Mechanical damage introduced into aluminum monocrystals during TEM thin-foil preparation

Abstract

The mechanical damage that is introduced into annealed aluminum by the various steps used in the preparation of thin foils for transmission electron microscopy (TEM) is discussed. These steps are: (1) preparation of 3-mm discs by mechanical punching; (2) preparation of 3-mm discs by spark-cutting; and (3) intermediate thinning by hand-grinding discs to thicknesses of 500, 375, 300, or 200 ..mu..m. Often these steps precede the final electrochemical jet-thinning used to obtain perforated TEM foils. The mechanical damage produced by these steps was evaluated by comparing, in the TEM, thin foils utilizing one of these steps with other thin foils of annealed (undamaged) aluminum. Damage was manifested by an increased dislocation density. The mechanical punching was performed on a device machined at the Lawrence Livermore National Laboratory that was very similar to smaller, commercially available punches. The spark-cutting was performed on a Metal Research LTD Servomet at a setting of 6 using a tubular brass cutting tool. Jet-thinning was done on a Struers Tenupol 2 using an electrolyte of 469 mL methyl alcohol, 25 mL H/sub 2/SO/sub 4/ and 6 mL HF at 265 K. Thinning was performed at 25 V. The aluminum (99.999% pure) was provided by Highways Internationalmore » as plate (1 x 100 x 100 mm). The plate was annealed at 723 K for 20 min in vacuum. The resulting average grain size was about 4 mm. Therefore, the discs that were punched, spark-cut, and ground were smaller than the typical grain or monocrystal.« less