Ultra trace analysis of refractory metals by solid state mass spectrometry — A comparison of GDMS,SSMS and SIMS

A high resolution glow discharge mass spectrometer (GDMS VG 9000) has been used to analyze tungsten and molybdenum. Detection limits have been shown to be typically of the order of 1 ng/g or better in these matrices for integration times of 60 s per element. The results demonstrate that precisions of approximately 10% can be obtained on trace concentrations at the 10 ng/g level.     

Investigation of the analytical performance of gliding spark source mass spectrometry (GSSMS) for the trace analysis of nonconducting materials

A radiofrequency (rf) spark discharge in vacuum developing across the surface of dielectrics – a so-called gliding spark – has been applied to the direct mass spectrometric trace analysis of nonconducting materials. The special configuration of the electrodes strengthened the electric field over the surface of a nonconducting sample and created optimum conditions for the sputtering and ionization of the sample material. Mass spectrometric investigations of the charge composition of atomic ion and molecular ion formation in radiofrequency gliding spark plasma showed a significant difference to that of the original rf spark discharge between two conducting electrodes. The analytical figures of merit (reproducibility, relative sensitivity factors and detection limits of chemical elements) of gliding spark source mass spectrometry have been studied by using the glass standard reference materials NIST SRM 610 and 611 for the determination of trace elements in glass matrix.     

Investigation of the analytical performance of gliding spark source mass spectrometry (GSSMS) for the trace analysis of nonconducting materials

A radiofrequency (rf) spark discharge in vacuum developing across the surface of dielectrics – a so-called gliding spark – has been applied to the direct mass spectrometric trace analysis of nonconducting materials. The special configuration of the electrodes strengthened the electric field over the surface of a nonconducting sample and created optimum conditions for the sputtering and ionization of the sample material. Mass spectrometric investigations of the charge composition of atomic ion and molecular ion formation in radiofrequency gliding spark plasma showed a significant difference to that of the original rf spark discharge between two conducting electrodes. The analytical figures of merit (reproducibility, relative sensitivity factors and detection limits of chemical elements) of gliding spark source mass spectrometry have been studied by using the glass standard reference materials NIST SRM 610 and 611 for the determination of trace elements in glass matrix. Received: 31 March 1999 / Revised: 10 May 1999 / Accepted: 13 May 1999     

Optimization of an rf-powered magnetron glow discharge for the trace analysis of glasses and ceramics

A radiofrequency (rf) powered planar magnetron glow discharge ion source has been designed and coupled to a double-focusing mass spectrometer. Superposition of the electrical field of the plasma in the cathode dark space and the magnetic field obtained from a ring-shaped magnet located directly behind the sample (cathode) form the electron traps and enhance the sputtering and ionization efficiency of the ion source. In order to establish optimum conditions for the trace analysis of nonconducting materials, mass spectrometric studies have been carried out on the ion signal intensities and energy distributions of analyte and discharge gas ions depending on pressure.     

Optimization of an rf-powered magnetron glow discharge for the trace analysis of glasses and ceramics

A radiofrequency (rf) powered planar magnetron glow discharge ion source has been designed and coupled to a double-focusing mass spectrometer. Superposition of the electrical field of the plasma in the cathode dark space and the magnetic field obtained from a ring-shaped magnet located directly behind the sample (cathode) form the electron traps and enhance the sputtering and ionization efficiency of the ion source. In order to establish optimum conditions for the trace analysis of nonconducting materials, mass spectrometric studies have been carried out on the ion signal intensities and energy distributions of analyte and discharge gas ions depending on pressure.     

