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Über dieses Buch

Following the biannual meetings in MUnster (1977) and Stanford (1979) the Third International Conference on Secondary Ion Mass Spectroscopy was held in Budapest from August 31 to September 5, 1981. The Conference was attended by about 250 participants. The success of the 1981 Conference in Budapest was especially due to the excellent preparation and organization by the Local Organizing Committee. We would also like to acknowledge the generous hospitality and cooperation of the Hungarian Academy of Sciences. Japan was chosen to be the location for the next conference in 1983. SIMS conferences are devoted to two main issues: improving the application of SIMS in different and especially new fields, and understanding the ion formation process. Needless to say, there is a very strong interaction be­ tween these two issues. The major reason for the rapid increase in SIMS activities in the last few years is the fact that SIMS is a powerful tool for bulk, thin-film, and surface analysis. Today it is extensively and successfully applied in such different fields as depth profiling and imaging of semiconductor devices, in isotope analysis of minerals, in imaging biological tissues, in the study of catalysts and catalytic reactions, in oxide-layer analysis on metals in drug detection, and in the analysis of body fluids.

Inhaltsverzeichnis

Frontmatter

Instrumentation

Frontmatter

Instrumental Aspects of Spatially 3-Dimensional SIMS Analysis

It has become clear from detailed ion optical analyses [1,2,3] that matching analyzer acceptance with secondary ion beam emittance is essential to obtain high transmission at given mass resolution, independent of the particular imaging principle used (scanning probe, microscope, image dissecting ion probe). Close-to-optimum matching can be obtained using a “transfer optic” system (consisting of an immersion lens immediately at the target and one or more image transfer lenses between immersion lens and mass spectrometer) as described by SLODZIAN [1,4]. Future scanning probes and microscopes therefore will have to incorporate such a system, taylored to the particular mode of analysis and primary beam illustration. When comparing in particular the ion microscope and the scanning ion microprobe mode of operation for their relative merits, it is only fair to assume the same type of double focusing spectrometer for both systems. We consider an instrument which is partially corrected for second-order aberrations [5], the most important remaining aberrations being second-order chromatic aberration and third-order aperture aberration. Without taking into account detailed ion optical properties of particular instrument designs, LIEBL [6] gives an estimate for the maximum tolerated divergence angle and the slit width s′ for such an instrument in dependence on the required mass resolution R (= M/ΔM) $$\begin{array}{*{20}{c}} {{}^{a}x = {{{(40R)}}^{{ - {{1} \left/ {3} \right.}}}}} \\ {s' = L/20R} \\ {L = 8{{r}_{m}}} \\ \end{array}$$where L is the total ion path length and rm the magnetic deflection radius. Owing to the second-order chromatic aberration coefficient Aδδ, the maximum allowed initial energy ΔΦch of the secondary ions is determined by $$\Delta {{\Phi }_{ch}}=0.45V{{(R.{{A}_{\delta \delta }})}^{-1/2}}$$ where V is the final energy of the secondary ions and it has been assumed that the chromatic aberration contribution to the width of the slit image, rmAδδ(Φ/V)2, is about half the slit width s′.

F. G. Rüdenauer

Some Problems of Construction Implied by Requirements of Up-To-Date SIMS Instrumentation

Recent advances in various instrument components and methods for SIMS bring us to the threshold of rapid growth in the application of SIMS. In spite of the present difficulties in quantitative analysis, the extreme sensitivity and promise of sub-micron imaging capability foreshadow its rapid growth in surface and thin film analyses. Here we will examine some of these new methods and components and predict the potential that might be realized in a few years for quadrupole microbeam SIMS instrumentation.

R. L. Gerlach

Description and Applications fo a New Design Cs+ Ion Source on the COALA Ion Microprobe for Negative Ion SIMS

In any mass spectrometric system, one of the key instrumentation components is the ion source, or stated similarly, the method of ionization. Apart from influencing the level at which the sought-for constituents can be quantitatively ionized, the ionization process should also preserve the native chemical integrity of the sample, that is, without inducing decomposition, compound formation, or falsifying sample structure. In the SIMS method, the practicing spectroscopist can often select a primary ion projectile species which affords advantages when sputtering into certain materials or when profiling specific elements. For example, negative primary ions can reduce the accumulation of electrostatic charge on the surface of poor-conducting samples [1]; molecular ions were used in one study to obtain information relative to damage density effects in the collision cascade [2]; and bombardment by 0 and Cs promotes ion yield enhancements for positive secondary ions [3] and negative secondary ions [4], respectively. The latter aspect — Cs bombardment SIMS — is of active interest in several research groups [5–7], including this laboratory [8]. We have recently designed and brought into operation a compact, microbeam Cs+ source for SIMS [9]. This brief report is intended to describe the source, and present first results of its coupling to a scanning ion microprobe mass analyzer developed at IPP.

B. L. Bentz, H. Liebl

Operational Data of a Simple Microfocus Gun Using an EHD-Type Indium Ion Source

When a liquid conductor (metal) is exposed to a high electrostatic field the liquid surface, under the action of surface tension and electrostatic polarization force, assumes an equilibrium shape, viz. a cone with a total apex angle of 98.6° (“Taylor cone” [1,2]). When the metal is positively polarized with respect to its surroundings, intense positive ion emission from the cone apex is observed [3,4]. The mechanism of ion emission is not yet fully understood; according to GOMER [5], ion emission appears to be initiated by field desorption from the liquid apex and, at higher emission currents, changes over to field ionization of thermally evaporated atoms in front of the cone apex. We can identify several critical parameters for ion emission: the “cone forming voltage” ΔV is to be applied between liquid metal and extractor electrode before a Taylor cone can develop; if both the microscopic cone apex and the extractor are assumed to be of ideal shape (according to the “sphere-on-cone”, SOC-model) ΔV is given by [5] V$$\Delta {{V}_{threshold}}=4.53\cdot {{10}^{5}}{{({{\gamma }_{0}})}^{1/2}}$$ where γ is the surface tension of the metal (N/m) and Ro the apex-extractor distance (m). The electrostatic field at the microscopic cone apex has to exceed the valueV/m$${{F}_{vap}}=6.96\cdot {{10}^{8}}{{\left( {{E}_{vap}}+{{E}_{i}}-\Phi -0.63 \right)}^{2}}$$ before ions can be field desorbed [3]; here Evap is the evaporation voltage of a metal atom, Ei the ionization voltage and Φ the voltage of the work function of the metal, all given in volt. Once ion emission is initiated, the emission current I+ seems to be space charge limited and follows a characteristic voltage dependence [3], $${{I}^{+}}=K\centerdot {{\left( \Delta V/\Delta {{V}_{threshold}} \right)}^{3/2}}-1for\Delta V\ge \Delta {{V}_{threshold}}$$ where ΔV is the tip/extractor voltage difference and k a constant, somewhat depending on geometry.

