Optical properties of CdS/PVA nanocomposite films synthesized using the gamma-irradiation-induced method

Monodispersed spherical CdS nanoparticles embedded into polyvinyl alcohol (PVA) films are synthesized by using an in-situ gamma-irradiation-induced method. The formation mechanism of CdS nanoparticles capped by two united cells of PVA is purposed by means of surrounding the CdS nanoparticles with OH bonds of the PVA chain. CdS nanoparticles are found to possess an unusual orthorhombic structure in monoclinic crystalline PVA. The polymer matrix affords protection from agglomeration and controls the particle size. It is found that the distribution of the prepared nanoparticles increases and a narrower size distribution is observed when the gamma radiation is varied from 10 to 50 kGy. While the average size of the nanoparticles is found to be less affected by the variation of the gamma radiation doses. The size range of the synthesized nanoparticles is 14±1 nm. The optical absorption spectra of synthesized CdS nanoparticles in a polymer matrix reveal the blue shift in the band gap energy with respect to CdS bulk materials owing to quantum confinement effect. The photoluminescence study of nanocomposite films shows the green emission arising from the crystalline defects

Preparation, characterization and thermal degradation of Polyimide (4-APS/BTDA)/siO2 composite films.

Polyimide/SiO2 composite films were prepared from tetraethoxysilane (TEOS) and poly(amic acid) (PAA) based on aromatic diamine (4-aminophenyl sulfone) (4-APS) and aromatic dianhydride (3,3,4,4-benzophenonetetracarboxylic dianhydride) (BTDA) via a sol-gel process in N-methyl-2-pyrrolidinone (NMP). The prepared polyimide/SiO2 composite films were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM) and thermogravimetric analysis (TGA). The FTIR results confirmed the synthesis of polyimide (4-APS/BTDA) and the formation of SiO2 particles in the polyimide matrix. Meanwhile, the SEM images showed that the SiO2 particles were well dispersed in the polyimide matrix. Thermal stability and kinetic parameters of the degradation processes for the prepared polyimide/SiO2 composite films were investigated using TGA in N2 atmosphere. The activation energy of the solid-state process was calculated using Flynn–Wall–Ozawa’s method without the knowledge of the reaction mechanism. The results indicated that thermal stability and the values of the calculated activation energies increased with the increase of the TEOS loading and the activation energy also varied with the percentage of weight loss for all compositions

Influence of exposure time on structural, optical and electrical properties of zinc sulphide nanoparticles synthesized by microwave technique

Zinc sulphide (ZnS) nanoparticles were synthesized via simple, rapid and energy efficient microwave technique. The obtained nanoparticles were found to possess a cubic structure with an average particle size of less than 5 nm. By changing the microwave irradiation time from 5 to 30 min, the average size of nanoparticles increased and a broader size distribution was obtained. The degree of crystallinity also increased with increasing irradiation time and reached to maximum at 25 min and then fell by rising further the irradiation time. The absorption spectra of prepared ZnS nanoparticles revealed a blue shift in the band gap energy with respect to the bulk counterpart owing to the quantum confinement effect. The photoluminescence study showed the emission intensity increased with increasing the irradiation time up to 25 min due to the increment in crystallinity of the obtained nanoparticles. Further study indicated that the microwave irradiation time has also influenced the electrical properties of nanoparticles, so that the DC conductivity increased from 1.08×10-6 to 1.67×10-4 S/m for irradiation time of 5-25min and decreased to 1.74×10-6 S/m for further irradiation time at 30 min. The dielectric constant showed a power law dispersion with no observed peak for all samples with different irradiation times

Pinch-off effect in p-type double gate and single gate junctionless silicon nanowire transistor fabricated by atomic force microscopy nanolithography

The spark of aggressive scaling of transistors was started after the Moors law on prediction of device dimensions. Recently, among the several types of transistors, junctionless transistors were considered as one of the promising alternative for new generation of nanotransistors. In this work, we investigate the pinch-off effect in double gate and single gate junctionless lateral gate transistors. The transistors are fabricated on lightly doped (1015) p-type Silicon-on-insulator wafer by using an atomic force microscopy nanolithography technique. The transistors are normally on state devices and working in depletion mode. The behavior of the devices confirms the normal behavior of the junctionless transistors. The pinch-off effect appears at VG +2.0 V and VG +2.5 V for fabricated double gate and single structure, respectively. On state current is in the order of 10-9 (A) for both structures due to low doping concentration. The single gate and double gate devices exhibit an Ion/Ioff of approximately 105 and 106, respectively

Single step thermal treatment synthesis and characterization of lithium tetraborate nanophosphor

This study includes the synthesis of nano-sized lithium tetraborate by an innovative single step thermal treatment method and characterization of the products. The heating temperature for the synthesis was varied between 200 and 850 °C with the retention time of 2 h. Polyvinyl pyrrolidone (PVP) with different concentrations was used as surfactant. Characterization of the samples was achieved by thermogravimetric analysis (TGA), derivative thermogravimetry analysis (DTG), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM) techniques and UV–vis spectroscopy. Thermal analysis of initial solution allowed the optimization of the heat treatment program and showed that the thermal stability of samples is started at 460 °C. FT-IR, XRD and TEM results proved the formation of pure nano-crystalline lithium tetraborate at temperature between 460 and 750 °C. Furthermore, the band gap investigation was performed using UV–vis spectra in the presence of different concentrations of PVP and in variety of calcination temperatures. The estimated optical bandgap was found to be between 5.2 and 6.2 eV

