44
T. B. Asafa et al.
them sufficient energy capable of passing through up to 1 mm of material (Kohl and
Reimer 2008). The operation of TEM requires the irradiation of the whole specimen,
which is thin enough to transmit at least 50% of the incident electrons (Bancroft
and Gamble 2008). The transmitted electrons are then directed by a series of lenses
resulting into a magnified, two-dimensional image of the sample. Meanwhile, every
TEM specimens must have areas of electron transparent material for transmission
of electrons. Preparation of TEM specimen is a diverse and highly complex task.
Several investigations have generated a series of methods for creating thin material
from a thick one (Ayache et al. 2010). Materials having heavy elements composition
(high Z-number) may require ≤100 nm thickness for transmission electrons. Hence,
non-destructive characterization using TEM is only feasible for specimens including
nanoparticles, nanofibers, and light materials such as molecules and nanocarbons
that are transparent to electron in their natural state. If some degree of destructive
specimen preparation is acceptable, then as it is in the case of the TEM in which
a wide range of thinning techniques such as electrochemical dissolution, chemical
etching, ion sputtering, mechanical abrasion, and controlled fracture can be applied
(Ayache et al. 2010; Echlin 1999).
TEM has been used to investigate the size and shape of nanomaterials which
are beyond the capability of SEM. For instance, the shape and size of nanoparticles such as gold, silver, gold–silver, and many more as well as those of nanotubes,
nanofibers, and several thin films have been investigated. Figure 22a, b presents the
TEM images of silver nanoparticles (AgNPs) produced from pod extract of Cola
nitida (Lateef et al. 2016) and silver–gold (Ag–AuNPs) alloy nanoparticles biosynthesized using cell extracted from B. safensis (Ojo et al. 2016). The particles are
considered spherical in shape with sizes range within 12–80 nm for AgNPs and 13–
80 nm for Ag–AuNPs. The hallow tubular structure of multiwalled carbon nanotubes
(MWCNTs) with an average diameter of 30–50 nm is shown in Fig. 22c (Palanisamy
et al. 2014). Figure 22d shows ultrathin poly-Si 11 Ge 89 film of columnar grain structure. The direction of the grain boundary (GB) explains the growth orientation (Asafa
et al. 2014).
In addition to its general function, TEM can also utilize the selected area electron
diffraction (SAED) mode to determine crystalline nature of the samples. In this case,
amorphous phase appears as diffused rings while crystalline phase is seen as bright
spots. Poly-nanocrystallines are viewed as small spots making up rings. The spot
arises from Bragg reflection from an individual crystallite. The crystalline phase of
each sample is obtained from its characteristic SAED pattern.
2.4 High-Resolution Transmission Electron Microscopy
The high-resolution transmission electron microscope (HRTEM), which utilizes the
high-resolution imaging mode of TEM, is an instrument used to directly image atomic
structure of a specimen (Spence et al. 2006). HRTEM has capacity for atomic scale
T. B. Asafa et al.
them sufficient energy capable of passing through up to 1 mm of material (Kohl and
Reimer 2008). The operation of TEM requires the irradiation of the whole specimen,
which is thin enough to transmit at least 50% of the incident electrons (Bancroft
and Gamble 2008). The transmitted electrons are then directed by a series of lenses
resulting into a magnified, two-dimensional image of the sample. Meanwhile, every
TEM specimens must have areas of electron transparent material for transmission
of electrons. Preparation of TEM specimen is a diverse and highly complex task.
Several investigations have generated a series of methods for creating thin material
from a thick one (Ayache et al. 2010). Materials having heavy elements composition
(high Z-number) may require ≤100 nm thickness for transmission electrons. Hence,
non-destructive characterization using TEM is only feasible for specimens including
nanoparticles, nanofibers, and light materials such as molecules and nanocarbons
that are transparent to electron in their natural state. If some degree of destructive
specimen preparation is acceptable, then as it is in the case of the TEM in which
a wide range of thinning techniques such as electrochemical dissolution, chemical
etching, ion sputtering, mechanical abrasion, and controlled fracture can be applied
(Ayache et al. 2010; Echlin 1999).
TEM has been used to investigate the size and shape of nanomaterials which
are beyond the capability of SEM. For instance, the shape and size of nanoparticles such as gold, silver, gold–silver, and many more as well as those of nanotubes,
nanofibers, and several thin films have been investigated. Figure 22a, b presents the
TEM images of silver nanoparticles (AgNPs) produced from pod extract of Cola
nitida (Lateef et al. 2016) and silver–gold (Ag–AuNPs) alloy nanoparticles biosynthesized using cell extracted from B. safensis (Ojo et al. 2016). The particles are
considered spherical in shape with sizes range within 12–80 nm for AgNPs and 13–
80 nm for Ag–AuNPs. The hallow tubular structure of multiwalled carbon nanotubes
(MWCNTs) with an average diameter of 30–50 nm is shown in Fig. 22c (Palanisamy
et al. 2014). Figure 22d shows ultrathin poly-Si 11 Ge 89 film of columnar grain structure. The direction of the grain boundary (GB) explains the growth orientation (Asafa
et al. 2014).
In addition to its general function, TEM can also utilize the selected area electron
diffraction (SAED) mode to determine crystalline nature of the samples. In this case,
amorphous phase appears as diffused rings while crystalline phase is seen as bright
spots. Poly-nanocrystallines are viewed as small spots making up rings. The spot
arises from Bragg reflection from an individual crystallite. The crystalline phase of
each sample is obtained from its characteristic SAED pattern.
2.4 High-Resolution Transmission Electron Microscopy
The high-resolution transmission electron microscope (HRTEM), which utilizes the
high-resolution imaging mode of TEM, is an instrument used to directly image atomic
structure of a specimen (Spence et al. 2006). HRTEM has capacity for atomic scale