M. J. Higatsberger, P. Pollinger, H. Studnicka, F. G. Rüdenauer

First Results on a Scanning Ion Microprobe Equipped with an EHD-Type Indium Primary Ion Source

Electrohydrodynamic ion sources have recently received increased attention in secondary ion mass spectrometry, owing to their potential of producing extremely small primary ion beams at relatively high focused ion currents. KROHN and RINGO were the first to suggest the use of such a source as primary ion gun in an ion microprobe [1,2,3] and have reported on ion gun tests using Ga+ and Cs+ ions [4]. The only paper so far actually describing experiments with an EHD source coupled to a secondary ion mass spectrometer was published by PREWETT and JEFFERIES [5]; these authors obtained 0.5 µm diameter primary beams of Ga+ at currents of 0.2 nA and were able to record secondary electron and mass separated secondary ion distribution maps from microelectronic circuits. LIEBL [6] has shown that spot currents (at spot sizes below 1 µm) are limited by chromatic aberration and calculated a limiting focusable current of 1.6.10−10 A at a spot size of 200 Å (ca. 50 A/cm2). Values approaching these theoretical limits have actually been obtained with a Ga+ ion gun designed for applications in ion lithography [7,8].

F. G. Rüdenauer, P. Pollinger, H. Studnicka, H. Gnaser, W. Steiger, M. J. Higatsberger

Simple Double-Channel SIMS Instrument

Secondary ion mass spectrometers serve currently as rather efficient tools for elemental and isotopic analysis of thin films, diffusion layers and other solids complex in composition and structure. Using a mass analyzer of the monopole type we have designed a compact double-channel secondary ion mass spectrometer. The objective was to produce simple, economical and technologically feasible ion optics with enhanced reliability of power supplies.

V. T. Cherepin, I. N. Dubinsky, Ya. Ya. Dyad’kin

Principles and Applications of a Dual Primary Ion Source and Mass Filter for an Ion Microanalyser

It is useful in some cases to filter the primary ion beam particularly when impurities are present in the primary beam. The primary ion beam from the duoplasmatron usually contains traces of non-desired ion species which may come from the feed gas or from the degassing of the source. In order to purify the primary ion beam from a duoplasmatron source, a magnetic mass filter has been designed for the CAMECA IMS 3F ion micro-analyser [1]. The features are: A symetrical magnetic mass filter which can mount two different ion sources.The ability to change rapidly between the duoplasmatron and cesium ion source which allows analysis of electropositive or electronegative elements in the same area.

J. J. Le Goux, H. N. Migeon

A Quadrupole Mass Spectrometer with Energy Filtering for SIMS Studies

In the last few years, the quadrupole mass filter has been widely used as mass analyser in secondary ion mass spectrometry. An energy pre-filter is generally added to reduce the background intensity and to reject the higher energy ions which degrade the mass resolution. As a very high energy resolution is not useful for such studies, the retarding-accelerating energy analyser [1,2] is very interesting because of its large angular acceptance, and is now effectively used in some modern apparatus [3,4] in spite of a rather poor knowledge of the energy transmission properties of such spectrometers.

R.-L. Inglebert, J.-F. Hennequin

Development and Operation of Special SIMS-Equipment for Use in Iron and Steel Analysis

Analysis of steel surfaces andin-depth profiling of the layer structure of different materials by SIMS often implies some compromises with the commercial instruments available today Ion microprobes with high sputtering rates and ion microscopes with similar possibilities are very successful in describing the distribution of phases and elements in micro-range, but they have no representative analysis area, most needed for technical information on products. Ion-scanning instruments with a larger area of analysis are often restricted by these conditions in fast sputtering in-depth.

J. Dittmann

Design Concept of a New Secondary Ion Optics System for Use with Quadrupole Mass Spectrometers

Most commercially available SIMS optics systems for use with quadrupole mass spectrometers suffer from the problems caused by mixing the parameters governing secondary ion emission with those related to the ion injection into the mass filter. In this paper, we propose a system which overcomes these difficulties. They have been partly solved by a previous design used for a dedicated SIMS instrument, which therefore has been a guideline for the present work. Because of the intended use in combination with XPS, this instrument is required to have a very large lateral acceptance of 10 mm diameter. In experiments where static conditions must be applied, this large acceptance allows reduced current density at a given sensitivity. On the other hand, in depth profiling the detection limits are improved at a given erosion Late. Additional requirements to be met have been energy filtering and reduction of the quadrupole mass discriminating effects. k detailed discussion of this system and its performance will be published elsewhere.

R. Jede, O. Ganschow, A. Benninghoven

Improved Analysis of Insulators in an ARL IMMA Using Positive Primary Ions and an Electron Gun

When analyzing insulating specimens by secondary ion mass spectrometry (SIMS) using positive primary ions as the bombarding species, a surface potential develops which partially or completely inhibits the extraction of ions into the secondary mass spectrometer. The result is that depth profiles, if measured intensities are observed at all, can be severely distorted, particularly when changes in composition lead to changes in conductivity of the specimen. Therefore surface charging limits the reliability of SIMS in analyzing insulators.

J. D. Brown, D. J. Gras

Performance and Use of Dissector Ion Microanalyzer

The solution of the problem of local in-depth analysis of solids using secondary ion emission encounters difficulties related to effects produced by the walls of the crater resulting from ion etching. One of the ways to overcome these difficulties might be the formation of an intermediate ion image of the surface of the sample under study with subsequent separation of the image element of the required locality and its analysis with the aid of a mass filter. This simultaneously decreases the effect of non-uniform distribution of current density of the primary beam. Just this way was chosen in the laboratory of the Institute of Metal Physics, Acad. Sci. UkrSSR to design a dissector ion microanalyzer for the in-depth local analysis of the isotopic composition of solids and for the determination of impurity concentration profiles through the depth of the sputtered layer.

V. T. Cherepin, V. L. Ol’khovsky

Distortion of Secondary Ion Extraction Due to Sample Surface Irregularities

Hitherto numerous publications concerning the analytical application of Secondary Ion Mass Spectroscopy (SIMS) have appeared. In contrast, a rather limited number of investigations dealing with the influence of instumental effects on quantitative analysis have been published till now. One of these is the interpretation of the results of the comparative SIMS study of selected glasses NEWBURY showed that the relative sensitivity factors for the same element obtained by 22 different laboratories vary over more than one order of magnitude. Under the assumption that well characterized standards had been distributed to all cooperating laboratories the main reasons for deviations of such an extent must be supposed in different primary ion (PI) beam parameters and instrumental conditions incomparable to each other. Solely standardized conditions for creation, extraction, analysis, and detection of the secondary ions (SI) and mathematical compensation of every discriminating effect will lead to data that can be handled successfully by quantitative models.

W. Bedrich, B. Koch, H. Mai, U. Seidenkranz, H. Syhre, R. Voigtmann

A Comined Direct Imaging Laser Ionization Secondary Ionization Mass Spectrometer

The advances in materials used for a wide variety of technologies place great demands on the characterization techniques developed for a study of these materials. At the present time, there exist only two techniques capable of the microanalysis of semiconductor and metallurgical and related materials. These are the well-known high performance secondary ion mass spectrometer or ion microanalyzer and the recently developed laser ionization microprobe mass spectrometer. The first technique, SIMS, is the topic of this conference and no more details are required except to say that, for the applications of this report, we used an instrument which employed direct imaging of the ion emission from the sample surface through stigmatic optics as exemplified by the Cameca IMS-3f ion microanalyzer [1]. In this instrument, images are formed not by the rastering of a finely focussed primary ion beam, but by optics which allows the transfer of an image of the emission areas from the sample surface through the entire mass spectrometry optics for detection. The images are detected by projecting this ion image onto a channel plate wherein the ions are converted into electrons, multiplied by impacting a fluorescent screen for visual observation and recording by photographic and video methods.

