A near-wearless and extremely long lifetime amorphous carbon film under high vacuum

Electrochemical investigation of ion-beam sputter-deposited carbon thin films for Li-ion batteries

Abstract

The C-rate capability of 230 nm- and 16 nm-thin ion-beam sputter-deposited amorphous carbon films, an interesting class of carbonaceous material for lithium-ion batteries, was investigated up to Li-platting. Stepwise ascending and descending constant Li+ currents after each fifth cycle, followed by hundreds of cycles with the highest current were applied. The carbon films show similar cycling with irreversible losses during the first five cycles, followed by reversible cycling with a capacity close to that of graphite. The capacity is significantly lower at high currents; however, it is restored for subsequent cycling again at low currents. Differential charge and differential capacity curves reveal three Li+ uptake and three Li+ release peaks located between 0 and 3 V. Irreversible as well as reversible Li bonding can be associated with all these peaks. Irreversibly bonded Li can be found at the surface (solid electrolyte interphase) and in the bulk of the carbon films (Li trapping). Reversible Li bonding might be possible inside the carbon films in graphite-like nano-domains and at defects. The thinner film reveals a more pseudo-capacitive cycling behavior, pointing to enhanced Li kinetics.

Graphical abstract

The influence of hydrogen concentration in amorphous carbon films on mechanical properties and fluorine penetration: a density functional theory and ab initio molecular dynamics study

Amorphous carbon (a-C) films have attracted significant attention due to their reliable structures and superior mechanical, chemical and electronic properties, making them a strong candidate as an etch hard mask material for the fabrication of future integrated semiconductor devices. Density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations were performed to investigate the energetics, structure, and mechanical properties of the a-C films with an increasing sp3 content by adjusting the atomic density or hydrogen content. A drastic increase in the bulk modulus is observed by increasing the atomic density of the a-C films, which suggests that it would be difficult for the films hardened by high atomic density to relieve the stress of the individual layers within the overall stack in integrated semiconductor devices. However, the addition of hydrogen into the a-C films has little effect on increasing the bulk modulus even though the sp3 content increases. For the F blocking nature, the change in the sp3 content by both atomic density and H concentration makes the diffusion barrier against the F atom even higher and suppresses the F diffusion, indicating that the F atom would follow the diffusion path passing through the sp2 carbon and not the sp3 carbon due to the significantly high barrier. For the material design of a-C films with adequate doped characteristics, our results can provide a new straightforward strategy to tailor the a-C films with excellent mechanical and other novel physical and chemical properties.

Anodic electrochemical regeneration of a graphene/titanium dioxide composite adsorbent loaded with an organic dye

A nanocomposite of graphene and titanium dioxide (G/TiO₂) was prepared using the sol-gel method for use in an electrochemical adsorption/regeneration process. The effect of annealing temperature on electrochemical characteristics of the nanocomposites was investigated by cyclic voltammetry and constant current electrochemical regeneration, using methylene blue (MB) as the adsorbate. The G/TiO₂ could be regenerated more rapidly and with less corrosion than the bare graphene. The G/TiO₂ annealed at 400 °C had a higher proportion of anatase phase TiO₂ (ca. 7% rutile TiO₂) compared to that annealed at 500 °C (ca. 40% rutile TiO₂). Cyclic voltammetry indicated that the G/TiO₂ annealed at 400 °C had a higher activity for MB oxidation than the nanocomposite annealed at 500 °C. Similarly, the regeneration of MB loaded G/TiO₂ annealed at 400 °C was much faster than for the nanocomposite annealed at 500 °C. Complete regeneration of the G/TiO₂ annealed at 400 °C was obtained after an electrochemical charge of 21 C per mg of adsorbate. The G/TiO₂ annealed at 400 °C was regenerated in half the time required for the bare graphene. TEM studies showed that the bare graphene was rapidly corroded, while corrosion was not observed for the G/TiO₂ nanocomposites.

First principles investigation on energetics, structure, and mechanical properties of amorphous carbon films doped with B, N, and Cl

Amorphous carbon (a-C) films have received significant attention due to their reliable structures and superior mechanical, chemical and electronic properties, making them a strong candidate as a hard mask material. We investigated the energetics, structure, and electronic and mechanical properties of the B, N, and Cl doped a-C films based on density functional theory (DFT) calculation. Our DFT calculated results clearly show that introducing B and N atoms into a-C films makes the bulk modulus slightly reduced as a function of the concentration increases. Interestingly, it is noted that introducing Cl atom into a-C films makes the bulk modulus is drastically reduced, which suggests that the films softened by Cl doping would relieve residual stress of the individual layers within the overall stacks in integrated semiconductor devices. These requirements become more important and increasingly more challenging to meet as the device integrity grows. In the perspective of F blocking nature, B doping into a-C films pulls in and captures the F atom due to the strong bonding nature of B‒F bond than C-F bond. Unlike the B doping, for the N doped a-C film, F atom has extremely large diffusion barrier of 4.92 eV. This large diffusion barrier is attributed to the electrostatically repulsive force between both atoms. The Cl doped a-C film shows consistently the similar results with the N doped a-C film because both N and Cl atoms have large electro-negativity, which causes F atom to push out. If one notes the optimized designing with the suitable doped characteristics, our results could provide a new straightforward strategy to tailor the a-C films with excellent mechanical and other novel physical and chemical properties.

