAs-GaAs multilayer structures. The best obtainable decay length of the Al+ signal with an iodine primary beam is 1.1 nm. At low impact energies, no mass dependence on the depth resolution is observed. In these conditions, a useful yield for Al+ of approximately 5×10−5 was obtained with the Cs+ beam and 10−2 with the iodine and oxygen beams.

Hydrogen passivation of shallow acceptors in p-type InP

Undoped GaInAs/zinc-doped InP structures grown by metal-organic chemical vapour deposition have been exposed to a RF hydrogen or deuterium plasma. Secondary ion mass spectrometry experiments show deuterium diffusion in both materials and the existence of a hydrogen-acceptor pairing effect in the p-type InP layer. After hydrogenation, the InP layer becomes highly resistive as a result of a strong passivation of acceptors by hydrogen. Hall effect and conductivity measurements performed on a lightly thermally reactivated InP layer indicate that the hole mobility is significantly higher than in the non-hydrogenated InP layer. This increase is attributed to a decrease of the ionised acceptor concentration under hydrogenation and is consistent with the existence of a pairing between the proton and the ionised acceptor giving rise to neutral Zn-H complexes. The relative thermal stability of Zn-H complexes in InP:Zn if compared to GaAs:Zn can be interpreted with the help of the microscopic model of these complexes, hydrogen being more tightly bonded to a phosphorus than to an arsenic atom.

Design and characteristics of SIPPI, an ion source for a long-distance SIMS analysis of the Phobos surface

The design, construction, and operating characteristics of SIPPI, a 2-mA, 3-keV krypton ion source, are described. This instrument will be part of a remote chemical analysis experiment of the surface of the Martian moon, Phobos. The composition of the surface will be evaluated at a distance of about 50 m by the mass analysis of ions ejected by the primary ion beam delivered by SIPPI. This long distance secondary ion mass spectrometry experiment is called DION and will be part of the Soviet space mission PHOBOS. The flight over Phobos is planned for the beginning of 1989. The ion source is based on a surface-wave-produced plasma from which the ions are extracted by means of a grid system. The ion beam is space-charge neutralized by the electrons emitted by heated tungsten filaments. SIPPI is composed of the ion source itself, its gas feed circuit, the power supplies for the discharge, the extraction system and neutralizing filaments, and the control and telemetry electronics. The dimensions of SIPPI are 45×32×13 cm; its mass is 10.7 kg.

Effects of rapid thermal processing on the formation of uniform tetragonal tungsten disilicide films on Si(100) substrates

Thin films of tungsten silicide with resistivities of 30–35 μΩ cm have been formed by sputter depositing 710 Å of W metal onto (100)–oriented, 3–7 Ω cm, p-type silicon wafers. The samples were fast radiatively processed in a rapid thermal processing (RTP) system under high vacuum for time anneals ranging from 15–20 s at two temperatures (∼1100 and ∼1150 °C). The inevitable oxide barrier at the interface is shown to decrease with increasing RTP time and temperature, evidenced by both Auger electron spectroscopy and secondary ion mass spectrometry experiments. The high film stress produced by thermal considerations does not seem to effect the resulting resistivity and, furthermore, appears to relax at higher temperatures when the film surface becomes ‘‘buckled.’’

Understanding the glycerol surface as it relates to the secondary ion mass spectrometry experiment. A review

A detailed understanding of the physical processes which can occur at the glycerol surface is essential to understanding the secondary ion mass spectra obtained from glycerol solutions. Because of differences in surface activity, the relative contribution of two solutes to the surface composition can differ dramatically with profound effects on the SIMS spectrum. Both first-order and secondary effects of this type are discussed. Also discussed is the preparation of surface active derivatives, the use of surfactants of opposite charge, and the use of surfactants as reagents and complexing agents.

Temperature dependence of electron mobility in GaAs-Ga1-xAlxAs modulation-doped quantum wells.

We report the temperature dependence of the drift mobility in GaAs-${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As modulation-doped quantum wells. A theoretical model is formulated that includes scattering by residual impurities located in the well, in the barrier, and at the ``inverted'' interface, by Si donors and acoustic phonons. Contributions to the total mobility arising from the segregated Si profile and background impurities piled up at the inverted interface are separated by secondary-ion mass spectrometry experiments and measurements of the temperature dependence of the scattering rate. The density of scattering centers trapped at the inverted interface increases with alloy composition x, independently of the ${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Al}}_{\mathrm{x}}$As barrier thickness.

Comparative study on desorption CI and molecular SIMS for aminoglycoside antibiotics containing aminoacyl group.

