Helical carbon nanofibers (HCNFs), such as the carbon nanocoil (CNC) and the carbon nanotwist (CNTw), were synthesized by catalytic chemical vapor deposition using a substrate. HCNFs are classified into round and angular types according to the fiber cross-sections. When four types of HCNFs (round-type CNC and CNTw, angular-type CNC and CNTw) were acidified in a 30% hydrogen peroxide solution, only the angular type CNC was found to show a drastic shape change. The shape change observed was a splitting followed by a flattening of the angular type CNCs. The CNC was split into two or three thinner flat fibers. As a function of the treatment temperature, the weight of the CNCs decreased above 80 degrees C and the CNCs were etched effectively at 140 degrees C. The longer the reaction time the lower the weight of the CNCs, and the weight loss reached a saturation point when the reaction time was greater than 45 min at 140 degrees C. The splitting and flattening of the CNC occurred during the weight loss process. To analyze the CNC structure, electron tomography of the as-grown and acid-treated CNCs was obtained using a computerized tomograph system with transmission electron microscopy (TEM). The 3D-images were constructed using the TEM images collected at different tilt angles. The 3D image reconstructions showed that the CNCs had a tubular structure and were composed of several helical fibers which act as frames.
Abstract. Twisted carbon nanofibers, named carbon nanotwists (CNTws), in a flocculated form were pasted, printed on the conductive silicon substrate, and then treated by dielectric barrier discharge using He and N 2 gases. Vertically upright nanofibers were clearly obtained by "filament discharge mode" in N 2 gas. As the treating time increased up to ~60 s, the height of the nanofiber tips became uniform. Consequently, the field emission property was greatly enhanced and showed a threshold electric field of 4.6 V/µm and maximum current of 0.433 mA/cm 2 at 8 V/µm.
A new technique to etch a substrate as a pre-treatment prior to functional film deposition was developed using a filtered vacuum arc plasma. An Ar-dominated plasma beam was generated from filtered carbon arc plasma by introducing appropriate flow rate of Ar gas in a T-shape filtered arc deposition (T-FAD) system. The radiation spectra emitted from the filtered plasma beam in front of a substrate table were measured. The substrate was etched by the Ar-dominated plasma beam. The principal results are summarized as follows. At a high flow rate of Ar gas (50 ml/min), when the bias was applied to the substrate, the plasma was attracted toward the substrate table and the 2 substrate was well etched without film formation on the substrate. Super hard alloy (WC), bearing steel (SUJ2), and Si wafer were etched by the Ar-dominated plasma beam. The etching rate was dependent on the kind of substrate. The roughness of the substrate increased, when the etching rate was high. A pulse bias etched the substrate without roughening the substrate surface excessively.
Abstract-We have successfully grown carbon nanotubes (CNTs) by plasma-enhanced chemical vapor deposition (PECVD) using alcohol. When 0.01-wt% ferrocene was added to the alcohol, vertically aligned CNTs grew at 650• C. By contrast, a few CNTs and mostly carbon nanoparticles were obtained by pure alcohol PECVD even though the Fe catalyst was coated on Si substrates. Comparing this PECVD experiment with thermal alcohol CVD showed that only the PECVD method can be used to grow CNTs under the reported experimental conditions. To understand the plasma properties for CNT growth, particularly plasma species contained in a gas phase of alcohol plasma, the plasma was analyzed using optical-emission spectroscopy (OES) and quadrupole mass spectrometry (QMS). From the OES measurement, emission peaks from the excitation states of C 2 , CH, CHO, CH 2 O, CO, H, O 2 , C + , and CO + were identified, while the QMS measurement also showed the existence of H 2 , O, and CO. These results indicate that, in alcohol plasma, oxidants and reductants exist together and potentially promote/suppress CNT growth depending on the process conditions. The contribution of C x H y (x ≥ 1, y ≥ 3) radicals, which were produced by decomposition reactions in alcohol plasma as a CNT precursor, is discussed. Index Terms-Carbon nanotube (CNT), ferrocene, mass spectrometry, optical-emission spectroscopy (OES), plasma-enhanced chemical vapor deposition (PECVD).
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