Amorphous Carbon Layer Research Articles

Encapsulated prussian blue analogs derived nanocubes with tunable yolk-shell structure enabling highly efficient microwave absorption

Pyrolytic Prussian blue analogs (PBAs) have attracted much attention in the field of microwave absorption (MA) because of their outstanding magnetic-carbon synergism effect. However, pure PBAs are prone to collapse and aggregate during pyrolysis, resulting in impedance mismatch that weaken the MA performance. Herein, the amorphous carbon layer with adjustable dielectric constant as the encapsulated layer, together with pyrolytic PBAs enables remarkable optimized performance via forming the classic yolk-shell structure. Specifically, the amorphous carbon obtained by quantitatively carbonizing phenolic resin, can not only avoid the collapse of pyrolytic PBAs but also optimize electromagnetic parameters to achieve optimum impedance matching by varying thickness. The NiFe alloys/graphite carbon core derived from pyrolytic NiFe–PBAs also enhance synergistic attenuation in the YS-NiFe/GC@C absorbers. According to experimental results, all YS-NiFe/GC@C absorbers exhibit impressive MA properties. When the thickness of the amorphous carbon shell is 50 nm, the minimum reflection loss value is as low as −56.3 dB and the maximum effective absorption bandwidth reaches 5.64 GHz, indicating that optimizing impedance matching via hierarchical and quantitative design can maximize the MA capability. The result is then verified by simulation calculations. Therefore, this promising work provides guidance for the sophisticated construction of tunable PBA-based MA materials.

Regeneration of graphite anode from spent lithium iron phosphate batteries: Microstructure and morphology evolution at different thermal-repair temperature

Recycling of graphite anode from spent lithium ion batteries is critical to the sustainability of the Li-ion battery industry. In this work, the effect of temperature on the microstructure morphology of graphite is studied systematically and the correspondence between the structure morphology and electrochemical properties is elucidated for the first time. The results show that heat treatment leads to the carbonization of organic impurities in spent graphite and the formation of an amorphous carbon layer on the graphite surface. The evolution of the carbon layer from formation to disappearance occurs at different heat-treatment temperatures, which is why the optimal heat-treatment temperature is not the highest heat-treatment temperature. Under optimal conditions, the regenerated graphite exhibits a charging capacity of 339.5 mAh g−1 at 0.1C, and displays a high retention rate of 97.7% after 60 cycles. Our work promotes the regeneration and utilization of spent graphite anode in the industry.

Role of Oxygen in Amorphous Carbon Hard Mask Plasma Etching.

In the current and next-generation Si-based semiconductor manufacturing processes, amorphous carbon layer (ACL) hard masks are garnering considerable attention for high-aspect-ratio (HAR) etching due to their outstanding physical properties. However, a current limitation is the lack of research on the etching characteristics of ACL hard masks under plasma etching conditions. Given the significant impact of hard mask etching on device quality and performance, a deeper understanding of the etching characteristics of ACL is necessary. This study aims to investigate the role of oxygen in the etching characteristics of an ACL hard mask in a complex gas mixture plasma etching process. Our results show that a small change of oxygen concentration (3.5-6.5%) can significantly alter the etch rate and profile of the ACL hard mask. Through our comprehensive plasma diagnostics and wafer-processing results, we have also proven a detailed mechanism for the role of the oxygen gas. This research provides a solution for achieving an outstanding etch profile in ACL hard masks with sub-micron scale and emphasizes the importance of controlling the oxygen concentration to optimize the plasma conditions for the desired etching characteristics.

Two-Step Thermal Transformation of Multilayer Graphene Using Polymeric Carbon Source Assisted by Physical Vapor Deposited Copper.

