Uniform Doping Research Articles

A uniform ion doping air-hole-assisted FM-EDF for low differential modal gain

An air-hole-assisted few-mode erbium-doped fiber (AH-FM-EDF) with a uniform erbium ion doping profile is proposed for gain equalization. By introducing the central air hole, the mode field distribution is strongly modified, contributing to a significant improvement in reducing the differential modal gain (DMG). Numerical results show that the gains of each mode can all reach 20 dB and the DMG is about 0.4 dB at 1550 nm in either core-pumping or cladding-pumping cases. Besides, the amplifier is well-behaved in gain-flattening with a noise figure (NF) of about 4.5 dB over the whole C-band. The proposed fiber shows much flexibility and robustness in gain equalization due to its simple uniform doping profile and pump-mode selection.

Two-dimensional multiband superconductivity of the optimally and uniformly Li-intercalated FeSe nanoflakes

We investigated the electrical transport properties of optimally Li+-intercalated FeSe nanoflakes. Using solid electrolyte gating, we obtained high and uniform electron doping up to ∼0.55 electrons per Fe sites in the FeSe nanoflakes, which exhibit a sharp superconducting transition at Tc ∼45.0 K. The temperature and magnetic-field dependent current-voltage characteristics clearly revealed the two-dimensional nature of the superconductivity in the intercalated FeSe nanoflakes. From the self-field critical current measurements, we found two distinct isotropic superconducting gaps with different gap ratios. These findings suggest that the highly electron-doped FeSe hosts two interband pairing channels between the hybridized electron pockets, in contrast to the case of pristine FeSe with electron and hole pockets.

Fabrication of Ga2O3 Schottky Barrier Diode and Heterojunction Diode by MOCVD.

In this article, we reported on a Ga2O3-based Schottky barrier diode and heterojunction diode from MOCVD. The Si-doped n-type Ga2O3 drift layer, grown by MOCVD, exhibited high crystal quality, flat surfaces, and uniform doping. The distribution of unintentional impurities in the films was studied. Then nickel Schottky barrier diode and p-NiO/n-Ga2O3 heterojunction diode were fabricated and measured. Without any electric field management structure, the Schottky barrier diode and heterojunction diode have specific resistances of 3.0 mΩ·cm2 and 6.2 mΩ·cm2, breakdown voltages of 380 V and 740 V, thus yielding power figures of merit of 48 MW·cm-2 and 88 MW·cm-2, respectively. Besides, both devices exhibit a current on/off ratio of more than 1010. This shows the prospect of MOCVD in power device manufacture.

Ordered mesoporous TiO2 framework confined CeSn catalyst exhibiting excellent high activity for selective catalytic reduction of NO with NH3 at low temperature

Synthesis of the cerium-based catalyst with excellent activity, selectivity, and toxicity resistance is one of the difficult problems for the selective reduction of NO by NH3 (NH3-SCR) at low temperature. Herein, we synthesize a novel and rational framework-confined ordered mesoporous CeSnOx/TiO2-E catalyst. Through a classical evaporation-induced self-assembly (EISA) strategy, the active components participate in the formation process of ordered mesoporous, which confines the catalytic active species into the interior of the overall structure. Via an array of microscopic characterizations and spectroscopic analysis, we have discovered that the presence of the ordered mesoporous structure makes the catalyst have a prominent confined effect on the framework. The high dispersion of nanoparticles in the system is realized here. Meanwhile, the cerium-based with Sn-doped catalyst system achieves the change of electronic structure and increases the charge exchange frequency, which enables the catalyst to acquire outstanding redox ability and abundant acidic sites. In addition, the ordered mesoporous structure of the catalyst guided the active components to produce a synergistic effect, and the uniform pore structure and metal doping enhanced the anti-poisoning ability. This strategy not only improves the low-temperature catalytic performance of the catalyst but also protects the nanoparticles from poisoning, which is beneficial to the long-time stability of the NH3-SCR reaction.