Inorganic trace analysis by mass spectrometry

Mass spectrometric methods for the trace analysis of inorganic materials with their ability to provide a very sensitive multielemental analysis have been established for the determination of trace and ultratrace elements in high-purity materials (metals, semiconductors and insulators), in different technical samples (e.g. alloys, pure chemicals, ceramics, thin films, ion-implanted semiconductors), in environmental samples (waters, soils, biological and medical materials) and geological samples. Whereas such techniques as spark source mass spectrometry (SSMS), laser ionization mass spectrometry (LIMS), laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), glow discharge mass spectrometry (GDMS), secondary ion mass spectrometry (SIMS) and inductively coupled plasma mass spectrometry (ICP-MS) have multielemental capability, other methods such as thermal ionization mass spectrometry (TIMS), accelerator mass spectrometry (AMS) and resonance ionization mass spectrometry (RIMS) have been used for sensitive mono- or oligoelemental ultratrace analysis (and precise determination of isotopic ratios) in solid samples. The limits of detection for chemical elements using these mass spectrometric techniques are in the low ng g⁻¹ concentration range. The quantification of the analytical results of mass spectrometric methods is sometimes difficult due to a lack of matrix-fitted multielement standard reference materials (SRMs) for many solid samples. Therefore, owing to the simple quantification procedure of the aqueous solution, inductively coupled plasma mass spectrometry (ICP-MS) is being increasingly used for the characterization of solid samples after sample dissolution. ICP-MS is often combined with special sample introduction equipment (e.g. flow injection, hydride generation, high performance liquid chromatography (HPLC) or electrothermal vaporization) or an off-line matrix separation and enrichment of trace impurities (especially for characterization of high-purity materials and environmental samples) is used in order to improve the detection limits of trace elements. Furthermore, the determination of chemical elements in the trace and ultratrace concentration range is often difficult and can be disturbed through mass interferences of analyte ions by molecular ions at the same nominal mass. By applying double-focusing sector field mass spectrometry at the required mass resolution—by the mass spectrometric separation of molecular ions from the analyte ions—it is often possible to overcome these interference problems. Commercial instrumental equipment, the capability (detection limits, accuracy, precision) and the analytical application fields of mass spectrometric methods for the determination of trace and ultratrace elements and for surface analysis are discussed.     

Application of RF GDMS for trace element analysis of nonconducting La0.65Sr0.3MnO3 ceramic layers

Radio-frequency glow discharge mass spectrometry (RF GDMS) has been applied to the determination of trace elements in ceramic perovskite layers (La_0.65Sr_0.3MnO₃) using synthetic standards. For the preparation of these standards high-purity powder of the basic material (La_0.65Sr_0.3MnO₃) was doped with trace elements in concentrations from 20 to 500 μg/g and the mixture was pressed to compact samples. The resulting calibration curves and the calculated relative sensitivity factors (RSF) differed only from 0.4 to 2 for different elements. For nearly all elements the standard deviations in the determination of trace elements in La_0.65Sr_0.3MnO₃ were better than 15% and detection limits (using the 3σ-criterion) were below 10 μg/g. Changes of the discharge parameters (RF power, pressure of the discharge gas (Ar) in the RF glow discharge) have no significant influence on the sensitivity to elements.     

Determination of trace concentrations of elements in high purity tellurium by radio frequency glow discharge optical emission spectrometer (RF-GDOES)

A method was established for the determination of trace impurities in high purity tellurium (Te) 99.9999 (6N) by radio frequency glow discharge optical emission spectrometry (RF-GDOES). The optimized parameters are power, argon pressure, pre-integration time, analysis time and selection of wavelength. Nine elements Se, Ca, Mg, Si, Fe, Cr, Cu, Ni and Pb were analysed in 6N Te, out of which only three elemental peaks (Se, Ca, and Mg) were detected and the remaining six elements ( Si, Fe, Cr, Cu, Ni and Pb) were below detection levels. Finally, the method was evaluated by the analysis of the above traces using inductively coupled plasma mass spectrometry (ICP-MS) and was found to be satisfactory. The detection limits for most of the elements were below 10 ng/g and R.S.D. was around 10%, which indicated that this method could fully satisfy the requirements for the trace analysis in high purity Te metal.     

