محمد صبائیان

In this study, ZnCdTeS quantum dots (QDs) with luminescent properties at different emission wavelengths were utilized to enhance the dielectric and electro-optical characteristics of nematic liquid crystal (NLC) cells. At various temperatures, the dielectric permittivity components (ɛ‖ and ɛꓕ) and dielectric anisotropy (Δɛ) of NLC samples containing ZnCdTeS QDs were measured. ɛ‖ increases considerably more than ɛꓕ in the nematic phase when QDs are introduced. The dielectric anisotropy of the system has increased by approximately 19% in the presence of QDs with red emission, which is a result of a significant enhancement of ɛ‖. The NLC environment induces one-dimensional arrays of QDs in the system, which enhances the dielectric properties of the system, as demonstrated by the dielectric results. The electro-optical findings indicate that including QDs substantially reduces the threshold voltage of NLC cells. Incorporating quantum dots into liquid crystal led to a reduction in the threshold voltage from 2.57 V for pure NLC to 2.21 V. QDs improve the effective field of a system by reducing the screening effects caused by ionic impurities in the system. Anisotropy enhancement, effective field increase within the cell, and QD-NLC interaction improvement all contribute to the enhancement of the cell's switching characteristics.

Seed germination is one of the most important and basic stages of plant growth and development so it has great importance and effect on other stages of its growth. Cassia is a plant from the legume family and has many medicinal properties. Cassia propagation is done by seeds, but no study and report on the tolerance of these seeds to salinity stress in the country have been presented yet. Two factorial experiments were performed in a completely randomized design at the Seed Technology Laboratory of Agricultural Sciences and Natural Resources University of Khuzestan. In the first experiment, the effect of hormone priming treatment with gibberellin, halopriming with potassium nitrate, and hydro priming on Cassia seed germination was investigated. The results of this experiment showed that the highest seed vigor was obtained in the treatment of 50 mg/l gibberellin for 12 hours of priming. After selecting the best treatment (gibberellin 50 mg/l for 12 hours), germination characteristics of primed seeds compared with no primed seeds under salinity stress (0, 4, 8, 14, 16, and 20 dS/m). The results showed that seed tolerance to salinity stress at the germination stage increased significantly with seed priming. The highest seed vigor was observed in priming treatment at no salinity stress condition (339.89) while the lowest seed vigor of primed treatment was observed in 20 dS/m. Unprimed seeds could not withstand salinity stress beyond 4 dS/m.

Remote spectroscopy of material plasmas can be used well to detect and identify the material identity especially the explosive and organic materials. The plasma can be generated either through the applying high power density laser radiations or high DC voltages in the vacuum circumstance. In this paper, to generate the material plasmas, a high DC voltage of 2 kV was applied in the T-shaped lamp with argon atmosphere. The plasmas of two explosive materials of TNT and picric acid and two organic materials of 4-nitrobenzoic acid and 3,5-dinitrobenzoic acid in quantities of 35 mg were at first generated and then their spectra were measured from distances of 1.55, 2, and 2.31 meters. The spectra of material plasmas ranged from 200 nm to 800 nm consisting of lines C2, H, O, N, and Ar. The limit-of-detection from a distance of 2 m was determined consequently. Finally, with the use of two methods, the explosive materials were distinguished from the organic ones and the calibration curve was also prepared.

In this study, colored glass was prepared using layer coating with silver nanostructures such as nanowire, spherical nanoparticles and dendritic. Silver nanowires were prepared by a solvo-thermal and polyol combination method with different molar ratios of poly-vinyl-pyrrolidone and silver nanoparticles by polyol and chemical reduction methods. The silver dendritic nanostructure was made by dip coating method in different sizes. Characterization of silver nanostructures was accomplished by X-ray diffraction, scanning electron microscopy and ultraviolet-visible spectroscopy. The cleaned glasses then were coated by immersion in a solution of silver nanostructures. In order to fix the color of the glasses after the coating operation, the glasses were heated at 700 °C. The colors of the glasses were in the yellow color range. The glass color characteristics, including the color parameters and color coefficients and the dominant wavelength, were studied using a spectrophotometer and color triangle. It was observed that the color coefficients (L*a*b*) for the same concentrations and different morphologies of the nanostructures were different and varied from (55.87, -8.39 and 9.94) for nanowires to (-66.85, -20.65 and 18.91) for dendritic and (46.69, -1.65 and -30.62) for nanoparticles. The effect of the concentration and size of nanostructures on the color of the glasses was also investigated.

