A comparative study of the synthesis of CdO nanoplatelets by an albumen-assisted isothermal evaporation method

Article abstract of DOI:10.1016/j.jallcom.2014.10.204

In this paper, the synthesis of CdO nanoplatelets by the isothermal evaporation method in the presence of egg white (albumen) as a bio-template agent is reported for the first time. The morphological and microstructural characteristics of products obtained after drying at 130 °C and annealing at 300 °C have been investigated by Fourier transform infrared (FT-IR) spectroscopy, Thermogravimetric analysis (TGA), X-ray diffraction (XRD), SEM (Scanning Electron Microscopy), Transmission Electron Microscopy (TEM), Energy Dispersive Spectroscopy (EDS), and compared with corresponding samples obtained in the absence of template. The characterization techniques evidenced remarkable differences between the two sample typologies. Specifically, crystalline CdO in the cubic phase was obtained only in the presence of albumen. The samples were further analyzed by electrical conductivity measurement, ultraviolet spectral studies (UV) and photoluminescence (PL) to ascertain their possible use for optical and electrical applications.

Full text of DOI:10.1016/j.jallcom.2014.10.204

Accepted Manuscript
A comparative study of the synthesis of CdO nanoplatelets by an albumen-as-
sisted isothermal evaporation method
T. Prakash, R. Jayaprakash, G. Neri
PII:
S0925-8388(14)02719-4
DOI:
http://dx.doi.org/10.1016/j.jallcom.2014.10.204
JALCOM 32625
Reference:
To appear in:
Journal of Alloys and Compounds
Received Date:
Revised Date:
Accepted Date:
6 June 2014
23 October 2014
31 October 2014
Please cite this article as: T. Prakash, R. Jayaprakash, G. Neri, A comparative study of the synthesis of CdO
nanoplatelets by an albumen-assisted isothermal evaporation method, Journal of Alloys and Compounds (2014),
doi: http://dx.doi.org/10.1016/j.jallcom.2014.10.204
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A comparative study of the synthesis of CdO nanoplatelets by an albumen-assisted
isothermal evaporation method
1
∗
2
T. Prakash , R. Jayaprakash , G. Neri
3
_
__________________________________________________________________________________________________________________
1
Department of Physics, Tamilnadu College of Engineering, Karumathampatti, Coimbatore-641 659, Tamil Nadu,
INDIA.
2
Nanotechnology Laboratory, Department of Physics, Sri Ramakrishna Mission Vidyalaya College of Arts and
Science, Coimbatore – 641020, Tamil Nadu, INDIA.
3
Department of Electronic Engineering, Chemistry and Industrial Engineering, University of Messina, 98166
Messina, ITALY.
_
____________________________________________________________________________
ABSTRACT
In this paper, the synthesis of CdO nanoplatelets by the isothermal evaporation method in
the presence of egg white (albumen) as a bio-template agent is reported for the first time. The
morphological and microstructural characteristics of products obtained after drying at 130 °C and
annealing at 300 °C have been investigated by Fourier transform infrared (FT-IR) spectroscopy,
Thermogravimetric analysis (TGA), X-ray diffraction (XRD), SEM (Scanning Electron
Microscopy), Transmission Electron Microscopy (TEM), Energy Dispersive Spectroscopy
(
EDS), and compared with corresponding samples obtained in the absence of template. The
characterization techniques evidenced remarkable differences between the two sample
typologies. Specifically, crystalline CdO in the cubic phase was obtained only in the presence of
albumen. The samples were further analyzed by electrical conductivity measurement, ultraviolet
spectral studies (UV) and photoluminescence (PL) to ascertain their possible use for optical and
electrical applications.
Key words: Albumen; Platelets; Quantum dots; Bio-template.
∗
Corresponding author Tel.: +91 0422 2692349
E-mail address: prakash_nano@rediffmail.com (T.prakash)
1

