Byung Soo Lee

Controlling the diameter, growth rate, and density of vertically aligned carbon nanotubes synthesized by microwave plasma-enhanced chemical vapor deposition

Vertically aligned carbon nanotubes were synthesized on Ni-deposited Si substrates using microwave plasma-enhanced chemical vapor deposition. The grain size of Ni thin films varied with the rf power density during the rf magnetron sputtering process. We found that the diameter, growth rate, and density of carbon nanotubes could be controlled systematically by the grain size of Ni thin films. With decreasing the grain size of Ni thin films, the diameter of the nanotubes decreased, whereas the growth rate and density increased. High-resolution transmission electron microscope images clearly demonstrated synthesized nanotubes to be multiwalled.

Effect of surface morphology of Ni thin film on the growth of aligned carbon nanotubes by microwave plasma-enhanced chemical vapor deposition

Aligned carbon nanotubes were synthesized on Ni-coated Si substrates using microwave plasma-enhanced chemical vapor deposition. The surface morphology of Ni thin films was varied with the rf power density during the rf magnetron sputtering process. It was found that the growth of carbon nanotubes was strongly influenced by the surface morphology of Ni thin film. Pure carbon nanotubes were synthesized on Ni thin film with uniformly distributed grain sizes, whereas large amounts of carbonaceous particles were produced in addition to the nanotubes, when the nanotubes were grown on Ni thin film with widely distributed grain sizes. With decreasing Ni-grain size, the diameter of nanotubes decreased and the length increased. High-resolution transmission electron microscope images clearly demonstrated the nanotubes to be multiwalled, and the graphitized structures were confirmed from the Raman spectra. Efficient field emission was observed from the diode structure with the nanotube tips.

Patterned growth and field emission properties of vertically aligned carbon nanotubes

Abstract Vertically aligned carbon nanotubes were grown selectively on patterned Ni thin films by microwave plasma-enhanced chemical vapor deposition and their field emission properties were investigated using a diode-structure. Ni thin films patterned with a form of dot-arrays were prepared using a shadow mask having an array of holes. The nanotubes were found to be well-graphitized with multiwalled structures. The measurements of field emission properties revealed that the carbon nanotube tips emitted high current density at low macroscopic electric field. The Fowler–Nordheim (F–N) plot clearly showed two characteristic regions where the current saturates at the high electric field region. It was found that the saturation behavior was caused by the adsorbates-enhanced field emission mechanism. Eliminating the adsorbates resulted in no saturation behavior, increasing turn-on field, decreasing current, and increasing field enhancement factor. Using ZnS/Cu,Al phosphor, very bright and uniform emission patterns were obtained.

Growth of carbon nanotubes by microwave plasma-enhanced chemical vapor deposition at low temperature

Carbon nanotubes have been grown on Ni-coated Si substrates by microwave plasma-enhanced chemical vapor deposition with a mixture of methane and hydrogen gases at temperatures ranging from 520 to 700 °C. The density and the length of the carbon nanotubes increased with increasing growth temperature. At a growth temperature of 520 °C, the carbon nanotubes were curly, whereas the nanotubes were straight and self-aligned upward at temperatures above 600 °C. Images from high-resolution transmission electron microscopy showed that the nanotubes were multiwalled, with a few wall structures. The graphitized structures were also confirmed by Raman spectra. We show that the size of Ni grains on Si substrates is correlated to the diameters of the grown carbon nanotubes.

Low temperature synthesis of carbon nanotubes by microwave plasma-enhanced chemical vapor deposition

Abstract We have synthesized pure carbon nanotubes at very low temperature using microwave plasma-enhanced chemical vapor deposition (MPECVD) with methane/hydrogen gas. Ratio of a gas mixture (CH4/H2) and deposition time at a substrate temperature below 520°C are optimized. Pure and dense carbon nanotubes are grown uniformly over a large area of Ni-coated silicon substrates without any pretreatment of substrates. The diameters and lengths of carbon nanotubes could be controlled by changing the ratio of gas mixture and the growth time. Raman spectrum clearly shows the peak at 1592 cm−1 (G-band), indicating the formation of graphitized carbon nanotubes.

Improvements of the Properties of Chemical-Vapor-Deposited (Ba,Sr)TiO3 Films through Use of a Seed Layer.