In this paper, three types of two-dimensional phononic crystals comprising of steel rods (with circular, square, and triangular cross-sections) in water-ground matter were investigated. The frequency band structure for the x-y mode was calculated using Finite Element Method. What the results show complete and incomplete gaps for phononic crystals with a circular and triangular cross-sections and for the square cross-section an incomplete gap appeared. The results show the maximum intensity for phononic crystal with circle, square and triangle cross section, 1.15 MHz, 1.11 MHz and 1.27 MHz, respectively. The effect of change of source distance to sheet, effect of sheet thickness change on focal point intensity and focal point distance to source were investigated. In general, the obtained results are in good agreement with other existing results.

In this study, waveguide properties of graphene nanoribbon on hBN and a substrate were investigated. Precisely, the plasmonic mode properties including real part of refractive index, propagation length, and figure-of-merit (FoM) on frequency, Fermi energy of graphene, and substrate in the mid-IR spectrum range were inspected. The simulated results show that graphene waveguide is intensively sensitive to the frequency, Fermi energy and structural geometry in the mid-IR range. Also, the propagation length for a Fermi energy of 0.3 (0.9) eV in the frequency range of 1375 cm-1 to 1600 cm-1 reachs from 0.1 (0.4) to 0.38 (4.15) µm, where shows a 3 (10) fold enhancement.

In this research, the synthesis of strontium aluminate nanoparticles (SrAl2O4) by using of combustion method assisted by microwave and doping them with dysprosium (SrAl2O4:Dy) have been investigated. Characterization of nanoparticles was performed by XRD, FT-IR, EDS, FESEM, UV-Vis and PL. In the synthesis stage, the data of XRDs confirmed the formation of the monoclinic phase of strontium aluminate with space group P1211, in the sample with the fuel to nitrate ratio of 3 to 1, pH value of 5.5, and microwave irradiation time of 5 minutes, calcination time of an hour and calcination temperature of 600 °C. By using the X-ray powder diffraction data and Scherrer's formula, the average size of nanocrystallites was obtained about 26 nm. In the substitution stage, in order to optimize the luminescence of SrAl2O4 nanoparticles, different percentages of doping were investigated. Among the synthesized nanoparticles, the sample of Sr0.9Al2O4: Dy0.1 nanoparticles with the average nanoparticles size 34±3 nm; most frequent distribution of nanoparticles between 30 and 35 nm; optical gap energy equal to 4.21 ± 0.01 eV and with the highest emission intensity in photoluminescence spectrum, was chosen as an optimal sample in terms of the structural and optical properties.

In this article, we present fabrication and characterization of two-layered polymer light emitting diode (PLED) with a structure of ITO/PEDOT:PSS/MEH:PPV/Al which emits a orange-colored light, with the aim of reduction of lightening voltage. In this work, the PEDOT:PSS layer, as hole injection layer, was coated with spin coating method and a rotating speed of 2000 rpm and the MEH:PPV layer, as an active layer (emission layer), was coated with four rotating speeds. The impact of change in layer thickness on the surface roughness, optical absorption, and most importantly, the lightening voltage was investigated. Eventually, a PLED with a structure of ITO/PEDO:PSS(2000 rpm)/MEH:PPV(6000 rpm)/Al (165 nm) was selected as the optimum structure with a minimum lightening voltage of 7.1 V. The emission light ranged from 550 nm to 650 nm and was observed as an orange light.

