Increase In Doping Concentration Research Articles

Joint Studies of Spin Frustration Induced by Doping Small ZnSe Nanoparticles with Fe Atoms

AbstractAs a 1.8 nm ZnSe nanocrystal is progressively doped with 1%, 5%, and 10% Fe, it shows a progressive change in its magnetic properties from a superparamagnetic FM‐dominated exchange type to an onset of AFM exchange with evidence of spin frustration. Magnetization measurements allow to obtain exchange coupling constants that are compared to the results of a Broken‐Symmetry Density Functional Theory (BS‐DFT) model of a doped (ZnSe)34 cluster. DFT shows a capability to reproduce the experimental pattern of the increasing influence of AFM exchange as doping concentration increases. The material phase segregates at the edges where strained rhombic surface sites are the preferred doping sites of iron. Large concentrations of iron leads to the formation of Fe clusters and complex exchange patterns that result in spin frustration in some iron trimers but none in the others. The spin frustration of these complex systems by assuming mirror symmetry of the sites when fitting by using BS‐DFT formalism is classified and analyzed. While some individual J constants obtained have significant errors, the averaged exchange constants are generally in good agreement with our experimental data.

Enhanced Red Emission from Amorphous Silicon Carbide Films via Nitrogen Doping.

The enhanced red photoluminescence (PL) from Si-rich amorphous silicon carbide (a-SiCx) films was analyzed in this study using nitrogen doping. The increase in nitrogen doping concentration in films results in the significant enhancement of PL intensity by more than three times. The structure and bonding configuration of films were investigated using Raman and Fourier transform infrared absorption spectroscopies, respectively. The PL and analysis results of bonding configurations of films suggested that the enhancement of red PL is mainly caused by the reduction in nonradiative recombination centers as a result of the weak Si-Si bonds substituted by Si-N bonds.

Correlation between local structure variations and critical temperature of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(TiO2)x superconductor

TiO2 doping content affects the critical temperature (Tc) and the variations of local structure on Bi1.6Pb0.4Sr2Ca2Cu3O10+δ. The (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(TiO2)x samples were fabricated with the solid-state reaction process, where x = 0, 0.002, 0.004, 0.006, 0.008, and 0.01. The Tc values of the samples were obtained by measuring resistivity versus temperature, indicating that Tc gradually decreased with increasing doping content (x). To explain the obtained degradation of Tc, carrier properties, role of interlayer coupling, and local structure were systematically investigated using Azlamozov–Larkin theory and its Lawrence–Doniach modification for strong anisotropic superconductors. The calculation of excess conductivity at the mean field region showed that the c-axis coherence length (ξc) and the effective inter-layering spacing (d) increased with increasing doping content. X-ray diffraction patterns also showed that the bond distances increased with increasing TiO2 content. The copper valence (V) and carrier concentration (p) of the samples were determined by analyzing the Cu L2,3-edge X-ray absorption near edge structure spectra. The values of V and p showed the same trend of decreasing with increasing x. A close correlation between the changes in local structure parameters and degradation of Tc of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(TiO2)x was then probably concluded.

Ultra-fast dynamic deposition of EuBa2Cu3O7−δ-BaHfO3 nanocomposite films: Self-assembly structure modulation and flux pinning behaviors

Structure modulation of rare-earth barium cuperates (REBCO) superconducting films plays an essential role in the flux pinning behaviors. In this paper, nano-composite EuBa2Cu3O7−δ-BaHfO3 (EuBCO/BHO) films were deposited by the ultra-fast pulsed laser deposition technique. All nano-composite films exhibited high-quality orientation under the growth rates up to 100 nm/s. TEM cross-sectional analysis reveals that the EuBCO/BHO films have a distinct lamellar structure, which is related to the periodic change of growth conditions during the multi-turn dynamic deposition. In addition, the morphology of BHO varies with dopant content, which suggests a strong correlation between dopant content and the BHO self-assembly mechanism. Consequently, the vortex behavior shifts from giant-flux creep to vortex-glass formation at the thermally activated flux flow region as the dopant content increases. The primary flux pinning behaviors change from random to correlated pinning with the increase of dopant content at 4.2 K. Due to the larger contribution of the correlated pinning machinimas, the 8% BHO-doped EuBCO film exhibits the highest Jc value at 4.2 K, with moderate fields (below 8 T) among all the three films. At 4.2 K and 14 T, the 6% BHO doped EuBCO film has the highest Fp value attributing to the predominate random pinning mechanism.

