Question 1

What is EDS and how does it work?

Accepted Answer

Energy dispersive x-ray spectroscopy (EDS/EDX) detects x-rays emitted from a sample when bombarded by electrons (usually in an SEM). Each element emits characteristic x-ray energies, enabling identification and quantification of elements present in the sample.

Question 2

What elements can EDS detect?

Accepted Answer

EDS typically detects elements from boron (Z=5) to uranium (Z=92). Light elements, like lithium (Li), are challenging due to low x-ray yields and absorption.

Question 3

How accurate is EDS for quantification?

Accepted Answer

Standardless (semi-quantitative): Routinely gives values with ~5 – 10% relative error.
Standards-based: Enables ~1 – 2% precision, but requires high-quality standards, more attention to detail, and a more complex workflow.

Question 4

What does “standardless quantification” mean?

Accepted Answer

Standardless quantification means that the software estimates composition using algorithms without physical standards. There are two common algorithms for this: ZAF (atomic number, absorption, fluorescence) and P/B-ZAF (peak to background-ZAF).

Question 5

What do I need to be aware of when using the ZAF standardless model?

Accepted Answer

There are three general assumptions that underlie the ZAF model.

The sample is flat.
The sample is homogenous at the scale of the interaction volume.
All the beam energy is deposited in the sample.

If any of these assumptions are not met, the model may have problems.

Question 6

What do I need to do to perform quantitative analysis?

Accepted Answer

Quantitative analysis, also known as standards-based, requires that the assumptions are met for the quantification model (for ZAF, see above) before use and that you utilize high-quality microanalytical standards.

To ensure accurate quantitative EDS analysis:

Sample and standard preparation: Polish both your samples and standards to a submicron finish and ensure they are mounted perfectly flat. This minimizes surface irregularities that can affect measurement accuracy.
Homogeneity: Use standards that are homogeneous at the scale of the electron beam’s interaction volume. Inhomogeneous standards can introduce significant errors in quantification.
Reference calibration: Incorporate a reliable reference value to correct for variations in beam current and instrument geometry. This step is essential for consistent and reproducible results.

Question 7

What's the difference between EDS and WDS?

Accepted Answer

Energy dispersive x-ray spectroscopy (EDS):

Rapid analysis as it collects all x-ray energies at once.
Simpler operation and faster results.
Lower spectral resolution (typically ~123 eV for Mn Kα), which can make it harder to distinguish between elements with closely spaced x-ray lines.

Wavelength dispersive x-ray spectroscopy (WDS):

Uses Bragg diffraction with crystals to separate x-ray wavelengths.
Offers much higher spectral resolution—usually at least ten times better than EDS—allowing for more precise identification of elements, especially those with overlapping peaks.
More sensitive for trace element detection.
Slower and more complex to operate.

Summary:

EDS is preferred for quick, routine analyses, while WDS is chosen when higher resolution and sensitivity are required, despite its slower and more involved process.

Question 8

Why do unexpected carbon or oxygen peaks appear in my EDS spectrum?

Accepted Answer

The presence of carbon or oxygen peaks in your spectrum, when these elements are not expected in your sample, is typically due to surface contamination. Common sources include:

Sample handling: Oils and residues from fingers or tools can transfer contaminants.
Sample preparation: Inadequate cleaning or exposure to air can introduce surface films.
Sample aging: Prolonged storage may allow atmospheric contaminants to accumulate.
Instrument cleanliness: A dirty microscope chamber or sample holder can contribute additional contaminants.

To minimize these unwanted peaks, handle samples with gloves or clean tools, ensure thorough cleaning during preparation, and maintain a clean instrument environment.

Question 9

What determines the lateral spatial resolution of WDS/EDS?

Accepted Answer

The lateral spatial resolution in both WDS and EDS is influenced by several factors:

Material density: Denser materials restrict the interaction volume, resulting in finer spatial resolution.
Accelerating voltage (kV): Higher beam voltages increase the interaction volume, reducing spatial resolution; lower voltages improve it.
X-ray energy and matrix effects: The energy of the x-ray line being measured, relative to the sample matrix, affects how localized the signal is.
Sample complexity: Irregular geometries or heterogeneous materials can further impact resolution.

For most bulk samples under standard conditions, you can expect a lateral spatial resolution of approximately 0.5 – 3 µm. For more precise estimation, Monte Carlo simulation models are often used to account for sample-specific variables.

Question 10

Can EDS perform elemental mapping?

Accepted Answer

Yes, EDS can generate elemental x-ray maps that visually display the spatial distribution of elements within your sample. These maps not only reveal where specific elements are located but can also be quantified to provide compositional information. Modern EDS detectors are particularly effective for mapping, as they can collect high-quality data rapidly and efficiently, even at elevated count rates.

