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Amaç: Bu araştırma, Eskişehir ili kabakgil ekim alanlarında virüs enfeksiyonlarını ve bazı yerel çerezlik kabak genotiplerinin Zucchini yellow mosaic potyvirus (ZYMV) ve Watermelon mosaic potyvirus (WMV)’ye reaksiyonlarının belirlenmesi amacıyla yapılmıştır. Materyal ve Metod: 2019 yılı Ağustos-Eylül aylarında Eskişehir ili kabakgil ekim alanlarında gerçekleştirilen surveyler sonucunda toplanan 164 adet bitki örneği DAS-ELISA yöntemi ile ZYMV, WMV, Cucurbit aphid borne yellows polerovirus (CABYV), Cucumber mosaic cucumovirus (CMV), Papaya ringspot potyvirus-watermelon (PRSV-W), Cucurbit green mottle mosaic virus (CGMMV) ve Squash mosaic comovirus (SqMV) etmenlerine karşı testlenmişlerdir. Bulgular: DAS-ELISA sonuçlarına göre, kabakgil bitkilerinde CABYV (%49.35), WMV (%44.87), ZYMV (%24.35), CMV (%17.30), PRSV-W (%1.28) ve SqMV (%1.92) ve yabancı ot örneklerinde ise ZYMV (%12.5) ve CABYV (%12.5) yaygın virüslerdir. Çerezlik kabak bitkilerinde mekanik inokulasyon çalışmalarının sonucuna göre, WMV’nin 5, 8 ve 9 numaralı genotipleri (%100) ve ZYMV’nin ise 9 (%95), 3 (%93) ve 7 (%91) numaralı genotipleri yüksek oranda hastalandırdığı belirlenmiştir. Eskişehir ilinde virüs hastalıklarının ortalama yaygınlık oranı %4.13 olarak belirlenmiştir. Sonuç: Eskişehir ilinde yapılan bu çalışma ile kabakgil üretimi yapılan alanlarda sorun olan virüs etmenleri ilk kez DAS-ELISA ile ortaya konulmuştur.

We propose a new type of self-referencing and multiplexed refractive index (RI) sensor based on a compound optical microresonator structure consisting of Fabry-Pérot (FP) resonators coupled with microring resonators. The transmission spectra shows resonant features that are superimposed on a background defined by FP oscillations. The resonances have asymmetric Fano-like non-Lorentzian shapes, which are used as sensing peaks, while the FP oscillations are used as reference peaks for internal self-referencing. The sensing peaks shift linearly with the increased RI of the cladding in the microring resonator, while FP peaks stay constant. When the temperature is increased, both the FP peaks and the Fano resonances shift linearly at the same rate, which eliminates the temperature effect on RI measurements. We theoretically analyzed that the two-mirror FP resonator coupled with a single microring resonator and optimized its sensing performance through finite-difference time-domain simulations. A sensitivity value of 220 nm/RIU and a maximum figure of merit of 4400 RIU-1 were achieved. We also proposed two possible multiplexing schemes consisting of two-mirror and three-mirror FP resonators coupled with two microring resonators of different radii. The proposed sensor concept is simple, easy-to-fabricate, self-calibrating and can be used for simultaneous measurements of different samples.

Here, we present the design and simulation of an ultrawide-bandwidth on-chip spectrometer that can be used in various applications, e.g. spectral tissue sensing. It covers 1200 nm wavelength range (400 nm-1600 nm) with 2 nm spectral resolution. The overall design size is only 3 × 3 cm2. The ultra-wide spectral range is made possible by using novel on-chip band-pass filters for the coarse wavelength division. The fine resolution is provided by the arrayed waveguide gratings. The band-pass filter is formed by using bend waveguides and adiabatic full-couplers. The additional loss caused by the band-pass filter is relatively small. The proposed spectrometer covers entire 400 nm-1600 nm range continuously with low crosstalk values. We envision that this design can be used in several different applications including food safety, agriculture, industrial inspection, optical imaging, and biomedical research.