Direct in situ growth of graphene on dielectric substrates is a reliable method for overcoming the challenges of complex physical transfer operations, graphene performance degradation, and compatibility with graphene-based semiconductor devices. A transfer-free graphene synthesis based on a controllable and low-cost polymeric carbon source is a promising approach for achieving this process. In this paper, we report a two-step thermal transformation method for the copper-assisted synthesis of transfer-free multilayer graphene. Firstly, we obtained high-quality polymethyl methacrylate (PMMA) film on a 300 nm SiO2/Si substrate using a well-established spin-coating process. The complete thermal decomposition loss of PMMA film was effectively avoided by introducing a copper clad layer. After the first thermal transformation process, flat, clean, and high-quality amorphous carbon films were obtained. Next, the in situ obtained amorphous carbon layer underwent a second copper sputtering and thermal transformation process, which resulted in the formation of a final, large-sized, and highly uniform transfer-free multilayer graphene film on the surface of the dielectric substrate. Multi-scale characterization results show that the specimens underwent different microstructural evolution processes based on different mechanisms during the two thermal transformations. The two-step thermal transformation method is compatible with the current semiconductor process and introduces a low-cost and structurally controllable polymeric carbon source into the production of transfer-free graphene. The catalytic protection of the copper layer provides a new direction for accelerating the application of graphene in the field of direct integration of semiconductor devices.

Characteristics of high aspect ratio SiO2 etching using C4H2F6 isomers

The present work used three C4H2F6 isomers (hexafluoroisobutylene [C4H2F6 - iso], (Z)-1,1,1,4,4,4-hexafluoro-2-butene [C4H2F6 - z], and cis-1,1,2,2,3,4-hexafluorocyclobutane [C4H2F6 - cyclo]) having the same chemical composition but different molecular structures, different components, and different global warming potentials (GWPs) to investigate the characteristics of plasmas and etch characteristics of SiO2 masked with an amorphous carbon layer (ACL). The different structures in the C4H2F6 isomers showed different fluorocarbon-based species (CF, CHF, CF2, CHF2, and CF3) and atomic species (H and F) in the plasma, therefore resulting in different characteristics of remaining fluorocarbon polymer on the sample surfaces after the etching and dielectric etch characteristics. Cyclic structured C4H2F6 showed a lower dissociation of molecules compared to the linear molecular structured C4H2F6, thus leading to differences in the concentration and species of high mass ions in the plasma and different etch profiles. These differences in plasma and etching characteristics among C4H2F6 isomers decreased in response to an increase in oxygen flow rate, which was attributed to a higher dissociation of isomer molecules by oxygen. Therefore, by controlling the oxygen flow rate, and using a low F/C ratio of C4H2F6 isomers, extremely selective SiO2 etching over the ACL mask can be applied to next-generation HARC etching.

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.

Noble gas effect on ACL etching selectivity to SiO2 films

AbstractIn this study, we investigated the effect of Ar/He mixing ratio in the tetrafluoromethane/perfluorocyclobutane/Ar/He gas mixture on plasma parameters, SiO2 etching kinetics, and etching selectivity with respect to the amorphous carbon layer (ACL) mask in the inductively coupled plasma system with the low frequency (2 MHz) bias source. It was found that the type of dominant carrier gas does influence the output process characteristics through changes in both ion flux and CFx/F ratio determining the plasma polymerizing ability. In particular, He‐rich plasmas exhibited better performance with respect to the faceting of ACL mask and SiO2/ACL etching selectivity.

Facile coating strategy of Si/C composite anode for high-performance lithium-ion battery

Attributed to its high capacity by alloying with lithium, silicon is considered to be new generation of anodes that can replace graphite and receives much attention. Alleviating the electrode failure caused by volume expansion during lithiation and shrink during delihiation in silicon anodes plays a pivotal role in promoting the industrial application of silicon anodes. In this article, we proposed a facile carbon coating strategy on the surface of silicon nanospheres to buffer the stress during charge and discharge. By controlling the low molecular weight, an ethanol-soluble phenolic resin was synthesized and further self-assembled on the surface of silicon nanoparticles to form the precursor. Uniform Si/C composites were fabricated via pyrolysis. Diffraction of x-rays confirmed that the silicon retained the pristine crystalline structure. Scanning electron microscopy revealed a homogeneous wrap of the amorphous carbon layer on the superficies of the silicon. The galvanostatic charge-discharge test proved the excellent durability of Si/C anodes. Undergoing 50 cycles of galvanostatic lithiation/delithiation at 0.2C, the retention capacity was 96%, as high as 800 mAh/g. This facile but efficient strategy is compatible with large-scale production and improves the feasibility of the practical application of silicon-based anodes.

