M Specimen Preparation:

TEM examination can only be carried out on solid materials.

TEM specimen preparation varies according to the form of the sample i.e, bulk, thin film, powder, cross sections, biological and polymeric forms.

Bulk specimens are prepared in two stages: first stage is pre-perforation stage, which is obtaning a 3 mm diameter, 60 µm thickness thin foil through a series of mechanical initial thinning followed by perforation to electron transparency, which is the second stage.

For intial thinning:

• Disc Grinder

• Dimple Grinder

• Disc Punch

• Diamond Saw (Struers Accutom 50 Precision Cutting and Grinding Machine)

For Perforation to Electron Transparency:

• PIPS (Gatan Precision Ion Polishing System):

• Electropolisher (Struers Tenupol 5 Twin-Jet Electropolisher): Only for Metallic Materials

Powder samples are prepared by obtaining a suspension in alcohol, water or methanol and then by dropping a small drop by means of a syringe or micropipet onto a suitable type of grid and finally by drying overnight at room temperature conditions. Initial powder size should be less than 100 nm in order to obtain a disperse and homogeneous distribution and electron transparent area. Otherwise, non-electron transparent, huge agglomerated areas will be observed during microscopic examination instead of distinct individual features.

Thin films, which are removed from the substrate by the applicant, are put into a sandwich type grid and then examined in the microscope.

Cross-sectional samples are generally prepared by Focused Ion Beam (FIB) Technique and by use of cross section kits. Gatan Cross Section kit is used to obtain cross section samples while FIB is not present at TEM Laboratories of METU Central Laboratory.

Biological samples are not prepared in Central Laboratory on the other hand, microscopic examination of as-ready biological TEM sections are carried out in High Contrast Transmission Electron Microscope.

Bulk polymeric materials are prepared by obtaining very thin slices by sectioning in an ultra-microtome and then by putting into a suitable grid.

Polymeric thin films can be prepared by spin coating technique, which is not available at TEM Laboratories of METU Central Laboratory.

Some tools used in TEM sample preparation are

• Various type and mesh size grids

i.e.

400 Square mesh Cu-grid, 3mm diameter,

100mesh/100mesh folding Cu-grids, 3mm diameter,

Very fine mesh grids

1500 mesh thin bar grids, 3mm diameter,

Holey carbon film on 400mesh Copper, 3mm diameter,

Lacey carbon film on 300mesh Copper, 3mm diameter,

Square quanti-foil 300 mesh, Copper, 3mm diameter,

Carbon Film Coated Copper, 3 mm diameter,

150 mesh Berillium Grid.

• Film forming solutions

i.e.

pioloform, formwar, butvar

• Subsidiary Tools

i.e.

Ultrasonic Cleaner (Bandelin RK-210H, 10 lt capacity),

Stereomicroscope (Olympus model SZ-61, light source)