Abstract: To attain both high energy density and power density in sodium-ion (Na+ ) batteries, the reaction kinetics and structural stability of anodes should be improved by materials optimization. In this work, few-layered molybdenum sulfide selenide (MoSSe) consisting of a mixture of 1T and 2H phases is designed to provide high ionic/electrical conductivities, low Na+ diffusion barrier, and stable Na+ storage. Reduced graphene oxide (rGO) is used as a conductive matrix to form 3D electron transfer paths. The resulting MoSSe@rGO anode exhibits high capacity and rate performance in both organic and solid-state electrolytes. The ultrafast Na+ storage kinetics of the MoSSe@rGO anode is attributed to the surface-dominant reaction process and broad Na+ channels. In situ and ex situ measurements are conducted to reveal the Na+ storage process in MoSSe@rGO. It is found that the MoS and MoSe bonds effectively limit the dissolution of the active materials. The favorable Na+ storage kinetics of the MoSSe@rGO electrode are ascribed to its low adsorption energy of -1.997 eV and low diffusion barrier of 0.087 eV. These results reveal that anion doping of metal sulfides is a feasible strategy to develop sodium-ion batteries with high energy and power densities and long life-span.

Abstract: The barrier layer in Cu technology is essential to prevent Cu from diffusing into the dielectric layer at high temperatures; therefore, it must have a high stability and good adhesion to both Cu and the dielectric layer. In the past three decades, tantalum/tantalum nitride (Ta/TaN) has been widely used as an inter-layer to separate the dielectric layer and the Cu. However, to fulfill the demand for continuous down-scaling of the Cu technology node, traditional materials and technical processes are being challenged. Direct electrochemical deposition of Cu on top of Ta/TaN is not realistic, due to its high resistivity. Therefore, pre-deposition of a Cu seed layer by physical vapor deposition (PVD) or chemical vapor deposition (CVD) is necessary, but the non-uniformity of the Cu seed layer has a devastating effect on the defect-free fill of modern sub-20 or even sub-10 nm Cu technology nodes. New Cu diffusion barrier materials having ultra-thin size, high resistivity and stability are needed for the successful super-fill of trenches at the nanometer scale. In this review, we briefly summarize recent advances in the development of Cu diffusion-proof materials, including metals, metal alloys, self-assembled molecular layers (SAMs), two-dimensional (2D) materials and high-entropy alloys (HEAs). Also, challenges are highlighted and future research directions are suggested.

Abstract: First-principles calculations were used to explore the effect of various Y-doping levels on the electrical conductivity of SrTiO3. Herein, we prepared ((Y0.07Sr0.93Ti0.6Fe0.4-xO3-δ)/x/3Co3O4 (x = 0.1, 0.2, 0.3)) composites using a solid state reaction method. The properties of these sensing materials and the fabricated sensors including crystal phase composition, microstructures, oxygen ionic conductivity, total conductivity and sensor performance were investigated in detail. XRD demonstrates the formation of a highly cubic perovskite structure. The introduction of Co3O4 promotes remarkably the electronic conductivity of the Y0.07Sr0.93Ti0.6Fe0.4-xO3-δ/x/3Co3O4 composites due to the formation of n-type CoO and p-type Co2O3. A limiting current oxygen sensor based on (Y0.07Sr0.93Ti0.6Fe0.4-xO3-δ)/x/3Co3O4 as a dense diffusion barrier shows excellent sensing performance. The recovery time is less than the response time, indicating that Co2O3 promotes the gas desorption reaction which results in a shorter recovery time. The obtained results demonstrate a direct relationship between limiting current (IL) and oxygen content.

Abstract: Herein, we illustrate a feasible strategy to strengthen the gas sensing of Y-doped CaZrO3 (YxCa1-xZr0.7O3-δ (x = 0.05, 0.06, and 0.07))/0.1Co3O4 used as sensing materials. This compound was prepared via a solid-state reaction technique. The structural, morphological, electrical, and sensing features such as phase identification, microstructure, ionic conductivity, total conductivity and sensitivity of the fabricated sensors were evaluated via X-ray diffraction, scanning electron microscopy, electron-blocking method, electrochemical impedance spectroscopy and cyclic voltammetry. In addition, the influence of the Y-dopant on the properties of YxCa1-xZr0.7O3-δ/Co3O4 was thoroughly studied. XRD results revealed the formation of the orthorhombic perovskite phase of YxCa1-xZr0.7O3-δ. Moreover, the obtained results from the electrical properties elucidated high electronic and low ionic conductivities, and small polaron conduction of YxCa1-xZr0.7O3-δ/Co3O4. Furthermore, the results confirmed an excellent limiting current plateau for the fabricated oxygen sensor based on YxCa1-xZr0.7O3-δ/Co3O4. In particular, experimental observation indicates that Y-doping at the Ca site and/or Zr site might be difficult.

