Secondary Ion Mass Spectrometry Experiments Research Articles

Chemical structure and bonding characteristics of metal hydrogen systems studied by the surface analytical techniques SIMS and XPS

Secondary ion mass spectrometry (SIMS) as well as photoelectron spectroscopy (XPS) are powerful tools for studying special properties of metal hydrogen systems and the interaction of hydrogen and metals. SIMS experiments have now also been extended to transition metal hydrogen systems with small hydrogen solubilities by using intelligent mass spectra accumulation. As known from studies on other metal hydrogen systems (V–H, Nb–H etc.) the cluster ion Me 2 H + is particularly characteristic for transition metal hydrogen systems. In AB 5 -type alloy hydrogen systems a quite different behavior is observed. We have focussed our attention on studying the properties of the LaNi 5 -alloy with nickel partially substituted by Al or Ag. The mass spectra, especially the negative ones, show a strong Ni–H, a weaker Ag–H and almost no Al–H bond, which explains the decrease in hydrogen storage capacity when going from pure LaNi 5 to LaNi 5− X Ag X and LaNi 5− X Al X . Pressure–concentration like isotherms are obtained for the LaNi 5− X Al X D Y system by SIMS with highest spectral purity when applying a synchronous in situ gasvolumetric hydrogen charging procedure during the SIMS analysis under Ar + ion bombardment. XPS studies on metal hydrogen systems yield valuable information concerning chemical and physical properties, which are complementary to the SIMS results. A hydrogen induced chemical shift and changes in the line shape of the valence band and the core electron levels are observed in LaNi 5 H Y photoelectron spectra if H 2 + ion implantation is used as an alternative hydrogen charging technique. The XPS results indicate the existence of a Ni–H bond in excellent agreement with the SIMS measurements.

Reconstruction of diffusion length distributions in semiconductors by photocurrent measurements with the depletion region modulation

The photocurrent measurements in combination with a modulation of the depletion region is a method which has the potentiality to determine the diffusion length profile in semiconductors directly. In this article the method is applied to strongly compensated (Au-doped) silicon. The expressions for signal description are derived and the situations in which the reconstruction of the diffusion length profile can be obtained are presented. An example of diffusion length profile reconstruction is given for a structure highly compensated by Au and the profile obtained has been compared with that calculated in the frame of the kick-out mechanism with the help of secondary ion mass spectrometry experiments.

Synergism between Cu and Zn sites in Cu/Zn catalysts for methanol synthesis

Three Cu-based catalysts prepared using RF plasma-sputtering (Cu/ZnO and Cu/Al 2O 3) and coprecipitation (Cu/Zn/Al oxide) methods were employed for the investigation of the synergism between Cu and Zn sites. The static secondary ion mass spectrometry (SIMS) experiments indicate that, on both Cu/ZnO/Al 2O 3 and Cu/ZnO catalysts, CO is adsorbed at Cu sites (SIMS peaks appear at 91 and 93 amu), and H is bound to ZnO sites (67, 69, 70, 71 and 81, 83, 84, 85 amu) when the catalyst surfaces are exposed to H 2, CO and CO 2. Methoxy, the intermediate species of methanol synthesis, is found to be bound at Zn sites (95, 97, 98, 99 amu). CO and CO 2 are found to induce Zn migration from sub-layers to the topmost layer while H 2 is heterolyzed easier due to the presence of Cu. The coexistence of ZnO with Cu could enhance the capability of Cu to adsorb CO species and itself to adsorb H 2 species. Al 2O 3 shows no synergetic effect with Cu in this experiment. No CO and H 2 are detected on the Cu/Al 2O 3 catalyst exposed to syngas. The synergetic effect between Cu and Zn in the course of methanol synthesis was discussed.