Magnetic Domain Characterization and Physical Properties of Gd-Doped and (Gd, Al) Co-Doped ZnO Thin Films.

Undoped ZnO, Gd-doped ZnO with various doping concentration (1, 3, 5, and 7 at%), and 3 at% (Gd, Al) co-doped ZnO films were prepared on a glass substrate using the co-reactive sputtering method. The influence of the doping and co-doping process on the films was characterized using X-ray diffraction, FESEM, EDX, MFM, VSM, UV-VIS spectroscopy, and the Hall Effect measurement at room temperature. XRD study confirmed that the Gd and Al ions are incorporated into a ZnO lattice. EDX analysis confirmed the existence of Zn, O, Al, and Gd elements in the prepared Gd-doped ZnO and (Gd, Al) co-doped ZnO films, which suggests the successful doping procedure. All the deposited films obtained maximum optical transmittance above 80%, showing a high transparency of the films in the visible region. The optical band gap was found red-shifted from 3.11 to 3.21 eV with the increase in Gd doping concentration. The increase in band gap energy from 3.14 eV to 3.16 eV was obtained for 3 at% Gd and 3 at% (Gd, Al) co-doped ZnO films. The MFM measurement proved the existence of room-temperature ferromagnetism and spin polarization in Gd and (Gd, Al) co-doped ZnO films. By co-doping with Al, the result obtained from MFM shows the enhancement of magnetic properties, as it exhibited a smaller domain size with a shorter magnetic correlation length L, a larger phase shift Φrms, and the highest value of δfrms compared to the sample with 3 at% Gd incorporated into ZnO. The carrier concentration and electrical conductivity increased with the increase in Gd concentration, whereas the electrical resistivity and hall mobility showed a reverse trend. The similar trend of results obtained for 3 at% (Gd, Al) co-doped ZnO as compared to 3 at% Gd-doped ZnO also indicates greater electrical properties after a shallow donor such as aluminum was incorporated into Gd-doped ZnO thin films. In conclusion, for future applications, one should consider the possible influence of other types of shallow donor incorporation in an attempt to enhance the properties of new types of diluted magnetic semiconductors (DMSs).

Stable lithium storage behavior observed in Mn-doped MgCo2O4 anode materials

Cation substitution strategy is considered to be an effective way to create defect structure in the spinel structure for improving the performance of Li-ion batteries. In this work, a series of MgMnxCo2-xO4 (x = 0, 0.5, 1, 1.5, 2) materials with Mn ions replacing Co ions were synthesized by a facile hydrothermal method. The collected X-ray diffraction and scanning electron microscope results show that the lattice parameters and particle size of the materials increase with the increase of Mn doping concentration. The O 1s X-ray photoelectron spectra results show that there are more oxygen vacancies and interstitial hydroxyl groups in MgMn0.5Co1.5O4 samples, which is conducive to the improvement of conductivity of the material. Analyses of XPS spectra of Mg 1s, Mn 2p and Co 2p reveal that magnesium exists as Mg2+ ions, manganese and cobalt exist in multivalent states (Mn2+/3+/4+ and Co2+/3+), and these ions are mixed and distributed in the spinel structure. The effect of Mn doping on the inversion degree of spinel and electrochemical performance of materials is discussed. Compared with pure MgCo2O4 material, Mn-doped MgCo2O4 anode materials exhibit good cycle stability. When x = 0.5, MgMn0.5Co1.5O4 anode material has the highest cycle capacity with an initial discharge capacity of 1165.2 mAh g−1, and a capacity of 427.6 mAh g−1 after 100 cycles. Mn-doped MgCo2O4 can significantly improve the cycle stability of the material while maintaining a high specific capacity.

