Additional Interlayer Research Articles

Contact Resistance Engineering in WS2-Based FET with MoS2 Under-Contact Interlayer: A Statistical Approach.

One of the primary factors hindering the development of 2D material-based devices is the difficulty of overcoming fabrication processes, which pose a challenge in achieving low-resistance contacts. Widely used metal deposition methods lead to unfavorable Fermi level pinning effect (FLP), which prevents control over the Schottky barrier height at the metal/2D material junction. We propose to harness the FLP effect to lower contact resistance in field-effect transistors (FETs) by using an additional 2D interlayer at the conducting channel and metallic contact interface (under-contact interlayer). To do so, we developed a new approach using the gold-assisted transfer method, which enables the fabrication of heterostructures consisting of TMDs monolayers with complex shapes, prepatterned using e-beam lithography, with lateral dimensions even down to 100 nm. We designed and demonstrated tungsten disulfide (WS2) monolayer-based devices in which the molybdenum disulfide (MoS2) monolayer is placed only in the contact area of the FET, creating an Au/MoS2/WS2 junction, which effectively reduces contact resistance by over 60% and improves the Ion/Ioff ratio 10 times in comparison to WS2-based devices without MoS2 under-contact interlayer. The enhancement in the device operation arises from the FLP effect occurring only at the interface between the metal and the first layer of the MoS2/WS2 heterostructure. This results in favorable band alignment, which enhances the current flow through the junction. To ensure the reproducibility of our devices, we systematically analyzed 160 FET devices fabricated with under-contact interlayer and without it. Statistical analysis shows a consistent improvement in the operation of the device and reveals the impact of contact resistance on key FET performance indicators.

Thermo-mechanically joined hybrids from carbon fiber-reinforced PA12 with die-cast alloy AlSi10Mg: how surface and interlayer design affect shear strength and fracture behavior

ABSTRACT Infrared radiation was used as a tool to heat laser-structured AlSi10Mg for subsequent fusion bonding with thermoplastic carbon fiber-reinforced PA12. When the two adherends are brought into contact, the bond is formed by melting of the surface-near polymer matrix and pressing it into the laser structure of the aluminum alloy. When investigating different fiber volume contents, the amount of fusible material was identified as a key parameter for the achievable bonding strength. Therefore, the best results were achieved with low fiber volume content (25 vol.-%) or under the use of an additional PA12 interlayer. Moreover, the influence of different surface texture parameters was investigated and the aspect ratio between structure depth and width was found to correlate best with the measured shear strengths. Aspect ratios from 0.18 to 1.15 increased the bond strength up to the interlaminar shear strength of the thermoplastic composite. Especially, aspect ratios of 0.61 or greater proved to be very effective, with resulting mean strength values of almost 30 MPa. While even lower ratios allowed higher loads on the joints compared with untreated surfaces, greater aspect ratios show lower bond strengths, as the laser structures were no longer completely filled with fused PA12.

Reinforcing 2D Single-Crystal Bi2O2CO3 with Additional Interlayer Carbonates by CO2-Assisted Solid-to-Solid Phase Transition.

A facile gaseous CO2 mediated solid-to-solid transformation principle is adopted to insert additional CO3 2- anions into the thin single-crystal nanosheets of Bi2O2CO3, which is built of periodic arrays of intrinsic CO3 2- anions and (Bi2O2)2+ layers. The additional CO3 2- anions create abundant defects. The Bi2O2CO3 nanosheets with rich interlayer CO3 2- exhibit superior electronic properties and charge transfer kinetics than the pristine single-crystal 2D Bi2O2CO3 and display enhanced catalytic activity in photocatalytic CO2 reduction reaction and the photocatalytic oxidative degradation of organic pollutants. This work thus illustrates interlayer engineering as a flexible means to build layered 2D materials with excellent properties.

Constructing 2D Phthalocyanine Covalent Organic Framework with Enhanced Stability and Conductivity via Interlayer Hydrogen Bonding as Electrocatalyst for CO2 Reduction.