Secondary ion mass spectrometry characterization of IrO2-Ta2O5 thin films: effect of relative composition on electrode properties

IrO2 and Ta2O5 mixed oxide coatings were deposited on Ti supports in order to fabricate dimensionally stable electrodes used in chloro-alkali technology. Secondary ion mass spectrometry (SIMS) and electrochemical experiments were carried out in order to characterize these materials. Electrochemical tests found the highest electrocatalytic activity for 50% IrO2–50% Ta2O5 electrodes. SIMS analyses are in harmony with these results, and it is shown that IrO2 is more diluted on the surface for noble metal oxide concentrations higher than 50%. Finally, it was observed by SIMS that support material migration was favoured at the highest concentrations of Ta2O5 stabilizer. © 1998 John Wiley & Sons, Ltd.

Total Differential Image Correction

Every imaging technique usually suffers more or less from two inaccuracies: nonhomogenous sensitivity of the recording device over the images area and spatial distortion. This work presents a method that corrects both errors by evaluating the changes of the images due to two small sample position shifts. The algorithm calculates a vector field that is used to determine the “undistorted” position of any point of the image and to determine the apparatus-caused inhomogeneities of the imaged intensities leading to an image that is free from both kinds of imaging errors. In this paper, the theoretical basis of the algorithm, the correction of a test image, and two images obtained from laterally resolved secondary ion mass spectrometry experiments are shown.

Magnetron Sputtered Ti-Basis Hard Material Coatings on Thermoplastic Polymers for Applications in Particle Sensitive Environments

AbstractEven under demanding environments, like clean rooms, polymers are already used in different-ranges of applications. The wear and particle generation within a specific particle size even under-mechanical stress is a limiting factor. So it was the aim to develop an innovative material-concept, that enables to apply a thermoplastic polymer coated with a thin hard material (thickness-up to 2.5 gm), which also prevents for electrostatical discharges and is usable for complex-bodies. Therefore it was necessary to improve the wear resistance and the adherence between the-polymer and the coating. To take also economic aspects into consideration a two step production-process sequence was required, consisting of the injection moulding process and then the plasma-deposition process including a plasma pre-treatment. In this investigation, poly(butyleneterephthalate)-(PBT) and poly(amide) 6.6 (PA) and polycarbonate (PC) were chosen as substrate-material. The coating materials used, which were mainly deposited by Magnetron Sputter Ion-Plating (MSIP), were on titanium basis (Ti-N). To get detailed chemical information about the-coatings and the interfacial region they were analyzed by X-Ray Photoelectron Spectroscopy-(XPS), additionally Secondary Ion Mass Spectrometry (SIMS) experiments were carried out to-confirm the results. The process parameter's influence on the microstructure, which extend from-amorphous to columnar (crystalline), and the film thickness were analyzed by SEM. It will be-shown and discussed, that it is possible to improve the coating's adherence by plasmapretreatment-as well as to reduce the particle generation after a suitable etching and coating process.

C−N Coupling in Reactions between Atomic Nitrogen and Ethylene on Rh(111)

Reactions between adsorbed atomic nitrogen and ethylene on Rh(111) have been investigated by temperature-programmed reaction spectroscopy (TPRS), secondary ion mass spectrometry (SIMS), and work function measurements. Coadsorption of a small amount of ethylene to 0.10 monolayer of atomic nitrogen results in the formation of a surface cyanide species, which is detected by SIMS through the Rh2CN+ cluster ion. Cyanide formation has been followed by measuring the decrease of the atomic nitrogen and carbon coverages and the accompanied increase in the CN coverage in temperature-programmed SIMS experiments. The CN formation kinetics is described by a preexponential factor and an activation energy of 1011±1 s-1 and 111 ± 10 kJ/mol, respectively. In the absence of surface hydrogen, CN groups are stable up to ∼700 K. CN decomposition results in reaction-limited desorption of N2 with a maximum at 800 K and is described by a preexponential factor and an activation energy of 1013±1 s-1 and 210 ± 15 kJ/mol. Coadsorption of large amounts of ethylene to 0.10 monolayer of Nads results in the desorption of almost all nitrogen in the form of HCN between 500 and 700 K. Cyanogen was also observed as a reaction product although the selectivity was small, 3% at maximum. Work function measurements indicate that surface cyanide is present as a negatively charged species on the Rh(111) surface.