Ultra-low power consumption and favorable reliability Mn-doped BiFeO3 resistance-switching devices via tunable oxygen vacancy

Due to the instability of Fe valence and the existence of a large number of oxygen vacancies in BFO films, a large leakage current, and comparatively low resistance value usually appear in BFO-based devices and high operating voltage and power consumption are demanded to form regular oxygen vacancy conductive channels, which restricts the application of BFO in resistive memory and memristor devices. In this paper, a series of Pt/BiFe1-xMnxO3/TiN (BFMO, x = 0, 0.05, 0.1, 0.15, 0.2) devices with different Mn doping concentrations were prepared by magnetron sputtering and lithography, and the microstructure and electrical characteristics of BFMO-based devices were investigated. As the amount of Mn doping increases, the resistive switching properties including operating voltage, power consumption, cycle stability, and retention of BFMO device first improve and then degrade. Interestingly, with the increase of Mn doping concentrations, the ratio of Fe2+ to Fe3+ and oxygen vacancies to lattice oxygen in BFMO devices analyzed by X-ray photoelectron spectroscopy initially diminishes reaching the minimum and then rises. Notably, BiFe0·9Mn0·1O3 device presents low DC operating voltage of −0.7 V and 0.8 V, preferable endurance of 104 pulse cycles, and low power consumption of only 0.45 pJ in a single set process. The remarkable electrical performance in BFMO-based devices likely originated from the inhibition of initial oxygen vacancies caused by Mn doping with appropriate content.

Metallic ferromagnetism of indium nitride nanosheets doped with Ce ions

• Ce 3+ doped indium nitride with room temperature ferromagnetism nanosheets were synthesized. • Ce 3+ doped InN nanosheets have single crystal properties. • Ce 3+ doping concentration can modulate the saturation magnetization values of sample. • Magnetism originates from d-f interaction between localized carriers of Ce 3+ ions. • Theoretical calculation prove Ce 3+ doped InN system has metallic characteristic. Herein, Ce-doped indium nitride nanosheets with room temperature ferromagnetism were prepared by high temperature nitration reaction. The saturation magnetization value of the InN system materials can controlled by the Ce doping concentration. With the increase of the Ce doping concentration, the saturation magnetization value first increases and then decreases. When the Ce doping concentration at 1.10 at. %, the saturation magnetization of the samples reach the maximum value of 0.125 emu/g. The first-principles calculation illustrate InN:Ce system display metallic characteristic. The magnetic properties of InN:Ce system originates from the interaction of d-f orbital electrons of Ce element. The synthesized Ce-doped InN nanosheets can expand the application range of InN materials in the field of magnetic semiconductors.

Effects of Fe doping on the magnetic and absorption spectrum of graphene-like ZnO monolayer from first-principles calculations

The stability, electronic structure, magnetic properties, and absorption spectrum of Fe doped ZnO monolayer have been investigated by first-principles calculation. The results show that Fe doped ZnO monolayer systems are stability. The band gap of ZnO monolayer is narrowed by Fe atom doping, and with the increase of Fe doping concentration, the band gap becomes more narrow(2.900 eV) in Zn14Fe2O16 monolayer, which may be due to the formation of the local built-in magnetic field by Fe atom doped in ZnO monolayer systems. Both of Zn15Fe1O16 and Zn14Fe2O16 monolayer systems are magnetic. The Curie temperature value has been estimated to be 916 K in figuration I of Zn14Fe2O16 monolayer systems. Moreover, the absorption spectrum has a red-shift in the wavelength range of 320–800 nm by Fe doping. These calculation results are helpful for the design of photoelectric and spintronic devices.

