Materials emitting light in the deep ultraviolet region around 200 nanometers are essential in a wide-range of applications, such as information storage technology, environmental protection, and medical treatment Hexagonal boron nitride (hBN), which was recently found to be a promising deep ultraviolet light emitter, has traditionally been synthesized under high pressure and at high temperature We successfully synthesized high-purity hBN crystals at atmospheric pressure by using a nickel-molybdenum solvent The obtained hBN crystals emitted intense 215-nanometer luminescence at room temperature This study demonstrates an easier way to grow high-quality hBN crystals, through their liquid-phase deposition on a substrate at atmospheric pressure

http://science.sciencemag.org/content/sci/317/5840/932.full.pdf

Deep Ultraviolet Light-Emitting Hexagonal Boron Nitride Synthesized at Atmospheric Pressure

The graphite die set in spark plasma system (SPS) is heated by a pulse direct current. Weak plasma, discharge impact, electric field and electric current, which are based on this current, induce good effects on materials in the die. The surface films of aluminum and pure WC powders are ruptured by the spark plasma. Pure AlN powder is sintered without sintering additives in the electric field. The spark plasma leaves discharge patterns on insulators. Organic fibers are etched by the spark plasma. Thermosetting polyimide is consolidated by the spark plasma. Insoluble polymonomethylsilane is rearranged into the soluble one by the spark plasma. A single crystal of CoSb3 is grown from the compound powders in the electric field by slow heating. Coupled crystals of eutectic powder are connected with each other in the electric field.

Sintering, consolidation, reaction and crystal growth by the spark plasma system (SPS)

A review, with 112 references, is given of the different ways to prepare cubic boron nitride (BN). The different crystal forms as well as the phase diagram of BN are described. The physical and chemical properties and the correlated industrial or potential applications are shown.

Cubic boron nitride: synthesis, physicochemical properties and applications

Revue des systemes de commutation representatifs et discussion detaillee d'une classe particuliere de ces systemes non identifiee correctement dans le passe. On presente les avantages de diodes planes MIM par rapport aux configurations fermees (sandwich) car la totalite de leur structure est ouverte et accessible directement a l'atmosphere gazeuse environnante ou au vide, qui affecte fortement le comportement

Bistable switching in electroformed metal–insulator–metal devices†

Luminescence Studies of Oxygen-Related Defects In Aluminum Nitride

The effect of the oxygen impurity on the densification behaviour of AlN was investigated AlN powders containing different amounts of oxygen were synthesized from alumina and hot-pressed The way in which oxygen accelerates densification is remarkable Contrary to what is expected from the densification equation, the sintering rate decreases during the holding time at temperatures above 1900° C This discrepancy is caused by the liberation of oxygen during the hot-pressing The compression test, conducted on the hot-pressed specimens, shows that oxygen impurity also improves the mechanical strength of sintered AlN The sintered specimens with more than 25 wt % of oxygen have compressive fracture stresses above 150kg mm−2, which are adequate for a refractory material

Effect of oxygen on sintering of AlN

The phase relations in the ternary system B-Mg-N resulting from the reaction between Mg and BN at 2.5 GPa were investigated by means ofin situ differential thermal analysis (DTA) supported by a conventional quenching technique. One compound, Mg3B2N4, was newly formed when melted Mg reacted with hexagonal BN (hBN) solid above 1150° C and formed the eutectic with Mg and hBNat 737 and 1295° C, respectively. It was also confirmed that hBN crystals were precipitated from the liquid above 1300° C. The catalytic mechanism controlling cBN formation in the system Mg-BN was discussed from the experimental results of the present work. The lower temperature limit of cubic BN (cBN) growth region appears to be closely related to the initial formation of liquid phase due to a eutectic of Mg3B2N4-BN.

Precipitation mechanism of BN in the ternary system of B-Mg-N

The phase relation of the system Ca-B-N was investigated at a pressure of 2.5 GPa by both differential thermal analysis (DTA) and a quenching method. When BN reacted with Ca at temperatures higher than 1150° C, Ca3B2N4 was formed together with small amounts of Ca3N2 and CaB6. The system of Ca3B2N4-BN has a eutectic relationship at 1316° C and 2.5 GPa. The synthesis of cBN was established by using Ca3B2N4 under the thermodynamic stable conditions of cBN. It could be seen that cBN crystals grew repeatedly in Ca3B2N4 melt, which advanced into the hBN layer. The cBN crystals obtained in this way were of outstanding purity and of good quality. This indicated that hBN dissolved and precipitated as cBN in Ca3B2N4 melt without any appreciable change of molar boron/nitrogen ratio. In the system of Ca-B-N, the low-temperature limit of cBN formation was closely related to the eutectic relationship between BN and Ca3B2N4.

The synthesis of cBN using Ca3B2N4

The growth pressure-temperature region of cBN in the system BN-Mg was determined under the conditions up to 8 GPa and 2300° C. Hexagonal BN with different oxygen contents (1.9 wt % for R-type and 7.9 wt % for N1-type) was used as a starting material. The lower temperature limit of the cBN region obtained from the R-type is about 1380° C under pressures of 6 to 8 GPa. This limit can be compared with the eutectic point in the system hBN-Mg3B2N4. The data suggest that cBN crystals grow through the dissolution and precipitation process from a eutectic liquid. The cBN region obtained from the N1-type is located at higher temperatures than that of the R-type, the lower limit of which is reached at about 1700° C at 6 GPa. MgO and/or Mg3 (BO3)2 are formed as by-products in such a system. The finding implies that Mg3B2N4, a solvent of BN, reacts with oxide impurities (especially B2O3) by the following reaction; Mg3B2N4+3/2O2=3MgO+2BN+N2 or Mg3B2N4+3O2=Mg3 (BO3)2+2N2. It is deduced that the cBN growth region shifts towards higher temperatures depending on the effect of oxygen.

Growth pressure-temperature region of cubic BN in the system BN-Mg

Cubic BN was synthesized by treating hexagonal BN(hBN) in the presence of Ca3B2N4 which acted as a flux for BN. After the high pressure and temperature treatments, cBN was obtained in a part of hBN layer initially charged, but hardly in the flux layer. The grains of cBN were precipitated accompanied with the advance of Ca3B2N4 flux into hBN zone. From these observations, it can be deduced that hBN dissociated beneath the thin layer of flux advanced, and crystallized as cBN under an isothermal condition. In this system, the mechanism was basically the same as that of the diamond growth in the metal flux such as nickel and cobalt. Namely, the crystal growth of cBN was governed by the difference of solubility between hBN and cBN in a melted Ca3B2N4, because of the eutectic relation between BN and Ca3B2N4. For the nucleation process, two types of features were observed; one was the preferential nucleation at the boundary of hBN-flux, and the other was the homogeneous nucleation in the part of hBN layer initially charged.

Minoru Iwata

Papers

Effect of oxygen on sintering of AlN

Precipitation mechanism of BN in the ternary system of B-Mg-N

The synthesis of cBN using Ca3B2N4

Growth pressure-temperature region of cubic BN in the system BN-Mg

Formation mechanism of cBN crystals under isothermal conditions in the system BN-Ca3B2N4