We report on a highly sensitive, selective, and flexible enzymatic sensor based on Zinc oxide nanoflakes (ZnO NFs) for noninvasive L-lactate sensing in sweat. A single step sonochemical process was used to synthesize ZnO NFs on gold-coated flexible polyethylene terephthalate (PET) substrates. The lactate oxidase enzyme (LOx) immobilized on the as-synthesized ZnO-NFs-based sensing electrode provided a high level of selectivity for lactate sensing. The sensor was tested in the range of 10 pM–20 mM, which covers the entire physiological range and demonstrated the sensitivity of $11.76~\mu \text{A}$ /decade/cm2 and the limit of detection (LoD) of 1.26 nM. The presented sensor does not require a linker due to the high isoelectric point of ZnO-NFs yet demonstrated ~55 times better response compared to conventional gold electrodes with a linker. Our statistical analysis showed that the sensor also has high reproducibility.

Here, we present a compact, high-resolution, and ultrabroad-bandwidth arrayed waveguide grating (AWG) realized in a silicon nitride (Si3N4) platform. The AWG has a cascaded configuration with a 1×3 flat-passband AWG as the primary filter and three 1×70 AWGs as secondary filters (i.e. 210 output channels in total). The primary AWG has 0.5-dB bandwidth of 45 nm over 190 nm spectral range. The ultrabroad-bandwidth is achieved by using an innovative design that is based on a multiple-input multi-mode interference (MMI) coupler placed at the entrance of the first free propagation region of the primary AWG. The optical bandwidth of the cascaded AWG is 190 nm, and the spectral resolution is 1 nm. The overall device size is only 1.1 × 1.0 cm2. Optical loss at the central channel is 4 dB, which is 3 dB less than a conventional design with the same bandwidth and resolution values but using a primary filter with Gaussian transfer function. To the best of our knowledge, this is the first demonstration of an ultrabroad-bandwidth cascaded AWG on a small footprint. We also propose a novel low-loss (∼ 0.8 dB) design using a small AWG instead of an MMI coupler in the primary filter part, which can be used in applications where the light intensity is very weak, such as Raman spectroscopy.

We report on a novel non-destructive testing method for integrated circuits (ICs) by measuring their response to scanning terahertz and sub-terahertz radiation at the pins. Analyzing the response using artificial intelligence (AI), counterfeit, altered, or damaged ICs can be identified as in-package and in-situ.

Increasing complexity of digital and mixed-signal systems makes establishing the authenticity of a chip to be a challenging problem. We present a new terahertz testing technique for non-destructive identification of genuine integrated circuits, in package, in-situ and either with no or under bias, by measuring their response to scanning terahertz and sub-terahertz radiation at the circuit pins. This novel, patent pending non-invasive nondestructive technology when merged with Artificial Intelligence (AI) engine will evolve and self-improve with each test cycle. By establishing and AI processing of the THz scanning signatures of reliable devices and circuits and comparing this signatures with devices under test using AI, this technology could be also used for reliability and lifetime prediction.

There have been extensive researches on terahertz (THz) plasmonic structures supporting resonant modes to demonstrate nano and microscale devices with high efficiency and responsivity as well as frequency selectivity. Here, using antisymmetric plasmonic fractal Y-shaped (FYS) structures as building blocks, we introduce a highly tunable four-member fractal assembly to support charge transfer plasmons (CTPs) and classical dipolar resonant modes with significant absorption cross section in the THz domain. We first present that the unique geometrical nature of the FYS system and corresponding spectral response allow for supporting intensified dipolar plasmonic modes under polarised light exposure in a standalone structure. In addition to classical dipolar mode, for the very first time, we demonstrated CTPs in the THz domain due to the direct shuttling of the charges across the metallic fractal microantenna which led to sharp resonant absorption peaks. Using both numerical and experimental studies, we have investigated and confirmed the excitation of the CTP modes and highly tunable spectral response of the proposed plasmonic fractal structure. This understanding opens new and promising horizons for tightly integrated THz devices with high efficiency and functionality.

We report for the first time on the growth of a homogeneous radial p–n junction in the ZnO core–shell configuration with a p-doped ZnO nanoshell structure grown around a high-quality unintentionally n-doped ZnO nanorod using sonochemistry. The simultaneous decomposition of phosphorous (P), zinc (Zn), and oxygen (O) from their respective precursors during sonication allows for the successful incorporation of P atoms into the ZnO lattice. The as-formed p–n junction shows a rectifying current–voltage characteristic that is consistent with a p–n junction with a threshold voltage of 1.3 V and an ideality factor of 33. The concentration of doping was estimated to be NA = 6.7 × 1017 cm–3 on the p side from the capacitance–voltage measurements. The fabricated radial p–n junction demonstrated a record optical responsivity of 9.64 A/W and a noise equivalent power of 0.573 pW/√Hz under ultraviolet illumination, which is the highest for ZnO p–n junction devices.

