Surface Trap Research Articles

Surface flashover in 50 years: II. Material modification, structure optimisation, and characteristics enhancement

AbstractSurface flashover is a gas–solid interface insulation failure that significantly jeopardises the secure operation of advanced electronic, electrical, and spacecraft applications. Despite the widespread application of numerous material modification and structure optimisation technologies aimed at enhancing surface flashover performance, the influence mechanisms of the present technologies have yet to be systematically discussed and summarised. This review aims to introduce various material modification technologies while demonstrating their influence mechanisms on flashover performances by establishing relationships among ‘microscopic structure‐mesoscopic charge transport‐macroscopic insulation failure’. Moreover, it elucidates the effects of chemical structure on surface trap parameters and surface charge transport concerning flashover performance. The review categorises and presents structure optimisation technologies that govern electric field distribution. All identified technologies highlight that achieving a uniform tangential electric field and reducing the normal electric field can effectively enhance flashover performance. Finally, this review proposes recommendations encompassing mathematical, chemical, evaluation, and manufacturing technologies. This systematic summary of current technologies, their influence mechanisms, and associated advantages and disadvantages in improving surface insulation performance is anticipated to be a pivotal component in flashover and future dielectric theory.

High-Performance CuInS2 Quantum Dot Sensitized Solar Cells Through I-/MPA Dual-Ligands Passivation.

High-efficiency quantum dot sensitized solar cells (QDSSCs) can be received by increasing quantum dot (QD) loading and mitigating QD surface trap states. Herein, the surface state of CuInS2 QDs is optimized through an I-/MPA dual-ligands passivation strategy. The steric hindrance and electrostatic repulsion between QDs can be effectively reduced, thereby enabling an increased QD loading capacity. Meanwhile, the I-/MPA dual-ligands passivation strategy can further lower the surface trap density, leading to substantially enhanced charge transfer efficiency of the solar cells. Interestingly, various iodized salts, including TBAI, MAI, and KI, are proved to possess comparable property, underscoring the versatility and broad applicability of this I-/MPA dual-ligands passivation strategy. Eventually, CuInS2 QDSSCs based on the NH4I/MPA dual-ligands exhibit a noteworthy enhancement in photovoltaic conversion efficiency, surpassing the benchmark of 5.71 % to reach 7.03 %.

Enhanced DC surface discharge characteristics of epoxy composites treated by dielectric barrier discharge plasma fluorination and its mechanisms

Surface flashover is a destructive high-voltage discharge phenomenon greatly limiting the update of modern power electronic and electrical equipment. Surface plasma treatment is a high-energy, eco-friendly, and convenience method, it changes the surface properties and owns potential to improve flashover voltage. In the present work, plasma fluorination (PF) technique are used to treat EP/Al2O3 composites, surface morphology, element and bonds content, surface trap, conductivity, charging, and DC flashover voltage are tested and simulated, the effects of plasma on surface discharge are explained through the investigation from microscopic molecular reactions to macroscopic flashover characteristics. It indicates the 20 min PF modified sample exhibits the superior DC flashover performance, increasing by 17 % compare to untreated sample. During PF modification, the epoxy chains are degraded and fluorinated, the degradation rather than fluorination of molecular chains introduce large amounts of shallow traps into the composites, accelerating carriers’ migration and improving surface conductivity, causing surface charges to dissipate through surface conductance. Consequently, the surface electric field distortion degree reduces, and the subsequent gas ionization and plasma formation in the gas phase is suppressed, leading to the improvement of DC flashover voltage after PF modifications.

Mechanism exploration of ion-implanted epoxy on surface trap distribution: An approach to augment the vacuum flashover voltages

Abstract The augmentation of the epoxy (EP) resin surface to advance flashover performance has become a pivotal point of global interest. This research introduces a novel surface modification method and its mechanism for insulation materials. The research follows an electron cyclotron resonance ion implantation system to subject the surface of EP insulation to ion beams with diverse energies, i.e., 6, 10, 20, 40, 50, and 60 keV for a consistent time of 300 s at an angle of 90°. The experimental phase includes the DC flashover examination under negative polarity. Besides, the simulation phase includes the Monte Carlo model constructed using SRIM software to examine the range and distribution of bombarded ions in the targeted insulation. Results reveal that the flashover properties are affected by the surface potential, surface conductivity, trap distribution, water contact angle, and elemental composition. Likewise, based on the outcomes and theoretical point of view, it is revealed that the bombardment of energetic ions enhances the trap depth, assisting in a reduction in surface conductivity, confining the surface charge movements, and extensively suppressing the secondary electron emission yield. Also, the enhanced trap depth induces homo-charge formation near triple junctions. Synergistically, the factors contribute to high flashover voltages.

