Asymmetric Planes Research Articles

Dual band notched superwideband MIMO antenna for 5G and 6G applications

In this article, a compact super wideband multiple input multiple output (MIMO) antenna with dual band elimination feature is presented. The antenna element comprises of modified square shaped radiating element and coplanar waveguide (CPW) with asymmetric ground planes. A dual-port MIMO configuration is proposed for spatial diversity. It has compact size of dimensions 18 × 37.5 × 1.6 mm3. It has frequency band of impedance matching (VSWR < 2) from 3.9– > 150 GHz (%BW > 189.86 %). The radiator and feedline are loadedwith modified M- and U-shaped slots to achieve a band notch at 5.5 GHz (WLAN) and 7.5 GHz (X-band satellite communication), respectively. A modified staircase shaped structure is used between the two ports to achieve an intraport isolation of > 20 dB at maximum frequencies. The MIMO antenna has envelope correlation coefficient based on scattering parameters < 0.005, envelope correlation coefficient based on farfield parameters < 0.08, peak gain of 8.63dBi, Mean Effective Gain (MEG) < -3dB, multiplexing efficiency > -4.0 dB, channel capacity loss (CCL) < 0.4bits/sec/Hz to signify its suitability for MIMO applications. The measured and the simulated outcomes are found to be close to each other. The proposed antenna element and MIMO antenna structure will be suitable for Internet of Things (IoT), 5G, and 6G due to their superwideband (SWB) bandwidth, desirable radiation properties and diversity performance.

Optical and Electrical Properties of AlxGa1-xN/GaN Epilayers Modulated by Aluminum Content.

AlGaN-based LEDs are promising for many applications in deep ultraviolet fields, especially for water-purification projects, air sterilization, fluorescence sensing, etc. However, in order to realize these potentials, it is critical to understand the factors that influence the optical and electrical properties of the device. In this work, AlxGa1-xN (x = 0.24, 0.34, 0.47) epilayers grown on c-plane patterned sapphire substrate with GaN template by the metal organic chemical vapor deposition (MOCVD). It is demonstrated that the increase of the aluminum content leads to the deterioration of the surface morphology and crystal quality of the AlGaN epitaxial layer. The dislocation densities of AlxGa1-xN epilayers were determined from symmetric and asymmetric planes of the ω-scan rocking curve and the minimum value is 1.01 × 109 cm-2. The (101¯5) plane reciprocal space mapping was employed to measure the in-plane strain of the AlxGa1-xN layers grown on GaN. The surface barrier heights of the AlxGa1-xN samples derived from XPS are 1.57, 1.65, and 1.75 eV, respectively. The results of the bandgap obtained by PL spectroscopy are in good accordance with those of XRD. The Hall mobility and sheet electron concentration of the samples are successfully determined by preparing simple indium sphere electrodes.

GaN/AlInN/AlN/Safir HEMT Yapılar için Mozaik Kusur ve AFM Çalışması

In this study, three samples of GaN/AlInN/AlN/Al2O3 high electron mobility (HEMT) structures are investigated with high resolution X-ray diffraction (HR-XRD) technique. Peak positions and peak broadenings are used in calculations, gained from rocking curves. Structural quality is determined from symmetric and asymmetric peak planes. Mosaic defects such as treadening dilocations (TDs), tilt and twist angles, lateral and vertical crystallite lengths are determined by using Williamson Hall (WH) method. In addition to these, surface morphology is also investigated by atomic force microscopy (AFM). It is noticed that crystal quality of epitaxial layers decrease in the order of samples C, B and A. Al compositions for samples A, B and C are found as %87.4, %86.6 and %86.4, respectively by using Vegard’s law.

A dual-band CPW-fed miniature planar antenna for S-, C-, WiMAX, WLAN, UWB, and X-band applications

A miniature planar antenna is a vital component of any portable wireless communication device. The antenna in portable devices should provide wide/multiple operating bands to cover a good number of narrowband services as a multi-band antenna not only reduces the number of antennas but also lessens the system complexity, cost, and device size. To operate over S-, C-, WiMAX, WLAN, UWB, and X-communication bands, in this paper, a dual-band CPW-fed antenna is presented. The anticipated antenna is made up of a vertical bow-tie-shaped patch and two asymmetric ground planes and etched on the same side of the single-sided standard substrate material. To generate two distinct operating bands, an inverted L-shaped parasitic element is inserted within the modified U-shaped coplanar ground plane. The antenna achieved dual operating bands of 3.24–8.29 GHz and 9.12–11.25 GHz in measurement which helps the proposed antenna to cover S-, C-, WiMAX, WLAN, 4G LTE, 5G sub-6 GHz, UWB, and X-communication bands. In the two operating bands, the antenna realized a peak gain of 4.33 dBi, and 4.80 dBi, the maximum radiation efficiency of 86.6%, and 72.6%, and exhibits symmetric radiation patterns. In the operating bands, the antenna also exhibits good time-domain behavior which helps it to transmit the signal with minimum distortion.