Catalytic Hydrogen Evolution from H2S Cracking over CrxZnS Catalyst in a Cylindrical Single-Layered Dielectric Barrier Discharge Plasma Reactor.

The use of non-thermal plasma technology in producing green fuels is a much-appreciated environmentally friendly approach. In this study, an Al2O3-supported CrxZnS semiconductor catalyst was tested for hydrogen evolution from hydrogen sulfide (H2S) gas by using a single-layered dielectric barrier discharge (DBD) system. The Al2O3-supported CrxZnS catalyst (x = 0.20, 0.25, and 0.30) was produced by using a co-impregnation method and characterized for its structural and photocatalytic characteristics. The discharge column of the DBD system was filled with this catalyst and fed with hydrogen sulfide and argon gas. The DBD plasma was sustained with a fixed AC source of 10 kV where plasma produced species and UV radiations activated the catalyst to break H2S molecules under ambient conditions. The catalyst (hexagonal-cubic-sphalerite structure) showed an inverse relationship between the band gap and the dopant concentration. The hydrogen evolution decreased with an increase in dopant concentration in the nanocomposite. The Cr0.20ZnS catalyst showed excellent photocatalytic activity under the DBD exposure by delivering 100% conversion efficiency of H2S into hydrogen. The conversion decreased to 96% and 90% in case of Cr0.25ZnS and Cr0.30ZnS, respectively.

Design and 3D FEM Analysis of a Flexible Piezoelectric Micromechanical Ultrasonic Transducer Based on Sc-Doped AlN Film.

In this paper, a flexible piezoelectric micromachined ultrasonic transducer (PMUT) based on Scandium (Sc)-doped Aluminum Nitride (AlN) film was designed and modeled by the three-dimensional finite element method (3D-FEM). The resonant frequency of 218.1 kHz was reported. It was noticeable that a high effective electromechanical coupling coefficient (k2eff) of 1.45% was obtained when a combination of a flexible PI and a thin Si layer was used as the PMUT supporting structure layer. Compared with a pure Si supporting layer counterpart, the coupling coefficient had been improved by 110.68%. Additionally, the increase of Sc doping concentration in AlN film further enhanced the device electromechanical coupling coefficient and resulted in an improvement for transmitting/receiving sensitivity of the proposed flexible PMUT. When the doping concentration of Sc reached 30%, the emission sensitivity was as large as 1.721 μm/V, which was 2.86 times greater than that of conventional AlN film-based PMUT. The receiving sensitivity was found to be 2.11 V/KPa, which was as high as 1.23 times the performance of an undoped device. Furthermore, the bending simulation result showed that the proposed flexible PMUT device can maintain a good mechanical stability when the bending radius is greater than 1.5 mm. The simulation of sound field characteristics demonstrated that the flexible PMUT based on AlScN could receive stable sound pressure signals under the bending radius of 1.5 cm.

Effects of N-doping and oxygen vacancies on electronic structure of LiFePO4

First-principle calculations were performed to study the crystal structure and electronic structure of nitrogen doped LiFePO4. The nitrogen dopant leaded to the formation of Fe–N covalent bond and some new electronic states emerged in the forbidden band, which decreased the band gap. With the increase of nitrogen doping concentration, more nitrogen atoms formed covalent bond with its adjacent iron atoms and the covalency of Fe–N bond was enhanced. The doping positions of nitrogen had little effect on the electronic structures. The removal of oxygen atoms destroyed the P–O covalent bond and increased the activity of phosphorus near the Fermi level. Both the nitrogen dopant and oxygen vacancies could increase the electronic conductive properties of LiFePO4 system.

