• Metals & Alloys
• Geology, Petrology & Mining
• Electronics & Semiconductors
• Energy Generation & Storage
• Forensics
• Environment

Here we present some data collected from a stainless steel with published compositions using AZtecWave. These measurements were made with an Ultim Max 100 mm² EDS detector and a Wave WDS spectrometer. Combined EDS-WDS analysis was carried out using an accelerating voltage of 20kV. The major constituent elements in the stainless steel were measured by EDS, and the concentrations of the trace constituents: Co and P, were measured by WDS. As shown in the data table, there is a good match between the measured and published compositions.

EDS-WDS Results

Table: Quantitative, combined EDS-WDS results obtained from a stainless steel of known composition using AZtecWave. 

Geology, Petrology, and Mining

Determining the minor and trace element concentrations in minerals and rocks is important in the fields of geological research, planetary research, natural hazard monitoring, mineral exploration, and mining. Minor and trace elements present in rocks and minerals can give information on their origin, evolution, age, and whether they are economically important. AZtecWave can be used to measure elements that are present in concentrations that are too low to measure accurately using EDS, or where overlaps between X-ray energy lines for different elements exist. Some specific examples include:

• The analysis of minor and trace element concentrations in minerals present in volcanic rocks, giving information on crystallisation and eruptive processes, such as variations in Sr concentrations from core to rim in plagioclase phenocrysts.
• Determining rare earth element (REE) concentrations in minerals such as monazite. The REE have multiple peak overlaps, and can occur in trace amounts, making them difficult to measure using EDS alone. The increased energy resolution and peak to background ratio provided by WDS allows these elements to be accurately quantified.

A simulated WDS spectrum for the mineral monazite, showing the high occurrence of peak line overlaps amongst the rare earth elements. This particular window shows the automatic line and background position selection, in this case for Praseodymium, available in AZtecWave. In this instance, AZtecWave has automatically selected to measure the Pr Lβ peak to avoid the inaccuracies caused by the overlap of the La Lβ peak on the Pr Lα peak.

• The analysis of platinum group elements that are typically present in low concentrations
• The accurate analysis of low levels of economically important elements that can be used to inform processing and production
• The non-destructive and accurate compositional analysis of rare samples or those that have not been measured before (e.g., meteorites)
• U-Th-Pb dating of minerals such as monazite. Accurate and quantitative determinations of the concentrations of U, Th and Pb present in minerals can be used to calculate crystallisation ages based on the U and Th radioactive decay schemes.

This is a comparison of U-Th-Pb chemical ages for monazite (determined by SEM-WDS) and isotopic ages (determined by SHRIMP and TIMS) showing a good correlation between the ages determined by the different techniques. Image from Slagstad (2006).

An example of using SEM-WDS to determine the age of an unknown monazite grain is presented here. U, Th and Pb concentrations were measured using a Wave WDS spectrometer. The analysis was conducted using an accelerating voltage of 20kV and a beam current of 49.5 nA. The overall analytical time was just over 2 hours, and this time is primarily made up of long peak and background counting times on U, which is in low concentration <0.01 wt.% in this particular monazite grain. The WDS counting times and results are shown in the below data table.

WDS Analytical Conditions and Results

*Table: WDS analytical conditions and quantitative results for U, Th and Pb obtained from an unknown monazite grain using AZtecWave.

These results, specifically the measured Pb concentrations, yield an age of 1385 Ma (i.e., million years old) for this particular monazite grain, when using the equation of Montel et al. (1996). Thus demonstrating that U-Th-Pb age dating of monazite is possible with the new generation Wave WDS spectrometer and AZtecWave.

Electronics and Semiconductors

In the development and manufacturing of key components accurate compositional information is required, at a confidence level that cannot be achieved with EDS analysis alone. Some specific examples, where WDS provides the sensitivity and resolution required, include:

• Concentrations of antimony and tin in solder
• Determining the compositions of bond wires, specifically the levels of platinum group elements that may exist at low concentrations
• Quantifying trace levels of elements in magnetic materials
• Investigating the composition of dopants in silicon wafers

To learn more on how to use SEM-based Wavelength Dispersive Spectroscopy (WDS) to measure highly doped semiconductor layers, click here.

Energy Generation and Storage

In the development of new materials for energy generation and storage, and in the production and maintenance of components, elemental compositions need to be determined with a high level of accuracy. This information goes on to inform future directions, and to ensure quality control and safety. Some specific examples, where WDS can achieve the degree of accuracy required, include:

• Determining the concentrations of many trace elements present in glass or ceramic materials related to nuclear waste storage
• Determining low concentrations of hafnium in zirconium oxides, where an overlap exists between the X-ray lines for these two elements

Forensics

Obtaining reliable and reproducible forensic evidence is critical to ensure it can undergo scrutiny in a court of law. Composition information is required on a wide range of forensics samples, from gunshot residue, to soil and minerals. This information can be obtained non-destructively using a SEM and X-ray microanalysis techniques (e.g., EDS, WDS). When key elements are present in low concentrations and EDS cannot produce an accurate enough result, or there is uncertainty over the presence of an element, WDS can provide the detection levels (<100ppm for many elements) required.

Here we present some data collected from glass of known composition using AZtecWave. These measurements were made using an Ultim Max 100 mm² EDS detector, combined with a Max+ interface, and a WaveWDS spectrometer. The combined EDS-WDS analysis was carried out using an accelerating voltage of 20kV and a beam current of 82 nA. The minor/trace element (Mg, S, Ti, Fe, As and Ba) compositions were measured using WDS, and the major elements were determined by EDS. Known pure elements and simple compounds were measured as WDS standards prior to the quantitative analysis of the glass sample. The in-built, factory standards, provided in the AZtec software, were used for the EDS. As demonstrated in the below table, a good match is observed between the measured and published compositions.

WDS Analytical Conditions and Results

*Table: Quantitative, combined EDS-WDS results obtained from a glass standard of known composition using AZtecWave. Oxygen has been calculated by stoichiometry.

Environment

WDS can be used for environmental studies when it is required to precisely and accurately measure small concentration of contaminants that could be introduced into biological systems after environmental disasters, such as oil spills.

Testing for the possible incorporation of Fe²⁺ ions in the crystalline structure of coralline algae after the world’s biggest mining disaster, which spilled up to 60 million m³ of ore tailing in Brazilian protected coastal areas. Measurements were performed using WDS due to better sensitivity and precision. WDS is an essential tool for the measurement of small amounts of contaminants in biological samples. The research can determine whether the contaminant ions can be trapped inside the crystalline structure.

Download this application note to learn:

• How WDS allows better sensitivity and precision in quantitative microanalysis
• How WDS can be used for study of natural disasters
• Highly sensitive and high precision measurements

References

• Slagstad, T.R.O.N.D., 2006. Chemical (U–Th–Pb) dating of monazite: Analytical protocol for a LEO 1450VP scanning electron microscope and examples from Rogaland and Finnmark, Norway. NGU-Bulletin, 443, pp.11-18
• Jean-Marc Montel, S.F., Veschambre, M. and Nicollet, C., 1996. Electron microprobe dating of monazite. Chemical Geology, 131, pp.37-53