B. K. Furman, C. A. Evans

Advances in Ion Probes A-DIDA

The basic concept of the ION PROBES A-DIDA was set up 10 years ago. While the basic concept proved to be highly successful, a number of advances in the A-DIDA design features could be introduced since the SIMS II conference, which considerably improved the analytical capability of the ION PROBES A-DIDA. The basic concept of the ION PROBES A-DIDA has already been described elsewhere [1,2]. Different to the horizontal configuration of the A-DIDA 2000 the new IONMICROPROBE A-DIDA 3000–30 is a vertical configuration, as commonly used in SEM design, with the primary ion beam coming from the top. The samples are mounted horizontally which allows running powder samples.

H. Frenzel, J. L. Maul

A Novel Ion Etching Unit Applicable for Depth Profiling with SIMS and IIR

During the past years, ion etching became a common means for removing surface layers from solid samples, for cleaning sample surfaces in UHV experiments, for depth profiling of multilayer structures, and for thinning specimens down to electron transparent thickness for investigations in transmission electron microscopy (TEM). Particularly in the case of the latter application, Balzers’ Ion Etching Unit IEU 100 has been developed as a compact easy-to-operate laboratory equipment, which also enables the possibility of attaching analytical equipment.

K. H. Guenther, E. Hauser, G. Hobi, P. G. Wierer, E. Brandstaetter

Improvements and Applications of the Riber MIQ 156

The techniques of in depth profile analysis have been improved considerably during the last few years. These methods include secondary ion mass spectrometry (SIMS) and surface analysis techniques combined with sputtering such as Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA) etc. We have put the emphasis on our equipment combining the three analytical methods mentioned above (LAS 3000): because comparison of the techniques indicates that, although unique in regard to certain applications, they all suffer from limitation regarding their general applicability in surface layer analysis. However a new ion gun has been designed [1] for the SIMS equipment because new needs have appeared, among these are a shorter time of analysis, a higher sensibility and an improvement in the dynamic range in depth profile.

F. Simondet, D. Kubicki

Fundamentals I. Ion Formation

Frontmatter

Molecule Formation in Oxide Sputtering

The understanding of the formation process of sputtered oxide molecules, in particular of MeO (Me: metal), is important for a number of reasons, such as an increased insight in surface processes induced by ion bombardment,oxidation studies at solid surfaces by mass spectrometric methods like SIMS or SNMS (Sputtered Neutral Mass Spectrometry [1]),the enhancement of secondary ion yields by oxygen exposure or bombardmentthe great fraction of MeO in the flux of oxide specific sputtered particles consisting mainly of neutrals also for oxides.

H. Oechsner

Dependence of Ionization Yields Upon Elemental Composition; Isotopic Variations

Owing to its great sensitivity secondary ion mass spectrometry is generally considered as a powerful technique for analyzing surfaces or microvolumes of solid samples despite many kinds of problems that remain to be solved. Among them, the ionization phenomena are directly responsible for the difficulties encountered in quantitative analysis. The subject will be restricted essentially to metallic alloys flooded with oxygen and silicate minerals bombarded with oxygen primary ions. In such experimental conditions, the elemental composition of the target controls the ionization yields which in turn prevents quantitative elemental analysis to be performed in a simple way. Moreover, it could very well be that the processes inducing the dependence of the ionization yields upon elemental composition affect isotopic abundance measurements as well.

G. Slodzian

Measurements of the Energy Distributions of Positive Secondary Ions in the Energy Range from 0 to About 500 eV

In this paper energy distributions of singly charged ions of Bi, Sb, W, Th, Cu, Zn and Cd as well as ions of some of their oxides emitted from the pure elements are presented. The purity of the target materials was ranged from 99 % (W, Th) to 99.999 % (other elements) ; all the materials had a polycrystalline structure and were mechanically polished.

C. Pahlke, H. Düsterhöft, U. Müller-Jahreis

Ion Dose Effects in Static SIMS

Ion bombardment of a solid surface may lead to significant changes of the surface, i.e. a change of the chemical or structural nature due to sputtering effects. Therefore static secondary ion mass spectroscopy has been developed in order to avoid damage of the topmost layers during measurement. Static SIMS means working with mean lifetimes of one monolayer of the order of 104 s [1]. Nevertheless, we want to show in this paper that we find dramatic changes in the SI spectrum although the conditions for static SIMS are fulfilled.

W. Speckmann, S. Prigge, E. Bauer

Current Density Effects on Secondary Ion Emission from Multicomponent Targets

The use of the Secondary Ion Mass Spectroscopy for determining in-depth distribution of selected elements requires sufficiently high erosion rates [1]. On the other hand when applying this technique to study surface phenomena, sputter etching has to be minimized in order to keep the investigated area relatively undisturbed [2]. The rate at which succesive layers sputter off the material is proportional to the current density (or flux) of the incoming particles, whereas the secondary ion current, in principle, is proportional to the primary current solely. It appears, however, that the magnitude of the applied beam density can influence strongly the quantitative interpretation of the SIMS analysis. Possible effects are: (i) Temperature rise under the impact of energetic high-flux beam. Usually, in commercially available devices the power dissipated in the near-surface region is not high enough to cause appreciable macro-thermal effects. (ii) Mutual interaction of the primary and the sputtered particles above the bombarded surface leads to modifications of the ionization efficiency of the latter [3]. (iii) Ion-induced desorption is the most pronounced phenomenon directly related to the primary flux. It is well known that the presence of reactive gases on the surface can drastically intensify the ion emission [4]. In the dynamic mode, oxygen coming either from the vacuum system or intentionally introduced in the vicinitiy of the target is continuously removed by impingent ions; the resulting coverage is determined by equilibrium between the gas pressure and the primary beam density.

A. Barcz, M. Domanski, B. Wojtowicz-Natanson

Isotope Effect in Secondary Ion Emission

Isotope abundance determination on small areas of standard polished sections appears to be one of the most interesting potentialities of secondary ion mass spectrometry. Key samples for the detection in natural samples of isotope effects of nuclear or radiogenic origin are indeed often rare phases of small dimensions. Secondary ion mass spectrometry offers the unique possibility of performing isotope ratio measurements on these phases with limited chemical contamination, and with the added advantage of allowing direct correlation of isotope data with chemical data (in particular on trace elements) and with mineralogical and textural features.