Mitigating interfacial recombination enabling efficient semitransparent organic photovoltaics

Charge recombination at the interface between top electrode and active layer is a substantial current loss pathway in semitransparent organic photovoltaics (STOPVs). Reducing interfacial traps is an effective strategy to mitigate interfacial recombination and promote charge extraction, and thereby improve the power conversion efficiencies (PCEs). Herein, a facile approach of depositing 11-mercapto-undecanoic acid (11-MUA) on zinc oxide (ZnO) cathode interlayer in conventional STOPVs is demonstrated. 11-MUA can form covalent interactions with both ZnO and silver (Ag) and thus can induce the formation of high-quality ultrathin Ag electrode. Compared with that deposited on bare ZnO, the Ag electrode on ZnO/11-MUA shows higher conductivity as well as higher optical transparency. The STOPVs based on ZnO/11-MUA/Ag exhibit 2 orders of magnitude lower surface trap density than the counterparts based on ZnO/Ag. Consequently, 11-MUA simultaneously improves the PCEs from 11.2% to 12.1% and average visible transmittance from 21.6% to 27.0% in the STOPVs. Furthermore, arising from the 11-MUA-modified interface, the thermal stability of STOPVs based on ZnO/11-MUA/Ag is also improved.

Unraveling the exceptional kinetics of Zn||organic batteries in hydrated deep eutectic solution

Intuitively, the solvation structure featuring stronger interacted sheath in deep eutectic solution (DES) electrolyte would result in sluggish interfacial charge transfer and intense polarization, which obstructs its practical application in emerging Zn based batteries. Unexpectedly, here we discover a Zn||organic battery with exceptional kinetics properties enabled by a hydrated DES electrolyte, which can render higher discharge capacity, smaller voltage polarization, and faster kinetics of charge transfer in comparison with conventional aqueous 3 M ZnCl2 electrolyte, though its viscosity is two orders of magnitude higher than the latter. The improved kinetics of charge transfer and ion diffusion is demonstrated to originate from the local electron structure regulation of cathode in hydrated DES electrolyte. Furthermore, the DES electrolyte has also been shown to restrict parasitic reaction associated with active water by preferential urea-molecular adsorption on Zn surface and stronger water trapping in solvation structure, giving rise to long-term stable dendrite-free Zn plating/stripping. This work provides a new rationale for understanding electrochemical behaviors of organic cathodes in DES electrolyte, which is conducive to the development of high-performance Zn||organic batteries.

In-situ synthesis of Fe phosphate layer on the porous hematite nanocube for efficient photoelectrochemical water splitting

Hematite (α-Fe2O3) is considered as an ideal photoanode material in photoelectrochemical (PEC) water splitting system due to its suitable band gap, excellent stability and abundant reserves. However, the actual PEC water oxidation performance of α-Fe2O3 is greatly limited by its severe charge recombination and sluggish water oxidation kinetics. Here, an in-situ generated Fe phosphate (Fe-Pi) coating strategy is applied on the surface of porous hematite nanocube (Fe2O3 NC) to realize PEC water oxidation effectively. The obtained Fe-Pi/Fe2O3 NC photoanode exhibits a remarkable PEC property with a photocurrent density of 2.7mAcm-2 at 1.23V vs. RHE, which was about 5.7-fold enlarged compared to the pristine nanorod-like hematite (Fe2O3 NR) photoanode. Detailed studies have shown that the porous Fe2O3 NC possesses an enhanced ability in light absorption and charge separation than the traditional Fe2O3 NR photoanode. In addition, the in-situ loading of Fe-Pi layer as a co-catalyst can not only effectively passivate the surface trapping states of Fe2O3 NC and suppress interfacial charge recombination, but also quickly extract the holes to participate in the water oxidation reaction. Our study suggests that the further surface modification based on morphological engineering is an effective strategy to improve the PEC performance of hematite.