Effect of Mg-doping and Fe-doping in lead zirconate titanate (PZT) thin films on electrical reliability

Uniformly acceptor doped Pb(Zr0.48Ti0.52)O3 (PZT) films with 2 mol. % Mg or Fe prepared by chemical solution deposition exhibited decreased dielectric constants and remanent polarizations relative to undoped PZT. For highly accelerated lifetime testing (HALT) at 200 °C and an electric field of 300 kV/cm in the field up direction, the HALT lifetimes (t50) for undoped, Mg-doped, and Fe-doped PZT films were shortened from 2.81 ± 0.1 to 0.21 ± 0.1 and 0.54 ± 0.04 h, respectively. Through thermally stimulated depolarization current measurement, significant VO∙∙ electromigration was found in homogeneously Mg-doped PZT thin films, a major factor in their short HALT lifetime. Because the concentration of oxygen vacancies increases with uniform acceptor doping, the lifetime decreases. In contrast, when a thin layer of Mg-doped or Fe-doped PZT was deposited on undoped PZT or Nb-doped PZT (PNZT), the HALT lifetimes were longer than those of pure PZT or PNZT films. This confirms prior work on PNZT films with a Mn-doped top layer, demonstrating that the HALT lifetime increases for composite films when a layer with multivalent acceptors is present near the negative electrode during HALT. In that case, the compensating electrons are trapped, presumably on the multivalent acceptors, thus increasing the lifetime.

Li diffusion and surface segregation in K0.5Na0.5NbO3 films grown by Pulsed Laser Deposition

Potassium Sodium Niobate has recently raised particular attention in the field of piezoelectric perovskites thanks to its remarkable piezoelectric properties and high Curie temperature. Previous works have shown that slight Lithium (Li) doping can improve the piezoelectric properties and reduce leakage of stoichiometric K0.5Na0.5NbO3 (KNN). In this paper, evidence is provided that this is not the case for thin films synthesized by Pulsed Laser Deposition, at growth temperature high enough to induce the (001) orientation on a Pt(111) /TiO2/SiO2/Si template. The high mobility of alkali ions leads to Li surface segregation and high non-uniformity of Li doping over the film thickness. This is accompanied by a degradation of KNN thin film electrical properties upon Li doping, with an increase in leakage currents by up to one order of magnitude which impedes a macroscopic piezoelectric characterization. On the other hand, local piezoelectric properties investigated by Piezoresponse Force Microscopy are unchanged upon doping. The results clearly point out the critical issues regarding the growth method to obtain a uniform doping of KNN with light elements such as Li. Due to the high mobility of this species, sizable migration phenomena can be thermally activated in physical vapor deposition processes with high thermal budget, ultimately hampering the envisaged benefits of Li on piezoelectric response.

Flexible pressure sensor based on graphene/PS microsphere/PDMS composite dielectric layer and activated carbon non-woven fabrics

• Fabrication of ultra-thin dielectric layers with surface microstructures and filler doping. • Offering new ideas for improving the sensitivity of flexible capacitive sensors. • Activated carbon non-woven fabrics are used to make flexible electrodes. • New dielectric layer fabrication process developed. • A number of dynamic tests have been completed using this sensor. With the widespread application of wearable devices, the demand for high-performance sensors has increased dramatically. This study proposes a novel capacitive sensor. By using polystyrene (PS) microspheres and the sacrificial layer method, the ultrathin dielectric layer with surface micro-dome structure and uniform graphene doping are fabricated. In addition, the activated carbon non-woven fabrics (ACNWF) electrode was prepared, and the device characteristics of the sensor were investigated. The sensor has a good capacitive response in a wide pressure range (0–150 kPa) and a sensitivity of 0.209 kPa −1 in the low-pressure range. The short response time (<25 ms) is suitable for real-time dynamic monitoring. Meanwhile, the sensor has good stability (3500 cycles) and performs well in mouse double-click, muscle contraction and arm swing. This sensor has great potential in wearable electronics and human-computer interaction.