We report on a mechanically tunable THz filter based on highly flexible and stretchable elastomer comprising metallic nanostructures. The detailed numerical studies show that the proposed structure provides band-pass filters with the linewidths of 23 GHz and 170 GHz at 0.15 THz and 0.825 THz, respectively.

A novel, compact, on-chip spectrometer based on cascaded EG, multiple AWGs as well as PIC foundry compatible components was designed and analyzed. The proposed device operates in the spectral range of 1050 nm −1250 nm, 0.5 nm resolution, −30dB cross talk and 400 output channels.

Ceramic-metal nanocomposites (NCs) are the one of the most promising materials for selective solar absorbers (SSAs) in renewable energy applications. Design of efficient SSAs demands precise modeling of light propagation in NCs. We report on the synthesis, detailed characterization, and analytical and numerical modeling of Molybdenum (Mo)-alumina (Al2O3) NCs. In this study, Mo–Al2O3 NC films with thicknesses of 45 nm and 60 nm and nominal metal volume fraction (f) of 30%, 40%, and 60% were grown on polished glass substrates, using sequential DC and RF sputtering. TEM analysis of the samples with f = 40% showed that most 2 nm-diameter Mo particles are spherical and isolated. The reflectance (R) and transmittance (T) curves of the NC were measured in the spectral range of 300 nm and 1700 nm. The measured R and T characteristics were compared with the calculated FDTD simulations to analyze the prediction accuracy of the approach.

In this letter, we report on the fabrication and DC/RF characterization of a novel Graphene Field-effect Transistor (GFET) with two additional contacts at the access regions. The additional contacts-Field Controlling Electrodes (FCEs), are capacitively coupled to the ungated access regions and independently biased to control the access resistance. The reduced access resistance resulted in an increased current-gain cutoff frequency (fT). The fabricated proposed device could be used for radio frequency (RF) applications.

In this paper, we have proposed and experimentally demonstrated engineering the bandgap of semi-metal zero bandgap single layer chemical vapor deposited graphene by decorating with randomly distributed nanoparticles. Decoration with two types of nanoparticles was investigated: zinc oxide nano-seed grown by sonication of zinc acetate dihydrate, and gold nanoparticles grown by thermal annealing of sputtered gold thin film. The proximity of nanoparticles and graphene break graphene’s sublattice symmetry and opens-up a bandgap. The grown nanoparticles were characterized by scanning electron microscopy and atomic force microscopy. The single layer graphene before and after decoration was characterized with Raman spectroscopy. The bandgap was engineered by simply adjusting the nanoparticle size and density, and the introduced bandgap was measured from the slope of temperature dependent conductivity characteristics. Graphene with significant bandgap introduced by the proposed methods could be used for devices intended for high speed digital and logic applications.

We report on numerical study of dispersion properties and frequency dependent absorption characteristics of asymmetric dual grating gate terahertz (THz) plasmonic crystals. The study shows that the dispersion relations of plasmons in a two-dimensional electron gas (2DEG) capped with asymmetric dual grating gates have energy band gaps in the Brillion zones. Depending on the wave vector, the plasmons can have symmetrical, anti-symmetrical, and asymmetrical charge distributions that are different from the ones for uniform gratings case. Plasmons in the studied plasmonic crystal exhibit both tightly confined/weakly coupled behavior and propagating/strongly coupled behavior depending on the plasmonic modes. The responsivity of the plasmonic detector based on asymmetric dual grating gate does not monotonically decrease with the frequency, which is in contrast to the responsivity of uniform grating THz detectors. The cross-section of an asymmetric dual grating gate terahertz plasmonic device under THz illumination is represented, where excited plasmons are shown in red.

We report on microring resonator with integrated photonic crystal that is capable of supporting discrete Raman signals with 7 orders of magnitude enhancement in the spectral range of 2-5 pm. The proposed platform can be used for advanced spectroscopic sensing applications.

Magnetic toroidal multipoles in 3D and planar resonators have been recently investigated for their unconventional characteristics and potential applications. We report on investigation of hybridized supertoroidal modes at terahertz frequencies in planar core shell structures along with their dependence on geometrical parameters.

