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The recent observation of superconductive effects in rhombohedral graphene and in pyrolytic graphite systems exhibiting stacking faults have attracted a significant attention. Here we report an advanced investigation of stacking faults in multilayered lamellae of natural graphite and grafoil, by employing a combination of Raman point/mapping spectroscopy, scanning and transmission electron microscopy (SEM, TEM/HRTEM). The presented work identifies significant local structural transitions and an anomalous stabilization of rhombohedral stacking order occurring within μm-scale ripplocation-like defect-structures (first-category of stacking fault). Interestingly, we demonstrate an abrupt enhancement in the intensity of the left shoulder of the 2D band (of the Raman spectra) in sample's regions exhibiting an intersection between these defect structures. Extensive Raman mapping analyses demonstrate coexistence of rhombohedral ABC and Bernal ABA phases also within other sample's regions (second category of stacking-fault). This interpretation is further supported by comparative analyses performed in as-purchased strain-rich grafoil films. Interestingly, no structural relaxation of rhombohedral ABC stacking into ABA Bernal ordering was found in the analysed defect-regions.

Fe3C filled carbon nanotubes (CNTs) self-organized into flexible-film-morphologies (buckypapers) have been proposed for numerous applications, these include flexible data-storage-devices, exchange-bias, spin-based-systems, flexible ferromagnetic-electrodes and others. However, despite the important progress, the significant concentration of Cl-containing-hydrocarbons which is needed for the buckypaper-growth (i.e. 1 to 10 ml) represents still an important challenge for industrial-production.Here we report the experimental-growth-parameters needed for the nucleation and growth of flexible Fe3C-filled-CNT buckypapers, under very-low-concentrations of dichlorobenzene, as low as 0.05 ml.By carefully estimating both the heating- and cooling-rate parameters of the chosen chemical-vapor-deposition (CVD) reactor, we demonstrate the identification of two active-growth-regions which allow for the simultaneous nucleation and growth of ferromagnetically-filled buckypapers. The obtained films comprise of selectively grown single-wall (active-region-1) and multiwall (active-region-2) CNTs. The simultaneous growth of the two types of buckypapers within the same reactor is discussed and attributed to the dynamics of dichlorobenzene-pyrolysis, which appears to yield a higher concentration of Cl-radicals in the active-region-1. In the buckypapers grown in the latter (active-region-1) we highlight an unusual separation between the first (inner) and second CNT-cylinders, with the HRTEM analyses revealing an anomalously-large interlayer-distance varying from ∼ 1.6 to ∼ 6.6 nm (an effective void between two CNT-cylinders).

We report the result of a novel structural-, electronic- and magnetic-investigation of exfoliated highly-oriented-pyrolytic-graphite (HOPG) samples exhibiting distorted-moiré-superlattices. Field-dependent-magnetometry of pre-selected lamellae revealed the presence of an anomalous-transition occurring from a vortex-like-ferrimagnetic-hysteresis to a ferromagnetic-behavior as the maximum-field was increased from 10 Oe to 800 Oe (T∼ 250 K). The observed as-acquired hysteresis resembled those intrinsic-signals reported by Scheike et al. and Shuai et al. in superconductive- and ferrimagnetic-HOPG. We highlight an anomalous field-dependent-magnetic-response from 10 Oe to 200 Oe, as also evidenced by susceptibility-plots, with a ferromagnetic-transition occurring at 120 Oe. Further, scanning-tunneling-microscopy (STM) and scanning-tunneling-spectroscopy (STS) acquisitions at T∼77 K highlighted an unusual broadening in the van Hove singularities, possibly a confirmation of disorder-induced-ferromagnetism.

The recent discovery of an innovative chemical vapour synthesis (CVS) approach for the encapsulation and stabilization of high-spin ferromagnetic γ-Fe nanocrystals inside carbon nano-onions (CNOs) has attracted significant attention. Stabilization of the γ-phase of iron is of particular interest for possible applications in self-regulating hyperthermic dissipative systems, under specific conditions of magnetic tuning. Here, we explore a further modification of the synthesis method, by adding controlled quantities of nickelocene into mixtures of ferrocene, dichlorobenzene and sulfur. In these experiments, sulfur plays a crucial role in stabilizing the face centred cubic (FCC) γ-FeNi phase, up to relative abundances of 94%. The structural and magnetic properties were investigated by employing SEM, TEM, HRTEM, XRD, Rietveld refinements, temperature dependent SQUID magnetometry and T-ESR. The presence of a transition from a high-temperature ferromagnetic state at TC1 ~ 400 K to a low-temperature disordered frozen magnetic state at TC2 ~ 60 K is further discussed. [ABSTRACT FROM AUTHOR]

homogenous membrane composed of chitosan (CS), sodium carboxymethyl cellulose (NaCMC) and nano hydroxyapatite (n-HA) was prepared by a gradual electrostatic assembling (GEA) method. The physical and chemical properties of the membranes with different n-HA contents and CS/NaCMC ratios were characterized by Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and mechanical test. The schematic formation mechanism of the membrane was discussed. The results show that GEA is an effective method to prepare the polyelectrolyte complex (PEC) membrane, in which oppositely charged CS-NaCMC polysaccharides can assemble mildly and gradually through electrostatic interaction to form the membrane framework, while the filled n-HA crystals can regulate the structure stability of the composite membrane. The optimum preparation condition for the PEC membrane can be fixed to a content of 60 wt% n-HA, an equivalent amount of CS to NaCMC and a drying temperature of 60°C. The PEC membrane may have good prospect for guided bone regeneration. [ABSTRACT FROM AUTHOR]

Developing high-capacity anode materials is urgent for next-generation lithium-ion batteries (LIBs) with the increasing need of larger scale applications. In order to obtain suitable anode materials, nitrogen-doped porous carbon microspheres (NPCMs) were prepared via spray drying followed by carbonization using chitosan as both carbon and nitrogen sources. The structure and properties of NPCMs were characterized by thermogravimetric, Raman spectroscopic, x-ray diffraction, scanning electron microscopic, transmission electron microscopic as well as x-ray photoelectron spectroscopic analysis, and the electrochemical performance of NPCM electrodes were also evaluated. The results show that the diameter of the obtained microspheres is 1–7 μm. When used as the anode material, the NPCMs display a reversible capacity of 443 mAh g−1 at 100 mA g−1 after 120 cycles and maintain a high capacity of 377 mAh g−1 at 1 A g−1 after 500 cycles. Even at a high current density of 4 A g−1, a discharge capacity of 256 mAh g−1 can also be obtained. The excellent rate performance and long cycle life of the electrode might be ascribed to the nitrogen-doping, porous and amorphous structure of NPCMs. The results suggest that the prepared NPCMs have the potential to be used as a promising anode material for high-capacity LIBs. [ABSTRACT FROM AUTHOR]