JEOL JSM-IT200 Instructions Manual page 216

6.1 FOR OBTAINING BETTER IMAGES
For the observation conditions of a specimen, you must select optimum values from various factors, such as
accelerating voltage, probe current, movable aperture, and working distance. You should also take into
consideration such as the sampling method (specimen preparation) and the specimen tilt. Moreover, in order
to obtain a more optimum image quality, the brightness adjustment, astigmatism correction adjustment and
focus adjustment become of importance.
6.1.1 Difference of image quality depending on the value of the
accelerating voltage
The higher the acceleration voltage, the thinner the electronic probe diameter, provided that only electronic
probe diameter is theoretically taken into account; however, drawbacks appearing when using a high
acceleration voltage cannot be disregarded. Some main points thereof are listed below:
a. The fine structure of the specimen surface is susceptible to damage.
b. Edge effect becomes significant.
c. Charge-up tends to easily occur.
d. Specimen damage tends to easily occur.
Generally, operation at low acceleration voltages results in fine structures more significantly appearing on the
specimen surface. At high voltages, the entry/diffusion area of the electron beam in the specimen is larger,
and accordingly unnecessary signals (e.g., reflected electrons) occurring from inside the specimen
deteriorate the contrast, thereby causing the fine structure on the specimen surface to be invisible. Thus,
low acceleration voltages are particularly preferred for observing low-density substances.
No.ISMIT200-1E
6-1