Amorphous Carbon Interlayer Research Articles

Interfacial Dynamics of Carbon Interlayers at Anode-Free Solid Electrolyte/Lithium Interfaces

Solid electrolytes (SEs) that incorporate lithium (Li) metal anodes provide a promising pathway to improve battery energy density and safety. However, Li metal anodes still suffer from multiple challenges, including 1) uniform Li deposition and dissolution, 2) continual formation of a solid-electrolyte interphase (SEI), and 3) limited rate capability. To control the interfaces, predefined interlayers such as gold, ZnO, carbon, and other coatings have been used tune the Li metal and SE interface. However, there is a need for improved fundamental understanding of the mechanistic role of these interlayers on performance and stability. In this work, we explore the application of an amorphous carbon interlayer in an argyrodite SE system, which is used for in situ Li metal formation in an “anode-free” configuration.The incorporation of a carbon interlayer has been previously shown to act as a physical barrier between the SE and in situ formed Li metal, improve the uniform contact and current distribution across the SE/anode interface, and potentially suppress dendrite propagation [1]. However, the mechanism of this improved performance is not fully understood. Therefore, to study the influence of the carbon interlayer on interfacial performance, a detailed electrochemical analysis was performed.First, the transition in reaction pathway from carbon lithiation to Li nucleation and growth was observed to change as a function of charging rates. To probe the lithiation effects of the carbon interlayer on subsequent Li deposition, incremental electrochemical impedance spectroscopy (EIS) and current-interrupt analysis was performed to study the dynamic changes of the carbon interlayer during the charging process prior to Li nucleation. To confirm the mode of metallic Li nucleation and growth, operando video microscopy and post-mortem focused ion-beam/scanning electron microscopy (FIB-SEM) was utilized. The preferential location of Li deposition and growth at the current collector and carbon interface confirms the transport of Li-ion through the lithiated carbon interlayer. Moreover, the Li metal deposition behavior was observed to depend on the electrochemical properties of the carbon interlayer during the lithiation process. These fundamental electrochemical studies will further our understanding of the design requirements for interlayers that can enable Li metal anodes in solid-state battery systems.[1] Y.G. Lee, S. Fujiki, C. Jung, N. Suzuki, N. Yashiro, R. Omoda, D. S. Ko, T. Shiratsuchi, T. Sugimoto, S. Ryu, J. H. Ku, T. Watanabe, Y. Park, Y. Aihara, D. Im, I. T. Han, Nat. Ener. 5, 299-308 (2020)

Amorphous carbon interlayer modulated interfacial thermal conductance between Cu and diamond

Introducing an interlayer is an effective method to improve the interfacial thermal conductance (G) of highly mismatched Cu/diamond interface. However, the relative role of interfacial bonding effect and vibrational bridging effect of the interlayer is still not clear. Herein, we introduce amorphous carbon (a-C) layer by Ar ion bombardment, oxygenated a-C layer by Ar/O2 mixture ion bombardment, and C-O bond by acid treatment at the Cu/diamond interface to regulate the interfacial bonding effect and vibrational bridging effect. The G of Cu/diamond is increased by 44% with increasing interfacial bonding strength from 12 mN to 17 mN and then is independent on interfacial bonding strength above 17 mN, which mainly comes from the interfacial bonding effect. Compared with the as-cleaned Cu/diamond interface, a 35% increase of G is obtained by inserting a 4.5 nm-thick a-C interlayer between Cu and diamond, which mainly comes from the vibrational bridging effect. The vibrational bridging effect overwhelms the interfacial bonding effect in improving the G of Cu/diamond interface when the interfacial bonding strength is relatively high. The findings give insights into the mechanisms dictating heat transfer of highly mismatched metal/non-metal interface and provide a new avenue for improving the G of Cu/diamond interface.

