Synthesis of nanoparticles of Cadmium Selenide(CdSe)Â  was carried out by using a microwave oven. Cadmium chloride and sodium selenite were used as the precursor materialsÂ  to prepare CdSe nanoparticles. Ethylene glycol was used as the capping agent to control the size of the nanoparticles.Â  Powder XRD pattern reveals the crystal structure of the prepared CdSe nanoparticles. The average particle size of the sample was found to be 54 nm. The morphology of the sample was studied byÂ Â  a SEM. UV-vis absorption spectrum for prepared CdSe sample was recorded. Dielectric studies were carried out for the pelltized sample of CdSe nanoparticles and AC conductivity and DC conductivityÂ Â  values have been measured. The obtainedÂ Â  results are discussed

Krishna ratnam3 and Chidambaradhanu4, S. Ganapathy Raman1, P. Selvarajan2*,

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Recent Research in Science and Technology 2010, 2(10): 72-76 ISSN: 2076-5061 www.recent-science.com  PHYSICS  STUDIES OF CADMIUM SELENIDE (CdSe) NANOPARTICLES SYNTHESIZED  BY SOLVO-THERMAL ROUTE  S. Ganapathy Raman1, P. Selvarajan2∗ Krishna ratnam3 and Chidambaradhanu4 1Department of Instrumentation, Sterlite Industries (I) Ltd,Tuticorin, Tamilnadu 2Department of Physics, Aditanar College of Arts and Science, Tiruchendur-628216, Tamilnadu, India 3Head of the department of QA, Sterlite Industries (I) Ltd, Tuticorin, India 4Physics Research Centre, S.T. Hindu College, Nagercoil 629 003, T.N., India    Abstract Synthesis of nanoparticles of Cadmium Selenide(CdSe)  was carried out by using a microwave oven. Cadmium chloride and sodium selenite were used as the precursor materials  to prepare CdSe nanoparticles. Ethylene glycol was used as the capping agent to control the size of the nanoparticles.  Powder XRD pattern reveals the crystal structure of the prepared CdSe nanoparticles. The average particle size of the sample was found to be 54 nm. The morphology of the sample was studied by   a SEM. UV-vis absorption spectrum for prepared CdSe sample was recorded. Dielectric studies were carried out for the pelltized sample of CdSe nanoparticles and AC conductivity and DC conductivity   values have been measured. The obtained   results are discussed.  Keywords: Nanomaterials; CdSe; X-ray diffraction; SEM; Microwave-assisted solution method; Electrical studies                                                           ∗ Corresponding Author, Email: pselvarajanphy@yahoo.co.in, Tel.:+91 04639 243289, Fax:  +91 04639 245247 Introduction During the last two decades, there has been an enormous interest in nanomaterials due to their novel physical and chemical properties that differ markedly from those of bulk materials. The novel properties of nanomaterials are due to quantum confinement of charge carriers in these materials. Most physico-chemical properties of these nanomaterials are sensitively dependent on their size and shape and researchers are now focusing on developing simple and effective methods for the preparation  of nanomaterials of controlled size and morphology[1-5]. Recently, there are many extensive studies on semiconductor nanocrystals because they exhibit strongly size dependent optical properties and from the viewpoint of fundmental physics, semiconductor nanocrystals provide us with an excellent stage for experimental studies of many-body effects in strongly photoexcited semiconductors[6-9]. Semiconductor nanocrystals are already commercially marketed for application as luminescent biolabels  and have been demonstrated as components in regenerative solar cells , optical gain devices, and electroluminescent devices[10-16]. Cadmium selenide (CdSe) is a useful semiconductor that is a binary compound of cadmium and selenium. It  has common names such as  cadmium(II) selenide, cadmium selenide and cadmoselite.  Three crystalline forms of cadmium selenide viz. wurtzite (hexagonal), sphalerite (cubic) and rock-salt (cubic) are available.  