High resolution depth profile analysis by elastic recoil detection with heavy ions

Elastic recoil detection (ERD) with energetic heavy ions (e.g. 60-120 MeV(127)I) is a suitable method to measure depth profiles of light and medium heavy elements in thin films. The advantages of this method are reliable and quantitative results and elementally and isotopically resolved depth profiles. A relative energy resolution of 0.07% has been measured in real ERD-experiments using the Q3D magnetic spectrograph at the Munich tandem accelerator and a large solid angle of detection of 5 msr. The good energy resolution allows atomic depth resolution near to the surface which has been obtained at flat and smooth carbon samples. A large solid angle of detection is necessary to measure a depth profile with the desired accuracy before the sample is significantly altered by the ion beam. As an example carbon profiles of thin carbon layers, prepared by a laser plasma ablation deposition process, have been investigated revealing the high depth resolution and its power to resolve elemental profiles at gradiated interfaces.     

Hydrogen profile analysis in a-C:H films by elastic recoil detection (ERD)

Summary The measurement of hydrogen profiles in diamond-like carbon films (a-CH) by elastic recoil detection (ERD) and the decrease of the H content after irradiation with Ni ions are described.

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Wasserstoffprofilanalyse in a-C:H-Filmen durch elastische Rückstoß-Detektion (ERD)

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Guest scientist from IMR of Academia Sinica, Shenyang, People's Republic of China     

Simultaneous analysis of low-Z impurities in the near-surface region of solid materials by heavy ion elastic recoil detection (HIERD)

A HIERD setup (HI-ERD=heavy ion elastic recoil detection) is introduced including a semiconductor -E-E telescope for the detection of hydrogen and helium isotopes and a Bragg Ionization Chamber (BIC) for the identification of heavier recoils. An optimum forward scattering geometry with respect to maximum analyzable depth and sensitivity is determined experimentally as well as by calculations for the analysis of oxygen and hydrogen using 35 MeV ³⁵Cl incident ions. As a relevant application of the method, the Na content of borosilicate glass is investigated in samples subject to anodic bonding procedures.     

Quantitative elastic recoil detection (ERD)

Elastic recoil detection with heavy ions is a well suited method to measure depth profiles of light and medium heavy elements in thin films. Due to known Rutherford scattering cross sections and stopping powers of ions in matter, measurements can be quantified with an accuracy of about 1%. The transformation of energy spectra to quantitative elemental depth profiles, however, is generally a non trivial task and therefore a transofrmation algorithm has been developed based on a similar one for RBS analysis and realised in the program KONZERD. The transformation procedure allows a fast conversion from raw spectra to concentration profiles for classical ERD measurements as well as for high resolution measurements with a depth resolution better than 1 nm.     

Elastic recoil detection analysis

This work briefly describes the basic principle of Elastic Recoil Detection Analysis. From a theoretical analysis of the physical process, we discuss the choice of the best experimental configuration for solid surface examination and particularly the advantages of the transmission geometry. Then, we propose a new calculation procedure for the collision cross section¹H(⁴He,⁴He)¹ H between 0.5 and 8 MeV helium ions energy, and finally we analyze in more detail the cross section results in the low energy range (1 to 2.5 MeV).     

SIMS depth profile analysis using MCs+ molecular ions

Summary The use of Cs⁺ primary ions in conjunction with the detection of MCs⁺ molecular ions (where M is the element to be monitored) in SIMS depth profiling is shown to be an efficient method of minimizing the variations of ion yields with sample composition, e.g., at the interface of multilayer structures. Depth profiles of several such samples demonstrate that MCs⁺ intensities follow closely the concentrations of the respective elements, providing the possibility of a (semi)quantitative analysis of major components by means of secondary ion mass spectrometry. As indicated by the similarity of their energy distribution data, the formation and emission process of MCs⁺ molecules seems coupled to that of Cs⁺ ions.     

High resolution depth profiling of non-conducting samples with SNMS

Beat-like signal modulations in sputter depth profiles of multilayer structures are shown to enable an estimation and the optimization of the homogeneity of the sputter erosion process. Using W-Si multilayer structures of 69 doublelayers with a thickness of 40 Å, it is shown that the high-frequency mode (HFM) of electron-gas SNMS (e^–-gas SNMS) for the analysis of insulators provides the same high depth resolution as the conventional direct-bombardment mode (DBM) of this technique.     