Controllable fabrication of Bi4Ti3O12/C/Bi2S3/MoS2 heterojunction with effective suppression of Bi2S3 assisted by amorphous carbon interlayer for significantly enhanced photocatalysis

BackgroundFabricating heterojunctions by combining with MoS2 is efficient to boost the visible light photocatalytic activity of Bi4Ti3O12 (BTO) but limited by the concurrent formation of Bi2S3 nanorods by in-situ ion exchange reaction. MethodsAn amorphous carbon interlayer that can effectively protect the BTO fibrous structure and suppress the Bi2S3 generation was introduced to construct Bi4Ti3O12/C/Bi2S3/MoS2 (BCBM) composites with enhanced photocatalytic activity. The BCBM fibers were fabricated by electrospinning and subsequent hydrothermal growth of carbon and MoS2. Significant findingsOwing to the important roles of carbon interlayer to keep the integrity of the BTO fibrous structure and provide charge transfer channel, fast separation of photoinduced carriers happens on the semiconductor interface between BTO and MoS2 to improve the visible light photocatalytic activity. The optimum BCBM displays a photocatalytic efficiency of 88.4% and apparent constant of 0.0148 min−1 towards degrading RhB, which are much higher relative to the Bi4Ti3O12/Bi2S3/MoS2 composites prepared without the carbon interlayer. Moreover, it is demonstrated that the thickness of carbon interlayer is crucial for fabricating high-performance BTO heterojunctions with MoS2. The design and results in this work may broaden the horizon to construct the Bi-based semiconductor photocatalyst with high photocatalytic performance.

High-Power Hybrid Solid-State Lithium–Metal Batteries Enabled by Preferred Directional Lithium Growth Mechanism

Solid electrolytes are revolutionizing the field of lithium–metal batteries; however, their practical implementation has been impeded by the interfacial instability between lithium metal electrodes and solid electrolytes. While various interlayers have been suggested to address this issue in recent years, long-term stability with repeated lithium deposition/stripping has been challenging to attain. Herein, we successfully operate a high-power lithium–metal battery by inducing the preferred directional lithium growth with a rationally designed interlayer, which employs (i) crystalline-direction-controlled carbon material providing isotropic lithium transports, with (ii) prelithium deposits that guide the lithium nucleation direction toward the current collector. This combination ensures that the morphology of the interlayer is mechanically robust while regulating the preferred lithium growth underneath the interlayer without disrupting the initial interlayer/electrolyte interface, enhancing the durability of the interface. We illustrate how these material/geometric optimizations are conducted from the thermodynamic considerations, and its applicability is demonstrated for the garnet-type Li7–xLa3–aZr2–bO12 (LLZO) solid electrolytes paired with the capacity cathode. It is shown that a lithium–metal cell with the optimized amorphous carbon interlayer with prelithium deposits exhibits outstanding room-temperature cycling performance (99. 6% capacity retention after 250 cycles), delivering 4.0 mAh cm–2 at 2.5 mA cm–2 without significant degradation of the capacity. The successful long-term operation of the hybrid solid-state cell at room temperature (approximately a cumulative deliverable capacity of over 1000 mAh cm–2) is unprecedented and records the highest performance reported for lithium–metal batteries with LLZO electrolytes until date.

Structure and characterization of carbonized cotton knitted fabric

Carbonized cotton fabrics have been used in the preparation of wearable sensors. However, there are few studies on the carbonization structure and properties of carbonized cotton fabric. This work provided a practical and effective method for the preparation of carbonized cotton knitted fabrics. The effects of impregnating agents and pre-oxidation on the carbonization structure and performances of the cotton knitted fabric were investigated systematically for the first time. Thermal gravimetry analysis revealed that cotton knitted fabric impregnated with 10% (NH4)2HPO4 had a higher carbonized yield of cotton knitted fabric than that with 5%, which was followed by 10% NH4H2PO4, and the worst was 10% (NH4)2SO4. The results also showed that the carbonized yield of cotton knitted fabric was enhanced considerably at 900°C for 120 min after impregnation with 10% (NH4)2HPO4 and pre-oxidation at 240°C for 60 min. The integrity of the cotton knitted fabric was maintained after carbonization. Scanning electron microscopy showed that the natural turn of carbonized cotton fiber was deepened after being impregnated with 10% (NH4)2HPO4 and pre-oxidized at 240°C for 60 min. With the increase of carbonization temperature, C-O and C-H were destroyed, and C=C bonds were formed. The amorphous carbon interlayer was created after carbonization. The structural order of these carbonized cotton fibers was improved with the enhancement of temperature. Pre-impregnation agent treatment and pre-oxidation greatly heightened the carbonized yield of cotton knitted fabric, maintained the integrity of the carbonized cotton fiber, and then increased the electrical conductivity of the carbonized cotton knitted fabric.

