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Specimen Coating Technique for the SEM--A Comparative Study.

DeNee PB; Walker ER
Proceedings of the Eight Annual Scanning Electron Microscope Symposium, IIT Research Institute, Chicago, Illinois 1975 Apr:225-232
Vacuum evaporation and sputtering specimen coating methods were compared. Human lung tissue sections were cut into matching halves and mounted on aluminum scanning electron microscopy (SEM) stubs. One of the halves was coated by the vacuum evaporation technique and the other half was coated by sputtering. The coatings used for both methods were carbon, gold (Au), gold/palladium 60:40 (Au/Pd), carbon followed by Au, or carbon followed by Au/Pd. In the vacuum evaporation method, the Au or Au/Pd material was heated in a tungsten wire basket, with a source to sample distance of 8 centimeters (cm) and a vacuum of 0.5 to 0.0003 torr. Carbon coating was performed in the vacuum evaporation using a carbon arc, at a vacuum of 5 to 0.0003 torr and a source to sample distance of 8cm. The sputtered coating of Au or Au/Pd was performed using an Au or Au/Pd cathode. The unit had been calibrated to give a coating thickness of 100 angstroms at a vacuum of 0.2 torr, 10 milliamps current, 5cm working distance and 1 minute coating time. The carbon sputtering procedures were identical but used a carbon cathode. The specimens were then micrographed in the SEM at a tilt of 45 degrees. Uniformity of coating, absence of charging and heating during SEM examination, clarity of detail and absence of excessive heating during coating were all measured. The sputter coating technique with either Au or Au/Pd was the superior method. The next best technique was vacuum evaporation of carbon followed by Au or Au/Pd. Coating by vacuum evaporation of carbon was best when either X-ray analysis on backscatter electron imaging was required.
Analytical-methods; Coatings; Materials-testing; Sampling; Sample-preparation; Sampling-equipment; Laboratory-techniques;
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Proceedings of the Eight Annual Scanning Electron Microscope Symposium, IIT Research Institute, Chicago, Illinois
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