Detailed computer simulation of ion implantation processes into crystals

A modified version of the binary collision computer code Marlowe that can deal with low energy implant simulations is presented. In this version the trajectories of the particles are calculated by numerically solving their equations of motion instead of simply using the asymptotes, which is the usual approach. The model has been applied to the simulation of 0·5 keV boron implants into amorphous and crystalline silicon. The agreement with the experimental secondary ion mass spectrometry profiles is better than that obtained using the asymptotic approximation.MST/3302

Novel chemical routes to silicon-germanium-carbon materials

We report the use of novel molecular precursors and ultrahigh vacuum chemical vapor deposition techniques to synthesize solid solutions of cubic SiC-GeC and diamond-structure Si1−x−yGexCy materials. Thin films with composition Si0.37Ge0.13C0.50 were deposited on Si by thermal decomposition of Ge[Si(CH3)3]4 at 650–700 °C. Electron microscope observations showed a polycrystalline zinc-blende-type structure and infrared (IR) analyses revealed carbide-type Si-C and Ge-C vibrations. The Si1−x−yGexCy (y≳2%) alloys were deposited at 550–600 °C on Si and SiO2 by interactions of (1) C(SiH3)4 and GeH4; (2) CH3GeH3 and SiH4; and (3) CH3GeH3 with mixtures of GeH4 and SiH4. A homogeneous alloy phase of composition Si56Ge30C14 with diamond cubic structure was obtained from reaction 1. Reactions 2 and 3 produced films with carbon compositions ranging from 2 to 27 at. %. The materials containing less than 10% carbon appeared to be exclusively diamond cubic, whereas those with greater carbon compositions showed mixtures of diamond cubic and carbide phases as indicated by vibrational and structural characterization. Secondary ion mass spectrometry experiments revealed that all materials had excellent chemical purity.

SIMS/XPS Investigations on Activated Carbon Catalyst Supports

The surface modifications of activated carbon catalyst supports due to HCl treatment were measured in investigations combining X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The surface properties of carbons derived from beech wood, pine wood, and bitumen were qualitatively characterized by analyzing selected positively and negatively charged fragment ions in SIMS experiments. Surface modification and lot-to-lot variations were found with respect to surface oxygen, aliphatic and aromatic/graphitic carbon, and surface C/H ratios. The surface characteristics of the supports correlated partly with properties of catalytic interest such as the valency and dispersion of precious metals which were deposited on these supports. The interaction between the activated carbon surfaces and precious metal compounds is apparently governed not only by the redox behavior of C/O and heterofunctional groups but also by the concentration of surface hydrogen. The surface hydrogen seems to enhance redox processes in the precious metal impregnation step of catalyst preparation. Therefore, surface hydrogen is an important parameter for controlling catalyst properties in catalyst preparation and should be carefully monitored.

Simultaneous detection of secondary ions and photons produced by the impact of keV polyatomic ions

(CsI) n I −( n=0−3), low mass organic negative clusters, and H −, in the 20–46 keV energy range, have been used in time-of-flight secondary ion mass spectrometry (TOF-SIMS) experiments to study the relationships between secondary ion and photon emission from a surface. We report on the simultaneous detection of secondary ions and photons produced by the impact of keV polyatomic ions. Our results indicate that, for a CsI target, secondary ions and photons are produced independently of each other through different mechanisms. Secondary ion emission is strongly dependent upon the complexity of the primary ion, i.e. monoatomic or polyatomic. However, photon emission appears to be independent of the primary ion's complexity and depends primarily upon the velocity of the primary ion. Unlike the secondary ion yields, no yield enhancements for the photons were observed due to polyatomic primary ions. Only broad band light emission from the bulk of the target was observed; no line emissions from sputtered species were detected. We compare the yields of both secondary ions and photons that were collected simultaneously, and present a simple model that describes the observed photon yields as a function of both the electronic and nuclear stopping powers of the primary ion.

