Junghoon Joo

Morphological change of multiwalled carbon nanotubes through high-energy (MeV) ion irradiation

Multiwalled carbon nanotubes (MWCNTs) were expanded by 2.5 times in diameter through high-energy (MeV) ion irradiation. Pristine MWCNTs were synthesized onto SiO2 substrate by chemical vapor deposition. The 4MeV Cl2+ ions with a dose of 3×1016ions∕cm2 were irradiated on MWCNTs. From high-resolution transmission electron microscopy (HR-TEM) images, the average diameter of the high-energy-ion-irradiated MWCNTs was ∼180nm, while that of the pristine MWCNTs was ∼70nm. The wall thickness of the pristine and the high-energy-ion-irradiated MWCNT samples was ∼20nm and 40–50nm, respectively. We observed the clear formation of nanocompartments with bamboolike structure inside the tubes after ion irradiation. The amorphous carbon structure in the ion-irradiated MWCNT shells was observed from Raman spectra. Based on the results of HR-TEM and Raman spectra, the expansion of the systems represents morphological transition from crystalline graphite structure to amorphous carbon or finite sized graphite structure due to ...

Multifunctional transducer using poly (vinylidene fluoride) active layerand highly conducting poly (3,4-ethylenedioxythiophene) electrode: Actuator and generator

Monomorph and bimorph multifunctional transducers such as actuators and generators were fabricated using a piezoelectric poly (vinylidene fluoride) (PVDF) films as the active layer and a highly conducting poly (3,4-ethylenedioxythiophene)∕poly (4-styrenesulfonate) [PEDOT∕PSS (DMSO for solvent)] as the electrode. In order to enhance the adhesion of the films, either the PVDF films or PEDOT∕PSS (DMSO) electrodes were modified using an ion-assisted-reaction (IAR) method. The direct (generator) and inverse piezoelectric (motor) effects as well as the pyroelectric effect in the PVDF-PEDOT∕PSS based devices were observed. The tip displacement of the 12mm by 30mm bimorph device made with the PEDOT∕PSS (DMSO) electrodes was 3.5mm at the resonance frequency with an appled potential of 40Vrms. The sinusoidal output voltage of the bimorph type generator consisting of the PVDF active layers and PEDOT∕PSS (DMSO) electrodes increased with increasing tip displacement induced by a vibrator. A maximum output voltage of 4....

Deposition of Ti–B–N films by ICP assisted sputtering

Abstract Ti–B–N coatings were prepared by inductively coupled plasma assisted DC magnetron sputtering using a TiB 2 target and a gas mixture of N 2 and Ar at 200 °C and a pressure of 60 mTorr. In addition to ICP, the effect of the substrate bias voltage on the structure and properties of the coating was investigated. By applying ICP the hardness of the TiB 2 coating was increased by more than 60 GPa, as a result of enhanced ionization in the plasma. By adding N 2 into the TiB 2 coating, the hardness decreased as reported previously. However, the hardness could be increased up to 76 GPa by applying ICP and a bias voltage to the substrate. The Ti–B–N coating, which had the highest hardness, showed the best surface uniformity and a very dense structure with a grain size of 3 nm. This sample also showed a high crystallinity compared to the coating prepared using other deposition parameters.

Mechanical properties of (Ti,Cr)N coatings deposited by inductively coupled plasma assisted direct current magnetron sputtering

Abstract (Ti,Cr)N coatings were deposited by inductively coupled plasma (ICP) assisted magnetron sputtering and the properties of the coatings were investigated. The (Ti,Cr)N coatings deposited by ICP assisted sputtering showed a much higher micro-hardness (>5000 HK0.01) compared to coatings produced by the conventional DC magnetron sputtering method. The ICP deposited (Ti,Cr)N coatings also showed superior properties in adhesion and wear compared to the DC sputtered (Ti,Cr)N coatings. The superior mechanical properties of ICP deposited (Ti,Cr)N coatings were attributed to the fine and dense micro-structure and high compressive residual stress.

High energy (MeV) ion-irradiated π-conjugated polyaniline: Transition from insulating state to carbonized conducting state

High energy (MeV)C2+,F2+, and Cl2+ ions were irradiated onto π-conjugated polyaniline emeraldine base (PAN-EB) samples. The energy of an ion beam was controlled to a range of 3–4.5MeV, with the ion dosage varying from 1×1012 to 1×1016ions∕cm2. The highest dc conductivity (σdc) at room temperature was measured to be ∼60S∕cm for 4.5MeV Cl2+ ion-irradiated PAN-EB samples with a dose of 1×1016ions∕cm2. We observed the transition of high energy ion-irradiated PAN-EB samples from insulating state to conducting state as a function of ion dosage based on σdc and its temperature dependence. The characteristic peaks of the Raman spectrum of the PAN-EB samples were reduced, while the D-peak (disordered peak) and the G peak (graphitic peak) appeared as the ion dose increased. From the analysis of the D and G peaks of the Raman spectra of the systems compared to multiwalled carbon nanotubes, ion-irradiated graphites, and annealed carbon films, the number of the clusters of hexagon rings with conducting sp2-bonded carb...

