Ultrathin Carbon Films Research Articles

Atomic scale in-situ observation of gas-solid interaction regulating the pre-nucleation process of Pd atomic clusters

Advancements in nanotechnology have propelled the understanding of atomic-scale nucleation processes, essential for the evolution of atomic manufacturing. The process of amorphous precursors nucleation showcases a complex transition influenced by various factors. Utilizing aberration-corrected ETEM and theoretical calculation, we explore the nucleation of amorphous Pd atomic clusters. This study examines the nucleation dynamics and gas-solid interaction regulating of Pd clusters on ultrathin carbon films, prepared via electron beam evaporation. HRTEM observation and FFT analysis reveal that, in the early stage of nucleation, Pd cluster growth predominantly follows an Ostwald ripening-like mechanism. Atoms from smaller clusters migrate and attach to larger ones, facilitating their progression to critical nucleation size. Environmental conditions significantly influence this process; hydrogen atmospheres lower the surface energy of Pd clusters, reducing the critical nucleation size, while argon atmospheres impede growth of Pd clusters by occupying migration sites on the carbon surface. These insights into atomic cluster behavior and environmental interactions are crucial for understanding the early stages of nucleation from amorphous to crystalline and can help opens new avenues for the controlled fabrication of materials with optimized functionalities.

Ultra-thin DLC diaphragm-based optical fiber sensor achieving a highly sensitive and broadband acoustic response.

In the design of an extrinsic Fabry-Perot interferometer (EFPI) acoustic sensor, broadband response and high-sensitivity sensing are usually conflicting and need to be carefully balanced. Here, we present a novel, to the best of our knowledge, optical fiber acoustic sensor based on an ultra-thin diamond-like carbon (DLC) film, fabricated using the plasma-enhanced chemical vapor deposition method, and transferred by a surface-energy-assisted method. The sensor exhibits a broadband response ranging from 200 Hz to 100 kHz, maintains an average sensitivity of 457.3 mV/Pa within the range of 6 to 30 kHz, and can detect weak acoustic signals down to 3.23 µPa/Hz1/2@16.19 kHz. The combination of an ultra-thin DLC film with a relatively high Young's modulus and internal stresses results in a trade-off between high sensitivity and a broadband response. This performance demonstrates that our sensor is among the most advanced in the EFPI acoustic sensor family, with significant potential for applications such as photoacoustic spectroscopy, defect diagnosis, and bio-imaging.

Atomic scale smoothing of nanoscale quartz mold using amorphous carbon films

Abstract Surface roughness control of end products is increasingly becoming significant, especially with the miniaturization trends in the semiconductor industry. Ultra-thin amorphous carbon (a-C) films offer a prime solution to optimize surface roughness due to their outstanding characteristics. In this study, hydrogenated a-C films are deposited on two-dimensional quartz plates and three-dimensional quartz molds to evaluate the growth mechanisms and changes in the surface roughness, which is supported by molecular dynamics simulations. Results reveal that surface roughness encounters multiple variations until it reaches stable values. These fluctuations are categorized into four different stages which provide a concrete understanding of various growing mechanisms at each stage. Different behavior of the atoms in the top layers is recorded in the cases of normal and grazing incidents of carbon atoms. Lower surface roughness values are obtained at low-angle deposition. Interestingly, surface smoothing is attained on the sidewalls of the nanotrench mold where the deposition occurs with high incident ion angles.

Ultrathin carbon film as ultrafast rechargeable cathode for hybrid sodium dual-ion capacitor

