Lesson 3.  What kind of samples can we measure?

Properties and sizes of measurable samples

Properties of the sample
You can measure almost anything around you, such as inorganic compounds, organic substances, solids, liquids, gases, films, powders, liquids, and glass, without special pretreatment.

Sample size
Depending on whether it can be put on the stage of the microscope and the working distance of the objective lens, the size of the slide glass can be a guide. If it is large, the plane direction can be about 10 cm square and the thickness can be about 2 to 3 cm. In addition, since the field of view that can be observed at one time with the low magnification of the microscope is 1 to 2 mm square, if the measurement target can be limited within the area of one rice grain size, location search is relatively smooth. The field of view at high magnification is about 100 μm square.

If you want to observe the sample surface, it is OK if it is the size to be on the stage. Put in a petri dish of glass or a sample bottle so as not to spill out liquid. It is possible to measure over the container. If it is powdery or creamy, placing it on a slide glass or painting it is complete.

Example of measurable sample

Inorganic compoundPiping rust (classification of iron oxide valence)
Semiconductor materialSemiconductor crystal (crystal form, stress strain)
Li-ion battery materialCoating agent for battery electrode plate (Evaluation of crystallinity, evaluation of dispersed state)
Pharmaceutical materialsTablet (crystal polymorphism, component distribution evaluation)
PolymerOpaque polymer film, bulk
Transparent resin laminated film
Evaluation of crystalline polymer (alignment, crystallinity)
Other (water-containing sample etc)Oil / water emulsion in gel
Evaluation of inorganic compounds in toothpaste
Evaluation of water / oil / protein distribution in food

A sample that can perform nondestructive sample internal measurement and XZ imaging (nondestructive tomographic observation) is required to be transparent to visible light (approximate transparency). In addition, the thickness of the object to be observed needs to be about 1 μm or more.

Samples that need to be devised for measurement

Constituent of several percent in bulk
Depending on the intensity of the Raman activity, a concentration of several percent or more is generally required. If it is less than that, use a microtome to make thin sections if it is solid, or if it is semi-solid, put it between cover glasses and perform pretreatment such as thin spreading. By doing so, you may be able to suppress and detect background signals.

When the sample size is 1 μm or less
There is a part that overlaps with how to measure low concentration components, but the trick is to reduce the influence of background as much as possible. When the sample itself is strong in Raman activity and there is little background effect, some samples can be detected even below 1 μm, but this is generally a difficult case.

Rubber or PVC
Rubber materials are generally used in practical cases where a large amount of additives are contained, and they often make it difficult to detect Raman scattered light. For example, carbon black makes the sample black, making it susceptible to sample laser heat damage. Also, since many additives emit fluorescence, some pretreatment such as removing additives is often required.

Not available sample

Pure metal (crystal of metal bond)
In principle, metal-bonded crystals also cause Raman scattering. However, light can not enter metal, so it is very weak compared to inorganic compounds and organic substances, and it is very difficult to measure practically.