Ions‐induced Assembly of Perovskite Nanocomposites for Highly Efficient Light‐Emitting Diodes with EQE Exceeding 30%

AbstractMetal halide perovskites, a cost‐effective class of semiconductos, hold great promise for display technologies that demand high‐efficiency, color‐pure light‐emitting diodes (LEDs). Early research on three‐dimensional (3D) perovskites showed low radiative efficiencies due to modest exciton binding energies. To inprove luminescence, reducing dimensionality or grain size has been a common approach. However, dividing the perovskite lattice into smaller units may hinder carrier transport, compromising electrical performance. Moreover, the increased surface area introduce additional surface trap states, leading to greater non‐radiative recombination. Here, an ions‐induced growth method is employed to assembe lattice‐anchored perovskite nanocomposites for efficient LEDs with high color purity. This approach enables the nanocomposite thin films, composed of 3D CsPbBr3 and its variant of zero‐dimensional (0D) Cs4PbBr6, to feature significant low trap‐assisted nonradiative recombination, enhanced light out‐coupling with a corrugated surface, and well‐balanced charge carrier transport. Based on the resultant 3D/0D perovskite nanocomposites, the perovskite LEDs (PeLEDs) achieving an remarkable external quantum efficiency of 31.0% at the emission peak of 521 nm with a narrow full width at half‐maximum of only 18 nm. This sets a new benchmark for color purity in high performance PeLED research, highlighting the significant advantage of this approach.

Enhancing broadband absorption and photocurrent generation in carbon dots via P3HT integration

The growing interest in carbon dots (CDs) arises from their diverse applications and unique properties. This study addresses challenges in CDs for photodetector (PD) applications, specifically surface defects and trap states hindering efficient charge transport. CDs/P3HT composites were prepared to overcome these issues by incorporating CDs in a poly(3-hexylthiophene) (P3HT) matrix. Broad absorption in spectroscopic characterization revealed its utility in fabricating a broadband PD. The CDs/P3HT PD displays a remarkable broadband photoresponse, spanning both UV and visible regions. The CDs and P3HT are effectively combined via non-covalent π-π interactions constituted by their conjugated systems. The π-π interaction increases electron delocalization and facilitates efficient charge transfer due to band alignment at the junction interface. Hence, fabricated CDs/P3HT PD demonstrated enhanced photocurrent compared to pure CDs, exhibiting high responsivity of 6.12 × 10−3 AW−1 and detectivity of 0.69 × 109 Jones. This study highlights the potential of CD/P3HT composites for broadband photodetector applications with enhanced photoelectric conversion.

Amino‐Arsine and Amino‐Phosphine Based Synthesis of InAs@InP@ZnSe core@shell@shell Quantum Dots

AbstractA colloidal synthesis protocol is demonstrated for InAs@InP core@shell quantum dots (QDs) with a tunable InP shell thickness (ranging from 3 to 8 monolayers), utilizing tris(diethylamino)‐arsine and ‐phosphine. Structural analysis reveals that the InP shell preferentially grows onto the tetrahedral InAs cores along the <‐1‐1‐1> directions, forming tetrapodal‐shaped InAs@InP QDs. Growth of the InP shell causes a red shift in the absorption spectrum of the QDs. This is explained by considering that electrons are delocalized throughout the whole core@shell QDs, while holes preferentially leak along the <‐1‐1‐1> directions, as indicated by the density functional theory calculations. This means such heterostructures cannot be described as type‐I or quasi type‐II, contrary to earlier assumptions. The overlap of carrier wavefunctions throughout the entire InAs@InP QD structure results in no significant reduction of the Auger recombination rate, which remains as fast as in InAs QDs. However, the InP shell enhances photoluminescence (PL) efficiency (up to ≈13%) by passivating surface trap states of the InAs QDs (mainly located close to the top of the valence band). The overgrowth of a ZnSe shell endows the QDs with a high PL efficiency (≈55%) and good stability upon air exposure (≈80% PL intensity retention after 14 days).

Superconducting surface trap chips for microwave-driven trapped ions

Microwave-driven trapped ion logic gates offer a promising avenue for advancing beyond laser-based logic operations. In future microwave-based operations, however, the joule heat produced by large microwave currents flowing through narrow microwave electrodes would potentially hinder improvements in gate speed and fidelity. Moreover, scalability, particularly in cryogenic trapped ion systems, is impeded by the excessive joule heat. To address these challenges, we present a novel approach: superconducting surface trap chips that integrate high-Q microwave resonators with large current capacities. Utilizing sub-ampere microwave currents in superconducting Nb resonators, we generate substantial magnetic field gradients with significantly reduced losses compared to conventional metal chips. By harnessing the high Q factors of superconducting resonators, we propose a power-efficient two-qubit gate scheme capable of achieving a sub-milliwatt external microwave input power at a gate Rabi frequency of 1 kHz.