The development of electrochemical energy storage devices has a decisive impact on clean renewable energy. Herein, novel ultrafast rechargeable hybrid sodium dual-ion capacitors (HSDICs) were designed by using ultrathin carbon film (UCF) as the cathode material. The UCF is synthesized by a simple low temperature catalytic route followed by an acid leaching process. UCF owns a large adsorption interface and number of additional active sites, which is due to the nitrogen doping. In addition, there exists several short-range order carbons on the surface of UCF, which are beneficial for anionic storage. An ultrafast rechargeable remarkable performance, remarkable anion hybrid storage capability and outstanding structure stability is fully tapped employing UCF as cathode for HSDICs. The electrochemical performance of UCF in a half-cell system at the operating voltage between 1.0 and 4.8 V, achieving an admirable specific discharge capacity of 358.52 mAh·g−1 at 500 mA·g−1, and a high capacity retention ratio of 98.42% after cycling 2500 times at 1000 mA·g−1, respectively. Besides, with the support of ex-situ TEM and EDS mapping, the structural stability principle and anionic hybrid storage mechanism of UCF electrode are investigated in depth. In the full-cell system, HSDICs with the UCF as cathode and hard carbon as anode also presents a super-long cycle stability (80.62% capacity retention ratio after cycling 1300 times at 1000 mA·g−1).

In-situ zinc vanadate layer derived from highly hydrophilic substrate for PEC performance enhancement of Zn-doped BiVO4 photoanode

Owing to serious concerns regarding environmental issues, extensive research is being conducted to develop eco-friendly and sustainable energy sources. One promising solution is the utilization of solar energy for energy production using photoelectrochemical (PEC) methods. However, the performance of photoanodes is frequently hindered by high recombination rates and inadequate charge transport. To address these issues, we designed an approach that incorporates an ultrathin hydrophilic carbon (UTHC) film on a substrate. The UTHC film enhanced the hydrophilicity of the FTO surface and enabled the synthesis of a zinc vanadate layer for efficient charge transfer. As a conductive bridge, the zinc vanadate layer promotes effective charge transfer for excellent PEC performance. The resulting carbon film/Zn-doped BiVO4 (CZB) photoanode exhibited significantly improved PEC performance, achieving a remarkable photocurrent density of 1.515 mA∙cm−2 and a separation efficiency of 9.58 % at 1.23 VRHE. This study demonstrates a potential method for enhancing PEC performance for sustainable energy conversion using a highly hydrophilic metal oxide layer on an FTO substrate.

Synergetic improvements in surface hydrophobicity and wear resistance of TC4 materials via the combination of rapid heating and EtOH quenching methods

Ti-6Al-4V (TC4) materials with high hydrophobicity and wear resistance improve anticorrosion performance when utilized in offshore conditions. In this work, a novel strategy for simultaneously enhancing the surface hydrophobicity and wear resistance of surface textured TC4 (selected laser melting, SLM-TC4) materials was proposed. An in-situ deposition of ultrathin carbon film is realized via rapid induction heating followed by the EtOH quenching (IHQ-TC4) process. After the IHQ process, the surface chemical composition evolves from Ti (SLM-TC4) to the mixture of carbon film and TiO2 nanoparticles (IHQ-TC4), and the corresponding surface roughness decreases, which results in a surface wettability transition from hydrophilicity (SLM-TC4) to hydrophobicity (IHQ-TC4, 125°). Molecular dynamics simulations were utilized to explore the wettability transition mechanism, and found that the surface chemical composition evolution is the dominant factor, and the carbon film is responsible for the hydrophobicity of IHQ-TC4. Moreover, the surface hardness and wear resistance of IHQ-TC4 are greatly enhanced compared to those of SLM-TC4. The collective enhancements to the hydrophobicity and wear resistance of TC4 materials via the IHQ process provide a novel and facile strategy for enhancing the anticorrosion performance of TC4 materials utilized in offshore conditions.

Anti-Stokes Raman spectroscopy for probing functional groups in amorphous carbon thin films

Ultra-thin amorphous carbon (a-C) films are well established protective coatings of optical fibers. These coatings allow one to prevent degradation of the SiO2 fiber, which occurs due to diffusion of the water and hydrogen molecules into cladding and core. The a-C films typically contain impurities, such as oxygen and hydrogen, which are attached to organic moieties via chemical bonding. The formation of hydrogen- and oxygen-containing functional groups reduces the hermeticity of a-C coatings, and therefore, monitoring these impurities is of great importance. In this work, we develop a method for probing O- and H- containing moieties based on resonance anti-Stokes Raman spectroscopy. We measured Raman spectra of a-C films and observed that anti-Stokes to Stokes ratios of Raman peaks differ from those predicted by Boltzmann law. This effect caused by resonance enhancement of the anti-Stokes Raman scattering in defects of graphite-like crystals. To quantify this effect, we used a resonance factor, which is defined as a ratio of the anti-Stokes and Stokes scattering cross sections. We show that this indicator can be used to assess degree of enrichment/depletion of a-C with O- and H- containing functional groups. Understanding the physical mechanisms of the anomalous anti-Stokes Raman scattering will improve Raman thermometry.