Abstract: In this Letter, in situ Mg doping in β-Ga2O3 was demonstrated via metalorganic chemical vapor deposition (MOCVD) epitaxy. The electrical insulating property of the Mg acceptors in β-Ga2O3 was found to be intrinsically activated in the as-grown Mg-doped β-Ga2O3 thin films. Growth conditions for MOCVD β-Ga2O3 were further explored and optimized at a lower growth temperature regime, leading to a better confinement of the Mg-doping profile. Detailed analysis of Mg diffusion characteristics revealed a diffusion barrier energy Ebarrier ∼ 0.9 eV for Mg in MOCVD β-Ga2O3, which is likely related to an interstitial-assisted process. Surface morphologies and electron transport were characterized on samples grown with different growth temperatures and Mg doping levels. The MOCVD growth method demonstrated its feasibility to grow semi-insulating Mg-doped β-Ga2O3 epilayers with controllable Mg incorporation while maintaining good material quality and smooth surface morphology. From capacitance-voltage charge profiling, it is verified that the Mg-doped buffer layer grown at the substrate-epilayer interface could effectively compensate the charge accumulation at the interface. The in situ acceptor doping of Mg in MOCVD β-Ga2O3 will provide versatility for designing β-Ga2O3 power devices.

Abstract: Gallium based liquid metals (GLMs) exist as atypical liquid-phase metals at and near room temperature while being electrical and thermal conductive, enabling copious applications in soft electronic...

Abstract: In this study, high-entropy alloy films, namely, AlCrTaTiZr/AlCrTaTiZr-N, were deposited on the n-type (100) silicon substrate. Then, a copper film was deposited on the high-entropy alloy films. The diffusion barrier performance of AlCrTaTiZr/AlCrTaTiZr-N for Cu/Si connect system was investigated after thermal annealing for an hour at 600 °C, 700 °C, 800 °C, and 900 °C. There were no Cu-Si intermetallic compounds generated in the Cu/AlCrTaTiZr/AlCrTaTiZr-N/Si film stacks after annealing even at 900 °C through transmission electron microscopy (TEM) and atomic probe tomography (APT) analysis. The results indicated that AlCrTaTiZr/AlCrTaTiZr-N alloy films can prevent copper diffusion at 900 °C. The reason was investigated in this work. The amorphous structure of the AlCrTaTiZr layer has lower driving force to form intermetallic compounds; the lattice mismatch between the AlCrTaTiZr and AlCrTaTiZ-rN layers increased the diffusion distance of the Cu atoms and the difficulty of the Cu atom diffusion to the Si substrate.

Abstract: The influence of the environment on the properties of TiAl alloys is a concern for elevated temperature applications. One element that stands out in improving the resistance of TiAl alloys against high-temperature oxidation is Nb. Nb promotes the activities of Al and favors the formation of a more protective Al2O3 surface oxide which subsequently stymies oxygen diffusion to the alloy. Ta is an equal replacement of Nb. Thus, this study aims to evaluate the effect of 0.8, 4, and 8 at. % Ta additions on the oxidation resistance of spark plasma sintered Ti-46.5Al (at. %) alloy. Isothermal oxidation tests were carried out for 360 and 100 h at 1123 and 1273 K respectively. Surface oxides examination include scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray diffractometry. The results show that 4 and 8 at. % Ta additions significantly support the formation of an interconnected, non-porous Al2O3 layer at the metal-oxide interface. The continuous non-porous Al2O3 layer serves as a diffusion barrier which leads to superior oxidation resistance of the TiAl alloys.

Abstract: Pulsed laser welding of TC4 Titanium alloy to SUS301 L stainless steel with V sheet as interlayer was applied. V does not form any intermetallic compound with Ti and Fe. V is used as an interlayer for joining Titanium alloy and stainless steel that the laser successively focused near the Titanium alloy-V and V-stainless steel interfaces. In this way, only two weld zones and unmelted V interlayer can be produced, but also by microstructure of residual solid V interlayer situated between two separately formed weld zones. The unmelted V interlayer acted as a barrier to mixing of the two base materials. The unmelted part of V interlayer also acted as a diffusion barrier between Ti and Fe to avoid the Ti-Fe intermetallics. The tensile strength of joint was 587 MPa accordingly.