Question 11

How can I collect elemental maps more quickly with EDS?

Accepted Answer

Total throughput for EDS is controlled by the amp time of the detector, the Deadtime and the beam current of the SEM. Max count rate is achieved at the 0.240 µs amp time. The user must be aware that at this amp time.

To reduce the time required for elemental mapping in EDS, focus on optimizing these key parameters:

Amplifier time (amp time):
Shorter amp times allow the detector to process signals more rapidly, increasing the total count rate. The maximum count rate is typically achieved at an amp time of 0.240 μs. However, be aware that very short amp times may slightly reduce energy resolution and cause the loss of lower energy peaks (Boron and Carbon ).
Deadtime:
Deadtime is the period when the detector cannot process new events because it is still handling previous signals. Aim to keep the deadtime within the recommended range (often 20–40%) to balance speed and data quality.
SEM beam current:
Increasing the electron beam current raises the number of x-rays generated, which can speed up mapping. However, too high a current may cause sample damage or detector saturation.

Tip: For the fastest high-quality maps, use the shortest amp time that maintains acceptable resolution, adjust the beam current appropriately, and monitor deadtime to avoid excessive data loss.

Question 12

What’s the difference between ROI, NET, and ZAF maps?

Accepted Answer

Region of interest (ROI) maps: These maps include all counts under the selected x-ray peak, including background signals. They do not correct for overlapping peaks from different elements. The region is defined as the peak plus or minus a set number of channels, determined by the peak’s resolution.
NET maps: NET maps subtract the background and mathematically deconvolve overlapping peaks, providing a more accurate representation of the element’s true signal.
ZAF maps: ZAF maps are fully quantified. Each pixel in the map is processed through the complete quantification routine, resulting in maps that show both weight percent and atomic percent for each element.

Question 13

What beam conditions should I use for EDS analysis?

Accepted Answer

The optimal beam conditions for EDS depend on your analytical goals:

Exciting x-ray lines: Select an accelerating voltage (kV) that is approximately twice the energy of the highest x-ray line you wish to detect. This ensures efficient excitation and maximizes x-ray generation for your elements of interest.
Balancing resolution and sensitivity: If your priority is higher spatial resolution—such as when analyzing fine features or thin layers—consider using a lower accelerating voltage. While this may reduce the overall x-ray yield, it limits the interaction volume and improves lateral resolution.

Summary:

For most analyses, use an accelerating voltage ≈ 2x the highest characteristic x-ray energy of interest. 15KV works for most day to day work.
For finer spatial resolution, reduce the voltage, but be aware of possible decreases in signal strength.

Adjust other parameters (such as beam current and working distance) as needed to further optimize for your specific sample and analytical requirements.

Question 14

Why is my gold (Au) peak so strong in the EDS spectrum?

Accepted Answer

A pronounced gold peak often indicates that your sample has been coated with a conductive layer (commonly gold (Au), carbon (C), or other element) to improve imaging and prevent charging during SEM analysis. If the coating is relatively thick, most of the detected x-ray signal may originate from the coating itself rather than the underlying sample. This can overshadow the elemental signals from your actual specimen and lead to misleading results.

Tip: To minimize this effect, apply the thinnest conductive coating necessary for your analysis and, if possible, use alternative methods (such as low-vacuum SEM modes) for non-conductive samples.

Question 15

Can EDS detect hydrogen or helium?

Accepted Answer

No, EDS cannot detect hydrogen or helium because these elements do not produce characteristic x-rays when bombarded by electrons. As a result, they are invisible to standard EDS analysis. To quantify hydrogen, EDS can be combined with other specialized techniques designed for light element detection (e.g., Cipher®).

Question 16

What are peak overlaps, and how can I resolve them?

Accepted Answer

Peak overlaps occur when two or more elements in your sample emit x-rays with energies that are very close together. This can make it difficult to distinguish between the elements in your EDS spectrum.

Minor overlaps: For small overlaps, modern EDS software can often separate (deconvolve) the signals accurately, provided there is enough statistical data.
Challenging overlaps: When overlaps are significant or involve elements with nearly identical x-ray energies, EDS may not be able to resolve them reliably. In these cases, wavelength dispersive spectroscopy (WDS) is recommended, as it offers much higher spectral resolution and can distinguish between closely spaced peaks.

Question 17

Can EDS be combined with EBSD or CL?