The Use of Sacrificial Graphite-like Coating to Improve Fusion Efficiency of Copper in Selective Laser Melting

Thin and ultrathin carbon films reduce the laser energy required for copper powder fusion in selective laser melting (SLM). The low absorption of infrared (IR) radiation and its excellent thermal conductivity leads to an intricate combination of processing parameters to obtain high-quality printed parts in SLM. Two carbon-based sacrificial thin films were deposited onto copper to facilitate light absorption into the copper substrates. Graphite-like (3.5 µm) and ultra-thin (25 nm) amorphous carbon films were deposited by aerosol spraying and direct current magnetron sputtering, respectively. The melting was analyzed for several IR (1.06 µm) laser powers in order to observe the coating influence on the energy absorption. Scanning electron microscopy showed the topography and cross-section of the thermally affected area, electron backscatter diffraction provided the surface chemical composition of the films, and glow-discharge optical emission spectroscopy (GDOES) allowed the tracking of the in-deep chemical composition of the 3D printed parts using carbon film-covered copper. Ultra-thin films of a few tens of nanometers could reduce fusion energy by about 40%, enhanced by interferences phenomena. Despite the lower energy required, the melting maintained good quality and high wettability when using top carbon coatings. A copper part was SLM printed and associated with 25 nm of carbon deposition between two copper layers. The chemical composition analysis demonstrated that the carbon was intrinsically removed during the fusion process, preserving the high purity of the copper part.

Freestanding Ultrathin Precisely Structured Hierarchical Porous Carbon Blackbody Film for Efficient Solar Interfacial Evaporation

Solar‐energy‐powered interfacial evaporation is the most meaningful strategy for energy utilization, water desalination, and mineral purification. It can achieve high efficiency, low‐density energy, and sustainable harvest and utilization. However, the microstructure and surface/interface design still lead to a balance between solar–thermal conversion, water conduction, and thermal management, which also determines the efficiency of photothermal interfacial evaporation. Here, a free‐standing, ultrathin carbon film with a tunable nanopore diameter is prepared and used as a blackbody layer for solar photothermal evaporation. By 3D reconstruction methods, the effect of pore structure on interfacial evaporation is systematically studied. Hierarchical porous carbon film with an average pore size of about 300 nm exhibits outstanding photothermal evaporation performance, reaching up to 1.96 kg m−2 h−1 with excellent stability. Ultra‐hydrophobic, optically enhanced absorption graphene array is constructed on the carbon film surface through femtosecond laser nanoprocessing, further increasing the evaporation rate to 2.12 kg m−2 h−1 (1 sun) and 5.55 kg m−2 h−1 (3 suns).

Nano- and Micro-Scale Impact Testing of Hard Coatings: A Review

In this review, the operating principles of the nano-impact test technique are described, compared and contrasted to micro- and macro-scale impact tests. Impact fatigue mechanisms are discussed, and the impact behaviour of three different industrially relevant coating systems has been investigated in detail. The coating systems are (i) ultra-thin hard carbon films on silicon, (ii) DLC on hardened tool steel and (iii) nitrides on WC-Co. The influence of the mechanical properties of the substrate and the load-carrying capacity (H3/E2) of the coating, the use of the test to simulate erosion, studies modelling the nano- and micro-impact test and performing nano- and micro-impact tests at elevated temperature are also discussed.