Recycling Single‐Crystal Perovskite Solar Cells With Improved Efficiency and Stability

AbstractMetal halide perovskite single crystals are promising for photovoltaic applications due to their outstanding properties. However, the high surface trap density causes severe nonradiative recombination and ion migration, hindering device performance and stability. Herein, mitigation of the deficient crystal surface is reported by optimized polishing engineering, resulting in stoichiometric lead‐iodine ratio with reduced iodide ion vacancies, increased ion migration activation energy, and suppressed nonradiative recombination. As a result, Cs0.05FA0.95PbI3 (FA = formamidinium) devices exhibit an impressive efficiency of 23.1%, which is one of the highest values for single‐crystal perovskite solar cells (PSCs). Moreover, multiple recycling of the degraded single‐crystal PSCs with higher efficiency and stability is achieved by removing the deteriorated surface, validating crystal surface dominates device degradation while the role of bulk and buried interface is negligible, which is different from polycrystalline devices. The T85 lifetime (remain 85% of initial efficiency) of Cs0.05FA0.95PbI3 devices increases to 1150 h after the recycling process, which is much better than that of previously reported single‐crystal PSCs. Since deficient crystal surface and ion migration are universal issues of perovskite materials, this work will promote the development of stable single‐crystal PSCs and other optoelectronic devices, such as X‐ray detectors, light‐emitting diodes, etc.

AC Zeeman effect in microfabricated surface traps.

Quantum processors and atomic clocks based on trapped ions often utilize an ion's hyperfine transition as the qubit state or frequency reference, respectively. These states are a good choice because they are insensitive in first order to magnetic field fluctuations, leading to long coherence times and stable frequency splittings. In trapped ions, however, these states are still subject to the second order AC Zeeman effect due to the necessary presence of an oscillating magnetic field used to confine the ions in a Paul trap configuration. Here, we measure the frequency shift of the 2S1/2 hyperfine transition of a 171Yb+ ion caused by the radio frequency (RF) electromagnetic field used to create confinement in several microfabricated surface trap designs. By comparing different trap designs, we show that two key design modifications significantly reduce the AC Zeeman effect experienced by the ion: (1) an RF ground layer routed directly below the entire RF electrode, and (2) a symmetric RF electrode. Both of these changes lead to better cancellation of the AC magnetic field and, thus, overall reduced frequency shifts due to the AC Zeeman effect and reduced variation across the device. These improvements enable a more homogeneous environment for quantum computing and can reduce errors for precision applications such as atomic clocks.

Influence mechanisms of ultraviolet irradiation aging on DC surface discharge properties of silicone rubber in dry and humid air

In the modern DC electrical transmission system, high-energy photons interact with silicone rubber (SIR) chains during long-term ultraviolet (UV) irradiation, it degrades the surface properties and triggers surface discharge (flashover) along the SIR-air interface, threatening the secure operation of the advanced electrical equipment. To further comprehend how UV-aging influences the flashover performance, in this work, the chemical bonds, surface charge transport parameters, and flashover performance of UV-aged SIR samples are characterized, and the influence mechanisms of UV-aging on surface discharge in dry and humid air are comprehensively clarified through the investigation from “molecular-mesoscopic-macroscopic” scales. The results indicate both degradation and oxidization reactions occur during UV-aging. The degraded molecular chains dominate the discharge in dry air, while oxidization reactions determine the discharge in humid environment: The degradation reactions reduce the surface trap depth and increase surface conductivity, leading to large surface leakage current and surface charge dissipation rate, causing flashover voltage in dry air increases and decreases as UV-aging time increasing. The oxidization of the chains introduces –OH and –COOH groups into chains, enhancing permittivity and adsorbing H2O molecules, significantly increasing surface leakage current, causing surface discharge voltage in humid air to decrease as UV-aging time increases.

Optimized Surface Ion Trap Design for Tight Confinement and Separation of Ion Chains

Qubit systems based on trapped ultracold ions win one of the leading positions in the quantum computing field, demonstrating quantum algorithms with the highest complexity to date. Surface Paul traps for ion confinement open the opportunity to scale quantum processors to hundreds of qubits and enable high-connectivity manipulations on ions. To fabricate such a system with certain characteristics, the special design of a surface electrode structure is required. The depth of the trapping potential, the stability parameter, the secular frequency and the distance between an ion and the trap surface should be optimized for better performance. Here, we present the optimized design of a relatively simple surface trap that allows several important high-fidelity primitives: tight ion confinement, laser cooling, and wide optical access. The suggested trap design also allows us to perform an important basic operation, namely, splitting an ion chain into two parts.

