Nanocharacterization Techniques

By Osvaldo de Oliveira Jr, Ferreira LG Marystela, Fábio de Lima Leite and Alessandra Luzia Da Róz

Nanocharacterization Techniques covers the main characterization techniques used in nanomaterials and nanostructures. The chapters focus on the fundamental aspects of characterization techniques and their distinctive approaches. Significant advances that have taken place over recent years in refining techniques are covered, and the mathematical foundations needed to use the techniques are also explained in detail. This book is an important reference for materials scientists and engineers looking for a through analysis of nanocharacterization techniques in order to establish which is best for their needs.

• Includes a detailed analysis of different nanocharacterization techniques, allowing readers to explore which one is best for their particular needs
• Provides examples of how each characterization technique has been used, giving readers a greater understanding of how each technique can be profitably used
• Covers the mathematical background needed to utilize each of these techniques to their best effect, meaning that readers can gain a full understanding of the theoretical principles behind each technique covered
• Serves as an important, go-to reference for materials scientists and engineers

• Language: English
• Publisher: Elsevier Science
• Release date: Mar 18, 2017
• ISBN: 9780323497794

Book preview

Nanocharacterization Techniques

Edited by

Alessandra L. Da Róz

Marystela Ferreira

Fabio de Lima Leite

Osvaldo N. Oliveira, Jr.

Table of Contents

Cover

Title page

Copyright

List of Contributors

Editor Biographies

1: Scanning Electron Microscopy

Abstract

1. Introduction

2. Scanning Electron Microscope

3. Using the SEM

4. Developments in Scanning Electron Microscopy

5. Low-Voltage Scanning Electron Microscopy

6. Environmental Scanning Electron Microscopy

7. Electron Backscatter Diffraction

8. Energy-Dispersive X-Ray Spectroscopy in Scanning Electron Microscopy

9. Electron Beam Lithography

10. Nanomanipulation

List of Symbols

2: Atomic Force Microscopy: A Powerful Tool for Electrical Characterization

Abstract

1. Introduction

2. Operating Principles

3. Operating Modes

4. Image Processing and Analysis

5. Electrical Nanocharacterization

List of Symbols

3: Spectroscopic Techniques for Characterization of Nanomaterials

Abstract

1. Ultraviolet–Visible Absorption

2. Fourier Transform Infrared Spectroscopy

3. Raman Scattering

4. Surface-Enhanced Raman Scattering

List of Symbols

4: Dynamic Light Scattering Applied to Nanoparticle Characterization

Abstract

1. Theory

2. Applications

List of Abbreviations and Symbols

5: X-Ray Diffraction and Scattering by Nanomaterials

Abstract

1. X-Ray Diffraction Applied to the Study of Nanocrystalline Powders

2. Small-Angle X-Ray Scattering

3. GISAXS and ASAXS

6: Surface Plasmon Resonance (SPR) for Sensors and Biosensors

Abstract

1. Introduction

2. Surface Plasmons

3. Surface Plasmon Resonance–Based Sensors

4. SPR Applications

5. Final Remarks

List of Symbols and Abbreviations

Index

Copyright

William Andrew is an imprint of Elsevier

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Copyright © 2017 Elsevier Inc. All rights reserved.

This English edition of Nanocharacterization Techniques by Alessandra L. Da Róz, Marystela Ferreira, Fabio de Lima Liete, Osvaldo N. Oliveira, Jr. is published by arrangement with Elsevier Editora Ltda.

Originally published in the Portuguese language as Tecnicas De Nanocaraterizacao 1st edition (ISBN 9788535280913) © Copyright 2015 Elsevier Editora Ltda.

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Notices

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary.

Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility.

