Dielectric properties of CdS-PVA nanocomposites prepared by ultrasound-assisted method

The electric and dielectric properties of ultrasound-assisted synthesized CdS nanocrystals-PVA mixture were studied in temperature range of 298 K to 498 K and frequency range from 200 Hz to 1 MHz. Scanning Electron Microscopy (SEM) shows that the morphology of CdS nanoclusters are formed in the form of mostly spherical nanoparicles with average size 10 nm. It was found that the nature of polarization processes in pure PVA and CdS-PVA nanocomposites are different. This is due to interfacial polarization in nanocompisites

The influence of the physicochemical processes on the electrical response of Al/p-Si structure with etched surface

In this paper, the electrochemical etching process is used for surface modifcation of the p-Si wafer, named as porous silicon (PS), in the metal–semiconductor (MS) type Schottky diode (SD) with a structure of Al/p-Si. Five regions of PS wafer with diferent etching rates are selected for comparison of them which are called P2, P3, P4, and P5 (P1 is the reference area without porosity). The morphological, structural, and electrical properties of the PS used in the MS-type SD are investigated using feld-emission scanning electron microscope (FE-SEM) images, energy dispersive X-ray (EDX) analysis, and current–voltage (I–V) characteristics, respectively. The FE-SEM images show a meaningful efect on the porosity. The EDX spectrum demonstrates the importance of the chemical efects in addition to the physical changes in the porosity process of the p-Si wafer. The reverse-saturation current (I0), ideality factor (n), barrier height at zero-bias (?B0), and series/shunt electrical resistances are also computed and compared. Some of these parameters (n, Rs, BH) are determined using diferent methods, namely Thermionic emission (TE), Cheung functions, and modifed Norde, and they exhibit strong agreement with each other. The energy-dependent profles of surface states (Nss) are estimated from the I–V data by considering the voltage dependence of ?B (V) and n(V). All the experimental fndings indicate that the etching process of the p-Si wafer signifcantly infuences the electrical performance of the Al/p-Si Schottky diode by increasing the extent of etching

Facile sonochemical preparation of size controlled bismuth hydroxide and oxide nanostructures in the presence of polyvinyl alcohol (PVA) as a capping agent

A simple ultrasound-assisted method involving polyvinyl alcohol (PVA) was employed to prepare the size controlled bismuth oxide and bismuth hydroxide nanostructures. The XRD study confirms the structure of the system as cubic with β-Bi2O3 phase. Scanning electron microscopy revealed that the β-Bi2O3 and bismuth hydroxide samples composed of cube like structures. The SEM micrographs also show the improvement in the particle size distribution upon PVA capping agent addition. Absorption spectra have been obtained using a UV-Vis spectrophotometer to find the optical direct band gap. The optical gap of pure and PVA capped bismuth oxide and bismuth hydroxide nanomaterials have been calculated using the Tauc’s relationship and blue shift in the optical gap has been reported. We also found that the optical band gap (Eg) increases with the increase in molar concentration of the PVA. Fourier transform infrared (FT-IR) spectra of the prepared samples show the presence of characteristic bands for the PVA in the spectrum and reveal the capping effect of PVA on bismuth oxide and hydroxide nanostructures

Comparison of quantum confinement effect on the reduced effective mass of CdSe nanocrystals prepared by different methods

Based on Effective Mass Approximation (EMA) and Hyperbolic Band Model (HBM), the effect of quantum confinement upon the energy band gap and reduced effective masses of CdSe nanoparticles has been examined. The size of nanoparticles were used from experimental data, such as X-ray diffraction (XRD), Scanning and transmission electron microscopy and the band gap also derived from optical spectroscopy. Also preparation of CdSe nanocrystals was achieved via ultrasound- assisted method. X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Uv-visible spectroscopy were used to characterize the structural and optical properties of as-prepared nanostructures. The experimental results showed that the as-prepared CdSe nanostructures are formed with very small nanometer size, which showed a blue shift of about 0.4eV in energy gap. Theoretical study showed that the value of the reduced effective mass of charge carriers in quantum sized CdSe materials differs from its bulk crystal. The comparative analyses and the main reasons of the changes in reduced effective mass value in the case of CdSe nanoparticles are briefly discussed

