36
T. B. Asafa et al.
nanoparticles. Within the sonication time range of 0–10 min, the smallest particle
sizes of 242 ± 41 nm and 436 ± 80 nm for TiO 2 and ZnO, respectively, were obtained
with 10 min of sonication indicating reduction of particle agglomeration (González
et al. 2017).
1.8 X-ray Photoelectron Spectroscopy
X-ray photoelectron spectroscopy (XPS) is a surface analytical technique that
measures the elemental composition, empirical formula, chemical state, and electronic state of elements that exist within the surface of material (Welker 2012). XPS
is the most commonly used technique in areas of materials science, chemistry, nanomaterial, and chemical engineering to assess surface chemistry, bonding structure,
and composition of surfaces and interfaces (Greczynski and Hultman 2020). XPS
spectra are obtained by irradiating a material with a beam of X-rays while simultaneously measuring the kinetic energy and number of electrons escaping within the
10 nm of the top surfaces. The strength of this technique relies on the fact that the
chemical environment of an atom has a pronounced effect on the assessed binding
energies of core-level electrons (termed chemical shift) (Sokolowski et al. 1958). XPS
can be deployed to analyze semiconductors, glasses, polymers, ceramics, catalysts,
metal alloys, and bones among others.
XPS is based on photoelectric effect in which the binding energy of a core-level
electron is overcome by the energy of an impinging soft X-ray photon, and the corelevel electron is excited and ejected from the surface of the material. The kinetic
energies of the ejected photoelectrons are measured by an electron spectrometer. By
invoking conservation of energy, the biding energy E B can be related to the kinetic
energy E k via the following equation (Lee and Flynn 2006; Einstein 1905; Rutherford
and Andrade 1914):
E B = hv − E k − ϕ
(13)
where h is the planks constant, ϕ is the spectrometer work function, and υ is the light
frequency.
In Fig. 16, an introduction of the light source over the sample generates the X-rays,
resulting into photoelectrons ejection and photons annihilation. Electron optics is
used as the collector of the photoelectrons. Energy in the electron energy analyzer will
then be employed to sort the collected photoelectrons. The number of electrons per
energy interval is then transduced to a current by an electron detector. Subsequently,
the spectrum of suitable electronics converts and processes the photocurrent. The
experiment is usually conducted under ultra high vacuum (UHV) conditions (Lee
and Flynn 2006).
Figure 17 shows the results of XPS characterization for surface compositions and
chemical states of pure ZnO and Ag doped ZnO films. It is observed that Zn 2p spectra
T. B. Asafa et al.
nanoparticles. Within the sonication time range of 0–10 min, the smallest particle
sizes of 242 ± 41 nm and 436 ± 80 nm for TiO 2 and ZnO, respectively, were obtained
with 10 min of sonication indicating reduction of particle agglomeration (González
et al. 2017).
1.8 X-ray Photoelectron Spectroscopy
X-ray photoelectron spectroscopy (XPS) is a surface analytical technique that
measures the elemental composition, empirical formula, chemical state, and electronic state of elements that exist within the surface of material (Welker 2012). XPS
is the most commonly used technique in areas of materials science, chemistry, nanomaterial, and chemical engineering to assess surface chemistry, bonding structure,
and composition of surfaces and interfaces (Greczynski and Hultman 2020). XPS
spectra are obtained by irradiating a material with a beam of X-rays while simultaneously measuring the kinetic energy and number of electrons escaping within the
10 nm of the top surfaces. The strength of this technique relies on the fact that the
chemical environment of an atom has a pronounced effect on the assessed binding
energies of core-level electrons (termed chemical shift) (Sokolowski et al. 1958). XPS
can be deployed to analyze semiconductors, glasses, polymers, ceramics, catalysts,
metal alloys, and bones among others.
XPS is based on photoelectric effect in which the binding energy of a core-level
electron is overcome by the energy of an impinging soft X-ray photon, and the corelevel electron is excited and ejected from the surface of the material. The kinetic
energies of the ejected photoelectrons are measured by an electron spectrometer. By
invoking conservation of energy, the biding energy E B can be related to the kinetic
energy E k via the following equation (Lee and Flynn 2006; Einstein 1905; Rutherford
and Andrade 1914):
E B = hv − E k − ϕ
(13)
where h is the planks constant, ϕ is the spectrometer work function, and υ is the light
frequency.
In Fig. 16, an introduction of the light source over the sample generates the X-rays,
resulting into photoelectrons ejection and photons annihilation. Electron optics is
used as the collector of the photoelectrons. Energy in the electron energy analyzer will
then be employed to sort the collected photoelectrons. The number of electrons per
energy interval is then transduced to a current by an electron detector. Subsequently,
the spectrum of suitable electronics converts and processes the photocurrent. The
experiment is usually conducted under ultra high vacuum (UHV) conditions (Lee
and Flynn 2006).
Figure 17 shows the results of XPS characterization for surface compositions and
chemical states of pure ZnO and Ag doped ZnO films. It is observed that Zn 2p spectra