A novel monoclinic phase and electrically tunable magnetism of van derWaals layered magnet CrTe2

Exploring the novel structural phase of van der Waals (vdW) magnets would promote the development of spintronics. Here, through first-principles calculations, we report a novel monoclinic structure of vdW layered 1T-CrTe2, which is one of the popular vdW magnets normally exhibiting a trigonal structure. The new monoclinic phase emerges from a switchable magnetic state between ferromagnetism and antiferromagnetism through changing hole doping concentration, which suggests a practical approach to obtain such a structure. The results of phonon dispersion and energy analysis convince us that the monoclinic structure is a metastable phase even without hole doping. When the hole doping concentration increases, the stability analysis indicates the preference for a novel monoclinic phase rather than a conventional trigonal phase, and meanwhile, the magnetic properties are accordingly tuned. This work provides new insights into the phase engineering of the chalcogenide family and the electrical control of magnetism of vdW layered magnets.

Effect of Transition Metal (Fe, Co) Ion Doping on TiO2 Nano Particles.

Keywords: Growth from solution, Nanomaterials, Oxides, Photocatalytic, Sol-Gel method, DMS. . we report the growth of [Fe, Co]xTiO2 (x=0.01, 0.02 & 0.04) Nano quantum dots prepared by Sol-Gel technique, followed by freeze-drying treatment at -30°C temperature for 12hrs. The obtained Gel was thermally treated at different temperature like 200,400,600, 800°C. The crystalline size of 4 to 40 nm is achieved. X-ray diffraction pattern of samples show anatase phases of TiO2, up to 600°C. At 800°C, the phase is Rutile. Figure 1 shows the XRD patterns acquired from different samples heated at different temperatures. The diffraction peak at 25.22°, 25.49°and 25.6° observed from the XRD pattern of the Fe, Co doped TiO2 shows that the main crystal phase is anatase, and the peak at 27.47° indicates the presence of the rutile phase. All the peaks in the XRD patterns of the sample calcined at 200°C, 400°C and 600°C of TM doped TiO2 can be designated to the anatase phase (most active phase) without any indication of other crystalline phases such as rutile or brookite . As a variant valence metal cation, Fe, Co ions can react with Ti4+ on the surface of TiO2, and Ti4+ is reduced to Ti3+ which inhibits the transformation of anatase to rutile [1]. It leads to the reduction in the oxygen vacancies on the TiO2 surface and suppresses the crystallization of other phases by adsorbing onto the surface of the TiO2 particles [2]. The photocatalytic degradation of formaldehyde has been successfully demonstrated using a 250 V UV lamp with TM doped TiO2 nano powder in a specific experimental setup. The degradation rate increases linearly with dopant content increases. This indicates that the photocatalytic reaction in this experiment was effected by dopant concentration. The results obtained in this research contribute to the understanding of binary doped transition metal ions in TiO2 nanoparticles can lead the efforts of enhancing their environmental application. Study of Magnatic proprty has been carried out by using VSM. The magnetic susceptibility of the Fe, Co doped TiO2 nanopowder increases with increase in doping concentration. Fe, Co doped TiO2 exhibits ferromagnetism at room temperature. Figure 1

Structural, electrical, and optical properties of rare-earth Sm3+ doped SnO2 transparent conducting oxide thin films for optoelectronic device applications: Synthesized by the spin coating method

Various concentrations of Sm (1, 2, 3, 4, and 5 at%) doped SnO2 thin films were synthesized by the sol-gel spin coating method and investigated the structural, optical, and electrical properties. According to X-ray diffraction studies, all deposited films exhibited the polycrystalline rutile tetragonal structure. The average crystallite size decreased with Sm doping concentration in SnO2, while the dislocation density and lattice strain values were increased. Both XPS and Raman spectra confirm that Sm3+ enters the host SnO2. The higher average optical transmittance is above 86% in pure SnO2, while Sm: SnO2 films exhibit a decreasing trend with the increase of Sm doping concentration and reached up to 77% in 5 at% Sm: SnO2 film. The optical bandgap energy increased with the increase of Sm doping concentration up to 3 at % Sm: SnO2 film (4.23 eV) which is attributed to the Moss-Burstein (MB) effect and then slightly decreased for 4 at% and 5 at% Sm: SnO2 films. Further, the room temperature sheet resistance and resistivity values were found to decrease with the increase of Sm doping concentration up to 3 at % Sm: SnO2 film then it slightly increased in 4 and 5 at% Sm: SnO2 films. Additionally, the efficiency parameter figure of merit (φ) for all the deposited films was calculated.

