Buffer Layer Design Research Articles

Ionic buffer layer design for stabilizing Zn electrodes in aqueous Zn-based batteries

Aqueous Zn-based batteries (AZBs) are hindered by issues associated with the Zn electrodeposition process (ZEDP) on electrode surfaces, including passivation, dendrite formation, and hydrogen evolution. One of the important reasons is the drastic fluctuation in the concentration of Zn2+ ions on the electrode surface during the charging and discharging process. In this work, an electrolyte with Zn2+ ion buffer layer (EZIBL) is proposed to regulate the ZEDP. First, numerical simulations and corresponding experiments are conducted to assess the impact of different thicknesses of the Zn2+ ion buffer layer (ZIBL) on the variation in Zn2+ ion concentration, from which the optimal thickness of the ZIBL is determined. Then, the regulation role of EZIBL in the cycling process is demonstrated by a Zn-Cu half cell. Further, combined with the potential profile of the symmetric cell and the experimental phenomena, the regulation role of EZIBL in ZEDP is systematically explained at the mechanistic level through the analysis of key parameters. Finally, a full battery composed of Zn-LiMn2O4 is assembled to evaluate the practical applicability of the EZIBL in real battery cycles, which shows great enhancement in capacity retention and Coulombic efficiency. This work proposes the design of the EZIBL used to regulate the ZEDP and provides a simple, low-cost regulation method for the development of high-performance AZBs.

Amorphous titanium dioxide and polyaniline dual modifying silicon for highly enhanced lithium-ion storage

Silicon (Si) anode material is promising in the next generation of lithium-ion batteries (LIBs) with high energy densities for its much higher capacity (4200 mAh/g) than that of commercial graphite (372 mAh/g). However, silicon anode material with low electronic conductivity suffers a huge volume variation and accompanies side reactions during alloyed and de-alloyed process. Here, we design an inner amorphous titanium dioxide (TiO2) and an outer flexible conductive polyaniline (PANI) network dual modified Si@TiO2@PANI material for LIBs, where the TiO2 avoids the side reactions and the PANI network layer buffers the volume expansion and increases the electronic conductivity. The as-prepared Si@TiO2@PANI exhibits a high initial discharge capacity of 3050 mAh/g and maintains 1583 mAh/g after 200 cycles at 0.5 A/g. It even delivers the discharge capacity of 1002 mAh/g after 600 cycles at 1 A/g, as well as an excellent rate ability with discharge capacity of 1890, 1260 and 432 mAh/g at the high current density of 1, 2 and 5 A/g, respectively. Our strategy shows that the innovative design of double buffer layers on Si can synergistically promote stability and accelerate kinetics of Li+ transport, offering novel resolution strategy to enhance the performance of Si-based anodes for LIBs.

Scalable CIGS Solar Cells Employing a New Device Design of Nontoxic Buffer Layer and Microgrid Electrode.

The efficiency of copper indium gallium selenide (CIGS) solar cells that use transparent conductive oxide (TCO) as the top electrode decreases significantly as the device area increases owing to the poor electrical properties of TCO. Therefore, high-efficiency, large-area CIGS solar cells require the development of a novel top electrode with high transmittance and conductivity. In this study, a microgrid/TCO hybrid electrode is designed to minimize the optical and resistive losses that may occur in the top electrode of a CIGS solar cell. In addition, the buffer layer of the CIGS solar cells is changed from the conventional CdS buffer to a dry-processed wide-band gap ZnMgO (ZMO) buffer, resulting in increased device efficiency by minimizing parasitic absorption in the short-wavelength region. By optimizing the combination of ZMO buffer and the microgrid/TCO hybrid electrode, a device efficiency of up to 20.5% (with antireflection layers) is achieved over a small device area of 5 mm × 5 mm (total area). Moreover, CIGS solar cells with an increased device area of up to 20 mm × 70 mm (total area) exhibit an efficiency of up to 19.7% (with antireflection layers) when a microgrid/TCO hybrid electrode is applied. Thus, this study demonstrates the potential for high-efficiency, large-area CIGS solar cells with novel microgrid electrodes.

