handbook of sample preparation for scanning electron microscopy and x ray microanalysis

Handbook of Sample Preparation for Scanning

Electron Microscopy and X-Ray Microanalysis

Handbook of Sample

Preparation for

Scanning Electron

Microscopy and X-Ray

Microanalysis

Patrick Echlin

Cambridge Analytical Microscopy, UK

Patrick Echlin

Cambridge Analytical Microscopy, UK

[email protected]

ISBN: 978-0-387-85730-5 e-ISBN: 978-0-387-85731-2

DOI: 10.1007/978-0-387-85731-2

Library of Congress Control Number: 2008942785

© Springer Science+Business Media, LLC 2009

All rights reserved. This work may not be translated or copied in whole or in part without the written permission of

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Printed on acid-free paper

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For Alexander, Charles, Patrick, Francesca, Maeve,

and William in the fond hope that some of them might

become scientists.

I am dedicating this book to my six grandchildren

and thanking a lot of people for their help and, finally for my wife's

patience over the past five years.

Books must follow science, and not science books.

–Francis Bacon, 1657

Acknowledgments

This book would not have been possible without the help of many

people. I am privileged to have been working in this field for the

past 45 years and am indebted to the many friends and colleagues

from all over the world who have listened to my ideas, corrected my

errors, and provided practical advice. I am also grateful to the many

people and manufacturers who have provided information and

illustrations for this book and who are acknowledged in the text.

I am particularly grateful to my colleagues with whom I have

taught at the Lehigh Microscopy School for the past 32 years.

They have been a constant source of enlightenment and their

constructive and critical analysis of my work and writings has

been very supportive.

Finally, gratitude to Joe Michael for the use of one of his micro￾graphs as a cover illustration for this book.

Patrick Echlin

Cambridge, January 2009

ix

Contents

Acknowledgments ........................................................................ ix

Chapter 1 Introduction ............................................................ 1

Chapter 2 Sample Collection and Selection ....................... 11

Chapter 3 Sample Preparation Tools .................................... 19

Chapter 4 Sample Support ..................................................... 31

Chapter 5 Sample Embedding and Mounting ................... 47

Chapter 6 Sample Exposure ................................................... 65

Chapter 7 Sample Dehydration ............................................. 97

Chapter 8 Sample Stabilization for Imaging

in the SEM............................................................... 137

Chapter 9 Sample Stabilization to Preserve

Chemical Identity .................................................. 185

Chapter 10 Sample Cleaning ................................................... 235

Chapter 11 Sample Surface Charge Elimination .................. 247

Chapter 12 Sample Artifacts and Damage ............................ 299

Chapter 13 Additional Sources of Information .................... 307

References ....................................................................................... 317

Index ................................................................................................ 323

xi

Scanning electron microscopy (SEM) and x-ray microanalysis can

produce magnified images and in situ chemical information from

virtually any type of specimen. The two instruments generally

operate in a high vacuum and a very dry environment in order to

produce the high energy beam of electrons needed for imaging and

analysis. With a few notable exceptions, most specimens destined

for study in the SEM are poor conductors and composed of beam

sensitive light elements containing variable amounts of water.

In the SEM, the imaging system depends on the specimen being

sufficiently electrically conductive to ensure that the bulk of the

incoming electrons go to ground. The formation of the image

depends on collecting the different signals that are scattered

as a consequence of the high energy beam interacting with the

sample.

Backscattered electrons and secondary electrons are generated

within the primary beam-sample interactive volume and are the

two principal signals used to form images. The backscattered

electron coefficient ( η ) increases with increasing atomic number

of the specimen, whereas the secondary electron coefficient ( δ ) is

relatively insensitive to atomic number. This fundamental differ￾ence in the two signals can have an important effect on the way

samples may need to be prepared. The analytical system depends

on collecting the x-ray photons that are generated within the

sample as a consequence of interaction with the same high

energy beam of primary electrons used to produce images.

1. The use of scanning electron microscopy and x-ray microa￾nalysis may be considered under three headings.It is first

necessary to understand the actual process of microscopy and

analysis. This is not considered here in any detail because my

colleagues and I have produced an excellent textbook that

covers these processes in great detail (Goldstein et al., 2004).

1

Introduction

P. Echlin, Handbook of Sample Preparation for Scanning Electron Microscopy

and X-Ray Microanalysis, DOI: 10.1007/978-0-387-85731-2_1,

© Springer Science + Business Media, LLC 2009

1

2 1. Introduction

2. It is necessary to consider how to prepare samples prior to

microscopy and analysis. These procedures are the topic of

this book.

3. It is necessary to be able to interpret the information obtained

from the SEM and attempt to relate the form and structure

of the two-dimensional images and the identity, validity, and

location of the chemical data back to the three-dimensional

sample from which the information was derived. This is a

topic of continuing debate.

There are two approaches to dealing with the frequent impasse

that may exist between the properties of the sample and the

optimal operating conditions of the SEM. We can either modify

the instruments so they employ less invasive procedures or we

can modify the specimen to make it more robust to the withering

beam of high energy electrons. The former approaches are dis￾cussed in the book by Goldstein et al. (2004); the latter approach

is considered here. With a few exceptions, both approaches are a

compromise.

Sample preparation is an absolute prerequisite for microscopy

and analysis.

Every specimen that goes into the SEM needs some form of

sample preparation. There are no exceptions.

Consider carrying out microscopy and analysis on the compo￾nents at our breakfast table. After drinking our fresh orange juice,

we use a knife to butter our toast before we drink our coffee. The

glass containing our juice is composed of a beam resistant, non￾conducting, non-crystalline, light element solid. The orange juice

and the coffee are wet, non-conducting, biopolymer composed of

light element materials that are very bean sensitive. The buttered

toast is a thermally and beam sensitive, non-conducting, damp,

light element biopolymer. The knife is made of a beam resistant

conducting metal that, in spite of being washed, is dirty. The

plastic plate is made of a beam sensitive, non-conducting, light

element polymer and the coffee cup is a beam resistant, non￾conducting inorganic ceramic. All of these objects need some form

of preparation before they may be examined properly by scanning

electron microscopy and x-ray microanalysis.

The preceding example shows that there is a very wide range of

specimen types. For convenience they are divided into six groups

on the basis that each group has distinct characteristics, and as a

consequence, may require different approaches to sample prepa￾ration. This sixfold division is somewhat artificial because many

specimens are composed of material from more than one of these

groups. For example, a human tooth is composed of hard dry,

inorganic material in a biological matrix, a car tire is a mixture of

metal and polymers, and deep sea oil is a mixture of brine, mud,

and organic material. The six groups are as follows.