Improving the GeAsSe Ovonic Threshold Switching Characteristics by Carbon Buffer Layers for Ultralow Leakage Current (∼0.4 nA) and Low Drift Characteristics

Volatile Ovonic threshold switching (OTS) selectors have been regarded as the critical component of highly integrated three-dimensional (3D) cross-point array nonvolatile memory systems. However, relatively high leakage current hinders the further reduction of power consumption in the crossbar array. In addition, the threshold voltage drift phenomenon hinders the improvement of device reliability. Utilizing the buffer layer can effectively reduce the interaction between electrodes and the active layer in the cross-point architecture. Here, it manifests that leakage current can be reduced to ∼0.4 nA with a 5 nm thick amorphous carbon layer as a buffer layer in the GeAsSe-based OTS device, where the carbon layer stabilizes the composition of GeAsSe during the electrical switching cycles. It is also found that the carbon layer leads to a lower threshold voltage drift (35.6 mv/dec) and excellent endurance (>109 cycles with ∼0.4 nA ON-state current). The conduction mechanism analysis demonstrates that the inhibition of the carbon layer on drift originates from the high barrier height from delocalized states transformed into localized states. This work clearly demonstrates the role of the carbon layer and facilitates future 3D crossbar-storage technology applications.

Contribution of Ion Energy and Flux on High-Aspect Ratio SiO2 Etching Characteristics in a Dual-Frequency Capacitively Coupled Ar/C4F8 Plasma: Individual Ion Energy and Flux Controlled.

As the process complexity has been increased to overcome challenges in plasma etching, individual control of internal plasma parameters for process optimization has attracted attention. This study investigated the individual contribution of internal parameters, the ion energy and flux, on high-aspect ratio SiO2 etching characteristics for various trench widths in a dual-frequency capacitively coupled plasma system with Ar/C4F8 gases. We established an individual control window of ion flux and energy by adjusting dual-frequency power sources and measuring the electron density and self-bias voltage. We separately varied the ion flux and energy with the same ratio from the reference condition and found that the increase in ion energy shows higher etching rate enhancement than that in the ion flux with the same increase ratio in a 200 nm pattern width. Based on a volume-averaged plasma model analysis, the weak contribution of the ion flux results from the increase in heavy radicals, which is inevitably accompanied with the increase in the ion flux and forms a fluorocarbon film, preventing etching. At the 60 nm pattern width, the etching stops at the reference condition and it remains despite increasing ion energy, which implies the surface charging-induced etching stops. The etching, however, slightly increased with the increasing ion flux from the reference condition, revealing the surface charge removal accompanied with conducting fluorocarbon film formation by heavy radicals. In addition, the entrance width of an amorphous carbon layer (ACL) mask enlarges with increasing ion energy, whereas it relatively remains constant with that of ion energy. These findings can be utilized to optimize the SiO2 etching process in high-aspect ratio etching applications.

Gas detonation-prepared nano-carbon-based capsule matrix materials: characterisation and microwave-absorption properties

Carbon-based capsule nanomaterials were synthesised through gas-phase detonation using acetylene gas, oxygen, and pentacarbonyl iron. The resulting nanoparticles consisted of a thin layer of capsule-like amorphous carbon with a high specific surface area and strong adsorption capacity. The products exhibited good electromagnetic properties with good reflection loss and absorption capabilities in the frequency range 2–18 GHz. The effective response frequency band ranged from 10.12 to 11.30 GHz, and the reflection loss reached 10.94 dB at 10.96 GHz. The absorption mechanism was mainly owing to dielectric loss as no significant magnetic loss was observed. These nanomaterials have the potential to be used as a matrix for carrying other nanomaterials and for adjusting the impedance-matching of composite materials, thereby enhancing electromagnetic-wave absorption.

