Question 1

How does micro-XRF differ from conventional XRF?

Accepted Answer

How does micro-XRF differ from conventional XRF?

While both conventional XRF and micro-XRF utilize x-ray fluorescence for elemental analysis, they differ significantly in spatial resolution and sample handling. Micro-XRF employs specialized focusing optics, such as polycapillary optics, to concentrate the x-ray beam into a small spot, typically around 30 µm. This enables high-resolution, spatially resolved analysis and is paired with a motorized stage for precise scanning across the sample surface.

In contrast, conventional XRF uses a broader x-ray beam to analyze bulk samples, resulting in lower spatial resolution. It lacks the capability for detailed stage scanning, making it more suitable for homogeneous samples.

Why does the coincidence of the high-magnification view and x-rays depend on focus in a traditional micro-XRF tool, but not with the EDAX Orbis II?

What can micro-XRF measure?

Is sample preparation required?

Is micro-XRF destructive?

How is data presented in micro-XRF?

What are the main differences between a tabletop micro-XRF and a micro-XRF integrated with SEM?

How does the sensitivity of micro-XRF compare to SEM EDS?

What is the spatial resolution of micro-XRF?

What is process time and how does it influence data quality?

Why is my spectrum noisy?

How do I improve map quality?

When is vacuum mode required?

In contrast, conventional XRF uses a broader x-ray beam to analyze bulk samples, resulting in lower spatial resolution. It lacks the capability for detailed stage scanning, making it more suitable for homogeneous samples.

Question 2

Why does the coincidence of the high-magnification view and x-rays depend on focus in a traditional micro-XRF tool, but not with the EDAX Orbis II?

Accepted Answer

As shown in the figure below, when the focal plane shifts from the top surface to the bottom of the specimen, the EDAX^® Orbis™ II system maintains precise alignment because its x-ray beam is perpendicular and coaxial with the high-magnification view of the specimen. This ensures that the x-ray beam always strikes the intended target, regardless of changes in focus.

In contrast, a traditional micro-XRF tool uses an angled x-ray path. When the focus changes, the intersection point of the angled x-ray beam and the optical axis moves, causing the x-rays to hit a different location on the sample. This misalignment can lead to measurements from the wrong area, reducing accuracy.

Question 3

What can micro-XRF measure?

Accepted Answer

Micro-XRF can detect a wide range of elements (from carbon or sodium to americium) and is suitable for analyzing solids, powders, liquids, as well as irregular or non-conductive samples. It’s especially useful in applications such as:

Forensics
Inclusion analysis
Cultural heritage
Electronics
Geology
Coating thickness measurement

Question 4

Is sample preparation required?

Accepted Answer

Minimal preparation is required. Samples can be solid, irregular, or coated. Flatness is preferred for optimal focus, but not mandatory. Non-conductive samples do not require coating.

Question 5

Is micro-XRF destructive?

Accepted Answer

No, it is a non-destructive technique, making it suitable for valuable or sensitive samples.

Question 6

How is data presented in micro-XRF?

Accepted Answer

Data is typically shown as elemental maps, spectra, and quantitative reports.

Question 7

What are the main differences between a tabletop micro-XRF and a micro-XRF integrated with SEM?

Accepted Answer

Another approach to micro-XRF involves integrating an x-ray source and x-ray optics with a scanning electron microscope (SEM). In this setup, the x-ray source excites the sample, and the energy dispersive spectroscopy (EDS) detector mounted on the SEM captures the resulting fluorescent x-rays. Together, the x-ray source and EDS detector function as a micro-XRF analyzer within the SEM.

This configuration allows for the generation of high-energy characteristic x-rays (typically above 20 kV), which can be advantageous for certain applications. However, samples must be specially prepared to be placed in the SEM chamber under vacuum conditions, which often requires polishing and coating. Additionally, the sample size is constrained by the physical limitations of the SEM chamber and stage, making it unsuitable for larger specimens.

In contrast, a standalone benchtop micro-XRF system offers greater flexibility. It can accommodate larger samples and typically requires less preparation, making it a more versatile option for a wider range of applications.

Question 8

How does the sensitivity of micro-XRF compare to SEM EDS?

