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Author's Accepted Manuscript

Growth and characterization of differentstructured CdO using a vapor transport

M. Zaien, A. Hmood, N.M. Ahmed, Z. Hassan

PII: S0167-577X(13)00422-9DOI: http://dx.doi.org/10.1016/j.matlet.2013.03.093Reference: MLBLUE15074

To appear in: Materials Letters

Received date: 6 March 2013Revised date: 16 March 2013Accepted date: 18 March 2013

Cite this article as: M. Zaien, A. Hmood, N.M. Ahmed, Z. Hassan, Growth andcharacterization of different structured CdO using a vapor transport, Materials

Letters, http://dx.doi.org/10.1016/j.matlet.2013.03.093

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Growth and characterization of different structured CdO using a vapor

transport

M. Zaiena,b,

*, A. Hmooda, N. M. Ahmed

a, Z. Hassan

a

a

Nano-Optoelectronics Research and Technology LaboratorySchool of Physics, Universiti Sains Malaysia, 11800 USM, Penang, Malaysia

b Department of Physics, College of Education for Pure Sciences, University of Anbar, IraqCorresponding author: mustafa1973_zzz@yahoo.com

H/P: 0060174596002, Fax: 00604-6579150

Abstract

Different structured of CdO ( nano- and micro ) were successfully synthesized using a vapor

transport process ( solid-vapor deposition ) method for CdO powder on p-type silicon substrates

at 1400 K with argon flow. Scanning electron microscopy revealed that the CdO morphology

exhibited various shapes depending on the position of the Si substrates from the CdO powder in

the furnace. Microstructured CdO included microrods and microcubes, microrods had diameters

in the range of 600 nm to 990 nm and different lengths of more than 10 m. The X-ray

diffraction pattern showed that the CdO has a cubic and polycrystalline structure.

The optical

properties of the different structured of CdO were investigated by photoluminescence

spectroscopy. Strong emission peaks were observed at 531 nm (2.34 eV) for the nanostructured

and 524 nm (2.37 eV) for the microstructured, which are ascribable to the near-band-edge

emission of CdO.

Keywords: Deposition ; CdO ; Microstructure ; Polycrystalline;Optical properties

1. Introduction

Cadmium oxide is a IIVI compound semiconductor consisting of cadmium from group

II and oxygen from group VI in the periodic table of elements [1]. The different structured CdO

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materials are now widely used as transparent conductive oxides (TCO) in various physical

applications [2], specifically in optoelectronic devices such as solar cells because of its high

transparency in the visible region of the solar spectrum [3]. These materials are also used in

diodes, gas sensors and transparent electrodes [4]. CdO has a narrow direct band gap ranging

from 2.2 eV to 2.5 eV [5]. In addition, it has several attractive properties, such as low resistivity,

high density (8150 Kg/m3), high melting point (1500 C ), and has a cubic crystal structure

[NaCl, face center cubic (fcc) type, and lattice constant a = 0.4695 nm] [6]. Numerous methods

have been adopted to grow different structured CdO, such as thermal evaporation in vacuum [7],

chemical bath deposition [8], vaporliquidsolid (VLS) [9]. Cadmium can be directly heated upto 900 C in air or with a trace amount of oxygen in an argon (Ar) flow [10]. In this study,

different structured CdO were synthesized via a solid-vapor deposition at 1400 K with Ar flow.

The morphological, structural, and optical properties of the nano- and micro-structured CdO

were also studied and investigated.

2. Materials and Methodology

The different structured CdO were synthesised by solid- vapor deposition, a method was

selected due to its lower cost and simplicity. The process of the Radio Corporation of America

was used to remove the oxide layer from a P-type Si wafers (1 cm 1 cm 283 m) with a

(111) orientation and a resistivity of 0.75 cm. CdO powder (purity: 99.99%, Aldrich) in a

quartz boat was placed at the center of a horizontal quartz tube furnace ( inner diameter, 20

mm). The Si substrates were placed downstream of the flowing gas (12 cm from the CdO

powder boat, with the polished side facing the source material) in another boat. The distance

between the Si substrates was approximately (1 cm). Fig. 1 shows the tube furnace setup. A flow

of Ar gas was initially used to purify the tube. When the temperature reached 1400 K, the CdO

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powder and Si substrates were placed inside the furnace for 2 h with an Ar flow of

approximately 350 Sccm. The samples were then cooled for 2 h at room temperature. X-ray

diffraction (XRD) measurements were carried out using a high- resolution X-ray diffractometer

system (XPert PRO MRD PW3040, PANalytical) to determine the CdO crystallite structure.

Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis (JSM-6460

LV, Japan) were conducted to determine the surface morphology and composition of the nano-

and micro-structured CdO. Photoluminescence (PL) study was carried out via a spectroscopy

system (HR 800UV, Jobin Yvon, USA) at room temperature using He-Cd laser ( = 325 nm).

3. Results and discussion

Fig. 2 (1S) shows the XRD patterns of the nanostructured CdO on the Si substrate. The

diffraction peaks observed at diffraction 2 angles of 33o, 38o, 55o, 65o, 69o, and 82o

corresponded to the (111), (200), (220), (311), (222), and (400) planes. These peaks also

corresponded to those observed for CdO (JCPDF File No. 03-065-2908). Fig. 2 (2S and 3S)

show the XRD patterns of the microstructured CdO on the Si substrates (rods and cubes). Thediffraction peaks observed at diffraction 2 angles of 33o, 38o, 55o, 65o, and 82o corresponded to

the (111), (200), (220), (311), and (400) planes. The spectrum indicates that the studied different

structured CdO are polycrystalline in nature with a cubic structure, except for two peaks at 44.5 o

and 31.8o. These two different peaks are related to the Si carbide of the XRD sample holder and

Cadmium element in (2S) microrods and (3S) microcubes CdO, respectively. Prominent peaks

were used to calculate the average crystallite sizes of the different structured CdO using the

Scherrer equation, which is expressed as follows [3,9]:

TE

O

COSD

94.0 (1)

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Where is the wavelength ( = 1.542 ) (CuK), is the full width at half maximum ( FWHM )

of the line, and is the diffraction angle. The average crystallite size decreased with an increase

in the lattice constant when the distance of the substrates from the CdO powder was increased.

The crystallization of the CdO and the intensity of the peaks decreased because of the structural

defects in the microstructured compared with the nanostructured without any defects due to (1S

sample) is near from the CdO powder at the center of a furnace tube as in Fig. 1, and there is a

high temperature with a prolonged time (2 h) to improve crystallization of the CdO same the

effects of annealing in the report [11]. The strain of different structured CdO grown on the Si

substrates along the c-axis can be calculated using the following equation [12]:

O

O

ZZ

C

CC%H (2)

Where C represents the lattice constant of the different structured CdO estimated from XRD

data, andO

C is the standard lattice constant for the unstrained CdO [7]. The negative values of

the strain reveal the compressive strain of the nanostructured and microrods CdO, whereas the

positive value of the strain reveals the tensile strain of the microcubes CdO. These extremely

low values of compressive and tensile strains suggest that the synthesized nano- and micro-

structured CdO have high-quality crystal geometry [3,13]. All results are presented in Table 1.

Fig. 3 shows the SEM images of the surface morphology of the different structured CdO

deposited on the Si substrates. The various shapes of the grown CdO structures depend on the

position of the Si substrates from the CdO powder in the furnace and the prolonged reaction

time (2 h). Fig. 3(1S) shows the growth of grass packs-like nanostructured CdO. Microstructured

CdO included microrods and microcubes, as shown in Fig. 3(2S and 3S), respectively. Microrods

had diameters ranging from 600 nm to 990 nm and various lengths greater than 10 m. The EDX

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spectrum and atomic composition of the nano- and micro-structured CdO on the Si substrates are

shown on the right side of SEM images. The tabulated atomic and weight percent values of the

elements in the CdO structures on the Si substrates are presented in Fig. 3. The concentrations of

these elements are indicated by the peaks, which clearly shows that the elements corresponding

to the peaks comprise the CdO on the Si substrate.

