Studies on the dielectric properties of CdS nanoparticles
- 5k Downloads
CdS is one of the most important II–VI semiconductors with applications in solar cells, optoelectronics and electronic devices. CdS nanoparticles were synthesized by the wet chemical method. The crystal structure and grain size of the particles were determined by X-ray diffraction. The optical properties were studied by the ultraviolet–visible absorption spectrum. The dielectric properties of CdS nanoparticles were studied in the frequency range of 50 Hz–5 MHz at different temperatures. The frequency dependence of the dielectric constant and dielectric loss is found to decrease with an increase in the frequency at different temperatures. The dielectric properties of CdS nanoparticles are found to be significantly enhanced specially in the low frequency range due to confinement. Further, electronic properties, such as valence electron plasma energy, average energy gap or Penn gap, Fermi energy and electronic polarizability of the CdS nanoparticles were calculated. The AC electrical conductivity measurements reveal that the conduction depends on both the frequency and the temperatures.
KeywordsNanoparticles CdS XRD UV–Vis absorption spectrum Dielectric constant and dielectric loss
Nanomaterials have attracted interest and attention due to their special characteristics that differ from those of bulk solids and molecules. Because the novel properties of nanomaterials depend on their size, structure and shape, an understanding of their mechanism as well as a new direction for synthetic methods are significant issues in nanoscience and nanotechnology (White et al. 2009). As a result of the high surface-to-volume ratio of the nanoparticles, the surface properties have significant effects on their structure, and in turn, have an influence on the nanoscale devices in electronics to target in drug delivery (Hullavarad et al. 2008). In recent years, semiconductor nanoparticles exhibit specific properties due to the quantum confinement effects. As a consequence of their size in the nanometric range and the special luminescent properties, a widening of the band gap is caused when the spatial dimension is reduced (Brus 1986; Rossetti et al. 1985; Hu and Zhang 2006). In semiconductors, the quantum confinement modulates the band structure of the nanoparticles, and hence, many properties can be tuned by changing the nanoparticles size. Owing to the quantum size effect of the semiconductor nanoparticles, the II–VI semiconductor nanoparticles in particular, exhibit size-dependent optical properties (Alivisatos 1996), which are of great importance for potential applications, such as light emitting diodes (Coe et al. 2002), biological labels (Zhang et al. 2003; Sato et al. 2008), optoelectronic devices (Duan et al. 2003) and solar cells (Huynh et al. 2002). Research in semiconducting nanoparticles is one of the most investigated subjects, due to their wide field of applications. Recently, the surface modification of fluorescent semiconductor nanoparticles by biomolecules and nucleic acids, has added a new dimension to nanoparticle research, with respect to their biological applications (Mamedova et al. 2001). This article deals with the preparation of CdS nanoparticles using the wet chemical method. The prepared nanoparticles were characterized structurally and optically using powder the XRD and the UV–Vis absorption spectrum. The dielectric studies have been carried out in the frequency range 50 Hz–5 MHz at different temperatures. Some of the electronic properties, such as plasma energy, Penn gap, Fermi energy and electronic polarizability of the CdS nanoparticles were determined.
Nanoparticles of CdS were synthesized by the wet chemical technique, starting from cadmium nitrate and sodium sulfide precursors. Glucose was used as a capping agent. After 12 h of constant stirring, a pale yellow coloured solution was obtained. The precipitates were washed several times with ethanol and centrifuged and dried at 50 °C for 3 h in vacuum. The structure and phase of the samples were determined by the XRD with CuKα radiation (λ = 1.5481 nm); the 2θ range used was from 10° to 70° at a scanning rate of 0.02 °/s. The UV–visible absorption spectrum of synthesised CdS nanoparticles was recorded using the Varian Cary Model 5000 spectrophotometer in the wavelength range of 400–700 nm. The dielectric constant and the dielectric loss of the pellets of CdS nanoparticles in disk form were studied at different temperatures using an HIOKI 3532 LCR HITESTER in the frequency region of 50 Hz–5 MHz.
Results and discussion
Electronic properties of the CdS nanoparticles
Plasma energy (hωp)
Penn gap (Ep)
Fermi energy (EF)
Electronic polarizability (using Penn analysis)
8.32 × 10−24 cm3
Electronic polarizability (using Clausius–Mossotti relation)
8.33 × 10−24 cm3
Electronic polarizability (using bandgap)
7.17 × 10−24 cm3
AC electrical conductivity studies
Nanoparticles of CdS are synthesized using the wet chemical method. The crystal structure and grain size of the particles are determined using the XRD studies and the particle size of the CdS nanoparticle is found to be 3.85 nm. From the optical absorption spectrum, it is seen that the blue shift of 480 nm with respect to the bulk counterpart is contributed by the quantum confinement effect. The value of the bandgap is found to be 2.58 eV. The dielectric constant and dielectric loss of the CdS nanoparticles are measured in the frequency range of 50 Hz–5 MHz at different temperatures. Dielectric studies reveal that both the dielectric constant and dielectric loss decrease with an increase in the frequency. The dielectric characterization shows the low value of the dielectric constant at higher frequencies. The dielectric constant of CdS nanoparticles is found to be much larger than that of the bulk CdS. Some of the electronic properties, such as the plasma energy, Penn gap, Fermi energy and electronic polarizability of the CdS nanoparticles have been calculated. AC electrical conductivity was found to increase with an increase in the temperatures and frequency. The results reveal that the AC electrical conductivity varies almost linearly with the applied frequency in the high range and increases with different temperatures.
- He R, Qian X, Yin J, Xi H, Bian L, Zhu Z (2003) Formation of monodispersed PVP-capped ZnS and CdS nanocrystals under microwave irradiation. Colloids Surf A 220:151–157Google Scholar
- Hullavarad NV, Hullavarad SS, Karulkar PC (2008) Review of Cadmium Sulfide CdS Nanotechnology: synthesis and Applications. J Nanosci Technol 8:3272–3299Google Scholar
- Smyth CP (1965) Dielectric Behavior and Structure. McGraw-Hill, New York, p 132Google Scholar
Open AccessThis article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.