Enhanced Pseudo-Capacitance Process in Nanoarchitectural Layered Double Hydroxide Nanoarrays Hollow Nanocages for Improved Capacitive Deionization Performance

Layered double hydroxides (LDHs) are perceived as a hopeful capacitive deionization (CDI) faradic electrode for Cl- insertion due to its tunable composition, excellent anion exchange capacity, and fast redox activity. Nevertheless, the self-stacking and inferior electrical conductivity of the two-dimensional structure of LDH lead to unsatisfactory CDI performance. Herein, the three-dimensional (3D) hollow nanocage structure of CoNi-layered double hydroxide/carbon composites is well designed as a CDI anode by cation etching of the pre-carbonized ZIF-67 template. C/CoNi-LDH has a unique 3D hollow nanocage structure and abundant pore features, which can effectively suppress the self-stacking of LDH sheets and facilitate the transport of ions. Moreover, the introduced amorphous carbon layer can act as a conductive network. When employed as the CDI anode, C/CoNi-LDH exhibited a high Cl- removal capacity of 60.88 mg g-1 and a fast Cl- removal rate of 18.09 mg g-1 min-1 at 1.4 V in 1000 mg L-1 NaCl solution. The mechanism of the Cl- intercalation pseudo-capacitance reaction of C/CoNi-LDH is revealed by electrochemical kinetic analysis and ex situ characterization. This study provides vital guidance for the design of high-performance electrodes for CDI.

Synthesis and Performance of NaTi2(PO4)3/VGCF@C Anode Composite Material for Aqueous Sodium-Ion Batteries

This study combines self-prepared NaTi2(PO4)3 (NTP) with commercial vapor-grown carbon fiber (VGCF) using a solid state calcination, then coats it with carbon to synthesize the composite anode material NaTi2(PO4)3/VGCF@C (NTP/VGCF@C). The microstructure and electrochemical properties of the composite material were then analyzed using microstructure analysis and electrochemical testing equipment. Single phase NTP shows nanoparticles with a polyhedral structure, and there is good contact at the interface between the nanoparticles and the VGCFs. The carbon coating formed on the NTP particles displays a nearly 6.5 nm thick layer of amorphous carbon. From the coin-cell battery performance measurements, after 850 cycles, the composite material NTP/VGCF@C exhibits an excellent retention rate of 96.3% compared to that of the pure NTP material when the current density is 200 mA/g. As a result, the composite material and lithium manganate (denoted as LMO) were assembled into an LMO-NTP/VGCF@C aqueous sodium-ion soft pack full battery system. The full battery shows an initial capacity of 31.07 mAh at a rate of 0.5C, and a reversible discharge capacity retention rate of 95.8% after 480 cycles, exhibiting a good long-cycle stability performance.

Nitrogen-Doped Carbon Coated Na3V2(PO4)2F3 Derived from Polyvinylpyrrolidone as a High-Performance Cathode for Sodium-Ion Batteries

Na super ionic conductor (NASICON)-type Na3V2(PO4)2F3 (NVPF) has been regarded as a prospective candidate of cathode materials for sodium-ion batteries due to its excellent structural stability, relatively high capacity and working voltage. However, the poor cyclability and rate capability, resulting from its low intrinsic electronic conductivity, have become a serious obstacle to their practical large-scale application. In this work, N-doped carbon coated NVPF composites (NVPF@NC) were successfully synthesized via a simple sol–gel method, in which low-cost polyvinylpyrrolidone was introduced as a nitrogen source. After high-temperature pyrolysis, a highly conductive N-doped carbon layer was in-situ constructed on the particle surface to enhance the sodium storage performance of NVPF. The optimized NVPF@NC cathode delivered high reversible capacity, excellent rate capability and long-term cycle life compared to pristine NVPF@C. The remarkable electrochemical performance of NVPF@NC cathode benefits from the modification strategy of introducing a heteroatom-doped carbon layer, triggering the formation of extrinsic defects and active sites in the N-doped amorphous carbon layer, which greatly enhances the electrical conductivity and the diffusion rate of sodium ions. This work provides a facile and effective approach for the preparation of N-doped carbon coated NVPF with remarkable sodium storage properties, which could be extended to other electrode materials electrochemical for energy storage.