1
. INTRODUCTION
In recent years, researchers have made many efforts for preparing semiconductor metal
oxide nanoparticles. In this respect, nanoparticles of CdO, an important n-type semiconductor
metal oxide with a direct band gap of 2.5 eV and an indirect band gap of 1.98 eV [1], have
attracted great interest because of their unique optical, electrical, chemical and physical
properties, which has led to use in advanced applications [2]. The unique properties of CdO
nanoparticles arise from their nanoscale structure, dimension and the large number of available
surface atoms [3].
CdO nanostructures have been used for solar cells, phototransistors, trasparent electrodes,
catalysts, gas sensors, optoelectronic devices, anode materials for litium ion batteries and
photodiodes [1, 4-10]. Numerous cadmium oxide nanostructures such as nanoparticles,
nanowires [11], nanoneedles, nanotubes [12], nanorods [13], have been synthesized by various
chemical and physical methods including vapour transport, chemical vapour deposition (CVD),
sol-gel, chemical bath deposition (CBD), spray pyrolysis, solvothermal/hydrothermal methods
and others [14-22]. In this paper, we reports a study finalized to synthetize CdO nanoplatelets by
the isothermal evaporation method with the use of egg albumen as a bio-template. At our
knowledge, this is the first attempts so far reported to obtain this important semiconductor
material via this simple synthesis method.
Many studies have examined the controlled synthesis of metal nanomaterials of various
sizes and morphologies through the use of biomolecules as templates [23-26]. Compared with
traditional chemical synthesis, biomolecule-assisted synthesis of metal nanoparticles have a
number of advantages [24-27]. The biomolecule-assisted synthesis are carried out at room
temperature and under aqueous conditions. Energy input of the process is reduced and the
2

solvents used are nontoxic, so minimizing environmental damage to human health. The structural
differences of the used biomolecules resulted in nanoparticles with a wide range of sizes, shapes
and polymorphisms, determining their physical-chemical properties [25-26]. Assisting the
synthesis of nanomaterials with a bio-template, i.e making use of a natural organic compound to
template inorganic materials, gives additional advantages and provides further promising routes
for fabricating nanoparticles for many applications [28]. Albumen, a protein with a long chain of
amino acids, is well known as a bio-template for its gelling, foaming and emulsifying
characteristics [29]. Due to its solubility in water and ability to associate with metal ions in
solution, it has been used as a binder gel for shaping material, particularly bulk and porous
2
+
3+
2+
3+
2+
2+
2+
ceramics [30]. Metal ions such as Mn /Mn , Fe /Fe , Cu , Zn and Ni have been
combined with egg white to obtain novel nanomaterials with interesting properties [31-36]. The
use of albumen as a bio-template [35,37-39,25] or as a fuel in combustion synthesis [40] is
recognized also as a convenient and cost-effective method.
Nowadays, utilization of the isothermal evaporation method is increasing because it is an
effective, useful, low-cost and a simple technique to synthesize different nanomaterials [41-42].
Moreover, compared to the competitive techniques, the advantage of this method is effective and
efficient in regards to time and produced quantity. For example, Prakash et al. synthesized ZnO
nanoparticles in more less time than that required by others methods reported in the literature
[
37]. In the current paper, we report a simple, nontoxic and eco-friendly green pathway to
prepare stable CdO nanoplatelets by using albumen as a bio-template and isothermal evaporation
method. The purpose of this work is to compare the morphological and microstructural
characteristics of CdO products obtained with the above method in the presence or not of the
albumen template. The analyses of products obtained after drying and annealing have been
3

performed by Fourier transform infrared (FT-IR) spectroscopy, Thermogravimetric analysis
TGA), X-ray diffraction (XRD) patterns, SEM (Scanning Electron Microscopy), Transmission
(
Electron Microscopy (TEM) and Energy dispersive spectrum (EDS). The samples were further
analyzed by electrical conductivity, ultraviolet spectral studies (UV) and photoluminescence
(
PL) measurement in view of their possible use for optical and electrical applications.
2
2
. EXPERIMENTAL
.1 Materials
Cadmium nitrate and ammonia were supplied from (Merk, 98%) Mumbai, India. All the
chemicals were of analytical grade and used as received without further purification. Hen egg
were purchased from local market. Double distilled water was used throught the experiments.
2
.2. Synthesis
The synthesis of CdO nanoplatelets by the isothermal evaporation method was carried out
as follows. First, a 0.1 M of cadmium hydroxyl solution was prepared by dissolving cadmium
nitrate (CdNO in deionized water. 5 ml of freshly extracted albumen was mixed with 25 ml of
)
3 2
deionized water and stirred. The obtained albumen suspension was added drop by drop in the
cadmium hydroxyl solution, maintaining pH of the solution at 8 by adding an ammonia solution
drop wise. The above mixture was stirred isothermally at 85 °C for 3h until the complete
removal of water content. The cadmium oxide powder obtained was was dried at 130 °C and
finally annealed at 300 °C for 5h in air. Table. 1 reports the main characteristics of the samples
investigated in this study.
2
.2.1. Characterization
4