Two dimensional (2D) Molybdenum disulfide (MoS2) has evolved as a promising material for next generation optoelectronic devices owing to its unique electrical and optical properties, such as band gap modulation, high optical absorption, and increased luminescence quantum yield. The 2D MoS2 photodetectors reported in the literature have presented low responsivity compared to silicon based photodetectors. In this study, we assembled atomically thin p-type MoS2 with graphene to form a MoS2/graphene Schottky photodetector where photo generated holes travel from graphene to MoS2 over the Schottky barrier under illumination. We found that the p-type MoS2 forms a Schottky junction with graphene with a barrier height of 139 meV, which results in high photocurrent and wide spectral range of detection with wavelength selectivity. The fabricated photodetector showed excellent photosensitivity with a maximum photo responsivity of 1.26 AW(-1) and a noise equivalent power of 7.8 × 10(-12) W/√Hz at 1440 nm.

In this study, we investigated numerically the plasmon response of a dimer configuration composed of a couple of split and concentric Au nanoshells in a complex orientation. We showed that an isolated composition of two concentric split nanoshells could be tailored to support strong plasmon resonant modes in the visible wavelengths. After determining the accurate geometric dimensions for the presented antisymmetric nanostructure, we designed a dimer array that shows complex behavior during exposure to different incident polarizations. We verified that the examined dimer was able to support destructive interference between dark and bright plasmon modes, which resulted in a pronounced Fano-like dip. Observation of a Fano minimum in such a simple molecular orientation of subwavelength particles opens new avenues for employing this structure in designing various practical plasmonic devices. Depositing the final dimer in a strong coupling condition on a semiconductor metasurface and measuring the effective refractive index at certain wavelengths, we demonstrate that each one of dimer units can be considered a meta-atom due to the high aspect ratio in the geometric parameters. Using this method, by extending the number of dimers periodically and illuminating the structure, we examined the isotropic, polarization-dependent, and transmission behavior of the metamaterial configuration. Using numerical methods and calculating the effective refractive indices, we computed and sketched corresponding figure of merit over the transmission window, where the maximum value obtained was 42.3 for Si and 54.6 for gallium phosphide (GaP) substrates.

In this study, a quadrumer cluster composed of Al nanodisks in both symmetric and antisymmetric orientations has been utilized to generate magnetic hot-spots by using coil-type Fano resonances. Determining the accurate geometrical sizes for the examined cluster, we calculated the spectral response of the structure numerically. Utilizing strong plasmon resonance hybridization between Al/Al2O3 nanodisks that are suited in a close proximity to each other, such a finite and simple nanocluster yields intensified hidden magnetic fields |H| as a dark mode and electric |E| as a bright modes. Using and placement of silicon nanospheres in the unoccupied gap distance between proximal Al nanodisks give rise to significant enhancement in the energy and quality of the induced multiple Fano dips. Appearing of multiple Fano resonant modes in a coil-type regime in the UV and visible spectrum helps us to optimize the energy of generated magnetic hot-spots, significantly. Ultimately, we examined the sensitivity of the proposed final quadrumer by considering the behavior of Fano minima. We plotted the linear figure of merit (FoM) based on the Fano resonance energy differences in various conditions over the refractive index. Quantifying the FoM for the studied nanostructure, then we compared the quality of structure with the analogous nanoclusters. This work paves novel methods toward the utilization of Al/Al2O3 nanoparticles as a potential substance to employ in designing nanoclusters that are able to support strong dark resonances as well as bright modes. Wide-range working region, optimized electric and magnetic fields, multiple and high quality Fano dips, high FoM and low-costs are the superior features of the proposed artificial structure in comparison to analogous configurations.

Plasmonic nanoparticles in complex clusters and in specific molecular orientations are able to support strong plasmon and Fano resonances in their nanoscale geometries. In this paper, we examine the spectral response of a symmetric necklace shape nanostructure composed of Au nanodisk heptamers that are located in a close proximity to each other. Determining the appropriate geometrical parameters for the proposed necklace, we analyzed the effect of geometrical variations on the Fano resonance position and quality by calculating the scattering cross-sectional profile, numerically. Considering the strong localization of surface plasmon resonances (LSPR) in the heptamer clusters, the LSPR sensitivity for the studied necklace has been determined. Moreover, we evaluated the performance of the structure for different medium conditions by plotting corresponding figure of merit (FoM). To this end, we measured the plasmon resonance energy differences (Δ E eV) over the refractive index (n) alterations, we quantified the corresponding FoM for the final necklace as 13.7, which can be utilized in designing precise and highly sensitive sensors. Ultimately, we proved that highly complex structures composed of metal nanoparticles clusters yield high sensitivity to the environmental perturbations.