Fabricating COFs-based electrocatalysts with high stability and conductivity still remains a great challenge. Herein, 2D polyimide-linked phthalocyanine COF (denoted as NiPc-OH-COF) is constructed via solvothermal reaction between tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalocyaninato nickel(II) and 2,5-diamino-1,4-benzenediol (DB) with other two analogous 2D COFs (denoted as NiPc-OMe-COF and NiPc-H-COF) synthesized for reference. In comparison with NiPc-OMe-COF and NiPc-H-COF, NiPc-OH-COF exhibits enhanced stability, particularly in strong NaOH solvent and high conductivity of 1.5×10-3Sm-1 due to the incorporation of additional strong interlayer hydrogen bonding interaction between the O-H of DB and the hydroxy "O" atom of DB in adjacent layers. This in turn endows the NiPc-OH-COF electrode with ultrahigh CO2-to-CO faradaic efficiency (almost 100%) in a wide potential range from -0.7 to -1.1V versus reversible hydrogen electrode (RHE), a large partial CO current density of -39.2mAcm-2 at -1.1V versus RHE, and high turnover number as well as turnover frequency, amounting to 45000 and 0.76S-1 at -0.80V versus RHE during 12h lasting measurement.

Gravity field induced composite solid electrolytes enabling enhanced Li+ transport kinetics of lithium metal battery

Multilayer composite solid electrolytes (CSEs) exhibit many advantages over uniform monolayer CSEs but are hindered by high interlayer resistance and complex preparation methods. Herein, for the first time, a natural sedimentation strategy was developed to construct concentration gradient CSEs (GCSEs) for lithium-metal batteries (LMBs). This method utilizes intrinsic gravity and photopolymerization to achieve multiple functions in the monolayer, avoiding additional interlayer resistance and reducing preparation time. Owning to the concentration gradient structure, the Li+ transport on the PolyIL-rich side relies on the weak solvation of Li+ with EMIMTFSI, while the Li+ transport on the LLZTO-rich side follows the 'vehicular diffusion' mechanism with the aid of TFSI−, improving the Li+ transport and enhances the Li+ transference number, leading to the high stability to 2300 h for the Li//Li cell and stable operation at 4.3 V with 89.6 % capacity retention after 100 cycles for the assembled LMB. Moreover, compared with the monolayer uniform hybrid CSEs, the gradient structure alleviates uncoordinated thermal expansion between LLZTO and PolyIL, avoiding stress increase during cycling and battery capacity fade. This gradient strategy mitigates high interlayer resistance and offers a universal path to address the sluggish Li+ transportation in multilayer CSEs and improves compatibility between the electrolyte and electrodes in fabricating solid-state batteries.

On the origin of epitaxial rhombohedral-B4C growth by CVD on 4H-SiC.

Rhombohedral boron carbide, often referred to as r-B4C, is a potential material for applications in optoelectronic and thermoelectric devices. From fundamental thin film growth and characterization, we investigate the film-substrate interface between the r-B4C films grown on 4H-SiC (0001̄) (C-face) and 4H-SiC (0001) (Si-face) during chemical vapor deposition (CVD) to find the origin for epitaxial growth solely observed on the C-face. We used high-resolution (scanning) transmission electron microscopy and electron energy loss spectroscopy to show that there is no surface roughness or additional carbon-based interlayer formation for either substrate. Based on Raman spectroscopy analysis, we also argue that carbon accumulation on the surface hinders the growth of continued epitaxial r-B4C in CVD.

Self-Assembly TiO2-Ti3C2Tx Ball-Plate Structure for Highly Efficient Electromagnetic Interference Shielding.

MXene is a promising candidate for the next generation of lightweight electromagnetic interference (EMI) materials owing to its low density, excellent conductivity, hydrophilic properties, and adjustable component structure. However, MXene lacks interlayer support and tends to agglomerate, leading to a shorter service life and limiting its development in thin-layer electromagnetic shielding material. In this study, we designed self-assembled TiO2-Ti3C2Tx materials with a ball-plate structure to mitigate agglomeration and obtain a thin-layer and multiple absorption porous materials for high-efficiency EMI shielding. The TiO2-Ti3C2Tx composite with a thickness of 50 μm achieved a shielding efficiency of 72 dB. It was demonstrated that the ball-plate structure generates additional interlayer cavities and internal interface, increasing the propagation path for an electromagnetic wave, which, in turn, raises the capacity of materials to absorb and dissipate the wave. These effects improve the overall EMI shielding performance of MXene and pave the way for the development of the next-generation EMI shielding system.