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A catalogue record for this book is available from the British Library

ISBN: 978-0-323-49778-7

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List of Contributors

Priscila Alessio,     State University of São Paulo, São Paulo, Brazil

Alvaro E. Aliaga,     State University of São Paulo, São Paulo, Brazil

Pedro H.B. Aoki,     State University of São Paulo, São Paulo, Brazil

Aldo F. Craievich,     Institute of Physics, University of São Paulo, São Paulo - Sp, Brazil

Marcelo de Assumpção Pereira-da-Silva

Institute of Physics of São Carlos, IFSC-USP

Central Paulista University Center, UNICEP, São Carlos, SP, Brazil

Fábio de Lima Leite,     Federal University of São Carlos, Sorocaba, Brazil

Mario de Oliveira Neto,     Institute of Biosciences, University of São Paulo State, Botucatu - Sp, Brazil

Daiana K. Deda,     Federal University of São Carlos, Sorocaba, Brazil

Marystela Ferreira,     Federal University of São Carlos (Ufscar), Sorocaba, Sp, Brazil

Fabio A. Ferri

Institute of Physics of São Carlos, IFSC-USP, São Carlos, SP

Federal University of Lavras, Lavras, MG

Federal University of São Carlos, São Carlos, SP, Brazil

Leonardo N. Furini,     State University of São Paulo, São Paulo, Brazil

Pâmela S. Garcia,     Federal University of São Carlos, Sorocaba, Brazil

Guinther Kellermann,     Department of Physics, Federal University of Paraná, Curitiba - Pr, Brazil

Diego G. Lamas,     Conicet/School of Science and Technology, National University of San Martín, San Martín, Argentina

Carlos J. Leopoldo Constantino,     State University of São Paulo, São Paulo, Brazil

Celina M. Miyazaki,     Federal University of São Carlos (Ufscar), Sorocaba, Sp, Brazil

Ana P. Ramos,     University of São Paulo, Ribeirão Preto, São Paulo, Brazil

Flávio M. Shimizu,     São Carlos Institute of Physics, University of São Paulo, São Carlos, Sp, Brazil

Ronald Tararam,     Multidisciplinary Center for the Development of Ceramic Materials, São Paulo State University, Araraquara, Brazil

José A. Varela,     Multidisciplinary Center for the Development of Ceramic Materials, São Paulo State University, Araraquara, Brazil

Editor Biographies

Alessandra L. Da Róz completed a degree in Sciences, with a major in Chemistry, and obtained her PhD in Materials Science and Engineering at the University of São Paulo, in São Carlos, Brazil. After a postdoc and a researcher positions at the São Carlos Institute of Physics, University of São Paulo, and at the Federal University of São Carlos, she now works in the coordination for research and development at the Federal Institute of Education, Science and Technology of São Paulo (IFSP) in Itapetininga, Brazil. Her main areas of research include polymers and their applications, such as in the processing of natural polymers, lignocellulosic biomass, and solid fuels.

Marystela Ferreira obtained her BSc in Chemistry in 1993, and MSc and PhD in Physical Chemistry in 1996 and 2000, respectively, at the University of São Paulo, São Carlos, Brazil. Her main fields of interest are preparation and characterization of nanostructured thin films for sensing, and layer-by-layer and Langmuir–Blodgett films of polymers for sensing different analytes in environmental and biological samples. She is a lecturer at the Universidade Federal de São Carlos, Sorocaba, Brazil, since 2007.

Fabio de Lima Leite obtained his PhD in Materials Science and Engineering from University of São Paulo, Brazil. Between 2006 and 2009, he was a Postdoctoral Fellow at the São Carlos Institute of Physics (IFSC-USP) in collaboration with Embrapa Agricultural Instrumentation. He was a FAPESP Young Researcher Fellow (2009–12). He has collaborated with Prof. Dr. Alan Graham MacDiarmid, winner of the Nobel Prize in Chemistry 2000, with whom he published the first article in the Journal of Nanoscience and Nanotechnology, in 2009. He is currently Adjunct Professor at the Federal University of São Carlos (UFSCar), Campus Sorocaba, and Coordinator of the Research Group in Nanoneurobiophysics and Future Scientist Program. He has conducted research in the areas of nanoscience and nanotechnology, with emphasis on nanoneuroscience and medical nanobiophysics. Currently, he leads research in neurological disorders, which has launched a new research area entitled nanoneurobiophysics.

