A Comparison of Herbarium Daried,Critical Point Daried and Fresh Plant Material Using High Vacuum and Variable Pressure SEM

摘要

In conventional high vacuum SEM, the vacuum is maintained throughout the column from the gun region at the top of the microscope to the specimen chamber below. However, in variable pressure SEM a differential pumping system, in conjunction with pressure limiting apertures, maintains high vacuum in the gun region while it is progressively reduced down through the column until a partial pressure of I mbar is achieved in the chamber (Figure I). Nitrogen gas is bled into the chamber and when the primary electron beam scans across the sample, some electrons will Figure I:A simple diagram showing the pressure zones of the variable pressure SEM.