We propose a novel Graphene FET (GFET) with two capacitively coupled field-controlling electrodes (FCEs) at the bottom of the ungated access regions between gate and source/drain. The FCEs could be independently biased to modulate sheet carrier concentration and thereby the resistance in the ungated regions. The reduction of source/drain access resistance results in increased cut off frequency compared to those of conventional GFETs with the same geometry. We studied the DC and improved RF characteristics of the proposed device using both analytical and numerical techniques and compared with the baseline designs.

We report a wearable, continuous and noninvasive monitoring of sweat pH platform. Recently there has been a surge in research to develop of highly stable and sensitive pH sensors for several biochemical and biological processes. pH is all a dynamic parameter in a comprehensive range of applications as monitoring of pH in sweat provides information about the body’s metabolic activity, as well as physiological responses. With the expansion of nano technology, pH sensors based on nanomaterials have been investigated by researchers. Among numerous metal oxide-based semiconductive nanomaterials, Zinc oxide (ZnO) has been considered as an attractive candidate for noninvasive wearable health-monitoring applications. Particularly, two-dimensional Zinc-oxide Nanoflakes (2D ZnO-NFs) attains technical interest for many biomedical applications. ZnO has a large direct energy band gap of 3.37eV with wurtzite structure and a large vibration in the binding energy of 60 meV. ZnO is an amphoteric oxide which reacts with H+ and OH- ions in pH solutions because of absorption by creating oriented dipoles or surface bonds. This absorption rate is proportional to the concentration of the free holes or electrons at the NFs surface. High surface-to-volume ratio of ZnO-NFS reduces the diffusion space of the analyte to the electrode surface, hence enhancing the signal-to noise ratio and increasing the sensitivity and reaction time. Thermal stability, biocompatibility, biosafety, high catalytic efficacy, chemical stability in functional environments, electrochemical activity, electron communication features, mechanical strength, low toxicity make it promising as a continuous pH sensing platform. The large surface area of nanoflakes makes them excellent candidates for pH sensing. Sonochemically synthesized ZnO-NFs are 20 nm thick and they have the average lateral dimensions of 5 um× 5 um. Using single step sonochemical technique, 2D ZnO-NFs are synthesized on gold deposited flexible polyethylene terephthalate (PET) substrates. Flexible polyethylene terephthalate (PET) substrate is used as it has achieved good reputation for wearables because of its thermal stability, excellent dielectric properties, intrinsic elasticity, hydrophobicity, structural resiliency against repeated bending forces, low coefficient of thermal expansion and compatibility with roll-to-roll fabrication processes for low price and scalable manufacturing. Sonochemical process permits synthetization of nanostructures (NSs) on a large variety of substrates (including flexible ones) in an atmospheric conditions (room temp, atmospheric pressure). This method offers simplification of fabrication procedure and improved long-term stability through large scale nanostructures synthesis. We choose this technique as it is fast, low-priced, catalyst free, complementary metal-oxide-semiconductor (CMOS) responsive and environmentally friendly. In comparison to other hydrothermal methods and the like well oriented NF synthesis with reaction rates up to 100 times higher can be achieved with the sonochemical method over a wide range of substrates. Selective area electron diffraction (SAED) characterization and high resolution transmission electron microscopy (HRTEM) images of ZnO-NFs ensure that ZnO-NFs have wurtzite structure and they are oriented in [0001] direction with a = 3.25 Å and c = 5.21 Å and they are single crystalline. The area of the working electrode is 5 mm ´ 5 mm. Using electrochemical studies and with the potential range of -0.6V – 0.6V at a scan rate of 50mVs-1, the specific pH measurements technique between reference electrode of Ag/AgCl and working electrode of ZnO-NFs have been explored. The designed pH sensor shows the sensitivity of 48.8 mV/pH/cm2 with a short response time of about 4.5s. The standard pH buffer solutions are applied to measure the performance of the pH sensor. The sensitivity of this sensor is determined in pH buffer solutions of the pH range from 4 to 10. A commercial pH glass-electrode sensor is used before every test to validate the pH value of the pH buffer solutions.The small form factor and biocompatibility of ZnO-NFs make this wearable, sweat based pH sensor a robust candidate for wearable and continuous pH monitoring device.