A scalable membrane electrode assembly architecture for efficient electrochemical conversion of CO2 to formic acid

The electrochemical reduction of carbon dioxide to formic acid is a promising pathway to improve CO2 utilization and has potential applications as a hydrogen storage medium. In this work, a zero-gap membrane electrode assembly architecture is developed for the direct electrochemical synthesis of formic acid from carbon dioxide. The key technological advancement is a perforated cation exchange membrane, which, when utilized in a forward bias bipolar membrane configuration, allows formic acid generated at the membrane interface to exit through the anode flow field at concentrations up to 0.25 M. Having no additional interlayer components between the anode and cathode this concept is positioned to leverage currently available materials and stack designs ubiquitous in fuel cell and H2 electrolysis, enabling a more rapid transition to scale and commercialization. The perforated cation exchange membrane configuration can achieve >75% Faradaic efficiency to formic acid at <2 V and 300 mA/cm2 in a 25 cm2 cell. More critically, a 55-hour stability test at 200 mA/cm2 shows stable Faradaic efficiency and cell voltage. Technoeconomic analysis is utilized to illustrate a path towards achieving cost parity with current formic acid production methods.

Achieving high strength friction lap spot joints of carbon fiber reinforced thermosetting composite to aluminum alloy with additional thermoplastic interlayer

The dissimilar materials of the 5182-aluminum alloy and continuous carbon fiber reinforced bismaleimide (CF-BMI) were joined by friction lap spot joining (FLSJ) directly and via the addition of the polyamide 6 (PA6) interlayer, and the effect of interlayer on the joining mechanism and the joint mechanical property was investigated. It was found that no effective joints were achieved by FLSJ directly, which was mainly attributed to the poor re-forming ability and liquidity of the thermosetting BMI, and its difficulty in reacting to metals. After the addition of the PA6 interlayer, the effective dissimilar joints were successfully realized by FLSJ. The maximum average tensile shear force of the joint reached 3.68 kN, with the average normal tensile shear strength of 20.9 MPa at the optimum parameter with the rotation rate of 2000 rpm, dwell time of 7 s, plunge depth of 0.7 mm and the PA6 interlayer of 0.3 mm. A new COAl chemical bond was found at the interface of the PA6 interlayer and aluminum alloy, which was the result of the chemical reaction between the amide polar function of PA6 and surface oxide of aluminum alloy. The great increase in the joint strength by the addition of the PA6 interlayer was mainly attributed to the great reduction of the interface defects and the formation of the chemical bonding, as the result of the great improvement of the interface fluidity and chemical reaction ability of PA6. This study provides an effective way to achieve high strength metal/continuous carbon fiber reinforced thermosetting composite joints.

Using an Interlayer to Toughen Flexible Colorless Polyimide-Based Cover Windows

Colorless polyimide (PI)-based flexible cover windows are a critical component of flexible electronics to protect devices from unwanted chemical and mechanical damage. The integration of flexible colorless PI-based windows into electronics applications is limited by the embrittlement of some colorless PI films when they are coated with hard coats. Here, we investigate the embrittlement mechanism of hard-coated colorless PI films and the role of interlayers in toughening the colorless PI-based cover windows for flexible electronics applications. A fracture mechanics approach combined with finite element analysis (FEA) models is employed to compute fracture strain, εc, for different crack cases in the bilayer (hard coated colorless PI) and trilayer (with an additional interlayer) cover windows. For the model inputs and validation, the material properties of the cover windows are characterized. We show that the embrittlement is attributed to the fracture behavior of the cover windows, and placing a ductile interlayer increases the εc of colorless PI films. Using the fracture analysis as a design guide, we fabricate a trilayer cover window with an acrylic thermoset interlayer and demonstrate an improvement of the εc of the colorless PI cover window by ~42%. We believe our analysis provides insights into design guides for mechanically robust cover windows using colorless PI films and flexible HCs for emerging flexible electronics.