Many researchers have reported their works on semiconducting nanocrystals [17-19]. The nanopowder  of CdSe  provides excellent and unique properties and these properties depend upon shape and size of nanostructures[20,21]. Various methods such as hydrothermal, sol-gel approach and surfactant-assisted approach etc  had been utilized for the synthesis of nanomaterials[22,23]. In this work, nanoparticles of CdSe was synthesized by solvo-thermal route using a microwave oven. Microwaves are   the electromagnetic waves with frequency range of 0.3-300 GHz and corresponding wavelength from 1 mm to 1000 mm. In the microwave irradiation region, the frequency of the applied irradiation is low enough so that the dipoles have time to respond to the alternating electric field and therefore respond to rotation. This method has been successfully applied for the preparation of a variety of nano-sized inorganic materials [24-26]. Compared with conventional heating, microwave heating has an advantage of high efficiency and rapid formation of nanoparticles with a nano-size distribution and less agglomeration. The fundamental mechanism of microwave heating involves agitation of polar molecules or ions that oscillate under the effect of an oscillating electric field. In the presence of an oscillating field, particles try to orient themselves. This constant re-orientation creates friction and collisions between molecules, thus producing heat[27]. The synthesized CdSe nanoparticles using the microwave oven were characterized by XRD method, SEM S. Ganapathy Raman et al./Rec Res Sci Tech 2 (2010) 72-76  method, UV-visible absorption technique,  dielectric studies and conductivity studies and results are reported.  Experimental Methods Synthesis Nanoparticles of CdSe was synthesized by microwave-assisted solution method. The chemicals such as  cadmium chloride and  sodium selenite were used as the precursor materials to prepare CdSe nanoparticles. Cadmium chloride and sodium selenite in 1:1 molar ratio were dissolved in de-ionized water and stirred well using a magnetic stirrer for 30 minutes. During stirring 20 %volume of ethylene glycol was added to the solution. This solution mixture was kept in a microwave oven for 45 minutes (ON for 4 minutes and OFF for 4 minutes). Then the solution was centrifuged, filtered and washed. The precipitate formed was collected and dried at 50 0C for 1 hour. The photograph of the prepared CdSe nanoparticles is displayed in the figure 1.                                  Fig.1: Photograph of CdSe nanoparticles        Instrumentation Powder X-ray diffraction measurement was taken using an automated X-ray powder diffractometer  (PANalytical) with nickel filtered, monchromated CuKa radiation ( λ =1.54056 0A ). The morphology of the nanoparticles was examined by Scanning Electron Microscopy and the SEM image of the synthesized CdSe  nanoparticles  was recorded using a Hitachi Scanning Electron Microscope. A Perkin Elmer UV-visible Spectrophotometer was used to carry out absorption spectrum in the 200-1000 nm wavelength range at room temperature. The pelletized samples of the synthesized nanoparticles were subjected to dielectric and  DC conductivity measurements. The dielectric constant and loss of the samples was measured using an LCR meter and a two probe arrangement [28]. The measurements were taken at fixed frequency of 1000 Hz and at different temperatures ranging from 30 to 100 oC.  AC conductivity of the pellet form of the prepared CdSe nanoparticles was determined using the measured values of dielectric constant and loss.  AC conductivity of the sample was determined using the σac= 2πf εr ε0 tan δ  where f is the frequency of a.c. signal εr is the dielectric constant, ε0 is the permitivity of free space or vacuum and tan δ is the dielectric loss. DC electrical conductivity of the pelletized nanoparticles was calculated using a two-probe arrangement and a megohm  digital meter. The resistance (R) of the sample was measured in the temperature range 30-100 oC and the conductivity was determined using the relation σdc  = d/(RA) where d is the thickness of the pellet, A is the area of cross section the pellet.   Results and Discussion  X-ray diffraction (XRD) studies Figure 2 shows  the XRD pattern  of the CdSe sample. From this figure, the characteristic peaks located at 2θ = 23.45, 25.56, 27.23, 41.21 and 49.87 0 are corresponding to (100), (002), (101), (110) and (112) planes respectively. These peaks match well with the peaks of hexagonal(wurtzite)  crystal structure. The particle size of nanoparticles was determined using the Scherrer’s relation d= (0.9 λ )/ ( β cosθ ) where β  is the full width at half maximum in radians, λ is the wavelength of X-rays used and θ  is the Bragg’s angle. For the various reflection peaks of the XRD pattern, the particle size was estimated and  the average size of nanoparticles of the sample was found to be around 54 nm. The indexing of the diffraction peaks has been carried out using the software “INDEXING” and the unit cell parameters have been found using the software “UNITCELL” [29] and these values are found to be  a= 4.231 Ao  and b= 7.0153 Ao.  