In this article, the report of design, construction and optimization of an xenon flash-lamp pumped solid-state Nd:YAG laser in a ceramic cavity are presented. A laser rod of Nd:YAG with a 1.1 wt% doping and a dimension of 80 mm×5 mm, as an active medium, and a xenon flash-lamp with a inner diameter of 7 mm, an arc length of 3 in, and a repetition frequency of 0.2 Hz, as the pump source, were used. At first, the laser was optimized with Findlay-Clay method, in terms of the output coupler reflectivity. The gain and the loss for pump energy of 4.9 J were achieved to be 0.9 and 0.005, respectively. Thus we calculated the optimum reflectivity as 32%. From a mirror with a reflectivity as 25% (which was the closest to our available reflectivity in laboratory) was used. A total electrical-to-optical efficiency of 3% was achieved at 1064 nm for 25% reflectivity for output coupler. For a 0.2 Hz repetition rate and a pumping energy of 9 J, a beam spot size of 3.98 and a quality factor of 17 were achieved. The results are valid for a cavity design with the mentioned parameters.

In this work, the optical absorption enhancement of the organic (P3HT:PCBM) solar cells in the presence of silver nanopyramids was investigated with a finite-difference time-domain method. The nanopyramids’ base lengths were changed from 40 to 160 nm. The results show for nanopyramids with a base length of 100 nm, the surface plasmon polariton as well as the effective forward scattering modes are excited effectively, which significantly contribute in enhancement of optical and electrical properties of organic solar cells. Due to the better light concentration in the absorption layer by nanopyramids, which are located under the ITO layer, this design is showed to be more influential in increasing the optical and electrical properties of the cells. The results show that for nanopyramids with a base length of 100 nm, the highest short-circuit current density enhancement are achieved.

In this article, plasmonic waveguides aimed to controlling the colloidal quantum dot spontaneous emission rate have been designed. To this end, with considering aluminum and silver waveguides, the dependence of plasmonic emission rate to the dimension, material, and the place of quantum dots have been investigated. The results show that for a quantum dot with a distance of 5 nm from the edge of a silver waveguide with a gap of 20 nm and width of 30 nm, the plasmonic emission rate enhancement reaches 209 at the wavelength of 480 nm. This value for aluminum is 30. This waveguide is appropriate for ZnCdS/ZnS colloidal quantum dot with a photoluminescence peak at cyan wavelength.

In this work, plasmonic bowtie nano-antennas (as two opposite nano-prisms) for enhancing the electric field and Purcell’s factor of InGaN/GaN quantum dot emitters have been designed. To this end, at first, gold, silver, copper, and aluminum bowties have been investigated. The primary results showed aluminum bowties are more suitable for low wavelength excitations near the green band. Then, the size, gap, and substrate of aluminum bowties have been examined. The results showed aluminum nano-antennas with the length of 63.6 nm, the thickness of 30 nm, top angle of 300, and gap of 20 nm, when are grown on GaN/glass as substrate, results in a Purcell;s factor of 81 with a resonance wavelength of 535 nm. Replacing the AlN/glass with GaN/glass substrate, results in a Purcell’s factor of 86.3 and resonance wavelength of 495 nm.

In this work the effect of size on the emission properties of InAs/GaAs conical-shaped quantum dot (QD) lasers coupled to wetting layer was investigated. At first, by use of numerical method of finite element and effective mass approximation, the Schrodinger equation for two types of QDs were solved and the envelop functions for the ground state, first excited state, and wetting layer state were obtained. Then, using the envelop functions, the transition dipole moments and spontaneous lifetimes were calculated and their dependence on size was investigated. In continue the output power of QD laser was calculated by use of semiconductor laser rate equations. The results show by increasing the QD size, the energy eigenvalues as well as the spontaneous lifetime decreases noticeably. We found out that the laser output decreases with increasing the size of QD. Respecting to this fact that the transition frequencies are also dependent on the size, the output frequency is revealed to shift by changing the QD size.

In this study، the efficiency of a self-doubler NYAB laser، which is simultaneously an active and a nonlinear crystal، in a double-pass cavity is investigated. To this end، first، a model based on the coupling of five differential equations describing the interaction of pump beam of 807 nm، laser beam of 1060 nm، and second harmonic beam of 530 nm is presented. In this model، the conversion of pump beam to laser beam through the fluorescence process is described by the laser rate-equations. The generation of second harmonic beam is performed through the nonlinear processes. The model consists the linear and nonlinear interactions of light as well as the optical absorption. The results give the laser and second harmonic generation efficiencies against the pump powers.