To investigate the thermal behavior of samples, thermal analysis (TG-DTA) was carried
out with a TA instruments (Mod. Q600 SDT), in air in the temperature range RT-900 °C. X-ray
diffraction data (XRD) were recorded on a Bruker (AXS D8 Advance) diffractometer with CuK
α
radiation (λ = 1.5406 Å) operating at 40kV and 30 mA. The crystallites average size was
determined by the Scherrer equation [43]:
0
.9λ
Dhkl
=
(1)
β cos(θ )
hkl
hkl
where λ is the X-ray wavelength, θhkl is the Bragg diffraction angle, and βhkl is the full width at
half-maximum (FWHM) of the main peak in the XRD pattern. Scanning electron microscopy
(
SEM) and energy dispersive X-ray (EDX) analysis were recorded on a JEOL Mod. JSM-
390LV instrument. Transmission electron microscopy (TEM), high resolution transmission
6
electron microscopy (HR-TEM) and selected area electron diffraction (SAED) images were
collected on a Philips (Mod. CM 200), electron microscope with an acceleration voltage of 80
kV. Fourier transform infrared spectroscopy (FT-IR) spectra were recorded using a Bio Rad
-1
Spectrometer (Mod. FTS-7) in KBr matrix in the range of 400-4000 cm . Diffuse reflectance
spectroscopy (DRS) spectra were recorded on a Perkin Elmer UV-visible DRS
spectrophotometer. Room-temperature photoluminescence (PL) spectra were registered on a
spectrofluorimeter Fluorolog (Mod. FL3-11). The electrical conductivity measurements were
carried out using a digital LCR Meter (Systronics Mod. 925).
3
3
3
. RESULTS AND DISCUSSION
.1 Morphological and microstructural analysis
.1.1. TGA analysis
5

The changes associated with the annealing process of the different samples were
investigated by thermal analysis measurements. Fig.1 (a) shows TGA of the albumen template,
Sample A. Different weight loss were observed during heat treatment from room temperature
(
RT) to 900 °C, revealing that the constituent proteins of the template were removed by the
heating process. The major weight loss was observed from 200°C to 450 °C due to the burning
of these organics in air [39].
Fig.1 (b-c) shows TGA curves of annealed CdO Sample C and Sample E, respectively.
Curve (b), related to Sample C, reveals a remarkable overall weight loss in the temperature range
from 100 to 450 °C. A three-step weight loss was observed. The first weight loss of 3.7 %
occurred below 125 °C and could be attributed to the release of water. The second and third
weight loss, about 21.4% in total, was attributed to release of water and carbon dioxide molecule
from decomposition of mixed cadmium(hydroxyl)carbonate Cd(OH)2-x(CO
cadmium oxide, CdO, according the following process:
Cd(OH) (CO ) → CdO + H O + CO
3
x
) phase to give
2
−x
3
x
2−x
2
x
2
In a previous paper, DSC analysis has confirmed that the above steps found in the TGA
pattern are associated at endothermic processes, as a result of the desorption of volatile
compounds from mixed cadmium hydroxyl carbonate [44]. Mixed cadmium hydroxide
carbonates species are well known and have been reported by other authors [45]. These mixed
non-stoichiometric compounds are formed by carbonation processes occurring in solution during
the synthesis step.
Curve (c), related to Sample E, reveals clearly a very low weight loss. The total weight
loss of less than 4%, observed between RT and 900 °C, may be attributed to the humidity release
and decomposition of trace albumen impurity. TGA analysis indicate then that pure cadmium
6