Low temperature TiN deposition by ICP-assisted chemical vapor deposition

Abstract TiN films were deposited by inductively coupled plasma (ICP)-assisted CVD using a gas mixture of TiCl 4 , H 2 , Ar and N 2 with a substrate temperature of 400 °C and room temperature. For ICP generation, r.f. power was applied using a dielectric-encapsulated coil antenna installed inside the deposition chamber. The ICP power was varied from 100 to 400 W. The deposition rate was as high as >1 μm/h in most deposition conditions. As the r.f. power was increased, the deposition rate decreased irrespective of the deposition temperature. It is believed that the decrease in the deposition rate at higher ICP powers is due to resputtering of the coatings as a result of ion bombardment as well as film densification. The hardness increased with increasing r.f. power, indicating the formation of a denser film at higher power. The decrease in the resistivity at high powers is related to the low Cl content in the film. The TiN film deposited by ICP-assisted CVD showed also a good step coverage on the trenches with a high aspect ratio.

Application of inductively coupled plasma to super-hard and decorative coatings

An inductively coupled plasma (ICP) assisted technique is expected to be the next generation deposition technique due to its many beneficial properties. In this paper, an internal type r.f. ICP process is presented. The core of this technology is the efficient production and control of self-depositing ions and reactive gas ions by an induced electric field. The properties of the immersed ICP can be tuned between the capacitively coupled and inductively coupled state by changing the antenna materials, the tuning network design, the driving frequency and the external magnetic field. Examples of applications of ICP to super-hard and decorative TiN and CrN coatings, which were produced by ICP magnetron sputtering and ICP evaporation, respectively, are presented.

The properties of (Ti, Al)N coatings deposited by inductively coupled plasma assisted d.c. magnetron sputtering

(Ti,Al)N coatings were deposited on M2 high speed steel substrates by inductively coupled plasma (ICP) assisted d.c. magnetron sputtering, and the structure and mechanical properties such as hardness, Youngs modulus, wear resistance and adhesion strength were investigated. A TiAl alloy target (Ti/Al — 50:50 at.%) was sputtered in an Ar and N2 atmosphere with 400 W for d.c. magnetron power as well as 400 W for ICP power at 80 mtorr of working pressure. Both the hardness and adhesion strength of the coating were found to increase with increasing substrate bias voltage. The hardness value was higher than 6500 HK0.01 at the bias voltage higher than –50 V. The Youngs modulus of the coating had a maximum value of approximately 450 GPa at −50 V. The wear properties of coatings also improved with the application of the substrate bias voltage. It was found that the grain size decreased (<100 nm), and the columnar structure, which was observed in the absence of bias, disappeared when a bias voltage was applied. The high hardness and good wear property was attributed to the microstructure change from a columnar structure with facet shaped grains to a denser one with small and round shaped grains.

Preparation of TiN films at room temperature by inductively coupled plasma assisted chemical vapor deposition

Abstract TiN films were deposited by inductively coupled plasma (ICP) assisted CVD using a gas mixture of TiCl 4 , N 2 , H 2 and Ar at room temperature. For ICP generation, the RF power was applied to a dielectric encapsulated RFI antenna installed inside the deposition chamber. The ICP power was varied from 100 to 400 W. With increasing RF power, the deposition rate, the resistivity, and the Cl concentration were decreased. Although the deposition of TiN was carried out at room temperature, the Cl content in the films was kept as low as approximately 2.5 at.%. TiCl 4 was injected at the hot spot, where the electron temperature was highest in the reactor. As a result, TiCl 4 could be more easily dissociated and TiN films with a low Cl concentration were produced with the deposition rate of 1 μm/h at room temperature. The coupling efficiency increased with increasing ICP power up to 85% at 400 W. The ion density was increased to approximately 6.34×10 11 /cm 3 at 400 W (only Ar).

Deposition of MgO films by ICP assisted evaporation

Crystalline MgO films could be prepared by ICP assisted evaporation without extra substrate heating. Mg was sublimated from a resistively heated Mo boat, while oxygen was introduced into the chamber with Ar during the deposition process. With increasing r.f.-power the structure and properties of the MgO films such as the crystallinity, the transmittance, the Mg/O ratio and surface uniformity were improved. The deposition pressure only changed the preferred orientation of MgO from (111) and (222) to (200). With the high growth rate of 800 A/min, the ICP assisted evaporation is thought to be a promising technique for MgO production in the PDP industry.