(Ba,Sr)TiO3 (BST) thin films were deposited on seed-layer/Pt/SiO2/Si substrates by chemical vapor deposition and the properties of the films were investigated. The effect of rapid thermal annealing (RTA) was also examined. The seed layer used in this experiment was the 10-nm-thick BST film fabricated by RF magnetron sputtering. Both the application of the seed layer and RTA increased the crystallinity of the BST films, which resulted in improved dielectric properties of the films. The seed layer suppressed the formation of an oxygen-deficient layer at the interface between BST and the bottom electrode, which resulted in a decrease of the current density of the Pt/BST/Pt capacitor. Furthermore, the current density was further decreased by RTA. With increasing deposition temperature, both the dielectric constant and the current density of the BST films deposited on the seed layers increased.

Properties of Ru and RuO2 Thin Films Prepared by Metalorganic Chemical Vapor Deposition

Ru and RuO2 thin films were deposited on Si substrates, using a metalorganic precursor of ruthenium carbonyl [Ru3(CO)12], by metalorganic chemical vapor deposition (MOCVD), and their properties were investigated. Ru or RuO2 single phase could be obtained by controlling the flow rate of the oxidant gas (O2). When the Ru film was annealed in oxygen atmosphere, oxygen atoms diffused through the Ru layer, resulting in the oxidation of ruthenium. The compositional uniformity of RuO2 thin films in the thickness direction was good, and interdiffusion at the interface between RuO2 and Si was not observable even after the post-annealing process. The deposition rate of RuO2 thin films is highest at 550°C. All RuO2 thin films showed a dense and smooth microstructure. It was demonstrated that a larger grain size of the film resulted in lower resistivity, and that post-annealing decreased the resistivity. The larger the grain size of the RuO2 film, the greater is the decrease in resistivity by annealing.

Nitrogen induced structure control of vertically aligned carbon nanotubes synthesized by microwave plasma enhanced chemical vapor deposition

Vertically aligned carbon nanotubes (CNT) were synthesized on Ni/Si substrates using microwave plasma-enhanced chemical vapor deposition, and the effects of nitrogen in the gas mixture of CH4+H2+N2 on the growth rate and the diameter of the nanotubes were studied. The growth rate and the diameter of CNT were systematically controlled by controlling the nitrogen content in the feed gas. With increasing the nitrogen content in the feed gas, the growth rate of the nanotubes increased, whereas the diameter decreased except for the case when nitrogen was not introduced. A model of roles of nitrogen in terms of etching carbon and Ni catalyst metal was suggested.

Role of PtO Electrode in Fatigue in Pb(Zr,Ti)O 3 Films

Two different structures of Pt/Pb(Zr,Ti)O3 (PZT)/Pt and PtO/PZT/PtO/Pt capacitors were fabricated by rf magnetron sputtering followed by rapid thermal annealing (RTA) in a N2 atmosphere. The ferroelectric properties of these two capacitors were compared mainly in terms of fatigue. The reduction of PtO to Pt after RTA was observed by X-ray diffraction (XRD) and this resulted in degradation-free capacitors for 5.0×1011 cycles of polarization reversals. The Pt/PZT/Pt capacitor, however, showed a sharp decrease in polarization in the range of 108 read and write cycles. It is thought that the improvement was due to compensation for oxygen vacancies in PZT, which are the source of fatigue during service, by oxygen atoms reduced and separated from the PtO layer that then diffuse to the dielectric layer to neutralize the vacancies.

Preparation of Pt/Ru Bilayers and Their Application to the Capacitor of Memory Devices

Pt(100 nm)/Ru(80 nm) bilayers were prepared on SiO2/Si substrates by RF magnetron sputtering. Pt films were deposited on Ru layers at temperatures ranging from 300°C to 450°C, while the deposition temperature of Ru films was fixed at 300°C. The Ru layer was found to act as a diffusion barrier as well as a glue layer. With increasing deposition temperature, the grain size of Pt increased. However, the Pt film deposited at 450°C had many voids. In the temperature range from 300°C to 400°C, the sheet resistance of Pt/Ru bilayers linearly decreased with temperature, which is ascribed to increasing crystallinity and grain size. The Pt(450°C)/Ru bilayer, however, showed much higher resistance, caused by voids. Three different capacitors with the structures of Pt/(Ba,Sr)TiO3(BST)/Pt, Pt/BST/RuO2, and Pt/BST/Pt/Ru were fabricated and their properties were characterized. The microstructures of BST films were found to be affected by those of bottom electrodes, and to have an important effect on the electrical properties of the capacitor. The electrical properties, such as dielectric constant and leakage current density, of the capacitor with Pt/Ru bottom electrodes are analogous to those with Pt bottom electrodes and better than those with RuO2 bottom electrodes.