J. C. Lorin, A. Havette, G. Slodzian

Caesiated Surfaces and Negative Ion Emission

The strong enhancement of the negative ion emission produced by caesium atoms is used now during analyses by secondary ion mass spectrometry more and more frequently. In most experiments, the caesium coverage results from the implantation into the target of the caesium positive ions that are producing the sputtering of the target itself [1,2,3]. After removal of a given thickness of the sample, an equilibrium is reached where the concentration of the implanted elements is controlled by the target sputtering yield. But, it is likely that the caesium concentration obtained that way is generally not sufficient to reach the saturation of the emission process. Another procedure consists of a chemisorption of neutral caesium atoms while the sample is simultaneously bombarded by a noble gas ion beam; thus the surface coverage can be adjusted by controlling the densities of either the primary ion beam or the neutral caesium jet [4,5].

M. Bernheim, G. Slodzian

Secondary Ion Mass Spectrometry of Organic Compounds; A Comparison with Other Methods (EI, CI, FI, FD, FAB)

In recent years secondary ion mass spectrometry (SIMS) has attained an increasing importance for the detection of organic compounds deposited on solid surfaces. In the static SIMS-method very low primary ion current densities are used in order to minimize the extent of fragmentation of the organic compounds deposited on metallic surfaces [1,2]. However, relatively fragment-free mass spectra of organic compounds have been also obtained applying high primary ion current densities [3,4]. A definite advantage of these secondary ionization (SI) techniques over more conventional ionization methods, like electron impact (EI), chemical ionization (CI), and field ionization (FI) lies in the fact that evaporation of the organic sample prior to analysis is not necessary. In this respect SI resembles the field desorption technique (FD) and many thus be preferentially applicable to the structure elucidation of organic salts and other labile, non—volatile compounds. Fragmentation patterns and ion intensities obtained by SI are, however, more readily controlled by varying parameters, such as current density, energy, and kind of primary ions, as well as nature and pretreatment of the target material. It has been shown that intensive cationic molecular ions are obtained by adding alkali halides to the organic target material [2,5].

K. D. Klöppel

Secondary Ion Emission from NbV-Alloys

In an attempt to establish quantitative analyses of solids by secondary ion mass spectrometry (SIMS), a series of samples in the niobium-vanadium binary alloy system was studied. Ejection of cluster particles, both electrically charged and neutrals, was recently reported to confirm closely to the stoichiometry of the targets [1]. In an extension of this and related work [2,3,4] the behaviour of monoatomic particles as well as the influence of surface morphology was investigated here.

J. Schou, G. Flentje, W. O. Hofer, U. Linke

Fundamentals II. Depth Profiling

Frontmatter

Depth Profiling by SIMS: Depth Resolution, Dynamic Range and Sensitivity

Secondary ion mass spectrometry (SIMS) utilizes a beam of energetic primary ions to sputter away a solid [1] surface producing ionized sputtered particles which can be mass spectrometrically detected. This technique provides in-depth information on atomic constituents by recording one or more mass peaks as the sputtering process erodes the sample, thus producing the detected signal from increasingly greater depths beneath the original sample surface. This depth profiling technique has become one of the most important uses of SIMS, but the accuracy with which the data reflect the original atomic profile within the sample depends on many parameters. Several critical reviews on depth profiling exist in the Ref. [2,3,36] which broadly cover most aspects of this mode of analysis. The present work is limited to three major aspects: 1) depth resolution, 2) dynamic range, and 3) sensitivity. The relationships between these areas will be discussed, as well as how they influence the accuracy of the final profile.

C. W. Magee, R. E. Honig, C. A. Evans

Disturbing Effects in Sputter Profiling

Sputtering by ion bombardment in combination with a suitable analysis technique is a universally applicable method to obtain the distribution of the elemental composition of a sample versus its distance perpendicular to the original surface. Although sputter depth profiling has found widespread application and numerous review articles on this subject have already appeared (e.g. [1–5,64,65]), we have not yet achieved a full understanding of the various distortions induced during profiling which impede a direct correlation between the measured profile and the original, true profile present in the sample prior to the analysis.

S. Hofmann

The Theory of Concentration Depth Profiling by Sputter Etching

Concentration depth profiling by controlled erosion of surface layers by sputtering is generally hampered by distorting effects due to recoil mixing and radiation enhanced migration. Emphasis is placed here on recoil mixing where we distinguish between two different collisional relocation processes: primary recoil mixing, on the one hand, and cascade recoil mixing on the other. In spite of the higher average energy/range of primary recoils, cascade recoils are the dominating cause for recoil mixing; this is by virtue of their much higher number [1].

W. O. Hofer, U. Littmark

Surface Topography Development During SIMS Investigations and Using it to Get Additional Information on Polycrystalline and Heterogeneous Solids

SIMS investigations are often confronted with problems of surface topography development resulting from the selective sputter-etch process in the bombarded region. Mainly the dynamical SIMS with emission or scanning ion microscopy of the sample surface has to consider contrast effects in the pictures, which are not only caused by concentration or orientation differences but also by topographic effects. However, also in macro-SIMS systems the sputtering process is accompanied by relief formation influencing the analysis, but, on the other hand, being also useful for subsequent scanning electron microscopical (SEM) investigations. The extended group of heterogeneous polycrystalline samples which are initially smooth and cleaned show characteristic ion-etch structures at phase and grain boundaries (Figs 1 and 2). Its knowledge is necessary to separate the topographic contrast from other influences and is favourable for getting information on the grain structure of the sample. Micro-scale features of the relief as facets are neglected here but can also influence the ion emission characteristics [4].

W. Hauffe

Sputtering of Metals with 20 keV O2 +; Characteristic Etch Patterns, Sputtered Atom Yields and Secondary Ion Mass Spectra

In secondary ion mass spectrometry an oxygen primary beam is frequently used because it enhances and stabilizes the yield of secondary sample ions [1,2]. But its role in the process of secondary ion emission is not yet fully understood [3–6].The purpose of the present paper is to investigate the surface structure, sputtered atom yields and secondary ion mass spectra of metals bombarded with O2+. Accumulation of these fundamental data will help to elucidate the effect of oxygen ion on sputtering and to establish the method of quantitative interpretation of mass spectra.

K. Tsunoyama, T. Suzuki, Y. Ohashi, M. Konishi

Depth Resolution of Ion Bombardment Technique Applied to NiPd, NiPt, PtPd, Thin Layer Systems

A lot of studies have been published already about the important questions in depth profiling: how the ion bombardment process itself can influence the accuracy of the measured depth profile, what depth resolution can be reached in an optical case, which parameters play a significant role in the profile measurement and how to get the real concentration profile from the measured one [1–4]. As the accuracy and reliability of SIMS measurements have to be subjects of both theoretical and experimental studies, one must examine depth profiles with respect to: a.)different layer producing techniquesb.)material, andc.)sputtering rate dependence.

J. Giber, D. Marton, J. László, J. Mizsei

The Influence of Ion Bombardment on the Results of AES-Depth Profiling on Silicides

The determination of quantitative concentration ratios of silicides with AES-depth profiling leads to results which are influenced by a strong sputter effect. We have investigated aspects of this problem by experiments on silicide-silicon systems. During sputtering two essential effects appear simultaneously, namely preferential sputtering and the knock-on effect [1,2]. In the literature preferential sputtering is regarded as the main effect [1,3–7]. However the knock-on effect can also influence concentration ratios [1,8,9]. I am reporting about investigations on the knock-on effect.