Thermally stable radio frequency power and noise behaviors of AlGaN/GaN high electron mobility transistor without voltage-blocking buffer layer design

Thermally stable radio frequency power and noise behaviors of AlGaN/GaN high electron mobility transistor without voltage-blocking buffer layer design

Mechanical testing and engineering applicability analysis of SAP concrete used in buffer layer design for tunnels in active fault zones

Abstract To tackle the challenge of dislocation damage when tunnels traverse active fault zones, this study introduces the concept of using brittle buffer materials for anti-dislocation. Building on this concept, we propose a novel concrete buffer material utilizing large-sized spherical super absorbent polymers (SAP) as a porogen, aimed at ensuring the safety of tunnel structures during active fault dislocations. To investigate the feasibility and superiority of SAP concrete as a buffer material compared to other similar materials, we prepared samples with three different SAP concrete proportions and conducted a series of physical and mechanical tests. The results show that SAP pre-hydrated with 0.2 mol·L−1 sodium carbonate solution exhibits a slower rate of moisture loss in the cement slurry, aiding the hydration reaction of concrete. The permeability coefficient of SAP concrete is approximately 10−7 cm·s−1, slightly lower than foam concrete of the same density level. SAP concrete buffer material demonstrates significant brittleness, in contrast to the mostly ductile nature of other buffers such as foam concrete and rubberized concrete. Utilizing the brittle nature of SAP concrete materials, when applied to tunnels affected by stick–slip active fault dislocations, its instantaneous loss of compressive capacity provides excellent yield performance, thus protecting the tunnel lining from damage. However, under certain circumferential pressure conditions, both the peak and residual strength of SAP concrete significantly increase. High peak and residual strengths do not favor the effective buffering effect of SAP concrete; therefore, an approach involving the intermittent arrangement of precast buffer blocks has been proposed for application.

Enhanced dielectric properties induced by the rational design of interfacial buffer layer in MoS2/poly(arylene ether nitrile) composites

Enhanced dielectric properties induced by the rational design of interfacial buffer layer in MoS2/poly(arylene ether nitrile) composites

Investigation of the Influence of the Buffer Layer Design in a GaN HEMT Transistor on the Breakdown Characteristics

Investigation of the Influence of the Buffer Layer Design in a GaN HEMT Transistor on the Breakdown Characteristics

Seismic design and performance analysis of perforated rubber buffer layer in tunnel

Tunnels may be damaged under earthquakes, which has been observed by many earthquake events, and the buffer layer is proposed and widely investigated as a damping measure. The rubber is considered as a qualified buffer layer material because of its small elastic modulus and super elasticity, but its high price makes it difficult to apply in practical engineering. Therefore, four types of rubber buffer layers are proposed in this study, including the common rubber buffer layer and three types of perforated rubber buffer layers (PRBL), which can reduce the seismic damage and cost of tunnels. A pseudo-static method for calculating the seismic response of tunnels under horizontal and vertical earthquake motions is proposed and verified. Based on proposed pseudo-static method, a seismic design method for the buffer layer is present, and the proposed seismic design process is used to study the seismic mitigation performance of buffer layers. The initial design of the buffer layer under earthquake action E1 is carried out by pseudo-static method, and then the seismic mitigation performance is verified through dynamic time history analysis method under earthquake action E2. The earthquake action E1 and earthquake action E2 are the earthquake actions with short and long return periods of the engineering site, respectively. The results show that the common rubber buffer layer has almost no seismic mitigation performance, and the three types of PRBLs have good seismic mitigation performance. The type IV buffer layer is strip-shaped PRBL and the holes are along the longitudinal direction of the tunnel, and it has optimal seismic mitigation performance. The effects of vertical earthquake motion and peak ground acceleration (PGA) on the seismic mitigation performance of the buffer layer are studied. The results show that vertical earthquake motion has little effect on the seismic mitigation performance of different types of buffer layers. For different PGAs, the type IV buffer layer is able to efficiently decrease the peak internal force of secondary lining. The results also prove the validity of design method.

