مهدی خواجه

Graphene transfer from a metal substrate to the dielectric one is often the first step in graphene device fabrication. in order to achieve the proper performance of these devices surface cleanliness and maximum coverage of transferred graphene are crucial. In this paper wet transfer method and the effects of each stage of the process on transferred graphene quality have been investigated and also the reasons of tear formation and contamination during transfer process have been studied. In this research scanning electron microscopy images has been employed because of graphene surface morphology observation. by applying van der pauw method and measuring electrical resistance which itself depends on coverage percentage and contamination area , the quality of transferred graphene has been evaluated. The results are confirmed by raman spectroscopy in which spectra peaks display crystalline network defects and doping concentration. Finally an optimal process with 95% coverage level and 700 ± 50 ohm electrical resistance has been presented.

In this research, design and fabrication of an integrated heterodyne electrooptic modulator in lithium niobate have been presented. In this modulator, the waveguide is made by using proton exchange process; to exert two high frequency signals, deposited electrodes with Mach-Zender arms between them are used. In this method, every electrical signal is applied on one of the Mach-Zender arms, so that it can be stimulated by one specific frequency; these two signals are united optically to create frequencies equal to sum and subtraction of the input signal frequencies in the output. Also, by using finite element method, the influence of proton diffusion scale in the output light mode, electrode dimension, and configuration in the overlap integral of the light mode and electrical field, as well as electrode impedance, is estimated.

Petrochemical wastewater from isocyanate units contains aromatic and hazardous compounds such as Diaminotoluenes, Mononitrotoluene, Dinitro-toluene, Nitro-phenol, Nitro-cresol. Persulfate and ferrous sulfate can produce sulfate radicals with strong standard oxidation potential. Clinoptilolite, a natural adsorbent; plus sulfate radicals can result in catalytic oxidation of these chemicals. The objective of this study is to evaluate the catalytic oxidation efficiency Fe2ﳷꮲ櫗 Clinoptilolite and cost effectiveness of this process for treatment of petrochemical wastewater containing aromatics.
The effect of study variables including persulfate and ferrous sulfate concentrations, zeolite dosages, pH and oxidation time were investigated. The type and amount of aromatic compounds as well as COD and TSS removal efficiencies were determined. All procedures in study were conducted ethically
The COD and TSS removal efficiencies using catalytic oxidative treatment processes by Fe,Persulfate, Clinoptilolite were 96% and 95%, respectively. The corresponding COD and TSS removal efficiencies using Fe and Persulfate, without zeolite were 85% and 80%, respectively.
The catalytic processes utilizing Fe2ﳷꮲ櫗 Clinoptilolite demonstrates an excellent COD and TSS removal efficiency. Due to its natural nature, low cost compared to chemical oxidants, as well as improvements in the efficiency of advanced oxidation processes, Zeolite can be considered as an efficient and cost-effective alternative to upgrade the catalytic oxidative treatment.

This paper reports on the photo detection properties of graphene nano layer, based on the fabrication of graphene-Si Schottky diode. To fabricate this Schottky junction, a graphene nano layer has been deposited on Si substrate. The Si substrate is oxidized to 270 nm thickness and is patterned with a specific mask after Cr/Au deposition (the thickness of Cr/Au are 50 nm and 150 nm, respectively). The current-voltage (C-V) curves of the diode are analyzed under 670, 700 and 1100 nm illuminations and also under yellow light radiations. To investigate the photo detection properties of graphene nano layer in Schottky diode structure, 700 and 1100 nm radiations are also illuminated to the backside of the diode and then the photo-generated current under both front and back side illuminations are compared. The experiment results demonstrate that the generated currents in the front side mode and under 700 and 1100 nm illuminations have been increased about 23 and 17 times in comparison with the backside mode. This rise in the current shows the graphene effect in photo detection mechanism and also shows the great amount of photo generated current in graphene in the front side illuminations. The C-V curves of the diode under 670 nm and yellow light illuminations demonstrate not only the photo-generated current but also the photo voltage which shows graphene potential for being used as the solar cell. The optical properties of graphene are also discussed in this paper and many theories which can describe the generation of photo current in graphene are presented.

The dual cured resin cements are conventionally used for cementing indirect restorations, such as composite and ceramic inlays and onlays. The aim of this investigation was to evaluate the efficacy of two light-curing units, LED & QTH in polymerization of dual cured resin cement that were placed beneath the ceramic onlays. This experimental study was conducted using 20 specimens. Ten specimens were cured with QTH and the rest with LED light curing devises. Metal rings with 5mm in diameter and 0.5mm in thickness were placed next to the surface of the curved dentin of the molar teeth that were mounted in self cured acrylic resin. A Mylar strip was placed beneath the metal rings and they were filled with Maxcem dual cured resin cement; they were then covered with another Mylar strip. Next, the ceramic onlays with 2mm thickness were placed over the Mylar strips. The specimens were stored in a dry and dark incubator at 37◦C for 24 hours, after cemented onlays were cured for 60 seconds. The Vickers hardness was determined for each sample and data were analyzed by using student T-test and SPSS statistical software. The mean Vickers hardness for QTH cured specimens was 24.75(± 3.59), and this value was 33.92 (±2.28) for the LED light cured specimens. The mean group difference was statistically significant (P<0.001). Based on these findings, the efficacy of LED light curing unit was significantly more efficient in polymerization of resin cements that were placed underneath the ceramic onlays compared with QTH light-curing unit. Key words: Resin cement - Micro hardness test - Radiation effects - Light curing units. Corresponding Author: Dr. Feiz A., Department of Operative Dentistry, School of Dentistry, Isfahan University of Medical Sciences. Isfahan, Iran.