Kenichi Motomiya

Magnetron-type radio-frequency plasma control yielding vertically well-aligned carbon nanotube growth

In order to understand the effects of plasma parameters on the nanotube formation and further controlled growth, we have investigated the optimal growth condition using a rf plasma-enhanced chemical vapor deposition method. The magnetic field introduced for a magnetron discharge enhances the nanotube growth as a result of the plasma-density increment and the self-bias reduction of a rf electrode. It is also found that the optimum ion flux and ion bombardment energy is a key parameter for the uniform, well-aligned, and density-controlled nanotube growth.

Structural deformation of single-walled carbon nanotubes and fullerene encapsulation due to magnetized-plasma ion irradiation

Positive and negative bias-voltages are applied to single-walled carbon nanotubes (SWNTs) in magnetized alkali–metal and alkali–fullerene plasmas. When accelerated ions are irradiated to the SWNTs through plasma sheaths, drastic structural deformations such as deflection and tube cutting of the SWNTs are observed to take place. Furthermore, this phenomenon is found to be accompanied by the fullerene encapsulation inside the SWNTs in the case of the positive-bias application in the alkali–fullerene plasma, giving the possibility that various kinds of atoms and molecules can effectively be intercalated by our plasma method.

Super-Robust, Lightweight, Conducting Carbon Nanotube Blocks Cross-Linked by De-fluorination

We produced large binder-free multi-walled carbon nanotube (MWNT) blocks from fluorinated MWNTs using thermal heating and a compressing method in vacuo. This technique resulted in the formation of covalent MWNT networks generated by the introduction of sp(3)-hybridized carbon atoms that cross-link between nanotubes upon de-fluorination. The resulting carbon nanotube blocks are lighter than graphite, can be machined and polished, and possess average bending strengths of 102.2 MPa, a bending modulus of 15.4 GPa, and an electrical conductivity of 2.1 x 10(2) S/cm. Although each nanotube exhibits a random structure in these blocks, the mechanical properties are 3 times higher than those obtained for commercial graphite. On the basis of theoretical molecular dynamics simulations, a model is presented for the nanotube interconnecting mechanism upon de-fluorination.

C60 encapsulation inside single-walled carbon nanotubes using alkali–fullerene plasma method

Abstract It is reported that alkali–fullerene plasmas consisting of positive alkali-metal ions, negative fullerene ions, and residual electrons are effective in encapsulating fullerenes inside single-walled carbon nanotubes (SWNTs). When positive or negative bias-voltages are applied to SWNTs in plasmas, accelerated negative fullerene or positive alkali-metal ions are irradiated to the SWNTs through the plasma sheath, respectively. Field emission gun transmission electron microscopy (FEG-TEM) clearly shows that drastic structural modifications such as severe bending of SWNT bundles, tube dislocation, and tube tip termination take place after the ion irradiation. Energy dispersive X-ray spectrometry (EDS) confirms the existence of the alkali-metal elements in the sample after the alkali-metal irradiation. In addition to this, the SWNTs encapsulating fullerene molecules are directly observed after only 1 h fullerene-ion irradiation. These results suggest that our experimental system could permit us to intercalate not only fullerenes but also other elements inside the SWNTs by the applied-bias control. Raman scattering spectroscopy is also adopted for the purpose of evaluating pure SWNTs and fullerene encapsulated SWNTs.

Long-term biopersistence of tangled oxidized carbon nanotubes inside and outside macrophages in rat subcutaneous tissue

Because of their mechanical strength, chemical stability, and low molecular weight, carbon nanotubes (CNTs) are attractive biological implant materials. Biomaterials are typically implanted into subcutaneous tissue or bone; however, the long-term biopersistence of CNTs in these tissues is unknown. Here, tangled oxidized multi-walled CNTs (t-ox-MWCNTs) were implanted into rat subcutaneous tissues and structural changes in the t-ox-MWCNTs located inside and outside of macrophages were studied for 2 years post-implantation. The majority of the large agglomerates were present in the intercellular space, maintained a layered structure, and did not undergo degradation. By contrast, small agglomerates were found inside macrophages, where they were gradually degraded in lysosomes. None of the rats displayed symptoms of cancer or severe inflammatory reactions such as necrosis. These results indicate that t-ox-MWCNTs have high biopersistence and do not evoke adverse events in rat subcutaneous tissue in vivo, demonstrating their potential utility as implantable biomaterials.