Studying structural, molecular, morphological and electrical properties of Co0.2 Zn0.8 Fe2O4 doped with Cadmium

A series of (Co0.2 Zn0.8-xCdxFe2O4) with (x = 0, 0.3, 0.6) were prepared by flash auto combustion method and annealed at 800 ℃ for 2hrs and morphological and structural using XRD, FTIR, and SEM characterization were studied. The cubic spinel structure is affirmed by XRD analysis of the samples. The XRD peaks elucidate that all synthesized ferrites have Fd3m phase group. The FTIR spectra evidenced two intensive absorption bands (ν1 and ν2) in the 400 – 600 cm−1 range corresponding to A and B sites. Peaks in FTIR analysis shift towards lower wavenumber as Cd doping concentration increases. Cd doping is essential for crystal growth, as evidenced by SEM images. The AC resistivity decreases by rising temperature whereas it increases by increasing Cd content up to × = 0.3 and after that decreases. The magnetic manner of our samples was distinguished by Vibrating Sample Magnetometer (VSM). Eventually, the hysteresis loop is small; So Co0.2 Zn0.8-xCdxFe2O4 nanoparticles are soft magnetic materials.

Charge Compensation Mechanism and Multifunctional Properties of Bi1−xBaxFeO3 (x = 0, 0.05, 0.1) Ceramics

The charge compensation mechanism of Ba2+ ion doped BiFeO3 (BFO) has been studied here in detail. The most common problem of high leakage current of ceramic BFO was noticeably resolved by significant reduction of charge defects through Ba2+ doping. The leakage current density of Bi1-xBaxFeO3 (x = 0, 0.05, 0.1) was found to be reduced to ∼3.13 × 10−8 A cm−2 for x = 0.1 from a value of 2.26 × 10−4 A cm−2 for x = 0 at an applied field of 500 V cm−1. This reduction of leakage current was caused by the reduction of charge defects which was verified through the X-ray photoelectron spectroscopy (XPS). The dielectric and ferroelectric properties of undoped and Ba2+ doped BFO were also studied here explicitly and correlated with charge compensation mechanism. The structural and vibrational characterization proved the phase pure formation and the presence of metal-oxide bonds. The optical characterization showed the reduction in energy band gap with increased Ba2+ doping in BFO (2.18, 1.71 and 1.56 eV for x = 0, 0.05 and 0.1, respectively). Another common problem of BFO, namely low remanent magnetization, was also significantly resolved through Ba2+ doping in it and the strong antiferromagnetic BFO started showing weak ferromagnetic nature with increased doping concentration.

Accumulation-Mode Device: Experimental of LDMOS With Folded Drift Region Achieving Ultralow Specific ON Resistance