Th. Wirth

A Study of Secondary Ion Energy Distributions During Sputtering of MIS Layer Structures

For several years we investigated the secondary ion mass spectra during the sputtering of MIS structures. It is known that these systems contain thin layers of metals, dielectrics and semiconductors, their properties (especially the structure) being strongly dependent on the growth conditions and subsequent treatment. There may be polycrystalline substances with the grain of various dimensions and monocrystalline ones. Such materials as SiO2 have a large number of modifications. In this work along with the results on the energy distribution of the secondary ions from the semiconductors and dielectrics also a qualitative model is presented of “the ensemble of cascades”, which makes it possible to explain non-contradictorily all the results obtained.

G. Ph. Romanova, P. I. Didenko, A. A. Yefremov, V. G. Litovchenko, R. I. Marchenko

Structural Effects in SIMS at the Depth Profiling of Boron Implanted Silicon

Secondary ion mass spectrometry is currently widely used to study the in-depth distribution of alloying additions in thin films and, in particular, for the in-depth profiling of implanted atoms in semiconducting materials.

V. T. Cherepin, A. K. Kosyachkov, A. D. Krasyuk, M. A. Vasiliev

Comparison of Compositional Thin Film Depth Profiling Obtained by SIMS, IIR and AES

Ion etching used in connection with surface-sensitive analytical techniques is a common method of determining the chemical composition of thin films and substrates. The method of surface analysis employed depends on the aims of the investigations and the information required. In this paper the advantages and limitations of AES, SIMS and IIR for the analysis of dielectric materials will be discussed. Each of the three analytical methods has been employed for parallel compositional investigations in a broad-band antireflection coating as well as in a dichroic beamsplitter.

E. Hauser, G. Hobi, K. H. Guenther, E. Brandstaetter

Quantification

Frontmatter

Quantifications of SIMS

The title of this paper refers to the quantification of SIMS or secondary ion mass spectrometry. More specifically we will be discussing the ion microprobe, a form of SIMS. The ion microprobe is presently one of the most sensitive methods for the in-situ characterization of elemental distributions in samples of limited dimensionality, often with detection limits in the parts per million range. The capabilities of lateral elemental imaging for defining microfeatures of interest(1 µm spatial resolution), and of elemental depth profiling with resolution of less than 100 Å make the ion microprobe unsurpassed in the field of three-dimensional trace element localization.

G. H. Morrison

Quantitative Chemical Analysis of Standard Iron Alloys by SIMS

SIMS technique is often used for the quantitative chemical analysis of alloys. It is considered to be a semiquantitative method. The models of plasma in the local thermal equilibrium at the surface (LTE) for 50% of the results have the factor of discrepancy smaller than 2, and only for 5% of the results it is higher than factor 5 [1–8]. The application of the non-equilibrium surface ionization model for the quantitative chemical analysis is of recent date [9,10]. Good agreement of theoretical and experimental results for ALCAN aluminium, ferro-niobium and basalt rock has been obtained [10]. For the majority of constituents the factor of discrepancy is smaller than 1.5, and only for niobium it is approximately 4.

Z. Jurela

Application of the LTE Model to Quantifying the Secondary Ion Spectra of Steels

The quantification of SIMS spectra obtained from steels was performed using the model based on the LTE concept, as proposed by ANDERSEN [1,2]. Since the calculation performed by this model requires the values of a large number of constants for each element and since all the constants are available with a sufficient accuracy, the calculations are done assuming some simplifications. SIMONS [3] described a model neglecting a correction for negative ions and introduced an empirical correction for molecular ions. The results obtained by such an analysis have approximately the same accuracy as those obtained on working with the more complex Anderson model. MORGAN and WERNER [4–8] introduced a further simplification, by assuming that the positive singly charged secondary ions only are representative for the sample composition. This simplification allowed to reduce the number of fitting parameters for the calculation of comparative concentrations. The quantity T described by ANDERSEN as the absolute temperature of the plasma generated by an impinging was denoted by the authors as a fitting parameter without a precise physical meaning. The method gives good results only when the bombarded surface is oxygen saturated. It fails in the determinations of elements showing high yields of monoxide ions (Cr, elements belonging to the IIIb to VIb groups of the periodic system, including lanthanides and actinides). In spite of numerous discussions resulting in critical comments [9–11] the LTE model useful for practical application gives results in practice.

J. Suba, A. Stopka

Modification of the MISR Method with the Use of Implantation of Standard Elements

The most accurate calibrational method for SIMS to date is that of the matrix ion species ratio indexed sensitivity factors (MISR) [1,2]. In this method the RSF’s are recorded against the relative secondary yields of two clusters or multiple charged atomic ions of the matrix species which characterize better the reactive gas surface concentration than the partial pressure of the reactive gas in the vacuum chamber [3]. The greatest problem in the practice of the calibrational methods is the selection of the most suitable standard sample with a close match to the one to be measured [4]. It has been demonstrated that ion implantation techniques may be used to incorporate a known amount of almost any element into the subsurface region of the sample [5], therefore LETA and MORRISON have proposed the application of ion implantation for the fabrication of internal standards in the sample itself [6].

J. Giber, A. Sblyom, L. Bori, J. Gyulai

Use of Ionic Implantation for Quantification of SIMS Analysis in Metals and Oxides — Application to Corrision Studies

Ionic implantation is a simple and reliable method for the preparation of standards containing well defined concentrations and in-depth distributions C(z) of dopants. This method, which is commonly used for quantification of secondary ion emissions of dopants in semiconductors [1,2] may be also of great interest in the field of corrosion studies, since transport of atoms and electric charges in oxide films is generally controlled by impurities low in concentration.

J. C. Pivin, D. Loison, C. Roques-Carmes, J. Chaumont, A. M. Huber, G. Morillot

Secondary Ion Emission from Binary and Ternary Amorphous Alloys

It is well known that quantitation of the SIMS method by the use of theoretically founded models results in only semiquantitative analytical data. The evaluation of SIMS spectra yields better analytical results when the method of relative sensitivity factors (RSF) is used [1–4]. Difficulties have however been reported concerning the commonly used standard samples [1,2,4,5]. We consider the metallic glasses to be suitable standards for quantitative SIMS for several reasons: 1.The standard alloys are often inhomogeneous on a micro-scale owing to the segregation of several elements and to the presence of insoluble phases. The metallic glasses can serve as better standards because they are single phase systems and are homogeneous also at the µm scale. The structure of metallic glasses is very close to that of liquids, i.e. without any crystalline order, but with internal friction of the same order of magnitude as that of solids [6].2.The concentration range of the alloying components is generally limited in crystalline standards. Metallic glasses can be prepared in a broader concentration range, and even insoluble elements can form an amorphous phase under suitable conditions [6].3.The ion yield of elements from crystalline samples depends also on the orientation of the bombarded surface [7]. In the isotropic amorphous alloys such effects which may cause errors in the analysis, cannot occur.4.Amorphous alloys are of metallic character. For similar reasons, NEWBURY [2] considers the silicon-based “conventional” glasses as suitable standards.