oxide phase can be obtained by thermal treatment at 300 °C using albumen as template, whereas
with the conventional procedure a more stable cadmium hydroxyl carbonate phase, which
decompose at higher temperature, has been formed.
3
.1.2. XRD
Fig. 2 (a-e) shows XRD patterns of Samples A-E. Pattern (a) indicated that the pure
albumen powder (Sample A) is essentially amorphous [46]. XRD patterns (b) and (c) of as-
prepared and annealed sample CdO without albumen added (Sample B and Sample C), reveal the
presence of many diffraction peaks of Cd(OH)
small amount of Cd(OH) hexagonal phase [JCPDS file no # 73-0969], few peaks of Cd(OH)
cubic phase [JCPDS file no # 11-0516], very few peaks of Cd hexagonal phase [JCPDS file no #
1-1175] and CdCO rhombohedral phase [JCPDS file no # 85-0989] indicating the crystalline
nature of the material synthesized. Unfortunately, most of these reflections could not be indexed
to any known phase related to Cd such as, Cd(OH) , CdCO , and so on. The average crystallite
2
monoclinic phase [JCPDS file no # 71-2137],
2
2
0
3
2
3
size, calculated by means of the Scherrer equation (1) of the Sample B and C is 39 and 43 nm,
respectively. On the basis of above reported data, and previous observations made by us and
others [44-45], we suggest that Sample B and C are mainly formed by a mixed cadmium
−
hydroxy carbonate compound, i.e. Cd(OH)2-x(CO
3
)
x
, derived from the coordination of OH and
2
−
CO
composition.
Fig.2 (d-e) show the diffraction peaks for the Sample D and E. Reflections observed on
both samples matches well with cubic cadmium oxide structure (JCPDS file no # 050640). The
presence of a small amount of CdO cubic phase (JCPDS file no # 781125) was also observed in
Sample D and E. We think that CdO
3
ions with cadmium ions. A more detailed analysis is however necessary to assign the right
2
2
nanoparticles might play an important role in the formation
7

of CdO nanoplatelets, which could be yielded according to the chemical reaction: CdO
CdO+1/2O [47].
As calculated from equation (2):
2
→
2
1
/ 2
2
h + k + l
2
2



1
=



(2)



2
dhkl

a

where d is the d- spacing value, h,k and l are Miller indices, the lattice parameter for
Sample D and Sample E, a = 4.67Å is comparable with standard lattice parameters for CdO
phase [48]. This indicates that the decomposition process of Cd(OH) into CdO starts at a
2
temperature below 130 °C, in agreement with our previous observations [44]. XRD
measurements indicates further the good crystalline nature of CdO particles obtained. As
expected, due to the higher treatment temperature, and according to the intensity of the XRD
pattern, the crystallization degree of Sample E is higher than that of Sample D. The mean
crystallite size of the CdO nanoplatelets in Sample D and E, estimated from the width at half
maximum of the main diffraction peak according to the Scherrer equation from (1), was about 27
and 29 nm, respectively.
3
.1.3. SEM
The morphology of the samples prepared was investigated by scanning electron
microscopy. Fig.3 (a) reports a micrograph showing the typical morphology of albumen used as
bio-template. The surface of the albumen appears to be untextured and amorphous. Fig.3 (b-c)
reports typical SEM images taken on Sample B and Sample C. Fig.3 (d-e) shows SEM images of
the Sample D and Sample E, respectively. From the comparison of the images, it appears evident
that using albumen as a template during the synthesis, the material obtained is less agglomerated.
The open structure is likely due to the decomposition of albumen template during the annealing
8

process. This is in agreement with previous literature data, which highlighted as the morphology
of nano-structures can change in the presence of albumen and also the particle size distribution
becomes more homogeneous [35, 37-39].
3
.1.4. TEM
TEM and HR-TEM micrographs, showing the nanostructure of the annealed cadmium
oxide Sample E, are reported in Fig. 4 (a-c). It can be observed the platelet morphology of these
particles. The images in Fig. 4 (a-b) clearly show that the platelet structure surfaces are
composed of agglomerated spherical-shaped particles with uniform size. The particle size can be
estimated from these images in the 18-37 nm range, in reasonable agreement with mean
crystallite size resulting from XRD analysis. The length of the platelets is in the order of hundred
of nanometer, whereas the thickness is in the range of 10-30 nm. SAED pattern inset of Fig. 4 (a)
shows bright spots which confirms the presence of the crystalline phase of the cubic CdO
structure [49]. Fig. 4 (d) reports the EDS analysis, showing the presence only of the elemental
component of cadmium oxide, i.e. Cd and O. The Cd atomic percentage is 79.93% and O atomic
percentage is 20.07%.
However, it is uncommon to obtain CdO nanoplatelets assembled by small-sized
spherical nanoparticles at a such a low synthesis temperature. On the other hand, in the presence
of the biotemplate albumen, interactions established between metallic ions in solution and
functional residues in the biotemplate could help the nucleation, growth and assembly of CdO
nanoplatelets.
3
.1.5. FT-IR
Fig. 5 shows the FT-IR spectra of the samples investigated. Curve (a) of the pure
-1
albumen powder exhibits characteristic peaks at 3258, 3020 and 1638 cm , attributed to the N-
9

