The sp2 and sp3 fractions of unknown carbon materials: electron energy-loss near-edge structure analysis of C-K spectra acquired under the magic-angle condition by the electron nanobeam technique

Spectral and microstructural analysis of the effect of the Ga+implantation on diamond: a CL-EELS study

Due to its capacity to achieve nanometre-scale machining and lithography, a focused ion beam (FIB) is an extended tool for semiconductor device fabrication and development, in particular, for diamond-based devices. However, some technological steps are still not fully optimized for its use. Indeed, ion implantation seems to affect the crystalline structure and electrical properties of diamond. For this study, a boron-doped ([B] ∼ 1017atoms·cm-3) diamond layer grown by chemical vapour deposition was irradiated using Ga+by FIB, with 1 nA current and 5, 20, and 30 keV of acceleration voltage. The Ga+implanted diamond layer has been analysed through cathodoluminescence (CL) and scanning transmission electron microscopy (STEM)-related techniques. The beam penetration depth has been simulated by Monte Carlo calculations of both Ga+(FIB) and e-(CL) beams at different energies. The comparative CL analysis of the layer as-grown and after implantation revealed peaks related to defects, such as A band, H3 centre, and defects present in the green band region. The STEM studies for the 30 keV implanted sample showed that the diamond lattice is affected by the damage, evidencing amorphisation in the layer with a sp2/sp3ratio of 1.37, estimated by electron energy loss spectroscopy. Therefore, this study highlights the effects of the Ga+implantation on the optical and structural characteristics of diamond, using different methods.

Highly cross-linked carbon tube aerogels with enhanced elasticity and fatigue resistance

Carbon aerogels are elastic, mechanically robust and fatigue resistant and are known for their promising applications in the fields of soft robotics, pressure sensors etc. However, these aerogels are generally fragile and/or easily deformable, which limits their applications. Here, we report a synthesis strategy for fabricating highly compressible and fatigue-resistant aerogels by assembling interconnected carbon tubes. The carbon tube aerogels demonstrate near-zero Poisson's ratio, exhibit a maximum strength over 20 MPa and a completely recoverable strain up to 99%. They show high fatigue resistance (less than 1.5% permanent degradation after 1000 cycles at 99% strain) and are thermally stable up to 2500 °C in an Ar atmosphere. Additionally, they possess tunable conductivity and electromagnetic shielding. The combined mechanical and multi-functional properties offer an attractive material for the use in harsh environments.

Abnormally High-Lithium Storage in Pure Crystalline C60 Nanoparticles

Li⁺ intercalates into a pure face-centered-cubic (fcc) C₆₀ structure instead of being adsorbed on a single C₆₀ molecule. This hinders the excess storage of Li ions in Li-ion batteries, thereby limiting their applications. However, the associated electrochemical processes and mechanisms have not been investigated owing to the low electrochemical reactivity and poor crystallinity of the C₆₀ powder. Herein, a facile method for synthesizing pure fcc C₆₀ nanoparticles with uniform morphology and superior electrochemical performance in both half- and full-cells is demonstrated using a 1 m LiPF₆ solution in ethylene carbonate/diethyl carbonate (1:1 vol%) with 10% fluoroethylene carbonate. The specific capacity of the C₆₀ nanoparticles during the second discharge reaches ≈750 mAh g^-1 at 0.1 A g^-1 , approximately twice that of graphite. Moreover, by applying in situ X-ray diffraction, high-resolution transmission electron microscopy, and first-principles calculations, an abnormally high Li storage in a crystalline C₆₀ structure is proposed based on the vacant sites among the C₆₀ molecules, Li clusters at different sites, and structural changes during the discharge/charge process. The fcc of C₆₀ transforms tetragonal via orthorhombic Li_x C₆₀ and back to the cubic phase during discharge. The presented results will facilitate the development of novel fullerene-based anode materials for Li-ion batteries.

Properties and Classification of Diamond-Like Carbon Films

Diamond-like carbon (DLC) films have been extensively applied in industries owing to their excellent characteristics such as high hardness. In particular, there is a growing demand for their use as protective films for mechanical parts owing to their excellent wear resistance and low friction coefficient. DLC films have been deposited by various methods and many deviate from the DLC regions present in the ternary diagrams proposed for sp³ covalent carbon, sp² covalent carbon, and hydrogen. Consequently, redefining the DLC region on ternary diagrams using DLC coatings for mechanical and electrical components is urgently required. Therefore, we investigate the sp³ ratio, hydrogen content, and other properties of 74 types of amorphous carbon films and present the classification of amorphous carbon films, including DLC. We measured the sp³ ratios and hydrogen content using near-edge X-ray absorption fine structure and Rutherford backscattering-elastic recoil detection analysis under unified conditions. Amorphous carbon films were widely found with nonuniform distribution. The number of carbon atoms in the sp³ covalent carbon without bonding with hydrogen and the logarithm of the hydrogen content were inversely proportional. Further, we elucidated the DLC regions on the ternary diagram, classified the amorphous carbon films, and summarized the characteristics and applications of each type of DLC.

Quantitative Analysis Method for Nitrogen Electron Energy-Loss Near-Edge Structures in Nanocarbons Based on Density Functional Theory Calculations and Linear Regression

Nonmetallic heteroatoms found in carbon nanomaterials act as active sites and exhibit excellent catalytic performance. Owing to structural complexity and the limitations of characterization technology, the identification of active sites in nanocarbon is challenging and controversial. Electron energy-loss spectroscopy is an electron microscope technique with high spatial resolution and a powerful tool for identifying the arrangement of heteroatoms. However, structural information regarding the configuration and distribution of heteroatoms is difficult to obtain using existing analytical methods. Herein, we have developed a method for the quantitative analysis of electron energy-loss near-edge structures to identify accurately nitrogen species in nanocarbon. Based on this approach, the relative amounts of nitrogen species were obtained from linear regression with calculated spectra. The concentration distribution of nanocarbon obtained by this method was consistent with the result of X-ray photoelectron spectroscopy analysis at different depths. Therefore, this fitting method can be used for the quantitative analysis of nitrogen K-edge structures. This provides a new strategy for studying the structure-activity relationships of carbon-based materials and the further design of custom nanocarbon catalysts with high active site densities.

Structural studies of carbons by neutron and x-ray scattering

Carbon can have many different forms and the characterisation of structural features on a length scale of 1 Å to 10 μm is important in defining its physical and chemical properties for the various forms. The use of either electro-magnetic (x-ray) or particle (neutron) beams plays an important role in determining these characteristics. In this paper, we review the various techniques that are used to determine the structural features by experimental means and how the data are processed to give the required information in a suitable form for detailed analysis by computer simulation. Diffraction methods are used for studies of the atomic arrangement and small-angle scattering techniques are used for studies of microporosity in the sample materials. The experimental data obtained from a wide range of different carbon materials are considered and how these results can be used as a basis for modelling the structures in a quantitative manner is also considered. This information underpins their use as active components in a wide range of functional materials.