Materials Characterization Using Nondestructive Evaluation (NDE) Methods

Gerhard Huebschen, Iris Altpeter, Ralf Tschuncky, Hans-Georg Herrmann

• Publisher: Woodhead Publishing
• Year: 2016
• Print ISBN:
  9780081000403
• eBook ISBN:
  9780081000571
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

Materials Characterization Using Nondestructive Evaluation (NDE) Methods discusses NDT methods and how they are highly desirable for both long-term monitoring and short-term assessment of materials, providing crucial early warning that the fatigue life of a material has elapsed, thus helping to prevent service failures. Materials Characterization Using Nondestructive Evaluation (NDE) Methods gives an overview of established and new NDT techniques for the characterization of materials, with a focus on materials used in the automotive, aerospace, power plants, and infrastructure construction industries. Each chapter focuses on a different NDT technique and indicates the potential of the method by selected examples of applications. Methods covered include scanning and transmission electron microscopy, X-ray microtomography and diffraction, ultrasonic, electromagnetic, microwave, and hybrid techniques. The authors review both the determination of microstructure properties, including phase content and grain size, and the determination of mechanical properties, such as hardness, toughness, yield strength, texture, and residual stress. - Gives an overview of established and new NDT techniques, including scanning and transmission electron microscopy, X-ray microtomography and diffraction, ultrasonic, electromagnetic, microwave, and hybrid techniques - Reviews the determination of microstructural and mechanical properties - Focuses on materials used in the automotive, aerospace, power plants, and infrastructure construction industries - Serves as a highly desirable resource for both long-term monitoring and short-term assessment of materials

1

Atomic force microscopy (AFM) for materials characterization

M.K. Khan¹, Q.Y. Wang¹, and M.E. Fitzpatrick^{2 1}Sichuan University, Chengdu, China ²Coventry University, Coventry, United Kingdom

Abstract

The use of high-resolution microscopic imaging is continuously increasing in engineering, medical, natural science, and other fields. In many applications, the characterization of surfaces requires spatial resolution of nanometers or lower. Atomic force microscopy (AFM), although a relatively newly developed technique, has now become a powerful technology for characterization of the surface of materials down to the atomic scale. AFM can be used to obtain nanoscale chemical, mechanical (modulus, stiffness, viscoelastic, frictional), electrical, and magnetic properties. In comparison with other microscopy techniques, AFM offers low cost, simplicity in operation, and imaging capability to atomic resolution. It is a powerful nondestructive analytical technique which can be used in air, liquid, or vacuum. This chapter discusses the effectiveness of AFM for material characterization.

Keywords

AFM; AFM probe; Material characterization; 3D scanning; Topography surface scanning

1.1. Introduction

The use of high-resolution microscopic imaging is widespread in engineering, medical, natural science, and various other fields. The local surface features and defects on the order of nanometers and lower play a crucial role in the functional performance of structures in service life. High-resolution microscopes are used to characterize the surface of materials down to the atomic scale. In many applications the characterization of materials, structures, microstructures, and damage requires spatial resolution of nanometers or lower. This has encouraged further development in capability of microscopes to characterize materials from real-space images.

In materials science and engineering, surface characterization data are usually obtained from a combination of conventional optical and electron microscopes such as scanning (SEM) and transmission (TEM) electron microscopes. However, the complete characterization process of any given material may require the application of various complementary characterization methods to obtain the information at various length scales.

Atomic force microscopy (AFM) is a relatively newly developed technique used for imaging local surface characteristics from submicron to nanometer length scale. It is a powerful nondestructive analytical technique which can be used in air, liquid, or vacuum (Bellitto, 2012; Takaharu et al., 2003; Kageshima et al., 2002; Yaxin and Bharat, 2007). The AFM has capability to generate very high-resolution topographic images of a surface down to atomic resolution. The AFM can be used to obtain the nanoscale chemical, mechanical (modulus, stiffness, viscoelastic, frictional), electrical, and magnetic properties (Bellitto, 2012; Hendrych et al., 2007; Zhang et al., 2004). In materials engineering and its allied fields, AFM can be used for 3D information of surface defects, scribes, scratches, gouges, corrosion pits, etc. The possibility to carry out imaging at such small scales, its small size, and ease in handling, makes AFM one of the very few tools capable of characterizing the surface properties around very small features. Fig. 1.1 shows a typical table-top AFM.

