فصلنامه نانو مقیاس
سال سوم شماره 3 (پیاپی 11، پاییز 1395)

Light-energy conversion by photoelectrochemical 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 effect the sensitivity. Optimizing these parameters, it is possible to sense the refractive index changes of 10^-5 .

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 semi-transparent 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 co-precipitation method. In these compositions the value of x varies from 0 to 0.7. Structural and magnetic properties of synthesized powder were characterized by X-ray diffraction XRD, Far-Infrared 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 cation-anion 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.