Studies of LA-ICP-MS on quartz glasses at different wavelengths of a Nd:YAG laser

The capability of LA-ICP-MS for determination of trace impurities in transparent quartz glasses was investigated. Due to low or completely lacking absorption of laser radiation, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) proves difficult on transparent solids, and in particular the quantification of measurement results is problematic in these circumstances. Quartz glass reference materials of various compositions were studied by using a Nd:YAG laser system with focused laser radiation of wavelengths of 1064 nm, 532 nm and 266 nm, and an ICP-QMS (Elan 6000, Perkin Elmer). The influence of ICP and laser ablation conditions in the analysis of quartz glasses of different compositions was investigated, with the laser power density in the region of interaction between laser radiation and solid surface determining the ablation process. The trace element concentration was determined via calibration curves recorded with the aid of quartz glass reference materials. Under optimized measuring conditions the correlation coefficients of the calibration curves are in the range of 0.9-1. The relative sensitivity factors of the trace elements determined in the quartz glass matrix are 0.1-10 for most of the trace elements studied by LA-ICP-MS. The detection limits of the trace elements in quartz glass are in the low ng/g to pg/g range.     

Studies of LA-ICP-MS on quartz glasses at different wavelengths of a Nd:YAG laser

The capability of LA-ICP-MS for determination of trace impurities in transparent quartz glasses was investigated. Due to low or completely lacking absorption of laser radiation, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) proves difficult on transparent solids, and in particular the quantification of measurement results is problematic in these circumstances. Quartz glass reference materials of various compositions were studied by using a Nd:YAG laser system with focused laser radiation of wavelengths of 1064 nm, 532 nm and 266 nm, and an ICP-QMS (Elan 6000, Perkin Elmer). The influence of ICP and laser ablation conditions in the analysis of quartz glasses of different compositions was investigated, with the laser power density in the region of interaction between laser radiation and solid surface determining the ablation process. The trace element concentration was determined via calibration curves recorded with the aid of quartz glass reference materials. Under optimized measuring conditions the correlation coefficients of the calibration curves are in the range of 0.9–1. The relative sensitivity factors of the trace elements determined in the quartz glass matrix are 0.1–10 for most of the trace elements studied by LA-ICP-MS. The detection limits of the trace elements in quartz glass are in the low ng/g to pg/g range.     

Parametric evaluation of laser ablation and ionization time-of-flight mass spectrometry with ion guide cooling cell

A novel laser ablation and ionization time-of-flight mass spectrometer has been used for direct elemental analysis of alloys. The system was incorporated with an ion guide cooling cell to reduce the kinetic energy distribution for the purpose of better resolution. Parametric studies have been conducted on the system with respect to the buffer gas pressure and the distance from sample to the nozzle to obtain the maximal signal intensities. In order to obtain satisfactory relative sensitivity coefficients (RSC) for different elements, the influence of the laser irradiance, nozzle voltage, rf frequency and voltage of the hexapole were also investigated. Under the optimized conditions, the RSC of different elements were available for direct semi-quantitative analysis. The mass resolving power (FWHM) of the spectrometer was approximately 7000 (m/Δm) and the limit of detection (LOD) was 10^− 6 g/g.     

Applications of inductively coupled plasma mass spectrometry and laser ablation inductively coupled plasma mass spectrometry in materials science

Inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) have been applied as the most important inorganic mass spectrometric techniques having multielemental capability for the characterization of solid samples in materials science. ICP-MS is used for the sensitive determination of trace and ultratrace elements in digested solutions of solid samples or of process chemicals (ultrapure water, acids and organic solutions) for the semiconductor industry with detection limits down to sub-picogram per liter levels. Whereas ICP-MS on solid samples (e.g. high-purity ceramics) sometimes requires time-consuming sample preparation for its application in materials science, and the risk of contamination is a serious drawback, a fast, direct determination of trace elements in solid materials without any sample preparation by LA-ICP-MS is possible. The detection limits for the direct analysis of solid samples by LA-ICP-MS have been determined for many elements down to the nanogram per gram range. A deterioration of detection limits was observed for elements where interferences with polyatomic ions occur. The inherent interference problem can often be solved by applying a double-focusing sector field mass spectrometer at higher mass resolution or by collision-induced reactions of polyatomic ions with a collision gas using an ICP-MS fitted with collision cell. The main problem of LA-ICP-MS is quantification if no suitable standard reference materials with a similar matrix composition are available. The calibration problem in LA-ICP-MS can be solved using on-line solution-based calibration, and different procedures, such as external calibration and standard addition, have been discussed with respect to their application in materials science. The application of isotope dilution in solution-based calibration for trace metal determination in small amounts of noble metals has been developed as a new calibration strategy. This review discusses new analytical developments and possible applications of ICP-MS and LA-ICP-MS for the quantitative determination of trace elements and in surface analysis for materials science.     