H, C-H and C=C stretching vibrational modes, respectively, confirming the presence of the bio-
template in the hybrid material [35]. Curves (b-c) are related to the as prepared and annealed
samples prepared in the absence of template, Sample B and Sample C, respectively. The strong
-1
and broad band appearing at 3200-3550 cm was due to the hydroxyl groups and water
molecules, where the broadening of this band was due to hydrogen bond formation between
-1
water molecules. The strong peaks in the region between 700 and 1700 cm were attributed to
2
-
the bending vibration of CO
3
, including a band arising from the bending mode H O of the water
2
-1
molecules observed at 1629 cm . No peak matching those indicated in the literature for CdO
were instead found on both samples.
Curves (d-e) report the spectrum of Samples D and E, respectively. Both samples are
characterized by the presence of absorption peaks of O-H groups and water in the wavenumber
-1
-1
range 3200-3550 cm , whereas C-H bands from alkyl groups between 2828 to 3000 cm , C=O
-
1
2-
and C-O-C bands from 1085 to 1750 cm derives from residual albumen and CO
3
ions [44-45,
in these latter
from the ambient air,
2
-
5
0-51]. Regarding the presence of absorption peaks characteristics of CO
3
samples, it should be remember that CdO based materials can absorb CO
2
leading to a carbonation of the surface. As suggested in a previous paper [44], the surface phases
formed are amorphous, and then not detectable by XRD, but easily seen in the FT-IR spectrum.
-1
The peak observed around 543 cm , well evidenced in the curve (d-e) is assigned to Cd-
O bond of CdO which confirms the formation of pure CdO nanoplatelets [52]. Hence, on the
basis of FT-IR analysis, it was concluded that the product obtained from the synthesis carried in
the presence of albumen is decomposed at below 130 °C. Furthermore, as proved comparing FT-
IR spectrum of Sample D and sample E, the cristallinity and purity of the formed CdO phase
improved after the annealing process, thus confirming the XRD results before presented.
10

3
.2 Optical and electrical properties
Pure and doped CdO has been largely studied for its optical, electrical and magnetic
properties [53-56]. Due to better microstructural characteristics of annealed samples, Sample C
and E were further investigated in order to exploit their optical and electrical properties. Optical
properties were investigated using a combination of UV-vis diffuse reflectance spectroscopy
(
UV-vis DRS) and photoluminescence characterization. The diffuse reflectance technique is
capable of collecting the reflected flux of light after interacting with the CdO nanopowders. As
shown in Fig. 6 (a-b), diffuse reflectance was measured in the wavelength range of 300-800 nm
at room temperature. The optical band gap values of the samples were determined from
reflectance spectra using the Kubelka-Munk equation (3):
1
)
/ 2
(αhν
= f (hν )
(3)
where, α is the absorption coefficient, hν is the incident photon energy and f is a constant
1
/ 2
depending on the transition probability [57]. The values of (αhν ) versus (hν ) were plotted
as illustrated in Fig. 6 (a-b). The optical band gap values calculated are 3.20 eV and 2.37 eV,
respectively. Then, the smaller value of band gap of the Sample E synthesized in the presence of
albumen can be attributed to a minor amount of defects, due essentially to its more ordered
crystalline structure. According to quantum size effect, as the particle size increases, the number
of atoms that form a particle increases, which consequently make conduction electrons more
attractive to the ions in the particles’ core, and hence decreasing the band gap of the particles.
From another perspective, the decline in the band gap can also be due to the transitions between
2
+
the partially forbidden valence and conduction band of the d-shell electrons of Cd ions [58-59].
The room-temperature photoluminescence properties of Sample E under an excitation
wavelength of 370 nm are shown in Fig.7. There is two emission peaks at 430 and 490 nm.
11

