Multi-layer graphene and graphite nanoflakes were produced through graphite liquid exfoliation using organic solvents. The nanoflakes size distribution was statistically analyzed, with the number of ...measured samples being high enough (from ∼200 to 900) for reliable evaluation of the statistical model. The nanoflakes size data were found to follow a log-normal distribution, with higher fraction of large size flakes as compared to a conventional normal distribution. The same kind of distribution was also obtained for nanoflakes thickness. Based on these findings, the detailed mechanism of the pristine polycrystalline graphite exfoliation in a liquid phase due to formation and collapse of cavitation bubbles was discussed. The high quality of nanoflakes was confirmed by Raman spectroscopy.
Defects induced by liquid-phase exfoliation of graphite using sonication were studied. It was shown that localized impact by cavitation shock waves can produce bulk ripplocations and various types of ...dislocations in graphite nanoplatelets. Formation of ripples is more pronounced in large aspect (length/width) ratio platelets or nanobelts. Quasi-periodical ripple systems were observed in many nanobelts after sonication. Mechanism of formation of ripples and dislocations during sonication was proposed. Surprisingly, fast high-temperature processing was found to anneal most of defects. This is consistent with our observations that defects associated with ripplocations are strongly localized and thus can be fast annealed.
The possibilities of doping carbon layers grown by pulsed laser deposition with transition-metal impurities are analyzed. The composition and optical and electrical parameters of structures on GaAs ...and Si/SiO
2
substrates are studied. It is shown that the introduction of such atoms as Fe ones modifies the magnetic properties of layers, which are responsible for nonlinear magnetic-field dependences of the Hall effect at temperatures of up to 300 K.
We present a facile and simple method for the large-scale synthesis of octahedral iron oxide nanocrystals (Fe3O4 ONCs) on the reduced graphene oxide nanosheets (rGO NSs). The Fe3O4-ONCs embedded on ...the rGO NSs surfaces (Fe3O4-ONCs@rGO hybrids) are synthesized by microwave assisted. The Fe3O4 nanoparticles (Fe3O4 NPs) decorated rGO NSs (Fe3O4-NPs@rGO hybrids) are also synthesized using same method for comparative studies in lithium ion storage. During the synthesis process, rGO NSs served as the structural platform to embed the positively charged Fe3O4-ONCs on the basis of the electrostatic assembly followed by the microwave reduction of rGO NSs. Compared to Fe3O4-NPs@rGO, Fe3O4-ONCs@rGO hybrids shows superior electrochemical performance, including better cycling stability and rate performances, which may be attributed to the embedded structure of the nano-size Fe3O4-ONCs in rGO NSs. The electrochemical performances of the hybrids material as anode for lithium storage are evaluated by cyclic voltammetry and constant current charging and discharging. The synthesized Fe3O4-ONCs@rGO hybrids exhibited high lithium storage capacity, outstanding cycling stability (540 mAh g−1 after 120 cycles at 100 mA g−1). This low-cost and fast synthesis strategy may be employed in other embedded structured hybrids design for high-performance lithium batteries.
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•The Fe3O4 –ONCs nanocrystals embedded into rGO NSs were synthesized.•The rGO NSs served as the structural platform for Fe3O4-ONCs.•The Fe3O4-ONCs@rGO hybrid shows superior electrochemical performance.•The Fe3O4-ONCs@rGO hybrid shows good lithium storage and cycling stability.
The self-assembled three dimensional (3D) hybrids nanostructure containing uniform growth of vertical carbon nanotubes (VCNTs) with faceted iron oxide nanoparticles (f-Fe3O4 NPs) on the surfaces of ...reduced graphene oxide nanosheets (rGO NSs) is achieved using microwave assisted approach. The formation of hierarchical 3D f-Fe3O4-VCNTs@rGO hybrids, using microwave method is a rapid, simple, and inexpensive synthetic route. First, the VCNTs grow with help of Fe NPs, and after oxidizing of Fe NPs in form of f-Fe3O4 NPs, the growth has terminated resulting in formation of small size (<500 nm) VCNTs containing f-Fe3O4 NPs on its tip. The defect- and oxygen-rich sites of rGO NSs favor the heterogeneous nucleation and growth of f-Fe3O4 NPs on the tip of VCNTs. The synthesized 3D f-Fe3O4-VCNTs@rGO hybrid shows the improved electromagnetic interference (EMI) for microwave shielding effectiveness (SE) as compared to both rGO NSs and Fe3O4 NPs@rGO NSs materials. This 3D f-Fe3O4-VCNTs@rGO hybrid demonstrates the shielding effectiveness value more than ∼25 dB as compared to Fe3O4 NPs@rGO NSs for 1.0 mm thin film of 3D f-Fe3O4-VCNTs@rGO hybrids in microwave X-band (8.2–12.4 GHz). This applied microwave synthesis approach for 3D f-Fe3O4-VCNTs@rGO hybrids is simple, fast, reproducible and scalable for advanced EMI shielding materials. It can be concluded that the faceted Fe3O4 NPs on the tip of VCNTs which are grown in-situ on rGO NSs shows synergetic performance for EMI shielding elements in advanced application areas like spacecraft and aircraft.
