Secondary Ion Mass Spectrometric Analysis Research Articles

Secondary ion mass spectrometric analysis of leaching behaviour of magnesium from chrysotile in oxalic acid solution

AbstractA study was made on the dissolution kinetics of chrysotile asbestos in 0.1 N oxalic acid over the temperature range 0–80°C. After treatment, the fractional release of magnesium from the fibre was measured using secondary ion mass spectrometry. Diffusion coefficients were determined assuming a plane sheet model. It appeared that the Arrhenius relation is obeyed over the entire temperature range, with an activation energy of 72.1 kJ mole−1, in agreement with earlier literature data.

Selection of calcium isotopes for secondary ion mass spectrometric analysis of biological material

The use of stable isotopes as tracers for elemental localization is a function of the background count rate which is dependent upon both the natural abundance and the quantity of interferences at the nominal mass. The occurrence of a variable and unpredictable high background count rate at mass 44+ in biological tissue, probably CO2+, limits the usefulness of this isotope for physiological problems.

Secondary ion mass spectrometric analysis of polymer and coal surfaces for trace inorganic elements

The application of secondary ion mass spectrometry (SIMS) to the study of organic polymeric surfaces has increased rapidly in recent years and has been extended to the organic constituents of coals. The detection of inorganic constituents in such organic matrices using SIMS is limited by the strong background contribution from molecular ions. A method for the suppression of molecular ions in SIMS spectra, known as specimen isolation (SI) has been introduced. The application of the SI-SIMS technique has now been extended to the analysis of some highly insulating organic polymer and coal surfaces. Examples of the results obtained are given.

Relative sensitivity factors of elements in quantitative secondary ion mass spectrometric analysis of biological reference materials.

Relative sensitivity factors of elements in quantitative secondary ion mass spectrometric analysis of biological reference materials.

SIMS profile analyses for Ge-, Co- and Fe-doped InP substrates used in epitaxial growth

Cockayne and co-workers [1, 2] have shown recently that germanium (Ge) or cobalt (Co) doping of liquid-encapsulation Czochralski (LEC) grown indium phosphide (InP) single crystals produces potentially useful properties in the application of this I I I -V compound as a substrate material for the manufacture of a number of electronic devices. At high concentrations (>1019 atoms cm-3), germanimn hardens the lattice sufficiently to inhibit dislocation generation during LEC growth and allows single crystals with dislocation densities close to zero to be obtained [1]. Cobalt, on the other hand, can be used at low doping levels (~3 x 101Satomscm-3) to induce resistivities in the region of 107ohmcm [2]. An important factor in determining applications for these materials is a knowledge of the extent to which cobalt and germanium migrate into epitaxial layers grown on to substrates doped with these elements. Here, we report the results of secondaryion mass spectrometric (SIMS) analysis of undoped layers grown on to such substrates by either vapour phase epitaxy (VPE) or molecular beam epitaxy (MBE). Comparison is made with layers grown similarly on to Fe-doped substrates. The single crystals used as substrates were all grown by the standard LEC technique using r.f. heating [3] from polycrystalline material supplied by MCP (Electronic Materials) Ltd. This yields undoped crystals with a residual donor concentration within the range 2 to 5 x l0 is cm -a at RT (room temperature) and with a corresponding mobility range of 4000 to 5000cm 2 V -1 sec -1. The highpurity dopants, germanium, cobalt or iron were added to the starting charge prior to melting and growth. The dopant levels, quoted subsequently, were determined either chemically by spark-source mass spectrometry or from electrical data obtained by the Van der Pauw technique. Epitaxial layers were grown on to (1 0 0) substrates from the crystals using either VPE or MBE techniques. Prior to growth polished substrates were degreased in propan-2-ol, dried, dipped in 0.3% bromine in methanol solution for 60 sec, rinsed in deionized water and then blow dried. The VPE process employed was the well established technique [4] based on the reaction between indium and PC13 in a stream of H2. In this process, the substrate is heated in H~ to the growth temperature of 650 ° C over a period of 30 min followed by growth for a further 40 rain to produce layers 2 to 3 #m thick. The MBE process used indium and P2 beams in ultra-high vacuum [5], wherein the substrates are heated for 5 min at 505 ° C in a P2 flux to facilitate cleaning without surface degradation followed by growth at 420 ° C for 3 h to produce layers 0.5 to 1 #m thick. SIMS analysis was performed with a Cameca 1MS3F instrument. All samples were analysed under standard conditions using an O~ primary beam to erode through the epitaxial layer into the substrate. The isotopes counted were S6Fe+, S9Co + and 72Ge+, all for a period of 30 sec at each sampling point. Each sample was analysed by rastering a beam of either 0.3/2A or 1 gA over an area of 500#m square. An aperture diaphragm was inserted into the secondary ion beam to restrict ions counted to a central area of 60gin diameter, to avoid crater edge effects. The energy discriminating slits between the electrostatic and magnetic analysers were opened to allow a 10 eV bandpass centred on the maximum energy of an aluminium standard specimen, no offset being used. All other apertures and slits were set for maximum trans-