In order to reduce the specific ON resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{R}_{\mathbf {{ \mathrm{\scriptscriptstyle ON}},sp}}$ </tex-math></inline-formula> ) of power device in the drift region, the folded accumulation lateral double-diffused MOSFET (FALDMOS) is manufactured and analyzed in this article. The drift region of the FALDMOS is etched to form the folded surface, which is similar to the FinFET structure. The oxide inside the trench optimizes the electric field in the drift region, so the doping concentration can be increased while maintaining the breakdown voltage (BV). In addition, the trench increases the area of the drift region covered by the extended gate electrode, which can introduce more accumulated electrons when the device is turned on. The increased doping concentration and accumulated electrons work together to substantially increase the conductivity of the drift region, thereby obtaining ultralow <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{R}_{ \mathrm{\scriptscriptstyle ON},sp}$ </tex-math></inline-formula> . Furthermore, the folded accumulation LDMOS with split gate (FSLDMOS) is proposed to solve the phenomenon that the BV of the FALDMOS cannot be improved by increasing the drift length with the fixed oxide thickness. The polysilicon above the drift region is etched apart to form an extended gate and a split electrode. The electric field concentration near the drain can be alleviated by adjusting the bias on the split electrode. The FALDMOS and FSLDMOS are manufactured by the 0.35- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> BCD technology and the key processes, such as trench etching and polysilicon filling, are shown. The experimental results show that <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{R}_{ \mathrm{\scriptscriptstyle ON},sp}$ </tex-math></inline-formula> of the FALDMOS is only 9.3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula> mm2, while that the conventional LDMOS is 36.2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula> mm2, which is reduced by 74.3% with the same BV of 36 V. Moreover, the current density of FALDMOS is five times higher than that of the conventional LDMOS in the same areas. The BV of the FSLDMOS is improved by 66% compared with FALDMOS.

Discharge Characteristics of Atmospheric Pressure Ar/N₂/O₂ a Plasma Jet Under a Square Wave Pulse

Plasma jets have broad application in the fields of sterilization and material processing. In recent years, studies have shown that adding a small amount of active gas into a single inert gas can change the distribution of active particles in the plasma. This not only produces the desired active species but also changes the length of the jet to make it more suitable for plasma applications. In this article, the characteristics of plasma jets were studied under an argon atmosphere with a small amount of nitrogen and oxygen. By measuring the voltage and current waveforms, luminescence images, and emission spectra under the three mixed gases, the main parameters such as discharge power, the three main particle emission spectrum intensities (the OH spectral line, the second positive band of nitrogen molecules and its diffraction band, argon atomic line), electron excitation temperature, molecular vibration temperature, and molecular rotation temperature are calculated. The results show two discharges in one cycle under the square wave pulse voltage. The addition of nitrogen and oxygen reduces the peak current of the Ar plasma jet but increases the power. The addition of N2 increases and stabilizes the length of the jet, while oxygen decreases the length. The spectral line intensities of OH and Ar atoms decrease with the increase in N2 doping concentration, while the spectral line intensity of nitrogen gas increases. The addition of oxygen reduces the intensity of all the three emission spectra. The electron excitation temperature is the highest in the mixed gas (Ar/N2/O2) and the lowest in pure argon. In the mixed gas (Ar/N2), the vibration temperature and rotation temperature are basically unchanged. After the addition of oxygen, the vibration temperature remained unchanged, but the rotation temperature increased slightly.

GeO2-doped ring-core photonic crystal fiber for supporting robust orbital angular momentum modes.

Orbital angular momentum (OAM)-mode-supported photonic crystal fibers (PCFs) have inspired intensive research in modern fiber optics due to the robust propagation and theoretically unlimited signal-carried channels. In this paper, a dual-cladding GeO2-doped ring-core PCF is designed, and a strategy for optimizing OAM mode properties is analyzed by structure parameters and GeO2-doping concentration. Numeric results show that high structural degrees of freedom are available to improve the effective refractive index separation (within the vector modes), chromatic dispersion, effective mode field area, nonlinear coefficient, and OAM mode purity in terms of inner cladding, outer cladding, and ring-core. In particular, the effective refractive index separation and chromatic dispersion can exhibit a high order magnitude of 10-3 and a low value in the broad band from 1.3 µm to 1.7 µm, respectively. In addition to structural optimization, doping high index material into the ring-core is another way to regulate the fiber performance by controlling the doping concentration. A systematic investigation shows that as the doping concentration increases, the effective refractive index separation and mode purity increase obviously, while the dispersion and mode field area gradually decrease. This flexible manipulation offers a method for customizing the optical properties of OAM-supported PCFs in communication and sensor systems.