Influence of buffer layer on nitrogen doped AZO relative humidity sensor with p-n heterojunction structure

A nitrogen doped AlZnO (N-doped AZO) relative humidity (RH) sensing p-n heterojunction structure on n-type silicon substrate using DC sputtering system and lift-off technique has been proposed in this research. N-doped AZO RH sensing film was adopted to enhance photocatalyst effect and realize the heterojunction structure in humidity sensing device. The carrier properties of N-doped AZO RH sensing film were evaluated in the carrier type, carrier mobility, carrier concentration, and carrier conductivity using Hall effect measurement. The N-doped AZO RH sensors were designed with a p-n heterojunction structure and embedded a buffer layer structure. The sensing properties of N-doped AZO RH sensors both with polymer buffer layer and without polymer buffer layer were respectively explored and evaluated in the hysteresis effect, sensitivity, linearity, sensing response and recover response characteristics using environment measurement system and measurement firmware. The research results revealed the carrier type, carrier mobility, carrier concentration, and carrier resistivity of the N-doped AZO RH sensing film deposited on p-n heterojunction structure with buffer layer respectively reached as p-type, 9.6✕101 cm2/Vs, 3.3✕1017 cm−3, and 5.0✕100 Ω-cm. The RH sensing hysteresis error of N-doped AZO RH sensor with buffer layer is approximately 4.57% at 60 %RH which is less than those at other relative humidity values. The sensitivity of N-doped AZO RH sensor with buffer layer reaches as more than 15.7 kΩ/%RH at desorption process which is better than that of sensor without buffer layer either at relative humidity value from 30 %RH to 90 %RH and from 30 %RH to 75 %RH. The adsorption linearity and desorption linearity of N-doped AZO RH sensor with buffer layer are respectively 0.31 and 0.27 between 30 %RH and 75 %RH which are better than those without buffer layer. The adsorption time and desorption time responses of N-doped AZO RH sensor with buffer layer measured during the measurement time of 2000 s with two measuring cycles were estimated about 235 s and 295 s at first cycle respectively less than those of the RH sensor without buffer layer. The design of polymer buffer layer embedded between N-doped AZO RH sensing p-n heterojunction structure and use of n-type silicon substrate revealed the better sensing characteristics and electrical properties both the molecular adsorption/desorption effects in chemical property and the carrier transport phenomena in physical property respectively.

Rational design of artificial interphase buffer layer with 3D porous channel for uniform deposition in magnesium metal anodes

Rechargeable magnesium (Mg) metal batteries (RMBs) have received extensive attention due to their high theoretical capacity and superior safety. However, the heterogeneous plating/stripping behavior and detrimental corrosion issues of Mg metal hinder the practical application of RMBs. The failure of the Mg metal anode when cycling under high areal capacity utilization is of rising concern. Herein, we have developed a facile and effective approach to realize stable Mg metal anode with artificial solid-electrolyte interphase (SEI) layers by in-situ dynamic self-assembly coordination of phytic acid (PA) with Mg2+. Especially, the 3D porous channel structure of interfacial PA skeleton could regulate ion flux via coordination, efficiently homogenizing the distribution of Mg2+ and successfully triggers uniform plating/stripping Mg by experimental results and theoretical calculation. Encouragingly, the symmetric cells using as-prepared Mg metal anode possess low voltage hysteresis (250 mV) and long cycle life (780 cycles) under harsh utilization condition (3 mA cm−2, 1 mAh cm−2). The effectiveness of 3D porous channel buffer artificial SEI is further demonstrated in the Mg-Mo6S8 full cells. Such an advanced strategy for modulating Mg2+ transport provides an avenue to addressing the basic challenges for RMBs, which can potentially be extended to other construction of highly tolerant and conductive artificial SEI layers.