Secondary ion mass spectrometric image depth profile analysis of thin layers

Image depth profiling is applied to the quantltative analysis of molecular beam epitaxlally grown gallium arsenide thin layers. The technique Involves the use of Ion implantation through a mask and subsequent analysla by secondary Ion mass spectrometry (SIMS). The proposed approach provides high accuracy results in the analysis of semlconductor thin layers. Semiconductor materials research has succeeded in steadily reducing the physical size of electronic devices. With the development of eptiaxial growth techniques, particularly molecular beam epitaxy (MBE) (1-3), layered structures of thicknesses on the order of 1-100 nm with precise composition profiles have been obtained. The fabrication of devices by MBE requires the ability to accurately add controlled quantities of electrically active dopants, a process which, in many cases, is not well understood. As experimentation continues, the need for accurate measurement of dopant concentration in such layers challenges the state-of-the-art of surface analytical techniques. Secondary ion mass spectrometry (SIMS) is currently recognized as one of the most sensitive techniques for the analysis of semiconductor materials (4,5), with detection limits in the parts per million range for most elements. The application of ion implant standards (6, 7) to SIMS has been developed to provide accurate quantitative concentration depth profiles. The method of solid-state standard addition by ion implantation has been shown to give excellent results (8). This method involves implanting the sample with a controlled dose of the element to be determined, profiling through the implantation zone, and then comparing the integrated signal obtained from the implant to the background signal arising from the dopant being determined. To ensure complete removal of the implanted species, the residual dopant signal is acquired at a depth of at least three to four times that of the implant peak (8). This places a restriction on the minimum sample thickness which can be analyzed by this method. Furthermore, dopant inhomogeneity in the sample presents difficulties to the conventional technique. Lateral (z-y) inhomogeneities can be dealt with only by the tedious process of running replicate analyses on several sampling areas. In-depth heterogeneity poses an even greater problem as all but gross inhomogeneities are masked within the implant region. Hence, effects such as diffusion toward the surface cannot be dealt with reliably. This problem can be circumvented in some instances by implanting with one isotope of the element of interest to serve as a standard and monitoring the residual component with another isotope. However, this is not always feasible, as in the case of beryllium which is monoisotopic. In order to reduce the thickness requirement to thinner layers, and to eliminate the problem of dopant inhomogeneity, we investigated the use of image depth profiling (9). This technique fully utilizes the advantages of the ion microscope (10) by providing simultaneous in-depth analysis of several features within the ion image. Therefore, if the field of view of the image contains both implanted and unimplanted regions, implant and background signal levels can be obtained simultaneously to give quantitative concentration data. The only thickness limitation then becomes that necesssary to contain the entire implant zone, while dopant heterogeneity can be visually assessed and determined quantitatively by proper choice of sampling areas within the ion image. This method was applied to two thin layer samples. First, a quantitative determination of the beryllium dopant concentration in a 1 pm MBE grown gallium arsenide layer was performed as a test sample. The technique yielded a precision of 24% and was accurate to within 13%, both comparable to the results achieved by the conventional solid-state standard addition method. Next a GaAs layer containing a diffused silicon dopant was quantitatively analyzed.

Structural investigation of thin films of diamondlike carbon

Diamondlike carbon films produced both by ion-beam technique and by radio-frequency (rf) plasma decomposition of hydrocarbon gases (C4H10, C2H6, C3H8, and CH4) have been examined using the technique of transmission electron microscopy. Although these examinations indicate that these films are predominantly amorphous, both single-crystal and polycrystalline diffraction patterns have been obtained from films of both types that indicate formation of several different phases. Some of these phases appear to be cubic and could be new forms of carbon. The results of secondary ion mass spectrometric analysis of carbon films produced by rf plasma decomposition of hydrocarbon gases are also discussed.

Compositional inhomogeneities along the growth direction of substituted yttrium iron garnet epilayers

Secondary ion mass spectrometric analyses calibrated by electron microprobe analyses reveal compositional inhomogeneities along the growth direction (thickness) of substituted yttrium iron garnet epilayers. Specially exaggerated growth conditions are induced by altering the substrate rotation rate during growth at high supercooling. These conditions cause changes of effective distribution coefficients with time.

Charging effects in the secondary ion mass spectrometric analysis of targets containing low-conductivity regions

Common ion sputtering techniques for depth profiles can cause buildup of charge in low-conductivity regions such as p-n junctions in semiconductors, leading to erroneous results. We analyzed Ga0.1Al0.9As liquid phase epitaxial (LPE) layers on GaAs with secondary ion mass spectrometry (SIMS) and observed that the profiles of 69Ga+ and 27Al+ in the low-conductivity region of these Zn-diffused LPE layers were a function of the sample bias. We noticed that this artifact was due to the shift and broadening of the secondary ion energy distributions caused by positive charging of the specimen surface. We also found that this could be effectively remedied by integrating the secondary ion yields over a wide energy range. The use of an electron flood gun reduced this charging effect, but complete charge compensation was not achieved even at electron current densities far exceeding the ion current density. This can be explained by the fact that the electron-induced secondary electron coefficient of GaAlAs is larger than unity.

Evaluation of several semi-theoretical methods for quantitative secondary ion mass spectrometric analysis after discrimination-correction of data

Evaluation of several semi-theoretical methods for quantitative secondary ion mass spectrometric analysis after discrimination-correction of data

A study of the interaction of oxygen with chromium using ion bombardment induced photon and secondary ion emission

Oxygen ion bombardment, or ion bombardment in an oxygen atmosphere is often used to enhance the ion yield from metallic targets, when secondary ion mass spectrometric analysis is being attempted. However, there exist few detailed studies of the effect of oxygen environment on the yields of various ions emitted from an ion bombarded surface. In this work we report detailed observations of the effect of a varying oxygen background pressure on the yield of ions of the form Cr + n and Cr m O + n from a polycrystalline Cr target. Observations of the variation of the photon yield from the same target, as the oxygen background pressure is changed are also reported. From these observations some conclusions regarding the effect of oxygen absorption on cluster ion yields and on the mechanisms of ion emission can be deduced. In particular it is shown that blocking of electronic transitions as a result of oxygen adsorption cannot account for the total variation of Cr + emission with increasing oxygen pressure.