Osvaldo N. Oliveira Jr. completed his PhD at the University of Wales, Bangor, United Kingdom. He is a professor at the São Carlos Institute of Physics, University of São Paulo. His main areas of expertise are in nanostructured organic films, and natural language processing. He is a member of the São Paulo State Academy of Sciences. He is a member of the editorial board of three journals, and is also associated editor of the Journal of Nanoscience and Nanotechnology. He received the Scopus Award 2006 awarded by Elsevier in Brazil and Capes, as 1 of 16 outstanding Brazilian researchers, based on the number of publications and citations.

1

Scanning Electron Microscopy

Marcelo de Assumpção Pereira-da-Silva*,**

Fabio A. Ferri*,†,‡

*    Institute of Physics of São Carlos, IFSC-USP, São Carlos, SP, Brazil

**    Central Paulista University Center, UNICEP, São Carlos, SP, Brazil

†    Federal University of Lavras, Lavras, MG, Brazil

‡    Federal University of São Carlos, São Carlos, SP, Brazil

Abstract

This chapter introduces the technique of scanning electron microscopy, a technique used for the visualization and characterization of surfaces. The initial part shows the general arrangement of scanning electron microscopy equipment, emphasizing the type of electron source and the main signals resulting from the interaction between the electron beam and the sample. The second part discusses the principles of the scanning electron microscopy technique and the solutions offered by the new technologies available in the scanning electron microscopy equipment market for morphological and structural characterization, including wet samples. Finally, the challenges already being superseded with the use of scanning electron microscopy on the nanoscale for nanofabrication and nanomanipulation are presented.

Keywords

diffraction

scattering

spectroscopy

lithography

microanalysis

microscopy

nanofabrication

nanomanipulation

nanomachine

nanoassembly

Chapter Outline

1 Introduction

2 Scanning Electron Microscope

2.1 Vacuum

2.2 Electron Gun

2.3 Electron Column

2.4 Sample Chamber

3 Using the SEM

4 Developments in Scanning Electron Microscopy

4.1 Electric Charge Buildup in the Sample

4.2 Nanoassembly

4.3 Electron Detectors

5 Low-Voltage Scanning Electron Microscopy

6 Environmental Scanning Electron Microscopy

7 Electron Backscatter Diffraction

8 Energy-Dispersive X-Ray Spectroscopy in Scanning Electron Microscopy

9 Electron Beam Lithography

10 Nanomanipulation

List of Symbols

References

1. Introduction

Microscopy is a technique used to visualize structures that cannot be observed with the naked eye. Its primary purpose is to form an image of the area intended to be observed.

Microscopy techniques allow visualization of structures present within the sample or on its surface, depending on the technique used and the characteristics of the sample. To visualize a sample, techniques to improve the resolution capacity of the human eye are used, which is on the order of 0.2 mm.

Until the first quarter of the 20th century, samples were observed using visible light with so-called optical microscopes, and this technique depended on the development of lens production techniques with appropriate optical qualities to achieve a resolution limit of half of the shortest wavelength of visible light.

Among the various ways to classify microscopy techniques, one of them relates to the excitation source for the sample. Currently, the three most used microscopy techniques—light microscopy, electron microscopy, and probe microscopy—use light, electrons, and a probe as excitation sources, respectively (Fig. 1.1).

Figure 1.1   Types of commonly used excitation sources in microscopy techniques.

When the excitation source hits the sample, various types of interactions take place, resulting in the emission of different signals. In some cases, these signals are emitted from the same side on which the sample’s excitation source is incident and are called scattered signals. In other cases, the signals are emitted from the opposite side to that on which the sample’s excitation source is incident and are referred to as transmitted signals. With an electron excitation source, the technique dedicated to capturing transmitted signals is called transmission electron microscopy, and the technique that captures scattered signals is called scanning electron microscopy, the subject of this chapter (Fig. 1.2).

Figure 1.2   The position of the captured signal defines the two types of electron microscopy.

2. Scanning Electron Microscope

The scanning electron microscope (SEM) consists of two major parts, the column and the cabinet (Fig. 1.3). The column is the extension that the electrons traverse from their emission until they reach the sample, where the installed detectors will capture the scattered signals resulting from the interaction between the electrons and the sample. The detectors are energy transducers that transform one type of signal into an electrical signal, which is sent to the control cabinet. The control cabinet has electronic systems able to quantify the electrical signals sent by the detectors and turn them into analyzable information such as images and graphs.