An asymmetric CPW‐fed modified bow tie‐shaped antenna with parasitic elements for ultra‐wideband applications

SummaryIn this paper, a modified bow tie‐shaped antenna for ultra‐wideband (UWB) communication applications is presented. The anticipated antenna consists of a CPW‐fed modified bow tie‐shaped patch and two asymmetric ground planes with dual parasitic elements. Electromagnetic computation on the antenna demonstrates that the patch and grounds are strongly linked, and the designed antenna can exhibit multiple resonances which overlap to reveal the UWB working spectrum. Experimental verification of the presented antenna shows that the antenna achieved a working band of 3.2–11.0 GHz, with a fractional bandwidth of 109.9%. The antenna also attained a peak gain of 4.32 dBi at 7.3 GHz and peak efficiency of 87.3% at 6.8 GHz and reveals excellent time‐domain behavior and omnidirectional radiation patterns throughout the operating band. A small‐size, large operating band, high gain and efficiency, high fidelity factor, omnidirectional radiation patterns, and very small group delay make the antenna ideal for portable communication devices in the UWB band.

High-quality AlN nucleation layer on SiC substrate grown by MOVPE: Growth, structural and optical characteristics

Thin AlN epi-layers (∼100 nm) were grown on a SiC substrate by MOVPE (Metal Organic Vapor Phase Epitaxy). The effect of V/III ratio and growth rate on the surface morphology, quality (crystalline/interface), and stress of AlN epi-layer were studied. It was found that the quality of AlN epi-layer depends strongly upon the V/III ratio and growth rate. Crystalline quality improved significantly as reflected by very low X-ray rocking curves FWHM values of symmetric (004) and asymmetric (204) planes, which are ∼355 arc-sec and ∼840 arc-sec, respectively for a high V/III ratio and low growth rate. The AlN/SiC interface quality and surface morphology of AlN epi-layer were also improved remarkably. Raman spectroscopy results indicated that dislocation density influenced the biaxial stress (0.75 to 1.05 GPa). The blue shift in Fourier Transform Infra-Red spectroscopy of E1(TO) mode of AlN epi-layer as compared to stress-free value (i.e. 670 cm−1) is in close agreement with the Raman results.

Compact Broadband Circularly Polarized CPW-Fed Antenna with Characteristic Mode Analysis

A compact circularly polarized (CP) antenna is proposed for low-profile and wideband operation based on characteristic mode analysis (CMA). A ring patch with a gap and two arc-shaped metallic stubs as the radiator is analyzed and optimized by CMA to figure out the orthogonal modes and operating frequency band for potential good axial ratio (AR) performance. The studies of these CP modes provide a physical insight into the property of broadband circular polarization. Such an in-depth understanding paves the way for the proposal of novel CP antenna with separation between the design of radiator and feeding network. A 50-Ω coplanar waveguide (CPW) is introduced and placed appropriately to excite the desired modes based on the information from CMA, which employs two asymmetric ground planes to improve the performance in terms of AR and impedance matching. The antenna with a compact size of 0.71λ0 × 0.76λ0 × 0.038λ0 (λ0 is the free-space wavelength at the center frequency of the 3-dB AR bandwidth) is fabricated and measured for validation. The realized gain varies from 1.6 to 3.1 dBic over the operating bandwidth characterized by the measured 10-dB impedance bandwidth of 83.8% (3.98–9.72 GHz) and 3-dB AR bandwidth of 70.3% (4.59–9.57 GHz), respectively.

Investigation of Structural, Optical and Electrical Properties of Al0.3Ga0.7N/GaN HEMT Grown by MOCVD

In this study, Al0.3Ga0.7N/GaN high electron mobility transistor (HEMT) structure is investigated grown over c- oriented sapphire substrate by using Metal Organic Chemical Vapor Deposition (MOCVD) method. Optical, morphological and electrical characteristics of this structure are determined by X-ray diffraction (XRD), Photoluminecanse (PL), Ultraviolet (UV-Vis.), Atomic Force Microscopy (AFM) and Hall- Resistivity measurements. By using XRD method, 2θ, Full Width at Half Maximun (FWHM), lattice parameters, crystallite size, strain, stress and dislocation values are calculated on symmetric and asymmetric planes. Direct band gap of GaN is determined by PL measurements as 3.24 eV. It is seen that conduction of AlGaN layer starts at 360 nm in UV-Vis. In Hall-Resistivity measurements, it is noticed that carrier density of HEMT structure is not effected by temperature and mobility value is high. Carrier density and mobility values are determined as 5.82x1015 1/cm3 and 1198 cm2/Vs at room temperature respectively. At the lowest temperature point (25 K) they are calculated as 5.19x1015 1/cm3 and 6579 cm2/Vs, respectively.