Accepted Answer

Micro-XRF generally offers higher sensitivity than SEM-EDS for heavier elements (higher atomic number, such as transition metals). Detection limits for micro-XRF often reach the ppm (parts per million) range, typically 10x better than those achievable with SEM-EDS.

However, for light elements (e.g., B, C, N, O, F), SEM-EDS provides better sensitivity. This is because the excitation of lower energy x-rays is more efficient in an SEM. Also, these low energy x-rays are more easily absorbed before detection. Many micro-XRF systems use a beryllium window, which blocks low-energy x-rays, making light elements difficult or impossible to detect.

Orbis II uses a thin silicon nitride (Si₃N₄) window instead of traditional beryllium, allowing better transmission of low-energy x-rays and improving light element detection. Nevertheless, SEM-EDS systems can employ windowless detectors, which are not available in micro-XRF systems.

Question 9

What is the spatial resolution of micro-XRF?

Accepted Answer

The spatial resolution of micro-XRF typically ranges from approximately 30 – 300 µm, depending on both the specimen characteristics and the type of x-ray optics used. In many practical cases, the specimen itself plays a more critical role in determining resolution than the optics. This is because the x-ray interaction volume is influenced by the specimen’s physical properties, such as composition and density. In addition, uneven surfaces can scatter x-rays unpredictably, broadening the excitation volume and reducing spatial resolution. Therefore, even with high-performance optics, the material’s nature often becomes the limiting factor in achieving fine spatial detail.

Question 10

What is process time and how does it influence data quality?

Accepted Answer

The process (also known as amp time or shaping time) refers to the duration the pulse processor in a silicon drift detector (SDD) takes to shape and filter the signal from each x-ray photon event.

Longer process times improve energy resolution by producing cleaner, more distinguishable peaks. They also reduce electronic noise and minimize pulse pile-up, but at the cost of a lower maximum count rate.
Shorter process times allow for higher count rates, which is beneficial for fast data acquisition such as elemental mapping. However, they introduce more electronic noise, leading to poorer energy resolution and increased risk of pulse pile-up at high count rates.

As a result:

High count rate applications (e.g., mapping) benefit from shorter process times.
High energy resolution applications (e.g., trace element analysis or peak deconvolution) require longer process times for optimal performance.

Question 11

Why is my spectrum noisy?

Accepted Answer

The most common reason is that the sample is not emitting enough x-rays. To improve the spectrum quality, you can:

Increase the measurement time to collect more x-ray events.
Raise the excitation power to stimulate stronger x-ray emission.
Use a shorter process (amp) time to increase data throughput, though this may slightly compromise energy resolution.

Question 12

How do I improve map quality?

Accepted Answer

To enhance the quality of elemental maps, focus on increasing the x-ray counts per pixel and improving spatial resolution:

Increase the x-ray counts per pixel

Extend dwell time: Collect more x-ray events at each pixel by increasing the time spent measuring.
Raise excitation power: Stimulate stronger x-ray emission for higher signal intensity.
Use a shorter process (amp) time: Boost data throughput, though this may slightly reduce energy resolution.

Improve spatial resolution

Use a smaller spot size: Focus the x-ray beam more tightly to resolve finer details.
Increase pixel density: Use smaller pixel sizes for a given area to capture more spatial detail.

Question 13

When is vacuum mode required?

Accepted Answer

Vacuum mode is recommended when analyzing lighter elements (e.g., C, N, O, F, Na, Mg, Al, Si). These elements emit lower-energy x-rays that are easily absorbed by air, so operating in vacuum helps minimize absorption and improves detection sensitivity.

Micro-XRF FAQs

How does micro-XRF differ from conventional XRF?

Why does the coincidence of the high-magnification view and x-rays depend on focus in a traditional micro-XRF tool, but not with the EDAX Orbis II?

What can micro-XRF measure?

Is sample preparation required?

Is micro-XRF destructive?

How is data presented in micro-XRF?

What are the main differences between a tabletop micro-XRF and a micro-XRF integrated with SEM?

How does the sensitivity of micro-XRF compare to SEM EDS?

What is the spatial resolution of micro-XRF?

What is process time and how does it influence data quality?

Why is my spectrum noisy?

How do I improve map quality?

When is vacuum mode required?