Coupled thermal-hydro model tests of double-layered buffer for nuclear waste repository

In the high-level radioactive waste disposal repository, bentonite is a preferred buffer material. As the buffer material, the hydraulic conductivity must be less than 10−13 m/s and the thermal conductivity should be higher than 0.8 W/(m·K) recommended by International Atomic Energy Agency (IAEA). Due to the decay heat of radionuclide and low thermal conductivity of bentonite, the released heat cannot be quickly transferred to the host rock through bentonite buffer layer and the repository may be in a high temperature state (>100 °C), which compromises both the hydro-mechanical performance of the bentonite and the anti-corrosion behavior of nuclear waste canister, therefore the barrier function of the buffer layer is severely damaged. Thus, a double-layered buffer concept which is based on the dual requirements of thermal conductivity and permeability was proposed for the nuclear waste disposal repository. In this paper, coupled thermal-hydro model tests of double-layered buffer with graphite-bentonite mixture layer and bentonite layer (the layer thickness ratio of graphite-bentonite to bentonite was 2:3) were carried out to investigate the temperature and relative humidity distribution laws and determine whether the physicochemical properties of double-layered buffer change after experiencing the coupled thermal-hydro process. In the model test, a heater simulating the decay heat generated by HLW was placed below the graphite-bentonite layer, and a hydration system simulating groundwater infiltration was installed above the bentonite layer, thus, the heat was transferred from the graphite-bentonite layer to the bentonite layer while water was permeated from the bentonite layer to the graphite-bentonite layer. The temperature and relative humidity distribution were synchronously measured by temperature-humidity sensors. After the model tests, the heater was switched off, and the tested bentonite/graphite-bentonite mixture samples were taken out for subsequent water content, scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The main conclusions from the test results are as follows. The distributions of temperature and relative humidity in the buffers were mainly governed by the competition between the thermal effect and the water permeation effect, the results of water content at different distances also indirectly verify this conclusion. And SEM results showed that macropores of the bentonite close to the water inlet side were significantly reduced and the pore distribution tended to be uniform along the water injection direction during wetting. XRD results indicated that the mineral composition of the graphite-bentonite mixtures close to the heater changed while that of the bentonite away from the heater remained unchanged. Obviously, even if the high thermal conductivity graphite was added to the buffer layer near the heat source, the mineral composition of the bentonite at the heat source side cannot be avoided completely unaffected. Therefore, it is necessary to conduct heat from the inner layer to outer layer to reduce the overall temperature in the repository and reduce adverse effects of temperature and water synchronization on outer bentonite layer. The research results in this paper can serve as a guideline for the buffer layer design in the high-level radioactive waste repository.

Research of Single-Event Burnout in 1.2-kV Rated CoolSiC Trench MOSFET

This paper presents the two-dimensional (2-D) numerical simulation results of heavy-ion induced reverse drain current degradation and single-event burnout (SEB) in the 1.2-kV rated CoolSiC Trench metal-oxide-semiconductor field-effect transistor (MOSFET). The physics models employed in simulations and critical failure conditions were validated by the heavy-ion irradiation experiments of the commercially available 1.2-kV rated SiC planar-gate MOSFET devices. The CoolSiC Trench MOSFET was proven to behave comparative SEB performance compared with the SiC planar-gate MOSFET. The robustness of the CoolSiC Trench MOSFET with different single buffer layer (SBL) designs against a heavy ion was simulated. Furthermore, the SBL-CoolSiC Trench MOSFET with low carrier lifetime control was investigated. According to the simulation results, the severe degeneration failure tolerance increased to 800 V; the SEB failure tolerance could reach 900 V.

Reducing Irreversible Performance Losses via a Graphene Oxide Buffer Layer for Proton-Exchange Membrane Fuel Cells.

Alloy catalysts are promising for proton-exchange membrane fuel cells but are difficult to realize high-durability operation because the dissolution of Pt-M (M = Co, Ni, etc.) metals inevitably accelerates irreversible performance degradation. Here, we propose a buffer layer solution that inserts a trace layer of a graphene oxide (GO) film between the PEM and the alloy catalyst layer to mitigate the poison effect. To distinguish the irreversible and reversible losses, two typical recovery procedures (shutdown and JRC-based protocols) being part of a fuel cell dynamic load cycle durability test are characterized. The electrochemical evaluation reveals that GO-1 μg/cm2 enables a higher initial performance and stability. Furthermore, the GO buffer layer design allows the realization of membrane electrode assemblies with a highly homogeneous current density distribution and a low accessible mass transport resistance. Thanks to the ion sieving effect in the GO buffer layer, high anti-poisoning and stability during the accelerated stress test process are ensured.