H. Gnaser, M. Riedel, J. Marton, F. G. Rüdenauer

Experimental Procedures for Quantitative Analysis of Silicate Minerals

Elemental analysis of silicon bearing minerals by secondary ion mass spectrometry is particularly useful when dealing with small mineral phases and low concentration elements. Many problems have to be solved before getting reliable results. In this paper, we describe some of the experimental procedures we have been using. The most important problems are the electrical charging up effects on insulating materials, the presence of polyatomic ions and matrix effect.

A. Havette, G. Slodzian

SIMS Isotopic Measurements at High Mass Resolution

One of the most promising capabilities of the ion microprobe mass analyzer which has not been fully realized so far is the measurement of isotopic ratios in small samples. In situ measurement of mineral assemblages in the ion probe avoids the time consuming desaggreagation of the sample into its mineral components [1]. However, the ubiquitous presence of interfering species (oxides, hydrides and other polyatomic ions as well as multiply charged ions) in the secondary ion spectrum has in the past restricted isotopic measurements by SIMS to elements like Li, Be, B [2] or Mg [3–8] where interferences are either virtually absent or their contributions can be corrected for. In all these studies interferences were small and/or the measured isotopic effects large. In the case of Pb in zircons [9] the number of interfering species is large and their contributions considerable. As a consequence the validity of correction procedures is questionable. Energy filtering offers the possibility of eliminating molecular interferences [10] but the method suffers from a large loss in the secondary ion signal and cannot be applied in the case of interfering hydrides and multiply charged ions. Another approach is to separate off interfering ions by using a secondary ion mass spectrometer capable of high mass resolution. The recently commercially available CAMECA IMS 3F achieves a mass resolving power which allows the elimination of most of the main molecular interferences in the atomic mass range 1–60. This opens the possibility to extend isotopic measurements to other elements and to cases where contributions from interfering ions are dominant [11].

E. Zinner, M. Grasserbauer

Computer Peak Identification and Evaluation of SIMS Spectra

The most important problems in computer peak identification and evaluation of SIMS spectra of multicomponent systems are: (i)to find the possible ion species: (“variables”) atomic, cluster and molecule ions(ii)the determination of the total isotopic currents of these species(iii)the reliability of the identification and evaluation process.

J. Antal, S. Kugler, M. Riedel

Application I. Depth Profiling

Frontmatter

Depth Profiling of Copper Atoms Gettered in Ion-Damaged GaP

The gettering process was introduced in the field of semiconductor technology by SHOCKLEY and GOETZBERGER [1]. The designation “gettering” comes from the valve technology. Gettering processes in semiconductors include (i)the binding of unwished-for electrically active impurities and/or crystal defects into electrically inactive complexes(ii)the outdiffusion of metal atoms from space charge regions into surface layers and into interfaces(iii)the outdiffusion of dopants or the addition of atoms to bind unwished-for electrically active atoms.

M. Griepentrog, H. Kerkow, H. Klose, U. Müller-Jahreis

The Optimisation of SIMS for the Analysis of Semiconductor Materials

The electronic properties of semiconductor materials such as conductivity, carrier mobility and carrier lifetime depend on the interactions between deliberately added impurity elements and contaminants, introduced during materials preparation and processing, at concentrations in the range 1013 to 1020 atoms cm−3. The correlation of physical properties with chemical concentrations in the thin films typically used for industrial electronic devices requires the determination of the distribution of trace impurity elements as a function of depth within layers that may be only 0.1 µm thick. Secondary ion mass spectrometry (SIMS) can in principle measure the in-depth distribution of a broad range of elements but in practice the absolute accuracy of the concentration measurements, the spacial accuracy of the profile, the dynamic range of the measurement and the limits of detection can be distorted by apparently minor secondary processes occurring in the system or at the sample. These include contamination by impurity ions in the primary ion beam or sputtered from the system or surrounding sample, memory effects and atomic mixing of the sample matrix atoms during the sputtering process.

J. B. Clegg

Impurity Redistribution in GaAS Epilayers

It is generally recognised that secondary ion mass spectrometry (SIMS) is one of the most powerful characterization techniques available in the electronics industry. Several problems have been solved thanks to SIMS techniques. In particular it contributes to the improvement of the expensive and difficult preparation and treatment of gallium arsenide, one of the basic materials of new semiconductor technology [1–6].

A. M. Huber, G. Morillot, P. Merenda, M. Bonnet, G. Bessonneau

Quantitative Distribution Analysis of B, As and P in Si for Process Simulation

For the development and improvement of process simulation accurate information about the (depth) distribution of dopant elements (electrically active fraction and total elemental concentration) as a function of process parameters has to be obtained. The analytical requirements for distribution analysis as applied for process simulation are stringent: i)high precision and accuracyii)high detection power and large dynamic rage (concentra-tion range of interest: 1014–5·1021 at/cm3)iii)high depth resolution (shallow p/n-structures in modern devices)

M. Grasserbauer, G. Stingeder, E. Guerrero, H. Pötzl, R. Tielert, H. Ryssel

High Spatial Resolution SIMS Depth Profiling of Cr Dopant in CdSe Thin Film Transistors

CdSe thin film transistors (TFTs) whose structure is illustrated in Fig. 1, have been fabricated with Cr source and drain electrodes having separations varying between 5 and 50 µm [1]. The thermal annealing process employed to activate the devices has been shown to cause diffusion of Cr from the electrodes into the CdSe layer in the gap, doping the film [1,2]. Auger electron spectroscopy [2] was unable to determine the detailed Cr distribution in the device. Since the conductivity behaviour of CdSe and other polycrystalline semiconductor TFTs depends critically on the doping level [3,4], an attempt was made to determine the Cr distribution across the source drain gap and throughout the depth of the CdSe film in annealed, operational devices.

J. D. Brown, F. R. Shepherd, W. D. Westwood

SIMS Investigation of p-n Junction Quality in Ion Implanted cw Laser Annealed Silicon

It is well established that silicon samples amorphized by ion implantation can be recrystallized by cw laser annealing [1,2]. The damaged surface layer is reconstructed by laser induced solid phase epitaxy [2,3,4]. In contrast to conventional furnace annealing and pulsed laser annealing the depth distribution of the implanted dopant remains unaltered during cw laser annealing [2,5], a distinct advantage for many device applications. Depending on laser power and dwell time, either optically perfect surface morphologies or surfaces showing slip lines are obtained [6,7]. Slip lines are observed at high laser power or long dwell time and indicate the generation of slip dislocations due to the thermally induced stresses [6,8]. At first sight samples with optically perfect surface morphology might be preferred for device fabrication. In contrast,the SIMS profiling studies of implanted and cw laser annealed diode structures reported here give clear evidence of much better quality of the p-n junctions in terms of lower reverse bias current for samples with the “slipped” surface morphology. TEM analysis reveals that the crystal quality of the p-n junction region (and not of the surface) is indeed decisive for the electrical behaviour of the diode.

M. Maier, D. Bimberg, H. Baumgart, F. Phillippi

Profiles of Implanted or Diffuses Dopants (Be, Zn, Cr, Se) in Indium Phosphide

Indium phosphide is of technological interest since it has been shown that optical fiber communications systems in the 1.1–1.6 µm range could be based on the InP/InGaAsP material. It is of primary importance to develop appropriate device fabricating techniques both for InP itself and alloys grown on it. The paper to be presented is concerned with the SIMS technique applied to the determination of some dopant profiles, i.e. Be, Zn as p-type, Se as n-type and Cr in semi-insulating substrates.

