Jung Sang Suh

Highly ordered two-dimensional carbon nanotube arrays

Highly ordered multiwalled carbon nanotube arrays have been fabricated by using porous anodic alumina templates prepared by a two-step anodization process. Nanotubes were very uniform in diameter. Two-dimensional tube arrays were highly ordered within domain boundaries, and their vertical alignment was nearly perfect. The density of nanotubes, 1.1×1010 tubes/cm2, was very high. Our fabrication technique enabled us to easily control the tube diameter, length, and density. There was no practical limitation to the size of the alumina template, so that very large panels of well-aligned carbon nanotubes could be made. Our results offer a potentially elegant technique for fabricating cold-cathode flat panel displays.

Study of the field-screening effect of highly ordered carbon nanotube arrays

We have studied the field-screening effect provoked by the proximity of neighboring tubes by changing the tube height of highly ordered carbon nanotubes fabricated on porous anodic aluminum oxide templates. The field emission was critically affected by the tube height that protruded from the surface. The field emission was optimal when the tube height was similar to the intertube distance. The intertube distance to the tube height for maximum field emission is about one half the intertube distance predicted by Nilsson et al. [Appl. Phys. Lett. 76, 2071 (2000)].

Surface enhanced Raman scattering for CdS nanowires deposited in anodic aluminum oxide nanotemplate

Abstract We report for the first time the SERS spectrum of CdS nanowires deposited electrochemically into the pores of anodic aluminum oxide, where silver has been predeposited. CdS grows epitaxially on the silver surface with a Raman spectrum dominated by a progression of the longitudinal optical phonon mode. The Raman intensity is enhanced by the enhanced local electric field near the silver surface.

Size-controllable and low-cost fabrication of graphene quantum dots using thermal plasma jet.

We report a size-controllable and low-cost fabrication method of graphene quantum dots (GQDs) using a thermal plasma jet. A carbon atomic beam was generated by injecting a large amount (2.5 L/min) of ethylene gas continuously into Ar plasma. The beam was then flowed through a carbon tube (5-20 cm in length) attached to the anode and then dispersed into a chamber. Carbon materials including GQDs were made by a gas phase collision reaction. The production rate of carbon soot was 40 g/h for a 2.5 L/min injection rate. Almost all of the carbon soot dispersed in ethanol by sonication, while isolated GQDs were dispersed in ethanol by stirring with a stirring rod. The weight percent of GQDs in carbon soot, based on the amount extracted in ethanol, was about 10%. This means that the production rate of GQDs was about 4 g/h. The average size of GQDs, with a relatively narrow size distribution, was controlled by varying the length of the carbon tube attached. It was about 10, 14, and 19 nm when the length was 5, 10, and 20 cm, respectively. The electric structure based on the photoluminescence data of our GQDs had a singlet ground state and was in good agreement with that of carbyne. Our GQDs will disperse in organic solvents such as toluene, but not in water. The dispersion properties also support that our GQDs have carbyne-like edges. We proposed that the PL peaks observed can be attributed to electronic transitions between energy levels of the GQDs having carbyne-like edges.

Fabrication of graphene flakes composed of multi-layer graphene sheets using a thermal plasma jet system

We have developed a method to fabricate graphene flakes composed of high quality multi-layer graphene sheets using a thermal plasma jet system. A carbon atomic beam was generated by injecting ethanol into Ar plasma continuously; the beam then flowed through a carbon tube attached to the anode. Graphene was made by epitaxial growth where a carbon atomic beam, having the proper energy, collided with a graphite plate. The graphene fabricated was very pure and showed a relatively good crystalline structure. We have demonstrated that the number of layers of graphene sheets could be controlled by controlling the rate of ethanol injection. Our process is a continuous process with a relatively high yield (approximately 8%).

Enhancement at the junction of silver nanorods.

The enhancement of surface enhanced Raman scattering (SERS) at the junction of linearly joined silver nanorods (31 nm in diameter) deposited in the pores of anodic aluminum oxide templates was studied systematically by excitation with a 632.8 nm laser line. The single and joined silver nanorod arrays showed a similar extinction spectrum when their length was the same. Maximum enhancement was observed from the junction system of two nanorods of the same size with a total length of 62 nm. This length also corresponded to the optimum length of single nanorods for SERS by excitation with a 632.8 nm laser line. The enhancement at the junction was approximately 40 times higher than that of the 31 nm single nanorod, while it was 4 times higher than that of the 62 nm single nanorod. The enhancement factor at the junction after oxide removal was approximately 3.9 x 10 (9).

Well-ordered Co nanowire arrays for aligned carbon nanotube arrays

Abstract Well-ordered Co nanowire arrays formed on the porous anodic aluminum oxide (AAO) templates prepared by a two-step anodization technique have been used in the fabrication of well-aligned carbon nanotubes. Designed Co nanowire arrays can be made by controlling the pore arrays on AAO templates. By using them as a catalyst it is possible to fabricate the designed carbon nanotube arrays. Carbon nanotubes fabricated by disproportionation of CO were well graphitized, uniform in diameter and aligned vertically with respect to the plane of the template. It has been suggested that CO is an ideal precursor in fabrication of carbon nanotubes.

Comparison of the field emissions between highly ordered carbon nanotubes with closed and open tips

We have studied the field emission from the closed and open tips of highly ordered carbon nanotubes fabricated on porous anodic aluminum oxide templates by changing the tube height. Due to the field-screening effect provoked by the proximity of the neighboring tubes, the field emission from both kinds of the tips was critically affected by the tube height that protruded from the surface. The field emission optimizes when the tube height is similar to the intertube distance for both kinds of tips. The field emission from the closed tips is much more efficient than that from the open ones.

Chemical sensors for sensing gas adsorbed on the inner surface of carbon nanotube channels

The authors have developed gas sensors that operate when gas flowing through carbon nanotube (CNT) channels is adsorbed on the inner surface of the channels. CNTs fabricated on anodic alumina membranes were used. The CNTs are well ordered and connected in parallel, forming parallel channels. The sensors are highly responsive to NH3 and NO2 molecules and the response times are relatively short. They are completely recovered within 10min when a dc voltage of 10V is applied for 2min. The fabrication processes are relatively simple and do not require special techniques such as e-beam lithography.

Minimum Enhancement of Surface-Enhanced Raman Scattering for Single-Molecule Detections

We have calculated the minimum enhancement factor for single-molecule detections from the surface-enhanced Raman scattering (SERS) data measured from well-defined silver nanorod arrays. Silver nanorods were fabricated by electrodepositing them evenly near the mouth of the pores of anodic aluminum oxide templates with a very shallow depth. The SERS intensity increased almost linearly with an increase in the concentration of the mother solution. From the data of the enhancement and the number of molecules irradiated by the laser beam at the detection limit, the minimum SERS enhancement factor for nonresonant single-molecule detections was calculated to be approximately 10(11).