Yoon Ho Song

Field emission properties from flexible field emitters using carbon nanotube film

Flexible carbon nanotube (CNT) field emitters are fabricated using CNT films on polyethylene terephthalate films. The flexible CNT emitters, which are made using double-walled CNTs, show high emission performance and also indicate stable field emission properties under several bending conditions. The flexible CNT emitters have a low turn-on field of about 0.82 V/μm and a high emission current density of about 2.0 mA/cm2 at an electric field of 1.6 V/μm. During stability tests, the flexible CNT emitters initially degrade over the first 4 h but exhibit no further significant degradation over the next 16 h testing while being continually bent. A flexible lamp made using the flexible CNT emitter displays uniform and bright emission patterns in a convex mode.

Tunable bandgap of a single layer graphene doped by the manganese oxide using the electrochemical doping

We studied the control of the bandgap energy of graphene by doping manganese oxide nanoparticles using an electrochemical method. The manganese oxide doping into the graphene was a main role for the bandgap opening and the defect generation was an effective method to increase the density of Mn doping on the graphene. The measured bandgap increased and finally saturated at 0.256 eV as the concentration of manganese oxide nanoparticles increased. The bandgap energies were 0.22, 0.244, 0.250, and 0.256 eV at the applied voltage of 0.5, 1.0, 1.5, and 2.0 V, respectively. In addition, the defect generation by the plasma treatment resulted in improved formations of the bandgap energy up to 0.4 eV. The combination of the manganese oxide doping and the defect generation can enhance the bandgap energy effectively in the graphene. It is considered that the electrochemical doping technique is an effective way to control the bandgap energy of graphene.

Excellent oxidation endurance of boron nitride nanotube field electron emitters

Boron nitride nanotubes (BNNTs) are considered as a promising cold electron emission material owing to their negative electron affinity. BNNT field emitters show excellent oxidation endurance after high temperature thermal annealing of 600 °C in air ambient. There is no damage to the BNNTs after thermal annealing at a temperature of 600 °C and also no degradation of field emission properties. The thermally annealed BNNTs exhibit a high maximum emission current density of 8.39 mA/cm2 and show very robust emission stability. The BNNTs can be a promising emitter material for field emission devices under harsh oxygen environments.

High performance field emission properties of graphite nanoplatelet field emitters

Graphite nanoplatelet (GNP) that consists of several tens of layers of graphene sheets is a promising candidate for electron field emission. The GNP emitter shows good field emission properties with a high emission current and a robust long-term stability because of the sharp edges, the high aspect ratio, and the stacked graphene sheets. Most of the electrons are emitted from the sharp edges of GNPs. The GNP emitters fabricated by the screen printing method reveal the turn-on electric field of 1.77 V/μm, the threshold electric field of 4.47 V/μm, the maximum emission current density of 39 mA/cm2, and the good emission stability for 20 h with little degradation rate of the emission current. The GNP field emitters can be a good candidate for several field emission applications such as flat lamps, field emission displays, and x-ray sources.

High-Performance Field-Emission Properties of Boron Nitride Nanotube Field Emitters

Boron nitride nanotubes (BNNTs) have attracted considerable attention as a field emission material because of their high mechanical strength, high negative electron affinity, and high oxidation resistance. Nevertheless, the obtained field-emission properties of BNNTs have indicated poor emission performance, which is a very high turn-on electric field with a low emission current. We fabricated BNNT field emitters and investigated their field-emission properties. The field-emission properties of the BNNT field emitters were considerably enhanced compared to those of other BN nanomaterial-based field emitters. The turn-on and the threshold electric fields of the BNNT field emitter were 3.1 and 5.4 V/μm at the gap distance of 750 μm, respectively. Both the turn-on and the threshold electric fields of the BNNT field emitters were decreased by increasing the gap distance between the emitter tip and the anode electrode. Degradation of the emission current during field emission operation for 20 h showed no significant difference according to the gap distance. Emission current fluctuation of the BNNT field emitters showed that the smaller gap was more unstable than the larger gap. The enhanced emission properties are mainly attributed to the small diameter, high-quality, and straight structure of BNNTs as well as the stable network formation of the BNNT film with good mechanical and electrical contact between the BNNTs and the cathode electrode. The remarkable emission performance of the BNNT field emitters might have promising applications for various field-emission devices.