Electrophysical parameter comparison of 2DEG in AlGaN/GaN heterostructures grown by the NH3-MBE technique on sapphire and silicon substrates

A comparative study of the structural properties of GaN layers and the electrophysical parameters of 2DEG in AlGaN/GaN heterostructures grown by ammonia molecular beam epitaxy on sapphire and silicon substrates using identical buffer layer designs has been carried out. It is demonstrated that GaN layers grown under the same growth conditions have the similar surface morphology, regardless of the substrate material. It is shown that the dislocation density of compressed GaN layers grown on sapphire substrates up to 5 times lower than in crack-free and stretched GaN layers grown on silicon substrates. The measured values of electron mobility in heterostructures with 2DEG grown on sapphire substrates are higher by 30% than on silicon substrates (∼1600 cm2/V × s and ∼1200 cm2/V × s).

Design of multifunctional near-infrared organic heterojunction and double hole transport layer to improve efficiency and stability of perovskite solar cells

• Single-walled carbon nanotubes acts as a double hole transport layer. • Multifunctional bulk organic heterojunction provides additional light harvesting. • Heterojunction and buffer layer enhance the stability of perovskite solar cells. Currently, the high-efficiency lead organic–inorganic hybrid perovskite solar cells (PSCs) can only utilize a relatively small fraction of sunlight (300–800 nm) due to the limited tunability of optical bandgap, which is the key factor limiting the further improvement of the photoelectric conversion efficiency (PCE) of PSCs. Here, we report a method to blend the narrow band gap non-fullerene acceptor molecule Y18 and the wide band gap donor molecule PM6 to form a multifunctional bulk organic heterojunction active layer. To avoid the loss of voltage and fill factor caused by the compromised hole transport layer (HTL), we introduce the single-walled carbon nanotubes as a buffer layer to fabricate a double HTL. The champion device displays a PCE improvement from 20.05% to 22.82% with a relative increase of 13.81%. After a deep examination of the mechanism, organic heterojunction provides the multifunctional roles as follows: (1) providing additional harvesting to the near-infrared light ranging of 800–950 nm; (2) passivating the perovskite surface and grain boundary to reduce the defect density; (3) promoting hole extraction from perovskite to HTLs by forming cascade energy levels. Moreover, the stability of PSCs is considerably enhanced because the introduction of organic heterojunction and buffer layer design isolated the natural degradation, which enhances the tolerance towards water and oxygen. Finally, a module group is fabricated by connecting two series modules in parallel, which is served as a power source to light the diode screen. This work demonstrates a buffer layer design for fabricating organic heterojunction-perovskite integrated solar cells to expand the near-infrared response, which provides a novel approach for designing integrated solar cells in the future.

High Mobility Cd3As2(112) on GaAs(001) Substrates Grown via Molecular Beam Epitaxy

The three-dimensional Dirac semimetal Cd3As2 exhibits ultrahigh electron mobilities that are attractive for optoelectronic devices. However, its strong propensity to grow in the (112) orientation limits the feasibility to epitaxially integrate it into semiconductor structures that are conventionally grown in the (001) orientation. Here, we demonstrate a route to epitaxially growing high mobility Cd3As2(112) layers on GaAs(001) substrates, opening up possibilities for device design. The (001) crystallographic orientation of the GaAs substrate is switched to the (111) orientation through a strain-driven process at a CdTe/GaAs interface, resulting in a CdTe(111) buffer layer on top of which Cd3As2 can be grown. Although the CdTe(111) buffer layer templates Cd3As2 in the (112) orientation, it is not sufficient for producing Cd3As2 with high electron mobility. We therefore demonstrate additional buffer layer design principles for realizing Cd3As2(112) epilayers with similar electron mobilities to those grown on lattice-mismatched III–V (111) substrates. Finally, we outline a pathway to use this approach to grow Cd3As2(112) epilayers on Si(001) substrates, further expanding the potential to integrate Cd3As2 into electronic devices.