M. Gauneau, A. Rupert, P. N. Favennec

Applications of SIMS in Studies of Slow Diffusion and Isotope Diffusion

Quantitative measurement of tracer diffusion coefficients by means of SIMS raises strict requirements of detection sensitivity, in-depth resolution and spectral purity [1]. During recent years, accurate measurements have been carried out on single-crystal metals and semiconductors [2–6], involving the determination of very low diffusion coefficients (as an example, see Fig. 1, from [3]) as well as the detection and identification of very dilute impurities (see e.g. Fig. 2, from [6]).

A. Lodding, H. Odelius, U. Södervall

Rapid Diffusion and Gettering Studies of Bulk Oxygen in Silicon by Cs/SIMS

The analysis of the light elements in materials has always been of ultimate importance due to their ubiquitous nature in nature and the environment. However, the analysis also is confounded or made more difficult by the presence of these species in the residual vacuum or sample environment of an analytical system. Modern instrumentation, in particular, high performance secondary ion mass spectrometers, employ a variety of experimental conditions which have made the analysis of these species more attainable. In this paper we would like to address the characterization of oxygen unintentionally incorporated in silicon during the CZOCHRALSKI (Cz) silicon growth method with the oxygen coming from the silica quartz crucible used to contain the melt. Although this oxygen is unintentionally incorporated in the silicon, it is known to have beneficial qualities on the resultant material. In particular, the oxygen supposedly adds structural strength to the silicon and through a variety of processing and thermal cycling the oxygen can be made to precipitate into regions which allow the stress resulting from this precipitation to getter impurities unintentionally incorporated during device fabrication.

C. A. Evans, B. K. Furman, T. J. Magee

Water Diffusion in Fused Silica and Iron-Making Slag

Secondary ion mass spectrometry is a powerful tool for analysis of hydrogen in small parts of a specimen. Purpose of this study is to measure diffusion coefficients of hydrogen in iron- and steel-making slags at high temperatures. As the first step, a preliminary investigation of heavy “water” diffusion in a silica glass was made. Here “water” diffusion means diffusion of hydrogen-bonding species which exist in a slag (or a silicate glass) through a reaction of water vapor with the slag on the surface.

M. Kobayashi, K. S. Goto, M. Someno

Combined SIMS-AES-XPS Investigation of the Composition and Interface Structure of Anodic Oxide Layers on Cd0.2Hg0.8Te (CMT)

Because of its small band gap, cadmium mercury telluride (CMT) is widely used as a material for IR detectors. The constancy and long-time stability of its composition, as well as a low impurity concentration are the crucial requirements for successful applications of this semiconductor. Anodic oxide layers are frequently used for passivation of the CMT surface. In the present investigation, the surface and in-depth composition of anodic oxide layers with different thickness from 20 to 230 nm on Cd0.2Hg0.8Te has been characterized by quasi simultaneous secondary ion mass spectrometry (SIMS), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS).

U. Kaiser, O. Ganschow, J. Neelsen, H. M. Nitz, L. Wiedmann, A. Benninghoven

Application II. Surface Studies, Ion Microscopy

Frontmatter

The Chemical Compositon of Oxide Films on Aluminium and Its Influence on Surface Properties Studied by SIMS, XPS and AES

The chemical composition of natural oxide films on aluminium foil and thin strip of technical purity has been studied using SIMS depth profiling, photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Special emphasis was placed on understanding diffusion processes leading to surface enrichment of low concentration impurities, in particular alkali and alkaline earth metals in technically pure aluminium.

M. Textor

Study of the Adsorption of Water on Titania by Secondary Ion Mass Spectrometry

Titania is known to dissociate water photocatalytically [1] but many aspects of the process are not fully understood. Complete agreement does not exist with respect to the character (associative, dissociative) of the water adsorption and the nature of the sites. In this paper, we report preliminary SIMS results concerning the adsorption of water on clean titania powders whose surface stoichiometry is varied and checked by a combination of Auger and SIMS. The main purpose of the present work is then to investigate the potentialities of SIMS as regarding the adsorption of water on oxides. Particularly, we are interested to see if the degree of coverage and the various phases of adsorption can be deduced from static SIMS.

J. Marien, E. De Pauw

SIMS Studies on Oxygen Adsorption on Aluminium and Its Alloys

SIMS has been used widely for surface chemistry studies, i.e. to try to identify species formed on metal or semiconductor surfaces during their reaction with the gaseous ambience, the latter being mostly oxygen. These studies can provide reliable information if the SIMS method is combined with other surface sensitive methods as TDMS [1], IRS [2], etc. One of us has developed a new method of using SIMS to measure oxygen adsorption on silicon surface [3]. The present paper deals with this method for the analysis of oxygen adsorption on aluminium and some aluminium alloys.

D. Marton, Á Csanády

Oxidation and Segregation at the Surfaces of Different Aluminium Foils and Sheets

Only a few SIMS investigations concerning bulk aluminium materials have been published in the literature. At the surface of differently heat treated Al-0.4 w% Fe and Al-0.4 w% Fe-0.06 w% Mg foils produced from 99.99 aluminium, Be, B and Mg impurities were observed by DORSEY [1] but their origin was not clearly understood. Aluminium sheets and foils were investigated by JANSSEN [2]. Deleterious effects on surface properties such as heat-seal adherence where explained by impurities (mainly magnesium) enriched in the surface oxide formed during annealing. DEGREVE et al. [3] have shown by an IMMA of extremely good mass resolution that Be enriches between amorphous oxid and metal in a heat treated Al-Zn-Mg alloy. To ensure advantageous surface properties i.e. corrosion behaviour of aluminium and aluminium alloy semiproducts, a detailed knowledge and understanding of the mechanism of surface processes are essential.

Á. Csanády, D. Marton, T. Turmezey

Oxygen Adsorption on Polycrystalline PT3Pb at Elevated Temperatures. A SIMS Study

The surface of solid platinum is an important subject of the modern methods of surface science caused by the special demands of research in catalysis [1]. Especially some work has been done to examine the oxygen adsorption on platinum single crystal surfaces at different temperatures reviewed by NIEHUS et al. recently [2]. The main feature is the experimental evidence for a chemisorption state of oxygen at temperatures below~800 K and for a second so-called “oxide” state above ~800 K. It was our aim to utilize the known advantages of SIMS to describe the temperature dependence of the oxygen adsorption phenomena at the surface of a binary alloy of platinum, polycrystalline Pt3Pb.