Boosting visible-light-driven photocatalytic H2 evolution of C/Znln2S4 hollow tubes by Ni doping

• A unique Ni doped CZIS photocatalyst was synthesized by a simply method. • Ni atoms partially replaced Zn atoms to form Ni/CZIS. • Ni/CZIS showed a high H 2 release capacity of 3537.04 μmol g -1 h −1 . • The good photocatalytic activity was attributed to Ni doping and special structure. An n-type nickel-doped carbon indium zinc sulfur (Ni/CZIS) hollow tube structure photocatalyst was synthesized for the first time through a simple solvothermal combination with an oil bath. Then it was characterized by a series of tests such as SEM, TEM, XRD, XPS, photoelectric properties and so on. The results showed that the addition of nickel acetate in the oil bath achieved uniform doping of nickel atoms and partially replaced the positions of zinc. The optimized Ni/CZIS material had lower overpotential, broadened the light absorption region, promoted photo-induced carrier separation and better hydrophilicity. Thus it showed an excellent visible-light photocatalytic hydrogen production rate (3035.75 μmol/g/h) and cyclic stability. In view of density functional theory calculations, Ni atomic doping narrowed the band gap width, changed the positions of the valence and conduction bands, and also generated a new hybridization level near the Fermi level. This energy level provided a new electronic channel for photo-generated electrons, facilitated the transfer of electrons and suppressed the recombination of carrier, thereby enhancing the photocatalytic hydrogen production performance.

Active Motif Change of Ni‐Fe Spinel Oxide by Ir Doping for Highly Durable and Facile Oxygen Evolution Reaction

AbstractThe oxygen evolution reaction (OER) is crucial for producing sustainable energy carriers. Herein, Ir (5 mol.%) doped inverse‐spinel NiFe2O4 (Ir‐NFO) nanoparticles deposited on Ni foam (NF) by scalable solution casting are considered a promising OER electrocatalyst for industrial deployments. The Ir‐NFO/NF (with minimal lattice distortion by uniform Ir doping) provides an OER overpotential of 251 mV (intrinsically outperforming NFO/NF and benchmarking IrO2/NF) and extraordinary robustness over 130 days at 100 mA cm−2. In situ X‐ray absorption spectroscopy reveals oxidation only for Fe on NFO, whereas concurrent generation of higher‐valent Ni and Fe occurs on Ir‐NFO during OER. Density functional theory calculations further demonstrate that Ir substitutes the sublayer Ni octahedral site and switches the main active reaction center from FeOhFeTd bridge site (FeOFe) on NFO to NiOh–FeTd bridge site (NiOFe active motif) on Ir‐NFO for a co‐catalytic OER. This study sheds new light on precious‐metal doped Ni‐Fe oxides, which may be applicable to other binary/ternary oxide electrocatalysts.

Simulation and Performance Evaluation of Charge Plasma Based Dual Pocket Biosensor using SiGe-Heterojunction TFET Design

Conventional biosensor designs are often vulnerable to issues like random dopant fluctuations (RDFs) and high thermal budgets due to their design and the device they are based on. The main reason behind such issues is the complexity of maintaining uniform doping levels throughout the device structure. This manuscript investigates a biosensor structure utilizing a dual pocket junctionless SiGe-Heterostructured TFET design to overcome such shortcomings. The implementation of the doping charge plasma technique with the uniform doping of mathrm {1}times mathrm {10}^{mathrm {15}} {cm}^{mathrm {-3}} along an integrated SiGe-Heterostructure layer has improved the tunneling process while also effectively eliminating issues like random dopant fluctuations (RDF). Again the overall performance also depends on the sensitivity of the sensor design. Increasing the trapping area for biomolecules at the same technological node by increasing the pocket length or by adding a pocket region leads to rapid changes in the sensor’s electric properties owing to shifting dielectric constants (k) and charge densities (in both positive and negative situations), improving in the overall detection process. The influence of these parameters on the device’s Drain current, Surface Potential, Electron Tunneling Rate (ETR), Subthreshold Swing (SS), and Ion/Ioff ratio is also explored. The introduction of the added pocket region gives us scalability while also showing a higher sensitivity of mathrm {5.38} times mathrm {10}^{mathrm {9}} for a dielectric constant being 12 and neutrally charged while rising to nearly mathrm {1.43} times mathrm {10}^{mathrm {10}} if the molecules are positively charged. With the improvement in drain current sensitivity due to the additional pocket and junctionless design, this work will undoubtedly give researchers a roadmap for the future generation of highly sensitive biosensor alternatives.