Preparation of cobalt hydroxide and cobalt oxide nanostructures using ultrasonic waves and investigation of their optical and structural properties

Nanocrystalline cobalt hydroxide and cobalt oxide compounds have been prepared using ultrasound-assisted method and some of their optical and structural properties have been characterized by thermogravimetric analyses(TGA), X-ray diffraction (XRD), scanning electron microscope (SEM), and UV-Visible spectroscopy. The results of thermogravimetric analyses show a sharp change in TGA peak, and the oneset of the peak (at 250°C) is transition temperature from hydroxide to oxide of the product. The optical absorption studies show that there are two direct band gaps in Co3O4 nanostructures. The XRD patterns of the prepared samples shows formation of pure cobalt oxide in cubic structure and cobalt hydroxide compound in hexagonal structure with average grain sizes are below 30 nm. Surface morphology of the prepared structures shows that the nanoparticles from nearly globular aggregates of microdimensions

Frequency and voltage dependence of electrical and dielectric properties in metal-interfacial layer-semiconductor (MIS) type structures

© 2020 Elsevier B.V.Zinc-ferrite nanostructures were fabricated using ultrasonic-assisted-method. FE-SEM, EDX and XRD were utilized for the investigation of morphological and structural properties. Au/(ZnFe2O4-PVP)/n-Si MPS structures were prepared for the purpose of characterizing electrical and dielectric properties via impedance-spectroscopy-method (ISM) between -2 V and 5 V in the frequency range of 10 kHz-5MHz. The frequency-dependent values of electrical parameters such as VD, ND, EF, WD and ΦC-V were extracted from the reverse bias C−2-V. Voltage-dependent profiles of Rs and Nss was calculated using Nicollian-Brews and high-low frequency capacitance (CLF-CHF) methods. Results showed Nss is more effective are depletion and inversion whereas accumulation region is the region at which Rs is more effective. The real and imaginary parts of ε* and M* were calculated and showed strong dependence on frequency and voltage. The higher values of C, G/ω or ϵ', ϵ" at low frequencies and observed peak in the M″-V and (tanδ)-V were associated with Nss

Dielectric and optical properties of CdS-polymer nanocomposites prepared by the successive ionic layer adsorption and reaction (SILAR) method

The successive ionic layer adsorption and reaction (SILAR) method has been used to grow epitaxial CdS-polymer nanostructures as thin films with different surface morphology and particle size. The main purpose of the study was to investigate the dielectric properties and a.c. electrical conductivity (σ a.c.), by a.c. impedance spectroscopy between 1 kHz and 1 MHz, at room temperature, of CdS-polymer nanocomposites produced by use of 2, 6, and 10 cycles of SILAR. The surface morphology and optical absorption of the samples were characterized by scanning electron microscopy (SEM) and UV-visible spectroscopy, respectively. Determination of the energy gaps of CdS-polymer nanocomposites prepared by use of different numbers of cycles of SILAR reveals that the band gap decreases with increasing number of cycles (J. Cryst. Growth 305, 175-180, 2007). This behavior is because of the growth of nanoparticles in the matrix materials, and can be explained by changes in the amount of confinement as a consequence of particle size variation. SEM images also confirm that different numbers of cycles lead to different morphology. Frequency-dependent dielectric properties and a.c. electrical conductivity of the samples prepared by use of different numbers of cycles of SILAR were investigated, and comparative studies on some electrophysical properties of the samples are reported. Experimental results show that values of the dielectric constant (ε), dielectric loss (ε′), dielectric loss tangent (tanδ), the real (M) and imaginary (M′) parts of electric modulus, and σ a.c. are highly dependent on the frequency and the number of cycles. It can be concluded that changing the frequency and the number of cycles substantially alters both the dielectric properties and a.c. electrical conductivity of the samples. © 2014 TMS