Eung Joon Chi

Fabrication of amorphous-carbon-nitride field emitters

To improve silicon field emitters, an amorphous-carbon-nitride (a-CN) coating was applied by helical resonator plasma-enhanced chemical vapor deposition. By this process, a-CN was very uniformly coated on silicon tips without any damage. Microstructural and electrical investigation of the silicon and a-CN coated field emitters were performed. a-CN coating lowered turn-on voltage and increased emission current. Negative electron affinity of carbon nitride is suggested for enhancing emission current.

Structural, Optical, and Field Emission Properties of Hydrogenated Amorphous Carbon Films Grown by Helical Resonator Plasma Enhanced Chemical Vapor Deposition.

Hydrogenated amorphous carbon films have been prepared by helical resonator plasma enhanced chemical vapor deposition using CH4 and H2 mixtures. Films with various physical properties were obtained from different deposition conditions. The structural and optical properties of hydrogenated amorphous carbon (a-C:H) films were more sensitive to the substrate bias than the substrate temperature. This reflects that the energetic ion bombardment modified the films more effectively than the thermal energy. The a-C:H films deposited with no bias applied show characteristics of polymeric films with a large content of C–H bond while the a-C:H films deposited as a function of the substrate temperature at a bias of 40 W show characteristics ranging from diamond-like carbon (DLC) to graphitic nature with a significantly reduced C–H bond. From elastic recoil detection analysis, the hydrogen content in the films also significantly reduced with an increase of substrate temperature at a bias of 40 W. The field emission from bare Si emitters and a-C:H coated Si emitters has been examined in an ultrahigh vacuum chamber. The field emission characteristic of the a-C:H coated Si emitters is better than that of the bare Si emitters. For the a-C:H coated Si emitters, the emission current of the a-C:H coated (at 150°C/40 W) Si emitters is higher than the that of the a-C:H coated (at 260°C/40 W) Si emitters. This difference in field emission characteristic is attributed to the structural and optical properties as well as hydrogen content.

Effects of heat treatment on the field emission property of amorphous carbon nitride

As a coating material for silicon field emitters, amorphous carbon nitride (a-C:N) by helical resonator plasma enhanced chemical vapor deposition has been proposed. Thermal annealing in nitrogen ambient up to 600 °C was carried out to investigate the effects of heat treatment on the field emission. The structural and compositional modifications induced by the annealing were followed by several analytical techniques: Fourier transformation infrared (FTIR) spectroscopy, elastic recoil detection analysis (ERDA), and x-ray photoelectron spectroscopy. FTIR and ERDA analyses indicate that hydrogen loss occurs for annealing temperatures higher than 300 °C. Amorphous-C:N films significantly lowered the turn-on voltage and increased the emission current of the silicon emitters. After annealing at 600 °C, the field emission property was further enhanced presumably due to the efficient conduction through the a-C:N films induced by an increase of the number and/or the size of the graphitic domains.

The Field Emission Characteristics of a-C:H Thin Films Prepared by Helical Resonator Plasma Enhanced Chemical Vapor Deposition

The field emission characteristics of hydrogenated amorphous carbon (a-C:H) films prepared by helical resonator-plasma enhanced chemical vapor deposition (HR-PECVD) are examined. a-C:H films are deposited with CH4/H2 and CH4/Ar gases under different substrate RF bias conditions. The properties of a-C:H films are investigated by Raman spectroscopy, Fourier transform IR (FT-IR), UV spectroscopy and elastic recoil detection (ERD). Field emission characteristics of a-C:H coated on Si whiskers which are grown by the vapor-liquid-solid (VLS) method are tested under ultrahigh vacuum. Highly efficient field emission characteristics are achieved in the specimen deposited at a substrate RF bias higher rather than in the ground deposition condition regardless of the nature of the reactant gas. As the substrate RF bias is changed from ground to a higher RF substrate bias, the deposited a-C:H films have lower hydrogen contents and higher sp2-bonds. Therefore, the field emission characteristics of a-C:H thin films are affected by the hydrogen contents of the films rather than by the sp3/sp2 ratio.