Rapid Gas-Phase Synthesis of the Perovskite-Type BaCe0.7Zr0.1Y0.1Yb0.1O3-δ Proton-Conducting Nanocrystalline Electrolyte for Intermediate-Temperature Solid Oxide Fuel Cells.

Perovskite-type proton-conducting materials, such as BaCe0.7Zr0.1Y0.1Yb0.1O3-δ (BCZYYb), are very attractive for the next-generation equipment of electrochemical energy conversion and storage owing to their excellent conductivity in the intermediate-temperature range (300-750 °C), as well as good thermo-chemical stability, coking resistance, and sulfur tolerance. However, the lack of a reliable and cost-effective synthesis method for such multi-component co-doping oxides limits their large-scale application. In this study, for the first time, we successfully synthesize BCZYYb electrolyte nanopowders by using a rapid, scalable flame-based gas-phase synthesis method with two different barium precursors Ba(NO3)2 and Ba(CH3COO)2, named as BCZYYb (N) and BCZYYb (CA). The as-synthesized nanoparticles exhibit good crystallinity of the pure orthorhombic perovskite BCZYYb phase. BCZYYb (CA) shows more uniform doping with the element ratio of 1:0.74:0.12:0.08:0.1, which is very close to the theoretical value. The shrinkage and surface SEM (scanning electron microscope) results indicate that the flame-made powders have superior sinterability compared to the sol-gel-made powders because of the smaller primary particle size (∼20 nm). Electrochemical impedance spectroscopy tests show that BCZYYb (CA) sintered at 1450 °C has the highest protonic conductivity of 1.31 × 10-2 S cm-1 in wet H2 when operating at 600 °C and still maintains a high-level conductivity of 1.19 × 10-2 S cm-1 even when the sintering temperature is reduced to 1350 °C, which is mainly attributed to uniform doping and good sinterability. The activation energy for the conductivity of BCZYYb (CA) is also significantly lower than that of conventional electrolytes, which suggests much better conductivity in the intermediate (∼600 °C) and even lower operating temperature. The excellent conductivity performance combined with the high-throughput production capability makes the swirling spray flame a promising synthesis method for promoting the BCZYYb electrolytes from lab to industrial-scale solid oxide fuel cells.

Introducing gallium in silicon and thin film polysilicon using self assembled monolayer doping

• Gallium compound synthesized to form Ga molecular monolayers on silicon surface. • Ga monolayer doping in silicon and thin film polysilicon demonstrated. • Junction depth of 200 nm with a dose 1.6*10 15 Ga atoms/cm 2 demonstrated in n -Si. • Near uniform doping in polysilicon films is achieved with 20% electrical activation. Monolayer Doping (MLD) is a technique involving the formation of a self-assembled dopant-containing layer on the substrate. The dopant is subsequently incorporated into the substrate by annealing, forming a diffused region. Following MLD, samples were capped with silicon dioxide and rapid thermal annealed (RTA). In this work, gallium doping using MLD has been demonstrated. Gallium containing compound Tris (2,4 pentanedionato) gallium(III) was synthesized, and shown to be suitable for monolayer doping silicon substrates and deposited thin film polysilicon. Secondary ion mass spectroscopy (SIMS) and spreading resistance probe (SRP) measurements were performed to determine the dopant profiles and dopant electrical activation. These results showed that a dose of 1.6*10 15 atoms/cm 2 was received, and the gallium dopant produced a 0.2 µm junction in n -type silicon. For polysilicon, the entire 0.4 μm film was evenly doped, with a concentration greater than 10 19 atoms/cm 3 throughout.