Compared to the previously reported data on the photoluminescence of CdO nanoparticles [60-
6
1], our PL results show an emission peak at shorter wavelengths with a narrow FWHM (about
7 nm), indicating a narrow distribution of nanoparticles diameter. However, the emission peaks
4
at 430 nm can be attributed to the surface-state emission or deep trap emission, which lied at the
longer wavelength range of the emission spectra [49]. For completeness of information, the
annealed Sample C, showed very different absorption UV-Vis pattern and PL properties, as
expected on the basis of the different composition.
Fig.8 shows the variation of dc resistivity with temperature of Sample E. At room
temperature, the electrical resistance was found to be around 20 MΩ. The plot resistance vs.
temperature shows two regions of resistance. Initially, the resistance decreases strongly with the
temperature increase suggesting a semiconductor behavior. The resistance decrease in the
temperature range from 110 to 150 °C is instead much more limited. This suggests that more
than one conduction mechanisms is involved. In the first region, at temperatures between RT and
110 °C, the electrical conduction is due to the increase in electron concentration and mobility
with rise in temperature while, above 110 °C and up to 150 °C, the conduction mechanism is
likely due to polaron hopping [62]. In the hopping mechanism electrons can ‘hop’ from one site
to another by acquiring the necessary activation energy. Such a thermally activated hopping
process is possible at sufficiently high temperatures [63]. The dc resistivity decreases with
increasing temperature because with the addition of thermal energy, electron could be set free
2
-
from O ions. When an electron is introduced in the sample it might be associated with cations,
which results in an unstable valence state [64]. In ionic crystals such as oxides, conduction
electrons (or positive holes) polarize the surrounding crystal lattice by strong electron-lattice
interactions, localizing themselves on the lattice points with inducing lattice distortion. Such
12

localized electrons are called small polarons, and travel by a hopping mechanism accompanied
by the surrounding lattice distortion. The mechanism results in the carrier mobility much lower
than that for the band conduction.
4
. CONCLUSIONS
The synthesis of CdO nanoplatelets by the isothermal evaporation method in the presence
of albumen as a bio-template agent is reported for the first time. The morphological and
microstructural characteristics of products obtained after annealing at 300 °C evidenced that
albumen strongly favour the formation of a pure crystalline cadmium oxide phase.
Characterization results showed indeed that, in the absence of albumen, a mixed cadmium
hydroxide carbonate phase was formed in the first step, whereas in the presence of bio-template
the formation of cadmium oxy(hydroxy) intermediate species was instead favoured (see Scheme
1). Due to the lower decomposition temperature of these latter intermediates, the sample
synthesized in the presence of albumen and annealed at 300 °C, lead to the formation of
nanocrystalline CdO nanoplatelets. Optical analysis has confirmed that the proposed way to
synthesize crystalline CdO nanoplatelets at relatively low temperature is very promising to
obtain this valuable semiconductor material for optical and electrical applications.
13

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21

Table 1: Sample code, composition and related treatment of the investigated samples.
Sample code
Sample A
Sample B
Sample C
Sample D
Sample E
Composition*
Albumen
Treatment
Template
-
None
Cd(OH)2-x(CO
Cd(OH)2-x(CO
CdO
3
)
)
x
x
Dried 130 °C
Annealed 300 °C
Dried 130 °C
Annealed 300 °C
None
3
None
Albumen
Albumen
CdO
*
On the basis of XRD analysis.
Scheme 1
22

FIGURE CAPTION
Fig. 1. TGA curves. (a) Sample A; (b) Sample C; (c) Sample E.
Fig. 2. XRD patterns. (a) Sample A; (b) Sample B; (c) Sample C; (d) Sample D; (e) Sample E.
Fig. 3. SEM images of albumen (a) Sample B; (b) Sample C; (c) Sample D; (d) Sample E (e).
Fig. 4. TEM micrograph (a-b) HR-TEM (c) and corresponding SAED (inset of Fig. 4 (a)) and
EDS (d) pattern of Sample E.
Fig. 5. FT-IR spectra of samples investigated: (a) Albumen; (b) Sample B; (c) Sample C; (d)
Sample D; (e) Sample E.
Fig. 6. UV-vis diffuse reflectance spectra of the cadmium oxide nanoplatelets in (a) Sample C
and (b) Sample E.
Fig. 7. PL spectra of cadmium oxide nanoplatelets in (a) Sample C and (b) Sample E.
Fig. 8. Variation of electrical resistance vs. temperature of Sample E.
23

Fig. 1
24

Fig. 2
25

a
b
c
d
e
Fig. 3
26

a
b
5
0 nm
1
00 nm
c
d
5
nm
Fig. 4
27

Fig. 5
28

Fig. 6
29