Radiochemical neutron activation analysis of ultra-pure molybdenum-based microelectronic materials for detrimental impurities

A radiochemical neutron activation analysis method, based on the separation of the radionuclides by anion-exchange from a 20 mol/l HF/3% H₂O₂ medium, was applied to the analysis of ultra-high purity molybdenum oxide and molybdenum metal and high-purity molybdenum silicide for 29 elements including the detrimental impurities Co, Cr, Fe, K, Na, Ni, Th, U and Zn. The achievable limits of detection for these elements are between 0.02 ng/g (for Co) and 50 ng/g (for K). The results were compared with those obtained by glow discharge mass spectrometry, inductively coupled plasma atomic emission and mass spectrometry, isotope dilution mass spectrometry and slurry sampling and direct solid sampling ETAAS. On the basis of the comparison of the results, the feasibility of the methods for analysis of these ultrapure materials is discussed.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Chemical analysis of thin films by means of SS-MS, GD-OES, and XPS demonstrated at Ir-Si thermoelectrica

Analytical methods with low detection limits were used for the investigation of Ir-Si thin films, the physical properties of which vary strongly with the chemical composition and the amount of impurities. It is demonstrated how to solve chemical characterization of different thermoelectric Ir-Si thin films by spark source mass spectrometry (SS-MS), glow discharge optical emission spectroscopy (GD-OES) and X-ray photoelectron spectroscopy (XPS). The combined use of the three different facilities allows the quantification of impurities of elements of the entire periodic system in the ppm range (down to 30 at.-ppm in dependence on the element) incorporated in thin film samples. Additional information about the in-depth distribution of elements or specifically bonded species can be achieved with a high depth resolution. Received: 6 April 1998 / Revised: 9 July 1998 / Accepted: 14 July 1998     

Direct Quantification of Major and Trace Elements in Geological Samples by Time-of-Flight Mass Spectrometry with a Pulsed Glow Discharge

A method has been developed for the determination of 24 elements (As, B, Ce, Co, Dy, Fe, K, La, Lu, Mg, Mn, Na, Nb, Nd, P, Pr, Rb, S, Sb, Si, Sm, Th, Ti, and U) in ore samples by pulsed direct current glow discharge time-of-flight mass spectrometry (PGD-TOF-MS). Sample treatment consisted of pressing the powdered samples into 10?mm diameter aluminum tablets. Quantification was performed using relative sensitivity factors with iron as the normalization element. PGD-TOFMS has low spectral interferences and low limits of detection and provides the quantification of the wide range of elements with a single method instead of a combination of several techniques. The limits of detection of the designed method were in the range 2–4?×?10^?6 mass %, depending on the element. The designed procedure was validated by the analysis of standard reference materials. The obtained results showed adequate repeatability (6–9% relative standard deviation), demonstrating high efficiency of the glow discharge mass spectrometry for the direct analysis of geological samples. The designed method requires a minimal sample pretreatment and is applicable for the determination of wide range of elements of the periodic table (e.g., metals, nonmetals, and rare earth elements) in a single analytical procedure without sample dissolution with adequate accuracy, sensitivity, and repeatability. The designed approach may replace the complex techniques that are normally required for this task.     

Chemical analysis of thin films by means of SS-MS, GD-OES, and XPS demonstrated at Ir-Si thermoelectrica

Analytical methods with low detection limits were used for the investigation of Ir-Si thin films, the physical properties of which vary strongly with the chemical composition and the amount of impurities. It is demonstrated how to solve chemical characterization of different thermoelectric Ir-Si thin films by spark source mass spectrometry (SS-MS), glow discharge optical emission spectroscopy (GD-OES) and X-ray photoelectron spectroscopy (XPS). The combined use of the three different facilities allows the quantification of impurities of elements of the entire periodic system in the ppm range (down to 30 at.-ppm in dependence on the element) incorporated in thin film samples. Additional information about the in-depth distribution of elements or specifically bonded species can be achieved with a high depth resolution.     

