Characterization Techniques in Nanotechnology …
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Table 1 Molecular orbital n,
σ, and π in electronic
transitions
Transition Range of wavelength
(nm)
Examples
σ → σ *
<200
C–H, C–C,
n → σ *
160–260
H 2 O, CH 3 OH, CH 3 Cl
π → π *
200–500
C=C, C=O, C=N, C≡C
n → π *
250–600
C=O, C=N, N=N, N=O
that absorb ultraviolet and visible radiation. The band gap (E g ) can be estimated by
assuming direct transition between conduction band and valence band. Theory of
optical absorption gives the correlation between the absorption coefficients α and
the photon energy hυ for direct allowed transition (Pankove and Kiewit 1972) as:
(αhυ)
2
= A
hυ − E g
(3)
The band gap (direct) is determined when straight line of the ‘(αhυ)
2 ’ against
‘hυ’ plot based on Eq. 3 is extrapolated to intercept the energy axis at α = 0.
A typical UV-vis absorption experiment for a material in liquid is described as
depicted in Fig. 2. A monochromatic beam of light from a source is split into two
beams, whereby one of them is moved through the sample and the other moves
through the reference. The two beams are directed back to the detectors, after transmission across the sample and reference, through which they are compared to give an
output (Kalantar-zadeh and Fry 2008). The basis for this measurement is the distinction between the two signals. The samples in liquid are usually analyzed in a cell
known as cuvette (made of flat and fused quartz faces). The quartz type of cuvette is
commonly employed because it is transparent to both UV and visible light.
UV-vis absorption spectra for AgNPs biosynthesized using cocoa bean extract
and Bacillus safensis cell-free extract (Fig. 3a, b) were reported elsewhere (Azeez
et al. 2017; Lateef et al. 2015). The absorption spectra for AgNPs showed maximum
Fig. 2 Schematic diagram for a double beam UV-vis spectrophotometer (Rocha et al. 2018)
23
Table 1 Molecular orbital n,
σ, and π in electronic
transitions
Transition Range of wavelength
(nm)
Examples
σ → σ *
<200
C–H, C–C,
n → σ *
160–260
H 2 O, CH 3 OH, CH 3 Cl
π → π *
200–500
C=C, C=O, C=N, C≡C
n → π *
250–600
C=O, C=N, N=N, N=O
that absorb ultraviolet and visible radiation. The band gap (E g ) can be estimated by
assuming direct transition between conduction band and valence band. Theory of
optical absorption gives the correlation between the absorption coefficients α and
the photon energy hυ for direct allowed transition (Pankove and Kiewit 1972) as:
(αhυ)
2
= A
hυ − E g
(3)
The band gap (direct) is determined when straight line of the ‘(αhυ)
2 ’ against
‘hυ’ plot based on Eq. 3 is extrapolated to intercept the energy axis at α = 0.
A typical UV-vis absorption experiment for a material in liquid is described as
depicted in Fig. 2. A monochromatic beam of light from a source is split into two
beams, whereby one of them is moved through the sample and the other moves
through the reference. The two beams are directed back to the detectors, after transmission across the sample and reference, through which they are compared to give an
output (Kalantar-zadeh and Fry 2008). The basis for this measurement is the distinction between the two signals. The samples in liquid are usually analyzed in a cell
known as cuvette (made of flat and fused quartz faces). The quartz type of cuvette is
commonly employed because it is transparent to both UV and visible light.
UV-vis absorption spectra for AgNPs biosynthesized using cocoa bean extract
and Bacillus safensis cell-free extract (Fig. 3a, b) were reported elsewhere (Azeez
et al. 2017; Lateef et al. 2015). The absorption spectra for AgNPs showed maximum
Fig. 2 Schematic diagram for a double beam UV-vis spectrophotometer (Rocha et al. 2018)