Field emission characteristic of diamond films grown by electron assisted chemical vapor deposition

Abstract By introducing positive substrate bias, ranging from 0 to 200 V, to the substrate during the growing procedure of diamond at 1, 2, and 3% CH4 concentration, we have investigated the effect of electron bombardment on modification of the structural property and the surface morphology of diamond films, and consequently the field emission properties. When increasing the bias voltage for each CH4 concentration, the structural properties of diamond films are significantly deteriorated together while the non-diamond carbon component increased and the surface morphologies of the films lost their unique facet shape. The reason for the deterioration of the structural property was attributed to both the increase of substrate temperature and the excessive generation of CHn radicals. Especially for the films deposited at 2% CH4 concentration under 100 V, it was observed that their morphological and structural characteristics approached those of graphitic carbon nature. The field emission properties of diamond films were substantially improved with increasing the CH4 concentration and with the application of bias voltage for each CH4 concentration. In order to investigate the correlation between the enhancement of field emission properties and the emission sites, we have examined the spatial distribution of the emission sites. From this result, a possible emission mechanism is discussed.

Enhancement of electron emission from silicon tips by nitrogen doped amorphous carbon coating

Silicon field emitters have been coated with nitrogenated amorphous carbon (a-C:N) in order to enhance the electron emission current. The coating was produced using a helical resonator plasma enhanced chemical vapor deposition system. The a-C:N film is amorphous and hydrogenated with about 30 at % hydrogen. Nitrogen is also included in the amorphous network and reduces the work function by doping. a-C:N coating enhances significantly the emission current of silicon tips.

Electrical characteristics of metal silicide field emitters

To improve silicon field emitter, Ti and Co silicides were formed on silicon tips. Silicides were produced by deposition of metal (Ti and Co) and subsequent annealing. I-V characteristics of as-grown silicon tips and silicide emitters were investigated. Turn-on voltage and emission current of silicon tips were 220 V and 10/sup -8/ A, respectively. Ti and Co silicide lowered turn-on voltage significantly. The emission current of Ti and Co silicide emitters were 140 V and 180 V, respectively. Both silicides increased emission current to order of 10/sup -7/ A. Ti and Co silicide emitters have enhanced field emission of silicon tips due to large emitting area and lower work function, respectively.

Effects of nitrogen addition on the structure and field emission properties of amorphous carbon

The films of amorphous carbon with different amount of incorporated nitrogen are deposited by helical resonator plasma enhanced chemical vapor deposition using CH/sub 4/, Ar, and N/sub 2/ gas mixture. As the increase of nitrogen in the films, the optical band gap and sp/sup 3/ bond fraction decreased. The higher field emission current and the lower turn-on voltage are obtained from the sample of the higher nitrogen content. The increase of the conducting part of the films and the role of nitrogen as an electrical donor are responsible for the enhanced field emission.

Effects of substrate bias on the structural and field emission properties of diamond films

The effect of electron bombardment on modification of the structural property and the surface morphology of diamond films, and consequently the field emission properties have been investigated by introducing positive substrate bias. When increasing the bias voltage, the structural properties of diamond films are significantly deteriorated together with the increase of nondiamond carbon component and the surface morphologies of the films lost their unique facet shape. The reason for the increase of nondiamond carbon content is described in terms of both the increase of substrate temperature and the excessive generation of CHn radicals. The field emission properties of diamond films were substantially improved with increasing bias voltage. Enhancement of field emission property for the films prepared by increasing bias voltage and/or methane concentration has been discussed by correlating between the substrate–diamond interface property and the slope of the Fowler–Nordheim plot.

Field emission characteristics of cesiated amorphous carbon films by negative carbon ion

Abstract Amorphous carbon (a-C) films and cesiated a-C films were synthesized on silicon substrate by Cs ion gun sputter deposition system (Cs IGSDS). The properties of a-C film were analyzed by X-ray photoelectron spectroscopy, Raman spectroscopy, and atomic force microscopy, As the negative carbon ion energy increased, relative sp 3 ratio in the a-C film increased, and surface roughness decreased. The field emission characteristics of the a-C films as a function of negative carbon ion energy were examined by diode type I – V measurement at ultra high vacuum system. From I – V measurements, the threshold voltage increased with the increase of negative carbon ion energy, and the range from 11 to 16 V/μm was obtained. To investigate the Cs effect, cesiated a-C films were prepared by Cs + ion and C - ion co-deposition and field emission characteristics of the cesiated a-C films were observed, too. Compared to non-cesiated a-C films, the threshold voltage is decreased by the Cs co-deposition and the value was about 6 V/μm. In this study, we investigate that the relation between carbon ion energy and field emission, and the effect of Cs in the a-C films were examined.