Shinobu Yamaoka

High temperature cubic boron nitride P-N junction diode made at high pressure

A p-n junction diode of cubic boron nitride was made by growing an n-type crystal epitaxially on a p-type seed crystal at a pressure of 55 kilobars and a temperature of about 1700�C. A temperature-difference solvent method was used for the crystal growth, and beryllium and silicon were doped as acceptors and donors, respectively. Formation of the p-n junction was clearly confirmed at 1 bar by rectification characteristics and by existence of a space charge layer of the junction as observed by electron beam induced current measurement. This diode operated at 530�C.

Ultraviolet light‐emitting diode of a cubic boron nitride pn junction made at high pressure

Injection luminescence in the ultraviolet is observed from a cubic boron nitride pn junction diode made at high pressure. Microscopic observation and spectroscopic studies show that the light emission occurs near the junction region only in the forward‐bias condition. The spectra extend from ∼215 nm to the red, having a few peaks mainly in the ultraviolet.

Synthesis of diamond from graphite-carbonate system under very high temperature and pressure

Abstract Although transition metals such as Fe, Co, Ni and their alloys have been used as diamond-producing solvent-catalysts under very high temperature and pressure, non-metallic compounds such as carbonates and oxides have also been claimed in the patents as the catalysts. In the present study, to make clear the catalytic effect of carbonates on the formation of diamond, high pressure experiments were carried out in the mixture of graphite and the carbonates of Li, Na, Mg, Ca and Sr. Diamond could reproducibly be synthesized from graphite in the presence of these carbonates at high pressure and temperature of 7.7 GPa and 2150°C. Although starting graphite was completely transformed to diamond in the presence of the carbonates, no transformation to diamond could be detected from graphite only at the same pressure and temperature condition. Therefore, it can be concluded that the carbonates have strong solvent-catalytic effect on the transformation of graphite to diamond.

Phosphorus: An Elemental Catalyst for Diamond Synthesis and Growth

As diamond-producing catalysts, 12 transition metals such as iron, cobalt, and nickel were first reported by General Electric researchers more than 30 years ago. Since then, no additional elemental catalyst has been reported. An investigation of the catalytic action of group V elements is of great interest from the viewpoint of producing an n-type semiconducting diamond crystal. In the present study, diamond was synthesized from graphite in the presence of elemental phosphorus at high pressure and temperature (7.7 gigapascals and 1800�C). Furthermore, single-crystal diamond was grown on a diamond seed crystal.

New catalysts for diamond growth under high pressure and high temperature

Diamond has been found to grow from copper, zinc, and germanium when temperatures and pressures in excess of those usually used for growth via conventional catalysts are used. Around their melting temperatures these metals are inert with respect to graphite. However, under the conditions used in this study, namely temperatures of 1600 °C and pressures of 6 GPa, they exhibit catalytic action. The conventional catalysts, which were first discovered by General Electric, act as catalysts immediately after melting in the presence of graphite, and this distinguishes them from the catalysts used in this study which should therefore be placed in a different category. A new model of diamond growth is proposed in order to explain the behavior of these new catalysts.

Appearance of N-type semiconducting properties of cBN single crystals grown at high pressure

Semiconducting properties of two types of cubic boron nitride (cBN) single crystals prepared at high pressure and high temperature were evaluated by Hall measurement. Sulfur was intentionally doped in one type as a donor and the other type contained no intentional dopants. Both crystals exhibit n-type conduction. Sulfur-doped and nonintentionally doped crystals show donor levels and carrier concentrations of 0.32 eV and 1014 cm-3, and 0.47 eV and 1012 cm-3 at room temperature, respectively. The origin of n-type conduction of nonintentionally doped crystal has not been elucidated but oxygen appears to be a candidate for the donor in the crystal.

Crystallization of diamond from a silicate melt of kimberlite composition in high-pressure and high-temperature experiments

In high-pressure and high-temperature experiments (1800- 2200 °C and 7.0-7.7 GPa), diamond crystallized and grew in a volatile-rich silicate melt of kimberlite composition. This diamond has well- developed {111} faces, and its morphologic characteristics resemble those of natural diamond but differ from those of synthetic diamond grown from metallic solvent-catalysts. The kimberlite melt has a strong solvent-catalytic effect on diamond formation, supporting the view that some natural diamonds crystallized from volatile-rich melts in the upper mantle.

Phase transformations in ABO 4 type compounds under high pressure

For ABO4 type ternary oxides, high pressure phase transformations known up to the present are reviewed, and an attempt is made to explain and predict crystal structures of their high pressure phases. When ABO4 type compounds are plotted based on the two variables, k=rA/rB and t=(rA+rB)/2rO, where rA, rB, and rO are the ionic radii of A and B cations and divalent oxygen, they can be classified into the major structure types. It is found empirically that a compound basically transforms to the structure type isostructural with a compound lying in a classified area with the same k and larger t values in the diagram.

Formation process of diamond from supercritical H2O-CO2 fluid under high pressure and high temperature conditions

Abstract The formation process of diamond from supercritical H 2 O–CO 2 fluid was studied using 13 C-graphitic carbon and oxalic acid dihydrate, (COOH) 2 ·2H 2 O, as starting materials under a diamond stable high pressure–high temperature (HP–HT) condition of 7.7 GPa and 1600°C. The exchange reaction between 13 C-graphitic carbon and 12 CO 2 in the supercritical H 2 O–CO 2 fluid, which was first formed by the decomposition of oxalic acid dihydrate, occurred very rapidly and became nearly equilibrated after 6 h. At the same time, graphite was recrystallized and coexistent with the fluid until traces of diamond were first observed after 8 h. All graphite transformed into diamond after 17 h, showing that a considerably long induction time was present for the formation of diamond in this fluid system.

High Pressure Synthesis of Diamond in the Systems of Grahpite-Sulfate and Graphite-Hydroxide

Diamonds were reproducively synthesized from graphite in the presence of Na2SO4, MgSO4, CaSO41/2H2O, Mg(OH)2 and Ca(OH)2 at high pressure of 7.7 GPa and a temperature of 2150°C. Although starting graphite was completely transformed to diamond in the presence of the sulfates or hydroxides, no transformation to diamond could be detected from graphite only at the same pressure and temperature condition. Therefore, we concluded that sulfates and hydroxides have a strong catalytic effect on the transformation of graphite to diamond.