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•Method for contacts improvement between carbon nanostructures and metal electrodes.•Gradual increase of the contact area during sample heating by focused laser beam.•Higher ...temperatures achieved for graphene flakes as compared to carbon nanotubes.•Temperatures achieved in the first stage of annealing up to 2000K for graphene flakes.•Areas of metal/graphene contacts increased up to 20times as a result of annealing.
A new approach for electrical and thermal improvement of contacts between carbon nanostructures (multi-wall carbon nanotubes – MWCNTs and multi-layer graphene – MLG) and metal electrodes by localized laser heating is presented. The nanostructures were deposited over electrodes using the dielectrophoresis (DEP) technique. A focused laser beam was used for direct heating the samples in ambient atmosphere. The Raman spectroscopy was used to determine the process temperature by observations of the graphitic G-line downshift. In the laser annealing experiments, the G-line position was found first to downshift linearly with laser power indicating gradual heating of the sample proportional to the absorbed power. However, with increasing power the shift was found to saturate at levels that depend on the metal and the contact area. This saturation was attributed to gradual increase of the contact area and improvement of the thermal contacts between the nanostructures and metal electrode that can occur during sample heating. The maximum sample temperature in the beginning of the annealing process was always higher for MLG samples, due to smaller area of contact established between rigid multi-layer graphene and initially rough metal surface. The final result is the increased heat losses to the electrodes and, subsequently, the reduction of the samples temperature.
The main advantage of this method, when compared with traditional and rapid thermal annealing, is that the thermal treatment is localized in a small pre-determined region, allowing individually controlled annealing process.
The highly conductive composite based on graphite nanobelts/ultra-high-molecular-weight polyethylene (UHMWPE) was developed using hot calendering at temperatures below the polymer melting point. The ...fabricated material exhibits excellent electrical conductivity (up to 40 S cm−1), high efficiency of electromagnetic interference shielding (near 35 dB for 100 μm thick samples) and good mechanical properties (flexibility and mechanical strength). These superior characteristics are the result of synergistic combination involving superior mechanical properties of the polymer, perfect transport characteristics of the filler and the specific method of fabrication allowing for formation of a segregated anisotropic conductive network with a low percolation threshold (0.42 vol %).
A significant (almost two orders of magnitude) increase in the intensity of photo- and electroluminescence of a diode structure with an InGaAs/GaAsSb/GaAs quantum well, GaMnAs layer as a spin ...injector, and contact coating of a multilayer graphene film has been experimentally detected. The result has been explained by the possible formation of a hybrid system of multilayer graphene and GaAs semiconductor under the influence of He–Ne laser radiation, which leads to a change in the band diagram of the heterostructure.
The combination of two highly versatile materials as reduced graphene oxide (rGO) and molybdenum disulfide (MoS 2 ) forms the layered rGO-MoS 2 hybrids that have great potential for sensing ...applications. In this paper, we developed a cost-effective, time-saving, and efficient microwave-assisted method to exfoliate rGO and MoS 2 nanosheets in a powder mixture for the formation of rGO-MoS 2 hybrids. The formation of hybrids with a combination of organic and inorganic 2-D layered materials offers new possibilities for the development of gas sensitive materials. The applied microwave treatment is a simple and fast process for the large-scale synthesis of rGO-MoS 2 hybrids. The synthesized rGO-MoS 2 hybrids were characterized by X-ray diffraction, scanning electron microscope, energy dispersive X-ray spectroscopy, Raman, X-ray photoelectron spectroscopy, and thermogravimetric analyses to determine the phase structure, surface morphology, defect formation, binding energy, thermal stability and so on. The synthesized rGO-MoS 2 hybrids were tested for sensing application and showed the good performance to detect gases such as O 2 , N 2 , and NH 3 at room temperature.
—Layers of InAs, InSb, and GaSb semiconductors highly doped with iron during their growth by the method of pulsed laser deposition are studied experimentally. The best temperatures for layer ...formation on GaAs (100) substrates are: 250°C (InSb : Fe), 300°C (InAs : Fe), and 350°C (GaSb : Fe). At high Fe concentration (over 10 at %) the layers display ferromagnetic properties expressed in emergence of a hysteresis curve within the magnetic field dependences of the Hall resistance, negative magnetoresistance, and in some cases, ferromagnetic-type magnetization at measurements at room temperature. The atoms of iron do not change the type of layer conductivity; InAs : Fe and InSb : Fe layers possess
n
-type conductivity, and GaSb : Fe layers display
p
-type conductivity due to their intrinsic point defects.
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