Tateki Kurosu

Formation Mechanism of p-Type Surface Conductive Layer on Deposited Diamond Films

A model of the formation of a p-type surface conductive layer on deposited diamond films is proposed. According to the model, the ionization of acid in water produces oxonium ion ( H3O+) which reacts with hydrogen on diamond films and causes the creation of holes in diamond films. The model also explains the disappearance of the p-type surface conductive layer by the action of alkaline substances. The experimental results concerning the change in electrical resistance at the surface of diamond films can be explained using the proposed model.

Characterization of Boron-Doped Diamond Film

Diamond films doped with boron were fabricated by the thermal filament CVD method. Powdered B2O3 was used as the doping source. The films were identified as diamond by means of several methods including Raman spectroscopy. The resistivity of the films was inversely proportional to the B/C ratio over four orders. The temperature dependence of current was measured and to fit this result to the theoretical calculation, the activation energy was evaluated.

Hall Effect Measurements of Surface Conductive Layer on Undoped Diamond Films in NO2 and NH3 Atmospheres

In order to clarify the mechanism of change in resistance of the surface conductive layer exposed to oxidizing and reducing gases, the Hall effect measurements of the surface conductive layer on as-grown undoped diamond films in NO2 and NH3 gas atmospheres were carried out. It was found that holes were generated in the surface conductive layer by the adsorption of NO2 gas, and the adsorption of NH3 gas resulted in the disappearance of the holes. Morever, the dependences of gas concentration on the sheet resistivity, carrier density per unit area and Hall mobility were observed. The mechanism of change in resistance of the surface conductive layer in gas atmospheres could be explained by the proposed model based on the experimental results.

Water Electrolysis Using Diamond Thin‐Film Electrodes

Thin, boron-doped diamond films formed on a silicon substrate were evaluated during water electrolysis in acidic solution in order to determine their potential for industrial use. Though the electrode exhibited overvoltages in excess of 2 V in the industrial current range, ozone gas was produced at a current efficiency of a few percent at ambient temperature. It was confirmed that the consumption rate of the highly doped sample was small and comparable with a platinum-plated anode, indicating that the diamond is dimensionally stable under extreme conditions. The failure mechanism in the test is discussed on the basis of scanning electron microscopy, X-ray diffraction, and Raman analyses. The spalling of the film from the substrate, which was observed in the deteriorated sample after the electrolysis, is attributed to the residual stress that accumulated during the production process carried out under high temperature.

Synthesis of n-type semiconducting diamond film using diphosphorus pentaoxide as the doping source

An n-type semiconducting diamond film has been synthesized by the hot filament CVD method using diphosphorus pentaoxide as the doping source. The obtained film was identified as polycrystalline diamond containing few sp2 components by means of several methods including Raman spectroscopy. From measurements of the Hall effect and the Seebeck effect, the film was found to be an n-type semiconductor.

Electrolytic decomposition of amaranth dyestuff using diamond electrodes

The electrolytic decomposition of an amaranth dyestuff solution using several combinations of electrodes with diamond and platinum is reported. It is observed that a portion of the amaranth is decomposed on the cathode surface while the other portion is decomposed to lower molecular weight components on the anode surface. The decolourizing rate is higher at diamond electrodes used as the anode and the cathode than with other combinations. This electrode combination also shows a rapid decrease in total organic carbon concentration. Acetic acid and oxalic acid are detected as the intermediate substances, and CO2 gas is generated as a final product corresponding to the decrease in the oxalic acid concentration.

Synthesis of Diamond Thin Films Having Semiconductive Properties

Semiconductive diamond films were fabricated by the thermal filament CVD method. A saturated solution of B2O3 powder in CH3OH mixed with acetone was used. The films deposited were identified as diamond by several methods including Raman spectroscopy. By the measurement of electrical properties, the obtained films were found to show p-type conduction.

ELECTRON FIELD EMISSION FROM DIAMOND-LIKE CARBON FILMS DEPOSITED BY ELECTROLYSIS OF METHANOL LIQUID

Electron field emission has been studied with diamond-like carbon (DLC) films deposited from a liquid phase. The DLC films were deposited on Si substrate by electrolysis of methanol liquid. The field emission measurements were carried out with a parallel plate configuration using the deposited DLC films on Si substrate as a cathode, and an indium tin oxide (ITO) coated glass plate as an anode. We found several bright spots on a luminescent screen mounted on the ITO anode, indicating that the electrons are emitted from the isolated emission sites on the deposited DLC film. The emission current density is more than 10−7 A/cm2 at the electric field as low as 1.2 V/μm. This result suggests that the DLC film deposited from the liquid phase has a potential advantage for field emitter applications.

Synthesis of B-doped diamond film

Abstract Boron-doped diamond films have been synthesized by the thermal filament CVD method. As the doping source, boron trioxide powder was used instead of diborane. The films obtained were identified as diamond by several methods including Raman spectroscopy. The resistivity of the films was inversely proportional to the doping concentration over four order. p-Type electrical conduction was also confirmed by measuring the Seebeck effect.

Fabrication of Metal-Insulator-Semiconductor Devices Using Polycrystalline Diamond Film

Metal-insulator-semiconductor (MIS) devices have been fabricated using a polycrystalline diamond film doped with boron. The diamond film has been deposited on Si substrate by a hot-filament chemical vapor deposition method. The SiO2 film has been deposited on the diamond by a plasma-assisted CVD method and aluminum has been evaporated as a gate on the SiO2 film. The MIS capacitance was varied as a function of voltage applied between the gate and substrate. Further, the metal-insulater-semiconductor field-effect transistor has indicated transistor operation capabilities at room temperature. These results suggest a possibility that the polycrystalline diamond film can be used as an electronics material.