Figure 1.3   The electron column shows all of the elements that pertain to the signals from their emission until their capture.

In the cabinet, the signals are processed for easy display.

2.1. Vacuum

In an SEM, a vacuum is required in the electron column and sample chamber because electrons can travel only a small distance through air. The vacuum is produced through a turbomolecular pump backed by a mechanical rotary pump. The turbomolecular pump starts operating only after a vacuum has been created by the mechanical pump, which is used to preevacuate or to roughly pump the sample chamber. After the preestablished vacuum, a valve is activated to allow the turbomolecular pump to evacuate the sample chamber.

2.2. Electron Gun

The electron gun at the top of the column is the electron source (Fig. 1.4). Electrons are emitted from a heated filament and are accelerated down the column. There are three electrically isolated parts in the gun (Goldstein et al., 2007). (1) The first part consists of a filament that emits the electrons (cathode) and creates a cloud of electrons around itself. (2) The second part consists of a metal cylinder (Wehnelt) with an aperture involving the emitter. This cylinder controls the number of electrons that leave the gun. A negative potential is applied to this cylinder, and around its aperture, field lines are formed, which will reduce the diameter of the electron cloud along the gun. (3) The third part comprises a disc with an aperture (anode) that accelerates the electrons at voltages of 0.5 and 30 kV. The disk with an aperture is placed to form an electric field with the cylinder capable of accelerating electrons along the gun.

Figure 1.4   Schematics of the electron source or electron gun. Adapted from Goldstein J, Newbury DE, Joy DC, Lyman CE, Echlin P, Lifshin E, Sawyer L, Michael JR: Scanning electron microscopy and X-ray microanalysis, New York, 2007, Springer.

2.2.1. Filament Types

The following are two types of electron guns: guns with a thermionic emission filament, having a filament of tungsten or lanthanum hexaboride (LaB6), and guns with field emission filaments, both thermal and cold (Fig. 1.5).

Figure 1.5   Illustration of the main types of filaments. Adapted from http://li155-94.members.linode.com/myscope/sem/practice/principles/gun.php; Goldstein J, Newbury DE, Joy DC, Lyman CE, Echlin P, Lifshin E, Sawyer L, Michael JR: Scanning electron microscopy and X-ray microanalysis, New York, 2007, Springer.

The most commonly used filament is the tungsten filament, which is heated to a temperature of 2800 K during operation. The high temperature provides kinetic energy for the electrons to overcome the surface energy barrier and leave the filament (Table 1.1).

Table 1.1

Comparison of the Electron Sources

Adapted from www.tedpella.com/apertures-and-filaments_html/yps-schottky.htm.

The lanthanum hexaboride (LaB6) filament requires less energy for the electrons to escape from the filament since it has a surface work function of 2 eV while tungsten has a value of 4.5 eV. The LaB6 filament provides greater beam intensity, but it must operate at a higher vacuum level. In the filaments for field emission, electrons are pulled from the filament surface by the tunneling effect instead of the thermionic effect through the application of a very high electric field that allows the electrons of the filament to overcome the surface energy barrier.

The field emission filaments made of a tungsten crystal with a very fine tip, on the order of 100 nm, provide an electron intensity 10,000 times greater than that of the common tungsten filament and at least 100 times higher than that of the LaB6 filament. The thermal field emission filaments operate in a temperature range of 1600–1800 K and provide an emission current with low noise. The cold field emission filament operates at room temperature, has a very small power distribution (0.3–0.5 eV), and is very sensitive to residual ions that collide with the filament, causing emission instability. This filament operates at a vacuum of 10−10 Torr and requires frequent maintenance to remove residues deposited by ions from the surface of the filament (Leng, 2008).