Fabrication of Foldable Metal Interconnections by Hybridizing with Amorphous Carbon Ultrathin Anisotropic Conductive Film

With the advent of foldable electronics, it is necessary to develop a technology ensuring foldability when the circuit lines are placed on the topmost substrate rather than in the neutral plane used in the present industry. Considering the potential technological impacts, conversion of the conventional printed circuit boards to foldable ones is most desirable to achieve the topmost circuitry. This study realizes this unconventional conversion concept by coating an ultrathin anisotropic conductive film (UACF) on a printed metal circuit board. This study presents rapid large-area synthesis of hydrogenated amorphous carbon (a-C:H) thin films and their use as the UACF. Since the synthesized a-C:H thin film has electrical transparency, the metal/a-C:H hybrid board reflects the complexity of the underlying metal circuit board. The a-C:H thin film electrically connects the cracked area of the metal line; thus, the hybrid circuit board is foldable without resistance change during repeated folding cycles. The metal/UACF hybrid circuit board can be applied to the fabrication of various foldable electronic devices.

Note: A compact microwave plasma enhanced chemical vapor deposition based on a household microwave oven

I designed an efficient and compact microwave plasma enhanced chemical vapor deposition (MW-PECVD) based on a household 2.45 GHz microwave oven. In the MW-PECVD, the microwave plasma was sparked by a piece of Cu foil in a low pressure down to 1 Pa. The SiC plate is not only used to realize rapid microwave heating-up but also to prevent the reflected power from damaging the magnetron. To test the performance of the system, vertically oriented graphene nanosheets were fabricated on the Cu foil. The products were characterized by Raman spectra and scanning electron microscope.

Superlubricity of hydrogenated carbon films in a nitrogen gas environment: adsorption and electronic interactions at the sliding interface

We proposed a superlubricity mechanism of hydrogenated carbon films based on surface hydrogen bonds. Theoretical calculations indicating the proposed is reasonable.

A sponge network-shaped Mn3O4/C anode derived from a simple, one-pot metal organic framework-combustion technique for improved lithium ion storage

Sponge shaped Mn₃O₄/C anode derived from simple, one-pot MOF-C technique exhibits excellent cyclability for lithium ion batteries.

Ab Initio Investigation on Cu/Cr Codoped Amorphous Carbon Nanocomposite Films with Giant Residual Stress Reduction

Amorphous carbon films (a-C) codoped by two metal elements exhibit the desirable combination of tribological and mechanical properties for widely potential applications, but are also prone to catastrophic failure due to the inevitable residual compressive stress. Thus far, the residual stress reduction mechanism remains unclear due to the insufficient understanding of the structure from the atomic and electronic scale. In this paper, using ab initio calculations, we first designed a novel Cu/Cr codoped a-C film and demonstrated that compared with pure and Cu/Cr monodoped cases, the residual stress in Cu/Cr codoped a-C films could be reduced by 93.6% remarkably. Atomic bond structure analysis revealed that the addition of Cu and Cr impurities in amorphous carbon structure resulted in the critical and significant relaxation of distorted C-C bond lengths. On the other hand, electronic structure calculation indicated a weak bonding interaction between the Cr and C atoms, while the antibonding interaction was observed for the Cu-C bonds, which would play a pivot site for the release of strain energy. Those interactions combined with the structural evolution could account for the drastic residual stress reduction caused by Cu/Cr codoping. Our results provide the theoretical guidance and desirable strategy to design and fabricate a new nanocomposite a-C films with combined properties for renewed applications.

Water Lubrication of Stainless Steel using Reduced Graphene Oxide Coating

Lubrication of mechanical systems using water instead of conventional oil lubricants is extremely attractive from the view of resource conservation and environmental protection. However, insufficient film thickness of water due to low viscosity and chemical reaction of water with metallic materials have been a great obstacle in utilization of water as an effective lubricant. Herein, the friction between a 440 C stainless steel (SS) ball and a 440 C stainless steel (SS) plate in water lubrication could be reduced by as much as 6-times by coating the ball with reduced graphene oxide (rGO). The friction coefficient with rGO coated ball in water lubrication was comparable to the value obtained with the uncoated ball in oil lubrication. Moreover, the wear rate of the SS plate slid against the rGO coated ball in water lubrication was 3-times lower than that of the SS plate slid against the uncoated ball in oil lubrication. These results clearly demonstrated that water can be effectively utilized as a lubricant instead of oil to lower the friction and wear of SS components by coating one side with rGO. Implementation of this technology in mechanical systems is expected to aid in significant reduction of environmental pollution caused by the extensive use of oil lubricants.