Enhanced van der Waals epitaxy of germanium by out-of-plane dipole moment induced from transferred graphene on TiN/AlN multilayers

Recent advances in 3D/2D heterostructures have opened up tremendous opportunities in building highly flexible and durable optoelectronic devices. However, the inherit lack of interfacial bonding and low surface energy of van der Waals surfaces limit the nucleation and growth of 3D materials. Enhancing wettability by providing a porous buffer is effective in growing compound semiconductors on graphene while van der Waals epitaxy of Ge remains challenging. Here, the nucleation of Ge has been significantly improved from an islanded mode to granular modes by using a TiN/AlN multilayered buffer prior to Ge/graphene integration. Highly textured Ge growth with dominating (111), (220), and (311) peaks are identified by x-ray diffraction. The microstructure of the buffer TiN/AlN demonstrates a polycrystalline quality with clean interfaces between each interlayer and the substrate. Kelvin probe force microscopy measurements along the lateral TiN/AlN interface identify a potential drop corresponding to the AlN phase. This contact potential difference between TiN and AlN is the key in generating the out-of-plane dipole moment that modifies the surface energy of the monolayer graphene, resulting in enhanced wettability of the Ge adatoms nucleated on top. Surface dipole induced nucleation of 3D semiconductor thin films on 2D materials via the proper design of buffer layer is fundamentally important to enhance the 3D/2D growth toward flexible optoelectronic applications.

Simulation Study on Single-Event Burnout in Rated 1.2-kV 4H-SiC Super-Junction VDMOS

This article presents the 2-D numerical simulation results of the heavy-ion-induced leakage current degradation and single-event burnout (SEB) in the rated 1.2-kV silicon-carbide (SiC) super-junction (SJ) vertical diffusion metal-oxide-semiconductor (VDMOS). The employed simulation physics models were validated by the heavy-ion irradiation experiments of the commercially rated 1.2-kV SiC common VDMOS (C-VDMOS), which indicated a severe degeneration threshold of 500 V. The SiC common SJ VDMOS (C-SJ VDMOS) was proven to be sensitive to high-energy heavy-ion and represents comparative SEB performance compared with the SiC C-VDMOS. The robustness of the SiC SJ VDMOS with different single buffer layer (SBL) designs against a heavy-ion was simulated. It is found that the maximum temperature in the source metal/SiC interface and bottom of the structure could be compromised by the thickness of the buffer layer. As a result, the SiC SJ VDMOS with an optimal SBL exhibited a severe degeneration threshold of 800 V, which was a 60% increase compared to the SiC C-SJ VDMOS.

Vertical GaN Power Devices: Device Principles and Fabrication Technologies—Part I

Recent years have witnessed a tremendous development of vertical gallium nitride (GaN) power devices, a new class of device technology that could be the key enabler for next-generation high performance power electronics. In this comprehensive review, we discuss the recent progress made on vertical GaN power devices, highlighting their important device design principles and fabrication processes. Part I of the two-part review series introduces the basic design principles of vertical GaN devices using Schottky barrier diodes (SBDs) and p-n diodes as examples. We provide a comprehensive review and in-depth analysis on their basic structures, fabrication processes, and device physics. Materials engineering, including buffer layer and drift layer design, and device engineering, including various edge termination methods, are elucidated. Key device topics, including avalanche breakdown and leakage mechanisms of vertical GaN power devices, are also discussed. We also examine various approaches and provide detailed descriptions of the key knowledge obtained. This timely review provides valuable information for the power electronics community and can inspire researchers for future interdisciplinary collaborations in this emerging and exciting research field.

The Characteristics of 6-Inch GaN on Si RF HEMT with High Isolation Composited Buffer Layer Design

In this study, a 50-nm Al0.05Ga0.95N back barrier (BB) layer was used in an AlGaN/GaN high-electron-mobility transistor between the two-dimensional electron gas channel and Fe-doped/C-doped buffer layers. This BB layer can reduce the channel layer. The BB layer is affected by doped carriers in the buffer layer and the conduction energy band between the channel and the buffer layers. The Ion/Ioff ratio of the BB device was 4.66 × 105, and the ratio for the device without BB was 1.91 × 103. Lower leakage currents were obtained in the BB device because of the higher conduction energy band. The 0.25-μm gate length device with the BB exhibited a high current gain cutoff frequency of 24.4 GHz, and power gain cutoff frequency of 73 GHz.