Simulation of transport in laterally gated junctionless transistors fabricated by local anodization with an atomic force microscope

In this paper, we have investigated the characteristics and transport features of junctionless lateral gate transistors via measurement and simulations. The transistor is fabricated using an atomic force microscopy (AFM) nanolithography technique on silicon-on-insulator (SOI) wafer. This work develops our previous examination of the device operation by using 3D numerical simulations to offer a better understanding of the origin of the transistor operation. We compare the experimental measurements and simulation results in the transfer characteristic and drain conductance. We also explore the behavior of the device in on and off states based on the variation of majority and minority carriers' density, electric-field components, and recombination/generation rate of carriers in the active region of the device. We show that the device is a normally on device that can force the current through a depleted region (off state) and uses bulk conduction instead of surface conduction. We also found that due to the lateral gate design, low-doped channel, and lack of the gate oxide the electrostatic squeezing of the channel effectively forces the device into the off state, but the current improvement by accumulation of carriers is not significant

Growth and characterization of La0.7Na0.3MnO3 thin films prepared by pulsed laser deposition on different substrates

Perovskite manganite La0.7Na0.3MnO3 thin films were directly grown on MgO (1 0 0), Si (1 0 0) and glass substrates by pulsed laser deposition. From the XRD patterns, the films are found polycrystalline single-phases rhombohedral. The surface appears porous and cauliflower-like morphology for all LNMO films. LNMO films deposited on the glass substrate were presented smooth morphologies of the top surfaces as compared with other films. The highest magnetoresistance value obtained was −18.86% for LNMO/MgO films at 80 K in a 1 T magnetic field. Phase transition temperature is 221 K for LNMO/Cg, 214 K for LNMO/Si and 144 K for films deposited on MgO substrates. The films exhibit ferromagnetic transition at a temperature around 286 K for LNMO/MgO, 304 K for LNMO/Si and 292 K for LNMO/Cg thin film. The Curie temperature of LNMO films deposited on the glass substrate, 292 K is the highest value that is reported in literature for LNMO films deposited on low-cost amorphous substrates

Structural, optical and electrical properties of ZnS nanoparticles affecting by organic coating

In this study the influence of the organic polymeric coating and its concentration on the structural, optical and electrical properties of ZnS nanocrystals has been investigated. In this matter, PVP-capped ZnS nanocrystals were prepared by a simple, rapid and energy efficient microwave method. The XRD results confirmed the formation of single phase cubic nano crystalline structure. TEM images showed the formation of well isolated spherical nanoparticles with the average size of less than 5.5 nm. The presence of tensile strain in all samples was determined from Williamson-Hall analysis. The elemental compositions of Zn, S and O were quantitatively obtained from EDX analysis, where the FT-IR spectra confirmed coordination with O atoms of PVP. The band gap and absorption edge shift was determined using UV–visible spectroscopy. The PL spectra of the PVP-capped ZnS nanoparticles appeared broadened from 370 to 500 nm due to the presence of multiple emission bands attribute to the sulfur and zinc vacancies or compounded effect of PVP. The electrical property study of samples indicated the conductivity enhancement from 2.981×10-6 to 7.014 ×10-6 S/m by increasing PVP concentration. Increasing of dielectric constant and decrease in the peak value of tan δ by raising the PVP concentration were observed

Field effect in silicon nanostructure fabricated by atomic force microscopy nano lithography

The electrical property of silicon nano-structure is highly considered in nanoelectronics. In this context we investigate the field effect in nanostructure Junctionless p-type silicon nanowire transistor under the lateral gate voltage. The device fabricated by means of Atomic Force microscopy (AFM) nano lithography on Silicon on Insulator (SOI) wafer. I-V characteristic and the Drain/Source current under the lateral gate voltage investigated. The subthreshold swing measured and hysteresis effect observed for the old sample compared to new one

High curie temperature for La5/8Sr3/8MnO3 thin films prepared by pulsed laser deposition on glass substrates

The manganite LSMO films were successfully grown on glass substrates without any additional buffer layer by pulsed laser deposition. The films have been investigated by X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), electrical and magnetic measurements. From the XRD pattern the film is found to be polycrystalline single-phase’s character. The LSMO thin films growth on glass substrate, follows the island growth model with average grain size of 44.46nm. The metal-insulator transition (TMI) temperature was above room temperature and electrical conduction mechanism of LSMO films below phase transition temperature (TP) is due to the electron-electron (major) and electron-magnon scattering processes. The Curie temperature of LSMO films is around 352 K, which is one of the high TC in all LSMO films and as our knowledge, is the highest value that is reported in literature for low cost amorphous substrates such as glass. The low resistivity, high TMI and high TC makes these LSMO films very useful for room temperature magnetic devices