Radiation Damage in (001) Diamond Induced by Phosphorus Ion Implantation

Microstructural evolution in ion‐implanted and postannealed (001) diamond is investigated using transmission electron microscopy. For 150 keV 31P+ ion implantation into diamond with a fluence of 1 × 1015 cm−2, an amorphous carbon interlayer about ≈80 nm thickness formed between damaged diamonds is observed. Postannealing at 1200 °C can recover some damaged diamond regions where the vacancy concentration is estimated below 3 × 1022 cm−3. However, graphitization from the amorphous carbon interlayer and the heavily damaged diamond regions with higher vacancy concentrations occurs to form an ≈85 nm‐thick graphite layer after annealing.

Preparation of novel high performance recoverable and natural sunlight-driven nanocomposite photocatalyst of Fe3O4/C/TiO2/N-CQDs

This work describes a sunlight-active photocatalyst capable of magnetically separating prepared by depositing various amounts of N-doped carbon quantum dots (N-CQDs) on the Fe3O4/C/TiO2 (FCT) nanocomposite. The photocatalytic activity of the resulting composites was investigated in the decolorization of methylene blue (MB), under UV, visible and sunlight irradiation. In the composites, the amorphous carbon interlayer is devised to prevent photodissolution of the Fe3O4 core. To coat the TiO2 nanoparticles on the insulated carbon surface of the magnetic core, a vapor phase hydrolysis method was used while a hydrothermal method was used to deposit N-CQDs on the Fe3O4/C/TiO2 nanocomposite surface. The prepared nanocomposites were characterized by photoluminescence (PL) spectroscopy, X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX) spectroscopy, Fourier transform infrared (FT-IR) spectrometry, diffuse reflectance spectroscopy (DRS) and vibrating sample magnetometry (VSM). The results revealed that the N-CQDs content of the FCT composite has a great influence on the photocatalytic activity of the nanocomposite. So that, the photocatalyst FCT/N-CQDs−4.5 wt% resulted in 95.5% MB decolorization within 80 min sunlight irradiation while pure TiO2 and FCT provided 20.3% and 31.8% decolorization, respectively. In addition, the results showed that sunlight has a significant effect on the photocatalytic activity of the composite, compared to visible and UV light irradiation. Moreover, the composite photocatalysts possessed superparamagnetic properties due to their good saturation magnetization value, i.e. 24.9 emu g−1. As a result, the developed composite photocatalyst was recovered by applying an external magnetic field without losing its activity even after five cycles. In general, this study provides new insights into the fabrication of a new generation of TiO2-based photocatalysts to overcome the main drawbacks of conventional TiO2 photocatalysts.

Constructing a continuous amorphous carbon interlayer to enhance dielectric performance of carbon nanotubes/polyvinylidene fluoride nanocomposites

Carbon nanotubes (CNTs) based percolative polymer nanocomposites own a high dielectric constant at a small amount of CNTs. However, CNTs are easy to connect with each other directly in the vicinity of percolation threshold (fc), which unavoidably leads to an abrupt increase in dielectric loss. Herein, we propose a facile way to fabricate core-shell structured CNTs@amorphous carbon (CNTs@AC) hybrids by chemical vapor deposition (CVD). The CNT@AC hybrids were subsequently integrated into polyvinylidene fluoride (PVDF) matrix to fabricate CNTs@AC/PVDF dielectric nanocomposites by the combination of solution casting and extrusion-injection procedures. The uniform AC shell provides an insulative interlayer for the adjacent CNTs, which not only hinders the direct contact of CNTs but also improves the dispersibility of CNTs in PVDF matrix. Compared with pristine CNTs (P-CNTs)/PVDF nanocomposites, the fc increases from 7.16 vol % to 11.81 vol % and the dielectric loss decreases from 83.66 to 1.35 for the CNTs@AC-60/PVDF nanocomposites, which indicates that the percolation behavior is delayed. The results indicate that the influence of AC interlayer on the dielectric performance of the nanocomposites after percolation is much more evident than that before percolation. All these results demonstrate that this strategy is effective to enhance the dielectric performance of polymer nanocomposites and the design concept could be extended to other carbon hybrids materials.