Influence of Ni interlayer on hydrogen absorption and cyclicity in Gd thin films

The Pd/Gd bilayers and Pd/Ni/Gd trilayers were prepared onto glass substrates by magnetron sputtering. Detailed XPS in-situ studies of the Pd/Gd bilayers allowed to estimate the thickness of the mixed layer at about 4 nm. Further studies showed that the additional Ni interlayer can significantly reduce the interface mixing during the deposition process, leading to the formation of a rather narrow Ni–Gd interface. The structure of the obtained layers before and after the hydrogenation was examined by the standard X-ray diffraction method. The hydrogenation kinetics was studied in-situ at room temperature and pressure up to 1 bar using simultaneous measurements of resistivity and optical transmittance. Furthermore, hydrogen absorption by electrochemical method was monitored using optical transmittance. It was found that the use of an additional 4 nm Ni layer significantly improved the cyclicity of the hydrogen absorption/desorption from the electrolyte, while maintaining low switching time (10 s).

Study on the SPCC and CFRTP Hybrid Joint Performance Produced with Additional Nylon-6 Interlayer by Ultrasonic Plastic Welding

Due to the high degree of dissimilarity in physicochemical properties between metal and carbon fiber, it presents a tremendous challenge to join them directly. In this paper, cold rolled steel (SPCC) and carbon fiber reinforced thermoplastic (CFRTP) chopped sheet hybrid joints were produced with the addition of Nylon 6 (PA6) thermoplastic film as an intermediate layer by the ultrasonic plastic welding method. The effect of ultrasonic welding energy and preheating temperature on the hybrid joint microstructure and mechanical behavior was well investigated. The suitable joining parameters could obtain a strong joint by adding the PA6 film as an intermediate layer between the SPCC and bare carbon fibers. Microstructural analysis revealed that the interface joining condition between the PA6 film and the SPCC component is the primary reason for the joint strength. The crevices generated at the interface were eliminated when the preheating temperature arrived at 200 °C, and the joint strength thus significantly increased. The lap shear test results under quasi-static loading showed that the welding energy and preheating temperature synergistically affect the joint performances. At 240 °C, the joint strength value reached the maximum. Through the analysis of the microstructure morphology, mechanical performance, and the failure mechanism of the joint, the optimized joining process window for ultrasonic plastic welding of SPCC-CFRTP by adding an intermediate layer, was obtained.

Effect of process parameters on performances of TWIP steel/Al alloy dissimilar metals butt joints by laser offset welding

In this paper, butt joints of twinning-induced plasticity (TWIP) steel and aluminum alloy dissimilar metals were carried out by the laser offset welding method, and the amount of the aluminum alloy that melted was controlled by adjusting the offset distance of the laser beam spot. The aim of this study was to regulate the influence of the intermetallic compounds (IMCs) layer thickness, crystal structure and crack defects on the tensile strength of the welded joint. The tensile strength of the welded joint was obviously improved by adjusting the welding process parameters without adding any alloying elements. The results demonstrated that the crack initiated at the junction between the aluminum base metal and the weld seam and propagated along with the interface. The increase in the recrystallized fraction was beneficial to improve the tensile strength of the joint. The tensile strength of welded joints with more low-angle grain boundaries was lower. The smaller the thickness of the IMCs layer was, the higher the welded joint strength was. The optimized welding process parameters were as follows: d = 0.2 mm, P = 900 W, V = 15 mm/s and △f = −2 mm in the present study, and the tensile strength of the joint reached 155 MPa. This study provides a theoretical basis for solving the welding cracking problem of steel/aluminum heterojunctions without additional interlayer material and so as to improve the strength of the steel/aluminum laser welded joint.

Lone-Pair-Induced Intra- and Interlayer Polarizations in Sillén-Aurivillius Layered Perovskite Bi4NbO8Br.