Fig. 4 (1S, 2S, and 3S) show the photoluminescence spectroscopy of the nanostructured,

microrods, and microcubes of CdO, respectively, at 325 nm excitation. The PL spectroscopy

show strong emission peaks were observed at 531 nm (2.34 eV) for the nanostructured and 524

nm (2.37 eV) for the microstructured (microrods and microcubes), which are ascribable to the

near-band-edge (NBE) emission of CdO [9,13]. These values indicate the quantum confinement

effect of the as-synthesized nano- and micro-structured CdO. The results also revealed that the

intensity of the emission peaks depends on the structure shape and the surface morphology.

4. Conclusion

Different structured CdO were successfullysynthesized by solid-vapor deposition of CdO

powder on a p-Si substrate at 1400 K. The XRD pattern showed that nano- and micro-structured

CdO are polycrystalline in nature with a cubic structure. The average crystallite sizedecreased

with an increase in the lattice constant when the distance of the substrates from the CdO powder

was increased. SEM results showed that the various shapes of the grown CdO structures depend

on the position of the Si substrates in the furnace. Microstructured CdO included microrods and

microcubes. The direct band gaps energy were 2.34 eV for nanostructured CdO and 2.37 eV for

microstructured (microrods and microcubes). These nano- and micro-structured CdO can be used

in various technological applications, especially in solar cells.

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Acknowledgement: The authors gratefully acknowledge the support of the School of Physics

in Universiti Sains Malaysia.

References

[1] Ortega M, Santane G, Morales-Acevedo A. Superficies y Vacio 1999;9:294-295.

[2] Sravani C, Reddy KTR, Hussain OMd, Reddy PJ. Thin Solid Films 1994;253:339-343.

[3] Zaien M, Ahmed NM, Hassan Z. Superlattices and Microstructures 2012;52:800-806.

[4] Hames Y, San SE. Solar Energy 2004;77 :291-294.

[5] Senthil K, Tak Y, Soel M, Yong K. Nanoscale Res Lett 2009;4:1329-1334.

[6] Reddy S, Kumara Swamy BE, Umesh Chandra, Sherigara BS, Jayadevappa H. Int J

Electrochem Sci 2010;5:10-17.

[7] Dantus C, Rusu RS, Rusu GI. Superlattices and Microstructures 2011;50:303-310.

[8] Dhawale DS, More AM, Latthe SS, Rajpure KY, Lokhande CD. Applied Surface Science

2008;254:3269-3273.

[9] Kuo Tz-Jun, Huang Michael H. J Phys Chem B 2006;110:13717-13721.

[10] Liu X, Li C, Han S, Han J, Zhou C. Appl Phys Lett 2003;82:1950.

[11] Vigil O, Cruz F, Morales-Acevedo A, Contreras-Puente G, Vaillant L, Santana G. Materials

Chemistry and Physics 2001;68:249252.

[12] Tsay C.-Y, Fan K.-S, Chen S.-H, Tsai C.-H. J Alloys Compd 2010;495:126-130.

[13] Zaien M, Ahmed NM, Hassan Z. Chalcogenide Letters 2012;9:115-119.

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Figures Captions

Fig. 1: Tube furnace setup.

Fig. 2 : XRD patterns of the (1S) nanostructured CdO, (2S) microrods CdO, and

(3S) microcubes CdO on silicon substrates.

Fig. 3: SEM images and EDX analysis of the (1S) nanostructured CdO, (2S)

microrods CdO, and (3S) microcubes CdO on silicon substrates.

Fig. 4: Photoluminescence spectroscopy of the (1S) nanostructured CdO, (2S)

microrods CdO, and (3S) microcubes CdO.

Table caption

Table 1: Values of the lattice constant (a), the crystallite size (D), and the strain

( zz) for CdO structures at different distances of the Si substrates from the CdO

powder in the furnace.

Table 1:

Highlights

>Different structured CdO were synthesized by vapor transport on Si substrate at

1400 K.> The XRD pattern showed that structured are polycrystalline in nature

with a cubic structure. >SEM results showed that the CdO structures depend on the

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position of the Si substrates in the furnace.> The direct band gaps energy were 2.34

eV for nanostructured and 2.37 eV for microstructured.

Fig. 1

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Fig. 2 Fig. 4

Fig. 3

ure(s)