Isotope dilution mass spectrometry of microelectronically relevant heavy metal traces in high-purity cobalt

Summary Because cobalt and its silicides are increasingly used in microelectronic devices, an isotope dilution mass spectrometric (IDMS) method has been developed for trace analysis of relevant heavy metals (U, Th, Fe, Zn, Tl, and Cd) in high-purity cobalt. The measurements of the isotope ratios were carried out with a small thermal ionization quadrupole mass spectrometer by producing positive thermal ions in a single- or double-filament ion source. For the trace/matrix separation and the isolation of the different heavy metals, anion-exchange chromatography and an extraction method for iron were applied. The detection limits obtained were (in ng/g): U=0.007, Th=0.017, Tl=0.06, Cd=1, Zn=8, and Fe=11, which demonstrates that the particularly critical radioactive impurities uranium and thorium could be analysed down to the low pg/g range. Three cobalt samples of different purity were analysed with concentrations ranging from about 0.1 ng/g for U and Th in an ultra high-purity material produced for microelectronic purposes, up to about 70 g/g for Cd in a cobalt sample with declared purity of 99.8%. Because IDMS usually results in accurate analytical results, it can be used in the future for calibration of other methods like glow discharge mass spectrometry, as could be shown by analysing one cobalt sample by both methods. IDMS can also be applied for the production of urgently needed certified standard reference materials in this important field of high technology.Presented at the ANAKON '93 conference     

A glow discharge ion source with fourier transform ion cyclotron resonance mass spectrometric detection

A glow discharge (CD) ion source has been coupled to a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer using a four-element electrostatic lens to accelerate and focus ions generated external to the instrument’s high magnetic field into its analyzer cell. Like other CD mass spectrometers, GD-FT-ICR can provide a quantitative measure of bulk analyte concentration with good precision and accuracy. Although detection limits currently attainable are several orders of magnitude higher than the commercially available magnetic sector-based instrument, CD-FT-ICR holds promise for ultrahigh resolving power elemental mass analysis. Several schemes are proposed to lower the detection limits of the technique while still providing high enough resolution to resolve isobaric interferences.     

Investigations on cluster and molecular ion formation by plasma mass spectrometry

The formation of molecular and cluster ions of different inorganic materials in plasma mass spectrometry – spark source mass spectrometry (SSMS), radiofrequency glow discharge mass spectrometry (rf GDMS), laser ionization mass spectrometry (LIMS), inductively coupled plasma mass spectrometry (ICP-MS) and laser ablation ICP-MS (LA-ICP-MS) – was investigated and compared. Similar abundance distributions of cluster ions were observed for a graphite sample, for boron nitride/ graphite and for metal oxide/graphite mixtures using different plasma mass spectrometric methods. A correlation of intensities of metal argide ions in ICP-MS with their bond dissociation energies was used to estimate unknown dissociation energies of molecular ionic species. For the elements of the 2nd or 3rd period in the periodic table, the intensities of most argon molecular ions (ArX⁺) measured by ICP-MS rise with increasing atomic number in a similar manner to the theoretically calculated bond dissociation energies of argon molecular ions.     

Application of the glow discharge mass spectrometry (GDMS) for the multi-element trace and ultratrace analysis of sputtering targets

Glow discharge mass spectrometry using a VG9000 high resolution mass spectrometer has been applied to both the multi-element trace and ultra trace analyses of sputtering target materials, i.e. aluminium-based alloys, cobalt-based alloys, titanium and platinum. Element dependent relative sensitivity factors (RSF) have been determined using reference materials in order to provide the possibility for quantitative analyses. Aluminium-based and cobalt-based alloys have been extensively analysed to demonstrate precision of GDMS analyses. Detection limits in the ng/g and sub-ng/g ranges, i.e. 0.2 ng/g for U and Th have been determined in aluminium-based alloys. Comparative analyses for alloy components in cobalt-based alloys as well as trace concentrations in titanium have been performed. GDMS has been also applied to multi-element depth profile analyses in contaminated and noncontaminated platinum targets.