In situ tensile and fracture behavior of monolithic ultra-thin amorphous carbon in TEM

Even while being important components in day-to-day life and in advanced technology, the wider application of amorphous solids is limited by their brittle behavior. Although amorphous solids have been reported to show plasticity at the nanoscale, studies have so far been limited to metallic and oxide glasses. Here, we report on the tensile and fracture behavior of monolithic ultra-thin amorphous carbon (a-C) films during in situ nanomechanical testing inside a transmission electron microscope (TEM). Our results show that ultra-thin a-C films exhibit large plastic strain under uniaxial tension while retaining high strength. Beam-off tests confirm that the plasticity is not induced by electron-beam effects during testing. Consecutive cyclic tests and Raman spectra reveal that the plasticity results from an increased nanoporosity, and graphitic cluster size increases and bond/cluster alignments along the tensile direction occur and likely contributes to stiffening of the a-C film. Despite the large plastic strain, catastrophic failure still occurred accompanied by the formation of multiple shear bands, which has never been reported for amorphous carbon. This study serves as a basis for our better understanding of the mechanical behavior of amorphous solids such as ultra-thin a-C, and provides new opportunities in design of flexible electronics, mechanical nanocomponents, and nanocomposites.

Multiple reinforcement effect induced by gradient carbon coating to comprehensively promote lithium storage performance of Ti2Nb10O29

The synchronous improvement of ionic diffusivity and electronic conductivity of Ti2Nb10O29 (TNO) is of enormous significance for boosting its high electrochemical performance. In our work, a novel gradient carbon coating strategy was first proposed to synthesize the pomegranate-type N-doped carbon coated TNO microspheres (TNO@NPC), in which not only TNO microspheres but also TNO secondary nanoparticles surfaces are uniformly coated with an ultrathin carbon film. The study results demonstrate that such ingenious configuration can combine conductive coatings, nanocrystallization technology, and defect engineering together to greatly improve the ionic diffusivity and electronic conductivity. Moreover, the carbon coatings as the armor can effectively inhibit the volume change of TNO, and thus enhance its cycling durability. Density functional theory (DFT) calculations were also employed to illustrate the nature influence on lithium-ion diffusion coefficient and electronic conductivity. Attributing to the synergistic effect, the TNO@NPC exhibit superior rate capability (328 mA h g−1 at 0.1 C and 258 mA h g−1 at 10 C) and remarkable cyclability (210 mA h g−1 at 10 C after 1000 cycles) in half-cells. The full-cell of LiFePO||TNO@NPC also show notable rate capability (271 mA h g−1 at 0.2 C and 211 mA h g−1 at 10 C) and remarkable cyclability (178 mA h g−1 at 10 C after 1000 cycles). This ingenious structural design may provide a new direction for the construction of other high-quality electrodes in lithium-ion batteries (LIBs).

Fullerphene Nanosheets: A Bottom‐Up 2D Material for Single‐Carbon‐Atom‐Level Molecular Discrimination

AbstractUltrathin 2D nanoporous materials offer enhanced sensitivity and high spatial resolution in sensing applications making them important for the selective discrimination of guest molecules. Here bottom‐up fabrication is reported of a novel molecularly‐thin nitrogen‐doped 2D fullerphene. Thermal annealing at 700 °C of a bottom‐up assembled fullerene C60‐ethylenediamine (EDA) thin film results in formation of a nitrogen‐doped ultrathin carbon film, fullerphene, which exhibits a hierarchically micro/mesoporous structure at its surfaces. N‐doping of fullerphene is dominated by pyrrolic and quaternary nitrogen atoms, which allow selective and repetitive adsorption and desorption of low‐molecular‐weight carboxylic acid vapors through noncovalent interactions. The large surface area (655.2 m2 g–1) and pore volume (0.659 cc g–1) offered by the hierarchical micro/mesoporous architecture leads to superior sensitivity of fullerphene to formic acid over acetic acid in the vapor phase demonstrating that novel 2D fullerphene provides an attractive platform for the discrimination of carboxylic acids at the single‐carbon‐atom level.