The direct analysis of underivatized aminoglycoside antibiotics containing an aminoacyl group, butirosins, amikacin, and HAPA-B and its analogues, by desorption chemical ionization (D/CI) and molecular secondary ion mass spectrometry (SIMS) has been demonstrated. The general features and unique characteristics of these two methods are discussed. The [MH]+ ions in D/CI is not as strong as in molecular SIMS, however, the D/CI spectra provide straightforward sequence information. Comparative sequence specific fragments can be obtained in the metastable ion spectra of the [MH]+ produced by SIMS, and thus obtained sequence information often complements that with D/CI method. Combination of D/CI and molecular SIMS experiments has enabled the unequivocal characterization for the structures of aminoglycoside antibiotics containing an aminoacyl group.

Properties of noble metal cluster ions X pn (X = Cu, Ag, Au; n < 20; p = −1, + 1, + 2) investigated by LMIS technique

Mass spectra of X p n cluster ions (with X = Cu, Ag, Au; n < 20; p = − 1, + 1, + 2) obtained in SIMS (secondary ion mass spectrometry) and LMIS (liquid metal ion source) experiments reveal remarkable behaviour. The X − n ions are more intense for odd n (observed in SIMS), the X + n ions are more intense for odd n (observed in SIMS and in LMIS), the X 2 n ions are more intense for even n ( n ⩾ 3, observed in LMIS). In seeded supersonic beams of neutral X n the intensities do not show any alternation. These findings are common to the three metals with small differences in the modulation of the effects. By using a Gutzwiller model (in which dielectronic correlation are taken into account) we calculate the stabilities of these clusters and show that the forementioned effects are due to the variations of this quantity with n: X − n and X + n cluster ions are more stable for odd n, X 2+ n are more stable for even n, X n clusters do not show such an effect.

Properties of noble metal cluster ions X pn (X= Cu, Ag, Au; n < 20; p = -1, +1, +2) investigated by LMIS technique

Abstract Mass spectra of X p n cluster ions (with X = Cu, Ag, Au; n p = − 1, + 1, + 2) obtained in SIMS (secondary ion mass spectrometry) and LMIS (liquid metal ion source) experiments reveal remarkable behaviour. The X − n ions are more intense for odd n (observed in SIMS), the X + n ions are more intense for odd n (observed in SIMS and in LMIS), the X 2 n ions are more intense for even n ( n ⩾ 3, observed in LMIS). In seeded supersonic beams of neutral X n the intensities do not show any alternation. These findings are common to the three metals with small differences in the modulation of the effects. By using a Gutzwiller model (in which dielectronic correlation are taken into account) we calculate the stabilities of these clusters and show that the forementioned effects are due to the variations of this quantity with n : X − n and X + n cluster ions are more stable for odd n , X 2+ n are more stable for even n , X n clusters do not show such an effect.

Vertical channeling of pyridine molecules ejected in ion bombardment experiments

Recent secondary ion mass spectrometry experiments of organic molecules on metal surfaces show that the bonding geometry of the molecule on the surface is reflected in the polar angle distributions. Specifically, the polar distribution of pyridine molecules ejected from a σ-bonded configuration on a Ag{111} is narrower than the polar distribution of benzene molecules ejected from a π-bonded configuration. Classical dynamics calculations presented here identify a new channeling mechanism in which the σ-bonded pyridine molecules on the surface focus the ejection direction of other pyridine molecules.

Energy distribution of secondary organic ions

The energy distribution of secondary organic ions is analyzed in relation to various parameters important for secondary ion mass spectrometry (SIMS) and fast-atom bombardment (FAB) experiments. The difference in the high-energy tails of peaks from organic ions compared with inorganics suggested that a direct knock-on mechanism plays a more important role with inorganics than with organic molecules. Application of the energy analyser as a selector for sample ions in SIMS/FAB experiments and a supressor for a matrix is demonstrated.

Excitation of molecules formed by ion bombardment of surfaces

We report the observation of optical emission from molecular species AB ∗ formed when a solid A is bombarded by energetic heavy ions B +. The vibrational spectra of CN, SiN, and A1N were observed during N 2 + bombardment of C, Si and Al. To confirm our identification of the observed spectra, we performed high resolution secondary ion mass spectrometry experiments. The possibility of formation of these molecules by recombination is examined and we propose a mechanism whereby the emitting species is ejected as an intact molecule in a vibrationally excited state.

Matrix effect and surface oxidation in depth profiling of AlxGa1−xAs by secondary ion mass spectrometry using O+2 primary ions

The dependence of the ionization probability in secondary ion mass spectrometry experiments of the dopants Be, Ge, and Sn and the matrix atoms Ga and As in AlxGa1−xAs with 0≤x≤0.83 on the matrix composition is determined using O+2 primary ions. The composition of the surface is analyzed for the first time by Auger electron spectrometry during O+2 bombardment. The ionization probability shows an approximately linear increase with increasing Al content ranging from a factor of 2.5 (for Ga+) to 7.5 (for Ge+). The variation of the ionization probability is a function of the degree of oxidation which depends on the metal-oxygen bond energy and on the availability of oxygen. The availability of oxygen is controlled by the implantation sputtering process during O+2 bombardment.