Fast growth of ultrananocrystalline diamond films by bias-enhanced nucleation and growth process in CH4/Ar plasma

This letter describes the fast growth of ultrananocrystalline diamond (UNCD) films by bias-enhanced nucleation and growth process in CH4/Ar plasma. The UNCD grains were formed at the beginning of the film's growth without the necessity of forming the amorphous carbon interlayer, reaching a thickness of ∼380 nm in 10 min. Transmission electron microscopic investigations revealed that the application of bias voltage induced the formation of graphitic phase both in the interior and at the interface regions of UNCD films that formed interconnected paths, facilitating the transport of electrons and resulting in enhanced electron field emission properties.

Synthesis of Tin Catalyzed Silicon and Germanium Nanowires in a Solvent–Vapor System and Optimization of the Seed/Nanowire Interface for Dual Lithium Cycling

Silicon and germanium nanowires are grown in high density directly from a tin layer evaporated on stainless steel. The nanowires are formed in low cost glassware apparatus using the vapor phase of a high boiling point organic solvent as the growth medium. HRTEM, DFSTEM, EELS, and EDX analysis show the NWs are single crystalline with predominant ⟨111⟩ growth directions. Investigation of the seed/nanowire interface shows that in the case of Si an amorphous carbon interlayer occurs that can be removed by modifying the growth conditions. Electrochemical data shows that both the tin metal catalyst and the semiconductor nanowire reversibly cycle with lithium when the interface between the crystalline phases of the metal and semiconductor is abrupt. The dually active nanowire arrays were shown to exhibit capacities greater than 1000 mAh g–1 after 50 charge/discharge cycles.

Microstructure investigation of positive/negative direct current bias-enhanced diamond deposition

A two step process, positive/negative direct current (dc) biasing during the substrate pretreatment stage without biasing during the subsequent deposition stage, was used in this study. Microstructure of positive/negative dc bias-enhanced diamond deposition by microwave plasma chemical vapor deposition on silicon substrate was investigated by Raman spectroscopy, scanning electron microscopy and high resolution transmission electron microscopy (HRTEM). In positive dc biasing pretreatment, high methane concentration (25.9% CH 4 in H 2) was used to enhance diamond nucleation and resulted in the co-deposition of diamond nuclei and amorphous carbon phase. Continuous polycrystalline diamond film was observed after positive dc biasing for 5 min and growth deposition. From HRTEM cross-section analysis, it is observed that an amorphous carbon interlayer was obtained between diamond–silicon interface after pretreatment and deposition processes. The process for negative dc biasing enhanced diamond deposition was also studied and discussed. HRTEM result shows that neither SiC nor other intermediate layer is revealed between the diamond and silicon after negative dc biasing and growth processes.

SiC TO SiC WAFER BONDING

ABSTRACTSiC wafers with an RMS roughness of 1.5 nm were bonded in a dedicated ultrahigh vacuum bonding chamber. Successful fusion of wafers was observed at temperatures as low as 800°C under a uniaxial mechanical stress of 20 MPa. Cross-section transmission electron microscopy (XTEM) of a specimen bonded at 1100°C revealed parts of the interface where wafers were in intimate contact, while other parts contained an up to 3 nm thick amorphous carbon interlayer. The bonded SiC retained its high crystalline quality; no extended defects emanating from the interface were observed within the sampling region. Electrical measurements showed that the azimuthal orientation of the bonded couple significantly influences the electrical character of the junction.

The surface properties on both sides of the isolated diamond film

The polycrystalline diamond films in this research were deposited on silicon substrates using a methane–hydrogen gas mixture by the microwave plasma chemical vapor deposition (MPCVD) system. Prior to deposition, the silicon wafers were pretreated by a photoresist in which 0.1 μm diamond powder is suspended. The isolated diamond film was then obtained by etching the backside of the silicon wafer with KOH solution. The bottom surface of the isolated diamond film exhibited a much smoother surface profile than the top surface of the isolated diamond film. From XPS analysis, the oxygenated phenomenon was detected for the as-deposited diamond film and increased for both surfaces of the isolated diamond film after the back-etching process. It was noted that the oxygenated phenomenon did not degrade the film quality since the quality of the isolated diamond film improved after the back-etching process. An estimated 600 Å thick SiC layer and an amorphous carbon interlayer was found on the bottom surface, which is in the diamond–Si interfacial region of the isolated diamond film. Experimental results showed that the film quality was not dependent on the grain size and roughness of the diamond film. The shift of the characteristic diamond peak was due to the strain force that was formed in the interface of diamond–Si during the cooling-down period of the deposition process. The thick layer of SiC and the amorphous carbon interlayer also affected the film quality in the interfacial region during diamond deposition and the noise of the Raman spectrum increased for the bottom surface of the isolated diamond film.