Hydrogen analysis by elastic recoil spectrometry: A new approach for absolute quantitative measurement

We have developed an absolute, quantitative procedure to determine the hydrogen content and to describe its concentration profile in the near-surface region of solids. The experimental technique used is the Elastic Recoil Detection Analysis of protons induced by helium-4 beam bombardment in the energy range 1.8 MeV. The deconvolution of the recoil spectra is obtained by means of a computer program which simulates all the physical processes of⁴He/¹H interaction. The hydrogen content is calculated using a new recoil cross section expression. The analyses are performed in silicon crystals implanted with hydrogen at 10 keV. The implantation dose is evaluated with an accuracy of 10% and the hydrogen depth profile is given with an accuracy of ±10 nm around 200 nm.     

Micro and surface analysis with fast heavy ions

The desorption of atomic and molecular species from surfaces bombarded by fast heavy ions (Z ? 20; E ? 0.5 MeV/amu) is attractive for surface and microscopic characterization. Only a low-intensity probe beam is needed, the escape depth of desorbed species is shallow (ca. 10 Å), and desorbed ions are efficiently detected with a time-of-flight mass spectrometer. Thus, particle-induced desorption mass spectrometry (PDMS) maintains sample integrity and charging effects are avoided. PDMS is useful for surface analysis of glasses and plastics by using californium-252 fission fragments for bombardment. Inorganic and organic surface constituents can be detected simultaneously; mass resolution is good. For lithium in glass, the detection limit is about 1 pg (ca. 100 μg g^?1. The PDMS technique can be combined with sequential ion etching for depth profiling. The feasibility of PDMS for microscopic analysis with a collimated 84-MeV Kr⁷⁺ beam (target diameter ca. 11 μm) is discussed.     

Trace analysis of heavy metal ions by ion chromatography

Summary An ion chromatographic separation technique for heavy metal ions is described. Using pressure-stable, silica-based, ion-exchange supports and standard HPLC equipment with post-column reaction detector high resolution is achieved as well as extremely high sensitivity in the parts per trillion (ppt)-range.     

Determination of heavy metal ions by microchip capillary electrophoresis coupled with contactless conductivity detection

An integrated detection circuitry based on a lock-in amplifier was designed for contactless conductivity determination of heavy metals. Combined with a simple-structure electrophoresis microchip, the detection system is successfully utilized for the separation and determination of various heavy metals. The influences of the running buffer and detection conditions on the response of the detector have been investigated. Six millimole 2-morpholinoethanesulfonic acid + histidine were selected as buffer for its stable baseline and high sensitivity. The best signals were recorded with a frequency of 38 kHz and 20 V(pp). The results showed that Mn(2+), Cd(2+), Co(2+), and Cu(2+) can be successfully separated and detected within 100 s by our system. The detection limits for five heavy metals (Mn(2+), Pb(2+), Cd(2+), Co(2+), and Cu(2+)) were determined to range from about 0.7 to 5.4 μM. This microchip system performs a crucial step toward the realization of a simple, inexpensive, and portable analytical device for metal analysis.     

Heavy‐ion elastic recoil detection analysis as a useful tool for tracking experimental modifications in bulk calcium silicates

Chemical modifications carried out on unique amorphous nano‐structured calcium silicate have been traced by time‐of‐flight heavy‐ion elastic recoil detection analysis (HERDA). It could be shown that this ion‐beam analysis method allows not only surface but also depth analysis of the silicate samples and the modifications effected upon it. While providing a challenge for standard analysis methods, the highly porous, low‐density nature of the calcium silicate proved to be an asset for the ion‐beam analysis technique chosen. Presented are depth profiles giving elemental compositions and providing the bases for representative chemical formula for the silicates studied. It was proven that a study of the surface composition of this nano‐structured silicate is sufficient for indicating the bulk composition of a sample of this material. Copyright © 2005 John Wiley & Sons, Ltd.     