Capacitive coupling and direct shuttling of charges in nanoscale plasmonic components across a dielectric spacer and through a conductive junction lead to excitation of significantly different dipolar and charge transfer plasmon (CTP) resonances, respectively. Here, we demonstrate the excitation of dipolar and CTP resonant modes in metallic nanodimers bridged by phase-change material (PCM) sections, material and electrical characteristics of which can be controlled by external stimuli. Ultrafast switching (in the range of a few nanoseconds) between amorphous and crystalline phases of the PCM section (here Ge2Sb2Te5 (GST)) allows for designing a tunable plasmonic switch for optical communication applications with significant modulation depth (up to 88%). Judiciously selecting the geometrical parameters and taking advantage of the electrical properties of the amorphous phase of the GST section we adjusted the extinction peak of the dipolar mode at the telecommunication band (λ~1.55 μm), which is considered as the OFF state. Changing the GST phase to crystalline via optical heating allows for direct transfer of charges through the junction between nanodisks and formation of a distinct CTP peak at longer wavelengths (λ~1.85 μm) far from the telecommunication wavelength, which constitutes the ON state.

Graphene plasmonics has been introduced as a novel platform to design various nano- and microstructures to function in a wide range of spectrum from optical to THz frequencies. Herein, we propose a tunable plasmonic metamaterial in the THz regime by using metallic (silver) concentric microscale split ring resonator arrays on a multilayer metasurface composed of silica and silicon layers. We obtained an absorption percentage of 47.9% including two strong Fano resonant dips in THz regime for the purely plasmonic metamaterial without graphene layer. Considering the data of an atomic graphene sheet (with the thickness of ~0.35 nm) in both analytical and experimental regimes obtained by prior works, we employed a graphene layer under concentric split ring resonator arrays and above the multilayer metasurface to enhance the absorption ratio in THz bandwidth. Our numerical and analytical results proved that the presence of a thin graphene layer enhances the absorption coefficient of MM to 64.35%, at the highest peak in absorption profile that corresponds to the Fano dip position. We also have shown that changing the intrinsic characteristics of graphene sheet leads to shifts in the position of Fano dips and variations in the absorption efficiency. The maximum percentage of absorption (~67%) was obtained for graphene-based MM with graphene layer with dissipative loss factor of 1477 Ω. Employing the antisymmetric feature of the split ring resonators, the proposed graphene-based metamaterial with strong polarization dependency is highly sensitive to the polarization angle of the incident THz beam.

We experimentally and numerically analyze the charge transfer THz plasmons using an asymmetric plasmonic assembly of metallic V-shaped blocks. The asymmetric design of the blocks allows for the excitation of classical dipolar and multipolar modes due to the capacitive coupling. Introducing a conductive microdisk between the blocks, we facilitated the excitation of the charge transfer plasmons and studied their characteristics along with the capacitive coupling by varying the size of the disk.

A novel label free, compact, fast and noninvasive absorbance based optical sensing technique was devised for the first time to detect cortisol, a physical and psychological stress biomarker, using ultraviolet (UV) LEDs. LEDs at three different UV wavelengths were employed to demonstrate cortisol sensing with different cortisol concentration. From the differential photoresponse versus concentration curves, we calculated the sensitivity of the sensors to be 1 mV/μM, 0.15 mV/μM and 0.08 mV/μM at 240 nm, 250 nm and 260 nm wavelength respectively. The developed sensing technique can be easily incorporated with microfluidic system for point-of-care cortisol detection and such developed protocol can be used in personalized health monitoring.

There have been extensive research to systematically tailor terahertz (THz) plasmonics structures to support strong resonant modes as platforms for designing practical nano and microscale devices with high efficiency and tunability. Here, using a symmetric four-member assembly of plasmonic vee-shaped structures, we introduce a quadratic, multiresonant plasmonic THz antenna to support significant resonant modes with high efficiancy. The effect of unique geometrical shape of the structure on the quality of the proposed structure is analyzed to provide ultrasharp resonant modes with high plasmon resonance confinement. Employing both numerical and experimental studies, we investigated and confirmed the tunable plasmonic response of the suggested antenna. In addition, by depositing an atomic graphene monolayer below the antenna, we enhanced the THz response of the proposed structure, including remarkable absorption cross-section correlating with the resonant frequencies. This understanding will contribute to a promising model for practical all-optical and optoelectronic devices operating in the THz spectrum.

