cBN Crystals Research Articles

A nanoindentation study of thick cBN films prepared by chemical vapor deposition

The mechanical properties of high-quality cubic boron nitride (cBN) films were systematically investigated by nanoindentation measurements performed in both cross-sectional and plan-view directions. The large film thickness (∼5 μm) allows the effective ruling out of both substrate and indenter size effects. The hardness and elastic modulus values were found to be 70 and 800 GPa, respectively, which are the highest values ever obtained on cBN films deposited by either PVD or CVD methods so far (comparable to those reported for cBN crystals synthesized by high-pressure high-temperature methods). The variation of hardness across the cBN film thickness was investigated. In conjunction with the transmission electron microscopic observations, the relationship of the hardness measured with the crystallinity and crystal size/grain boundaries was discussed.

Structure analysis of cBN films prepared by DC jet plasma CVD from an Ar–N 2–BF 3–H 2 gas system

The structure of the cBN films deposited by DC jet plasma CVD from an Ar-N 2-BF 3-H 2 gas system was investigated by transmission electron microscopy and electron-energy-loss spectroscopy. A sequent layered-structure of Si/amorphous /hexagonal/cubic BN was revealed, which was also confirmed by the confocal Raman technique. For comparison, the phase composition, crystal size and crystallinity of cBN films deposited for different times at initial growth stage were studied by infrared spectroscopy, Raman spectroscopy and glancing-angle X-ray diffraction. A columnar growth of the cBN grains with the average column width of approximately 0.2 μm was observed. The columns were proved to be cBN single crystals elongated from the nucleation sites on the hexagonal BN to the film surface. High-density twins and stacking faults were observed on the {111} planes of the cBN crystals, which subdivided the crystals into many lamellae of several to about 20 nm in thickness.

High pressure synthesis of cubic boron nitride from Si-hBN system

Cubic boron nitride (cBN) was synthesized from hexagonal boron nitride (hBN) in the presence of silicon. The cBN forming pressure-temperature region was determined at pressures up to 7.7 GPa. Near perfect octahedral cBN crystals could be synthesized under the P-T conditions near the low temperature boundary of the cBN-forming region. When the temperature was above 1700°C at 6.5 GPa, the transformation rate of cBN from hBN was very high and the cBN crystals had an oriented columnar morphology. This suggests that silicon has strong catalytic ability for cBN formation from hBN. The energy-disperse X-ray analysis (EDXA) identified that silicon was homogeneously distributed in the cBN crystals.

Raman and photoluminescence spectra of indented cubic boron nitride and polycrystalline cubic boron nitride

Abstract The use of Raman spectroscopy, and in particular Raman line shifts, to measure stress in diamond and nitrides such as gallium nitride (GaN), is well known. In both diamond and GaN the application is principally to study stresses in thin films and at the substrate–thin film interface. Stresses in polycrystalline diamond composites have also been measured by this method. Typically stresses of the order of GPa can be determined with a spatial resolution of a few micrometers. In this paper, Raman spectra of indentations on cubic boron nitride (cBN) crystals and polycrystalline cubic boron nitride (PcBN) composites are presented. Shifts of the cBN Raman lines from their unstressed positions quantify the residual stresses in the boron nitride due to the deformation brought about by the indentation. Making use of the measured coefficient of shift of 3.39 cm−1/GPa for the transverse optical Raman peak, these are of the order of 1 GPa. These measurements illustrate, for the first time, the use of Raman spectroscopy to study residual stresses in boron nitride. Plastic deformation is usually associated with the creation of vacancies. To investigate the possible presence of vacancy defects and vacancy-related defects, the indented boron nitride samples were also studied with photoluminescence spectroscopy.

