Hassan Ghafoorifard

Graphene nanoscroll, because of attractive electronic, mechanical, thermoelectric and optoelectronics properties, is a suitable candidate for transistor and sensor applications. In this research, the electrical transport characteristics of high-performance field effect transistors based on graphene nanoscroll are studied in the framework of analytical modeling. To this end, the characterization of the proposed device is investigated by applying the analytical models of carrier concentration, quantum capacitance, surface potential, threshold voltage, subthreshold slope and drain induced barrier lowering. The analytical modeling starts with deriving carrier concentration and surface potential is modeled by adopting the model of quantum capacitance. The effects of quantum capacitance, oxide thickness, channel length, doping concentration, temperature and voltage are also taken into account in the proposed analytical models. To investigate the performance of the device, the current-voltage characteristics are also determined with respect to the carrier density and its kinetic energy. According to the obtained results, the surface potential value of front gate is higher than that of back side. It is noteworthy that channel length affects the position of minimum surface potential. The surface potential increases by increasing the drain-source voltage. The minimum potential increases as the value of quantum capacitance increases. Additionally, the minimum potential is symmetric for the symmetric structure (V_fg = V_bg). In addition, the threshold voltage increases by increasing the carrier concentration, temperature and oxide thickness. It is observable that the subthreshold slope gets closer to the ideal value of 60 mV/dec as the channel length increases. As oxide thickness increases the subthreshold slope also increases. For thinner gate oxide, the gate capacitance is larger while the gate has better control over the channel. The analytical results demonstrate a rational agreement with existing data in terms of trends and values.

The experimental results of dielectric barrier discharge (DBD) plasma treatment on barley (Hordeum Valgare L cv. Yusef) seed germination and seedling growth are analyzed and presented. The seeds were exposed to DBD plasma with 40-, 80-, and 120-W powers for 15 s. All treatments showed positive effects on seed germination, seedling growth, and vigor index. The scanning electron microscope (SEM) images and water imbibition evaluations of plasma-treated seeds revealed that the treatments improved water absorption in the seeds. Similar positive improvements were observed for the plasma-treated seeds in the seedling stage. The best germination characteristics were obtained in 80-W DBD plasma, which included an 18.28% increment in total germination percentage, and 13.35%, 66.83%, 38.55%, and 31.93% increment on the seed germination potential, vigor index, shoot height, and root length, respectively. Moreover, the seed germination of the plasma-treated barley was studied after 2, 7, 14, and 30 days of storage, which indicated the desirable effect of plasma over the storage time. It is concluded that the use of cold plasma can significantly improve the germination and seedling growth of barley seeds.

This paper presents a new resonator for class-C oscillators which not only decreases the phase noise, but solves their inevitable start-up problem. The aforementioned resonator has two separate nodes that increasing inductance energy factor (IEF) in output node provides lower phase noise. By connecting a class-B active pair to the other node of the resonator, with larger equivalent impedance, start-up problem has been solved. By reaching the steady state, the auxiliary class-B active pair transistors will be switched off in order to achieve lower phase noise besides power consumption goals. The proposed oscillator, implemented in 130 nm standard CMOS technology, oscillates at the frequency of 3.4 GHz and its phase noise is about -136.8 dBc/Hz at 3 MHz offset. The power consumption and FoM are 9.5 mW and 188.1 dBc/Hz, respectively.

This work deals with the fluorescence properties of the methylene blue (MB) fluorophores loaded on metal oxide nanoparticles, such as TiO₂, ZnO, and Al₂O₃ based on laser-induced fluorescence (LIF) spectroscopy. At first, MB is provoked by diode laser at 665 nm, then the fluorescence emissions are recorded using a Czerny-Turner spectrometer. The lucid red shift appears during the right angle LIF measurements of (MB + TiO₂NPs) suspensions, where NP are well distributed among the fluorophores. Despite that, the LIF of (MB + TiO₂) demonstrates notable red shift in terms of NP concentrations; however, (MB + ZnO) and (MB + Al₂O₃) exhibit a negligible one. The larger red shift occurs for the NPs with greater refractive indices due to the optical elongation. Furthermore, the quenching coefficients KTiO₂, K_ZnO, and KAl₂O₃ are measured according to the linear Stern-Volmer formalism. The quenching effect in a (TiO₂+MB) attests to be much stronger than that of other nanoparticles of interest. The discrepancy in the fluorescence emissions of MB at the attendance of different metal oxide NPs is very significant during simultaneous imaging/diagnosis and treatment of tumors.

This letter presents a low-power small-footprint low-noise amplifier (LNA) that operates over the frequency band of 55-64 GHz. Using a resistor between bulk and substrate (ground) nodes, these two nodes are isolated. This bulk isolation technique is introduced to achieve the maximum gain of the transistor at the desired frequency band. Also, a methodology is proposed to determine the optimal size of transistors to achieve the maximum possible gain. As a proof of concept, the proposed LNA is fabricated in a 65-nm bulk CMOS process, and the design features 12.8 ± 0.5 dB power gain and an average noise figure of 3.8 dB. The output 1-dB compression point of the LNA is -6 dBm. The LNA consumes 8.8 mW from a 1-V supply and excluding the pads occupies a silicon area of 0.23 mm ² .

Graphene has originally low absorption at telecommunication wavelengths. Therefore it is necessary to overcome this hurdle to use graphene as absorption media in many optoelectronic devices. In this paper, a narrow-bandwidth graphenebased total absorber is numerically and theoretically investigated.The proposed structure consists of a graphene sheet on a Si rectangular grating, which is placed on SiO2 spacer backed with the gold substrate. Due to the absence of plasmonic response of graphene in near infrared wavelengths, the method of critical coupling with guided mode resonance is employed to realize highly efficient absorption of light in the graphene sheet. The simulation results show that the maximum magnitude of absorption reaches near 100% (43-fold enhancement compared to isolated monolayer graphene absorption of 2.3%). Also, based on calculated results, the absorption of the proposed structure can be controlled by altering the geometrical parameters and chemical potential of graphene. In particular, the absorption spectrum is modulated by the external gate voltage. Moreover, we find that the operating wavelength is adjusted flexibly by incident source angle. As a result, the proposed absorber has high directivity and can act similar to an antenna. The control ability of total absorption in the proposed structure provides potential applications for the realization of ultra-compact and high-performance optoelectronic devices, such as sensors and narrow-band filters.

An adjustable continuous-wave single-mode double-clad ytterbium (Yb)-doped silica fiber laser is numerically investigated in the form of a master-oscillator fiber power-amplifier (MOFPA) array. An optically-tunable coupler is suggested based on the nonlinear electromagnetically induced transparency (EIT) within fiber Bragg grating (FBG). Here, the Si nanocrystals is embedded in SiO2 over the selected regions of the output coupler. The transmittance is adjusted using a low power control field by modulating the refractive index in the EIT material.