Accepted Answer

Yes, modern scanning electron microscopes (SEMs) can integrate energy dispersive x-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), and cathodoluminescence (CL) detectors. This allows you to simultaneously collect complementary data on elemental composition (EDS), crystallographic structure (EBSD), and luminescence properties (CL) from the same region of your sample. Combining these techniques provides a more comprehensive understanding of your material’s chemistry, structure, and optical behavior.

Question 18

What is the difference between SNIP and Bremsstrahlung backgrounds?

Accepted Answer

Statistical non-linear iterative peak (SNIP) clipping: SNIP is a mathematical filtering method used to estimate the background in x-ray spectra. It does not require user input and provides consistent, visually appealing fits regardless of sample geometry or surface condition. SNIP is especially useful for qualitative analysis of non-ideal samples, such as fracture surfaces or particles. However, because it is a filtering approach, it may mask underlying issues (“red flags”) in the data.
Bremsstrahlung background: This approach uses a physical model that considers the sample’s geometry and composition to calculate the theoretical background signal. If the Bremsstrahlung model produces a poor fit, it often indicates that the model’s assumptions (which are similar to those used in quantitative analysis) are not met. In such cases, quantification results may be unreliable.

Summary: SNIP is fast, user-friendly, and robust for qualitative work, but may hide data quality issues. Bremsstrahlung modeling is more rigorous and diagnostic—if the fit is poor, it signals potential problems with sample preparation or analysis assumptions. For more details, see: Tips and tricks: Background analysis and modeling.

Question 19

What are sum peaks in EDS spectra?

Accepted Answer

Sum peaks are spectral artifacts that occur when two x-ray photons strike the detector almost simultaneously. The detector electronics cannot distinguish them as separate events, so it records a single event with an energy equal to the sum of the two individual x-ray energies. This results in an artificial peak at a higher energy, which does not correspond to any real element in the sample. Recognizing sum peaks is important for accurate interpretation of EDS data.

Question 20

How can I simplify my EDS analysis?

Accepted Answer

EDS analysis can be complex, but there are tools and workflows designed to make it easier. EDAX APEX™ software streamlines the process, offering intuitive features for data collection, interpretation, and reporting. For practical tips and a detailed guide on how APEX can help simplify your EDS analysis, read our Insight article: Tips and tricks: Analysis is easier with APEX.

Question 21

Why is the background signal in EDS analysis important, and how can APEX™ help interpret it?

Accepted Answer

Read our Tips and Tricks article on Background analysis and modeling.

Question 22

How can I improve EDS quantification when analyzing small structures or surface contaminants at low overvoltage?

Accepted Answer

Read our Tips and Tricks article on Low overvoltage quantification with SCC.

Question 23

Why is the background signal in EDS analysis important, and how can APEX help interpret it?

Accepted Answer

The background signal in EDS analysis plays a crucial role in accurate data interpretation. Understanding and modeling the background helps distinguish real elemental peaks from artifacts, leading to more reliable results. EDAX APEX™ software offers advanced tools for background analysis and modeling, making it easier to interpret complex spectra. For a detailed guide and practical tips, read our Tips and Tricks article:
Background analysis and modeling

Question 24

How can I improve EDS quantification when analyzing small structures or surface contaminants at low overvoltage?

Accepted Answer

Accurate EDS quantification of small structures or surface contaminants at low overvoltage can be challenging. Specialized workflows and tools, such as those described in the SCC method, can help improve results. For practical tips and a detailed guide on low overvoltage quantification, read our Tips and Tricks article:
Low overvoltage quantification with SCC.

EDS FAQs

What is EDS and how does it work?

What elements can EDS detect?

How accurate is EDS for quantification?

What does “standardless quantification” mean?

What do I need to be aware of when using the ZAF standardless model?

What do I need to do to perform quantitative analysis?

What's the difference between EDS and WDS?

Why do unexpected carbon or oxygen peaks appear in my EDS spectrum?

What determines the lateral spatial resolution of WDS/EDS?

Can EDS perform elemental mapping?

How can I collect elemental maps more quickly with EDS?

What’s the difference between ROI, NET, and ZAF maps?

What beam conditions should I use for EDS analysis?

Why is my gold (Au) peak so strong in the EDS spectrum?

Can EDS detect hydrogen or helium?

What are peak overlaps, and how can I resolve them?

Can EDS be combined with EBSD or CL?

What is the difference between SNIP and Bremsstrahlung backgrounds?

What are sum peaks in EDS spectra?

How can I simplify my EDS analysis?

Why is the background signal in EDS analysis important, and how can APEX™ help interpret it?

How can I improve EDS quantification when analyzing small structures or surface contaminants at low overvoltage?

Why is the background signal in EDS analysis important, and how can APEX help interpret it?

How can I improve EDS quantification when analyzing small structures or surface contaminants at low overvoltage?