April 2, 2012

Fingerprint analysis via SEM

Analysis of fracture surfaces of samples is sometimes complicated by inadvertent contamination the the sample surfaces during sample preparation. Dust and other debris from the lab bench, in addition to particles generated from cutting instruments, can contaminate an otherwise clean surface. If gloves are not worn during sample preparation, finger oils and salts can be left behind. As an example, a prepared polymer surface was freshly prepared by cryofracturing the sample, so that no tooling was used. The sample was then briefly touched with a bare fingertip. The sample, when imaged under SEM, shows the crystalline structure outlined in the white rectangle shown above. The elemental composition of this crystalline material is shown below, and contains salt, chlorine, and potassium. The carbon and oxygen may be from the polymer background, and/or from finger oils transmitted with the fingerprint.