MoC quantum dots embedded in ultra-thin carbon film coupled with 3D porous g-C3N4 for enhanced visible-light-driven hydrogen evolution

The main purpose of photocatalytic hydrogen evolution is to fundamentally solve the problem of energy shortage and environmental pollution. In this experiment, based on the adjustment of the density of MoC quantum dots (MoC-QDs) on carbon film and the morphology of 3D porous g-C3N4, this exploring aimed at exploring the influence of various morphology combinations on the hydrogen evolution performance. Using bulk g-C3N4 (CN-B) as a reference, the tubular and honeycomb g-C3N4 were prepared by solvothermal and chemical vapor deposition methods. The experimental results show that the hydrogen production of MoCT-7 and MoCH-5 composite catalysts are 1.54 and 1.76 times that of MoCB-15, respectively, which proves that the ingenious morphology matching is an effective strategy to improve the catalytic performance. It is believed that CN-H and CN-T have unique slow photo effect and directional electron transfer characteristics, respectively. The well-dispersed MoC-QDs provide abundant active sites, and the thin carbon film is conducive to the adsorption of dye molecules and electrons transfer. This experiment is expected to provide some references for the in-depth study of g-C3N4 and the design of novel photocatalysts.

Ultra-thin N-doped carbon coated SnO2 nanotubes as anode material for high performance lithium-ion batteries

Tin dioxide nanotubes coated with ultrathin N-doped carbon film (N-doped SnO2/C NTs) are prepared through a sacrificial template method for the first time. It was employed as anodes for lithium-ion batteries (LIBs) and delivered a high reversible capacity of 909.5 mAh g−1 at 0.5 A g−1 after 200 cycles, outstanding stability 551.7 mAh g−1 after 500 cycles at 1 A g−1, and excellent rate performance of 1069.2 mAh g−1 after 280 cycles. Such superior electrochemical performance is owning to the N-doped carbon coating which improved the conductivity of the NTs, which is essential for higher performance LIBs. The special designed whole nanotube structure provides extensive surface and pores to accommodate Li, meanwhile, prohibited the volume expansion during cycling test. The electrochemical performanceof pouch-type cells further demonstrates the SnO2/C NTs as a promising candidate for LIBs anode. This study has shed a light on the LIB anode materials design and preparation and made such hollow nanostructured materials a potential candidate to replace commonly used graphite materials.

MoC quantum dots modified by CeO2 dispersed in ultra-thin carbon films for efficient photocatalytic hydrogen evolution

MoC quantum dots are dispersed in a carbon film by the temperature-programmed method. The hybrid catalyst is obtained by the mixed solution method, and the hybrid catalyst is optimized by adjusting the content of CeO2 to obtain the composite catalyst 15%-COMCC with the best photocatalytic hydrogen evolution activity. SEM and TEM show that there is an intimate interface contact between CeO2 and MoC-QDs/C, which provides the basis for smooth electron transfer. It is proved by XPS that there is a strong interaction force between the catalysts, which provides a evidence for electron transfer between semiconductors. It is proved by electrochemistry that the introduction of CeO2 can effectively reduce the hydrogen evolution potential and provide powerful conditions for the hydrogen production of the hybrid catalyst. The carbon film has excellent conductivity, can effectively suppresses the recombination of photo-generated carriers, and accelerate the separation of carriers between the interfaces. MoC quantum dots with high dispersibility embedded in the carbon film provide a lot of active sites for photocatalytic hydrogen production. This research provides an effective strategy for the application of ultra-thin carbon film in photocatalytic hydrogen evolution, the loading of quantum dots, and the design and synthesis of non-noble metals.

Thermal stability and diffusion characteristics of ultrathin amorphous carbon films grown on crystalline and nitrogenated silicon substrates by filtered cathodic vacuum arc deposition

Amorphous carbon (a-C) films are widely used as protective overcoats in many technology sectors, principally due to their excellent thermophysical properties and chemical inertness. The growth and thermal stability of sub-5-nm-thick a-C films synthesized by filtered cathodic vacuum arc on pure (crystalline) and nitrogenated (amorphous) silicon substrate surfaces were investigated in this study. Samples of a-C/Si and a-C/SiNx/Si stacks were thermally annealed for various durations and subsequently characterized by high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The TEM images confirmed the continuity and uniformity of the a-C films and the 5-nm-thick SiNx underlayer formed by silicon nitrogenation using radio-frequency sputtering. The EELS analysis of cross-sectional samples revealed the thermal stability of the a-C films and the efficacy of the SiNx underlayer to prevent carbon migration into the silicon substrate, even after prolonged heating. The obtained results provide insight into the important attributes of an underlayer in heated multilayered media for preventing elemental intermixing with the substrate, while preserving the structural stability of the a-C film at the stack surface. An important contribution of this investigation is the establishment of an experimental framework for accurately assessing the thermal stability and elemental diffusion in layered microstructures exposed to elevated temperatures.