β -Ga2O3 MESFETs with insulating Mg-doped buffer grown by plasma-assisted molecular beam epitaxy

In this work, we develop in situ Mg doping techniques in plasma-assisted molecular beam epitaxy (PAMBE) of β-Ga2O3 to compensate Si dopants at the substrate epilayer growth interface and eliminate parasitic leakage paths. Both abrupt and uniform Mg doping profiles over a wide range of concentrations were achieved in β-Ga2O3 epilayers grown by PAMBE. Capacitance–voltage characteristics of Si and Mg co-doped samples confirmed the compensating effect of the Mg dopants. Mg delta-doping was then integrated into a β-Ga2O3 metal-semiconductor field effect transistor structure and shown to be effective in eliminating source leakage. The results presented here show that Mg doping is a promising way to engineer insulating buffer layers for β-Ga2O3 lateral devices grown by PAMBE.

Bilateral gradient defect engineering integrated atomic in-layer homojunctions for efficient photoelectrochemical water splitting

Severe recombination of photo-generated carriers restricts the application of photoelectrochemical water splitting. Designing carrier spatial separation paths at the atomic level is an innovative but challenging strategy to address this problem. Herein, we first propose a gradient defect model confined in atomic layers. Bilateral gradient Cd doping terminated at the outer surfaces of five-atomic-layer BiOI nanosheets was achieved by a linear pressurized gas-assisted (LPGA) technique with self-adapting oxygen vacancies generated unexpectedly. Different doping concentrations between layers trigger the rearrangement of energy levels, resulting in distributed atomic homojunctions with “pyramid-like” band alignment to synergistic modulate carrier separation. Thus, the gradient Cd doping BiOI displays a charge separation efficiency of 78.1%, which is 12.0 and 7.9 times higher than those for pristine BiOI and uniform doping BiOI. Furthermore, the record photocurrent density of 4.68 mA cm−2 at 0 VRHE is the highest absolute value of BiOI photocathodes reported to date and outperforms most bismuth-based photocathodes. Our work provides a new method to modulate photo-generated carrier separation at the atomic level and deepens the understanding of homojunction semiconductors.

Effect of Gradient Doping on Charge Collection Efficiency of EBCMOS Devices

We investigated the effect of different gradient doping methods on the charge collection efficiency of the electron multiplication layer of EBCMOS devices. Exponential doping of the electron multiplication layer can form a built-in electric field in the electron multiplication layer that is favorable for photoelectron transport, so exponential doping instead of uniform doping in the electron multiplication layer of EBCMOS can effectively improve the charge collection efficiency. It is shown that exponential heavy doping on the side of the electron multiplication layer near the dead layer and exponential light doping on the side near the depletion region can improve the built-in electric field structure and increase the lifetime of the multiplied electrons, thereby improving the charge collection efficiency of EBCMOS. The optimized device achieves a charge collection efficiency of 94.48% at an incident electron energy of 4 keV, an electron beam diameter of 20 nm, a dead layer thickness of 60 nm, and a P-type silicon epitaxial layer thickness of 10 μm.

Scalable-doped Nanoporous 1T″ ReSe2 via a General Surface Co-Alloy Strategy.

Reliable and controllable doping of 2D transition metal dichalcogenides is an efficient approach to tailor their physicochemical properties and expand their functional applications. However, precise control over dopant distribution and scalability of the process remains a challenge. Here, we report a general method to achieve scalable in situ doping of centimeter-sized bicontinuous nanoporous ReSe2 films with transition metal atoms via surface coalloy growth. The distinct strains induced by the bending curvature of nanoporous structures and uniform dopants result in a local 1T' to 1T″ structure phase transition over nanoporous ReSe2 films. The as-prepared nanoporous Ru-ReSe2 with high 1T″ phase exhibits preferable electrochemical activity in hydrogen evolution reaction. The work demonstrates a unique and general approach to synthesize uniformly-doped transition metal dichalcogenides with 3D bicontinuous nanoporous structure, which can be scaled up to batch production for various applications.

