Characterization Techniques in Nanotechnology …
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3 Other Characterization Techniques
3.1 Mechanical Characterization
Mechanical characterization refers to testing performed to precisely measure the
mechanical properties of materials. For nanotechnology applications, it is essential
to measure the exact mechanical properties as a means of evaluating the reliability of
products developed with nanomaterials, as these properties are closely related with
their reliability metrics, such as the service life of the product. There are several
tests in existence, many of which are standardized and vary for the material to be
tested and the intended area of application. In this section, the testing procedures for
four different mechanical characterization techniques including Young’s modulus,
abrasive wear measurement, nanoindentation, and microhardness are presented.
3.1.1 Young’s Modulus or Modulus of Elasticity
Young’s modulus is a measure of material stiffness using the rate of change of strain
as a function of stress. Generally, Young’s modulus can be obtained from the slope
of the tensile stress and tensile strain or the compressive stress and compressive
strain retrieved during tension/compression tests conducted using a universal testing
machine (Asafa et al. 2015). However, at nanoscale, this approach is not feasible
because sample of interest is either a thin film deposited or a substrate or nanoparticles
that cannot be mounted on tensile machine. Several studies have shown that the
properties of nanomaterials differ from those of the bulk due to enhanced surfaceto-volume ratio (Asafa et al. 2014; Namba 2008; Reiss et al. 1991). Also, these
properties are influenced when the structural dimensions are scaled down to a length
scale that is comparable to the electron mean free paths (Asafa et al. 2014; Namba
2008; Reiss et al. 1991). In this case, predictions based on classical theories such as
Euler–Bernoulli theory and Hooke’s law become invalid as the results differ from
ones.
The use of surface acoustic wave (SAW) (Schneider et al. 2000) and nanoindentation techniques (Oliver and Pharr 1992) are considered accurate and reliable
for characterizing Young’s moduli of ultrathin films. In SAW experiment, a nitrogen
laser with pulse duration of 3 ns and a wavelength of 337 nm is used to generate wide
band surface wave pulses. Example of such a step is shown in Fig. 29a (Schneider
et al. 1998). These surface acoustic waveforms are then detected at different distance
across the sample. The Fourier transform of the waveforms results into the frequencydependent phase from where the phase velocity and modulus are obtained via dispersion equation (Asafa et al. 2014; Schneider et al. 1998). The values of the Young’s
modulus obtained by SAW have been established to be accurate and close to those
obtained by membrane deflection method (Fig. 29b) for metallographically polished
and annealed steel 42CrMo4 (Schneider et al. 1998). Another good example of SAW
technique is shown in Fig. 29c where evolutionary study was conducted on influenced
53
3 Other Characterization Techniques
3.1 Mechanical Characterization
Mechanical characterization refers to testing performed to precisely measure the
mechanical properties of materials. For nanotechnology applications, it is essential
to measure the exact mechanical properties as a means of evaluating the reliability of
products developed with nanomaterials, as these properties are closely related with
their reliability metrics, such as the service life of the product. There are several
tests in existence, many of which are standardized and vary for the material to be
tested and the intended area of application. In this section, the testing procedures for
four different mechanical characterization techniques including Young’s modulus,
abrasive wear measurement, nanoindentation, and microhardness are presented.
3.1.1 Young’s Modulus or Modulus of Elasticity
Young’s modulus is a measure of material stiffness using the rate of change of strain
as a function of stress. Generally, Young’s modulus can be obtained from the slope
of the tensile stress and tensile strain or the compressive stress and compressive
strain retrieved during tension/compression tests conducted using a universal testing
machine (Asafa et al. 2015). However, at nanoscale, this approach is not feasible
because sample of interest is either a thin film deposited or a substrate or nanoparticles
that cannot be mounted on tensile machine. Several studies have shown that the
properties of nanomaterials differ from those of the bulk due to enhanced surfaceto-volume ratio (Asafa et al. 2014; Namba 2008; Reiss et al. 1991). Also, these
properties are influenced when the structural dimensions are scaled down to a length
scale that is comparable to the electron mean free paths (Asafa et al. 2014; Namba
2008; Reiss et al. 1991). In this case, predictions based on classical theories such as
Euler–Bernoulli theory and Hooke’s law become invalid as the results differ from
ones.
The use of surface acoustic wave (SAW) (Schneider et al. 2000) and nanoindentation techniques (Oliver and Pharr 1992) are considered accurate and reliable
for characterizing Young’s moduli of ultrathin films. In SAW experiment, a nitrogen
laser with pulse duration of 3 ns and a wavelength of 337 nm is used to generate wide
band surface wave pulses. Example of such a step is shown in Fig. 29a (Schneider
et al. 1998). These surface acoustic waveforms are then detected at different distance
across the sample. The Fourier transform of the waveforms results into the frequencydependent phase from where the phase velocity and modulus are obtained via dispersion equation (Asafa et al. 2014; Schneider et al. 1998). The values of the Young’s
modulus obtained by SAW have been established to be accurate and close to those
obtained by membrane deflection method (Fig. 29b) for metallographically polished
and annealed steel 42CrMo4 (Schneider et al. 1998). Another good example of SAW
technique is shown in Fig. 29c where evolutionary study was conducted on influenced