Sillén-Aurivillius layered perovskite oxyhalides Bi4MO8X (M = Nb, Ta; X = Cl, Br) are of great interest because of their potential as lead-free ferroelectrics in addition to their function as visible-light-responsive photocatalysts. In this work, we revisited the crystal structure of Bi4NbO8Br (space group: P21cn), revealing that the intralayer polarization is not based on the reported NbO6 octahedral tilting but is derived from the stereochemically active Bi3+ lone pair electrons (LPEs) and the octahedral off-centering of Nb5+ cations. The revised structure (space group: Ic) has additional interlayer polarizations (calculated: 0.6 μC/cm2), in agreement with recent experiments on Bi4NbO8Br. The occurrence of polarization due to stereochemically active LPEs and Nb-site off-centering is similar to Aurivillius-type ferroelectrics (e.g., Bi2WO6), with comparable spontaneous polarizations in the in-plane direction (calculated: 43.5 μC/cm2). This, together with the out-of-plane polarization, indicates that Sillén-Aurivillius compounds have great potential as ferroelectric materials.

Effect of the Surface Polarity, Through Employing Nonpolar Spacer Groups, on the Glass-Transition Dynamics of Poly(phenyl methylsiloxane) Confined in Alumina Nanopores

Broadband dielectric spectroscopy and differential scanning calorimetry were used to study the effect of changes in the surface conditions on the segmental dynamics of poly(phenylmethylsiloxane) confined in alumina nanopores. Functionalization was done using highly polar propyl phosphoric units separated by the assumed concentration of triethoxysilane groups (from N = 0 to N = 24). By adjusting the proportion between polar units and nonpolar spacers, it was possible to control the surface polarity. Modification of the surface conditions does not inhibit the formation of the adsorbed layer, as revealed by the presence of two Tg’s in calorimetric results. However, changes in the surface polarity will prevent the growth of the additional interlayer in between the core volume and the interfacial layer. Finally, we also found that the changes in the surface polarity affect the equilibration kinetics and can be used to control the time scale of the structural recovery toward the equilibrium state.

XY magnetism, Kitaev exchange, and long-range frustration in the Jeff=12 honeycomb cobaltates

The quest for Kitaev quantum spin liquids has led to great interest in honeycomb quantum magnets with strong spin-orbit coupling. It has been recently proposed that even Mott insulators with $3d$ transition metal ions, having nominally weak spin-orbit coupling, can realize such exotic physics. Motivated by this, we study the rhombohedral honeycomb cobaltates CoTiO$_3$, BaCo$_2$(PO$_4$)$_2$, and BaCo$_2$(AsO$_4$)$_2$, using $\textit{ab initio}$ density functional theory, which takes into account realistic crystal field distortions and chemical information, in conjunction with exact diagonalization numerics. We show that these Co$^{2+}$ magnets host $j_\text{eff}=1/2$ local moments with highly anisotropic $g$-factors, and we extract their full spin Hamiltonians including longer-range and anisotropic exchange couplings. For CoTiO$_3$, we find a nearest-neighbor easy-plane ferromagnetic $XXZ$ model with additional bond-dependent anisotropies and interlayer exchange, which supports three-dimensional (3D) Dirac nodal line magnons. In contrast, for BaCo$_2$(PO$_4$)$_2$ and BaCo$_2$(AsO$_4$)$_2$, we find a strongly suppressed interlayer coupling, and significant frustration from additional third-neighbor antiferromagnetic exchange mediated by P/As. Such bond-anisotropic $J_1$-$J_3$ spin models can support collinear zig-zag or coplanar spiral ground states; we discuss their dynamical spin correlations which reveal a gapped Goldstone mode, and argue that the effective parameters of these pseudospin-$1/2$ models may be strongly renormalized by coupling to a low energy spin-exciton. Our results call for re-examining proposals for realizing Kitaev spin liquids in the honeycomb cobaltates.