First-principles study of structural and opto-electronic characteristics of ultra-thin amorphous carbon films

Most amorphous carbon (a-C) applications require films with ultra-thin thicknesses; however, the electronic structure and opto-electronic characteristics of such films remain unclear so far. To address this issue, we developed a theoretical model based on the density functional theory and molecular dynamic simulations, in order to calculate the electronic structure and opto-electronic characteristics of the ultra-thin a-C films at different densities and temperatures. Temperature was found to have a weak influence over the resulting electronic structure and opto-electronic characteristics, whereas density had a significant influence on these aspects. The volume fraction of sp3 bonding increased with density, whereas that of sp2 bonding initially increased, reached a peak value of 2.52 g/cm3, and then decreased rapidly. Moreover, the extinction coefficients of the ultra-thin a-C films were found to be density-sensitive in the long-wavelength regime. This implies that switching the volume ratio of sp2 to sp3 bonding can effectively alter the transmittances of ultra-thin a-C films, and this can serve as a novel approach toward photonic memory applications. Nevertheless, the electrical resistivity of the ultra-thin a-C films appeared independent of temperature. This implicitly indicates that the electrical switching behavior of a-C films previously utilized for non-volatile storage applications is likely due to an electrically induced effect and not a purely thermal consequence.

Characterization of Ultra-Thin Diamond-Like Carbon Films by SEM/EDX

A novel, high throughput method to characterize the chemistry of ultra-thin diamond-like carbon films is discussed. The method uses surface sensitive SEM/EDX to provide substrate-specific, semi-quantitative silicon nitride/DLC stack composition of protective films extensively used in the hard disk drives industry and at Angstrom-level. SEM/EDX output is correlated to TEM to provide direct, gauge-capable film thickness information using multiple regression models that make predictions based on film constituents. The best model uses the N/Si ratio in the films, instead of separate Si and N contributions. Topography of substrate/film after undergoing wear is correlatively and compositionally described based on chemical changes detected via the SEM/EDX method without the need for tedious cross-sectional workflows. Wear track regions of the substrate have a film depleted of carbon, as well as Si and N in the most severe cases, also revealing iron oxide formation. Analysis of film composition variations around industry-level thicknesses reveals a complex interplay between oxygen, silicon and nitrogen, which has been reflected mathematically in the regression models, as well as used to provide valuable insights into the as-deposited physics of the film.

High hydrogen uptake by a metal-graphene-microporous carbon network

High-surface area carbon nanomaterials are promising candidate as reversible physisorption materials for hydrogen storage in personal transportation vehicles at moderate temperatures and pressures. Metal-incorporated graphitic microporous carbon is considered to be an excellent H2 storage material due to high molecular hydrogen uptake at the micropores coupled with considerable H2 adsorption at the graphitic network. A simple, cost-effective sputtering technique is adopted to fabricate metal-incorporated graphitic microporous carbon film and differential resistance measurements are carried out in H2 ambient to observe the high hydrogen uptake within the samples. Ultrathin amorphous carbon film is irradiated with metal nanoparticles which converts it into graphitic carbon, whereas sputtering plasma acts as dry-etchant to activate it into microporous carbon. Average number of graphene layer formation is observed to be dependent on sputtering parameters (current/voltage/time), which manifest bi-layer to multi-layer graphene sheets. With increase in the graphene layers, hydrogen adsorption also increases due to a four-fold effect - higher molecular hydrogen uptake at the graphene layers, more active sites into the micropores, promotion of molecular dissociation into atomic hydrogen by the metal nanoparticles, followed by adsorption at the active surface sites and the formation of hydrogenated carbon via destruction of the π-bonds.