Surface electronic structure of nitrogen-doped semiconducting single-walled carbon nanotube networks

We investigated the effects of vacuum annealing on the surface electronic structure and the work function of single-walled carbon nanotubes (SWCNTs). We changed the doping type of semiconducting single-walled carbon nanotubes (semi-SWCNTs) from p-type to n-type, and investigated their optical properties. The HNO3 treated p-type SWCNT network was converted to n-type after vacuum annealing due to formation of C-N bond. The C 1s sp2 binding energy of the vacuum annealed semi-SWCNTs was shifted toward a higher binding energy about 0.42 eV, which indicates a raising Fermi level as much as 0.42 eV compared with the intrinsic semi-SWCNTs. In addition, the work function of the vacuum annealed semi-SWCNT was observed towards lower energies. It is considered that the C-N bonding of semi-SWCNTs creates a donor level near the bottom of the conduction band, thus raising the Fermi level. The ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy revealed that the increased binding energy of C 1s sp...

Field emission behavior of boron nitride nanotubes

The field emission properties of boron nitride nanotube (BNNT) field emitters according to vacuum pressure were demonstrated. During the short-term emission operation, the field emission behaviors were almost similar, regardless of the vacuum pressure, even though the turn-on electric field of the BNNT field emitter was slightly increased as the vacuum pressure increased. On the other hand, during the long-term emission operation, both the degradation and fluctuations of the emission current of the BNNT field emitters were dramatically increased as the vacuum pressure increased. The degradation of field emission properties of the BNNT emitters according to vacuum pressure is mainly attributed to the ion bombardment effect, rather than the oxidation effect. The field emission behavior under Ar ambient also strongly demonstrates that the degradation and the fluctuation of the emission current are largely dependent on the ion bombardment effect.

Field electron emission of boron nitride nanotube emitters

Field emission properties of boron nitride (BN) nanomaterials have been studied for years to apply it at harsh ambient condition. However, the field emitters fabricated using the BN nanomaterials have limitations to utilize it as field emission devices due to their poor emission performances. Here, we report much enhanced field emission properties of the BN nanomaterial with low turn-on electric field, high emission current density, and long term emission stability.

Polycrystalline Silicon Films Formed by Solid-Phase Crystallization of Amorphous Silicon: the Substrate Effects on Crystallization Kinetics and Mechanism

The substrate effects on the solid-phase crystallization of amorphous silicon (a-Si) have been extensively investigated. The a-Si films were prepared on two kinds of substrates, a thermally oxidized Si wafer (SiO 2 /Si) and a quartz, by low-pressure chemical vapor deposition (LPCVD) using Si 2 H 6 gas at 470 °C and annealed at 600 °C in an N 2 ambient for crystallization. The analysis using XRD and Raman scattering shows that crystalline nuclei are faster formed on the SiO 2 /Si than on the quartz, and the time needed for the complete crystallization of a-Si films on the SiO 2 /Si is greatly reduced to 8 h from ˜15 h on the quartz. In this study, it was first observed that crystallization in the a-Si deposited on the SiO 2 /Si starts from the interface between the a-Si film and the thermal oxide of the substrate, called interface-induced crystallization, while random nucleation process dominates on the quartz. The very smooth surface of the SiO 2 /Si substrate is responsible for the observed interface-induced crystallization of a-Si films.

Field emission properties of triode structure CNT film emitter

We reported fabrication and field emission properties of carbon nanotube (CNT) field emitters which indicated the point-type CNT film emitter and line-type CNT film emitter. The CNT film field emitters were made by cutting CNT film using a razor. The CNT film emitters showed good emission properties such as the low turn-on field, the high emission current in a triode configuration. Especially, the line-type CNT film emitter was effective to realize an electron sheet beam with high density.