CDrift: An Algorithm to Correct Linear Drift From A Single High-Resolution STEM Image.

In this work, a new method to determine and correct the linear drift for any crystalline orientation in a single-column-resolved high-resolution scanning transmission electron microscopy (HR-STEM) image, which is based on angle measurements in the Fourier space, is presented. This proposal supposes a generalization and the improvement of a previous work that needs the presence of two symmetrical planes in the crystalline orientation to be applicable. Now, a mathematical derivation of the drift effect on two families of asymmetric planes in the reciprocal space is inferred. However, though it was not possible to find an analytical solution for all conditions, a simple formula was derived to calculate the drift effect that is exact for three specific rotation angles. Taking this into account, an iterative algorithm based on successive rotation/drift correction steps is devised to remove drift distortions in HR-STEM images. The procedure has been evaluated using a simulated micrograph of a monoclinic material in an orientation where all the reciprocal lattice vectors are different. The algorithm only needs four iterations to resolve a 15° drift angle in the image.

A CPW-fed compact monopole antenna with defected ground structure and modified parasitic hilbert strip having wideband circular polarization

A novel CPW-fed monopole antenna with wideband circular polarization is proposed. The antenna consists of a basic rectangular monopole, fed by a 50 Ω microstrip line, through partial asymmetric impedance steps to attain wideband characteristics. On either side of the feed line, there are sections of partial, asymmetric ground planes. The ground plane on the left is appended with a rectangular stub and a step notch. Wideband circular polarization is achieved by using a strip around the upper end of the monopole and also by a parasitic modified Hilbert strip to the right of the monopole. The monopole, the upper parasitic strip and the modified parasitic Hilbert strip are coupled together by proximity coupling yielding the wide bandwidth. The antenna has been fabricated and the simulated and measured results were compared. The antenna has an impedance bandwidth ranging from 2.04 GHz to 7.95 GHz (118.2%) and an axial ratio bandwidth ranging from 3.6 GHz to 6.84 GHz (62%), thus covering the Wireless Local Area Network (WLAN) 5.2/5.8 GHz, the Worldwide interoperability for Microwave Access (WiMAX) 3.5/5.5 GHz and also partially covering the C-band (4–8 GHz). The antenna shows good radiation characteristics and obtains a reasonable gain over the entire operating frequency band.

High x-ray resolving power utilizing asymmetric diffraction from a quartz transmission crystal measured in the 6 keV to 22 keV energy range.

A Cauchois-type spectrometer utilizing the (203) lattice planes at an oblique angle of 11.53° to the normal to the surface of a quartz transmission crystal recorded the Kα and Kβ spectral lines of six elements from Fe to Ag in the 6-22keV energy range from a laboratory x-ray source. After deconvolving the natural lifetime widths and the image plate detector broadening from the observed spectral linewidths, the intrinsic crystal resolving power was determined to be 4000 at the lower energies and decreasing to 1000 at the higher energies. Previously, a Si wafer crystal exhibited twice this resolving power when the (331) planes had been used in asymmetric geometry. The investigation of diffraction with this quartz crystal, with a very similar lattice spacing and therefore spectral coverage, was motivated by the larger integrated reflectivity of quartz due to its well-known quasimosaicity upon elastic bending. The measured spectral linewidths were in good agreement with the widths calculated by accounting for various broadening mechanisms, including source size, crystal thickness, crystal height, crystal rocking curve width, geometrical aberrations, and possible spectrometer configuration errors. This is the first, to the best of our knowledge, demonstration of high resolving power achieved by asymmetric diffraction over a wide energy range (6-22keV) and with detailed comparisons with theoretical broadenings. Based on these results, Cauchois spectrometers employing asymmetric planes of perfect quartz and silicon crystals can be reliably designed and optimized for high-resolution spectroscopy in the >6 keV energy range.