Plasmonic ultraviolet (UV) photodetectors have witnessed ongoing and tremendous enhancements in quantum efficiency and responsivity. Here, we go beyond regular plasmonic detectors by using periodic arrays of fractal aluminum nanostructures as Cayley trees deposited on a Ga 2 O 3 substrate to generate photocurrent. We show that the proposed aluminum Cayley trees are able to support and intensify strong broad plasmon resonant modes across the UV to the visible spectrum. It is shown that the Cayley trees can be tailored to facilitate strong absorption at high energies (short wavelengths), resulting formation of hot carriers. Having perfect compatibility to operate at the UV spectrum, fractal aluminum structures and Ga 2 O 3 substrate help to increase the produced photocurrent remarkably. Presence of Ga 2 O 3 layer blue-shifts the peak of absorption to higher energies and helps to generate hot carriers at deeper UV wavelengths.

In this paper, we have experimentally demonstrated the engineering of semi-metal single layer CVD Graphene’s bandgap by decorating with randomly distributed ZnO nano-seed grown by sonication of Zinc acetate dehydrate. The proximity of nanoparticles and Graphene breaks Graphene’s sublattice symmetry and opens-up a bandgap. The 2-D/G ratio of Raman spectroscopy of decorated Graphene along with a peak at 432.39 cm-1 confirmed presence of ZnO on single layer Graphene. The introduced bandgap was measured from the slope of Arrhenius plot. Graphene with significant bandgap introduced by the proposed methods could be used for devices intended for digital and logic applications.

This work proposes a novel geometry field effect transistor with graphene as a channel—graphene field-effect transistor (GFET), having a hybrid contact that consists of an ohmic source/drain and its extended part towards the gate, which is capacitively coupled to the channel. The ohmic contacts are used for direct current (DC) biasing, whereas their capacitive extension reduces access region length and provides the radio frequency (RF) signal a low impedance path. Minimization of the access region length, along with the paralleling of ohmic contact’s resistance and resistive part of capacitively coupled contact’s impedance, lower the overall source/drain resistance, which results in an increase in current gain cut-off frequency, fT. The DC and high-frequency characteristics of the two chosen conventional baseline GFETs, and their modified versions with proposed hybrid contacts, have been extensively studied, compared, and analyzed using numerical and analytical techniques.

This chapter summarizes the optical and electrical properties of plasmonic photodetectors in the spectral range of UV to the near infrared. Different types of plasmonic photodetectors are described with fundamental operation principles, relative advantages, applications and challenges. The chapter also reviews the state of the art for the plasmonic photodetectors and provides an outlook for the future.

In this work, we propose a novel Graphene field effect transistor (GFET) with ohmic Source/Drain contacts having capacitive extension towards the Gate. The ohmic contacts of the proposed GFET are used for DC biasing as like as conventional GFETs whereas their extended parts which are capacitively coupled to the channel reduce access region length as well as the access resistance and provide a low impedance route for the high frequency RF signal. Reduction of access resistance along with the paralleling of ohmic contact resistance and real part of capacitive impedance result in an overall lower Source/Drain resistance which eventually increases the current gain cut-off frequency, f T . We have studied and compared the DC and RF characteristics of the baseline conventional GFET and proposed GFET using analytical and numerical techniques.

We propose and systematically investigate a novel tunable, compact room temperature terahertz (THz) source based on difference frequency generation in a hybrid optical and THz micro-ring resonator. We describe detailed design steps of the source capable of generating THz wave in 0.5–10 THz with a tunability resolution of 0.05 THz by using high second order optical susceptibility (χ(2)) in crystals and polymers. In order to enhance THz generation compared to bulk nonlinear material, we employ a nonlinear optical micro-ring resonator with high-Q resonant modes for infrared input waves. Another ring oscillator with the same outer radius underneath the nonlinear ring with an insulation of SiO2 layer supports the generated THz with resonant modes and out-couples them into a THz waveguide. The phase matching condition is satisfied by engineering both the optical and THz resonators with appropriate effective indices. We analytically estimate THz output power of the device by using practical values of susceptibility in available crystals and polymers. The proposed source can enable tunable, compact THz emitters, on-chip integrated spectrometers, inspire a broader use of THz sources and motivate many important potential THz applications in different fields.