W. Unger, L. Bori, D. Marton

SIMS Investigation on TiFe Nitrided by NH3-Pretreatment

TiFe has been found in the last years to be one of the best materials for hydrogen storage and purification [1]. The idea to use hydrogen storage materials as hydrogenation catalysts [2] has been picked up to investigate the catalytic activity of TiFe specially pretreated for the ammonia synthesis [3]. The apparent activation energy has been found to be only 62 kJ/mol for TiFe compared to values of 150 kJ/mol for pure Fe and 90 kJ/mol for technical contacts. The special pretreatment is a cycling hydrogenation and dehydrogenation followed by a nitridation with ammonia at temperatures of about 450°C. The total nitridation leads to a compound of a stoichiometry TiFeN1. 8. X-ray DebyeScherrer patterns from this material only show reflexes which can be appointed to TiN, no iron containing compounds can be identified and no X-ray reflexes of TiFe occur [3]. Thus it has to be assumed, that a reconstruction of the original TiFe lattice into a new phase, probably nitrided Ti and finely dispersed Fe, has taken place. The Fe shows the high catalytic activity. These results are confirmed by magnetic and Mössbauer measurements which clearly show a disappearance of the original TiFe [3,4].

G. Kirch, H. Züchner

SIMS/TDMS Studies of Hydrocarbon Interaction with Nickel

As compared with other surface analytical techniques, static secondary ion mass spectrometry offers the following advantages: hydrogen sensitivityisotope sensitivityhigh detection sensitivity (< 10−6 ML)compound detection by molecular ions The latter feature is of special interest in conjunction with the investigation of surface reactions. It is, however, also connected with serious problems. Firstly, there is no straightfoward relationship between the composition of secondary ions and that of corresponding surface complexes. Secondly, an adsorbate induced change of ionization probability hinders the quantitative interpretation of SIMS results.

M. Schemmer, P. Beckmann, D. Greifendorf, A. Benninghoven

SIMS Investigation of Adsorption and Chemical Modification of C2H4 and C2H2 on a Polycrystalline Ni-Surface

Nickel is an important catalyst in the hydrogenation and dehydrogenation of hydrocarbons. As with other transition metals, this feature is connected with the capability of the catalytic active surface to adsorb H2 dissociatively. In the study of these catalytic processes the chemical changes in ethylene have often served as a relatively simple example and many investigations on this system with different methods are reported in the literature [1–7]. For surface temperatures below 150 K, molecular adsorption of C2H4 is observed [1] whereas for temperatures between 200 K and 400 K hydrogenation as well as dehydrogenation could be detected [1–3]. Some authors were able to demonstrate the simultaneous existence of both corresponding species. Furthermore, also polymerization and cracking could be found [4,5]. For temperatures above 400 K most commonly a complete dehydrogenation of C2H4 is observed with the formation of a carbon layer on the Ni-surface [3]. With increasing temperature this carbon layer diminishes and disappears at temperatures above 700 K [3]. Some interest is also concentrated on the influence of preadsorption of hydrogen [4,5]. Very similar findings are reported for acetylene on Ni [6]. At a temperature of 150 K, molecular adsorption and partial dehydrogenation coexist. For temperatures near and above 300 K cracking and formation of a CH-species are quoted. Hydrogenation and polymerization were found at temperatures above 400 K, also the formation of a graphite layer. A special feature seems to be the fact that the CH-species only looses hydrogen at the substantially higher temperature of 670 K (as compared to the case of ethylene on Ni).

H. Kaarmann, B. Leidenberger, H. Hoinkes, H. Wisch

Secondary Ion Emission from UHV-Deposited Amino Acid Overlayers on Clean Metal Surfaces

In SIMS work on organic materials samples are usually prepared under atmospheric conditions using aqueous or alcoholic solutions (e.g. dipping technique [1], electrospray [2], micropipette [3]). Major drawbacks of these methods are possible chemical reactions occuring between the target material and some components of the solution, and contaminations with e.g. hydrocarbons. Furthermore, it is not possible to produce well-defined substrate surfaces. Therefore, when investigating the influence of surface chemistry on secondary ion formation, it is necessary to perform sample preparation under UHV-conditions.

W. Lange, M. Jirikowsky, D. Holtkamp, A. Benninghoven

SIMS Investigation of Adsorption of O2, H2O, CO, CO2, CH2O, and CH3OH and Coadsorption of O2 with CH2O and CH3OH on Polycrystalline Silver Surfaces

In the past few years, the importance of a surface analytical approach to the study of heterogeneous catalysis has become evident [1]. In order to ensure the relevance of the surface physical results obtained in ultra-high vacuum for the catalytic processes under technical conditions (usually high pressure and temprature), we have set up an instrument which is a combination of a technical microreactor and a surface analytical system incorporating SIMS, AES, XPS, ISS and TDMS. The details of this combined system will be published elsewhere. It should, however, be pointed out that three kinds of experiments can be conducted in this instrument, which are essential for the understanding of catalytic processes: (1)well-defined reactions on model surfaces under “clean” conditions,(2)surface analytical characterization of catalysts as drawn from the plant,(3)catalytic reactions in the microreactor and subsequent surface characterization of the catalyst after transferring it into the surface analysis section in vacuum and within a few minutes.

L. Wiedmann, N. L. Wang, R. Jede, L. D. An, O. Ganschow, A. Benninghoven

Distribution of Ni, Co, Ga, and Cu in Iron Meteorities

Distribution of nickel in taenite veins of iron meteorites have been thoroughly investigated by J.A. WOOD [1], J.I. GOLDSTEIN and J.M. SHORT [2] using electron probe microanalyzers (EPMA) in connection with the problem of cooling rates of meteorite parent bodies. M. SHIMA et al. [3] reported the results of the line analyses by EPMA for iron, nickel and cobalt on the four iron meteorites. Studies on the distributions of minor components such as gallium, germanium and copper in taenite veins have been limited due to a lack of microanalytical techniques with high sensitivities. Recently, ion microprobe mass analyzer (IMMA) has been developed and proved to have a much higher sensitivity compared with EPMA. In 1979, S.J.B. REED et al. [4] reported the results on line analyses using IMMA for gallium in iron meteorites and they found M type profiles that were strongly correlated with the profiles for nickel.

J. Okano, H. Nishimura

Metallurgical Applications of Ionic Microscopy

Mechanical and physico-chemical properties of metallic materials are greatly affected by the distribution of impurities or minor additions in the matrix structure on a microscopic scale. Most information on the composition of precipitates or diffusion gradients can be obtained by EMA. But light elements such as B, Be, C, N are important constituents of metallic materials, of which detection is almost impossible by EMA. The study of submicroscopic precipitations and atomic segregations at interfaces are also out of the field of this microanalytical method. Auger scanning microscopy is the most appropriate non-destructive method to study segregations at interfaces and submicroscopic precipitations, because of its high spatial resolution and of its better sensibility to light elements (for local contents over 1%).

E. Darque-Ceretti, R. Dennebouy, J. C. Pivin, C. Roques-Carmes

Secondary Ion Mass Spectrometry of Organic Compounds

Parent-like secondary ions of the general composition (M+H)+ and (M-H)−, where M stands for an organic molecule, are emitted with very high absolute yields from corresponding molecular layers on solid surfaces during ion bombardment. That was the surprising result of two systematic SIMS investigations of amino acids (1), and further groups of organic compounds (2,3) published in 1976 and 1977. Besides these and other parent-like ions as (M+cation)+ e.g. (4), many characteristic fragment ions are emitted too (Fig. 1).

A. Benninghoven

Backmatter

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