Abstract: The size of the advanced Cu interconnects has been significantly reduced, reaching the current 7.0 nm node technology and below. With the relentless scaling-down of microelectronic devices, the advanced Cu interconnects thus requires an ultrathin and reliable diffusion barrier layer to prevent Cu diffusion into the surrounding dielectric. In this paper, amorphous carbon (a-C) layers of 0.75-2.5 nm thickness have been studied for use as copper diffusion barriers. The barrier performance and thermal stability of the a-C layers were evaluated by annealing Cu/SiO2/Si metal-oxide-semiconductor (MOS) samples with and without an a-C diffusion barrier at 400 °C for 10 h. Microstructure and elemental analysis performed by transmission electron microscopy (TEM) and secondary ion mass spectroscopy showed that no Cu diffusion into the SiO2 layer occurred in the presence of the a-C barrier layer. However, current density-electric field and capacitance-voltage measurements showed that 0.75 and 2.5 nm thick a-C barriers behave differently because of different microstructures being formed in each thickness after annealing. The presence of the 0.75 nm thick a-C barrier layer considerably improved the reliability of the fabricated MOS samples. In contrast, the reliability of MOS samples with a 2.5 nm thick a-C barrier was degraded by sp2 clustering and microstructural change from amorphous phase to nanocrystalline state during annealing. These results were confirmed by Raman spectroscopy, X-ray photoelectron spectroscopy and TEM analysis. This study provides evidence that an 0.75 nm thick a-C layer is a reliable diffusion barrier.

Abstract: Increasing requirements on hard coatings in high-performance machining processes like high speed and dry cutting demands further developments even of the already well established TiAlN coatings. The aim of this work is to present a comparative study on oxidation behavior of Ti0·5Al0·5N coatings alloyed with X (X = V, Hf, Si) elements. Ab initio molecular dynamics results showed that a pronounced layered oxide appears due to the incorporation of these alloying elements thus affecting the thermal stability and antioxygenic properties. The additions of Hf and Si facilitate the formation of layered oxides with Ti-rich and Al-rich oxides, respectively, which improves the antioxidant performance at high temperatures. Contrarily, the Al-rich layer is absent during oxidation of V-containing coating. The Ti-oxides on the surface of TiAlVN and TiAlHfN coatings have different structures due to the discrepancy of O–Ti–O angle. The present findings clearly show that the V-addition results in more rutile-like TiO2 whereas the Hf-addition leads to more anatase-like2 with O–Ti–O angle of 156.3°. With further oxidation, the structures of coatings vary significantly with the alloying elements, which indicates that the alloying of Hf and Si retards the inward diffusion of O atoms, especially, the alloying of Si leads to an earlier formation of a dense sublayer rich in Al2O3, and thus promotes the oxidation resistance. The different diffusion barrier energies of Ti and Al in TiN bulk contribute to the formation of layered oxides on the surface of coating and the different oxidation behaviors. This study provides an atomistic insight to the initial as well as further stages of the oxidation process of quaternary TiAlXN, which together with the electronic structure analysis and diffusion of metal atoms gives a new basis for understanding of its oxidation behaviors.

Abstract: Copper-metallized gallium nitride (GaN) high-electron-mobility transistors (HEMTs) using a Ti/Pt/Ti diffusion barrier layer are fabricated and characterized for Ka-band applications. With a thick copper metallization layer of 6.8 μm adopted, the device exhibited a high output power density of 8.2 W/mm and a power-added efficiency (PAE) of 26% at 38 GHz. Such superior performance is mainly attributed to the substantial reduction of the source and drain resistance of the device. In addition to improvement in the Radio Frequency (RF) performance, the successful integration of the thick copper metallization in the device technology further reduces the manufacturing cost, making it extremely promising for future fifth-generation mobile communication system applications at millimeter-wave frequencies.

Abstract: LiBH4 is one of the most promising solid electrolyte materials for use in solid-state batteries because its hexagonal phase above 110 °C offers Li-ion conductivity of almost 10−3 S cm−1. However, near room temperature, its orthorhombic phase delivers Li-ion conductivity of only 10−8 S cm−1, which considerably hampers its further applications. In the present study, a highly disordered interface between LiBH4 and two-dimensional MoS2 in the composite material was formed, yielding ionic conductivity of 10−4 S cm−1 at room temperature. LiBH4 and MoS2 are found to be in close contact without the formation of any intermediate phase at the interface. First-principles calculations employing density functional theory (DFT) and the nudged elastic band (NEB) method reveal that the migration energy barrier on three specific pathways could be established via microstructure analyses. It was found that the interface between the two phases yields the lowest Li-ion diffusion barrier among all the possible Li-ion pathways; further, the superior conductivity of the composite could be attributed to the interface with high Li-ion conductivity. This study proposes a new strategy for designing solid electrolytes and provides certain possibilities for two-dimensional materials to serve as superior solid electrolytes.

Abstract: An in-depth understanding of lithium (Li) diffusion barriers is a crucial factor for enabling Li-ion-based devices such as three-dimensional (3D) thin-film batteries and synaptic redox transistors ...