Novel pure‐metal tri‐axis CMOS‐MEMS accelerometer design and implementation

This work proposed a pure-metal, single-proof-mass structure fabricated by the standard 0.18 μm one-poly-silicon six-metal (1P6M) CMOS process along with one in-house post-CMOS wet-etching approach. The implemented state-of-the-art symmetrical tri-axis accelerometer consists of the disk-like mezzanine proof-mass and four diagonal double-layered springs. Three sets of the addressable quadrant electrodes underneath the proof-mass with additional interlayer inter-digital comb-conductors help to fulfil the high sensibilities of 248.6, 250.8, and 220.1 mV/G for the x-, y-, and z-axes, respectively. Symmetrical-structure and addressable-electrode design of the device also effectively eliminates the cross-coupling effects. The thin-film composite springs can be width-trimmed for the necessities of specification changes, and the optional calibration pads also provide the on-chip accuracy compensations. The fabricated tri-axis accelerometer reveals stable and consistent results and exemplifies a potential platform design for the highly integrated monolithic CMOS-MEMS system-on-chip applications.

Bandgap engineered Cu2ZnGexSn1−xS4 solar cells using an adhesive TiN back contact layer

Kesterite-based solar cells are mainly restricted by their lower than expected open-circuit voltage (Voc) due to non-radiative recombination. Therefore, an approach to reduce bulk and interface recombination through band gap grading to induce a back surface field is attempted. This contribution presents the challenges in the formation of compositional grading of the wide bandgap material Cu2ZnGexSn1−xS4 (CZGTS) and successful fabrication of solar cells with an additional adhesive TiN interlayer. It is observed that the TiN interlayer improves adhesion between CZGTS and the back contact. The microstructure of the Cu2ZnSnS4 (CZTS) film is significantly affected by the concentration of Ge, and the existence of a Ge concentration gradient is strongly correlated to the formation of smaller Ge-rich and larger Sn-rich grains. The bandgap grading is exploited with a moderate Ge concentration of up to (Ge/(Ge+Sn) = 0.25) in CZTS. As the Ge profile stretched all the way to the front interface, the cliff-like band alignment at the front interface of the absorber could negate the beneficial effect of Ge inclusion in the bulk and back interface of the absorber. Ordering the absorber can introduce an additional downward shift in the valence band. In one of the samples, the increased ordering and high concentration of Ge in CZTS are suggested to enhance the hole barrier at the back interface. It is concluded that the effect of the bandgap grading with Ge can only be realized with optimization of interface band alignment and back contact formation.

Friction stir spot welding of AA5052 with additional carbon fiber-reinforced polymer composite interlayer

AbstractIn this study, similar aluminum alloys AA5052 with additional carbon fiber-reinforced polymer composite (CFRP) interlayer were selected to investigate the effect of welding parameters (rotational speed and dwell time) on the mechanical properties, joint efficiency, and microstructure of friction stir spot weld joint. The maximum tensile shear load was 1779.6 N with joint efficiency of 14.6% obtained at rotational speed of 2,000 rpm and 2 s dwell time, which is 39.5% higher than the value at low rotational speed 850 rpm and 2 s dwell time. Meanwhile, the maximum microhardness 58 HV was attained in the keyhole region at rotational speed of 2,000 rpm and dwell time of 5 s, which is 22.4% higher compared to low rotational speed. The SEM-EDS results reveal the presence of intermetallic compounds (Al–Mg–C), which enhance the intermetallic bonding between elements.

Enhancing upconversion of manganese through spatial control of energy migration for multi-level anti-counterfeiting.

The upconversion of manganese (Mn2+) exhibits a green light output with a much longer lifetime than that of lanthanide ions, showing great potential in the frontier applications like information security and anti-counterfeiting. Mn2+ can be activated by energy migration upconversion. However, there exists serious quenching interactions between Mn2+ and the lanthanides at the core-shell interfacial area, which would markedly reduce the role of Tm3+ as a ladder to facilitate the up-transition and subsequently limit the upconversion of Mn2+. Here, we propose a mechanistic strategy to enhance the upconversion luminescence of Mn2+ by spatial control of energy migration among Gd sublattice through introducing an additional migratory NaGdF4 interlayer within the commonly used core-shell nanostructure. This design can not only isolate the interfacial quenching interactions between the sensitized core and luminescent shell, but also allow an efficient channel for energy transport, resulting in enhanced upconversion of Mn2+. Moreover, the relatively long lifetime of Mn2+ (around 32.861 ms) provides new possibilities to utilize the temporal characteristic for the frontier application of multi-level anti-counterfeiting through combining the time-gating technology.