Atomically stepped, pseudomorphic, corundum-phase (Al1-xGax)2O3 thin films (0 ≤ x &amp;lt; 0.08) grown on R-plane sapphire

Atomically smooth, pseudomorphic (Al1−xGax)2O3 thin films were grown for 0 ≤ x &amp;lt; 0.08 on R-plane sapphire (01.2) by pulsed laser deposition at growth temperatures up to 1000 °C. Films up to 720 nm thickness show atomically stepped surfaces with monolayer terraces, similar to the substrates prior to growth, in wide ranges of growth pressure and temperature. A careful analysis of 13 symmetric, skew-symmetric, and asymmetric X-ray peaks agrees quite well with the continuum elastic strain theory of pseudomorphic distortion in corundum heterostructures by M. Grundmann [J. Appl. Phys. 124, 185302 (2018)]. The Ga-contents x and weak deviations from the expected ratios of rhombohedral c/a lattice constants are obtained from the best fits of the spacing of the (02.4), (04.8), and (00.6), (00.12) film and substrate reflections, in reasonable agreement with chemical energy dispersive X-ray spectrometry analyses. In addition, the measured tilts of the asymmetric film lattice planes corroborate the elastic theory.

An Alternative X-ray Diffraction Analysis for Comprehensive Determination of Structural Properties in Compositionally Graded Strained AlGaN Epilayers

In this letter, a standard deviation based optimization technique has been applied on High Resolution X-ray Diffraction symmetric and asymmetric scan results to accurately determine the Aluminum molar fraction and lattice relaxation of Molecular Beam Epitaxy grown compositionally graded Aluminum Gallium Nitride (AlGaN)/Aluminum Nitride/Gallium Nitride (GaN) heterostructures. Mathews–Blakeslee critical thickness model has been applied in an alternative way to determine the partially relaxed AlGaN epilayer thicknesses. The coupling coefficient determination has been presented in a different perspective involving sample tilt method by offset between the asymmetric planes of GaN and AlGaN. Sample tilt is further increased to determine mosaic tilt ranging between 0.01° and 0.1°.

Structural properties of InGaN/GaN/Al2O3 structure from reciprocal space mapping

By using metal organic chemical vapor deposition technique, InGaN/GaN solar cell (SC) structure is deposited over sapphire (Al2O3) wafer as GaN buffer and GaN epitaxial layers. Structural properties of InGaN/GaN/Al2O3 SC structure is investigated by using high resolution X-ray diffraction technique dependent on In content. By using reciprocal space mapping, reciprocal space data are converted to w–θ data with a software. These w–θ data and full width at half maximum data are used for calculating lattice parameters. When compared with w–θ measurements in literature it is seen that especially a- lattice parameter is found very near to universal value from RSM. It is calculated as 3.2650 nm for sample A (S.A) GaN layer and 3.2570 nm for sample B (S.B) GaN layer on (105) asymmetric plane. Strain and stress calculations are made by using these lattice parameters. Strain and stress are calculated as 0.02363 and 8.6051 GPa for S.A GaN layer respectively. Other results are given in tables in the results and discussion section of this article. Edge, screw and mixed type dislocations are calculated as mosaic defects. All these calculations are made for two samples on (002) symmetric and (105) asymmetric planes. As a result it is seen that measurements by using RSM give more sensitive results. a- lattice parameter calculated with this technique is the best indicator of this result.

Effect of nitridation time on structural, optical and electrical properties of InN films grown on c-sapphire substrates by PAMBE

We have investigated the effect of nitridation time of the sapphire substrates on the structural, morphological, optical, and electrical characteristics of InN thin films grown by plasma assisted molecular beam epitaxy technique. Three sets of the films were prepared with nitridation times of 1, 2.5 and 3 h, respectively. Full width at half maximum (FWHM) of ω-scans around X-ray diffraction peaks of different symmetric and asymmetric planes were drastically reduced with increasing nitridation time, hence the threading dislocation densities were also reduced by order of magnitude (2.4 × 1011 cm−2 to 6.7 × 1010 cm−2). The atomic force microscopy also showed improvement in surface roughness. But interestingly, on increasing the nitridation time, a prominent blue shift in the photoluminescence (PL) spectra (~ 60 meV) was observed which has also been confirmed by infrared absorption spectroscopy (blue shift of ~ 120 meV). This phenomenon of blue shift of PL peak was attributed to increase in electron concentration (n) in InN layer and was further confirmed by the Hall measurement. Carrier concentration (n) is seen to increase from 6.8 × 1018 cm−3 to 1.8 × 1019 cm−3 while the highest mobility was estimated to be 164 cm2/V-s which is observed to decrease considerably upon longer nitridation time. Thus there is a trade-off between structural and electrical qualities of InN film upon prolonged nitridation.