A computational analysis of the impact of thin undoped channels in surface-related current collapse of AlGaN/GaN HEMTs

Abstract This study provides an insight into the impact of thin purely undoped GaN channel thickness (t ch) on surface-related trapping effects in AlGaN/GaN high electron mobility transistors. Our TCAD study suggests that in cases where parasitic gate leakage is the driving trapping mechanism that promotes the injection of electrons from the Schottky gate contact into surface states, this effect can be alleviated by reducing t ch of the undoped GaN channel. We show that by decreasing t ch from 130 to 10 nm, devices exhibit a reduction in gate-related current collapse under the specific class-B RF operating bias conditions as a consequence of a substantial decrease in the off-state gate leakage with reducing t ch. Large-signal simulations revealed an increase by 3 W mm−1 and about 12% output power and power-added efficiency due to the decrease of gate-related collapse. This work, for the first time, highlights the role of a proper purely undoped GaN t ch selection to alleviate gate-related surface trapping in the design of GaN-based microwave power amplifiers.

High-Performance Ideal Bandgap Sn-Pb Mixed Perovskite Solar Cells Achieved by MXene Passivation.

Ideal bandgap (1.3-1.4eV) Sn-Pb mixed perovskite solar cells (PSC) hold the maximum theoretical efficiency given by the Shockley-Queisser limit. However, achieving high efficiency and stable Sn-Pb mixed PSCs remains challenging. Here, piperazine-1,4-diium tetrafluoroborate (PDT) is introduced as spacer for bottom interface modification of ideal bandgap Sn-Pb mixed perovskite. This spacer enhances the quality of the upper perovskite layer and forms better energy band alignment, leading to enhanced charge extraction at the hole transport layer (HTL)/perovskite interface. Then, 2D Ti3C2Tx MXene is incorporated for surface treatment of perovskite, resulting in reduced surface trap density and enhanced interfacial electron transfer. The combinations of double-sided treatment afford the ideal bandgap PSC with a high efficiency of 20.45% along with improved environment stability. This work provides a feasible guideline to prepare high-performance and stable ideal-bandgap PSCs.

In-Situ Growth of One-Dimensional Blocking Layer to Mitigate Deficient Surface of Single-Crystal Perovskites.

Organic-inorganic halide perovskite (OIHP) single crystals are promising for optoelectronic application, but their high surface trap density and associated ion migration hinders device performance and stability. Herein, a one-dimensional (1D) perovskites are designed and proposed as blocking layer at the crystal/electrode interface to mitigate the surface issues. As a model system, the interface ion migration in Cs0.05FA0.95PbI3 (FA=formamidinium) single-crystal perovskite solar cells (PSCs) is obviously suppressed, leading to increase of T90 lifetime from 260 to 1000 hours, five times better than previously reported results. Besides, the reduction of surface iodide ion vacancies inhibits nonradiative recombination, thus increasing the efficiency from 22.1% to 23.8%, which is one of the highest values for single-crystal PSCs. Since the deficient crystal surface is a universal and open issue, our strategy is instructive for optimizing diverse single-crystal perovskite devices.

Green light all the way: Triple modification synergistic modification effect to enhance the photoelectrochemical water oxidation performance of BiVO4 photoanode

The recombination of photogenerated electron-hole pairs of the photoanode seriously impairs the application of bismuth vanadate (BiVO4) in photoelectrochemical water splitting. To address this issue, we prepared a Yb:BiVO4/Co3O4/FeOOH composite photoanode by employing drop-casting and soaking methods to attach Co3O4/FeOOH cocatalysts to the surface of ytterbium-doped BiVO4. The prepared Yb:BiVO4/Co3O4/FeOOH photoanode demonstrates a high photocurrent density of 4.89 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (RHE), which is 5.1 times that of bare BiVO4 (0.95 mA cm−2). Detailed characterization and testing demonstrated that Yb doping narrows the band gap and significantly enhances the carrier density. Furthermore, Co3O4 serves as a hole transfer layer to expedite hole migration and diminish recombination, while FeOOH offers additional active sites and minimizes surface trap states, thus boosting stability. The synergistic effects of Yb doping and Co3O4/FeOOH cocatalyst significantly improved the reaction kinetics and overall performance of PEC water oxidation. This work provides a strategy for designing efficient photoanodes for PEC water oxidation.

Robust and fast microwave-driven quantum logic for trapped-ion qubits

Microwave-driven logic is a promising alternative to laser control in scaling trapped-ion based quantum processors. We implement Mølmer-Sørensen two-qubit gates on 43Ca+ hyperfine clock qubits in a cryogenic (≈25 K) surface trap, driven by near-field microwaves. We achieve gate durations of 154 µs [with 1.0(2)% error] and 331 µs [0.5(1)% error], which approaches the performance of typical laser-driven gates. In the 331 µs gate, we demonstrate a Walsh-modulated dynamical decoupling scheme which suppresses errors due to fluctuations in the qubit frequency as well as imperfections in the decoupling drive itself. Published by the American Physical Society 2024