Phosphine sensing mechanism in conducting Langmuir-Blodgett films based on tetracyanoquinodimethane and ethylenedithiotetrathiofulvalene derivatives

This paper presents the results of X-ray photoelectron spectroscopy and secondary ion mass spectrometry experiments performed to obtain information about the sensing mechanism involved in the detection of phosphine by conducting Langmuir-Blodgett (LB) films based on TCNQ and EDT-TTF derivatives. In contrast to the EDT-TTF based LB films, it is shown that with the TCNQ derivative the action of phosphine (PH 3) results in the insertion of phosphine subproducts in the LB film. This information is correlated with the general behaviour of each film towards phosphine detection.

A spontaneous desorption-based polyatomic ion source

We describe an ion source based on the spontaneous desorption process. The production, acceleration, and separation processes allow for the production of keV energy polyatomic ions while maintaining a high signal-to-background ratio. Both atomic and polyatomic ions with up to 37 keV energy were generated. Because the spontaneous desorption process is naturally pulsed, the ion source was attached to a dual time-of-flight mass spectrometer for secondary ion mass spectrometry experiments. In this article, we describe the design of both the polyatomic ion source and the mass spectrometer.

Physical properties of semi-insulating polycrystalline silicon. III. Infrared diagnosis of the polycrystalline-Si/c-Si interface

In order to investigate the interface between polycrystalline-silicon (poly-Si) and crystalline silicon (c-Si), which is of crucial importance for the passivation of high-voltage devices, an infrared diagnostic method has been developed which is based on a modified attenuated total reflection configuration. This interface is shown to consist of silicon oxides (mainly SiO2) in the monolayer range with a thickness of 7±2 Å. The interpretation of the experimental results is based on a direct comparison of the infrared reflectivity spectrum of the interface to be studied with that of a reference sample containing a 100-Å thick SiO2 interface layer, as well as on extensive computer calculations. Such calculations have been performed for a three-layer system as well as for a simplified system consisting of a single absorbing layer sandwiched between two transparent half-spaces. The latter system can be solved analytically and provides detailed insight into the physics of the interaction of light with the vibrational excitations of the interface layer. The existence and properties of such a silicon oxide interface layer are compatible with our secondary ion mass spectrometry experiments (oxygen segregation at the interface) and its thickness is in excellent agreement with the thickness of the amorphous interface layer observed by transmission electron microscopy.

Dimerization of polystyrene during static SIMS measurements

AbstractIn this work we report on the results of some static time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) experiments performed on low‐molecular‐weight narrow distribution polystyrene. Evidence of cross‐linking during analysis is found, as indicated by the presence of peaks corresponding to molecules formed by linking of two initial polymer chains. The effect, which can be easily taken into account, does not appreciably affect the molecular weight distribution parameters obtained. However, the observed phenomenon gives the indication that, at least in the case of particularly sensitive systems, ion beam‐induced modification can occur also in static SIMS experiments. In addition, the observed phenomenon can be of relevance in modelling the sputtering of large molecules.

On the secondary ionic emission of polyatomic ions from C 60 samples

We present secondary ion mass spectrometry experiments on a C 60 sample bombarded with a Cs + primary beam. The obtained spectrum exhibits an odd-even alternation of the C − n intensities with even n species favoured. This alternation is not so regular as for graphite samples. We give a qualitative explanation of the difference between the C 60 and the graphite samples by using the Radi results on the photonic fragmentation of C + n clusters in the gas phase and also by taking into account the electron-affinities of C n clusters which, in the n ≲ 10 range, are larger for even n. We then introduce a theoretical model allowing the calculation of C n , C + n and C − n properties ( n ≲ 60). Preliminary results on the cohesive energy, the electron-affinity and the ionization potential of C 3 and C 60 are given.

