Sample Preparation Guidelines
Good sample preparation is essential for high-quality materials characterization. Most users will prepare their samples before accessing our facilities, but specialized equipment is available for those who need it.
The Department of Materials Engineering houses many sample preparation and polishing facilities. Consultation on your specific preparation needs is available upon request.
General Requirements
X-ray diffraction:
The goal of XRD sample preparation is to achieve a random distribution of crystallite orientations, a sufficient crystallite density, and a flat, well-defined surface. The right approach depends on your sample form.
Bulk solids can often be analyzed directly by cleaving or breaking off a representative piece with a reasonably flat surface. This is best suited to qualitative phase identification, as surface texture and preferred orientation can affect peak intensities.
Pulverization is the most reliable route to accurate, quantitative results. Grinding with a pestle and mortar (or ball mill for harder materials) to below ~10 μm is recommended. Wet grinding — using a compatible fluid such as ethanol — reduces heat-induced lattice strain and promotes uniform particle size. The fluid is then evaporated, leaving a dry powder for mounting.
Powder mounting options include:
- Back-loading into a holder ring for a smooth, flat surface — preferred for quantitative Rietveld analysis
- Top-loading/pressing with a glass slide — quick, but risks introducing preferred orientation if over-compacted
- Adhesive tape — dusting powder onto double-sided tape on a sample puck, suitable for very small quantities
- Smear mounts are useful for very small sample volumes. A small amount of powder is suspended in a mounting grease (e.g., petroleum jelly or silicone grease) and smeared thinly onto a glass slide or zero-background disc. The grease contributes a broad amorphous background, which should be accounted for in interpretation. Intentionally oriented smears can also be prepared for materials such as clay minerals.
Thin films and single crystals can typically be mounted and measured directly with minimal preparation.
Electron Microscopy:
All samples submitted for electron microscopy must be high-vacuum compatible — dry and free of oils or greases. In general, samples should be:
- As small as reasonably possible
- Structurally stable and non-degassing under moderate vacuum (chamber pressures are typically 10⁻³ to 10⁻⁵ Pa)
- Clean — wash using an ultrasonic bath with a suitable solvent, and handle only with gloves afterward
- Electrically conductive where possible; we can apply carbon or metallized coatings to assist with this
You should never handle your samples with bare hands, as you will transfer oils and grease to the sample. This impacts your analysis, and also makes our instruments dirty (impacting yourself and other users). We recommend the use of tweezers or gloves.
Sample Preparation Equipment
The following equipment is available to trained users or under our fee-for-service model.
Sectioning
Diamond Wafering Saw — A slow-speed, load-controlled diamond saw. Samples are cut using a lubricant and diamond wafering blade after being attached to an aluminum mounting post with a suitable adhesive.
Mounting
We maintain a stock of several cold mounting systems, suitable for fracture surfaces, as-prepared surfaces, and polished cross sections. Available systems include:
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Spurr-type low-viscosity resin
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Standard polyester epoxy resins
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LECOSet 100 cold-curing acrylic
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Technovit 5000 conductive polymer resin
A vacuum desiccator is available to remove bubbles from specimen mounts.
For SEM and FIB work, samples can be mounted on aluminum stubs (typically 12.5 mm diameter, pin-mount style — compatible with Zeiss, FEI, Thermo Fisher Scientific, and TESCAN instruments). Users are encouraged to supply their own stubs, though a small supply is available to get you started.
Samples can be secured using several adhesives. We recommend TEM wax, a hot wax that melts on a hot plate and dissolves in a suitable solvent. Alternatives include superglue, copper tape, or carbon tape.
All samples must have an electrical ground path to the pin stub, achieved via silver or carbon paint/dag, or copper tape.
A dedicated dry workspace with a long working-distance optical microscope is available to support sample mounting.
We have holders for a variety of different sample types, including a series of ‘vice grips’ and dedicated holders for SEM/EDX and EBSD of geological thin sections.
Polishing
Mechanical Polishing — For metal samples, a typical sequence involves SiC papers in decreasing grit size, followed by diamond slurry on a polishing cloth, and optionally a final polish with colloidal alumina or silica for high-quality finishes.
The EM lab has one dedicated polishing wheel for trained users. Members of the Department of Materials Engineering may also access additional wheels in the undergraduate laboratories when classes are not in session. Specialized equipment such as vibropolishing may be available through specific research groups — contact Heli Eunike for guidance on access.
Electropolishing — A dedicated Struers Tenupol 5 is available for automated electrolytic thinning, primarily used to prepare thin foils for (S)TEM studies of metals. It can also be used for conventional electropolishing (additional safety protocols apply when handling acids and/or cryogenic fluids).
Ion-Beam Polishing — A Gatan PECS II Broad Ion Beam (BIB) system is available, using Ar-ions to gently remove surface material with a variety of recipes. This is particularly useful for EBSD sample preparation. The PECS II can also prepare cross sections and coat single samples using a Cr or C target, which is ideal for very thin coating layers.
Note that chemical use in the lab requires suitable safety training, consult our policies page for more information.
Coating
A dedicated carbon coater is operated by Heli Eunike. Please provide your samples at least one business day before your session; multiple samples can be coated in a single run.
A new gold-coating system is expected to arrive approximately June 2026.
The PECS II can coat single samples using a Cr or C target, which is ideal for very thin coating layers.
(S)TEM sample preparation
In addition to mechanical polishing methods, TEM samples can be prepared using FIB cross sectioning using the AMBER-X (Xenon) plasma focussed ion beam system. This provides site specific lift out, but can be time consuming for multiple samples.
Sample preparation – charging:
For small, and one-off tries, we can often supply some of the items required but we may require reimbursement. For more substantial use, users should provide their own consumables. We can discuss compatibility with our equipment as required.
Materials Engineering reserachers can obtain many of the consumables directly from stores, and we maintain a modest range of supplies in the lab. For other users, we can discuss your needs.
For use of the coaters, typically the costs are ‘per sample’. Some users can be trained for more routine operation (e.g. of the PECS2 system) and this is subsequently charged per hour. You can find our rates on the charging page.