2.3. Electron Column

The electron column is located just below the disc aperture. In the electron column, there are the condenser lenses, objective lenses, and scanning lenses. The lenses nearest to the electron gun are called condenser lenses, while lenses nearest to the sample are called objective lenses. The condenser lenses, magnetic lenses located below the electron gun, are used to reduce the electron beam to a small cross-section of 5–50 nm in diameter from an initial cross-sectional diameter more than 1000 times greater. The electron beam enters as a cylindrical shape with a diameter on the order of millimeters and is condensed to form a cone whose vertex is a few nanometers. Next, the objective lenses alter the vertical position of the vertex and allow focusing through the different vertical positions of the sample. The function of the objective lenses is to move the smallest cross-section of the beam up and down to find the sample surface, which corresponds to focusing the image. The scanning lenses deflect the electron beam in both directions over the sample surface, causing the electron beam to hit and interact with an array of sample points.

The final aperture is a platinum disc with a small hole (±100 μm diameter) located just before the sample chamber, and its function is to limit the angular width (solid angle) of the electron beam to reduce the effects of spherical aberration and improve the depth of field in the image.

Another lens system is responsible for beam scanning, and its scanning coils are used to deflect the beam across the sample in sync with the video monitor that displays the image.

2.4. Sample Chamber

The sample chamber connected to the vacuum line is located just below the objective lenses. Furthermore, the moving sample stage, electron signal detectors, and X-ray detectors are located within the chamber.

To insert a sample into the chamber, the electron beam must be turned off; the vacuum is released from the sample chamber and dry nitrogen is vented into it. Then, a new sample can be inserted into the sample stage, and the chamber is again evacuated. A good vacuum is very important, and every place in the evacuated area, including the sample, should be handled only with dust-free gloves.

The stage and detectors are located inside the chamber. The stage is where the samples are placed for analysis. The detectors are responsible for capturing the signals that were scattered by the sample and act as transducers of these signals into an electrical signal.

The electrical signal will be sent to the control cabinet that has electronic systems able to quantify the electrical signals sent by the detectors and turn them into analyzable information such as images and graphs.

3. Using the SEM

The SEM is used to observe and modify the sample’s surface. It is used to capture and interpret some signals emitted during the interaction of the electron beam with the sample (Fig. 1.6). Among these signals, there are electrons [Auger electrons, secondary electrons (SEs), and backscattered electrons], X-rays (characteristic X-rays and Bremsstrahlung X-ray radiation), light (ultraviolet, visible, and infrared), heat, electrons conducted through the sample, and electrons absorbed by the sample. With some of these signals, it is possible to observe and characterize the sample in terms of its (1) surface morphology, (2) structural organization, and (3) chemical composition.

Figure 1.6   Main signals emitted as a result of the interaction between the electron beam and the sample. Adapted from Goldstein J, Newbury DE, Joy DC, Lyman CE, Echlin P, Lifshin E, Sawyer L, Michael JR: Scanning electron microscopy and X-ray microanalysis, New York, 2007, Springer.

Surface modification occurs because the electron beam, when it has sufficient energy, is able to locally change the sample’s surface material, which may generate nanometer-sized structures. The most commonly used technique for sample surface modification using an electron beam as a writing and design tool with a resolution of a few nanometers, known as electron beam lithography (EBL).

4. Developments in Scanning Electron Microscopy

The developments in scanning electron microscopy have brought important changes to the observation of surface morphology, including the use of low-voltage scanning electron microscopes (LVSEMs), the use of variable pressure or environmental scanning electron microscopes (ESEMs), the use of sources capable of providing greater brightness than scanning electron microscopy with field emission filaments [field emission scanning electron microscopes (FESEMs)], and electron detectors within the lenses.

4.1. Electric Charge Buildup in the Sample

In general, the samples examined in an SEM must be electrically conductive to minimize charge buildup on the sample caused by the electron beam. The charge buildup can degrade the sample and distort the image data (Sawyer et al., 2008). During imaging, electrons are continuously bombarding the sample, and a negative charge can build up in areas of the sample under the beam. This negative charge, when sufficiently large, can deflect the incident and emitted electrons, thus ruining the image. To prevent this effect, each sample must be electrically conductive so that the current deposited by the electron beam on the sample can pass through the sample stage to the electrical ground. Some samples, such as metals, are already conductors; however, other samples, such as ceramics, polymers, and biological materials, are not conductive. Thus, the sample surface is coated with a thin layer of an inert conductive substance, such as gold or carbon, using evaporation or