Structural defects of GaN deposited on (111) Si with Gd2O3-related buffer layers

The structural defects of GaN deposited on (111) Si with Gd2O3-related rare earth oxide buffer layers were investigated using a double-crystal x-ray rocking curve (DCXRC), high resolution transmission electron microscopy (HRTEM). By comparing the DCXRC signals of (11¯02)GaN and (12¯12)GaN asymmetric planes and (0002)GaN symmetric plane, respectively, it was found that most of the threading dislocations (TDs) in GaN of the GaN on (111) Si using Gd2O3 or Er2O3/Gd2O3 buffer layer are type a TDs in nature. Based on the results of DCXRC studies, it is believed that the full-width at half maxima of the DCXRC signals of (11¯02)GaN and (12¯12)GaN asymmetric planes are primarily due to the contributions of the 1/3⟨12¯10⟩GaN components of the Burgers vectors of type a and type c + a TDs on the interplanar spacing distortions of (11¯02)GaN and (12¯12)GaN planes in GaN of the GaN/Er2O3/Gd2O3/(111) Si samples. HRTEM observations also revealed the presence of extrinsic stacking faults and Frankel partial dislocations in GaN of the GaN on the (111) Si sample with Gd2O3 or Er2O3/Gd2O3 buffer layer.

Effect of thermal annealing on structural properties of GeSn thin films grown by molecular beam epitaxy

GeSn alloy with 7.68% Sn concentration grown by molecular beam epitaxy has been rapidly annealed at different temperatures from 300°C to 800°C. Surface morphology and roughness annealed below or equal to 500°C for 1 min have no obvious changes, while the strain relaxation rate increasing. When the annealing temperature is above or equal to 600°C, significant changes occur in surface morphology and roughness, and Sn precipitation is observed at 700°C. The structural properties are analyzed by reciprocal space mapping in the symmetric (004) and asymmetric (224) planes by high resolution X-ray diffraction. The lateral correlation length and the mosaic spread are extracted for the epi-layer peaks in the asymmetric (224) diffraction. The most suitable annealing temperature to improve both the GeSn lattice quality and relaxation rate is about 500°C.

A Mutation in the bHLH Domain of the SPCH Transcription Factor Uncovers a BR-Dependent Mechanism for Stomatal Development.

The asymmetric cell divisions necessary for stomatal lineage initiation and progression in Arabidopsis (Arabidopsis thaliana) require the function of the basic helix-loop-helix (bHLH) transcription factor SPEECHLESS (SPCH). Mutants lacking SPCH do not produce stomata or lineages. Here, we isolated a new spch-5 allele carrying a point mutation in the bHLH domain that displayed normal growth, but had an extremely low number of sometimes clustered stomata in the leaves, whereas the hypocotyls did not have any stomata. In vivo tracking of leaf epidermal cell divisions, combined with marker lines and genetic analysis, showed that the spch-5 leaf phenotype is dosage dependent and results from the decreased ability to initiate and amplify lineages, defects in asymmetric cell fate allocation, and misorientation of asymmetric division planes. Notably, application of brassinosteroids (BRs) partly rescued the stomatal leaf phenotype of spch-5 Transcriptomic analysis combining spch-5 with BR treatments revealed that the expression of a set of SPCH target genes was restored by BRs. Our results also show that BR-dependent stomata formation and expression of some, but not all, SPCH target genes require the integrity of the bHLH domain of SPCH.

Structural properties of GeSn thin films grown by molecular beam epitaxy

GeSn thin films on Ge (001) with various Sn concentrations from 3.36 to 7.62% were grown by molecular beam epitaxy and characterized. The structural properties were analyzed by reciprocal space mapping in the symmetric (004) and asymmetric (224) planes by high resolution X-ray diffraction (XRD). The lateral correlation length (LCL) and the mosaic spread (MS) were extracted for the epi-layer peaks in the asymmetric (224) diffraction. With the increase of Sn concentration, the LCL reduces while the MS increases, indicating degrading crystalline quality. Dislocations were observed in the sample with 7.62% Sn concentration by transmission electron microscope, consistent with the strain relaxation found in XRD mapping. Besides, the surface morphologies were investigated.

High-quality AlN template grown on a patterned Si(111) substrate

To obtain a high-quality AlN template on a Si substrate for high-quantum efficiency AlGaN-based deep-UV LED applications, we fabricated a high-density micro-patterned Si(111) substrate. An about 8-µm-thick AlN template was grown on the Si(111) substrate in a metal-organic chemical vapor deposition reactor by using NH3 pulsed-flow multilayer AlN growth and epitaxial lateral overgrowth methods. The template had a small X-ray full width at half-maximum with rocking curves of 620 and 1141″ for the symmetric and asymmetric (002 and 102) planes. A threading dislocation density at the best region as low as 107cm−2 was also obtained.