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A Guide to Scanning Microscope Observation
1
A Guide to
Scanning Microscope
Observation
JEOL
Ser ving Advanced Technology 2
A Guide to
Scanning Microscope
Observation
Table of contents
Preface
....................................................................................................................................................... 3
1.
Types of Image Disturbances .................................................................................................................... 4
2.
Image Changes Caused by Interactions Between Electron Probe and Specimen ............................... 5
2-1 Influence of accelerating voltage on image quality .......................................................................... 5
2-2 Probe current, probe diameter and image quality ............................................................................ 8
2-3 Influence of edge effect on image quality ......................................................................................... 9
2-4 Use of specimen tilt ........................................................................................................................... 10
a) Dependence of image quality on tilt angle ................................................................................. 10
b) Stereo micrographs ...................................................................................................................... 10
c) Detector position and specimen direction .................................................................................. 11
2-5 Use of backscattered electron signals ............................................................................................ 12
2-6 Influence of charge-up on image quality ......................................................................................... 14
a) Charge-up and countermeasures against it ............................................................................... 14
b) Prevention of charge-up by sampling ......................................................................................... 15
2-7 Specimen damage by electron beam ............................................................................................. 16
2-8 Contamination ................................................................................................................................... 17
3.
The Influence on Images, of Operational Technique, Specimen Preparation Technique,
External Disturbances, Etc ....................................................................................................................... 18
3-1 Working distance and objective aperture ........................................................................................ 18
a) Influence of working distance on images .................................................................................... 18
b) Influence of objective aperture diameter on images .................................................................. 18
3-2 Influence of astigmatism ................................................................................................................... 20
3-3 Optimum contrast and brightness of micrographs ......................................................................... 22
3-4 Exposure time for X-ray images ........................................................................................................ 23
3-5 Influence of external disturbances on images ................................................................................ 24
3-6 Deformation and impurity precipitation during specimen preparation process ........................... 25
3-7 Image distortion and its cause ......................................................................................................... 26
3-8 Coating .............................................................................................................................................. 28
a) Sputtering device .......................................................................................................................... 28
b) Vacuum evaporator ...................................................................................................................... 28
4.
Disturbances Caused by Intrumental Defects ........................................................................................ 30
4-1 Insufficient filament heating .............................................................................................................. 30
4-2 In correct alignment and centering of objective aperture .............................................................. 31
4-3 10 kV discharge of detector ............................................................................................................. 32
4-4 Burnt or dusty CRT ........................................................................................................................... 33
Technical terms ................................................................................................................................................ 34
Closing words/References .............................................................................................................................. 35 3
Preface
Preface
Preface
Preface
Preface
Today, the scanning electron microscope (hereinafter ab-
breviated to SEM) is utilized not only in medical science and
biology, but also in diverse fields such as materials develop-
ment, metallic materials, ceramics, and semiconductors.
This instrument is getting easier to use with the progress
of electronics and introduction of new techniques. Anybody
can now take micrographs after short-time training in its op-
erational procedure. However, when one has begun to use
the instrument, he cannot always take satisfactory photos.
When the photo is not sharp enough, or when necessary
information cannot be obtained, it is necessary to think what
causes it.
To help make a correct judgment in such a case, the first
edition of A Guide to Scanning Microscope Observation was
published and it has since been used by many people. To-
day, when several years have passed since the publication
of the first edition, some parts of the edition need amend-
ment with instrumental improvements. This is the reason
why we bring this revised edition to you.
We included in this book as many application examples as
possible so that they can be used as criteria for judging what
causes unsatisfactory image factors (hereinafter referred to
as image disturbances). Although this edition does not de-
scribe all about image disturbances, it carries application
photos to allow you to consider their causes. It is also im-
portant to correctly select the optimum observation condi-
tions fcr various specimens. For instance, this book carries
matters which are considered to be useful for using the in-
strument, such as the accelerating voltage, probe current
and working distance (hereinafter abbreviated to WD).
We shall be pleased if this publication is of help to people
who are now using or going to use SEMS. 4
Lack of sharpness
Low image quality
Noises
Image distortion and deformation
the basis of the data available at hand, for cases such as the
following:
1) The mutual interaction between the specimen and
the electron beam involves a problem.
2) Selection of observation conditions and specimen
preparation involve a problem.
3) The instrument itself involves a problem.
Table 1. Image Disturbances and Their Causes Improper accelerating voltage setting. Instability of gun emission caused by insufficient heating of filament. Improper electron probe diameter. Improper setting and incorrect centering of objective aperture. Insufficient astigmatism correction Improper focal depth Too large magnification Specimen charge-up and magnetization Defocus of camera system Improper accelerating voltage setting Improper probe current setting Incorrect astigmatism correction Noise caused by excessive photomultiplier (PMT) gain Improper contrast and brightness Improper specimen preparation process Improper photographic material Improper positional relation between specimen and detector No specimen tilting Instability of accelerating voltage anci gun emission Discharge of detector Charge-up of specimen surface Burnt CRT or dusty CRT screen External stray magnetic field Mechanical vibration Specimen charge-up External stray magnetic field Electron beam damage Deformation of specimen itself during its preparation Image drift caused by column interior charge-up Specimen drift on heating and cooling stages
Types of Image Disturbances
Image disturbances, though diverse in types, can be classified
by the following expressions:
1) Images lacking sharpness and contrast
2) Unstable images
3) Generally poor-quality images
4) Noisy images
5) Images showing jagged edges
6) Unusual-contrast images
7) Distorted or deformed images.
The above-listed image disturbances, besides being attributed
to defects in the instrument itself, are occasionally caused by the
operators lack of experience, improper specimen preparation and
external influences such as the installation room conditions.Table
1 shows various image disturbances and their causes.
In this booklet, how im