Bombarding energy dependence of bonding structure in amorphous carbon interlayer and its effect on diamond nucleation

The bombarding energy dependence of bonding structure in amorphous carbon interlayer and its effect on diamond nucleation density (Nd) were studied. Amorphous carbon (a-C) interlayer was deposited by magnetron sputtering. Interestingly, the intensity ratio (ID/IG) of the D band (∼1400 cm−1) to the G band (∼1570 cm−1) in the Raman spectra and the optical band gap of the a-C film were found to be inversely proportional to the sputtering power, that is, to bombarding energy. When diamond was subsequently deposited at 800 °C by microwave plasma chemical vapor deposition (CVD), diamond could be grown only on the interlayers with higher ID/IG (≥2.20), and Nd was increased up to 2 × 106/cm2 with the increase of ID/IG ratio, that is, with the decrease of the bombarding energy. We experimentally confirmed that the amount of the sp3 bonded carbon clusters within the interlayer was dependent on the bombarding energy of the particles, determining the diamond nucleation density. We suggest that the transformation of the amorphous carbon into graphitic carbon should be effectively prevented for the diamond nucleation on the a-C interlayer.

スパッタ法による垂直面内複合型媒体の作製

Perpendicular/longitudinal composite media were fabricated by sputtering. It is hard to deposit a perpendicular upper layer on a longitudinal underlayer because of the epitaxy between the layers. Therefore, it is important to prevent the epitaxial growth between the perpendicular upper layer and the longitudinal underlayer. For this purpose, we attempted to apply an amorphous carbon interlayer. First, the magnetic properties of perpendicular single media with Ti-Cr and C underlayers were compared. As a result, it was found that a perpendicular single medium with a C underiayer had the same property as a medium with a Ti-Cr underlayer. In accordance with these results, a perpendicular layer was deposited onto a longitudinal layer with a C interlayer. Consequently, the thickness of the C interlayer was optimized. As a result, a perpendicular/longitudinal composite medium was successfully fabricated using 5-nm C interlayer.

Effects of hydrogenated amorphous carbon interlayer on diamond nucleation

Diamond was deposited at 850 °C by microwave plasma chemical vapor deposition (CVD) on the interlayers with various intensity ratios (ID/IG) of the D band (~1400 cm-1) to the G band (~1570 cm-1) in the Raman spectra. Diamond could be grown only on the interlayers with higher ID/IG (≤1.95), and Nd was slightly increased to 3 × 106/cm2with ID/IG. The predeposition at 350 °C, which decreased the full-width at half-maximum of the broad D band, further increased Nd to 5 × 107/cm2. With 300 ÅA Pt overlayer on the interlayer, Nd was much more enhanced to 8 × 107/cm2. We suggest the sp3 bonded carbon clusters within the interlayer contribute to diamond nucleation, but they should be survived against atomic hydrogen etching during diamond deposition by increasing the sp3/sp2 ratio, by increasing the degree in clustering, or by protecting them with overlayer.

Aluminum Wiring Reliability of Fluorinated Amorphous Carbon Interlayer

ABSTRACTWe investigated the aluminum wiring reliability of fluorinated amorphous carbon (a-C:F) interlayer dielectrics (ILD) using electromigration tests at the wafer level under accelerated stress conditions with current density ranging from 25–32 MA/cm2 and a the substrate temperature of 300 K. The a-C:F film is one of the low-k organic materials with a dielectric constant of 2.5. The thermal conductivity of the a-C:F film (0.108 W/m·K) is about one order lower than that of SiO2 (1.2 W/m.K). We found that joule heating effect is enhanced by the lower thermal conductivity of a-C:F and that the wiring lifetime for a-C:F ILD is about one order lower than that for SiO2 ILD under high current stress. However, when the wiring lifetime is plotted as a function of the wiring temperature, the wiring lifetimes for both a-C:F ILD and SiO2 ILD became almost the same. The degradation of the wiring lifetime for a-C:F ILD is explained by the increase of the wiring temperature which is caused from joule heating. Moreover, the activation energy of the electromigration for a-C:F ILD has the same value as that of SiO2 LD at a temperature.