NANOSCALE
Year:2016 | Volume:3 | Issue:3|Papers Count:8

Light-energy conversion by photo electrochemical cells has been extensively studied in the past 50 years using various combinations of semiconductors. Organic–inorganic perovskites have recently attracted increasing attention as light absorber. A direct band gap, strong light absorption, and high carrier mobility make them excellent absorber in solar cells. The morphology, stoichiometry and crystallinity of perovskites have significant effect on the device performance significantly, then deposition techniques are critical to achieve high efficiency solar cells. Efficiency of perovskite solar cells improve from 9% to 15% in two years due to change of deposition method. In this research, the two step technique was employed for the deposition of perovskite films. Different parameters of this method such as TiO2 thickness, concentration of the CH3NH3I solution and dipping time in the CH3NH3I solution were optimized. Finally, in optimized condition, we obtained a power conversion efficiency of 11.9%.

In this work, we have optimized the performance of the 1D photonic crystal based biosensor. The photonic crystal contains the layers A, B and F which are ZnSe, SiO2 and a microfluidic channel, respectively. Also, there is a radial gradient refractive index defect layer in the center of the structure. By irradiating a plane beam to the proposed structure, a ring-shaped intensity profile is achieved on the output plane of the structure. Any changed in the effective refractive index of the fluid inside of microfluidic channels can cause a change in the radius of the intensity ring. There are different parameters such as number and thickness of the layers and the rate of the refractive index variation in the D layer that can affect the sensitivity. Optimizing these parameters, it is possible to sense the refractive index changes of  Dn=1×10-5 RIU.

In this paper, a mesoscopic-scaled system is proposed based on the embedded graphene layers inside a dielectric medium in order to improve the presentation of optical bistability in THz range. It is firstly shown that the nonlinearity is considerably enhanced in comparison to the visible range. It is also shown that the nonlinear behavior can be increased by increasing the number of graphene layers. For the purpose of analyzing these issues, we use Boltzmann equation to describe the optical conductivity. Then, THz light wave is traced through the embedded graphene layers via Maxwell equations. This yields the optical bistability hysteresis. The results show that the optical bistability is enhanced with increasing the number of graphene layers. The important issue in THz range is the tunability of nonlinearity with an external bias voltage.

In recent two decades, a large share of lighting research has been assigned to investigation on organic light emitting diodes (OLEDs). The basic structure of OLEDs consist of an organic emissive layer and another layers as injection or transporting layers which can be organic or inoarganic. In this report, with varying of silver thickness which acts as anode layer we could fabricated a semitransparent hybrid LED. The minimum thickness which OLED with structure of “ITO/ZnO/Cs2Co3/PDY/MoO3/Ag” emits light both side was about 30 nm. The optical transmittance analysis showed Ag layers with thickness lower than 20 nm has been grown in island mode. In thick Ag layers, atomic force microscopy demonstrated that roughness is increased as Ag thickness is increased. The maximum brightness for semi-transparent hybrid LED was about 2290 cd/m2 with current efficiency of about 1 cd/A.

In this researcher, the MnxFe0.7-xZn0.3Fe2O4 ferrite nanoparticles prepared by coprecipitation method. In these compositions the value of x varies from 0 to 0.7. Structural and magnetic properties of synthesized powder were characterized by Xray diffraction (XRD), FarInfrared spectroscopy (Far-FTIR), Transmission Electron Microscopy (TEM) and vibration sample magnetometer (VSM). The XRD results show that all of the samples have single phase spinel structure. The average crystallite size estimated of about 12 to 7 nm, using Scherrer's formula. The Far-FTIR measurements show, two frequency bonds within the rang 300 to 600 cm-1 indicate the presence of cationanion interactions in the octahedral and tetrahedral sites, respectively. Also Transmission Electron Microscope images show particles size uniform distribution. The VSM results show that the saturation magnetization for all the samples decrease by increasing the manganese content.

In this study, CdWO4 nanoparticles with acetate cadmium (as a starting material) synthesized by hydrothermal method and their photoluminescence emission spectra were investigated. The photoluminescence (PL) spectra showed a peak at 460 nm which is in agreement with the results of cadmium tungstate nanoparticles synthesized by cadmium nitrate (as a starting material). The FTIR spectra confirmed the Cd-O, W-O and O-W bands in the CdWO4 structure. The X-ray diffraction pattern indicated that CdWO4 with a single phase of wolframite structure was synthesized. The SEM images showed that cadmium tungstate nanoparticles with the 35nm average size were synthesized. The results showed that cadmium acetate can be used as a cheaper material for the synthesizing cadmium tungstate.

In this research, three copper sulfide thin films using three different copper-source precursors including: copper sulfate, copper chloride and copper acetate (M1, M2 and M3 samples, respectively) are prepared by spray pyrolysis method at 285oC on glass substrate and their physical properties were investigated. The physical study on these three layers showed that using different copper source precursors lead to various properties not only in morphologies of the samples, but also on their structural, electrical and optical properties. From structural study (XRD) we found that M1 and M2 samples are crystalline in covellite phase with preferred direction of (200) and (102), respectively, but M3 has an amorphous structure. Also from optical properties point of view it is found that all samples have a relatively high absorbance ( ~ 105 cm-1). Electrical properties study showed all samples have p-type conductivity and among these samples M3 has the highest hole concentration (about 1×1019 cm-3). Due to exclusive properties of the sample prepared by copper acetate precursor, i.e. M3, in continue we have investigated the spray rate effect on physical properties of this sample. It was revealed that with decreasing the spray rate the optical properties of the layers are improved and this could be useful in transmitting solar light control device applications.

In this paper, a new physical model is presented to describe the relation between carbon nanotube and catalytic nanoparticle diameter and environmental temperature. This relation is obtained by considering the rate of fenced surface of catalytic nanoparticle in nanotube, which leads to an appropriate formula. Obtained results of the formula show that the diameter of carbon nanotube is increased by increasing of temperature. This happens because catalyst particle has been grown, and carbon atoms which bond to catalyst during growth, will be bonded to the external catalyst atoms. So the nanotube diameter is increased. Furthermore, investigation of dependence of nanotubes diameter on catalyst type during growth shows that if thermal expansion coefficient of catalytic nanoparticle is decreased, the diameter of nanotube at each variation of temperature will be decreased.