Oxidized graphene fabrication from oil palm shell at different exposure time

Biochar made from Oil Palm Shell (B-OPS) can release bio-gaseous compounds such as methane and carbon dioxide during thermal pressure. A percentage of these bio-gaseous compounds can be used as precursors in the carbon deposition process during Chemical Vapor Deposition (CVD) to synthesize oxidized graphene. By manipulating the exposure time during the CVD process, one can observe varying nucleation, growth, and exfoliation differences. The highest exposure time results in exfoliation, observable crystallinity, high carbon content, low defects, and a reduction in oxygen within the intercalated layers. Furthermore, oxidized graphene synthesized at different exposure times can be characterized using various methods such as Atomic Force Microscope (AFM), Scanning Electron Microscope – Field Emission Gun (SEM- FEG), Energy Dispersive X-ray (EDX), micro-Raman, X-Ray Diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS). Observing the carbon characteristics at 30-minute intervals allows one to speculate on the relationship between carbon deposition and exposure time. As the exposure time increases, the initial amorphous carbon layer deposition changes to a higher sp2 hybridized layer deposition. G-65 has shown optimized properties, such as a high hybridization trend, a high surface area porous-wavelike structure, an observable crystallinity, and the highest sp2 compared to sp3 deconvoluted peaks.

C+ ion implanted single crystal diamond with amorphous surface for efficient oxygen evolution catalysis

Oxygen evolution reaction (OER) is critical in water splitting for green hydrogen gas production due to its sluggish kinetics; however, commercial OER catalysts commonly suffer from high cost, low catalytic activity and poor stability. Herein, we developed a C+ ion implantation method to modify single crystal diamond, and the resultant surface amorphous layer not only raised the active site number but also increased the content of the C=O group, thus significantly improving the OER activity. The C+ ion implanted high-temperature and high-pressure (C+-HTHP) and chemical vapor deposition (C+-CVD) diamonds both exhibit low OER overpotential with η10 of 317 mV and 325 mV respectively, superior to those of HTHP diamond (360 mV), CVD diamond (395 mV) and RuO2 (364 mV). The potentiostatic testing shows that the C+ implanted diamonds almost didn't undergo the rise of OER overpotential upon catalysis for more than 12 h at a current density of 10 mA cm−2, suggesting a high catalytic stability, owing to the strong bonding between single crystal diamond and amorphous carbon layer. For the first time, we utilized carbon ion implantation to prepare diamond-based high-performance OER catalyst, which broadens the understanding of carbon-based materials in OER catalysis.

Extraordinary radiation tolerance of a Ni nanocrystal-decorated carbon nanotube network encapsulated in amorphous carbon

Nanostructured materials with abundant defect sinks show good radiation tolerance due to their efficient absorption of irradiation-induced interstitials and vacancies. However, the poor thermal stability and limited size of such nanomaterials severely limit their practical applications. Herein, we report a novel flexible free-standing network-structured hybrid consisting of amorphous carbon encapsulated nickel nanocrystals anchored on a single-wall carbon nanotube scaffold with excellent radiation tolerance up to 5 dpa at 673 K and exceptional thermal stability up to 1073 K. The nano-scale Ni-SWCNT network with abundant Ni-SWCNT interfaces and grain boundaries provides effective sinks and fast transportation channels for defects, which effectively absorb irradiation-induced defects and improved the irradiation tolerance. Furthermore, the formation of a low-energy Ni-C interface and surface thermal grooves significantly reduces the system free energy and increased thermal stability. The amorphous carbon layer produces an external compressive radial stress that inhibits Ni grain boundaries from migrating, which greatly improves the thermal stability of the hybrid by pinning GBs at grooves between grains and facilitates the annihilation of irradiation-induced defects at the sinks. This work provides a new strategy to improve the thermal stability and radiation tolerance of nano-materials used in an irradiation environment.