We propose and extensively analyze a novel graphene-FET (GFET) with two capacitively coupled field-controlling electrodes (FCE) at the access region. The dc and RF characteristics of the proposed device are studied using analytical and numerical techniques and compared with the baseline designs. The independently biased FCEs could control the electric field and sheet carrier concentration at the ungated region, and thus reduce the access resistance effectively. The reduction of source/drain access resistance results in improved fT and fMAX compared with those of conventional GFETs of the same geometry. The proposed device with improved characteristics of GFET can be used for high-frequency applications.

This study reports on a reconfigurable antenna platform based on vanadium dioxide (VO2), a phase-change material (PCM) with low transition temperature, integrated with an addressable microheater matrix. For the first time, it is shown that an entire planar antenna can be thermally reconfigured virtually to any pattern by switching the phase of the selected regions of the VO2 layer from insulator to metallic state by indirect thermal stimuli generated by individually addressable nichrome resistive microheaters. Careful selection of the individual pixels to start the phase transition from insulator (OFF) to metallic (ON) state allows creating different antenna patterns with unique resonance properties. Reconfiguring the antenna into different patterns, operating frequency can be tuned from C-band (4–8 GHz) to X-band (8–12 GHz), and S-band (2–4 GHz) frequencies which cover the entire ultra wideband spectrum (3.1–10.6 GHz). The proposed approach provides a promising platform for designing monolithically integrated reconfigurable antennas, radio frequency devices, and circuits for various applications.

We theoretically investigated and designed a tunable, compact THz source in 1-10 THz range based on a nonlinear optical microdisk resonator. The lack of tunable THz source operating at room temperature is still one of the major impediments for the applications of THz radiation. The proposed device on an insulated borosilicate glass substrate consists of a nonlinear optical disk resonator on top of another disk capable of sustaining THz modes. A pair of Si optical waveguides is coupled to the nonlinear microdisk in order to carry the two input optical waves. Another pair of Si THz waveguides is placed beneath the input optical waveguides to couple out the generated THz radiation from the disk to receiver antenna. Both optical and THz disks are engineered optimally with necessary effective mode indices in order to satisfy the phase matching condition. We present the simulation results of our proposed device using a commercial finite element simulation tool. A distinguished THz peak coincident exactly with the theoretical calculations involving DFG is observed in frequency spectrum of electric field in the microdisk resonator. Our device has the potential to enable tunable, compact THz emitters and on-chip integrated spectrometers.

Analytical and numerical studies of the dispersion properties of grating gated THz plasmonic structures show that the plasmonic crystal dispersion relation can be represented in terms of effective index of the dielectric medium around the 2DEG for the plasmons. Forbidden energy band gaps are observed at Brillion zone boundaries of the plasmonic crystal. FDTD calculations predict the existence of the plasmonic modes with symmetrical, antisymmetrical and asymmetrical charge distributions. Breaking the translational symmetry of the crystal lattice by changing the electron concentration of the two dimensional electron gas (2DEG) under a single gate line in every 9th gate induces a cavity state. The induced cavity state supports a weekly-coupled cavity mode.

We designed and theoretically investigated nonlinear optical micro-ring resonators for tunable terahertz (THz) emission in 1-10 THz range by using difference frequency generation (DFG) phenomenon with large second order optical nonlinearity (χ(2)). Our design consists of a nonlinear ring resonator and another ring underneath capable of sustaining high-Q resonant modes for infrared pump beams and the generated THz radiation, respectively. The nonlinear ring resonator generates THz through DFG by mixing the input waves carried by a pair of waveguides. The proposed device can be a viable platform for tunable, compact THz emitters and on-chip integrated spectrometers.

We report on sub-wavelength THz plasmonic split ring resonators on 2 dimensional electron gas (2DEG) at AlGaN/GaN hetero-interface and on oxide coated high mobility graphene. The investigated in this study guide THz electric field into deep sub-wavelength scale by plasmonic excitations. Propagation of a broadband pulse of EM waves was simulated by using a commercial FDTD simulation tool. The results show that split ring resonator structures can be used to guide THz into deep sub-wavelength down λ/200 and achieve relatively higher quality factors than grating gate devices by plasmonic confinement which can be used for THz detection, filtering and possibly for THz on-chip-spectrometer. Moreover, ring resonator modes supported by system can be tuned with an applied voltage to gratings.