Each instrument translates a different interaction into evidence. Compare what the signal reveals, what the specimen demands, and where interpretation can go wrong.
Surface shape, molecular labels, optical anisotropy, and crystal structure are different questions. Magnification alone cannot tell you which method to choose.
The methods below are currently available at Phoenix College. Use the comparisons to understand what each signal can reveal, then contact Dr. Ong about specimen suitability, training, and access arrangements.
In an April 2024 college profile, Dr. Eddie Ong directed the Center for Microscopy and mentored student SEM work on Sonoran ironwood. The story also described student learning with AFM, FTIR, and XRD. Phoenix College’s academic affairs directory lists Ong as Chair of Physical Sciences.
These methods are currently available. Contact Dr. Ong to discuss your specimen, training, and access arrangements.
Begin with the property you need to measure, then follow the signal that can reveal it.
SEM maps fine surface form. Detector choice can add composition-related contrast.
02 / TRANSMITTED ELECTRONSWhat lies within a thin specimen?TEM uses electrons passing through a thin sample to reveal internal structure.
03 / TIP–SAMPLE FORCEHow high, rough, or mechanically different?AFM follows topography with a probe and can map local properties in suitable modes.
04 / FLUORESCENT LIGHTWhere is a labeled structure in depth?Confocal detection excludes much out-of-focus fluorescence to form optical sections.
05 / POLARIZED LIGHTDoes orientation change the light?Crossed polarizers reveal birefringence in minerals and other anisotropic materials.
06 / COMPLEMENTARY TOOLSWhich bonds or crystal phases are present?FTIR supplies a molecular spectrum; XRD investigates crystalline structure.
A focused electron beam scans a specimen. Secondary electrons emphasize near-surface detail; backscattered electrons can provide contrast related to material differences.
SEM with energy-dispersive X-ray spectroscopy (EDS) is available at Phoenix College. The characteristic X-rays add elemental evidence to the image; spectra and maps still require careful interpretation.
Mount securely. Poorly conductive samples may charge; grounding, a conductive coating, lower beam energy, or a low-vacuum mode may help, depending on the instrument.
Coatings, drying, beam exposure, and charging can change the image or introduce artifacts. Preserve detector, voltage, preparation, and scale information.
An SEM image and an elemental map answer related, but different, questions. Secondary electrons emphasize near-surface shape. Backscattered-electron contrast can reflect material differences as well as geometry. EDS adds characteristic X-rays that provide evidence about elements in the sampled region.
At Phoenix College SEM with EDS is available. Contact Dr. Ong to discuss sample preparation, training, and access arrangements.
Transmission electron microscopy (TEM) records electrons passing through an electron-transparent specimen. It can reveal internal ultrastructure rather than only the near-surface form seen in a typical SEM image.
What appears in a TEM image depends on scattering, specimen thickness, preparation, and electron dose. A two-dimensional view can superimpose features at different depths. Any color added after acquisition is a display choice, not the specimen’s natural color.
Prepare a very thin section or small particles on a support grid, using a method appropriate to the material. Staining, drying, and freezing can each affect what is preserved.
Record preparation and imaging conditions, look for beam or processing artifacts, and rely on a calibrated scale rather than display magnification.
Atomic force microscopy measures interactions between a sharp tip and a surface. A cantilever’s response becomes a height map rather than a conventional photograph.
In contact mode, the tip stays against the sample. In tapping mode it touches intermittently, reducing lateral forces that can disturb softer or loosely attached specimens. Specialized modes can map other local properties, but the available modes depend on the instrument and probe.
A stable, accessible surface and a suitable probe matter. Choose the scan area and imaging force to suit the material.
The tip has finite width: narrow raised features may appear wider, while trenches may appear narrower. Check probe condition before treating lateral dimensions as exact.
Fluorophores absorb light and emit it at longer wavelengths. In confocal microscopy, a detection pinhole rejects much of the out-of-focus fluorescence.
Serial optical sections can show where labeled structures sit within a thicker specimen. The labeled target, controls, objective, and acquisition settings determine what those bright regions mean.
Label selectively and choose mounting conditions that preserve the structure of interest. A thicker sample may need a series of focused planes.
Repeated excitation can bleach fluorophores and damage living specimens. Use the lowest practical illumination and document exposure and image processing.
Between crossed polarizers, birefringent material splits light into components that recombine as changes in brightness and interference color.
Rotate the specimen to see how the contrast changes with orientation. This is especially useful for mineral thin sections, but also applies to suitable polymers and other anisotropic materials.
For transmitted-light mineral work, prepare a suitably thin section. Uniform thickness makes comparison more meaningful.
Interference color depends on birefringence, thickness, and orientation. Color alone is not a unique mineral identity.
Microscopy locates and describes features. Spectra and diffraction patterns can answer different questions about the same material.
Fourier-transform infrared spectroscopy records which infrared frequencies a sample absorbs. The pattern reflects molecular vibrations and can help identify materials or functional groups.
Choose it for a chemical fingerprint, while remembering that a conventional FTIR spectrum does not show where a feature sits in the image.
Bruker: FTIR fundamentals ↗X-ray diffraction measures patterns produced by ordered atomic planes. Compare those patterns with reference data to identify crystalline phases and investigate structure.
Choose it when composition alone cannot distinguish crystal forms; diffraction does not replace an image of morphology.
NIST: crystalline phase identification ↗FTIR and XRD are currently available at Phoenix College. Its 2024 student profile describes earlier learning with these methods under Dr. Ong. Contact him about specimen suitability, training, and access arrangements.
See labeled visual examples, then ask Dr. Ong about a specimen, training, or access arrangements.