The values of   2θ (degrees), Full Width at Half Maximum(FWHM), hkl  and particle size are provided in the table 1.   Fig.2: Powder XRD pattern for the prepared CdSe sample             S. Ganapathy Raman et al./Rec Res Sci Tech 2 (2010) 72-76    Table 1: Values of XRD data and particle size              SEM studies    The SEM image of the synthesized CdSe nanopaticles is displayed in the figure 3. It is observed that different structures have been formed when microwave oven was used to prepare the particles of CdSe and in this case most of  the particles are agglomerated.   Fig. 3: SEM image of CdSe nanoparticles               UV-visible absorption studies UV-Visible-absorption spectrum of  CdSe nanoparticles  in the wavelength range 300-750 nm is  shown in figure 4. The spectrum consists of an absorption shoulder at 606 nm and an absorption edge at 668 nm for the CdSe sample.   This spectral study may be assisted in understanding electronic structure of the optical band gap   of the material.  Absorption in the near ultraviolet region arises from electronic transitions associated within the sample.  The study of the absorption edge is important especially in connection with the theory of electronic structure, which predicts that the band structure is mostly affected near the band extreme. A major objective of this study is   to determine the magnitude of the optical energy band gap. The broadness of the absorption shoulder is attributed to the self-assembly of the nanoparticles and the formation of elongated particles            Fig.4: UV-vis absorption spectrum for the prepared CdSe sample       Electrical studies      Temperature dependence of dielectric constant, AC conductivity and DC conductivity of the disc form of  CdSe nanoparticles  are shown in the figures 5, 6 and 7. It is observed from results that dielectric constant, AC conductivity and DC conductivity of CdSe nanoparticles increase with increase in temperature. The measured values of the dielectric parameters are observed to be larger than those of conventional CdSe   material.      Fig.5:  Temperature dependence of dielectric constant for pellet form of CdSe nanoparticles         Peak No. 2θ (degrees) FWHM (degrees) hkl  Particle size (nm) 1. 2.  3.  4.  5. 23.45235 25.56412 27.23674 41.21453 49.87341  0.02617 0.02442 0.02960 0.02250 0.02967  100 002 101 110 112 54.16 58.23 48.31 58.83 51.52 S. Ganapathy Raman et al./Rec Res Sci Tech 2 (2010) 72-76  Fig.6: Temperature dependence of AC conductivity for pellet form of CdSe nanoparticles               Fig.7: Variation of DC conductivity with temperature for pellet form of CdSe particles            The increase in AC  and DC conductivity values  with temperature shows the semiconducting nature of the sample. Due to thermionic emission and tunneling of charge carriers across the barrier, the conductivity increases with temperature. Because of small size of the particles, the charge carriers reach the surface of the particles more and easily enabling easy electron transfer by thermionic emission or tunneling to enhance the conductivity [30]. The conductivity values are fitted in the equation  σac or dc =  σ0 e-E/KT where σ0 is the constant which depends upon the type of material and K is the Boltzmann’s constant, T is the absolute temperature and E is the activation energy.  Taking natural logarithm on both side of the above equation,  ln σac or dc = ln σ0 –E/KT This is an   equation of a straight line with a slope E/K. The activation energies  of  the synthesized nanoparticles of CdSe  for AC and DC conduction processes  were obtained to be 0.112 and 0.165 eV  respectively.   Conclusion Nanoparticles of CdSe were synthesized   by using a domestic microwave oven.  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Studies of Cadmium Selenide (CdSe) Nanoparticles Synthesized  by Solvo-thermal Route

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Studies of Cadmium Selenide (CdSe) Nanoparticles Synthesized by Solvo-thermal Route

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