Fluoride and Mineral Content in Hyper-Remineralized Coronal Bovine Dentine in vitro after an Acid Challenge

In this paper the acid resistance of hyper-remineralized dentine was quantified by means of fluoride and mineral measurements. Hyper-remineralization was achieved by demineralization of dentine in an acidic gel system (pH 5) for 3 weeks, followed by remineralization in a solution containing 1.5 mM Ca, 0.9 mM phosphate and 10 ppm F at pH 7 and 37 degrees C for 8 days. The samples were subsequently again demineralized in the gel system mentioned for 1, 2 and 3 weeks. Analysis for fluoride was done by means of the microdrill biopsy technique and to obtain information on the fluoride distribution by secondary ion mass spectrometry (SIMS); mineral was assessed by microradiography. The results showed that in hyper-remineralized dentine the original fluoride content was approximately 30,000 ppm F. This value was still in the same order after the acid challenge of 3 weeks at pH 5. These values were substantially higher than the baseline values in sound or in demineralized dentine being about 900 ppm F. The main microradiographic result was that there was no significant mineral change in the hyper-remineralized dentine due to the acid challenges. There was, however, a tendency for mineral redistribution deeper into the dentine lesion leading to lamination phenomena. The SIMS experiments on some of the samples showed a fluoride distribution in agreement with the microdrill fluoride data. Furthermore a fluoride redistribution took place in deeper parts of the lesion due to the acid challenges. The combined fluoride concentration and microradiographical data indicate that fluoride-enriched and highly mineralized hyper-remineralized dentine is more acid resistant than sound or demineralized dentine.

Defect-induced redistribution of Fe- or Ti-implanted and annealed GaAs, InAs, GaP, and InP

The structural properties of GaAs, InAs, GaP, and InP implanted by Fe or Ti at 150 keV/400 keV and doses of 1012–1×1015 cm−2 and the depth distribution of the implants are comparatively studied before and after annealing with and without a Si3N4 cap. Results of Rutherford backscattering, x-ray double-crystal diffractometry, and secondary-ion mass spectroscopy experiments are presented. Fe redistributes strongly in all materials upon annealing, Ti does not redistribute at all. The driving force of redistribution of Fe is not classical diffusion but reaction with implantation-induced defects and stoichiometric imbalances. The actual defect chemistry of the as-implanted arsenides is found to be fundamentally different from the as-implanted phosphides since in the latter case the mass ratio of the constituents is much larger and the specific energy for amorphization is much lower. Consequently, redistribution of Fe in the phosphides and the arsenides differs qualitatively from each other.

Lateral and in-depth junction delineation of buried Sb-doped layers following silicidation

The demarcation of Sb‐doped Si buried layer structures has been investigated following silicidation‐enhanced diffusion. After Co and Ti silicidation at 700 and 800 °C, respectively, two‐dimensional perspectives of the two buried n/p junction interfaces have been obtained by optical microscopy of bevel‐polished and etched (or stained) cross sections. Greatly enhanced and asymmetric diffusion of Sb buried layers is observed under silicided regions, as well as at large distances from the edges of silicided stripes. Excellent correlation of micrographs with one‐dimensional experimental secondary ion mass spectrometry profiles was obtained. Metrology and shallow junction processing/characterization issues are discussed.

Lunar surface composition and solar wind‐Induced secondary ion mass spectrometry

The Moon has no strong global magnetic field and only a tenuous atmosphere, so solar wind ions (∼95% H+, 5% He++) directly bombard the lunar surface, sputtering atoms and secondary ions from the exposed grains of the regolith. The secondary ions potentially provide surface composition information through secondary ion mass spectrometry (SIMS), a standard laboratory surface composition analysis technique. In this paper we report the results of laboratory SIMS experiments on lunar soil simulants using solar wind‐like ions. We find that H+ and He++, while not efficient sputterers, nevertheless produce significant fluxes of secondary lunar ions, including Na+, Mg+, Al+, Si+, K+, Ca+, Ti+, Mn+ and Fe+. We predict that lunar surface secondary‐ion fluxes range between ∼10 and 104 ions cm−2 s−1, depending on the species.