Surface yttrium-doping induced by element segregation to suppress oxygen release in Li-rich layered oxide cathodes

Doping electrochemically inert elements in Li-rich layered oxide cathodes usually stabilizes the structure to improve electrochemical performance at the expense of available capacity. Here, we use an element segregation principle to realize a uniform surface doping without capacity sacrifice. On the basis of Hume-Rothery rule, element yttrium is chosen as a candidate dopant to spontaneously segregate at particle surface due to mismatched ionic size. Combined with X-ray photoelectron spectroscopy and electron energy loss spectroscopy mapping, yttrium is demonstrated uniformly distributed on particle surface. More importantly, a significant alleviation of oxygen release after surface doping is detected by operando differential electrochemical mass spectrometry. As a result, the modified sample exhibits improved reversibility of oxygen redox with 82.1% coulombic efficiency and excellent cycle performances with 84.15% capacity retention after 140 cycles. Postmortem analysis by transmission electron microscopy, Raman spectroscopy and X-ray diffraction reveal that the modified sample maintains the layered structure without a significant structure transformation after long cycles. This work provides an effective strategy with a series of elements to meet the industrial application.

Nitrogen-Doped Porous MXene (Ti3C2) for Flexible Supercapacitors with Enhanced Storage Performance.

Flexible supercapacitors (FSCs) are limited in flexible electronics applications due to their low energy density. Therefore, developing electrode materials with high energy density, high electrochemical activity, and remarkable flexibility is challenging. Herein, we designed nitrogen-doped porous MXene (N-MXene), using melamine-formaldehyde (MF) microspheres as a template and nitrogen source. We combined it with an electrospinning process to produce a highly flexible nitrogen-doped porous MXene nanofiber (N-MXene-F) as a self-supporting electrode material and assembled it into a symmetrical supercapacitor (SSC). On the one hand, the interconnected mesh structure allows the electrolyte to penetrate the porous network to fully infiltrate the material surface, shortening the ion transport channels; on the other hand, the uniform nitrogen doping enhances the pseudocapacitive performance. As a result, the as-assembled SSC exhibited excellent electrochemical performance and excellent long-term durability, achieving an energy density of 12.78 Wh kg−1 at a power density of 1080 W kg−1, with long-term cycling stability up to 5000 cycles. This work demonstrates the impact of structural design and atomic doping on the electrochemical performance of MXene and opens up an exciting possibility for the fabrication of highly FSCs.

A new insight characterization analysis and two photon absorption behaviour of pure and doped vanadium oxide

Pure and (7, 12 and 17 wt%) fluorine doped vanadium oxide was synthesized by simple one-step hydrothermal treatment. XRD confirms the formation of mixed phases of orthorhombic V2O5 and monoclinic V3O7. Increasing trend in crystallite size with fluorine content was observed due to the replacement of fluorine in oxygen sites of vanadium oxide lattices. FESEM and EDX analysis ascertains the formation of platelets with uniform doping of vanadium pentoxide. Both samples exhibit maximum absorption in UV region and the band gap slightly decreases due to fluorine doping. The impedance characterization signal was analysed in the specific frequency range from 100 KHz to 0.01 Hz. The dielectric parameters are dependent on the frequency and different dopant ratios. The dielectric dispersion signal shows to decrease in dielectric values as frequency increases. The microstructure properties are successfully studied using Raman and FTIR spectroscopy. Under Q-switched frequency doubled Nd:YAG laser (532 nm, 9 ns, 100 μJ) excitation, both pure and fluorine doped vanadium oxide exhibit reverse saturable absorption. 17 wt% F doped V2O5 possesses a higher 2PA coefficient which arises mainly from the synergetic effect from the contribution of nanoplatelet morphology and incorporation of F as decorative element upon V2O5. Also two-photon absorption induced optical limiting action was witnessed and this makes them potential candidate for fabrication of laser safety googles.

Numerical analysis of beam self-cleaning in multimode fiber amplifiers

Recent experimental results have reported the observation of beam self-cleaning or, more generally, nonlinear beam reshaping in active multimode fibers. In this work, we present a numerical analysis of these processes by considering the ideal case of a diode-pumped signal amplifier made of a graded-index multimode fiber with uniform Yb doping. Simulations confirm that beam cleaning of the signal may take place even in amplifying fibers, in the absence of beam power conservation. Moreover, we show how the local signal intensity maxima, which are periodically generated by the self-imaging process, may influence the population inversion of the doping atoms, and locally saturate the amplifier gain.