Figure 1.1 A typical atomic force microscope (AFM).

1.2. Comparison of AFM with other microscopy techniques

The best technique for characterization of any material requires knowledge of the properties of the material being analyzed, the length scale of the required information, and the limitations of the technique in use. In material characterization, SEM and TEM are mostly preferred to obtain the submicron or lower scale information. These electron microscopes are very expensive tools. The surface imaging from these microscopes requires samples to be in a vacuum and sometimes preparation to ensure electrical conductivity. The conduction of the electron beam through some samples may damage the surface. The sample chamber of these microscopes is generally very small, which does not allow the observation on large samples. In comparison, AFM has several advantages over SEM and TEM for characterizing materials at very small length scales. The fundamental advantage of AFM is its capability to provide 3D information from the probed surface. 3D information with direct height measurement enables scientists and engineers to make better decisions about the functional performance of the materials. In addition, the AFM can be used in various environments, which make measurement of some sensitive materials possible in their operating environments. Table 1.1 shows the comparison of AFM with conventional SEM and TEM. It can be seen that AFM provides substantial advantages over these techniques. Fig. 1.2 shows the cost comparison of the various surface measurement tools. It can be seen that AFM is much lower in capital cost as compared to other tools. In addition, the operating cost of the AFM is much less than the other techniques.

AFM tips or probes play a key role in measurement of the high-resolution topography. The benefits of sharper tips are numerous, such as smaller contact area and reduced long-range forces. Most conventional tips are made from silicon nitride and silicon. Now new nanotips produced through whiskers or carbon fiber are capable of providing much higher resolution images (Marcus et al., 1989). The quality of images will keep increasing in the future due to further advancements being made in the tip–surface interaction mechanisms. Combined AFM and STM with tips made up of novel materials are a potential future development which will increase the versatility of AFM data acquisition.

Table 1.1

Comparison of attributes of various surface characterization tools

Parameter	SEM	TEM	AFM
Measurement environment	Vacuum	Vacuum	Air, water, gas, vacuum, etc.
Surface height	Not possible	Not possible	Possible
Measurement dimension	2D	2D	3D
Size of equipment	Large	Large	Very small
Cost	Expensive	Expensive	Cheap
Usage	Skilled operator required	Skilled operator required	Easy to use
Measurement speed	Fast	Fast	Slow

SEM, Scanning electron microscope; TEM, transmission electron microscope; AFM, atomic force microscopy.

Figure 1.2 Comparison of capital cost of various surface measurement tools.

1.3. Principles of AFM technique

In AFM scanning, a cantilever with a sharp tip is used to scan over the surface of the sample. The cantilever probes the surface by sensing the force between surface and tip. The atoms respond to the developed van der Waals force, which can be either short-range repulsive exchange interactio...

Table of contents

• Cover image
• Title page
• Table of Contents
• Related titles
• Copyright
• List of contributors
• Woodhead Publishing Series in Electronic and Optical Materials
• 1. Atomic force microscopy (AFM) for materials characterization
• 2. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for materials characterization
• 3. X-ray microtomography for materials characterization
• 4. X-ray diffraction (XRD) techniques for materials characterization
• 5. Microwave, millimeter wave and terahertz (MMT) techniques for materials characterization
• 6. Acoustic microscopy for materials characterization
• 7. Ultrasonic techniques for materials characterization
• 8. Electromagnetic techniques for materials characterization
• 9. Hybrid methods for materials characterization
• Index