Surface studies of (111) facets of cBN mini-crystals

Surface analysis techniques, including x-ray photoelectron spectroscopy with small-spot analysis (down to 100 μm 2 ) capabilities, field emission scanning Auger microscopy, electron energy-loss spectroscopy in association with these two techniques and micro-Raman spectroscopy, have been used to collect surface information on specific facets of commercially available submillimetre-sized cubic boron nitride (cBN) crystals. With the freedom of choosing a specific facet with a known orientation relative to the probing beam and detector, it is possible to obtain accurate information on the surface compositional structure of a cBN crystal before and after a surface reaction.

Heteroepitaxial Growth of Cubic Boron Nitride Single Crystal on Diamond Seed Under High Pressure

ABSTRACTSingle crystal cubic boron nitride(cBN) was heteroepitaxially grown on a seed crystal of diamond under static high pressure and high temperature of 5.5GPa and 1600–1700°C, respectively, for 10–100 hour. A temperature gradient method was employed for the crystal growth by using lithium boron nitride as a solvent. Initial growth feature of cBN crystal was found on the diamond seed surface after the growing time of 10 minutes. The nucleation sites of the crystals seem to be near the etch pits on the diamond surface which were introduced by the surface dissolution by the solvent for cBN growth. Two types of growth features, island and step growth were typically shown on the surface. It can be seen that grown crystal appearing as a (111) nitrogen face was exhibited with the step growth feature, while the (11n) face exhibited the island growth feature. Considering the growth process under constant P-T growing condition, growth rate of cBN crystal was significantly small as compared to that of diamond.

Microscopic investigations of silicon surfaces pretreated for use in diamond deposition

The influence of pretreatment of silicon by diamond powder and cubic coron nitride (cBN) powder, as well as by substrate biasing, was investigated. The uncoated silicon surfaces were investigated by scanning electron microscopy, transmission electron microscopy and electron energy loss spectroscopy. The mechanical pretreatment was carried out in an ultrasonic water bath. Polished silicon wafers were dipped in a beaker containing an ethanol-powder mixture. It has been shown that very small diamond or cBN crystals are pressed into the silicon surface. These crystals are not removable even with thorough post-treatment. The size of the crystals, which were pressed into the silicon surface, is between 2 nm and 50 nm, and the density is in the range 10 9–10 10 crystals cm −2. Increasing pretreatment time causes an increase in crystal number density. All substrates were coated in a microwave chemical vapour deposition system in order to determine the nucleation density. Under the same conditions non-pretreated silicon substrates were coated with the help of substrate biasing. It has been supposed that the nature and the density of residues left on the silicon surface after mechanical pretreatment are important for nucleation. Clusters of diamond microcrystals were formed on the surface of biased pretreated substrates. After deposition a silicon carbide film can be observed in areas not occupied by diamond particles.

Synthesis of cubic boron nitride from hexagonal boron nitride with AlMg alloy solvent under high pressures and high temperatures

An AlMg metallic alloy solvent has been proved to be an effective solvent for the synthesis of cubic BN(cBN) from hexagonal BN(hBN) under high pressures and temperatures. The Mg content in the AlMg solvent ranged from 30 to 70% by weight. The conversion rate from hBN to cBN and morphology of the cBN crystals could be controlled by varying the amount of solvent in the hBN-solvent mixture and the Mg content in the solvent, respectively. The conversion rate increased as the amount of solvent in the hBN-solvent mixture or the Mg content in the solvent increased. The large blocky cBN crystals with well-developed crystallographic surfaces were synthesized by the solvent with high Mg content and the fine cBN crystals, with irregular shape, by the solvent with low Mg content.