Te-doped NiFe2O4 stabilized by amorphous carbon layers derived from one-step topological transitions of NiFe LDHs with significantly enhanced oxygen evolution reaction

Constructing efficient oxygen evolution reaction (OER) electrocatalysts that can stably operate under high temperatures and strong alkaline conditions still faces great challenges for industrial hydrogen production from water electrolysis. Herein, a self-supported tellurium (Te)-doped spinel NiFe2O4 with a carbon-stabilized nanosheet structure anodic catalyst on nickel foam (NF) (Te-NiFe2O4@C/NF) is successfully synthesized by calcination of a layered double hydroxide precursor (NiFe LDH). Benefiting from Te doping as well as coupling with the amorphous carbon layer and the unique superhydrophilic/aerophobic surface property, which provides efficient mass transport channels and rapid electron transport, the optimized Te-NiFe2O4@C/NF requires an overpotential of 220 mV to achieve a current density of 10 mA cm−2 for the OER in 1 M KOH at 25 ℃. Furthermore, an extremely low overpotential of 180 mV is required to achieve 500 mA cm−2 in 6 M KOH at 80 ℃ and maintains superior stability over 60 h under such harsh quasi-industrial conditions. Density functional theory calculations further reveal that Te doping can effectively modulate the local electronic environment of the Ni and Fe sites, which optimizes the intermediate (*OH) adsorption and facilitates the OER kinetics. This work may open up opportunities to explore efficient electrocatalysts for scalable hydrogen production.

Synergetic Contributions from the Components of Flexible 3D Structured C/Ag/ZnO/CC Anode Materials for Lithium‐Ion Batteries

Low electronic conductivity and large volume changes during the (de)lithiation process are the two main challenges for ZnO anode materials used for lithium‐ion batteries (LIB). Here, a free‐standing, flexible, and binder‐free LIB electrode composed of ZnO nanorods and carbon cloth (CC) is fabricated. This is then decorated with Ag nanoparticles and finally coated by an amorphous carbon layer to form the hybrid electrode: (C@(Ag&ZnO)). The voids among the nanorods are sufficient to accommodate the volume expansion of the ZnO while the flexible CC, which acts as the current collector, relieves the volume change‐induced stress. The Ag nanoparticles are effective in improving the conductivity. This composite electrode shows excellent LIB performance with a stable long cycling life over 500 cycles with a reversible capacity of 1093 mAh g−1 at a current density of 200 mA g−1. It also shows good rate performance with reversible capacity of 517 mAh g−1 under a high‐current density of 5000 mA g−1. In situ Raman spectroscopy is conducted to investigate the contributions of the amorphous carbon layer to the capacity of the whole electrode and the synergy between the CC and ZnO nanorods.

Direct regeneration of degraded lithium-ion battery cathodes with a multifunctional organic lithium salt

The recycling of spent lithium-ion batteries is an effective approach to alleviating environmental concerns and promoting resource conservation. LiFePO4 batteries have been widely used in electric vehicles and energy storage stations. Currently, lithium loss, resulting in formation of Fe(III) phase, is mainly responsible for the capacity fade of LiFePO4 cathode. Another factor is poor electrical conductivity that limits its rate capability. Here, we report the use of a multifunctional organic lithium salt (3,4-dihydroxybenzonitrile dilithium) to restore spent LiFePO4 cathode by direct regeneration. The degraded LiFePO4 particles are well coupled with the functional groups of the organic lithium salt, so that lithium fills vacancies and cyano groups create a reductive atmosphere to inhibit Fe(III) phase. At the same time, pyrolysis of the salt produces an amorphous conductive carbon layer that coats the LiFePO4 particles, which improves Li-ion and electron transfer kinetics. The restored LiFePO4 cathode shows good cycling stability and rate performance (a high capacity retention of 88% after 400 cycles at 5 C). This lithium salt can also be used to recover degraded transition metal oxide-based cathodes. A techno-economic analysis suggests that this strategy has higher environmental and economic benefits, compared with the traditional recycling methods.