Strict preparation and evaluation of water-soluble hat-stacked carbon nanofibers for biomedical application and their high biocompatibility: influence of nanofiber-surface functional groups on cytotoxicity

Water-soluble H-CNFs modified with a carboxyl group possessed the ability to induce TNF-alpha, whereas CHAPS-treated H-CNFs possessed significantly greater activity and were also found to activate NF-kappaB reporter activity, to a significantly greater level than H-CNFs; furthermore the functional group modified or coated on the surface of H-CNFs was a significant cytotoxic factor that affected cell activation.

Experimental study of fullerene-family formation using radio-frequency-discharge reactive plasmas

Abstract A formation regime of fullerenes and carbon nanotubes in glow-discharge reactive plasmas is investigated in order to gain sharp insight into the relation between plasma characteristics and the generation processes of the fullerene families. The plasma is produced in a mixture of CH 4 and a small fraction of H 2 by the radio-frequency (RF) discharge across an externally-applied magnetic field. The plasma is found to be apparently localized around the RF electrode under certain conditions determined by the magnetic field strength and reactive-gas pressure. In this case, it is demonstrated that fullerenes and carbon nanotubes are most effectively generated on the RF electrode, which is negatively self-biased, and exposed to a strong plasma-sheath drop. Our results indicate that the creation of radical species, such as hydrocarbon precursors, due to the local discharge around the RF electrode, the sheath acceleration of positively-charged particles such as carbon ions, and the abstraction of the hydrogen from hydrogenated-carbon species or clusters, are important in the nucleation, formation, and growth of the fullerene families.

Production of carbon nanotubes by controlling radio-frequency glow discharge with reactive gases

Abstract Relations between plasma characteristics and formation processes of carbon nanotubes (CNTs) are investigated in order to develop an effective method for producing CNTs using glow discharge reactive plasmas. The plasma generated by the radio-frequency (RF) discharge in a crossed magnetic field is found to be apparently localized around an RF electrode under a certain condition determined by the magnetic-field strength and mixed gas (CH 4 +H 2 ) pressure. In this case, it is demonstrated that CNTs are most effectively produced on the RF electrode which is negatively self-biased and exposed to a strong plasma-sheath drop.

Formation and structural observation of cesium encapsulated single-walled carbon nanotubes

Cesium encapsulation inside single-walled carbon nanotubes (SWNTs) is for the first time realized by ion irradiation of SWNTs immersed in a magnetized alkali-metal plasma, the configuration of which is confirmed to comprise three varieties by field emission type transmission electron microscopy (FE-TEM) and scanning TEM (STEM) observation.

Polycarbosilane-derived SiC/single-walled carbon nanotube nanocomposites

One of the key issues for the development of high toughness carbon nanotube (CNT) reinforced composites is the control of the interfacial bond between the CNT and the matrix. Here, we introduce a novel technique to facilitate the homogeneous coating of single-walled carbon nanotube (SWCNT) bundles with polycarbosilane (PCS)-derived SiC nanoparticles. The PCS dissolved in n-hexane was used as a precursor for SiC nanoparticles. The results obtained from XRD, TEM and EDXS analyses confirmed the formation of β-SiC nanoparticles of about 20 nm in diameter, which possessed a relatively homogeneous distribution on the SWCNT bundles. It was shown that the number of SiC nanoparticles per unit of SWCNT surface area could be adjusted by changing the weight ratio of PCS and SWCNTs. This approach may provide a useful route for the preparation of SiC/SWCNT nanocomposites that have a tunable interface property with the matrix and potentially with an enhanced anchor effect, which may have potential applications as a reinforcing element in CNT/ceramic composites.