Synthesis of cubic boron nitride using Mg and pure or M?-doped Li3N, Ca3N2 and Mg3N2 with M?=Al, B, Si, Ti

The growth pressure-temperature region of cubic boron nitride (cBN) in the systems Mg-BN and MxNy-BN (MxNy=Li3N, Ca3N2, Mg3N2) has been redetermined using well-crystallized hexagonal BN (hBN) with low oxygen content (0.2%) as the starting material. The data on the MxNy-BN systems are compatible with the existence of two growth regions: a high-temperature region where cBN grows from a liquid phase, and a low-temperature region where cBN forms from solid-solid reactions. Previous data are discussed according to this model and possible solid-state reactions are proposed on the basis of thermodynamic considerations. The results for the Mg-BN system confirm the effect of the O2 content of the starting BN on the cBN growth region. The systems (MxNy + M′)-BN (M′=Al, B, Si, Ti) have been shown to produce cBN crystals of increased size and improved morphology (more compact and perfect) compared to those obtained with the MxNy-BN systems. Their colour is dark or black and their size reaches 0.6 mm. The effect of the relative proportions of M′ and MxNy on the growth region and yield has been determined and is discussed on the basis of the chemical reactions likely to occur.

On Performance of Chemically Bonded Single-Layer CBN Grinding Wheel

Electroplated superabrasive wheels made of a single layer of CBN crystals have in general 60 to 80% of the grit height covered by the galvanic embedding layer for effective grit retention. This height is required because of the inherent mechanical nature of bonding. In a newly developed grinding wheel less grit coverage is sufficient to retain the grit on the wheel. This has been made possible by forming a chemical bond between the grit surface and the bonding material to the wheel thus ensuring large chip clearance space. The performance OF such grinding wheel while grinding unhardened 100Cr6 steel, cast iron and high speed steel, respectively, is reported in this paper.

Cubic Boron Nitride Crystals Grown at High Pressure: PN Junction, Crystallographic Polarity and Some Properties

ABSTRACTStudies on the cubic boron nitride (cBN) crystals grown by the temperature difference method at high pressure are reviewed. The electron beam induced current measurement, the electrical measurement, and the optical measurement demonstrated that the cBN is a good potential candidate as a wide-gap semiconductor material. The Raman spectrum and the reflectance and transmittance spectra of the cBN were obtained. The crys-tallographic polarity of cBN crystals was directly determined from the Rutherford backscattering spectroscopy (RBS).The RBS experiment showed that the (111) surface which adjoins to the (100) surface at an obtuse angle so that the edge between the (111) and the (100) is parallel to the <110> direction of striations on the (100) face is a triply bonded nitrogen-terminating face. The result seems to disagree with that derived from other semiconductor compounds.

Crystal growth of cubic boron nitride using Li 3BN 2 solvent under high temperature and pressure

A temperature gradient method was applied to grow a large cubic boron nitride (cBN) crystal under 5.5 to 6 GPa and 1700 to 1950°C using Li 3BN 2 as a solvent. The crystals, free from inclusions and cracks, were grown successfully on a seed crystal without spontaneous nucleation. The grown crystals consists of large { 1 1 l̄}, mostly { 1 1 3 }, faces, a nd small {111}, { 1 1 1 } and {100} faces, in contrast to the latter three faces being predominant in commercial cBN, Borazon. The { 1 1 l̄} and {100} faces are characterized by striations parallel to 〈110〉 and estimated to correspond to the nitrogen-terminating surfaces. Most crystals contain many { 1 1 1 } twin lamellae, resulting in complicated habit.

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

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.

The synthesis of cBN using Ca3B2N4

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.

Effect of oxygen on the growth of cubic boron nitride using Mg3N2 as catalyst

Cubic boron nitride (cBN) was synthesized from hexagonal boron nitride (hBN) under high pressure and high temperature using Mg3N2 as catalyst. The yield and morphology of cBN were investigated in relation to the oxygen impurity of the BN-Mg3N2 system. Magnesium oxide precipitated as a by-product in this system and the amount of the precipitate increased with an increase in the oxygen content of the starting materials. The morphology and surface patterns of cBN crystals synthesized using an hBN which contained oxygen showed unusual features. It was confirmed that the precipitation of MgO interfered with the free growth of cBN crystals. Purification of starting materials and addition of zirconium powder to the catalyst as an oxygen getter increased the yield of cBN crystals showing smooth surfaces.

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

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.