Reflection electron microscopy (REM) of NaCl crystals

NaCl and other alkaline halide crystals are unstable under the electron beam and therefore have seldom been examined with the various electron beam techniques. Surfaces of these crystals, however, are of fundamental and application interests. There has been a considerable effort in studying these surfaces using the replica methods. Reflection high energy electron diffraction (RHEED) and reflection electron microscopy (REM) have been successfully applied to the study of stable insulators. Since direct observation on an uncoated surface is always desirable, we tried RHEED and REM on cleaved NaCl(100) surfaces. The experiment was carried out on a JEOL JEM-200CX electron microscope with a high tilt side-entrystage. The accelerating voltage of lOOkV was used throughout the experiment. There is no special protection to the specimen except the standard anti-contamination cold finger. The initial effort of doing ordinary REM on NaCl was a failure: When the electron beam and the specimen were properly tilted toget a good RHEED pattern, the bright pattern remained for only a couple of seconds and then turned into a pattern of weak spots and high diffuse background. The bright REM image also lost its contrast in a few seconds.