Q: Do all samples need coating?

Non-conductive samples typically need a thin conductive coating (gold, platinum, or carbon) to prevent charging artifacts. Gold and platinum provide excellent signal but may obscure fine surface detail. Carbon coating is preferred for EDS analysis to avoid interference with elemental peaks. Low vacuum mode can image some non-conductive samples without coating, though resolution may be reduced.

Q: How do I prepare biological samples?

Biological samples require fixation (typically glutaraldehyde), dehydration through an ethanol or acetone series, and critical point drying to preserve structure without collapse. After drying, mount on stubs with conductive adhesive and sputter coat. For quick imaging, some samples can be air-dried and examined in low vacuum mode, though structural preservation is not as good.

Q: What is the best way to mount samples?

Use conductive mounting materials: carbon tape, silver paint, or conductive epoxy. Carbon tape is convenient for most samples. Silver paint provides excellent conductivity for powders and small particles. Ensure good electrical contact between the sample and stub to prevent charging.

Q: How do I handle powder samples?

Sprinkle powders onto carbon tape or apply with a fine brush. For better dispersion, suspend in ethanol or isopropanol and drop onto a stub. Blow off loose particles with compressed air or nitrogen before inserting into the chamber. Consider using conductive adhesive tabs for very fine powders.

Q: Can I image wet or hydrated samples?

Standard SEM requires dry samples due to the vacuum environment. Wet samples will outgas and contaminate the chamber. Options include: critical point drying for biological samples, freeze-drying for some applications, or using an environmental SEM (ESEM) that operates at higher pressures.

Q: How do I reduce charging artifacts?

Several strategies can minimize charging: (1) Lower accelerating voltage reduces charge accumulation, (2) Apply conductive coating, (3) Use low vacuum mode to neutralize charge with gas ions, (4) Reduce beam current, (5) Scan faster to prevent charge buildup, (6) Ensure good grounding between sample and stub.

Q: When should I use BSE vs SE imaging?

Use SE (secondary electrons) for topography—surface texture, edges, and morphology. SE images look three-dimensional with shadowing. Use BSE (backscattered electrons) for compositional contrast—phases with different average atomic numbers appear with different brightness. Heavy elements appear bright; light elements appear dark. BSE is excellent for identifying inclusions, precipitates, and multi-phase materials.

Q: What accelerating voltage should I use?

It depends on your goal. Lower voltages (1-5kV) provide surface-sensitive imaging with reduced charging and beam damage. Higher voltages (15-30kV) penetrate deeper, provide better resolution, and are necessary for EDS analysis of heavy elements. For EDS, use 1.5-2× the energy of the highest X-ray peak you need to analyze.

Q: How do I get the best resolution?

Optimize resolution by: (1) Using a clean, well-prepared sample, (2) Reducing working distance, (3) Using appropriate accelerating voltage, (4) Minimizing vibration, (5) Ensuring the column is well-aligned and the filament is properly saturated, (6) Using slower scan speeds with frame averaging for final images.

Q: Why is my image drifting?

Image drift can be caused by: (1) Thermal expansion as the sample or stage warms up, (2) Sample outgassing, (3) Charging effects, (4) Mechanical instability, (5) Magnetic interference. Let samples stabilize in vacuum for a few minutes before high-magnification imaging. Ensure samples are fully dry and properly grounded.

Q: What causes image contamination (dark rectangles)?

Contamination buildup occurs when hydrocarbons in the chamber polymerize under the electron beam. To reduce contamination: (1) Use clean samples, (2) Avoid fingerprints and organic residues, (3) Plasma clean samples before imaging, (4) Keep the chamber clean, (5) Use lower beam currents when possible.

Q: What is the detection limit for EDS?

Typical detection limits are 0.1-1% by weight, depending on the element, matrix, and acquisition conditions. Light elements (B, C, N, O) have higher detection limits due to low X-ray yields and absorption. Longer acquisition times improve detection limits by improving counting statistics.

Q: Why can’t I detect light elements well?

Light elements produce low-energy X-rays that are easily absorbed by the sample, detector window, and any contamination. To improve light element detection: (1) Use lower accelerating voltage to reduce absorption path length, (2) Ensure clean, flat samples, (3) Use a windowless or thin-window detector, (4) Acquire for longer times.

Q: How accurate is EDS quantification?

Standardless quantification is typically accurate to ±5-10% relative. Using standards improves accuracy to ±1-2% relative. Accuracy depends on sample preparation, peak overlap correction, and appropriate ZAF matrix corrections. For highest accuracy, use well-characterized standards similar to your samples.

Q: What is the sampling volume for EDS?

X-rays are generated from a pear-shaped interaction volume that extends 0.5-5 micrometers into the sample, depending on accelerating voltage and material density. This means EDS samples subsurface material, not just the surface. Lower voltage reduces the interaction volume for better spatial resolution.

Q: How often should I change the filament?

Tungsten filaments typically last 40-100 hours of operation, depending on usage conditions. Signs of filament aging include reduced brightness, unstable emission, and degraded image quality. Keep a log of operating hours and change the filament before it fails to avoid contaminating the column.

Q: How do I clean the SEM chamber?

Periodically clean the chamber with lint-free wipes and isopropanol. Remove any debris or sample fragments. Vacuum the stage area gently. For persistent contamination, plasma cleaning can remove hydrocarbon deposits. Avoid touching the detector or any optical components.

Q: What routine maintenance is required?

Regular maintenance includes: (1) Filament changes as needed, (2) Periodic chamber cleaning, (3) Checking and topping off any cooling water, (4) Monitoring vacuum levels, (5) Annual service for pump maintenance and column alignment. Keep the SEM area clean and climate-controlled for best performance.

Q: How does a desktop SEM compare to a floor-model?

Desktop SEMs achieve 5nm or better resolution—sufficient for most applications. Main differences: smaller chamber limits sample size, some desktop SEMs have fewer detector options, and maximum accelerating voltage may be lower. Benefits include lower cost, smaller footprint, faster pump-down, and simpler operation.

Q: What sample sizes can I image?

The SNE-Alpha accommodates samples up to 70mm diameter on the standard stage. Height clearance depends on working distance requirements. Larger samples may need to be sectioned. The 5-axis stage allows imaging of tilted samples for topographic views.

Q: Do I need special facility requirements?

Desktop SEMs have minimal requirements: standard electrical outlets, a stable bench, and reasonable temperature and humidity control. No water cooling, compressed air, or special vibration isolation is typically required. Avoid locations near heavy machinery, elevators, or other vibration sources.