Goo-Hwan Jeong

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.

Size control of catalytic nanoparticles by thermal treatment and its application to diameter control of single-walled carbon nanotubes

The authors report size control of catalytic nanoparticles by thermal annealing for diameter-controlled growth of single-walled carbon nanotubes (SWNTs). They found that Co nanoparticle-size gradually decreased through repetitive annealing at 1000°C in Ar ambient. Results of x-ray photoelectron spectroscopy and secondary ion mass spectroscopy show that thermal evaporation is responsible for the decrease. After SWNT growth using this phenomenon, the authors found that thinner SWNTs with a narrower diameter distribution grew as the nanoparticles became smaller. Their results provide a rational and straightforward technique to prepare catalysts having a desirable size and uniformity toward diameter-controlled SWNT growth.

Effect of nanoparticle density on narrow diameter distribution of carbon nanotubes and particle evolution during chemical vapor deposition growth

Single-walled carbon nanotubes (SWNTs) were synthesized by chemical vapor deposition (CVD) using catalytic nanoparticles both on the substrates and above the substrates in order to investigate the effect of nanoparticle density on diameter-controlled SWNT growth. As the density of the catalytic nanoparticles increased, tube-diameter distribution broadened and the diameter itself also increased. SWNTs observed in this study were grown by the base-growth mechanism and their diameters were much smaller than those of the nanoparticles. Based on elaborate diameter measurements, we reasonably conjecture that the time evolution of catalytic nanoparticles during CVD growth can explain these large size differences.

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.

Low temperature transfer and formation of carbon nanotube arrays by imprinted conductive adhesive

This letter demonstrates the transfer and formation of aligned carbon nanotube (CNT) arrays at low temperature by imprinted conductive adhesive. A thermoplastic isotropic conductive adhesive is patterned by an imprint and heat transfer process. The CNTs grown by thermal chemical vapor deposition are then transferred to another substrate by the conductive adhesive, forming predefined patterns. The current-voltage response of the transferred CNT bundles verifies that good electrical connection has been established. This process can enable the integration of CNTs into various temperature-sensitive processeses and materials.

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.

Encapsulation of cesium inside single-walled carbon nanotubes by plasma-ion irradiation method

Positive Cs ions are irradiated to a negatively biased substrate, which is covered with the dispersed single-walled carbon nanotubes (SWNTs) and immersed in the Cs plasma. Field emission type transmission electron microscopy (FE-TEM) and Z-contrast technique by scanning TEM (STEM) are used for the precise observation. FE-TEM gives high resolved images of structurally modified SWNTs such as irreversible bending of tube bundles, tube dislocation, and cutting due to the positive Cs ion irradiation. Moreover, this structural modification becomes severe with an increase in the acceleration energy of irradiating Cs ions. Especially, the Cs encapsulation inside SWNTs is directly observed, the configuration of which is confirmed to comprise three varieties by FEG-TEM and STEM. In addition to these experimental results, ab initio study is used to investigate the static stable configurations due to Cs ion irradiation.

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.