E.A. Skryleva

Carbon nanomaterial produced by microwave exfoliation of graphite oxide: new insights

We present detailed characterization of graphene-like material obtained through microwave stimulated exfoliation of graphite oxide (GO). Properties of this material were studied by multiple techniques including, among others, X-ray photoelectron spectroscopy, mass-spectroscopy, infrared and Raman spectroscopy, scanning electron microscopy and broadband dielectric spectroscopy. Specific surface area and volume of microwave exfoliated graphite oxide reached 600 m2 g−1 and 6 cm3 g−1, respectively. It is shown that during such an explosive reduction process the sample emits CO2, CO and H2O and, in some cases, SO2 gases. The resulting reduced material exhibits IR spectra similar to that of graphite and a dc-conductivity of 0.12 S cm−1.

XPS characterization of MWCNT and C60-based composites

ABSTRACT X-ray photoelectron spectroscopy was used for characterization of MWNT-C60 composites with assistance of scanning and transmission electron microscopy. The composites were received by immerison of nanotubes into fullerene solution in CS2 with consequent processing with green laser irradiation at aproximately 10 W/cm2. It was shown that C1s spectra of composites are different from simple addition of MWNT and C60 features. It found that preliminary nanotube purification by oxidative treatment influences strongly the nature of fullerene-nanotube bonding. Hydrophilic surface of oxidized nanotube material has lower affinity to C60 molecules and provides for concentration of C60 molecules into clusters, which show differential charging effect in XPS spectra. The differential charging effect disappears after laser processing, which induces photopolymerization of fullerene clusters. The as-synthesized nanotubes form composites with more evenly distributed fullerene.

XPS Characterization Onion-Like Carbon from Nanodiamonds and Carbon Structure from Onion-Like Carbon after High-Pressure High-Temperature Treatment

In this work, we report the results of X-ray photoelectron spectroscopy research into the relative concentrations of sp3 and sp2 hybridization type atoms in onion-like carbon (ONC) specimens and in structures synthesized by high pressure and high temperature treatment (HPHT structures). The experimental method was based on the analysis of C1s core line and plasmon loss spectra. ONC specimen graphitization degree was analyzed as a function of treatment temperature for the 1000–1600°C range. Reverse processes, that is, sp3 bond formation, were observed in HPHT structures at 7.7 and 15 GPa and 500–1500°C.

Transformation of multiwall carbon nanotubes to onions with layers cross-linked by sp3 bonds under high pressure and shear deformation

A pressure-induced phase transition of multiwall carbon nanotubes (MWNT) to a new structure at room temperature is studied using a shear diamond anvil cell, X-ray photoelectron spectra (XPS), transmission electron microscope (TEM) and Raman procedures. We observe a cardinal pressure-induced change in the nanoparticles shape from multi-shell tubes to multi-shell spheres. MWNT transforms to onions with layers cross-linked by sp3 bonds under the 45-65 GPa compressive stress combined with shear deformation at room temperature. TEM and XPS results show that about 40% of the carbon atoms in the new phase are sp3-bounded.

Properties of nanosilicon obtained by plasma chemical decomposition of monosilane in a microwave discharge

Investigations of nanoscale silicon powders obtained by plasma chemical synthesis in various process parameters were carried out by transmission electron microscopy, X-ray photoelectron spectroscopy, and infrared (IR) spectroscopy. It was demonstrated that the powders consist of spherical particles with an average diameter from 20 to 30 nm. Each particle includes a single-crystal silicon core and amorphous shell whose chemical composition is defined by bonds of silicon with oxygen and hydrogen. The measurements of photoluminescence (FL) show the presence of dim near-infrared FL in the specimen powders, and more intensive emission around 420 nm in the suspension of the powder in ethanol. The character of this emission has not been determined yet.

C60 fullerene decoration of carbon nanotubes

A new fully carbon nanocomposite material is synthesized by the immersion of carbon nanotubes in a fullerene solution in carbon disulfide. The presence of a dense layer of fullerene molecules on the outer nanotube surface is demonstrated by TEM and XPS. Fullerenes are redistributed on the nanotube surface during a long-term action of an electron beam, which points to the existence of a molecular bond between a nanotube and fullerenes. Theoretical calculations show that the formation of a fullerene shell begins with the attachment of one C60 molecule to a defect on the nanotube surface.