New synthesized ligands for detection of heavy metal ions

Some new chemo-sensors (4,4'-((1E,1′E)-(2,2′-dichloro-[1,1′-biphenyl]-4,4′-diyl)bis(diazene-2,1-diyl))bis(3,5-dihydroxybenzoic acid), 4-((E)-(4-(N-(4-((E)-(4-carboxy-2,6-dihydroxyphenyl)diazenyl)phenyl)sulfamoyl)phenyl)diazenyl)-3,5-dihydroxybenzoic acid, 4-((E)-(4-((4-((E)-(4-carboxy-2,6-dihydroxyphenyl)diazenyl)-2-sulfophenyl)amino)phenyl)diazenyl)-3,5-dihydroxybenzoic acid) were synthesized. These synthesized sensors were then characterized by FTIR, TLC, UV–Visible spectrophotometry, and NMR techniques. The sensors showed the best results for detection of all type of heavy metal ions simply by changing the colour of metal ion solution and by shifting in the λ_max values of sensors due to interactions.     

High resolution recycle gas chromatography with off-line flame ionization detection

Preliminary results of a recycle system employing fused silica capillary columns are discussed. The unit, which can be operated with a pre-column for multidimensional GC, utilizes continuous stream splitting for off-line flame ionization detection. Commercially available rotary valves were used for recirculation of the chromatographic zone between column loops. Adsorptive activity, which is shown to be additive, is a serious limitation in the analysis of polar compounds. The successful application of recycle chromatography to increase resolution on non-polar mixtures is demonstrated.     

Errors in activation analysis by nuclear recoil

The recoil energies of up to several MeV developed during nuclear reactions involving particle emission lead to the radionuclides used in the analysis being redistributed between adjacent materials. In aluminum irradiated by reactor neutrons,²⁴Na losses were observed up to a depth of 8·10⁻⁶ m; in the adjacent silicon, a²⁴Na penetration depth was observed up to 4·10⁻⁶ m. Similar results were obtained from reaction products deriving from irradiation of Ti, Ni, N, S and Cl. This means that the results of activation analysis investigations performed for the purpose of evaluating this type of reaction might contain significant errors if thin layers, boundary zones of very small sample volumes are examined. In the analysis of surface layers on silicon devices, completely erroneous results have been obtained in some cases due to the recoil phenomena described.     

Determination of heavy metal ions by capillary electrophoresis with contactless conductivity detection after field-amplified sample injection.

A method has been developed for determining of heavy metal ions by field-amplified sample injection capillary electrophoresis with contactless conductivity detection. The effects of the 2-N-morpholinoethanesulfonic acid/histidine (MES/His) concentration in the sample matrix, the injection time and organic additives on the enrichment factor were studied. The results showed that MES/His with a low concentration in the sample matrix, an increase of the injection time and the addition of acetonitrile improved the enrichment factor. Four heavy metal ions (Zn2+, Co2+, Cu2+ and Ni2+) were dissolved in deionized water, separated in a 10 mM MES/His running buffer at pH 4.9 and detected by contactless conductivity detection. The detection sensitivity was enhanced by about three orders of magnitude with respect to the non-stacking injection mode. The limits of detection were in the range from 5 nM (Zn2+) to 30 nM (Cu2+). The method has been used to determine heavy metal ions in tap water.     

Non-destructive depth profile analysis using synchrotron radiation excited XPS

We have used synchrotron radiation as excitation source in an X-ray photoelectron spectroscopy (XPS) experiment to analyse surface-near element depth profiles non-dectructively. By tuning the photon energy one can vary the kinetic energy of the photoelectrons and in turn the information depth of the measurement. To quantify the sample geometry (e.g. layer thicknesses) model calculations similar as for angle-resolved XPS (ARXPS) measurements are necessary. We have successfully applied this technique to several samples. We will show how to calculate the relative intensities of the peaks, using photoionization cross sections and an experimentally determined analyzer transmission function and the procedure to quantify the geometry for a model sample: natively oxidized Ta covered by carbon contamination. At Sn-doped indium oxide samples we found a sub-monolayer of segregated Sn at the surface which was expected from previous investigations.     

Characterization of metallic layer composites by means of AES/depth profile analysis

The adherence mechanism of arc sprayed Ni layers on structure steel St37 is investigated. AES depth profiles are obtained on single Ni particles still adhering to the substrate after the Ni layer has been separated from it. A comparison of interface shapes and results of adherence measurements reveals Fe-Ni layered structures for the best adhering layers, whereas less adhering layers are characterized by narrower interfaces caused by diffusion. Areas with no adherence are covered with oxidic layers.