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.
We report the design and fabrication of microreactors and sensors based on metal nanoparticle-decorated carbon nanotubes. Titanium adhesion layers and gold films were sputtered onto Si/SiO2 ...substrates for obtaining the electrical contacts. The gold layers were electrochemically thickened until 1 μ m and the electrodes were patterned using photolithography and wet chemical etching. Before the dielectrophoretic deposition of the nanotubes, a gap 1 μ m wide and 5 μ m deep was milled in the middle of the metallic line by focused ion beam, allowing the fabrication of sensors based on suspended nanotubes bridging the electrodes. Subsequently, the sputtering technique was used for decorating the nanotubes with metallic nanoparticles. In order to test the as-obtained sensors, microreactors (100 μ L volume) were machined from a single Kovar piece, being equipped with electrical connections and 1/4′′ Swagelok-compatible gas inlet and outlets for controlling the atmosphere in the testing chamber. The sensors, electrically connected to the contact pins by wire-bonding, were tested in the 10−5 to 10−2 W working power interval using oxygen as target gas. The small chamber volume allowed the measurement of fast characteristic times (response/recovery), with the sensors showing good sensitivity.
The possibility of fabricating high-quality thin (10–100 nm), flexible, semitransparent films of multilayer graphene and graphite nanoplates (ultrathin graphite) using a modified Langmuir-Blodgett ...method is demonstrated. The high quality of the resulting samples is confirmed via Raman spectroscopy and high-resolution scanning electron microscopy. Sheet resistance measurements for the films show values of ∼100 Ω/sq and lower.
The thermal resistance of the contact between a metal and carbon nanotubes (CNTs) and between CNT layers is estimated by the local heating of CNT arrays (films) of different thicknesses using a ...focused laser beam and measuring their local temperature via Raman spectroscopy. It is demonstrated that thermal contacts between nanotubes, and also between CNTs and an electrode, can be formed by means of laser annealing.
Liquid phase exfoliation of natural graphite to produce high quality micron scale multi-layer graphene sheets (flakes) in two different solvents (n,n - dimethylformamide and isopropyl alcohol) has ...been studied. The effects of process parameters (basically, sonication time, bath temperature, and centrifugation time) have been investigated. By adjusting the process parameters, high-density solutions containing graphene sheets with lateral sizes from 0.5 to 10 µm (with lateral size-to-thickness ratios up to 200-300) were obtained. For characterization, graphene sheets were deposited over holey carbon TEM grids. The statistic analysis for large number of sheets was performed to show a log-normal lateral graphene size distribution. High quality of graphene sheets was confirmed using scanning electron microcopy and 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.
In this work we present the performance of metallic (copper and aluminum) and graphene buckypaper based microstrip transmission lines and the comparison between these device configurations. The ...graphene buckypapers were deposited by a simple vacuum filtration method, leading to freestanding paper with 350 Dm thickness and diameter up to 1.2 inches. After deposition and drying, the graphene paper and the metallic bands were strips cut by UV laser. The transmission line strips were fixed over alumina substrates with gold backside metallic ground. The S-parameter of these graphene microstrips allows to know the conductivity behavior of carbon electronics when compared with copper and aluminum transmission lines over a wide band of frequencies (from 0.5 to 10 GHz).
Fabrication of novel micron-scale structures based on multi-layer graphene and quantum dots (QD) hybrids is presented. Two types of CdSe/ZnS (core/shell) QDs with diameters of 5.3 and 2.5 nm and ...photoluminescence peaks at 630 and 530 nm, respectively, were used. The photoresponse for illumination by a 473 nm wavelength laser was found to change polarity for these two types of QDs, being positive for larger and negative to smaller ones. The presented photo-resistive devices can be used for studies of the mechanisms responsible for photoinduced change of graphene layer conductivity in presence of QDs.
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